Source and Migration of Short-Chain Chlorinated Paraffins in theCoastal East China Sea Using Multiproxies of Marine OrganicGeochemistryZongshan Zhao,†,‡ Huijuan Li,†,‡ Yawei Wang,† Guoliang Li,† Yali Cao,‡ Lixi Zeng,†,§ Jing Lan,∥

Thanh Wang,† and Guibin Jiang*,†

†State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, ChineseAcademy of Sciences, Beijing 100085, China‡Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100,China§College of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, China∥College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, P. R. China

*S Supporting Information

ABSTRACT: Multiple proxies of terrestrial organic matters (TOM)were introduced to study the migration behaviors of short-chainchlorinated paraffins (SCCPs) in the coastal East China Sea (ECS).The contents of SCCPs in the surface sediment collected fromChangjiang (Yangtze) River Delta (CRD) and along the Zhejiang−Fujian coastline ranged from 9.0 to 37.2 ng/g (dry weight, d.w.),displaying a “band-style” distribution trend. Spatial distributionpatterns of SCCP congeners presented an increasing trend seawardand southward along the coastline for shorter carbon length (C10 +C11) and lower chlorinated (Cl5 + Cl6 + Cl7) congeners, suggesting aspreading tendency seaward and southward from the CRD and thenorth of the inner shelf. The significant relationship between ΣSCCPsand total organic carbons (TOC) (r2 = 0.402, p < 0.05) indicated thatthe migration of SCCPs in sediments was markedly affected by TOC.The spatial patterns of the TOM proxies of TOC δ13C, the contents of ΣC27 + C29 + C31 n-alkanes, terrestrial marine biomarkerratio (TMBR), and terrestrial TOC (T-TOC) were all similar to that of ΣSCCPs. Linear relationships between SCCP contentsand both the contents of ΣC27 + C29 + C31 n-alkanes (r

2 = 0.537, p < 0.05) and T-TOC (r2 = 0.495, p < 0.05) were also observed.The consistence demonstrated that a major portion of sedimentary SCCPs in the coastal ECS should be from the river input ofChangjiang River and deposited in the CRD and along the inner shelf of the ECS, but only a minor fraction was transported tothe offshore areas.

■ INTRODUCTION

In marine environments, sediments constitute the mostimportant carriers for marine organic matters (MOM) andterrestrial organic matters (TOM). As the intensity of humanactivities has increased, more and more anthropogeniccontaminants are transported to the ocean environment, buriedin the marine sediments, and might threaten the marineecosystems during the migration processes.1,2 To date, somemarine environmental surveys on anthropogenic pollutantshave been carried out to investigate their contents and toidentify their characteristics.2−4 Geographical features and theproxies of TOC and grain size are important features forstudying the source identification and distribution/accumu-lation characteristics.5 However, some abnormal levels orcharacteristics of pollutants in some regions are still difficult tounderstand due to the lack of detailed and comprehensive data.

Thence, the introduction of other indicators is necessary andmeaningful for study of the sources, migration path, andtransformation mechanisms of anthropogenic contaminants,and even their fate in the marine environment.Generally, organic matters buried in the sediments of

estuaries and their adjacent areas are mainly composed ofMOM from marine primary production and TOM via riverinput.6 If sharing similar migration paths and depositioncharacteristics, then the spatial and temporal distributions ofriver-derived contaminants should resemble those of TOM.The proxies of TOM can then provide valuable information

Received: November 30, 2012Revised: April 23, 2013Accepted: April 23, 2013

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when investigating potential sources, migration path, andenvironmental fate of these contaminants. The δ13C of organiccarbon and C/N ratio of TOC are traditional proxies used todetermine the relative amounts of TOM in marine sediments.Usually, TOM has a more negative δ13C value (∼ −27‰) anda higher C/N ratio (>12) than MOM (−20‰ and 6−8respectively),7 and the values of δ13C and C/N ratio canprovide useful information on the relative contributions ofTOM to the TOC. Recently, proxies based on biomarkercontents and ratios have also been introduced to distinguishTOM from sedimentary TOC and have shown high potentialas alternative approaches. The long-chain odd-carbon n-alkanes,long-chain even-carbon n-alkanols, and fatty acids produced byhigher plants are the most used TOM biomarkers.8,9 Thecontent ratios of these terrestrial biomarkers to marinephytoplankton biomarkers (such as brassicasterol, dinosterol,and C37 alkenones) can be directly used to estimate the relativecontributions of TOM to sedimentary TOC in both open andcoastal sea regions.10−12

The East China Sea (ECS), one of the largest shelf seas inthe world, is an important terrestrial organic carbon sink. Largeamounts of terrestrial particulate matters (∼0.5 Gt per year)13

with ∼2.5 Mt of organic matters14 are discharged into the ECSvia the Changjiang River (CR). In recent years, anthropogenicactivities have altered the nature and amounts of terrestrialmatter delivered by the CR15 and resulted in coastaleutrophication and the burial of marine organic matter inshelf sea sediments.16 Meanwhile, a large number of organiccontaminants are transported into the ECS such aspolybrominated diphenyl ethers (PBDEs),17 organochlorinepesticides (OCPs),18,19 and polycyclic aromatic hydrocarbons(PAHs),20 etc.Short-chain chlorinated paraffins (C10−C13, SCCPs), with

the formula of CnH2n+2‑zClz and chlorine content ranging from30% to 72% by weight,21 are a group of widely used industrialadditives.22 In the past decade, they have attracted increasingattention23−25 as a result of potential properties in long-rangetransport,23 persistence in the environment,24 and toxicity toaquatic organisms.25 Our previous study has shown theoccurrence of SCCPs in the sediment in the ECS, with ageneral decreasing trend with distance from the coast.26 Spatialdistributions and correlation analysis demonstrated that TOC,riverine input, ocean current, and atmosphere deposition mightcontribute to the accumulation of sedimentary SCCPs.However, their main source and migration path are still notclear due to lack of necessary supporting data in the studiedregion.This study is a continuation of our previous work to further

investigate the possible sources and migration paths of SCCPsin the coastal ECS by introducing organic geochemistryindicators. The studied region is concentrated in theChangjiang River Delta (CRD) and along Zhejiang−Fujiancoastline, which is heavily affected by CR after the Holocene.To our knowledge, this is the first work to employ multiproxiesof organic geochemistry to study the environmental behaviorsof chlorinated paraffins.

■ EXPERIMENTAL SECTIONSampling Area and Sample Collection. The ECS is a

typical Western Pacific marginal seas open shelf, with theworld’s broadest continental shelf. A major portion of thesediments discharged from the CR is ultimately deposited inthe CR estuary and southern inner shelf of the ECS, forming a

ribbon of mud area.27,28 The surface currents of the ECSconsist of a northward flow of the warm and saline Taiwanwarm current (TWC), relatively cold and brackish southwardflowing Jiangsu and Zhejiang−Fujian coastal current (JCC andZFCC), and the Changjiang diluted freshwater (CDFW)(Figure 1). Three cruises were conducted in July 2010, and

July and August 2011. In all, 37 surface sediment samples (0−3cm) from the CRD to the middle shelf of the ECS (Figure 1)were collected using a Van Veen stainless steel grab sampler.Samples of MZ14, MZ15, MZ16, MZ17, MZ18, and MZ19 arefrom the same batch of Zeng’s work, but they are reanalyzed inthis study. All the samples were immediately stored in arefrigerator at −20 °C until analysis.

Extraction and Cleanup. The pretreatment procedure forSCCPs was based on a previous report with somemodifications.29 Homogenized dry sediment (2 g) was spikedwith the surrogate standard (1 ng of 13C10-trans-chlordane) andextracted by accelerated solvent extraction (ASE) with theextraction solvent of dichloromethane and n-hexane (1:1).Activated copper granules were added to the extraction toremove elemental sulfur. The extract was rotary-evaporated toabout 2 mL and then cleaned and fractionated on a multilayersilica−Florisil composite column, which consisted of 3 g ofFlorisil, 2 g of activated silica gel, 5 g of acid silica gel (30%, w/w), and 4 g of anhydrous sodium sulfate from bottom to top.The column was precleaned with 50 mLof hexane and theextract was eluted in sequence with 40 mL of hexane (first

Figure 1. Sampling sites in the coastal ECS, modified from ref 26.Mud areas are marked in gray and major surface currents are indicatedby large arrows: CDFW (Changjiang diluted freshwater), ZFCC(Zhejiang−Fujian coastal current), TWWC (Taiwan warm current),and KC (Kuroshio current).

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fraction) and 100 mL of dichloromethane/hexane (1:1, v/v)(second fraction). The second fraction was concentrated tonear dryness and then reconstituted in 50 μL of cyclohexane.Prior to analysis, ε-HCH was added in order to determine therecoveries.For biomarkers, deuterium-substituted C24 n-alkane and C19

n-alkanol were added as internal standards to the homogenizeddry sediments (∼2 g), which were then extracted ultrasonicallywith a 3:1 mixture of dichloromethane and methanol fourtimes. The extracts were first hydrolyzed with 6% KOH inMeOH and then extracted with hexane. The extracts weresubsequently separated into fractions using silica gelchromatography. The nonpolar lipid fraction (containing n-alkanes) was eluted with 8 mL of hexane and dried under agentle N2 stream for instrumental analyses. The neutral lipidfraction (containing the three marine phytoplankton bio-markers) was eluted with 12 mL of dichloromethane/methanol(95:5, v/v), dried under a gentle N2 stream, and derivatizedusing N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) at 70°C for 1 h before instrumental analysis.Instrument Analysis, Identification, and Quantifica-

tion. SCCPs analysis was performed on a 7890A gaschromatograph (GC) coupled with a 7000B triple quadruplemass spectrometer (Agilent, USA) as described by a previousstudy.29 One μL of the final extract was injected with a 7683BSeries Injector (Agilent, USA) in splitless mode into a DB-5MScapillary column (30 m length, 0.25 mm i.d., 0.25 μm filmthickness) at an injector temperature of 275 °C. Helium wasused as carrier gas at a flow of 1.0 mL/min. The oventemperature program was as follows: 1 min isothermal at 100°C, increased to 160 °C at 30 °C/min, held for 5 min, thenramped to 310 °C at 30 °C/min and held for 17 min. The low-resolution mass spectrometer was employed in the ECNI modewith methane as reagent gas. The transfer line temperature andion source temperature were set to 275 and 200 °C,respectively. The most abundant isotope was used forquantification and the second-most abundant isotope wasused for identification. To ensure the instrument sensitivity,SCCP congeners were divided into four groups by theoptimized combinations (C10, C11, C12, and C13) and subjectedto analysis by four individual injections. Identification of CPcongener groups was performed by comparison of retentiontime, signal shape, and correct isotope ratio according to Rethand Oehme.30 The actual relative integrated signals for eachcongener were obtained by correcting the SIM signals of [M −Cl]− ions from isotopic abundance and response factors.Congener group abundance profiles were established using theactual relative integrated signals, followed by internal standardmethod to determine the relative concentrations of thecongener group content in the commercial standards andenvironmental samples.The quantification of biomarkers analysis was performed on

an Agilent 6890N GC with FID detector, using a HP-1 capillarycolumn (50 m × 0.32 mm i.d., 0.17 μm film thickness, J&WScientific) and hydrogen as the carrier gas at a flow rate of 1.2mL/min. The oven temperature program was as follows: 1 minisothermal at 80 °C, increased to 200 °C at 25 °C/min, to 250°C at 4 °C/min, and to 300 °C at 4 °C/min, and then held for15 min. The identification and structure verification ofbiomarkers were performed on GC/MS (Thermo) bycomparisons with the retention times of the standards. TheMS was operated in the electron ionization (EI) mode (70 eV),and the mass scanning ranged between m/z 50 and 650 amu,

using an EQUITY-5 capillary column (30 m × 0.25 mm i.d.,0.25 μm film thickness) with helium as the carrier gas. Oventemperature programming for GC/MS was 60−200 °C at 15°C/min, 200−300 °C at 2.5 °C/min, and holding at 300 °C for5 min.All the results are reported on a dry weight (d.w.) basis.Quality Assurance and Quality Control (QA/QC) on

SCCPs. Quality assurance and control measures wereperformed to ensure the identification and quantification ofthe analysis. Glassware and sodium sulfate were solvent-rinsedand heated at 450 °C prior to use. A procedural blank wasprocessed with each batch of eight samples and no quantifiableSCCPs were detected in these blanks; the results were thereforenot blank corrected. The recoveries for the surrogate standard,13C10-trans-chlordane, were in the range of 81−106%.

TOC and Total Nitrogen (TN) Analysis. Prior to analysis,the homogenized dry sediment samples were decalcified with 4N HCl at room temperature for 24 h, and then rinsed withdeionized water and dried in an oven at 55 °C. The TOC andTN analysis were performed using a Thermal Flash 2000Elemental Analyzer, with standard deviations of ±0.02 wt % (n= 6) and ±0.002 wt % (n = 6), respectively. The standard usedin the EA Analysis is Soil Reference (C = 3.5%, N = 0.37%,Santis Analytical AG).

■ RESULTS AND DISCUSSIONPrevious studies have indicated that the occurrence of highlevels of sedimentary contaminants in the Mud Area Southwestof Cheju Island is mainly attributed to atmosphericdeposition.20,26 Terrestrial matters buried in this region aredominated with sediments from the Old Yellow River.31

Therefore in this study, the coastal ECS including the CRD, theZhejiang−Fujian coastline, and their adjacent regions, whichare significantly affected by CR, were chosen as the samplingregion to further study the source and the migration path ofsedimentary SCCPs (Figure 1).

Contents and Spatial Distributions of SCCPs. Similar toour previous study,26 SCCPs were detected in all the surfacesediment samples. ΣSCCPs (total SCCP content) and degreeof chlorination (Cl%) in all the samples are listed in Table SI-1in the Supporting Information. Generally, ΣSCCPs varied from9.0 to 37.2 ng/g d.w., with an average value of 24.0 ng/g d.w. inthe sediments, which were much lower than those in sedimentsfrom Liaohe River Basin (39.8−480.3 ng/g)32 and the PearlRiver Delta in China (320−6600 ng/g).33 Compared with ourprevious work,26 most of the SCCP contents of the 6 samplesfrom the same batch (MZ14, MZ15, MZ16, MZ17, MZ18, andMZ19) were slightly lower (−13% to 50%), with the averagedifference of 25%, indicating that the method we used issatisfactory. The relatively lower levels of SCCPs in this area aremost likely due to the “dilution effect” of terrestrial matters andmarine matters. Previous work reported that about 0.5 Gt/yrterrestrial particulate matters is discharged into the ECS byCR,15 and there is a significant increase of the production andburial of marine organic matters in the shelf sediments due tocoastal eutrophication from increased human activities.16 Thevery high sedimentation rate in the CRD and along the innershelf of the ECS might be another reason for the “dilutioneffect” in the specific hydrodynamic conditions.34 Similarresults have also been reported for the terrestrial organicmatters preserved in the ECS.18,35

The spatial distribution of SCCPs in the coastal ECS displaysa “band-type” distribution, which decreased vastly from the

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inner shelf to the outer shelf, but remained consistent in thenorth−south direction (Figure 2). For example, the areas with

higher contents of ΣSCCPs were located in CRD (such as ES4(37.2 ng/g d.w.)), the inner shelf of the ECS (such as MZ5(35.1 ng/g d.w.), MZ6 (32.1 ng/g d.w.), and MZ10 (34.3 ng/gd.w.)), while lower levels of ΣSCCPs was distributed in themiddle and outer shelf (such as MZ9 (10.1 ng/g d.w.) andMZ13 (19.5 ng/g d.w.)). This distribution characteristicdemonstrated a direct influence of river input by CR and theimpact of the proximity to land-based sources of the coast. Also,the pattern with higher ΣSCCPs in the CRD and alongZhejiang−Fujian coastline resemble the southward flowingdirection of ZFCC and the elongated inner-shelf mud wedgepattern from the Yangtze mouth into the Taiwan Strait (Figure1). The results indicated that a major portion of thesedimentary ΣSCCPs along the coastline are most likely fromthe river input by CR from its basin, which was similar to boththe terrestrial inorganic and organic matters preserved in theECS.18,35

Spatial Distribution Patterns of SCCP CongenerGroups. The congener group profiles of all sedimentarySCCPs showed a significant variation in both the differentcarbon congener groups and degree of chlorine (Figure SI-1).C10 homologue was the most dominant carbon chain group,accounting for 40.5−57.9% of ΣSCCPs, followed by C11homologue (21.2−32.1%), C12 homologue (11.1−17.8%),and C13 homologue (6.7−12.3%). Based on the chlorinegroups, the predominant congeners were of the lowerchlorinated congener groups (Cl5−Cl7) at 16.6−36.4%, 30.9−42.7%, and 16.3−27.3%, respectively, and cumulativelyaccounted for 76.7−96.4% of ΣSCCPs. The patterns ofSCCP congener groups in this study are similar to those

found in the soils from the rural areas of the Liaohe RiverBasin,32 the sediments from the lower industrial areas of thePearl River Delta,33 marine mollusks from the Chinese BohaiSea,36 and marine mammals from the remote Arctic,37 butobviously different from those found in the sediments from thehighly industrialized areas of the Pearl River Delta;33 thesediments of Lake Ontario;3 soils, sediments, and sewagesludge related to municipal wastewater treatment plants;29,38,39

and marine mammal samples from urbanized and industrializedareas.37

It has been reported that log Kow of SCCPs increases linearlywith the increasing carbon atom numbers,40 whereas vaporpressures (VPs) tend to decrease with increasing carbon chainlength and degree of chlorination. The shorter carbon chainand lower chlorinated congener group of SCCPs are moreprone to migrate to regions far away from the emission sourcesthan those of longer carbon chain and higher chlorinatedcongener groups.32,33 Therefore, the spatial distributions ofdifferent SCCP congener groups can provide useful informa-tion on the potential sources and the migration path. Figure 3shows the spatial patterns of the relative abundance of differentSCCP congener groups. The areas with relative higherabundance of long carbon chain (C12 + C13) are concentratedin the CRD and the north of the Zhejiang−Fujian mud area(Figure 3A), while the short carbon chains (C10 + C11) showedan increasing trend seaward and southward along theZhejiang−Fujian coastline (Figure 3B). The similar patternfor SCCP congener groups based on chlorine groups was alsoobserved, with relatively higher amounts of Cl8 + Cl9 + Cl10groups in the CRD and the north of the Zhejiang−Fujian mudarea (Figure 3C,D). The seaward increasing trend of relativeamounts of short carbon (C10 + C11) and lower chlorinatedcongeners (Cl5 + Cl6) along the profile of sites of YRE, DH2-1,DH2-3, and DH2-5 in the ECS was consistent with ourprevious study,26 further demonstrating the possible transportpath of SCCPs from land to the ocean. Additionally, thesouthward increasing trend along the Zhejiang−Fujian coastlinefor short carbon chains (C10 + C11) and lower chlorinatedcongeners (Cl5 + Cl6) with higher volatility and solubility21

resembles the ZFCC southward flow (Figure 1), suggestingthat SCCPs in the CRD or the north of Zhejiang−Fujian mudarea could be transported southward along the coastline andthen buried in the inner shelf.

TOC and TOC-Based Proxies. Many studies haveindicated that TOC could be responsible for the distribution/accumulation of organic pollutants in the aquatic environ-ment,18,33,41,42 although no such correlation was found betweenTOC and organic contaminants in some regions.17,32,43 Usually,high contents of organic pollutants are related to high TOClevels since these organic pollutants can be removed from thewater column and adsorbed onto the particular matters becauseof the high affinity between these materials.44 In this study,TOC of the sediment samples (Figure 4A, Table SI-1) variedfrom 0.12% to 0.69%, with an overall trend of higher valuesalong the coastline including the CRD and the inner shelf, butlower values away from the coast. Significant linear relation-ships were found between the TOC and SCCP contents (r2 =0.402, p < 0.05) (Figure SI-2) in the coastal ECS, which isconsistent with our previous study in the whole ECS,26 whereasit is different from that between TOC and some hydrophobichalogenate organics in the inshore areas of the ECS,17 in thePearl River Delta,33 and in the Daliao River Estuary45 of China.The consistency further indicated that the distribution or

Figure 2. Spatial distributions of SCCP contents (ng/g d.w.) in surfacesediments of the ECS. The gradient distributions were calculated usingKriging by Surfer 8.0.

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accumulation of SCCPs in the marine environment wassignificantly affected by TOC. In addition, the spatialdistribution of grain size (sand%) also displayed a “band-type” distribution along the coastline, with <10% sanddominated in the CRD and 10−30% sand in the innershelf,46 resembling that of SCCP levels (Figure 2). Theterrestrial input, including organic matters and minerals fromCR, is mainly transported southward and preserved along the

Zhejiang−Fujian coastline, forming a depositional mud area inthe ECS inner shelf.28,47 Thence, the similar patterns betweenSCCPs and fine-grained percentage indicated that the surfacesedimentary SCCPs in the coastal ECS are mainly from theriver input of CR and implied that the grain size should beanother key factor influencing the sedimentary SCCPs due tothe high affinity between fine-grained minerals and organicmatter.14,46

Figure 3. Spatial distributions of (SCCP congener groups)% in surface sediments of the ECS: (A) (C12 + C13 groups)%; (B) (C10 + C11 groups)%;(C) (Cl8 + Cl9 + Cl10 groups)%; (D) (Cl5 + Cl6+Cl7 groups)%. The gradient distributions were calculated using Kriging by Surfer 8.0.

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Because both anthropogenic contaminants and TOM arefrom the land and the contribution of TOM or MOM on theTOC is very different in the ECS,12,14 the traditional indicatorsused to distinguish the contribution of TOM are alsointroduced to study whether they are suitable to trace thesource and migration path of these contaminants. In this work,the C/N ratios of the samples ranged from 4.18 to 7.53, with an

average value of 6.04 (Table SI-1). The values suggest apredominant marine origin for TOC in the ECS surfacesediments, even in the CRD and the inner shelf of the ECSwith abundant TOM supply.12,28,48 The C/N ratios alsodisplayed an apparent seaward decreasing trend (Figure 4B),with higher values concentrated in the CRD and alongZhejiang−Fujian coastline. However, they might not be used

Figure 4. Spatial distributions of TOC (%) (A), C/N ratio (B), and TOC δ13C value (C) (modified from previous report12) in surface sediments ofthe ECS. The gradient distributions were calculated using Kriging by Surfer 8.0.

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to study the distribution of SCCPs because of the inability toestimate the contribution of TOM in the ECS.12 TOC δ13Cvalues in the ECS from some other reports range from−20.1‰ to −22.9‰,12,49 displaying a significant seawardenrichment (Figure 4C),12 which is similar to SCCPs and TOCdecreasing trends in our study. The f Terr values (the fraction ofTOM as a percentage of TOC-based δ13C) which is calculatedby a two end-member mixing model, ranged from 48% along

the coast to near 0% in the outer shelf,12 suggesting higherTOM contributions in the CRD and along the Zhejiang−Fujiancoastline. The consistent spatial distributions between ΣSCCPsand f Terr indicated that they are likely to share the same sourceand migration path and these sedimentary SCCPs are mainlyfrom the CR, and mostly deposited in the CRD and along theZhejiang−Fujian coastline.

Figure 5. Spatial distributions of the contents of C27 + C29 + C31 n-alkanes (ng/g d.w.) (A), TMBR value (B), and T-TOC (%) (C). The gradientdistributions were calculated using Kriging by Surfer 8.0.

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Biomarker-Based Proxies. Terrestrial high plants producelong-chain n-alkanes C25−C35 with a strong odd-to-even carbonperformance and C27, C29, and C31 are the most abundant n-alkanes,8 and thus the total contents of C27 + C29 + C31 n-alkanes can be used as a useful TOM indicator.12,50 In the ECS,the indicator has been successfully used to indicate the relativeamounts of TOM and to evaluate their input in the ECS,12,48,51

despite the occurrence of their origin from marinephytoplankton, microorganisms, and oil pollution. In ourstudy, the contents of C27 + C29 + C31 n-alkanes ranged from64.4 to 451.3 ng/g d.w., with high values in the CRD and alongZhejiang−Fujian coastline, displaying a decreasing trendseaward (Table SI-1 and Figure 5A). Linear relationshipsbetween the contents of ΣSCCPs and total contents of C27 +C29 + C31 n-alkanes (r2 = 0.537, p < 0.05, Figure SI-3).Compared to TOC, the contents of C27 + C29 + C31 n-alkanesseem to better indicate the distribution of SCCPs. Theresemblance of pattern and linear relationship also demon-strated that most SCCPs share a similar source and migrationpath with that of C27 + C29 + C31 n-alkanes, which is mainlyfrom the river input by CR and transported southward alongthe Zhejiang−Fujian coastline.In recent years, a new proxy of terrestrial and marine

biomarkers ratio (TMBR) based on terrestrial and marinebiomarkers has been proposed to estimate the relative TOMcontribution.12 Therefore, the total contents of C27 + C29 + C31n-alkanes are defined as the TOM indicator, whereasbrassicasterol, dinosterol, and C37 alkenones, the major lipidcomponents produced by the diatoms, dinoflagellates, andcocolithophrorids, respectively, are used as the MOM indicator.Like other indexes based on biomarker ratios,11,52 the TMBRindex is less affected by degradation because of synchronousdecomposition of both terrestrial and marine biomarkers andtherefore it is also suitable to estimate the quantitativecontributions of TOM and MOM. The TMBR index isexpressed as follows:

= + + ‐

+ + ‐ + + +

n

n B D A

TMBR (C C C alkanes)

/((C C C alkanes ( ))27 29 31

27 29 31

where TMBR stands for terrestrial and marine biomarker ratio,and B, D, and A stand for brassicasterol, dinosterol, and C37alkenones, respectively.In the present study, the TMBR proxy reveals that TOM

accounted for nearly 50% of TOC in the CRD and along thecoast, whereas it accounted for less than 10% in the outer shelf(Table SI-1), displaying a decreasing trend away from the coast(Figure 5B). The percentage terrestrial TOC (T-TOC) basedon this proxy, the product of TOC and TMBR, were alsocalculated, and were at a range of 0.02−0.23% (Table SI-1,Figure 5C). The spatial trends of the TMBR index and T-TOCare similar to the trends of SCCPs (Figure 2), TOC (Figure4A), and other TOM proxies of TOC δ13C (Figure 4C) andΣC27 + C29 + C31 n-alkanes (Figure 5A). Linear relationships(r2 = 0.495, p < 0.05) (Figure SI-4) were observed between thecontents of ΣSCCPs and T-TOC (%). The similarity againindicated the same sources and migration paths betweenSCCPs and TOM and further implied that a major portion ofSCCPs was mostly deposited in the CRD and in the inner shelfof the ECS but a minor fraction was transported to the offshoreareas.In summary, this study provides a foundation for under-

standing the possible sources and migration paths of

anthropogenic pollutants in the marine environment usingmultiproxies of organic geochemistry. However, the estimationof the contribution of atmospheric deposition/river input andthe fate of organohalogen compounds preserved in thesediments still need further investigation.

■ ASSOCIATED CONTENT*S Supporting InformationDetailed contents of ΣSCCPs and congeners, degree ofchlorination of SCCPs, TOC, TOC/TN ratio, contents ofΣC27 + C29 + C31 n-alkanes,∑(Brassi + Dino + Alken), TMBR,and T-TOC in surface sediments (Table SI-1); compositionprofiles of SCCP congeners in the surface sediments from theECS (Figure SI-1); correlations between SCCP contents andTOC (Figure SI-2); correlations between SCCP contents andthe contents of C27 + C29 + C31 n-alkanes (Figure SI-3);correlations between SCCP contents and the contents of TOMbased on TMBR (Figure SI-4). This material is available free ofcharge via the Internet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*Tel: 8610-6284-9334; fax: 8610-6284-9339; e-mail: gbjiang@rcees.ac.cn.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank Meixun Zhao and Lei Xing for samples andconstructive comments on organic geochemistry, and HailongZhang and Li Li for technical assistance. This work was jointlysupported by the National Natural Science Foundation(21007062, 21007078, 41020164005), SKLECE Open Fund(KF2009-21), Young Teachers Special Fund, Ocean Universityof China (201013018), and SOA Open Fund (MESE-2011-07).

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