Environ Monit Assess (2015) 187:4159 DOI 10.1007/s10661-014-4159-x
Vertical distributions of organochlorine pesticides and polychlorinated biphenyls in an agricultural soil core from the Guanzhong Basin, China Hongxuan Lu & Weiguo Liu
Received: 4 June 2014 / Accepted: 10 November 2014 / Published online: 25 November 2014 # Springer International Publishing Switzerland 2014
Abstract The concentrations and distributions of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and polychlorinated biphenyls (PCBs) in an agricultural soil core in the Guanzhong Basin, China were determined. Overall, p,p’-DDT and p,p’-DDE were dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. Low chlorinated PCBs (PCB 28 and PCB 52) were generally detected at higher concentrations and more frequently than high chlorinated PCBs. The peak values of ∑DDT (12.92 ng/g), ∑HCH (2.25 ng/g), and ∑PCB (3.44 ng/g) occurred in the 10–15, 15–20, and 5– 10 cm sections, respectively. The negative correlation between the organochlorine pesticide (OCP) concentrations and the soil depths and the relatively high p,p’DDT/p,p’-DDE ratios in the surface soils indicated that these chemicals were recently used illegally, despite their official ban in 1983. The increase in the ratio of α-/γ-HCH with increasing soil depth indicated that the use of lindane decreased relative to the use of technical HCHs in recent years.
H. Lu (*) : W. Liu State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China e-mail: [email protected] W. Liu School of Human Settlement and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Keywords Soil core . Residue . Source . OCPs . PCBs . Guanzhong Basin
Introduction Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are typical and persistent organic pollutants (POPs) that have been widely produced and used over several decades. Due to their high lipophilic content, low vapor pressure, low reactivity, and low water solubility, OCPs and PCBs have become a popular topic of study worldwide (Jiang et al. 2009; Meijer et al. 2003; Nakata et al. 2005; Ren et al. 2007; Wang et al. 2012). Soils have a high retention capacity relative to other environmental phases, such as air and water, and are generally considered as important reservoirs for many POPs, including OCPs and PCBs, in terrestrial systems. Although the official use of OCPs was banned in 1983 and the use of PCBs had been restricted in China since the mid-1970s, they are still detected in air, dust, soil, sediment, and biota samples and may continue to impact the environment and ecosystems (Jiang et al. 2009; Nakata et al. 2005; Wang et al. 2009, 2012; Xu et al. 2005; Zhang et al. 2007). Extensive studies have been conducted regarding OCP and PCB contamination in surface soils worldwide (Jiang et al. 2009; Meijer et al. 2003; Mishra et al. 2012; Nakata et al. 2005; Ren et al. 2007; Shi et al. 2013; Toan et al. 2009; Wang et al. 2012); however, the depth distributions of these pollutants in soils have rarely been
4159, Page 2 of 8
determined. In this study, we investigated the vertical concentrations and distributions of OCPs and PCBs in an agricultural soil core collected from the Guanzhong Basin, China. As one of the major grain producing areas in China, OCPs have been used in the Guanzhong Basin since the 1980s. Additionally, the sampling site is approximately 30 miles from Xi’An, an important industrial center in China that could cause PCB contamination of the area through long-range transport. Our result may provide useful information regarding contamination levels and the transformation processes of these POPs and help governments take effective measures to minimize their potential health and ecological risks.
Materials and methods Sample collection and extraction Soil core samples were collected from farmland in the Guanzhong Basin during March 2013. Samples were collected at 5 cm depth intervals from 0–100 cm using a soil borer. The OCPs and PCBs were extracted from all samples using an accelerated solvent extractor (Dionex ASE 350). Approximately 20–30 g of the samples were subjected to DCM and hexane (2:3, v/v) extraction at 100 °C and 7.6×106 Pa. This process was conducted in three cycles with 5 min of heating followed by 5 min of static extraction. Next, the extracts were concentrated to approximately 0.5 ml under a gentle stream of N2 before eluting with 45 ml of DCM/hexane (3:7, v/v) and using Florisil (5 g) as an adsorbent. The extracts were solventexchanged to hexane and reduced to 0.5 ml under a gentle stream of N2 before analysis. Instrumental analysis A HP 6890 GC system equipped with a 63Ni electron capture detector (GC-μECD) was used to perform a quantitative analysis of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and PCBs in the splitless mode as described by Lu and Liu (2013). An injection volume of 2 μL was used for each sample. Solution chromatography was performed using a HP-5 (30 m×0.25 mm i.d. with 0.25 mm film thickness) capillary column to separate the target analytes. The oven was set at 60 °C for 1 min, increased from 60 to 150 °C at a rate of 10 °C/min, from 150 to 210 °C at a rate of 2 °C/min, and to 290 °C at a rate of 20 °C/min
Environ Monit Assess (2015) 187:4159
(held for 10 min). Nitrogen was used as the carrier gas with a flow rate of 2.5 ml/min under the constant flow mode. The injector and detector temperatures were maintained at 290 and 300 °C, respectively. Quality control and quality assurance (QC/QA) Stock solutions of eight OCPs (α-HCH, β-HCH, γ-HCH, δ-HCH, o,p’-DDT, p,p’-DDT, p,p’-DDD, and p,p’-DDE) were purchased from the National Research Center for Certified Reference Materials of China. Stock solutions of seven PCBs (PCB-28, PCB-52, PCB-101, PCB-118, PCB-152, PCB-138, and PCB-180) were purchased from the national research center of the Agro-environmental Protection Institute, Ministry of Agriculture, China, at concentrations of 2 μg/ml. Surrogate standards (TCMX and PCB191) were purchased from o2si Smart Solutions (USA). The average OCP and PCB recoveries (70–119 and 75–115 %, respectively) were obtained to evaluate the method performance by using multiple analyses of the six replicated spiked soil samples with OCP and PCB stock solutions of 50 ng/g. The instrument detection limits for quantifying the individual OCPs and PCBs, which are defined as the standard concentrations required for generating a peak with a signal/noise ratio of 3, varied from 0.01 to 0.04 ng/g. Quantification was performed using the five-point calibration method (from 2 to 200 ng/ml, r2 > 0.995). The reporting limit was defined as the lowest concentration level from the calibration curve for a specific analyte. Concentrations that were less than the reporting limit were considered as below the detection level (BDL). For each batch of 10 field samples, a procedural blank, a spiked blank, a pair of spiked matrix sample/duplicates, and a sample replicate were processed. The recoveries of the surrogate standards from all of the samples and blanks were 73–110 %, and the variation of the OCP and PCB concentrations in the duplicate samples was less than 20 %.
Results and discussion HCH, DDT, and PCB concentrations in the soil core from the Guanzhong Basin In all soil samples, OCPs and PCBs were identified (Table 1). Among these pollutants, the ∑DDT concentrations were generally the highest, varying from 1.66 to 12.92 ng/g with a mean value of 5.89 ng/g. In contrast,
7.64
1.03
1.66
0.06
0.12
2.13
0.39
1.05
2.19
0.45
5.75
6.20
0.57
0.17
0.23
BDL BDL BDL
0.15
BDL BDL BDL
0.12
BDL 0.04
0.67
p.p’-DDE
p.p’-DDD
o.p’-DDT
p.p’-DDT
HCHs
DDTs
OCPs
p,p’-DDT/p,p’-DDE 1.03
1.61
δ-HCH
α-HCH/γ-HCH
α-HCH/β-HCH
PCB 28
PCB 52
PCB 101
PCB 118
PCB 138
PCB 153
PCB 180
PCBs
3.44
0.15
0.30
2.77
0.17
0.53
7.07
0.57
2.65
1.36
0.50
2.56
0.12
0.08
0.10
0.70
BDL
0.14
0.19
0.20
0.18
0.48
1.31
3.27
13.41
12.92
0.49
7.66
1.42
1.51
2.34
0.11
0.07
0.21
γ-HCH
0.13
0.24
0.10
0.18
α-HCH
0.25
BDL
0.10
BDL
BDL
BDL
BDL
0.15
0.10
2.03
1.14
10.06
7.81
2.25
3.15
1.36
0.54
2.76
0.30
0.08
1.71
0.17
0.48
BDL
0.09
BDL
BDL
BDL
0.14
0.25
0.35
1.06
1.39
5.96
5.07
0.89
1.96
1.15
0.55
1.41
0.26
0.12
0.38
0.13
0.63
0.19
0.11
BDL
BDL
BDL
0.16
0.17
0.47
2.24
1.83
8.75
7.97
0.78
3.88
1.47
0.50
2.12
0.11
0.08
0.40
0.19
0.54
BDL
0.13
BDL
BDL
BDL
0.28
0.14
0.41
1.74
2.54
4.78
4.24
0.54
2.14
1.01
0.25
0.84
0.10
0.06
0.27
0.11
0.14
BDL
BDL
BDL
BDL
BDL
0.04
0.11
0.47
2.14
3.04
7.19
6.43
0.76
3.19
1.81
0.39
1.05
0.09
0.09
0.40
0.19
0.40
0.07
0.17
BDL
BDL
BDL
BDL
0.16
0.42
1.70
2.52
5.97
5.41
0.56
2.71
1.31
0.31
1.08
0.10
0.07
0.27
0.12
1.26
0.07
0.24
0.11
0.24
0.27
0.20
0.15
0.53
2.15
3.35
6.87
6.14
0.73
3.24
1.57
0.36
0.97
0.11
0.09
0.35
0.18
0.41
BDL
0.09
BDL
BDL
BDL
0.20
0.12
0.43
1.74
2.64
4.45
3.77
0.68
1.98
0.78
0.25
0.75
0.12
0.08
0.34
0.15
1.14
BDL
0.35
BDL
BDL
0.31
0.26
0.22
0.50
1.96
4.06
8.26
7.30
0.96
4.00
1.93
0.39
0.98
0.14
0.12
0.47
0.23
0.81
BDL
0.12
BDL
0.11
0.20
0.22
0.16
0.48
1.72
3.24
4.90
4.25
0.65
2.19
1.13
0.25
0.68
0.13
0.08
0.30
0.14
1.59
BDL
0.36
BDL
0.36
0.34
0.24
0.29
0.47
1.99
4.68
8.18
7.40
0.78
4.14
1.99
0.39
0.88
0.13
0.09
0.38
0.18
0.67
BDL
0.04
BDL
0.02
0.18
0.22
0.21
0.43
1.85
1.95
3.42
2.86
0.56
1.44
0.44
0.24
0.74
0.09
0.07
0.28
0.12
0.23
BDL
0.04
BDL
BDL
BDL
0.14
0.05
0.43
1.92
1.31
2.13
1.66
0.47
0.84
BDL
0.18
0.64
0.06
0.06
0.25
0.11
1.38
0.06
0.14
BDL
BDL
BDL
0.81
0.37
0.49
3.06
2.06
5.72
4.74
0.98
2.15
1.19
0.35
1.05
0.24
0.07
0.44
0.22
0.49
BDL
0.10
BDL
BDL
BDL
0.16
0.24
0.56
2.09
2.28
4.72
4.02
0.70
1.96
0.92
0.29
0.86
0.12
0.09
0.32
0.18
0.28
BDL
BDL
BDL
BDL
BDL
BDL
0.28
0.36
2.28
2.12
8.87
7.64
1.23
3.55
1.87
0.55
1.67
0.16
0.11
0.71
0.25
0.21
BDL
BDL
BDL
BDL
BDL
BDL
0.21
0.37
2.21
2.07
6.18
5.32
0.86
2.44
1.32
0.39
1.18
0.11
0.08
0.48
0.18
5–10 10–15 15–20 20–25 25–30 30–35 35–40 40–45 45–50 50–55 55–60 60–65 65–70 70–75 75–80 80–85 85–90 90–95 95–100
β-HCH
0–5
Compounds
Depths of soil (cm)
Table 1 Concentrations of OCPs and PCBs at different soil depths (ng/g d.w.)
Environ Monit Assess (2015) 187:4159 Page 3 of 8, 4159
4159, Page 4 of 8
the ∑HCH and ∑PCB concentrations were lower, varying from 0.45 to 2.25 ng/g with a mean value of 0.79 ng/ g and from 0.14 to 3.44 ng/g with a mean value of 0.79 ng/g, respectively. Among the DDTs and their metabolites, p,p’-DDT and p,p’-DDE were the dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. The p,p’-DDT concentration was the highest, ranging from 1.44 to 7.66 ng/g with a mean value of 2.87 ng/g and a detection frequency of 100 %. In addition, β-HCH was the most abundant HCH in the soil core, ranging from 0.18 to 1.71 ng/g with a mean value of 0.42 ng/g and a detection frequency of 100 %. The α-HCH, γ-HCH, and δ-HCH concentrations varied from 0.10 to 0.23 ng/g (mean 0.16 ng/g), 0.06 to 0.12 ng/g (mean 0.08 ng/g), and 0.09 to 0.30 ng/g (mean 0.14 ng/g), respectively (Table 1). In contrast with the HCHs and DDTs, some of the PCB congeners had relatively low detection frequencies (PCB 101 25 %, PCB 138 5 %, PCB 180 25 %) (Table 1). However, the low chlorinated PCBs (PCB 28) still showed high detection frequencies (100 %), which suggested a wide occurrence of PCBs in the farmland of the Guanzhong Basin, China. In addition, PCB 28 and PCB 52 were the dominant PCB congeners, with concentrations ranging from 0.11 to 0.29 ng/g with mean value of 0.19 ng/g, and from BDL to 2.77 ng/g with a mean value of 0.31 ng/g, respectively. The concentrations of OCPs and PCBs at different depths in the farmland soil are shown in Fig. 1. The maximum DDT and HCH concentrations were observed in the 10–15 cm and 15–20 cm sections, respectively. The higher POP concentrations, including HCHs and DDTs, in the surface soils (
Vertical distributions of organochlorine pesticides and polychlorinated biphenyls in an agricultural soil core from the Guanzhong Basin, China Hongxuan Lu & Weiguo Liu
Received: 4 June 2014 / Accepted: 10 November 2014 / Published online: 25 November 2014 # Springer International Publishing Switzerland 2014
Abstract The concentrations and distributions of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and polychlorinated biphenyls (PCBs) in an agricultural soil core in the Guanzhong Basin, China were determined. Overall, p,p’-DDT and p,p’-DDE were dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. Low chlorinated PCBs (PCB 28 and PCB 52) were generally detected at higher concentrations and more frequently than high chlorinated PCBs. The peak values of ∑DDT (12.92 ng/g), ∑HCH (2.25 ng/g), and ∑PCB (3.44 ng/g) occurred in the 10–15, 15–20, and 5– 10 cm sections, respectively. The negative correlation between the organochlorine pesticide (OCP) concentrations and the soil depths and the relatively high p,p’DDT/p,p’-DDE ratios in the surface soils indicated that these chemicals were recently used illegally, despite their official ban in 1983. The increase in the ratio of α-/γ-HCH with increasing soil depth indicated that the use of lindane decreased relative to the use of technical HCHs in recent years.
H. Lu (*) : W. Liu State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China e-mail: [email protected] W. Liu School of Human Settlement and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Keywords Soil core . Residue . Source . OCPs . PCBs . Guanzhong Basin
Introduction Organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) are typical and persistent organic pollutants (POPs) that have been widely produced and used over several decades. Due to their high lipophilic content, low vapor pressure, low reactivity, and low water solubility, OCPs and PCBs have become a popular topic of study worldwide (Jiang et al. 2009; Meijer et al. 2003; Nakata et al. 2005; Ren et al. 2007; Wang et al. 2012). Soils have a high retention capacity relative to other environmental phases, such as air and water, and are generally considered as important reservoirs for many POPs, including OCPs and PCBs, in terrestrial systems. Although the official use of OCPs was banned in 1983 and the use of PCBs had been restricted in China since the mid-1970s, they are still detected in air, dust, soil, sediment, and biota samples and may continue to impact the environment and ecosystems (Jiang et al. 2009; Nakata et al. 2005; Wang et al. 2009, 2012; Xu et al. 2005; Zhang et al. 2007). Extensive studies have been conducted regarding OCP and PCB contamination in surface soils worldwide (Jiang et al. 2009; Meijer et al. 2003; Mishra et al. 2012; Nakata et al. 2005; Ren et al. 2007; Shi et al. 2013; Toan et al. 2009; Wang et al. 2012); however, the depth distributions of these pollutants in soils have rarely been
4159, Page 2 of 8
determined. In this study, we investigated the vertical concentrations and distributions of OCPs and PCBs in an agricultural soil core collected from the Guanzhong Basin, China. As one of the major grain producing areas in China, OCPs have been used in the Guanzhong Basin since the 1980s. Additionally, the sampling site is approximately 30 miles from Xi’An, an important industrial center in China that could cause PCB contamination of the area through long-range transport. Our result may provide useful information regarding contamination levels and the transformation processes of these POPs and help governments take effective measures to minimize their potential health and ecological risks.
Materials and methods Sample collection and extraction Soil core samples were collected from farmland in the Guanzhong Basin during March 2013. Samples were collected at 5 cm depth intervals from 0–100 cm using a soil borer. The OCPs and PCBs were extracted from all samples using an accelerated solvent extractor (Dionex ASE 350). Approximately 20–30 g of the samples were subjected to DCM and hexane (2:3, v/v) extraction at 100 °C and 7.6×106 Pa. This process was conducted in three cycles with 5 min of heating followed by 5 min of static extraction. Next, the extracts were concentrated to approximately 0.5 ml under a gentle stream of N2 before eluting with 45 ml of DCM/hexane (3:7, v/v) and using Florisil (5 g) as an adsorbent. The extracts were solventexchanged to hexane and reduced to 0.5 ml under a gentle stream of N2 before analysis. Instrumental analysis A HP 6890 GC system equipped with a 63Ni electron capture detector (GC-μECD) was used to perform a quantitative analysis of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and PCBs in the splitless mode as described by Lu and Liu (2013). An injection volume of 2 μL was used for each sample. Solution chromatography was performed using a HP-5 (30 m×0.25 mm i.d. with 0.25 mm film thickness) capillary column to separate the target analytes. The oven was set at 60 °C for 1 min, increased from 60 to 150 °C at a rate of 10 °C/min, from 150 to 210 °C at a rate of 2 °C/min, and to 290 °C at a rate of 20 °C/min
Environ Monit Assess (2015) 187:4159
(held for 10 min). Nitrogen was used as the carrier gas with a flow rate of 2.5 ml/min under the constant flow mode. The injector and detector temperatures were maintained at 290 and 300 °C, respectively. Quality control and quality assurance (QC/QA) Stock solutions of eight OCPs (α-HCH, β-HCH, γ-HCH, δ-HCH, o,p’-DDT, p,p’-DDT, p,p’-DDD, and p,p’-DDE) were purchased from the National Research Center for Certified Reference Materials of China. Stock solutions of seven PCBs (PCB-28, PCB-52, PCB-101, PCB-118, PCB-152, PCB-138, and PCB-180) were purchased from the national research center of the Agro-environmental Protection Institute, Ministry of Agriculture, China, at concentrations of 2 μg/ml. Surrogate standards (TCMX and PCB191) were purchased from o2si Smart Solutions (USA). The average OCP and PCB recoveries (70–119 and 75–115 %, respectively) were obtained to evaluate the method performance by using multiple analyses of the six replicated spiked soil samples with OCP and PCB stock solutions of 50 ng/g. The instrument detection limits for quantifying the individual OCPs and PCBs, which are defined as the standard concentrations required for generating a peak with a signal/noise ratio of 3, varied from 0.01 to 0.04 ng/g. Quantification was performed using the five-point calibration method (from 2 to 200 ng/ml, r2 > 0.995). The reporting limit was defined as the lowest concentration level from the calibration curve for a specific analyte. Concentrations that were less than the reporting limit were considered as below the detection level (BDL). For each batch of 10 field samples, a procedural blank, a spiked blank, a pair of spiked matrix sample/duplicates, and a sample replicate were processed. The recoveries of the surrogate standards from all of the samples and blanks were 73–110 %, and the variation of the OCP and PCB concentrations in the duplicate samples was less than 20 %.
Results and discussion HCH, DDT, and PCB concentrations in the soil core from the Guanzhong Basin In all soil samples, OCPs and PCBs were identified (Table 1). Among these pollutants, the ∑DDT concentrations were generally the highest, varying from 1.66 to 12.92 ng/g with a mean value of 5.89 ng/g. In contrast,
7.64
1.03
1.66
0.06
0.12
2.13
0.39
1.05
2.19
0.45
5.75
6.20
0.57
0.17
0.23
BDL BDL BDL
0.15
BDL BDL BDL
0.12
BDL 0.04
0.67
p.p’-DDE
p.p’-DDD
o.p’-DDT
p.p’-DDT
HCHs
DDTs
OCPs
p,p’-DDT/p,p’-DDE 1.03
1.61
δ-HCH
α-HCH/γ-HCH
α-HCH/β-HCH
PCB 28
PCB 52
PCB 101
PCB 118
PCB 138
PCB 153
PCB 180
PCBs
3.44
0.15
0.30
2.77
0.17
0.53
7.07
0.57
2.65
1.36
0.50
2.56
0.12
0.08
0.10
0.70
BDL
0.14
0.19
0.20
0.18
0.48
1.31
3.27
13.41
12.92
0.49
7.66
1.42
1.51
2.34
0.11
0.07
0.21
γ-HCH
0.13
0.24
0.10
0.18
α-HCH
0.25
BDL
0.10
BDL
BDL
BDL
BDL
0.15
0.10
2.03
1.14
10.06
7.81
2.25
3.15
1.36
0.54
2.76
0.30
0.08
1.71
0.17
0.48
BDL
0.09
BDL
BDL
BDL
0.14
0.25
0.35
1.06
1.39
5.96
5.07
0.89
1.96
1.15
0.55
1.41
0.26
0.12
0.38
0.13
0.63
0.19
0.11
BDL
BDL
BDL
0.16
0.17
0.47
2.24
1.83
8.75
7.97
0.78
3.88
1.47
0.50
2.12
0.11
0.08
0.40
0.19
0.54
BDL
0.13
BDL
BDL
BDL
0.28
0.14
0.41
1.74
2.54
4.78
4.24
0.54
2.14
1.01
0.25
0.84
0.10
0.06
0.27
0.11
0.14
BDL
BDL
BDL
BDL
BDL
0.04
0.11
0.47
2.14
3.04
7.19
6.43
0.76
3.19
1.81
0.39
1.05
0.09
0.09
0.40
0.19
0.40
0.07
0.17
BDL
BDL
BDL
BDL
0.16
0.42
1.70
2.52
5.97
5.41
0.56
2.71
1.31
0.31
1.08
0.10
0.07
0.27
0.12
1.26
0.07
0.24
0.11
0.24
0.27
0.20
0.15
0.53
2.15
3.35
6.87
6.14
0.73
3.24
1.57
0.36
0.97
0.11
0.09
0.35
0.18
0.41
BDL
0.09
BDL
BDL
BDL
0.20
0.12
0.43
1.74
2.64
4.45
3.77
0.68
1.98
0.78
0.25
0.75
0.12
0.08
0.34
0.15
1.14
BDL
0.35
BDL
BDL
0.31
0.26
0.22
0.50
1.96
4.06
8.26
7.30
0.96
4.00
1.93
0.39
0.98
0.14
0.12
0.47
0.23
0.81
BDL
0.12
BDL
0.11
0.20
0.22
0.16
0.48
1.72
3.24
4.90
4.25
0.65
2.19
1.13
0.25
0.68
0.13
0.08
0.30
0.14
1.59
BDL
0.36
BDL
0.36
0.34
0.24
0.29
0.47
1.99
4.68
8.18
7.40
0.78
4.14
1.99
0.39
0.88
0.13
0.09
0.38
0.18
0.67
BDL
0.04
BDL
0.02
0.18
0.22
0.21
0.43
1.85
1.95
3.42
2.86
0.56
1.44
0.44
0.24
0.74
0.09
0.07
0.28
0.12
0.23
BDL
0.04
BDL
BDL
BDL
0.14
0.05
0.43
1.92
1.31
2.13
1.66
0.47
0.84
BDL
0.18
0.64
0.06
0.06
0.25
0.11
1.38
0.06
0.14
BDL
BDL
BDL
0.81
0.37
0.49
3.06
2.06
5.72
4.74
0.98
2.15
1.19
0.35
1.05
0.24
0.07
0.44
0.22
0.49
BDL
0.10
BDL
BDL
BDL
0.16
0.24
0.56
2.09
2.28
4.72
4.02
0.70
1.96
0.92
0.29
0.86
0.12
0.09
0.32
0.18
0.28
BDL
BDL
BDL
BDL
BDL
BDL
0.28
0.36
2.28
2.12
8.87
7.64
1.23
3.55
1.87
0.55
1.67
0.16
0.11
0.71
0.25
0.21
BDL
BDL
BDL
BDL
BDL
BDL
0.21
0.37
2.21
2.07
6.18
5.32
0.86
2.44
1.32
0.39
1.18
0.11
0.08
0.48
0.18
5–10 10–15 15–20 20–25 25–30 30–35 35–40 40–45 45–50 50–55 55–60 60–65 65–70 70–75 75–80 80–85 85–90 90–95 95–100
β-HCH
0–5
Compounds
Depths of soil (cm)
Table 1 Concentrations of OCPs and PCBs at different soil depths (ng/g d.w.)
Environ Monit Assess (2015) 187:4159 Page 3 of 8, 4159
4159, Page 4 of 8
the ∑HCH and ∑PCB concentrations were lower, varying from 0.45 to 2.25 ng/g with a mean value of 0.79 ng/ g and from 0.14 to 3.44 ng/g with a mean value of 0.79 ng/g, respectively. Among the DDTs and their metabolites, p,p’-DDT and p,p’-DDE were the dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. The p,p’-DDT concentration was the highest, ranging from 1.44 to 7.66 ng/g with a mean value of 2.87 ng/g and a detection frequency of 100 %. In addition, β-HCH was the most abundant HCH in the soil core, ranging from 0.18 to 1.71 ng/g with a mean value of 0.42 ng/g and a detection frequency of 100 %. The α-HCH, γ-HCH, and δ-HCH concentrations varied from 0.10 to 0.23 ng/g (mean 0.16 ng/g), 0.06 to 0.12 ng/g (mean 0.08 ng/g), and 0.09 to 0.30 ng/g (mean 0.14 ng/g), respectively (Table 1). In contrast with the HCHs and DDTs, some of the PCB congeners had relatively low detection frequencies (PCB 101 25 %, PCB 138 5 %, PCB 180 25 %) (Table 1). However, the low chlorinated PCBs (PCB 28) still showed high detection frequencies (100 %), which suggested a wide occurrence of PCBs in the farmland of the Guanzhong Basin, China. In addition, PCB 28 and PCB 52 were the dominant PCB congeners, with concentrations ranging from 0.11 to 0.29 ng/g with mean value of 0.19 ng/g, and from BDL to 2.77 ng/g with a mean value of 0.31 ng/g, respectively. The concentrations of OCPs and PCBs at different depths in the farmland soil are shown in Fig. 1. The maximum DDT and HCH concentrations were observed in the 10–15 cm and 15–20 cm sections, respectively. The higher POP concentrations, including HCHs and DDTs, in the surface soils (
