Contamination of polychlorinated biphenyls and hexachlorobutadiene in greenhouse and open-field agricultural soils across China

Contamination of polychlorinated biphenyls and hexachlorobutadiene in greenhouse and open-field agricultural soils across China | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Contamination of polychlorinated biphenyls and hexachlorobutadiene in greenhouse and open-field agricultural soils across China Li Yaru, Jing Lan, Zongshan Zhao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2297064/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Combined with the physical isolation feature of greenhouse, the popularization of greenhouse throughout China makes the pollution of greenhouse soils more noteworthy as a result of its high yielding food exposed to human beings. Here, a national-scale survey was conducted to evaluate the contamination status, contaminated sources and human health risks of polychlorinated biphenyls (PCBs) and hexachlorobutadiene (HCBD) in greenhouse and open-field soils of 20 regions across China. The PCBs contents ranged from <LOD to 673.78 ng/g with the mean content of 77.38 ng/g in greenhouse soils and ranged from <LOD to 552.53 ng/g with the mean content of 61.90 ng/g in open-field soils. The HCBD contents ranged from 0.85 ng/g to 24.18 ng/g with the mean content of 8.33 ng/g in greenhouse soils and ranged from <LOD to 20.19 ng/g with the mean content of 6.39 ng/g in open-field soils. Among divided seven regions, higher levels of PCBs in greenhouse and open-field soils were found in north and south China. Furthermore, in most regions, correlation analysis indicated that soil PCBs in greenhouse and open-field were likely from the same emission sources. Higher levels of soil pollutants in greenhouse than in open-field may be contributed to the limited air-soil exchange. Compared with higher levels of ΣPCBs in greenhouse soils, the health risks of ΣPCBs in open-field soils were higher due to the higher percentages of high-toxicity PCBs, especially for the carcinogenic risks to children (> 10 -6 ). This study provided a full insight into the contamination status and risks of PCBs and HCBD when guiding greenhouse agriculture activities. Polychlorinated biphenyls Hexachlorobutadiene Agricultural soils Contamination status Contaminated sources Health risks Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Agricultural soil for crop production is generally used under two cultivated models, open-fields and greenhouses. Especially for greenhouses, it is a technology-based approach, which have been widely popularized and applied in fields of vegetables, fruits and flowers by creating a micro-scale environment (Wu et al. 2020 ). It has been characterized by strong risk resistance, highly concentrated knowledge and technology, and multiple effects in the economy, society and ecology (Kumar et al. 2006 ). As a consequence, they have been supported by the Food and Agriculture Organization (FAO) of the United Nations worldwide (Khoshnevisan et al. 2014 ; Hanan 2017 ). Since its first introduction into China in late 1970s, the total area of greenhouse cultivation projects had reached 4.708 million hectares in 2019 (Yang et al. 2013 ; Wang et al. 2022 ). The extensive applications of greenhouse enhance resource utilization and land productivity, and further improve the economic efficiency. However, the improved yields and the shortened agricultural production cycle are achieved by inputting plenty of material and energy, which would lead to severe soil contamination and hence pose adverse effects to the environment (Badrudin et al. 2022 ). Agricultural soil is a major source and sink for persistent organic pollutants (POPs) (Tao et al. 2008 ). For example, POPs can enter agricultural soils through irrigation wastewaters, chemical fertilizer, atmospheric deposition and so on (Khuman et al. 2020 ; Pena et al. 2020 ). Once entering soils, some POPs are more persistent in greenhouse soils than in open-field soils and present different contaminated statuses (Lehmann et al. 2015; Wu et al. 2012 ). Previous studies reported that higher contaminations of POPs were found in greenhouse soils than in open-field soils, such as pyrethroids, atrazine, organophosphorus pesticides (OPPs), phthalate esters (PAEs) and polycyclic aromatic hydrocarbon (PAHs) (Sun et al. 2018a ; Dou et al. 2020 ; Li et al. 2021a ). This result was likely caused by the limited environmental behaviors of POPs in greenhouses, such as volatilize from soil to air (Ali et al. 2015 ; Xu et al. 2019 ). Furthermore, compared with in open-fields, there were more significant effects of human activities on the contamination of POPs in greenhouse soils, via the soil properties, heavy metals and so on (Li et al. 2021a ). Therefore, the contamination status, affected factors and environmental risk of these pollutants in greenhouses should be more concerned. Polychlorinated biphenyls (PCBs) and hexachlorobutadiene (HCBD) belonging to persistent organic pollutants (POPs), have been widely utilized in various areas, such as heat-exchange fluids, dielectric, pesticide additives, transformers, herbicides, and fungicides, etc. (Breivik et al. 2007 ; van der Gon et al. 2007; Wang et al. 2018 ; Luo et al. 2020 ). Due to improper disposal and environmental migration, they have been frequently detected in almost all environmental medium on the earth. For PCBs, in the Pearl River Delta, the concentration ranged from 0.30 to 202.00 ng/g with predominant homologues of low-chlorinated biphenyls (Zhang et al. 2013 ). Even in some remote areas such as Siberia and Tibet, the occurrence of PCBs has also been reported (Mamontova et al. 2007 ; Wang et al. 2016). For HCBD, among China’s three economic hubs, namely, Yangtze River Delta, Beijing-Tianjin-Hebei region and Pearl River Delta, the Yangtze River Delta showed the highest soil contents of HCBD (8.47 ng/g dry weight) (Tang et al. 2016; Sun et al. 2018c ). With the high bioaccumulation, semi-volatile, high toxicity, and teratogenic, carcinogenic, and mutagenic effects, PCBs and HCBD can easily enter the crops, and present adverse effects to human health and ecological environment. As a result, PCBs were classified as A Class iiA human carcinogen by the International Agency for Research on Cancer and HCBD has also been listed in Annex A of the Stockholm Convention, respectively (Zeeb et al. 2006 ; Wang et al. 2018 ). Though the contamination of PCBs and HCBD has already been reported many times in some developed regions, such as the Yangtze River Delta, the Pearl River Delta, the Liaohe River and the southeast China, and others (Fu et al. 2010 ; Teng et al. 2013 ; Tao et al. 2020 ), there is only a few reports with various pollution levels on these POPs in greenhouse. Due to the popularization of greenhouse throughout China, the disorderly discharge of pollutants and the physical isolation inside and outside of the greenhouse, greenhouse soils are likely to undergo different pollutions from open-field soils, even facing more serious pollution and ecological risks. In this study, we aimed to identify the typical distribution characteristics of soil PCBs and HCBD, and compare the pollution differences between two land farming patterns of greenhouse and open-field soils across China. This work was conducted by (1) characterizing the contamination status and spatial distribution of PCBs and HCBD in greenhouse and open-field soils, (2) analyzing the correlation between pollutants and soils physicochemical properties, and the potential sources of pollutants, (3) evaluating the human health risks of pollutants in greenhouse and open-field soils. These results would provide a comprehensive assessment of PCBs and HCBD in greenhouse and open-field soils across China. 2. Materials And Methods 2.1. Sample collection In total, 51 pairs of surface soil samples (0–20 cm) were collected from the greenhouses and nearby open vegetable fields in 20 provinces, municipalities and autonomous regions across China from November 2014 to February 2015. The investigated 20 provinces, municipalities and autonomous regions with two or three sampling sites included Heilongjiang (HLJ), Jilin (JL), Liaoning (LN), Beijing (BJ), Hebei (HB), Shanxi (SX), Inner Mongolia (IM), Jiangsu (JS), Shandong (SD), Zhejiang (ZJ), Shanghai (SH), Hunan (HN), Jiangxi (JX), Guangdong (GD), Qinghai (QH), Gansu (GS), Xinjiang (XJ), Yunnan (YN), Sichuan (SC), and Tibet (TB). The detailed information of the sampling sites, including GPS location, crop cultivation, cultivation age, main fertilizer and soil type, was listed in Table S1. For each sample site, soils were collected from five cores using a bamboo scoop and they were later composited to form a single sample. Then the soil samples were packed with aluminum foil, sealed in Kraft bags, and immediately delivered to the laboratory on ice. The remaining soil was stored at -20°C for the analysis of the soil properties and the target contaminants (Sun et al. 2018a ). 2.2. Sample pretreatment The extraction and cleanup procedures for PCBs were adopted from the reported methods (Wang et al. 2013 ). All freeze-dried samples were ground and sieved through a stainless steel 75-mesh sieve. A portion of soil samples (5 g) were spiked with recovery surrogate PCB-65, followed by ultrasonic extraction for 30 min using hexane/dichloromethane (1:1 v/v, 40 mL). After three extractions, the extracts were concentrated to 1 mL, and then subjected to cleanup by a multilayer silica column as follows (from bottom to top): 1 g silica, 4 g basic silica (1.2%, w/w),1 g silica, 8 g acidic silica (30%, w/w), 2 g silica, and 4 g anhydrous sodium sulfate. Before used, the column was pre-washed with hexane. The extract was eluted with 100 mL of hexane, and then was concentrated by rotary evaporation to a final volume of 200 µL prior to instrumental analysis. The extractions of HCBD were also adopted from the reported methods (Zhang et al. 2014). A portion of soil samples (10 g) were spiked with surrogate standard 2,4,5,6-tetrachlori- m -xylene, followed by ultrasonic extraction 30 min using a mixture solvent of dichloromethane/hexane (1:1, v/v, 30 mL). The procedure was repeated two times, and all the extract was collected. Then the extract was concentrated to 1 mL by rotary evaporation and was cleaned up by a multilayer silica-Florisil composite column as follows (from bottom to top): 6 g Florisil, 4 g activated silica gel, and 5 g anhydrous sodium sulfate. Similarly, the columns were pre-washed with 50 mL hexane. Finally, the extract was eluted with 150 mL of petroleum ether and was thereafter concentrated to 200 µL prior to instrumental analysis. 2.3. Chemical analysis In all samples, the target PCBs included 12 dioxin-like PCBs (DL-PCBs) (including PCB-77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189), and six indicator PCBs (including PCB-28, 52, 101, 138, 153, and 180) (Table S2). The quantitative analysis of PCBs and HCBD were performed on gas chromatography/mass spectrometry (GC/MS) (7890B/5977A, Agilent Technologies, Santa Clara, CA, USA) with an electron ionization source. A DB-5 MS capillary column was used (30 m × 0.25 mm i.d. with 0.25 mm film thickness). All data were obtained in the selective ion monitoring (SIM) mode. High purity helium was used as carrier gas with a flow rate of 1.0 mL/min. Oven temperature program for PCBs was as follows: initial column temperature at 80 ℃ for 3 min, ramped to 150 ℃ at 15 ℃/min and held for 2 min, increased to 270 ℃ at 2.5 ℃/min and held for 3 min, increased to 300 ℃ at 15 ℃/min and held for 5 min. Another program for HCBD was as follows: initial oven temperature at 80°C for 2 min and increased to 140°C at a rate of 10°C/min linearly, then ramped to 280°C at 4°C/min and held for 5 min. 2.4. Environmental factors and pollution sources analysis In order to determine the correlation of environmental factors with the levels of PCBs and HCBD, the data including the soil physicochemical properties and the content of co-existing pollutants for these soil samples reported by Sun et al. ( 2018a ) has been extracted in this paper. The soil physicochemical properties including soil moisture (SM), soil total carbon (STC), soil total phosphor (STP), soil total nitrogen (STN), and pH value were measured. The co-existing pollutants were quantified, including POPs (organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs)) and heavy metals (cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb)). Redundancy analysis and correlation analysis were carried out to evaluate the correlations of these factors. And principal component analysis (PCA) on soil PCBs has been performed to identify their mainly emission sources using. 2.5. Health risk assessment The exposure noncancer and carcinogenic risk of PCBs and HCBD to human health were evaluated using the methods recommended by the U.S. Environmental Protection Agency (EPA). Generally, there are three types of exposure pathways, including soil ingestion, dermal contact and inhalation. By considering these pathways, two primary indices were determined to assess the health risk, namely the hazard index (HI) and carcinogenic risks. The methods employed to calculate the two primary indices were presented in SI. The relative parameters were shown in Tables S3 and S4. The noncancer risks of chemical contaminants are considered as relatively high when HI > 1.0, while the risk may be negligible when the value of HI is below 1.0. The carcinogenic risks of chemical contaminants are considered to be very low when the risk value is below 10 − 6 , low in the range of 10 − 6 and 10 − 4 , moderate from 10 − 4 to 10 − 3 , high from 10 − 3 to 10 − 1 , and very high when it is over 10 − 1 . 3. Results And Discussions 3.1. Levels and spatial distributions of pollutants All the contents of PCBs and HCBD were presented on a dry weight (dw) basis. At a national-scale, the PCBs contents ranged from < LOD to 241.22 ng/g with the mean contents of 62.33 ng/g in greenhouse soils, and ranged from < LOD to 192.89 ng/g with the mean contents of 51.09 ng/g in open-field soils (Table S5 and Fig. 1 ). Furthermore, the detection frequencies of PCBs were 84.31% in greenhouse soils and 76.47% in open-field soils. In contrast, the contamination of PCBs in greenhouse soils was more serious than in open-field soils. Different from their contamination levels and detection frequencies, the compositions of total PCBs (ΣPCBs) were similar in greenhouse and open-field soils. The major PCB homologue was tetra-CBs, followed by penta-CBs and hexa-CBs, which took over > 80% of ΣPCBs in greenhouse and open-field soils (Figure S1). The similar compositions indicated the possible homology of greenhouse and open-field soil’s pollution from human activities. Totally, the ΣPCBs levels in this study was at the same levels as previous reports in China, such as in agriculture soils of south Jiangsu and Taiyuan (Zhang et al. 2017; Sun et al. 2019 ). In order to further identify the distribution characteristics, all the soil samples were classified as seven regions in China, including northeastern (HLJ, JL and LN), northwestern (XJ, GS and QH), northern (BJ, IM, SX and HB), central (HN, JX), eastern (SD, JS, ZJ and SH), southern (GD), and southwestern (YN, TB and SC). As shown in Table S6, the north and south China showed higher PCBs levels in open-field soils, especially in IM, BJ and HB, while the north, southwest and south China presented higher PCBs levels in greenhouse soils. But it should be noted that the PCBs levels in greenhouse soils were higher than in open-field soils in most regions, which may be attributed to the limited soil-air exchange in greenhouse (Gao et al. 2008 ; Hu et al. 2021). Usually, the polluted sources of soil PCBs are mainly from wastewater discharge, solid waste leakage, waste incineration, atmospheric deposition, etc. (Cetin et al. 2017 ). And the source/sink tendency of soil PCBs depended on their volatility. For example, the low-chlorinated PCBs tended to volatilize from soil, and high-chlorinated PCBs tended to sink into soil, until reached the balanced state in open-field soils (Ali et al. 2015 ; Xu et al. 2019 ). Therefore, the volatility was inhibited by the limited soil-air exchange due to the physical isolation in greenhouse. For all the soil samples, the HCBD contents ranged from 0.85 to 24.18 ng/g with the mean contents of 8.19 ng/g in greenhouse soils, and ranged from < LOD to 20.19 ng/g in greenhouse and open-field soils with the mean contents of 6.52 ng/g in open-field soils (Table S5 and Fig. 1 ). Compared with PCBs, though HCBD showed lower contamination levels, the detection frequencies of HCBD were higher both in greenhouse (100%) and open-field soils (96.08%). Furthermore, the contamination of HCBD in greenhouse soils were also higher than in open-field soils in most regions, which also may be attributed to the limited soil-air exchange in greenhouse (Ali et al. 2015 ; Xu et al. 2019 ) (Table S6). Totally, the HCBD contents in this work were at comparable levels to that in agricultural soil of east China (Tang et al. 2014 ), the Yangtze River Delta (Sun et al. 2018c ) and southwest China (Tang et al. 2016). According to the investigation results of soil PCBs and HCBD, it could be easily found that both of them presented their unique characteristics in spatial distributions, such as more serious pollution in greenhouse of north China. The reasons may be attributed to their pollution sources and regional environmental factors (including other pollutants and soil physicochemical properties) (Nieuwoudt et al. 2009 ; Habibullah-Al-Mamun et al. 2019 ; Niu et al. 2022 ). 3.2. Correlation between pollutants and environmental factors The linkages between pollutants and environmental factors in greenhouse and open-field soils were obtained through redundancy analysis (Fig. 2 ). At a national-scale, the positive correlations were only obtained between OCPs and PCBs (r = 0.298, p༜0.05) in greenhouse soils (Table S7), indicating that they were likely to share the same pollution paths, such as irrigation (Meng et al. 2017 ). The positive correlations between Pb and PCBs (r = 0.311, p < 0.05) were also obtained in open-field soils (Table S8), suggesting that they were likely to share same pollution sources, such as industrial metal smelting (Diop et al. 2017 ). But there was no any environmental factor correlated with HCBD in greenhouse and open-field soils (Table S7, S8). In this study, no correlation between soil PCBs and properties can be attributed to the variety of pollution levels and region distributions across China (Niu et al. 2022 ). Meanwhile, there were no correlation between soil HCBD and other pollutants/soil properties. To further study the relationships between pollutants and environmental factors, the correlation analysis between PCBs homologues and soil properties were also carried out in some economically developed regions, such as the north China and the east China. In north China, ΣPCBs were correlated with tetra-CBs (r = 0.907, p < 0.01 in greenhouse soils; r = 0.830, p < 0.01 in open-field soils) and hexa-CBs (r = 0.609, p < 0.05 in greenhouse soils; r = 0.881, p < 0.01 in open-field soils) (Table S9, S10). In east China, the total PCBs were correlated with tetra-CBs (r = 0.921, p < 0.01 in greenhouse soils; r = 0.904, p < 0.01 in open-field soils) and penta-CBs (r = 0.860, p < 0.01 in greenhouse soils; r = 0.569, p < 0.05 in open-field soils) (Table S11, S12). The correlations between ΣPCBs and homologues verified the same sources/paths for greenhouse and open-field soils pollution in these regions (Hu et al. 2021). 3.3. Regional source analysis of pollutants Traceability analysis on soil PCBs in north and east China has been performed to identify their mainly emission sources using principal component analysis (PCA). The compositions of PCBs homologues were also compared with the Aroclor series products, including Aroclor 1016, 1221, 1232, 1242, 1248, 1254, 1260, 1262. Factors with eigenvalues greater than 1.0 were extracted and 3 principal components (> 80% variance) were acquired. In north China, the compositions of PCBs were less consistent with the Aroclor series products (Fig. 3 a, 3 b). In both greenhouse and open-field soils, hexa-CBs and hepta-CBs presenting larger loading in PC1 (> 0.53), were likely attributed to the recycling and disposal of electrical equipment containing PCBs (Li et al. 2019). Tetra-CBs and tri-CBs showing larger loading in PC2 (> 0.48), corresponded to the domestic coal, wood burning emissions, non-ferrous metal smelting and regeneration, and high temperature incineration of industrial as well as municipal waste (Lee et al. 2005 ; Nieuwoudt et al. 2009 ; Habibullah-Al-Mamun et al. 2019 ). Penta-CBs with loading of > 0.83 in PC3 were mainly from oil additives and metallurgy industry (Ba et al. 2009 ). This result revealed the silimar pollution sources of greenhouse soils and open-field soils in north China. In east China, the compositions of PCBs were similar to the Aroclor series products in partial sample sites (Fig. 3 c, 3 d). For example, in both greenhouse and open-field soils of Shanghai, PCBs (G1, O1, O2) possibly derived from Aroclor 1242, which was identical with the result of Jiang et al. (2010). In rest greenhouse soils, tri-CBs and tetra-CBs showed larger loading in PC1 (> 0.53), indicated the mainly sources of the domestic coal, wood burning emissions, high temperature incineration of industrial and municipal waste, etc. (Lee et al. 2005 ; Nieuwoudt et al. 2009 ; Habibullah-Al-Mamun et al. 2019 ). And hepta-CBs and hexa-CBs showed larger loading (> 0.61) in PC2 and PC3, indicating the source from the recycling and disposal of electrical equipment containing PCBs (Li et al. 2019). In open-field soils, hexa-CBs and hepta-CBs showed larger loading in PC1 (> 0.42) in open-field soils, and hexa-CBs and tri-CBs presented larger loading (> 0.53) in PC2 and PC3. This indicated that the recycling and disposal of electrical equipment containing PCBs was the main source. Previous reports have indicated that the e-waste dismantling areas distributed in east China, such as Taizhou, were one of the most important sources for soil PCBs (Sun et al. 2018b ; Liu et al. 2020 ). 3.4. Human health risk assessments The health risks of pollutants in greenhouse and open-field soils were estimated via soil ingestion, dermal contact and inhalation exposure pathways (Niu et al. 2013 ; Li et al. 2021b). As shown in Fig. 4 a, the non-cancer exposure risks of PCBs to children and adults in open-field soils were both higher than in greenhouse soil. Meanwhile, the non-cancer exposure risks of PCBs to children were higher than to adults both in greenhouse and open-field soils. The average HI values of PCBs were 0.022 for adults and 0.222 for children in greenhouse soils, and 0.030 for adults and 0.274 for children in open-field soils, respectively. In all these samples, lower HI values ( 1.0) for children both in greenhouse and open-field soils indicated the potential non-cancer risks of PCBs to children were not negligible. Among PCBs homologues, the average HI value of PCB-126 was the highest in greenhouse soils (HI = 0.010 for adults, HI = 0.121 for children) and in open-field soils (HI = 0.016 for adults, HI = 0.146 for children), followed by PCB-81 (Figure S2). For HCBD, all the HI values were below 1.0 for adults and children, implying the negligible non-cancer risks in soil samples (Fig. 4 c). The carcinogenic risks of PCBs to children were higher than that to adults (Fig. 4 b). In greenhouse soils, the average values of PCBs to adults and to children were 8.37 × 10 − 7 and 1.38 × 10 − 6 , respectively. Compared with in greenhouse soils, the carcinogenic risks of PCBs to children and adults in open-field soils presented higher risks (Fig. 4 b). In open-field soils, the average values of PCBs to adults and children were 1.03 × 10 − 6 and 2.13 × 10 − 6 respectively. And the values in large number of samples (25.5% to adults and 37.3% to children) were between 10 − 6 and 10 − 4 , implying relatively low carcinogenic risks to human beings. Among these PCB homologues, the most significant carcinogenic risks were also attributed to PCB-126 (Figure S1). In contrast, the carcinogenic risks of HCBD to adults and children were both below 10 − 6 in greenhouse and open-field soils (Fig. 4 d), corresponding to the negligible carcinogenic risks. In this study, the non-cancer risks and carcinogenic risks of PCBs were similar to the Yellow River irrigation area and Lanzhou soils (Ding et al. 2018; Li et al. 2021b). However, the different patterns were found between the health risks and PCBs levels. For example, samples from IM presented the higher PCBs levels and the lower health risks in greenhouse soils. The reason could be explained by different toxic equivalency factor (TEF) of measured PCBs, which order was PCB-126 > PCB-169 > PCB-81 > PCB-77 > other PCBs (Van den et al. 2006; Niu et al. 2022 ). Compared with that in open-field, low-chlorinated (≤ 4) PCBs presented increasing ratios in ΣPCBs in greenhouse soils, corresponding to their lower risks. This might be attributed to the faster dechlorination of high-chlorinated PCBs in greenhouse, as greenhouse environment factors (moisture and temperature) were more favorable for microbial growth (Dou et al. 2020 ; Tao et al. 2022 ). 4. Conclusion In this study, 51 pairs of surface soil samples collected from 20 regions were analyzed to investigate the contamination status of PCBs and HCBD in both greenhouse and open-field soils across China. At a national-scale, the PCBs and HCBD pollutions in greenhouse soils presented a slightly higher level than in open-field soils as a result of the limited air-soil exchange in greenhouse. Positive correlations between ΣPCBs and PCBs homologues indicated their similar sources/paths in greenhouse and open-field soils. The regional source analysis showed that the soil PCBs sources consisted of domestic coal, wood burning emissions, disposal of electrical equipment, oil additives and metallurgy industry. Meanwhile, the low-toxicity PCBs in greenhouse soils contributed to the lower risks when comparing with that in open-field soils. This study provided valuable information to understand the contamination status, sources and risks of PCBs and HCBD in greenhouse and open-field soils when changing the farmland farming modes, especially for greenhouse cultivation. Declarations Acknowledgments This study was financially supported by the Natural Science Foundation of Shandong Province (ZR2022QB167) and the National Natural Science Foundation of China (No. 21976185). Funding The authors have not disclosed any funding. 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J Agr Food Chem 68:10542-10549. doi: 10.1021/acs.jafc.0c00479 Mamontova EA, Tarasova EN, Mamontov AA, Kuzmin MI, McLachlan MS, Khomutova MI (2007) The influence of soil contamination on the concentration of PCBs in milk in Soberia. Chemosphere 67(9):71-78. doi: 10.1016/j.chemosphere.2006.05.092 Meng J, Hong S, Wang TY, Li QF, Yoon SJ, Lu YL, Giesy JP, Khim JS (2017) Traditional and new POPs in environments along the Bohai and Yellow Seas: An overview of China and South Korea. Chemosphere 169:503-515. doi: 10.1016/j.chemosphere.2016.11.108 Nieuwoudt C, Quinn LP, Pieters R, Jordaan I, Visser M, Kylin H, Borgen AR, Giesy JP, Bouwman H (2009). Dioxin-like chemicals in soil and sediment from residential and industrial areas in central South Africa. Chemosphere 76(6):774-783. doi: 10.1016/j.chemosphere.2009.04.064 Niu LL, Xu C, Yao YJ, Liu K, Yang FX, Tang ML, Liu WP (2013) Status, influences and risk assessment of hexachlorocyclohexanes in agricultural soils across China. Environ Sci Technol 47(21):12140-12147. doi: 10.1021/es401630w Niu LL, Mao SD, Zhou JY, Zhao L, Zhu YQ, Xu C, Sun XH, Sun JQ, Liu WP (2022) Polychlorinated biphenyls (PCBs) in soils from typical paddy fields of China: Occurrence, influencing factors and human health risks. Environ Pollut 307(15):119567. doi: 10.1016/j.envpol.2022.119567 Pena A, Delgado-Moreno L, Rodriguez-Liebana JA (2020) A review of the impact of wastewater on the fate of pesticides in soils: effect of some soil and solution properties. Sci Total Environ 718:134468. doi: 10.1016/j.scitotenv.2019.134468 Sun JT, Pan LL, Li ZH, Zeng QT, Wang LW, Zhu LZ (2018a) Comparison of greenhouse and open field cultivations across China: soil characteristics, contamination and microbial diversity. Environ Pollut 243:1509-1516. doi: 10.1016/j.envpol.2018.09.112 Sun JT, Pan LL, Tsang DCW, Zhan Y, Zhu LZ, Li XD (2018b) Organic contamination and remediation in the agricultural soils of China: A critical review. 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J Hazard Mater 439:129625. doi: 10.1016/j.jhazmat.2022.129625 Tao S, Liu WX, Li Y, Yang Y, Zuo Q, Li BG, Cao J (2008) Organochlorine pesticides contaminated surface soil as reemission source in the Haihe plain, China. Environ Sci Technol 42:8395-8400. doi: 10.1021/es8019676 Tao YM, Meng J, Li QQ, Shi B, Su JG, Guo LX (2020) Sources and distribution characteristics of HCBD in rapid economic development areas. Environ Sci 42(03):1053-1064. doi: 10.13227/j.hjkx.202009084 Teng M, Zhang HJ, Fu Q, Lu XB, Chen JP, Wei FS (2013) Rigation-induced pollution of organochlorine pesticides and polychlorinated biphenyls in paddy field ecosystem of Liaohe River Plain, China. Chinese Sci Bull 58(15):1751-1759. doi: 10.1007/s11434-013-5815-1 Van den Berg M, Birnbaum LS, Denison M, De Vito M, Farland W, Feeley M, Fiedler H, Hakansson H, Hanberg A (2006) The 2005 World Health Organization reevaluation of human and Mammalian toxic equivalency factors for dioxins and dioxin-like compounds. Toxicol Sci 93(2):223-241. doi: 10.1093/toxsci/kfl055 van der Gon HD, van het Bolscher M, Visschedijk A, Zandveld P (2007) Emissions of persistent organic pollutants and eight candidate POPs from UNECE-Europe in 2000, 2010 and 2020 and the emission reduction resulting from the implementation of the UNECE POP protocol. Atmos Environ 41:9245-9261. doi: 10.1016/j.atmosenv.2007.06.055 Wang CF, Gong P, Wang XP, Yang TD (2016) Distribution, environmental behavior, and health risks of polychlorinated biphenyls in the Tibetan agricultural soil and crops. Asian J Ecotoxicol 11(02):339-346. doi: 1673-5897(2016)11:22.0.TX;2-J Wang L, Bie PJ, Zhang JB (2018) Estimates of unintentional production and emission of hexachlorobutadiene from 1992 to 2016 in China. Environ Pollut 238:204-212. doi: 10.1016/j.envpol.2018.03.028 Wang P, Zhang HD, Fu JJ, Li YM, Wang T, Wang YW, Ren DW, Ssebugere P, Zhang QH, Jiang GB (2013) Temporal trends of PCBs, PCDD/Fs and PBDEs in soils from an E-waste dismantling area in East China. Environ Sci-Porc Imp 15(10):1897-1903. doi: 10.1039/c3em00297g Wang XB, Wang XL, Sheng HJ, Wang XZ, Zhao HT, Feng K (2022) Excessive nitrogen fertilizer application causes rapid degradation of greenhouse soil in China. Pol J Environ Stud 31(2):1527-1534. doi: 10.15244/pjoes/143293 Wu CW, Sun JQ, Zhang AP, Liu WP (2012) Dissipation and enantioselective degradation of plant growth retardants paclobutrazol and uniconazole in open field, greenhouse, and laboratory soils. Environ Sci Technol 47:843-849. doi: 10.1021/es3041972 Wu RL, He W, Li YL, Li YY, Qin YF, Meng FQ (2020) Residual concentrations and ecological risks of neonicotinoid insecticides in the soils of tomato and cucumber greenhouses in Shouguang, Shandong province, East China. Sci Total Environ 738, 140248. doi: Xu C, Niu LL, Zou DL, Zhu SY, Liu WP (2019) Congener-specific composition of polychlorinated biphenyls (PCBs) in soil-air partitioning and the associated health risks. Sci Total Environ 684:486-495. doi: 10.1016/j.scitotenv.2020.140248 Yang LQ, Huang BA, Hu WY, Chen Y, Mao MC (2013) Assessment and source identification of trace metals in the soils of greenhouse vegetable production in eastern China. Ecotoxicol Environ Saf 97:204-209. doi: 10.1016/j.ecoenv.2013.08.002 Zeeb BA, Amphlett JS, Rutter A, Reimer KJ (2006) Potential for phytoremediation of polychlorinated biphenyl-(PCBs)contaminated soil. Int J Phytoremediation 8(3):199-221. doi: 10.1080/15226510600846749 Zhang HB, Luo YM, Teng Y, Wan HF (2013) PCB contamination in soils of the Pearl River Delta, South China: levels, sources, and potential risks. Environ Sci Pollut Res 20:5150-5159. doi: 10.1007/s11356-013-1488-1 Zhang HY, Wang YW, Sun C, Yu M, Gao Y, Wang T, Liu JY, Jiang GB (2014) Levels and distributions of hexachlorobutadiene and three chlorobenzenes in biosolids from wastewater treatment plants and in soils within and surrounding a chemical plant in China. Environ Sci Technol 48(3):1525-1531. doi: 10.1021/es405171t Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2297064","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":161115733,"identity":"0ebf00bb-d688-424b-b510-53481fb0de12","order_by":0,"name":"Li Yaru","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAArUlEQVRIiWNgGAWjYFAC5oYDHxiYQSwDYrUwNhycQbIWZh6StBjcPth42KbMOrGBvXmbBEPNHSK0nEtsOJxzLj2xgedYmQTDsWdEaDnD2HA4t+1wYoNEjpkEkE2kFkuQFvk3pGhhBNvCQ6QWSaCWgz3n0o3beNKKLRKOEaGF7wzz4Q8/yqxl+9kPb7zxoYYILQoHQCQbGDEwJBDWwMAg3wDVMgpGwSgYBaMAJwAAF4o8QtQ+Q1wAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-6197-0391","institution":"Qingdao University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Yaru","suffix":""},{"id":161115734,"identity":"34f09d09-02ec-4b8d-8bd9-59fd648e56ca","order_by":1,"name":"Jing Lan","email":"","orcid":"","institution":"Qingdao University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Lan","suffix":""},{"id":161115735,"identity":"74761c68-739f-4adc-8ca0-265a595fe871","order_by":2,"name":"Zongshan Zhao","email":"","orcid":"","institution":"Qingdao University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zongshan","middleName":"","lastName":"Zhao","suffix":""}],"badges":[],"createdAt":"2022-11-21 12:39:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2297064/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2297064/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":30628990,"identity":"32e16bcb-ac1f-4b9e-b629-a5088f6d0d43","added_by":"auto","created_at":"2022-12-21 15:06:29","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":613237,"visible":true,"origin":"","legend":"\u003cp\u003eSpatial distributions of PCBs and HCBD in greenhouse and open-field soils in the investigated regions in mainland China. In most regions, the concentrations of PCBs and HCBD in greenhouse soils are higher than in open-field soils.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/fecb48f6a0a47ea872465cf7.jpeg"},{"id":30628994,"identity":"39881f70-ad5a-491e-bc65-496460b3ab6c","added_by":"auto","created_at":"2022-12-21 15:06:30","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":226022,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of soil physicochemical properties and other pollutants on the levels of PCBs and HCBD in greenhouse soils and open-field soils through redundancy analysis.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/2b13c9726014fc47895ab31e.jpeg"},{"id":30628995,"identity":"14fac85f-3861-475e-ad12-715ccd824053","added_by":"auto","created_at":"2022-12-21 15:06:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":198788,"visible":true,"origin":"","legend":"\u003cp\u003eResults of principal component analysis (PCA) of PCBs homologous: (a) greenhouse soils in north China; (b) open-field soils in north China; (c) greenhouse soils in east China; (d) open-field soils in east China.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/c937b8632f3d98d6b5711a8e.png"},{"id":30628989,"identity":"bf60c7fa-9603-4fbb-81fc-ca2fae2e10fe","added_by":"auto","created_at":"2022-12-21 15:06:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":132449,"visible":true,"origin":"","legend":"\u003cp\u003eComparison the non-cancer exposure risk (a) and carcinogenic exposure risks (b) of PCBs, and the non-cancer exposure risk (c) and carcinogenic exposure risks (d) of HCBD to adults and children in greenhouse and open-field soils, respectively. The health risks of ΣPCBs in open-field soils were higher than in greenhouse soils, especially for the carcinogenic risks to children (\u0026gt; 10\u003csup\u003e-6\u003c/sup\u003e).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/ab0cb313bc470d87ad0bbc21.png"},{"id":38560216,"identity":"ac32335f-6a9e-4472-9683-fc2cf3393273","added_by":"auto","created_at":"2023-06-14 19:38:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":824451,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/ab3099fe-0c7b-4288-a437-a5ab0f04cd8d.pdf"},{"id":30628993,"identity":"a1800855-8ef1-4b9d-82e2-183b82ce7309","added_by":"auto","created_at":"2022-12-21 15:06:29","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":510097,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-2297064/v1/ff28fd13fff8b46a95b5d680.docx"}],"financialInterests":"","formattedTitle":"Contamination of polychlorinated biphenyls and hexachlorobutadiene in greenhouse and open-field agricultural soils across China","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAgricultural soil for crop production is generally used under two cultivated models, open-fields and greenhouses. Especially for greenhouses, it is a technology-based approach, which have been widely popularized and applied in fields of vegetables, fruits and flowers by creating a micro-scale environment (Wu et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). It has been characterized by strong risk resistance, highly concentrated knowledge and technology, and multiple effects in the economy, society and ecology (Kumar et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). As a consequence, they have been supported by the Food and Agriculture Organization (FAO) of the United Nations worldwide (Khoshnevisan et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Hanan \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Since its first introduction into China in late 1970s, the total area of greenhouse cultivation projects had reached 4.708\u0026nbsp;million hectares in 2019 (Yang et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The extensive applications of greenhouse enhance resource utilization and land productivity, and further improve the economic efficiency. However, the improved yields and the shortened agricultural production cycle are achieved by inputting plenty of material and energy, which would lead to severe soil contamination and hence pose adverse effects to the environment (Badrudin et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAgricultural soil is a major source and sink for persistent organic pollutants (POPs) (Tao et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). For example, POPs can enter agricultural soils through irrigation wastewaters, chemical fertilizer, atmospheric deposition and so on (Khuman et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Pena et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Once entering soils, some POPs are more persistent in greenhouse soils than in open-field soils and present different contaminated statuses (Lehmann et al. 2015; Wu et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Previous studies reported that higher contaminations of POPs were found in greenhouse soils than in open-field soils, such as pyrethroids, atrazine, organophosphorus pesticides (OPPs), phthalate esters (PAEs) and polycyclic aromatic hydrocarbon (PAHs) (Sun et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e; Dou et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e). This result was likely caused by the limited environmental behaviors of POPs in greenhouses, such as volatilize from soil to air (Ali et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Xu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Furthermore, compared with in open-fields, there were more significant effects of human activities on the contamination of POPs in greenhouse soils, via the soil properties, heavy metals and so on (Li et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e). Therefore, the contamination status, affected factors and environmental risk of these pollutants in greenhouses should be more concerned.\u003c/p\u003e \u003cp\u003ePolychlorinated biphenyls (PCBs) and hexachlorobutadiene (HCBD) belonging to persistent organic pollutants (POPs), have been widely utilized in various areas, such as heat-exchange fluids, dielectric, pesticide additives, transformers, herbicides, and fungicides, etc. (Breivik et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; van der Gon et al. 2007; Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Luo et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Due to improper disposal and environmental migration, they have been frequently detected in almost all environmental medium on the earth. For PCBs, in the Pearl River Delta, the concentration ranged from 0.30 to 202.00 ng/g with predominant homologues of low-chlorinated biphenyls (Zhang et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Even in some remote areas such as Siberia and Tibet, the occurrence of PCBs has also been reported (Mamontova et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Wang et al. 2016). For HCBD, among China\u0026rsquo;s three economic hubs, namely, Yangtze River Delta, Beijing-Tianjin-Hebei region and Pearl River Delta, the Yangtze River Delta showed the highest soil contents of HCBD (8.47 ng/g dry weight) (Tang et al. 2016; Sun et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2018c\u003c/span\u003e). With the high bioaccumulation, semi-volatile, high toxicity, and teratogenic, carcinogenic, and mutagenic effects, PCBs and HCBD can easily enter the crops, and present adverse effects to human health and ecological environment. As a result, PCBs were classified as A Class iiA human carcinogen by the International Agency for Research on Cancer and HCBD has also been listed in Annex A of the Stockholm Convention, respectively (Zeeb et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Though the contamination of PCBs and HCBD has already been reported many times in some developed regions, such as the Yangtze River Delta, the Pearl River Delta, the Liaohe River and the southeast China, and others (Fu et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Teng et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tao et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), there is only a few reports with various pollution levels on these POPs in greenhouse.\u003c/p\u003e \u003cp\u003eDue to the popularization of greenhouse throughout China, the disorderly discharge of pollutants and the physical isolation inside and outside of the greenhouse, greenhouse soils are likely to undergo different pollutions from open-field soils, even facing more serious pollution and ecological risks. In this study, we aimed to identify the typical distribution characteristics of soil PCBs and HCBD, and compare the pollution differences between two land farming patterns of greenhouse and open-field soils across China. This work was conducted by (1) characterizing the contamination status and spatial distribution of PCBs and HCBD in greenhouse and open-field soils, (2) analyzing the correlation between pollutants and soils physicochemical properties, and the potential sources of pollutants, (3) evaluating the human health risks of pollutants in greenhouse and open-field soils. These results would provide a comprehensive assessment of PCBs and HCBD in greenhouse and open-field soils across China.\u003c/p\u003e"},{"header":"2. Materials And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Sample collection\u003c/h2\u003e \u003cp\u003eIn total, 51 pairs of surface soil samples (0\u0026ndash;20 cm) were collected from the greenhouses and nearby open vegetable fields in 20 provinces, municipalities and autonomous regions across China from November 2014 to February 2015. The investigated 20 provinces, municipalities and autonomous regions with two or three sampling sites included Heilongjiang (HLJ), Jilin (JL), Liaoning (LN), Beijing (BJ), Hebei (HB), Shanxi (SX), Inner Mongolia (IM), Jiangsu (JS), Shandong (SD), Zhejiang (ZJ), Shanghai (SH), Hunan (HN), Jiangxi (JX), Guangdong (GD), Qinghai (QH), Gansu (GS), Xinjiang (XJ), Yunnan (YN), Sichuan (SC), and Tibet (TB). The detailed information of the sampling sites, including GPS location, crop cultivation, cultivation age, main fertilizer and soil type, was listed in Table S1. For each sample site, soils were collected from five cores using a bamboo scoop and they were later composited to form a single sample. Then the soil samples were packed with aluminum foil, sealed in Kraft bags, and immediately delivered to the laboratory on ice. The remaining soil was stored at -20\u0026deg;C for the analysis of the soil properties and the target contaminants (Sun et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Sample pretreatment\u003c/h2\u003e \u003cp\u003eThe extraction and cleanup procedures for PCBs were adopted from the reported methods (Wang et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). All freeze-dried samples were ground and sieved through a stainless steel 75-mesh sieve. A portion of soil samples (5 g) were spiked with recovery surrogate PCB-65, followed by ultrasonic extraction for 30 min using hexane/dichloromethane (1:1 v/v, 40 mL). After three extractions, the extracts were concentrated to 1 mL, and then subjected to cleanup by a multilayer silica column as follows (from bottom to top): 1 g silica, 4 g basic silica (1.2%, w/w),1 g silica, 8 g acidic silica (30%, w/w), 2 g silica, and 4 g anhydrous sodium sulfate. Before used, the column was pre-washed with hexane. The extract was eluted with 100 mL of hexane, and then was concentrated by rotary evaporation to a final volume of 200 \u0026micro;L prior to instrumental analysis.\u003c/p\u003e \u003cp\u003eThe extractions of HCBD were also adopted from the reported methods (Zhang et al. 2014). A portion of soil samples (10 g) were spiked with surrogate standard 2,4,5,6-tetrachlori-\u003cem\u003em\u003c/em\u003e-xylene, followed by ultrasonic extraction 30 min using a mixture solvent of dichloromethane/hexane (1:1, v/v, 30 mL). The procedure was repeated two times, and all the extract was collected. Then the extract was concentrated to 1 mL by rotary evaporation and was cleaned up by a multilayer silica-Florisil composite column as follows (from bottom to top): 6 g Florisil, 4 g activated silica gel, and 5 g anhydrous sodium sulfate. Similarly, the columns were pre-washed with 50 mL hexane. Finally, the extract was eluted with 150 mL of petroleum ether and was thereafter concentrated to 200 \u0026micro;L prior to instrumental analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Chemical analysis\u003c/h2\u003e \u003cp\u003eIn all samples, the target PCBs included 12 dioxin-like PCBs (DL-PCBs) (including PCB-77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189), and six indicator PCBs (including PCB-28, 52, 101, 138, 153, and 180) (Table S2). The quantitative analysis of PCBs and HCBD were performed on gas chromatography/mass spectrometry (GC/MS) (7890B/5977A, Agilent Technologies, Santa Clara, CA, USA) with an electron ionization source. A DB-5 MS capillary column was used (30 m \u0026times; 0.25 mm i.d. with 0.25 mm film thickness). All data were obtained in the selective ion monitoring (SIM) mode. High purity helium was used as carrier gas with a flow rate of 1.0 mL/min. Oven temperature program for PCBs was as follows: initial column temperature at 80 ℃ for 3 min, ramped to 150 ℃ at 15 ℃/min and held for 2 min, increased to 270 ℃ at 2.5 ℃/min and held for 3 min, increased to 300 ℃ at 15 ℃/min and held for 5 min. Another program for HCBD was as follows: initial oven temperature at 80\u0026deg;C for 2 min and increased to 140\u0026deg;C at a rate of 10\u0026deg;C/min linearly, then ramped to 280\u0026deg;C at 4\u0026deg;C/min and held for 5 min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Environmental factors and pollution sources analysis\u003c/h2\u003e \u003cp\u003eIn order to determine the correlation of environmental factors with the levels of PCBs and HCBD, the data including the soil physicochemical properties and the content of co-existing pollutants for these soil samples reported by Sun et al. (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e) has been extracted in this paper. The soil physicochemical properties including soil moisture (SM), soil total carbon (STC), soil total phosphor (STP), soil total nitrogen (STN), and pH value were measured. The co-existing pollutants were quantified, including POPs (organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs)) and heavy metals (cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb)). Redundancy analysis and correlation analysis were carried out to evaluate the correlations of these factors. And principal component analysis (PCA) on soil PCBs has been performed to identify their mainly emission sources using.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Health risk assessment\u003c/h2\u003e \u003cp\u003eThe exposure noncancer and carcinogenic risk of PCBs and HCBD to human health were evaluated using the methods recommended by the U.S. Environmental Protection Agency (EPA). Generally, there are three types of exposure pathways, including soil ingestion, dermal contact and inhalation. By considering these pathways, two primary indices were determined to assess the health risk, namely the hazard index (HI) and carcinogenic risks. The methods employed to calculate the two primary indices were presented in SI. The relative parameters were shown in Tables S3 and S4. The noncancer risks of chemical contaminants are considered as relatively high when HI\u0026thinsp;\u0026gt;\u0026thinsp;1.0, while the risk may be negligible when the value of HI is below 1.0. The carcinogenic risks of chemical contaminants are considered to be very low when the risk value is below 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, low in the range of 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e and 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e, moderate from 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, high from 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and very high when it is over 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results And Discussions","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Levels and spatial distributions of pollutants\u003c/h2\u003e \u003cp\u003eAll the contents of PCBs and HCBD were presented on a dry weight (dw) basis. At a national-scale, the PCBs contents ranged from \u0026lt;\u0026thinsp;LOD to 241.22 ng/g with the mean contents of 62.33 ng/g in greenhouse soils, and ranged from \u0026lt;\u0026thinsp;LOD to 192.89 ng/g with the mean contents of 51.09 ng/g in open-field soils (Table S5 and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Furthermore, the detection frequencies of PCBs were 84.31% in greenhouse soils and 76.47% in open-field soils. In contrast, the contamination of PCBs in greenhouse soils was more serious than in open-field soils. Different from their contamination levels and detection frequencies, the compositions of total PCBs (ΣPCBs) were similar in greenhouse and open-field soils. The major PCB homologue was tetra-CBs, followed by penta-CBs and hexa-CBs, which took over \u0026gt;\u0026thinsp;80% of ΣPCBs in greenhouse and open-field soils (Figure S1). The similar compositions indicated the possible homology of greenhouse and open-field soil\u0026rsquo;s pollution from human activities. Totally, the ΣPCBs levels in this study was at the same levels as previous reports in China, such as in agriculture soils of south Jiangsu and Taiyuan (Zhang et al. 2017; Sun et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn order to further identify the distribution characteristics, all the soil samples were classified as seven regions in China, including northeastern (HLJ, JL and LN), northwestern (XJ, GS and QH), northern (BJ, IM, SX and HB), central (HN, JX), eastern (SD, JS, ZJ and SH), southern (GD), and southwestern (YN, TB and SC). As shown in Table S6, the north and south China showed higher PCBs levels in open-field soils, especially in IM, BJ and HB, while the north, southwest and south China presented higher PCBs levels in greenhouse soils. But it should be noted that the PCBs levels in greenhouse soils were higher than in open-field soils in most regions, which may be attributed to the limited soil-air exchange in greenhouse (Gao et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Hu et al. 2021). Usually, the polluted sources of soil PCBs are mainly from wastewater discharge, solid waste leakage, waste incineration, atmospheric deposition, etc. (Cetin et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). And the source/sink tendency of soil PCBs depended on their volatility. For example, the low-chlorinated PCBs tended to volatilize from soil, and high-chlorinated PCBs tended to sink into soil, until reached the balanced state in open-field soils (Ali et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Xu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Therefore, the volatility was inhibited by the limited soil-air exchange due to the physical isolation in greenhouse.\u003c/p\u003e \u003cp\u003eFor all the soil samples, the HCBD contents ranged from 0.85 to 24.18 ng/g with the mean contents of 8.19 ng/g in greenhouse soils, and ranged from \u0026lt;\u0026thinsp;LOD to 20.19 ng/g in greenhouse and open-field soils with the mean contents of 6.52 ng/g in open-field soils (Table S5 and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Compared with PCBs, though HCBD showed lower contamination levels, the detection frequencies of HCBD were higher both in greenhouse (100%) and open-field soils (96.08%). Furthermore, the contamination of HCBD in greenhouse soils were also higher than in open-field soils in most regions, which also may be attributed to the limited soil-air exchange in greenhouse (Ali et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Xu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) (Table S6). Totally, the HCBD contents in this work were at comparable levels to that in agricultural soil of east China (Tang et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), the Yangtze River Delta (Sun et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2018c\u003c/span\u003e) and southwest China (Tang et al. 2016). According to the investigation results of soil PCBs and HCBD, it could be easily found that both of them presented their unique characteristics in spatial distributions, such as more serious pollution in greenhouse of north China. The reasons may be attributed to their pollution sources and regional environmental factors (including other pollutants and soil physicochemical properties) (Nieuwoudt et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Habibullah-Al-Mamun et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Niu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Correlation between pollutants and environmental factors\u003c/h2\u003e \u003cp\u003eThe linkages between pollutants and environmental factors in greenhouse and open-field soils were obtained through redundancy analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e2\u003c/span\u003e). At a national-scale, the positive correlations were only obtained between OCPs and PCBs (r\u0026thinsp;=\u0026thinsp;0.298, p༜0.05) in greenhouse soils (Table S7), indicating that they were likely to share the same pollution paths, such as irrigation (Meng et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The positive correlations between Pb and PCBs (r\u0026thinsp;=\u0026thinsp;0.311, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) were also obtained in open-field soils (Table S8), suggesting that they were likely to share same pollution sources, such as industrial metal smelting (Diop et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). But there was no any environmental factor correlated with HCBD in greenhouse and open-field soils (Table S7, S8). In this study, no correlation between soil PCBs and properties can be attributed to the variety of pollution levels and region distributions across China (Niu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Meanwhile, there were no correlation between soil HCBD and other pollutants/soil properties.\u003c/p\u003e \u003cp\u003eTo further study the relationships between pollutants and environmental factors, the correlation analysis between PCBs homologues and soil properties were also carried out in some economically developed regions, such as the north China and the east China. In north China, ΣPCBs were correlated with tetra-CBs (r\u0026thinsp;=\u0026thinsp;0.907, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in greenhouse soils; r\u0026thinsp;=\u0026thinsp;0.830, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in open-field soils) and hexa-CBs (r\u0026thinsp;=\u0026thinsp;0.609, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 in greenhouse soils; r\u0026thinsp;=\u0026thinsp;0.881, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in open-field soils) (Table S9, S10). In east China, the total PCBs were correlated with tetra-CBs (r\u0026thinsp;=\u0026thinsp;0.921, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in greenhouse soils; r\u0026thinsp;=\u0026thinsp;0.904, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in open-field soils) and penta-CBs (r\u0026thinsp;=\u0026thinsp;0.860, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01 in greenhouse soils; r\u0026thinsp;=\u0026thinsp;0.569, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 in open-field soils) (Table S11, S12). The correlations between ΣPCBs and homologues verified the same sources/paths for greenhouse and open-field soils pollution in these regions (Hu et al. 2021).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3. Regional source analysis of pollutants\u003c/h2\u003e \u003cp\u003eTraceability analysis on soil PCBs in north and east China has been performed to identify their mainly emission sources using principal component analysis (PCA). The compositions of PCBs homologues were also compared with the Aroclor series products, including Aroclor 1016, 1221, 1232, 1242, 1248, 1254, 1260, 1262. Factors with eigenvalues greater than 1.0 were extracted and 3 principal components (\u0026gt;\u0026thinsp;80% variance) were acquired. In north China, the compositions of PCBs were less consistent with the Aroclor series products (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). In both greenhouse and open-field soils, hexa-CBs and hepta-CBs presenting larger loading in PC1 (\u0026gt;\u0026thinsp;0.53), were likely attributed to the recycling and disposal of electrical equipment containing PCBs (Li et al. 2019). Tetra-CBs and tri-CBs showing larger loading in PC2 (\u0026gt;\u0026thinsp;0.48), corresponded to the domestic coal, wood burning emissions, non-ferrous metal smelting and regeneration, and high temperature incineration of industrial as well as municipal waste (Lee et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nieuwoudt et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Habibullah-Al-Mamun et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Penta-CBs with loading of \u0026gt;\u0026thinsp;0.83 in PC3 were mainly from oil additives and metallurgy industry (Ba et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This result revealed the silimar pollution sources of greenhouse soils and open-field soils in north China.\u003c/p\u003e \u003cp\u003eIn east China, the compositions of PCBs were similar to the Aroclor series products in partial sample sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). For example, in both greenhouse and open-field soils of Shanghai, PCBs (G1, O1, O2) possibly derived from Aroclor 1242, which was identical with the result of Jiang et al. (2010). In rest greenhouse soils, tri-CBs and tetra-CBs showed larger loading in PC1 (\u0026gt;\u0026thinsp;0.53), indicated the mainly sources of the domestic coal, wood burning emissions, high temperature incineration of industrial and municipal waste, etc. (Lee et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Nieuwoudt et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Habibullah-Al-Mamun et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). And hepta-CBs and hexa-CBs showed larger loading (\u0026gt;\u0026thinsp;0.61) in PC2 and PC3, indicating the source from the recycling and disposal of electrical equipment containing PCBs (Li et al. 2019). In open-field soils, hexa-CBs and hepta-CBs showed larger loading in PC1 (\u0026gt;\u0026thinsp;0.42) in open-field soils, and hexa-CBs and tri-CBs presented larger loading (\u0026gt;\u0026thinsp;0.53) in PC2 and PC3. This indicated that the recycling and disposal of electrical equipment containing PCBs was the main source. Previous reports have indicated that the e-waste dismantling areas distributed in east China, such as Taizhou, were one of the most important sources for soil PCBs (Sun et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4. Human health risk assessments\u003c/h2\u003e \u003cp\u003eThe health risks of pollutants in greenhouse and open-field soils were estimated via soil ingestion, dermal contact and inhalation exposure pathways (Niu et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Li et al. 2021b). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the non-cancer exposure risks of PCBs to children and adults in open-field soils were both higher than in greenhouse soil. Meanwhile, the non-cancer exposure risks of PCBs to children were higher than to adults both in greenhouse and open-field soils. The average HI values of PCBs were 0.022 for adults and 0.222 for children in greenhouse soils, and 0.030 for adults and 0.274 for children in open-field soils, respectively. In all these samples, lower HI values (\u0026lt;\u0026thinsp;1.0) for adults indicated the negligible non-cancer risks to adults. But in some provinces, such as BJ, XJ, SD and GD, higher HI values (\u0026gt;\u0026thinsp;1.0) for children both in greenhouse and open-field soils indicated the potential non-cancer risks of PCBs to children were not negligible. Among PCBs homologues, the average HI value of PCB-126 was the highest in greenhouse soils (HI\u0026thinsp;=\u0026thinsp;0.010 for adults, HI\u0026thinsp;=\u0026thinsp;0.121 for children) and in open-field soils (HI\u0026thinsp;=\u0026thinsp;0.016 for adults, HI\u0026thinsp;=\u0026thinsp;0.146 for children), followed by PCB-81 (Figure S2). For HCBD, all the HI values were below 1.0 for adults and children, implying the negligible non-cancer risks in soil samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eThe carcinogenic risks of PCBs to children were higher than that to adults (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). In greenhouse soils, the average values of PCBs to adults and to children were 8.37 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e and 1.38 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e, respectively. Compared with in greenhouse soils, the carcinogenic risks of PCBs to children and adults in open-field soils presented higher risks (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). In open-field soils, the average values of PCBs to adults and children were 1.03 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e and 2.13 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e respectively. And the values in large number of samples (25.5% to adults and 37.3% to children) were between 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e and 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e, implying relatively low carcinogenic risks to human beings. Among these PCB homologues, the most significant carcinogenic risks were also attributed to PCB-126 (Figure S1). In contrast, the carcinogenic risks of HCBD to adults and children were both below 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e in greenhouse and open-field soils (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ed), corresponding to the negligible carcinogenic risks.\u003c/p\u003e \u003cp\u003eIn this study, the non-cancer risks and carcinogenic risks of PCBs were similar to the Yellow River irrigation area and Lanzhou soils (Ding et al. 2018; Li et al. 2021b). However, the different patterns were found between the health risks and PCBs levels. For example, samples from IM presented the higher PCBs levels and the lower health risks in greenhouse soils. The reason could be explained by different toxic equivalency factor (TEF) of measured PCBs, which order was PCB-126\u0026thinsp;\u0026gt;\u0026thinsp;PCB-169\u0026thinsp;\u0026gt;\u0026thinsp;PCB-81\u0026thinsp;\u0026gt;\u0026thinsp;PCB-77\u0026thinsp;\u0026gt;\u0026thinsp;other PCBs (Van den et al. 2006; Niu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Compared with that in open-field, low-chlorinated (\u0026le;\u0026thinsp;4) PCBs presented increasing ratios in ΣPCBs in greenhouse soils, corresponding to their lower risks. This might be attributed to the faster dechlorination of high-chlorinated PCBs in greenhouse, as greenhouse environment factors (moisture and temperature) were more favorable for microbial growth (Dou et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Tao et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, 51 pairs of surface soil samples collected from 20 regions were analyzed to investigate the contamination status of PCBs and HCBD in both greenhouse and open-field soils across China. At a national-scale, the PCBs and HCBD pollutions in greenhouse soils presented a slightly higher level than in open-field soils as a result of the limited air-soil exchange in greenhouse. Positive correlations between ΣPCBs and PCBs homologues indicated their similar sources/paths in greenhouse and open-field soils. The regional source analysis showed that the soil PCBs sources consisted of domestic coal, wood burning emissions, disposal of electrical equipment, oil additives and metallurgy industry. Meanwhile, the low-toxicity PCBs in greenhouse soils contributed to the lower risks when comparing with that in open-field soils. This study provided valuable information to understand the contamination status, sources and risks of PCBs and HCBD in greenhouse and open-field soils when changing the farmland farming modes, especially for greenhouse cultivation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was financially supported by the Natural Science Foundation of Shandong Province (ZR2022QB167) and the National Natural Science Foundation of China (No. 21976185).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have not disclosed any funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors agree with the publication of this paper in Environmental Chemistry Letters.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYaru Li: Writing - Investigation, Original Draft, Editing and Writing.\u003c/p\u003e\n\u003cp\u003eJing Lan: Formal analysis and Review.\u003c/p\u003e\n\u003cp\u003eZongshan Zhao: Editing and Review.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cbr\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAli U, Syed JH, Mahmood A, Li J, Zhang G, Jones KC, Malik RN (2015) Influential role of black carbon in the soil-air partitioning of polychlorinated biphenyls (PCBs) in the Indus River Basin, Pakistan. 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Environ Sci Technol 48(3):1525-1531. doi: 10.1021/es405171t\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Polychlorinated biphenyls, Hexachlorobutadiene, Agricultural soils, Contamination status, Contaminated sources, Health risks","lastPublishedDoi":"10.21203/rs.3.rs-2297064/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2297064/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCombined with the physical isolation feature of greenhouse, the popularization of greenhouse throughout China makes the pollution of greenhouse soils more noteworthy as a result of its high yielding food exposed to human beings. Here, a national-scale survey was conducted to evaluate the contamination status, contaminated sources and human health risks of polychlorinated biphenyls (PCBs) and hexachlorobutadiene (HCBD) in greenhouse and open-field soils of 20 regions across China. The PCBs contents ranged from \u0026lt;LOD to 673.78 ng/g with the mean content of 77.38 ng/g in greenhouse soils and ranged from \u0026lt;LOD to 552.53 ng/g with the mean content of 61.90 ng/g in open-field soils. The HCBD contents ranged from 0.85 ng/g to 24.18 ng/g with the mean content of 8.33 ng/g in greenhouse soils and ranged from \u0026lt;LOD to 20.19 ng/g with the mean content of 6.39 ng/g in open-field soils. Among divided seven regions, higher levels of PCBs in greenhouse and open-field soils were found in north and south China. Furthermore, in most regions, correlation analysis indicated that soil PCBs in greenhouse and open-field were likely from the same emission sources. Higher levels of soil pollutants in greenhouse than in open-field may be contributed to the limited air-soil exchange. Compared with higher levels of ΣPCBs in greenhouse soils, the health risks of ΣPCBs in open-field soils were higher due to the higher percentages of high-toxicity PCBs, especially for the carcinogenic risks to children (\u0026gt; 10\u003csup\u003e-6\u003c/sup\u003e). This study provided a full insight into the contamination status and risks of PCBs and HCBD when guiding greenhouse agriculture activities.\u003c/p\u003e","manuscriptTitle":"Contamination of polychlorinated biphenyls and hexachlorobutadiene in greenhouse and open-field agricultural soils across China","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-12-21 15:06:24","doi":"10.21203/rs.3.rs-2297064/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"fbb4cb48-d1e8-49e5-9dc8-044c158372c2","owner":[],"postedDate":"December 21st, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-06-14T19:38:05+00:00","versionOfRecord":[],"versionCreatedAt":"2022-12-21 15:06:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2297064","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2297064","identity":"rs-2297064","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}