Arch Environ Contam Toxicol (2016) 71:359–364 DOI 10.1007/s00244-016-0296-2
Spatial and Vertical Distribution of Dechlorane Plus in Mangrove Sediments of the Pearl River Estuary, South China Yu-Xin Sun1 • Zai-Wang Zhang1 • Xiang-Rong Xu1 • Qin-Wei Hao1,4 • Yong-Xia Hu1,4 • Xiao-Bo Zheng2 • Xiao-Jun Luo3 • Zeng-Hui Diao1 • Bi-Xian Mai3
Received: 7 March 2016 / Accepted: 29 June 2016 / Published online: 15 July 2016 Ó Springer Science+Business Media New York 2016
Abstract Thirty surface sediments and three sediment cores were collected from mangrove wetlands in the Pearl River Estuary of South China to investigate the spatial and vertical distribution of Dechlorane Plus (DP). DP concentrations in the mangrove surface sediments ranged from 0.0130 to 1.504 ng/g dry weight (dw). DP concentrations in sediments from Shenzhen were significantly greater than those from Guangzhou and Zhuhai. Anti-Cl11-DP, the dechlorinated product of anti-DP, was also detected in the mangrove sediments with concentrations ranged from not detected to 0.0198 ng/g dw. Significant positive relationship between anti-Cl11-DP and anti-DP levels was observed in the mangrove sediments, suggesting that photo and/or microbial degradation of anti-DP might occur in the sediments. The fanti values in the mangrove sediments were close to those in the technical DP products, suggesting that stereoselective enrichment of anti-DP may not exist in the mangrove sediments. DP concentrations in the mangrove sediment cores generally showed an increasing trend from the bottom to top layers. This is the first study to report the
& Xiang-Rong Xu
[email protected] 1
Key Laboratory of Tropical Marine Bio-resources and Ecology, Guangdong Provincial Key Laboratory of Applied Marine Biology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
2
College of Natural Resources and Environment, South China Agricultural University, Guangzhou 510642, China
3
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
4
University of Chinese Academy of Sciences, Beijing 100049, China
occurrence of DP and its degradation product in the mangrove wetlands.
Dechlorane Plus (DP; C18H12Cl12) is an additive chlorinated flame retardant used primarily in coating electrical wires and cables, plastic roofing materials, automotive lubricants, and hard connectors in computers and televisions for more than 40 years (Tomy et al. 2007). DP has three types of commercial formulations: DP-25, DP-35, and DP-515. These three products share a similar syn-/antiisomer composition, but they differ from each other in particle size (Zhu et al. 2007). The annual production of technical DP products is estimated to be as high as 10 million pounds (Yu et al. 2010). The occurrence of DP was first reported in air, fish, and sediment samples from the Great Lakes region in 2006 (Hoh et al. 2006). Since then it has been detected in various environmental matrices (Sverko et al. 2011; Xian et al. 2011). Monitoring data indicate that DP may be persistent, bioaccumulative, and subject to long-range transport and thus can be considered as a candidate for Annex D evaluation under the United Nations Stockholm Convention on Persistent Organic Pollutants (Sverko et al. 2011). Mangrove ecosystems, the intertidal wetlands generally confined to the tropical and subtropical areas, are unique transitional coastal ecosystems between terrestrial and marine environments. Although mangrove ecosystems have important ecological services and socioeconomic value, they have been subjected to increasing pollution pressure from human activities due to rapid urbanization and industrialization in coastal areas (Lewis et al. 2011; Bayen 2012). Mangrove sediments have been reported to be capable of acting as sinks for varieties of organic pollutants because of their unique properties such as high
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organic carbon content and abundant detritus (Tam 2006; Vane et al. 2009). Until now, the occurrence of brominated flame retardants, including polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), and 1,2bis(2,4,6-tribromophenoxy)ethane (BTBPE), in mangrove sediments has been reported (Binelli et al. 2007; Zhu et al. 2014, Zhang et al. 2015), but information on the distribution of DP in mangrove ecosystems is rather scarce. In the present study, sediments from three mangrove wetlands in the Pearl River Estuary (PRE) of South China were collected and analyzed for DP. The objectives of this study were to (1) explore the levels and isomer profiles of DP and (2) to investigate the spatial and vertical distribution of DP in mangrove sediments of the PRE. To the best of our knowledge, this is the first study to investigate the occurrence of DP in mangrove ecosystems.
Materials and Methods Sample Collection A total of 30 surface sediments and 3 sediment cores were collected from Futian Mangrove Nature Reserve in Shenzhen, Qi’ao Island Mangrove Nature Reserve in Zhuhai, and Tantou Mangrove Nature Reserve in Guangzhou between October and November 2012 (Fig. 1). Kandelia obovata, Sonneratia apetala, and Aegiceras corniculatum are the dominant mangrove species in mangrove wetlands of Shenzhen, Zhuhai, and Guangzhou, respectively. The top 5-cm layer of surface sediment was taken with a stainlesssteel grab sampler, and five subsamples were randomly collected to mix a composite sample at each sampling point with an area of 5 9 5 m2. The sediment cores were collected in the middle of the natural swamps of each mangrove ecosystem using a gravity corer and sliced at 4-cm intervals. All of the samples were immediately transferred to the laboratory and frozen at -20 °C until chemical analysis. Sample Extraction and Clean-Up The procedure for sample extraction was similar to that reported in a previous study (He et al. 2014). Briefly, mangrove sediment samples were freeze-dried, ground, and homogenized by sieving through a stainless steel 80-mesh sieve. Approximately 10 g samples were spiked with surrogate standards (13C12-PCB 141, BDE 77 and 181) and then Soxhlet-extracted with a mixture of acetone and hexane (v/v = 1:1) for 24 h. Activated copper granules were added to the extraction flasks to remove element sulfur. The extract solution was concentrated to 1 mL with a rotary evaporator and then purified using a multilayer column filled with 8 cm neutral silica, 8 cm acidified silica,
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and 1 cm anhydrous sodium sulfate from bottom to top. The column was eluted with 30 mL hexane and dichloromethane (v/v = 1:1). The eluate was concentrated to near dryness under a gentle nitrogen flow, reconstituted in 200 lL isooctane, and spiked with internal standards (BDE 118 and 128, 3-Fluoro-BDE 153) before instrumental analysis. Instrumental Analysis DP was analyzed by an Agilent 6890 gas chromatograph coupled with an Agilent 5975C mass spectrometer using electron-capture negative ionization in selective ion-monitoring mode and separated by a DB-XLB capillary column (30 m 9 0.25 mm 9 0.25 lm; J&W Scientific, USA). The initial oven temperature was set as 110 °C (held for 1 min), ramped at 8 °C/min to 180 °C (held for 1 min), and then 2 °C/min to 240 °C (held for 5 min), 2 °C/min to 280 °C (held for 15 min), and finally 10 °C/min to 310 °C (held for 10 min). One lL of the sample was injected in the pulsed splitless mode. The monitored and quantitative ions were as follows: m/z 653.8 and 651.8 for syn- and anti-DP, m/z 618; and 620 for anti-Cl11-DP; m/z 372 and 374 for 13 C12-PCB 141; m/z 79 and 81 for 3-Fluoro-BDE 153 and BDEs 77, 118, 128, and 181. A subsample of the surface sediment was treated with 10 % hydrochloric acid solution to remove inorganic carbon, washed with purified water to remove chlorine ion, and dried to constant weight at 60 °C before the determination of total organic carbon (TOC) by a CHN-O Rapid Elemental Analyzer (Heraus, Germany). Acetanilide used as the external standard was analyzed with each batch of 20 samples to ensure the relative SD at \5 %. Quality Assurance and Quality Control A procedural blank was processed for each batch of 11 samples, and the target compounds were not detected in the procedural blanks (n = 6). Recoveries of DP were evaluated by spiking known amounts of syn- and anti-DP in solutions and matrices, which were passed through the entire analytical procedure. The mean recoveries of synand anti-DP in the spiked blanks and matrices were 94.8 % ± 3.6 % and 98.0 % ± 2.4 % (mean ± SD), and 106.7 ± 3.0 % and 102.0 % ± 4.1 %, respectively. The average recoveries of surrogate standards in all samples were as follows: 101.2 % ± 14.3 % for 13C12-PCB 141, 96.4 % ± 9.8 % for BDE 77, and 106.8 % ± 14.6 % for BDE 181. Reported concentrations were not corrected by the surrogate recoveries. Limit of quantification (LOQ) for DP was defined as a signal of five times the noise level. Based on the mean dry weight (dw) of sediment samples, the LOQs for syn-DP, anti-DP, and anti-Cl11-DP were 0.00067, 0.00081, and 0.00039 ng/g dw, respectively.
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Fig. 1 Map of mangrove sampling sites
Data Analysis All concentration data were presented on a dry-weight basis. Statistical analysis was performed with SPSS 16.0 (SPSS, Chicago, Illinois, USA). One-way analysis of variance (ANOVA) was used to determine the spatial variations in DP concentrations among mangrove wetlands in the PRE. Simple linear correlation analysis was used to investigate the relationships between DP levels and TOC contents, and between anti-Cl11-DP and anti-DP concentrations, in mangrove sediments of the PRE. The level of significance was set at p \ 0.05.
Results and Discussion Levels and Spatial Distribution of DP Concentrations of DP in mangrove surface sediments of the PRE are listed in Table 1. Syn- and anti-DP were detected in all sediment samples. The total DP concentrations (sum of
syn- and anti-DP) in mangrove sediments of the PRE ranged from 0.0130 to 1.504 ng/g dw, which was significantly lower than those of PBDEs (1.25–206 ng/g dw) and DBDPE (0.364–34.9 ng/g dw) in mangrove sediments of the PRE (Zhu et al. 2014; Zhang et al. 2015). One possible explanation for this observation might be linked to the wide use of PBDEs and DBDPE in the Pearl River Delta (PRD). DP was reported in surface sediments of the PRE close to the mangrove wetlands with concentrations ranging from not detected (ND) to 2.13 ng/g dw (Chen et al. 2013) and from 0.15 to 4.2 ng/g dw (Liu et al. 2014), which is comparable with the results of the present study. DP concentrations in this study were slightly greater than those in surface sediments from the Songhua River (ND to 0.16 ng/g dw [Qi et al. 2010]), Qiantang River (ND to 1.1 ng/g dw [Sun et al. 2013]), and Yellow Sea (\0.00012–0.187 ng/g dw [Zhao et al. 2011]) in China, but they were much lower than those in sediments from the Great Lakes (0.061–586 ng/g dw [Sverko et al. 2008; Shen et al. 2011]). These results suggested that mangrove sediments of the PRE had been slightly contaminated by DP.
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Guangzhou
Zhuhai
Shenzhen
N
9
12
9
TOC (%)
1.77 ± 0.48
2.87 ± 0.33
4.35 ± 0.27
syn-DP
0.0121 (0.0008–0.0565)
0.0491 (0.0103–0.0697)
0.2783 (0.1724–0.4583)
anti-DP
0.0602 (0.0126–0.1213)
0.1334 (0.0624–0.1933)
0.6511 (0.4337–1.045)
Total DPa
0.0819 (0.0130–0.1778)
0.1830 (0.0756–0.2531)
0.9136 (0.6061–1.504)
0.0011 (ND–0.0025)
0.0102 (0.0058–0.0198)
0.737 (0.683–0.864)
0.711 (0.695–0.770)
anti-Cl11-DP
ND (ND–0.0009)
fanti
0.755 (0.561–0.969)
Sum of syn- and anti-DP
b
Not detected
1.8
r2 = 0.37, p = 0.00022 1.5
DP concentrations (ng/g dw)
a
The median concentrations of DP in mangrove surface sediments of the PRE decreased in the order of Shenzhen (0.9136 ng/g dw) [ Zhuhai (0.1830 ng/g dw) [ Guangzhou (0.0819 ng/g dw) (Table 1). A significant difference for DP concentrations was found in sediments among the three mangrove ecosystems in the PRE (F2,29 = 97.7, p \ 0.0001). The total DP concentrations in mangrove sediments from Shenzhen were significantly greater than those from Zhuhai and Guangzhou (p \ 0.001). Futian mangrove wetland, located in the center of Shenzhen, which is characterized by high levels of industrialization and high population densities (a population of 6500 km-2), received a large amount of municipal and industrial wastewater discharged directly (Tam 2006). Thus, the highest DP concentrations were expectedly observed in the surface sediments of Futian mangrove wetland. Relatively greater levels of PBDEs and DBDPE were also found at this sampling site (Zhang et al. 2015). In addition, total DP concentrations were positively and significantly correlated with TOC contents (Fig. 2; r2 = 0.37, p = 0.00022), indicating that TOC may also be an important factor determining the DP levels in mangrove sediments. Therefore, greater levels of DP in Futian mangrove sediments might be partly attributed to high contents of TOC. A similar relationships between DP levels and TOC contents was also observed in sediments of the Qiantang River in eastern China (Sun et al. 2013). Anti-Cl11-DP (C18H13Cl11), the dechlorination product of anti-DP, was detected in 66.7 % of mangrove surface sediments at concentrations ranging from ND to 0.0198 ng/ g dw (Table 1). Anti-Cl11-DP was also found in the surface sediments of the Lower Great Lakes and the Yellow Sea of North China, but this was not quantified (Sverko et al. 2008; Zhao et al. 2011). Correlation analysis showed that anti-Cl11-DP concentrations were positively and significantly correlated with anti-DP levels in mangrove sediments of the PRE (Fig. 3, r2 = 0.83, p \ 0.0001), indicating that anti-Cl11-DP in mangrove surface sediments might originate from the photodegradation and/or microbial degradation of anti-DP.
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b
1.2
0.9
0.6
0.3
0.0 0
1
2
3
4
5
6
7
TOC (%)
Fig. 2 Correlations between DP levels and TOC contents in mangrove sediments of the Pearl River Estuary
Isomeric Profiles of DP The fraction of anti-DP (fanti), defined as the concentration of anti-DP divided by sum of syn- and anti-DP levels, was calculated to evaluate the possible stereoisomer selective
0.025
r2 = 0.83, p < 0.0001 0.020
anti-Cl11-DP (ng/g dw)
Table 1 Concentrations of DP (ng/g dw) in mangrove surface sediments of the Pearl River Estuary, South China
Arch Environ Contam Toxicol (2016) 71:359–364
0.015
0.010
0.005
0.000 0.0
0.3
0.6
0.9
1.2
anti-DP (ng/g dw)
Fig. 3 Correlation of anti-Cl11-DP concentrations plotted against anti-DP levels in mangrove sediments of the Pearl River Estuary
Arch Environ Contam Toxicol (2016) 71:359–364
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PRE. A similar result was also found in sediments of the PRE (Chen et al. 2013).
1.0
0.9
Vertical Distribution of DP fanti
0.8
0.7
0.6
0.5 Guangzhou
Zhuhai
Shenzhen
Fig. 4 The fanti values in mangrove sediments of the Pearl River Estuary
enrichment of DP isomers in mangrove sediments. The average fanti values in mangrove sediments of Guangzhou, Zhuhai, and Shenzhen were 0.790, 0.736, and 0.717, respectively (Fig. 4). The mean fanti values in the present study were consistent with those in commercial DP products manufactured by China (0.65–0.79 [Wang et al. 2010]) and North America (0.65–0.80 [Hoh et al. 2006; Tomy et al. 2007]), suggesting that stereoselective enrichment of anti-DP may not exist in the mangrove sediments of the
Vertical distribution of DP concentrations in the mangrove sediment cores of the PRE is shown in Fig. 5. DP was detected in 67.7 % of the segments in the mangrove sediment cores with concentrations ranging from ND to 1.351 ng/g dw. The sediment cores from Shenzhen (ND to 1.351 ng/g dw) had greater concentrations of DP than those from Guangzhou (ND to 0.0821 ng/g dw) and Zhuhai (ND to 0.2431 ng/g dw). DP concentrations in the sediment cores collected from Guangzhou and Shenzhen showed an increasing trend from the bottom to top layers. A rapid increase of DP concentrations started in the segment 12–16 cm for Guangzhou. For Shenzhen, DP levels in the upper segment 0–20 cm (0.6209–1.351 ng/g dw) were significantly greater than those in the deeper segment 20–32 cm (0.0368–0.3647 ng/g dw). These results indicated that DP commercial products are still being used in Guangzhou and Shenzhen. An increased trend of DP levels was also observed in sediment cores collected from the Dongjiang River located the upstream of the PRE, which runs through the largest manufacturing base for electronic/electrical products of the PRD (He et al. 2014). A
Concentrations (ng/g dw) 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0
4
4
8
8
0
0.0
0.3
0.6
0.9
1.2
1.5
4
8 12
12
16
16
20
20
16
24
24
20
28
28
Depth (cm)
12
24 32
32
36
36
40
40
28
Guangzhou 44
32
Zhuhai 44
Shenzhen 36
Fig. 5 Vertical distribution of DP concentrations in mangrove sediment cores of the Pearl River Estuary
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rapid increase of DP concentrations started in segment 24–28 cm for Zhuhai. An unexpectedly high level was found in segment 20–24 cm (0.2653 ng/g dw) for Zhuhai, and the cause is worth further investigation.
Conclusions DP and its degradation product were determined in mangrove sediments of the PRE, South China. Relatively lower concentrations of DP were observed in mangrove sediments of the PRE. Mangrove sediments from Shenzhen contained greater levels of DP than those from Guangzhou and Zhuhai. A significant relationship between anti-Cl11DP and anti-DP levels was found in mangrove sediments. The fanti values in mangrove sediments were close to the reported values in technical DP products. An increasing trend for DP levels was observed in the mangrove sediment cores of the PRE. Acknowledgments This study was financially supported by the National Natural Science Foundation of China (Grants Nos. 41573084, 41401576, 41230639, and 21407155), the National Basic Research Program of China (Grant No. 2015CB452902), the Hong Kong Scholars Program (Grant No. XJ2015046), China Postdoctoral Science Foundation (Grant No. 2016M590823) and Science and Technology Planning Project of Guangdong Province, China (Grant No. 2014B030301064).
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