SVENSK STANDARD SS-ISO 17924:2018

SVENSK STANDARDSS-ISO 17924:2018Fastställd/Approved: 2018-10-17Utgåva/Edition: 1Språk/Language: engelska/EnglishICS: 13.080.30

Markundersökningar – Bedömning av humanexponering för jord och jordmaterial genom intag – Metod för uppskattning av human biotillgänglighet av metaller i jord (ISO 17924:2018, IDT)

Soil quality – Assessment of human exposure from ingestion of soil and soil material – Procedure for the estimation of the human bioaccessibility/bioavailability of metals in soil (ISO 17924:2018, IDT)

This preview is downloaded from www.sis.se. Buy the entireThis preview is downloaded from www.sis.se. Buy the entireThis preview is downloaded from www.sis.se. Buy the entireThis preview is downloaded from www.sis.se. Buy the entirestandard via https://www.sis.se/std-80007311standard via https://www.sis.se/std-80007311standard via https://www.sis.se/std-80007311standard via https://www.sis.se/std-80007311

Standarder får världen att fungeraSIS (Swedish Standards Institute) är en fristående ideell förening med medlemmar från både privat och offentlig sektor. Vi är en del av det europeiska och globala nätverk som utarbetar internationella standarder. Standarder är dokumenterad kunskap utvecklad av framstående aktörer inom industri, näringsliv och samhälle och befrämjar handel över gränser, bidrar till att processer och produkter blir säkrare samt effektiviserar din verksamhet.

Delta och påverkaSom medlem i SIS har du möjlighet att påverka framtida standarder inom ditt område på nationell, europeisk och global nivå. Du får samtidigt tillgång till tidig information om utvecklingen inom din bransch.

Ta del av det färdiga arbetetVi erbjuder våra kunder allt som rör standarder och deras tillämpning. Hos oss kan du köpa alla publikationer du behöver – allt från enskilda standarder, tekniska rapporter och standard-paket till handböcker och onlinetjänster. Genom vår webbtjänst e-nav får du tillgång till ett lättnavigerat bibliotek där alla standarder som är aktuella för ditt företag finns tillgängliga. Standarder och handböcker är källor till kunskap. Vi säljer dem.

Utveckla din kompetens och lyckas bättre i ditt arbeteHos SIS kan du gå öppna eller företagsinterna utbildningar kring innehåll och tillämpning av standarder. Genom vår närhet till den internationella utvecklingen och ISO får du rätt kunskap i rätt tid, direkt från källan. Med vår kunskap om standarders möjligheter hjälper vi våra kunder att skapa verklig nytta och lönsamhet i sina verksamheter.

Vill du veta mer om SIS eller hur standarder kan effektivisera din verksamhet är du välkommen in på www.sis.se eller ta kontakt med oss på tel 08-555 523 00.

Standards make the world go roundSIS (Swedish Standards Institute) is an independent non-profit organisation with members from both the private and public sectors. We are part of the European and global network that draws up international standards. Standards consist of documented knowledge developed by prominent actors within the industry, business world and society. They promote cross-border trade, they help to make processes and products safer and they streamline your organisation.

Take part and have influenceAs a member of SIS you will have the possibility to participate in standardization activities on national, European and global level. The membership in SIS will give you the opportunity to influence future standards and gain access to early stage information about developments within your field.

Get to know the finished workWe offer our customers everything in connection with standards and their application. You can purchase all the publications you need from us - everything from individual standards, technical reports and standard packages through to manuals and online services. Our web service e-nav gives you access to an easy-to-navigate library where all standards that are relevant to your company are available. Standards and manuals are sources of knowledge. We sell them.

Increase understanding and improve perceptionWith SIS you can undergo either shared or in-house training in the content and application of standards. Thanks to our proximity to international development and ISO you receive the right knowledge at the right time, direct from the source. With our knowledge about the potential of standards, we assist our customers in creating tangible benefit and profitability in their organisations.

If you want to know more about SIS, or how standards can streamline your organisation, please visit www.sis.se or contact us on phone +46 (0)8-555 523 00

This preview is downloaded from www.sis.se. Buy the entire standard via https://www.sis.se/std-80007311

© Copyright/Upphovsrätten till denna produkt tillhör SIS, Swedish Standards Institute, Stockholm, Sverige. Användningen av denna produkt regleras av slutanvändarlicensen som återfinns i denna produkt, se standardens sista sidor.

© Copyright SIS, Swedish Standards Institute, Stockholm, Sweden. All rights reserved. The use of this product is governed by the end-user licence for this product. You will find the licence in the end of this document.

Upplysningar om sakinnehållet i standarden lämnas av SIS, Swedish Standards Institute, telefon 08-555 520 00. Standarder kan beställas hos SIS som även lämnar allmänna upplysningar om svensk och utländsk standard.

Information about the content of the standard is available from the Swedish Standards Institute (SIS), telephone +46 8 555 520 00. Standards may be ordered from SIS, who can also provide general information about Swedish and foreign standards.

Den internationella standarden ISO 17924:2018 gäller som svensk standard. Detta dokument innehåller den officiella engelska versionen av ISO 17924:2018.

The International Standard ISO 17924:2018 has the status of a Swedish Standard. This document contains the official English version of ISO 17924:2018.

Denna standard är framtagen av kommittén för Karaktärisering av avfall, mark och slam, SIS/TK 535.

Har du synpunkter på innehållet i den här standarden, vill du delta i ett kommande revideringsarbete eller vara med och ta fram andra standarder inom området? Gå in på www.sis.se - där hittar du mer information.

This preview is downloaded from www.sis.se. Buy the entire standard via https://www.sis.se/std-80007311

Contents Page

Foreword ........................................................................................................................................................................ vIntroduction .................................................................................................................................................................vi1 Scope ................................................................................................................................................................... 72 Normative references ................................................................................................................................... 73 Termsanddefinitions ................................................................................................................................... 74 Bioaccessibility/Bioavailability as a concept in assessment of soils and sites with

respect to human exposure ......................................................................................................................... 95 Description of the mechanisms of human contaminant uptake ..................................................116 Description of metal binding mechanisms (speciation of metals) in soil .................................137 Use and interpretation of in vitro tests for risk assessment ..........................................................148 Description of test method ........................................................................................................................15

8.1 Test principle ....................................................................................................................................................... 158.2 Apparatus .............................................................................................................................................................. 158.3 Reagents ................................................................................................................................................................ 168.4 Preparationofsimulatedfluids ................................................................................................................... 17

8.4.1 General .................................................................................................................................................. 178.4.2 Simulatedsalivafluid(1000ml) .............................................................................................. 178.4.3 Simulatedgastricfluid(1000ml) ............................................................................................ 198.4.4 Simulatedduodenalfluid(1000ml) ....................................................................................... 198.4.5 Simulatedbilefluid(1000ml) ..................................................................................................208.4.6 pHcontrolofmixedfluids ............................................................................................................ 21

8.5 Sample pre-treatment ...................................................................................................................................... 218.5.1 General .................................................................................................................................................. 218.5.2 Preparation of test samples ......................................................................................................... 218.5.3 Typical analysis protocol .............................................................................................................. 21

8.6 Sample preparation procedure .................................................................................................................... 229 Data handling, quality control and presentation of results ...........................................................23

9.1 General ................................................................................................................................................................... 239.2 Bioaccessibility calculation ........................................................................................................................... 24

Annex A (informative) Sample preparation procedure ..................................................................................26Bibliography ................................................................................................................................................................27

iv

SS-ISO17924:2018(E)This preview is downloaded from www.sis.se. Buy the entire standard via https://www.sis.se/std-80007311

Foreword

ISO(theInternationalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies(ISOmemberbodies).Theworkofpreparing InternationalStandards isnormallycarriedoutthrough ISO technical committees. Eachmember body interested in a subject forwhich a technicalcommittee has been established has the right to be represented on that committee. Internationalorganizations, governmental and non-governmental, in liaisonwith ISO, also take part in thework.ISO collaborates closelywith the International Electrotechnical Commission (IEC) on allmatters ofelectrotechnicalstandardization.

The procedures used to develop this document and those intended for its furthermaintenance aredescribedintheISO/IECDirectives,Part1.Inparticular,thedifferentapprovalcriterianeededforthedifferenttypesofISOdocumentsshouldbenoted.ThisdocumentwasdraftedinaccordancewiththeeditorialrulesoftheISO/IECDirectives,Part2(seewww .iso .org/directives).

Attentionisdrawntothepossibilitythatsomeoftheelementsofthisdocumentmaybethesubjectofpatentrights.ISOshallnotbeheldresponsibleforidentifyinganyorallsuchpatentrights.DetailsofanypatentrightsidentifiedduringthedevelopmentofthedocumentwillbeintheIntroductionand/orontheISOlistofpatentdeclarationsreceived(seewww .iso .org/patents).

Anytradenameusedinthisdocumentisinformationgivenfortheconvenienceofusersanddoesnotconstitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms andexpressions related to conformity assessment, as well as information about ISO's adherence to theWorld Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) seewww .iso .org/iso/foreword .html.

This documentwas prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 7,Impact assessment.

This first editionof ISO17924 cancels and replaces ISO/TS17924:2007,whichhasbeen technicallyrevised.Thechangescomparedtothepreviouseditionareasfollows:

— 7.1"General",7.2"Choosinganappropriatetest",7.3"Descriptionofapplicabletestmethods"and7.4 "Recommendations" have been deleted. 7.5 "Use and interpretation of in vitro tests for riskassessment"hasbeenretainedandrenumberedtoClause7;

— Clause8"Descriptionoftestmethod"hasbeenadded;

— Clause9(formerlyClause8)"Datahandling,qualitycontrolandpresentationofresults"hasbeencompletely revised;

— Annex A "Human bioaccessibility testing" has been replaced by Annex A "Sample preparation procedure";

— thefigureshavebeenrevised;

— thecompletedocumenthasbeeneditoriallyrevised;

— theScopehasbeenadapted.

Anyfeedbackorquestionsonthisdocumentshouldbedirectedtotheuser’snationalstandardsbody.Acompletelistingofthesebodiescanbefoundatwww .iso .org/members .html.

v


https://www.iso.org/directives-and-policies.html

https://www.iso.org/iso-standards-and-patents.html

https://www.iso.org/foreword-supplementary-information.html

https://www.iso.org/foreword-supplementary-information.html

https://www.iso.org/members.html

Introduction

Whenassessingsoilscontaminatedwith,forexample,potentiallyharmfulelements(e.g.arsenic),soilingestion (especially by children) is often considered to be themost important exposure pathway.Thisassessmentisoftencarriedoutonthebasisoftotalcontentofthepotentiallyharmfulelementsinquestioninthesoil.However,severalstudiessuggestthattheavailabilityofthepotentiallyharmfulelements (e.g. arsenic) in gastrointestinal tract is dependent on the formof the potentially harmfulelements present and the site-specific soil chemistry. Testmethods based on in vivo testswith, forexample, juvenile swine or mini pigs are time consuming and expensive and not very compatiblewiththedecisionprocessesconnectedwiththeassessmentandclean-upofcontaminatedsites.Testmethods have thus been developed and validated, which involve in vitro laboratory tests aimed at simulating in vivoresults.Thiswillreducethecostandpracticalitiesrelatedtotheuseofsuchtestingon contaminated land.

Duetothelargeexpenditurenecessaryforbothprivatelandownersandpublicfundssetasidefortheremediation of contaminated land, International Standards on the assessment of contaminated soil,especiallywithregardtohumanhealth,areingreatdemand.InternationalStandardsinthiscomplexfieldwillsupportacommonscientificbasis fortheexchangeofdata,developmentofknowledgeandsoundevaluation.Theaimofthisdocumentistodescribetheelementsofsuchanin vitro test system andgiveadviceastotheappropriatecombinationanduseoftheseelementsinthespecificsituation.ThemethodisbasedontheBioaccessibilityResearchGroupofEurope,UnifiedBioaccessibilityMethod(BARGEUBM),whichhasbeendevelopedandagreeduponbytheBARGEgroup.

Inhumanhealthriskassessment,“bioavailability”isspecificallyusedinreferencetoabsorptionintosystemiccirculation,consistentwiththetoxicologicaluseoftheterm.Thisencompassesbioaccessibility,whichagain isacombinedmeasureof theprocessesdeterminingthe interactionbetweenthemetalassociatedwith the soil and the liquid in the human digestion system. Bioavailability furthermoreincludestheabsorptionofthecontaminantthroughaphysiologicalmembraneandthemetabolismintheliver.Thebioavailablefractionisthusthefractionleftafterreleaseintothehumandigestiveliquid,transport across the intestinal epitheliumandmetabolism in the liver. Further description of theseprocesses is given in Clause4.

When considering bioavailability as the fraction of the chemical that is absorbed into systemiccirculation, twooperationaldefinitionsare important:absoluteandrelativebioavailability.Absolutebioavailabilityisthefractionoftheapplieddosethatisabsorbedandreachesthesystemiccirculation(and can never be greater than 100 percent). Relative bioavailability represents a comparison ofabsorptionundertwodifferentsetsofconditions,forexamplefromasoilsamplevs.foodoranothermatrixusedinatoxicitystudy,andcanbegreaterthanorlessthan1.Thisfactorcanbeusedinexposureassessmentsforexposurebydirectingestionofsoil,forinstanceiftheabsolutebioavailabilityofthemetalinthespecificsoilissuspectedtodiffersignificantlyfromtheabsolutebioavailabilityimplicitinthetoxicityvalue/qualitycriteriaused.

vi


Soil quality — Assessment of human exposure from ingestion of soil and soil material — Procedure for the estimation of the human bioaccessibility/bioavailability of metals in soil

1 Scope

Thisdocumentdealswiththeassessmentofhumanexposurefromingestionofsoilandsoilmaterials.Itspecifiesaphysiologicallybasedtestprocedurefortheestimationofthehumanbioaccessibilityofmetals from contaminated soil in connectionwith the evaluation of the exposure related to humanoraluptake.

The method is a sequential extraction using synthetic gastrointestinal fluids and can be used toestimateoralbioaccessibility.Soilsorothergeologicalmaterials, insieved form,areextracted inanenvironmentthatsimulatesthebasicphysicochemicalconditionsofthehumangastrointestinaltract.

Thisdocumentdescribesamethodtosimulatethereleaseofmetalsfromsoilandsoilmaterialsafterpassagethroughthreecompartmentsofthehumangastrointestinaltract(mouth,stomachandsmallintestine). It produces extracts that are representative of the concentration of potentially harmfulelementsinthehumangastrointestinaltractforsubsequentchemicalcharacterization.

NOTE 1 Bioaccessibility can be used to approximate oral bioavailability.

NOTE2 Thetesthasbeenvalidatedforarsenic,cadmiumandleadinaninterlaboratorytrial.Themethodhasbeen in vivo validatedtoassesstheoralbioavailabilityofarsenic,cadmiumandlead.

2 Normative references

The followingdocuments are referred to in the text in such away that someor all of their contentconstitutes requirements of this document. For dated references, only the edition cited applies. Forundatedreferences,thelatesteditionofthereferenceddocument(includinganyamendments)applies.

ISO11074,Soil quality — Vocabulary

3 Termsanddefinitions

Forthepurposesofthisdocument,thetermsanddefinitionsgiveninISO11074andthefollowingapply.

ISOandIECmaintainterminologicaldatabasesforuseinstandardizationatthefollowingaddresses:

— ISOOnlinebrowsingplatform:availableathttps: //www .iso .org/obp

— IECElectropedia:availableathttp: //www .electropedia .org/

3.1absorptionprocessbywhichabodytakesinsubstanceandmakesitapartofitself

3.2bioaccessibilityfractionofasubstanceinsoilorsoilmaterialthatisliberatedin(human)gastrointestinaljuicesandthusavailableforabsorption

3.3bioavailabilityfractionofasubstancepresentiningestedsoilthatreachesthesystemiccirculation(bloodstream)

7


https://www.iso.org/obp

http://www.electropedia.org/

3.4contaminantsubstanceoragentpresentinthesoilasaresultofhumanactivity

Note1toentry:Thereisnoassumptioninthisdefinitionthatharmresultsfromthepresenceofthecontaminant.

3.5dermal contactcontactwith(touching)theskin

3.6exposuredoseofachemicalthatreachesthehumanbody

3.7exposure pathwayrouteasubstancetakesfromitssourcetoareceptor

3.8ingestionactoftakingsubstances,suchassoilandsoilmaterial,intothebodybymouth

3.9in vitro bioaccessibility testbioaccessibility test carried out outside a living organism

3.10no observed adverse effect levelNOAELdoseatwhichnoadverseeffectonareceptorcanbeobserved

3.11picaeating habit where usually strange and unpalatable material such as soil material and stonesare consumed

Note1toentry:ThetermpicastemsfromtheLatinnamepica pica fortheravenbirdmagpiewhichpicksuprandomlyanykindofmaterialfornestconstruction.

3.12provisional tolerable weekly intakePTWIprovisionalweeklytolerableamountofasubstancewhichcanbetakeninbyahumanbodyduringalifetimethroughthefoodchainwithoutaffectinghumanhealth

3.13receptor<human>potentiallyexposedperson

3.14relative absorption fractionRAFratio between the amount of a contaminant reaching systemic circulation when ingested with, forexample, soil and the same amount obtained when ingested in the toxicity experiment underlyingthecriteria

3.15speciesdifferentformsofasubstancealwaysarisingwitheachotherinareactionequilibrium

8


3.16tolerable daily intake valueTDIdailytolerableamountofasubstancewhichcanbetakeninbyahumanbodyduringalifetimethroughthefoodchainwithouteffectinghumanhealth

4 Bioaccessibility/Bioavailability as a concept in assessment of soils and sites with respect to human exposure

Thecharacterizationofbioaccessibility/bioavailabilityisusuallyperformedasapartofariskand/orexposure assessment.

Riskassessmentcomprisesthefollowingelements:

— hazardidentification;

— dose-response assessment;

— exposure assessment;

— andbasedontheabove:riskcharacterization.

An exposure assessment is the process wherein the intensity, frequency, and duration of humanexposureofacontaminantareestimated,andcomprises:

— sourceidentificationandcharacterization;

— identificationofexposureroutes;

— identificationofrelevantreceptors/targetgroups;

— andbasedonthis:theactualexposureassessment.

For the assessment of possible effects on human health, an analysis of the exposure routes is aprerequisite.Wherereceptorsarenotdirectlyexposedtoacontaminant,exposureassessmentneedstoconsiderthevariouswaysbywhichindirectexposuremightoccurandthesignificanceofthem.

Humanexposurefromsoilcontaminationcanoccurthroughdifferentmedia.

Directlyfromthesoil,thefollowingexposureroutesexist:

— soilingestion,bothdietaryandthroughadherencetohandsandunwashedvegetables,etc.;

— dermal contact;

— ingestionofhousedustthatpredominantlyconsistsofsoilmaterial.

Airborneexposurecomprisesthefollowing:

— inhalationandingestionoffugitivedust;

— inhalationofelevatedoutdoor-concentrations;

— inhalationofvapoursthathaveintrudedintobuildings.

Exposurethroughfoodchaincomprisesthefollowing:

— consumptionofplantsincludingcrops,wildplantsandfungi;

— consumptionofanimalsandanimalproducts,includingwildanimals;

— consumptionofcontaminatedwater.

9


Withinthisdocument,directuptakeofsoilviaingestionand/oringestionoffugitivedustisconsidered.Oralingestionisoneofthemostimportantexposureroutesforhumanstosoilcontaminants.

Qualitycriteriaforsoil(themaximumconcentrationlimitsforsoil)areusuallycalculatedonthebasisofatolerabledailyintakevalue(TDI)oraprovisionallytolerableweeklyintake(PTWI),thatcanbederivedfromthenoobservedadverseeffectlevel(NOAEL)foundinhumandataorexperimentalanimaldata.Forgenotoxiccarcinogensforwhichnolowerthresholdforincreasedriskforcancerisassumed,theTDIvalueissetatalevelthatcorrespondstoatolerablelow(negligible)cancerrisklevel.

For determining the TDI, data on oral toxicity are primarily considered. These data often pertaintoanimalexperimentswhere thesubstance isadministrated to theanimalsmixed in the feedor indrinkingwater(thevehicleortransporterofthecontaminant).Theamountofcontaminantneededtoproduceadversehealtheffectsintheanimalisthenrecorded.Asanalternative,epidemiologicalstudiesrelating observed human health effects to recorded exposures have been used. Most toxicologicalstudiesreportthetotalingestedamountandseldomindicateexactvaluesforthebioavailabilityofthesubstances administered.

When extrapolating from such experimental conditions to other conditions, e.g. to intake ofcontaminatedsoil,thisapproachassumesthattheuptakeefficiencyisequalforallscenarios,i.e.thatthe absolute bioavailability of the contaminant is constant. The absolute oral bioavailability can bedefinedasthefractionofanorallyingestedcontaminantthatreachessystemiccirculation,i.e.entersthebloodstream.Theabsoluteoralbioavailabilityofacontaminantmayrangefromcloseto0toalmost1(i.e.100%)dependinguponthephysiochemicalformofthecontaminant.Inthiscontext,theuseoftheconceptofabsolute,oralbioavailabilityrestsupontheassumptionthatadversehealtheffectsaresystemicandthustriggeredbythecontaminantsreachingthebloodstream,i.e.theinternalexposureasopposedtotheexternalexposuremeasureddirectlyasintakeofacontaminatedmediummultipliedbytheconcentrationofthecontaminantinthemedium,seeFigure 1.

Theabsolutebioavailability canbemeasuredas the ratiobetweenamounts in thebloodofanimalsor man after intravenous injection (100 % bioavailability) and after oral ingestion (uptake ofbioavailablefraction).

Figure 1 — Schematic presentation of oral uptake processes

A more feasible approach is to measure the relative bioavailability or relative absorption fraction(RAF),which is the ratiobetween theamountofa contaminant reachingsystemiccirculationwhen

10


ingestedwith,forexample,soilandthesameamountobtainedwheningestedinthetoxicityexperimentunderlyingthecriterion.

Itshouldbenotedthatalthoughmostrelativebioavailabilitiesarelessthan1andwouldresultinanincreasedacceptable levels,RAFvaluesabove1couldbe found thatwould result inademand foradecreased acceptable level.

5 Description of the mechanisms of human contaminant uptake

A series of compartments are involved in human bioavailability of ingested soil contaminants, asdescribed in Clause4.

Theoverallpathway leadsthe foodandsoilwithcontaminants fromthemechanicalgrinding in themouththroughaseriesofchemicalandmicrobiologicalprocesses topartialdissolutionthroughtheentire gastrointestinal tract (bioaccessibility processes). Thedissolved components are transportedthrough themembranes of the gastrointestinal epithelium (absorption) and into the blood stream.During transport through the membranes, degradation can occur (metabolism). The blood passesthe liverbefore entering the systemic circulation, allowing fordegradationor removal ofunwantedcompoundsintheliver(metabolism,firstpasseffect).Mostofthedissolutionprocessesarecompletedbefore thematerial leaves the small intestine, and it is generally accepted thatmost of the uptaketakesplaceinthesmallintestine.Towhichextentuptaketakesplaceinthestomachdependsonthecompound.Theenvironmentinthecompartmentsdiffersandaccordinglyimpactsthebioaccessibilityprocessdifferently,seeTable 1.

Table 1 — Functions and conditions in the compartments involved in bioaccessibility processes

CompartmentPrimary digestion functions

Main added “reagents” pH Residence

timeContaminant dissolution

function

Mouth GrindingCleavageofstarch

MoistureAmylase

6,5 Seconds to minutes

Grindingenhancessubsequentdissolution

Gullet Transport None 6,5 Seconds NoneStomach

Cleavageofpro-teins and fats

HydrochloricacidProteasesLipases

1 - 5 8minto3hAcid dissolves labile mineral oxides,sulphidesandcar-bonates to release metals.

Small intestineCleavageofoligosaccha-rides,proteins,fatsandotherconstituents

Solubilizationoffats

BicarbonateBile

ProteasesLipases

OligosaccharasesPhosphatases

4-7,5 2hto10h

Organic matter is dissolved and bound contaminants releasedCationicmetalsaresolubilisedbycomplexationwithbileacidsSome metals are precipitated bythehighpHorbyphosphate

ThepHinthestomachmayvaryfromcloseto1underfastedconditionstoashighas5afterfeeding.Residence time (1/2-time for emptying) in the stomach varies similarly from 8min to 15min and30minto3hforfastedandaveragefedconditions,respectively.Furthermore,bilereleasevariesaswell,withhigh releasesunder fed conditions. Finally, thepH in the stomach canbe lower for smallchildrenthanforadults.

Thegastrointestinaltractconstitutesacomplexecosystemwithaerobicandanaerobicmicroorganisms.Thedensityofmicroorganismsislessinthehumanstomachandintheupperpartofthesmallintestinebut increases towards and in the large intestine. Anaerobic microorganisms dominate in humanfaeces,whereas aerobic bacteria are found in high densities in the large intestine. Sulfate reducingbacteriahavebeendetected in thehuman large intestinewhilehigh concentrationsof oxygenhave

11


Documents

SVENSK STANDARD SS-ISO 17924:2018