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Distribution and region-specific sources of Dechlorane Plus in marine sediments from the coastal East China Sea
Science of the Total Environment 573 (2016) 389–396
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Distribution and region-specific sources of Dechlorane Plus in marine sediments from the coastal East China Sea Guoguang Wang, Jialin Peng, Ting Hao, Yao Liu, Dahai Zhang, Xianguo Li ⁎ Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education, Qingdao 266100, China
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• The first records of DP were reported in coastal East China Sea. • Higher levels of DP were detected in the southern inner shelf. • Regional sources of DP were identified by using lignin and n-alkanes. • Enrichment of syn-DP was found in marine sediments. • anti-DP was more vulnerable to degradation during LRAT and after burial.
a r t i c l e
i n f o
Article history: Received 29 June 2016 Received in revised form 13 August 2016 Accepted 13 August 2016 Available online xxxx Editor: Jay Gan Keywords: Dechlorane Plus Region-specific source Environmental behavior Lipid biomarker Lignin East China Sea sediment
⁎ Corresponding author. E-mail address: [email protected] (X. Li).
http://dx.doi.org/10.1016/j.scitotenv.2016.08.090 0048-9697/© 2016 Elsevier B.V. All rights reserved.
a b s t r a c t Dechlorane Plus (DP) is a highly chlorinated flame retardant and found to be ubiquitously present in the environment. We reported here the first record of DP in sediments from the coastal East China Sea (ECS). DP was detected in most of the surface sediments, and the concentrations ranged from 14.8 to 198 pg/g dry weight (dw) with a mean value of 64.4 pg/g dw. Overall, DP levels exhibited a seaward decreasing trend from the inshore toward outer sea. The fractional abundance of anti-DP (fanti) showed regional discrepancies, attributing to different environmental behaviors of DP isomers. Depth profiles of DP in a sediment core from estuarine environment showed distinct fluctuation, and the core in open sea had stable deposition environment with two peak values of DP in ~1978 and 2000. The fanti exhibited downward decreasing trend prior to mid-1950s, indicating a preferential degradation of anti-DP and/or a greater adsorption capacity of syn-DP after its burial. Lignin and lipid biomarkers (∑C27 + C29 + C31 n-alkanes) of terrestrial organic matters were introduced to identify region-specific sources of DP, and the results showed that DP in the northern inner shelf, southern inner shelf of 29 °N and mud area southwest of Cheju Island was mainly come from Yangtze River (YR) input, surface runoffs after discharge of local sources close to the Taizhou-Wenzhou Region and the atmospheric deposition from the North China and East Asia, respectively. The coastal ECS was an important reservoir of DP in the world, with mass inventory of approximately 310.7 kg in the surface sediments (0–5 cm). © 2016 Elsevier B.V. All rights reserved.
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1. Introduction Dechlorane Plus (DP), a highly chlorinated flame retardant, has been widely used in commercial and industrial polymer materials, such as electronic wires and cables, plastic roofing materials and computer connectors (Betts, 2006; Sverko et al., 2011). The technical DP mixture primarily comprises of two conformers, syn-DP and anti-DP. There are two major DP manufacturing facilities in the world, namely, OxyChem in Niagara, USA and Anpo Electrochemical Co. (Anpo) in Huai'an, China, with annual production as high as 5000 tons (Sverko et al., 2011) and 300– 1000 tons (Wang et al., 2010b), respectively. The United States Environmental Protection Agency has classified DP as a high production volume chemical (Ren et al., 2008). Although DP has been produced and used for almost 50 years, its occurrence was first detected in air, sediment and fish from the Laurentian Great Lakes in 2006 (Hoh et al., 2006). Thereafter, DP has been reported in various environmental matrices, such as air (Liu et al., 2016; Möller et al., 2010), sediments (Sühring et al., 2016; Yang et al., 2011), water (Mahmood et al., 2015; Qi et al., 2010), soils (Ma et al., 2014; Yu et al., 2010), dust (Li et al., 2015; Zhu et al., 2007), animals (Sun et al., 2012; Von Eyken et al., 2016) and even human beings (Kim et al., 2016; Siddique et al., 2012) in all major continents except Africa (Wang et al., 2016b). In marine environments, organic matters buried in the sediments of estuaries and their surrounding areas mainly contain terrestrial organic matters (TOM) from land through river input or/and atmospheric deposition and marine organic materials derived from marine primary productivity. If sharing similar migration pathways and deposition characteristics to those of TOM, the distribution of anthropogenic organic pollutants should be similar, and a significant correlation should also be observed between them. Xing et al. (2011) reported that lignin and long-chain odd-carbon n-alkanes (C27 + C29 + C31 n-alkanes) showed higher potential as precise proxies of TOM compared with traditional proxies of C/N ratio and δ13C. The East China Sea (ECS), one of the largest shelf seas in the western Pacific of the northern hemisphere, is a river-dominated marginal sea and annually receives large quantities of sediments from the dominated Yangtze River (YR) and some small rivers in south of YR (Qiantang River, Qu River and Min River) (Guo et al., 2003b; Lim et al., 2007). Additionally, the coastal ECS is adjacent to Shanghai, Fujian and Zhejiang Provinces in China, which are highly urbanized and industrialized. More importantly, a booming electronic-waste (e-waste) recycling center is located at the Zhejiang Province. Although DP is widely used and produced in China, environmental data of DP are mostly derived from studies in the e-waste recycling, industrial and DP manufacturing areas (Helm et al., 2008; Wang et al., 2010a; Yu et al., 2010; Zhang et al., 2011), and information on marine environments in coastal China
seas is very limited. Only Jia et al. (2011) and Zhao et al. (2011) investigated DP in the sediments and oyster from the inshore area of Dalian and sediments from coastal Yellow Sea, respectively. Moreover, the historical records of DP have not been reported in marine environments in China until now. Therefore, the present study aimed to investigate the distribution and environmental fate of DP in ECS sediments. More importantly, multiple proxies of TOM were introduced to identify the regional sources and migration pathways of DP in the coastal ECS sediments. To our knowledge, we reported the first record of DP in the ECS, and this was also the first work to introduce biomarkers of TOM to identify DP sources. 2. Materials and methods 2.1. Sample collection A detailed illustration of the sampling sites was shown in Fig. 1. A total of 34 surface sediments (0–5 cm) from the inner shelf and mud area southwest of Cheju Island in the ECS were collected during a cruise conducted by R/V Dong Fang Hong 2 of Ocean University of China in April 2010. Briefly, the sediments were collected by a Van Veen stainless steel grab sampler (Qingdao Orson). Then, the surface layers (0–5 cm) were cut using a stainless steel blader. Meanwhile, two sediment cores, P01 (122°21′36″ E and 31°14′24″ N, 24 cm long) and P14 (122°28′20″ E and 28°30′14″ N, 20 cm long) (Fig. S1) were also collected in 2010 and 2011, respectively. The cores were separated into 2 cm (for core P01) and 1 cm (for core P14) intervals along the length using a stainless steel cutter aboard the ship. All samples were wrapped in aluminum foil and stored at −20 °C until further analysis. 2.2. Chemicals, sample preparation and instrumental analysis Chemicals, sediment pretreatment and analytical procedures (including DP, ∑C27 + C29 + C31 n-alkanes, lignin, grain size, total organic carbon (TOC) and dating of the sediment cores) were given in detail in Supplementary materials. Briefly, The individual anti-DP and syn-DP standards were used for identification and quantification, 2,4,5,6tetrachloro-m-xylene (TCmX) and PCB-209 were added as surrogates, and BDE-77 was used as an internal standard. All of the standards were purchased from AccuStandards, Inc. (USA). For DP determination, dried sediments (approximately 10 g) were spiked with TCmX and PCB209, and processed in an ultrasonic bath in 2.0 M NaOH-methanol solution for 30 min. Activated copper granules were added to remove sulfur potentially existed in the sediments during the extraction. Then 50 mL Milli-Q water and 50 mL n-hexane, in turn, were added. The extracts of organic phase were separated from the mixture, concentrated in a
Fig. 1. Location of the sampling sites (violet dots) and regional ocean circulation patterns in the coastal ECS. Mud areas are marked in pink. YDW (Yangtze Diluted Water), YSCC (Yellow Sea Coastal Current), ZFCC (Zhejiang-Fujian Coastal Current), TWC (Taiwan Warm Current) and KC (Kuroshio Current). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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rotary vacuum evaporator and purified on a multi-layer silica column packed with neutral silica gel (4 g, 5% water deactivated), 50% (w/w) sulfuric acid silica (3 g) and anhydrous sodium sulfate (3 g) from bottom to top. The DP fraction was eluted with 70 mL n-hexanes, concentrated to about 0.5 mL and dried out under a gentle stream of nitrogen. Finally, the eluent was solvent-exchanged to isooctane to a constant volume of 60 μL with a known amount of BDE-77 prior to instrumental analysis. DP was measured by a Shimadzu 2010plus gas chromatograph coupled with an electron capture detector (GC-ECD). A DB-5 capillary column (15 m × 0.25 mm i.d. × 0.10 μm film thickness) was used for separation. 2.3. Quality assurance and quality control For each batch of 10 samples, a procedural blank (in which aluminum foil identical to that used to wrap the samples was solvent-extracted and processed in the same way as the samples), a matrix-spiked sample (a sediment spiked with anti-DP and syn-DP, together with the same sediment without DP spiked, was used for calculation of matrixspiked recoveries) and a sample duplicate were processed. The method detection limits of DP was calculated by multiplying the final extract volume by the concentration of target compounds that could produce a chromatographic peak with a S/N ratio of 5 and subsequently divided by the dry weight (dw) of the sediment samples, and was 0.2 pg/g (dw) for syn-DP and 0.7 pg/g (dw) for anti-DP. No target compounds were detected in the procedural blanks. The matrix-spiked recoveries of DP ranged from 88.2% to 104%, and the surrogate recoveries ranged from 81.5% to 95.7% and from 84.9% to 100% for TCmX and PCB-209, respectively. The relative percentage differences for duplicated samples were b14.7%. All the reported concentrations of DP were not corrected for the surrogate recoveries, and expressed based on the dry weight of the sediment samples. 3. Results and discussion 3.1. Occurrence of DP The detection rates, concentration ranges, and mean values of DP as well as TOC contents in the 34 surface sediments from the coastal ECS were presented in Table 1, with detailed data in Table S1. DP was detected in almost all samples with the detection rates of 97% for syn-DP and 100% for anti-DP, indicating the ubiquitous presence of DP in the ECS. The total concentrations of DP isomers varied from 14.8 to 198 pg/g dw, with a mean value of 64.4 pg/g dw. Reports on DP in sediments from different locations around the world were summarized in Table S2. Note that comparisons were made with not only the results of available studies on marine sediments but also the values of similar matrix (river sediments) since data on DP levels in marine sediments were currently very limited. Overall, the ECS was at a low level of DP contamination among the compared regions. The relatively low level of contamination in this area was also observed for polybrominated diphenyl ethers (Wang et al., 2016a), polychlorinated biphenyls (Duan et al., 2013) and short-chain Table 1 Concentrations of DP isomers (pg/g dw), TOC (%) and fanti in the surface sediments (n = 34) from the ECS. Compound
DF (%)a
Range
Mean (SD)b
Median
syn-DP anti-DP ∑DP fanti TOC (%)
97% 100
nd-137c 11.2–82.4 14.8–198 0.21–1.0 0.16–0.99
31.9 (29.9) 28.7 (17.2) 64.4 (37.9) 0.42 (0.20) 0.64 (0.19)
42.7 28.8 72.1 0.43 0.69
a b c
DF: detection frequency. Mean: the geometric average. nd: not detection.
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chlorinated paraffins (Zhao et al., 2013), which might be attributed to the potential “dilution effect” resulted from the large quantities of terrestrial and marine matters as well as the high sedimentation rate in the YR estuary and inner shelf of the ECS (Bouloubassi et al., 2001; Paerl, 2006; Zhao et al., 2013). 3.2. Spatial and temporal distribution of DP 3.2.1. Spatial distribution The spatial distributions of DP, TOC and median grain size were shown in Fig. 2. In the inner shelf, the relatively higher levels of ∑DP were found in the nearshore areas, with an offshore decreasing trend toward the outer shelf (Fig. 2a), and correspondingly DP showed a significantly negative correlation (r2 = 0.263, p b 0.05) with the longitude of the sampling sites. The spatial pattern was consistent with polybrominated diphenyl ethers (Li et al., 2012) and polychlorinated biphenyls (Duan et al., 2013) in this region, indicating the direct influence of the land-based sources. Additionally, there was a distinctly spatial discrepancy between the northern and southern inner shelf of the 29 ° N. Overall, the DP levels in the southern part were higher than those in the northern part (Fig. 2a). The southern inner shelf with the highest DP content was close to the Taizhou-Wenzhou Region, which is a highly urbanized and industrialized region. Elevated levels of DP were usually observed in the urban and industrial areas, and showed a decreasing trend with increasing distance from these areas (Helm et al., 2008; Ma et al., 2014; Qi et al., 2010), indicating that these regions were the significant local sources of DP for the adjacent environmental compartments. Moreover, Taizhou and Wenzhou are two of the well-known electronic/ electrical manufacturing and e-waste recycling cities. With outdated technologies for e-waste recycling, large quantities of DP were detected in environmental matrices in these regions (Chen et al., 2011; Yu et al., 2010; Zheng et al., 2010). These results indicated that Taizhou-Wenzhou Region should be responsible for the high DP levels in the southern inner shelf. In the northern inner shelf, relatively higher levels of DP were found in the area near Hangzhou Bay, which is a significant deposition center of YR-derived fine-grained sediments (Liu et al., 2007). In addition, Hangzhou Bay is a large multifunction harbor and mariculture zone, and consumption of products with different additives would inevitably bring serious pollution to the coastal areas (Nakata et al., 2005). Pollutants transported by Qiantang River were also discharged into the Hangzhou Bay (Sun et al., 2013). Therefore, DP in the northern inner shelf might be influenced by the input of YR and Qiantang River. Over the entire studied area, high levels of DP were also detected in the mud area southwest of Cheju Island, associated with higher TOC contents and smaller particle sizes (Fig. 2b and c). This mud area was also a significant sink of polychlorinated biphenyls (Fan et al., 2014) and short-chain chlorinated paraffins (Zeng et al., 2012). The sediments in this region are mainly derived from the Old Yellow River estuary, which contained only a small amount of anthropogenic pollutant (Guo et al., 2001; Zeng et al., 2012). According to the studies by Guo et al. (2003a) and Wilkening et al. (2000), pollutants adsorbed on aerosols from the North China and East Asia could be transported to the northern Pacific Ocean by East Asian monsoon. The mud area is located at downwind of the Chinese mainland and the pathway for terrestrial contaminants to the northern Pacific Ocean, resulting in large quantities of contaminants entering this region through the atmospheric deposition of particles (Guo et al., 2006; Guo et al., 2003a). In addition, Cheju Island has been developed as a tourist area for many years, which inevitably resulted in release of pollutants from the consumption of industrial, tourist and household products, which may contain DP as flame retardant. Therefore, the high DP levels in the mud area southwest of Cheju Island might be from the atmospheric deposition and local sources. Due to the hydrophobicity of organic pollutants, TOC and grain size were two important factors controlling their distributions in aquatic environments (Hung et al., 2006; Zhao et al., 2013). In the present study, the TOC contents ranged from 0.16% to 0.99%, with an average of
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Fig. 2. Spatial distributions of DP (pg/g dw) (a), TOC (%) (b) and median grain size (Ф) (c) in the coastal ECS sediments using Kriging by Surfer 11.0.
0.64% (Table 1). The TOC distributions only resembled those of DP in the northern inner shelf of 29 °N and the mud area southwest of Cheju Island (Fig. 2a and b), and significantly positive correlations (r2 = 0.316, p b 0.05 for northern inner shelf; r2 = 0.469, p b 0.05 for mud area southwest of Cheju Island) were also found between TOC and DP. In addition, the resemblance was also found between the distributions of DP and grain size in these two areas (Fig. 2a and c), and DP showed strong correlations (r2 = 0.322, p b 0.05 for northern inner shelf; r2 = 0.378, p b 0.05 for mud area southwest of Cheju Island) with grain size. However, neither such correlation (r2 b 0.1) nor similar distribution was found between DP and TOC as well as grain size in the southern inner shelf, which might be attributed to the direct discharge of local sources. 3.2.2. Temporal distribution The historical records of DP in the sediment cores from coastal ECS were shown in Fig. 3. DP was detected in almost all the sediment segments, indicating that DP had been discharged into the coastal ECS for a long time. As shown in Fig. 3, trace levels of DP were detected from early 1930s to mid-1940s in both cores, which was prior to the starting production of DP in the 1970s in OxyChem, in agreement with the results in the Great Lakes (Qiu et al., 2007; Yang et al., 2011). This phenomenon might be explained by the sediment resuspension, bioturbation, and downward smearing and migration after DP burial (Qiu et al., 2007; Zhu et al., 2014). However, considerable discrepancies
in temporal trends were observed between the two sediment cores, which might be attributed to different deposition environments in these two areas. In Core P01, a considerable fluctuation of DP concentrations along with core depth was found (Fig. 3a), which was consistent with organochlorine pesticides in this region (Lin et al., 2016), attributing to mixed effects of varied sedimentation rates, shallow water depth (b 20 m) and strong resuspension. In spite of this, there was an identifiably general trend in the vertical distribution. The DP levels showed a rapid increasing from mid-1940s, peaked in ~1965, and decreased thereafter, while with another peak in ~ 1991 (Fig. 3a). Since no DP data was available in sediment cores in China, the temporal trends of DP in the core P01 were compared with those in Great Lakes (Shen et al., 2011; Yang et al., 2011). No similarity was observed, indicating different deposition environments between these two areas. However, the periods of higher DP levels coincided with those of the higher Yangtze sediment loading associated with extraordinary flooding (1954, 1971, 1991 and 1998) (Guo et al., 2006; Lin et al., 2016). The accumulation of pollutants in the river-ocean boundary zone was sensitive to elevated outflow of sediment loading, because sediments and associated pollutants were rapidly deposited and well-preserved in the estuary mud area during the flooding (Lin et al., 2016). In Core P14, the DP levels started increasing in mid-1950s with a maximum concentration occurred in ~1978, followed by a distinct decline (Fig. 3a). The increasing trend was also found in sediment cores
Fig. 3. Historical records of DP (pg/g dw) in the sediment cores P01 (a) and P14 (b) from the coastal ECS using B-spline curve fitting.
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from the Great Lakes (Hoh et al., 2006; Zhang et al., 2011). Since DP was starting to be produced in late 1990s in China (Wang et al., 2010b), the increasing trend was believed to be resulted from the import of DP-containing electronic equipments and the rapid economic development in China. DP levels showed a decreasing trend after ~ 1980, consistent with the results in Lake Ontario and Lake Michigan (Hoh et al., 2006; Shen et al., 2011), which might be attributed to the decreasing production volume of DP during the period of 1986 to 2006 (USEPA, 2006). With the extensively e-waste recycling and extensive DP production by Anpo in late 1990s, large quantities of DP were released, and another peak occurred in around 2000. However, the levels of DP rapidly decreased after 2000, and the decreasing trend was also observed in Core P01, which might reflect the decrease in production and/or an improvement in controlling the discharge in recent years in China. Compared with Core P01, Core P14 could more significantly imply the overall trend of DP input into the ECS, and the sedimentary records fitted better with available data of historical application as well as the signal of economic development in China. 3.3. Isomer profiles of DP DP has two conformers, syn- and anti-DP. The isomer ratios of DP can be described by the fractional abundance, and anti-DP fraction (fanti) was calculated as the concentration of anti-DP divided by the concentration of total DP. Previously reported fanti in technical DP mixture ranged from 0.59 to 0.80, depending on the manufacturer (Hoh et al., 2006; Tomy et al., 2007; Wang et al., 2010b). Due to the different physicochemical properties of syn- and anti-DP such as octanol-water partition coefficient (Kow) and solubility (Fang et al., 2014), the fanti variations between the environment matrices and the technical DP mixture were generally used to explore the differences in environmental behaviors and fates of the two isomers in the studied matrices. As shown in Table 1, the fanti was in the range of 0.21–1.00, with a mean value of 0.42, which was distinctly lower than that of the technical DP mixture. To better understand the fanti variation in the studied area, the fanti was compared among all the sampling sites (Fig. 4). As shown in Fig. 4, the fanti showed significantly region-specific discrepancies (p b 0.01, one way analysis of variance). Among the studied area, the mud area southwest of Cheju Island had the lowest fanti (0.32), corresponding with the longest distance from the Chinese mainland. Previous studies reported that anti-DP was more vulnerable to photodegradation than syn-DP during long-range atmospheric transport (LRAT) (Möller et al., 2010; Sverko et al., 2011; Tao et al., 2015). Moreover, Fang et al.
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(2014) estimated the octanol-air partitioning coefficient (log Koa) of syn- and anti-DP, and found that log Koa of syn-DP was lower than that of anti-DP, indicating a greater LRAT partitioning potential into air for syn-DP. The reduced fanti was also observed in marine environments in Arctic and Antarctic and attributed to the LRAT (Möller et al., 2010). Therefore, DP with enriched syn-DP might mainly come from the atmospheric deposition in the mud area. In the northern inner shelf of 29 °N, the mean fanti was 0.49, and the fanti showed a decreasing trend from the north to south except for two extraordinarily high fanti (1.00 in P05 and 0.78 in P06, close to Zhoushan Island). In winter, most of the fine particles derived from the YR were resuspended by the strong hydrodynamic conditions in the Yangtze River Estuary, and transported southward along the Zhejiang-Fujian Coastal Current (Liu et al., 2007). Due to the higher log Kow of syn-DP, it preferentially adsorbed on the fine particles (Fang et al., 2014), which was also supported by the significantly positive correlations between the syn-DP fraction and TOC (r2 = 0.427, p b 0.05) as well as grain size (r2 = 0.361, p b 0.05) in the northern inner shelf. Consequently, a north to south decreasing trend of fanti could be attributed to the southward transport of fine particles with the abundance of syn-DP. In contrast, fanti in the southern inner shelf was 0.63, which is close to that of the technical DP mixture, and there was no distinct variation between sampling sites. Thus, the direct discharge of local sources should be responsible for DP in the southern inner shelf. The isomer profiles of DP in Core P01 and P14 were shown in Fig. 5. During the period of mid-1950s to 2011, the fanti fluctuated in the range of reported technical DP values in both cores. The similar phenomenon was also observed in sediment cores from Great Lakes (Hoh et al., 2006; Yang et al., 2011), indicating the contribution of DP commercial sources for a long time. However, the fanti was lower than that in technical DP mixture prior to mid-1950s (Fig. 5b). The linear regression showed that fanti was positively correlated with the deposition year in both cores significantly (r2 = 0.313, p b 0.05 for P01 and r2 = 0.604, p b 0.01 for P14, Fig. S2a and b). This result indicated that fanti decreased with increasing depth, which might be attributed to the greater adsorption capacity of syn-DP (Kow: syn-DP N anti-DP) (Fang et al., 2014) by organic matters and/or the preferential biodegradation of anti-DP after sedimentation (Sverko et al., 2015; Sverko et al., 2011). On the contrary, there was no significant change in fanti associated with depth in sediment cores from Lake Erie (Sverko et al., 2007), and fanti increased with depth in sediment cores from Lake Ontario (Qiu et al., 2007). These discrepancies might be attributed to different depletion/enrichment mechanism of syn- and anti-DP in marine sediments versus freshwater sediments (Jia et al., 2011).
Fig. 4. The fanti values at different sampling sites from the coastal ECS.
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Fig. 5. Historical trends of fanti values in the sediment cores P01 (a) and P14 (b) from the coastal ECS using B-spline curve fitting.
3.4. Source identification of DP implied by biomarkers of TOM Terrestrial high plants can produce long-chain (C25–C35) n-alkanes with a strong preference of odd-to-even carbon, and C27, C29 and C31 n-alkanes are the most abundant congeners (Rao et al., 2008; Xing et al., 2011). Lignin is a naturally occurring and widely abundant biopolymer found almost exclusively in terrestrial vascular plants, and essentially absent from marine organisms (Jex et al., 2014; Kuzyk et al., 2008). In general, lignin is intrinsically stable and relatively resistant to microbial degradation, and therefore serves to be a specific tracer in sediments for TOM (Goñi and Hedges, 1995; Tesi et al., 2007). Previous studies reported that ∑ C27 + C29 + C31 n-alkanes could enter the oceans through fluvial and atmospheric inputs (Gagosian et al., 1981; Xing et al., 2011), and lignin reflected only fluvial TOM entering into the marine environment via surface runoffs (Jex et al., 2014; Tesi et al., 2007). The spatial distributions of ∑C27 + C29 + C31 n-alkanes and lignin in the sediments from the coastal ECS were shown in Fig. 6. In the northern inner shelf of 29 °N, ∑C27 + C29 + C31 n-alkanes had the highest contents, and exhibited a decreasing trend from inshore to offshore (Fig. 6a). A similar pattern was also found in this region by Xing et al. (2011), indicating that YR-derived TOM mainly deposited in Yangtze River Estuary and the northern inner shelf. In addition, relatively higher
contents of ∑C27 + C29 + C31 n-alkanes were also detected in the mud area southwest of Cheju Island. The distributions of ∑C27 + C29 + C31 n-alkanes resembled to those of DP in the northern inner shelf and the mud area southwest of Cheju Island (Fig. 2a). Linear regression showed that DP also had significantly positive correlations with ∑C27 + C29 + C31 n-alkanes in the northern inner shelf (r2 = 0.592, p b 0.01, Fig. S3a) and the mud area southwest of Cheju Island (r2 = 0.839, p b 0.01, Fig. S3c). However, neither r esemblance nor correlation was found between DP and ∑C27 + C29 + C31 n-alkanes in the southern inner shelf (Fig. 2a, Fig. 6a and Fig. S3b). These results indicated that DP and ∑ C27 + C29 + C31 n-alkanes shared similar sources and migration pathway in the northern inner shelf and the mud area southwest of Cheju Island, and mainly derived from YR input and atmospheric deposition, respectively. However, in the southern inner shelf, DP was mainly come from the discharge of local sources. The lignin content presented a seaward decreasing trend in the inner shelf (Fig. 6b), consistent with that of DP (Fig. 2a). Moreover, DP and lignin showed strong positive correlations in the area (r2 = 0.557, p b 0.01 for northern inner shelf and r2 = 0.306, p b 0.05 for southern inner shelf, Fig. S4). These results implied that DP in the inner shelf was potentially derived from YR input and surface runoffs after discharge from local sources. Compared with DP and ∑C27 + C29 + C31
Fig. 6. Spatial distributions of ∑C27 + C29 + C31 n-alkanes (ng/g) (a) and lignin (mg/10 g) (b) in the coastal ECS sediments using Kriging by Surfer 11.0.
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n-alkanes, no high values of lignin were observed in the mud area southwest of Cheju Island, and the correlation between DP and lignin was weak (r2 b 0.1, Fig. S4c). Therefore, atmospheric deposition should be responsible for DP in the mud area. According to the region-specific deposition conditions, distribution patterns and isomer profiles of DP and biomarkers of TOM, we concluded that DP in the northern inner shelf, southern inner shelf of 29 °N and the mud area southwest of Cheju Island were mainly come from the YR input, surface runoffs after discharge of local sources from the TaizhouWenzhou region and atmospheric deposition of DP from the North China and East Asia, respectively. 3.5. Mass inventory of DP To assess the contamination extent and potential of sediments as a pollutant source to the nearby environment, the mass inventory of DP in the coast ECS were tried to estimate according to Zhao et al. (2011) and Zhou et al. (2014). The study region was divided into 34 compartments, and make sure that each of the sampling site was located at the center of its own compartment. The inventory (I, in kg) was calculated by the following equation: I ¼ CAdp where C is the DP concentration in the sediment sample; A is the area of water body (7.8 × 104 km2) (Li et al., 2012); p is the sediment dry density of 1.2 g/cm3 recommended by Liu et al. (2007); and d is the thickness of sediment sample of 5 cm (surface sediments). The mass inventory in the surface sediments from the coastal ECS was estimated to be approximately 310.7 kg for DP. The data on DP inventory in marine environments were limited in the world. Zhao et al. (2011) reported that the DP inventory per unit area in bays adjacent to the Yellow Sea was 8.5, 20.1 and 37.7 pg/cm2 for Jiaozhou Bay, Taozi Bay and Sishili Bay, respectively. Qiu et al. (2007) estimated that DP inventory was approximately 120,000 pg/cm2 in Lake Ontario (about 10,000 kg in total), where it is close to the DP manufacturing plant. In the present study, the DP inventory based on per unit area was 39.8 pg/cm2 in the coastal ECS, which was comparable to that in Sishili Bay, slightly higher than Jiaozhou Bay and Taozi Bay, but much lower than Lake Ontario. Consequently, we believe that sediment is an important sink of DP in the ECS. 4. Conclusions The surface sedimentary DP in the coastal ECS showed a seaward decreasing trend from inshore to offshore in the inner shelf, with the highest levels in Taizhou-Wenzhou Region, and fanti showed the region-specific discrepancies. In the sediment cores, a decreasing trend in recent years was revealed for DP, and fanti decreased with increasing the depth. Lignin and ∑C27 + C29 + C31 n-alkanes were introduced to identify the regional sources of DP, and the results showed that DP in the northern inner shelf, southern inner shelf of 29 °N and the mud area southwest of Cheju Island were mainly come from YR input, surface runoffs after discharge of local sources and atmospheric deposition, respectively. Biomarkers of TOM provided new valuable information to identify region-specific sources and migration pathways of DP in the present study. However, marine organic materials may alter the DP distribution and behavior and thus may have a potential influence on the DP sources and migration. Further studies are needed to investigate this question. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (Grant No. 41276067). Grain size data were supported by Dr. Xiaodong Zhang (Marine Geosciences College of the
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Ocean University of China) and the core sedimentation rates were supported by Prof. Liguang Sun (University of Science and Technology of China), to whom we owe our thanks. We also thank the crew members of R/V Dong Fang Hong 2 for helps in collecting samples. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2016.08.090. References Betts, K.S., 2006. A new flame retardant in the air. Environ. Sci. Technol. 40, 1090–1091. Bouloubassi, I., Fillaux, J., Saliot, A., 2001. Hydrocarbons in surface sediments from the Changjiang (Yangtze river) estuary, East China Sea. Mar. Pollut. Bull. 42, 1335–1346. Chen, S.-J., Tian, M., Wang, J., Shi, T., Luo, Y., Luo, X.-J., Mai, B.-X., 2011. Dechlorane Plus (DP) in air and plants at an electronic waste (e-waste) site in South China. Environ. Pollut. 159, 1290–1296. Duan, X., Li, Y., Li, X., Li, M., Zhang, D., 2013. 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Distribution and region-specific sources of Dechlorane Plus in marine sediments from the coastal East China Sea Guoguang Wang, Jialin Peng, Ting Hao, Yao Liu, Dahai Zhang, Xianguo Li ⁎ Key Laboratory of Marine Chemistry Theory and Technology (Ocean University of China), Ministry of Education, Qingdao 266100, China
H I G H L I G H T S
G R A P H I C A L
A B S T R A C T
• The first records of DP were reported in coastal East China Sea. • Higher levels of DP were detected in the southern inner shelf. • Regional sources of DP were identified by using lignin and n-alkanes. • Enrichment of syn-DP was found in marine sediments. • anti-DP was more vulnerable to degradation during LRAT and after burial.
a r t i c l e
i n f o
Article history: Received 29 June 2016 Received in revised form 13 August 2016 Accepted 13 August 2016 Available online xxxx Editor: Jay Gan Keywords: Dechlorane Plus Region-specific source Environmental behavior Lipid biomarker Lignin East China Sea sediment
⁎ Corresponding author. E-mail address: [email protected] (X. Li).
http://dx.doi.org/10.1016/j.scitotenv.2016.08.090 0048-9697/© 2016 Elsevier B.V. All rights reserved.
a b s t r a c t Dechlorane Plus (DP) is a highly chlorinated flame retardant and found to be ubiquitously present in the environment. We reported here the first record of DP in sediments from the coastal East China Sea (ECS). DP was detected in most of the surface sediments, and the concentrations ranged from 14.8 to 198 pg/g dry weight (dw) with a mean value of 64.4 pg/g dw. Overall, DP levels exhibited a seaward decreasing trend from the inshore toward outer sea. The fractional abundance of anti-DP (fanti) showed regional discrepancies, attributing to different environmental behaviors of DP isomers. Depth profiles of DP in a sediment core from estuarine environment showed distinct fluctuation, and the core in open sea had stable deposition environment with two peak values of DP in ~1978 and 2000. The fanti exhibited downward decreasing trend prior to mid-1950s, indicating a preferential degradation of anti-DP and/or a greater adsorption capacity of syn-DP after its burial. Lignin and lipid biomarkers (∑C27 + C29 + C31 n-alkanes) of terrestrial organic matters were introduced to identify region-specific sources of DP, and the results showed that DP in the northern inner shelf, southern inner shelf of 29 °N and mud area southwest of Cheju Island was mainly come from Yangtze River (YR) input, surface runoffs after discharge of local sources close to the Taizhou-Wenzhou Region and the atmospheric deposition from the North China and East Asia, respectively. The coastal ECS was an important reservoir of DP in the world, with mass inventory of approximately 310.7 kg in the surface sediments (0–5 cm). © 2016 Elsevier B.V. All rights reserved.
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1. Introduction Dechlorane Plus (DP), a highly chlorinated flame retardant, has been widely used in commercial and industrial polymer materials, such as electronic wires and cables, plastic roofing materials and computer connectors (Betts, 2006; Sverko et al., 2011). The technical DP mixture primarily comprises of two conformers, syn-DP and anti-DP. There are two major DP manufacturing facilities in the world, namely, OxyChem in Niagara, USA and Anpo Electrochemical Co. (Anpo) in Huai'an, China, with annual production as high as 5000 tons (Sverko et al., 2011) and 300– 1000 tons (Wang et al., 2010b), respectively. The United States Environmental Protection Agency has classified DP as a high production volume chemical (Ren et al., 2008). Although DP has been produced and used for almost 50 years, its occurrence was first detected in air, sediment and fish from the Laurentian Great Lakes in 2006 (Hoh et al., 2006). Thereafter, DP has been reported in various environmental matrices, such as air (Liu et al., 2016; Möller et al., 2010), sediments (Sühring et al., 2016; Yang et al., 2011), water (Mahmood et al., 2015; Qi et al., 2010), soils (Ma et al., 2014; Yu et al., 2010), dust (Li et al., 2015; Zhu et al., 2007), animals (Sun et al., 2012; Von Eyken et al., 2016) and even human beings (Kim et al., 2016; Siddique et al., 2012) in all major continents except Africa (Wang et al., 2016b). In marine environments, organic matters buried in the sediments of estuaries and their surrounding areas mainly contain terrestrial organic matters (TOM) from land through river input or/and atmospheric deposition and marine organic materials derived from marine primary productivity. If sharing similar migration pathways and deposition characteristics to those of TOM, the distribution of anthropogenic organic pollutants should be similar, and a significant correlation should also be observed between them. Xing et al. (2011) reported that lignin and long-chain odd-carbon n-alkanes (C27 + C29 + C31 n-alkanes) showed higher potential as precise proxies of TOM compared with traditional proxies of C/N ratio and δ13C. The East China Sea (ECS), one of the largest shelf seas in the western Pacific of the northern hemisphere, is a river-dominated marginal sea and annually receives large quantities of sediments from the dominated Yangtze River (YR) and some small rivers in south of YR (Qiantang River, Qu River and Min River) (Guo et al., 2003b; Lim et al., 2007). Additionally, the coastal ECS is adjacent to Shanghai, Fujian and Zhejiang Provinces in China, which are highly urbanized and industrialized. More importantly, a booming electronic-waste (e-waste) recycling center is located at the Zhejiang Province. Although DP is widely used and produced in China, environmental data of DP are mostly derived from studies in the e-waste recycling, industrial and DP manufacturing areas (Helm et al., 2008; Wang et al., 2010a; Yu et al., 2010; Zhang et al., 2011), and information on marine environments in coastal China
seas is very limited. Only Jia et al. (2011) and Zhao et al. (2011) investigated DP in the sediments and oyster from the inshore area of Dalian and sediments from coastal Yellow Sea, respectively. Moreover, the historical records of DP have not been reported in marine environments in China until now. Therefore, the present study aimed to investigate the distribution and environmental fate of DP in ECS sediments. More importantly, multiple proxies of TOM were introduced to identify the regional sources and migration pathways of DP in the coastal ECS sediments. To our knowledge, we reported the first record of DP in the ECS, and this was also the first work to introduce biomarkers of TOM to identify DP sources. 2. Materials and methods 2.1. Sample collection A detailed illustration of the sampling sites was shown in Fig. 1. A total of 34 surface sediments (0–5 cm) from the inner shelf and mud area southwest of Cheju Island in the ECS were collected during a cruise conducted by R/V Dong Fang Hong 2 of Ocean University of China in April 2010. Briefly, the sediments were collected by a Van Veen stainless steel grab sampler (Qingdao Orson). Then, the surface layers (0–5 cm) were cut using a stainless steel blader. Meanwhile, two sediment cores, P01 (122°21′36″ E and 31°14′24″ N, 24 cm long) and P14 (122°28′20″ E and 28°30′14″ N, 20 cm long) (Fig. S1) were also collected in 2010 and 2011, respectively. The cores were separated into 2 cm (for core P01) and 1 cm (for core P14) intervals along the length using a stainless steel cutter aboard the ship. All samples were wrapped in aluminum foil and stored at −20 °C until further analysis. 2.2. Chemicals, sample preparation and instrumental analysis Chemicals, sediment pretreatment and analytical procedures (including DP, ∑C27 + C29 + C31 n-alkanes, lignin, grain size, total organic carbon (TOC) and dating of the sediment cores) were given in detail in Supplementary materials. Briefly, The individual anti-DP and syn-DP standards were used for identification and quantification, 2,4,5,6tetrachloro-m-xylene (TCmX) and PCB-209 were added as surrogates, and BDE-77 was used as an internal standard. All of the standards were purchased from AccuStandards, Inc. (USA). For DP determination, dried sediments (approximately 10 g) were spiked with TCmX and PCB209, and processed in an ultrasonic bath in 2.0 M NaOH-methanol solution for 30 min. Activated copper granules were added to remove sulfur potentially existed in the sediments during the extraction. Then 50 mL Milli-Q water and 50 mL n-hexane, in turn, were added. The extracts of organic phase were separated from the mixture, concentrated in a
Fig. 1. Location of the sampling sites (violet dots) and regional ocean circulation patterns in the coastal ECS. Mud areas are marked in pink. YDW (Yangtze Diluted Water), YSCC (Yellow Sea Coastal Current), ZFCC (Zhejiang-Fujian Coastal Current), TWC (Taiwan Warm Current) and KC (Kuroshio Current). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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rotary vacuum evaporator and purified on a multi-layer silica column packed with neutral silica gel (4 g, 5% water deactivated), 50% (w/w) sulfuric acid silica (3 g) and anhydrous sodium sulfate (3 g) from bottom to top. The DP fraction was eluted with 70 mL n-hexanes, concentrated to about 0.5 mL and dried out under a gentle stream of nitrogen. Finally, the eluent was solvent-exchanged to isooctane to a constant volume of 60 μL with a known amount of BDE-77 prior to instrumental analysis. DP was measured by a Shimadzu 2010plus gas chromatograph coupled with an electron capture detector (GC-ECD). A DB-5 capillary column (15 m × 0.25 mm i.d. × 0.10 μm film thickness) was used for separation. 2.3. Quality assurance and quality control For each batch of 10 samples, a procedural blank (in which aluminum foil identical to that used to wrap the samples was solvent-extracted and processed in the same way as the samples), a matrix-spiked sample (a sediment spiked with anti-DP and syn-DP, together with the same sediment without DP spiked, was used for calculation of matrixspiked recoveries) and a sample duplicate were processed. The method detection limits of DP was calculated by multiplying the final extract volume by the concentration of target compounds that could produce a chromatographic peak with a S/N ratio of 5 and subsequently divided by the dry weight (dw) of the sediment samples, and was 0.2 pg/g (dw) for syn-DP and 0.7 pg/g (dw) for anti-DP. No target compounds were detected in the procedural blanks. The matrix-spiked recoveries of DP ranged from 88.2% to 104%, and the surrogate recoveries ranged from 81.5% to 95.7% and from 84.9% to 100% for TCmX and PCB-209, respectively. The relative percentage differences for duplicated samples were b14.7%. All the reported concentrations of DP were not corrected for the surrogate recoveries, and expressed based on the dry weight of the sediment samples. 3. Results and discussion 3.1. Occurrence of DP The detection rates, concentration ranges, and mean values of DP as well as TOC contents in the 34 surface sediments from the coastal ECS were presented in Table 1, with detailed data in Table S1. DP was detected in almost all samples with the detection rates of 97% for syn-DP and 100% for anti-DP, indicating the ubiquitous presence of DP in the ECS. The total concentrations of DP isomers varied from 14.8 to 198 pg/g dw, with a mean value of 64.4 pg/g dw. Reports on DP in sediments from different locations around the world were summarized in Table S2. Note that comparisons were made with not only the results of available studies on marine sediments but also the values of similar matrix (river sediments) since data on DP levels in marine sediments were currently very limited. Overall, the ECS was at a low level of DP contamination among the compared regions. The relatively low level of contamination in this area was also observed for polybrominated diphenyl ethers (Wang et al., 2016a), polychlorinated biphenyls (Duan et al., 2013) and short-chain Table 1 Concentrations of DP isomers (pg/g dw), TOC (%) and fanti in the surface sediments (n = 34) from the ECS. Compound
DF (%)a
Range
Mean (SD)b
Median
syn-DP anti-DP ∑DP fanti TOC (%)
97% 100
nd-137c 11.2–82.4 14.8–198 0.21–1.0 0.16–0.99
31.9 (29.9) 28.7 (17.2) 64.4 (37.9) 0.42 (0.20) 0.64 (0.19)
42.7 28.8 72.1 0.43 0.69
a b c
DF: detection frequency. Mean: the geometric average. nd: not detection.
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chlorinated paraffins (Zhao et al., 2013), which might be attributed to the potential “dilution effect” resulted from the large quantities of terrestrial and marine matters as well as the high sedimentation rate in the YR estuary and inner shelf of the ECS (Bouloubassi et al., 2001; Paerl, 2006; Zhao et al., 2013). 3.2. Spatial and temporal distribution of DP 3.2.1. Spatial distribution The spatial distributions of DP, TOC and median grain size were shown in Fig. 2. In the inner shelf, the relatively higher levels of ∑DP were found in the nearshore areas, with an offshore decreasing trend toward the outer shelf (Fig. 2a), and correspondingly DP showed a significantly negative correlation (r2 = 0.263, p b 0.05) with the longitude of the sampling sites. The spatial pattern was consistent with polybrominated diphenyl ethers (Li et al., 2012) and polychlorinated biphenyls (Duan et al., 2013) in this region, indicating the direct influence of the land-based sources. Additionally, there was a distinctly spatial discrepancy between the northern and southern inner shelf of the 29 ° N. Overall, the DP levels in the southern part were higher than those in the northern part (Fig. 2a). The southern inner shelf with the highest DP content was close to the Taizhou-Wenzhou Region, which is a highly urbanized and industrialized region. Elevated levels of DP were usually observed in the urban and industrial areas, and showed a decreasing trend with increasing distance from these areas (Helm et al., 2008; Ma et al., 2014; Qi et al., 2010), indicating that these regions were the significant local sources of DP for the adjacent environmental compartments. Moreover, Taizhou and Wenzhou are two of the well-known electronic/ electrical manufacturing and e-waste recycling cities. With outdated technologies for e-waste recycling, large quantities of DP were detected in environmental matrices in these regions (Chen et al., 2011; Yu et al., 2010; Zheng et al., 2010). These results indicated that Taizhou-Wenzhou Region should be responsible for the high DP levels in the southern inner shelf. In the northern inner shelf, relatively higher levels of DP were found in the area near Hangzhou Bay, which is a significant deposition center of YR-derived fine-grained sediments (Liu et al., 2007). In addition, Hangzhou Bay is a large multifunction harbor and mariculture zone, and consumption of products with different additives would inevitably bring serious pollution to the coastal areas (Nakata et al., 2005). Pollutants transported by Qiantang River were also discharged into the Hangzhou Bay (Sun et al., 2013). Therefore, DP in the northern inner shelf might be influenced by the input of YR and Qiantang River. Over the entire studied area, high levels of DP were also detected in the mud area southwest of Cheju Island, associated with higher TOC contents and smaller particle sizes (Fig. 2b and c). This mud area was also a significant sink of polychlorinated biphenyls (Fan et al., 2014) and short-chain chlorinated paraffins (Zeng et al., 2012). The sediments in this region are mainly derived from the Old Yellow River estuary, which contained only a small amount of anthropogenic pollutant (Guo et al., 2001; Zeng et al., 2012). According to the studies by Guo et al. (2003a) and Wilkening et al. (2000), pollutants adsorbed on aerosols from the North China and East Asia could be transported to the northern Pacific Ocean by East Asian monsoon. The mud area is located at downwind of the Chinese mainland and the pathway for terrestrial contaminants to the northern Pacific Ocean, resulting in large quantities of contaminants entering this region through the atmospheric deposition of particles (Guo et al., 2006; Guo et al., 2003a). In addition, Cheju Island has been developed as a tourist area for many years, which inevitably resulted in release of pollutants from the consumption of industrial, tourist and household products, which may contain DP as flame retardant. Therefore, the high DP levels in the mud area southwest of Cheju Island might be from the atmospheric deposition and local sources. Due to the hydrophobicity of organic pollutants, TOC and grain size were two important factors controlling their distributions in aquatic environments (Hung et al., 2006; Zhao et al., 2013). In the present study, the TOC contents ranged from 0.16% to 0.99%, with an average of
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Fig. 2. Spatial distributions of DP (pg/g dw) (a), TOC (%) (b) and median grain size (Ф) (c) in the coastal ECS sediments using Kriging by Surfer 11.0.
0.64% (Table 1). The TOC distributions only resembled those of DP in the northern inner shelf of 29 °N and the mud area southwest of Cheju Island (Fig. 2a and b), and significantly positive correlations (r2 = 0.316, p b 0.05 for northern inner shelf; r2 = 0.469, p b 0.05 for mud area southwest of Cheju Island) were also found between TOC and DP. In addition, the resemblance was also found between the distributions of DP and grain size in these two areas (Fig. 2a and c), and DP showed strong correlations (r2 = 0.322, p b 0.05 for northern inner shelf; r2 = 0.378, p b 0.05 for mud area southwest of Cheju Island) with grain size. However, neither such correlation (r2 b 0.1) nor similar distribution was found between DP and TOC as well as grain size in the southern inner shelf, which might be attributed to the direct discharge of local sources. 3.2.2. Temporal distribution The historical records of DP in the sediment cores from coastal ECS were shown in Fig. 3. DP was detected in almost all the sediment segments, indicating that DP had been discharged into the coastal ECS for a long time. As shown in Fig. 3, trace levels of DP were detected from early 1930s to mid-1940s in both cores, which was prior to the starting production of DP in the 1970s in OxyChem, in agreement with the results in the Great Lakes (Qiu et al., 2007; Yang et al., 2011). This phenomenon might be explained by the sediment resuspension, bioturbation, and downward smearing and migration after DP burial (Qiu et al., 2007; Zhu et al., 2014). However, considerable discrepancies
in temporal trends were observed between the two sediment cores, which might be attributed to different deposition environments in these two areas. In Core P01, a considerable fluctuation of DP concentrations along with core depth was found (Fig. 3a), which was consistent with organochlorine pesticides in this region (Lin et al., 2016), attributing to mixed effects of varied sedimentation rates, shallow water depth (b 20 m) and strong resuspension. In spite of this, there was an identifiably general trend in the vertical distribution. The DP levels showed a rapid increasing from mid-1940s, peaked in ~1965, and decreased thereafter, while with another peak in ~ 1991 (Fig. 3a). Since no DP data was available in sediment cores in China, the temporal trends of DP in the core P01 were compared with those in Great Lakes (Shen et al., 2011; Yang et al., 2011). No similarity was observed, indicating different deposition environments between these two areas. However, the periods of higher DP levels coincided with those of the higher Yangtze sediment loading associated with extraordinary flooding (1954, 1971, 1991 and 1998) (Guo et al., 2006; Lin et al., 2016). The accumulation of pollutants in the river-ocean boundary zone was sensitive to elevated outflow of sediment loading, because sediments and associated pollutants were rapidly deposited and well-preserved in the estuary mud area during the flooding (Lin et al., 2016). In Core P14, the DP levels started increasing in mid-1950s with a maximum concentration occurred in ~1978, followed by a distinct decline (Fig. 3a). The increasing trend was also found in sediment cores
Fig. 3. Historical records of DP (pg/g dw) in the sediment cores P01 (a) and P14 (b) from the coastal ECS using B-spline curve fitting.
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from the Great Lakes (Hoh et al., 2006; Zhang et al., 2011). Since DP was starting to be produced in late 1990s in China (Wang et al., 2010b), the increasing trend was believed to be resulted from the import of DP-containing electronic equipments and the rapid economic development in China. DP levels showed a decreasing trend after ~ 1980, consistent with the results in Lake Ontario and Lake Michigan (Hoh et al., 2006; Shen et al., 2011), which might be attributed to the decreasing production volume of DP during the period of 1986 to 2006 (USEPA, 2006). With the extensively e-waste recycling and extensive DP production by Anpo in late 1990s, large quantities of DP were released, and another peak occurred in around 2000. However, the levels of DP rapidly decreased after 2000, and the decreasing trend was also observed in Core P01, which might reflect the decrease in production and/or an improvement in controlling the discharge in recent years in China. Compared with Core P01, Core P14 could more significantly imply the overall trend of DP input into the ECS, and the sedimentary records fitted better with available data of historical application as well as the signal of economic development in China. 3.3. Isomer profiles of DP DP has two conformers, syn- and anti-DP. The isomer ratios of DP can be described by the fractional abundance, and anti-DP fraction (fanti) was calculated as the concentration of anti-DP divided by the concentration of total DP. Previously reported fanti in technical DP mixture ranged from 0.59 to 0.80, depending on the manufacturer (Hoh et al., 2006; Tomy et al., 2007; Wang et al., 2010b). Due to the different physicochemical properties of syn- and anti-DP such as octanol-water partition coefficient (Kow) and solubility (Fang et al., 2014), the fanti variations between the environment matrices and the technical DP mixture were generally used to explore the differences in environmental behaviors and fates of the two isomers in the studied matrices. As shown in Table 1, the fanti was in the range of 0.21–1.00, with a mean value of 0.42, which was distinctly lower than that of the technical DP mixture. To better understand the fanti variation in the studied area, the fanti was compared among all the sampling sites (Fig. 4). As shown in Fig. 4, the fanti showed significantly region-specific discrepancies (p b 0.01, one way analysis of variance). Among the studied area, the mud area southwest of Cheju Island had the lowest fanti (0.32), corresponding with the longest distance from the Chinese mainland. Previous studies reported that anti-DP was more vulnerable to photodegradation than syn-DP during long-range atmospheric transport (LRAT) (Möller et al., 2010; Sverko et al., 2011; Tao et al., 2015). Moreover, Fang et al.
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(2014) estimated the octanol-air partitioning coefficient (log Koa) of syn- and anti-DP, and found that log Koa of syn-DP was lower than that of anti-DP, indicating a greater LRAT partitioning potential into air for syn-DP. The reduced fanti was also observed in marine environments in Arctic and Antarctic and attributed to the LRAT (Möller et al., 2010). Therefore, DP with enriched syn-DP might mainly come from the atmospheric deposition in the mud area. In the northern inner shelf of 29 °N, the mean fanti was 0.49, and the fanti showed a decreasing trend from the north to south except for two extraordinarily high fanti (1.00 in P05 and 0.78 in P06, close to Zhoushan Island). In winter, most of the fine particles derived from the YR were resuspended by the strong hydrodynamic conditions in the Yangtze River Estuary, and transported southward along the Zhejiang-Fujian Coastal Current (Liu et al., 2007). Due to the higher log Kow of syn-DP, it preferentially adsorbed on the fine particles (Fang et al., 2014), which was also supported by the significantly positive correlations between the syn-DP fraction and TOC (r2 = 0.427, p b 0.05) as well as grain size (r2 = 0.361, p b 0.05) in the northern inner shelf. Consequently, a north to south decreasing trend of fanti could be attributed to the southward transport of fine particles with the abundance of syn-DP. In contrast, fanti in the southern inner shelf was 0.63, which is close to that of the technical DP mixture, and there was no distinct variation between sampling sites. Thus, the direct discharge of local sources should be responsible for DP in the southern inner shelf. The isomer profiles of DP in Core P01 and P14 were shown in Fig. 5. During the period of mid-1950s to 2011, the fanti fluctuated in the range of reported technical DP values in both cores. The similar phenomenon was also observed in sediment cores from Great Lakes (Hoh et al., 2006; Yang et al., 2011), indicating the contribution of DP commercial sources for a long time. However, the fanti was lower than that in technical DP mixture prior to mid-1950s (Fig. 5b). The linear regression showed that fanti was positively correlated with the deposition year in both cores significantly (r2 = 0.313, p b 0.05 for P01 and r2 = 0.604, p b 0.01 for P14, Fig. S2a and b). This result indicated that fanti decreased with increasing depth, which might be attributed to the greater adsorption capacity of syn-DP (Kow: syn-DP N anti-DP) (Fang et al., 2014) by organic matters and/or the preferential biodegradation of anti-DP after sedimentation (Sverko et al., 2015; Sverko et al., 2011). On the contrary, there was no significant change in fanti associated with depth in sediment cores from Lake Erie (Sverko et al., 2007), and fanti increased with depth in sediment cores from Lake Ontario (Qiu et al., 2007). These discrepancies might be attributed to different depletion/enrichment mechanism of syn- and anti-DP in marine sediments versus freshwater sediments (Jia et al., 2011).
Fig. 4. The fanti values at different sampling sites from the coastal ECS.
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Fig. 5. Historical trends of fanti values in the sediment cores P01 (a) and P14 (b) from the coastal ECS using B-spline curve fitting.
3.4. Source identification of DP implied by biomarkers of TOM Terrestrial high plants can produce long-chain (C25–C35) n-alkanes with a strong preference of odd-to-even carbon, and C27, C29 and C31 n-alkanes are the most abundant congeners (Rao et al., 2008; Xing et al., 2011). Lignin is a naturally occurring and widely abundant biopolymer found almost exclusively in terrestrial vascular plants, and essentially absent from marine organisms (Jex et al., 2014; Kuzyk et al., 2008). In general, lignin is intrinsically stable and relatively resistant to microbial degradation, and therefore serves to be a specific tracer in sediments for TOM (Goñi and Hedges, 1995; Tesi et al., 2007). Previous studies reported that ∑ C27 + C29 + C31 n-alkanes could enter the oceans through fluvial and atmospheric inputs (Gagosian et al., 1981; Xing et al., 2011), and lignin reflected only fluvial TOM entering into the marine environment via surface runoffs (Jex et al., 2014; Tesi et al., 2007). The spatial distributions of ∑C27 + C29 + C31 n-alkanes and lignin in the sediments from the coastal ECS were shown in Fig. 6. In the northern inner shelf of 29 °N, ∑C27 + C29 + C31 n-alkanes had the highest contents, and exhibited a decreasing trend from inshore to offshore (Fig. 6a). A similar pattern was also found in this region by Xing et al. (2011), indicating that YR-derived TOM mainly deposited in Yangtze River Estuary and the northern inner shelf. In addition, relatively higher
contents of ∑C27 + C29 + C31 n-alkanes were also detected in the mud area southwest of Cheju Island. The distributions of ∑C27 + C29 + C31 n-alkanes resembled to those of DP in the northern inner shelf and the mud area southwest of Cheju Island (Fig. 2a). Linear regression showed that DP also had significantly positive correlations with ∑C27 + C29 + C31 n-alkanes in the northern inner shelf (r2 = 0.592, p b 0.01, Fig. S3a) and the mud area southwest of Cheju Island (r2 = 0.839, p b 0.01, Fig. S3c). However, neither r esemblance nor correlation was found between DP and ∑C27 + C29 + C31 n-alkanes in the southern inner shelf (Fig. 2a, Fig. 6a and Fig. S3b). These results indicated that DP and ∑ C27 + C29 + C31 n-alkanes shared similar sources and migration pathway in the northern inner shelf and the mud area southwest of Cheju Island, and mainly derived from YR input and atmospheric deposition, respectively. However, in the southern inner shelf, DP was mainly come from the discharge of local sources. The lignin content presented a seaward decreasing trend in the inner shelf (Fig. 6b), consistent with that of DP (Fig. 2a). Moreover, DP and lignin showed strong positive correlations in the area (r2 = 0.557, p b 0.01 for northern inner shelf and r2 = 0.306, p b 0.05 for southern inner shelf, Fig. S4). These results implied that DP in the inner shelf was potentially derived from YR input and surface runoffs after discharge from local sources. Compared with DP and ∑C27 + C29 + C31
Fig. 6. Spatial distributions of ∑C27 + C29 + C31 n-alkanes (ng/g) (a) and lignin (mg/10 g) (b) in the coastal ECS sediments using Kriging by Surfer 11.0.
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n-alkanes, no high values of lignin were observed in the mud area southwest of Cheju Island, and the correlation between DP and lignin was weak (r2 b 0.1, Fig. S4c). Therefore, atmospheric deposition should be responsible for DP in the mud area. According to the region-specific deposition conditions, distribution patterns and isomer profiles of DP and biomarkers of TOM, we concluded that DP in the northern inner shelf, southern inner shelf of 29 °N and the mud area southwest of Cheju Island were mainly come from the YR input, surface runoffs after discharge of local sources from the TaizhouWenzhou region and atmospheric deposition of DP from the North China and East Asia, respectively. 3.5. Mass inventory of DP To assess the contamination extent and potential of sediments as a pollutant source to the nearby environment, the mass inventory of DP in the coast ECS were tried to estimate according to Zhao et al. (2011) and Zhou et al. (2014). The study region was divided into 34 compartments, and make sure that each of the sampling site was located at the center of its own compartment. The inventory (I, in kg) was calculated by the following equation: I ¼ CAdp where C is the DP concentration in the sediment sample; A is the area of water body (7.8 × 104 km2) (Li et al., 2012); p is the sediment dry density of 1.2 g/cm3 recommended by Liu et al. (2007); and d is the thickness of sediment sample of 5 cm (surface sediments). The mass inventory in the surface sediments from the coastal ECS was estimated to be approximately 310.7 kg for DP. The data on DP inventory in marine environments were limited in the world. Zhao et al. (2011) reported that the DP inventory per unit area in bays adjacent to the Yellow Sea was 8.5, 20.1 and 37.7 pg/cm2 for Jiaozhou Bay, Taozi Bay and Sishili Bay, respectively. Qiu et al. (2007) estimated that DP inventory was approximately 120,000 pg/cm2 in Lake Ontario (about 10,000 kg in total), where it is close to the DP manufacturing plant. In the present study, the DP inventory based on per unit area was 39.8 pg/cm2 in the coastal ECS, which was comparable to that in Sishili Bay, slightly higher than Jiaozhou Bay and Taozi Bay, but much lower than Lake Ontario. Consequently, we believe that sediment is an important sink of DP in the ECS. 4. Conclusions The surface sedimentary DP in the coastal ECS showed a seaward decreasing trend from inshore to offshore in the inner shelf, with the highest levels in Taizhou-Wenzhou Region, and fanti showed the region-specific discrepancies. In the sediment cores, a decreasing trend in recent years was revealed for DP, and fanti decreased with increasing the depth. Lignin and ∑C27 + C29 + C31 n-alkanes were introduced to identify the regional sources of DP, and the results showed that DP in the northern inner shelf, southern inner shelf of 29 °N and the mud area southwest of Cheju Island were mainly come from YR input, surface runoffs after discharge of local sources and atmospheric deposition, respectively. Biomarkers of TOM provided new valuable information to identify region-specific sources and migration pathways of DP in the present study. However, marine organic materials may alter the DP distribution and behavior and thus may have a potential influence on the DP sources and migration. Further studies are needed to investigate this question. Acknowledgment This work was financially supported by the National Natural Science Foundation of China (Grant No. 41276067). Grain size data were supported by Dr. Xiaodong Zhang (Marine Geosciences College of the
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Ocean University of China) and the core sedimentation rates were supported by Prof. Liguang Sun (University of Science and Technology of China), to whom we owe our thanks. We also thank the crew members of R/V Dong Fang Hong 2 for helps in collecting samples. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2016.08.090. References Betts, K.S., 2006. A new flame retardant in the air. Environ. Sci. Technol. 40, 1090–1091. Bouloubassi, I., Fillaux, J., Saliot, A., 2001. Hydrocarbons in surface sediments from the Changjiang (Yangtze river) estuary, East China Sea. Mar. Pollut. Bull. 42, 1335–1346. Chen, S.-J., Tian, M., Wang, J., Shi, T., Luo, Y., Luo, X.-J., Mai, B.-X., 2011. Dechlorane Plus (DP) in air and plants at an electronic waste (e-waste) site in South China. Environ. Pollut. 159, 1290–1296. Duan, X., Li, Y., Li, X., Li, M., Zhang, D., 2013. 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