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Lipid biomarkers profile—presence of coprostanol:recent sediments from Rodrigo de Freitas Lagoon—Riode Janeiro, BrazilJosemar Luis Stefens a , João Henrique Z. dos Santos a , João Graciano Mendonça Filho b ,Carla Graziele Azevedo da Silva a & Maria do Carmo Ruaro Peralba aa Instituto de Química , Universidade Federal do Rio Grande do Sul , Porto Alegre, RS, Brazilb Instituto de Geociências , Universidade Federal do Rio de Janeiro , Rio de Janeiro, RJ,BrazilPublished online: 19 Oct 2007.

To cite this article: Josemar Luis Stefens , João Henrique Z. dos Santos , João Graciano Mendonça Filho , Carla GrazieleAzevedo da Silva & Maria do Carmo Ruaro Peralba (2007) Lipid biomarkers profile—presence of coprostanol: recent sedimentsfrom Rodrigo de Freitas Lagoon—Rio de Janeiro, Brazil, Journal of Environmental Science and Health, Part A: Toxic/HazardousSubstances and Environmental Engineering, 42:11, 1553-1560, DOI: 10.1080/10934520701513423

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Journal of Environmental Science and Health Part A (2007) 42, 1553–1560Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934520701513423

Lipid biomarkers profile—presence of coprostanol: recentsediments from Rodrigo de Freitas Lagoon—Rio de Janeiro,Brazil

JOSEMAR LUIS STEFENS,1 JOAO HENRIQUE Z. DOS SANTOS,1 JOAO GRACIANO MENDONCAFILHO,2 CARLA GRAZIELE AZEVEDO DA SILVA1 and MARIA DO CARMO RUARO PERALBA1

1Instituto de Quımica, Universidade Federal do Rio Grande do Sul, Porto Alegre (RS), Brazil2Instituto de Geociencias, Universidade Federal do Rio de Janeiro, Rio de Janeiro (RJ), Brazil

Coprostanol (contribution characteristic from anthropogenic pollution) and other lipid biomarkers (sterols, fatty alcohols and fattyacids) were identified and quantified in recent sediment extracts from Rodrigo de Freitas Lagoon, a touristy spot of Rio de Janeiro—Brazil, using gas chromatography with mass selective detector (GC-MSD). The determination of lipid biomarkers profile indicatesan autochthonous biogenic contribution due to the presence of phytoplankton, zooplankton, bacteria and dinoflagellates. Theallochthonous biogenic contribution was confirmed by detection of biomarkers from higher plants in the sediments due to theinfluence of the Atlantic Forest inserted in the studied region. The concentration of the studied compounds varied from 5.53 to 216.47μg.g−1 for sterols, 0.47 to 5.35 μg.g−1 for fatty alcohols, 20.15 to 66.22 μg.g−1 for fatty acids and 0.08 to 3.98 μg.g−1 for coprostanol.The presence of coprostanol was attributed to illegal untreated sewage discharge in the pluvial collector which ends up in the Lagoon.

Keywords: Biomarkers, sediments, lagoon, sterols, fatty acids, fatty alcohols, coprostanol.

Introduction

The organic matter of lakes comprises a complex mixtureof compounds from different origins, especially where thereis a contribution from sea material and pluvial water. Thebiogenic sources of organic matter includes the primaryproduction of aquatic organisms, introduction of materialfrom higher plants and products associated to microbiolog-ical activity in water and sediments.[1] On the other hand,the discharge of industrial and domestic effluents in thelacustrine system, due to the urban development of the re-gion, is the main source of anthropogenic contributions.[2]

Lipid compounds are very often employed as biomarkersof the organic matter origin due to their specificity and sta-bility in aquatic sediments.[3] Some lipid compounds foundin sediments, like sterols, fatty alcohols, fatty acids and hy-drocarbons, can be associated to biogenic and/or anthro-pogenic activities of a region.

Address correspondence to Maria do Carmo Ruaro Peralba, In-stituto de Quımica—UFRGS. Av. Bento Goncalves 9500; CEP91501-970 Porto Alegre/RS, Brazil. E-mail: mcarmo@iq.ufrgs.bror schifino@terra.com.brReceived March 8, 2007.

Sterols are common chemical constituents of terres-trial and marine plants and are frequently used as mark-ers for geochemical interpretations. Sterols with 27 car-bon atoms (C27), with the exception of coprostanol andepicocoprostanol, indicate the contribution of organismsof non specific aquatic origin, including phytoplankton,zooplankton and dinoflagellates, while C29 sterols indicatecontribution from higher plants from which they are themajor constituents.[4,5] In sewage impact studies the most-cited sterols are coprostanol and epicoprostanol, knownas faecal sterols, since they are not natural from aquaticsediments.[6] Coprostanol is produced in the digestive sys-tem of higher animals by microbial reduction of cholesterol.Isobe et al.[7] have reported that coprostanol concentrationcorrelate well with coliform bacteria in sewage contami-nated environments. Since coprostanol is the predominant5β-stanol present in human faeces, representing about 60%of the total sterols, it is the main interest compound in stud-ies of pollution by domestic sewage.[8−10] Faecal sterols havebeen largely used as molecular markers to indicate and dis-criminate contamination sources by sewage in several envi-ronments like water and sediments due to their specificityand stability.[11]

Phytol (3,7,11,15-tetramethyl-2-hexadecen-1-ol) is an al-cohol derived from the hydrolysis of chlorophyll-a and

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frequently used as biomarker for phytoplankton while far-nesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) is derivedfrom the hydrolysis of bacteriochlorophyll-e, a pigmentconstituent of green photosynthetic sulphur bacteria, andcan be used as a biomarker for this type of bacteria insediments.[12−14]

Fatty acids are compounds abundant in the majority oforganisms, being the most encountered lipids in recent sed-iments. Sources of fatty acids include bacteria, microalgae,higher plants and aquatic fauna (phytoplankton and zoo-plankton). Each of these organisms presents a characteristicfatty acid profile.[15]

Fatty acids, as well as fatty alcohols, present predomi-nantly an even number of chain carbon atoms due to theirenzymatic biosynthesis. The chain length of fatty acids en-countered in sediments is largely used as indicator of thistype of source. However, more specific information on theorganic matter origin are obtained by the unsaturation andbranching degree of fatty acids found in sediments.[16] Un-saturated fatty acids, mainly the monounsaturated (MU-FAs) n-C16:1, n-C18:1, and n-C20:1, are indicatives of recentdiagenesis and are generally present in all recent sedimentsamples. Fatty acids with distributions n-C14:0, n-C16:0, n-C16:1, are abundant in phytoplankton, while n-C16:0, n-C18:1and n-C18:0 are frequently predominant in zooplankton.The zooplankton generally contributes in greater propor-tion to the saturated fatty acids (SFAs) n-C16 e n-C18 ascompared to phytoplankton.[17−19]

Diatoms, like zooplankton, are also rich in fatty acidswith distribution n-C14:0, n-C16:0 and n-C16:1, but presentlow composition in homologues n-C18. On the other hand,acids n-C18:1, n-C18:2, n-C18:3, n-C18:4 predominate in di-noflagellates and freshwater algae.[20] Branched fatty acids(brFAs) with odd number of chain carbon atoms (iso- andanteiso- C13–C17) are generally present in several bacteria,allowing their use as bacterial biomarkers.[21] The fact ofbranching fatty acids being found in low concentrations inother organisms makes them useful indicators for bacte-rial contribution in sediments.[2] Compounds generally at-tributed to bacterial sources (branched fatty acids iso- andanteiso- C15:0 e C17:0, C17:0 and C18:1ω7) are lost or present insmall amounts in sediments due to the bacterial decompo-sition process which occurs when particles cross the watercolumn.[19,22,23]

Polyunsaturated fatty acids (PUFAs) with 16, 18, 20 and22 carbon atoms are frequently used as planktonic organ-isms biomarkers. Among the PUFAs, eicosapentanoic acid(C20:5ω3) predominates in the majority of diatoms species insediments, with small contribution from fatty acids C22:6ω3,C16:3 and C16:2.[21] While the octadecatrienoic acid (C18:3ω3)predominates in most of the green algae, compounds withdistribution C20:5ω3 and C22:6ω3are also the mainly polyun-saturated found in zooplanktonic species. [2,24]

PUFAs are biosynthesized from fatty acids by enzymeaction.[16] However, the concentration of these compoundsin sediments is generally low since they are degraded faster

than any other fatty acid, even in anoxic conditions.[17]

Therefore, the presence of PUFAs indicates a recent algaeintroduction due to their susceptibility to the degradationprocess. Notwithstanding, the concentration of these com-pounds in sediments is generally low since they are degradedfaster than saturated compounds.[17]

The scope of the present work was to characterize qual-itatively and quantitatively the distribution profile of lipidbiomarkers (sterols, fatty alcohols and fatty acids) in sedi-ments from Rodrigo de Freitas Lagoon, an area of perma-nent environmental protection, which has suffered severalproblems in the last decade affecting the water and sedimentquality, in order to identify the biogenic and anthropogeniccontributions to the region.

Materials and methods

Study area and sampling

Rodrigo de Freitas Lagoon is situated in the urban area ofthe city of Rio de Janeiro (RJ), Brazil. A detailed descrip-tion of lagoon has been reported in the previous work.[25]

Ten sediment samples were collected from the bottom ofRodrigo de Freitas Lagoon using a punctual bottom sam-pler Van Veen in the period of October 2001, according toFigure 1. After collection, sediment samples were frozenand kept at −15◦C until being analyzed.

Analytical procedure

Chemicals and treatment

All glassware was submitted to a rigorous washing pro-cess [tap water and neutral soap followed by rinsing withultra pure water (MilliQ system)] plus sterilization in a fur-nace at 300◦C for 2 hours previous to utilization. Pesti-cide grade solvents (dichloromethane, n-hexane, toluene,ethyl acetate and methanol), purchased from Mallinckrodt,were used for sample preparation and analysis. Anhydroussodium sulfate (Merck) was baked at 400◦C and granu-lated metallic copper (Leco) was treated with hydrochloricacid p.a. (Merck), methanol and acetone p.a. (Merck) forposterior use. Silica gel preparative liquid chromatographygrade (0.063–0.200 mm – Merck) was dried at 180◦C for 12hours and deactivated by the adding 5% in weigh of ultrapure water (Milli-Q System). The derivatization agent bis-(trimethylsilyl)-trifluoroacetamide (BSTFA, 98+%), pur-chased from Acros Organics, was used to derivatize sterolsand fatty alcohols while diazomethane was employed toderivatize fatty acids. As internal standards, the compoundsd4-C27ααα(20R)-cholestane (99,9%), purchased from Ch-iron, linoleic acid methyl ester (99%) from Sigma and n-octyl trimethylsilyl ether obtained in laboratory throughthe derivatization of 1-octanol (Riedel-de-Haen, 98%) withBSTFA, were used.

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Coprostanol and lipid biomarkers in Rio de Janeiro 1555

Fig. 1. Map of the studied area with location of the sediment sampling points.

Sample preparation

Sediment samples were thawed and dried at room temper-ature. After grinding in agate pestle, weighing and additionof the sufficient amount of anhydrous sodium sulphate,the samples were extracted with 30 mL of a mixture ofdichloromethane (DCM) and methanol (2:1) in an ultra-sonic bath (cycles 3 × 30 min). The combined extracts wereconcentrated in a rotary evaporator and passed through acopper column, previously activated, for elemental sulphurremoval. After volume reduction to 1 mL, the extract wasesterified with 50 mL of KOH 1 mol.L–1 in methanol/water(3:2) under reflux at 80◦C for 2 h. Neutral lipids were re-covered from the basic solution with n-hexane (3 × 10 mL).After acidifying the aqueous phase to a residual pH < 2,the fatty acids were extracted with n-hexane (3 × 10 mL).Water traces were removed from extracts by addition ofanhydrous sodium sulphate followed by filtration, volumereduction to 1 mL and derivatization with diazomethane.The neutral lipids were fractionated by preparative liq-uid chromatography according to the method proposed byJaffe et al.[26] in order to obtain the pure fractions fattyalcohols and sterols, which were derivatized with 300 μLof BSTFA [bis(trimethylsilyl-trifluoroacetamide)] at 40◦Cduring 45 minutes. The extracts volume was reduced to 1mL under a gentle nitrogen flow for posterior analysis byGC-MSD.

Instrumental analysis and quantification

The identification and quantification were carried out in agas chromatograph Agilent 6890 with automatic injection,capillary column of fused silica (30 m×0.25 mm×0.25μm;stationary phase 5% phenyl −95% dimethylpolysiloxane—

DB5), mass selective detector (Agilent 5976), operationmode SCAN and electronic impact (75 eV). A sample of 1μL was injected in splitless mode (Tinjector = 290◦C) usingthe following oven conditions: initial temperature = 40◦C,isothermal for 1 min, heating rate 6◦C/min up to 290◦Cand isothermal for 20 min.

The quantitative analysis was carried out using theinternal standard technique using the standards: d4-C27ααα(20R)-cholestane for sterols, linoleic acid methyl es-ter for fatty acids and octyl trimethylsilyl ether for fatty alco-hols. The quantification limits were 0.07 μg.g–1 for sterols,0.02 μg.g–1 for fatty alcohols and 0.06 μg.g–1 for fattyacids.

Results and discussion

Sterols

Table 1 shows the concentration of sterols, fatty alcoholsand fatty acids found in Rodrigo de Freitas Lagoon sedi-ments. The total concentration of sterols in sediments var-ied between 5.53 and 216.47 μg.g–1. The sampling point10 showed the greater concentration and preservation ofsterols, probably due to the high stagnation of water in thisregion (Fig. 1). Chromatogram of sterols from samplingpoint 10 is presented in Figure 2.

According to the data obtained , a predominance ofsterols of terrestrial origin (C29)in all analyzed sedimentsfrom Rodrigo de Freitas Lagoon was observed (Table 1).Sterols of terrestrial origin correspond to 34 to 60% of to-tal sterols found in sediments indicating strong influenceof high plants near the studied area while the sterols ofaquatic origin (C27) represent 9 to 22% of the total found

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Table 1. Concentration of lipidic compounds (μg.g−1) found in sediments from Rodrigo de Freitas Lagoon

Sites

1 2 3 4c 5c 6 7d 8 9 10

SterolsCoprostanol 0.08 0.17 0.39 < 0.07 < 0.07 0.85 0.53 0.60 0.08 3.98Campesterol 0.15 0.81 0.69 0.12 1.02 2.13 1.03 1.06 0.32 12.84Stigmasterol 0.37 2.88 2.32 0.66 2.88 4.72 2.67 2.18 0.82 34.67Sitosterol + 23,24-dimethylcholestanol 2.71 5.22 4.21 1.61 4.83 13.68 4.09 3.62 1.28 26.10Dinosterol 0.66 3.78 4.48 1.38 0.64 5.69 4.91 2.00 1.13 35.70Total (μg.g−1) 5.53 23.20 23.39 7.66 17.00 48.77 28.28 20.85 8.08 216.47% C27 12 9 13 11 16 9 15 22 18 10% C29 58 47 39 57 60 52 34 41 41 39Cholesterol/cholestanol 2.2 1.6 1.8 4.0 1.7 0.9 2.6 3.8 1.7 0.7

Fatty alcoholsn-C14 0.08 0.22 0.28 < 0.02 0.07 0.22 0.70 0.40 0.03 0.29n-C16 0.19 1.24 1.80 0.19 0.60 0.96 1.81 0.87 0.38 1.94n-C18 0.10 0.21 0.37 0.03 0.19 0.32 0.45 0.34 0.15 0.89TOTAL (μg.g−1)a 0.49 2.78 3.18 0.47 1.83 2.51 3.80 3.93 0.80 5.35Phytolb 5.40 12.92 17.42 0.02 0.18 8.12 43.84 100.08 5.59 51.75Farnesolb 1.30 1.63 3.46 < 0.02 < 0.02 0.81 7.52 6.87 0.94 2.17�(C12-C20)/(�C21–C28)e 3.3 1.6 6.0 0.9 1.0 2.3 4.1 0.7 2.3 1.4

Fatty acidsSFAs 15.83 27.37 39.76 — — 18.12 — 47.95 21.38 42.27brFAs 1.64 6.63 10.87 — — 2.41 — 4.66 3.25 6.57MUFAs 1.51 10.10 13.65 — — 6.57 — 10.26 7.48 10.62PUFAs 1.17 1.95 1.94 — — 0.68 — 2.92 0.51 2.52TOTAL (μg.g−1) 20.15 46.05 66.22 — — 27.78 — 65.79 32.62 61.98

aexcept phytol and farnesol; blipid extracts submitted to saponification; cnon saponified lipidic extracts; d the acid extract of sediment from samplingpoint 7 was not obtained; elinear saturated fatty alcohols; SFAs: saturated linear fatty acids; brFAs: branched fatty acids; MUFAs: monounsaturatedfatty acids; PUFAs: polyunsaturated fatty acids.

in sediments (Table 1). Among the sterols of terrestrial ori-gin, sitosterol and stigmasterol are predominant in all sed-iment samples from Rodrigo de Freitas Lagoon (Table 1).Campesterol was also encountered in the analyzed sedi-ments and contributed for the increase in the concentrationof sterols originated from high plants. The predominance ofsterols of terrestrial origin (C29) in all sediment samples wasdue to the influence of the Atlantic Forest characteristic ofthe Rio de Janeiro region. The Atlantic Forest contributeswith a large variety of plants species in this region.

The presence of dinoflagellates, a class constituted mainlyby dinosterol (4,23,24-trimethyl-5α-colest-22-en-3β-ol)[15],was detected in significant concentration in sediments fromsampling points 2, 3, 6, 7 and 10 (Table 1). Dinosterol givesa great specificity in relation to the source of organic mattersince it is synthesized only by a type of marine algae nameddinoflagellates.[1] The proliferation of dinoflagellates is re-sponsible for a phenomenon known as red tide, arising fromthe excess of organic matter in the aquatic environment. Theintroduction of organic matter may have contributed to thefish mortality occurred in Rodrigo de Freitas Lagoon dueto excess of oxygen consume and production of toxins bydinoflagellates.[27]

Concentrations of cholestanol higher than those ofcholesterol were observed in sediments from samplingpoints 6 and 10 (Table 1). Values for the relation choles-terol/cholestanol lower than 1, found in sediments fromsampling points 6 and 10 (Table 1), may indicate a recentdiagenetic transformation in sediments due to microbialactivity in the organic matter, since the 5α(H)-stanols ap-peared in very low concentrations in living organisms andtheir presence in sediments is mainly due to the microbialreduction of stenols.[5,17,28]

Coprostanol as an indicator of contamination by sewage

Coprostanol was detected in all analyzed samples withconcentration varying from 0.08 to 3.98 μg.g−1 (Table 1).The greater concentration was found in sampling point 10.Levels of coprostanol found in sediments are similar tothose of regions contaminated by sewage.[7,29−32] Highercoprostanol levels have been reported in highly urbanizedareas due to discharge of untreated sewage in rivers, sea andestuaries.[11,33−36]

Small amounts of coprostanol (<0.01 μg.g–1) havebeen reported for anaerobic sediments uncontaminated by

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Coprostanol and lipid biomarkers in Rio de Janeiro 1557

Fig. 2. Chromatogram of sterols found in sediments from sampling point 10. Peak assignement: (1) coprostanol, (2) cholesterol, (3)cholestanol, (4) brassicasterol, (5) brassicastanol, (6) campesterol, (7) campestanol, (8) stigmasterol, (9) stigmastanol, (10) sitostanol+ 23,24-dimethylcholestanol, (11) sitostanol, (12) dinosterol, (13) 4-methyl-stenol, (14) 4-methyl-stanol, (15) dinostanol, i.s.: d4-C27ααα(20R)-cholestane.

faecal pollution, a phenomenon caused by hydrogenationin situ of cholesterol.[8,28,29,37,38] Some researchers considerthat concentrations of coprostanol in sediments higherthan 0.5 μg.g–1 are indicative of significant pollution bysewage.[29,39] Based on these studies, it can be concludedthat the areas most affected by pollution from untreatedsewage were those corresponding to sampling points 6, 7,8 and 10, due to significant concentrations of coprostanol(Table 1). The presence of epicoprostanol was not detectedin the analysed sediments which indicates that the sewagereceived no previous treatment of any kind.

Due to the dependence of coprostanol with particle sizeand organic carbon content, some researchers have beensuggesting the use of molecular indexes to evaluate contam-ination degree in sediments.[6,33,37] However, there is no con-sensus on a preferential evaluation method, other param-eters being necessary to confirm environmental pollutionby sewage. Furthermore, relations between faecal sterolspresent limited applicability in tropical estuarine systems,probably due to the influence of the intensive primary pro-duction and to the microbial degradation processes.[40]

The use of sterols as biomarkers for pollution by sewagecan be compared to the traditional counting of faecal co-liforms to evaluate contamination of a specific region.[7,39]

Data on bacteriological monitoring of water from Rodrigode Freitas Lagoon showed a very high number of faecalcoliforms, reaching 1.6 × 106 MPN/100 mL in the pe-riod 1996 to 2001.[27] Values for faecal coliforms frequentlyreached values above the maximum allowed by the Brazil-ian environmental legislation (1000 MPN/100 mL)[41] dur-ing rainy periods due to the water discharge in Rodrigo deFreitas Lagoon.[27] The bathing condition of Ipanema andLeblon Beaches, located near the Jardim de Alah, was af-fected during these periods. The Ambiental Engenharia e

Consultoria[27] quite frequently detected pollution by un-treated sewage in Rodrigo de Freitas Lagoon due to un-lawful discharges of domestic sewage into the pluvial wa-ter collecting system. Specific areas of continual contam-ination by sewage were not observed by faecal coliformanalyses.[27] However, by determining coprostanol in sedi-ments, it was possible to identify sites which significantlycontribute for contamination by domestic sewage. Sam-pling points 6, 7, 8 and 10, near the exits of the pluvialcollecting system showed high coprostanol concentrationsdue to sewage discharge (Fig. 1). Sediment sample collectedin point 10 showed the highest coprostanol concentration,indicating that this site has chronic problems of contami-nation by sewage discharged into the pluvial collecting sys-tem. The water stagnation in this site contributed to theaccumulation of coprostanol in the sediments. However,the physical transport of organic matter in sediments mayhave contributed for dilution of sterols in other samplingpoints.

The chromatographic identification of coprostanol hasgreat advantages over classical microbial techniques likethe use of coliform bacteria in determining contaminationby sewage in a marine environment. Some advantages inthe use of faecal sterol as biomarkers are: specificity in theidentification of the contamination source, relative resis-tance to microbial alterations and the high residence timeof coprostanol in the aquatic environment.[7,9]

Fatty alcohols

The distribution of fatty alcohols in the sediments variedfrom n-C12 to n-C28 (Table 1), showing a strong predom-inance of even chains over the odd ones (even-over-odd).The fatty alcohols concentration in sediments varied from

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Fig. 3. Sterols, fatty alcohols and fatty acids concentration insediments from Rodrigo de Freitas Lagoon.

0.47 to 5.35 μg.g–1 which corresponds to the lowest con-centration among the analyzed lipids (Fig. 3).

Phytol has been detected in all samples. Farnesol wasanother alcohol found in significant amounts in all ex-tracts submitted to esterification. The co-occurrence ofbacteriochlorophyll-e together with chlorophyll-a in sedi-ments indicates the development of anoxide conditions andproductive activity in the aquatic environment.[42]

In sediments from sampling points 4 and 5, farnesol wasnot detected and phytol was found in low concentrations,since these extracts were not submitted to esterification (Ta-ble 1). Sampling points 7, 8 and 10 showed high phytol con-centrations indicating elevated productivity of microalgae,mainly phytoplankton, in these sites. The highest concen-tration of farnesol was found in sediments from samplingpoints 3, 7 and 8, suggesting the possibility of anoxic con-ditions in determined periods (Table 1).

In order to distinguish between the terrestrial and aquaticorigin of sediments the ratio between short chain and

Fig. 4. Distribution of fatty acids in sediments from Rodrigo de Freitas Lagoon according to the saturation and branching degree.

long chain saturated n-alkanols ((�C12–C20)/(�C21–C28))was used. A ratio higher than 1 indicates the predomi-nance of aquatic organisms in the sediments while val-ues lower than 1 are indicative of the predominanceof higher plants.[9] Values higher than 1 were found inmost of the analysed sediments, indicating the predomi-nance of autochthonous sources (Table 1). This distribu-tion of n-alkanols in the sediments is attributed mainly tophytoplankton and zooplankton although the bacterial ori-gin can not be discarded.[9,43,44] Sampling points 4 and 8showed values lower than 1 indicating the contribution ofhigher plants, although short chain n-alkanols n-C16 andn-C18 were also found in these sediments (Table 1).

Fatty acids

Different types of fatty acids were found in the analysedsediments. The concentration of fatty acids in the sedi-ments ranged from 26.15 to 66.22 μg.g–1 (Table 1). Thesecompounds presented a distribution ranging from C8 toC28 with strong predominance of even chain carbon atoms.Sampling points 3, 8 and 10 showed the highest concentra-tions of fatty acids in the analysed sediments. (Table 1, Fig.3).

The saturated linear fatty acids (SFAs), mainly the com-pounds n-C16 and n-C18, predominate in the sedimentcomposition (Fig. 4). Beside the saturated linear fattyacids, a significant amount of monounsaturated fatty acids(MUFAs), n-C16:1 and n-C18:1 was found in the samples.This distribution generally indicates the contribution ofzooplanktonic algae and bacteria in the sediments.[4,16] Thepredominance of hexadecanoic acid (n-C16) followed byoctadecanoic (n-C18) and octadecenoic (n-C18:1) in all sam-ples. This distribution of acids indicates the presence of zoo-plankton in the aquatic environment since these organismscontribute in higher proportion for saturated fatty acidsn-C16 and n-C18 as compared to phytoplankton.[17−20]

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Coprostanol and lipid biomarkers in Rio de Janeiro 1559

The compounds iso- and anteiso- C15 and C17 predomi-nated among the branched fatty acids (brFAs) in the an-alyzed sediments from sampling 2, 3 and 10, indicatingintense bacterial activity in these sites. The recent intro-duction of algae was confirmed by the presence of polyun-saturated fatty acids (PUFAs) in all sampling points.

Conclusions

The autochthonous and allochthonous contributions werefound in all sediment samples of Rodrigo de Freitas La-goon as indicated the biogenic biomarkers mixture found.Rodrigo de Freitas Lagoon was characterized as a highlyeutrophic environment due to the high primary production.This fact was clearly shown by the presence in the sedimentsof phytoplankton, zooplankton, bacteria and dinoflagel-lates, precursors of the biomarkers found in the sediments.This highly complex medium allows the proliferation of agreat variety of organisms due to the salty characteristic ofthe water and the introduction of nutrients. The introduc-tion of material from high plants, due to the Atlantic Forest,has possibly caused the dilution of some of the biomarkersgiving a complex interpretation of the depositional envi-ronment.

Contamination by sewage in Rodrigo de Freitas Lagoonwas detected by the presence of coprostanol in the analysedsediments. The contamination was assigned to the illegalsewage discharge in the pluvial system that reaches the la-goon near the sampling points. Anthropogenic activities,typical of urbanization and industrialization have been fre-quent in this region in the past years. Some chronicle prob-lems, like connection deficiency to the sea, introduction oforganic matter, illegal sewage discharge and water stagna-tion are responsible for the eutrophication of the lagoonwater. Under more critical circumstances these problemsfrequently lead to the lack of water oxygenation and to theconsequent fish mortality. Periods of water anoxity weredetected due to the presence of farnesol in the sedimentextracts submitted to saponification. The proliferation ofdinoflagellates, responsible for the phenomena of red tide,has also contributed to fish mortality due to the excess oforganic matter.

The lipid compounds found in sediments from Rodrigode Freitas Lagoon were quite useful for depositional envi-ronment evaluation, allowing identification of the biogenicand anthropogenic origin of the past events.

Acknowledgments

This work was supported by CAPES and CNPq. FEMMA(Fundacao Estadual de Engenharia e Meio Ambiente—Rio de Janeiro) is acknowledged for bibliographical supporton Rodrigo de Freitas Lagoon.

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