Chemosphere 111 (2014) 304–311

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Hexabromocyclododecanes in surface sediments from Shanghai, China: Spatial distribution, seasonal variation and diastereoisomer-specific profiles Ming-Hong Wu, Jian-Yao Zhu, Liang Tang, Ning Liu, Bing-Quan Peng, Rui Sun, Gang Xu ⇑ Institute of Applied Radiation of Shanghai, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, PR China

h i g h l i g h t s  Much higher proportion of

a-HBCD was found in the surface sediments compared to technical HBCD product.

 The concentrations of

RHBCD in the summer were significantly higher than those in the winter (paired t test, p < 0.01).  No significant correlation was observed between RHBCD levels and TOC content in sediments.

a r t i c l e

i n f o

Article history: Received 30 November 2013 Received in revised form 2 April 2014 Accepted 13 April 2014

Handling Editor: Klaus Kümmerer Keywords: Hexabromocyclododecanes Sediment Spatial distribution Seasonal variation Diastereoisomer profiles Shanghai

a b s t r a c t The concentrations, spatial distribution, diastereoisomer-specific profiles of hexabromocyclododecanes (HBCDs) in surface sediments from three major rivers in Shanghai as well as the seasonal variation of HBCDs were investigated. The concentrations of total HBCD diastereoisomers ranged from 0.05 to 6.87 ng g1 dw. Significant spatial distribution of total HBCDs concentrations were observed. The mean concentration of total HBCDs followed the order of Suzhou Creek (2.00 ng g1) > Huangpu River (1.59 ng g1) > Yunzao Creek (0.77 ng g1). The concentration was a relatively low HBCDs level compared to levels measured in domestic and other parts of the world. The proportions of a-HBCD in sediment samples were generally higher than that of commercial formulations. This might be due to thermal isomerization from c-HBCD to a-HBCD and slower degradation rate of a-HBCD compared to c-HBCD in anaerobic conditions. The concentrations of RHBCD in the summer were significantly higher than those in the winter (paired t test, p < 0.01). This seasonal variation could probably be attributed to a combined effect of temperature and wet deposition. Moreover, a poor and no significant correlation between RHBCD levels and TOC content in sediments was observed, suggesting that the spatial distributions of HBCDs were not constrained by the TOC in sediments of Shanghai. Ó 2014 Published by Elsevier Ltd.

1. Introduction As one of the most important brominated flame retardants (BFRs), hexabromocyclododecanes (HBCDs) are used in polystyrene thermal insulation foams in the building industry, in textile coatings, and to a minor extent, in electrical and electronic equipment and appliances (BSEF, 2012). Commercial HBCDs are mainly made up of a-, b-, and c-HBCD with percentage of 10–13%, 1– 12% and 75–89%, respectively (Law et al., 2005). With restrictions for polybrominated diphenyl ethers (PBDEs), the use of HBCDs have increased over the past few years. In 2003, the estimated

⇑ Corresponding author. Tel.: +86 21 66138250. E-mail address: [email protected] (G. Xu). http://dx.doi.org/10.1016/j.chemosphere.2014.04.031 0045-6535/Ó 2014 Published by Elsevier Ltd.

worldwide market demand of HBCDs was about 22 000 tons (de Wit et al., 2010). As flame retardant additives are not chemically bound to the products, HBCDs can easily be released into the environment media and become ubiquitous in the environment. HBCDs are of environmental concern because of its potential toxicity, bioaccumulation, persistency and long-range environmental transport (Darnerud, 2003; Morris et al., 2004; Murvoll et al., 2006; van der Ven et al., 2006; Ema et al., 2008). In 2013, HBCD was listed as one of persistent organic pollutants (POPs) by the Stockholm Convention (UNEP, 2013). HBCDs have been identified in a wide variety of biota and abiotic environmental samples around the world, including sediment, indoor dust, sewage sludge, egg, fish and marine mammal (Sellstrom et al., 1998; Lindberg et al., 2004; Morris et al., 2004; Marvin et al., 2006; Frederiksen et al.,

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2007; Harrad et al., 2009a; Gorga et al., 2013). Interestingly, HBCDs have been detected in samples from the Arctic (McKinney et al., 2011; Jörundsdóttir et al., 2013), providing persuasive evidence of long-range transport of the chemicals. In China, HBCDs have also been detected in various environmental media such as sediments (Zhang et al., 2013), soils (Thanh et al., 2013), particulate phase of air (Ni and Zeng, 2013) and biotic samples (Xian et al., 2008; Shi et al., 2009; Sun et al., 2012; Zheng et al., 2012). Due to the rapid development of economy in the past decades, China had been expected to become a large HBCDs manufacturer and consumer. Shanghai is the largest city in China. It is located in the Yangtze River Delta, which is the most highly urbanized and industrialized region in China. Three major rivers flow through Shanghai City. The Huangpu River is a tributary of the Yangtze River and the most important source of water for both industrial and residential purposes. In addition, it is a crucial waterway for transporting merchandise in Shanghai. The Suzhou Creek and the Yunzao Creek are also two important navigable rivers. Sediment is an important sink. Varieties of hydrophobic organic contaminants, including HBCDs, undergo atmospheric deposition, riverine inputs and accumulation in sediments. Further, these hydrophobic compounds in sediments are transferred to organisms and are bioaccumulated along the food chain (Tomy et al., 2004; Law et al., 2006). However, up to now, no systematic study on HBCDs in surface sediments has been conducted in Shanghai, China. Therefore, we investigated the concentrations, seasonal variation and diastereomer-profiles of HBCDs in surface sediments from the Huangpu River, the Suzhou Creek and the Yunzao Creek in Shanghai. 2. Materials and methods 2.1. Sample collection The surface sediment samples were collected using a stainless steel grab sampler from 17 sites in three major rivers in December 2011 and July 2012 (Huangpu River, 10 sites; Suzhou Creek, 5 sites; Yunzao Creek, 2 sites). July is the wet season (summer) and December is the dry season (winter) in Shanghai. Fig. 1 and Table 1

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show sampling locations and information of surface sediment. The top 5-cm loamy sediment was taken for the chemical analyses. At each sampling site, at least three subsamples were randomly collected in the near-shore regions and combined as one sample. Immediately after collection, the samples were wrapped in several layers of aluminum foil and transported to the laboratory, then freeze-dried. All the dried samples were homogenized, sieved to 50-mesh and stored at 20 °C until the time of analysis. 2.2. Reagents and standards Native a-, b-, and c-HBCD were purchased from AccuStandard, Inc (New Haven, USA). 13C-labeled c-HBCD was obtained from Cambridge Isotope Laboratories (Andover, MA, USA). Acetonitrile, methanol and acetone were obtained from Merck (Darmstadt, Germany). Dichloromethane and n-hexane were supplied by CNW (Shanghai, China). All solvents were of HPLC grade. SiliaFlashÒ ultrapure silica gels (0.12–0.2 mm) obtained from Silicycle (Quebec City, Canada) were activated by heating at 130 °C for 12 h and further stored in a desiccator. Anhydrous sodium sulfate was stored in a desiccator after baking at 450 °C for 4 h. Pelletized diatomaceous earth added to samples as dispersant and desiccant in the extraction was bought from Dionex (Silicon Valley, USA). 2.3. Extraction and cleanup The extraction and cleanup procedures described by Gao et al. (2011) were followed with some modifications. Briefly, 15 g of sediment samples spiked with the recovery standards (10 ng of 13Clabeled c-HBCD) were mixed with 3.5 g pelletized diatomaceous earth. The samples were extracted with n-hexane: acetone (1:1, v/v) using an accelerated solvent extraction (ASE 150, Dionex, USA). The extraction conditions were as follows: temperature: 100 °C; pressure: 1500 psi; static time: 8 min; purge time: 120 s; rinse volume: 60%; static cycles: 2. The extracts were subsequently concentrated to about 2 mL by rotary evaporator and elemental sulfur was removed from the extracts by activated copper. Each extract was cleaned up through a multilayer column packed from

Fig. 1. Sampling location of surface sediments in Shanghai, China.

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Table 1 Information of sediment samples and the concentrations of HBCD (ng g1 dw). Site

Latitude

Longitude

a-HBCD (ng g1 dw) Winter

Summer

Winter

Summer

Winter

Summer

Winter

Summer

Winter

Summer

H1 H2 H3 H4 H5 H6 H7 H8 H9 H10 S1 S2 S3 S4 S5 Y1 Y2

31°060 30°570 30°590 31°010 31°040 31°060 31°140 31°150 31°190 31°230 31°160 31°170 31°140 31°130 31°140 31°190 31°210

120°590 121°130 121°210 121°290 121°280 121°280 121°290 121°320 121°330 121°300 121°040 121°100 121°190 121°220 121°270 121°210 121°270

0.17 0.20 0.49 0.32 0.84 0.63 0.58 0.32 0.46 0.25 1.02 0.66 0.09 0.39 0.05 0.43 0.20

0.31 0.38 0.79 1.02 2.00 2.06 0.40 0.20 0.75 0.27 3.61 0.24 0.46 0.28 1.87 0.29 0.47

0.03 0.04 0.16 0.15 0.23 0.18 0.15 0.09 0.19 0.06 0.25 0.15 0.03 0.08 Nd 0.08 0.03

0.05 0.11 0.14 0.24 0.34 0.49 0.04 0.08 0.18 0.29 0.77 0.20 0.17 0.06 0.63 0.06 0.16

0.26 0.06 0.76 2.15 0.68 0.92 1.11 0.32 0.42 0.27 2.02 1.06 0.21 0.44 Nd 0.39 0.27

0.30 0.63 0.94 0.85 1.19 2.22 0.28 1.16 1.29 0.21 2.49 1.05 0.83 0.29 0.57 0.24 0.46

0.46 0.30 1.42 2.61 1.75 1.73 1.84 0.73 1.07 0.58 3.30 1.87 0.32 0.91 0.05 0.90 0.50

0.66 1.11 1.88 2.11 3.53 4.77 0.73 1.44 2.22 0.77 6.87 1.50 1.46 0.62 3.06 0.60 1.09

1.15 0.60 2.78 0.10 5.63 0.10 0.95 1.81 1.87 0.66 0.94 1.43 0.41 0.64 1.14 0.60 0.38

0.47 0.10 3.23 1.21 1.45 1.16 0.10 2.48 1.89 0.10 3.06 0.76 0.87 0.79 1.00 0.50 0.55

N N N N N N N N N N N N N N N N N

E E E E E E E E E E E E E E E E E

b-HBCD (ng g1 dw)

c-HBCD (ng g1 dw)

RHBCD (ng g1 dw)

TOC %

Nd: below detection limit.

bottom to top with the following: neutral silica gel (2 cm, previously activated at 130 °C for 12 h), basic silica gel (6 cm, 1.2% (w/ w) 1 mol L1 NaOH solution), neutral silica gel (2 cm), acid silica gel (12 cm, 44% (w/w) concentrated H2SO4), anhydrous Na2SO4 (2 cm). The column was washed with 100 mL dichloromethane/ n-hexane (1:1, v/v). The eluate was concentrated under a gentle nitrogen stream at room temperature until dryness and redissolved in 1 mL methanol before instrumental analysis. 2.4. Instrumental analysis The analysis of HBCDs were performed on an Agilent 1260 liquid chromatograph coupled to an Agilent 6460 triple quadrupole mass spectrometer. Calibration curves were used for identification and quantification of HBCD diastereoisomers (7 calibration standards ranging in concentration from 0.05 to 20 ng mL1 for b-HBCD and from 0.2 to 60 ng mL1 for a- and c-HBCD, respectively). A Poroshell 120 EC-C18 reversed-phase column (3  100 mm, 2.7 lm, Agilent) was used for the determination of HBCD diastereoisomers and the column temperature was set to 40 °C. Sample injection volume was 5 lL and the flow rate was 0.4 mL min1. The mobile phases used for the analysis were methanol/acetonitrile (1:1, v/v) as eluent A and water as eluent B. The elution gradient program started at 80:20 A/B and held for 1 min, gradually increased to 90:10 A/B at 3 min and kept for 1 min, then changed linearly to 100:0 A/B at 4.8 min and held for 3.2 min, finally returned to 80:20 A/B within 0.1 min and equilibrated for further 5 min. The mass system was operated in electro-spray ionization (ESI) negative ion mode with multiple reaction monitoring (MRM). Transitions selected for HBCD isomers were m/z 640.7 ? 78.9 and m/z 640.7 ? 80.9, and transitions selected for 13C-labeled cHBCD were m/z 652.6 ? 78.9 and m/z 652.6 ? 80.9. The crucial MS/MS parameters were as follows: drying gas temperature: 300 °C, drying gas flow: 8 L min1, nebulizer Pressure: 40 psi, sheath gas temperature: 370 °C, sheath gas flow: 12 L min1, capillary voltage (–): 3000 V, nozzle voltage (–): 2000 V, DEMV (–): 500 V, cell accelerator voltage: 3 V, fragmentor: 80 V, collision energy were 16 ev for m/z 640.7 ? 78.9 and m/z 652.6 ? 78.9, and 6 ev for m/z 640.7 ? 80.9 and m/z 652.6 ? 80.9. 2.5. TOC analysis Total organic carbon (TOC) content of each sediment sample was analyzed using an elemental analyzer (EA3000, EuroVector,

Italy). Approximately 100 mg of freeze-dried sediment sample was treated with 1 M HCl to remove inorganic carbon portion, washed with milli-Q water three times, and then dried at 40 °C. After cooling to room temperature, the TOC content was measured. 2.6. Quality assurance/quality control Laboratory glassware was washed with acetone and hexane prior to use. For all the sediment samples, the recovery of surrogate standard (13C-labeled c-HBCD) spiked into each sediment sample before the extraction was ranging from 73% to 115%. One procedural blank was simultaneously conducted with each batch of seven samples to monitor interferences and contamination. Results showed that HBCDs in blanks were below the detection limits. The mean recoveries of a-, b-, and c-HBCD were 95%, 95% and 96% in the spiked blanks and 81%, 88% and 93% in the spiked matrices, respectively. The relative standard deviations (RSD) of replicated analysis (n = 3) generally were 620%. The method detection limits (MDL), defined as a signal-to-noise ratio of 5:1, were 0.068, 0.019, 0.076 ng g1 for a-, b-, and c-HBCD, respectively. 2.7. Statistical analysis Values below the limit of detection (LOD) and the non-detects were treated as zero. All of the concentrations were expressed on a dry weight (dw) basis. Simple regression analysis was used to obtain p and r values. Spearman’s rank test was used to investigate correlations among individual diastereoisomer and the total of HBCDs (designed as RHBCD). All statistical analysis were performed with SPSS 18.0 statistical software (IBM company, Chicago, IL, USA). The significance level was p 6 0.05. 3. Results and discussion 3.1. Concentration levels and spatial distribution The spatial distribution of HBCDs concentrations determined in surface sediments is shown in Table 1 for samples collected from the Huangpu River, the Suzhou Creek and the Yunzao Creek in 2011 and 2012. HBCDs were detected in all surface sediment samples. It shows that HBCDs are ubiquitous environmental contaminants in this area. The levels of RHBCD ranged from 0.05 to 6.87 ng g1 on a dry weight basis (dw). Overall, the highest mean

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M.-H. Wu et al. / Chemosphere 111 (2014) 304–311 Table 2 Comparison of HBCD concentrations in sediment samples among different regions. Location

Concentration (ng g1 dw)

a-HBCD North Sea (Dutch) Detroit River (USA) Korea Åsefjorden (Norway)

b-HBCD

References

c-HBCD

RHBCD