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PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets
Chemosphere xxx (2014) xxx–xxx
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PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets Xitao Liu ⇑, Ying Jiao, Chunye Lin, Ke Sun, Ye Zhao State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, 100875 Beijing, PR China
h i g h l i g h t s Presence of polybrominated compounds in bivalves from Beijing markets was studied. Levels of PBDEs in this study were higher than those in Baltic blue mussels. Levels of OH- and MeO-PBDEs in this study were lower than in Baltic blue mussels. Polybrominated compounds showed significant seasonal variations in blue mussels. Acidic components displayed different seasonal variations from neutral components.
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Article history: Received 5 February 2013 Received in revised form 23 January 2014 Accepted 6 February 2014 Available online xxxx Keywords: PBDEs OH-PBDEs MeO-PBDEs Bivalves Seasonal variations
a b s t r a c t The structural analogues of polybrominated diphenyl ethers (PBDEs), hydroxylated PBDEs (OH-PBDEs) and methoxylated PBDEs (MeO-PBDEs) have been attracting increasing concern in recent years. Five bivalve species (blue mussel, short-necked clam, surf clam, ark shell and razor clam) were collected from Beijing markets, and the concentrations of seven PBDEs, four OH-PBDEs and fourteen MeO-PBDEs in the bivalves were measured. The seasonal variations of these three types of polybrominated compound in blue mussels were also monitored. The results indicate that the levels of RPBDEs in this study were comparable to those in short-necked clams from Liaodong Bay, China, with BDE47 as the dominant congener. For the ortho-MeO-PBDEs, 6-MeO-BDE47 was found at higher concentrations than the others, while for the metaand para-MeO-PBDEs, 40 -MeO-BDE17 was found at higher concentrations. 6-OH-BDE-47 was the most abundant congener among the 4 measured OH-PBDEs, followed by 6-OH-BDE-137 and 6-OH-BDE-85. The levels of OH-PBDEs and MeO-PBDEs in bivalves from Beijing markets were much lower than the corresponding compounds in blue mussels from the Baltic Sea. In the blue mussels collected in April, June and September of 2012, apparent seasonal variations were observed for these three types of polybrominated compounds, but the acidic components displayed different trends from the neutral components, with PBDEs and MeO-PBDEs showing the highest concentrations in June, while OH-PBDEs had the lowest concentrations in June. This difference in seasonal variations between the neutral components and the acidic components may be explained by their different sources and transformation/elimination mechanisms. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Polybrominated diphenyl ethers (PBDEs) have been extensively used as additive flame retardants in a wide range of products. Because the physicochemical properties of PBDEs render them persistent and bioaccumulative, there has been increasing concern over PBDE contamination, and many studies have been conducted to monitor levels in various environmental and biological samples (Routti et al., 2009; Kim and Stapleton, 2010). ⇑ Corresponding author. Tel.: +86 10 58805080; fax: +86 10 58807743. E-mail address: [email protected] (X. Liu).
Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are known to be both natural products from marine environments and metabolites of anthropogenic PBDEs, whereas methoxylated polybrominated diphenyl ethers (MeO-PBDEs) appear to be solely natural in origin (Malmvärn et al., 2008; Erratico et al., 2010). OH-PBDEs with the hydroxyl group predominantly attached in an ortho-position to the ether bridge are primarily of natural origin (Marsh et al., 2004; Malmvärn et al., 2005). Among PBDE metabolites in rats, the OH-group is mainly in the meta- and para-positions (Malmberg et al., 2005). MeO-PBDEs have never been observed as metabolites following exposure to PBDE flame retardants in animal studies (Kelly et al., 2008b), but they may
http://dx.doi.org/10.1016/j.chemosphere.2014.02.019 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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be formed naturally byO-biomethylation of the corresponding halogenated phenols (Malmvärn, 2007). Recently, seven OH-PBDEs (6-OH-BDE-47, 20 -OH-BDE-68, 6-OH-BDE-85, 6-OH-BDE-90, 6-OHBDE-99, 2-OH-BDE-123, and 6-OH-BDE-137) and four MeO-PBDEs (6-MeO-BDE-47, 20 -MeO-BDE-68, 6-MeO-BDE-85 and 6-MeO-BDE137) were detected both in red algae and blue mussels from the Baltic Sea and structurally identified as natural products (Malmvärn et al., 2005). The formation of OH-PBDEs is of concern because there is growing evidence that OH-PBDEs have a potential to disrupt the endocrine system (Routti et al., 2009). In vitro studies suggested that in humans, meta- and para- OH-substituted PBDEs have relative binding potencies toward transthyretin (TTR) 160–1600 times higher than BDE-47 itself (Hamers et al., 2008). It has also been reported that OH-PBDEs have greater affinity and more potent competitive binding to gull TTR compared to the natural ligands (Ucán-Marín et al., 2009). Studies have shown that some ortho-substituted OH-PBDEs and MeO-PBDEs (6-OH-BDE-47, 6OH-BDE-99, 6-MeO-BDE-47) have an inhibitory effect on aromatase (CYP19) activity at low micromolar concentrations in the H295R human adrenocortical carcinoma cells, and 6-OH-BDE47 also causes a statistically significant increase in cytotoxicity at concentrations >2.5 lM (Song et al., 2009). Compared to 6-OH-BDE47, 6-MeO-BDE47 does not elicit a cytotoxic effect, but can still significantly inhibit CYP19 (Cantón et al., 2005). Moreover, Wan et al. (2009) reported the production of OH-PBDEs from MeO-PBDEs by in vitro biotransformation in microsomes of liver from rainbow trout, chicken and rat, and they suggested that human exposure to MeO-PBDEs that occur naturally in marine organisms should be considered in risk assessments. In the present work, the existence of PBDEs, along with selected OH-PBDEs and MeO-PBDEs, in five bivalve species from Beijing markets was investigated, and efforts were made to explore any seasonal variations. Structures of the target compounds are given in the electronic (Supplementary material (Table S1)). Currently, information on the occurrence of PBDEs, especially OH-PBDEs and MeO-PBDEs, in seafood products from China is scarce. Data obtained in this study will be helpful for the health risk assessment of these edible bivalves for local residents. 2. Materials and methods 2.1. Chemicals Five OH-PBDEs (20 -OH-BDE28, 6-OH-BDE47, 20 -OH-BDE68, 6-OHBDE85, and 6-OH-BDE137), one mixture standard BDE-CSM (BDE28, BDE47, BDE99, BDE100, BDE153, BDE154, BDE183 and BDE209) and fourteen MeO-PBDEs (40 -MeO-BDE17, 30 -MeO-BDE68, 20 -MeO-BDE 28, 4-MeO-BDE42, 40 -MeO-BDE49, 3-MeO-BDE47, 5-MeO-BDE47, 6-MeO-BDE47, 20 -MeO-BDE68, 4-MeO-BDE90, 6-MeO-BDE85, 6MeO-BDE82, 60 -MeO-BDE99 and 6-MeO-BDE137) were purchased from AccuStandard Inc., USA. 2-propanol, n-hexane, dichloromethane and methanol were of HPLC grade and obtained from Amethyst Chemicals. Ethanol and sulfuric acid were purchased from J.T. Baker NEUTRASORB, USA. Silica gel (70–230 mesh size, SILICYCLE SiliaFlash, Canada) was heated at 300 °C for 4–5 h before use. Sodium chloride and sodium hydroxide were obtained from Sinopharm Chemical Reagent Co., Ltd., China. The derivatization reagent, pentafluorobenzoyl chloride (PFBCl, 98%), and the derivatization buffer, tetra-n-butylammonium hydroxide (40% w/w aq.), were acquired from Alfa Aesar, USA. 2.2. Samples Five bivalve species (blue mussel, short-necked clam, surf clam, ark shell, and razor clam) were bought from four seafood markets
located in different areas of Beijing City in April, 2012. To investigate the seasonal variations, the blue mussels were also collected in June and September of 2012. The bivalves were kept frozen at 20 °C until analysis. 2.3. Extraction and cleanup procedure Approximately 10 g (wet weight) of each sample was spiked with surrogate standards BDE138 and 20 -OH-BDE28 and extracted with isopropanol, n-hexane and diethyl ether as described by Jensen et al. (2003). The organic phase was evaporated until dry and weighed for lipid content determination. The dried compounds were resuspended in n-hexane, and the phenolic compounds were separated from the neutral compounds by partitioning with a sodium hydroxide solution (0.5 M, in 50% ethanol) and re-extracted with n-hexane and diethyl ether after acidification with hydrochloric acid (2 M). All phenolic compounds were derivatized with PFBCl according to the method provided by Jensen et al. (2009). Both the neutral and phenolic fractions were treated with sulfuric acid (98%). The subsequent cleanup was performed on a 10-mm i.d. multilayer silica column packed, from bottom to top, with 44% acidic silica (6 cm), neutral silica gel (10 cm, 3% deactivated), and anhydrous sodium sulfate (1 cm). The column was prewashed with n-hexane, and as the solvent reached the top layer, the sample was added and slowly eluted with 100 mL of 50% dichloromethane in n-hexane (v/v). The effluent was concentrated, changed to n-hexane and further concentrated. Finally, the internal standards (BDE85 for PBDEs and MeO-PBDEs, BDE138 for derivatized OHPBDEs) were added before instrumental analysis. 2.4. Instrumentation Analyses were performed using a gas chromatograph coupled to a mass spectrometer (GC/MS, Shimadzu QP2010 plus) equipped with a non-polar DB-5MS column (30 m 0.32 mm i.d. and 0.25 lm film thickness; J&W Scientific, Folsom, CA, USA) with helium as the carrier gas (column flow 1.50 mL min1). The MS analyses were performed in an electron capture negative ionization (ECNI) mode. Selected ion monitoring (SIM) was used to monitor the bromine isotope ions (m/z 79 and 81). The interface and ion source temperatures were 280 °C and 200 °C, respectively. A splitless injector was used and held at 280 °C. To confirm the presence of derivatized OH-PBDEs, the oven temperature was programmed from 80 °C (held for 2.0 min), raised to 180 °C at 15 °C min1, increased to 280 °C at 10 °C min1, and finally ramped to 300 °C at 15 °C min1 (held at 300 °C for 8 min). The temperature of the GC oven for MeO-PBDEs and PBDEs (BDE-209 was not quantified) analyses was raised from 80 °C (2.00 min) to 180 °C at a rate of 15 °C min1, then increased to 280 °C at a rate of 4 °C min1, and finally raised to 300 °C at a rate of 15 °C min1, where it was held for 10 min. Quantification was carried out with an internal calibration procedure. 2.5. Quality control The mean recoveries based on the surrogate standards added were 62.86% ± 20.15% for PBDEs and MeO-PBDEs, and 48.74% ± 25.70% for OH-PBDEs. The results were recovery corrected. Method blanks were simultaneously analyzed to monitor interferences and contamination, showing an absence of background interference for all compounds. Duplicate samples were extracted and analyzed to ensure the accuracy of the results. The instrumental detection limit (IDL) was calculated as 3 times the signal-to-noise ratio. Because the objective compounds were not detected in procedural blanks, the method detection limit (MDL) was set to the IDL. MDLs of PBDEs and their structural analogues in the various samples ranged from 0.001–0.030 ng g1 lipid for PBDEs, 0.002–0.051 ng g1 lipid for
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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MeO-PBDEs, and 0.029–8.442 (approximately 10% higher than 5) ng g1 lipid for OH-PBDEs. 3. Results and discussion 3.1. PBDEs, MeO-PBDEs and OH-PBDEs present in the bivalves As an excellent bioindicator, mussels have been extensively investigated worldwide to assess the residual levels of organic contaminants (including PBDEs) in the global environment (Guo et al., 2007). Measured concentrations of PBDEs, MeO-PBDEs and OHPBDEs in the bivalves collected from Beijing markets are shown in Supporting Information Table S2 (n = 8, duplicate samples for each type of bivalve from each market), which indicates that most of the target polybrominated compounds were detected. 3.1.1. PBDEs All the studied PBDE congeners (BDE28, BDE47, BDE99, BDE100, BDE153, BDE154 and BDE183) could be detected in samples of the bivalves. RPBDEs for the different bivalves ranged between 4.98 ng g1 lipid and 29.75 ng g1 lipid. Concentrations of RPBDEs in the bivalves from Beijing markets were clearly higher than those found in blue mussels (Löfstrand et al., 2011) but lower than those in salmon muscle (49.5 ng g1 lipid) from the Baltic Sea (Sinkkonen et al., 2004). A possible reason for the higher concentrations in salmon may be that salmon belongs to a higher trophic level relative to blue mussels. Zhang et al. (2010a) reported the concentrations ofRPBDEs in short-necked clams collected from Liaodong Bay, China, in the range of 3.09–20.95 ng g1 lipid, which were comparable to those in the bivalves of this study and in the bivalves of a Canadian Arctic marine food web (RPBDEs 5.4 ng g1 lipid) (Kelly et al., 2008a). The average lipid weight of bivalves in this study was approximately 1.3%, so the concentrations of RPBDEs expressed in wet weight were approximately 68.25–386.75 pg g1. The sum of five PBDEs in market fish collected from Swedish cities was reported to be approximately 634 pg g1 wet weight (Darnerud et al., 2006). Meng et al. (2007) reported relatively lower PBDEs levels in fish from China than in those from other countries or regions, which they attributed to the smaller amount of penta-BDE consumption in China. Fig. 1a shows the relative abundances (%) of individual components to the RPBDEs consistently detected in the five bivalve species. The congener profile of PBDEs was dominated by BDE47, followed by BDE28 and BDE 99. The predomination of BD47 has also been reported in bivalves from Korean coastal waters (Moon et al., 2007), in blue mussels from the Bo Sea, China (Wang et al., 2009), and in Arctic Glaucous Gulls and Polar Bears (Wolkers et al., 2004; Verreault et al., 2005). 3.1.2. MeO- and OH-PBDEs Similar to PBDEs, MeO-PBDEs are neutral, lipophilic, non-volatile and biplanar compounds, and they are chemically non-reactive (Malmvärn, 2007). In Fig. 1, the profile of MeO-PBDEs was divided into two parts: Fig. 1b displaying ortho-MeO-PBDEs, of which 6MeO-BDE47 was found at somewhat higher concentrations than the other MeO-PBDEs in the five bivalve species, and Fig. 1c displaying meta- and para-MeO-PBDEs, of which 40 -MeO-BDE17 was found at the highest concentrations. Fig. 1d shows the relative abundances (%) of individual components (6-OH-BDE-47, 20 -OHBDE68, 6-OH-BDE-85 and 6-OH-BDE-137) to the ROH-PBDEs consistently detected in the five bivalve species. Based on some recent reports, Wiseman et al. (2011) found that profiles of OH-PBDEs in marine organisms were generally dominated by 6-OH-BDE-47 and, to a lesser extent, 20 -OH-BDE68. However, in this study, although 6-OH-BDE-47 was the most abundant congener in different bivalves, the concentrations of 6-OH-BDE-85 and 6-OH-BDE-137
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were much higher than those of 20 -OH-BDE68. Verreault et al. (2005) reported that 20 -OH-BDE68 was not detected in two Norwegian Arctic top predators, glaucous gulls and polar bears. Compared to the observations of OH-PBDEs and MeO-PBDEs in blue mussels from the Baltic Sea, reported by Löfstrand et al. (2011), the concentrations of these two types of PBDEs in bivalves from Beijing Markets were quite low. One reason may be attributed to high concentrations of these compounds in the Baltic alga (Malmvärn et al., 2008), and the other may be that most of the bivalves in Beijing Markets were from mariculture plants and therefore did not solely fed on natural alga. In recent years, Chinese researchers have paid more and more attention to OH-PBDEs and MeO-PBDEs in various biotic samples. Zhang et al. (2010a) detected MeO-PBDEs (5-MeO-BDE47, 6-MeOBDE47, 60 -MeO-BDE49, 20 -MeO-BDE68, 40 -MeO-BDE103, 40 -MeOBDE101 and 50 -MeO-BDE99) in biota from Liaodong Bay and found that the highest average concentrations were in fish, followed by bivalves (15.96 ± 11.82 ng g1 lipid), seabirds, and crustaceans. They reported the detection of OH-PBDEs (6-OH-BDE47, 20 -OH-BDE68, 3-OH-BDE47, 4-OH-BDE49, and 5-OH-BDE47) with average concentrations of ROH-PBDEs in invertebrates being 1.7 ± 0.002 ng g1 lipid (Zhang et al., 2012), which are much lower than the concentrations of ROH-PBDEs in our samples. They also reported tissue concentrations of these three types of polybrominated compound in Chinese sturgeon from the Yangtze River. The highest concentrations of PBDEs and MeO-PBDEs occurred in adipose tissue followed by liver and eggs, and the highest concentration of OH-PBDEs was observed in liver and eggs (Zhang et al., 2010b). Su et al. (2010) reported the detection of some MeO-PBDEs in anchovy (Coilia sp.) from the Yangtze River Delta, China. They found that the concentrations of RMeO-PBDEs in anchovy ranged from non-detectable (ND) to 48 ng g1 lipid. Liu et al. (2010) detected some MeO-PBDEs and OH-PBDEs in the sera of eight bird species collected from an e-waste recycling region in South China. 3-OH-BDE47 and 20 -OH-BDE68 were detected in more than 80% of the collected bird serum samples, while 6-OH-BDE47 and 6-MeO-BDE47 were occasionally detected in bird sera at concentrations ranging from ND to 2.5 ng g1 lipid. Naturally originated MeO-BDEs and OH-BDEs share a common structural property in that the OH or MeO group is located in the ortho position relative to the diphenyl ether bond (Athanasiadou et al., 2008). The ortho-OH-PBDEs and ortho-MeO-PBDEs have been detected in the Baltic ecosystem in cyanobacteria, red alga, blue mussels, and salmon (Marsh et al., 2004; Malmvärn et al., 2008; Löfstrand et al., 2011). It should be noted that the orthoOH-PBDEs cannot be completely allocated to natural origin, as ortho-OH-PBDEs have been detected in rats (Marsh et al., 2006; Hamers et al., 2008) and fish (Zeng et al., 2012; Zeng et al., 2013) exposed to PBDEs. The meta- and para-substituted OH-PBDEs are more likely to be metabolites of anthropogenic PBDEs, such as the biologically predominant BDE47 congener, because metaand para-substituted OH-PBDEs have not been detected in marine algae or other microorganisms (Malmvärn et al., 2008). As can be seen in Table S2, the sum of the four ortho-OH-PBDEs is about 2–5 times higher than the sum of the seven PBDEs in different bivalves, which supports the hypothesis that most of the ortho-OHPBDEs in this study were derived from natural origin. There was a weak negative correlation between concentrations of 6-OH-BDE47 and 6-MeO-BDE47 in bivalves (R = 0.335, p = 0.012); this correlation is inconsistent with the interconversion of the two compounds in Japanese medaka reported recently (Wan et al., 2010), which indicates that 6-OH-BDE47 may not be solely from natural origin. Another interesting finding is that there was significant correlation between the levels of 6-MeO-BDE47 and BDE47 (R = 0.675, p < 0.01), suggesting that 6-MeO-BDE47 is a possible metabolic product of BDE47. However, MeO-BDEs have not been observed to be formed in controlled exposure studies with
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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Fig. 1. Relative abundances (%) of individual compounds to the sum of each class of brominated compound (PBDEs, MeO-PBDEs, and OH-PBDEs) consistently detected in the five bivalve species. (a) Provides results for the seven PBDEs; (b) represents the MeO-PBDEs with the methoxy group attached in the ortho-position to the ether bridge; (c) shows the MeO-BDEs with the methoxy group attached in the meta or para-position to the ether bridge; and (d) indicates the OH-PBDEs. The horizontal line represents 10th, median, and 90th percentiles, and the box represents 25th and 75th percentiles. Outliers exceeding 1.5 and 3 times of the height of box are shown as individual circles and asterisks, respectively.
PBDEs, performed either in vitro or in vivo (Wiseman et al., 2011). The concentrations of BDE47, 6-MeO-BDE47 and 6-OH-BDE47 in different bivalve species are shown in Fig. 2, and they generally followed the order 6-OH-BDE47 > BDE47 > 6-MeO-BDE47. 3.2. Seasonal variations of PBDEs, MeO-PBDEs and OH-PBDEs in blue mussels It was reported that clear seasonal variations in biologically active secondary metabolites were observed for some macroalgal species from the southern coasts of India (Padmakumar and
Ayyakkannu, 1997). Löfstrand et al. (2011) found that the OH-PBDE and MeO-PBDE levels in the mussels from the Baltic Sea showed seasonal variations from May to October, with the highest concentration of each congener appearing in June. This study also concentrated on seasonal variations of polybrominated compounds in blue mussels from Beijing markets. As shown in Fig. 3, apparent seasonal variations are observed for these three types of polybrominated compound in blue mussels, although the acidic components display different trends from the neutral components. In the PBDEs cluster, BDE47 has a more significant seasonal variation than other congeners, while for
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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Fig. 2. Mean concentrations of BDE47, 6-MeO-BDE47 and 6-OH-BDE47 (ng g1 lipid) in bivalves from Beijing markets. The vertical bars represent the 95% confidence interval.
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MeO-PBDEs, the variation of 20 -MeO-BDE68 is more apparent. The concentration of 20 -MeO-BDE68 rises rapidly from 1.03 ng g1 lipid in April to 3.88 ng g1 lipid in June, then drops to 2.23 ng g1 lipid in September (data shown in Table S3). The similar, though less apparent, trends of seasonal variation are observed for other congeners. It seems that 6-MeO-BDE137 has no significant seasonal variation compared to other congeners, with the average concentration in blue mussels remaining almost the same in different seasons. It is notable that the OH-PBDEs in blue mussels in this study show converse seasonal variations compared to PBDEs and MeOPBDEs, with the lowest values observed in June. The congener pattern of OH-PBDEs is also different from that of MeO-PBDEs, with 20 OH-BDE68 being the least abundant congener for OH-PBDEs while 20 -MeO-BDE68 is one of the most abundant congeners for the MeO-PBDEs. The difference between patterns of OH-PBDEs and MeO-PBDEs in blue mussels might be due to the difference in bioavailability, source and transformation/elimination mechanism. The neutral MeO-PBDEs are lipophilic and bioaccumulative as indicated by the high log Kow values determined for some MeO-PBDEs (Teuten et al., 2005), which are not apt to be excreted by blue mussels. In summer (June), the blue mussels may consume more alga and accumulate more polybrominated compounds, but the metabolic process may also be fast in this period, and the OH-PBDEs are more easily excreted. For the MeO-PBDEs and OH-PBDEs detected in marine sponges, salmon, mussels, alga and cyanobacteria, a plausible explanation is that OH-PBDEs are the primary products,
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2'-Meo-BDE-28 2'-Meo-BDE-68 6-Meo-BDE-47 6'-Meo-BDE-99 6-Meo-BDE-85 6-Meo-BDE-82 6-Meo-BDE-137
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Fig. 3. Seasonal variations of average concentrations of PBDEs, MeO-PBDEs and OH-PBDEs in blue mussels from Beijing markets. (a) Provides results for the seven PBDEs; (b) represents the MeO-PBDEs with the methoxy group attached in ortho-position to the ether bridge; (c) shows the MeO-BDEs with the methoxy group attached in meta or para-position to the ether bridge; and (d) indicates the OH-PBDEs.
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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while MeO-PBDEs may be formed as the secondary products by methylation of the corresponding OH-PBDEs in liver or intestinal microflora in vertebrates or directly by organisms in sediments (Asplund et al., 1999; Teuten et al., 2005; Valters et al., 2005; Malmvärn, 2007). This may be a detoxification mechanism, as methyl derivatives exhibit less bioactivity than the corresponding alcohols (Teuten et al., 2005). Based on this hypothesis, another potential explanation for the decreases of OH-PBDEs and the increases of MeO-PBDEs in blue mussels collected in June is the transformation between the analogues. For polybrominated compounds, it is known that the more highly brominated ones can be transformed into less brominated compounds when subjected to reducing conditions (Bastos et al., 2008). Debromination has been observed to occur in several fish species; for example, common carp converts BDE-99 to BDE-47, and pike, trout and carp can transform BDE-209 to less highly brominated PBDEs (Malmvärn, 2007). Therefore, the interconversion between polybrominated compounds in bivalves may be very complicated.
3.3. Potential effects OH-PBDEs have been reported to have the potential to elicit a variety of effects on organisms. 6-OH-BDE47 was confirmed by microarray analysis to be acutely toxic in developing and adult zebrafish at concentrations in the nanomolar (nM) range, and the findings indicated that 6-OH-BDE47 causes disruption of oxidative phosphorylation (van Boxtel et al., 2008). Hamers et al. (2006) also revealed in vitro anti-estrogenic effects for 6-OH-BDE-47. In addition to those that are naturally produced, another important origin of OH-PBDEs is that of the metabolites of PBDEs or MeO-PBDEs. Although the concentrations of these three types of polybrominated compound in bivalves from Beijing markets are not very high, a biomagnification effect via the food chain may exist. Consequently, consumption of marine products could mean an significant exposure of polybrominated compounds. However, part of the polybrominated compounds may be decomposed during the cooking of marine products. Therefore, it would be interesting to investigate the decomposition of polybrominated compounds in different marine products by different cooking methods.
4. Conclusions The concentrations of some PBDEs, OH-PBDEs and MeO-PBDEs were measured in five bivalve species from Beijing markets. Compared with the values of these compounds in blue mussels from the Baltic Sea, the higher concentrations of PBDEs and lower concentrations of OH-PBDEs and MeO-PBDEs in this study might be partly attributed to the fact that the bivalves were from mariculture plants and therefore did not solely feed on natural alga. The concentrations of MeO-PBDEs in blue mussels from Beijing markets showed similar trends in seasonal variation to those in blue mussels from the Baltic Sea. However, the concentrations of OHPBDEs displayed the converse seasonal variation trends. The results presented in this study could be useful for health risk assessments.
Acknowledgements This study was supported by the National Natural Science Foundation (Project No. 20977011), the Ministry of Environmental Protection (Project No. 201309044), and the Ministry of Science and Technology of China (Project No. 2013AA06A305).
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PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets Xitao Liu ⇑, Ying Jiao, Chunye Lin, Ke Sun, Ye Zhao State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, 100875 Beijing, PR China
h i g h l i g h t s Presence of polybrominated compounds in bivalves from Beijing markets was studied. Levels of PBDEs in this study were higher than those in Baltic blue mussels. Levels of OH- and MeO-PBDEs in this study were lower than in Baltic blue mussels. Polybrominated compounds showed significant seasonal variations in blue mussels. Acidic components displayed different seasonal variations from neutral components.
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Article history: Received 5 February 2013 Received in revised form 23 January 2014 Accepted 6 February 2014 Available online xxxx Keywords: PBDEs OH-PBDEs MeO-PBDEs Bivalves Seasonal variations
a b s t r a c t The structural analogues of polybrominated diphenyl ethers (PBDEs), hydroxylated PBDEs (OH-PBDEs) and methoxylated PBDEs (MeO-PBDEs) have been attracting increasing concern in recent years. Five bivalve species (blue mussel, short-necked clam, surf clam, ark shell and razor clam) were collected from Beijing markets, and the concentrations of seven PBDEs, four OH-PBDEs and fourteen MeO-PBDEs in the bivalves were measured. The seasonal variations of these three types of polybrominated compound in blue mussels were also monitored. The results indicate that the levels of RPBDEs in this study were comparable to those in short-necked clams from Liaodong Bay, China, with BDE47 as the dominant congener. For the ortho-MeO-PBDEs, 6-MeO-BDE47 was found at higher concentrations than the others, while for the metaand para-MeO-PBDEs, 40 -MeO-BDE17 was found at higher concentrations. 6-OH-BDE-47 was the most abundant congener among the 4 measured OH-PBDEs, followed by 6-OH-BDE-137 and 6-OH-BDE-85. The levels of OH-PBDEs and MeO-PBDEs in bivalves from Beijing markets were much lower than the corresponding compounds in blue mussels from the Baltic Sea. In the blue mussels collected in April, June and September of 2012, apparent seasonal variations were observed for these three types of polybrominated compounds, but the acidic components displayed different trends from the neutral components, with PBDEs and MeO-PBDEs showing the highest concentrations in June, while OH-PBDEs had the lowest concentrations in June. This difference in seasonal variations between the neutral components and the acidic components may be explained by their different sources and transformation/elimination mechanisms. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Polybrominated diphenyl ethers (PBDEs) have been extensively used as additive flame retardants in a wide range of products. Because the physicochemical properties of PBDEs render them persistent and bioaccumulative, there has been increasing concern over PBDE contamination, and many studies have been conducted to monitor levels in various environmental and biological samples (Routti et al., 2009; Kim and Stapleton, 2010). ⇑ Corresponding author. Tel.: +86 10 58805080; fax: +86 10 58807743. E-mail address: [email protected] (X. Liu).
Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are known to be both natural products from marine environments and metabolites of anthropogenic PBDEs, whereas methoxylated polybrominated diphenyl ethers (MeO-PBDEs) appear to be solely natural in origin (Malmvärn et al., 2008; Erratico et al., 2010). OH-PBDEs with the hydroxyl group predominantly attached in an ortho-position to the ether bridge are primarily of natural origin (Marsh et al., 2004; Malmvärn et al., 2005). Among PBDE metabolites in rats, the OH-group is mainly in the meta- and para-positions (Malmberg et al., 2005). MeO-PBDEs have never been observed as metabolites following exposure to PBDE flame retardants in animal studies (Kelly et al., 2008b), but they may
http://dx.doi.org/10.1016/j.chemosphere.2014.02.019 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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be formed naturally byO-biomethylation of the corresponding halogenated phenols (Malmvärn, 2007). Recently, seven OH-PBDEs (6-OH-BDE-47, 20 -OH-BDE-68, 6-OH-BDE-85, 6-OH-BDE-90, 6-OHBDE-99, 2-OH-BDE-123, and 6-OH-BDE-137) and four MeO-PBDEs (6-MeO-BDE-47, 20 -MeO-BDE-68, 6-MeO-BDE-85 and 6-MeO-BDE137) were detected both in red algae and blue mussels from the Baltic Sea and structurally identified as natural products (Malmvärn et al., 2005). The formation of OH-PBDEs is of concern because there is growing evidence that OH-PBDEs have a potential to disrupt the endocrine system (Routti et al., 2009). In vitro studies suggested that in humans, meta- and para- OH-substituted PBDEs have relative binding potencies toward transthyretin (TTR) 160–1600 times higher than BDE-47 itself (Hamers et al., 2008). It has also been reported that OH-PBDEs have greater affinity and more potent competitive binding to gull TTR compared to the natural ligands (Ucán-Marín et al., 2009). Studies have shown that some ortho-substituted OH-PBDEs and MeO-PBDEs (6-OH-BDE-47, 6OH-BDE-99, 6-MeO-BDE-47) have an inhibitory effect on aromatase (CYP19) activity at low micromolar concentrations in the H295R human adrenocortical carcinoma cells, and 6-OH-BDE47 also causes a statistically significant increase in cytotoxicity at concentrations >2.5 lM (Song et al., 2009). Compared to 6-OH-BDE47, 6-MeO-BDE47 does not elicit a cytotoxic effect, but can still significantly inhibit CYP19 (Cantón et al., 2005). Moreover, Wan et al. (2009) reported the production of OH-PBDEs from MeO-PBDEs by in vitro biotransformation in microsomes of liver from rainbow trout, chicken and rat, and they suggested that human exposure to MeO-PBDEs that occur naturally in marine organisms should be considered in risk assessments. In the present work, the existence of PBDEs, along with selected OH-PBDEs and MeO-PBDEs, in five bivalve species from Beijing markets was investigated, and efforts were made to explore any seasonal variations. Structures of the target compounds are given in the electronic (Supplementary material (Table S1)). Currently, information on the occurrence of PBDEs, especially OH-PBDEs and MeO-PBDEs, in seafood products from China is scarce. Data obtained in this study will be helpful for the health risk assessment of these edible bivalves for local residents. 2. Materials and methods 2.1. Chemicals Five OH-PBDEs (20 -OH-BDE28, 6-OH-BDE47, 20 -OH-BDE68, 6-OHBDE85, and 6-OH-BDE137), one mixture standard BDE-CSM (BDE28, BDE47, BDE99, BDE100, BDE153, BDE154, BDE183 and BDE209) and fourteen MeO-PBDEs (40 -MeO-BDE17, 30 -MeO-BDE68, 20 -MeO-BDE 28, 4-MeO-BDE42, 40 -MeO-BDE49, 3-MeO-BDE47, 5-MeO-BDE47, 6-MeO-BDE47, 20 -MeO-BDE68, 4-MeO-BDE90, 6-MeO-BDE85, 6MeO-BDE82, 60 -MeO-BDE99 and 6-MeO-BDE137) were purchased from AccuStandard Inc., USA. 2-propanol, n-hexane, dichloromethane and methanol were of HPLC grade and obtained from Amethyst Chemicals. Ethanol and sulfuric acid were purchased from J.T. Baker NEUTRASORB, USA. Silica gel (70–230 mesh size, SILICYCLE SiliaFlash, Canada) was heated at 300 °C for 4–5 h before use. Sodium chloride and sodium hydroxide were obtained from Sinopharm Chemical Reagent Co., Ltd., China. The derivatization reagent, pentafluorobenzoyl chloride (PFBCl, 98%), and the derivatization buffer, tetra-n-butylammonium hydroxide (40% w/w aq.), were acquired from Alfa Aesar, USA. 2.2. Samples Five bivalve species (blue mussel, short-necked clam, surf clam, ark shell, and razor clam) were bought from four seafood markets
located in different areas of Beijing City in April, 2012. To investigate the seasonal variations, the blue mussels were also collected in June and September of 2012. The bivalves were kept frozen at 20 °C until analysis. 2.3. Extraction and cleanup procedure Approximately 10 g (wet weight) of each sample was spiked with surrogate standards BDE138 and 20 -OH-BDE28 and extracted with isopropanol, n-hexane and diethyl ether as described by Jensen et al. (2003). The organic phase was evaporated until dry and weighed for lipid content determination. The dried compounds were resuspended in n-hexane, and the phenolic compounds were separated from the neutral compounds by partitioning with a sodium hydroxide solution (0.5 M, in 50% ethanol) and re-extracted with n-hexane and diethyl ether after acidification with hydrochloric acid (2 M). All phenolic compounds were derivatized with PFBCl according to the method provided by Jensen et al. (2009). Both the neutral and phenolic fractions were treated with sulfuric acid (98%). The subsequent cleanup was performed on a 10-mm i.d. multilayer silica column packed, from bottom to top, with 44% acidic silica (6 cm), neutral silica gel (10 cm, 3% deactivated), and anhydrous sodium sulfate (1 cm). The column was prewashed with n-hexane, and as the solvent reached the top layer, the sample was added and slowly eluted with 100 mL of 50% dichloromethane in n-hexane (v/v). The effluent was concentrated, changed to n-hexane and further concentrated. Finally, the internal standards (BDE85 for PBDEs and MeO-PBDEs, BDE138 for derivatized OHPBDEs) were added before instrumental analysis. 2.4. Instrumentation Analyses were performed using a gas chromatograph coupled to a mass spectrometer (GC/MS, Shimadzu QP2010 plus) equipped with a non-polar DB-5MS column (30 m 0.32 mm i.d. and 0.25 lm film thickness; J&W Scientific, Folsom, CA, USA) with helium as the carrier gas (column flow 1.50 mL min1). The MS analyses were performed in an electron capture negative ionization (ECNI) mode. Selected ion monitoring (SIM) was used to monitor the bromine isotope ions (m/z 79 and 81). The interface and ion source temperatures were 280 °C and 200 °C, respectively. A splitless injector was used and held at 280 °C. To confirm the presence of derivatized OH-PBDEs, the oven temperature was programmed from 80 °C (held for 2.0 min), raised to 180 °C at 15 °C min1, increased to 280 °C at 10 °C min1, and finally ramped to 300 °C at 15 °C min1 (held at 300 °C for 8 min). The temperature of the GC oven for MeO-PBDEs and PBDEs (BDE-209 was not quantified) analyses was raised from 80 °C (2.00 min) to 180 °C at a rate of 15 °C min1, then increased to 280 °C at a rate of 4 °C min1, and finally raised to 300 °C at a rate of 15 °C min1, where it was held for 10 min. Quantification was carried out with an internal calibration procedure. 2.5. Quality control The mean recoveries based on the surrogate standards added were 62.86% ± 20.15% for PBDEs and MeO-PBDEs, and 48.74% ± 25.70% for OH-PBDEs. The results were recovery corrected. Method blanks were simultaneously analyzed to monitor interferences and contamination, showing an absence of background interference for all compounds. Duplicate samples were extracted and analyzed to ensure the accuracy of the results. The instrumental detection limit (IDL) was calculated as 3 times the signal-to-noise ratio. Because the objective compounds were not detected in procedural blanks, the method detection limit (MDL) was set to the IDL. MDLs of PBDEs and their structural analogues in the various samples ranged from 0.001–0.030 ng g1 lipid for PBDEs, 0.002–0.051 ng g1 lipid for
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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MeO-PBDEs, and 0.029–8.442 (approximately 10% higher than 5) ng g1 lipid for OH-PBDEs. 3. Results and discussion 3.1. PBDEs, MeO-PBDEs and OH-PBDEs present in the bivalves As an excellent bioindicator, mussels have been extensively investigated worldwide to assess the residual levels of organic contaminants (including PBDEs) in the global environment (Guo et al., 2007). Measured concentrations of PBDEs, MeO-PBDEs and OHPBDEs in the bivalves collected from Beijing markets are shown in Supporting Information Table S2 (n = 8, duplicate samples for each type of bivalve from each market), which indicates that most of the target polybrominated compounds were detected. 3.1.1. PBDEs All the studied PBDE congeners (BDE28, BDE47, BDE99, BDE100, BDE153, BDE154 and BDE183) could be detected in samples of the bivalves. RPBDEs for the different bivalves ranged between 4.98 ng g1 lipid and 29.75 ng g1 lipid. Concentrations of RPBDEs in the bivalves from Beijing markets were clearly higher than those found in blue mussels (Löfstrand et al., 2011) but lower than those in salmon muscle (49.5 ng g1 lipid) from the Baltic Sea (Sinkkonen et al., 2004). A possible reason for the higher concentrations in salmon may be that salmon belongs to a higher trophic level relative to blue mussels. Zhang et al. (2010a) reported the concentrations ofRPBDEs in short-necked clams collected from Liaodong Bay, China, in the range of 3.09–20.95 ng g1 lipid, which were comparable to those in the bivalves of this study and in the bivalves of a Canadian Arctic marine food web (RPBDEs 5.4 ng g1 lipid) (Kelly et al., 2008a). The average lipid weight of bivalves in this study was approximately 1.3%, so the concentrations of RPBDEs expressed in wet weight were approximately 68.25–386.75 pg g1. The sum of five PBDEs in market fish collected from Swedish cities was reported to be approximately 634 pg g1 wet weight (Darnerud et al., 2006). Meng et al. (2007) reported relatively lower PBDEs levels in fish from China than in those from other countries or regions, which they attributed to the smaller amount of penta-BDE consumption in China. Fig. 1a shows the relative abundances (%) of individual components to the RPBDEs consistently detected in the five bivalve species. The congener profile of PBDEs was dominated by BDE47, followed by BDE28 and BDE 99. The predomination of BD47 has also been reported in bivalves from Korean coastal waters (Moon et al., 2007), in blue mussels from the Bo Sea, China (Wang et al., 2009), and in Arctic Glaucous Gulls and Polar Bears (Wolkers et al., 2004; Verreault et al., 2005). 3.1.2. MeO- and OH-PBDEs Similar to PBDEs, MeO-PBDEs are neutral, lipophilic, non-volatile and biplanar compounds, and they are chemically non-reactive (Malmvärn, 2007). In Fig. 1, the profile of MeO-PBDEs was divided into two parts: Fig. 1b displaying ortho-MeO-PBDEs, of which 6MeO-BDE47 was found at somewhat higher concentrations than the other MeO-PBDEs in the five bivalve species, and Fig. 1c displaying meta- and para-MeO-PBDEs, of which 40 -MeO-BDE17 was found at the highest concentrations. Fig. 1d shows the relative abundances (%) of individual components (6-OH-BDE-47, 20 -OHBDE68, 6-OH-BDE-85 and 6-OH-BDE-137) to the ROH-PBDEs consistently detected in the five bivalve species. Based on some recent reports, Wiseman et al. (2011) found that profiles of OH-PBDEs in marine organisms were generally dominated by 6-OH-BDE-47 and, to a lesser extent, 20 -OH-BDE68. However, in this study, although 6-OH-BDE-47 was the most abundant congener in different bivalves, the concentrations of 6-OH-BDE-85 and 6-OH-BDE-137
3
were much higher than those of 20 -OH-BDE68. Verreault et al. (2005) reported that 20 -OH-BDE68 was not detected in two Norwegian Arctic top predators, glaucous gulls and polar bears. Compared to the observations of OH-PBDEs and MeO-PBDEs in blue mussels from the Baltic Sea, reported by Löfstrand et al. (2011), the concentrations of these two types of PBDEs in bivalves from Beijing Markets were quite low. One reason may be attributed to high concentrations of these compounds in the Baltic alga (Malmvärn et al., 2008), and the other may be that most of the bivalves in Beijing Markets were from mariculture plants and therefore did not solely fed on natural alga. In recent years, Chinese researchers have paid more and more attention to OH-PBDEs and MeO-PBDEs in various biotic samples. Zhang et al. (2010a) detected MeO-PBDEs (5-MeO-BDE47, 6-MeOBDE47, 60 -MeO-BDE49, 20 -MeO-BDE68, 40 -MeO-BDE103, 40 -MeOBDE101 and 50 -MeO-BDE99) in biota from Liaodong Bay and found that the highest average concentrations were in fish, followed by bivalves (15.96 ± 11.82 ng g1 lipid), seabirds, and crustaceans. They reported the detection of OH-PBDEs (6-OH-BDE47, 20 -OH-BDE68, 3-OH-BDE47, 4-OH-BDE49, and 5-OH-BDE47) with average concentrations of ROH-PBDEs in invertebrates being 1.7 ± 0.002 ng g1 lipid (Zhang et al., 2012), which are much lower than the concentrations of ROH-PBDEs in our samples. They also reported tissue concentrations of these three types of polybrominated compound in Chinese sturgeon from the Yangtze River. The highest concentrations of PBDEs and MeO-PBDEs occurred in adipose tissue followed by liver and eggs, and the highest concentration of OH-PBDEs was observed in liver and eggs (Zhang et al., 2010b). Su et al. (2010) reported the detection of some MeO-PBDEs in anchovy (Coilia sp.) from the Yangtze River Delta, China. They found that the concentrations of RMeO-PBDEs in anchovy ranged from non-detectable (ND) to 48 ng g1 lipid. Liu et al. (2010) detected some MeO-PBDEs and OH-PBDEs in the sera of eight bird species collected from an e-waste recycling region in South China. 3-OH-BDE47 and 20 -OH-BDE68 were detected in more than 80% of the collected bird serum samples, while 6-OH-BDE47 and 6-MeO-BDE47 were occasionally detected in bird sera at concentrations ranging from ND to 2.5 ng g1 lipid. Naturally originated MeO-BDEs and OH-BDEs share a common structural property in that the OH or MeO group is located in the ortho position relative to the diphenyl ether bond (Athanasiadou et al., 2008). The ortho-OH-PBDEs and ortho-MeO-PBDEs have been detected in the Baltic ecosystem in cyanobacteria, red alga, blue mussels, and salmon (Marsh et al., 2004; Malmvärn et al., 2008; Löfstrand et al., 2011). It should be noted that the orthoOH-PBDEs cannot be completely allocated to natural origin, as ortho-OH-PBDEs have been detected in rats (Marsh et al., 2006; Hamers et al., 2008) and fish (Zeng et al., 2012; Zeng et al., 2013) exposed to PBDEs. The meta- and para-substituted OH-PBDEs are more likely to be metabolites of anthropogenic PBDEs, such as the biologically predominant BDE47 congener, because metaand para-substituted OH-PBDEs have not been detected in marine algae or other microorganisms (Malmvärn et al., 2008). As can be seen in Table S2, the sum of the four ortho-OH-PBDEs is about 2–5 times higher than the sum of the seven PBDEs in different bivalves, which supports the hypothesis that most of the ortho-OHPBDEs in this study were derived from natural origin. There was a weak negative correlation between concentrations of 6-OH-BDE47 and 6-MeO-BDE47 in bivalves (R = 0.335, p = 0.012); this correlation is inconsistent with the interconversion of the two compounds in Japanese medaka reported recently (Wan et al., 2010), which indicates that 6-OH-BDE47 may not be solely from natural origin. Another interesting finding is that there was significant correlation between the levels of 6-MeO-BDE47 and BDE47 (R = 0.675, p < 0.01), suggesting that 6-MeO-BDE47 is a possible metabolic product of BDE47. However, MeO-BDEs have not been observed to be formed in controlled exposure studies with
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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Fig. 1. Relative abundances (%) of individual compounds to the sum of each class of brominated compound (PBDEs, MeO-PBDEs, and OH-PBDEs) consistently detected in the five bivalve species. (a) Provides results for the seven PBDEs; (b) represents the MeO-PBDEs with the methoxy group attached in the ortho-position to the ether bridge; (c) shows the MeO-BDEs with the methoxy group attached in the meta or para-position to the ether bridge; and (d) indicates the OH-PBDEs. The horizontal line represents 10th, median, and 90th percentiles, and the box represents 25th and 75th percentiles. Outliers exceeding 1.5 and 3 times of the height of box are shown as individual circles and asterisks, respectively.
PBDEs, performed either in vitro or in vivo (Wiseman et al., 2011). The concentrations of BDE47, 6-MeO-BDE47 and 6-OH-BDE47 in different bivalve species are shown in Fig. 2, and they generally followed the order 6-OH-BDE47 > BDE47 > 6-MeO-BDE47. 3.2. Seasonal variations of PBDEs, MeO-PBDEs and OH-PBDEs in blue mussels It was reported that clear seasonal variations in biologically active secondary metabolites were observed for some macroalgal species from the southern coasts of India (Padmakumar and
Ayyakkannu, 1997). Löfstrand et al. (2011) found that the OH-PBDE and MeO-PBDE levels in the mussels from the Baltic Sea showed seasonal variations from May to October, with the highest concentration of each congener appearing in June. This study also concentrated on seasonal variations of polybrominated compounds in blue mussels from Beijing markets. As shown in Fig. 3, apparent seasonal variations are observed for these three types of polybrominated compound in blue mussels, although the acidic components display different trends from the neutral components. In the PBDEs cluster, BDE47 has a more significant seasonal variation than other congeners, while for
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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Fig. 2. Mean concentrations of BDE47, 6-MeO-BDE47 and 6-OH-BDE47 (ng g1 lipid) in bivalves from Beijing markets. The vertical bars represent the 95% confidence interval.
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BDE28 BDE47 BDE-100 BDE-99 BDE-154 BDE-153 BDE-183
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MeO-PBDEs, the variation of 20 -MeO-BDE68 is more apparent. The concentration of 20 -MeO-BDE68 rises rapidly from 1.03 ng g1 lipid in April to 3.88 ng g1 lipid in June, then drops to 2.23 ng g1 lipid in September (data shown in Table S3). The similar, though less apparent, trends of seasonal variation are observed for other congeners. It seems that 6-MeO-BDE137 has no significant seasonal variation compared to other congeners, with the average concentration in blue mussels remaining almost the same in different seasons. It is notable that the OH-PBDEs in blue mussels in this study show converse seasonal variations compared to PBDEs and MeOPBDEs, with the lowest values observed in June. The congener pattern of OH-PBDEs is also different from that of MeO-PBDEs, with 20 OH-BDE68 being the least abundant congener for OH-PBDEs while 20 -MeO-BDE68 is one of the most abundant congeners for the MeO-PBDEs. The difference between patterns of OH-PBDEs and MeO-PBDEs in blue mussels might be due to the difference in bioavailability, source and transformation/elimination mechanism. The neutral MeO-PBDEs are lipophilic and bioaccumulative as indicated by the high log Kow values determined for some MeO-PBDEs (Teuten et al., 2005), which are not apt to be excreted by blue mussels. In summer (June), the blue mussels may consume more alga and accumulate more polybrominated compounds, but the metabolic process may also be fast in this period, and the OH-PBDEs are more easily excreted. For the MeO-PBDEs and OH-PBDEs detected in marine sponges, salmon, mussels, alga and cyanobacteria, a plausible explanation is that OH-PBDEs are the primary products,
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2'-Meo-BDE-28 2'-Meo-BDE-68 6-Meo-BDE-47 6'-Meo-BDE-99 6-Meo-BDE-85 6-Meo-BDE-82 6-Meo-BDE-137
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Fig. 3. Seasonal variations of average concentrations of PBDEs, MeO-PBDEs and OH-PBDEs in blue mussels from Beijing markets. (a) Provides results for the seven PBDEs; (b) represents the MeO-PBDEs with the methoxy group attached in ortho-position to the ether bridge; (c) shows the MeO-BDEs with the methoxy group attached in meta or para-position to the ether bridge; and (d) indicates the OH-PBDEs.
Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019
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while MeO-PBDEs may be formed as the secondary products by methylation of the corresponding OH-PBDEs in liver or intestinal microflora in vertebrates or directly by organisms in sediments (Asplund et al., 1999; Teuten et al., 2005; Valters et al., 2005; Malmvärn, 2007). This may be a detoxification mechanism, as methyl derivatives exhibit less bioactivity than the corresponding alcohols (Teuten et al., 2005). Based on this hypothesis, another potential explanation for the decreases of OH-PBDEs and the increases of MeO-PBDEs in blue mussels collected in June is the transformation between the analogues. For polybrominated compounds, it is known that the more highly brominated ones can be transformed into less brominated compounds when subjected to reducing conditions (Bastos et al., 2008). Debromination has been observed to occur in several fish species; for example, common carp converts BDE-99 to BDE-47, and pike, trout and carp can transform BDE-209 to less highly brominated PBDEs (Malmvärn, 2007). Therefore, the interconversion between polybrominated compounds in bivalves may be very complicated.
3.3. Potential effects OH-PBDEs have been reported to have the potential to elicit a variety of effects on organisms. 6-OH-BDE47 was confirmed by microarray analysis to be acutely toxic in developing and adult zebrafish at concentrations in the nanomolar (nM) range, and the findings indicated that 6-OH-BDE47 causes disruption of oxidative phosphorylation (van Boxtel et al., 2008). Hamers et al. (2006) also revealed in vitro anti-estrogenic effects for 6-OH-BDE-47. In addition to those that are naturally produced, another important origin of OH-PBDEs is that of the metabolites of PBDEs or MeO-PBDEs. Although the concentrations of these three types of polybrominated compound in bivalves from Beijing markets are not very high, a biomagnification effect via the food chain may exist. Consequently, consumption of marine products could mean an significant exposure of polybrominated compounds. However, part of the polybrominated compounds may be decomposed during the cooking of marine products. Therefore, it would be interesting to investigate the decomposition of polybrominated compounds in different marine products by different cooking methods.
4. Conclusions The concentrations of some PBDEs, OH-PBDEs and MeO-PBDEs were measured in five bivalve species from Beijing markets. Compared with the values of these compounds in blue mussels from the Baltic Sea, the higher concentrations of PBDEs and lower concentrations of OH-PBDEs and MeO-PBDEs in this study might be partly attributed to the fact that the bivalves were from mariculture plants and therefore did not solely feed on natural alga. The concentrations of MeO-PBDEs in blue mussels from Beijing markets showed similar trends in seasonal variation to those in blue mussels from the Baltic Sea. However, the concentrations of OHPBDEs displayed the converse seasonal variation trends. The results presented in this study could be useful for health risk assessments.
Acknowledgements This study was supported by the National Natural Science Foundation (Project No. 20977011), the Ministry of Environmental Protection (Project No. 201309044), and the Ministry of Science and Technology of China (Project No. 2013AA06A305).
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Please cite this article in press as: Liu, X., et al. PBDEs, hydroxylated PBDEs and methoxylated PBDEs in bivalves from Beijing markets. Chemosphere (2014), http://dx.doi.org/10.1016/j.chemosphere.2014.02.019