Environ Sci Pollut Res DOI 10.1007/s11356-015-4126-2
RESEARCH ARTICLE
Changes of polybrominated diphenyl ethers and polychlorinated biphenyls in surface soils from urban agglomeration of the Yangtze River Delta, in China between 2003 and 2012 Shuang-Xin Shi & Ye-Ru Huang & Li Zhou & Li-Fei Zhang & Liang Dong & Wen-Long Yang & Xiu-Lan Zhang
Received: 1 September 2014 / Accepted: 12 January 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Surface soil samples were collected from urban agglomeration of the Yangtze River Delta (YRD), China in 2003 and 2012, respectively. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were analyzed to determine if there were any changes in their levels and compositional profiles between the two sampling years. The concentrations of Σ 8PBDEs ranged from 0.553 to 13.0 μg kg−1(with the mean of 3.31 μg kg−1) in the 2003 samples and from 1.01 to 43.2 μg/kg (with the mean of 10.0 μg kg−1) in the 2012 samples. The concentrations of Σ32PCBs ranged from 0.301 to 3.29 μg kg−1(with the mean of 1.01 μg kg−1) in the 2003 samples and from 0.205 to 3.96 μg/kg (with the mean of 0.991 μg kg−1) in the 2012 samples. The comparisons between the 2012 and 2003 data showed that PBDEs concentrations increased over the years, but PCB concentrations did not change much. BDE-209 was the major BDE congener in both the 2003 and 2012 samples, indicating that the dominant PBDE mixture production and usage in the YRD had been the commercial deca-BDE mixture. Investigation of the PBDE congener profiles indicated that there had been new input of octa-BDEs in this region in recent years. Little change was found for the pattern of PCBs congener profiles between 2 years’ samples. As such, spatial distributions of PBDEs or PCBs in surface soil samples reflected a gradient (from high to low) from the central cities Responsible editor: Hongwen Sun S.BDE-153(81.8 %)>BDE-154(66.7 %)>BDE-100 (51.5 %), while in the 2003 samples, followed a pattern of BDE-209 (100 %)>BDE-99 (88.9 %)>BDE-47 (77.8 %)> BDE-28 (58.3 %)>BDE-183=BDE-154 (27.8 %)>BDE153=BDE-100(25.0 %). The detection frequency for BDE209 was 100 % in both samples, indicating that BDE-209 was already a ubiquitous environmental pollutant in the YRD soils almost 10 years ago. However, the frequencies of the lowbrominated congeners and BDE-183 detected in the 2012 samples were higher than those in the 2003 samples, suggesting that these compounds have been becoming widespread environmental pollutant in soils of the YRD in recent years. Some PCB congeners, including PCB-8, 166, 156, 126, 114, 189, and169 were not detected in all samples, while most other PCB congeners were detected in the samples, especially for PCB-28, 52, 49, 101, 118, 153, 138, and 180, for which detection frequency were higher than 80.6 % in all samples. Similar PCB congeners and detection frequency were found in the 2003 and 2012 samples. Descriptive statistics for concentrations of BDE-209, Σ32PCBs, and Σ7PBDEs in the samples are summarized in Table 1. To establish if there were any changes of the PBDE and PCB concentrations between the 2003 and 2012 samples, independent sample group T tests were applied. The results show that the data obtained followed a normal distribution and the concentrations of Σ7PBDE and BDE-209 in the 2012 soils were significantly higher than in the 2003 soils with P0.05) between BDE-153 and BDE183 in the 2012 samples, indicating the possible additional input from octa-BDE sources in this region. However, because BDE-153 had low detection frequency (27.8 %) and low concentration in the 2003 samples, it is inappropriate to reach robust conclusions based on such data. It has been noted that BDE-47and 99 are major congeners of penta-BDE products (la Guardia et al. 2006), with the BDE47/BDE-99 ratios of 1.05 in Bromkal 70-5DE and 0.76 in DE71. Because BDE-99 has a higher KOA (octanol-air partition coefficients) relative to BDE-47, the ratio of BDE-47 to BDE99 usually falls below a value of 0.8 in soils (Harrad and Hunter. 2006). The ratio of our 2003 data was 0.73±0.34, indicating that there might have been input from penta-BDE sources in 2003. However, the ratio obtained from the 2012 data was1.12±0.33, different from that in penta-BDE product and background soils reported in other literatures (Harrad and Hunter. 2006). In addition, the proportions of BDE-28 and BDE-154 in the 2012 samples were higher than those in penta-BDE products. Such difference might be a result from BDE congener fractionation changing during transportation, mixing, microbial degradation, or photodegradation from higher brominated congeners as well as depositional mechanisms in the environment. Another plausible explanation for
this compositional profile might be indicate that a Bspecific penta-BDE formulation^ has been produced or used in this region over the recent years (Qiu et al. 2010). But, these explanations are speculative and a more detailed investigation of penta-BDE sources in this region should be carried out in the future. PCBs The compositional patterns of PCBs in soils have changed little over the passing 9 years. The major homolog in all samples was penta-PCBs, followed by tetra-PCBs and hexaPCBs. The proportions of lighter weighted molecular PCBs (di-, tri-, tetra-PCB) in the 2003 and 2012 samples were 33.6 and 29.8 %, respectively. This was due to the fact that lower chlorinated congeners are more mobile and thus have permeated deeper into the soil (Backe et al. 2004). Another factor could be that the lower congeners are more volatile and hence more likely to diffuse into the atmosphere (Backe et al. 2004). Principal component analysis (PCA) was used to evaluate the distribution pattern of PCBs and to determine their possible origins. Homolog from di-PCBs to hepta-PCBs were selected as variables for principal component analysis. The first principal component (PC1) accounted for 46.5 % of the variability in the 2003 data, while the second principal component (PC2) accounted for 22.9 %. PC1 had higher loading for the homolog di, tri-, and tetra-PCBs, which were mostly associated with lower chlorinated PCBs. PC2 had higher loading for the higher chlorinated congeners, namely, homolog hexa- and hepta-PCBs. Similar results were found in the 2012 data, with PC1 and PC2 accouting for 46.5 and 29.3 % of the variability, respectively. The principal component scores for each site and PCBs mixtures are displayed in Fig. 3 It can be observed from the loading plot that several samples as well as Aroclor1254 constituted similar scores of PC1 and
Environ Sci Pollut Res
Fig. 3 Score plot of PCA for the 2003 soil samples from the Yangtze River Delta, China
PC2. The possible source of PCBs in these samples might be the emission from Aroclor1254. In China, Aroclor1242 and Aroclor 1254 were the two major PCBs mixture, with production of 9000 and 1000 tons prior to 1974, respectively (Xing et al. 2005). These soil samples might have been polluted by primary or secondary sources containing Aroclor1254, such as outdated equipment and contaminated water and air. This observation is consistent with the finding that the surface water samples from this region have been more or less polluted by Aroclor1254 (Zhang et al. 2011). However, although the PC1 and PC2 scores of Aroclor1242
were significantly different among sample sites, it is difficult to make a conclusion that there was no input from Aroclor1242 in this region. This could be mostly due to the penetration of the low-chlorinated PCBs from the surface soil into the deeper soi, or the volatilization into the atmosphere. The consequence was then a relatively higher proportion of the higher chlorinated PCBs stored in soils. In addition, the majority of sample sites had different PC values of Aroclor1260 or Aroclor1248, consistent with the finding that there had not been large-scale use of them in China (Xing et al. 2005).
Fig. 4 Spatial distributions of PBDEs in surface soils from the Yangtze River Delta. Error bars correspond to 95th percentiles of levels; boxes correspond 25th to 75th percentiles of levels. U urban area, R rural area, S suburban area
Fig. 5 Spatial distributions of PCBs in surface soils from the Yangtze River Delta. Error bars correspond to 95th percentiles of levels; boxes correspond to 25th to 75th percentiles of levels. U urban area, R rural area, S suburban area
Environ Sci Pollut Res
Spatial distribution of PBDEs and PCBs in the Yangtze River Delta As a whole, the spatial distributions of PBDEs or PCBs in the surface soil samples reflect a gradient (from high to low) from the central cities out to rural areas in both the 2003 and 2012 data (Figs. 4 and 5). The soil samples with higher PBDEs concentrations were observed in the urban sites, while most samples with lower concentrations were observed in the rural or suburb sites which are normally far away from factories and residential areas. This finding lends support to the hypothesis that urban area are sources of PBDEs or PCBs pollutants to surrounding areas (Harrad and Hunter 2006; Qin et al. 2010; Zhang et al. 2013). Normally, PBDE emission sources are concentrated in urban areas with large-scale production, use, and disposal of PBDE-containing products, industrial combustion processes, transportation, and building activities (de Wit. 2002; Wang et al. 2011). Therefore, the PBDEs concentrations in soils were higher in urban areas than in urban-rural transition and rural areas. It has also been found that PBDE pollution in the YRD was not limited to the large cities with high population density but also in small cities. For example, many samples collected in 2012 with high PBDE concentrations were found in Kunshan(11.5 μg kg−1), Zhangjiagang(26.5 μg kg−1), Jiangyin(17.4 μg kg−1), etc. In fact, the urban system in this region is made up of many secondary cities as mentioned above. Since 1991, the development of rural industries and the construction of small cities and towns have led to the emergence of rural economic development zones and many small cities groups (Gu et al. 2011). With the industrialization and urbanization process in this region, these small cities and rural economic development zones are facing serious PBDE pollution problems, which should be of a serious concern. The spatial distributions of the soil PCBs in the urban, suburban, and rural area are similar to those of PBDEs. The spatial variability in the concentrations of PCBs suggestes that the PCBs in urban soils are mainly from particular sites. Based on the investigation to sample sites, it is evident that the samples with higher PCBs concentrations were all observed in or near the industrial areas of the cities. This indicates that significant PCB pollution in urban soils might have come from PCB stationary sources in the industrial areas or particular sites where the soils had been historically contaminated by PCB-containing products, improper disposal, and leakage of oil from transformers and capacitors.
Conclusions Overall, soil PBDE concentrations in the study region increased significantly between the sampling years of 2003
and 2012, but PCBs demonstrated little changes. The study indicates that there have been large amount of inputs from deca-BDE during the 9-year period, and there was likely additional input from octa-BDE sources in recent years. The results of principal component analysis show that a few surface soil samples have been polluted by Aroclor1254. Generally, urban centers had higher PBDE concentrations in soils than suburban areas in this region. Moreover, PBDE pollution in the YRD region was not limited to highly populated cities, but also found in small cities in this region. Acknowledgments We are grateful for financial support from the National Basic Research Program of China (no. 2009CB42160X).
References Aries E, Anderson DR, Fisher R, Fray TAT, Hemfrey D (2006) PCDD/F and BDioxin-like^ PCB emissions from iron ore sintering plants in the UK. Chemosphere 65(9):1470–1480 ATSDR (Agency for Toxic Substances and Disease Registry) (2000) Toxicological profile for polychlorinated biphenyls (PCBs). ATSDR, Atlanta. Available at http://www.atsdr.cdc.gov/ toxprofiles/tp17.pdf Backe C, Cousins IT, Larsson P (2004) PCB in soils and estimated soil– air exchange fluxes of selected PCB congeners in the south of Sweden. Environ Pollut 128(1–2):59–72 Breivik K, Sweetman A, Pacnya JM, Jones KC (2002) Towards a global historical emission inventory for selected PCB congeners—a mass balance approach: 1. Global production and consumption. Sci Total Environ 290(1–3):181–198 Cai ZW, Jiang GB (2006) Determination of polybrominated diphenyl ethers in soil from e-waste recycling site. Talanta 70(1):88–90 De Wit CA (2002) An overview of brominated flame retardants in the environment. Chemosphere 46(5):583–624 Frederiksen M, Vorkamp K, Thomsen M, Knudsen LE (2009) Human internal and external exposure to PBDEs—a review of levels and sources. Int J Hyg Environ Health 212(2):109–134 Duan YP, Meng XZ, Yang C, Pan ZY, Chen L, Yu R, Li FT (2010) Polybrominated diphenyl ethers in background surface soils from the Yangtze River Delta (YRD), China: occurrence, sources, and inventory. Environ Sci Pollut Res 17(4):948–956 Gerecke AC, Hartmann PC, Heeb NV, Kohler HPE, Giger W, Schmid P, Zennegg M, Kohler M (2005) Anaerobic degradation of decabromodiphenyl ether. Environ Sci Technol 39(4):1078–1083 Gu CL, Hu LQ, Zhang XM, Wang XD, Guo J (2011) Climate change and urbanization in the Yangtze River Delta. Habitat Int 35(4):544–552 Hassanin A, Breivik K, Meijer SN, Steinnes E, Thomas GO, Jones KC (2004) PBDEs in European background soils: levels and factors controlling their distribution. Environ Sci Technol 38(3):738–745 Harrad S, Hunter S (2006) Concentrations of polybrominated diphenyl ethers in air and soil on a rural–urban transect across a major UK conurbation. Environ Sci Technol 40(15):4548–4553 Jones KC, De Voogt P (1999) Persistent organic pollutants (POPs): state of the science. Environ Pollut 100(1–3):209–221 La Guardia MJ, Hale RC, Harvey E (2006) Detailed polybrominated diphenyl ether (PBDE) congener composition of the widely used penta-, octa-, and deca-PBDE technical flame-retardant mixtures. Environ Sci Technol 40(20):6247–6254 Luo Y, Luo XJ, Lin Z, Chen SJ, Liu J, Mai BX, Yang ZY (2009) Polybrominated diphenyl ethers in road and farmland soils from
Environ Sci Pollut Res an e-waste recycling region in southern China: concentrations, source profiles, and potential dispersion and deposition. Sci Total Environ 407(3):1105–1113 Leung AOW, Luksemburg WJ, Wong AS, Wong MH (2007) Spatial distribution of polybrominated diphenyl ethers and polychlorinated dibenzo-p-dioxins and dibenzofurans in soil and combusted residue at Guiyu, an electronic waste recycling site in southeast China. Environ Sci Technol 41(8):2730–2737 Ma J, Qiu XH, Zhang JL, Duan XL, Zhu T (2012) State of polybrominated diphenyl ethers in China: an overview. Chemosphere 88(7):769–778 Mai BX, Chen SJ, Luo XJ, Chen LG, Yang QS, Sheng GY, Peng PG, Fu JM, Zeng EY (2005) Distribution of polybrominated diphenyl ethers in sediments of the Pearl River Delta and adjacent South China Sea. Environ Sci Technol 39(10):3521–3527 McDonald TA (2002) A perspective on the potential health risks of PBDEs. Chemosphere 46(5):745–755 Qin PH, Ni HG, Liu YS, Shi YH, Zeng H (2010) Occurrence, distribution and source of polybrominated diphenyl ethers in soil and leaves from Shenzhen special economic zone, China. Environ Monit Assess 174(1–4):259–270 Qiu XH, Zhu T, Hu JX (2010) Polybrominated diphenyl ethers (PBDEs) and other flame retardants in the atmosphere and water from Taihu Lake, East China. Chemosphere 80(10):1207–1212 Ren N, Que M, Li YF, Liu Y, Wan X, Xu D, Sverko E, Ma J (2007) Polychlorinated biphenyls in Chinese surface soils. Environ Sci Technol 41(11):3871–3876 Schuster JK, Gioia R, Moeckel C, Agarwal T, Bucheli TD, Breivik K, Steinnes E, Jones KC (2011) Has the burden and distribution of PCBs and PBDEs changed in European background soils between 1998 and 2008? Implications for sources and processes. Environ Sci Technol 45(17):7291–7297 Shen M, Yu YJ, Zheng GJ, Yu HX, Lam PKS, Feng JF, Wei ZB (2006) Polychlorinated biphenyls and polybrominated diphenyl ethers in surface sediments from the Yangtze River Delta. Mar Pollut Bull 52:1299–1304 Shi SX, Dong L, Yang WL, Zhou L, Zhang LF, Zhang XL, Huang YR (2014) Monitoring of airborne polybrominated diphenyl ethers in
the urban area by means of road dust and camphor tree barks. Aerosol Air Qual Res 14:1106–1113 UNEP (2009) Fourth meeting of the conference of the parties of the Stockholm convention. United Nations Environment Programme, Geneva, Switzerland. Available at http://chm.pops.int/Portals/0/ download.aspx?d=UNEP-POPSCOP.4-38.English.pdf Wang DL, Cai ZW, Jiang GB, Leung A, Wong MH, Wong WK (2005) Determination of polybrominated diphenyl ethers in soil and sediment from an electronic waste recycling facility. Chemosphere 60 (6):810–816 Wang LC, Lee WJ, Lee WS, Chang-Chien GP (2011) Polybrominated diphenyl ethers in various atmospheric environments of Taiwan: their levels, source identification and influence of combustion sources. Chemosphere 84(7):936–942 Xing Y, Lu Y, Dawson RW, Shi Y, Zhang H, Wang T (2005) A spatial temporal assessment of pollution from PCBs in China. Chemosphere 60(6):731–739 Xu J, Gao ZS, Xian QM, Yu HX, Feng JF (2009) Levels and distribution of polybrominated diphenyl ethers (PBDEs) in the freshwater environment surrounding a PBDE manufacturing plant in China. Environ Pollut 157(6):1911–1916 Zhang JY, Qiu LM, He J, Liao Y, Luo YM (2007) Occurrence and congeners specific of polychlorinated biphenyls in agricultural soils from Southern Jiangsu, China. J Environ Sci 19(3):338–342 Zhang HJ, Zhao XF, Ni YW, Lu XB, Chen JP, Su F, Zhao L, Zhang N, Zhang XP (2010) PCDD/Fs and PCBs in sediments of the Liaohe River, China: levels, distribution, and possible sources. Chemosphere 79(7):754–762 Zhang LF, Shi SX, Dong L, Zhang T, Zhou L, Huang YR (2011) Concentrations and possible sources of polychlorinated biphenyls in the surface water of the Yangtze River Delta, China. Chemosphere 85(3):399–405 Zhang LF, Zhang T, Dong L, Shi SX, Zhou L, Huang YR (2013) Assessment of halogenated POPs and PAHs in three cities in the Yangtze River Delta using high-volume samplers. Sci Total Environ 454–455:619–626 Zhang YF, Fu S, Dong Y, Nie HF, Li Z, Liu XC (2014) Distribution of polychlorinated biphenyls in soil around three typical industrial sites in Beijing, China. Bull Environ Contam Toxicol 92(4):466–471
RESEARCH ARTICLE
Changes of polybrominated diphenyl ethers and polychlorinated biphenyls in surface soils from urban agglomeration of the Yangtze River Delta, in China between 2003 and 2012 Shuang-Xin Shi & Ye-Ru Huang & Li Zhou & Li-Fei Zhang & Liang Dong & Wen-Long Yang & Xiu-Lan Zhang
Received: 1 September 2014 / Accepted: 12 January 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Surface soil samples were collected from urban agglomeration of the Yangtze River Delta (YRD), China in 2003 and 2012, respectively. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were analyzed to determine if there were any changes in their levels and compositional profiles between the two sampling years. The concentrations of Σ 8PBDEs ranged from 0.553 to 13.0 μg kg−1(with the mean of 3.31 μg kg−1) in the 2003 samples and from 1.01 to 43.2 μg/kg (with the mean of 10.0 μg kg−1) in the 2012 samples. The concentrations of Σ32PCBs ranged from 0.301 to 3.29 μg kg−1(with the mean of 1.01 μg kg−1) in the 2003 samples and from 0.205 to 3.96 μg/kg (with the mean of 0.991 μg kg−1) in the 2012 samples. The comparisons between the 2012 and 2003 data showed that PBDEs concentrations increased over the years, but PCB concentrations did not change much. BDE-209 was the major BDE congener in both the 2003 and 2012 samples, indicating that the dominant PBDE mixture production and usage in the YRD had been the commercial deca-BDE mixture. Investigation of the PBDE congener profiles indicated that there had been new input of octa-BDEs in this region in recent years. Little change was found for the pattern of PCBs congener profiles between 2 years’ samples. As such, spatial distributions of PBDEs or PCBs in surface soil samples reflected a gradient (from high to low) from the central cities Responsible editor: Hongwen Sun S.BDE-153(81.8 %)>BDE-154(66.7 %)>BDE-100 (51.5 %), while in the 2003 samples, followed a pattern of BDE-209 (100 %)>BDE-99 (88.9 %)>BDE-47 (77.8 %)> BDE-28 (58.3 %)>BDE-183=BDE-154 (27.8 %)>BDE153=BDE-100(25.0 %). The detection frequency for BDE209 was 100 % in both samples, indicating that BDE-209 was already a ubiquitous environmental pollutant in the YRD soils almost 10 years ago. However, the frequencies of the lowbrominated congeners and BDE-183 detected in the 2012 samples were higher than those in the 2003 samples, suggesting that these compounds have been becoming widespread environmental pollutant in soils of the YRD in recent years. Some PCB congeners, including PCB-8, 166, 156, 126, 114, 189, and169 were not detected in all samples, while most other PCB congeners were detected in the samples, especially for PCB-28, 52, 49, 101, 118, 153, 138, and 180, for which detection frequency were higher than 80.6 % in all samples. Similar PCB congeners and detection frequency were found in the 2003 and 2012 samples. Descriptive statistics for concentrations of BDE-209, Σ32PCBs, and Σ7PBDEs in the samples are summarized in Table 1. To establish if there were any changes of the PBDE and PCB concentrations between the 2003 and 2012 samples, independent sample group T tests were applied. The results show that the data obtained followed a normal distribution and the concentrations of Σ7PBDE and BDE-209 in the 2012 soils were significantly higher than in the 2003 soils with P0.05) between BDE-153 and BDE183 in the 2012 samples, indicating the possible additional input from octa-BDE sources in this region. However, because BDE-153 had low detection frequency (27.8 %) and low concentration in the 2003 samples, it is inappropriate to reach robust conclusions based on such data. It has been noted that BDE-47and 99 are major congeners of penta-BDE products (la Guardia et al. 2006), with the BDE47/BDE-99 ratios of 1.05 in Bromkal 70-5DE and 0.76 in DE71. Because BDE-99 has a higher KOA (octanol-air partition coefficients) relative to BDE-47, the ratio of BDE-47 to BDE99 usually falls below a value of 0.8 in soils (Harrad and Hunter. 2006). The ratio of our 2003 data was 0.73±0.34, indicating that there might have been input from penta-BDE sources in 2003. However, the ratio obtained from the 2012 data was1.12±0.33, different from that in penta-BDE product and background soils reported in other literatures (Harrad and Hunter. 2006). In addition, the proportions of BDE-28 and BDE-154 in the 2012 samples were higher than those in penta-BDE products. Such difference might be a result from BDE congener fractionation changing during transportation, mixing, microbial degradation, or photodegradation from higher brominated congeners as well as depositional mechanisms in the environment. Another plausible explanation for
this compositional profile might be indicate that a Bspecific penta-BDE formulation^ has been produced or used in this region over the recent years (Qiu et al. 2010). But, these explanations are speculative and a more detailed investigation of penta-BDE sources in this region should be carried out in the future. PCBs The compositional patterns of PCBs in soils have changed little over the passing 9 years. The major homolog in all samples was penta-PCBs, followed by tetra-PCBs and hexaPCBs. The proportions of lighter weighted molecular PCBs (di-, tri-, tetra-PCB) in the 2003 and 2012 samples were 33.6 and 29.8 %, respectively. This was due to the fact that lower chlorinated congeners are more mobile and thus have permeated deeper into the soil (Backe et al. 2004). Another factor could be that the lower congeners are more volatile and hence more likely to diffuse into the atmosphere (Backe et al. 2004). Principal component analysis (PCA) was used to evaluate the distribution pattern of PCBs and to determine their possible origins. Homolog from di-PCBs to hepta-PCBs were selected as variables for principal component analysis. The first principal component (PC1) accounted for 46.5 % of the variability in the 2003 data, while the second principal component (PC2) accounted for 22.9 %. PC1 had higher loading for the homolog di, tri-, and tetra-PCBs, which were mostly associated with lower chlorinated PCBs. PC2 had higher loading for the higher chlorinated congeners, namely, homolog hexa- and hepta-PCBs. Similar results were found in the 2012 data, with PC1 and PC2 accouting for 46.5 and 29.3 % of the variability, respectively. The principal component scores for each site and PCBs mixtures are displayed in Fig. 3 It can be observed from the loading plot that several samples as well as Aroclor1254 constituted similar scores of PC1 and
Environ Sci Pollut Res
Fig. 3 Score plot of PCA for the 2003 soil samples from the Yangtze River Delta, China
PC2. The possible source of PCBs in these samples might be the emission from Aroclor1254. In China, Aroclor1242 and Aroclor 1254 were the two major PCBs mixture, with production of 9000 and 1000 tons prior to 1974, respectively (Xing et al. 2005). These soil samples might have been polluted by primary or secondary sources containing Aroclor1254, such as outdated equipment and contaminated water and air. This observation is consistent with the finding that the surface water samples from this region have been more or less polluted by Aroclor1254 (Zhang et al. 2011). However, although the PC1 and PC2 scores of Aroclor1242
were significantly different among sample sites, it is difficult to make a conclusion that there was no input from Aroclor1242 in this region. This could be mostly due to the penetration of the low-chlorinated PCBs from the surface soil into the deeper soi, or the volatilization into the atmosphere. The consequence was then a relatively higher proportion of the higher chlorinated PCBs stored in soils. In addition, the majority of sample sites had different PC values of Aroclor1260 or Aroclor1248, consistent with the finding that there had not been large-scale use of them in China (Xing et al. 2005).
Fig. 4 Spatial distributions of PBDEs in surface soils from the Yangtze River Delta. Error bars correspond to 95th percentiles of levels; boxes correspond 25th to 75th percentiles of levels. U urban area, R rural area, S suburban area
Fig. 5 Spatial distributions of PCBs in surface soils from the Yangtze River Delta. Error bars correspond to 95th percentiles of levels; boxes correspond to 25th to 75th percentiles of levels. U urban area, R rural area, S suburban area
Environ Sci Pollut Res
Spatial distribution of PBDEs and PCBs in the Yangtze River Delta As a whole, the spatial distributions of PBDEs or PCBs in the surface soil samples reflect a gradient (from high to low) from the central cities out to rural areas in both the 2003 and 2012 data (Figs. 4 and 5). The soil samples with higher PBDEs concentrations were observed in the urban sites, while most samples with lower concentrations were observed in the rural or suburb sites which are normally far away from factories and residential areas. This finding lends support to the hypothesis that urban area are sources of PBDEs or PCBs pollutants to surrounding areas (Harrad and Hunter 2006; Qin et al. 2010; Zhang et al. 2013). Normally, PBDE emission sources are concentrated in urban areas with large-scale production, use, and disposal of PBDE-containing products, industrial combustion processes, transportation, and building activities (de Wit. 2002; Wang et al. 2011). Therefore, the PBDEs concentrations in soils were higher in urban areas than in urban-rural transition and rural areas. It has also been found that PBDE pollution in the YRD was not limited to the large cities with high population density but also in small cities. For example, many samples collected in 2012 with high PBDE concentrations were found in Kunshan(11.5 μg kg−1), Zhangjiagang(26.5 μg kg−1), Jiangyin(17.4 μg kg−1), etc. In fact, the urban system in this region is made up of many secondary cities as mentioned above. Since 1991, the development of rural industries and the construction of small cities and towns have led to the emergence of rural economic development zones and many small cities groups (Gu et al. 2011). With the industrialization and urbanization process in this region, these small cities and rural economic development zones are facing serious PBDE pollution problems, which should be of a serious concern. The spatial distributions of the soil PCBs in the urban, suburban, and rural area are similar to those of PBDEs. The spatial variability in the concentrations of PCBs suggestes that the PCBs in urban soils are mainly from particular sites. Based on the investigation to sample sites, it is evident that the samples with higher PCBs concentrations were all observed in or near the industrial areas of the cities. This indicates that significant PCB pollution in urban soils might have come from PCB stationary sources in the industrial areas or particular sites where the soils had been historically contaminated by PCB-containing products, improper disposal, and leakage of oil from transformers and capacitors.
Conclusions Overall, soil PBDE concentrations in the study region increased significantly between the sampling years of 2003
and 2012, but PCBs demonstrated little changes. The study indicates that there have been large amount of inputs from deca-BDE during the 9-year period, and there was likely additional input from octa-BDE sources in recent years. The results of principal component analysis show that a few surface soil samples have been polluted by Aroclor1254. Generally, urban centers had higher PBDE concentrations in soils than suburban areas in this region. Moreover, PBDE pollution in the YRD region was not limited to highly populated cities, but also found in small cities in this region. Acknowledgments We are grateful for financial support from the National Basic Research Program of China (no. 2009CB42160X).
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