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SHEN Beibei, WU Jinglu, ZHAO Zhonghua. Organochlorine pesticides and polycyclic aromatic hydrocarbons in water and sediment ofthe Bosten Lake, Northwest China. Journal of Arid Land, 2017, 9(2): 287-298.  
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Received:2016-03-01 Revised:2016-11-24
Organochlorine pesticides and polycyclic aromatic hydrocarbons in water and sediment ofthe Bosten Lake, Northwest China
SHEN Beibei1,2, WU Jinglu1,*, ZHAO Zhonghua1
1State Key Laboratory of Lake and Environmental Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing210008, China
2 University of ChineseAcademy of Sciences, Beijing100049, China
*Corresponding author: WU Jinglu (E-mail: w.jinglu@niglas.ac.cn)
Abstract

We evaluated organic pollution in Bosten Lake, Xinjiang, China, by measuring the concentrationsand distributionsof organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs). Water and sediment samples were collected from 19 sites (B1-B19) in the lakefor analysis. Our analytical results show that the concentrations of total OCPs in water rangesfrom 30.3 to 91.6 ng/L and the concentrations of PAHsrangesfrom undetectable (ND) to 368.7 ng/L. The concentrations of total OCPs in surface (i.e., lake bottom) sediment rangesfrom 6.9 to 16.7ng/g and the concentrations of PAHs rangesfrom 25.2 to 491.0 ng/g. Hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) account for large proportions of the OCPs. Low α- to γ-HCH ratios in both water and sediment samples indicate possible contributions from both industrial products and lindane. DDTs in water are probably from historical input, whereas DDTs in sediments are from bothhistorical and recent inputs. Moreover, DDT products in both water and sediments were from multiple sources in the northwestern part of the lake (B11, B12, B13, and B14). Fugacity ratios for DDT isomers ( p, p′-DDEand p, p′-DDT) at these sites were generally higher than equilibrium values. These results suggest that the input from the Kaidu River and diffusion of DDTs from the sediment to the water are responsible for DDT pollution in the water. Lower-molecular-weight PAHs, which originate primarily from wood and coal combustion and petroleum sources, represent the major fraction of the PAHs in both water and sediment samples. Our findings indicate that OCPs and PAHs in BostenLake can be attributed primarily to human activities. A risk assessment of OCPs and PAHs in water and sediment from BostenLake, however, suggests that concentrations are not yet high enough to cause adverse biological effects on the aquatic ecosystem.

Key words: organochlorine pesticides (OCPs); polycyclic aromatic hydrocarbons (PAHs); Bosten Lake; surface water and sediment; spatial distribution
1 Introduction

Organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) have attracted widespread attentionsbecause of their persistence, toxicity, bioaccumulation, and semi-volatility. OCPs were used as insecticides, herbicides and fungicides in agriculture, but have been designated as persistent organic pollutants and banned for many years in some countries.However, OCPsare still detected in water, soil, and sedimentsin some regions. PAHs are derived mainly from anthropogenic origin, e.g., incomplete burning of fuels, garbage, or other organic substances (Kim et al., 2013).OCPs and PAHs enter the aquatic environment via discharge of industrial wastewater and domestic sewage, runoff from non-point sources, wet or dry depositions, etc., whichare hydrophobic and tend to accumulate in sediments. Nevertheless, sediments can also besources, from which OCP and PAHresidues can bereintroduced into the water(Liu et al., 2013; Li et al., 2014).

In the past few decades, many studies have beenconducted on the occurrence, fate, and transport of OCPs and PAHs invarious environmentsassociated withintense human activities (Iwata et al., 1995; Helm et al., 2011; Lu et al., 2012; Liu et al., 2013, 2014). Little informationisavailable regarding OCPs or PAHs in arid areas of China.

Bosten Lake, the largest inland freshwater lake in China, is located in thearid region of Xinjiang.It is an important water source thatsupports local ecological services and economic development. Recent anthropogenic activities in the drainage basin have, however, caused environmental problems in Bosten Lake.Previous studies of Bosten Lake focused mainly onthe history of PAH pollution, climateand environmental changes, and water quality(Guo et al., 2010; Zhang et al., 2010; Ma et al., 2011; Wu et al., 2014), but the OCP and PAH concentrations had not been scrutinized thoroughly. In this study, wedetermined the concentrations of OCPs and PAHs in surface water and sediments of Bosten Lake to:(1) identify their sources and delineate the spatial distributionsin the lake; and (2) examine the potential eco-toxicitiesof these pollutants.

2 Materials and methods
2.1 Study area

Bosten Lake (41° 56′ -42° 14′ N, 86° 40′ -87° 56′ E; 1051 m a.s.l.), the largest inland freshwater lake in China, is located in the southeastern part of the Yanqi Basin(Fig. 1). It has a maximum length of 81 km anda maximum width of 42 km. It coversa surface area of 1005 km2(Wu et al., 2014).There are 13 riversaround the lake and Kaidu River is the only non-seasonal one that is the most important water contributorof the Lake, accounting for about 83% of the lake’ s water inflow. Bosten Lake is also the headwaters of the KonqiRiver. The lake plays an important role in mitigatingfloodsfrom theKaiduRiver.It also serves as a potable water supply and provides water for agriculture andnaturalecosystems. Besides the agricultural wastewater discharges into the lake from the northwestern corner, the lake also acts as asink for municipal sewage and industrial wastewater, leading to a continuousdeterioration of the water quality(Liu et al., 2015).

Fig. 1 Location of Bosten Lake and its river system

2.2 Sampling and sample pretreatment

Water and sediment samples were collected from 19 samplingsites inBosten Lake (Fig. 2)in July 2014 for OCP and PAH analysis.The global positioning system was used to identify the location of each sampling site. Surface water samples were collected at 0.5 m below the water surface, filtered through a GF/C glass fiber filter and stored in 2-L pre-cleaned amber glass bottles at 4° C. And, they were analyzed within 12 h after the sampling. The water samples were then forced through solid-phase extraction(SPE) columns that were eluted sequentially with 10 mL methanol and 10 mL deionized water. The samples were eluted twice with 10 mL dichloromethane solution. The SPE extracts were evaporated to a near-dry state by a rotary evaporator (Buchi R-200, Flawil, Switzerland), re-dissolved in 5 mL hexane and then concentrated to 1 mL under a gentle stream of nitrogen, transferred into a vial and kept at -20° C before instrumental analysis.

Fig. 2 Location of sampling sitesin Bosten Lake

Surface sediment (i.e., 5 cm from the lake bottom) samples were collected in polyethylene bags with a Peterson grab sampler and stored at 4° C during transport to the laboratory. Sediment samples were freeze-dried and ground witha mortar and pestle to obtain 100-μ samples. Five-gram samples of homogenized sediment were extracted by accelerated solvent extraction (ASE-100, Dionex, USA) using dichloromethane, and mixed with copper to remove sulfur. The extracts were collected in a bottle and evaporated to a near-dry state by a rotary evaporator (Buchi R-200, Flawil, Switzerland), then re-dissolved with 5 mL hexane to remove dichloromethane. Solutions were purified by passing them through a glass column filled with silica gel-alumina (2:1) at the top and anhydrous sodium sulfate (1 cm) at the bottom. The column was eluted with 70 mL n-hexane/dichloromethane (v/v=5/2). The n-hexane/dichloromethane elution was evaporated to a near-dry state by a rotary evaporator, re-dissolved in 5 mL hexane, concentrated to 1 mL under a gentle stream of nitrogen, then transferred to a vial and kept at -20° C before instrument analysis.

2.3 Chemicals and reagents

A mixture of standard OCPs (containing α -HCH, β -HCH, γ -HCH, δ -HCH, heptachlor, aldrin, heptachlor epoxide, α -chlordane, γ -chlordane, dieldrin, endrin, endrin aldehyde, endrin ketone, α -endosulfan, β -endosulfan, p, p′ -DDE, p, p′ -DDD, p, p′ -DDT, endosulfan sulfate, and methoxychlor), recovery surrogates standard (2-, 4-, 5-, 6-tetrachloro-m-xylene (TCmX)) and decachlorobiphenyl (PCB209) and internal standard (pentachloronitrobenzene (PCNB)) was purchased from Supelco (USA). Standards of 16 United States Environmental Protection Agency (USEPA) priority PAHs (containing naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorine (Fl), phenanthrene (Phe), anthracene (Ant), fluoranthene (Flu), pyrene (Pyr), benzo[a]anthracene (BaA), chrysene (Chr), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1, 2, 3-cd]pyrene (IcdP), dibenzo[ah]anthracene (DahA), and benzo[ghi]perylene (BghiP)), deuterated recovery surrogates standard (consisting of naphthalene-D8, acenaphthene-D10, phenanthrene-D10, chrysene-D12, and perylene-D12) and the internal standard (hexamethylbenzene) were purchased from Supelco (USA). Dichloromethane, methanol, and n-hexane were also obtained from Supelco. All organic solvents were HPLC grade.

2.4 Instrumental analysis

OCPconcentrations were determined by gas chromatography equipped with a63Ni electron capture detector (GC-ECD: 7890 GC Agilent, USA). A DB-5MS capillary column (30 m× 0.25 mm× 0.25 µ m) was used for separation. The oven temperature was programmed to range from 60° C to 170° C (2 min hold) at the rate of 10° C/min, and from 170° Cto 280° C (3 min hold) at the rate of 5° C/min, and finally from 280° Cto 300° C at the rate of 15° C/min. Temperatures of the injector and detector were 250° Cand 320° C, respectively. Helium was used as the carrier gas (1.5 mL/min) and nitrogen as the make-up gas (60 mL/min). Oneµ L of sample was injected in thesplitless mode for analysis. Identification of OCPs was confirmed using GC-MS (Agilent 7890-5975C) equipped with a HP-5MS capillary column (30 m× 0.32 mm× 0.25 µ m).

PAHs analyses were carried out using a high performance liquid chromatograph (HPLC) (Agilent 1200 HPLC) equipped with diode array detection (DAD, 238 nm) coupled with a fluorescence detector (FLD). The separation column was a WATERS PAH C18 (5 µ m× 460 mm× 0.25 µ m). The mobile phase was a gradient of acetonitrile and purified water (60% acetonitrile at first; after 20 min, linear gradient to 100% acetonitrile held for 10 min; flow rate: 1 mL/min). The injection volume was 20 µ L.

2.5Quality assurance and quality control

Concentrations of OCPs and PAHs were quantified by peak identification and retention times of corresponding standard components. Blanks, duplicate samples, and internal standard additions were employed for analytical assurance. The surrogate recoveries were 68%-112% for OCPs and 76%-103% for PAHs. The detection limitswere 0.01-2.00ng/L and 0.01-2.81 ng/gfor OCPs, and 0.02-0.08ng/L and 0.03-3.57 ng/g for PAHs.

2.6Fugacity ratios calculation

The fugacity value can be used to estimate the net flux direction of a pollutant between compartments (Mackay, 2001).The sediment-water fugacity ratio (fs/fw) iscalculated as Equation 1 (Mackay, 2001; Dai et al., 2014):

fs/fw=Cs/(Cw× 0.41OC× Kow× ρ s). (1)

Where fw and fs are the fugacity(Pa)in water and sediment, respectively.Cw and Cs are the concentrations of the DDT isomer in water (ng/L) and sediment (ng/g), respectively. OC, the organic carbon content (%); Kow, the octanol-water partition coefficient; ρ s, the sediment density (kg/L). The Kow values for p, p′ -DDT, p, p′ -DDE and p, p′ -DDD were taken from Unitednations Environment Programme (UNEP) Chemicals (2002). The valueof fs/fw at 1.0 impliesthat the DDTs in water and sediment are at equilibrium and the net flux is therefore zero. fs/fw> 1.0 andfs/fw< 1.0 indicate net diffusion from the sediment to the water and net deposition from the water to the sediment, respectively (Dai et al., 2014).

3 Results
3.1Concentration and composition of OCPs in water and sediments

The concentration of total OCPs in water ranged from 30.3 to 91.6 ng/L, with an average concentration of 55.2 ng/L. The concentrationranged from 6.9to 16.7ng/g in sediments, with a mean value of 11.1 ng/g(Table 1). Among OCPs, DDTs and HCHs were the most abundant compounds both in water and sediments. DDTs (p, p′ -DDD, p, p′ -DDE and p, p′ -DDT) were in the range of 0.7-40.0 ng/L and 0.1-4.5 ng/gin water and sediments, respectively. HCHs (α -HCH, β -HCH, γ -HCH, and δ -HCH) were in the range of 14.2-24.5ng/L and 2.0-7.1ng/gin water and sediments, respectively. In terms of individual component distributions, p, p′ -DDT wasthe major pollutant of DDTs both in waterand sediments. Andα -HCH and β -HCH were the major pollutants of HCHsin water and sediments, respectively.

Table 1 Concentrations of organochlorine pesticides(OCPs) in surface water and sediments (dry weight) in Bosten Lake
3.2Concentration and composition of PAHs in water and sediments

Total concentration of PAHs in water ranged from ND (not detectable) to 368.7 ng/L, with an average concentration of 189.7 ng/L (Table 2). The detected PAHs ranged from ND to 93.2 ng/Lfora 2-ring compound (Nap; average 54.9ng/L), from ND to 269.0 ng/L for 3-ring compounds (Phe, Fl, Ace, Acy, Ant; average 116.4ng/L), and from ND to 111.5 ng/L for 4-ring compounds (Flu, Pyr, BaA, Chr; average 18.4ng/L). However, 5- and 6-ring PAHs (BbF, BkF, BaP, DahA, BghiP and IcdP) were not detected at any site.The compositional profile of PAHs in water showed that 2- and 3-ring PAHs were abundant, accounting for 29% and 61% of total PAHs, respectively (Fig. 3). For the individual compounds, Nap and Phe were the major pollutants, accounting for 29% and 38% of total PAHs, respectively.

Table 2 Concentrationsof polycyclic aromatic hydrocarbons(PAHs) in surface water and sediments (dry weight) in Bosten Lake

Fig. 3 Distribution of polycyclic aromatic hydrocarbons (PAHs) withdifferent ring numbersin water (a) and sediments (b) inBosten Lake

Concentration of PAHs ranged from 25.2 to 491.0 ng/g, with a mean value of 145.3 ng/g insediments(Table 2). Concentration of the 2-ring compound ranged from 1.7 to 98.9 ng/g (average 26.5ng/g), concentration of 3-ring compounds ranged from 12.8 to 343.4 ng/g (average 100.6 ng/g), concentration of 4-ring compounds ranged from ND to 46.7 ng/g (average 17.6 ng/g), and concentration of 5-ring compounds ranged from ND to 2.0 ng/g (average 0.5ng/g). However, 6-ring PAHs were not detected in any sediment sample. The compositional profile of PAHs in sediments showed that 3-ring PAHs were abundant, accounting for 69% of total PAHs (Fig. 3). Among the individual compounds, Nap, Acy and Phe were the major pollutants, accountingfor 18%, 19% and 37% of total PAHs, respectively.

4 Discussion
4.1 Residual OCP and PAH concentrations in BostenLake

We evaluated organic pollutantlevels in BostenLake (i.e., the concentrations of OCPs and PAHs in water and sediments)and comparedthe values withthose fromother lakes (Table 3). DDTs and HCHs inBostenLakewater and sediments were slightly higher than those of the lakes in developed countries, whereas PAHs were comparativelylower(Helm et al., 2011; Montuori and Triassi, 2012; Ok et al., 2013; Montuoriet al., 2014).In addition, DDTs in BostenLakewater were slightly higher than those measured in PoyangLakeand Baiyangdian Lake, China, and HCHs were higher than those in BaiyangdianLake. PAHs were only higher than those in PoyangLake. In terms of sediment samples, DDTs, HCHs andPAHs were generallylower than those in otherlakes in China. It can beconcluded that DDT and HCH levels in BostenLake are generally lower compared with the other lakes in China, but are on the high endwith respect to worldwide lakes. PAHs in BostenLakewere lower than those in all of other lakes (China and worldwide).Relative to Bosten Lake, water systemswith higher OCP levels in Chinalie within major agricultural areas andthe high OCPs detected in those regions are consequences of crop production although they were banned over 30 years ago (i.e., 1983).Slightly higherDDT andHCHs in Bosten Lakewater may be contributed partiallyby OCP residues from soils transported into the lake via enhanced surface runoff(Santschi et al., 2001; Franců et al., 2010). Concentrations of PAHs in the environmentwere closely correlated with local human population, gross domestic product, number of vehicles and power generation, and thus can serveas a proxy foranthropogenic activities, especially industrial activities(Liu et al., 2012).The BostenLakearea lies ina remote and arid area and its social and economic development levels were lower than in other regions ofChina. This explains the relatively low PAHs in BostenLake.

Table 3 Comparison of HCH (dichlorodiphenyltrichloroethane), DDT (hexachlorocyclohexane) and PAH (polycyclic aromatic hydrocarbon) concentrations in surface water (ng/L) and sediments (ng/g, dry weight) of selected lakes
4.2 Spatial distributions and sources of OCPs and PAHs in BostenLake

4.2.1OCPs

The spatial distribution of OCPs in BostenLakeis shown in Figure 4. High OCP concentrations occurred in the northwestern part of the lake, with the highest concentrations of OCPs in the water and sediments at sites B11 and B19, respectively. Yanqi is an agricultural area and there is some agricultural draining water around B11. Higher OCPs in water at site B11 can be explained by agricultural runoff. High OCPs in the sediment at site B19 may be a consequence of the fact that water from B11 and the Kaidu River (B14) mixednear site B19, leading to deposition of more pollutants in the sediment over time(Zhang et al., 2003).In addition, relatively high OCP concentrations in water also occurred near the estuary of Huangshui Ditch (B7 and B8). The lowest concentration of OCPs in water was found at site B18, located in the outlet of Bosten Lake to the Konqi River, whichmay be affected by massivewater exchange. The spatial distributions of OCPs in water and sediments suggest that the KaiduRiver, agricultural runoff and Huangshui Ditch were the main sources of pollution.

Fig. 4 OCP(organochlorine pesticide) concentrationsofwater and sedimentsinBosten Lake

Generally, HCHs were produced by industrial products (technical HCHs) and pesticide lindane. Technical HCHs contain 60%-70% α -, 5%-12% β -, 10%-15% γ - and 6%-10% δ -HCH; and lindane contains nearly 99% of γ -HCH. The value of α -/γ -HCH is 4.64-5.83 for technical HCHs, and a value ofα -/γ -HCH< 1 indicates lindaneinput (Zhang et al., 2009).In this study, the ratios in water and sediment samples were about 1, indicatingthe inputs of technical HCHs and lindane at most sites.α -HCH and β -HCH predominated HCHs both in water and sediments.The resultssuggest thatlong-distance transportprovided the enhancedsource of HCHsin the water, given the high volatility ofα -HCH, and historical use of HCHs, because β -HCH is more stable than other HCH isomers and can accumulate in the environment over time(Willett et al., 1998).

p, p′ -DDT can degrade top, p′ -DDE and p, p′ -DDD under aerobic and anaerobic conditions, respectively. Therefore, a value of (p, p′ -DDE+p, p′ -DDD)/DDTs> 0.5 indicates the historical use of DDT(Qiu et al., 2004). The ratio of (p, p′ -DDE+p, p’ -DDD)/DDTs inwater and sediments in Bosten Lake ranged from 0.05 to 1.00 and 0.04 to 1.00, respectively. The ratios in 80% of the water samples were> 0.5 and the ratiosin 40% of the sediment sampleswere> 0.5, indicating the main source of DDT was weathered agricultural soils. Only at sites B11, B12, B13 and B14 were the ratios < 0.5 in both water and sediments, indicating there was possible new pollution from the Kaidu River and agricultural runoff. Recent observations of OCPs in China revealed that a significant contributionof fresh DDT to the environmentdicofolwas the major contributor of DDT (Qiu et al., 2004, 2005). Dicofol is mainly used as an insecticide/herbicide in cotton crop. TheBosten Lake is surrounded bylarge areas of cotton fields and dicofol is of a great concern. Given that Bosten Lake is used for fishing and aquaculture, another potential DDT source is fishing boats, which in China are often tainted with antifouling material containing DDT(Lin et al., 2009). The ratios atother sites (B4, B5, B15, B16, B17, B18 and B19) were > 0.5 in water and < 0.5 in sediments, which may be a consequence of new inputs from the other sources, such as pollutant re-suspension resulted from sediment disturbances.

In this study, fs/fw valueswere calculated to assessthe direction of DDT exchangebetween the water and sediments. The values in Bosten Lake ranged from 0.76 to 4.03forp, p′ -DDE and 0.96 to 2.50 for p, p′ -DDT(Fig. 5). Ratios within the range 0.79-1.21 represent values that are equivocal or uncertain with respect to contaminant movement (Dai et al., 2014).In Bosten Lake, with the exception of four values forp, p′ -DDE and one value forp, p′ -DDT, calculated fugacity ratios fall outside this uncertainty range, and we concluded that for p, p′ -DDEand p, p′ -DDT, the water and sedimentswere not in equilibrium. Therefore, fugacity ratios for p, p′ -DDE and p, p’ -DDTin Bosten Lake indicatednet transfers from the sediments to overlying water.

Fig. 5 Sediment-water fugacity ratios of p, p′ -DDE and p, p′ -DDTin Bosten Lake (the dotted line represented the range from 0.79 to 1.21). fw and fs are the fugacity (Pa)in water and sediment, respectively.

4.2.2PAHs

Concentrations of PAHs in water in the centerof the lake were lower than those in water from theeast and westareas of the lake. SedimentaryPAHs gradually declined from the westernpart to the eastern part of the lake (Fig.6). HigherPAHconcentrations in water were found at B19 (368.7ng/L), B14(324.0 ng/L)and B16 (355.3 ng/L), and in sediments atB14 (491.0ng/g)and B5 (246.8 ng/g). Spatial distributions of PAHs in water and sediments indicatethat they entered the lake mainlyvia the KaiduRiver. B5 is located near the fisheries factory where powerboats are often used. Ogata and Fujisawa(1990) reported that oil spilled from such boats could be the main source of PAH pollution.And combustion of petroleum fuels may have also contributed to PAH pollution. Pollutants in water near B16 may beattributable to the fishing and aquaculture industries, but this needs further investigation.

Fig. 6 Polycyclic aromatic hydrocarbon (PAH)concentrations of water and sediments inBosten Lake

Anthropogenic PAHs come mainly from combustion of fossil fuels (pyrogenic) and discharge of petroleum-related materials (petrogenic). Petroleum-derived residues and low-temperature combustion, such as that of wood and coal, yield abundantlow-molecular-weight (LMW)PAH compounds (including 2- and 3-ring PAHs), whereas high-temperature combustion processes, such as burning of petroleum fuels, can yield high concentrations of high-molecular-weight (HMW)PAHs(including 4-, 5- and 6-ring PAHs) (Harrison et al., 1996).In this study, LMWPAHs were the predominant compounds, accounting for 91% and 88% of the total PAHs in water and sediments, respectively (Fig. 2). This pattern of similar PAH abundance inwater and sediments of Bosten Lake suggests that the pollution came primarily from the same petrogenicsources or/and from low-temperature combustion of wood and coal. Furthermore, the ratio of Ant/(Ant+Phe) was used to distinguish between combustion and petroleum sources of PAHs. The ratios in water and sediments ranged from ND to 0.2 and from ND to 0.18, respectively. In the samples fromsites B5, B11, B14, B16 and B17, the ratios showed a combustion source of PAHs in water, whereas input to sediments was from a mixture of pyrolyticand petrogeniccontamination. For samples at siteB15, the ratios in water and sediment were > 0.1, suggestingthat PAHs from that site were of pyrolytic origin and implying that PAHswere probably air-transported. Ant and Phe were the major PAH pollutants in water and sediments, indicating wood and coal combustion sources (Khairy and Lohmann, 2012).

4.3 Ecological risk assessment of OCPs and PAHs in BostenLake

To determine whether OCP and PAH concentrationshave reached toxic levels inBostenLake, we comparedthe pollutant valueswith several environmental quality guideline values. According to recommendations for water samples provided by the USEPA (2002), γ -HCH concentrations in Bosten Lake were within guideline values (Criterion Continuous Concentration (CCC): 80ng/L); concentrationsof p, p′ -DDT were between the CCC and Criterion Maximum Concentration (CMC) guideline values (USEPA, 2002); and the predominant PAHs, Nap and Phe, were below the CCC standards (< 620, 000 ng/L for Nap, < 630 ng/L for Phe). The concentrations of HCHs, DDTs and PAHs were below the corresponding CMC and CCC. Therefore, HCH, DDT and PAH residues in BostenLake water are generally within safe levels.

The concentrations of primary OCPs and PAHs were compared with consensus-based sediment quality guidelines, including the threshold effect concentration (TEC) and probable effect concentration (PEC; MacDonald et al., 2000). The TEC represents the concentration below which adverse effects are not expected to occur. PEC represents the concentration above which adverse effects are expected to occur (MacDonald et al., 2000).For p, p′ -DDE, p, p′ -DDT and total DDTs in the sediments of Bosten Lake, none of the samples surpassed the TEC value (p, p′ -DDE, 3.16 ng/g; p, p′ -DDT, 4.16 ng/g; total DDTs, 5.28 ng/g). Concentrations of γ -HCH(ND-1.0 ng/g)were all lower than the TEC (2.37 ng/g). For PAHs, concentrations of total PAHs and main compounds (Nap and Phe) in sediments were all belowtheTEC levels (total PAHs, 1, 610 ng/g; Nap, 176 ng/g; Phe, 204 ng/g). It can be concluded that the concentrations of DDTs, HCHs and PAHs were also lower than the values that could cause ecologicalrisks.

5Conclusions

We analyzed the contamination status and possible sources of OCPs and PAHs in the surface water and sediments of BostenLake, in Xinjiang of China. Compared to lakes in the other regions of Chinathat have experiencedintensive agricultural or industrial activities, residues of OCPs in BostenLake are relatively low. But, they are relatively higher compared to the values of the lakesin developed countries. PAH concentrations in BostenLakewere relatively lower than those in lakes surrounded by intensive industrial activities. The spatial distributions of contaminants in Bosten Lake suggest that local agricultural runoff, domestic sewage, and industrial wastewater caused most of the pollution. Composition analysis showed that both industrial products and lindane uses were the main pollution sources for HCHs.DDT pollution was primarily derived from the historical residues in water and recent inputs of DDTs in sediments. The main sources of PAHs were petroleum and low-temperature combustion of wood and coal. Comparison of OCP and PAH concentrations in Bosten Lake with existing quality guideline values suggests that risks from these pollutants are relatively low in Bosten Lake.

Acknowledgements

This research was funded by the National Natural Science Foundation of China (41471173; 41671200;U1603242)and the Specific Scientific Research Fund from the Ministry of Environmental Protection of the People’s Republic of China (201309041).We thank Prof. GAO Guang, Dr. TANG Xiangming and Dr. ZENG Hai’aofor their helps in the field, and Professor Mark BRENNER for his valuable supports in language improvements. We also thank anonymous reviewers andthe journal editors for their helpful comments and suggestions.

The authors have declared that no competing interests exist.

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