Sources, transport, reservoirs and fate of dioxins, PCBs ... · SWEDISH ENVIRONMENTAL PROTECTION AGENCY Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic

Naturvårdsverket 106 48 Stockholm. Besöksadress: Stockholm – Valhallavägen 195, Östersund – Forskarens väg 5 hus Ub, Kiruna – Kaserngatan 14. Tel: +46 8-698 10 00, fax: +46 8-20 29 25, e-post: [email protected] Internet: www.naturvardsverket.se Beställningar Ordertel: +46 8-505 933 40, orderfax: +46 8-505 933 99, e-post: [email protected] Postadress: CM Gruppen AB, Box 110 93, 161 11 Bromma. Internet: www.naturvardsverket.se/bokhandeln

Sources, transport, reservoirs and fate of dioxins, P

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eport 59

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Sources, transport, reservoirs and fate of

dioxins, PCBs and HCB in the Baltic Sea environment

Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic Sea environment

A better knowledge of sources, transport, reservoirs and fate of

persistent organic pollutants (POPs) in the Baltic Sea environment is

crucial for the identification of effective actions against these com-

pounds.

In this report the present situation regarding sources and current

fluxes of persistent pollutants in the Baltic Sea ecosystem is presented.

The compounds selected for the study were: polychlorinated biphe-

nyls (PCBs), hexachlorobenzene (HCB), polychlorinated dibenzofu-

rans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). These

classes of compounds represent a broad range of physical-chemical

properties, and hence their environmental behaviour encompasses the

spectrum of most chemicals listed in the Stockholm Convention.

Based on current knowledge and some new field measurements

in air, sea water and sediments, mass balances for the selected POPs

were calculated. These mass balances indicate that the atmosphere

is the major source of PCDD/Fs to the Bothnian Sea and the Baltic

Proper and also the dominant external source of HCB and PCBs to

the Baltic Sea. These findings emphasise the need for further interna-

tional agreements to prevent long-range transboundary transport of

these POPs.

REpoRt 5912

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REpoRt 5912 • JANUARY 2009

SWEDISH ENVIRONMENTAL PROTECTION AGENCY

Sources, transport, reservoirs and fate of dioxins, PCBs and HCB

in the Baltic Sea environment

Main authors: Karin Wiberg,

Department of Chemistry, Umeå University, Michael McLachlan,

Department of Applied Environmental Science, Stockholm University, Per Jonsson,

Department of Applied Environmental Science, Stockholm University, Niklas Johansson,

Swedish Environmental Protection Agency

Contributing authors: Sarah Josefsson, Eva Knekta, Ylva Persson and Kristina Sundqvist,

Department of Chemistry, Umeå University; James Armitage, Dag Broman, Gerard Cornelissen,

Anna-Lena Egebäck and Ulla Sellström, Department of Applied Environmental Science, Stockholm University

and Ingemar Cato, Geological Survey of Sweden

OrdersPhone: + 46 (0)8-505 933 40

Fax: + 46 (0)8-505 933 99 E-mail: [email protected]

Address: CM Gruppen AB, Box 110 93, SE-161 11 Bromma, Sweden Internet: www.naturvardsverket.se/bokhandeln

The Swedish Environmental Protection AgencyPhone: + 46 (0)8-698 10 00, Fax: + 46 (0)8-20 29 25

E-mail: [email protected] Address: Naturvårdsverket, SE-106 48 Stockholm, Sweden

Internet: www.naturvardsverket.se

ISBN 978-91-620-5912-5 ISSN 0282-7298

© Naturvårdsverket 2009

Print: CM Gruppen AB, Bromma, 2009Cover photo: Titus Kyrklund, Naturvårdsverket

SWEDISH ENVIRONMENTAL PROTECTION AGENCYReport 5912 • Sources, transport, reservoirs

and fate of dioxins, PCBs and HCB in the Baltic Sea environment

3

PrefaceThe importance of the persistence of a compound released to the environ ment became apparent in 1966 when PCBs were demonstrated to be abun dant in biota. This was the first time a non-intentionally spread chemical was found to accumulate and cause effects in the environment. Unfortu nately, since then, many other compounds with similar properties have been detected in the environ ment.

During the last decades, the environmental pollution of PCBs, dioxins and other persistent organic pollutants (POPs) has been extensively studied in numerous media in many countries all over the world. In Sweden, there has been much focus on the situation in the Baltic Sea and its surroundings. Since around the 1970s, the levels of dioxins and PCBs have shown de creasing environmental trends. For some POPs, these trends have levelled off in many areas since the mid-1980s and have remained more or less stable since then. In 1972, the use of PCBs in open systems was banned and thereafter many other actions have been taken in order to reduce emissions of dioxins and other POPs. These measures obviously had a great impact on the situation. The lack of profound improvement during the last fifteen years is, however, troublesome and suggests the presence of hitherto unknown sources and/or that the importance of some known (primary and secondary) sources has been misjudged.

The aim of the current work was to identify the sources that contribute to the present pollutant situation including current fluxes of POPs to, from and within the Baltic Sea. Some well-known POPs were selected (PCBs, dioxins and HCB) as representatives for a broad range of physical-chemical proper-ties. These compounds are also known to have different (primary) sources and they represent both intentionally and unintentionally formed pollutants. Based on current knowledge and new measurements, the current pollution scenario of the Baltic Sea ecosystem was modelled in order to get an over view of the relative impact of various sources. Future scenarios were also predicted inclu-ding varying pollution source strengths.

The results from this study are intended to be used together with other rele vant information to form an up-to-date basis for a new Swedish strategy on POPs with special emphasis on POPs formed unintentionally.

Swedish EPA, January, 2009



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AbbreviationsAOC amorphous organic carbonBC black carbon; also referred to as soot carbonb.w. body weightDF dibenzofuranDD dibenzo-p-dioxinDL-PCBs dioxin-like PCBsDOM dissolved organic matterd.w. dry weightEC European CommissionEMEP European Monitoring and Evaluation Program

(Co-operative programme for monitoring and evalua-tion of the long-range transmission of air pollutants in Europe)

EOCl extractable organic chlorinefg femtogram (1 fg = 0.001 pg) H Henry’s law constantHCB hexachlorobenzeneHELCOM Helsinki conventionHxCDD hexachlorinated dibenzo-p-dioxinHxCDF hexachlorinated dibenzofuranHpCDD heptachlorinated dibenzo-p-dioxinHpCDF heptachlorinated dibenzofuranIMO International Maritime OrganizationI-TEF toxic equivalency factors according to NATO/CCMS

1988I-TEQ toxic equivalents according to I-TEFsKAW air – water partition coefficient KOA octanol – air partition coefficientKOW octanol – water partition coefficientl.w. lipid weightmg milligram (1 mg = 0.001 g)NDL-PCBs non-dioxin-like PCBs NERI National Environmental Research Institute

of Denmarkng nanogram (1 ng = 0.001 μg)NODC National Oceanographic Data Centre of GermanyOC organic carbonOCDD octachlorinated dibenzo-p-dioxinOCDF octachlorinated dibenzofuranOM organic matterPAHs polycyclic aromatic hydrocarbonsPCB(s) polychlorinated biphenyl(s)PCDD(s) polychlorinated dibenzo-p-dioxin(s)



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PCDD/F(s) polychlorinated dibenzo-p-dioxin(s) and polychlori-nated dibenzofuran(s); commonly known as dioxins

PCDF(s) polychlorinated dibenzofurans(s)PCP pentachlorophenolPeCDD pentachlorinated dibenzo-p-dioxinPeCDF pentachlorinated dibenzofuranpg picogram (1 pg = 0.001 ng)POC particulate organic carbonPOM polyoxymethylene (material used for passive sampling)POP(s) persistent organic pollutant(s)PUF polyurethane foamPVC polyvinyl chlorideSPM settling (or suspended) particulate matterSTP sewage treatment plantTCDD tetrachlorinated dibenzo-p-dioxinTCDF tetrachlorinated dibenzofuranTDI tolerable daily intake (for humans)TEF toxic equivalency factor; factor indicating the esti mated

toxic potency of an individual DD, DF or dioxin-like compound as compared to 2,3,7,8-TCDD. Note that many different sets of TEFs have been pro posed since the 1980s.

TEQ toxic equivalent; concept developed to express the overall toxicity of a mixture of dioxins and dioxin-like compounds as a single value. The TEQ value is obtained by adding the product of the concentration or amount and the TEF for each toxic compound.

TOC total organic carbonTWI tolerable weekly intake (for humans)WHO World Health OrganizationWHO-TEF toxic equivalency factor according to WHO; two sets

issued, in 1998 and 2006WHO-TEQ toxic equivalents according to one of the WHO-TEF

setsw.w. wet weightμg micrograms (1 μg = 0.001 mg) ΣPCB7 sum of the PCB congeners 28, 52, 101, 118, 138, 153

and 1802,3,7,8-chlorinated the 17 congeners with chlorines at position 2,3,7 and dioxins 8 (2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 1,2,3,4,7,8-

HxCDD, 1,2,3,6,7,8-HxCDD, 1,2,3,7,8,9-HxCDD, 1,2,3,4,6,7,8-HpCDD, OCDD, 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, 2,3,4,7,8- PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, 1,2,3,7,8,9-HxCDF, 2,3,4,6,7,8-HxCDF, 1,2,3,4,6,7,8-HpCDF, 1,2,3,4,7,8,9-HpCDF, OCDF)



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Innehåll

1 SAmmAnfATTning 111.1 Trender och den nuvarande situationen i Östersjöns miljö, samt för den

svenska befolkningen 111.2 Utsläpp från industrin 121.3 Nya mätningar i fält 141.4 Massbalansmodellering 161.4.1 Bassängerna som helhet: 171.4.2 Områden med förhöjda halter (till exempel nära industrier, städer och

förorenad mark) 181.5 Rekommendationer för framtida forskning 19

2 SummAry 212.1 Trends and the current situation in the Baltic Sea environment including the

Swedish population 212.2 Industrial emissions 222.3 New field measurements 242.4 Mass balance modelling 262.4.1 The basins as a whole: 272.4.2 Non-pristine areas (e.g. near industries, cities and contaminated land) 28

2.5 Recommendations for future research 29

3 inTrOducTiOn 31

4 ThE BAlTic SEA EnvirOnmEnT 324.1 Physical environment of the Baltic Sea 324.2 Sediment dynamics in the Baltic Sea 334.2.1 Erosion bottoms 344.2.2 Transportation bottoms 344.2.3 Areas of accumulation 35

5 ThE SElEcTEd POPS And ThEir TrEndS in BAlTic SEA BiOTA 385.1 PCDD/Fs 385.2 PCBs 425.3 HCB 45

6 POPS in ThE BAlTic SEA EnvirOnmEnT 466.1 Distribution between environmental compartments 466.2 Industrial emissions 506.2.1 Previous and current PCDD/F emissions in Europe 506.2.2 Atmospheric emissions of PCDD/Fs in the Baltic Sea area 506.2.3 Emissions of PCDD/Fs in Sweden 516.2.4 Emissions of PCBs and HCB in Sweden 516.2.5 PCDD/F, PCB and HCB emissions from various branches 516.2.6 Emissions of PCDD/Fs and HCB in Denmark and Finland 53



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6.3 POPs in the atmosphere 536.3.1 PCDD/Fs in air – previous measurements 536.3.2 PCDD/Fs in air – new measurements 546.3.3 PCBs and HCB 57

6.4 POPs in soils 586.5 POPs in the water body 596.5.1 Advective water in- and outflow of POPs to the Baltic Sea 596.5.2 Surface water – previous measurements 606.5.3 Surface and deep water – new measurements 60

6.6 POPs in sediments 636.6.1 Sediment-water exchange – new measurements 646.6.2 Levels of POPs in Baltic sediments – new measure ments 666.6.3 Levels and trends of POPs in Baltic sediments 676.6.4 Relation between total organic carbon, black carbon and POP levels 786.6.5 Sediment burial of POPs in the Baltic Sea 806.6.6 The impact of bioturbation on POP fluxes in the sedi ment 82

6.7 Influence of temperature 836.8 Degradation 83

7 mEThOdOlOgy EmPlOyEd TO mOdEl POP BEhAviOur in ThE BAlTic SEA 857.1 Introduction to chemical fate modelling 857.2 The POPCYCLING-Baltic model 867.3 Model parameterization 877.4 PCDD/Fs 887.4.1 Physical-chemical properties 887.4.2 Enhanced sorption to organic carbon 897.4.3 Initial concentrations 897.4.4 Concentrations in air 89

7.5 PCBs 907.5.1 Physical-chemical properties 907.5.2 Enhanced sorption to organic carbon 907.5.3 Initial concentrations 907.5.4 Concentrations in air 91

7.6 HCB 917.6.1 Physical-chemical properties 917.6.2 Initial concentrations 917.6.3 Concentrations in air 92

8 currEnT invEnTOriES, SOurcES, And fATE Of POPS: A mOdEl- And STATiSTicS-BASEd SynThESiS 93

8.1 PCDD/F s 948.1.1 PCDD/F inventories 948.1.2 PCDD/F flows 958.1.3 Evaluation of model predictive power for PCDD/F 988.1.4 Congener pattern analysis of the PCDD/Fs 102



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8.2 PCBs 1068.2.5 PCB inventories 1068.2.6 PCB flows 1068.2.7 Evaluation of model predictive power for PCBs 109

8.3 HCB 1118.3.1 HCB inventories 1118.3.2 HCB flows 1118.3.3 Evaluation of model predictive power for the HCB 113

8.4 Summary and comparison of the behaviour of the POPs 1148.5 Linking POP levels in water and sediment to levels in Baltic Sea fish 115

9 EvAluATiOn Of ThE fuTurE dEvEl OPmEnT Of ThE cOnTAminA TiOn Of ThE BAlTic SEA 117

9.1 PCDD/Fs 1179.2 PCBs 1199.3 HCB 1219.4 Uncertainties in the assessment 122

10 cOncluSiOnS And fuTurE rESEArch 12610.1 New field measurements 12610.1.1 Air and atmospheric deposition measurements 12610.1.2 Surface sediments: 12610.1.3 Surface, deep sea and sediment pore-water: 12710.1.4 Sediment-water exchange: 127

11 rEfErEncE liST 131



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1 SammanfattningDen här rapporten behandlar persistenta organiska föroreningar (POP) i Östersjöns miljö – deras källor, förekomst och omsättning. Den är resultatet av ett uppdrag som Naturvårdsverket fick från Miljödepartementet. Projekt-gruppen bestod av medlemmar från Umeå universitet, Stockholms univer si tet, Naturvårdsverket och Sveriges geologiska undersökning (SGU).

Uppdraget var att bedöma källor, beskriva den rådande situationen och under söka nuvarande flöden av POP i Östersjöns ekosystem. Ämnena som valdes ut för studien var polyklorerade bifenyler (PCB), hexaklorbensen (HCB), polyklorerade dibenso furaner (PCDF) och polyklorerade dibenso-p- dioxiner (PCDD); de två senare allmänt kända som dioxiner (PCDD/F). Substanserna som ingår i dessa ämnes grupper täcker ett brett spektrum av fysikalisk-kemiska egenskaper, och deras beteenden i miljön är därmed repre sentativa för de flesta ämnen som tas upp i Stockholms konventionen. Ämnena har olika källor. PCDD/F bildas oavsiktligt i många olika pro cess er, till exempel vid förbränning och som biprodukter i kemikalie industrin. HCB bildas också vid förbränning, men har dessutom tillverkats och använts som fungicid. PCB är industri kemikalier med ett flertal användnings områden, till exempel som isolerolja. Ytterligare ett skäl för att välja att undersöka PCDD/F och PCB är att halterna av dessa ämnen i fisk överskrider EU:s gränsvärden. Halterna av PCDD/F i miljön har inte minskat i samma utsträckning som hal-terna av till exempel PCB och HCB, vilket har setts som en indikation på att det finns pågående, ännu inte identifierade, utsläpp av PCDD/F.

Tillvägagångssättet som projektgruppen valde var att göra massbalanser för de ut valda föroreningarna genom att använda en modifierad version av en existerande massbalansmodell (POPCYCLING-Baltic). I ett första skede utfördes en osäkerhets analys för att identifiera de viktigaste kunskaps brist -erna. Sedan gjordes mätningar i fält av luft, havsvatten och sediment för att minska dessa osäkerheter.

1.1 Trender och den nuvarande situationen i Östersjöns miljö, samt för den svenska befolkningenÖstersjöns biota: Sedan miljöövervakningen startade på 1970-talet har minsk ande halter av PCB och HCB observerats i biota från Östersjön (sill-grissle ägg från Egentliga Östersjön och strömming från Bottenhavet). För PCDD/F sågs en trend av avtagande TEQ-nivåer på 1970-talet, men minsk-ningen planade ut i mitten av 1980-talet och nivåerna har sedan dess varit tämligen stabila. Ny forskning har visat att från 1990 och 15 år framåt har halterna av vissa dioxin (PCDD)-kongener (till exempel 2,3,7,8-TCDD och OCDD) minskat signifikant i sillgrissleägg från Östersjön, medan stabila eller till och med ökande trender observerats för de flesta andra toxiska PCDD/F-kongener.



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Sveriges befolkning: I början av 2000-talet hade över 10 % av den svenska befolkningen ett dagligt intag av PCDD/F och dioxin-lika PCB som över skred gränsen för tolerabelt dagligt intag rekommenderad av den Europeiska kom-missionen. Forskning har visat att de allmänna nivåerna av PCB och PCDD/F i svensk mat har minskat sedan 1970-talet. I överensstämmelse med dessa observationer har koncentrationerna av PCB, PCDD/F och HCB i bröstmjölk uppvisat en avtagande trend sedan 1970-talet. Tydligt avtagande koncentra-tioner av PCB och HCB har också uppmätts i blodserum från svenska män under perioden 1991 till 2001. Däremot har TEQ-nivåerna i samma befolk-ning inte minskat signifikant mellan 1987 och 2001. Detta tillskrivs stabila eller ökande nivåer av flera furan (PCDF)-kongener.

Ytsediment: Längs Östersjöns kust finns flera tungt industrialiserade områ den, och det har framkommit att den svenska kusten har ett flertal så kallade hot spots för PCDD/F förknippade med industriell aktivitet.

Vad gäller PCDD/F-trenderna i utsjösediment finns det begränsat med information. Medan nivåerna tydligt avtar i utsjöområden i Finska viken på grund av omfattande utsläppsminskningar, är situationen i Bottenhavet och Egentliga Östersjön oklar. Det finns få mätningar, men dessa indikerar att det har skett en minskning sedan 1970-talet. Minskningen har emellertid planat ut i Egentliga Östersjön, och i Bottenhavet verkar halterna av dioxin (PCDD)-kongener minska, medan furan (PCDF)-kongenerna inte visar någon avtagande trend.

För PCB finns det mer data tillgängligt. Under de senaste 10–20 åren har en tydlig minskning av PCB-koncentrationerna observerats i sediment i Botten havet och Egentliga Östersjön. I Bottenhavet minskade koncentra-tionerna i medeltal med en faktor 5.6 och i Egentliga Östersjön med 4.5. Att PCB-koncentrationerna minskar i utsjösediment ligger i linje med de minskande halterna i strömming från Bottenhavet samt i sill/strömming och sillgrissle ägg från Egenliga Östersjön. Det finns även indikationer på minskande HCB -koncentrationer i Östersjösediment.

Det har tidigare föreslagits att den avsevärt lägre PCB-koncentrationen i sedi ment i dag kan vara en följd av ökad sedimentackumulation, orsakad av en ökad frekvens av kraftiga stormar på 1990-talet. Under 2000-talet har man emellertid fortsatt att observera lägre koncentrationer, trots lugnare väder-förhållanden, vilket motsäger denna hypotes. Den uppmätta minsk ning en av PCB-koncentrationer är således mest troligt ett resultat av ett minskat inflöde av PCB till Östersjön.

1.2 Utsläpp från industrinEuropa och Östersjöregionen: Den så kallade ”Europeiska dioxinemissions-inventering en”, som organiserades av den Europeiska kommissionen, om fattade en storskalig inventering av europeiska PCDD/F-utsläpp från 1985 till 2005. I allmänhet har avsevärda reduktioner uppnåtts för industri-ella utsläpp under den studerade tids perioden, och inom en nära framtid



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kommer de icke-industriella utsläppen troligtvis att överskrida utsläppen från industrin. I dag anses sintring av järnmalm vara den viktigaste utsläpps källan, följt av den källa som tidigare var viktigast, förbränning av kommun alt avfall. Målet för EU:s femte aktionsprogram var att minska utsläppen av PCDD/F med 90 % från 1985 till 2005, och slutsatsen blev att detta mål endast kan uppnås för några av källtyperna. Bland länderna runt Östersjön rapporterade Tyskland, Ryssland och Polen de högsta utsläppen av PCDD/F till luft i Östersjö regionen; sammantaget stod de för mer än 95 % av de totala utsläp-pen. Aktuell information om utsläppen i Östersjöregionen är emellertid osäker på grund av brist på data.

PCDD/F-utsläpp i Sverige: I en kartläggning av PCDD/F-källor i Sverige beräknades de totala utsläppen från alla industrisektorer i Sverige vara 160–480 g WHO-TEQ år-1 till avfall/deponi, 16–84 g WHO-TEQ år-1 till luft och 1,9–2,4 g WHO-TEQ år-1 till vatten och sediment. Merparten av utsläp-pen till luft tros fortfarande härröra från förbränning. Bland förbrännings-källorna tros storskalig biobränsleförbränning, mer eller mindre småskalig icke-industriell förbränning (så kallad ”backyard burning”) och förbränning av fossila bränslen vara de dominerande källorna, medan utsläpp från för-bränning av kommunalt avfall nu anses vara obetydliga. Å andra sidan kan avfall (främst aska) från förbränning av kommunalt avfall innehålla betydande mängder PCDD/F. Avfallet deponeras och kan ge upphov till utsläpp till land och vatten.

Naturvårdsverket genomförde nyligen en kartläggning av halterna av diox in er och andra POP i närheten av flera pappers- och massafabriker, ned-lagda eller i bruk. Den fokuserade på POP-halterna i olika miljömatriser (fisk, vatten och sedimenterande partiklar) i närheten och på avstånd från dessa anläggningar. Slutsatsen blev att även om inte alla mätningar visade på för-höjda halter fanns det klara indikationer på lokal miljöpåverkan från några av anläggningarna, och uppföljningsstudier krävdes vid vissa av platserna för att ytterligare klargöra situationen. Nyligen genomförde även Skogs industrierna en dioxinkartläggning som omfattade mätningar vid nio an läggningar. Avloppsvatten, rökgaser, luft och slam analyserades. Några pågående PCDD/ F-utsläpp upptäcktes. Undersökningen fastslog att bidrag av PCDD/F från punktkällorna tillsammans med bidrag från inflöden till recepienterna på ett ungefär kunde förklara skillnaderna i PCDD/F-halter mellan fiskar fångade nära industrierna och på referensplatser.

PCB- och HCB-utsläpp i Sverige: Tidigare har de huvudsakliga utsläppen av PCB till miljön uppkommit under produktion och genom läckage och för-luster från produkter och system som innehåller PCB. I dag är förmod lig en sekundära källor, som avdunstning från mark, ansvariga för en stor del av halterna i luft. PCB-utsläppen i Sverige har beräknats uppgå till 10–31 kg år-1 till avfall/deponi, 0,4–1,1 kg år-1 till luft och 0,1 kg år-1 till vatten och sedi-ment. De största utsläppen bedömdes komma från förbränning och från



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kemikalieindustrin. HCB-utsläppen beräknades till 13–32 kg år-1 till luft, 3–26 kg år-1 till avfall/deponi och 0,01 kg år-1 till vatten och sediment. För-bränning och kemikalieindustrin rapporterades vara ansvariga för den största delen av utsläppen.

1.3 Nya mätningar i fält Mätningar i Östersjön av luft, våt- och torrdeposition, ytsediment, sediment-porvatten samt yt- och djupvatten genomfördes i denna studie. Dessa mät-ning ar var nöd vändiga för att minska osäkerheten i de massbalans beräkning ar som skulle utföras.

Luft och atmosfärisk deposition: Under vintern 2006/2007 togs luft- och bulk depositions prover i Aspvreten (södra Sverige) och Pallas (norra Fin land) för att identifiera de regioner som var de största källorna till atmosfär iskt inflöde av PCDD/F till Östersjön. Då koncentrationerna av PCDD/F i atmo-sfären är högre under vintern än under sommaren, inträffar den största delen av den årliga depositionen under vinterhalvåret. Korta provtag nings tider användes och endast prover där luftmassans ursprung säkert kunde spåras valdes ut för analys av 2,3,7,8-substituerade PCDD/F-kongener. Flera prover samlades också in under sommar halvåret.

Regionen som luftmassorna kunde härröra från delades in i sju sektorer. De högsta koncentrationerna uppmättes i luft som hade passerat över den euro peiska kontinent en. I luft som hade passerat över de brittiska öarna och i luft från norr var koncentrationerna låga. PCDF-koncentrationerna var högre än PCDD-koncentration erna i luft som kom från söder och öster, medan det motsatta förhållandet rådde i luft från väst-nordväst. Variationen i koncent-rationerna var mycket lägre inom en sektor än mellan sektorer.

Var PCDD/F som våtdeponerades i Östersjön under de sex månader som studien ägde rum (d v s under vintern) härrörde från beräknades också. Resultaten visade att ~40 % av våtdepositionen av PCDD/F hade sitt ur sprung i den sydvästra sektorn, medan ~20 % kom från luft från den södra sektorn. Den partikelbundna torrdeposi tion en av PCDD/F förväntas vara liten jämfört med våtdepositionen under de för hållanden som råder i Europa.

Våt- och torrdepositionen av PCDD/F som uppmättes under samma tid uppgick till ~200 pg WHO-TEQ m–2 eller 1,1 pg WHO-TEQ m–2 dag–1. Beräkning ar av ursprung et till den gasformiga depositionen till Östersjön indikerar att bidragen från de olika regionsektorerna var jämförbara.

Detta delprojekt visar tydligt att halterna av PCDD/F över Östersjön och den atmosfär iska depositionen av PCDD/F till Östersjön huvudsakligen bestäms av luftströmmar nas rörelsemönster. Dessa kan variera betydligt från år till år, och därmed också depositionen. För att kunna göra en bättre extra polering av resultaten i tid och rum undersöktes korrelationen mellan PCDD/ F-koncentrationer och atmosfärsparametrar som är enklare/mer rutin-artade att bestämma. En stark korrelation mellan koncentra tion en av partikel-bundna PCDD/F och koncentrationen av sotkol (så kallade soot carbon eller black carbon, BC) upptäcktes, med en korrelationskoefficient (r2) på 0,80.



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Ytsediment: Kustnära och utsjösediment från Egentliga Östersjön och Botten-havet samlades in under 2007 och dess innehåll av PCDD/F, PCB och HCB analyserades. För att få ett stort dataset inkluderades även data från andra studier i utvärderingen.

I allmänhet var sedimentens koncentrationer av PCDD/F, normaliserade till sedi ment torrvikt, ungefär en faktor 2-3 högre i Egentliga Östersjön än i Bottenhavet. Om de däremot normaliserades till organiskt kol (OC), med hänsyn till att sediment i Egentliga Östersjön har en avsevärt högre halt totalt organiskt kol, fanns det inga skillnader mellan de två bassängerna. I likhet med detta var koncentrationerna av ΣPCB7, normaliserade till torrvikt, i medel 4–5 gånger lägre i Bottenhavet än i Egentliga Östersjön. Denna skill-nad blev mindre tydlig om data normaliserades till OC. Koncentration erna av HCB verkade inte skilja sig nämnvärt åt mellan sediment från Botten havet och Egentliga Östersjön.

Variationen i halterna av PCDD/F och PCB i utsjösediment visade sig till stor del kunna förklaras med variationer i halten organiskt kol. Innehållet av OC förklarade 80–90 % av variationen i PCDD/F och PCB, medan innehåll et av sotkol (black carbon) bara svarade för 50–70 % av variationen. En låg korrelation mellan OC-innehåll och HCB-koncentration observerades (r2=0,28).

Ytvatten, djupvatten och sedimentporvatten: Koncentrationen av så kallade fritt lösta (freely dissolved) POP i yt- och djupvatten mättes genom använd-ning av passiva provtagare (av typen POM). Provtagarna utplacerades på olika platser i Egentliga Östersjön och Bottenhavet under våren och somma-ren 2007, och hämtades in efter tre månader. Medelkoncentrationen av dioxin i kustnära och utsjövatten var 1,1 respektive 2,5 pg WHO-TEQ m–3. De mot-svarande ΣPCB7-koncentrationerna var 5,8 och 24 ng m–3. Det fanns inga signifikanta skillnader i koncentrationer mellan yt- och djupvatten i varken Egentliga Östersjön eller Bottenhavet.

Koncentrationerna i sedimentporvatten från samma platser i Östersjön som vatten proverna togs på bestämdes genom användning av passiva prov-tagare (av typen POM) i skaktest. Koncentrationerna av POP i porvatten samvari erade i allmänhet med koncentrationerna i sediment.

Utbyte mellan sediment och vatten: För de kustnära stationerna var medel-värdet av kvoten mellan koncentrationerna i porvatten och överliggande vatten 3,6 ± 1,6 för PCDD/F och 1,0 ± 0,6 för PCB. Detta indikerar att de kustnära sedimenten fungerar som en PCDD/F-källa för överliggande vatten, medan det inte finns någon koncentra tions gradient för PCB och de kustnära sedimenten inte utgör vare sig betydande sänkor för eller källor till PCB. För PCDD/F i djupvatten var kvoten 1,1 ± 0,5, vilket tyder på att det inte finns en koncen-trationsgradient och att sedimenten i utsjöområden varken utgör betydande sänkor eller källor för ett diffusivt utbyte av lösta PCDD/F. För PCB var denna kvot 0,7 ± 0,3, vilket antyder att koncentra tions gradienten för PCB är liten. Gradientens riktning indikerar att sedi menten kan vara en sänka för PCB.



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Mätningarna i sediment och vatten möjliggjorde beräkningar av fördelnings-koefficienter mellan totalt organiskt kol och vatten (KOC) för dessa Öster sjö -sediment. Totalt organiskt kol innefattar amorft organiskt kol (amorphous organic carbon, AOC) och sotkol (black carbon, BC). Den observerade bind-ningen till AOC+BC i Östersjösediment var starkare än vad bindningen till enbart AOC beräknades vara utifrån standardmetoder för riskbedömning. Detta indikerar att de ekotoxikologiska riskerna från PCB och PCDD/F i Östersjösediment är 10–30 gånger lägre än vad uppskattningen skulle bli om riskbedömingen baserades på enbart bindning till AOC.

1.4 Massbalansmodellering För modelleringen användes de nya data som presenterades i föregående avsnitt samt data från en omfattande litteraturstudie. Beräkningarna genom-fördes för hela Öster sjön, men den detaljerade utvärderingen av resultaten fokuserade på de två största bassängerna, Bottenhavet och Egentliga Öster-sjön. Arbetet utfördes i flera steg:

1) Den nuvarande förekomsten av och uppehållstiden för de utvalda föro rening arna i Östersjöns miljö beräknades.

2) Den nuvarande storleken på sänkor, källor och flöden av förorening ar i och mellan bassängerna i Östersjön uppskattades.

3) Modellens tillförlitlighet utvärderades.4) Modellen användes för att utvärdera de framtida föroreningsnivå-

erna i Östersjöns miljö. Avsikten med dessa simuleringar var att under söka den möjliga effekten av minskade koncentrationer i atmosfären på den framtida koncentrationen av dessa föroreningar i Östersjön.

Nedanstående tabell sammanfattar de huvudsakliga resultaten av mass balans-modellering en.

hcB PcB Pcdd/f

Nuvarande situation i Östersjön

Mängd (vatten + ytsediment*) 540 kg 2800 kg (ΣPCB7) 10 kg TEQ

% av mängd i vatten 40 9 4

Uppehållstid (år)** 0,34 1,8 11

Största källa Atmosfär Atmosfär Atmosfär

Största sänka Atmosfär Atmosfär Begravning i sediment

Framtida utveckling i Östersjöns ytvatten

Scenario 1***

Botten havet Oförändrat Oförändrat År 2025: ~40 % lägre än nuvarande nivå

Egentliga Östersjön Oförändrat Oförändrat År 2025: ~15 % lägre än nuvarande nivå

Scenario 2**** Botten havet År 2025: ~90 % lägre än nuvarande nivå

År 2025: ~90 % lägre än nuvarande nivå


Egentliga Östersjön År 2025: ~90 % lägre än nuvarande nivå



*Översta 2 cm; **Bottenhavet; *** Oförändrade koncentrationer i atmosfären; ****Koncentrationerna i atmosfären minskade linjärt till 10 % av initialvärdet under en tioårsperiod.



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De huvudsakliga slutsatserna som kan dras från massbalansmodelleringen, osäkerhetsanalyserna, mönsteranalyserna och jämförelser med andra studier och mätdata finns summerade nedan.

1.4.1 Bassängerna som helhet:• Atmosfären är den dominerande yttre källan till HCB och PCB i

Östersjön, och koncentrationerna av HCB och PCB i vattenmassan kommer att reagera snabbt när koncentrationerna i atmosfären ändras. Dessa slutsatser ansågs vara högst säkra för HCB och myck et säkra för PCB. Den atmosfäriska depositionen av dessa ämnen är mycket större än det beräknade inflödet från floder och kända direkta inflöden. Bra överensstämmelse mellan modellerade och uppmätta koncentrationer i vatten och sediment över en tidsserie stöder denna slutsats. Inflödet till vattenmassan från atmosfären är tydligt större än inflödet från sedimenten, även när hänsyn tas till osäkerheter i modellen. Följ aktligen fungerar inte sedimenten som en buffert för vattenmassan mot yttre påverkan från luft. Dessutom visar miljö övervak ningsdata att koncentration erna av PCB i ytsedi-ment har minskat parallellt med koncentrationerna i luft.

• Atmosfären är den största källan till PCDD/F i Bottenhavet och Egentliga Östersjön. Denna slutsats anses vara ganska säker. Modellerings resultaten tyder på att inflödena från atmosfären är större än inflödena från andra kända källor. De indikerar också att inflödena från atmosfären är tillräckligt stora för att förklara dagens halter av PCDD/F i vattenmassan. Dessutom indikerar analysen av kongenermönstret att PCDD/F i utsjösediment i Bottenhavet och Egentliga Östersjön huvudsakligen har atmosfäriskt ursprung.

• Koncentrationerna av fritt lösta PCDD/F i Bottenhavet och Egentliga Östersjön minskar om koncentrationerna av PCDD/F i atmosfären förblir på dagens nivåer. Denna slutsats anses vara ganska säker. Processen som kontroll erar tidsfördröjningen mellan minskningen av koncentrationerna i luft och minskningen i vatten är transporten av PCDD/F från sediment till vatten. Koncentrationerna i ytsediment har en responstid på flera årtionden på för ändringar i inflödet av föroreningar till Östersjön. Detta beror på den långa uppehållstiden PCDD/F har i Östersjöns system. Därför reagerar också flödet från sediment till vattenmassa långsamt på förändringar. Eftersom den atmo sfär iska depositionen av PCDD/F har minskat under de sista år tiondena kommer det troligen att ske en successiv minskning av de fritt lösta koncentrationerna under de kommande årtiondena. Detta är inte helt säkert eftersom det kan finnas andra, ännu inte identifierade, stora källor till PCDD/F som inte har mins-kat de senaste åren. En annan osäkerhet är kopplad till storleken på den förutsagda minsk ningen. Detta kommer att bero på i) storleken på minskningen i in flödet från atmosfären under de senaste årtiondena



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ii) uppehålls tiden för PCDD/F i bassängerna. Scenariot för minsk-ning av PCDD/F-koncentrationerna i luft under de senaste 20 åren baseras på empi riska observationer och bedöms vara ganska tillför-litligt.

• En minskning av PCDD/F-koncentrationerna i luft kommer att skynda på minskningen av koncentrationerna av fritt lösta PCDD/F i Bottenhavet och Egentliga Östersjön. Denna slutsats anses vara ganska säker. Detta är en konsekvens av att den atmosfäriska de positionen är den dominerande källan till PCDD/F i dessa bassänger. Den kvarvarande osäkerheten beror på möjligheten att det finns andra stora, oidentifierade, källor.

• Hastigheten med vilken koncentrationerna av fritt löst PCDD/F minskar kommer att vara som modellen förutsagt. Denna slutsats anses vara ganska osäker. Hastigheten på minskningen i Östersjöns ytvatten misstänks vara överskattad på grund av den enkla modell-strukturen i POPCYCLING-Baltic. Minskningshastigheten i de övriga vattenmassorna är tätt kopplad till uppehållstiden för PCDD/F, vilken i sin tur är kopplad till modellens antagande an gående ytarea och det sedimentdjup som står i kontakt med vatten massan, liksom hastigheten med vilken föroreningarna begravs i sedimentet. Även om dessa antaganden har en empirisk grund är de osäkra, och det har ännu inte varit möjligt att utvärdera deras till förlitlighet, till exempel genom att mäta elimineringshastigheten för mycket hydrofoba ämnen i dessa vattenmassor. Dessutom kan uppehålls tiden påverkas av störningar i miljön, som kraftiga stormar, vilka kan resuspendera ackumulerat sediment och sålunda göra att begravda PCDD/F åter kommer i omlopp

• Hastigheten på minskningen av koncentrationerna i fisk kommer att vara parallell med hastigheten på minskningen av de fritt lösta koncentrationerna i vattenmassorna. Denna slutsats anses vara myck et osäker. Mätningarna på sill/strömming under de senaste 15 åren har visat att så inte behöver vara fallet. Minskningen i tillväxt hastighet för sill/strömming tros ha orsakat en större bioackumuler ing av PCDD/F, med konsekvensen att koncentratio-nerna av PCDD/F i sill/strömming inte minskade under denna period, trots att de fritt lösta koncentrationerna (förmodligen) minskade. Det är således möjligt att ekossystemförändringar kan sakta ner eller öka den förväntade responsen hos fisk på en minsk-ning av de fritt lösta koncentrationerna.

1.4.2 Områden med förhöjda halter (till exempel nära industrier, städer och förorenad mark)• Analyseravytsedimentlängsdensvenskakustenharvisatattmönst

ret av PCDD/F i sediment från områden nära urbaniserade eller industrialiserade zoner ofta skiljer sig signifikant från mönstret i



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atmosfären. Receptor modellering har visat sig vara ett effektivt redskap för att spåra och kvanti fiera PCB- och PCDD/F-källor, så kallad källfördelning (source apportioning). En receptormodellering-studie av PCDD/F-källor i Öster sjön pågår för närvarande. Preliminära resultat stöder de observationer som gjorts i denna undersökning, nämligen att det atmosfäriska inflödet är större för utsjöområden medan kustnära områden ofta har ett mer komplext bidrag från olika källor, och att icke-atmosfäriska källor kan vara betydande lokalt/regionalt.

1.5 Rekommendationer för framtida forskningFöroreningssituationen i Östersjön fortsätter att vara ett problem, speciellt vad gäller PCDD/F och dioxinlika PCB. Halterna av dessa ämnen i fisk gör att det finns restriktioner för försäljningen av fisk från Östersjön.

Även om detta projekt har bidragit till en större förståelse av förorenings-situationen i Östersjön, finns det ett flertal områden där kunskap saknas eller är osäker. Det är främst för PCDD/F som det finns stora osäkerheter. De största kunskapsbristerna inkluderar:• NuvarandeutsläppavPCDD/Ftillluft.Dennaundersökninghar

tyd ligt visat att problemen med PCDD/F i Östersjön på det hela taget orsakas av långväga lufttransport, där källor i kontinentala Europa är viktiga. Följ aktligen är det viktigt att fastställa huruvida dagens bild av PCDD/F-utsläpp stämmer med det atmosfäriska inflödet av PCDD/F till Östersjön.

• NuvarandeutsläpptillÖstersjönsvatten.Dessainkluderarinflödenmed sötvatten, industriutsläpp och läckage från förorenad mark. Det finns stora osäkerheter i alla dessa kategorier. Det är troligt att de främst påverkar föroreningssituationen i kustnära områden.

• Dettyckssomomdioxinerna(PCDD)minskarmeränfuranerna(PCDF) i flera matriser, inklusive biota från Östersjön, blodserum från svenska män, och möjligen också i Östersjösediment. Börjar utsläppen domineras av PCDF istället för PCDD, eller beror detta skifte på andra faktorer?

• TidstrenderförPCDD/FkoncentrationeriÖstersjösedimentoch-luft. Dessa behövs för att utvärdera resultaten av modelleringar.

• HalterochföroreningaravPCDD/FochdioxinlikaPCBiÖstersjönsytsediment. Stora områden av Östersjön har aldrig undersökts. Analys av föroreningsmönstret i ytsediment kan användas för att spåra källor. För närvarande finns det bara data för källfördelning i begränsade områden av Östersjön (Sveriges kust).

• Enstörreförståelseavytsedimentensackumuleringochomblandning. Detta är nödvändigt för att få fram mer tillförlitliga uppskatt-ningar av hur lång tid det tar för Östersjön att svara på förändringar i inflöden av PCDD/F.



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• Enstörreförståelseavföroreningsdynamikenmellansediment,vatten och biota. Varför ser vi en variation i tid och rum hos förorenings nivåerna i fisk i Östersjön? Beror det på biologiska faktorer (till exempel tillväxthastighet och födomönster)? Hur viktiga är föroreningsnivåerna i sediment för nivåerna i biota?



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2 SummaryThis report deals with sources, transport, reservoirs and fate of selected persistent organic pollutants (POPs) in the Baltic Sea environment. It is the result of a commission that the Swedish Environmental Protection Agency was given by the Swedish Ministry of Environment. The project group in cluded members from Umeå University, Stockholm University, the Swedish Environmental Protection Agency and the Geological Survey of Sweden.

The commission was to estimate sources, describe the present situation, and investigate the current fluxes of persistent pollutants (POPs) in the Baltic Sea ecosystem. The compounds that were chosen for the study were poly-chlorinated biphenyls (PCBs), hexachlorobenzene (HCB), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). These classes of compounds represent a broad range of physical-chemical pro-perties, and hence their environmental behaviour encompasses the spectrum of most chemicals listed in the Stockholm Convention. The sources of the com-pounds differ. PCDD/Fs are formed unintentionally in a number of different processes, e.g. during combustion and as by-products in the chemical industry. HCB is also formed during combustion, but in addi tion it was produced and used as a fungicide. PCBs are industrial chemicals with a wide range of uses, e.g. as insulating fluids. A further reason for se lecting PCDD/Fs and PCBs is that currently, the levels of these compounds in fish exceed the limit for mar-keting of fish within the EU. The environ mental levels of PCDD/Fs have not decreased to the same extent as e.g. PCBs and HCB, which has been interpre-ted as an indication that there are ongoing, not yet identified, PCDD/F emis-sions.

The approach chosen by the project group was to calculate mass balances for the selected POPs by using a modified version of an existing mass balance model (POPCYCLING-Baltic). In a first stage, an uncertainty analysis was conducted to identify the most important knowledge deficits. Thereafter field measurements in air, sea water and sediments were under taken to reduce these uncertainties.

2.1 Trends and the current situation in the Baltic Sea environment including the Swedish population Baltic biota: Decreasing trends of HCB and PCB concentrations have been observed in Baltic biota (guillemot egg from the Baltic Proper and her-ring from the Bothnian Sea) since the monitoring started in the 1970s. For the PCDD/Fs, a decreasing trend of the TEQ levels was seen in the 1970s, but the decrease has levelled out since the mid-1980s and TEQ levels have re mained rather stable since then. Recent research has shown that from 1990 and 15 years onward, some dioxin (PCDD) congener levels have decreased significantly in Baltic guillemot egg (e.g. 2,3,7,8-TCDD and OCDD), while stable or even increasing trends were observed for most other toxic PCDD/F congeners.



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Swedish population: In the early 2000s, >10% of the Swedish population had a daily intake of dioxin and dioxin-like PCBs above the tolerable daily intake (TDI) limit recommended by the European Commission. It has been shown that the general levels of PCBs and PCDD/Fs in Swedish food have decreased since the 1970s. In accordance with these observations, the con centrations of PCBs, PCDD/Fs and HCB in human milk have shown de creasing trends since the 1970s. Distinct decreasing concentrations of PCBs and HCB have also been observed in blood serum from Swedish men during the period 1991– 2001. In contrast, the TEQ levels in the same population did not decrease significantly between 1987 and 2001. This is mostly attrib uted to stable or increasing trends of several of the furan (PCDF) congeners.

Surface sediments: The coast of the Baltic Sea includes several heavily industri-alized zones, and it has been shown that the Swedish coast includes a number of PCDD/F hot spots associated with industrial activity.

There is limited information on PCDD/F trends in Baltic offshore sedi-ments. While levels are clearly declining in offshore areas of the Gulf of Finland due to extensive reduction of emissions, the situations in the Both nian Sea and the Baltic Proper are unclear. Measurements are few, but these indi-cate that there has been a decrease since the 1970s. However, in the Baltic Proper, the decrease seems to have levelled off, and in the Bothnian Sea, the concentrations of dioxin (PCDD) congeners appear to be declining, while the furan (PCDF) congeners do not show a declining trend.

For the PCBs, more data are available. During the last 10–20 years, a dis tinct decrease of PCB concentrations has been observed in sediments in the Bothnian Sea and the Baltic Proper. In the Bothnian Sea, the decrease was on average a factor of 5.6 while in the Baltic Proper it was a factor of 4.5. These decreasing PCB concentrations in offshore sediments are in line with the decreasing trends in herring from the Bothnian Sea and herring and guille-mot egg from the Baltic Proper. There are also indications of decreas ing HCB concentrations in Baltic sediments.

It has previously been suggested that the distinctly lower PCB concentra-tions in sediments today could be caused by an increased bulk sediment accu-mulation rate as a result of an increased frequency of severe storms in the 1990s. However, the lower concentrations have continued to be observ ed through the 2000s despite calmer conditions, refuting this hypothesis. Hence, the registered decrease in PCB concentration is most likely the result of decreased input to the Baltic Sea.

2.2 Industrial emissionsEurope and the Baltic area: The so called “European Dioxin Emission Inventory”, organised by the European Commission, included a large scale inventory of European PCDD/F emissions from 1985 to 2005. In general, considerable emission reduction has been achieved for the industrial sources over the studied period, and in the near future the non-industrial emission



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sources will probably exceed those from industrial installations. Today, iron ore sintering is believed to be the most important emission source type fol-lowed by the former “No. 1”, municipal waste incineration. The goal of the 5th Action Programme was to reduce PCDD/F emissions by 90% from 1985 to 2005, and it was concluded that this goal can only be achieved for some source types. Among the Baltic countries, the highest air emissions of PCDD/ Fs to the Baltic Sea area were reported by Germany, Russia and Poland, which together contributed more than 95% of the total emissions. However, current data on emissions in the Baltic Sea region are uncertain due to missing information.

PCDD/F emissions in Sweden: In a survey of PCDD/F sources in Sweden, the total annual emission from all industrial sectors in Sweden was esti mated to be 160–480 g WHO-TEQ yr-1 to waste/landfills, 16–84 g WHO-TEQ yr-1 to air and 1.9–2.4 g WHO-TEQ yr-1 to water and sediments. Most emissions of PCDD/Fs to air are still believed to originate from combustion. Among the combustion sources, it is believed that large scale bio-fuel incin eration, back-yard burning and combustion of fossil fuels are the dominant sources, while emissions from municipal waste incineration are today con sidered insignifi-cant. On the other hand, waste from municipal waste incin eration (mainly ash) contains significant amounts of PCDD/Fs. The waste is deposited at land-fills and may cause emissions to soil and water.

The Swedish EPA recently conducted a survey of the levels of dioxins and other POPs in the vicinity of a number of operating and closed pulp and paper plants. It focused on POP levels in various environmental compart ments (fish, water and settling particulate matter) at sites near and distant from these sites. It was concluded that, although not all measurements showed elevations, there are clear indications of local environmental im pacts from some of the mills, and follow-up studies are needed at selected sites to further elucidate the situation. The Swedish Forest Industries Fed eration also recently conducted a dioxin survey including measurements at 9 mills. Waste water, flue gases, air and sludge were analysed. Some current PCDD/F emissions were detected. It was stated that the contributions of PCDD/F from the point sources together with tributary inflows to the re ceiving recipients could roughly explain the differences in PCDD/F levels in fish caught near the industries compared to reference locations.

PCB and HCB emissions in Sweden: Previously, the primary emissions of PCBs to the environment occurred during production and through leakage and losses from PCB-containing products and systems. Today, secondary sources, such as re-volatilisation from soils, probably contribute a large part of the levels in air. Emissions of PCBs in Sweden have been estimated to be 10–31 kg yr-1 to waste/landfills, 0.4–1.1 kg yr-1 to air and 0.01 kg yr-1 to water and sediments. The largest emissions were estimated to originate from com-bustion and from the chemical industry. The emissions of HCB were estima-



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ted to be 13–32 kg yr-1 to air, 3–26 kg yr-1 to waste/landfills and 0.01 kg yr-1 to water and sediment. Combustion sources and the chemical indus try were reported to be responsible for the largest emissions.

2.3 New field measurementsField measurements of Baltic air, bulk deposition, surface sediment, sedi ment pore-water and surface and deep sea water were undertaken within this study. These measurements were needed for reduction of the uncertainties in the mass balance calculations that were to be done.

Air and atmospheric deposition: During the winter of 2006/2007, air and bulk deposition samples were collected in Aspvreten (southern Sweden) and Pallas (northern Finland) in order to identify the major source regions for atmosphe-ric input of PCDD/Fs to the Baltic Sea. Note that atmospheric con centrations of PCDD/Fs are much higher during winter than during summer, so that most of the annual deposition occurs during the winter half-year. Short sampling times were employed and only samples with stable air mass back-trajectories were selected for the analysis of the 2,3,7,8-substituted PCDD/F congeners. Several samples were also collected during the summer half-year.

The region for air mass origin was divided into 7 compass sectors. The highest concentrations were found in air that had passed over the European continent. In air that had passed over the British Isles and air from northerly directions, the concentrations were low. The PCDF concentrations were higher than the PCDD concentrations in air from the south and east, while the opposite was true in air from the west-northwest. The variability in the con-centrations was much lower within a sector than it was between the sec tors.

The origin of the wet deposition of PCDD/Fs to the Baltic Sea was esti-mated for the 6-month study period (winter). The results indicate that ~40% of the wet deposition of PCDD/F derived from air that originated from the southwest sector, while ~20% derived from air from the south sector. The dry particle-bound deposition of PCDD/Fs is expected to be small compared to wet deposition under European conditions.

The PCDD/F bulk deposition measured during the same period amounted to ~200 pg WHO-TEQ m–3 or 1.1 pg WHO-TEQ m–2d–1. Estimates of the ori-gin of the gaseous deposition to the Baltic Sea indicate that the contributions from the various compass sectors were quite comparable.

This subproject clearly indicates that the levels of PCDD/Fs over the Baltic Sea and the atmospheric deposition of PCDD/Fs to the Baltic Sea are pri-marily determined by the air flow pattern. The air flow pattern can vary con-siderably from year to year, and hence so may the deposition. In order to be able to better extrapolate these results in space and time, correlations be tween the PCDD/F concentrations and the concentrations of more easily/ routinely determined atmospheric parameters were explored. A strong cor relation bet-ween the concentration of particle-bound PCDD/F and the soot carbon con-centration was found, with a correlation coefficient (r2) of 0.80.



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Surface sediments: Offshore and coastal Baltic Proper and Bothnian Sea sedi-ments were sampled during 2007 and analysed for PCDD/Fs, PCBs and HCB. To obtain an extensive data set, data from other studies were also in cluded in the evaluation.

In general, the PCDD/F concentrations in sediment, when normalised to dry weight (d.w.), were approximately a factor 2–3 times higher in the Baltic Proper than in the Bothnian Sea. However, if normalised to organic carbon (OC), taking into account the substantially higher TOC content in the Baltic Proper sediments, there were no differences between the two basins. Simi larly, the dry weight normalised ΣPCB7 concentrations were on average 4–5 times lower in the Bothnian Sea than in the Baltic Proper. This difference was less pronounced if the data were normalised to OC. The HCB concen trations seemed to be quite similar in Bothnian Sea and Baltic Proper sedi ments.

It was shown that the variability in PCDD/F and PCB levels in offshore sediments could largely be explained by variation in organic carbon (OC) levels, while a low correlation was observed between OC content and HCB concentration.

Surface, deep sea and sediment pore-water: The freely dissolved concen-trations of POPs in deep water and surface water were measured by using passive sampler strips (POM). The samplers were deployed at different sites in the Baltic Proper and Bothnian Sea during the spring-summer of 2007 and harvested after three months. The average dioxin concentrations were 1.1 and 2.5 pg WHO-TEQ m–3 in coastal and offshore waters, respectively. The corre-sponding ΣPCB7 concentrations were 5.8 and 24 ng m–3. There were no signi-ficant concentration differences between surface and deep sea water in either the Baltic Proper or the Bothnian Sea.

Pore-water concentrations in Baltic sediments from the same sampling sites as the water samples were determined by employing passive samplers (POM) in a batch shaking test. The POP concentrations in the pore-waters generally co-varied with the sediment concentrations.

Sediment-water exchange: For the coastal stations, the average ratio of the pore-water/overlying water concentration was 3.6 ± 1.6 for the PCDD/Fs and 1.0 ± 0.6 for the PCBs. This indicates that the coastal sediments act as a source of PCDD/Fs to the overlying water, whereas for the PCBs there is no concentration gradient and the sediments in the coastal areas neither consti-tute strong sinks nor strong sources of PCBs. For PCDD/Fs in deep water, the ratio was 1.1 ± 0.5, which suggests that there is no concentration gradi ent and that the sediments in the offshore areas constitute neither strong sinks nor strong sources for the diffusive exchange of dissolved PCDD/Fs. For PCBs this ratio was 0.7 ± 0.3, suggesting that there is only a slight con centration gradient for PCBs. The direction of the gradient indicates that the sediments could be a PCB sink.



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The sediment and water measurements allowed calculation of the total orga-nic carbon–water partition coefficients (KOC) for these Baltic Sea sedi ments, where total organic carbon refers to amorphous organic carbon (AOC) and soot (black) carbon (BC). The observed binding to AOC+BC in Baltic Sea sediments was stronger than the binding to AOC alone predicted using stan-dard risk assessment methodologies. This indicates that the ecotoxicological risk from PCBs and PCDD/F in the Baltic Sea sediments is 10–30 times lower than would be predicted if the risk assessment would be based on sorption to AOC alone.

2.4 Mass balance modellingFor the modelling, the new data presented in the previous section and data from an extensive literature search were used. The calculations were con-ducted for the whole Baltic Sea, but the detailed assessment of the results focused on the two largest basins, the Bothnian Sea and the Baltic Proper. The work was conducted in several steps:

1) The current inventory and residence time of the selected contami-nants in the Baltic Sea environment was estimated.

2) The current magnitude of the sources, sinks, and flows of contami-nants in and between the basins of the Baltic Sea was assessed.

3) The reliability of the model was evaluated.4) The model was applied to evaluate the future development of the

contaminant levels in the Baltic Sea environment. The purpose of these simulations was to investigate the potential impact of re duced atmospheric concentrations on the future concentrations of these contaminants in the Baltic Sea environment.

The table below summarises the principal outcome of the mass balance modelling.

hcB PcBs Pcdd/fs

current situation in the Baltic Sea

Inventory (water + surface sediment*) 540 kg 2 800 kg (ΣPCB7) 10 kg TEQ

% of inventory in water 40 9 4

Residence time (yr)** 0.34 1.8 11

Major source Atmosphere Atmosphere Atmosphere

Major sink Atmosphere Atmosphere Sediment burial

future development in Baltic surface water

Scenario 1***

Bothnian Sea Unchanged Unchanged At year 2025: ~40% below current level

Baltic Proper Unchanged Unchanged At year 2025: ~15% below current level

Scenario 2**** Bothnian Sea At year 2025: ~90% below current level

At year 2025: ~90% below current level


Baltic Proper At year 2025: ~90% below current level



*Upper 2 cm; **Bothnian Sea; *** Unchanged atmospheric concentrations; ****Atmospheric concen-trations were linearly reduced to 10% of the initial values over a 10-year period



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The main conclusions that can be drawn from the mass balance modelling, the uncertainty analyses, the pattern analyses and comparisons with other studies and measurement data are summarised below.

2.4.1 The basins as a whole:• The atmosphere is the dominant external source of HCB and PCBs

to the Baltic Sea, and the concentrations of HCB and PCBs in the water column will react quickly to changes in the concentrations in the atmosphere. These conclusions were considered to be highly certain for HCB and very certain for PCBs. The atmospheric deposi-tion of these chemicals is much larger than the estimated riverine inputs and known direct inputs. Good agreement between predicted and measured concentrations in water and sediment including time trends supports this. The input to the water column is clearly larger from the atmosphere than from the sedi ments, even given the uncer-tainties in the model. Consequently, the sediment reservoir does not significantly buffer the water column against changes in the external forcing from air. Furthermore, the monitoring data show that the PCB concentrations in surface sediments have de creased in parallel to the air concentrations.

• The atmosphere is the major source of PCDD/Fs to the Bothnian Sea and the Baltic Proper. This conclusion is considered to be quite certain. The modelling results indicate that the inputs from the atmosphere are larger than the inputs from other known sources. They also indicate that the atmospheric inputs are sufficiently large to explain the current levels of PCDD/Fs in the water column. Furthermore, the congener pattern analy sis indicates that the PCDD/ Fs in offshore surface sediments of the Both nian Sea and the Baltic Proper are largely of atmospheric origin.

• The freely dissolved PCDD/F concentrations in the Bothnian Sea and the Baltic Proper decrease if the PCDD/F concentrations in the atmosphere remain at current levels. This conclusion is considered to be quite certain. The process determining the lag between the decrease in the concentra tions in air and in water is the transfer of PCDD/Fs from surface sedi ment to water. The concentrations in the surface sediment respond over a period of several decades to changes in the rate of input due to the long residence time of the PCDD/Fs in the Baltic Sea system. Thus the flow of PCDD/Fs from the sediment into the water column also responds over a time period of decades to changes in the rate of input. Since the atmo spheric deposition of PCDD/Fs has decreased over the last decades, there is likely to be an ongoing decrease of the freely dissolved concentrations in the next decades. The major uncertainty associated with this conclu sion is that there could be other unidentified large sources of PCDD/Fs that have not decreased over recent years. There is further uncertainty



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associated with the magnitude of the predicted decrease. This will depend on i) the magnitude of the decrease in the atmospheric input over the last decades; ii) the residence time of the PCDD/Fs in the basins. The sce nario for the decrease in PCDD/F concentrations in air over the last 20 years is based on empirical observations and is judged to be quite reli able.

• Reducing the PCDD/F concentrations in the atmosphere will accele-rate the reduction in the freely dissolved PCDD/F concentrations in the Both nian Sea and the Baltic Proper. This conclusion is considered to be quite certain. This is a consequence of atmospheric deposition being the domi nant source of PCDD/Fs to these basins. The residual uncertainty lies in the possibility that there are other major unidenti-fied sources.

• The rate of decrease of the freely dissolved PCDD/F concentrations will be as predicted. This conclusion is considered to be quite uncer-tain. The rate of decrease in the surface water of the Baltic Sea is suspected to be overestimated due to the simple structure of the POPCYCLING-Baltic model. The rate of decrease in the other water bodies is closely linked to the PCDD/F residence time, which is in turn linked to the assumptions in the model regarding the surface area and mixed depth of the surface sediments as well as the sedi-ment burial rates. Although these assump tions have an empirical basis, they are uncertain, and it has not yet been possible to evaluate their correctness, e.g. by measuring the elimination rate of very hydrophobic chemicals from these water bodies. In addition, the residence time may be modified by environmental disturbances such as intense storms which resuspend accumulation sediments and thus bring buried PCDD/Fs back into circulation.

• The rate of decrease in the concentrations in fish will parallel the rate of decrease in the freely dissolved concentrations in the water bodies. This conclusion is considered to be very uncertain. The observations of levels in herring over the last 15 years have shown that this need not be the case. The decrease in the rate of growth of the herring is believed to have resulted in stronger bioaccumulation of the PCDD/Fs, with the con sequence that the PCDD/F concentrations in herring did not decrease during this period, although the freely dissolved concentrations (pre sumably) did. Hence it is possible that changes in the ecosystem may slow down or accelerate the expected response of the fish to a decrease in the freely dissolved concentrations.

2.4.2 non-pristine areas (e.g. near industries, cities and contaminated land)• AnalysesofsurfacesedimentsalongtheSwedishcoasthasshown

that the PCDD/F patterns in sediments sampled near urbanised and industri alised areas often differ significantly from atmospheric patterns. For source apportioning, receptor modelling has been



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shown to be an effect ive tool for tracing and quantifying PCB and PCDD/F sources. A recep tor modelling study for PCDD/Fs sources in the Baltic Sea area is under way. Preliminary results support the findings in this study, namely that the atmospheric inputs are large for offshore sites, while in coastal zones, the contribution from various sources is often much more complex and non-atmospheric sources can be significant on a local/regional scale.

2.5 Recommendations for future researchThe POP pollution situation in the Baltic Sea continues to be a problem, espe-cially for PCDD/Fs and dioxin-like PCBs, which contaminate the fish so that marketing of Baltic fish in the EU is restricted.

Although the current project has contributed to a better understanding of the contamination situation in the Baltic Sea, several areas for which know-ledge is uncertain or lacking have also been identified. It is primarily for the PCDD/Fs that the uncertainties are high. The major knowledge deficits in clude:• CurrentemissionsofPCDD/Fstoair.Thisworkhasclearlydemon

strated that the PCDD/F problem in the Baltic as a whole is caused by long range atmospheric transport, whereby sources in continental Europe play a major role. Consequently, it is important to establish whether current understanding of PCDD/F emissions is consistent with the atmospheric input of PCDD/Fs to the Baltic.

• CurrentemissionstoBalticSeawater.Theseincludefreshwaterin flow, industrial effluents and leakage from contaminated land. There are large uncertainties in all these categories. It is likely that they pri marily affect the contamination situation in coastal zones.

• ItappearsthatthePCDDsaredecliningmorethanthePCDFsinanumber of matrices including Baltic biota, blood serum of Swedish men, and possibly also in Baltic sediments. Is there a shift towards emissions rich in PCDFs rather than PCDDs, or can this be attributed to other factors?

• TimetrendsofPCDD/FconcentrationsinBalticsedimentsandBalticair. These are needed for the evaluation of retrospective/perspective predictions.

• LevelsandcontaminationofPCDD/FsanddioxinlikePCBsinBalticsurface sediments. Large areas of the Baltic Sea have never been in vestigated. Contaminant pattern analysis of surface sediments can be used for tracing sources. Currently, the data available only allow for source apportionment in limited parts of the Baltic Sea (along the Swedish coast).

• Abetterunderstandingofsurfacesedimentaccumulationand mixing. This is needed to produce more reliable estimates of the response time of the Baltic Sea to changes in PCDD/F inputs.



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• Abetterunderstandingofsedimentwaterbiotacontaminantdynamics.Why do we see spatial and temporal variation in contaminant levels in fish in the Baltic Sea? Is it due to biological factors (e.g. growth rate and feeding habits)? How important are the contaminant levels in sediment for the levels in biota?



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3 IntroductionBy direction of the Swedish Ministry of Environment, the Swedish Envi-ronmental Protection Agency was given a commission to estimate sources, describe the present situation and investigate the current fluxes of persistent pollutants in the Baltic Sea ecosystem.

The project was performed during 2007 by a group including Karin Wiberg (project coordinator), Sarah Josefsson, Eva Knekta, Ylva Persson and Kris tina Sundqvist (Umeå University); James Armitage, Dag Broman, Gerard Cornelissen, Anna-Lena Egebäck, Per Jonsson, Michael McLachlan and Ulla Sellström (Stockholm University); Niklas Johansson (Swedish Envi ronmental Protection Agency) and Ingemar Cato (Geological Survey of Sweden).

Two groups of contaminants and one individual compound were chosen as representatives for POPs, including both intentionally and unintentionally produced pollutants. The compounds that were chosen to act as model sub-stances were: polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). PCDFs and PCDDs are commonly designated as dioxins. The selected compounds are all priority substances and are globally distrib-uted organic contaminants. These three classes of compounds represent a broad range of physical-chemical properties, and hence their environmental behaviour encompasses the spectrum of most chemicals listed in the Stock-holm Convention. The sources of the compounds differ. Dioxins are formed un intentionally in a number of different processes, e.g. during combustion and as by-products in the chemical industry. HCB is also formed during combus-tion, but in addition it was produced and used as a fungicide. PCBs are indu-strial chemicals with a wide range of uses, e.g. as insulating fluids.

Dioxins and PCBs are present in high concentrations in fish from the Baltic Sea, and a large portion of the catch exceeds the limits for dioxins and dioxin-like compounds in food set by the European Commission (The Commission of the European Communities 2006). This has resulted in marketing restric-tions for the fish industry in the EU countries surrounding the Baltic Sea. The environmental levels of dioxins have not decreased to the same extent as e.g. PCBs, which have been interpreted as an indication that there are ongoing, not yet identified, emissions.

The approach chosen by the project group was to calculate mass balan-ces for the selected POPs by using an existing mass balance model, the POPCYCLING-Baltic (Wania et al. 2001). In a first stage, an uncertainty analysis was conduct to identify the most important knowledge deficits. Thereafter field measurements in air, sea water and sediments were under-taken to reduce these uncertainties. For the modelling, these new data and data from an extensive data search were used. The calculations focused on the Bothnian Sea and the Baltic Proper.



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4 The Baltic Sea environment The Baltic Sea is classified as a particularly sensitive sea area by the United Nations’ International Maritime Organization (IMO) due to criteria such as vulnerability and the uniqueness of the ecosystem. The following chapter aims to give an introduction to the physical environment of the Baltic Sea.

4.1 Physical environment of the Baltic SeaThe drainage area of the Baltic Sea is 1 729 000 km2, and its surface area including the Danish sounds (Belt Sea) is 370 000 km2 (Stigebrandt 2001). It is a shallow sea with an average depth of approximately 60 m. The Baltic Sea can be divided into different basins: the Bothnian Bay, Bothnian Sea, Gulf of Finland, Baltic Proper, Gulf of Riga and Belt Sea. The two northern most basins, the Bothnian Bay and the Bothnian Sea, constitute the Gulf of Bothnia. Often the Kattegat Sea is included as part of the Baltic Sea (Figure 1). The Baltic Sea is semi-enclosed with limited exchange of water through the shal-low Belt Sea between the Baltic Proper and the Kattegat (Stige brandt 2001). It has a positive freshwater balance; i.e. the inflow of fresh water from rivers and precipitation is higher than the inflow of saline water from the Kattegat. This has created a brackish sea. The turnover time for the entire water mass has been estimated to be 25–35 years (Sjöberg 1992).

Figure 1. The drainage area and the seven basins of the Baltic Sea (HELCOM 2002).



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The density difference between salt water and fresh water creates a perma nent stratification of water in the Baltic Proper. Dense saline water is over laid by less saline surface water. The two layers are separated by a halo cline, a sharp gradient in salinity and density that inhibits mixing of the water bodies. The halocline is found in the Baltic Proper at a depth of 60–70 m (Stigebrandt 2001). The presence of the less saline surface water and the shallowness of the Belt Sea contribute to a limited inflow of saline seawater into the Baltic Proper. Since seawater inflow is the major engine of water exchange in the deep water layer, periods of limited inflow result in large areas of the seabed under the deep water becoming anoxic.

The major basins are interconnected by straits through which the exchange of water takes place. Each basin has a positive fresh water balance, which creates a gradient of decreasing salinity towards the Gulf of Bothnia. The halocline diminishes towards the Gulf of Bothnia due to vertical mixing of saline and fresh waters that decreases the salinity differences between the water masses.

The climate in the Baltic is mainly influenced by winds from the west or southwest. In the winter, the air flow from the south-west is strong, in cont-rast to the weaker and more westerly air flow in the summer. The annual precipitation in the area is usually between 400 to 600 mm yr-1, with areas of high precipitation, e.g. 1 500 to 2 000 mm yr-1, in the Scandinavian highlands (Bergström et al. 2001). Parts of the Baltic Sea are normally cov ered with ice in the winter. During mild winters the ice coverage is limited to the Bothnian Bay, while during severe winters the ice covers most of the sea except parts of the Baltic Proper.

Nine countries border on the Baltic Sea, and the drainage area encompas-ses fourteen countries. The drainage area covers both highly populated and industrialized regions as well as remote areas. Examining land use from a national perspective, the contribution of urban areas to the Baltic drainage basin varies from 14% for Denmark to 2% for Finland. Forests account for 16% of the Danish part of the drainage basin and 70% of the Swedish (Sweitzer et al. 1996). The German part of the drainage basin consists of 72% farmland, while only 6% of the Swedish portion is farmland. The Baltic Sea drainage basin has about 85 million inhabitants, of which 45% live in Poland. The long water turnover time (25–35 years) in combination with a dense population and heavy industry has resulted in rather severe pollution of the Baltic Sea with a number of hazardous substances as well as high nutrient loads.

4.2 Sediment dynamics in the Baltic Sea The sediments in the Baltic Sea are the final sink for the emitted POPs. Thus, it would be preferable if the POPs associated with the sediments were perma-nently buried. The following chapter will discuss some im portant aspects of this burial and some processes that may remobilize POPs from sediment.



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There are several different systems to classify bottom types based on their physical and chemical properties. The following sediment classi fication system (Håkanson and Jansson 1983) has been used:

- Accumulation areas dominate where fine materials with grain sizes less than 0.006 mm are continuously deposited.

- Transportation areas are characterised by a discontinuous depo si tion of fine particles/aggregates, i.e. periods of accumula tion are interrup-ted by periods of resuspension and transporta tion.

- Erosion areas prevail where there is no deposition of fine matter.Obviously any classification is a simplification of reality, and there is a

con tinuum of sediments ranging over all three sediment types. This chapter addresses the importance of sediment dynamics when interpreting temporal trend data on contaminants in sediments.

4.2.1 Erosion bottomsIn the Baltic Sea, erosion is a significant process not only in coastal areas but also in shallow offshore areas. In total, erosion bottoms are estimated to con-stitute approximately 30% of the bottom area. The occurrence of erosion bottoms is strongly associated with water depth. In shallow waters near the coasts, Christiansen et al. (1997) found that resuspension occurred during 15–35% of the year, whereas in deeper areas, the bottoms were resuspended during less than 3% of the year.

Suspended matter derived from wave-induced resuspension has been shown to be of significant importance for the sedimentation process (e.g. Christian sen et al. 1997). It was found that the resuspended portion com-monly ex ceed ed 50% of the total sedimented matter in a coastal area of the Baltic Sea (Brydsten 1993, Axelsson and Norrman 1977, Brydsten 1990, Jonsson et al. 1990). Eckhéll et al. (2000) found that between 1969−1993 ero-sion/resus pension accounted for on average 70% of the deposited matter in the open NW Baltic Proper. During individual windy years, the eroded/resus-pended portion may increase to 85%.

4.2.2 Transportation bottomsApproximately 40% of the bottom area of the Baltic Sea is classified as trans-portation bottoms. The transportation bottoms may be characterised as the transition zone in which eroded sediments are transported to the final accu-mulation areas in the deep offshore bottoms of the Baltic. Due to the large share of erosion and transportation bottoms (2/3 in the Baltic Proper), one has to keep in mind that the delay time for contaminant changes to be mani-fested in the deep accumulation areas may be substantial (Jonsson 2000). A contaminant-carrying particle may have passed through a number of re suspension events before being trapped in the anoxic sediments years to decades after it first enters the water column. Particle-associated contami nants may be retained in long-term transportation bottoms until strong energy input from waves, currents or sub-marine slides resuspends the sediments years to decades after the first deposition.



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4.2.3 Areas of accumulationLarge areas of the Baltic Sea are classified as accumulation areas for fine mate-rial. Although it may vary in different parts of the Baltic Sea, in off shore areas an average of 30% of the bottom area is considered to constitute this type of bottom. In general, accumulation bottoms are found at depths greater than 75–80 m, although in more shallow areas accumulation can occur in topo-graphic depressions as shallow as 50 m in wind-exposed areas. The yearly accumulation rate in the surface sediment is generally between 1 mm and 4 mm. Some characteristics of the Baltic Sea accumulation sedi ments are sum-marised in Table 1. The accumulation areas may be divided into: 1) bioturba-ted sediments and 2) azooic laminated sediments. In the bioturbated sediments animals are causing a more or less effective mixing of the upper sediment. This process is discussed further in Chapter 6.6.6.

LAMINATED SEDIMENTS

In areas where poor oxygen conditions (< 2 mg O2 L–1) cause elimination of

the benthic fauna, laminated sediments are often created. The seasonal chan-ges in the composition of sedimenting matter are preserved in the sedi ments as more or less distinct annual varves or lamina (Figure 2).

In the deepest parts of the major basins of the open Baltic Proper, lami-nated sediments have been deposited on anoxic bottoms for more than a hundred years, indicating natural oxygen deficiency in these areas (Jonsson et al. 1990). The area of laminated sediments has expanded since the 1940s, and in the late 1980s approximately one third of the Baltic Proper at depths ex ceeding 75–80 m had laminated surface sediments. Due to the lack of ben-thic macrofauna and subsequently low bioturbation, laminated sediments can be used to study changes in the contaminant levels with a high temporal reso-lution.

However, it is important to bear in mind that the lamination is not a static phenomenon. In 1993 a major inflow of saline water occurred through the Danish Sounds into the Baltic Sea. The oxygenation of the sea floor allowed benthic fauna to recolonise, causing bioturbation down to a couple of centi-metres below the sediment surface. The oxic episode after 1993 may be seen in the sediment column as a 1–2 cm thick bioturbated layer, over-layered by laminated sediments.

Table 1. Brief characteristics of the Baltic Sea accumulation sediments. grain size Mainly <60 μm

mud content >90%

TOc content 2−10%

redox conditions Upper cm temporarily oxic, temporarily anoxic

dynamics Sedimentation rate offshore: mean 1–3 (range 0.5–20) mm yr–1 Sedimentation rate archipelago: mean 17 (range 1–70) mm yr–1



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Storm-induced erosion causes changed sediment accumulation rates From long-term registration of waves along the German Baltic coast it has been shown that the annual frequency of storm waves increased from 1831 to 1990 (Baerens and Hupfer 1994). A strong relationship was shown be tween dry matter deposition and the frequency of wind speeds in excess of ≥14 m s–1 expressed as annual means. Figure 3 shows the strong relationship bet-ween the gale frequency and the deposition of dry matter. Changes in storm frequency may be used to indicate whether extra care should be taken when interpreting temporal trend monitoring.

Resuspension of old clays affects sediment carbon content In numerous investigations it has been shown that the sediment carbon con-tent is of great importance for the sediment burial of hydrophobic organic contaminants. There fore, processes/mechanisms that may alter the organic carbon content have to be taken into consideration in trend monitoring.

Figure 2. Typical laminated sediment from the open N Baltic Proper. In situ image taken with a sediment profile imaging camera at 125 m depth. The total length of the image is approximately 10 cm.



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In Figure 4, it is demonstrated that the dry matter accumulation rate de creased by approximately 50% in the 1980s. This was accompanied by an increase in total organic carbon (TOC) content from 3–4% to 7–8% during the same period of time. The interpretation of this is that the erosion/ resus pension of mainly minerogenic matter from glacial and postglacial clays increases during windy years, whereas the carbon input from primary production is more con-stant and thus makes a stronger contribution to the dry matter flux during calm years with low dry matter sedimentation rates.

Figure 3. Dry matter deposition (3-year running average, each year the mean of measurements from 3 cores) and the frequency of wind velocities ≥ 14 m s–1 (gale force; individual years and 3-year running mean) for the period 1969–1993 (from Eckhéll et al. 2000).

Figure 4. Dry matter deposition and TOC content in sediment from the NW Baltic Proper versus time. A 3-year running average of the means of the 3 cores is shown (from Eckhéll et al. 2000 and Jonsson, unpublished data).

0

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5 The selected POPs and their trends in Baltic Sea biota

The substances included in this study (PCDD/Fs, PCBs and HCB) were emit-ted mainly prior to the 1980s. However, despite the considerable emission reductions during the 1980s, these substances are still present and affecting the Baltic Sea environment. This is due to a number of reasons, e.g. the Baltic Sea being a rather closed ecosystem as described in the previ ous chapter (Bergström et al. 2001, Stigebrandt 2001). The hydrophobic properties result in the compounds accumulating in the fatty tissues of orga nisms. Humans are consequently exposed by intake of food. This chapter describes the pollutants, their origin, the human exposure/risk and the con centration trends in Baltic Sea biota.

5.1 PCDD/FsPolychlorinated s (PCDDs) are a group of 75 compounds with the same che-mical backbone (congeners), and the similarly structured polychlorinated dibenzofurans (PCDFs) are a group of 135 congeners. The various PCDD/F congeners differ in chlorination degree (from 0 up to 8 chlorines per congener) and chlorination pattern. Among these 210 con geners, 17 congeners are con-sidered biologically active and toxic.

Commonly, when dioxins are analysed, only the toxic congeners, i.e. the 17 PCDD/Fs that have a 2,3,7,8-chlorine substitution pattern, are quantified and reported. Of the 17, the 2,3,7,8-tetra-chlorinated (TCDD), exhibits the highest toxicity. To compare the risk of different con geners, toxic equivalency factors (TEFs) were introduced. These factors relate the toxicity of each toxic congener to 2,3,7,8-TCDD. The 2,3,7,8-TCDD toxic equivalence (TEQ) of a mixture of compounds is calculated by adding the products of the concen-tration and the TEF for each toxic con gener. The TEF values have evolved over time. The values most commonly referred to in the literature are the WHO-TEFs, the current standard which was adopted by the World Health Organization in 1998 and revised in 2006 (van den Berg et al. 1998, 2006), and the international TEFs (I-TEFs), which were adopted by NATO/CCMS and employed through much of the 1990s (NATO/CCMS 1988). The three TEF schemes are listed in Table 2.

In the WHO-TEF concept, dioxin-like (DL) PCBs are also included, and reported values may refer to PCDD/F-TEQs, DL-PCB-TEQs or total (PCDD/F and DL-PCB) TEQs.



39

Dioxins are unintentionally formed in various processes, often in high tem-perature processes and in the presence of chlorine. The most important known sources are:• Chemicalmanufacturing,especiallytheproductionofchlorinegasin

the chlor-alkali industry, as well as the production of chlorophenols and PCBs.

• Industrialprocessessuchaschlorinebleachinginthepulpandpaperindustry.

• Combustionprocessessuchasmunicipalwasteincinerationandmetallurgic processes.

• Secondarysources,suchassedimentleakagetowaterandvolatilisation from soil and vegetation surfaces.

In the Baltic Sea region, the pulp and paper industry, metallurgic industry and combustion processes are believed to have been the major dioxin emission sources during the last decades. However, in the Gulf of Finland, the produc-tion of chlorophenols has been a major regional source. The contaminated sediments of River Kymijoki still act as important secondary sources of diox-ins to the Gulf of Finland (Isosaari et al. 2002).

The historically high emissions of POPs have resulted in high loads of con taminants to the Baltic Sea ecosystem. In 1991, the Swedish National Food Administration introduced food recommendations for the consump-tion of Baltic Sea fish to reduce the intake of dioxin-like compounds. In 1998–1999, the average daily intake for the Swedish population was 1.1 pg

Table 2. TEf schemes according to i-TEf, WhO-TEf (2006) and WhO-TEf (1998).congener i-TEf

NATO/CCMS 1988WhO-TEf van den Berg 2006

WhO-TEf van den Berg 1998

2378-TCDD 1 1 1

12378-PeCDD 0.5 1 1

123478-HxCDD 0.1 0.1 0.1

123678- HxCDD 0.1 0.1 0.1

123789- HxCDD 0.1 0.1 0.1

1234678-HpCDD 0.01 0.01 0.01

OCDD 0.001 0.0003 0.0001

2378-TCDF 0.1 0.1 0.1

12378-PeCDF 0.05 0.03 0.05

23478-PeCDF 0.5 0.3 0.5

123478-HxCDF 0.1 0.1 0.1

123678-HxCDF 0.1 0.1 0.1

123789-HxCDF 0.1 0.1 0.1

234678-HxCDF 0.1 0.1 0.1

1234678-HpCDF 0.01 0.01 0.01

1236789-HpCDF 0.01 0.01 0.01

OCDF 0.001 0.0003 0.0001



40

WHO- TEQ kg–1 body weight (b.w.) for women and 1.0 pg WHO-TEQ kg–1 b.w. for men (Lind et al. 2002). Fish from the Baltic Sea contributed 15–18% of the daily intake, while fish in total contributed 50–55% of the daily intake.

In an attempt to lower the general exposure of dioxins and dioxin-like compounds to the European Union populations, the European Commission introduced maximum allowed limits for food and feed. Currently, a large portion of the fish caught in the Baltic Sea exceeds the limit for marketing of fish within the EU. The EU Scientific Committee for Food has set a tole-rable weekly intake (TWI) of dioxins and dioxin-like compounds of 14 pg WHO- TEQ kg–1 b.w. week-1 (The Commission of the European Commu-nities 2006). This limit is commonly referred to as a tolerable daily intake (TDI) of 2 pg WHO-TEQ kg–1 b.w. d–1. In Sweden 12% of the population has a daily intake above the European Commission TDI (Lind et al. 2002).

In a risk exposure study by the National Food Administration of Sweden (2007), it was concluded that the levels of dioxins in food have decreased since the 1970s. In accordance with these observations, the concentrations in human milk have decreased since 1996 (National Food Administration 2007). In contrast to the decreasing dioxin levels in food and human milk, the TEQ concentration in blood serum from Swedish men (n=26) did not show any significant decreasing trend between 1987 and 2001 (Hagmar et al. 2004; Rylander et al. 2008). On the other hand, the concentration of seve-ral dioxin (PCDD) congeners decreased significantly (five out of seven of the 2,3,7,8-substituted PCDDs). Among the PCDFs, it was only the 2,3,7,8-TCDF that decreased significantly, while OCDF showed significant increase. Among the 26 men, nine were classified as high consumers of fatty fish from the Baltic Sea. The serum levels of this group did not deviate from the average time trend levels of TEQ.

The major part of the daily intake of dioxins originates from animal foods, and in particular fish. In contrast to the general food levels, the levels of dioxin in herring from the Baltic Sea have not decreased since the 1990s (Figure 5) and it has been shown that fishermen’s families from the east coast have higher concentration of dioxins and PCBs in blood as compared to fishermen’s families from the west coast (National Food Administration 2007).

Figure 5 and Figure 6 show the trends of TEQ-levels in Baltic herring muscle and guille mot egg (Bignert et al. 2007a, Olsson et al. manuscript A). As seen in Figure 6, there were decreasing trends from the 1970s in guille-mot egg from the Baltic Proper and herring from the Bothnian Sea, but these decreasing trends have levelled out since the 1980s. The TEQ trends in herring from other Baltic locations (Bothnian Bay and Baltic Proper) have only been re corded since the end of the 1980s, and these show increasing (Bothnian Bay on lipid weight (l.w.) basis) or stable (Bothnian Bay on wet weight (w.w.) basis and Baltic Proper on w.w and l.w. basis) trends (Figure 5). The 2,3,4,7,8-PeCDF is the major contributor to the TEQ value in Baltic biota. Since the level of this congener has been relatively stable from around 1980 in Baltic



41

guillemot egg, this is the reason why also the TEQ levels have been stable for the last decades (Olsson et al. manuscript B). Recent re search has shown that from 1990 and 15 years onward, some PCDD con gener levels have decreased significantly in Baltic guillemot egg (e.g. 2,3,7,8-TCDD and OCDD), while stable or even increasing trends (although not statistically significant) have been observed for most other toxic PCDD/F congeners (Olsson et al. manu-script B).

Figure 5. Concentrations (geometric mean) and 95% confidence interval of dioxin concentra-tions in herring muscle (pg TEQ g–1 w.w.; n=10) from fish caught in Haru fjärden (Bothnian Bay), Utlängan (Baltic Proper) and Fladen (Kattegat) from 1989 to 2005 (Bignert et al. 2007a and Olsson et al. manu script A). The dotted line represents the geometric mean of the annual means.

Figure 6. Time trends of dioxin concentrations in guillemot eggs from Stora Karlsö (ng TEQ g–1 l.w.; n=10; Baltic Proper; Bignert et al. 2007a) and herring from Ängskärsklubb (pg TEQ g–1 w.w.; n=12–20; Bothnian Sea; Olsson et al. manuscript A). Geometric means and 95% confidence inter-vals are given.

pg TEQ g-1 w.w. TCDD-equivalents, pg/g fresh wt, herring muscleHarufjarden

.0

.5

1.0

1.5

2.0

90 95 00 05

Utlangan

.0

.5

1.0

1.5

2.0

90 95 00 05

Fladen

.0

.5

1.0

1.5

2.0

90 95 00 05

pia - 08.04.19 16:08, tcddecwo

ng/g l.w.

TCDD equivalents, ng/g fat, Guillemot egg, early

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06

TCDD equivalents, ng/g fat, guillemot egg, early laöGuillemot egg PCDD/F-TEQ, ng/g l.w.

Herring musclePCDD/F-TEQ, pg/g w.w.

0

1

2

3

4

5

6

7

80 85 90 95 00 05

Guillemot egg PCDD/F-TEQ ng g-1 l.w.

Herring muscle PCDD/F-TEQ pg g-1 w.w.



42

It is interesting to note that there is a concentration difference between herring from Harufjärden (Bothnian Bay) and Utlängan (Baltic Proper) compared to herring from Fladen (Kattegat), with significantly higher dioxin concentra-tions in fish from the north-eastern sites. Spatial differences have also been observed in the congener composition of the dioxins and dioxin-like PCBs in herring going from the North Sea to the Baltic Proper (Karl and Ruoff 2007). The contribution of dioxin-TEQ to the total TEQ increases in an easterly direction, going from the North Sea to the Skagerrak and Kattegat and further into the Baltic Proper (Karl and Ruoff 2007). As pointed out in section 6.5.2, the concentrations of dissolved PCBs decrease moving from the Kattegat into the Baltic Proper, which may explain the west-to-east trend in the contribution of the dioxin-TEQ in herring. A com parison with herring levels reported by Bignert et al. (2007b) confirms this trend and verifies the high levels in Baltic fish (Figure 7). Bignert et al. (2007b) discussed the geographical distribution of dioxins in the Gulf of Bothnia and showed that fish from the southern part of the Bothnian Sea exhibit 30% higher concentrations as compared to fish from the northern part of the Baltic Proper, the central and northern parts of the Bothnian Sea, and the Bothnian Bay (Figure 7).

5.2 PCBsPolychlorinated biphenyls (PCBs) are a group of compounds consisting of 209 congeners with one to ten chlorine atoms. Among these, there are twelve congeners with a structure and toxic mechanism similar to the diox ins (PCBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189). These are often referred to as dioxin-like PCBs (DL-PCBs) or co-planar PCBs, and they have been assigned TCDD toxic equivalence factors (Table 3). The TEFs for DL-PCB are generally lower than those for the toxic PCDD/Fs, but since the prevalence of PCBs generally is higher, the contri bution of DL-PCBs to the

Figure 7. Dioxin and dioxin-like PCB TEQ (pg TEQ g–1 w.w.) in herring from the North Sea, the Skagerrak Sea and various basins of the Baltic Sea. The figures are based on data from A) Karl and Ruoff (2007) and B) Bignert et al. (2007b).

0

2

4

6

8

10

12

North

Sea

Skage

rrak

Katteg

att

Coast

of M

eckle

nburg

Rügen

are

a

South

of B

ornh

olm

East o

f Born

holm

Coast

of P

oland

Coast

of L

atvia

South

of G

otlan

d

pg

/g w

.w.

dioxin-like PCBs

Dioxins

0

2

4

6

8

10

12

Baltic

Proper

South

Both

nian S

ea

Centra

l Both

nian S

ea

North

Bothnia

n Sea

Bothn

ian B

ay

pg

/g w

.w.

dioxin-like PCBs

Dioxins

A) B)

0

2

4

6

8

10

12

North

Sea

Skage

rrak

Katteg

att

Coast

of M

eckle

nburg

Rügen

are

a

South

of B

ornh

olm

East o

f Born

holm

Coast

of P

oland

Coast

of L

atvia

South

of G

otlan

d

pg

/g w

.w.

dioxin-like PCBs

Dioxins

0

2

4

6

8

10

12

Baltic

Proper

South

Both

nian S

ea

Centra

l Both

nian S

ea

North

Bothnia

n Sea

Bothn

ian B

ay

pg

/g w

.w.

dioxin-like PCBs

Dioxins

A) B)



43

total TEQ is significant in most environmental compartments (e.g. in Baltic herring; Figure 7). To date, the non-dioxin-like PCBs (NDL-PCBs) have not been assigned TEFs, but ongoing discussions within the EC indicate that NDL may be included in the TEF scheme in the near future.

In environmental monitoring and scientific research, seven PCB congeners are typically analysed, the so-called indicator PCBs (ΣPCB7). The industrial pro-duction of PCBs started in the 1920s; it increased up to the 1970s and was ceased out in the 1990s (Breivik et al. 2002). Major fields of applica tions were as heat resistant oils and lubricants in electrical equipment and hydraulic sys-tems, and in carbon paper. Previously, the primary emissions of PCBs to the environment occurred mainly during production and through leakage and losses from PCB containing products and systems. Today, sec ondary sources, such as re-volatilisation from soils, probably contribute to a large part of the levels in air.

As for the dioxins, the major human PCB exposure pathway is through in take of animal food in general and fish in particular (National Food Admini stration 2007). The levels of PCBs in food have decreased since the 1970s. In contrast to dioxins, the PCBs displayed distinct decreasing blood con centrations from 1991 to 2001 (Hagmar et al. 2004); however, there was considerable variation between individuals included in the study. The con centration of PCB #153 in human milk has also been decreasing since the 1970s (National Food Administration 2007). Interesting to note is that there are indications of higher levels of some PCBs (118, 153, 156 and 180) in human milk from women living on the east coast of Sweden compared to women living on the west coast (Lignell et al. 2006). These women had declared a higher intake of Baltic fish compared to women on the west coast during their childhood. Studies conducted by Karl and Ruoff (2007) and

Table 3. TEf schemes for dl-PcBs according to WhO-TEf (2006) and WhO-TEf (1998).congener WhO-TEf

van den Berg 2006WhO-TEf van den Berg 1998

non-ortho substituted

PCB 77 0.0001 0.0001

PCB 81 0.0003 0.0001

PCB 126 0.1 0.1

PCB 169 0.03 0.03

mono-ortho substituted

PCB 105 0.00003 0.0001

PCB 114 0.00003 0.0005

PCB 118 0.00003 0.0001

PCB 123 0.00003 0.0001

PCB 156 0.00003 0.0005

PCB 157 0.00003 0.0005

PCB 167 0.00003 0.00001

PCB 189 0.00003 0.0001



44

Bignert et al. (2007b) have shown that the DL-PCBs have a lower variation in herring concentrations between basins as compared to dioxins (Figure 7). Fish from the southern parts of the Baltic Proper (samples taken outside Born holm Island, Poland and Latvia) showed the highest concentrations of DL-PCBs. Figure 8 shows the time trend of ΣPCB7 in herring muscle from fish caught at four locations in the Baltic Sea (Bignert et al. 2007a) and Figure 9 shows the trend in guillemot eggs from Stora Karlsö (Baltic Proper). In both herring muscle and guillemot egg, the ΣPCB7 levels have decreased since the start of the monitoring in 1978.

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

,

sPCB, µg/g lipid w., herring muscle

Harufjärden Angskarsklubb Landsort Utlängan

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

, p

.0

.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

78 83 88 93 98 03

,





μg ΣPCB7 g

-1 l.w.

Figure 8. Concentrations (geometric mean) and 95% confidence interval of PCB con centrations in herring muscle (μg ΣPCB7 g

–1 l.w.; n=12–20). The fish were caught in Harufjärden (Bothnian Bay), Ängskärsklubb (Bothnian Sea), Landsort (Baltic Proper) and Utlängan (Baltic Proper) between 1978 and 2005 (Bignert et al. 2007a). The dotted line represents the geometric mean of the an-nual means.

0

100

200

300

400

68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06

, psPCB, µg/g lipid w., guillemot eggs, early laid. St Karlso

0

100

200

300

400

68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06

, psPCB, µg/g lipid w., guillemot eggs, early laid. St Karlso μg ΣPCB7 g

-1 l.w.

Figure 9. Concentrations (geometric mean) and 95% confidence interval of PCB concentrations (μg ΣPCB7 g

–1 l.w.; n=10) in early laid guillemot eggs sampled between 1968 and 2006 at Stora Karlsö (Baltic Proper) (Bignert et al. 2007a). The dotted line represents the geometric mean of the annual means.



45

5.3 HCBHexachlorobenzene (HCB) has been used intentionally as a fungicide, a lubri-cant, a wood preservative, and in the production of printing ink (USEPA 2000). It is also unintentionally formed during combustion and in proces-ses in the chemical industry. In Sweden, the use of HCB was banned in 1980 (Swedish Chemical Agency 2007). HCB is moderately toxic to humans and wild life at low doses, but is not included in the TEF scheme.

HCB has been monitored since 1979 in guillemot egg and since 1987 in herring muscle. As with PCBs, the levels have decreased over time (Figure 10 and Figure 11) (Bignert et al. 2007a). In human blood the HCB levels showed a clear decreasing trend between 1991 and 2001 (Hagmar et al. 2004). Regardless of the fish consumption (low, medium or high fish con sumption), the HCB concentrations in blood from Swedish men decreased by more than 50% during this period (Hagmar et al. 2004).

Figure 11. Concentrations (geometric mean) and 95% confidence interval of HCB levels (μg g–1 l.w.; n=10) in early laid guillemot egg from Stora Karlsö (Baltic Proper) sampled between 1979 and 2006 (Bignert et al. 2007a). The dotted line represents the geometric mean of the annual means.

Figure 10. Concentrations (geometric mean) and 95% confidence interval of HCB concentra-tions (μg g–1 l.w.) in herring muscle (n=10). The fish were caught in Haru fjärden (Bothnian Bay), Ängskärsklubb (Bothnian Sea), Landsort (Baltic Proper) and Utlängan (Baltic Proper) between 1987 and 2005 (Bignert et al. 2007a). The dotted line represents the overall geometric mean.

.00

.02

.04

.06

.08

.10

.12

87 92 97 02

( ) , ,

.00

.02

.04

.06

.08

.10

.12

87 92 97 02

( ) , ,

.00

.02

.04

.06

.08

.10

.12

87 92 97 02

( ) , p ,

.00

.02

.04

.06

.08

.10

.12

87 92 97 02

( ) , ,

HCB, µg/g lipid w., herring muscle


.00

.02

.04

.06

.08

.10

.12

87 92 97 02

( ) , ,

.00

.02

.04

.06

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.00

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87 92 97 02

( ) , p ,

.00

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.04

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.12

87 92 97 02

( ) , ,





μg HCB g-1 l.w.

0

1

2

3

4

5

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06

HCB, µg/g lipid w., guillemot egg, early laid. St Karlso

0

1

2

3

4

5

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06

HCB, µg/g lipid w., guillemot egg, early laid. St Karlso μg HCB g-1 l.w.



46

6 POPs in the Baltic Sea environmentThis chapter gives an overview of the fate and fluxes of environmental pollu-tants. It also summarises the present situation regarding emissions and levels of dioxins, PCBs and HCB in the Baltic Sea environment.

6.1 Distribution between environmental compartmentsThe environmental fate of chemicals is governed by the chemical’s proper ties and the properties of the receiving media. This results in differences in environ mental distribution between compound classes and between con geners within compound classes. The most important chemical properties affecting the distribution of persistent environmental pollutants are the partition coef-ficients (Mackay 2001). These describe the distribution of a compound in a two phase system at equilibrium, i.e. air-water, lipid-water, sediment-water, etc. A selection of physical-chemical properties of dioxins, PCBs and HCB is shown in Table 4, and an overview of important fluxes and partition coeffi-cients is shown in Figure 12.

The pollutants can be dissolved in water, sorbed to particles or present in the gaseous phase. The gains and losses (inflows and outflow) can be classified as i) diffusive fluxes, ii) advective fluxes and iii) fluxes due to degradation of the pollutant. Diffusive fluxes include dry gaseous deposition, evapora tion, sorp-tion and dis solution. The magnitude of the diffusive fluxes be tween compart-ments depends on differences in chemical potential (or fuga city) between compartments. These differences, in turn, depend on the de gree of pollution, inherent properties of the chemical and characteristics of the various compart-ments. Advective fluxes refer to transport of pollutants with a moving media. Examples of advective fluxes are: wet and dry atmo spheric deposition, inflow via air masses and fresh water, sedimentation, resuspension and erosion.

Table 4. range of physical–chemical properties for selected POPs (Swedish Environmental Protection Agency 2007*)Substance log KOW

Molecular weight (g mol-1)

H (m3 Pa mol-1)

Chlorinated dioxins (mono-octa CDDs)

4.8 – 8.2 219 – 460 0.68 – 49

Chlorinated furans (mono-octa CDFs)

4.4 – 8.6 203 – 444 0.19 – 34

Chlorinated PCBs (mono-deca CBs)

4.5 – 9.1 189 – 499 0.91 – 952

HCB 5.7 285 172

KOW = octanol-water partition coefficient; H = Henry’s law constant *The data are from the database PhysProp and the calculation program The Estimation program Interface (EPI) SuiteTM, v.3.12 (US-EPA).



47

Hydrophobic compounds like dioxins, PCBs and HCB tend to accumulate in organic carbon rich compartments (e.g. soils and sediments) or lipid rich organisms (e.g. animals and humans). The accumulation can be enhanced if the soils and sediments have a high content of black carbon (soot). For fish and other aquatic biota, the important uptake routes are diffusion across the gills and ingestion of feed. The main POP elimination routes of aquatic orga-nisms are through diffusion across the gills, excretion and biotransform ation. POPs have differing susceptibility to bio transformation. The net result of uptake and elimination of POPs is called bio accumulation. Bioaccumula tion often results in increased concentration of POPs with increasing age of the organism. For highly persistent POPs such as dioxins, PCBs and HCB, bio-magnification is also seen. Biomagnification is an increase in lipid normalised concentration from lower to higher trophic levels in the food web.

The relative abundance of congeners within a compound class (e.g. PCDD/ Fs and PCBs) in an environmental compartment is described as the congener pattern. In this report, the congener pattern of dioxins relates to abundance of individual 2,3,7,8-substituted PCDD/F congeners in relation to the sum of all seventeen 2,3,7,8-substituted PCDD/Fs. Correspondingly, the congener pattern of PCBs describes the abundance of the individual PCB7- congeners in relation to the sum of all PCB7-congeners (ΣPCB7).

The congener pattern present in emissions is often modified during trans-port and fate. Figure 13 illustrates the dioxin congener pattern in several environ mental compartments. For example, the aerosol compartment was domi nated by OCDD and 1,2,3,4,6,7,8-HpCDD, while the gaseous phase con tained a larger contribution from 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF and 2,3,4,7,8-PeCDF (results from this study). Figure 14 shows the correspond ing mean ΣPCB7 composition of the different compartments.

Advection

Inflow/outflow

Atmosphere

Water Body

Terrestrial System

Inflow

Outflow

Sediment

Diffusion

Sorbed to particles

Disolved

Gaseous

Kow

Koa

Kow

Koa

Outflow KowKow

Emissions

Emissions EmissionsKoa

Run off

Temperature

Degradation

Kaw

Kaw

Kaw

Advection

Inflow/outflow

Atmosphere

Water Body

Terrestrial System

Inflow

Outflow

Sediment

Diffusion

Sorbed to particles

Disolved

Gaseous

Kow

Koa

Kow

Koa

Outflow KowKowKow

EmissionsEmissions

EmissionsEmissions EmissionsEmissionsKoa

Run off

Temperature

DegradationDegradation

Kaw

Kaw

Kaw

Inflow

Advection

Inflow/outflow

Atmosphere

Water Body

Terrestrial System

Inflow

Outflow

Sediment

Diffusion

Sorbed to particles

Disolved

Gaseous

Kow

Koa

Kow

Koa

Outflow KowKow

Emissions

Emissions EmissionsKoa

Run off

Temperature

Degradation

Kaw

Kaw

Kaw

Advection

Inflow/outflow

Atmosphere

Water Body

Terrestrial System

Inflow

Outflow

Sediment

Diffusion

Sorbed to particles

Disolved

Gaseous

Kow

Koa

Kow

Koa

Outflow KowKowKow

EmissionsEmissions

EmissionsEmissions EmissionsEmissionsKoa

Run off

Temperature

DegradationDegradation

Kaw

Kaw

Kaw

InflowInflow

Figure 12. Schematic picture of partition coefficients (KAW, KOW, KOA) and impor tant fluxes in a multimedia environmental system.



48

Figure 13. Congener patterns of 2,3,7,8-chlorinated dibenzo-p-dioxins (DDs) and dibenzofurans (DFs) plotted as fraction of the sum of the 2,3,7,8-substituted DDs and DFs in background soil in Denmark, Sweden, Norway and Estonia (Vikelsoe 2004, Matscheko et al. 2002, Hassanin et al. 2005, Roots et al. 2004), herring from the Gulf of Bothnia (Sundqvist et al. 2007, Bignert un-published data), offshore sedi ment from the Bothnian Sea and the Baltic Proper (Sundqvist et al. manuscript, and results from this study), the atmospheric gas phase and aerosols (results from this study; average over a six-month period, the average was weighted to correct for variation in com-position due to air mass origin), dissolved phase in offshore water of the Bothnian Bay and Baltic Proper (results from this study using passive sampling) and the particulate and dissolved phases in fresh water from seven Swedish rivers (Wiklund, personal communication; Andersson, personal commu nication). Error bars indicate one standard deviation.

Bothnian Sea sediment

0.0

0.1

0.2

0.3

0.4

fresh water dissolved+particulate

0.0

0.2

0.4

0.6

soil

0.0

0.2

0.4

0.6

0.8

herring

0.0

0.2

0.3

0.5

0.6

aerosol

0.0

0.1

0.2

0.3

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air gaseous

0.00

0.05

0.10

0.15

0.20

marine water dissolved

0.0

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0.2

0.3

0.4

Baltic Proper sediment

0.0

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Fra

ctio

n of

sum

Aerosol

Soil


Atmospheric gas phase (PUF adsorbtion)

Dissolved and particulate phase in fresh water Dissolved phase in marine water (passive sampling)

Baltic Sea herring

Bothnian Sea sedimentBothnian Sea sediment

0.0

0.1

0.2

0.3

0.4

fresh water dissolved+particulate

0.0

0.2

0.4

0.6

soil

0.0

0.2

0.4

0.6

0.8

herring

0.0

0.2

0.3

0.5

0.6

aerosol

0.0

0.1

0.2

0.3

0.4

air gaseous

0.00

0.05

0.10

0.15

0.20

marine water dissolved

0.0

0.1

0.2

0.3

0.4


0.0

0.1

0.2

0.3

0.4

Fra

ctio

n of

sum

Aerosol

Soil


Atmospheric gas phase (PUF adsorbtion)

Baltic Sea herring

Bothnian Sea sediment

Dissolved and particulate phase in fresh water Dissolved phase in marine water (passive sampling)

2378

-D12

378-

D12

3478

-D12

3678

-D12

3789

-D12

3467

8-D

OC

DD

2378

-F

1237

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2347

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1236

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2346

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3478

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2378

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378-

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3478

-D12

3678

-D12

3789

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3467

8-D

OC

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1236

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3478

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OC

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2378

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3478

-D12

3678

-D12

3789

-D12

3467

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OC

DD

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-F

1237

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1236

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2346

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1237

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2347

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1234

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1236

78-F

2346

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1237

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1234

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F12

3478

9-F

OC

DF



49

Figure 14. The calculated mean congener pattern of ΣPCB7 plotted as frac tion of ΣPCB7 in herring from the Gulf of Bothnia (Bignert unpublished data, Bignert et al. 2007b), soil from Sweden and Norway (Meijer et al. 2003, Armitage et al. 2006), sediment from the Bothnian Bay and Baltic Proper (results from this study; Sund qvist et al. manuscript; Cato and Kjellin 2005; Cato, perso-nal communication) dissolved phase in water from the Baltic Proper and Bothnian Bay (results from this study) and the particulate (>0.7μm) fraction in marine water from the Baltic Proper (McLachlan et al. 2003, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, Smith and McLachlan 2006, Wodarg et al. 2004, Sobek et al. 2004), in air from Sweden and Finland and in precipita-tion from Sweden and Germany (EMEP 2007). Error bars indicate one standard deviation.

soil

0.0

0.1

0.2

0.3

0.4

P C B _ 2 8 P C B _ 5 2 P C B _ 1 0 1 P C B _ 1 1 8 P C B _ 1 3 8 P C B _ 1 5 3 P C B _ 1 8 0


0.0

0.1

0.2

0.3


marine dissolved water (<0.7um)

0.0

0.2

0.4

0.6

0.8

1.0


marine particulate water (>0.7um)

0.0

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0.2

0.3

0.4


precipitation

0.0

0.1

0.2

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0.4


air+aerosol

0.0

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Gulf of Bothnia sediment

0.0

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0.3


PC

B 2

8

PC

B 5

2

PC

B 1

01

PC

B 1

18

PC

B 1

38

PC

B 1

53

PC

B 1

80

PC

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8

PC

B 5

2

PC

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01

PC

B 1

18

PC

B 1

38

PC

B 1

53

PC

B 1

80

Aerosol

Soil

Baltic Proper sedimentBothnian Sea sediment

Atmospheric gas phase (PUF adsorption)

Particulate phase in marine water (>0.7µm) Dissolved phase in marine water (passive sampling)

Fra

ctio

n of

sum

Herring

0

0.1

0.2

0.3

0.4


Baltic Sea herringsoil

0.0

0.1

0.2

0.3

0.4



0.0

0.1

0.2

0.3


marine dissolved water (<0.7um)

0.0

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0.6

0.8

1.0


marine particulate water (>0.7um)

0.0

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0.2

0.3

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precipitation

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0.1

0.2

0.3

0.4


air+aerosol

0.0

0.1

0.2

0.3

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Gulf of Bothnia sediment

0.0

0.1

0.2

0.3


PC

B 2

8

PC

B 5

2

PC

B 1

01

PC

B 1

18

PC

B 1

38

PC

B 1

53

PC

B 1

80

PC

B 2

8

PC

B 5

2

PC

B 1

01

PC

B 1

18

PC

B 1

38

PC

B 1

53

PC

B 1

80

Aerosol

Soil

Baltic Proper sedimentBothnian Sea sediment

Atmospheric gas phase (PUF adsorption)

Particulate phase in marine water (>0.7µm) Dissolved phase in marine water (passive sampling)

Fra

ctio

n of

sum

Herring

0

0.1

0.2

0.3

0.4


Baltic Sea herring



50

6.2 Industrial emissions

6.2.1 Previous and current Pcdd/f emissions in EuropeThe so called “European Dioxin Emission Inventory”, organised by the European Commission, include a large scale inventory of European PCDD/F emissions from 1985 to 2005. In general, considerable emission reduction has been achieved for the industrial sources over the studied period, in contrast to the non-industrial sources (Quaß et al. 2004). In a near future, the emissions from non-industrial sources will probably exceed those from industrial instal-lations. Today, iron ore sintering is believed to be the most important emission source type followed by the former “No. 1”, municipal waste incineration The goal of the 5th Action Programme was to reduce PCDD/F emissions by 90% from 1985 to 2005, and it was concluded that this goal can only be achieved for some source types, and particularly not for the non-industrial ones. Measurements from a large number of in stallations are missing, especi-ally from metal industries in Spain and Italy.

6.2.2 Atmospheric emissions of Pcdd/fs in the Baltic Sea areaThe total emissions of dioxins to air by Baltic Sea countries were recently esti-mated to be 4.6 kg WHO-TEQ yr-1 (HELCOM 2006). The annual emis sion of dioxins decreased between 1990 and 2004. The decrease varied be tween 9% in Poland and up to 39% in Sweden (HELCOM 2006). On the contrary, some countries reported on an increase in emissions in 2004 as compared to 1990, e.g. Lithuania and Germany. The reason for the reported increase in Germany is connected to the fact that emissions for some sectors (e.g. petro-leum refining) were estimated and submitted for the period 2000-2005, but not for 1990-1999. The highest emissions of dioxins to the Baltic Sea area were reported by Germany, Russia and Poland, which together contributed more than 95% of the emissions (HELCOM 2006). Estonia, Lithuania and Latvia reported low yearly dioxin emissions (HELCOM 2006). Current data on the emission of POPs in the Baltic Sea region are uncertain. Some countries have not reported data at all, and emission data from some industrial sectors were rough estimates rather than based on measurements, or they were based on old measure ment data.

According to a recent HELCOM report, understanding of the concerns re lated to POPs is still low in some Baltic countries (e.g. Latvia, Lithuania, Poland and Russia; HELCOM 2007). These countries often lack informa tion on releases of hazardous compounds from industrial sources. In Poland, a substantial part of the dioxin emissions stem from the use of coal in the resi-dential sector (HELCOM 2007). In a recommended action plan, it was stated that the Polish emissions to air could be reduced by more than 40% by cea-sing backyard burning, by using dry hardwood instead of coal, and by optimi-zing the stove conditions in residential homes (HELCOM 2007). Furthermore, the emissions could be substantially reduced by pre venting landfill fires and by installing the best available technology for flue gas cleaning (HELCOM 2007).



51

6.2.3 Emissions of Pcdd/fs in SwedenIn a survey of PCDD/F sources in Sweden, the total yearly emissions from all industrial sectors in Sweden were estimated to be 160 to 480 g WHO- TEQ yr-1 to waste/landfills, 16 to 84 g WHO-TEQ yr-1 to air and 1.9 to 2.4 g WHO-TEQ yr-1 to water and sediments (Swedish Environmental Protection Agency 2005). The main emissions of PCDD/Fs to air are still believed to ori-ginate from combustion. Among the combustion sources, it is believed that large scale bio-fuel incineration, backyard burning and combustion of fossil fuels are the dominant sources (Umeå University 2005). The emis sions from municipal waste incineration are today considered as insignifi cant. On the other hand, waste from municipal waste incineration (mainly ashes) contain significant amounts of PCDD/Fs. The waste is deposited at landfills and may cause emissions to soil and water.

6.2.4 Emissions of PcBs and hcB in SwedenEmissions of PCBs in Sweden were estimated to be 10 000–31 000 g yr-1 to waste/landfills, 370–1 100 g yr-1 to air and 13 g yr-1 to water and sediments (Swedish Environmental Protection Agency 2005). The largest emissions were estimated to origin from combustion and from the chemical industry. The emissions of HCB were estimated to be 13 400–32 400 g yr-1 to air, 2 600–26 000 g yr-1 in waste/landfill and 14 g yr-1 to water and sediment (Swedish Environmental Protection Agency 2005). Combustion sources and the chemical industry were reported to be responsible for the largest emis-sions.

6.2.5 Pcdd/f, PcB and hcB emissions from various branchesThe forest industry, and in particular the pulp and paper industry, has histo-rically been responsible for high emissions of dioxins to water. Some PCB emission has also been observed, probably due to the use of recycled paper in the production. Despite strong reductions of emissions, primarily by changing the bleaching process, high levels of dioxins are still found in surface sedi-ments sampled near pulp and paper mills (Sundqvist et al. 2006). The highest levels in herring and sediment are found in the southern Bothnian Sea, an area with a high concentration of pulp and paper industry (Sundqvist et al. 2006, Bignert et al. 2007b).

The Swedish Environmental Protection Agency has, from 2005 to 2008, conducted a survey of the levels of dioxins and other POPs in the vicinity of a number or existing and closed pulp and paper industries. The survey focused on POP levels in various environmental compartments, mainly fish (perch and viviparous blenny), water and settling particulate matter (SPM). Fish samples were taken near industrial effluents (“near-sites”) and 5–20 km away from the industrial discharges (“distant-sites”). The authors chose to divide the mills into the following three categories: i) ECF: chlorine dioxide (ClO2) used in the bleaching process, ii) TCF: chlorine free bleaching proc ess and in this study also production of non-bleached pulp, iii) TMP: thermo-mechanic pro-



52

duction of pulp and in this study also board produc tion. In addition, samples were taken at sites where chlorine gas (Cl2) was formerly used in the bleaching process. In a draft version of a report about contamination levels in the vici-nity of pulp and paper industries (Swedish Environmental Protection Agency unpublished) and in Olsson et al. (2005), it is shown that the concentrations of HCB, PCB and WHO-TEQ in perch (but not viviparous blenny) sampled near some of the ECF and TMP sites were elevated in relation to the samples representing more distant locations. An elevation of the dioxin levels, expres-sed as TEQs, at “near-site” vs. “distant-site”, of >30% was seen at 7 out of 13 sites (range –50% to +225%). In the TCF category, none of the 4 sites showed clear elevation (range –30% to +17%) and at mills that formerly used chlorine gas in the bleaching process (n=4) the range was –18% to +33%. There were no statistically significant differences in the near/distant perch level ratios between cate gories. The PCDD/F levels in water and SPM samples showed deceasing trends in transects taken from sites connecting to pulp & paper and board industry (inner, intermediate and outer measurements). Elevations (inner/ outer) were seen at 4 out of 5 sites, and for these 4 sites the elevations ranged from 20% to 770% for SPM and from 19% to 120% for dissolved water concentrations. The authors of the draft report conclude that, although not all measurements showed elevations, there are clear indications of a local environmental impact from some of the mills, and follow-up studies are needed at selected sites to further elucidate the situation.

The Swedish Forest Industries Federation also recently conducted a dioxin survey including measurements at 9 mills. Waste water, flue gases, air and sludge were sampled (ÅF 2008). Some current PCDD/F emissions were detected. In a draft report (IVL 2008a), it is stated that the contri butions of PCDD/F from the point sources together with tributary inflows to the re ceiv-ing recipients could roughly explain the differences in PCDD/F levels in fish caught near the industries compared to reference conditions. Tentative mass balances were made for two recipients and the mill effluents accounted for 2% and 25%, respectively, of the total PCDD/F loads (in cluding e.g. inflowing sea water and atmospheric deposition).

In Sweden, the emissions of dioxins to water and air from the chemical industry have mainly been from the chlor-alkali industry (Swedish Envi ron-mental Protection Agency 2005). The chemical industry has also con tributed to dioxin emissions by production of hydrochloric acid and poly vinyl chloride (PVC). The production of PVC is also associated with emissions of PCBs and HCB (Swedish Environmental Protection Agency 2005). HCB can also be formed in chlor-alkali processes. Emissions from the chemical industry mainly occur through disposal of contaminated sludge and release of polluted water and air.

The metallurgic industry has emitted large quantities of dioxins to air. In a recent report from Jernkontoret (2006), it was stated that the air emis-sion from the Swedish steel producers is 3–5 g WHO-TEQ yr-1, including the DL-PCBs, which contribute with 10–20% to the total TEQ-value.



53

6.2.6 Emissions of Pcdd/fs and hcB in denmark and finlandThe atmospheric PCDD/F emissions in Denmark were estimated to 11–163 g I-TEQ yr-1 in 2002 (Hansen and Libak Hansen 2003). The major sources were from waste treatment (mainly municipal waste incineration), fires and energy production (mainly biomass combustion) (Hansen and Libak Hansen 2003). In Finland, the PCDD/F and HCB air emissions were recently esti mated to be 26.2 g I-TEQ yr-1 and 35.7 kg yr-1, respectively (SYKE 2007). For PCDD/Fs, the major sources were from the energy sector (71%), par ticularly from public energy and heat production, and for HCB, 94% of the emissions were from the industrial section, mainly the chemical industry.

6.3 POPs in the atmosphereIn the atmosphere, POPs are present in the vapour phase, attached to aerosol particles or dissolved in precipitation. As air-borne pollutants they can origi-nate from sources within the catchment area as well as from sources located outside the catchment.

The degree of adsorption of POPs to aerosols in the atmosphere depends on the octanol-air partition coefficient (KOA), the temperature and the avai-lable surface of aerosols. Most of the selected POPs will preferably partition into organic phases in aerosols rather than occur as vapours. However, the limit ed amount of particles in the atmosphere results in significant amounts of POPs in the vapour phase (Axelman et al. 2001; Swedish Environmental Protection Agency 2007).

The transfer of POPs from the atmosphere to the Baltic Sea catchment area occurs by dry and wet deposition. Wet deposition includes deposition by rain or snow, where the pollutant is either dissolved in droplets or attached to particles captured by precipitation. Dry deposition occurs either with the pollutant attached to particles or as gaseous diffusion. The dry gaseous depo-sition is a diffusion process driven by the chemical disequilibrium be tween the atmosphere and the surface medium. If there is a net diffusive transport to the surface one speaks of absorption, while a net diffusive transport to the atmosphere is referred to as volatilisation.

6.3.1 Pcdd/fs in air – previous measurementsA recent study of dioxins in the atmosphere in Sweden reported a decrease of dioxin concentrations by a factor of three compared to the 1980s (IVL 2006). The monitor ing took place in 2004 and 2005 at Råö at the Swedish west coast and the atmo spheric concentrations ranged between 0.5 and 10 fg WHO-TEQ m–3 for bulk air (particle-bound and gaseous). The correspond ing average concentration at a Danish air monitoring site within the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air pollutants in Europe (EMEP) was 27 fg WHO-TEQ m–3 (Hovmand et al. 2007). The average dioxin deposition at Råö was reported to be 1.3 and 0.5 pg WHO-TEQ m–2d–1 in winter and summer respectively (IVL 2006). The Danish deposition data varied between 2.2 and 3.5 pg WHO-TEQ m–2yr–1 (Hovmand et al. 2007).



54

6.3.2 Pcdd/fs in air – new measurementsDuring the winter of 2006/2007, air samples were collected in Aspvreten (southern Sweden) and Pallas (northern Finland) in order to identify the major source regions for atmospheric input of PCDD/Fs to the Baltic Sea. Short sampling times (24 h) were employed and only samples with stable air mass back-trajectories were selected for the analysis of the 2,3,7,8-substituted PCDD/F congeners. Several samples were also collected during the summer half-year.

In Figure 15 and Figure 16, the PCDD and PCDF concentrations (TEQs) in air samples from Aspvreten (particle-bound and gaseous, respectively) are shown grouped according to the compass sector from which the air mass primarily originated. The highest concentrations were found in air that had passed over the European continent (southwest, south and east: sectors A2, B1 and B2). In air that had passed over the British Isles and air from north-erly directions, the concentrations were low. The PCDF TEQ-concentrations were higher than the PCDD concentrations in air from southwest, south, east and northeast (sectors A2, B1, B2 and C), while the opposite was true in air from west-northwest (sectors A1, D2 and D1) (Figure 15). The variabil ity in the concentrations was much lower within a sector than it was be tween the sectors.

Figure 15. Particle-bound PCDD and PCDF concentrations (fg WHO-TEQ m–3) in air samples from Aspvreten collected during October 2006–April 2007. The samples were grouped according to the compass sectors of the origin of the air sampled. The boundaries of the compass sectors employed are illustrated by the dotted lines. Samples marked with * are from May 2005 (i.e. the summer season), and samples marked with # are from the winter season of 2005–2006.

A2 B1

C

D1

D2

B2

A1

PCDD PCDF

0

5

10

15

20

(fg TEQ/m3 )

#

*

#

*



55

The origin of the wet deposition of PCDD/Fs to the Baltic Sea was esti mated for the 6-month study period. Note that atmospheric concentrations of PCDD/Fs are much higher during winter than during summer, so that most of the annual deposition occurs during the winter half-year. For each day, the compass sector of air mass origin was determined and the average particle-bound PCDD/F concentration for this compass sector was multi plied by the amount of precipitation on that day and a constant scavenging ratio. The total deposition for the 6-month period was estimated and then the fractio-nal contribution of air from each compass sector to this total deposi tion was determined. The results are plotted in Figure 17. They indicate that ~40% of the wet deposition of PCDD/F derived from air that originated from the southwest sector (A2), while ~20 % derived from air from the south sector (B1). Bulk deposition samples were also collected (on a monthly basis) during the air sampling campaign. The total PCDD/F bulk deposition for this period was ~200 pg WHO-TEQ m–2 or 1.1 pg WHO-TEQ m–2d–1. Good agreement between the measured bulk deposition and the wet deposition estimated from the air concentrations was obtained when a scav enging ratio of 154 000 was used, which is similar to scavenging ratios re ported in the literature (Mackay et al. 1986).

Gaseous deposition is also a major pathway of PCDD/Fs into the Baltic Sea (Chapter 8.1.2.). The origin of the gaseous deposition to the Baltic Sea was roughly estimated for the 6-month study period by multiplying the aver-age gaseous PCDD/F concentration in air from each compass sector by the

Figure 16. Gaseous PCDD and PCDF concentrations (fg WHO-TEQ m–3) in air samples from Aspvreten collected during October 2006–April 2007. The samples were grouped according to the compass sectors of the origin of the air sampled. The boundaries of the compass sectors employed are illus trated by the dotted lines. Samples marked with * are from May 2005 (i.e. the summer season), and samples marked with # are from the winter season of 2005-2006.

A2 B1

C

D1

D2

B2

A1

PCDD(fg TEQ/m3 )

*

#

#

*

PCDF

0

0.5

1

1.5

2

2.5

3



56

fre quency with which the air over the Baltic Proper originated from that sector. The results indicate that the contributions from each sector to gaseous depo sition were quite comparable (Figure 18). There is, however, considerable uncertainty in the contribution from the west, northwest, and north sectors due to the small number of data points for these sectors.

Figure 17. Relative contribution (in percent) of different sectors of air mass origin to the wet depo-sition of PCDDs and PCDFs (WHO-TEQs) to the southern Baltic Sea.

Figure 18. Relative contribution (in percent) of different sectors of air mass origin to the gaseous PCDD and PCDF concentrations (WHO-TEQ) in air over the southern Baltic Sea.

A2 B1

C

D1

D2

B2

A1

PCDD PCDF

0

10

20

30

40

50

%

A2 B1

C

D1

D2

B2

A1

PCDD PCDF

0

5

10

15

20

25

30

%



57

Note that dry particle-bound deposition of PCDD/Fs is expected to be small compared to wet deposition under European conditions, even at landlocked sites more affected by local emissions of large particles with short atmo spheric residence times (Kaupp and McLachlan 1999).

This work clearly indicates that the levels of PCDD/Fs over the Baltic Sea and the atmospheric deposition of PCDD/Fs to the Baltic Sea are primarily deter-mined by the air flow pattern. The air flow pattern can vary considera bly from year to year, and hence so may the deposition. In order to be able to better extrapolate these results in space and time, correlations between the PCDD/F concentrations and the concentrations of more easily/routinely determined atmospheric parameters were explored. A strong correlation between the con-centration of particle-bound PCDD/F and the soot carbon concentration was found, with a correlation coefficient (r2) of 0.80 (Figure 19). In Aspvreten, the soot concentration is measured continuously, and so it should be possible to estimate PCDD/F concentrations in air from the soot data.

6.3.3 PcBs and hcBΣPCB7 is routinely monitored in air and precipitation in European countries by EMEP. The mean concentrations of ΣPCB7 for the years 2000–2007 was calculated within this study based on monthly EMEP-data covering Sweden, Germany and Finland. In precipitation, the mean concentration was 2.8 ng L–1 (standard deviation 5.0 ng L–1; n=314) and in bulk air it was 11 pg m–3 (stan-dard deviation 9.9 pg m–3; n=257). The corresponding concentrations for the years 1990–1999 were 1.3 ng L–1 (standard deviation 1.5 ng L–1; n=262) in

Figure 19. Correlation of the concentration of particle-bound PCDD/Fs with the concentration of soot in air.

r2 = 0.80

-0.5

0

0.5

1.0

1.5

-1.5 -1.0 -0.5 0.5

log soot (µg/m )3

log

PCD

D/F

-TEQ

(fg/

m)3



58

precipitation and 15 pg m–3 (standard deviation 16 pg m–3; n=183) in bulk air. The atmospheric wet and dry deposition of ΣPCB7 in Sweden was reported to be 1.5 and 1.3 ng m–2d–1 in winter and summer respectively (IVL 2006).

Similar to ΣPCB7, HCB is routinely monitored in European air and precipi tation by EMEP. The calculated mean concentration of HCB in pre-cipitation sampled at two German EMEP stations was 0.58 ng L–1 (standard deviation 0.60 ng L–1, n=94). The corresponding concentration for the years 1990-1999 was 0.15 ng L–1 (standard deviation 0.42 ng L–1, n=93). The HCB con centration in bulk air was monitored at a EMEP station in Finland, and the calculated average was 38 pg m–3 (standard deviation 13 pg m–3, n=11).

6.4 POPs in soilsChlorinated dioxins, furans and biphenyls and HCB are hydrophobic chemi-cals with octanol-water partition coefficients (KOW) ranging from 4.4 up to 9.1 (Table 4). This means that they tend to partition into organic matter (OM) of soil and sediments. In soil, OM will reduce the mobility of POPs by acting as a sink. With increasing hydrophobicity of the POPs, the strength of the asso-ciation with OM increases. OM of different origin and level of decay differs in hydrophobicity and POPs will have a correspond ingly different tendency to associate with them. Black carbon, a soot frac tion of OM formed from anthropogenic and natural combustion sources, has been shown to possess a strong sorption capacity for POPs (Cornelissen et al. 2005). Planar POPs, e.g. PCDD/Fs and polycyclic aromatic hydro carbons (PAHs), have a particularly strong affinity for black carbon.

Although most POPs have low mobility in soil due to their high affinity for OM, POPs may still move through soils via migration of colloids (small OM particles) and dissolved organic matter (DOM; Persson 2007, Isosaari et al. 2000). For highly hydrophobic compounds, such as PCDD/Fs, PCBs and HCB, this co-transport is important for the mobility (Persson 2007). Eleva-tion of particulate and dissolved organic matter has been shown to occur in streams during snowmelt and other hydrological events (Laudon et al. 2004). Thus, an elevation of POP fluxes during such events is likely to occur. For instance, a study of PAHs and PCBs after severe floods in the Czech Republic in 1997 showed a relocation of the POPs (Hilscherova et al. 2007). Sediment-associated contaminants were mobilized and deposited on the flooded areas. In addition, washout of contaminants from the flooded soils was observed. The mobility of POPs from soils to surrounding waters is poorly investigated in contrast to other substances that also associate with OM, e.g. radionuclides and metals.

Measurements of background levels of POPs in soil are scarce. Average soil concentrations of PCDD/Fs were calculated based on results from stu-dies conducted in Norway, Denmark, Sweden and Estonia (Hassanin et al. 2005, Vikelsoe 2004, Matscheko et al. 2002, Roots et al. 2004), and it was found to be 53 pg WHO-TEQ g-1 d.w. (standard deviation 50 pg WHO-TEQ



59

g–1 d.w.; n=20). The average ΣPCB7 concentration in soils from Norway and Sweden was 3.1 ng g–1 d.w. (standard deviation 6.2 ng g–1 d.w.; n=50; Meijer et al. 2003; Armitage et al. 2006), and for HCB, the mean concen tration in Norwegian background soil was 1.0 ng g–1 d.w. (standard devia tion 0.9 ng g–1 d.w.; n=46; Meijer et al. 2003).

6.5 POPs in the water bodyAs shown in Figure 12, POPs reach the Baltic Sea water by many routes: • directemissionsfromindustries(seealso6.2)• airwatergasexchange(seealso6.3)• atmosphericwetanddrydeposition(seealso6.3)• sedimentwatergasexchange(seealso6.6.1)• sedimentresuspensionandparticlewatergasexchange(seealso6.6)• advectivefreshwaterinflowviarivers,precipitationandground

water.• advectiveinflowfromconnectingseasandfromdeepwater(if

exist ing)

In the water phase, the POPs can be present either in the freely dissolved form or adsorbed to surfaces (primarily particulate organic matter). Hydro-phobic compounds associate only to a small extent with mineral matter (Schwarzenbach and Westall 1981).

6.5.1 Advective water in- and outflow of POPs to the Baltic SeaThe major inflow of water to the Baltic Sea occurs via precipitation, inflow from rivers and water intrusions from the North Sea. The latter plays an im portant role for the ecosystem, but due to the relatively low flow of water, it does not contribute significantly to the input of POPs to the Baltic Sea (Assmuth and Jalonen 2005).

Secondary sources include leakage from contaminated soils, sediments and landfills through the groundwater to a water course. Contaminated soil in cludes e.g. dioxin-contaminated sawmill soils, where chlorophenols have been used as preservatives. Dioxins and HCB are also present at former chlor-alkali sites. The contribution from contaminated soils is difficult to estimate. However, rough estimates have been made for some sites. At the former sawmill site in Marieberg (Kramfors municipality), representing one of the major chlorophenol contaminated sites in Sweden, the dioxin leakage from the site was estimated to be 15 to 40 mg WHO-TEQ yr-1 to the con necting bay (Kramfors municipality 2007). A similar estimate was made at the former chlor-alkali site in Bengtsfors (Bengtsfors municipality), and the outflow of dioxins was calculated to be 1.7 to 8.3 mg I-TEQ yr-1 (Sundberg et al. 2003).

There are few studies that have reported POP concentrations in river water. Dioxin concentrations for some Swedish rivers (Dalälven, Husån, Delånger ån, Hamrångsån, Emån, Ljusnan and Göta älv) were reported to be



60

in the range 7 to 120 pg WHO-TEQ m–3 (Andersson, personal communi-cation; Wiklund, personal communication). These are bulk concentrations (dissolv ed and particulate fractions).

There is an outflow of brackish water from the Baltic Sea through the Danish Belt and Kattegat. The estimated outflow is 15 500 km3 yr-1 (Sjöberg 1992). This surface water carries POPs and discharges POPs from the Baltic Sea.

6.5.2 Surface water – previous measurementsIn a study by Broman et al. (1991), the concentration range of dioxins in marine water from the Bothnian Bay, Bothnian Sea and Baltic Proper was found to be 0.3-3.6 pg WHO-TEQ m–3 in the dissolved fraction (<0.7 μm) and 0.6-2.9 pg WHO-TEQ m–3 in the particulate fraction (>0.7 μm). The sampling technique was active water sampling, i.e. pumping water through filter and adsorbent (polyurethane foam; PUF). The fraction adsorbed on the PUF was defined as the dissolved fraction.

The mean concentration of ΣPCB7 and HCB in marine water from the Baltic Proper was calculated within this study. The ΣPCB7 is based on data from a number of studies (NODC 2007, McLachlan et al. 2003, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, Smith and McLachlan 2006, Wodarg et al. 2004, Sobek et al. 2004). The average dissolved water concentration was 11 ng m–3 (standard deviation 8 ng m–3; n= 170; <0.7 μm), while the parti-culate fraction (>0.7 μm) contained 4.3 ng m–3 water (standard deviation 5.0 ng m–3; n=144). Monitoring cruises conducted in four consecutive years each showed decreasing concentrations of PCBs moving eastward from the Mecklenburg Bight to the Baltic Proper (McLachlan et al. 2003, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, Wodarg et al. 2004).

A mean HCB concentration in dissolved marine water was calculated based on results from environmental monitoring in the Baltic Proper (Wodarg et al. 2004, Schulz-Bull et al. 2003, Schulz-Bull et al. 2004, McLachlan et al. 2003). The calculated mean was 7.5 ng m–3 (standard deviation 0.8 ng m–3; n=83; <0.7 μm). The particulate fraction (>0.7 μm) contained 0.6 ng m–3 water (standard deviation 0.8 ng m–3 water, n=83).

6.5.3 Surface and deep water – new measurementsWithin this project, the freely dissolved concentrations of POPs in Baltic deep and surface water were analysed by using passive sampler strips. Con-taminants distribute between the water and the passive sampler by diffu-sion, and the quantification of the water concentrations relies on empirically de termined equilibrium partition coefficients.

The passive sampler strips were made of polyoxymethylene (POM). They were placed at three coastal and three offshore sites (Figure 25; Table 5) in the spring- summer of 2007. For the coastal sites, it was assumed that the water mass was well-mixed and that the contaminants were homogenously distributed. Therefore, the samplers were placed at one level (a couple of



61

meters above the sea bottom). In deeper areas, the water may be less mixed, or even distinctly stratified, as is the case in the Baltic Proper. The offshore samplers were therefore placed at two levels: 25 m and 60–120 m below the surface, where the latter depth corresponds to a couple of meters above sea bottom. The construction of an offshore rig is shown in Figure 20. A buoy placed at approximately 25–30 m below the surface was used to keep the rig in an upright position. Stainless frames (Figure 21) were deployed 3 m below the buoy and 1 m above the sediment surface. A 150–200 m long line was attached to the main anchor and a small anchor was deployed at the end of the line. This line was dragged up with a small anchor from the ship when the rig was taken in. The samplers were exposed for at least 3 months, which is the time required for reaching equilibrium between the sampler and the water. After harvesting, the POM strips were immediately cut into pieces and put in glass flasks which were stored deep-frozen until extraction and analysis.

The dissolved water concentration of ΣPCB7 (including all stations, both coastal and offshore) ranged from 3 to 44 ng m–3. The corresponding value for dioxins ranged from 0.8 to 3.2 pg WHO-TEQ m–3. The concentration of dioxins may be slightly overestimated due to a possible chromatographic co-elution between a non-2,3,7,8-substituted PeCDF-congener and the 2,3,4,7,8-PeCDF congener. The overestimation was judged to be maximum 25%.

The average dioxin concentrations at the different sites were:Coastal: 1.0 pg WHO-TEQ m–3 (n=6; range 0.79-1.5 pg WHO-TEQ m–3)Offshore: 2.4 pg WHO-TEQ m–3 (n=12; range 1.7–3.2 pg WHO-TEQ m–3).

The average ΣPCB7 concentrations at the different sites were:Costal: 5.7 ng m–3 (n=6; range 3.0-10 ng m–3)Offshore: 20 ng m–3 (n=12; range 5.5-44 ng m–3).

The concentrations of HCB could not be determined as a measured passive sampler/water equilibrium partition coefficient was not available.

Figure 20. The construction of the POM rig. In deep waters, sampling was conduct ed at two depths (as shown) and in coastal waters at one depth.

25-30 m

1 m

Stainless frame with POM

Stainless frame with POM



62

As can be seen in Table 5, there were no distinct concentration differences between surface and deep sea water, neither in the Baltic Proper nor in the Bothnian Sea. An interesting result, however, is that the dioxin levels are somewhat higher in the Baltic Proper than in the Bothnian Sea, while the opposite is true for PCBs. The reason for this geographical pattern is un known, and more measurements are needed before definite conclusions can be drawn.

Table 5. concentration ranges for dissolved Pcdd/fs and ΣPcB7 at differ ent depths in the Bothnian Sea and the Baltic Proper.Sampling depth

Bothnian Sea Pcdd/fs

(pg WHO-TEQ m-3)

Baltic Proper Pcdd/fs

(pg WHO-TEQ m-3)

Bothnian Sea ΣPcB7

(ng m-3)

Baltic Proper ΣPcB7

(ng m-3)

25 m 1.8–2.2 2.6–3.2 25–37 5.5–8.1

60–120 m 1.7–2.1 2.5–3.2 20–44 8.2–9.1

Figure 21. A stainless steel frame with POM strip.



63

6.6 POPs in sediments As in soil, hydrophobic pollutants will primarily partition into the organic matter of sediments and suspended material. Particles suspended in the water body will be deposited when they reach calm water or through aggre gation. This formation of sediments will eventually result in permanent burial. However, sediments deposited in shallow water may be subject to resuspen-sion. Thus, the sediment-associated POPs may be brought back into solution. Furthermore, the bioturbation of sediments by organisms can bring POPs back into suspension. The extents of bioturbation, wave- and current-induced resuspension, mineralisation, deposition of particles, diffusion and degrada-tion of the chemical determine whether the sediments act as a sink or as a source of the pollutant.

The coast of the Baltic Sea includes several heavily industrialized zones. Along the Gulf of Bothnia there are a number of pulp and paper mills and steel mills. Several chemical factories are situated both on the coast of the Gulf of Finland and the Baltic Proper. These industries have been known to emit dioxins and other POPs. Sediments sampled near industrialized and urban areas often show higher concentrations as compared to sediments from back-ground sites. This is shown by the distribution of dioxins in sur face sediment samples along the Swedish coast in Figure 22 (Sundqvist et al. 2006). The Swedish coast includes a number of dioxin hot spots associ ated with industrial activity (Sundqvist et al. manuscript).

Figure 22. Sediment sampling locations in the Baltic Sea and Σ tetra through octa-chlorinated DD/F concentrations (each bar unit equals 5 ng g–1 d.w.). The highest value was decreased 4 times for clarity (TISS, Thematic Images and Spatial Statistics) (Sundqvist et al. 2006).

x 4

Bothnian Sea



64

6.6.1 Sediment-water exchange – new measurementsPOPs in sediments equilibrate between sediment particles, pore-water and overlying water. The POPs present in the pore-water constitute a potentially mobile and bioavailable fraction. The relation between freely dissolved con-centration in the overlying water and pore-water gives an indication of the net flow of dissolved POPs between the two compartments. If pore-water concen-tration > overlying water concentration, one can expect a net diffu sive trans-port of dissolved POPs from the sediment to the water column. Note that the overall mass transfer of POPs between sediment and water is also influenced by particle deposition and resuspension.

Within the scope of this study, the pore-water concentrations in 14 sedi-ments were determined. The sediments were sampled during 2007 from the same sampling sites as the water samples described earlier (Figure 25). The pore-water concentrations were determined by using passive samplers (POM), where the POMs were allowed to equilibrate by shaking a sediment-water slurry for 30 days at room temperature.

As expected, the POP concentrations in the pore-waters generally co-varied with sediment concentrations. The average pore-water concentration was 3.5 pg WHO-TEQ m–3 (n=14; range 1.6–7.4 pg WHO-TEQ m–3). These values may be slightly overestimated due to a possible chromatographic co-elution between a non-2,3,7,8-substituted PeCDF-congener and the 2,3,4,7,8-PeCDF congener. The overestimation was judged to be maximum 25%.

For the coastal stations, the average ratio of the pore-water/overlying water dioxin concentration was 3.6 ± 1.6 (average for all congeners; 3 sites; tripli cates). For the PCBs the average ratio was 1.0 ± 0.6. This indicates that the coastal sediments act as a source for PCDD/Fs to the overlying water, whereas for the PCBs there is no concentration gradient and the sediments in the coastal areas neither constitute strong sinks nor strong sources for PCBs.

For PCDD/Fs in deep water, the ratio was 1.1 ± 0.5, which suggests that there is no concentration gradients and that the sediments in the offshore areas constitute neither strong sinks nor strong sources for the diffusive ex change of dissolved PCDD/Fs. For PCBs this ratio was 0.7 ± 0.3, sugges-ting that there is only a slight concentration gradient for PCBs, but that the di rection of the gradient indicates that the sediments could be a PCB sink.

The sediment and water measurements allowed calculation of total orga-nic carbon–water partition coefficients (KOC) for these Baltic Sea sediments, where total organic carbon refers to amorphous organic carbon (AOC) and soot (black) carbon (BC). Previously, the partition coefficient KOC was used to describe the partitioning between AOC and water. Here, we use the KOC to describe the partitioning between BC+AOC and water and KAOC is used to describe partitioning between AOC and water. In Figure 23, the log KOC of various dioxin congeners are plotted vs. their log KOW (Sacan et al. 2005) and in Figure 24, the log KOC of various PCB congeners are plotted vs. their log KOW (Schenker et al. 2005). In addition, the figures show the equi lib rium partition coefficient between amorphous organic carbon and water (KAOC)



65

as predicted by the regression of Seth et al. (1999). It was observed that the binding to BC+AOC in Baltic Sea sediments is stronger than for AOC alone. These high KOC values (a factor of 10–30 times higher than KAOC) indicate that the ecotoxicological risk for PCDD/F and PCBs in the Baltic Sea sediments is 10–30 times lower than would be predicted if the risk assessment would be based on KAOC.

Figure 23. Log KOC vs. log KOW for various PCDD/F congeners (average for all sediments; n=14). The line shows a regression for predicting KAOC, i.e. the parti tioning between amorphous organic carbon (without BC) and water according to the regression suggested by Seth et al. (1999). Log KOW values are from Sacan et al. (2005).

Figure 24. Log KOC vs. log KOW for various PCB congeners (average for all sedi ments; n=14). The line shows a regression for predicting KAOC, i.e. the partition ing between amorphous organic carbon (without BC) and water according to the re gression suggested by Seth et al. (1999). Log KOW values are from Schenker et al. (2005).

5

6

7

8

9

10

11

6 7 8log KOW

log

KO

C(L

/kg

)

LFER-KAOC OC Baltic sediments, PCDD/Fs

9

5

6

7

8

9

5 6 7 8log KOW

log

KO

C(L

/kg

)

LFER-KAOC OC Baltic sediments, PCBs



66

6.6.2 levels of POPs in Baltic sediments – new measure mentsWithin this study, offshore and coastal sediments were sampled and ana-lysed for PCDD/Fs, PCBs and HCB. The offshore sampling was performed at seven accumulation bottom stations in the Bothnian Sea and at five sta-tions in the Baltic Proper in June–July 2007 (Figure 25). Two of the stations in the Bothnian Sea were later classified as transport bottoms due to low carbon content and were therefore rejected in the evaluation. In the Baltic Proper, coastal sediments were sampled from transport bottoms in three areas (Figure 25). Differential GPS (DGPS) was used for the positioning, with an accuracy of ±10 m or better.

Before sampling, a measuring grid of approximately 500×500 m was run by means of echosounding at each sampling site to describe the topographical conditions in the area before the exact position for sediment sampling was chosen. Surface sediment samples (0–2 cm) were taken with a modified Ponar sampler (Håkanson and Jansson 1983; Figure 26), which allows free water passage through the sampler during descent and sediment penetration. Great care was taken to ensure that the sediment surface was intact, e.g. that a bac-terial film of Beggiatoa and clear supernatant water were present.

At each offshore station sediment cores were taken with a Gemini double corer (Figure 27). The core was only accepted if the sediment surface was intact. These cores were used for description of the sediment type, down-core stratification, lamination, bioturbation structures etc. The samples and intact cores were stored cold until analysis. The results from this study are presented in the next chapter (6.6.3).

Figure 25. Sediment and water sampling locations used in this study. POM (polyoxymethylene) was used as a passive water sampler.



67

6.6.3 levels and trends of POPs in Baltic sedimentsThe levels of POPs in Baltic sediments including their spatial distribution and time trends were investigated. To obtain an extensive data set, data from one offshore station in the Bothnian Sea and five stations in the Baltic Proper were included from Sundqvist et al. (manuscript and unpublished data). Furthermore, for PCBs, eight offshore stations in the Baltic Proper and two in

Figure 26. Sediment sampling by the Ponar sampler.

Figure 27. The Gemini corer ready for operation.



68

the Bothnian Sea from the national Swedish sediment monitoring programme (Cato and Kjellin 2005) were included in the evaluation of the large-scale dist-ribution patterns and time trends.

PCDD/FS

Spatial distributionIn Table 6 and Table 7, average concentrations and ranges of selected PCDD/ Fs in surface sediments obtained in this study and by Sundqvist et al. (manuscript) are compiled together with previous measurement data for off-shore sediments from the Bothnian Sea (Verta et al. 2007, Rappe et al. 1989) and the Baltic Proper (Koistinen et al. 1997, Rappe et al. 1989, Kjeller and Rappe 1995). The concentrations of HpCDF and OCDF from Rappe et al. (1989) were left out of the compilation due to uncertain data quality (no internal standard in combination with unstable GC-column).

Different analytical methods were used to determine the PCDD/Fs. In some of the studies, a co-elution occurred between a 2,3,7,8-substituted con-gener and a non-2,3,7,8-substituted congener. These data were not included in the calculation of mean concentrations. As seen in Table 6 and Table 7, the con centrations found in this study and by Sundqvist et al. agree well with data from other studies of recent samples (from the 2000s).

Table 6. concentrations (pg g–1 d.w.; average and range) of selected Pcdd/fs in surface sediments sampled at offshore sites in the Bothnian Sea. The data are from this study and Sundqvist et al. (manuscript) together with data from verta et al. (2007) and rappe et al. (1989).

Bothnian Sea (offshore)

reference and site

This study and Sundqvist et al.

(manuscript)

verta et al.

(2007)

uS5B

verta et al.

(2007)

Sr5

rappe et al.

(1989)

Sr5

rappe et al. (1989)

iggesund 30 km

n=10 n=1 n=1 n=1 n=1

Sampling period 2005–2007 2000s 2000s 1986 1986

2378-TCDD 0.55 (0.24–0.68)a 0.40 0.47 1.0 1.9

12378-PeCDD 1.3 (0.6–1.9) 1.5 1.8 3.5 3.6

OCDD 53 (24–76) 63 73 89 96

2378-TCDF 8.4 (3.0–12) 4.7 6.0 8.3 11

23478-PeCDF 6.2 (4.8–7.0)b 5.5 6.6 7.7 5.7

1234678-HpCDF 33 (15–54) 80 38 - -

OCDF 44 (17–74) 115 59 - -

a Data from this study only, n=5 b Data from Sundqvist et al. (manuscript) only, n=5



69

In general, PCDD/F sediment concentrations normalised to dry weight are approximately a factor 2–3 times higher in the Baltic Proper as compared to the Bothnian Sea (Table 6 and Table 7). If normalised to carbon, however, taking into account the substantially higher TOC content in the Baltic Proper (Table 8), there are no differences between the two basins.

Table 7. concentrations (pg g–1 d.w.; average and range) of selected Pcdd/fs in surface and sub-surface (2–4 cm) sediments sampled at off shore sites in the Baltic Proper. The data are from this study and Sundqvist et al. (manuscript) together with data from Koistinen et al. (1997), rappe et al. (1989), Kjeller and rappe (1995).

Baltic Proper (offshore)

reference and site

This study and Sundqvist

et al. (manuscript)

Koistinen et al. (1997)

By15

rappe et al. (1989)

40

Kjeller and rappe (1995)

P18

Kjeller and rappe (1995)

P18

n=10 n=1 n=1 n=1 n=1

Sampling period 2005–2007 1993 1986 1988 (core) 0–2 cm

(corresponds to an average sampling year

of 1985)

1988 (core) 2–4 cm

(corresponds to an average sampling year

of 1978)

2378-TCDD 0.93 (0.37–1.6)a <2 1.4 1.0 0.55

12378-PeCDD 3.4 (1.3–7.3) 5.0 6.5 3.5 5.2

OCDD 204 (74–355) 265 250 273 273

2378-TCDF 18 (5.8–44) 42 14 13 16

23478-PeCDF 15 (7.6–28)b 19 15 16 20

1234678-HpCDF

83 (32–154) 118 - 87 141

OCDF 95 (37–167) 58 - 73 190

a Data from this study only, n=5

b Data from Sundqvist et al. (manuscript) only, n=5

Table 8. Average TOc content (% d.w.) of Baltic Sea sediments sampled during 1989–1993 and 2003–2007.Sampling period n Average TOc content (% d.w.)

Bothnian Sea

1989–1993 5 3.1

2003–2007 8 2.9

Baltic Proper

1989–1993 13 6.1

2003–2007 19 7.8



70

Time trendsDecreasing trends of PCDD/F concentrations have been registered towards the sediment surface in cores from Gulf of Finland (sites K15, LL3a and JML1b: Isosaari et al. 2002; site AKL: Verta et al. 2007) and in offshore cores from the Bothnian Sea and the Baltic Proper (site SR5: Verta et al. 2007; site P18: Kjeller and Rappe 1995). Verta et al. (2007) concluded that this indicates a general and clear decrease in input of dioxins to the Baltic Sea. The data from this study and Sundqvist et al. (manuscript) confirm the decreasing trend in the Bothnian Sea (Table 6) for the PCDDs, but suggest that the PCDF levels have been relatively stable. The data from the Baltic Proper, however, do not indicate any substantial decrease when the few available historical data (n=3) are compared to the recent data (Table 7). Considering the few measurement data available and considering also that the core from the Baltic Proper was sampled in the 1980s (Kjeller and Rappe 1995), it is difficult to draw any conclusions about the recent time trend for PCDD/Fs in Baltic Proper surface sediments.

PCBS

Spatial distributionSince the sum of PCBs is often based on different congeners and different numbers of congeners, comparisons between data sets are difficult. How ever, for some studies the large-scale spatial distribution of PCB concentra tions in Baltic Sea could be assessed. Based on a limited number of surface sedi-ment samples (n=11), Gustavson and Jonsson (1999) showed slightly increa-sing concentrations of PCBs from north to south in a data set from 1989. However, Axelman et al. (2001) sampled a larger number of surface sediments (n=44) and suggested a uniform distribution of PCBs in the Baltic Sea when the concentrations were normalised to organic carbon. Also, the atmospheric input of total PCB indicated a uniform deposition of PCBs to the Baltic Sea (Agrell 1999). On the other hand, Jonsson (2000) found a small but relati-vely clear gradient with almost two times higher sPCB concentrations (sum of congeners 52, 101, 105, 118, 138, 153 and 180) in the S Baltic Proper (lat 540000–560000; mean 382 ng g–1 OC) compared to the Gulf of Bothnia (lat 602000–650000; mean 213 ng g–1 OC).

Time trendsIn contrast to the decreasing trends of PCBs in Baltic biota, increasing sedi-ment concentrations of PCBs were registered in the 1970–80s (Niemistö and Voipio 1981, Perttilä and Haahti 1986, Nylund et al. 1992, Blanz et al. 1999), coinciding in time with a large-scale expansion of laminated sedi ments in the Baltic Proper (Jonsson 1992). In the 1980s, decreasing concen trations were registered as shown by several studies of sediments from the NW Baltic Proper (Kjeller and Rappe 1995, Axelman et al. 1995, Broman et al. 1994; also dis-played in Figure 28, from Jonsson et al. 2000).



71

Jonsson (2000) demonstrated that the general down-core concentration trend on dry weight basis for sPCBs in the Baltic Proper was an increase from the early 1970s and up to around 1990 (Figure 29), which is in contrast to the decreasing concentrations trends for PCBs in pelagic biota from the Baltic Proper (Chapter 5). There was no trend between 1970 and 1990 if PCB data were normalised to organic carbon (Figure 29).

Figure 28. Concentration plots of sPCBs obtained from former investiga tions of dated sediment cores in different parts of the Baltic Proper and the Gulf of Finland (from Jonsson et al. 2000). Figures refer to the following cores and papers: 1 = P18 in Kjeller and Rappe (1995), 2 = Axelman et al. (1995), 3 = TEILI in Perttilä and Haahti (1986), 4 = XV-1 in Perttilä and Haahti (1986), 5 = Nylund et al. (1992), 6 = 18021 in Blanz et al. (1999).



72

If bioturbated and laminated cores were treated separately, slight increases were found in bioturbated cores, whereas laminated cores showed decreases of 20–50% from 1979-1981 to the early 1990s (Figure 30).

Jonsson (2000) argued that the degradation of PCBs is probably insignifi-cant in the laminated sediments. This was demonstrated by the absence of major changes in the congener composition with increasing sediment depth in the cores (Figure 31).

In chapter 4.2, the importance of considering the sediment dynamics was emphasised when down-core trends are interpreted. Changes of the overall sediment accumula tion rate in the depositional areas most likely affect the carbon content, which sub sequently affects the burial of hydrophobic con-taminants. By assuming a constant sediment accumulation rate during the last decades, which has been the common way of presenting deposition data by several authors, Jonsson (2000) found that the sPCB deposition increased gradually in the 1940–60s, thereafter levelling out at 15–20 g sPCB (km)–2 yr–1 (Figure 32). These deposition trends were re-evaluated after publication of the results of Eckhéll et al. (2000). They demonstrated a significant varia tion in the bulk sedimentation rate from the 1960s and onwards that was highly correlated with the annual frequency of wind speeds ≥ 14 m s–1. Following this re-evaluation, the PCB deposition gradually increased in the 1940–1960s,

Figure 29. Mean sPCB concentrations (ng g–1) in time intervals in eight cores from the Baltic Proper and Gulf of Finland normalised to dry weight (d.w.) and organic carbon (OC). (From Jonsson 2000).

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

0

100

200

300

400

sPCB (ng g-1 OC)

sPCB*10 (ng g-1 dw)

sPC

B

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

0

100

200

300

400

0

100

200

300

400

sPCB (ng g-1 OC)

sPCB*10 (ng g-1 dw)

sPCB (ng g-1 OC)

sPCB*10 (ng g-1 dw)

sPC

B



73

Figure 30. Concentration of sPCB (ng g–1 OC) in dated laminated and bioturb ated sediment cores from the Baltic Sea. (From Jonsson 2000).

Laminated cores

0

100

200

300

400

500

600

1965 1970 1975 1980 1985 1990 1995

sPC

B(n

gg-1

OC

)

171, E. Gotland Deep178, W. Gotland Deep180, N. Baltic proper182, C. Gulf of Finland187, NE Gulf of Finland

Bioturbated cores

0

100

200

300

400

500

600

1965 1970 1975 1980 1985 1990 1995

sPC

B(n

gg-1

OC

)

169, Gdansk Bay170, Off Lithuania167, Bornholm

Laminated cores

0

100

200

300

400

500

600

1965 1970 1975 1980 1985 1990 1995

sPC

B(n

gg-1

OC

)

171, E. Gotland Deep178, W. Gotland Deep180, N. Baltic proper182, C. Gulf of Finland187, NE Gulf of Finland

Bioturbated cores

0

100

200

300

400

500

600

1965 1970 1975 1980 1985 1990 1995

sPC

B(n

gg-1

OC

)

169, Gdansk Bay170, Off Lithuania167, Bornholm

reaching peak values in the 1970s, and thereafter substantially decreasing during the late 1970s and 1980s (Figure 32). Around 1990, the PCB depo-sition increased again, coinciding in time with the increasingly windy con-ditions and increased dry matter deposition in the early 1990s. The trend in PCB deposition, assuming inter-annually variable deposition rates, clearly resembles PCB concentration trends in Baltic biota (Bignert et al. 1998).



74

Figure 31. Mean PCB congener composition in time intervals from eight dated sediment cores from the Baltic Proper and the Gulf of Finland (From Jonsson 2000). The data are presented as the fraction (%) in relation to PCB 153.

1990-1993

020406080

100

PCB#52 PCB#101 PCB#118 PCB#105 PCB#138 PCB#153 PCB#180

1980-1989

020406080

100


1970-1979

020406080

100


1940-1969

020406080

100


1900-1939

0

50

100


(%)

(%)

(%)

(%)

(%)



75

In Table 9, PCB concentration data for surface sediments from 1989-1993 (Gustavson and Jonsson 1999, Jonsson 2000) and 2003-2007 (this study, Sundqvist unpublished, Cato and Kjellin 2005) are compiled. The dry weight normalised ΣPCB7 concentrations are on average 4–5 times lower in the Bothnian Sea as compared to the Baltic Proper, and this was also the case some decades ago.

Figure 32. Deposition rates of sPCB in sediment cores. Mean values from the Baltic Proper and the Gulf of Finland assuming a constant sedimentation rate (yellow bars) and a variable sedimentation rate accounting for the inter-annual variability reported by Eckhéll et al. 2000 (blue bars) (from Jonsson 2000).

0

5

10

15

20

25

2000

1995

1990

1985

1980

1975

1970

1965

1960

1955

1950

1945

1940

ΣPC

B7

depo

sitio

n (g

km

-2 y

r-1)

sPCB - Constant sed. rate

sPCB - Variable sed. rate

sPC

B d

epos

ition

ng

km-2

yr-1

0

5

10

15

20

25

2000

1995

1990

1985

1980

1975

1970

1965

1960

1955

1950

1945

1940

ΣPC

B7

depo

sitio

n (g

km

-2 y

r-1)

sPCB - Constant sed. rate

sPCB - Variable sed. rate

sPC

B d

epos

ition

ng

km-2

yr-1

Table 9. mean concentrations (ng g–1 d.w.) of PcBs in Baltic Sea surface sedi ments sampled in 1989–1993 (gustavson and Jonsson 1999, Jonsson 2000) and 2003–2007 (this study, Sundqvist unpublished, cato and Kjellin 2005).

(ng g-1 d.w.) PCB 28 PCB 52 PCB 101 PCB 118 PCB 138 PCB 153 PCB 180 ΣPCB7

Bothnian Sea 1989–1993 (n=5)Mean 0.32 0.78 0.61 0.39 1.7 2.1 1.4 6.7SD % 50 117 59 92 104 91 55 86% ΣPCB7 4.8 11.6 9.1 5.8 25 31 21 100

Bothnian Sea 2003–2007 (n=7)Mean 0.09 0.08 0.16 0.19 0.29 0.29 0.17 1.2SD % 66 64 45 37 41 41 48 47% ΣPCB7 7.6 6.7 13 16 24 24 14 100

Baltic Proper 1989–1993 (n=9)Mean 1.1 3.4 3.2 1.9 5.6 6.4 3.4 24SD % 79 89 70 98 50 62 37 47% ΣPCB7 4.6 14 13 8.1 24 27 15 100

Baltic Proper 2003–2007 (n=13)Mean 0.35 0.47 0.91 0.74 1.3 1.1 0.59 5.3SD % 109 104 96 64 74 81 80 81% ΣPCB7 6.6 8.9 17 14 24 21 11 100



76

A distinct decrease in sediment concentrations has occurred in both basins during the last 10-20 years. In the Bothnian Sea, the decrease was on aver age a factor of 5.6 while in the Baltic Proper it was a factor of 4.5. These decrea-sing PCB concentra tions in offshore sediments are in line with the decreases in herring from the Bothnian Sea (3.5 times) and the Baltic Proper (2-4 times). Also the PCB concentra tions in guillemot eggs from the Baltic Proper (Stora Karlsö) have decreased by a factor 3 during the same time period.

As was discussed earlier (Chapter 4.2), a change in the bulk sedimentation rate might affect the sediment concentrations of hydrophobic substances, and furthermore, there is a highly linear relationship between annual bulk accu-mulation rate and annual frequency of wind speeds ≥ 14 m s-1. In Figure 33, the gale (≥14 m s–1) frequency at Gotska Sandön in the North Baltic Proper is plotted vs. time. The 1950–70s were characterised by a high fre quency of gales. These windy decades were followed by a very calm decade (the 1980s). In the early 1990s, the frequency of gale force winds increased substantially with a peak value in 1993. The decade from the mid 1990s until the present has been the calmest period recorded since 1950.

The two data sets compared in Table 5 are 1989–1993 and 2003–2007, i.e. one data set that can be considered to represent a windy period and one that repre sents a much less windy period. Theoretically, the carbon content in the sediments would be higher in the 2000s due to a smaller portion of eroded minerogenic matter in the sediments. Taking into account that POPs show an affinity for organic matter, a higher carbon content would lead one to expect higher POP concentrations in the early 2000s. However, the opposite was observed for PCBs in both the Bothnian Sea and the Baltic Proper. A compari-

Figure 33. Gale frequency (≥14 m s–1) at Gotska Sandön (N Baltic Proper). Red line = 3-year average. (Data from SMHI 2007).



77

son between the average TOC contents during the two periods showed no dif-ference in the Bothnian Sea. In the Baltic Proper, on the other hand, the TOC content increased by 28 % from 1989–1993 to 2003–2007. This increase has to be considered with due reservation because of the pos sible problems with the TOC analyses in the 2003–2007 data (Cato and Kjellin 2005). In any case, the calm conditions during the 2000s refutes the hypothesis that the dis-tinctively lower PCB concentrations found in recent surface sediments could be caused by an increased bulk sediment accumu lation rate . Thus, the registe-red decrease in ΣPCB7 concentration is con firmed and most likely depends on a decreased input to the Baltic Sea.

HCB

The HCB concentrations found in this study were quite similar in Bothnian Sea and the Baltic Proper with mean values of 356 and 404 pg g–1 d.w., re spectively. Former investigations of HCB in sediments sampled between the 1990s and early 2000s indicate quite variable sediment concentrations. These data were compiled together with the data from this study and are presented in Table 10.

Due to the scatter of the data in space and time, limited information on spa tial and temporal trends could be obtained. However, most of the data indi cate a general level of a few hundred pg HCB g–1 d.w. From the results in the SE Baltic Proper, there are indications of decreasing concentrations in recent years (Sapota 2006). Similarly, de creasing trends are indicated if data from the Gulf of Bothnia collected in the 1990s (Strandberg et al. 1998) are compared with the Bothnian Sea data from this study.

Table 10. hcB concentrations (pg g–1 d.w.; range) in surface sediments from different areas of the Baltic Sea.Area Sampling

yearn hcB

(pg g–1 d.w.)reference

Baltic Proper and Gulf of Finland

2001–2002 7 2–360 Pikkarainen 2007

SE Baltic Proper 1996–2005 3 670–1330 Sapota 2006

SW Baltic Proper 1993 19 10–750* Dannenberger 1996

Gulf of Bothnia 1990s 2 790/840 Strandberg et al. 1998

Bothnian Sea 2007 5 169–514 This work

Baltic Proper 2007 5 264–790 This work

* Mainly sandy sediment



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6.6.4 relation between total organic carbon, black carbon and POP levels RELATION BETWEEN PCBS AND OC

In several local/regional investigations of Baltic Sea surface sediments, the concentrations of organic contaminants normalised to dry weight were highly correlated with the organic carbon content. However, in the Baltic Sea sedi-ment baseline study (Jonsson 2000), which covered the entire Baltic Sea, the concentrations of ΣPCB7 and individual PCB congeners showed rather poor relationships with TOC in surface sediments (r2=0.41–0.59) and sediment cores (r2=0.25–0.33). The regression for surface sediments did not explain more than approximately half of the variation, which suggests that other fac-tors are of importance for the burial of PCBs in the sediments.

The data from this study (n=25) including data from Sundqvist (unpub-lished data) (n=6) and data from the national Swedish sediment monito-ring (Cato and Kjellin 2005) (n=10) showed no relationship between TOC (% d.w.) and ΣPCB7 (ng g–1 d.w.) at all (r2=0.05; Figure 34). A thorough data check showed that the poor correlation was caused by the data set from Cato and Kjellin (2005), belonging to the Baltic Proper. The mean ΣPCB7 con-centration in these data was approximately a factor 2 lower than the mean of the rest of the data set. If these data were excluded, the relationship im proved substantially (r2=0.49, Figure 35). The PCB concentrations reported in the study by Cato and Kjellin (2005) agree with the other data if normal ised on a dry weight basis. Due to the possible problems with the TOC de terminations we have chosen to present the PCB data on a dry weight basis when descri-bing the distribution in space and time.

Figure 34. Relationship between OC (% d.w.) and ΣPCB7 (ng g–1 d.w.) in surface sediments from the Bothnian Sea and the Baltic Proper. The data included are from this study, Sundqvist (unpu-blished), and Cato and Kjellin (2005).

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18

r2=0.05

(n=25)

OC (% d.w.)

ΣP

CB

7(n

g g-1

d.w

.)



79

Correlations between PCDD/Fs, PCBs, HCB, OC and BCIn many contexts, it has been argued that the content of black carbon (BC) can better explain the variation of organic pollutant concentrations in sedi-ments than total organic carbon (OC), which is the sum of amorphous OC and BC. In this investigation, both OC and BC were analysed in the surface sediment samples from the Baltic Proper (n=7) and the Bothnian Sea (n=5). In Table 11, data for six 2,3,7,8-substituted PCDD/F congeners, ΣPCB7, HCB, TOC and BC are compiled. It should be noted that this correlation study is based on data from this study only (n=12), and correlation values therefore differ from the statistical analyses discussed above. High correla tion values (r2) were obtained between OC and the PCDD/F congeners (r2=0.81–0.94) as well as between OC and ΣPCB7 (r

2=0.92). Low correlation was shown bet-ween OC and HCB (r2=0.28). In general, substantially lower r2 values were obtained between the different compounds and BC. However, this lower cor-relation was primarily attributed to one sample. By excluding this outlier, the correlation values increased to similar values as for OC.

Figure 35. Relationship between OC (% d.w.) and ΣPCB7 (ng g–1 d.w.) in surface sediments from the Bothnian Sea and the Baltic Proper. The data included are from this study and Sundqvist (un-published). Data from Cato and Kjellin (2005) are excluded.

OC (% d.w.)

ΣP

CB

7(n

g g-1

d.w

.)

r2=0.49

(n=15)

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12



80

6.6.5 Sediment burial of POPs in the Baltic SeaBased on bulk sediment accumulation data from Jonsson et al. (1990), Borg and Jonsson (1996), Perttilä et al. (2003), Jonsson (Ed. 2003) and Algesten et al. (2005), the sediment accumulation rates in the different basins of the Baltic Sea were calculated and compiled (Table 12). These basin-related accu-mulation rates were used to calculate the annual sediment burial of ΣPCB7 and sum of the 2,3,7,8-substituted PCDD/Fs (Table 13).

PCDD/FS

So far, to our knowledge, no reliable calculation of the total sediment burial of PCDD/Fs in the Baltic Sea has been presented. The number of data has been too small to allow such a calculation. Although our set of data on PCDD/Fs still is limited, the number of data points was considered to be sufficient to roughly estimate the total PCDD/F burial. Considering the rea sonably small variation in PCDD/F concentrations in the Bothnian Sea and the Baltic Proper, 2 and 4 times respectively, and the good correlation with OC (Table 11), the

Table 11. correlation matrix (r2) for selected Pcdd/fs, ΣPcB7, hcB, TOc and Bc from 12 stations in the Baltic Proper (n=7) and the Bothnian Sea (n=5) (data from this study only).

2378-TCDD

12378-PeCDD OCDD

2378-TCDF

23478-PeCDF OCDF ∑PCB7 HCB OC BC

2378-TCDD 1

12378-PeCDD 0.93 1

OCDD 0.86 0.97 1

2378-TCDF 0.98 0.96 0.91 1

23478-PeCDF 0.93 0.99 0.98 0.96 1

OCDF 0.86 0.94 0.94 0.88 0.94 1

PCB7 0.87 0.96 0.97 0.93 0.98 0.88 1

HCB 0.58 0.43 0.32 0.57 0.43 0.26 0.41 1

OC 0.81 0.93 0.94 0.88 0.94 0.92 0.92 0.28 1

BC 0.51 0.65 0.68 0.53 0.63 0.56 0.56 0.02 0.73 1

BC excl. outlier 0.68 0.93 0.93 0.78 0.92 0.95 0.94 0.01 1

Table 12. Estimated average TOc content (% d.w.) and dry matter and carbon deposition (ton yr-1) in the basins of the Baltic Sea.

n

dry matter deposition

(ton yr-1)

Organic carbon deposition (ton yr-1)

Average TOc content (% d.w.)

Bay of Bothnia 16 6,720,0001 252,0001 3.81

Bothnian Sea 68 37,900,0001 1,430,0001 3.81

Baltic Proper 17 37,200,0002 2,830,0002 7.62

gulf of finland 6 10,500,0003 618,0003 5.93

gulf of riga 4 3,200,0004 189,0004 5.94

Total Baltic Sea 95,520,000 5,319,000

1 Compiled from analyses in Jonsson et al. 1990, Borg and Jonsson 1996, Algesten et al. 2005, Jonsson unpublished material; and assuming the same deposition rate and TOC content in the Archipelago Sea as in 17 bays from Stockholm archipelago (Jonsson, Ed., 2003). 2 Compiled from analyses of dated cores in Jonsson et al. 1990 and Perttilä et al. 2003. 3 Data from Perttilä et al. 2003. 4 From Borg and Jonsson 1996 assuming the same TOC content as in the Gulf of Finland.



81

estimate is probably fairly good. Offshore data from the Gulf of Finland were also included (Verta et al. 2007). The PCDD/F burial in the Gulf of Finland (Table 13) constitutes 33% of the total burial in the Baltic Sea. In contrast to the ΣPCB7 concentrations of Gulf of Finland, the PCDD/F concentrations are new data from around 2000. The calculation implies that the relative importance of the Gulf of Finland as a sink for PCDD/Fs is significant. The down-core trends, however, indicates a more rapid decrease in this area com-pared to e.g. the Bothnian Sea.

PCBS

Based on analyses of PCBs in surface (0–2 cm) sediments and estimates of dry matter accumulation rates in different parts of the Baltic Sea, Jonsson (2000) estimated the annual sediment burial of ΣPCB7 for the period 1990-1993 to 923 kg yr-1, and the total sediment inventory of ΣPCB7 in Baltic Sea sediments was calculated to be 75 tons. Axelman et al. (1997) calcula ted the inventory of ΣPCB7 in the water mass to 570 kg. Based on these calcu lations, Jonsson (2000) estimated the average retention time for ΣPCB7 in the water mass to be <1 year, and suggested that this indicates that the Baltic Sea is an efficient trap of PCBs, and that the Baltic Proper laminated sediments more efficiently trap PCBs than bioturbated sediments.

The sediment burial calculated from recent data (Table 13) is approxima-tely 2.5 times lower than the rate calculated by Jonsson (2000), which is in rea sonable agreement with the general decreasing concentration trend from around 1990 to the early 2000s. According to the calculations, the Baltic Proper constitutes the main sink, accounting for 55% of the total burial. The other basins contribute less, except the Gulf of Finland, where the sediment burial was calculated to be 29% of the total burial in the Baltic Sea although it constitutes only 8% of the total area. The data from the Gulf of Finland and Gulf of Riga were derived from the Baltic Sea sediment baseline study in 1993 and probably overestimate the situation in the 2000s. If we assume a decrease

Table 13. Estimated annual sediment burial of ΣPcB7 (kg yr–1) and sum of the 2,3,7,8-substituted Pcdd/fs (kg yr–1) in the basins of the Baltic Sea.

Area dry matter deposition (ton yr-1)

no. of samp-les for ΣPcB

n

mean conc. ΣPcB7 (ng g–1

d.w.)

no. of samples

for ΣPcdd/fs

n

mean conc.

ΣPcdd/fs (pg g–1 d.w.)

Annual sediment burial of ΣPcB7 (kg yr–1)

Annual sediment burial of ΣPcdd/fs (kg yr–1)

Bay of Bothnia 6720000 1.21 1951 8 1

Bothnian Sea 37900000 7 1.2 10 195 45 7

Baltic Proper 37200000 13 5.3 10 574 197 21

gulf of finland 10500000 6 102 2 17533 105 18

gulf of riga 3200000 3 1.82 17534 6 6

Total Baltic Sea 95520000 361 541 Assuming the same concentration as in the Bothnian Sea 2 Assuming the same concentration as in 1993. From Perttilä et al. 2003. 3 LL3a and JML1b. From Verta et al. 2007. 4 Assuming the same concentration as in the Gulf of Finland



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similar to that observed in the Bothnian Sea and the Baltic Proper between 1990 and the early 2000s, the burial in the Gulf of Finland and the Gulf of Riga concerning the early 2000s may be recalculated to 21 and 1.2 kg yr-1 respectively. Subsequently, the total sediment burial of ΣPCB7 in the Baltic Sea is then reduced to 272 kg yr-1.

6.6.6 The impact of bioturbation on POP fluxes in the sedi mentThe movement of POPs across the sediment-water interface is of great im portance for their fate. By permanent burial in the sediments the pollutants are removed from the aquatic ecosystems, while mechanisms which facili tate the transport of pollutant from the sediment into the water will increase the load in the water.

One activity influencing the transport across the sediment-water interface is bioturb ation. Bioturbation can be defined as the mixing of particles and pore-water in sedi ment by macrofauna (Thibodeaux 2005). It is more in tense in the surface layers of the sediment, but the depth to which the bio turbated layer extends is highly species-specific. The Baltic Sea has rela tively low spe-cies diversity, with a few species dominating the benthic community. During the last twenty years the invading poly chaete Maren zelleria spp. has spread in the entire Baltic Sea and become a domi nant species in many areas. It can dig deeper in the sediment than previously present species, down to around 35 cm (Zettler et al. 1995). It thus has the potential to affect deeper layers of conta-minated sediment.

Research on bioturbation and its effect on contaminant fate point at an in creased outflow of contaminants from sediment as a result of bioturba-tion. In a study by Gunnarsson et al. (1999), the release rate of a tetrachloro-biphenyl added to the sediment surface was 220% higher in bioturbated systems compared to non-bioturbated. Karickhoff and Morris (1985) noticed an increased flux of chlorinated hydrocarbons, including HCB, from the sedi-ment to the surface in the presence of bioturbating tubificid worms. In systems without worms the flux out of the sediments was controlled by diffusion, and subsequently very low.

There are different types of bioturbation. Some species rework particles, while others bioirrigate, i.e. pump water, for instance to oxygenate their bur-rows. Generally, it can be assumed that POPs which partition strongly to particles will be more affected by particle reworking than by bioirrigation. Ciarelli et al. (1999) found that the increased release of PAH was mostly due to an increase of the suspended particles and the particle-bound con taminant in the aqueous phase, not an increase of the freely dissolved con centration of the contaminants.

In addition to a direct influence on POP movement, bioturbation can also affect the fate of POPs by its influence on microfauna and nutrient cycling in the sediment. The importance of bioturbation on the transformation of organic matter can be a result of increased oxygenation of the sediment (e.g. Kristensen 2000). Since POPs preferentially sorb to organic matter, a change



83

in the organic matter quality will also affect the sorption of POPs. The quanti-tative effects of bioturbation on the fate of POPs in the Baltic Sea, either as a result of direct resuspension/solubilisation or as a result of a change in the organic matter quality, remain to be investigated.

Another activity that has the potential to affect the sediment-water inter-face is trawling. It stirs up the top centimetres of sediment and disturbs the benthic macrofaunal community. Investigations in the Gulf of Maine, USA, showed that during periods of intense trawling the amounts of resuspended sediment and benthic worms collected in sediment traps 25 m above the bottom increased greatly (Pilskaln et al. 1998). How large impact trawling has on the fate of POPs in the Baltic Sea has not been determined.

6.7 Influence of temperatureTemperature is an important environmental factor affecting the distribution and fate of POPs. The ambient temperature affects several important prop-erties such as vapour pressure, water solubility, degradation processes and the Henry’s law constant. The average air temperature above the Baltic Sea ranges from 0.3°C in the Bothnian Bay to 7.2°C in the Baltic Proper (HELCOM 2002). The determination of physico-chemical properties is normally carried out at +20–25°C, and they must be corrected to the ambient temperatures (Beyer et al. 2002). Temperature also affects environmental processes, e.g. rate of evaporation, production of biomass, vertical water movements, ice cover and currents.

6.8 DegradationPOPs are persistent and will thus be present in the environment for a long time. Persistence is evaluated using half-lives (h), defined as the time it takes to reduce a concentration to half of the initial concentration. In model ling, the degradation rate constant (h–1) is used, which is calculated from the half-life assuming first order degradation kinetics. Degradation will be sub stantial if the half-life of the substance in the compartment is short and that compart-ment has high capacity to store the substance.

The overall degradation rate constants in a certain media include all impor tant degradation processes. They are compartment- and temperature-specific, and often also site-specific (Mackay 2001, Sinkkonen and Paasi virta 2000). Therefore, degradation rates measured at one location are not always applicable at other locations. Furthermore, degradation rates de termined in the laboratory are not easily extrapolated to environmental con ditions (Sinkkonen and Paasivirta 2000, Wania et al. 2001). Low tempera tures, lower OH radical concentrations and partitioning to particles generally cause longer atmospheric lifetimes of POPs compared to lifetimes calcu lated from laboratory-derived reaction rate constants. Thus, degradation rates are not



84

only an essential property but difficult to determine accurately. Sinkkonen and Paasivirta (2000) showed that data on degradation rates for PCBs and dioxins are generally very scarce, especially for biodegradation at low temperatures. Aronson et al. (2006) also stressed the lack of biodegra dation data for organic chemicals.

Photodegradation includes direct photolysis and reactions with OH radi-cals, ozone, nitrogen oxides and other radicals and can occur in air, water and soils. Since photodegradation in soils solely occurs close to the surface and the photodegradation rate in natural water is low (due to low OH radi-cal concentration), the atmosphere is the most important compartment for photo degradation of POPs (Sinkkonen and Paasivirta 2000). The degrada tion in the atmosphere is faster for POPs in the gas phase than for POPs ad sorbed to particles. Atmospheric degradation half-lives for various PCBs in the Baltic Proper environ ment have been estimated to be 3 days–1.4 years and for diox-ins 1 week–1 year.

Biodegradation can occur in water, soil and sediments. The rate of bio-degradation depends on several characteristics of the surrounding environ-ment such as tempera ture, moisture content, diversity and activity of the microorganism community, and concentration of oxygen. Biodegradation of PCBs and PCDD/Fs in soils and sedi ments in the Baltic Sea environment is very slow (Sinkkonen and Paasivirta 2000, Kjeller and Rappe 1995). Sink-ko nen and Paasivirta (2000) estimated the degradation half-lives in soil and sediments to be 3–38 years for PCBs and 17–274 years for dioxins. They also suggested degradation half-lives for PCBs and PCDD/Fs in water to be ten times longer than in air. Table 14 summarises half-lives for PCBs, diox in and HCB in air, water, soil and sediment.

Table 14. range of suggested degradation half-lives (h) for PcBs, hcB and Pcdd/fs in air, water, soil and sediment for Baltic Proper environment (Sinkkonen and Paasivirta 2000, mackay et al. 2006).

PCBs HCB PCDD/Fs

Air (h) 72 – 12 000 3 753 – 37 530 200 – 9600

Water (h) 1 450 – 240 000 23 256 – 50 136 4000 – 192 000

Soil (h) 26 000 – 330 000 23 256 – 50 136 150 000 – 2 400 000

Sediment (h) 26 000 – 330 000 150 000 – 2 400 000



85

7 Methodology employed to model POP behaviour in the Baltic Sea

7.1 Introduction to chemical fate modellingMultimedia fate and transport models are mathematical tools for prediction of transport, distribution and fate of compounds that have been introduced into the environment (Mackay 2001). Physico-chemical properties of the compound, environmental characteristics and emission data are used for the calculations. The environment is divided into a number of different com-partments, e.g. air, water, soil and sediment, which are considered to be well-mixed and homogeneous with respect to both environmental charac teristics and chemical contaminants. The model simulates emissions of the chemical to the different compartments and degradation of the chemical therein. The compartments are linked by the relevant inter-compartmental chemical trans-port processes (Figure 36).

Multimedia fate and transport models are used to integrate the information on chemical emissions, levels, reservoirs, and mass flows described in the pre-vious chapters. Through such models the multitude of information and the complexity of chemical behaviour in the environment can be synthesized to give an overall picture of the chemical fate, to identify key factors con trolling the levels in the environment, and to evaluate the impact of different manage-ment scenarios on chemical levels in the future.

In the next three chapters, a multimedia fate and transport model for POPs in the Baltic Sea called POPCYCLING-Baltic is used to assess the major sources of three different chemical groups: PCDD/Fs, PCBs, and HCB. The assessment was conducted for the whole of the Baltic Sea, but the

Figure 36. Schematic picture of a multimedia model. The environment is divided into a num-ber of compartments (e.g. air, aerosols, soil, biota, water, suspended sediments and sediments). Degradation and different transport processes can be included.

Air

Soil

Water

Biota

Aerosols

Sediments

Suspended sediments

Transport in and out of the unit world

Degradation

Transport between compartments

Air

Soil

Water

Biota

Aerosols

Sediments

Suspended sediments

Transport in and out of the unit world

Degradation

Transport between compartments



86

presenta tion of the results focuses on the two largest basins, the Bothnian Sea and the Baltic Proper. This work addresses basin scale contamination; it does not deal with hot spots that may have a local infl uence but that do not con tribute signifi cantly to contamination at the basin scale. In this chapter the POPCYCLING-Baltic model is presented and the model input parame-ters for each chemical group are summarized. Chapter 8 contains the model assessment of the current contamination situation, focusing on the quantity and location of the chemicals in the Baltic Sea (the inventory), the major pat-hways by which the chemicals are entering and leaving the Baltic Sea (the mass fl ows), and evaluating the predictive ability of the model by com paring model predictions with empirical observations. Finally, in Chapter 9 the future contamination of the Baltic Sea is assessed using different model scenarios that simulate the effects of reductions in emissions.

7.2 The POPCYCLING-Baltic modelThe model employed to simulate the environmental fate of PCDD/Fs, PCBs and HCB in the Baltic Sea environment was a modifi ed version of POPCYCLING-Baltic (Wania et al. 2000). POPCYCLING-Baltic is a non-steady state multi-compartment mass balance model that includes the entire drainage basin of the Baltic Sea as its model domain. The terrestrial envi-ronment (10 zones) includes freshwater and associated sediments, vegeta tion (forest canopy) and soil (forest, agricultural) while the aquatic envi ronment (16 zones) includes water and sediments. The aquatic environment is divided into coastal (10) and open water (6) zones in order to represent shallow areas (< 20 m) and deeper areas of the Baltic Sea separately. The terrestrial and aqua-tic environments are overlaid by atmospheric compart ments (4 zones), which represent the troposphere covering the drainage basin. Full details of the ratio-nale determining the model domain and inter nal subdivisions are presented in Wania et al. (2000) and a map of the model domain is presented in Figure 37.

Figure 37. Maps showing the compartmentalisation of the terrestrial (A), marine (B) and atmosphe-ric (C) environments of the Baltic Sea drainage basin in the POPCYCLING-Baltic model. Each of the ten terrestrial units is represented by fi ve compartments (agricultural soil, forest soil, forest can opy, fresh water, fresh water sediment), each of the marine units by a water and a sediment compartment (from Wania et al. 2000).



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The model code of POPCYCLING-Baltic as described in Wania et al. (2000) and downloadable from http://www.utsc.utoronto.ca/~wania/ downloads.html was modified to incorporate the following features:• Initialconcentrationsinallcompartmentscanbedefinedbytheuser.• Atmosphericconcentrationscanbe‘decoupled’fromtherestofthe

model domain (i.e. atmospheric concentrations become boundary conditions that are specified as model input).

• Scenarioscanbedefinedforatmosphericconcentrationswherebytheinitial concentrations can be reduced (or increased) over a certain period of time to a fraction of the initial values over the course of the model simulation (e.g. reduced to 10% of initial concentration over a period of 10 years).

• Atermtorepresentenhancedsorptiontoorganiccarbonwasintroduced to account for situations where contaminants exhibit greater sorption to sediments and suspended solids than would be predicted by the default algorithm used in the model code (i.e. the generic lin ear free-energy relationship between the octanol-water (KOW) and organic carbon-water (KOC) partition coefficients proposed by Karickhoff (1981)).

7.3 Model parameterizationA complete description of the model parameterization process and a compi-lation of the default values for environmental characteristics of the Baltic Sea environment are presented in Wania et al. (2000). The default parameter values can also be accessed through the user interface of the POPCYCLING-Baltic model itself, which is available to the public upon request. One of the more important considerations affecting the fate and distribution of organic chemicals in the marine environment is the cycling of particulate organic carbon (POC). The production (i.e. primary productivity) and subsequent pro-cessing of POC (e.g. sedimentation, mineralization, re suspension, and burial) have a strong influence on the behaviour of hydro phobic contaminants due to the high proportion of the total mass typically associated with particulate carbon. In light of more recent information about POC dynamics in the Baltic (e.g. the OC burial rates given in Table 12, the thickness of the bioturbated layer in the sediment discussed in Chapter 8), the model input parameters describing the mass balance of POC were ad justed to more accurately repre-sent these processes. Apart from these ad justments, default values were used for the environmental parameters.

In addition to environmental characteristics, the model requires as inputs physical-chemical properties of the chemical of interest, the direct emissions of the chemical to water, the initial concentration of the chemical in the dif ferent media (for each of the compartments), and the concentration of the chemical in air during the whole time period of the simulation.



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The physical-chemical properties required by the model are described in detail by Wania et al. (2000). They include phase partition coefficients (two of the following: air/water partition coefficient (KAW), the octanol/water partition coefficient (KOW), octanol/air partition coefficient (KOA)), the corresponding heats of phase transfer, and rate constants for chemical de gradation in diffe-rent environmental media.

Reliable estimates of the direct emissions of the chemicals of interest were not available. Consequently they were set to zero and the potential relevance of direct emissions was assessed by comparing available estimates of direct emissions with the model predictions of other mass flows of the chemical into the Baltic Sea (Chapter 8).

Two different sets of initial concentrations were used: one for retrospective model simulations, for which early measurements of the substances in sam-ples collected in the late 1980s and 1990s were used, and one for prospec tive model simulations, for which data from recent sampling campaigns were employed. Available data were carefully screened for quality and representati-veness. For each set of data, summary statistics were calculated and then used to initialize concentrations in each environ mental medium. Initial concentra-tions in geographical areas where no recent monitor ing data were available were assumed to be equal to concentrations in the closest neighbouring area. The initial concentrations in the forest canopy and water were not important for the simulations, as these concentrations responded quickly to the control-ling influence of the concentrations in air and sedi ments. The initial concentra-tions in sediments were based on measured concentrations normalised to the organic carbon content.

Seasonal variability in atmospheric concentrations was included. The ini-tial concentrations in all zones were varied around the median value using a sinusoidal function.

The selection of the physical-chemical properties, initial concentrations, and air concentrations is summarized for each of the chemical groups in the fol lowing three sections.

7.4 PCDD/Fs

7.4.1 Physical-chemical propertiesSimulations were conducted separately for the seven 2,3,7,8-substituted dibenzo-p-dioxins and the ten 2,3,7,8-substituted dibenzofurans. The results (e.g. predicted concentrations, mass flows) were summed after adjusting the predicted values by the appropriate toxic equivalency factor (WHO-TEF; Van den Berg et al. 2006) to give 2,3,7,8-TCDD toxicity equivalents (TEQs). The physical-chemical properties (e.g. partition coefficients, their tempera-ture dependencies, degradation rates) for the 17 congeners were taken from literature sources (Govers and Krop 1998, Beyer et al. 2002, Sinkkonen and Paasivirta 2000).



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7.4.2 Enhanced sorption to organic carbonEnhanced sorption to black carbon (BC) has previously been suggested for PCDD/Fs in marine environments (Persson 2003). In the model simulations it was initially assumed that there was no enhanced sorption to black carbon, and a sensitivity analysis of the influence of this parameter on the model out-comes was conducted.

7.4.3 initial concentrationsSince there were very few data available for PCDD/F concentrations in accu-mulation sediments prior to 2000, the modelling approach employed for the PCDD/F was different than for the other chemical groups. Reversed modelling was employed, whereby an initial concentration in sediment for the year 1986 was selected such that the model simulation gave a good pre diction of the cur-rent concentration in sediment. The thus obtained initial concentrations in sediments were compared with measurements of samples collected in 1985 and 1986 (Rappe et al. 1989, Kjeller and Rappe 1995). The current concen-trations in sediment were taken from data collected be tween 2005 and 2007 (this study, Sundqvist et al. manuscript). Initial con centrations in soils were based on EU reference background concentrations (Gawlik et al. 2007) due to a lack of reliable background data for the Baltic Sea watershed. No distinction was made between agricultural and forest soils.

7.4.4 concentrations in airThe current PCDD/F concentrations in air were derived from the recent data summarised in 6.3.2. The measurements allowed an estimate of the average atmospheric concentrations during the winter half-year of 2006/2007 at Aspvreten and Pallas. The average concentration for the whole year was esti-mated assuming that the average concentration during the summer half-year was a factor of 4 lower than during the winter half-year. The seasonal ity in the concentrations was assumed to be a factor of 9 with maximum values in January. The concentration scenario for Aspvreten was applied to the atmospheric compartments A2, A3, and A4, while the average of the scenarios for Aspvreten and Pallas was applied to compartment A1 (Figure 37).

For the retrospective simulations, the atmospheric concentrations were assumed to have decreased in a linear manner between 1986 and 2006 by a factor of 4. This assumption was based on estimates of the time trends of PCDD/F emissions during this period (Quaß et al. 2004) and on time trends of PCDD/F concentrations in tree foliage from Germany (Rappolder et al. 2007). Note that most of the PCDD/F in the air over the Baltic Sea is from air that originates from the European continent (Chapter 6.3).



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7.5 PCBs

7.5.1 Physical-chemical propertiesSimulations were conducted separately for 7 PCB congeners (IUPAC #28, 52, 101, 118, 138, 153 and 180) and then the results were summed. The physical- chemical properties for these seven PCBs were included in the database accompanying the original POPCYCLING-Baltic model. This database can be accessed through the user interface of the model. All default values presented in the model database were adopted with the exception of the degradation half-lives, which were based on Sinkkonen and Paasivirta (2000) instead. In general, the degradation half-lives proposed by Sinkkonen and Paasivirta were longer than the default values accompanying the model.

7.5.2 Enhanced sorption to organic carbonEnhanced sorption to black carbon may also be an important factor for some PCBs, particularly for co-planar PCBs such as PCB 28 and PCB 118, which were included in these simulations. However, measurements of the distribu-tion of PCBs between suspended particulate matter and the water column in the Baltic Proper (Wodarg et al. 2004, Smith and McLachlan 2006) did not indicate any significant degree of enhanced sorption to organic carbon for any measured PCB congener. Based on this empirical evidence, no en hanced sorp-tion to organic carbon was introduced.

7.5.3 initial concentrationsFor the retrospective calculations, initial concentrations of PCBs in sedi ments were based on data from Gustavson and Jonsson (1999) and Jonsson (2000). For the prospective simulations, initial concentrations of PCBs in sediments were based on reported measurements from NODC (2007), NERI (2007) and published reports by Cato (2006) and Verta et al. (2007). Repre sentative background measurements for this period were available from locations cor-responding to the Bothnian Sea, Baltic Proper, Danish Straits, Kattegat and Skagerrak zones of the model domain (Figure 37).

Representative background concentrations in freshwater sediment covered only a limited geographical area (multiple sites in Sweden, two sites in Poland). However, since the reported measurements in freshwater sediments in Sweden (Sundin et al. 2000) and the few in Poland (Kowalewska et al. 2003; Falandysz et al. 2006) were generally within the interquartile range (IQR) of the marine sediments, it was assumed that the PCB concentrations in fresh-water sediments were equal to those in marine sediments in the clos est geo-graphical region.

Initial concentrations in soil were based on representative background con centrations taken from Meijer et al. (2003) and Armitage et al. (2006).



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The monitoring sites were limited to locations in Sweden and Norway and were assumed to be broadly representative of conditions across the model domain. Furthermore, no distinction was made between agricultural and forest soils. The model endpoints evaluated were not sensitive to the mag-nitude of the initial soil concentration.

7.5.4 concentrations in airPCB concentrations in the atmosphere were based on data from stations in Sweden (Rörvik, Råö, and Aspvreten) and Finland (Pallas). Atmospheric concentrations in compartments A2 – A4 were extracted from the data from the three southerly stations only, while the concentrations in compartment A1 (Figure 37) were estimated as the average of the median values for the three southerly stations and the data from the northerly station (Pallas). The seasonal variability in the simulated concentrations reflected the seasonality in the observations, with peak concentrations in August and a difference bet-ween the concentrations in August and February of a factor of 3-8, depending on the congener.

For the retrospective simulations the concentrations were assumed to have decreased by a factor of 3 between 1989 and 1999 and remained constant after that.

7.6 HCB

7.6.1 Physical-chemical propertiesPhysical-chemical properties (e.g. partition coefficients, temperature depen-dencies, degradation rates) for HCB were included in the database accompa-nying the original POPCYCLING-Baltic model. No changes were made to these default values.

7.6.2 initial concentrationsThere were insufficient data of documented quality on HCB levels in recent accumulation sediments from the Bothnian Sea and the Baltic Proper. Con-centrations measured in sediments from nearby waters (Kattegat, Skagerrak, Nordic freshwater systems) were used as a guideline to initialize the model, but the initial concentrations in sediment were an unimportant parameter for simulating HCB behaviour as the HCB concentrations in sediment respon ded within several years to the concentrations in the atmosphere (Chapter 6.3). Since the concentrations in the atmosphere have been rela tively con stant over the last decade, the predicted current concentrations in water were nearly independent of the initial concentration assumed in sedi ment.

Due to the lack of reliable background data for the Baltic watershed, HCB concentrations in background soil from Norway (Meijer et al. 2003) were used to initialize all geographical regions of the Baltic.



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7.6.3 concentrations in airDue to the absence of evidence of strong time trends in HCB levels in the Baltic Sea region in the last two decades and the large quantity of high qua-lity data from the current decade, the historical simulations for HCB were re stricted to the period 2000-2005. The HCB concentrations in air collected at the EMEP monitoring stations in Lista and Birkenes, Norway, and at Pallas were used. The average annual concentration was 55 pg m–3 in the atmo-spheric compartments A2, A3, and A4, while it was 46 pg m–3 in A1. The average concentration was overlain by a sinusoidal seasonal varia bility with a maximum in October and a max:min range of a factor of 2.



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8 Current inventories, sources, and fate of POPs: A model- and statistics-based synthesisIn this chapter different aspects of the past and current behaviour of the three groups of POPs are assessed with the help of the available data and the POPCYCLING-Baltic model.

First, the current inventory of contaminants in the Baltic Sea environ-ment was estimated. The inventories were calculated using the best estimates of current concentrations of the PCDD/Fs, PCBs, and HCB in seawater and surface sediments, together with the volumes of these compartments. The surface sediments were assumed to be 2 cm deep based on field observa tions showing this to be a typical thickness of the bioturbated layer of sedi ments in the Baltic Sea (Per Jonsson, personal communication). There is a much larger inventory of the chemicals stored in sediments below this depth. Under some conditions, this deeper reservoir may also be returned to the active circulation in the Baltic Sea (e.g. via unusual resuspension events, sediment slumping, deeper bioturbation), so the numbers given here may be underestimates. The results are presented for the whole of the Baltic Sea. They provide insight into the magnitude of the contaminant reservoirs in the Baltic Sea and the relative importance of seawater and sediment for con taminant storage.

Second, the current magnitude of the sources, sinks, and flows of contami-nants in and between the basins of the Baltic Sea was assessed. The flows and the inventories were calculated from the historical simulations con ducted to evaluate the model (see below). The results from the final year of the simu-lation were used to calculate the annual flows. This approach was justified because of the good agreement between simulated and measured current con-centrations of the chemicals. The results are presented below for two basins: the Bothnian Sea and the Baltic Proper. Note that the simula tions were not conducted assuming steady-state (i.e. dM/dt = 0), and hence the sum of the inflows/sources to a given compartment may not balance the outputs/losses. The contaminant flows provide insight into the main proces ses and sources controlling the long-term fate of contaminants in the Baltic Sea.

Third, the reliability of the model was assessed. This was done by initialis-ing the model with measured or estimated earlier contaminant concentra tions in sediment (from the 1980s for PCDD/Fs and PCBs, from 2000 for HCB), and running the models using the best estimates of air concentrations from this time point until 2007 as a boundary condition (Chapter 9). The predicted concentrations of the contaminants in water and surface sediments over this time period were then compared with contaminant concentrations that have been measured. In addition, available measurements of contami nant flows were compared with model predictions. This assessment gives insight into the model’s capability to predict the contaminant fate, and hence into the relia-



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bility of the evaluation of the current sources, sinks and flows of contami-nants (above) as well as the predictions of their concentrations in the future (Chapter 9).

Finally, for the PCDD/Fs a statistical analysis of the congener patterns that have been measured in different matrices was undertaken. The congener pat-terns found in the major PCDD/F reservoir in the Baltic Sea (the sedi ments) were compared with the patterns present in a range of potential sources. Since the PCDD/Fs are very persistent in the environment, many features of the PCDD/F congener patterns in the emissions should be con served in the environ ment. Consequently, this comparison is another tool to identify the major source(s) of PCDD/Fs to the Baltic Sea.

8.1 PCDD/Fs

8.1.1 Pcdd/f inventories The total PCDD/F inventory in Baltic Sea surface sediments was 10 kg TEQ, while the water column contained 4% of this quantity (0.4 kg TEQ). Note again that the inventory in sub-surface sediments is much greater than the inventory in the surface sediments. However, only the surface sediments are included here, as only they are considered to be available for recircula tion back into the water column.

The large size of the inventory in surface sediments compared with water indicates that the surface sediments are a potential major source of PCDD/Fs to the water column. Indeed, they could potentially buffer the concentrations in the water column. In evaluating the potential impact of PCDD/F sources on the contamination of the pelagic environment of the Baltic, one should com-pare the magnitude of the sources with this inventory in the surface sediments (i.e. 10 kg TEQ). Sources that do not markedly in crease the inventory in the surface sediments will not markedly increase the contamination of the pelagic environment of the Baltic Sea as a whole.

For instance, it has been estimated that the sediments of the Kymijoki River in Finland contain 17.3 kg TEQ (Verta et al. 2006). If a significant portion of this sediment was to be mobilized and transported to the Gulf of Finland in the next years, then it would have a sizeable impact on the PCDD/F in ventory in the surface sediments there. On the other hand, a former sawmill site with contaminated soil containing 0.24 kg TEQ of PCDD/Fs (Kramfors municipality 2007) would not have a measurable impact on the PCDD/F levels in the Baltic Sea as a whole, even in the extremely unlikely event that all of this contamination is transferred to the Baltic in a short period of time. Indeed, the total inventory in surface sediments of 10 kg can be compared with the 5–50 kg TEQ estimated to be present in soil from pressure treat-ment and dipping at sawmills in Sweden (Swedish Environmental Protec tion Agency 2005). Since only a very small fraction of this soil can be ex pected to be transported to the Baltic Sea over a period of several decades (i.e. within a



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period similar to the residence time of PCDD/Fs in the Baltic Sea system, see below), this source of PCDD/Fs is highly unlikely to con tribute significantly to the contamination of the Baltic Sea as a whole. This does not preclude that a local contamination of Baltic Sea sediments of lim ited geographical extent may occur in some cases.

8.1.2 Pcdd/f flows The current magnitude of the flows of PCDD/F TEQs between the various compartments in the Baltic Proper and the Bothnian Sea (Figure 37) are pre-sented in Figure 38 and Figure 39, respectively.

Figure 38. Model estimates of current mass flows of PCDD/F in the coastal (a) and open water (b) compartments of the Baltic Proper (in g TEQ yr-1).

Degradation

Riverine Input

Degradation

Interbasin ExchangeCoastal/Open Exchange

VolatilizationVolatilization

Water-Sediment

Sediment-Water

Burial Degradation

Burial

Degradation Sediment-Water

Water-Sediment

Degradation

Surface-Deep Exchange

Deep-SurfaceExchange

Total Atmospheric DepositionTotal Atmospheric Deposition82.623.0

9.5

2.0

21.0

152.1

143.4

0.61.2

20.9

63.6(a)

(a)

(b)

(b)

504.9

9.8

19.2

8.1

378.8345.0

14.9

120.5

8.7

2.6

19.2

Figure 39. Model estimates of current mass flows of PCDD/F in the coastal (a) and open water (b) compartments of the Bothnian Sea (in g TEQ yr-1).

Degradation

Riverine Input

Degradation



Water-Sediment

Sediment-WaterBurial Degradation

Burial

Degradation

Sediment-Water

Water-Sediment

Total Atmospheric DepositionTotal Atmospheric Deposition

(a)

(a)

(b)

(b)

7.0 20.3

11.1 29.6

14.1

5.1 8.1

1.0

110.0

113.2

0.30.9

78.2

15.8

5.070.862.6

6.9

8.2



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Considering the marine environment as a whole (i.e. the water and the sedi-ment compartments), the major external source of PCDD/Fs to all the model regions is atmospheric deposition. This conclusion is not surprising, since it was not possible to obtain reliable estimates of the direct emissions of PCDD/ Fs to the Baltic Sea, and these were not included in the simula tions. However, the potential relevance of other sources can be explored by compa-ring those estimates that are available with the total atmospheric deposition to the Bothnian Sea and the Baltic Proper, which is estimated to be 133 g TEQ yr-1 (Figure 38 and Figure 39). It has been estimated that the highly con-taminated Kymijoki River in Finland emitted 44 g I-TEQ yr-1 to the Gulf of Finland in 2001 (Verta et al. 2006). This is greater than the atmospheric depo-sition to the Gulf of Finland and indicates that this river continues to be an important source of PCDD/Fs to this basin. On the other hand, the emissions of PCDD/Fs from the Marieberg sawmill site, one of the major chlorophenol contaminated sites in Sweden, which were estimated to be 0.013 g TEQ yr-1 (Kramfors municipality 2007), are negligible com pared to the atmospheric deposition to the Bothnian Sea.

The major sink for PCDD/Fs in the marine environment is sediment burial. Volatilisation back to the atmosphere is smaller than deposition as a con sequence of the strong tendency of PCDD/Fs to associate with particles in the atmosphere and the water column. Gaseous deposition is nevertheless an important deposition mechanism, contributing the majority of the atmo-spheric deposition of the lower chlorinated congeners. The degradation of PCDD/Fs is also small compared to sediment burial. Since sediment burial occurs on a time scale of decades, this means that once PCDD/Fs enter the Baltic Sea they will remain available in the marine environment for a long time. The PCDD/F residence time in the basins (both water and sediments together) was estimated by dividing the current inventory in the basin by the current loss rates, yielding values of 11 years for both the Bothnian Sea and the Baltic Proper. This indicates that PCDD/F levels in the Baltic Sea envi-ronment as a whole will react slowly to changes in PCDD/F inputs. More insight into the expected response of the different phases (sediment, surface water, deep water) is given in Chapter 9.

The potential for inter-basin migration of PCDD/Fs can be assessed in a similar manner. Comparing the rate of export from the deep water basins in Figure 38 and Figure 39 with the inventories in the respective basins indi cates that 0.06% and 0.7% of the inventory in the Baltic Proper and the Bothnian Sea, respectively, is transported to adjacent basins annually. This indicates that PCDD/F contamination will move only very slowly between the major basins of the Baltic Sea.

It is also instructive to examine the sources and sinks to the water column alone, since the concentrations in the water column determine the PCDD/F levels in most fish species including herring. The sediments are the most important sources to the water column, followed by the atmosphere.

The relative importance of sediment to water transfer is greatest in the coastal areas. This is a consequence of the more intensive cycling of POC



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between the water column and the sediment in the shallower water. Since there are few accumulation sediments in the shallow coastal areas, the coastal surface sediments do not contain a large PCDD/F reservoir that can serve as a long term source of PCDD/F to the water column. The sediment to water transfer is largely the result of resuspension of recently deposited sediments on transportation bottoms. Export to the open water is the major net loss mechanism for the water column in the coastal compartment. Simplified, the mass balance indicates that the sum of the riverine/direct inputs and the net atmospheric deposition is exported to the open water compartment. The PCDD/F concentrations in the coastal water are governed by the intensity of the mixing with the open water. The assumptions con cerning this mixing made in the model represent a large scale average; they are not applicable to specific riverine or point sources. These kinds of sources will typically be cha-racterised by strong concentration gradients close to the point of discharge, with the steepness of the gradient governed by the local hydrology.

For the open water of the Bothnian Sea, the sediment is the most important source of PCDD/Fs. Atmospheric deposition is about 3 times less. Sedi mentation is the dominant removal process. Degradation is of secondary importance, and inter-basin exchange plays no significant role. This indi cates that the concentrations in water (and hence herring) are governed by both the PCDD/F concentrations in the atmosphere and the PCDD/F reser voirs in the sediments. The relative importance of these sources will be ex plored in more detail in Chapter 9.

The open water of the Baltic Proper shows a different behaviour due to the presence of the halocline. The halocline acts as a barrier to the upward transport of POC from the deep water to the surface water. As a conse-quence, atmospheric deposition is the dominant source to the surface water, and POC sedimentation to the deep water is the dominant sink. Hence the concentrations in the surface water are closely linked to the concentrations in the atmosphere, while the level of contamination in the sediments plays almost no role. In the deep water, on the other hand, the PCDD/F input from sediments is three times larger than the indirect atmo spheric input from the surface water, so it can be expected that both the PCDD/F concentrations in the atmosphere and the PCDD/F inventory in the sediments will affect the PCDD/F concentrations in the deep water. Note that the model exaggerates this aspect of PCDD/F behaviour by assuming that the deep water compart-ment has the same surface area as the surface water compartment.

In summary, atmospheric deposition is the major known external source of PCDD/Fs to the Baltic Sea, while the PCDD/F inventory in the surface sedi-ments also has a major influence on the PCDD/F levels in the water column. The Kymijoki River has been and continues to be a major source to the Gulf of Finland, and it cannot be ruled out that there are other important riverine or direct sources in the less well studied regions of the Baltic Sea. The section on congener pattern analysis (Chapter 8.1.4) gives more insight into this issue.



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8.1.3 Evaluation of model predictive power for Pcdd/f Several PCDD/F datasets were available that allowed the evaluation of a number of key features of the model. These features included the model’s abi-lity to predict the atmospheric deposition, the dissolved water concentra tions, and the time trend in sediment concentrations. In addition, a bio accumulation model was used to predict the concentrations in herring from the output from the POPCYCLING-Baltic model, and these concentrations were compared with measured values.

Recently, bulk atmospheric deposition was measured at Aspvreten, a moni toring station located on the Swedish Baltic coast to the south of Stockholm, for 5 months between November 2006 and April 2007 (Chapter 6.3.2). The bulk deposition measurements captured the PCDD/Fs associated with wet deposition and dry sedimentation of aerosols. The deposition fluxes ranged between 0.37 and 4.3 pg TEQ m–2d–1 with a mean of 1.1 pg TEQ m–2d–1. This compares favourably with the predictions of the model, which gave an aver age of 0.7 pg TEQ m–2d–1 for wet deposition and dry depo-sition of aerosols for this period. This indicates that the model does a satis-factory job predict ing the atmospheric deposition from the air concentrations; however, it would appear to somewhat underpredict this source of PCDD/Fs to the Baltic Sea.

The ability of the model to predict time trends was assessed by initializing it in 1986 with a PCDD/F concentration in surface sediments and running it using a scenario for the PCDD/F concentrations in air from 1986 until 2006 (Figure 40, top panel). During this period the concentrations in air were assu-med to decrease linearly by a factor of 4 to current levels based on time trend information from the European Dioxin Emissions Inventory (Quaß et al. 2004) and time trends of PCDD/Fs in bioindicators of atmospheric depo sition (spruce and pine needles) in Germany (Rappolder et al. 2007). The initial (1986) concentrations in sediment were selected such that the model gave good predictions of the current (2005-2007) concentrations in sedi ment.

The model predicts the water concentrations based on the external for-cing from the PCDD/F concentrations in the atmosphere and the internal for-cing from the PCDD/F concentrations in the sediments. During 2006–2007, measured data for PCDD/F concentrations in the water of the Baltic Sea were gathered (Chapter 6.5.3). The samples were collected using a passive sampler that sampled only the dissolved phase of the water column. The measured concentrations averaged 2.0, 2.7, and 2.6 pg TEQ m–3 in the Bothnian Sea, Baltic Proper surface water, and Baltic Proper deep water, respectively. The dissolved concentrations predicted by the model for 2006–2007 were ~2.5 pg TEQ m–3 for all 3 water bodies (Figure 40, middle panel). The good agreement indicates that the model does an acceptable job at predicting the PCDD/F con-centrations in the dissolved phase. This is a key output of the model, since the concentration in the dissolved phase gov erns the bioaccumulation of PCDD/Fs through the food chain.

One of the uncertainties in modelling PCDD/F fate is the degree of en hanced sorption of these chemicals to organic carbon (Chapter 7.4.2). A sensitivity analysis was conducted to assess the impact that enhanced sorp-



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tion would have on the long term fate of PCDD/Fs in the water column. The results showed that enhanced sorption to the sediments had very little in fluence on either the PCDD/F concentrations in the water column or in the sediments (although it did strongly influence the freely dissolved concentra-tion in sediment pore-water and hence the availability of PCDD/Fs to benthic organisms). This can be explained by the fact that the diffusion of PCDD/Fs between the sediment and the overlying water, the process that is influenced by enhanced sorption, plays an insignificant role in the fate of PCDD/Fs in the Baltic Sea. Instead, sediment-water exchange of these chemicals is dominated by deposition and resuspension of particulate matter.

On the other hand, enhanced sorption of PCDD/Fs to the organic mate-rial in the water column had a strong influence on chemical fate. Although the total concentration of PCDD/Fs in the water column was not influenced, enhanc ing the sorption reduced the magnitude of the key model endpoint, the freely dissolved concentration, which in turn reduced both volatilisation and de grada tion of the PCDD/Fs. Without enhanced sorption in the water column, the model over-predicted the measured freely dissolved concentra-tions of PCDD/Fs in the Bothnian Sea and in the deep water of the Baltic Proper. Enhancing the sorption in these two water bodies by a factor of 2 gave the good prediction of the freely dissolved concentrations shown in Figure 40. For the surface water of the Baltic Proper, however, an excellent prediction was obtained with no enhanced sorption. This could be inter preted as an indication that the aging of the organic material in the water column results in an increase in its sorption capacity for PCDD/Fs, i.e. the fresher organic material from recent primary production in the surface water of the Baltic Proper has a lower sorption capacity than the more aged organic material in the deep water or in the Bothnian Sea, where the lack of stratification results in mixing of fresh organic material with resuspended, aged material. Given the pioneering nature of the measurements of the PCDD/F concentrations in the water, this interpretation should be regarded as preliminary. Note that the enhanced sorption in the water column was of no consequence for the major conclusions drawn from this study (see below).

Returning to the PCDD/Fs in surface sediments, the simulations suggested that the concentrations decreased by a factor of ~3 between 1986 and 2006. Measurements of PCDD/Fs in surface sediments collected between 1986 and 1988 indicate that the concentrations at that time were similar to the concen-trations today (Table 6 and Table 7), but the limited number of sam ples (2 for each basin), the considerable natural variability in surface sedi ment concen-trations, the fact that the analyses were made two decades ago, and the fact that the organic carbon content was not measured but estimated mean that these data give an uncertain estimate of average PCDD/F levels. As noted in Chapter 6.6.30, one recently analysed sediment core from the Bothnian Sea indicates that the PCDD/F levels in surface sediments have decreased during the last 2 decades (Verta et al. 2007). We conclude that the model predictions are not inconsistent with the empirical observations when the uncertainties in the latter are taken into account.



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Figure 40. Comparison of the model prediction of the PCDD/F concentrations in the Baltic Sea compared with measurements. The upper panel shows the PCDD/F concentrations in air that was used as input to the model for compartments A2 – A4. The middle panel shows the freely dissol-ved PCDD/F concentration in the water of the Bothnian Sea and the Baltic Proper predicted by the model (lines) compared to the concentrations measured in this study (symbols showing mean ±1 standard deviation). The lower panel shows the PCDD/F concentrations in surface sediment of the Bothnian Sea and the Baltic Proper predicted by the model (lines) compared with monitoring data (symbols showing mean ±1 standard deviation, data from Rappe et al. 1989, Kjeller and Rappe 1995, Sundqvist et al. manu script; this work). All concentrations are expressed on a TEQ basis. Note that the simula tions presented here included enhancing sorption by a factor of 2 to organic matter in the water column of the Bothnian Sea and the deep water of the Baltic Proper.

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The uncertainty in the model predictions of time trends of PCDD/F concen-trations in sediment was assessed by rerunning the model simulations using the new estimates of sediment burial of organic carbon that were made for this report (see Chapter 6.6.4, Table 12). These estimates were higher by a factor of 2 for the Baltic Proper and a factor of 5 for the Bothnian Sea than the values used for the initial simulations that were based on Jonsson (2000). The time trends in PCDD/F concentrations in surface sediments predicted by the two different simulations are compared in Figure 41. The influence of the higher burial rates was relatively small in the Baltic Proper, but in the Bothnian Sea the PCDD/F concentrations in surface sediments were predic-ted to be 10 times higher during the late 1980s than for the de fault scenario. Over the past 20 years the concentrations were postulated to have decreased by a factor of 30. This is clearly inconsistent with the empirical observations. A similar comparison for the PCBs also revealed results inconsistent with empirical observations, which were otherwise pre dicted well by the model (see Chapter 8.2.3). Hence it was concluded that the high burial scenario was not realistic.

This comparison highlights the importance of sediment burial for the fate of PCDD/Fs in the Baltic, particularly in the Bothnian Sea. The time constant for burial of PCDD/F is equal to the rate of accrual of new sediment mate rial divided by the depth of the surface sediment layer. The depth of the mixed surface sediment layer was assumed to be 2 cm based on observa tions of the thickness of the bioturbated surface layer in sediment cores from the Baltic Proper sampled several months after transition from anoxic to oxic condi-tions (Per Jonsson, personal communication). The diversity of accumulation sediments in the Baltic Sea is large. In the anoxic stratified sediments of the Gotland Deep in the Baltic Proper, the mixed layer depth will be <2 cm, while in the oxic sediments in the shallower Bothnian Sea there is evidence that the mixed layer depth is considerably greater. Two thirds of the cores taken in accumulation sediments from the Bothnian Sea fail to show a distinct Cs-137 peak as a result of the fallout from the Cherno byl accident in 1986 (Per Jonsson, personal communication). This indicates that there is intense vertical mixing of these sediments. Deeper mixing will lengthen the residence time of contaminants in the surface sediment. A better understanding of surface sedi-ment accumulation and mixing is needed to produce more reliable estimates of the response time of the Baltic Sea to changes in PCDD/F inputs.

In summary, the evaluation indicates that the model gives reasonable pre-dictions of the atmospheric deposition and the freely dissolved concentra tions of PCDD/Fs in water. There is some uncertainty regarding the model predic-tions of time trends in sediments. It is possible that the recovery time of the Baltic Sea sediments following reduction of PCDD/F inputs may be different than predicted by the model.



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8.1.4 congener pattern analysis of the Pcdd/fs In addition to the mass balance modelling, a second method was used to gain insight into the sources of PCDD/F contamination in the Baltic Sea. The congener pattern of the PCDD/Fs in the Baltic Sea was compared with the congener pattern present in different potential sources of the PCDD/F conta-mination. PCDD/Fs lend themselves to a congener pattern analysis because:

- 17 different congeners of PCDD/Fs are commonly analysed;- the congener patterns of emitted PCDD/Fs vary widely from source

to source and are often unique to a source type;- PCDD/F congeners are very persistent in the physical environment,

and therefore the source pattern tends to be conserved in the physi-cal environment.

There is, however, one major caveat to the above. Although the PCDD/F pattern of congeners with similar physical chemical properties (i.e. within a homologue group) tends to be conserved, changes can occur between con-geners with widely different physical chemical properties. This is because dif-ferences in partitioning behaviour can lead to fractionation of the PCDD/F mixture during its passage through the environment. This was taken into account in the data normalization.

The assessment of the PCDD/F inventory in the Baltic Sea indicated that the surface sediments contain >99 % of the PCDD/F in the Baltic marine envi ronment. Therefore the congener pattern in the surface accumulation sedi ments best represents the pattern of the PCDD/F contamination in the Baltic Sea. The data from both the older surface accumulation sediments (1985/1986) and the more recent surface accumulation sediments (2005–2007) were included in the analysis.

Figure 41. Comparison of the model prediction of recent PCDD/F concentra tions in the surface sediments of the Baltic Sea using different assumptions for the burial rate of sediment organic carbon. The default scenario and the measured data are the same as in Figure 40 and are based on the sediment organic carbon burial rates of Jonsson (2000). The high burial scenario is based on the sediment organic carbon burial rates from Table 12.

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The congener patterns in these sediment samples were compared with the pat-terns from 14 source and effluent samples. The majority of the effluent samp-les were collected in Sweden as part of the Swedish Dioxin Survey (Cynthia de Wit, personal communication). These samples included effluent from the pulp & paper and other industries. A contaminated soil from a plant that used the chlor-alkali process, a sediment heavily polluted with Ky-5 (technical chlorophenol-product dominated by 2,3,4,6-tetra-chloro phenol; Koistinen et al. 1995; site KRSE2) and four different pentachloro phenol (PCP) technical products were also used.

Given the finding in the modelling work indicating that the atmosphere was the major external source of PCDD/Fs to the Baltic Sea, ambient air (com bined gas-phase and particle-bound) and bulk deposition samples were also included in the comparison. The 24 h ambient air samples collected in the framework of this project at Aspvreten during 2006 and 2007 were em ployed together with 30-day bulk deposition samples from the same period and loca-tion.

In order to minimize the effect of pattern changes caused by physical chemical fractionation of the PCDD/F (see above), the data were normalised as follows:• thetetra- and penta-chlorinated DD/F congeners were normalised to

the sum of the 5 tetra- and penta-chlorinated DD/F congeners• thehexa-chlorinated DD/F congeners were normalised to the sum of

the 7 hexa-chlorinated DD/F congeners• thehepta- and octa-chlorinated DD/F congeners were normalised to

the sum of the 5 hepta- and octa-chlorinated DD/F congeners

The normalised data were then subject to principle component analysis using the software package SIMCA-P Version 10 (Umetrics AB). The data were scaled to unit variance and mean centred.

Figure 42 shows plots of the first two principle components. They yielded cumulative r2 and q2 values of 0.53 and 0.20, respectively. The object plot (Figure 42, bottom plot) shows a tight cluster at the intersection of the axis that contains the current surface sediment samples. The tightness indicates that the congener pattern in these samples is very uniform. One of the sur face sediment samples from 1985/86 also lies in this cluster, but the other three are spread out above and to the right. This may indicate more hetero geneity in the PCDD/F pattern in the surface sediments at that time. The two samples to the right are both from the Bothnian Sea (SR5 and Iggesund 30 km, Rappe et al. 1989, see also Table 6), and both contain comparatively higher levels of the more chlorinated DDs.

The object plot further shows that the air samples form a half circle above and to the left of the current sediments. The comparatively large spread in the air samples indicates that there is considerable variation in the PCDD/F pat-tern. This likely reflects variation in the PCDD/F emissions sources to the air. Each of the air samples had a stable air mass origin during the short sampling



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period. Since the sampling strategy minimized the mixing of different air masses, it is likely to have maximized the differentiation in the PCDD/F pat-terns in the air. The bulk deposition samples, which were inte grated over a longer period of time, are grouped closer together. They lie within the space covered by the air samples, a short distance above the sediment cluster.

All of the other potential sources included lie very distant from the sedi-ment cluster. These include three of the technical PCP mixtures, two pulp and paper plant effluents, effluents from two bleached sulphate mills, effluent from a paper recycling plant, scrubber water from the rubber industry and PVC burning, the soil contaminated by the chlor-alkali process and the sediment polluted by Ky-5 (the last two points lie to the lower left in the object plot). There are two exceptions. One is a PCP technical product with an unusual pattern (Witophen P, see Hagenmaier and Brunner 1987), which lies to the right of the sediment cluster. The second is effluent from the Rönnskärsverken, which groups with the atmospheric samples above the cluster. Since this source is located in the north of the Baltic, it is unlikely that it is the dominant source of the PCDD/F contamination of the sediments of the Baltic Proper.

The loading plot (Figure 42, top plot) provides insight into the differen-ces between the samples. The PCDDs all lie to the right in the plot, together with most of the sources, while the PCDFs lie to the left, together with the sediment and atmospheric samples and the chlor-alkali and Ky-5 sediment sources. The vertical downward differentiation is most strongly influenced by 2,3,7,8-TCDF, 1,2,3,7,8,9-HxCDF, 1,2,3,4,7,8,9-HpCDF and OCDF, while vertical upward differentiation is most strongly influenced by 2,3,4,7,8-PeCDF 1,2,3,6,7,8-HxCDF, 2,3,4,6,7,8-HxCDF, and 1,2,3,4,6,7,8-HpCDD. High contributions of the latter congeners would tend to place ob jects higher in the plot, while high contribution from the other group, would tend to place objects lower in the plot. Indeed, the sediment samples had consistently higher contributions of OCDF than the atmospheric samples did, which may partly explain the vertical separation of the sediment sam ples from many of the atmospheric samples in the object plot. The four air samples that lie at or below the x-axis also all had high OCDF contributions. The concentrations of 1,2,3,4,7,8,9-HpCDF and 1,2,3,7,8,9-HxCDF were low in all samples, and below the limit of quantification in many of the air samples, which may also have contributed to the vertical separation.

It is possible that some of the differences arise from analytical artefacts re lated to the congeners discussed above. The atmospheric samples were ana-lysed in one laboratory, while the sediment samples were analysed in a second laboratory.

The similarity between the PCDD/F congener patterns in accumulation sediments and in ambient air/atmospheric deposition provides further evi-dence that atmospheric deposition has been the major source of the current basin scale PCDD/F contamination of surface sediments in the Baltic Proper and the Bothnian Sea. This hypothesis is strengthened by the fact that the pat-terns in the two industrial sources that are believed to have been most signifi-



105

cant, namely pulp and paper mill effl uent and use of chlorophenol for wood treatment, are clearly different from the patterns in remote surface sediments. Note that the contribution from various sources to surface sedi ments in coas-tal areas affected by human activities is often more complex than at offshore sites.

Figure 42. Loading plot (top) and object plot (bottom) showing the fi rst and second compo nents from the PCA analysis of PCDD/F patterns in surface accumulation sediments from 2005/07 (05– 07 Sed; this study and Sundqvist et al. manuscript) and 1985/86 (85 Sed; Rappe et al. 1989, Kjeller and Rappe 1995), in atmospheric deposition samples (AD; this study), in air samp-les (ITM Air; this study) and in samples representative of sources (Sources).



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8.2 PCBs

8.2.5 PcB inventoriesThe total inventory of PCBs (ΣPCB7, kg) in Baltic Sea surface sediments (top 2 cm) was 2500 kg, while the water column contained ~10% of this quantity (285 kg). Like the PCDD/Fs, the surface sediments contain a large inventory of PCBs compared with the water column. Thus the surface sedi ments must be considered to be a potential major source and buffer of the PCB contami-nation in the water column.

8.2.6 PcB flowsThe magnitude of the mass flows of PCBs (ΣPCB7, kg yr-1) between the various compartments in the Baltic Proper and Bothnian Sea are presented in Figure 43 and Figure 44, respectively.

Considering the marine environment as a whole, the major external source is atmospheric deposition, which exceeds the estimated riverine inputs by 2 orders of magnitude. There was insufficient information available to esti-mate direct emissions of PCBs to the Baltic Sea for the model simulations. However, available information on emissions from specific sources or source classes can be compared with the atmospheric deposition. For in stance, it was estimated that the total quantity of ΣPCB7 in sewage sludge produced in Stockholm County in 2003 was 2.2 kg (Swedish Environmental Protection Agency 2005). It can be assumed that <1% of this quantity was released via the sewage treatment plant (STP) effluent to water, i.e. <0.02 kg. Compared to the annual atmospheric deposition of ΣPCB7 to the Baltic Proper of 500 kg, this quantity is negligible. In another example, total annual emissions of PCBs from the Swedish chemical industry to water were estimated to be 1.1–16 g TEQ for the period 2001–2004 (Swedish Environmental Protection Agency 2005). Assuming a conversion factor for TEQ to ΣPCB7 of 100, this would amount to 0.11–1.6 kg ΣPCB7 yr-1. This is also very small compared to the atmospheric deposition to the Baltic Proper of 500 kg ΣPCB7 yr-1. Based on available information, the input of PCB from point sources is much less than the atmospheric deposition. Note that this does not mean that emissions of PCBs are trivial. To the contrary, the dominance of atmospheric deposition is a consequence of the persistence and mobility of PCBs in the environment. New emissions of PCBs contrib ute to the pool of PCBs circulating in the environ ment.

The major sink for the PCBs in the marine system is volatilisation. Sediment burial is also significant, but about 3.5 times less than volatilisa-tion. De gra dation amounts to about one third of the burial, while inter-basin ex change is negligible. The large volatilisation of the PCBs stands in contrast to the behaviour of the PCDD/Fs. It can be attributed to the weaker tendency of the PCBs to associate with POC in the water column and to their higher



107

air/water partition coefficients. The presence of volatilisation as a major sink means that PCBs are dispersed from the Baltic Sea marine envi ronment more quickly than the PCDD/Fs. Using the current inventories and current loss rates, the PCB residence time was estimated to be 2.4 years for the Baltic Proper and 1.8 years for the Bothnian Sea.

Figure 43. Model estimates of current mass flows of ΣPCB7 in the coastal (a) and open water (b) compartments of the Baltic Proper (in kg yr-1).

Figure 44. Model estimates of current mass flows of ΣPCB7 in the coastal (a) and open water (b) compartments of the Bothnian Sea (in kg yr-1).

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Examining the sources and sinks to the water column alone, atmospheric deposition (largely gaseous deposition) is the most important source and vola-tilisation is the most important sink in all basins. In most cases the atmosphe-ric deposition and the volatilisation are very similar. This is an indication that the PCBs in the atmosphere and the Baltic Sea are close to a partitioning equi-librium. This implies that there is an intimate link between the concentrations of PCBs in the atmosphere and in the water column of the Baltic Sea.

Despite this common feature, there are important qualitative differences in the water column mass balances between the coastal and open water compartments and between the Bothnian Sea and the Baltic Proper. The rela-tive importance of sediment-to-water transfer is greatest in the coastal areas. As discussed previously, this is a consequence of the more intensive cycling of POC between the water column and the sediment due to the shallower water. Since there is little accumulation sediment in the shallow coastal areas, the sediments do not contain a large PCB reservoir that can serve as a long term source of PCBs to the water column. Instead, over a time scale of years the inputs are governed by atmospheric deposition and, to a lesser extent, by riverine/direct inputs and inflow from the open water. Volatilisation is the major loss mechanism, while advection to the open water is also considerable. Simplified, the mass balance indicates that the concentrations in the coastal water are largely governed by equilibration with the atmosphere, although there is a net transfer of riverine inputs and excess atmospheric deposition to the open water.

For the open water of the Bothnian Sea, the input from sediment is negligi-ble compared to atmospheric deposition, and volatilisation is large com pared to transfer to the sediment. This indicates that the PCB concentrations in the water are almost completely controlled by atmospheric exchange.

The open water of the Baltic Proper shows once again a different beha-viour due to the presence of the halocline. Atmospheric deposition is prac-tically the only source in the surface water due to the very low transport upwards through the halocline. Volatilisation is the dominant sink, as for the Bothnian Sea. However, in contrast to the Bothnian Sea the volatilisation in the Baltic Proper is considerably lower than the atmospheric deposition. This can be attributed to the sedimentation of some of the PCBs out of the surface water into the deep water, where it is no longer available for ex change with the atmosphere. This can be viewed as a “stripping” process that lowers the PCB concentrations in the surface water and hence reduces volatilisation. In the deep water, on the other hand, the input from sediments is of comparable magnitude to the indirect atmospheric input from the sur face water, so it can be expected that both the PCB concentrations in the atmosphere and the PCB inventory in the sediments will affect the PCB concentrations in the deep water.

In summary, atmospheric deposition is the major external source of PCBs to the Baltic Sea. Atmospheric concentrations control the concentrations in the water column. The large PCB reservoir in sediments has little influence on the water concentrations, with the possible exception of the deep water of the Baltic Proper.



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8.2.7 Evaluation of model predictive power for PcBsThe different environmental behaviour of the PCBs compared to the PCDD/Fs means that a somewhat different approach must be taken to evaluating model performance for this set of chemicals. Because the atmo spheric deposition to the Baltic Sea occurs largely via gaseous diffusion, wet and dry particle-bound deposition is of little relevance for the mass bal ance. However, the ability of the model to predict the water concentrations is of central importance.

The model was employed to predict the PCB concentrations in the dissol-ved phase of the Baltic Proper by conducting a simulation from 1989 to 2007 as described in Chapter 7. The approximation of the ΣPCB7 concentration in air that was used as model input is shown in the upper panel of Figure 45 together with the monitoring data that were used to derive this approxima-tion. The middle panel shows the dissolved concentration in the surface water of the Baltic Proper predicted by the model and compares it with the monito-ring data (the ΣPCB6 plotted as the monitoring data do not include PCB 28). Only in recent years has the quality of the sampling and analytical methods been sufficient to reliably measure PCBs in seawater. The agree ment is very good, demonstrating that the model predicts the PCB concen trations in water well.

The ability of the model to predict time trends was evaluated using the PCB concentrations in sediment, as measured data were available from the late 1980s. The lower panel of Figure 45 shows the results for the Bothnian Sea and Baltic Proper open water compartments. Both the model predictions and the measurements indicate a decrease in the PCB concentrations in surface sediment by a factor of ~5 during this period. The good agreement indicates that the model predicts the time trends of PCB levels in the Baltic Sea well.

In summary, the model evaluation indicates that the model gives good pre dictions of the PCB concentrations in water. These predictions, when com-bined with a bioaccumulation model, give good estimates of the PCB levels in herring. In addition, the time trend of PCB levels in the surface sedi ments, the major reservoir of available PCBs in the Baltic, is predicted well by the model.



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Figure 45. Comparison of the model prediction of the ΣPCB7 concentra tions in the Baltic Sea with measurements. The upper panel shows the ΣPCB7 concentrations in air measured in southern Sweden and Norway (symbols, data from EMEP 2007) and the concentration that was used as input to the model for compartments A2 – A4 (line). The middle panel shows the freely dissolved ΣPCB6 concentration in the surface water of the Baltic Proper predicted by the model (line) compared to the concentrations measured in the German monitoring program and a Swedish research pro ject (symbols showing mean ±1 standard deviation, data from McLachlan et al. 2003, Wodarg et al. 2004, Sobek et al. 2004, Schulz-Bull et al. 2004, Schulz-Bull et al. 2005; PCB 28 was not quantified and hence the sum of just 6 PCB congeners is plotted). The lower panel shows the ΣPCB7 con centrations in surface sediment of the Bothnian Sea and the Baltic Proper predicted by the model (lines) compared with monitoring data (symbols showing mean ±1 standard deviation) (Gustavson and Jonsson 1999, Jonsson 2000, Cato and Kjellin 2005, Sundqvist unpublished, this work).

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8.3 HCB

8.3.1 hcB inventoriesThe total inventory of HCB in the Baltic Sea was estimated for the water column and surface sediments based on the most current (2000–2006) con-centrations in each geographical area and the volume of each compartment. The resulting HCB inventory in Baltic Sea surface sediments (top 2 cm) was 320 kg, while the water column contained 220 kg. The ratio of the quantity in the water column and the quantity in surface sediments is much higher for HCB than for PCDD/Fs and PCBs.

8.3.2 hcB flows The magnitude of the mass flows of HCB (kg yr-1) between the various compartments in the Baltic Proper and Bothnian Sea are presented in Figure 46 and Figure 47, respectively.

Considering the marine environment as a whole, the major source of HCB is atmospheric deposition, which exceeds the estimated riverine inputs by al most three orders of magnitude. There was insufficient information avail-able to estimate direct emissions of HCB to the Baltic Sea for the model simu-lations. However, available information on emissions from specific sources or source classes can be compared with the atmospheric deposition. For instance, total annual emissions of HCB from the Swedish chemical industry to water were recently estimated to be 50–70 g (Swedish Environ mental Protection Agency, 2005). This is very little compared to the annual atmospheric deposi-tion of 890 kg to the Baltic Proper. Based on available information, the input of HCB from point sources is much smaller than the atmospheric deposition. Note that this does not mean that emissions of HCB are trivial. As with the PCBs, the dominance of atmospheric deposition is a consequence of the persis-

Figure 46. Model estimates of current mass flows of HCB in the coastal (a) and open water (b) compartments of the Baltic Proper (in kg yr-1).

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tence and mobility of HCB in the environment. New emissions of HCB contri-bute to the pool of HCB circulating in the environment.

The major sink for HCB in the marine system is volatilisation. Sediment burial is insignificant, which is a reflection of the low affinity of HCB for sus-pended particulate material in the water column. Degradation and inter-basin exchange are also negligible compared to volatilisation. The presence of vola-tilisation as a major sink and the fact that there is no large sediment reservoir means that HCB levels in the Baltic Sea marine environment can drop even more quickly than PCB levels. Using the current inventories and current loss rates, the HCB residence time was estimated to be 0.24 years for the Baltic Proper and 0.34 years for the Bothnian Sea.

Examining the sources and sinks to the water column alone, atmospheric deposition (gaseous deposition) is by far the most important source and vola-tilisation by far the most important sink in all cases. No other processes play a significant role in HCB fate in the Baltic Sea. In most cases the atmo spheric deposition and the volatilisation are very similar. This is an indica tion that the HCB in the atmosphere and the Baltic Sea are close to a parti tioning equili-brium. This implies that there is an intimate link between the concentrations of PCBs in the atmosphere and in the water column of the Baltic Sea. It is only in the deep water of the Baltic Sea where this link be comes weaker, since the transport of HCB across the halocline is slow.

In summary, atmospheric deposition is the major external source of HCB to the Baltic Sea, and atmospheric concentrations control the concentrations in the water column. The HCB reservoir in sediments is insignificant and has almost no influence on the water concentrations.

Figure 47. Model estimates of current mass flows of HCB in the coastal (a) and open water (b) compartments of the Bothnian Sea (in kg yr-1).

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72.1 228.2

1.7 4.8

4.7

73.6 228.0

0.03

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0.040.01

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8.3.3 Evaluation of model predictive power for the hcBAs shown above, the behaviour of HCB in the Baltic Sea is governed by gaseous exchange with the atmosphere; sediments play a negligible role. Hence, the key aspect of model performance is its ability to predict the HCB concentrations in water from the concentrations in the atmosphere.

The model was employed to predict the HCB concentrations in the dis-solved phase of the Baltic Proper by conducting a simulation from 2000 to 2005, initializing the HCB concentrations in sediment with measured data from the Kattegat, and using a scenario for the HCB concentrations in air based on weekly measurements from the EMEP monitoring stations (Chap ter 7.6 and Figure 48). The modelled HCB concentrations in water were compared with measured values (Figure 48). Since 2000, a large number of measure ments have been made of HCB concentrations in the water of the Baltic Proper. The modelled and measured concentrations in water show good agreement. This demonstrates that the model predicts the HCB con centrations in water well.

Figure 48. Comparison of the model prediction of the HCB concentrations in the Baltic Sea com-pared with measurements. The upper panel shows the HCB concen trations in air measured at the EMEP stations in Lista and Birk enes, Norway (symbols, data from EMEP 2007) and the concentra-tion that was used as input to the model for compartments A2 – A4 (line). The lower panel shows the freely dis solved HCB concentration in the surface water of the Baltic Proper predicted by the model (line) compared to the concentra tions measured in the German monitor ing program (sym-bols showing mean ±1 standard deviation) (data from McLachlan et al. 2003, Wodarg et al. 2004, Schulz-Bull et al. 2004, Schulz-Bull et al. 2005).

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8.4 Summary and comparison of the behaviour of the POPsTable 15 summarises some key characteristics of the environmental behav iour of the three classes of POPs in the Baltic Sea identified in this chapter.

One common feature of all three POP classes is that they enter the Baltic Proper and the Bothnian Sea primarily via the atmosphere. For HCB the atmospheric input is so large that it is implausible that other sources make a major contribution. The atmospheric input of PCBs is also much larger than other known sources. For PCDD/Fs, the situation is less clear. There is a pos-sibility that there are other, as yet unidentified major riverine or direct sources of PCDD/Fs. However, analyses of congener patterns in offshore sediments and atmospheric samples indicate that atmospheric deposition of PCDD/Fs is a major source. It should be noted that sediments sampled near industrialised and urbanised areas have shown PCDD/F patterns that are distinctly different from the atmospheric pattern.

The residence time of the chemicals in the basins also influences the poten-tial role of non-atmospheric sources. The residence time is much shorter for HCB and PCBs than it is for PCDD/Fs. This means that the levels of these che-micals in the Baltic Sea will respond rapidly (within several years) to changes in the inputs. This coupled with the intensive air – water exchange of gaseous HCB and PCBs means that the concentrations of these chemicals in the water column are essentially regulated by the concentrations in the atmosphere. Even if there would be major riverine or direct sources, their impact on the Baltic Sea would be reduced by volatilisation.

For the PCDD/Fs, on the other hand, a long residence time is coupled with a low potential for volatilisation. Once PCDD/Fs enter the Baltic Sea, sedi-ment burial is the major loss mechanism. They accumulate in sediments, and the large chemical inventory in the sediment can become a major source to the water column, particularly when levels in the atmosphere decrease. This can be amplified if deeper bioturbation or increased gale frequency lengthens the PCDD/F residence time by increasing the active layer of the surface sediments.

Table 15. Summary of key characteristics of POP behaviour in the Bothnian Sea and the Baltic Proper.

hcB PcB Pcdd/f

inventory (water + surface sediment)

540 kg 2 800 kg (ΣPCB7) 10 kg TEQ

% of inventory in water 40 9 4

residence time (yr)* 0.34 1.8 11

major source Atmosphere Atmosphere Atmosphere

major sink Atmosphere Atmosphere Sediment burial

* Bothnian Sea



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8.5 Linking POP levels in water and sediment to levels in Baltic Sea fishCurrent understanding of POP bioaccumulation in pelagic fish indicates that the concentrations in the fish are linearly proportional to the freely dissolved concentrations in the water column. Hence, for a given food chain a de crease in the dissolved concentrations of the POPs would result in a pro portional decrease in the concentrations in the fish.

Several mechanistically based mathematical models of bioaccumulation in aquatic ecosystems have been assembled. One, the ACC-HUMAN model (Czub and McLachlan 2004), has been employed to model the bioaccumu-lation of PCBs in herring in the Baltic Proper. A historical scenario for the freely dissolved PCB concentrations in the Baltic Proper was constructed based on the recent measurements discussed above as well as time trend infor-mation. This was used as input for the ACC-HUMAN model, which then predicted the lipid-normalised concentrations in herring. In Figure 49, the predicted concentrations of the individual congeners in 4-year old herring and cod are compared with the concentration of PCB 153 measured in the Swedish Environmental Monitoring Program (IVL 2008b). The agreement is good, which indicates that the understanding of POP bio accumulation in the Baltic and its link to the freely dissolved concentration is sound.

Peltonen et al. (2007) applied a different bioaccumulation model to predict the concentrations of PCDD/Fs in herring from the Bothnian Sea. Although this model had no direct link to the concentrations in the physical environ ment (the model input was the concentration in the fish’s prey), this work illustrates the importance of fish growth rates and feeding habits on the PCDD/F concentrations in herring. It shows how changes in these variables can result in time trends in PCDD/F concentrations in herring that differ from the time trends of the PCDD/F concentrations in the physical environ ment. Hence, a decrease in the freely dissolved concentrations of the PCDD/Fs may not result in a proportional decrease in the concentrations in herring if the structure of the ecosystem changes; the decrease may be larger or smaller, or the concentrations could even increase.

At this point it is instructive to return to the spatial trends in PCDD/F levels in herring that were discussed in Chapter 5.1 and to explore whether they are related to gradients in contamination of the physical environment or in the structure of the ecosystem. One observation was an increase in the lipid-normalized concentrations moving from the Baltic Proper into the Bothnian Sea. Peltonen et al. (2007) show that this may be explained by the slower growth rates of the northern herring populations, i.e. that this spa-tial trend is related to differences in the structure of the ecosystem. Another demonstra tion that gradients in concentration in biota need not be related to gradients in contamination of the physical environment is provided in Figure 7a. PCB concentrations in herring are seen to increase moving from the Kattegat to the open Baltic Proper. However, as discussed in Chapter 6.5.2,



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a decreas ing (i.e., opposite) gradient in PCB concentration in water between the Mecklenburg Bight and the Baltic Proper has been consistently observed. Hence, the even stronger west to east gradient in PCDD/F concentrations in herring compared to PCBs (Figure 7a) could be explained by there being no gradient in the PCDD/F contamination of the water column. Alternatively, it may be a consequence of the fact that PCDD/F concentrations in herring are more strongly influenced by differences in growth dilution than PCBs due to their greater hydrophobicity.

Figure 49. Concentrations of PCB 153 in 4-year old herring and cod from the Baltic Proper over time as predicted by the ACC-HUMAN model and as measured in the Swedish environmental mo-nitoring program (IVL 2008b). See Czub and McLachlan (2004) for details on the model and the scenario employed.



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9 Evaluation of the future devel opment of the contamina tion of the Baltic SeaThe modified POPCYCLING-Baltic model was applied to evaluate the future development of the contaminant levels in the Baltic Sea environment. Two dif-ferent scenarios were chosen based on the finding that atmospheric deposition is the major source of all 3 chemical groups. In Scenario 1, no changes to con-taminant levels in the atmosphere were made, while in Scenario 2 atmospheric concentrations of the contaminants of interest were linearly reduced to 10% of the initial values over a 10-year period. The pur pose of these simulations was to investigate the potential impact of reduced atmospheric concentrations on the long-term dynamics of these contami nants in the Baltic Sea environ-ment. The results for each scenario are pre sented in the following sections.

9.1 PCDD/FsFor scenario 1 (unchanged atmospheric concentrations) the predicted future PCDD/F concentrations in the water column (pg TEQ L–1) and in surface sedi-ments (pg TEQ g–1 dry weight) of the Baltic Proper (surface water and deep water) and Bothnian Sea are shown in the left panels of Figure 50. The con-centrations in the surface sediments continue to decrease gradually, largely as a result of burial by less contaminated new sediment. The con centrations in water also decrease slowly to a level ~60% below current levels. The concen-trations in the Baltic Proper surface water stabilize most rapidly – by about 2015 – while the decrease in the Baltic Proper deep water and in the Bothnian Sea is more gradual, continuing over at least 40 years.

For scenario 2 (reduced atmospheric concentrations), the reduction in PCDD/F concentrations in the atmosphere is followed by a decrease in the water column (the right panels of Figure 50). This decrease is most immedi-ate for the Baltic Proper surface water, and by 2025 (when the concentration in the atmosphere has again stabilized) the concentration in water has al ready dropped to ~20% of its value in 2015. The decrease in the Bothnian Sea water is more gradual as a result of the buffering effect of the surface sediments; after 10 years the concentration has only dropped ~45%, and it takes 25 years for it to approach 20%. The response in the deep water of the Baltic Proper is also slow, but somewhat more rapid than in the Bothnian Sea. The PCDD/F concentrations in the surface sediments also decrease, but more gradually. This is in accordance with the long residence times of PCDD/F in the Baltic marine environment.

The simulations suggest that the freely dissolved PCDD/F concentrations in the water of the Baltic Proper and the Bothnian Sea will continue to de crease over the next 20 years to about a factor of two below current



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levels as a result of the slow response of the Baltic system to the decreases in atmo spheric inputs that have already occurred over the last decades. Since the dissolved concentrations in water determine the concentrations in fish, a parallel decrease in the concentrations in the fish stocks would be expected, barring changes in the food web structure and energetics. Eventually the con-centrations in most fish would lie below the current EU guidelines for marke-ting as food.

The simulations also show that this gradual reduction in PCDD/F concen-trations could be markedly accelerated by reducing the concentra tions in the atmosphere, and that the final steady state concentrations would also be redu-ced. Indeed, the absence of other known major current sources of PCDD/Fs to the Baltic Proper and the Bothnian Sea suggests that this is the only option for positively influencing the PCDD/F concentrations in the water.

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Figure 50. Simulations of future PCDD/F concentrations in the Baltic Sea assum ing that the PCDD/F concentrations in air remain at current levels (left hand panels) or that the PCDD/F con-centrations in air decrease from their current levels beginning in 2015 to 10% thereof in 2025 (right hand panels). The upper panels show the concentrations in air for compartments A2 – A4 (model input). The middle panels show the dissolved concentra tions in the water of the Baltic Proper and the Bothnian Sea. The lower panels show the concentrations in the corre sponding sur-face sediment. All concentrations are for PCDD/F TEQs.



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Regarding the possibilities for reducing atmospheric deposition to the Baltic Sea, there is evidence that regional emissions of PCDD/Fs to air have an impact on the PCDD/F concentrations in air over the Baltic Sea. The PCDD/F concentrations in air are much higher in air masses that have passed over the industrialized areas to the south, southeast, and southwest of the Baltic Sea than in air that has come from the north, northeast, or north west (Chapter 6.3.2). This suggests that the PCDD/F emissions in central, eastern, and wes-tern Europe significantly impact the concentrations in air over the Baltic Sea. It was estimated that air from these southerly, south-easterly, and south-westerly directions accounted for ~80% of the wet depo sition and ~50% of the gaseous deposition of PCDD/F to the Baltic Sea during the study period (October 2006 to April 2007). Thus it is likely that reducing PCDD/F emis-sions to air in industrialized Europe would result in a reduction of PCDD/F levels in the Baltic Sea. Further insight into the most important source areas could be provided by atmospheric dispersion model ling, but that was beyond the scope of this study.

Moreover, it may also be possible to reduce the PCDD/F concentra-tions in the fish stocks by fisheries management techniques. This approach builds on reducing the water-to-fish bioaccumulation of the PCDD/Fs, which could mean lower concentrations in fish, even if the PCDD/F concentrations in water were not to change. This could be achieved by e.g. increasing the growth rate of the fish (Peltonen et al. 2007).

9.2 PCBsThe model predictions for ΣPCB7 for scenario 1 (unchanged ΣPCB7 con-centrations in the atmosphere) are shown in the left panels of Figure 51. The ΣPCB7 concentrations in the Bothnian Sea and the surface water of the Baltic Proper remain at their current levels. The concentrations in the sur-face sediments continue to decrease somewhat, particularly in the Baltic Proper, as does the concentration in the deep water of the Baltic Proper, but the decrease is small compared to that observed and modelled for the last years (Figure 45). This suggests that the PCB distribution in the Baltic Sea/ atmosphere system has approached a steady state.

The predictions for scenario 2 (a 90% decrease in ΣPCB7 concentrations in the air beginning in 2015) are shown in the right panels of Figure 51. The ΣPCB7 concentrations in the water of the Bothnian Sea and in the surface water of the Baltic Proper react quickly to the change in the concentrations in the atmosphere; they also decrease to ~10% of the original level with little time delay with respect to the concentrations in air. The ΣPCB7 con centrations in the deep water also decrease, albeit more slowly, while the sediments show an even slower decrease that extends over several decades. Eventually the con-centrations in all compartments approach a new steady state where the con-centrations are 10% of the current levels.



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The simulations clearly demonstrate that reducing the PCB concentrations in air is an effective way to reduce the PCB levels in the Baltic Sea. The concentra-tions in the water column are more closely coupled to the concen trations in the atmosphere than is the case for the PCDD/Fs, which causes the concentrations in water to respond more quickly to changes in the con centrations in air. For PCBs it is even clearer that there are no effective alternatives to reduce the water con-centrations; they will stay close to their present levels if the inputs do not change, and atmospheric deposition is the only PCB source that has a significant impact on the PCB mass balance, at least for the Bothnian Sea and the Baltic Proper.

Reducing the atmospheric concentrations of PCBs requires not just regional, but hemispheric efforts. PCBs have a longer residence time in the atmo sphere than PCDD/Fs, and hence they are more subject to long range atmospheric transport. Hence, a substantial portion of the PCBs in the atmosphere over the Baltic Sea may not originate from the Baltic drainage basin. In addition, PCBs are subject to secondary emissions from reservoirs in the environment such as soils. It is possible that a considerable portion of the PCBs entering the atmosphere over the European continent originate from these sources and not from primary emissions.

Figure 51. Simulations of future PCB concentrations in the Baltic Sea assum ing that the PCB concen-trations in air remain at current levels (left hand panels) or that the PCB concentrations in air decrease from their cur rent levels beginning in 2015 to 10% thereof in 2025 (right hand panels). The upper pa-nels show the concentra tions in air for compartments A2 – A4 (model input). The middle panels show the dissolved concentrations in the water of the Baltic Proper and the Bothnian Sea. The lower panels show the concentrations in the corresponding surface sedi ment. All concentrations are for ΣPCB7.

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9.3 HCBThe model predictions for HCB for scenario 1 (unchanged HCB concentra-tions in the atmosphere) are shown in the left panels of Figure 52. The HCB concentrations in the water column remain at their current levels.

The predictions for scenario 2 (a 90% decrease in HCB concentrations in the air beginning in 2015) are shown in the right panels of Figure 52. The HCB concentrations in the water of the Bothnian Sea and in the surface water of the Baltic Proper react in step with the change in the concentrations in the atmosphere; they also decrease to ~10% of the original level with virtually no time delay with respect to the levels in air.

The HCB contamination of the Baltic Sea is closely tied to the levels in the atmosphere. However, the opportunities to reduce HCB levels in the atmo-sphere by local or regional actions are limited. HCB is an organic contami-nant with an extremely high long range transport potential. It also partitions readily from the air into other media such as soil and water which buffer its concentrations in the atmosphere. Consequently, HCB is truly a global con-tamination problem; similar concentrations are measured in air around the Northern Hemisphere (Barber et al. 2005). The only realistic possibility for reducing its levels in air are successful action to reduce emissions interna-tionally (e.g. through the implementation of the Stockholm Convention), and time. Following elimination of HCB sources on a global scale, the HCB inven-tory currently circulating in the environment will slowly decrease as the HCB is removed to more permanent sinks like deep sea sediments. However, this process is slower than for other POPs, as suggested by the comparatively small fraction of HCB in Baltic Sea sediment in relation to the water column when compared with PCBs and PCDD/Fs (Chapter 8.4).

Figure 52. Simulations of future HCB concentrations in the Baltic Sea assuming that the HCB con-centrations in air remain at current levels (left hand panels) or that the HCB concentrations in air decrease from their current levels beginning in 2015 to 10% thereof in 2025 (right hand panels). The upper panels show the concentra tions in air for compartments A2–A4 (model input). The lower panels show the dissolved concentrations in the water of the Baltic Proper and the Bothnian Sea.

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9.4 Uncertainties in the assessmentIn the following the uncertainty of the modelling results is explored. The dis-cussion is structured around the major conclusions of Chapters 8 and 9 using a 6-level qualitative scale (highly certain, very certain, quite certain, quite uncertain, very uncertain, and highly uncertain):

a) Air is the dominant external source of HCB and PCBs to the Baltic Sea. This conclusion is considered to be highly certain for HCB and very certain for PCBs. The atmospheric deposition of these chemi cals is much larger than the estimated riverine inputs and known direct inputs. There is a lack of information on PCB and HCB inputs along the south-eastern coast between the Neva and the Oder rivers, so it cannot be ruled out with certainty that there are significant sources. However, the good agreement between predicted and meas ured concentrations in water and sediment including time trends supports this conclusion. Note that the highest PCB concentrations in water have not been measured in the south-eastern parts of the Baltic Proper, but rather in the south-western parts (e.g. Wodarg et al. 2004).

b) The concentrations of HCB and PCBs in the water column will react quickly to changes in the concentrations in the atmosphere. This conclusion is considered to be highly certain for HCB and very cer tain for PCBs. The input to the water column is clearly larger from the atmosphere than from the sediments, even given the uncer-tainties in the model. Consequently, the sediment reservoir does not signifi cantly buffer the water column against changes in the external forcing from air. Furthermore, the monitoring data show that the PCB concentrations in surface sediments have decreased in parallel to the air concentrations. A residual uncertainty for the PCBs is the possibility of major riverine/direct inputs along the south-eastern coast (which is considered unlikely, see a) above), inputs that must also have decreased in parallel with the air concentrations during the last 20 years.

c) The atmosphere is the major source of PCDD/Fs to the Bothnian Sea and the Baltic Proper. This conclusion is considered to be quite certain. The modelling results indicate that the inputs from the atmo sphere are larger than the inputs from other known sources. They also indicate that the atmospheric inputs are sufficiently large to ex plain the current levels of PCDD/Fs in the water column. Further more, the congener pattern analysis indicates that the PCDD/ Fs in offshore surface sediments of the Bothnian Sea and the Baltic Proper are largely of atmospheric origin. It should be noted that other sources can be dominant on a local scale. Analyses of surface sedi ments along the Swedish coast has shown that the



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PCDD/F patterns in sediments sampled near urbanised and industri-alised areas often differ significantly from atmospheric patterns. While there is compelling evidence for the importance of atmo-spheric deposition, there is a major riverine source in the Gulf of Finland, and it is conceiv able that there are also major non-atmospheric sources in less well studied parts of the Bothnian Sea or the Baltic Proper. The pattern analysis suggests that any such major source(s) would have a pattern similar to the atmospheric pattern or dominated by selected toxic congeners. A river could for instance be a recipient for combustion residues with high PCDD/F levels. Information on the PCDD/F discharge of the major rivers entering the Baltic is needed to assess this possibility. For source apportioning, so called receptor modelling has been shown to be an effective tool for tracing and quantifying PCB and PCDD/F sources (Masunaga et al. 2003, Du and Rodenburg 2007, Sundqvist et al. 2008). This technique utilizes comprehensive con-gener patterns and multivariate statistical tools (e.g. positive matrix factorization) to reconstruct source patterns in a region, which then can be linked to specific sources. A receptor modelling study for PCDD/Fs sources in the Baltic Sea area is under way (Sundqvist un published). Sediment from >140 sites along the Swedish coast was analysed for all tetra- through octa-CDD/F congeners and these data constitute the basis for the study. For each sampling location, the contribution from various sources are being quantified and appor-tioned. Preliminary results support the findings in this study, namely that the atmospheric inputs are large for offshore sites. In coastal zones, the contribution from various sources is often much more complex. It should also be noted that the congener pattern analysis has its shortcomings. By focusing on the similarity of the pattern of all seventeen 2,3,7,8-substituted congeners (as was done in the current study), this approach can miss meaningful contributions of specific sources to one or several congeners if these sources did not signifi-cantly distort the overall pattern. For instance, it is conceivable that the chlor-alkali source pattern, which is dominated by the lower chlorinated furans, could significantly contribute to the levels of 2,3,7,8-TCDF, 1,2,3,7,8-PeCDF, and 2,3,4,7,8-PeCDF in Baltic Sea sediments without markedly affecting the (atmospheric) pattern of the remaining 14 congeners. Different techniques are required that focus on key “signature” components of the sources in question and on the key congeners from a risk perspective (i.e. 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 2,3,7,8-TeCDF, and 2,3,4,7,8-PeCDF). Finally, it could be better to use environmental samples (e.g. sediments, soils) in highly impacted source areas to characterize the source signatures, rather than product or effluent samples.



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d) The freely dissolved PCDD/F concentrations in the Bothnian Sea and the Baltic Proper will decrease if the PCDD/F concentrations in the atmosphere remain at current levels. This conclusion is consid ered to be quite certain. The process determining the lag between the decrease in the concentrations in air and in water is the transfer of PCDD/Fs from surface sediment to water. The concentra-tions in the surface sediment respond over a period of several decades to changes in the rate of input due to the long residence time of the PCDD/Fs in the Baltic Sea system (Table 15). Thus the flow of PCDD/Fs from the sediment into the water column also responds over a time period of decades to changes in the rate of input. The un certainties in the degree of sorption of the PCDD/F to the surface sediments do not alter this fact. Since the atmospheric deposition of PCDD/Fs has decreased over the last decades, there is likely to be an ongoing decrease of the freely dissolved concentrations in the next decades. The major uncertainty associated with this conclusion is the same as that discussed under c) above, namely that there could be other un identified major sources of PCDD/Fs that have not decreased over recent years. There is further uncertainty associated with the magni-tude of the predicted decrease. This will depend on i) the magnitude of the decrease in the atmospheric input over the last decades; ii) the residence time of the PCDD/Fs in the basins. The scenario for the decrease in PCDD/F concentrations in air over the last 20 years is based on empirical observations and is judged to be quite reliable. The uncertainty in the residence time of the PCDD/Fs is discussed in f) below.

e) Reducing the PCDD/F concentrations in the atmosphere will acceler-ate the reduction in the freely dissolved PCDD/F concentra tions in the Bothnian Sea and the Baltic Proper. This conclusion is conside-red to be quite certain. This is a consequence of atmospheric deposi-tion being the dominant source of PCDD/Fs to these basins. The residual uncertainty lies in the possibility that there are other major unidentified sources (see c) above).

f) The rate of decrease of the freely dissolved PCDD/F concentrations will be as illustrated in Figure 50. This conclusion is considered to be quite uncertain. The rate of decrease in the surface water of the Baltic Sea is suspected to be overestimated due to the simple struc-ture of the POPCYCLING-Baltic model. The rate of decrease in the other water bodies is closely linked to the PCDD/F residence time, which is in turn linked to the model assumptions regarding the sur face area and mixed depth of the surface sediments as well as the sediment burial rates. Although these assumptions have an empirical



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basis, they are uncertain, and it has not yet been possible to evaluate their correctness, e.g. by measuring the elimination rate of very hydrophobic chemicals from these water bodies. In addition, the residence time may be modified by environmental disturbances such as intense storms which resuspend accumulation sediments and thus bring buried PCDD/Fs back into circulation.

g) The rate of decrease in the concentrations in fish will parallel the rate of decrease in the freely dissolved concentrations in the water bodies. This conclusion is considered to be very uncertain. The ob servations of levels in herring over the last 15 years have shown that this need not be the case. The decrease in the rate of growth of the herring is believed to have resulted in stronger bioaccumulation of the PCDD/Fs, with the consequence that the PCDD/F concentrations in herring did not decrease during this period, although the freely dissolved concentrations (presumably) did. Hence it is possible that changes in the ecosystem may slow down or accelerate the expected response of the fish to a decrease in the freely dissolved concentra tions.



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10 Conclusions and future research10.1 New field measurements10.1.1 Air and atmospheric deposition measurements• ThehighestPCDD/Fconcentrations(TEQ)werefoundinairthat

had passed over the European continent. • AirthathadpassedovertheBritishIslesandairfromnortherly

direc tions showed lower concentrations. • ThePCDFconcentrations(TEQ)werehigherthanthePCDD

concentra tions in air from southwest, south, east, and northeast, while the opposite was generally true in air from west-northwest.

• Thevariabilityintheconcentrationswasmuchlowerwithinacompass sector than it was between the sectors.

• Approximately40%ofthewetdepositionofPCDD/Fderivedfromair that originated from the southwest sector, while ~20% derived from air from the south sector.

• ThePCDD/Fbulkdepositionwas1.1pgWHOTEQm–2d–1 during a 6-month study period (winter 2006/2007). Estimates of the origin of the gaseous deposition to the Baltic Sea indicate that the contribu-tions from various sectors to gaseous deposition were quite compa-rable.

• AstrongcorrelationbetweentheconcentrationofparticleboundPCDD/F and the soot carbon concentration was found, with a correlation coefficient (r2) of 0.80.

10.1.2 Surface sediments: • PCDD/Fconcentrationsinoffshoreareasareapproximately2–3

times higher in the Baltic Proper than in the Bothnian Sea if normali-sed to dry weight. The organic carbon (OC) levels are on average substantially higher in Baltic Proper offshore sediments. If normali-sed to OC, there are no differences in PCDD/F-levels between the two basins.

• TheΣPCB7 concentrations normalised to dry weight are on average 4-5 times lower in the Bothnian Sea as compared to the Baltic Proper. This difference is less pronounced if the data are normalised to OC. The con centrations of HCB in sediment seem to be quite similar in the Bothnian Sea and the Baltic Proper.

• ThevariabilityofPCDD/FandPCBlevelsinoffshoresedimentsislargely explained by variation in OC levels. The OC content explai-ned 80–90% of the PCDD/F and PCB variation, while the BC con-tent ex plained 50–70% of the variation. If one outlier was excluded, the BC content could explain 70–90% of the OC level variation. There was a low correlation between OC content and the concentra-tion of HCB (r2=0.28).



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• ThevariabilityinPCDD/Flevelsandcontaminationpatternsincoastal zones is large. The coast of the Baltic Sea includes several heavily industrialized zones, and it has been shown that the Swedish coast in cludes a number of PCDD/F hot spots associated with indu-strial activi ties.

• ThereislimitedinformationonPCDD/FtimetrendsinBalticoff-shore sediments. While levels are clearly declining in offshore areas in the Gulf of Finland due to extensive reduction of emissions, the situations in the Bothnian Sea and the Baltic Proper are unclear.

• Duringthelast10–20years,adistinctdecreaseofPCBconcentra-tions in surface sediments of the Bothnian Sea and the Baltic Proper has occurred. In the Bothnian Sea, the decrease was on average a factor of 5.6, while in the Baltic Proper it was a factor of 4.5. These decreasing PCB concentrations in offshore surface sediments are in line with the de creases in PCB concentrations in herring from the Bothnian Sea and in herring and guillemot egg from the Baltic Proper. There are also indica tions of decreasing HCB concentrations in Baltic sediments.

10.1.3 Surface, deep sea and sediment pore-water: • Averagedioxinconcentrationsincoastalandoffshorewaterswere

found to be 1.1 and 2.5 pg WHO-TEQ m-3, respectively, and the corresponding levels for average ΣPCB7 concentrations were 5.8 and 24 ng m-3.

• Therewerenosignificantconcentrationdifferencesbetweensurfaceand deep sea water, neither in the Baltic Proper nor in the Bothnian Sea.

• ThePOPconcentrationsintheporewatergenerallycovariedwithsedi ment concentrations.

10.1.4 Sediment-water exchange: • Forthecoastalstations,theaverageratiooftheporewater/overlying

water concentration was 3.6 ± 1.6 and 1.0 ± 0.6 for PCDD/Fs and PCBs, respectively. This indicates that the coastal sediments act as a source of PCDD/Fs to the overlying water, whereas for the PCBs there is no con centration gradient and the sediments in the coastal areas constitute neither strong sinks nor strong sources of PCBs.

• Atdeepwatersites,theaverageratiooftheporewater/overlyingwater was 1.1 ± 0.5 for PCDD/Fs, which suggests that there are no concentra tion gradients and that the sediments in the offshore areas constitute neither strong sinks nor strong sources for the diffusive exchange of dis solved PCDD/Fs. For PCBs, this ratio was 0.7 ± 0.3, suggesting that there is only a slight concentration gradient for PCBs. The direction of the gradient indicates that the sediments could be a PCB sink.



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• ThebindingofPCDD/FstoBalticSeasedimentsis10–30timesstronger than predicted by the equation typically used in risk assess-ment. The ecotoxicological risk from PCBs and PCDD/Fs in the Baltic Sea sedi ments is 10–30 times lower than would be predicted if the risk assessment would be based on the binding to AOC alone.

MASS BALANCE MODELLING, PATTERN ANALYSES AND UNCERTAINTY ANALYSES

Offshore and other pristine areas:• The atmosphere is the dominant external source of HCB and PCBs

to the Baltic Sea, and the concentrations of HCB and PCBs in the water column will react quickly to changes in the concentrations in the atmosphere. These conclusions were considered to be highly certain for HCB and very certain for PCBs. Good agreement between predicted and measured concentrations in water and sediment including time trends supports this. The atmospheric deposition is much larger than the estimated riverine in puts and known direct inputs, and the input to the water column is also clearly larger from the atmosphere than from the sediments.

• The atmosphere is the major source of PCDD/Fs to the Bothnian Sea and the Baltic Proper. This conclusion is considered to be quite certain. The modelling results indicate that the inputs from the atmosphere are larger than the inputs from other known sources. They also indicate that the atmospheric inputs are sufficiently large to explain the current levels of PCDD/Fs in the water column. Furthermore, the congener pattern analy sis indicates that the PCDD/Fs in offshore surface sediments of the Both nian Sea and the Baltic Proper are largely of atmospheric origin.

• The freely dissolved PCDD/F concentrations in the Bothnian Sea and the Baltic Proper will decrease if the PCDD/F concentrations in the atmo sphere remain at current levels. This conclusion is conside-red to be quite certain. The process determining the lag between the decrease in the con centrations in air and in water is the transfer of PCDD/Fs from surface sediment to water. The concentrations in the surface sediment respond over a period of several decades to changes in the rate of input due to the long residence time of the PCDD/Fs in the Baltic Sea system. Thus the flow of PCDD/Fs from the sediment into the water column also responds over a time period of decades to changes in the rate of input. The scenario for the decrease in PCDD/F concentrations in air over the last 20 years is based on empirical observations and is judged to be quite reli able. Since the atmospheric deposition of PCDD/Fs has decreased over the last deca-des, there is likely to be an ongoing decrease of the freely dissolved concentrations in the next decades. The major uncertainty associated



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with this conclusion is that there could be other unidentified major sources of PCDD/Fs that have not decreased over recent years.

• Reducing the PCDD/F concentrations in the atmosphere will accele-rate the reduction in the freely dissolved PCDD/F concentrations in the Both nian Sea and the Baltic Proper. This conclusion is conside-red to be quite certain. This is a consequence of atmospheric deposi-tion being the domi nant source of PCDD/Fs to these basins. The residual uncertainty lies in the possibility that there are other major unidentified sources.

• The rate of decrease in the concentrations in fish will parallel the rate of decrease in the freely dissolved concentrations in the water bodies. This conclusion is considered to be very uncertain. The observations of levels in herring over the last 15 years have shown that this need not be the case. PCDD/F concentrations in herring did not decrease, although the freely dissolved concentrations (presumably) did. This is believed to be due to a stronger bioaccumulation of PCDD/Fs as a result of a decrease in the rate of growth of the herring. Hence ecosystem changes may slow down or accelerate the expected response of the fish to a decrease in the freely dissolved concentra-tions.

Non-pristine areas (e.g. near industries, cities and contaminated land)• AnalysesofsurfacesedimentsalongtheSwedishcoasthasshown

that the PCDD/F patterns in sediments sampled near urbanised and industri alised areas often differ significantly from atmospheric patterns. For source apportioning, so called receptor modelling has been shown to be an effective tool for tracing and quantifying PCB and PCDD/F sources. A receptor modelling study for PCDD/Fs sources in the Baltic Sea area is under way. Preliminary results support the findings in this study, namely that the atmospheric inputs are large for offshore sites, while in coastal zones, the contribution from various sources is often much more complex and non-atmospheric sources can be significant on a local/regional scale.

RECOMMENDATIONS FOR FUTURE RESEARCH

The POP pollution situation in the Baltic Sea continues to be a problem, espe-cially for the PCDD/F and dioxin-like PCBs, which contaminate the fish so that marketing of Baltic fish is restricted in the EU.

Although the current project has contributed to a better understanding of the contamination situation in the Baltic Sea, several areas for which know-ledge is uncertain or lacking have also been identified. It is primarily for the PCDD/Fs that the uncertainties are high. The major areas of interest include:• AbetterunderstandingofcurrentemissionsofPCDD/Fstoair.This

work has clearly demonstrated that the PCDD/F problem in the Baltic as a whole is caused by long range atmospheric transport,



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whereby sources in continental Europe play a major role. Con-sequently, it is important to establish whether our current under-standing of PCDD/F emissions is consistent with the atmospheric input of PCDD/Fs to the Baltic. As an example, a comparison of the EMEP model predictions of PCDD/F concentrations in air, which are based on current emissions inventories for European countries, with the ambient air concentrations measured in this project would be a good point of departure. This could be followed up by a revision of the emissions estimates or an assessment of how planned emis sions reductions measures can be expected to reduce PCDD/F inputs to the Baltic Sea in the future (both on a European scale).

• AbetterknowledgeofriverineinputsofPCDD/FstotheBalticSea.This is essential for assessing whether transfer of PCDD/Fs from the watershed, for instance via soil erosion, is a significant source of PCDD/Fs to the Baltic that could greatly lengthen the response time of concentrations in Baltic biota to reductions in PCDD/F emissions to air. This potential source was not addressed in this report as there is a lack of data.

• AbetterknowledgeofcurrentindustrialemissionstoBalticSeawater. These include industrial effluents and leakage from contami-nated land. There are large uncertainties in all these categories, which primarily affect the contamination situation in coastal zones.

• ItappearsasthePCDDshaveabetter(i.e.declining)trendthanthePCDFs in Baltic biota, blood serum of Swedish men, and possibly also in Baltic sediments. Is there a shift towards emissions rich in PCDFs rather than PCDDs, or can this be attributed to other fac-tors?

• AbetterknowledgeoftrendsforPCDD/FsinBalticsedimentsandBaltic air. This is needed for the evaluation of retrospective and pro spective model predictions.

• AbetterknowledgeoflevelsandcompositionofPCDD/Fsanddioxin-like PCBs in Baltic surface sediments. Large areas of the Baltic Sea have never been investigated. Contaminant pattern analy-sis of surface sediments can be used for tracing sources. Currently, the data available only allow for source apportionment in limited parts of the Baltic Sea (along the Swedish coast).

• Abetterunderstandingofsurfacesedimentaccumulationandvertical mixing. This is needed to produce more reliable estimates of the response time of the Baltic Sea to changes in PCDD/F inputs.

• Abetterunderstandingofsedimentwaterbiotacontaminantdynamics. Why do we see spatial and temporal variation in PCDD/F levels in fish from the Baltic Sea? Is it due to biological factors (e.g. growth rate, feeding habits, etc.), other factors or a combination of factors? How important are the PCDD/F levels in sediment for the PCDD/F levels in biota?



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Sources, transport, reservoirs and fate of dioxins, P

CB

s and HC

B in the B

altic Sea environm

ent R

eport 59

12

Sources, transport, reservoirs and fate of

dioxins, PCBs and HCB in the Baltic Sea environment

Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic Sea environment

A better knowledge of sources, transport, reservoirs and fate of

persistent organic pollutants (POPs) in the Baltic Sea environment is

crucial for the identification of effective actions against these com-

pounds.

In this report the present situation regarding sources and current

fluxes of persistent pollutants in the Baltic Sea ecosystem is presented.

The compounds selected for the study were: polychlorinated bi phenyls

(PCBs), hexachlorobenzene (HCB), polychlorinated dibenzo furans

(PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs). These

classes of compounds represent a broad range of physical- chemical

properties, and hence their environmental behaviour encompasses the

spectrum of most chemicals listed in the Stockholm Convention.

Based on current knowledge and some new field measurements

in air, sea water and sediments, mass balances for the selected POPs

were calculated. These mass balances indicate that the atmosphere

is the major source of PCDD/Fs to the Bothnian Sea and the Baltic

Proper and also the dominant external source of HCB and PCBs to

the Baltic Sea. These findings emphasise the need for further interna-

tional agreements to prevent long-range transboundary transport of

these POPs.

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Sources, transport, reservoirs and fate of dioxins, PCBs ... · SWEDISH ENVIRONMENTAL PROTECTION AGENCY Sources, transport, reservoirs and fate of dioxins, PCBs and HCB in the Baltic