Chemosphere 88 (2012) 1292–1299

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Determination and partitioning behavior of perfluoroalkyl carboxylic acidsand perfluorooctanesulfonate in water and sediment from Dianchi Lake, China

Yuan Zhang a,b, Wei Meng a,b,⇑, Changsheng Guo a,b, Jian Xu a,b, Tao Yu a,b, Wenhong Fan c, Lei Li a,b

a State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, Chinab Laboratory of Riverine Ecological Conservation and Technology, Chinese Research Academy of Environmental Sciences, Beijing 100012, Chinac Department of Environmental Science and Engineering, School of Chemistry and Environment, Beihang University, Beijing 100191, China

a r t i c l e i n f o

Article history:Received 26 October 2011Received in revised form 16 March 2012Accepted 31 March 2012Available online 11 May 2012

Keywords:Perfluorinated compounds (PFCs)HPLC–MS/MSPartitionDianchi Lake

0045-6535/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.chemosphere.2012.03.103

⇑ Corresponding author at: State Key Laboratory oRisk Assessment, Chinese Research Academy of Env100012, China. Tel.: +86 10 84915237; fax: +86 10 84

E-mail address: mengwei@craes.org.cn (W. Meng)

a b s t r a c t

Perfluorinated compounds (PFCs) have received much attention on their distribution in various matricesincluding water bodies, precipitations, sediment and biota in different areas globally, however, littleattention has been paid to their occurrence and distribution in urban lakes. In this study, water and sed-iment samples collected from 26 sites in Dianchi Lake, a plateau urban lake in the southwestern part ofChina were analyzed via high performance liquid chromatography–tandem mass spectrometry(HPLC–MS/MS) for ten analytes involving nine perfluoroalkyl carboxylic acids (PFOAs) and perfluorooc-tanesulfonate (PFOS). Total levels of PFCs were 30.98 ± 32.19 ng L�1 in water and 0.95 ± 0.63 ng g�1 insediment. In water samples PFOA was the dominant PFC contaminant, with concentrations ranging from3.41 to 35.44 ng L�1, while in sediments PFOS was the main PFC contaminant at levels from 0.07–0.83 ng g�1 dry weight. Field-based sediment water distribution coefficients (KD) were calculated andcorrected for organic carbon content (Koc), which reduced variability among samples. The log Koc rangedfrom 2.54 to 3.57 for C8–C12 perfluorinated carboxylic acids, increasing by 0.1–0.4 log units with eachadditional CF2 moiety. The log Koc of PFOS was 3.35 ± 0.32. Magnitudes and trends in log KD or log Koc

appeared to agree well with previously published laboratory data. Results showed that different PFCcomposition profiles were observed for samples from the lake water and sediments, indicating the pres-ence of dissimilar characteristics of the PFCs compounds, which is important for PFC fate modeling andrisk assessment.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Perfluorinated compounds (PFCs) consisting of perfluorosulfo-nates (PFSAs) and perfluorocarboxylates (PFCAs) are a new classof emerging organic pollutants, and make up a group of surfactantsthat have been in production for more than 50 years (Prevedouroset al., 2005; Teng et al., 2009). These PFCs have attractiveproperties for industrial applications, such as interfacial activity,resistance to acid and high temperatures, and water and oil repel-lency. They are highly stable, bio-accumulative and resistant todegradation in the environment. The widespread applications ofPFCs coupled with their unique characteristics make them ubiqui-tously distributed in various types of environmental matricesincluding river and ocean water (Yamashita et al., 2008; Zushiand Masunaga, 2009), sediments (Zushi et al., 2010), wildlife biota(Senthil et al., 2009), and the human body (Zhang et al., 2010).

ll rights reserved.

f Environmental Criteria andironmental Sciences, Beijing926073.

.

They were even found in remote areas, such as the Arctic (Martinet al., 2003) and Tibetan Plateau (Shi et al., 2010).

Identifying the transport and fate of PFCs in aquatic environ-ment is necessary for strategy designing of pollution control. Theunderstanding of PFCs fate in aquatic systems is still incompleteand so far there is only limited data on their distribution betweenwater and sediment (Kwadijk et al., 2010; Li et al., 2011). PFCs canaccumulate in aquatic systems and are readily transported by typ-ical hydrological or adsorbable processes (Houde et al., 2006; Lauet al., 2007; Eschauzier et al., 2010). There are a few laboratorystudies on sorption processes providing sorption data under con-trolled laboratory conditions (Higgins et al., 2005; Higgins andLuthy, 2006, 2007; Johnson et al., 2007; Ochoa-Herrera and Sier-ra-Alvarez, 2008). Hydrophobic interaction was reported to playan important role in PFCs sorption on sediment (Higgins and Luthy,2006). The partitioning behavior of PFCs has also demonstratedthat the sediment–water distribution depends on solution param-eters such as pH (Higgins and Luthy, 2006) and sediment organiccarbon fraction (foc) (Liu and Lee, 2005; Ahrens et al., 2010). How-ever, adsorption parameters of PFCs obtained from laboratorystudies were different from field based sediment–water

Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299 1293

distribution coefficients (Liu and Lee, 2005; Ahrens et al., 2010;Kwadijk et al., 2010). The extent to which the resulting distributionparameters and mechanistic inferences apply to field conditions isnot yet clear. Besides, limited data show that the distribution ofdifferent PFC homologues between sediment and water were dif-ferent. The short-chain perfluorinated carboxylic acids (PFCAs)(<C8) were exclusively detected in the dissolved phase, whereasthose long-chain PFCAs (>C8) and perfluoroalkyls sulfonates(PFASs) appeared to be bound to sediment (Ahrens et al., 2009,2010). There is still a relative lack of field-based PFC distributioncoefficients, which is essential for environmental fate modeling.

Dianchi Lake (24�280–25�280N, 102�300–103�000E) is located inthe middle of Yunnan-Guizhou Plateau in Southwest China. Theentire basin has a total area of approximately 2920 km2, includingpart of Kunming City (the capital of Yunnan Province), Songming,Chenggong, Jinning, and Xishan Counties. The lake serves many so-cial and economic purposes, with 2.68 million residents in theDianchi Basin, and yearly burden of 216 million m3 of householdwastewater and 47.6 million m3 of industrial waste water (Yanget al., 2010). Previous researches performed in Dianchi Lake weremostly focused on high COD, TN and TP contents which causedthe serious eutrophication in the lake (Lu et al., 2007; Yang et al.,2010). The information on PFCs contamination, however, to thebest of our knowledge, is not available in this region. In this study,the occurrence and spatial distribution of PFCs in water and sedi-ments from Dianchi Lake was determined, and the compositionprofiles of PFCs in both water and sediment samples were investi-gated. Partition coefficients were also calculated to investigate thepartition behavior of these PFCs compounds between water andsediment.

2. Experimental

2.1. Chemicals and regents

The standards, perfluorobutanoate (PFBA, 99.5%), perfluoro-pentanoate (PFPeA, 95%), perfluorododecanoate (PFDoA, 95%) andperfluorooctane sulfonate (PFOS, 99%) were purchased from Sig-ma–Aldrich (St. Louis, MO, USA). Perfluorohexanoate (PFHxA,98%), perfluoroheptanoate (PFHpA, 98%) and perfluoroundecanoate(PFUnA, 96%) were purchased from Matrix Scientific (Columbia, SC,USA). Perfluorooctanoate (PFOA, 98%), perfluorononanoate (PFNA,98%) and perfluorodecanoate (PFDA, 98%) were purchased fromWellington Laboratories (Guelph, Ontario, Canada). 13C8-labeledPFOA (Cambridge Isotope Laboratories, Andover, MA, USA) and13C4-labeled sodium PFOS (Wellington Laboratories, Guelph,Ontario, Canada) were used as the internal standards. All stocksolutions were prepared in methanol and stored in polypropylene(PP) tubes or vials at 4 �C. Methyl tert-butyl ether (MTBE), acetone,methanol, acetic acid and ammonium acetate were of HPLCreagent grade and purchased from Beijing Chemical Reagent Fac-tory (Beijing, China).

2.2. Sample collection and preparation

Water and sediment samples were collected from Dianchi Lakein October, 2010 (Fig. 1), with their geographic information givenin Table SI-1 in Appendix Supplemental Information (SI). Two par-allel water samples were collected at a depth of approximately0.5 m below the surface water with a stainless steel bucket, andstored in 5 L polypropylene (PP) bottles. Surface sediment samples(0–10 cm) were collected with a stainless steel grab sampler andplaced in PP bags. Samples were transported to laboratory on icefor further treatment. All sampling vessels were pre-cleaned with

methanol, Milli-Q water, and water from the specific site beforesampling.

Temperature of the water sample was from 17.2–20.7 �C duringsampling campaign. The pH and total dissolved solids (TDS) ofwater samples were determined and the values are listed in TableSI-1. The TDS of water samples from Dianchi Lake did not vary alot, ranging from 204 (S14) to 310 mg L�1 (S1 and S2). pH valuesranged from 7.08 (S1) to 9.87 (S11, and S13). foc of sediments weredetermined by the method of potassium dichromate–sulfuric acidoxidation (Li et al., 2011), and are also listed in Table SI-1.

2.3. Extraction and cleanup

Water samples (1500 mL) were filtered through GF/A glass fiberfilter (Whatman Inc., USA) to remove large particles and biota, andthen spiked with internal standards (including 5 ng of 13C8-PFOAand 5 ng of 13C4-PFOS), followed by solid phase extraction (SPE)by Oasis HLB cartridges (500 mg, 6 mL, Waters Corp., Milford,MA, USA). Prior to SPE extraction, the cartridge was preconditionedby 10 mL of methanol and 10 mL of Milli-Q water. The filteredwater samples were passed through the cartridges at a flow rateof 5 mL min�1, and the cartridge was then rinsed by 5 mL of 40%methanol in water. Finally, the target fraction was eluted with8 mL of methanol. The extract was reduced to 1 mL under a gentleN2 stream, and transferred into a polypropylene vial for chemicalanalysis.

PFCs in the sediment were analyzed according to the methodreported by Naile et al. (Higgins et al., 2005; Naile et al., 2010) withsome modifications. The extraction procedure consisted of twosteps, (a) extraction of the PFCs from the sediments by sonicationand (b) enrichment and clean-up of the extract by SPE. 2.0 g ofhomogenized freeze-dried sediment (from Dianchi Lake) weretransferred to 50 mL PP centrifuge tubes and spiked with 5 nginternal standard, to which 10 mL of 1% acetic acid solution(pH = 3) was added. Each tube was vortexed, and placed in aheated sonication bath (40 �C) for 15 min. The tubes were thencentrifuged at 4000 rpm for 5 min and the supernatant was dec-anted into a new clean 50 mL PP tube. 2.5 mL of 90:10 (v/v) meth-anol and 1% acetic acid mixture was then added to the originaltube. The mixture was sonicated for 15 min, centrifuged, and thesupernatant was combined into the second tube. This processwas repeated one more time, and a final 10 mL of extracting solu-tion was preformed. All extracts were combined in the second tubebefore SPE. To test the extraction efficiency of different solvents, inthis study pure methanol instead of the above extraction solventswas used to extract PFCs from sediments, following the similarprocedure described above.

2.4. HPLC–MS/MS analysis

PFCs were analyzed by HPLC–MS/MS. The HPLC separation wasperformed on an Agilent 1200 series (Palo Alto, CA, USA) equippedwith an Agilent Zorbax Eclipse XDB-C18 column (2.1 � 100 mm,5 lm). The column was maintained at 40 �C during the sampleanalysis. The mobile phase consisted of eluent A (methanol) andeluent B (2.5 mM ammonium acetate solution). Flow rate was keptat 0.25 mL min�1, and the injection volume was 20 lL. The separa-tion of PFCs was achieved with a gradient program, with an initialgradient of 30% A, and increased to 40% A at 4 min, and continu-ously increased to 90% A at 9 min. The gradient was reverted to30% A at 13 min and was maintained for 2 min.

Mass spectrometric analyses were performed on an Agilent6410 triple quadrupole mass spectrometer equipped with an elec-trospray ionization (ESI) source that operated in the negative ion-ization mode. The nebulizer pressure was set to 35 psi and the flowrate of drying gas was 3 L min�1. The capillary and nozzle voltages

Fig. 1. Sampling sites in Dianchi Lake.

1294 Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299

were 4000 and 0 V, respectively. The flow rate and temperature ofthe sheath gas (nitrogen) were 7 L min�1 and 350 �C, respectively.The collision gas was argon, and the collision energies are listed inTable SI-2.

Multiple responses monitoring (MRM) analysis was used toidentify analytes. For each analyte, quantification was based onthe response of a single product ion (Table SI-2). Internal calibra-tion was used to quantify analytes. 13C8-PFOA and 13C4-PFOS wereused as the internal standards for PFCAs and PFOS, respectively.The analytical procedure was carried out in triplicates to evaluatethe precision.

2.5. Quality assurance

During the sampling and analytical processes, Teflon coated labwares were avoided to minimize contamination. Along with eachbatch of ten samples, one procedure blank was run to make surethe analytical procedure was operating correctly. Solvent blankscontaining Milli-Q water and methanol (1:1, v/v) were preparedto run after every ten samples for monitoring the instrumentalbackground. Recoveries of the PFCs were tested with the waterand sediment from Dianchi Lake. Per matrix, a sample was spikedwith 2 and 20 ng of each PFC. A duplicate of the unspiked samplewas also performed in the case of the sediment, and calculatedas the percentages of the measured concentrations relative to thespiked concentrations. Quantification of each PFCs compoundwas obtained using the internal standard method. Calibrationcurves were constructed for the range of 0.2–50 lg L�1 for thePFCs, with linearity of r2 > 0.995. Limit of detection (LOD) and limitof quantification (LOQ) of the PFCs were calculated with signal/

noise ratios (S/N) of 3 and 10, respectively. The S/N ratios were ob-tained by using the software Masshunter (Agilent) processing theresults of the recovery test done at the concentration of0.2 lg kg�1.

3. Results and discussion

3.1. Recoveries of PFCs from sediment

The extraction solvent is crucial on the extraction of PFCs fromsediments, as PFCs tend to complexate with organic matters andadsorb strongly onto sediment (Powley et al., 2005; Voogt andSáez, 2006). In 2005 Higgins et al. for the first time developed anacetic acid extraction method to analyze PFCs in sediment anddomestic sludge (Higgins et al., 2005; Naile et al., 2010), whichwas used in many following studies. The half dry alkaline methodwas also used to extract the PFCs from the sediment with NaOH in20% H2O/80% methanol solvents (Powley et al., 2005; Ahrens et al.,2009). In the present study, the effect of the extraction solvent wasevaluated by extracting the PFCs from spiked sediments by acidsolution and by pure methanol solvent. For each extraction meth-od, triplicate samples of sediment (2 g) were spiked with 20 lL and200 lL of 100 ng mL�1 mixture solution (containing PFCAs andPFOS), and recoveries of two-step extraction for various PFCAsand PFOS were determined. Results were summarized in Table 1.

It indicated that the efficiencies of acetic acid solution andmethanol extraction method for PFOS and short-chain PFCAs weresimilar, with recoveries ranging from 61% to 100%. However, forsome long-chain PFCAs, methanol extraction gave better recoveries

Table 1Recoveries, LODs and LOQs for individual PFCs in sediment.

Analyte % Recovery (SD) from sediment LODa LOQb Linearity (r2)c

Acid method Pure methanol method Sediment (ng g�1 dw) Water (ng L�1) Sediment (ng g�1 dw) Water (ng L�1)

2 ng g�1 20 ng g�1 2 ng g�1 20 ng g�1

PFBA 74 (4) 71 (3) 75 (4) 76 (2) 0.029 0.23 0.096 0.55 0.9953PFPeA 67 (3) 79 (2) 100 (2) 86 (2) 0.028 0.11 0.066 0.43 0.9994PFHxA 61 (3) 63 (3) 83 (8) 79 (7) 0.020 0.24 0.066 0.63 0.9995PFHpA 83 (2) 76 (6) 97 (7) 76 (2) 0.028 0.35 0.092 0.92 0.9988PFOA 74 (8) 62 (2) 90 (4) 89 (3) 0.011 0.33 0.02 0.94 0.9987PFNA 79 (4) 64 (2) 81 (6) 82 (4) 0.014 0.22 0.033 0.86 0.9982PFDA 62 (2) 55 (3) 67 (3) 79 (3) 0.018 0.17 0.059 0.38 0.9988PFUnA 41 (3) 53 (3) 99 (7) 86 (2) 0.014 0.24 0.046 0.72 0.9998PFDoA 47 (5) 36 (2) 101 (2) 77 (3) 0.013 0.16 0.043 0.31 0.9982PFOS 75 (7) 69 (4) 74 (5) 88 (3) 0.010 0.22 0.020 0.74 0.9989

a Limit of detection.b Limit of quantification.c Calibration curves (0.2–50 lg L�1 for each compound).

Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299 1295

than acetic acid solution. As shown in Table 1, recoveries of PFDA,PFUnA and PFDoA (C10–C12) ranged from 67–101% by methanolextraction, while by acetic acid extraction, the recoveries werefrom 36–62%. Long-chain PFCs tend to strongly adsorb to sedi-ments, causing it difficult to be extracted (Yang et al., 2011). Meth-anol extraction method provided better recovery for most PFCsthan the acid method, especially for long-chain PFCAs. In thisstudy, PFCs in sediments were extracted by methanol.

Fig. 2. Spatial distribution of PFCs in surface water (a) and sediment (b) fromDianchi Lake.

3.2. Spatial distribution of PFCs in water samples

Although 10 different PFCs compounds were determined in thisstudy, in the following sections PFOS and PFOA would be primarilydiscussed since these two compounds were consistently found atthe greatest concentrations. The occurrence and concentrationsof PFCs in surface water samples collected from Dianchi Lake weresummarized in Fig. 2a. PFOA and PFOS were detected in all sam-ples. For long-chain PFAs (C9–12), PFNA, PFDA, PFUnA and PFDoA,their detection frequencies (chance to be detected) in water sam-ples were from 19.2% to 30.7%, while short-chain PFAs (C4–7) weredetected in much higher frequency (30.8–34.6%).

The profiles of relative concentrations of 10 PFCs in water fromDianchi Lake were shown in Fig. 3a. In the study sites, PFOA con-tributed 10.8–87.8% of the total PFCs, however, relatively smallercontributions of PFOS were determined between 6.0% and 60.9%of all analytes. Comparable to PFOS, PFHxA and PFHpA contributed7.9–34.2% and 10.0–39.0% of the total target analytes in these loca-tions (Fig. 3a). The other six PFAs including PFBA, PFPeA, PFNA,PFDA, PFUnA and PFDoA were measured with less frequency andat lower concentrations. For instance, PFUnA and PFDoA were notdetected in most of the water samples, and their levels were rang-ing from <LOD to 1.75 ng L�1 (Fig. 2a).

It is notable that the total concentration of PFCs (RPFCs) innorthern lake (S1–S6) was higher than in the south part of the lake(Fig. 2a). As shown in Fig. 1, Dianchi Lake is divided into two partsby an artificial dam as Caohai (north part, 10.7 km2) and Waihai(south part, 297.9 km2). Caohai is a small lake surrounded by Kun-ming City and has poor ability of water exchange with Waihai. Itreceives direct discharge of effluent of municipal sewage treatmentplants and river flows containing contaminants, resulting in its rel-atively high levels of RPFCs ranging from 35.76 ng L�1 to135.88 ng L�1. The highest concentration of PFCs was observed atS2, where PFOS (40.90 ng L�1) was the highest and PFOA was alsohigh. In contrast, lower RPFCs in S8–S26 were probably due to thedilution effect of larger volume of water in Waihai.

PFOS and PFOA were the dominant compounds in surface waterfrom Dianchi Lake, with concentrations ranging from 1.71–40.90 ng L�1 and 3.4–35.44 ng L�1, respectively, which was compa-rable to the levels in other aquatic environments around the world.As shown in Table 2, the levels of PFOA and PFOS in Dianchi Lakewere similar to those reported in Taihu Lake and Liao River in Chi-na (Yang et al., 2011), and relatively lower than those reported in

Fig. 3. Average contribution of each compound to the total PFCs in water (a) and sediment (b) from Dianchi Lake.

Table 2Concentrations of PFOS and PFOA in water (ng L�1) and sediment (ng g�1 dw) in samples around the world.

Sampling Type Year n Concentration References

PFOS PFOA

Yangtzi River Estuary, China Water 2008 4 36.3–703.3 NA (Pan and You, 2010)Sediment 2008 4 72.9–536.7 NA

Orge River near Paris, France Water 2010 12 17.4 ± 2.2 9.4 ± 0.6 (Labadie and Chevreuil, 2011)Sediment 2010 12 4.3 ± 0.3 <0.07

Estuarine and coastal areas of Korea Water 2008 15 4.11–450 59 ± 112 2.95–68.6 20.6 ± 19.8 (Naile et al., 2010)Sediment 2008 12 Nd-2.0 Nd-2.0

Several River of Japan water 2003 5 7.9–110 4.1–10 (Senthilkumar et al., 2007)Sediment 2005 9 Nd-3.9 Nd-6.4

Daliao River system of northeast China Sediment 2008 10 0.06–0.37 0.09–0.17 (Bao et al., 2009)San Francisco Bay, USA Sediment 2004 17 n.d.-3.76 n.d.-0.625 (Higgins et al., 2005)Pearl River Delta, China water 2003–2004 8 0.02–12 0.24–16 (So et al., 2004)Yangtzi River near Shanghai Water 2005 12 0.62–14 22–260 (So et al., 2007)

Sediment 2009 9 ND-0.46 0.20–0.64 (Bao et al., 2010)Zhujiang River, Guangzhou, China Water 2004 6 0.90–99 0.85–13 (So et al., 2007)

Sediment 2009 22 n.d.�3.1 0.09–0.28 (Bao et al., 2010)Taihu Lake, China Water 2009 32 3.6–394 10.6–36.7 (Yang et al., 2011)

Sediment 2009 32 0.06–0.31 <0.02–0.52Haihe River, Tianjin China Water 2010 16 2.02–7.62 14.4–42.1 (Li et al., 2011)

Sediment 2010 16 1.76–7.32 0.92–3.69Dianchi Lake, China Water 2010 26 1.71–15.12 ND-35.44 This study

Sediment 2010 26 0.07–0.83 ND-0.71

1296 Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299

Great Lakes of North America (Boulanger et al., 2004; Kannan et al.,2005), Mississippi River Basin (Nakayama et al., 2010), South ChinaSea (So et al., 2004), Tokyo Bay and coastal areas of Korea (Yamash-ita et al., 2005; Naile et al., 2010). The highest concentration ofPFOA detected in Dianchi Lake (35.44 ng L�1) was much lower thanthe highest level found in Yangtzi River (206 ng L�1) (So et al.,2007) and the rivers from Tokyo Bay (192 ng L�1) (Yamashitaet al., 2005). The mean concentrations of PFOA and PFOS in Dianchi

Lake were approximately 10.31 ng L�1 and 7.78 ng L�1, respec-tively.

3.3. Spatial distribution of PFCs in sediment

Distribution of PFCs in the sediment of Dianchi Lake was shownin Fig. 2b. The RPFCs ranged between 0.21 and 2.45 ng g�1 dryweight. Similar to the spatial distribution tendency of PFCs in sur-

Table 3Average log KD and log Koc (L kg�1) at sediment–water interface from Dianchi Lake.

Compound Sampling locations log KD logKoc

PFBA S1–S26 1.18 ± 0.096 (n = 3) 2.62 ± 0.10 (n = 3)PFPeA S1–S26 1.14 ± 0.38 (n = 3) 2.54 ± 0.51 (n = 3)PFHxA S1–S26 1.33 ± 0.37 (n = 5) 2.72 ± 0.40 (n = 5)PFHpA S1–S26 1.24 ± 0.15 (n = 7) 2.62 ± 0.21 (n = 7)PFOA S1–S26 1.27 ± 0.40 (n = 24) 2.63 ± 0.45 (n = 24)PFNA S1–S26 1.18 ± 0.21 (n = 8) 2.75 ± 0.22 (n = 8)PFDA S1–S26 1.64 ± 0.28 (n = 6) 3.05 ± 0.30 (n = 6)PFUnA S1–S26 1.89 ± 0.11 (n = 4) 3.28 ± 0.21 (n = 4)PFDoA S1–S26 1.95 ± 0.35 (n = 6) 3.57 ± 0.25 (n = 6)PFOS S1–S26 1.80 ± 0.29 (n = 26) 3.35 ± 0.32 (n = 26)

Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299 1297

face water, relatively higher RPFCs were found in Caohai, with thehighest RPFCs appeared in S2 with a concentration up to2.45 ng g�1 dw. Corresponding low RPFCs were observed in sedi-ments of Waihai area.

In contrast to the similarity of spatial distribution with watersamples, the PFCs in the sediment showed a different compositeprofile, as shown in Fig. 3b. In aqueous phase long-chain PFCs wereless detected, while in sediments more PFCs including the long-chain PFCAs such as PFNA, PFDA, PFUnA and PFDoA were detectedwith high detection frequencies (57.7–69.2%). Different compositeprofiles observed between water and sediment indicated that thedistribution of individual PFCs was closely dependent on theirphysicochemical characteristics. Short-chain PFCAs tend to existin water phase, while long-chain PFCAs and PFOS seem to bindmore strongly to sediment. This suggests that long-chain PFCsare prone to partition to sediment, which may act as a sink forthese chemicals in the environment.

PFOS was the predominant PFC and was detected in all sedi-ment samples, which contributed 24.0–84.8% of the total PFCs inthe sediments. However, relatively smaller contribution of PFOAwas determined between 11.5% and 41.2% of the total detectableanalytes, followed by PFHpA (8.3–24.7%) and PFNA (3.7–22.9%).Levels of PFOS were determined between 0.07 and 0.83 ng g�1 dw,with a median value of 0.25 ng g�1, while levels of PFOA were ran-ged below LOD to 0.71 ng g�1 dw with a median value of0.12 ng g�1 dw. For PFNA, PFDA, PFUnA and PFDoA, their concen-trations in sediments were from below LOD to 0.30 ng g,0.18 ng g�1, 0.17 ng g�1 and 0.14 ng g�1 dw, respectively. The con-centrations of PFBA and PFPeA in sediments were measured belowtheir LOQs in most of the sampling sites. The highest concentrationof PFOA and PFOS up to 0.71 ng g�1 and 0.83 ng g�1 dw appeared insite S1 and S2 that was placed close to the conventional city centreas mentioned earlier. Nevertheless, PFOA contaminations were notobserved in sites S16 and S25, where in sites S16 only PFOS andPFUnA was determined as the PFCs contaminant. Although thelong-chain PFCAs were still at low levels, the detection frequencyand concentrations increased with longer carbon chains.

Table 2 summarized the concentrations of PFOA and PFOS in thesediments in some other study areas. PFOA in the sediments ofDianchi Lake was comparable to that in the Taihu Lake, China withmean concentration of 0.16 (0.02–0.52) ng g�1 (Yang et al., 2011),slightly higher than that found in the Daliao River system with amean concentration of 0.12 (0.09–0.17) ng g�1 dw (Bao et al.,2009) and in the rivers by San Francisco Bay, USA with a mean con-centration of 0.25 (n.d.�0.625) ng g�1 dw (Higgins et al., 2005).Sediment concentration of PFOA was lower than that in Kyoto Riv-er in Japan with the concentration from 1.30–3.90 ng g�1 dw (Sent-hilkumar et al., 2007), much lower than that in Huangpu River inShanghai and Haihe River in Tianjin, China, where a mean concen-tration of PFOA was found to be 34.60 (5.20–203) ng g�1 and 1.80(0.90–3.70) ng g�1 dw, respectively (So et al., 2007; Li et al., 2011).As for PFOS, its sediment concentration was comparable to those inTaihu Lake, China (0.11 (0.09–0.14) ng g�1 dw) (Yang et al., 2011),Roter Main River, Germany (0.201 (0.09–0.348) ng g�1) (Beckeret al., 2008) and Daliao River (0.21 (0.06–0.37) ng g�1) (Bao et al.,2009), but lower than in the San Francisco Bay, USA(n.d.�3.76 ng g�1 dw) (Higgins et al., 2005), Haihe River, China(5.20(1.80–7.30) ng g�1 dw), and Orge River, France (mean concen-tration of 4.30 ng g�1 dw) (Labadie and Chevreuil, 2011).

3.4. Partition of PFCs between sediment and water

Partition coefficient was calculated to understand the relativeimportance of sediment and aqueous PFCs concentrations fromDianchi Lake, according to the following equation:

KD ¼ Csediment=Cwater

where Csediment is the concentration in sediment as expressed inmicrograms per kilogram, Cwater is the water concentration inmicrograms per liter, and KD is in liters per kilogram. The organiccarbon normalized partition coefficient (Koc) was also calculatedwith the following equation because the organic carbon contentof sediments was reported to influence the transport of PFCs in sed-iments by previous studies (Ahrens et al., 2010; Kwadijk et al.,2010).

Koc ¼ KD � 100=foc

where foc is the organic carbon fraction in sediment.The log KD and log Koc values for PFCs were shown in Table SI-3

and Table 3. The average log KD of 1.80 ± 0.29 (n = 26) for PFOS inDianchi Lake was similar to the reported field log KD values (1.2–1.6; 2.1 ± 0.1; 2.53 ± 0.35) in literatures (Becker et al., 2008; Ahrenset al., 2010; Kwadijk et al., 2010), and much lower than that re-ported in Haihe River and Dagu River (3.1 ± 0.2) in China (Liet al., 2011). For PFOA, the average value of log KD (1.3 ± 0.4) washigher than previous reports, i.e. 0.04 ± 0.03 (Ahrens et al., 2010)and 0.18–0.48 (Becker et al., 2008), but agreed with the report va-lue (1.83 ± 0.40) in Netherlands (Kwadijk et al., 2010). It should benoted that the values of log KD of the PFOA varied from differentsampling points. For example, log KD of PFOA was 0.56 at site S4,but 2.05 at site S9. The sediment properties and water conditionsmay affect the partition of PFCs in real environment (Yang et al.,2011).

The difference of log KD values in different studies was probablyrelated to the different physicochemical characteristics of PFCs.The special physical and chemical properties of anionic PFCs makeboth hydrophobic and electrostatic effects co-influence their sorp-tion behavior (Li et al., 2011). For a given PFC class, perfluoroalkylchain length was the dominant structural feature influencing sorp-tion onto river sediments (Higgins and Luthy, 2006). Water chem-istry may also influence the sorption of PFCs on sediment. Asignificant correlation was found between pH and sedimentaryconcentrations of some PFCs, showing increasing sorption of PFCswith decreasing pH of approximately 0.37 log units per unit pH(Higgins and Luthy, 2006; Ahrens et al., 2009; You et al., 2010).Other parameters such as Ca2+ and salinity were also reported toenhance PFC sorption onto sediment, which can be explained thatthe increased concentration of CaCl2 could neutralize the negativecharge on the sediment surface, and reduced the electrostaticrepulsion between the negative charged sediment surface andthe anionic PFOS. The decreased electrostatic repulsion would cer-tainly promote the sorption of anionic PFOS molecule to the sedi-ment surface through electrostatic attraction (Higgins and Luthy,2006; You et al., 2010). Another important influencing factor wasthe sediment property, for instance, the organic carbon contentof sediments (Ahrens et al., 2010; Li et al., 2011). The sediment or-ganic carbon was the dominant sorbent-specific parameter affect-ing sorption of PFCs in the dilute solution range, which was

Fig. 4. Correlation between log Koc and perfluoroalkyl chain length.

1298 Y. Zhang et al. / Chemosphere 88 (2012) 1292–1299

employed to normalize partition coefficients of PFCs to minimizedeviations.

In this study, the average log Koc values (Table 3) increased withan increasing perfluoroalkyl chain length. From PFNA to PFUnA,log Koc values increased by 0.1–0.4 log units with each CF2 moiety(Fig. 4), which was consistent with previous studies (Higgins andLuthy, 2006, 2007; Ahrens et al., 2010; Li et al., 2011). It is notablethat the slope of the regression of log Koc vs. f(alkyl chain length)was 0.26 (Fig. 4), which was different from 0.45 reported by Hig-gins and Luthy (2006). This variation may be due to the differencein sediment properties, and that different PFAs were considered(Labadie and Chevreuil, 2011). For PFOS, the average log Koc of3.35 ± 0.32 (n = 26) was rather high when compared to the valuesreported by Johnson et al. (Johnson et al., 2007) and Higgins andLuthy (Higgins and Luthy, 2006, 2007), i.e. log Koc = 2.4–3.1 and2.57, respectively, and was consistent with the values reportedby Kwadijk et al. and Li et al., i.e. log Koc = 3.61 and 4.4 (Kwadijket al., 2010; Li et al., 2011). In addition to the difference in sedi-ment characteristics, this variation may be partially attributed tothe sediment–water equilibrium status.

4. Conclusions

A sensitive and reliable analytical method was developed tosimultaneously determine the concentration of ten PFCs in waterand sediment samples from Dianchi Lake, China. Methanol solutionshowed better extraction efficiency of PFCs from the sedimentsthan the acetic acid method. Pollution of PFCs in Dianchi Lakewas in a moderate level, compared with their occurrence in otherareas around the world. This study also provided field-based distri-bution coefficients (KD and Koc) for a wide range of PFCs, whichwere still relatively scarce and useful for a better understandingof the fate of PFCs in aquatic ecosystems.

Acknowledgements

This work was financially supported by China’s national basicResearch Program: ‘‘Water environmental quality evolution andwater quality criteria in lakes’’ (2008CB418201).

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.chemosphere.2012.03.103.

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