Chemosphere 83 (2011) 1391–1397

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Chemosphere

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Occurrence of polybrominated diphenyl ethers in soil from the central LoessPlateau, China: Role of regional range atmospheric transport

Xiang-Zhou Meng, Zhao-Yu Pan, Jun-Jie Wu, Yan-Ling Qiu, Ling Chen ⇑, Guang-Ming LiState Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China

a r t i c l e i n f o

Article history:Received 11 October 2010Received in revised form 30 January 2011Accepted 27 February 2011Available online 2 April 2011

Keywords:Polybrominated diphenyl ethers (PBDEs)SoilThe Loess PlateauHuan CountyAtmospheric transport

0045-6535/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.chemosphere.2011.02.057

⇑ Corresponding author. Tel./fax: +86 21 65984261E-mail address: chenling@tongji.edu.cn (L. Chen).

a b s t r a c t

Very few studies were conducted in highland and depositional areas in studying the transport and behav-ior of polybrominated diphenyl ethers (PBDEs). In this study, surface soils were collected from HuanCounty to investigate the level, profile, and potential influence of PBDEs via regional range atmospherictransport in the central part of the Loess Plateau (CLP) of China, one of the most extensive areas of loessdeposition in the world. PBDEs were ubiquitous and log-normally distributed in soils from the CLP withmean concentrations of 0.91 and 0.54 ng g�1 for RPBDEs (sum of PBDE congeners except for BDE-209)and BDE-209, respectively. BDE-209 was predominated congener (43.5%), followed by BDE-47 (15.7%),99 (10.7%), and 153 (7.5%). Further principal component analysis on congener profiles showed that PBDEsin the CLP originated from similar source(s). Additionally, significant differences in the ratios of BDE-47 to99 and BDE-153 to 154 were found between soil samples and commercial products, indicating that theyhave undergone fractionation during the process of regional range atmospheric transport. The depositionof PBDEs in the CLP could be influenced by the sources from surrounding regions. For example, Xi’an mayhave potential influence to the CLP based on geographical analysis and concentrations comparison ofPBDEs in gaseous. Therefore, more studies are needed to clarify the atmospheric transport and fate ofPBDEs in this region.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Polybrominated diphenyl ethers (PBDEs) are a class of additivebrominated flame retardants that are added to plastics, polyure-thane foam, textiles, and electronic equipment to reduce the mate-rial flammability (Hites, 2004). Despite their benefits, PBDEs isqualified as persistent, bioaccumulative, and toxic substances andis widely concerned by environmental researchers and policy-makers (Birnbaum and Staskal, 2004; Hites, 2004). Currently, thePenta- and Octa-formulations have been voluntarily withdrawnfrom the United States (USA) marketplace since the end of 2004.Deca-BDEs have also been banned in some countries from the Eur-ope Union (EU) and North America. In contrast, in China, thedomestic demand of brominated diphenyl ethers (includingPBDEs) has increased annually at a rate of �8% (Mai et al., 2005).In addition, China is the world’s largest importer and recycler ofwaste electrical and electronic equipments (Ni and Zeng, 2009).During the electronic waste (e-waste) dismantled with crudemethods, PBDEs was released into the environment (Leung et al.,2007; Meng et al., 2008; Luo et al., 2009).

Persistent organic pollutants (POPs) can be diffused frompoint source area to surrounding and remote areas undergo long/

ll rights reserved.

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regional range atmospheric transport (Wania and Dugani, 2003;Zhao et al., 2009). Therefore, remote regions are beginning toreceive increased attention in studying the transport and behaviorof POPs (Liu et al., 2010). Currently, to the best of our knowledge,no study on POPs was conducted in the Loess Plateau (LP) of China.

The LP, also known as the Huangtu Plateau, is one of the mostextensive areas of loess deposition in the world. Historically, theLP was created by the deposition of wind-blown dust and by gla-cial till, called loess. Present eolian dust is mainly transported bylow level winds in step-wise way to deposit in this area (Sunet al., 2001). The LP (between 33–40�N and 98–115�E) is high-land area in north-central China, covering much of Shanxi, north-ern Henan, Shaanxi, eastern Gansu provinces, and the middlepart of the Yellow River basin (Fig. 1). The average elevation isabout 1200 m and the area is about 400,000 km2. Precipitationtotals from 500 mm per year in the east to 250 mm in the north-west. Huan County, located at the central part of the LP (CLP; be-tween 36�010–37�090N and 106�210–107�440E), has the area of9236 km2 and the population of 351,000, of which 93% arefarmers. The annual precipitation is about 300 mm and theelevation ranged from 1136 to 2089 m. The objectives of presentstudy are to investigate the levels and compositions of PBDEs insurface soil from the CLP and to examine the potential influenceof regional range atmospheric transport for PBDEs deposition inthis area.

Fig. 1. Map of the study area and sampling sites.

1392 X.-Z. Meng et al. / Chemosphere 83 (2011) 1391–1397

2. Materials and methods

2.1. Soil sampling

Between July and August 2009, soil sampling was conducted 20locations in Huan County, including of Tianshui, Shancheng,Qintuanzhuang, Nanjiu, Luoshanchuan, Gengwan, Siheyuan, Xiao-nangou, Hongde, Maojing, Hudong, Huancheng, Fanjiachuan, Baz-hu, Lujiawan, Hedao, Mubo, Quzi, Tianchi, and Yanwu. Prior tosoil collection, any overlying vegetation was removed. Compositesurface agricultural soil samples (0–10 cm depth) were collectedusing the cleaned handheld corer from 45 sites in Huan County,the CLP (Fig. 1 and Table S1, ‘‘S’’ designates Supplemental Informa-tion here and thereafter). The first two cores were discarded, thenthe following three cores (taken over an area of several m2) werecombined as one sample. The samples were wrapped in aluminumfoil and sealed in polyethylene bag, and then transported to the

laboratory. Before extraction, the samples were freeze-dried,mixed thoroughly, sieved to 100 mesh and kept at �18 �C.

2.2. Standard materials

Our targets, including BDE-17, 28, 33, 47, 49, 66, 99, 100, 138,153, 154, 183, 190, 196, 203, 206, 207, 208, and 209, were pur-chased from AccuStandards (New Haven, CT, USA). Surrogates(BDE-50 and 172) and internal standards (BDE-118 and 128) werealso purchased from AccuStandards (New Haven, CT, USA).

2.3. Analytical procedure

The detailed analytical procedure was presented elsewhere(Mai et al., 2005; Duan et al., 2010). Briefly, spiked with BDE-50and 172, about 10 g soil was Soxhlet extracted with a mixture ofacetone and hexane (1:1 in volume) for 48 h. Activated copper

X.-Z. Meng et al. / Chemosphere 83 (2011) 1391–1397 1393

were added into samples prior to extraction to remove elementalsulfur. The concentrated extract was further purified on a 1 cmi.d. silica/alumina column packed, from the bottom to top, with3% deactivated basic alumina oxide (6 cm) and 3% deactivated neu-tral silica gel (12 cm). PBDEs of interest were eluted in the 50 mLfraction of 50% DCM in hexane (v:v), and the final extract volumewas reduced to 500 lL under a gentle N2 stream. BDE-118 and128 were added before instrumental analysis.

A gas chromatography and mass spectrometry (Shimadzu Mod-el QP 2010 plus; Shimadzu, Japan) was used to analysis all targetsat negative chemical ionization (NCI) in selected ion monitoringmode (SIM). The separation was performed using A DB-5(15 m � 0.25 mm i.d., 0.15 lm film thickness) capillary column(J&W Scientific, Folsom, CA, USA) at different temperature pro-grams. For tri- to hepta-BDEs, the column temperature was initi-ated at 80 �C (held for 2 min) and increased to 140 �C at12 �C min�1, 280 �C at 5 �C min�1 (held for 20 min), and 290 �C at20 �C min�1 (held for 5 min). For octa- to deca-BDEs, the oven tem-perature was initiated at 110 �C (held for 1 min) and increased to290 �C at a rate of 10 �C min�1 (held for 20 min). The limit of detec-tion (LOD), defined as a signal/noise ratio (S/N) = 5, ranged from 3to 5 pg g�1 dry weight for tri- to nona-congeners and 50 ng g�1 forBDE-209 based on dry weight, respectively.

2.4. Total organic carbon measurements

Total organic carbon (TOC) was analyzed with the ShimadzuTOC-VCPN with solid sample module (SSM-5000A) (Shimadzu,Japan). The overall standard deviation of measurements was betterthan 3% (n = 3).

2.5. Quality assurance/quality control (QA/QC)

A procedural blank, a spiked blank, a matrix spiking sample (19PBDE congeners spiked into sample), and a matrix spiking dupli-cate were processed for each batch of 12 soil samples. The recover-ies of BDE-50 and BDE-172 were 75.4 ± 8.5% and 74.2 ± 11.7%,respectively. The relative standard deviation for individual BDEcongeners measured in triple duplicate samples were <20%. OnlyBDE-47 and 99 with level lower than LOD were found in proce-dural blanks and not subtracted from the sample. Reported con-centrations were not surrogate recovery corrected.

2.6. Data analysis

For samples with concentrations below the LOD, 1/2 LOD wereused in the calculation thereafter. The normality of the distributionwas tested using nonparametric test (Kolmogorov–Smironov Z).Principal component analysis (PCA) was conducted to further clas-sify the possible relationship among PBDEs congeners and to ex-plore the similarity of PBDEs sources in soils. Independent onesample t-test was used to compare the population mean with aspecified value. The level of significance was set to 5% (a = 0.05)throughout the present study. All statistical analyses were per-formed with SPSS software (Ver 13.0; SPSS, Chicago, IL, USA).

3. Results and discussion

3.1. PBDEs concentrations

As shown in Fig. 2 and Table S1, PBDEs were found in all soilsamples (n = 45) collected from the CLP, suggesting that these pol-lutants were ubiquitous in this rural region. For specific congeners,the detection frequencies varied widely. BDE-17, 28, 47, 49, 66, 99,100, 153, 154, and BDE-209 were detected in more than 70% of the

samples. For other congeners, including BDE-138, 183, 196, 203,206, 207, and 208, the detection frequencies ranged from 17.8%to 53.3%. BDE-190 was found only in one sample and no BDE-33was detected in any soil sample. Here we defined ‘‘Total PBDEs’’as the sum of all congeners analyzed in this study. Meanwhile,for the comparison of our data with other studies, RPBDEs was alsodefined as the sum of all congeners except for BDE-209. The meanand median concentrations of RPBDEs were 911 pg g�1 and444 pg g�1, respectively, with a range from 35.1 to 12,100 pg g�1.For BDE-209, the concentration was slightly lower than RPBDEs,and the mean and median levels were 538 pg g�1 and 252 pg g�1,respectively, with a range from not detected to 5760 pg g�1

(Fig. 2 and Table S1). Overall, RPBDEs and BDE-209 in surface soilsfrom the CLP were log-normally distributed as determined by one-sample Kolmogorov–Smirnov test (p > 0.05; Fig. 2b and d).

3.2. PBDEs congener profiles

BDE-209 was the predominated congener (43.5%), followed byBDE-47 (15.7%), 99 (10.7%), and 153 (7.5%) (Fig. 3). This composi-tion pattern was similar to the previous studies (Offenberg et al.,2006; Leung et al., 2007; Zou et al., 2007; Jin et al., 2008; Liet al., 2008, 2009; Yun et al., 2008; Luo et al., 2009; Duan et al.,2010). BDE-209 is the main congener in two Deca-formulations(Saytex 102E and Bromkal 82-0DE with the percentages of 96.8%and 91.6%, respectively), which was widely used in electrical andelectronic equipment and textiles (Birnbaum and Staskal, 2004;La Guardia et al., 2006). In 2001, Deca-BDE accounted for 83.3%of total production worldwide (Hites, 2004). On the other hand,BDE-209 is extremely hydrophobic (Log KOW � 10), thus it was ex-pected to possess low bioavailability and tendency to strongly bindto sediment and soil (Hale et al., 2002). BDE-47, 99, and 153 arethree main components in two Penta-formulations, which contrib-uted to 38.2%, 48.6%, and 5.44% in DE-71 and 42.8%, 44.8%, and5.32% in Bromkal 70-5DE, respectively (La Guardia et al., 2006).Despite of the Penta-BDE was banned to use in EU and the USA,PBDEs can be released from finished and discarded products con-taining PBDEs into the environment (Kemmlein et al., 2003; Hites,2004). In addition, Penta-BDE commercial products is still beingused in China. For BDE-183, as a marker of Octa-BDE products,the percentage in this study was 1.4%, which was higher than thosein the Penta-BDE products (0.1% in DE-71 and 0.33% in Bromkal70-5DE, respectively) (La Guardia et al., 2006). Hence we thoughtthat additional input from Octa-BDE products co-occurred in theCLP.

PCA was used to further examine the sources of PBDEs in soils ofthe CLP. As shown in Fig. 4a, the PCA classified the PBDE congenersinto two distinct clusters (Clusters I and II), accounting for 85.1% ofthe variation. Principal component 1, explaining 57.4% of the vari-ance, shows positive loadings for the relative abundances of BDE-17, 28, 47, 49, 66, 99, 100, 138, 153, 154, and 183, which are themain components of Penta-BDE and Octa-BDE, respectively. Princi-pal component 2, explaining 27.7% of the variance, contains a highpositive loading of BDE-196, 203, 206, 207, 208, and 209, which arethe main components of Deca-BDE. From Fig. 4b, over 90% of sam-ples are gathered and located near the origin, indicating that thePBDEs congener profiles in soils from the CLP were a combinationof the three commercial formulations (Penta-BDE, Octa-BDE, andDeca-BDE). Only two samples scatter far away from the origin,probably due to the sampling sites are close to PBDEs local pointsources. One sample (#35) collected in Hedao contained very highlower-brominated congeners, where the concentrations of BDE-47and BDE-99 were 3830 ng g�1 and 3360 ng g�1, respectively. Ashigh as 5760 ng g�1 of BDE-209 was found in another sample(#38) collected in Mubo (Fig. 1). Despite of the occurrence ofvery few local point sources, the results above imply that the

0 3000 6000 9000 12000

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Fig. 2. Histograms showing the distributions of (a) RPBDEs; (b) LogRPBDEs; (c) BDE-209; (d) LogBDE-209 concentrations (pg g�1, dry weight) in farmland soils from the CLP,China. The green line in (a) marks the median of RPBDEs (444 pg g�1), and the red line marks the mean of RPBDEs (911 pg g�1). The green line in (c) marks the median BDE-209 (252 pg g�1), and the red line marks the mean concentration (538 pg g�1). (For interpretation of the references to color in this figure legend, the reader is referred to theweb version of this article.)

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Fig. 3. Compositional profiles of PBDEs congeners in farmland soils. Error bars represent 1sd.

1394 X.-Z. Meng et al. / Chemosphere 83 (2011) 1391–1397

compositions of PBDEs in most sampling sites in the CLP weresimilar, possibly originating from the same source(s).

3.3. Global comparisons of PBDEs levels

Although different PBDE congeners were analyzed, PBDE con-centrations in surface soils from global range can be compared

due to similar composition pattern, as mentioned above. Clearly,as shown Table S2, RPBDEs (mean: 0.91 ng g�1; range: 0.035–12.1 ng g�1) and BDE-209 (mean: 0.54 ng g�1, range: not de-tected-5.8 ng g�1) in this study were much lower than those insoils from e-waste dismantling sites in China (i.e., Guiyu, Taizhou,and Qingyuan) (Cai and Jiang, 2006; Leung et al., 2007; Luo et al.,2009). In addition, our results were lower than those in soils from

Principal component 1 (57.4%)

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Fig. 4. Loading plot (a) and score plot (a) of the relative abundances of PBDEscongeners (except for BDE-33 and BDE-190 due to low detection frequencies) in allsoil samples.

X.-Z. Meng et al. / Chemosphere 83 (2011) 1391–1397 1395

industrial sites (Zou et al., 2007; Jin et al., 2008; Li et al., 2008,2009; Luo et al., 2009). Globally, our data fall into a similar rangereported in background soils in Europe and the USA (Hassaninet al., 2004; Harrad and Hunter, 2006; Offenberg et al., 2006;Yun et al., 2008). As we expected, our data were much higher thanPBDEs in surface soils (including upland soil, agriculture soils, mea-dow soil, and moraine soils) from remote area of China (TibetanPlateau; mean: 0.011 ng g�1; range: 0.004–0.035 ng g�1) (Wanget al., 2009).

Among all studies conducted in urban/rural areas, BDE-209 insoil from the CLP were one order of magnitude lower than thosein Taiyuan (mean: 25.5 ng g�1) (Li et al., 2008), Chongming Island(mean: 5.0–14.0 ng g�1) (Duan et al., 2010), the Pearl River Delta(PRD) (mean: 13.8 ng g�1) (Zou et al., 2007), Qingyuan (mean:19.7 ng g�1) (Luo et al., 2009), and 15 states and Michigan of theUSA (mean: 0.6–21.1 ng g�1) (Offenberg et al., 2006; Yun et al.,2008). However, unexpectedly, our RPBDEs were similar to thosein other regions in China (Zou et al., 2007; Li et al., 2008, 2009;Luo et al., 2009; Duan et al., 2010). Generally, PBDEs were largelyused in human-related products like textiles and electronic equip-ments to reduce flammability. Soils in rural, sparsely populated,and underdeveloped regions should contained lower PBDEs thanthose in developed, populous, and/or industrial regions as a resultof less PBDEs local consumption and/or production. In HuanCounty, not like the Yangtze River Delta (YRD) and the PRD (twoof the most developed regions in China), very few industries existexcept for agricultural activity. The per capita gross domestic prod-uct was only 2333 Yuan in 2009, which was much lower than thoseof the YRD and PRD (35,262–84,810 Yuan and 67,321 Yuan, respec-tively). Very few electronic equipments, like TVs and computers,were used in residents house in Huan County. In addition, the

population density of Huan County was 38 people km�2, contribut-ing to about one fifteenth to twentieth of 779 and 590 people km�2,respectively, for the YRD and PRD. Therefore, except for very fewlocal sources, we postulated that regional range atmospherictransport is a dominant pathway for PBDEs input into the CLP soil.

3.4. Preliminary evidence of regional range atmospheric transport ofPBDEs

It is interesting to note that the mean percentage of BDE-209was 43.5% in this study, which was highly different with those re-ported in Chongming Island (>90%) (Duan et al., 2010), the PRD(93%) (Zou et al., 2007), Linfen (>65%) (Li et al., 2009), Taiyuan(>70%) (Li et al., 2008), and in Michigan of the USA (79% in the Shi-awassee River and 90% in the Saginaw River) (Yun et al., 2008). Thisfindings may due to the fact that the lower-brominated congenershave a significant potential of regional range transport, whereasthe highly brominated congeners have a very low potential toreach remote areas (Wania and Dugani, 2003). Moreover, the aver-age of ratios of BDE-47 to BDE-99 in soils was 1.6 with a range of0.69–3.1, which is significantly different with those in Penta-BDEproducts based on independent one sample t-test (�0.79 in DE-71 and �0.96 in Bromkal 70-5DE; t = 8.2 and 10.5, respectively,both p = 0.000) (La Guardia et al., 2006). Furthermore, the ratiosof BDE-153 to BDE-154 in this study (mean: 5.6) were inconsistentto the ratio found in Octa-BDE based on independent one sample t-test (i.e., 8.1 in DE-79; t = �2.8, p = 0.01) (La Guardia et al., 2006).

Such these difference may due to PBDE congeners fractionationchanging during their transport in the environment and partition-ing in various environmental media/surfaces due to their differentphysicochemical properties (Harner and Shoeib, 2002; Palm et al.,2002; Wania et al., 2002), i.e., volatilization, octanol–air partitioncoefficient (Koa), and water solubility, or vegetation absorption(Gouin and Harner, 2003), microbial degradation (Gerecke et al.,2005), photodegradation (Ahn et al., 2006), and air-to-soil ex-change (Cetin and Odabasi, 2007). Gouin et al. developed a modelon the environmental fate of PBDEs illustrated that congeners mayundergo different degradation processes in soil at the presence ofvegetation (Gouin and Harner, 2003). Gerecke et al. reported high-er-brominated BDEs can degrade to lower-brominated BDEs byanaerobic mesophilic microorganisms (Gerecke et al., 2005). Ahnet al. suggested that photodegradation of BDE-209 on mineralaerosols during long range atmospheric transport may be animportant fate process for BDE-209 in the environment (Ahnet al., 2006).

3.5. Potential PBDE source(s) for regional range atmospheric transport

As a major sink and environmental reservoir, soil can receivePBDEs via deposition of dry particle, wet, and dry gaseous. Cetinand Odabasi found positive relationships between the PBDE conge-ner profile in soil and air (r2 = 0.13–0.79, p < 0.01), thus furthersupporting the assumption of a close link between air and soil.They measured average dry deposition fluxes of total PBDEs forsuburban and urban sites (67.6 and 128.8 ng m�2 day�1, respec-tively) in Izmir, Turkey and indicated dry particle, wet, and gasdeposition contribute 60%, 32%, and 8%, respectively, to annualPBDEs flux to the suburban soil (Cetin and Odabasi, 2007). As asemiarid region with annual precipitation of �300 mm, the CLPwas formed by the deposition of dust historically and dustfallcontinuing in step-wise way with the accumulation rate of0.75 g m�2 day�1 in recent years (Sun et al., 2001). Therefore, wethought dry deposition is the main way for the input of PBDEs insoil.

Assuming the transfer of PBDEs in the soil–air system ap-proached equilibrium, we further explored the potential PBDEs

1396 X.-Z. Meng et al. / Chemosphere 83 (2011) 1391–1397

source(s) for the CLP via regional range atmospheric transport. Theequilibrium partitioning of a chemical between air and soil is de-scribed by the dimensionless soil–air partition coefficient KSA,which is related to Koa in the following model proposed byHippelein and McLachlan (Hippelein and McLachlan, 1998).

KSA ¼ 0:411f ocqKoa ð1Þ

where q is the average density of the dry soils (g cm�3) and foc is thefraction of organic carbon on a dry soil basis. We calculated the gas-eous concentrations of PBDEs congeners in the CLP using the Eq. (1)and the Koa values at 25 �C obtained from a previous study (Harnerand Shoeib, 2002). As shown in Table S3, the maximum concentra-tions of BDE-17, 28, 47, 99, and 100 were 14.0, 14.5, 47.7, 6.90, and0.44 pg m�3, respectively. Clearly, our data were much lower thanthe reported data from an urban station in Xi’an (420 km south ofHuan County; Fig. 1), a city with the largest electronics industryin northwestern China (Table S3) (Jaward et al., 2005). Thus, on ageographical and regional scale, we suggested Xi’an is a potentialsource of PBDEs to soil of the CLP via regional range atmospherictransport. Moreover, other surrounding industrial cities, includingLanzhou (480 km west of Huan County) and Yinchuan (260 kmnorth of Huan County), may have potential influence to the soilPBDEs in the CLP. Harrad and Hunter also showed the PBDE concen-trations in soils usually reflect a gradient (high to low) from thecentral city out to rural areas consistent with atmospheric measure-ments (Harrad and Hunter, 2006). More studies are needed toinvestigate the factors (like wind direction) and pathway on howthe surrounding cites to influence PBDEs levels in soils from theCLP.

4. Conclusions

PBDEs with log-normal distribution were ubiquitous in surfacesoil of the CLP, one of the most extensive areas of loess depositionin the world. BDE-209, 47, 99, and 153 were the predominatedcongeners and PBDEs in most of soil samples have the similarsources, including of Penta-, Octa, and Deca-BDE. As a sparselypopulated, undeveloped, and agricultural region, PBDEs levels (ex-cept for BDE-209) in soil were similar to those in very developedregions in China, suggesting regional range atmospheric transportmay play an important role for input of PBDEs in the CLP. Mean-while, the characteristics of percentage of BDE-209 to the total,the ratio of BDE-47 and 99, and the ratio of BDE-153 and 154 in soilprovided the preliminary evidence for the regional range atmo-spheric transport. Potential PBDEs sources may from the surround-ing industrial cities of the CLP. Therefore, more studies are neededto explore the atmospheric transport and fate of PBDEs in thisregion.

Acknowledgements

We are grateful to the students from Tongji University whohelped with soils collection in Huan County. Financial supportfrom the National Key Technology R&D Program in the 11th Five-Year Plan of China (No. 2008BAC46B02), the National Natural Sci-ence Foundation of China (No. 40901251), the Foundation of theState Key Laboratory of Pollution Control and Resource Reuse(No. PCRRY09001), and the Program for Young Excellent Talentsin Tongji University (No. 2009KJ049).

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.chemosphere.2011.02.057.

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