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Environ Earth Sci (2015) 74:5001–5008 DOI 10.1007/s12665-015-4512-6

ORIGINAL ARTICLE

Occurrence and assessment of organochlorine pesticides in the agricultural topsoil of Three Gorges Dam region, China Minxia Liu1,2 • Yuyi Yang1 • Xiaoyan Yun1,2 • Miaomiao Zhang1 • Jun Wang1

Received: 10 October 2014 / Accepted: 6 May 2015 / Published online: 22 May 2015 Ó Springer-Verlag Berlin Heidelberg 2015

Abstract Sixteen organochlorine pesticides (OCPs) were investigated in the 80 agricultural topsoil samples of Three Gorges Dam region, China. The concentration of OCPs ranged from 1.26 to 22.15 ng g-1, with a mean concentration 6.49 ng g-1. Dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) were predominant compared to other OCPs, with mean concentrations 1.80 and 1.27 ng g-1, respectively, accounting for 28 and 20 % of the total OCPs. Ratio analysis indicated that there is new input of DDTs in this study area. However, HCHs residual was mainly from historical use and atmospheric deposition. Other OCPs were due to the historical use in the studied area. Based on the soil quality guideline, both DDTs and HCHs pollution were in the low pollution level. Cancer risk assessment indicated that OCPs concentrations in this area presented a low cancer risk level. The study can offer some reference to the land management in the Three Gorges Dam region. Keywords OCPs  DDTs  HCHs  Three Gorges Dam region  Agricultural topsoil

& Jun Wang [email protected] 1

Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China

2

University of Chinese Academy of Sciences, Beijing 100049, China

Introduction In the last century, large amounts of chlorinated persistent organics have been produced, such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). As artificial pesticides, OCPs are known for their high lipophilicity, persistence, long-range transportation, and toxic biological effects in the environment (Zhang et al. 2004) and still detectable in different environment media, such as water (Yang et al. 2013), sediments (Hu et al. 2009; Sun et al. 2010; Zhao et al. 2010), soils (Yang et al. 2012; Zhao et al. 2013) and animals (Guo et al. 2008). Due to the low cost and versatility in controlling various insects, OCPs are still being produced and consumed in some developing countries, although they had been banned in developed countries (Pandit et al. 2001; Zhou et al. 2006). Although dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs) were officially banned for agricultural activities in 1983 in China, DDTs were also used for malaria and dicofol production. Because of the hydrophobic property, OCPs are readily absorbed onto soils. For higher yield, plenty of pesticides are applied to protect crops. So, agricultural soil is the important repository of OCPs. It was reported that residue of OCPs accumulated only on the surface of the agricultural soil and almost all the plant roots concentrated in the surface soil (Shi et al. 2009). Thus, OCPs in the agricultural soil can be easily introduced into plants, which can pose a risk to ecosystems and human health via food chain (Nakata et al. 2002). OCPs residual in the agricultural soil can also enter into aquatic ecosystem through surface runoff and get deposited in the sediment which becomes a secondary pollution source of aquatic ecosystem. China is the largest producer and consumer of pesticides in the world; the residual of OCPs in agricultural soil has been

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reported in many regions, such as Beijing (Shi et al. 2009), shanghai (Jiang et al. 2009), Guangzhou (Gao et al. 2008), Zhangzhou (Yang et al. 2012). The Three Gorges Dam region is located from Badong County to Yichang City along the Yangtze River in Hubei province, China. Environment quality worsened in this area due to the Three Gorges Dam construction and rapid industrialization. Recently, pollution studies in this area are mainly focused on water body, sediments, and water-levelfluctuating zone (Li et al. 2012; Luo et al. 2010; Xu et al. 2007; Zhao et al. 2007). Because most agricultural fields were reclaimed in the mountain, pollution of OCPs in agricultural soil of Three Gorges Dam region was less noticed. The objectives of this study were to investigate the distributions, sources, and risk of OCPs in the agricultural topsoil of Three Gorges Dam region, which could provide information for soil management.

Materials and methods Sample collection Agricultural topsoil samples were collected in March 2013. Totally, 80 agricultural soil samples were collected at 16 sites from Badong County to Yichang City along the Yangtze River. The sketch map of sampling sites is shown in Fig. 1. At each sampling sites, five topsoil samples were randomly taken within a range of 200 m2. All samples were lyophilized, ground, and then passed through a sieve of 0.15 mm stainless steel, and stored in an amber glass container at -20 °C for analysis. Reagents A 1000 mg L-1 standard solution of OCPs including aHCH, b-HCH, c-HCH, d-HCH, p,p0 -DDE, p,p0 -DDD, p,p0 -DDT, heptachlor, aldrin, heptachlor-exo-epoxide, aendosulfan, dieldrin, endrin, b-endosulfan, endrin-aldehyde and methoxychlor was purchased from AccuStandard Inc., USA and diluted to the working concentrations. Dichloromethane and n-hexane are of chromatographic grade (Fisher Scientific, USA). Other chemicals are of analytical reagent grade. The recovery surrogate and internal standard were 2,4,5,6-tetrachloro-m-xylene (TCmX) and pentachloronitrobenzene (PCNB), respectively, in this study. Extraction and cleanup Organochlorine pesticides were extracted followed by the modified matrix solid-phase dispersion extraction method (Rallis et al. 2012). Matrix solid-phase dispersion

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extraction method is a recent extraction method developed by Baker in 1989 for extraction of solid and semisolids samples (Barker 2000). Matrix solid-phase dispersion was widely adopted for its flexibility, selectivity, sample fraction, and purification in one step, and a small amount of organic solvent. The method requires blending the sample with dispersion sorbent, which isolates target compounds and absorbs them on the sorbent; then the target compounds were desorbed from the absorbent with organic solvent (Kristenson et al. 2006; Rallis et al. 2012). Two grams of soil were blended thoroughly with 3.00 g C18 as dispersion sorbent in a glass mortar for 5 min using a glass pestle to obtain a homogeneous mixture. The homogeneous mixture was completely transferred by using a funnel into a syringe barrel-column (10 mL) with a 0.22-lm membrane filter. One gram of anhydrous sodium sulfate (Na2SO4), 1.00 g of florisil, 1.00 g of silica gel, and 1.00 g of activated copper power were placed into the column from bottom to top. After the mixture was transferred into the column, another membrane filter was added on the top of the column. Na2SO4, florisil, and silica gel were packed as a clean-up adsorbent and activated copper powder was used for desulphurization. Finally, the column was compressed with the syringe plunger for air removal to avoid undesirable channels. The sample column was eluted with 20 mL of dichloromethane to yield a fraction containing OCPs. The eluent was collected into a conical tube and evaporated under a gentle stream of nitrogen till dry. The residue was re-dissolved in 100 lL of n-hexane containing (PCNB) as internal standard.

Gas chromatograph/mass spectrometer/electron capture detection (GC/ECD/MS) Qualitative and quantitative analyses of OCPs were carried out with an agilent 7890A gas chromatography equipped with an electron capture detector (GC-ECD) and a Model 5975 mass spectrometer (MS) using electron-ionization ion source (EI) in the selected ion monitoring (SIM) mode. One microliter of aliquots of the sample extracts was automatically injected into an HP-5 capillary column (30 m 9 0.25 mm 9 0.25 lm). Helium gas was used as the carrier gas at 1.0 mL min-1 under the constant flow mode. The injector and the detector were operated at 250 and 300 °C, respectively. The ion source and interface temperatures were set to 300 and 280 °C, respectively. The GC oven temperature for OCPs was programmed as follows: initial temperature was maintained at 80 °C for 1 min, and then programmed at 20 °C min-1–150 °C, at 5 °C min-1–300 °C, holding the final temperature for 5 min. The data were acquired and processed with Chemstation software (Hewlett-Packard).

Environ Earth Sci (2015) 74:5001–5008

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Fig. 1 Sketch map of sampling sites

Quality assurance and quality control (QA/QC) All analytical procedures were monitored under strict quality assurance and control measures. Average OCP recoveries and relative standard deviation (RSD) were first obtained to evaluate the method performance. Procedural blanks and spiked samples with standard were used to monitor procedural performance and matrix effects. All experiments were carried out in duplicate. The limits of detection (LOD) were defined as the minimum detectable peaks of individual species with a signal-tonoise ratio (S/N) of 3:1. The LODs of individual OCPs ranged from 0.01 to 0.03 ng g-1. The average recoveries of the surrogate standards 2,4,5,6-tetrachloro-m-xylene (TCmX) were 81 ± 8 % and the recoveries of individual OCPs ranged from 83 to 106 %. Reported 16 OCPs concentrations were corrected according to the recoveries of the standards. Cancer risk assessment The estimated cancer risks of residential exposure for direct ingestion, dermal contact, and inhalation were calculated according to the Eqs. 1–3, respectively.

Cs  IR  CF  EF  ED ð1Þ BW  ED Cs  IAR  EF  ED CRDermal ¼ ð2Þ BW  AT  PEF Cs  CF  SA  AF  ABS  EF  ED CRInhalation ¼ : BW  AT ð3Þ

CRIngestion ¼

Total cancer risk was obtained by summing individual risks calculated for the three exposure routes. The parameters in these equations can be obtained from the US EPA documents (US 2013). In these equations, Cs is the concentrations of OCPs in the soils (mg kg-1); IR is the average daily ingestion of soil (100 mg day-1); CF is the conversion coefficient (1 9 10-6 kg mg-1); EF is the exposure frequency (350 day year-1); ED is the exposure duration (30 year); BW is the body weight (70 kg); AT is the average lifespan (70 9 365 days); PEF is the dust production factor (1.36 9 109 m3 kg-1); IAR is the inhalation of air (15 m3 day-1); SA is the area of dermal contact with soil (5700 cm2 day-1); AF is the soil adsorption coefficient of dermal [0.07 mg (cm2)-1]; and ABS is the contaminant’s adsorption coefficient of dermal (0.1). According to the US EPA, the cancer risk was estimated

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Environ Earth Sci (2015) 74:5001–5008

into five levels: very low (value lower than 10-6), low (value between 10-6 and 10-4), moderate (value between 10-4 and 10-3), high (value between 10-3 and 10-1), and very high (value higher than 10-1).

10–10.5 years), while the half-life time of a-HCH and cHCH is only 20 weeks and 20–50 days (Gong et al. 2004; Manz et al. 2001). DDTs are likely to be more persistent in P soil. So, it is not amazing that DDTs was the dominant contaminant in the study area.

Results and discussion Distribution profile and possible sources of DDTs Concentrations of OCPs in the agricultural topsoil samples

The concentrations of p,p0 -DDT, p,p0 -DDE, and p,p0 -DDD were all detected in the agricultural topsoil from the study area. The total concentration of DDTs (sum of p,p0 -DDT, p,p0 -DDE and p,p0 -DDD) ranged from 0.31 to 5.36 ng g-1 with a mean concentration of 1.80 ng g-1, accounting for 9–40 % of total OCPs. The highest concentration of DDTs was detected at S11 and the lowest appeared at S9. The levels of DDTs in other regions published in the literature were compared with those of the analyzed soils in this study (Table 2). Concentrations of DDTs in soils of this study were much lower than the levels of DDTs in soils of Shanghai (Jiang et al. 2009), Northwest China (Huang et al. 2014), Guangzhou (Gao et al. 2008), and Zhangzhou (Yang et al. 2012). The distribution profile of DDTs is exhibited in Fig. 2. Among DDTs and its metabolites, p,p0 DDT was the most dominant, and its concentrations were in the range of 0.14–3.01 ng g-1 with a mean concentration of 0.78 ng g-1, accounting for 43 % (in a range of 6–69 %) of the total DDTs. The mean concentrations of p,p0 -DDE and p,p0 -DDD were 0.55 and 0.47 ng g-1, accounting for 31 and 26 % of the total DDTs.

Table 1 shows the mean, median, concentration ranges, and detection frequencies of OCPs in agricultural topsoil samples of Three Gorges Dam region. It can be seen in Table 1 that except dieldrin and b-HCH, other 14 OCPs were detected in agricultural topsoil. The detection frequencies of HCHs, DDTs, a-endosulfan, and b-endosulfan in the soils are up to 100 %, indicating widespread occurrence of these compounds in the agricultural topsoil of Three Gorges Dam region. The total concentrations of OCPs in the agricultural topsoil ranged from 1.26 to 22.15 ng g-1 with a mean concentration of 6.49 ng g-1. Total DDTs (1.80 ng g-1) exhibited high mean concentration, followed by total HCHs (1.27 ng g-1) and other OCPs. DDTs was the dominant compound of OCPs in the agricultural topsoil. It was also reported that DDTs were the dominant contaminants in Tianjin (Wang et al. 2006), Shanghai (Jiang et al. 2009), and soil of arid and semiarid areas of northwest China (Huang et al. 2014). In agricultural soils, the half-life time of DDT is 4–35 years (mean Table 1 Concentrations of OCPs (ng g-1) in agricultural topsoil samples

Compound

Mean

Median

Range

Detection frequency (%)

a-HCH

0.49

0.65

0.03–3.37

100

c-HCH

0.22

0.20

nd–0.54

94

d-HCH P HCHs

0.55

0.35

nd–1.50

94

1.27

0.96

0.23–3.77

100

p,p0 -DDE

0.55

0.22

0.06–3.04

100

p,p0 -DDD

0.47

0.22

nd–2.13

100

p,p0 -DDT P DDTs Heptachlor

0.78

0.37

0.14–3.01

100

1.80 0.04

0.98 0.01

0.31–5.36 nd–0.25

100 50

Aldrin

0.35

0.29

nd–1.08

88

Heptachlor-exo-epoxide

0.33

0.23

nd–1.13

94

a-Endosulfan

0.79

0.33

0.1–7.32

100

Endrin

0.20

nd

nd–2.08

19

b-Endosulfan

0.40

0.34

0.18–0.98

100

Endrin-aldehyde

0.43

0.06

nd–2.82

56

Methoxychlor P Other OCPs P OCPs

0.77

0.13

nd–7.23

56

3.26

1.54

0.66–15.02

100

6.49

4.81

1.26–22.15

100

nd not detected

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Environ Earth Sci (2015) 74:5001–5008 Table 2 Concentrations of P P DDTs and HCHs in soils of different areas in China (ng g-1)

5005 P DDTs

Area

P HCHs

Range 0.44–247.45a

References

Mean

Range

Mean

21.41

nd–10.38b

2.41

Jiang et al. (2009)

Northwest China

c

0.1–120.49

12.52

0.17–9.38b

1.45

Huang et al. (2014)

Guangzhou

7.60–66.29d

67.30

0.20–103.9b

4.40

Gao et al. (2008)

Zhangzhou

0.64–78.08a

3.86

0.72–30.16b

9.79

Yang et al. (2012)

1.43

This study

Shanghai

Three Gorges Dam region

d

0.31–5.36

1.80

0.23–3.77

b

a

Sum of p,p -DDT, p,p -DDD, p,p -DDE and p,p -DDT

b

Sum of a-HCH, b-HCH, c-HCH, and d-HCH Sum of p,p0 -DDE, p,p0 -DDE, p,p0 -DDD, p,p0 -DDD, p,p0 -DDT, and p,p0 -DDT

c d

0

0

0

0

Sum of p,p0 -DDD, p,p0 -DDE, and p,p0 -DDT

Fig. 2 Distribution profile of DDTs with its metabolites in agricultural topsoil

The ratio between the parent compounds and its metabolite can provide some information on the pollution source (Wang et al. 2007). The ratio between p,p0 -DDE, p,p0 -DDD, and p,p0 -DDT had been regarded as an indication of increasing or decreasing inputs to the environment (Ge et al. 2013). The ratio value of p,p0 -DDT/(p,p0 DDE ? p,p0 -DDD) lower than 1.0 indicated historical DDT input while the value greater than 1.0 indicated fresh DDT application (Hitch and Day 1992). p,p0 -DDE and p,p0 DDD were the two main products of p,p0 -DDT. Therefore, aerobic metabolism of p,p0 -DDT was indicated when the ratio value of p,p0 -DDD/p,p0 -DDE was less than 1.0, and anaerobic metabolism of p,p0 -DDT was indicated when the ratio was greater than 1.0 (Sun et al. 2005).The triangular graph of DDTs, DDDs, and DDEs (Fig. 3) indicated the historical use and metabolic environment of DDTs. According to the ratio analysis, sixteen sampling sites could be divided into three groups: (1) the ratio values of p,p0 DDT/(p,p0 -DDE ? p,p0 -DDD) at six sites (S2, S5, S8, S11, S12, and S16) were greater than 1.0, indicated fresh DDTs

Fig. 3 Triangle diagrams of p, p0 -DDE, p, p0 -DDD, and p, p0 -DDT in the agricultural topsoil

application, (2) two sites (S6 and S14) with dominant aerobic metabolic of DDTs, (3) eight sites (S1, S3, S4, S7, S9, S10, S13, and S15) with anaerobic and aerobic

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metabolism of DDTs. Positive correlation (p \ 0.05) was found between DDTs and TOCs (total carbon organic), a probable interpretation is that the DDTs were brought in with the organic matters input (Fig. 4). Distribution profile and possible sources of HCHs Four HCH isomers were investigated in the analyzed soils and three of which were detected, including a-HCH, cHCH, and d-HCH and the detection frequency of a-HCH was 100 %. The total concentration of HCHs (sum of aHCH, c-HCH, and d-HCH) was between 0.23 and 3.77 ng g-1 with a mean concentration of 1.27 ng g-1, accounting for 7–43 % of the total OCPs. The highest concentration of HCHs was found at S12 and the lowest concentration was at S10. Figure 5 shows the distribution profile of HCHs in the agricultural topsoil samples. Among the three isomers, the most dominant d-HCH varied from nd to 1.5 ng g-1, with a mean concentration of 0.55 ng g-1, accounting for 0–84 % (mean 43 %) of the total HCHs. The mean concentrations of a-HCH and cHCH were 0.49 and 0.22 ng g-1, accounting for 39 and

Environ Earth Sci (2015) 74:5001–5008

18 % of the total HCHs, respectively. The concentration levels in the analyzed soils were far below the soils in other areas of China (Table 2). When the reports were compared, HCHs in the agricultural topsoil of Three Gorges Dam region was lower. Technical HCH contains 60–70 % a-HCH, 5–12 % bHCH, 10–12 % c-HCH, and 6–10 % d-HCH, while lindane mainly contains c-HCH (99 %). Among the four isomers, b-HCH is easily absorbed on the soil organic matter and difficult to evaporate from the soil (Mackay et al. 2010). Moreover, a-HCH and c-HCH can be transformed into bHCH in the environment. The ratio of a-HCH/c-HCH has been used to identify the possible HCH source. The ratio value of a-HCH/c-HCH higher than three indicated input of technical HCH and atmospheric deposition, while a ratio close or lower than one was characteristic of lindane source (Qiu et al. 2005). The ratio values of a-HCH/c-HCH in the soil of S12 and S16 were higher than three, indicating HCHs in the soil samples of S12 and S16 may be from historical use of technical HCHs or atmospheric deposition. While HCHs in the soil samples of other sites may have lindane input, concentration of HCHs had a significant positive correlation with TOC (p \ 0.01), indicating TOC played an important role in the partitioning and retention of HCHs (Fig. 4). Other OCPs

Fig. 4 Distribution profile of HCHs in agricultural topsoil

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The concentrations of other OCPs varied from 0.66 to 15.02 ng g-1 with a mean concentration of 3.26 ng g-1. The concentrations were in an order a-Endosulfan [ Methoxychlor [ Endrin-aldehyde [ b-Endosulfan [ Aldrin [ Heptachlor-exo-epoxide [ Endrin [ Heptachlor. Concentrations of a-Endosulfan were between 0.1–7.32 ng g-1 with a mean concentration of 0.79 ng g-1, which was higher than the concentration of b-Endosulfan (mean concentration 0.40 ng g-1). Generally, a concentration of a-Endosulfan higher than b-Endosulfan indicated historical input of Endosulfan. The concentration of Heptachlor was in the range of nd-0.25 ng g-1 with mean concentration 0.04 ng g-1, while the concentration of its degradation product Heptachlor-exo-epoxide was in the range of nd-1.13 ng g-1 with a mean concentration 0.33 ng g-1. The concentration of Heptachlor lower than the concentration of Heptachlor-exo-epoxide indicated that there was no recent use of this pesticide in the agricultural soil of Three Gorges Dam region. The concentrations of endrin-aldehyde, Endrin, and Aldrin in the analyzed soils all lower than other soils (Jiang et al. 2009) indicated that agricultural soil in this area was slightly polluted by these pesticides.

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5007

Fig. 5 The correlation analysis between HCHs and TOC, DDTs, and TOC

Table 3 Cancer risk assessment for OCPs

Compounds

Pathways

DDTs

Ingestion Dermal

HCHs

Median

9.0 9 10-7 -13

2.7 9 10

-13

1.5 9 10

2.7 9 10-6

1.6 9 10-7

-13

4.8 9 10-14

-9

8.1 9 10

5.3 9 10

2.9 9 10

1.7 9 10-14

Total

9.1 9 10-7

5.0 9 10-7

2.8 9 10-6

1.7 9 10-7

-7

-7

-6

4.3 9 10-7

-13

1.3 9 10-13

-9

4.7 9 10-10

4.9 9 10

-6

2.0 9 10

4.4 9 10-7

2.4 9 10-6

1.1 9 10-5

6.3 9 10-7

Inhalation Total Ingestion Dermal Inhalation Total

Pollution assessment The soil quality for DDTs and HCHs was classified as three grades according to national environmental quality standard in China (GB15618-1995): low-level (DDTs or HCHs residual concentration lower than 50 ng g-1), mid-level (DDTs or HCHs residual concentration between 50 and 500 ng g-1), and high-level (DDTs or HCHs residual concentrations higher than 1000 ng g-1). Compared to the national environmental quality, total DDTs and HCHs residual concentrations in the present soil were all lower than 50 ng g-1, which fell into the low-level. Based on the Canadian Soil Quality Guidelines, the threshold value of total DDTs for agricultural soil was 700 ng g-1. If concentration of total DDTs is lower than the threshold value, the soil is suitable for agricultural activities. In this study, the concentration of total DDTs in agricultural topsoil of Three Gorges Dam region was far below the threshold value.

6.3 9 10

-13

1.9 9 10

-10

6.9 9 10

-7

6.4 9 10

3.24 9 10-6 -13

9.8 9 10

-9

3.5 9 10

-6

3.3 9 10

-14

Minimum

9.8 9 10

Ingestion

-10

4.9 9 10-7

Maximum

Inhalation

Dermal

OCPs

Mean

4.8 9 10

-13

1.5 9 10

-10

5.3 9 10

-7

-13

7.26 9 10

-9

2.6 9 10

-6

2.5 9 10

1.9 9 10 5.7 9 10 2.1 9 10

-12

1.9 9 10-13

-8

6.9 9 10-10

-5

6.4 9 10-7

3.3 9 10 1.2 9 10 1.2 9 10

Cancer risk of OCPs in the agricultural topsoil was calculated according to the Eqs. 1–3. The cancer risks via ingestion, dermal contact, and inhalation are shown in Table 3. The estimated cancer risk values of total OCPs were between 10-7 and 10-5 with a mean value 10-6, which fell in the low cancer risk rank. The estimated cancer risk values of DDTs and HCHs were below 10-6, indicating no adverse effect of these compounds. For different exposure pathways, the cancer risk for total DDTs, total HCHs, and total OCPs was in the order: dermal \ inhalation \ ingestion.

Conclusion Fourteen OCPs were detected in the agricultural topsoil of Three Gorges Dam region. DDTs exhibited high concentration, followed by HCHs and other OCPs. The ratio analysis suggested both current and historical use of DDTs

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that had occurred in the study area, while HCHs residuals were mainly due to the historical and atmospheric deposition. Both DDTs and HCHs had a low pollution level based on the soil quality guideline. The cancer risk of total OCPs fell in the low risk rank and had slightly adverse effects on humans. Acknowledgments This project was supported in part by Natural Science Foundation of Hubei Province of China (NO. 2012FFB07301), and the Hundred Talents Program of the Chinese Academy of Sciences (Y329671K01), and open Funding Project of the Key Laboratory of Aquatic Botany and Watershed Ecology, Chinese Academy of Sciences.

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