Spatial distributions and homolog profiles of chlorinated nonane paraffins, and short and medium chain chlorinated paraffins in soils from Yunnan, China

Chemosphere 247 (2020) 125855

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Spatial distributions and homolog profiles of chlorinated nonane paraffins, and short and medium chain chlorinated paraffins in soils from Yunnan, China Kunran Wang a, b, Lirong Gao a, b, *, Shuai Zhu c, Lili Cui a, b, Lin Qiao a, b, Chi Xu a, b, Di Huang a, b, Minghui Zheng d, ** a

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China University of Chinese Academy of Sciences, Beijing, 100049, China c National Research Center for Geoanalysis, Beijing, 100037, China d Jianghan University, Wuhan, 430056, China b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Chlorinated nonane paraffins (C9CPs) were analyzed in soils from Yunnan, China.
Short and medium chain chlorinated paraffins (SCCPs and MCCPs) were detected.
C10Cl6e7 were the major SCCP congeners and C14Cl6e7 were the major MCCP congeners.
The spatial distributions were related to human activities and atmosphere deposition.
The sources of SCCPs and MCCPs were different.

a r t i c l e i n f o Article history: Received 22 October 2019 Received in revised form 2 January 2020 Accepted 4 January 2020 Available online 6 January 2020 Handling editor: J. de Boer

Keywords: Chlorinated nonane paraffin Short chain chlorinated paraffin Medium chain chlorinated paraffin

a b s t r a c t To preliminarily investigate the occurrence, spatial distributions, homolog compositions, and ecological risks of chlorinated paraffins (CPs) in Yunnan, China, 110 soil samples were collected from an area part of Yunnan, representative of the whole Yunnan area, where had similar characteristics to most parts of Yunnan and 22 pooled soil samples were analyzed for 50 CP congener groups (C9e17Cl5e10). The chlorinated nonane paraffin (C9-CP), short chain (SCCP), and medium chain chlorinated paraffin (MCCP) concentrations in soil samples were 8e109 ng/g (average 39 ng/g), 79e948 ng/g (average 348 ng/g), and 20e1206 ng/g (average 229 ng/g), respectively. The C9-CP homologs contributed 5%e16% of the C9e13-CP concentrations in soils. No significant correlation was found between CP concentrations and the total organic carbon content (P > 0.05). The CP levels in soils from Yunnan were at a medium level compared with those in other areas worldwide. Human activity and atmosphere deposition would influence the levels and spatial distributions of CPs in this area. The concentrations of CPs in east area were higher than those in west area. C10Cl6e7 were the major SCCP congeners and C14Cl6e7 were the major MCCP congeners. Principal component analysis indicated that SCCPs and MCCPs came from different sources. A

* Corresponding author. State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China. ** Corresponding author. E-mail address: [email protected] (L. Gao). https://doi.org/10.1016/j.chemosphere.2020.125855 0045-6535/© 2020 Elsevier Ltd. All rights reserved.

2 Yunnan Soil

K. Wang et al. / Chemosphere 247 (2020) 125855

preliminary risk assessment indicated that these concentrations of CPs in soil from Yunnan do not pose a significant ecological risk for soil organisms. © 2020 Elsevier Ltd. All rights reserved.

1. Introduction Chlorinated paraffins (CPs), also known as polychlorinated nalkanes, are industrial mixtures with chlorine contents ranging from 40% to 70%. According to the carbon chain length, CPs can be divided into short chain chlorinated paraffins (SCCPs, C10eC13), medium chain chlorinated paraffins (MCCPs, C14eC17), and long chain chlorinated paraffins (LCCPs, C18eC30) (Fiedler and Heidelore, 2010). They have received increasing attention in recent years because of their long-range mobility (Tomy et al., 1999), persistence (Iozza et al., 2008), accumulation (Ma et al., 2014a), and biotoxicity (Bezchlebova et al., 2007). In May 2017, SCCPs were officially added to the controlled list of Annex A of the Stockholm Convention (POPRC, 2017). CPs have been produced in high quantities as plasticizers, lubricant additives, metal-cutting fluids, sealants, and flame retardants (Bayen et al., 2006). During the production, transportation, and use of CP-containing products, CPs are released into the surrounding environment, resulting in environmental pollution (Bayen et al., 2006). CPs have been found in various environmental matrices, such as air (Wang et al., 2013b; Wu et al., 2019a), dust (Friden et al., 2011; He et al., 2019; Brits et al., 2020), soil (Wang et al., 2014; Aamir et al., 2019), water (Zeng et al., 2011b), sediments (Marvin et al., 2003; Chen et al., 2011), and biota (Tomy et al., 1998; Sun et al., 2017; Li et al., 2019; Zhou et al., 2019), even in human blood (Li et al., 2017; Qiao et al., 2018). Therefore, it is important to enhance awareness of the pollution levels and potential risks of CPs. Soil is a vast reservoir for CPs, which are deposited from the atmosphere or sewage irrigation (Wang et al., 2017). From 1935 to 2012, the global releases of SCCPs during production and use were 1690e41400 t to air, 1660e105000 t to surface water, and 9460e8100 t to soil, respectively (Gluge et al., 2016). In China, the total estimated release of SCCPs in 2016 was 2563 t (Xu et al., 2014). Contaminated soil is both a source and matrix for exchange with other environmental media. Several studies have investigated CPs in typical polluted areas, such as areas receiving effluent from a sewage treatment plant (Zeng et al., 2011b) and contaminated by ewaste (Sun et al., 2017; Xu et al., 2019), in rivers (Chen et al., 2011; Wang et al., 2013b), surface soils surrounding a CP production plant (Xu et al., 2016), and sewage sludge from wastewater treatment plants (Zeng et al., 2012). Few studies have investigated CPs in soils from areas with no obvious industrial pollution sources in China (Wang et al., 2014, 2017; Huang et al., 2016). It is necessary to investigate the CP pollution status and atmospheric migration in those areas. Yunnan is remote and at a high altitude, and there are few manufacturers producing CPs in this area. Because of their physicochemical properties, CPs are persistent in the environment and able to undergo long-distance atmospheric transport to remote and high-altitude areas (Ma et al., 2014b). As the carbon chain becomes shorter, the toxicity of CPs increases (Fiedler and Heidelore, 2010). Therefore, CPs with shorter chain lengths might be more toxic than SCCPs. Chlorinated nonane paraffins (C9-CPs) have been detected in many CP products, including the three main commercial CP products in China (CP-42, CP-52, and CP-70) (Xia et al., 2019), hand blenders (Yuan et al., 2017b), and lubricants (Yuan et al., 2016). In China, C9-CPs were also ubiquitous in air (Xia et al., 2019), soil (Wu et al., 2019b),

sediment (Yuan et al., 2017a), fish (Huang et al., 2017), and even in human serum (Qiao et al., 2018). This means that C9-CPs may have been released into the environment during the production and use of CP products. To date, SCCPs have been widely investigated but little is known about C9-CPs in soil. The present study aimed to investigate the occurrences, spatial distributions, and homolog profiles of C9-CPs, SCCPs, and MCCPs. Two-dimensional gas chromatography (GC  GC) coupled with electron-capture negative-ionization mass spectrometry (ECNIMS) was used to detect CPs in soils from Yunnan. The results were used to explore the environmental behavior and sources of the CPs. Finally, a preliminary ecological risk assessment of CPs was conducted. This research will be useful for studying the environmental fate of CPs and the risks posed by CPs to humans living in this area. 2. Materials and methods 2.1. Sampling Yunnan is a province in Southwest China and the mountainous area accounts for 88.64% of the total area of Yunnan. There are only two CP manufacturing plants in this region. Taking into account the terrain characteristics in Yunnan, the surface soil samples were collected in a mountainous area far from any CP manufacturers. According to grid sampling method, the sample density was about one site/km2. To increase the representativeness of the soil samples, five soil columns (depth of 0e20 cm) were collected using a stainless steel scoop at each sampling site within an area of 100 m2. These subsamples were mixed together to form one pooled sample. In total, 22 pooled surface soil samples were collected in Yunnan in June 2016 (Fig. 1 (a)). The collected soil samples were dried at room temperature in where was separated from the laboratory and sieved through a 60-mesh sieve. Weeds, grass roots, gravel, and fertilizer pellets were removed. The samples were then stored in brown glass bottles at 20  C until required for analysis. 2.2. Chemicals and materials Three SCCP standard mixtures with chlorine contents of 51.5%, 55.5%, and 63.0%, and three standard MCCP mixtures with chlorine contents of 42.0%, 52.0%, and 57.0%, were bought from Dr. Ehrenstorfer (Augsburg, Germany). 13C10-trans-chlordane (Cambridge Isotope Laboratories, Tewksbury, MA, USA) and ε-hexachlorocyclohexane (Dr. Ehrenstorfer) were used as surrogate and internal standards, respectively. Silica gel (63e100 mm) and Florisil (60e100 mesh) from Merck (Kenilworth, NJ, USA) were activated at 550  C for 6.5 h and 12 h before use, respectively. Anhydrous sodium sulfate (Sinopharm Chemical Reagent Company, Beijing, China) was baked at 660  C for 6.5 h before use. Activated silica gel (100 g) was mixed with 43 mL of concentrated sulfuric acid thoroughly to obtain an acidic silica gel (44%, w/w). 2.3. Sample preparation The extraction and cleanup procedures for the soil samples were based on those used in a previous study (Gao et al., 2012). Briefly, 2.5 ng of 13C10-trans-chlordane was added to 10 g of dry soil, then

K. Wang et al. / Chemosphere 247 (2020) 125855

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Fig. 1. Map of the location of soil samples from Yunnan, China in 2016 (a) and the spatial distribution of C9-CPs, SCCPs, and MCCPs in the soil samples (b).

the soil was extracted using accelerated solvent extraction (ASE350; Dionex, Sunnyvale, CA, USA) with a mixture of n-hexane and dichloromethane (1:1, v/v) at 1.03  104 kPa and 100  C, and three extraction cycles were performed. The extract was evaporated to approximately 2 mL and cleaned up using a multilayer chromatography column, which contained (from bottom to top) 4 g of activated Florisil, 3 g of activated silica gel, 6 g of acidified silica gel (44%, w/w), and 6 g of anhydrous Na2SO4. Before adding the extraction, the multi-layer silica gel column was rinsed by 50 mL of n-hexane. Then, the extract was added to the column, and the column was eluted using 40 mL of n-hexane. The eluent from this step was discarded. Next, the sample was eluted using 100 mL of a mixture of n-hexane/dichloromethane (1:1 v/v), and the eluate was retained and evaporated to approximately 2 mL. Finally, the sample was concentrated to near dryness under a low flow of nitrogen gas, and 2.5 ng of ε-hexachlorocyclohexane and 50 mL of cyclohexane were added. 2.4. Instrumental analysis The C9-CPs, SCCPs and MCCPs in the soil samples were analyzed by GC  GC (Agilent Technologies, Santa Clara, CA, USA) equipped with a ZX2004 loop cryogenic modulator (Zoex, Houston, TX, USA) and coupled to an electron capture negative ion mass spectrometer (ECNI-MS) (Agilent Technologies). DB-5MS (30 m  0.25 mm  0.25 mm) (Agilent Technologies) was used as the first-dimension column, and BPX-50 (1 m  0.1 mm  0.1 mm) (SGE, Austin, TX, USA) as the second-dimension column. The GC parameters were further optimized based on our previous study (Xia et al., 2014). Briefly, the injection and transfer line temperatures were both 280  C, and the temperature of the ion source was 200  C. The injection volume was 1 mL and the sample was injected in splitless mode. The temperature program for the oven was as follows: held at an initial temperature of 100  C for 1 min, increased to 140  C at 10  C/min, and then increased to 310  C at 1.5  C/min and maintained for 5 min. The solvent delay time and the modulation period were 7 min and 7 s, respectively. The carrier gas was helium at a flow rate of 0.8 mL/min. Methane was used as the reagent gas. Selected ion monitoring mode was adopted. The method we used to quantify C9-CPs, SCCPs and MCCPs was similar to a previous study (Reth et al., 2005). The most abundant

ion, [M  Cl] was used as the quantification ion, and the next most abundant ion as the qualification ion (Table S1). The relative total response was calculated by dividing the congener response by the internal standard response. Calibration curves between the total response factor of CP standard mixture and the calculated chlorine content of CP standard mixtures with different chlorine contents were established. This could compensate for the influence on different total response factors of SCCPs caused by samples and standards with different chlorine contents. The CP content was calculated using the calibration curve and the relative total response. GC Image® R2.1 Software (GC Image, Lincoln, NE, USA) was used to process the GC  GC data. And statistical analysis was performed by SPSS Statistics 24 (IBM Corp., Armonk, NY, USA). 2.5. Quality control and quality assurance Anhydrous methanol, acetone, and dichloromethane were used to clean the glassware before use and each solvent rinsed three times. A process blank was analyzed with each batch of seven samples to monitor background contamination. The extraction, cleanup, and analysis of blanks were performed as for the samples. The CP concentrations in the blanks were less than 10% of the concentrations in the samples. Three of the 22 soil samples were extracted randomly for parallel testing, and the relative standard deviations of the samples were less than 15%. The method detection limit (MDL) was defined as the mean value of CPs detected in the blanks plus 3 times the standard deviation. And the MDLs of SCCPs and MCCPs were 8 and 16 ng/g, respectively. The recovery of 13C10trans-chlordane from all soil samples ranged from 70.6% to 105.6%. 3. Results and discussion 3.1. Concentrations and spatial distributions of C9-CPs, SCCPs, and MCCPs in soils 24 SCCP congener groups (C10e13Cl5e10), and 24 MCCP congener groups (C14e17Cl5e10) were detected in the soils from Yunnan. Two C9-CP congeners (C9H14Cl6 and C9H13Cl7) found in previous studies (Qiao et al., 2017) were also detected in the present study. The concentrations are reported on a dry weight (dw) basis (Table 1). The C9-CP, SCCP, and MCCP concentrations in the soil samples were

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K. Wang et al. / Chemosphere 247 (2020) 125855

Table 1 C9-CP, SCCP, and MCCP concentrations and relative abundances of congener groups in Yunnan soil samples. Sample no

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22

ng/g (dw) P C9

P C10

P C11

% P C12

P C13

ng/g (dw) P SCCP

P C14

P C15

P C16

P C17

ng/g (dw) P MCCP

35 37 10 44 34 14 10 81 47 61 24 56 27 43 109 47 23 21 8 20 52 66

75.0 60.5 58.9 73.1 52.4 61.9 56.0 73.8 69.9 69.5 69.8 71.7 70.1 69.6 74.6 72.3 60.0 41.0 63.7 39.2 74.5 67.0

19.3 24.8 24.4 19.8 19.0 24.4 24.6 20.2 21.8 21.6 21.5 20.6 21.9 21.9 19.7 19.7 22.8 32.5 23.2 16.9 19.5 22.4

4.1 7.9 9.3 4.4 9.8 8.1 10.3 4.3 5.5 5.8 5.4 4.9 5.1 5.6 3.9 4.8 7.7 14.0 7.5 9.3 4.0 6.0

1.6 6.8 7.5 2.8 18.8 5.5 9.1 1.8 2.8 3.2 3.3 2.8 2.9 3.0 1.7 3.1 9.6 12.5 5.6 34.6 2.1 4.6

192 300 113 307 308 153 134 575 495 451 221 376 247 394 948 397 288 363 79 326 383 615

27.4 51.7 65.9 60.0 60.9 67.1 71.3 54.1 79.6 75.9 55.1 72.8 55.0 40.4 57.4 63.8 68.0 51.6 63.4 72.4 52.8 77.8

22.5 21.5 19.4 21.2 22.5 21.3 15.7 18.0 14.7 15.8 19.3 14.7 18.8 23.3 17.6 16.7 22.3 24.2 17.7 19.1 20.9 17.0

23.3 14.7 9.2 11.9 11.6 7.9 7.0 13.8 3.9 6.0 13.1 7.0 13.9 20.4 14.5 11.3 7.0 15.2 10.4 6.4 14.7 3.9

26.8 12.1 5.5 7.0 5.0 3.8 6.0 14.1 1.8 2.3 12.5 5.5 12.3 15.8 10.6 8.1 2.7 8.9 8.5 2.1 11.6 1.3

20 31 45 71 495 93 54 82 248 156 33 149 1080 44 34 202 725 53 63 120 27 1206

8e109 ng/g (average 39 ng/g), 79e948 ng/g (average 348 ng/g), and 20e1206 ng/g (average 229 ng/g), respectively. Spatial distributions of the C9-CPs, SCCPs, and MCCPs in the soil samples are shown in Fig. 1 (b). The highest SCCP concentration (948 ng/g) was found in sample 15. High SCCP concentrations were found at sites 8e10 and 22, with an average value of 534 ng/g over these sites. The site with the highest SCCP concentration was located in east area. The sites with high concentrations were all located in east area, too. The east area has a higher population density than other areas. CPs might be widely used as plasticizers and flame retardants, which could contribute to the high CP concentrations in soils from the east area. Sites 8e10, 15 and 22 with the higher SCCP concentrations were all located in the valley. The atmospheric deposition might affect the CP content in the valley soil samples. The average of the low SCCP concentrations in the remaining 17 soil samples was 269 ng/g which were collected mostly in central and west area. Human activity and atmospheric deposition might affect the CP concentration there. The spatial distribution of C9-CPs was very similar to that of SCCPs. The highest C9-CP concentration (109 ng/g) was found in sample 15, which also had the highest SCCP concentration. High C9CP concentrations were also found in soils at sites 8, 10, and 22, with an average of 69 ng/g over these sites, and this distribution was very similar to that observed for SCCPs. Lower C9-CP concentrations were found in the remaining 18 soil samples, and the average value over these sites was 31 ng/g. The site with the highest SCCP concentration was located in east area. The samples with the high C9-CP concentrations were mainly from the east area, which had a higher population density than other areas. Sites 8, 10, 15 and 22 which had the higher C9-CP concentrations were almost all located in the valley. Like SCCPs, human activity and atmospheric deposition might lead to the high CP levels in the valley soil. The samples with low C9-CP concentrations were collected mostly in central and west Yunnan. The C9-CP contamination levels in this area soil may be related to human activities and atmospheric deposition. For the MCCPs (Fig. 1 (b)), the highest concentrations were found in samples 13 and 22, with an average value of 1143 ng/g over these sites. High MCCP concentrations were found in samples 5 and 17, with an average value of 607 ng/g. The other soil samples had

%

low MCCP concentrations, with an average value of 85 ng/g. Highest MCCP concentrations were found in samples collected in central and southeast area. The samples (13 and 22) with the highest MCCP concentrations were collected in valleys. The atmospheric deposition might affect the CP concentration in the valley soils. Furthermore, all the samples with high MCCP concentrations were collected at an altitude of above 2000 m and had much higher MCCP concentrations than the other soil samples. This finding is consistent with an earlier report that MCCP homologs are more sensitive to mountain cold-trapping, which may lead to high MCCP concentrations in highland surface soils (Aamir et al., 2019). Higher MCCP concentrations were also found in areas that had more human activity, which could be attributed to CPs release into the surrounding environment during products used by humans. In the present study, the lowest MCCP concentrations were found in samples from west area. Relatively low MCCP concentrations and low MCCP/SCCP ratios were found in soils from west area, and these could be ascribed to the small quantities of CPs used in this sparsely populated area compared with east area. In addition, because of their relatively low octanolewater partition coefficients (KOW) and octanoleair partition coefficients (KOA), SCCPs are more volatile and undergo long-range migration more readily than MCCPs. The C9-CP concentrations obtained in the present study were higher than those found in soil samples from Antarctica (3.0e25.6 ng/g) (Xia et al., 2019). The SCCP concentrations obtained in this study were lower than those found in soil samples from areas irrigated with wastewater (159.9e1450 ng/g) (Zeng et al., 2011a), agricultural areas (39e1609 ng/g) (Aamir et al., 2019), and the area around a CP production plant (218.7e2196.9 ng/g dry weight) (Xu et al., 2016), but higher than those in soil samples from the Pearl River Delta in China (1.9e236 ng/g) (Wang et al., 2013b), the UK (<0.8e179 ng/g), Western Europe (Halse et al., 2015), and Switzerland (3.0e3.26 ng/g) (Bogdal et al., 2017). The MCCP concentrations in this study were higher than those soil samples from Switzerland (5.1e160 ng/g) (Bogdal et al., 2017) and Shanghai (not detectede666 ng/g) (Wang et al., 2017), but lower than those in agricultural soils (127e1969 ng/g) (Aamir et al., 2019), surface soils from the area around a CP production plant (337.8e4388.4 ng/g dry weight) (Xu et al., 2016), and topsoil from the Pearl River Delta in China (2.1e1530 ng/g) (Wang et al., 2013b). Overall, the CP

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concentrations in soils from Yunnan were at a medium level compared with those in other regions around the world. Therefore, the soil environment in this area is not seriously polluted. This result could be attributed to production and use of only small quantities of CPs in this region. The MCCP/SCCP ratios in the soil samples from Yunnan ranged from 0.03 to 3.94, with most of them less than 1. In recent years, MCCP/SCCP ratios were greater than 1 in some area soils (Wang et al., 2013a, 2014; Aamir et al., 2019). Commercial CP products exhibit quite different congener group profiles in different areas in China. The present study showed that SCCPs may be the main source of pollution in this area. The total organic carbon (TOC) content of soil is an important factor affecting the accumulation of CPs (Huang et al., 2016). The TOC contents in the Yunnan soil samples are reported on a dry weight basis (Table S2). The TOC content range in the soil samples was 0.32%e4.91% (average 1.57%). An earlier study found a significant relationship between TOC contents and CP concentrations in soil cores from wastewater-irrigated farmland but not in topsoil (Zeng et al., 2011a). Huang et al. (2016) found that SCCP concentrations were significantly correlated with the organic matter content in topsoil in vegetable fields but not in other types of topsoil. In other studies, significant correlations were not found in soils (Gao et al., 2012; Wang et al., 2013a, 2013b; Aamir et al., 2019). In the present study, the SCCP and MCCP concentrations were not significantly correlated with the soil TOC contents (P > 0.05) (Table S3). 3.2. Congener group profiles of C9-CPs, SCCPs, and MCCPs in soils The congener group profiles of C9-CPs, SCCPs, and MCCPs in all

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the samples are shown in Fig. 2. In the Yunnan soil samples, the C9CP homologs contributed 5.4%e15.6% of the C9e13-CP concentrations. C10-CPs was the predominant SCCP congener group and P contributed 36.9%e66.9% of the SCCPs. The major chlorine congener groups were Cl6-and Cl7-CPs, which accounted for 58.0%e P 79.9% of the SCCPs. The SCCP patterns in the present study are similar to those found in air samples from the Pearl River Delta, Guangzhou (Wang et al., 2013b; Huang et al., 2016) where C10Cl6-7 were dominant homologs. However, they are different to those fround in the Liao River Basin (Gao et al., 2012) and Shandong Peninsula (Zhao et al., 2019). This could be caused by the use of different raw materials for CP production in different places, which could lead to difference in the composition characteristics for CPs in soils. In addition, the relative abundances of short chain and low chlorinated congeners in this study were high, perhaps because they were more prone to transport than long chain and high chlorinated congeners because of their high solubility and volatility. In the transportation process, low chlorinated homologs can be formed by dechlorination of high chlorinated homologs, which is consistent with previous results (Chen et al., 2011). The C14-CPs were the most abundant MCCP congener group and contributed 27.4%e79.6% of the SMCCPs. The Cl6-CPs and Cl7-CPs were the predominant chlorine congener groups, accounting for 35.9%e77.5% of the SMCCPs. The MCCP patterns were similar to those found in soil samples from Shanghai (Wang et al., 2014, 2017), pine needle samples from Shanghai (Wang et al., 2016) where C14e15Cl7-8 were the dominant homologs, and air samples taken in the Pearl River Delta (Wang et al., 2013b) where C14Cl6-8 were the dominant homologs. This homolog profile may be caused by the use of commercial CP products with similar compositions or the

Fig. 2. Carbon and chlorine congener group profiles of C9-CPs, SCCPs (a, b) and MCCPs (c, d) in Yunnan soil samples.

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fractionation of carbon congeners, and further study is needed to clarify the cause. For further analysis of the CP composition profiles in Yunnan soils, hierarchical cluster analysis was carried out. All 22 soil samples were clustered by the relative contents of two C9-CP homolog groups (C9 with 6e7 chlorines), 24 SCCP homolog groups (C9eC13 with 5e10 chlorines), and 24 MCCP homolog groups (C14eC17 with 5e10 chlorines) (Fig. S1). In addition, to compare the compositions of C9-CP and SCCP congeners at different sampling sites, correspondence analysis was performed according to the relative abundances of C9-CP and SCCP congeners (Fig. 3). For SCCPs (Fig. S2), C10Cl7 was the most abundant congener group in cluster 1 (n ¼ 12). In cluster 2 (n ¼ 10), the predominant congeners were C10e11Cl6e7. The samples in cluster 1 were mostly collected in east Yunnan, and the samples in cluster 2 were mainly collected in west Yunnan. The soils in cluster 1 had high relative abundances of C10- and Cl5e6-CPs (Fig. 3). These results might be related to the compositions of CP products in this area. Moreover, because of their relatively high vapor pressures, CPs with shorter carbon chains and lower chlorine numbers are more likely to undergo long-range atmospheric transport than other CPs, which may lead to higher relative abundances of C10- and Cl5e6-CPs in soils in east Yunnan. Compared with the soil samples in cluster 1, the soil samples in cluster 2 had significantly higher relative abundances of C11-12-CPs and Cl8-10-CPs (Fig. 3); however, the total chlorinated paraffin content decreased. This might be caused by acceleration of the deposition rates of long chain SCCPs on mountains by the mountain cold-trapping effect. In addition, the homolog profiles may be affected by the degradation of CPs(Chen et al., 2011; Gao et al., 2012). SCCP homologs with long carbon chains do not degrade rapidly, which increases the relative abundances of C11-12CPs (Omori et al., 1987). For the MCCPs, C14Cl6e7 were the major congeners in both cluster 1 (n ¼ 15) and cluster 2 (n ¼ 7) (Fig. S2). In cluster 1, C16e17Cl8e9 accounted for a slightly larger proportion as the mountain cold-trapping effect accelerated the deposition rate of long-chain congeners on the mountains. The soil samples in cluster 1 were mainly collected in central and west Yunnan. However, C14CPs and Cl6-7-CPs in cluster 2 accounted for a larger proportion than in cluster 1. The samples in cluster 2 were mostly collected in east

Yunnan, and the MCCP concentrations were relatively high in this area. This means that the sampling sites in cluster 2 may be located closer to the pollution source than those in cluster 1. Because MCCPs are more persistent in soils (log KOW ¼ 6.2e8.0) and less transportable (log KOA ¼ 8.4e12.7) than SCCPs, the main factor influencing the distribution of MCCPs is location near the pollution source rather than migration and transformation from highly industrialized areas to less industrialized areas like SCCPs(Aamir et al., 2019). Moreover, the complex geomorphology of alpine canyons and climate patterns may also influence the SCCP and MCCP homolog group profiles in the Yunnan samples, and this should be investigated in detail in future research. To further investigate the sources of C9-CPs, SCCPs, and MCCPs in Yunnan soils, principal component analysis was carried out (P < 0.001). Principal components (PCs) with eigenvalues > 1 were extracted and the first two factors (PC 1 and PC 2) accounted for 97.5% of the total variance (Fig. S3). PC 1 explained 70.0% of the total variance and was characterized by high loadings of MCCPs, implying similar sources for these MCCP congeners. PC 2 accounted for 27.5% of the total variance and was highly associated with the C9-CP and SCCP congener groups, suggesting that the C9-CP and SCCP congeners had similar sources. These results indicate that SCCPs and MCCPs in Yunnan soils come from different contamination sources. Earlier studies have reported that urban soils from Shanghai and sediments from the Yangtze River and the Yellow River also have different sources for SCCPs and MCCPs (Wang et al., 2014; Qiao et al., 2016, 2017). 3.3. Risk assessment A preliminary risk assessment was conducted using the CP concentrations in the soil samples and reported toxicological thresholds. Previous studies have indicated that the predicted no effect concentrations of SCCPs and MCCPs for soil-dwelling organisms are 5280 ng/g and 28 mg/g, respectively (Bezchlebova et al., 2007; Gluege et al., 2018). The concentrations of SCCPs and MCCPs in all soil samples in this study were lower than the corresponding predicted no effect concentrations, suggesting that the present concentrations of SCCPs and MCCPs in Yunnan soils do not pose a significant ecological risk to soil organisms. However, because the mass load of CPs, especially MCCPs, in soil increases over time, further attention should be paid to CPs in the soil environment and regulatory action should be considered. 4. Conclusions C9-CPs, SCCPs, and MCCPs were detected by GC  GC-ECNI-MS in all soil samples collected in Yunnan, China. The concentrations of SCCPs and MCCPs in these samples were at a medium level compared with those in soils from other regions around the world. Soil samples collected in east Yunnan had higher concentrations of C9-CPs, SCCPs, and MCCPs, and samples collected in west Yunnan had lower C9-CP, SCCP, and MCCP concentrations. Human activity and atmosphere deposition would influence the levels and spatial distributions of CPs in this area. The results of principal component analysis showed that C9-CPs and SCCPs in the region’s soils were derived from similar contamination sources, but MCCPs and SCCPs came from different contamination sources. A preliminary risk assessment indicated that the present concentrations of SCCPs and MCCPs in Yunnan soils do not pose a significant ecological risk to soil organisms. Declarations of competing interest

Fig. 3. Two-dimensional scatter plots of correspondence analysis for the relative abundances of C9-CP and SCCP congeners.

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CRediT authorship contribution statement Kunran Wang: Formal analysis, Investigation, Writing - original draft. Lirong Gao: Project administration, Conceptualization, Investigation, Writing - review & editing. Shuai Zhu: Investigation, Methodology. Lili Cui: Investigation, Data curation. Lin Qiao: Investigation, Methodology. Chi Xu: Investigation, Methodology. Di Huang: Data curation, Formal analysis. Minghui Zheng: Resources, Supervision. Acknowledgements This work was supported by the State Key Project of Research and Development Plan [grant number 2018YFC1801601] and the National Natural Science Foundation of China [grant numbers 21577152, 91543106, and 21377140]. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.chemosphere.2020.125855. References Aamir, M., Yin, S., Zhou, Y., Xu, C., Liu, K., Liu, W., 2019. Congener-specific C-10-C-13 and C-14-C-17 chlorinated paraffins in Chinese agricultural soils: spatio-vertical distribution, homologue pattern and environmental behavior. Environ. Pollut. 245, 789e798. Bayen, S., Obbard, J.P., Thomas, G.O., 2006. Chlorinated paraffins: a review of analysis and environmental occurrence. Environ. Int. 32, 915e929. Bezchlebova, J., Cernohlavkova, J., Kobeticova, K., Lana, J., Sochova, I., Hofman, J., 2007. Effects of short-chain chlorinated paraffins on soil organisms. Ecotoxicol. Environ. Saf. 67, 206e211. Bogdal, C., Niggeler, N., Gluge, J., Diefenbacher, P.S., Wachter, D., Hungerbuhler, K., 2017. Temporal trends of chlorinated paraffins and polychlorinated biphenyls in Swiss soils. Environ. Pollut. 220, 891e899. Brits, M., de Boer, J., Rohwer, E.R., De Vos, J., Weiss, J.M., Brandsma, S.H., 2020. Short, medium-, and long-chain chlorinated paraffins in South African indoor dust and cat hair. Chemosphere 238, 124643-124643. Chen, M.Y., Luo, X.J., Zhang, X.L., He, M.J., Chen, S.J., Mi, B.X., 2011. Chlorinated paraffins in sediments from the Pearl River Delta, south China: spatial and temporal distributions and implication for processes. Environ. Sci. Technol. 45, 9936e9943. Fiedler, Heidelore, 2010. Short-chain chlorinated paraffins: production, use and international regulations. In: Boer, J. (Ed.), Chlorinated Paraffins. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 1e40. Friden, U.E., McLachlan, M.S., Berger, U., 2011. Chlorinated paraffins in indoor air and dust: concentrations, congener patterns, and human exposure. Environ. Int. 37, 1169e1174. Gao, Y., Zhang, H.J., Su, F., Tian, Y.Z., Chen, J.P., 2012. Environmental occurrence and distribution of short chain chlorinated paraffins in sediments and soils from the liaohe River Basin, P. R. China. Environ. Sci. Technol. 46, 3771e3778. Gluege, J., Schinkel, L., Hungerbuehler, K., Cariou, R., Bogdal, C., 2018. Environmental risks of medium-chain chlorinated paraffins (MCCPs): a review. Environ. Sci. Technol. 52, 6743e6760. Gluge, J., Wang, Z., Bogdal, C., Scheringer, M., Hungerbuhler, K., 2016. Global production, use, and emission volumes of short-chain chlorinated paraffins - a minimum scenario. Sci. Total Environ. 573, 1132e1146. Halse, A.K., Schlabach, M., Schuster, J.K., Jones, K.C., Steinnes, E., Breivik, K., 2015. Endosulfan, pentachlorobenzene and short-chain chlorinated paraffins in background soils from Western Europe. Environ. Pollut. 196, 21e28. He, C., Brandsma, S.H., Jiang, H., O’Brien, J.W., van Mourik, L.M., Banks, A.P., Wang, X., Thai, P.K., Mueller, J.F., 2019. Chlorinated paraffins in indoor dust from Australia: levels, congener patterns and preliminary assessment of human exposure. Sci. Total Environ. 682, 318e323. Huang, H., Gao, L., Xia, D., Qiao, L., 2017. Bioaccumulation and biomagnification of short and medium chain polychlorinated paraffins in different species of fish from Liaodong Bay, North China. Sci. Rep. 7. Huang, Y., Chen, L., Feng, Y., Ye, Z., He, Q., Feng, Q., Qing, X., Liu, M., Gao, B., 2016. Short-chain chlorinated paraffins in the soils of two different Chinese cities: occurrence, homologue patterns and vertical migration. Sci. Total Environ. 557, 644e651. Iozza, S., Mueller, C.E., Schmid, P., Bogdal, C., Oehme, M., 2008. Historical profiles of chlorinated paraffins and polychlorinated biphenyls in a dated sediment core from Lake Thun (Switzerland). Environ. Sci. Technol. 42, 1045e1050. Li, H., Bu, D., Fu, J., Gao, Y., Cong, Z., Zhang, G., Wang, Y., Chen, X., Zhang, A., Jiang, G., 2019. Trophic dilution of short-chain chlorinated paraffins in a plant-plateau

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