Article pubs.acs.org/est
Using Compound-Specific Stable Carbon Isotope Analysis to Trace Metabolism and Trophic Transfer of PCBs and PBDEs in Fish from an e‑Waste Site, South China Yan-Hong Zeng,†,‡ Xiao-Jun Luo,*,† Le-Huan Yu,†,‡ Hua-Shan Chen,† Jiang-Ping Wu,† She-Jun Chen,† and Bi-Xian Mai† †
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People’s Republic of China ‡ Graduate University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China S Supporting Information *
ABSTRACT: Two fish species (mud carp and northern snakehead) forming a predator/prey relationship and sediment samples were collected from a pond contaminated by e-waste. The concentrations and stable carbon isotope ratios (δ13C) of individual polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) congeners were measured to determine if compound-specific carbon isotope analysis (CSIA) could be used to provide insight into the metabolism and trophic dynamics of PCBs and PBDEs. Significant correlations were found in the isotopic data of PCB congeners between the sediment and the fish species and between the two fish indicating identical origin of PCBs in sediment and fish. Most PCB congeners in the fish species were enriched in 13C compared with the PCB congeners in the sediments as a result of isotopic fractionation during the metabolism of PCBs in fish. The isotopic data of several PCB congeners showing isotopic agreement or isotopic depletion could be used for source apportionment or to trace the reductive dechlorination process of PCBs in the environment. The PCB isotopic data covaried more in the northern snakehead than in the mud carp when compared to the sediment, implying that a similar isotopic fractionation occurs from the prey to the predator fish for a PCB congener possibly due to similar metabolic pathways. The PBDE congener patterns differed in the three sample types with a high abundance of BDE209, 183, 99, and 47 in the sediment, BDE47, 153, and 49 in the mud carp and BDE47, 100, and 154 in the northern snakehead. The isotopic change of BDE congeners, such as BDE47 and BDE49, in two fish species, provides evidence for biotransformation of PBDEs in biota. The results of this study suggest that CSIA is a promising tool for deciphering the fate of PCBs and PBDEs in the environment.
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PBDE congeners in fish11 and birds,12 and the hydroxylation of PBDEs in fish, birds, and marine mammals were also previously reported.13 These biochemical processes present new concerns because the toxicity of the transformation products may be greater than that of their parent compounds.14 Furthermore, the biotransformation of these compounds adds an additional layer of complexity when assessing their bioavailability and bioaccumulation potential. For example, some studies suggest that the ratios of BDE47 to BDE99 and BDE100 to BDE99 observed in fish were higher than those observed in the surrounding samples and could be related to the low bioavailability of BDE99 in fish.15 However, other studies have
INTRODUCTION Polychlorinated biphenyls (PCBs) have been used as heat transfer fluids, hydraulic lubricants, and dielectric fluids for transformers and electrical/electronic equipment.1 Polybrominated diphenyl ethers (PBDEs) are used as flame retardant additives in various consumer products, such as plastic electrical appliances, furniture, and textiles.2 The PCB and PBDE additives can leach out of the products, which has resulted in the widespread introduction of these compounds into the environment.1,3 Moreover, PCBs and PBDEs can bioaccumulate and can undergo biotransformation in wildlife and humans and pose a serious threat to biota.4,5 Due to the biotransformation of PCBs and PBDEs, the biogeochemical behavior of these organic compounds is often complicated and variable.1,6 To date, numerous reviews have described the biodegradation of PCBs by bacteria, either aerobically or anaerobically,7 and several studies have shown the biotransformation of PCBs in fish.8−10 The debromination of © 2013 American Chemical Society
Received: Revised: Accepted: Published: 4062
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carp samples and 4 composite northern snakehead samples were obtained. Sample Preparation. The sediment samples were freezedried, pulverized, and homogenized by sieving through a stainless steel sieve. Approximately 100 g of dry sediment was extracted using a Soxhlet extractor with 350 mL of acetone/hexane (1/1, V/V). An aliquot of the extract (one-tenth of the extract) was used to quantify the PCB and PBDE concentrations. The method used to purify the sediment extract for PCB and PBDE quantification has been previously described.26,27 The remainder of the extract was used for CSIA studies and was concentrated and purified with a multilayer silica gel column. The extract was further purified by an alumina/silica column. Finally, the extracts were purified using column chromatography with florisil as the stationary phase. Details of the column chromatography and elution are given in the Supporting Information (SI). The purified extracts were concentrated to 0.5 mL for GC-C-IRMS analysis. In the present study, only the fish carcasses were analyzed, and the heads and internal organs were removed to avoid PCBs and PBDEs from undigested food and particles in the gills. The dry weights of the samples used for analysis were between 100 and 122 g for each mud carp sample and between 66 and 74 g for each northern snakehead sample. The fish carcasses were extracted using a Soxhlet extractor with 350 mL acetone/hexane (1/1, V/ V) for 24 h. An aliquot of extract (one-tenth of the extract) was used to determine the lipid content and the concentration of PCBs and PBDEs. A detailed description of the method used to purify the extract for PCB and PBDE quantification in fish was previously published.25 The remaining extract was used for CSIA after being concentrated. The solvent was also exchanged to hexane before being treated with concentrated sulfuric acid. Then, the extract was purified on a complex silica gel column followed by an alumina/silica column. Detailed information on the purification of PCBs and PBDEs in fish for CSIA was reported previously.24,28 No significant isotopic fraction of the target compounds was found during the purification processes.28 The extracts used for GC-C-IRMS for each fish species were further pooled into two composite samples to be concentrated enough for isotopic analysis. PCB and PBDE Quantification. The PCBs were quantified on an Agilent 6890 GC coupled with a 5975 mass selective detector using an electron impact (EI) ion source. A DB-5 MS column (60 m × 0.25 mm i.d. × 0.25 μm film thickness) was used for PCB separation. A total of 209 PCB congeners were detected. PBDEs were analyzed on an Agilent 6890 GC-5975 MS using electron capture negative ionization (ECNI) in selected ion monitoring mode (SIM). Tri- to hepta-BDE congeners were separated by a DB-XLB (30 m × 0.25 mm i.d. × 0.25 μm film thickness) and octa- to deca-BDE congeners were separated by a DB-5 HT (15 m × 0.25 mm i.d. × 0.10 μm film thickness) capillary column. Details of the GC conditions and the ions monitored for PCB and PBDE analysis were previously published.25 Quantification was based on internal calibration curves made from standard solutions at six concentrations. GC-C-IRMS Analysis. The extracts used for CSIA were first checked the purification by an Agilent 6890 GC-5975 MS system with electron impact (EI) ion source in full scan mode. A secondary Aroclors mixture 1242/1248/1254/1260 (1:1:1:1) standard and Penta-BDE mixtures (DE-71) were used as standards for the qualitative analysis of PCBs and PBDEs. The individual congeners of PCBs and PBDEs were identified by
suggested that the observed differences can be attributed to metabolic congeners.7,16,17 In this study, compound-specific isotope analysis (CSIA) using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) was used to expand our current understanding on the biotransformation processes of PCBs and PBDEs in wild life. CSIA is based on the determination of the isotopic composition of carbon, hydrogen, and nitrogen, among other elements in the compounds. Typically, this isotopic composition is reported in the delta (δ) notation, δ13C(‰) = (R sample/R standard − 1) × 1000 (in units of ‰)
where Rsample and Rstandard are the 13C/12C ratios of the sample and reference standard for the carbon isotopic analysis. The heavier molecules have higher binding energies and lower mobility.18 Thus, the heavier isotopes react more slowly than the light isotopes in most chemical and biological reactions. These effects are called isotopic fractionation, which may be expressed during production and postproduction. Consequently, the δ13C values can be used to infer contaminant sources and specific biotransformation processes. CSIA has developed into a mature analytical method for many applications, particularly for stable carbon isotope analysis.19 However, isotope studies of PCBs and PBDEs are limited. Most studies that have performed CSIA on PCBs and PBDEs have focused on reporting the δ13C values of PCB and PBDE congeners in commercial mixtures.20−22 Drenzek et al.23 observed an absence of stable carbon isotopic fractionation during the reductive dechlorination of PCBs in the laboratory. In a field study, Yanik et al.24 found that the PCBs extracted from biota in the Housatonic River were rich in 13C relative to the PCB source. To the best of our knowledge, no study that tracks the biotransformation of PBDE in environmental biota using CSIA has been reported, and little is known about the isotope composition of PCB congeners during trophic transfer of PCBs in the food web. In the present study, sediment and two fish species forming a predator/prey relationship, were collected from a natural pond contaminated by e-waste. Our specific objectives were to determine the δ13C values of PCBs and PBDEs in different media by CSIA, to monitor the possible biotransformation of PCBs and PBDEs in a natural system using isotope data and concentration information, and to eventually provide information regarding the fate of these compounds in the natural environment.
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MATERIALS AND METHODS Sampling. A total of 23 aquatic biota samples were collected, including 15 northern snakeheads (Ophicephalus argus), 24 ± 1 cm in length and 130 ± 10 g in wet weight, and 8 mud carp (Cirrhinus molitorella), 31 ± 1 cm in length and 390 ± 30 g in wet weight, along with three composite sediment samples from a pond located in Longtang, Qingyuan County, Guangdong Province, South China, in 2010. This pond had been seriously impacted by discarded e-waste from the surrounding e-waste recycling workshops. A variety of organisms collected from this pond were shown to have elevated levels of PCBs and PBDEs.25 Detailed information regarding this pond can be found in previous publications.25 Two mud carp were pooled into one composite sample, and three to four northern snakeheads were pooled into one composite sample. Overall, 4 composite mud 4063
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comparing the mass spectrum and the retention time of the target compounds with the standards. CSIA studies were performed on an Agilent 6890 gas chromatography coupled to a GV Isoprime isotope ratio mass spectrometer (GV Instruments, U.K.) via a modified GC combustion interface. Samples were injected at 290 °C in splitless mode (split opened after 1 min). PCBs were separated on a DB-5 MS column (60 m × 0.25 mm i.d. × 0.25 μm film thickness). The following oven temperature program was used: the initial oven temperature was 120 °C with a ramp to 180 °C at 6 °C/min, another ramp to 240 °C at 1 °C/min, and finally a ramp to 290 °C at 6 °C/min (held for 17 min). Helium was used as the carrier gas at 1.1 mL/min for PCB separation. PBDEs were separated on a DB-5 MS column (30 m × 0.25 mm i.d. × 0.25 μm film thickness). The following oven temperature program was used: 110 °C (held for 1 min), followed by increases to 200 °C at 8 °C/min (held for 1 min), 240 °C at 3 °C/min (held for 2 min), 280 °C at 5 °C/min (held for 10 min), and finally 310 °C at 10 °C/min (held for 10 min). Helium was used as the carrier gas at 1.3 mL/min for PBDE separation. The combustion interface was maintained at a temperature of 940 °C. For calculation purposes, a CO2 reference gas was automatically introduced into the isotopic ratio mass spectrometer in a series of pulses at the beginning and the end of each run. The stable carbon isotope data are reported in the delta (δ) notation, and all values reported are relative to the international standard, V-PDB (Vienna Pee Dee Belemnite). The reliability of IRMS was verified by injecting a standard mixture containing 10 n-alkanes with a known isotopic composition (provided by Indiana University, Bloomington, U.S.) at the beginning of the analysis and a coinjected standard, 2,4,6-trichlorobiphenyl (PCB30), obtained from Ultra Scientific, North Kingstown, RI. The δ13C of the coinjected standard was off-line determined by EA-IRMS (Flash 2000 EA-DELTA V PLUS IRMS, Thermo-Fisher). The differences between the values (−29.17−29.03‰) of online measured for the coinjected standard in each sample and the values of off-line measured (−28.80‰) were less than 0.5‰. In addition, the stability of the system was tested daily, and the performance of the GC-C-IRMS system was determined regularly by analyzing Penta-BDE standards and PCB standard mixtures. Each extract was analyzed in triplicate, and the data were only considered if the δ13C values of the three injections did not vary by more than 0.5‰.
Figure 1. Relative homologue proportions of PCBs in sediments, mud carp, and northern snakehead samples from a natural pond in an e-waste site, South China. Error bars represent the standard deviations of replicates (n = 3 pool samples for sediment; n = 4 pool samples for fish species).
(BMFs > 2) were found mainly among the penta-PCB congeners (n = 12) and hex-PCB congeners (n = 14). The bioaccumulation potential observed is in line with the prediction that congeners with log KOW values of 6−7 (penta-hepta CBs) have the highest bioaccumulation potential.29 Our results demonstrate that the PCB homologue pattern may be linked to the trophic level of the species studied. PCB Carbon Isotope Data. Although more than 100 PCB congeners were detected in the samples, accurate δ13C values can only be obtained for a congener having a well-resolved peak and a high concentration. A subset of PCB congeners (30 congeners) were chosen for detailed isotopic analysis (Figure S3 of the SI). The δ13C values of the PCBs from the sediment ranged from −34.85 to −17.85‰, while the mud carp samples ranged from −32.79 to −18.64‰ and the northern snakehead samples ranged from −30.25 to −16.26‰ (Table S1 of the SI). The isotopic composition of the two pooled mud carp extracts was similar for most of the PCB congeners. This finding was also true for the two northern snakehead extracts and the two sediment extracts (Figure 2a−c). The high degree of reproducibility between similar samples with similar histories verifies the robustness of the technique and fosters confidence in the isotopic values derived from this approach. Sediments are thought to be a major source of pollutants for fish since e-wastes were dumped and deposited in the bottom of the pond in the studied pool. A comparison of the PCB δ13C values from the two fish species and the δ13C values from the sediment could provide insight into the PCB bioaccumulation and biotransformation in fish. Significant correlations in the isotopic data between the sediment and the mud carp (r = 0.93, p < 0.0001) and between the mud carp and the northern snakehead (r = 0.78, P < 0.0001) were observed (Figure 3). The isotopic data of the northern snakehead were also significantly correlated (p = 0.002) with those of the sediment, but the correlation coefficient (r = 0.58) was lower than the previous comparisons. The good relationships in PCB isotopic data between the sediment and the two fish species imply that the origins of PCBs in these samples are identical. It might also indicate the same partition behavior, in addition to common sources. Generally, mud carp feed on organic detritus or decomposed organic matter and like to disturb bottom sediments during feeding. Incidental ingestion of sediment particles could contribute to the PCBs in their body. Northern snakehead is a voracious predatory species25 that feeds on mud carp. The significant correlation in the isotopic data between the
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RESULTS AND DISCUSSION PCB Concentrations and Homologue Patterns. A total of 119 PCB congeners were detectable in both the sediment and the fish samples. The PCB concentrations (sum of 119 PCB congeners) in the sediment ranged from 14 000 to 19 000 ng/g dry weight. The total PCB concentrations varied from 290 000 to 340 000 ng/g lipid in the mud carp and from 420 000 to 760 000 ng/g lipid in the northern snakehead. These concentrations were in the same range as previously reported for similar samples collected from the same pond.25 Compared with the sediment samples, the abundance of penta- to hepta-substituted homologues in the two fish species increased while the di- to tetra-substituted homologues decreased (Figure 1, Figure S1 of the SI). The calculated biomagnification factors (BMFs) (mean of PCB congeners in northern snakehead divided by mean in the mud carp) were less than 1 for all di- and tri- PCB congeners with the exception of PCB37 but were larger than 1 for most of the penta- to octa- PCB congeners (Figure S2 of the SI). Furthermore, the high BMFs 4064
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Figure 2. Comparison between the isotopic values (δ13C) of the determined individual PCB congeners in the sediment (a), the mud carp (b), and the northern snakehead (c) extracts. Δδ13C was expressed as the isotopic differences of PCB congeners in fish relative to the sediment samples (d).
Figure 3. Correlations of δ13C of PCB congeners among the sediment and the two fish species.
Most PCB congeners from the fish samples were isotopically enriched relative to the sediment PCBs when there was isotopic deviation between the fish and the sediment samples (Figure 2d). These results are in agreement with observations of fish and duck samples collected from the Housatonic River, Massachusetts.24 In that study, most of the PCBs extracted from the grass carp and duck samples were isotopically enriched compared to the source material. Enrichment in the fish samples indicates that some isotopic fractionation occurred during the bioaccumulation
northern snakehead and mud carp confirmed the predator−prey relationship between these two fish species. Three PCB congeners, including PCB8, 110, and 105 in the two fish species, show isotopic agreement with the PCBs in the sediment samples (the isotopic differences between the fish and the sediment is less than 1‰) (Figure 2d). This result indicates that these congeners are more resistant than others. Thus, these congeners have great potential as markers in future source appointment studies if they are conserved in other species. 4065
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processes. The metabolism of PCBs could cause fractionation. Previous studies have demonstrated that PCB congeners with vicinal hydrogen atoms at meta−para position can readily be metabolized in fish.8 The PCB congeners which show a significant enrichment in δ13C compared to sediment (Δδ13C > 1‰, PCB17, 18, 31, 33/20, 22, 44, 42, 64, 101, and 136, Figure 2d) all have vicinal hydrogen atoms at the meta−para position or ortho−meta position in molecular structure. PCB153 without vicinal hydrogen but it coelute with PCB132 which have meta− para vicinal hydrogen. In fact, in a previous study, 16 methylsulfonyl-PCB congeners were detected in mud carp and northern snakehead collected from the same pond and the methylsulfonyl all insert at a meta−para vicinal hydrogen location.30 Therefore, the observed enrichment in δ13C for PCB congeners in the present study could be attributed to the degradation in fish. During the metabolism of PCBs, an isotopically depleted molecule would be preferentially biotransformed due to lower bonding energy,18 resulting in an isotopic enrichment in the remaining PCB reservoir. The δ13C values of PCB49, 48/47/75, 87/115/81, and 138 were isotopically depleted compared to the sediment (Figure 2d). This depletion implies that dechlorination from highly chlorinated congeners might make larger contributions to these congeners. The δ13C values of congeners in PCB technical mixtures generally decrease with increasing chlorine content. Therefore, reductive dechlorination will create congeners with more negative δ13C values than native PCB congeners with the same degree of chlorination, which will result in a lower δ13C for the original PCB congener pool. To date, both aerobic and anaerobic bacteria have been found with the ability to dechlorinate PCBs. Three major pathways of reductive dechlorination were demonstrated in the previous study.31 These are as follows: (2,3,4) remove meta-position (3) to form (2,4), (2,4,5) remove para-position (4) to form (2,5) and (3,4) remove para-position (4) to form (3). According to these pathways, PCB91 and PCB138 can be dechlorinated production of PCB132 and PCB170, respectively. However, it should bear in mind that the dechlorination pathways mentioned above were mainly induced from microbiological degradation. The reductive dechlorination in fish has not been established. Therefore, further studies are needed to clarify whether the depletion observed in these congeners was caused by dechlorination process in the fish. Furthermore, as shown in Figure 2d, when there was isotopic deviation between the sediment and fish samples, the PCBs from the northern snakehead were isotopically covaried with those from the mud carp, with the exception of congener PCB52 and PCB99. Similar isotopic fractionation for PCB congeners in mud carp and northern snakehead indicates that the metabolic pathways of PCB congeners are the same in the two fish species, but it occurs to a different extent. This speculation was confirmed by evidence that the congener profile of methylsulfonyl-PCBs in the mud carp was similar to that in northern snakehead but the ratio of metnysulfonyl-PCBs to PCBs (0.63 × 10−3) in the mud carp was lower than that in the northern snakehead (1.28 × 10−3).30 PBDE Concentrations and Congener Profiles. A total of 30 PBDE congeners were detected in the three sediment samples at concentrations ranging from 3000 ng/g to 3700 ng/g dry weight. BDE209, 183, 99, and 47 were the main congeners found in the sediment, accounting for 64.9%, 6.8%, 3.5%, and 3.1%, respectively, of the total PBDEs (Figure 4). All PBDE congeners found in the sediments were also detected in the mud carp and
Figure 4. Relative contributions of the PBDE congeners in sediment, mud carp, and northern snakehead from a natural pond in an e-waste site, South China. Error bars represent the standard deviations of replicates (n = 3 pool samples for sediment; n = 4 pool samples for fish species).
the northern snakehead. The total PBDE concentrations in the mud carp and the northern snakehead were between 32 000 and 39 000 ng/g lipid and between 53 000 and 92 000 ng/g lipid, respectively. The congener profiles in the mud carp and the northern snakehead have major contributions from lower brominated PBDE congeners, such as BDE28, 49, 47, 100, 154, and 153, which were different from that in the sediment. These results can be attributed to the combined effects of lower bioavailability and debromination of highly brominated congeners.32,33 There were some differences in PBDE profiles between the two fish species. For the mud carp, BDE47 (45.5%) was the most abundant congener, followed by BDE153 (15.3%), BDE49 (9.8%), BDE154 (7.8%), BDE100 (7.7%), and BDE28 (4.9%) (Figure 4). Common carp can debrominate BDE99 to BDE47 and 49 as well as BDE183 to BDE154.34 A similar debromination pathway could also exist in mud carp, which could contribute to the increased abundance of BDE47, 49, and 154 compared to the sediment. BDE28, 47, 100, and 154 were found to be resistant to metabolism in fish, which increases their potential to bioaccumulate in fish.34 High abundance of BDE153 has been previously reported in terrestrial bird species.35 The high abundance of this congener in mud carp could be related to its low elimination rate in organism.36 Compared to mud carp, the northern snakehead has a relatively higher BDE47 abundance (60.4%) but lower BDE153 (2.1%) and BDE49 (3.7%) abundances. There are two possible explanations for these differences. First, the prey of northern snakehead includes a wide range of fish species. The prey that contain a high abundance of BDE47 but a low abundance of BDE153 could contribute to the observed PBDE congener profile in the northern snakehead.25 Second, the metabolic transformation of PBDEs in northern snakehead could alter the PBDE profile. BDE153 was found to be metabolized to BDE101 and/or BDE47 in fish.34 Thus, if this metabolic pathway exists in northern snakehead, an increased abundance of BDE47 and a decreased abundance of BDE153 will result. The metabolism of PBDE in northern snakehead is currently unknown. The calculated BMFs of PBDEs ranged between 0.3 and 4.5 (Figure S4 of the SI). PBDE congeners such as BDE28, 47, 100, 154, and 155, are thought to be resistant to metabolism in fish and had BMFs larger than 1, suggesting biomagnification of these congeners. BMFs of several PBDE congeners, including BDE153 4066
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Table 1. Isotopic Ratio Values of PBDE Congeners in Sediment, Mud Carp, and Northern Snakehead Extracts sediment 1 BDE49 BDE47 BDE100 BDE99
−23.76 ± 0.09 −28.08 ± 0.32 −28.69 ± 0.27
sediment 2 −24.05 ± 0.68 −27.00 ± 0.11 −31.24 ± 0.14
mud carp 1
mud carp 2
northern snakehead 1
northern snakehead 2
−26.80 ± 0.01 −26.75 ± 0.23 −27.60 ± 0.28
−27.27 ± 0.13 −26.44 ± 0.42 −27.62 ± 0.03
−25.25 ± 0.08 −26.84 ± 0.47 −27.16 ± 0.11
−24.49 ± 0.47 −26.65 ± 0.08 −27.77 ± 0.52
biogeochemical processes occur from environmental matrixes to fish. From mud carp, which has a low trophic level, to northern snakehead, which has a high trophic level, the isotopic fractionation of PCB congeners was enlarged, suggesting similar metabolic pathways of PCBs in the studied prey/predator relationship. This isotopic fractionation during trophic transfer was not well recorded for PBDE congeners. The species−specific metabolism of PBDE in fish adds to the difficulty of tracking the trophic transfer of PBDEs using stable carbon isotope analysis, especially when a predator has various prey species. However, CSIA is an innovative approach to identify intrinsic biotransformation of PCBs and PBDEs and to characterize the sources of these pollutants in the environment.
and BDE183 were less than 1. This is probably due to their metabolism in fish.34 It appears that the metabolic debromination pathway influences the PBDE biomagnification pattern to a large extent in the fish food web. PBDE Carbon Isotope Data. The chromatography profiles of the extracts used for CSIA in GC/EI-MS in full scan mode are shown in Figure S5 (SI). The stable carbon isotope composition could only be determined for congeners BDE47, 100, and 99 in the sediment samples and for BDE49, 47, and 100 in the fish samples (Table 1). The δ13C values of BDE47, 100, and 99 in the sediments were −23.91‰ ± 0.21‰, −27.54‰ ± 0.76‰, and −29.97 ± 1.80‰, respectively. BDE100 and BDE99 were more depleted in 13 C than BDE47, which is in good agreement with reports on the stable carbon isotope composition of PBDE technical mixtures.22 Compared to the sediments, the δ13C values of BDE47 in the mud carp (−26.59‰ ± 0.21‰) were significantly lower. BDE99 can debrominate to BDE47 in cyprinidae. BDE47 originated from the debromination of BDE99 would has the same as or lower δ13C value than that of BDE99 due to specific isotope ratios of individual congeners and the isotopic fractionation effects during the debromination process. Consequently, the pool of BDE47 in the fish shows a decrease in the δ13C value compared to its origination. A decrease in the δ13C value of BDE47 in several fish species (common carp, tiger barb, and oscar fish) occurs because of the debromination of highly brominated congeners, which was observed in our laboratory exposure experiments.37 The decrease in the δ13C of BDE47 provides evidence for the metabolic debromination of PBDE in the cyprinidae fish species. The δ13C values of BDE47 in northern snakehead were similar to those in mud carp, which was an unexpected finding. However, this result does not rule out the possibility that BDE153 debrominate to BDE47 in northern snakehead. Although debromination of BDE153 to BDE47 would result in δ13C depletion in pool BDE47, other prey species that have high BDE47 δ13C values could also offset this depletion. The δ13C values of BDE49 in northern snakehead are isotopically enriched relative to mud carp. Metabolism of BDE49 in northern snakehead, such as hydroxylation, and/or a contribution from other prey species could explain this enrichment. No significant differences in the δ13C values of BDE100 were observed in the sediment, the mud carp, and the northern snakehead. In our previous laboratory experiments, the δ13C values of BDE100 were also found to be constant in food and different fish species.37 BDE100 has no meta-bromine in its molecular structure. It was reported that this structure cannot undergo metabolic debromination in fish.34 Therefore, the δ13C value of BDE100 can be used for source apportionment of PBDEs in future studies. In conclusion, the results from this study indicate that stable carbon isotopes of PCBs and PBDEs can provide insight into biochemical processes and allow us to study the fate of these pollutants at the trophic level. The changes in the δ13C values of most PCB congeners imply that biotransformation or other
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ASSOCIATED CONTENT
* Supporting Information S
A detailed description of the sample preparation and additional figures and tables. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +86-20-85290146; fax: +86-20-85290706; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This study was supported financially by the National Basic Research Program of China (No. 2009CB4216604), the National Nature Science Foundation of China (Nos. 20890112, 40873074, 41230639, 81273118), and the Chinese Academy of Sciences (No. KZCX2-EW-QN 105). This is contribution No. IS-1667 from GIGCAS.
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dx.doi.org/10.1021/es304558y | Environ. Sci. Technol. 2013, 47, 4062−4068
