Environ. Sci. Technol. 2008, 42, 3634–3639
Enantioselective Bioaccumulation of Hexabromocyclododecane and Congener-Specific Accumulation of Brominated Diphenyl Ethers in an Eastern Canadian Arctic Marine Food Web G R E G G T . T O M Y , * ,†,‡ K E R R I P L E S K A C H , † T Y L E R O S W A L D , †,| T H O R H A L L D O R S O N , †,⊥ P A U L A . H E L M , †,# GORDIA MACINNIS,§ AND CHRIS H. MARVIN§ Department of Fisheries and Oceans, Arctic Aquatic Research Division, Winnipeg, MB R3T 2N6 Canada, Departments of Chemistry, and Environment and Geography, University of Manitoba, Winnipeg, MB, R3T 2N6 Canada, and Aquatic Ecosystem Management Research Branch, Environment Canada, Burlington, ON L7R 4A6 Canada
Received December 9, 2007. Revised manuscript received February 23, 2008. Accepted February 25, 2008.
The extent of trophic transfer of the three diastereoisomers of hexabromocyclododecane (HBCD) and seven brominated diphenyl ether (BDE) congeners was examined in components of an Arctic marine food web from eastern Canada. R and γ-HBCD diastereoisomers were detected in all species and total (Σ) HBCD concentrations ranged from 0.6 ( 0.2 pg/g (geometric mean ( 1 × standard error (SE), lipid weight (lw)) in arctic cod to 3.9 ( 0.9 ng/g (lw) in narwhal. β-HBCD was below method detection limits in all the samples. Mean ΣBDE (sum of seven congeners) concentrations ranged from 0.4 ( 0.2 ng/g (lw) in walrus to 73 ( 10 ng/g (lw) in zooplankton. The relative trophic status of biota was determined by nitrogen stable isotopes (δ15N), and results indicated clear differences in HBCD isomer and BDE congener profiles with trophic level (TL). Trophic magnification was observed for the R-diastereoisomer and BDE-47 as concentrations increased with increasing TL in the food web, whereas there was trophic dilution of γ-HBCD and BDE-209 through the food web. Only the (-)R-enantiomer showed a strong positive relationship between concentration and TL (p < 0.01) with a trophic magnification factor (TMF) value of 2.2. A small but significant increase in the enantiomeric fraction value of the R-enantiomers with TL was also observed (r2 ) 0.22, p < 0.005), implying that there is an overall
preferential enrichment of the (-)R-enantiomer relative to the (+)R-enantiomer likely due to the greater bioaccumulation potential of the (-)R-enantiomer and/or to the greater susceptibility of the (+)R-enantiomer to metabolism.
Introduction Persistent organic pollutants (POPs) such as chlorinated biphenyls and brominated diphenyl ethers (BDEs) which have sufficiently long atmospheric half-lives and can travel long distance in relatively short periods of time, are transported by atmospheric and oceanic mechanisms to remote regions like the Arctic. Cold annual temperatures, large areas of ice cover, and reduced sunlight are some of the conditions that make the Arctic an ideal environment for POPs to accumulate. In Arctic biota, fat (or lipid) is considered the energy “currency” and lipid-rich animals tend to thrive more so than lipid-poor ones. However, it is within the lipids of these animals where hydrophobic POPs tend to accumulate. As such, indigenous people in the Arctic that subscribe to a traditional diet rich in nutritionally beneficial fat, are in turn exposed to elevated levels of these compounds. Together, these factors make the Arctic a good sentinel-environment for examining occurrence, fate, and exposure in assessing the significance of chemical compounds of concern. Few studies have examined the trophodynamics of brominated flame retardants (BFRs) in the Arctic. Wolkers et al. reported on the congener-specific accumulation of BDEs in two Norwegian Arctic food chains; the first food chain consisted of polar cod-ringed seal-polar bear and the other of polar cod-beluga whale (1). In another study, Sømro et al. investigated the biomagnification of BDEs and hexabromocyclododecane (HBCD) in a Norwegian Arctic marine food chain consisting of four invertebrates, polar cod, ringed seals, and polar bears (2). More recently, Morris et al. assessed the distribution of BDEs and HBCD in a Canadian Arctic food chain consisting of water, zooplankton, phytoplankton, arctic cod, and ringed seals from Barrow Strait (Nunavut) (3). None of these studies used stable isotope of nitrogen (δ15N) to assess the relative trophic status of biota samples. Our earlier work reported on the occurrence and behavior of a suite of polyfluorinated alkyl acids in a similar food web (4). In this study, we hypothesized that BFRs including HBCD and BDEs bioaccumulate in the Arctic food web and that trophic transfer might be enantioselective for HBCD. Our objective then was to build on our earlier work and specifically to assess the occurrence and extent of trophic transfer of the isomers of HBCD and BDEs in biota which were representative of an eastern Canadian Arctic marine food web and whose trophic position was determined by δ15N. Particular emphasis was placed on understanding the behavior of the enantiomers of HBCD in the food web.
Experimental Section * Corresponding author phone: 204-983-5167; fax: 204-984-2403; e-mail:
[email protected]. † Arctic Aquatic Research Division. ‡ Departments of Chemistry, and Environment and Geography, University of Manitoba. § Environment Canada. | Current Address: Department of Medicine, University of Manitoba, Winnipeg, MB R3T 2N2 Canada. ⊥ Current Address: Health Products and Food Branch, Health Canada, Winnipeg, MB, R2J 3Y1 Canada. # Current Address: Ontario Ministry of the Environment, Environmental Monitoring and Reporting Branch, Toronto, ON, M9P 3V6 Canada. 3634
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Standards and Reagents. Native and mass labeled (13C12 and d18) R-, β-, γ- HBCD (99.8% purity), and chlorinated diphenyl ether (CDE) congeners 2,2′,4-triCDE (CDE-17), 2,2′,4,4′,5pentaCDE (CDE-99), 2,2′,3,3′,4,4′,5-heptaCDE (CDE-170) (each >96%) and a fish tissue standard reference material (SRM, WMF-01) were obtained from Wellington Laboratories (Guelph, ON). The BDE analytical standard consisted of a 36 congener mix including BDE-209, both obtained from Cambridge Isotope Laboratories (Andover, MA). The beluga SRM (1945) was obtained from the National Institute for Science and Technology (NIST, Gaithersburg, MD). Distilled 10.1021/es703083z CCC: $40.75
2008 American Chemical Society
Published on Web 04/18/2008
in glass methanol, isooctane, 2-propanol, dichloromethane (DCM), hexane, and acetone were obtained from Caledon (Edmonton, AB). Optima grade water and methanol were obtained from Fisher Scientific (Nepean, ON). Study Area and Sample Details. BDEs and HBCD were analyzed in the blubber of the beluga whale (Delphinapterus leucas, n ) 5), narwhal (Monodon monoceros, n ) 5) and walrus (Odobenus rosmarus, n ) 5). Whole organism homogenates of Arctic cod (Boreogadus saida, n ) 8), shrimp (Pandalus borealis and Hymenodora glacialis, n ) 5), clams (Mya truncate and Serripes groenlandica, n ) 5), deepwater redfish (Sebastes mentella, n ) 5) and, mixed zooplankton (n ) 5) were analyzed. Sampling locations are noted on the map in the Supporting Information (SI) (Figure SI-1). Mammal tissues were collected from Frobisher Bay near Iqaluit (beluga; 1996), from Cape Dorset (walrus; 1998), and from Broughton Island (narwhal; 2000) and archived. The beluga (aged 3.5-10.5 years) and narwhal were all males, whereas walrus samples consisted of both sexes. Arctic cod (young of the year and 2 years of age), deepwater redfish (aged from 4 to 7 years), and shrimp were collected from Davis Strait in October of 2000 and 2001 by trawling from the Greenland Institute of Natural Resources research vessel, Paamiut. Clams (collected by diver) and zooplankton samples were collected from Frobisher Bay in May 2002. Zooplankton samples consisted of bulk sieved mixed species (predominantly copepods with fifth stage Calanus hyperboreus removed) collected using 350 and 500 µm mesh nets. Extraction and Clean-Up. Marine mammal blubber (approximately 1 g) was extracted using a ball mill shaker with 10 g anhydrous sodium sulfate (baked 6 h at 600 °C) and 25 mL of 1:1 hexane:dichloromethane (DCM). Each cell was spiked with recovery internal standards (RIS: 13C12-HBCD and CDE congeners), then shaken for 15 min, left to stand 2-4 h before centrifuging, then decanted to a round-bottom flask. The extraction was repeated twice, combining the decanted extracts. The remaining biota samples were extracted as described elsewhere (5). Briefly, fish, shrimp, and clam tissues were homogenized with dry ice in a laboratory blender, then stored overnight in a –20 °C freezer to allow for sublimation of the CO2. Thawed tissue was weighed and mixed with pelleted diatomaceous earth (Hydromatrix; Varian Canada, Mississauga, ON; baked 6 h at 600 °C) then added to a 100 mL cell along with the RISs and extracted using an accelerated solvent extractor (ASE 300, Dionex Canada Ltd., Oakville, ON). Zooplankton samples were weighed frozen and homogenized by directly mixing with Hydromatrix prior to ASE extraction. Void space was filled with Ottawa sand (Fischer Scientific, Ottawa, ON; baked 6 h at 600 °C). After extraction, anhydrous sodium sulfate was added to the collection bottles to remove water, then samples were transferred to round-bottom flasks for volume reduction. Extracts were reduced in volume and filtered using 1 µm PTFE syringe filters (Fisher Scientific Company, Ottawa, ON). Lipid content was determined gravimetrically in an aliquot of extract, while lipid was removed from the remainder of the extract by gel permeation chromatography. After volume reduction, samples were further cleaned using Florisil according to Law et al. (5). Fraction 1 (F1; BDEs) and fraction 2 (F2; HBCD) were both reduced in volume to 200 uL and instrument performance internal standards (10 µL of 2 ng/ uL aldrin to F1; 5 µL of 1 ng/µL d18 R- and γ-HBCD to F2) were added. Instrumental Analysis. BDEs were analyzed by gas chromatography electron capture negative ion mass spectrometry (GC-ECNIMS) on an Agilent 5973 GC-MSD fitted with a 10 m × 0.25 mm i.d. DB-5 capillary column (0.25 µm film thickness, J&W Scientific, CA) using instrument conditions as described previously (5). BDEs were detected in selected ion monitoring (SIM) mode using the [Br]- ions
(m/z 79, 81) and an external standard solution containing the BDE-mix (36 BDE congeners) and BDE-209 for quantification. Of the 36 BDEs analyzed, seven (47, -85, -99, -100, -153, -154 and -209) were consistently detected in our samples. Our data analysis was restricted, therefore, to these congeners. Details of the diastereoisomer and enantiomer analysis of HBCD are found in Tomy et al. and Marvin et al., respectively (6, 7). In brief, diastereoisomer separations were achieved using high performance liquid chromatography (HPLC) on a Genesis C18 analytical column (10.0 cm × 2.1 mm i.d., 4 µm particle size; Jones Chromatography, Chromatographic Specialties Inc.) with a methanol:water (70:30%) mobile phase at a flow rate of 300 µL/min. MS analysis was done on a Sciex API 4000 triple quadrupole. Quantification was achieved by monitoring the specific m/z 640.6 [M-H]-f m/z 79 (Br-) ion transition. MS/MS detection of d18-HBCD and 13C12-HBCD isomers was based on the analogous ([MH]-) f Br- reaction monitored for the native HBCD (m/z d18: 657.6 and 13C12: 652.4 ([M-H]-)). Enantiomer separations were achieved on a NUCLEODEX β-PM chiral LC column (4.0 cm × 200 mm, 5 µm particle size) containing permethylated β-cyclodextrin on silica (Macherey-Nagel, Duren, Germany). MS analysis was done on a Sciex API 4000 triple quadrupole instrument. Quality Assurance/Quality Control. Procedural blanks were run with every batch of 10 samples for both HPLC and GC. Eight procedural blanks were ball milled and contained DCM:hexane and sodium sulfate (baked for 6 h at 600 °C), four were intentionally fortified with the RIS standard. The other four blanks were not fortified. There were eight procedural blanks for the other species that were ASE that contained Ottawa sand and Hydromatrix (both baked for 6 h at 600 °C), four were fortified with RIS standard and four were unfortified. These were extracted using the same methods as the samples. Instrument blanks for HPLC and GC were injections of optima-grade methanol (after every six samples) and isooctane (after every 10 samples), respectively. These blanks were used to monitor contamination between each injection. The seven routinely detected BDE congeners were also measured in the procedural blanks, at amounts typically much smaller than observed in samples, with the following mean ((1 × standard error (SE) amounts: 97 ( 26 pg (BDE-47), 12 ( 3 pg (BDE-100), 50 ( 14 pg (BDE-99), not detected (BDE-85), 19 ( 9 pg (BDE-154), 8 ( 5 pg (BDE-153), and 61 ( 56 pg (BDE-209). All samples were blank corrected for BDEs. All HBCD isomers were redfish ≈ clams > shrimp > beluga > zooplankton > walrus > arctic cod. Sørmo et al. and Morris et al. were unable to detect HBCD in four different invertebrate species from the Norwegian Arctic and in zooplankton from Barrow Strait (Canada), respectively (2, 3). In polar cod from Svalbard, mean HBCD concentrations were 1.9 ng/g (lw) (1) while Morris et al. were unable to detect HBCD in arctic cod from Barrow Strait (3), similar to our results. Σ2HBCD concentrations in beluga in our study ranged from 0.71 to 2.15 ng/g (lw). Using a GC-based method, Muir et al. reported significantly greater ΣHBCD concentrations in male beluga from eastern Hudson Bay and Hudson Straight, 12 ( 5.0 (n ) 3) and 17 ( 14 (n ) 7) ng/g (lw), respectively (12). Differences in sampling locations, age of the animals, exposure, and the analytical approach taken in the latter study may partly explain this discrepancy. The HBCD diastereoisomer profile in the animals is shown in Figure 1 (top panel). No clear discerning trend in the diastereoisomer profile was observed in the animals; however, the R-diastereoisomer contributes greater than 70% of the total burden in shrimp, redfish, arctic cod, narwhal, and beluga, whereas zooplankton, clams, and walrus contain >60% of the γ-diastereoisomer. The observed HBCD diastereoisomer signature can be explained in part by what is known about their environmental fate and behavior. For example, the γ-diastereoisomer is the least water soluble of the three isomers [R: 48 µg/L; β: 15 µg/L; γ: 2 µg/L (13)] thus passive diffusion from the water column into zooplankton, which may be considered floating-globules of lipid, is most likely to occur for the γ-HBCD relative to the other two isomers. Clams are benthic filter feeders and likely get their contaminant exposure from sediment; the γ-diastereoisomer is known to be the dominant isomer in sediment (14). Clams also 3636
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FIGURE 1. Profiles of HBCD diastereoisomers (top panel) and PBDE congeners (bottom panel) in biota from the eastern Arctic. HBCD was not detected in arctic cod. make up the bulk of the diet of walrus which are thought to have a low metabolic capability (15). The predominance of the R-diastereoisomer in upper TL organisms like beluga and narwhal is consistent with the enhanced metabolic capability of these animals. Zegers et al. have shown that the R-diastereoisomer dominated profile in higher TL organisms from Western Europe is due in part to a stereoisomer-specific biotransformation of the γ-diastereoisomer mediated by cytochrome P450 enzymes (11). Law et al. have shown that bioisomerization of isomers in a rainbow trout results in predominantly the R-diastereoisomer; the predominance of the R-diastereoisomer in redfish indicates that this species might have similar metabolic capabilities to trout (16). It remains unclear why shrimp show a HBCD diastereoisomer profile dominated by the R-isomer. Σ7BDE concentrations (lipid weight; lw) ranged from 72.9 ( 10.1 ng/g in zooplankton to 0.4 ( 0.2 ng/g in walrus. Concentrations of Σ7BDE were similar in the shrimp (16 ( 9 ng/g) and clam (21 ( 9 ng/g) samples. In top TL organisms, Σ7BDE concentrations in beluga (12 ( 2 ng/g) were ∼1.5 times smaller than in narwhal (18 ( 2 ng/g). For the pelagic fish, Σ7BDE concentrations in arctic cod (23 ( 13 ng/g) were ∼8 times greater than those in redfish (3 ( 1 ng/g). It is surprising that Σ7BDE concentrations in zooplankton from our study were greater than those of the other animals. However, Morris et al. also found a similar result in which Σ14BDE concentrations in zooplankton (18.6 ng/g, lw) were greater than those of higher TL organisms like amphipods (16.6 ng/g, lw) and ringed seal (4.9 ng/g, lw) from a Canadian Arctic marine food web (3). Conversely, Sørmo et al. found small concentrations (lw) of ΣBDE (range: 0.16–0.53 ng/g) in
invertebrates from Svalbard (2), and Wolkers et al. and Sørmo et al. measured similar BDE concentrations (lw) in polar cod (3.5 and 1.9 ng/g, respectively) from a similar geographic region (1, 2). The Σ14BDE concentrations (lw) measured in arctic cod by Morris et al. was 23 ( 13 ng/g (3), similar to our study. Taken together these results indicate that there may be broad geographical differences in BDE contamination at the base of Arctic marine food webs. Reasons for these differences are unclear and further work is warranted to try and resolve this disparity. Muir et al. found ΣBDE concentrations (lw) in male belugas from Hudson Straight (30 ( 9 ng/g, n ) 7) and east Hudson Bay (41 ( 4 ng/g, n ) 3) that were approximately 2.5-3 times greater than the concentrations of belugas found in our study (12 ( 2 ng/g), respectively (12). Significantly higher concentrations were measured in animals (male) from Norway (161 ( 23 ng/g) (1). Whereas BDE concentrations are greater in animals at the base of the food chain in the Canadian Arctic relative to Norway, it appears that in high TL animals like beluga, BDE concentrations are much greater in Scandinavian animals than animals from the Canadian Arctic. This latter spatial difference in BDE concentrations was also observed in polar bears (17). The relative percent contribution of the individual BDE congeners in the animals is presented in Figure 1 (bottom panel). BDE-209 was found to contribute significantly to the body burden of total BDEs in the lower TL organisms; 60% in redfish and 75% in arctic cod, for example. Morris et al. also found BDE-209 to be the dominant congener in arctic cod from Barrow Strait (3). The greater proportions of BDE209 in the redfish and arctic cod may reflect greater exposure to this compound through zooplankton and also suggest that these organisms may have limited metabolic capabilities in eliminating/metabolizing this congener. Conversely, in the upper TL organisms like beluga and narwhal, BDE-209 accounts for less than 2% of the total BDE burden, whereas the BDE-47 accounts for over 40% in these samples. These results are consistent with other studies that have shown that BDE-209 is not an abundant congener in high TL animals (2, 17, 18). This can be explained in part by greater assimilation efficiency of the lower brominated congener (19) and also potentially by the enhanced metabolic capability of high TL organisms to convert BDE-209 to lower Br-congeners, e.g., BDE-47 (20). The observations of greater ΣBDE concentrations in zooplankton and greater BDE-209 proportions in lower TL organisms seem somewhat anomalous, although very recent observations confirm our findings (3). Carlson and Swackhamer (21) observed differing accumulation trends of BDEs between lake trout in Lake Superior, a colder lake, than in the other Laurentian Great Lakes, resulting in a hypothesis that colder temperatures foster a more rapid establishment of equilibrium with phytoplankton due to much lower growth, and favoring greater proportions of the more brominated congeners. For example, they observed that ratios of BDE-99 to BDE-47 (99:47) were approximately 2:3 (0.67) in Lake Superior lake trout, but in lake trout from the other lakes, the 99:47 ratios were approximately 0.2. In this study, mean 99: 47 ratios were 1.7, 0.9, and 0.6 in zooplankton, shrimp, and clams; also indicating a relative enrichment of BDE-99. In fish, this ratio dropped to 0.1 (redfish) and 0.3 (arctic cod), and was 0.2 and 0.3 in the beluga and narwhal, respectively. Trophic Transfer. Figure 1 suggests that there are differences in the profiles of BDE congeners and HBCD isomers with TL. Furthermore, as there was no relationship between Σ7BDE and Σ2HBCD concentrations in animals from the food web, the pathways of exposure or bioaccumulation potentials of these compound classes may differ. To further explore the trophic magnification behavior of the BFRs throughout the entire food web log-normalized concentra-
tions of the individual compounds were plotted against TL as defined by δ15N. Based on the plots in Figure SI-3 and Table 1, concentrations of both the R-HBCD diastereoisomer and BDE-47 show significant positive relationships with TL (p < 0.01 in both cases) with respective TMFs of 2.1 (lowerupper 95% CI: 1.3–3.4) and 2.5 (lower-upper 95% CI: 1.6–3.7). Our earlier study on perfluoroalkyl acids in a similar food web found a TMF of 3.1 for PFOS (4). Interestingly, while the TL-log normalized concentration relationship of BDE-47 shows a significant positive slope, BDE-209 shows a statistically significant negative slope (r2 ) 0.25, p ) 0.002, TMF ) 0.3). Biotransformation of BDE-209 has been suggested and is becoming more accepted (19, 20, 22). Bhavsar et al. recently proposed a biotransformation pathway for BDE-209 in lake trout suggesting that BDE-183 and -190 are good chemical markers to indicate in vivo biotransformation of BDE-209 (23), although some contributions of BDE183 and -190 in wildlife could arise from abiotic degradation of BDE-209 to these congeners followed by accumulation in animals. The fact that BDE-183 and -190 were undetectable in higher TL animals like beluga and narwhal in our study (chromatogram not shown) does not rule out biotransformation of BDE-209 as a possible loss of this congener. More likely it suggests that the metabolic capability of these mammals is more enhanced than lake trout and perhaps biotransformation is occurring more rapidly. Nevertheless, trophic dilution of BDE-209 with increasing TL in the food web does lend support to metabolism of this isomer by animals higher up the food chain. However, the role of assimilation efficiencies of the congeners can not be ruled out. Similar to BDE-209, the γ-HBCD also shows a statistically significant negative relationship between concentrations and TL (r2 ) 0.10, p < 0.05, TMF ) 0.5, Table 1). This observation is consistent with our earlier discussion on the susceptibility of this isomer to metabolism by higher TL organisms (11, 16). Lipid-corrected and TL-adjusted BMFs of individual predator/prey feeding relationships are presented in Table SI3. Normalizing BMFs to TL allows for BMFTL comparisons among different food webs to be made. In general, the individual BMF values are greatest for all of these chemicals within the narwhal to arctic cod predator–prey interaction, with BDE-85 having the greatest BMFTL(b:w) value of 40. As mentioned in our earlier study on polyfluorinated compounds, there may be a bias for some of the BMF values as different tissues were analyzed for contamination (i.e., blubber in marine mammals versus muscle tissue in fish versus whole organism for invertebrates) (4). Like other contaminants, accumulation and biotransformation of BFRs is likely to be species-specific and related to the presence and activity of enzymes of the cytochrome P450 system. This may partly explain why BMFs are greater than 1 for some trophic interactions and not others. Differences in sampling year and location of samples collected may also affect the magnitude of BMF values; however, these differences could not be assessed in our study. Enantiomeric Fractions and Enantioselective Bioaccumulation of HBCD. Nonstereospecific synthesis of chiral compounds results in a racemic mixture which has an enantiomer fraction (EF), expressed relative to the first eluting enantiomer (i.e., EF ) amount first enantiomer/(sum of both enantiomers)), with a value equal to 0.5. The integrity racemic mixtures are preserved when it is subjected to achiral interactions such as hydrolysis, photolysis, volatization, and atmospheric deposition. Deviation from an EF of 0.5, however, is indicative of a stereospecific-enantiomeric shift from biologically mediated processes. As mentioned, EFs are expressed fractionally relative to the first eluting enantiomer. This is noteworthy as the (-)R, (-)β and (+)γ-enantiomers are the first eluting peak of each VOL. 42, NO. 10, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Trophic Magnification Factors (TMFs) (Lower-Upper 95% Confidence Intervals) and Regression Parameters for Seven BDE-Congeners and the Diastereoisomers and Enantiomers of HBCD Examined in the Present Studya
BDE-47 BDE-85 BDE-99 BDE-100 BDE-153 BDE-154 BDE-209 R-HBCD γ-HBCD (-)R-HBCD (+)R-HBCD (-)γ-HBCD (+)γ-HBCD a
r2
p-value
TMF
lower-upper 95% CI
0.3801 0.0254 0.0010 0.0400 0.0024 0.0072 0.2666 0.2265 0.1008 0.2820 0.0840 0.0990 0.1019
0.0002 0.3389 0.9534 0.2604 0.7642 0.6221 0.0010 0.0022 0.0459 0.0005 0.0740 0.0483 0.0447
2.5
1.6–3.7
ln [BDE-47] ) 0.9078 (TL) - 2.1764
0.3 2.1 0.5 2.2
0.1–0.6 1.3–3.4 0.3–0.9 1.5–3.4
ln ln ln ln
0.5 0.5
0.3–0.9 0.3–0.9
ln [(-)γ-HBCD] ) –0.5924 (TL) - 0.1543 ln [(+)γ-HBCD] ) –0.6088 (TL) – 0.0461
[BDE-209] ) –1.2109 (TL) + 4.8712 [R-HBCD] ) 0.7624 (TL) – 3.0690 [γ-HBCD] ) –0.6013 (TL) + 0.5981 [(-)R-HBCD] ) 0.8043 (TL) – 3.7513
TMFs and regression equation given only for statistically significant relationships.
FIGURE 2. Enantiomer fraction of the r- and γ-HBCD isomers in biota. Error bars are ( standard error. Dotted lines represent the measured EF in the racemic mixture. corresponding enantiomeric pair. Interestingly, work in our laboratory and by others has demonstrated that EFs of racemic standard solutions of HBCD can result in EF-values that deviate from 0.5 (7, 24). For example, the EF values for the R-, β-, and γ-HBCD enantiomers in an external standard solution was determined to be 0.48 ( 0.03, 0.51 ( 0.03, and 0.51 ( 0.02, respectively (7). Our previous work has indicated that mobile phase composition and column bleed are factors that can contribute to the variability of EF-values for HBCD (7). As such, careful consideration must be given to interpretation of EF values for HBCD. Figure 2 shows the EF values for the R- and γ-isomers in the animals examined (β-isomer was not detected in the samples). For the R-isomer, narwhal, beluga, and walrus, all have EF values that were statistically greater (p > 0.05, t-test) than for an external standard (n ) 8) suggesting that there is a selective enrichment of the (-)R-enantiomer relative to the (+)R-enantiomer in these animals. Although arctic cod, clams, and shrimp all have EF values that were smaller than 0.48, only in clams (EF ) 0.47 ( 0.03) was the EF-value statistical different from that of the external standard (p ) 0.006). Narwhal, walrus, clams, and shrimp all have EF-values greater than 0.51 for the γ-isomer, but they were not significantly different from standard values (p > 0.05). To examine whether trophic magnification of HBCD may be enantioselective, the log-normalized concentrations of the individual enantiomers were plotted against TL (see Figure SI-4 and Table 1). Only the (-)R-enantiomer showed a strong positive relationship between concentration and TL 3638
regression equation
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FIGURE 3. Plot of enantiomer fraction (EF) of r-HBCD versus trophic level within the eastern Arctic food web. (p < 0.005) with a TMF value of 2.2 (lower-upper 95% CI: 1.5–3.5). Based on this observation, we hypothesized that there might be an overall change in EF throughout the entire food web. A plot of EF-values versus TL does reveal a small but significant (p < 0.005) increase in the EF with TL and suggests there may be preferential enantioselective accumulation of the (-)R-enantiomer (Figure 3). It remains unclear whether this arises from a lower bioaccumulation potential of the (+)R-enantiomer relative to the (-)Renantiomer and/or to the greater susceptibility of the (+)Renantiomer to metabolism. In summary, the trophodynamics of BDEs and HBCD were examined in a food web from the eastern Canadian Arctic. Both the BDE-47 and the R-isomer of HBCD showed a strong increase in concentration with increasing trophic level. Conversely, the BDE-209 showed a decrease in concentration with trophic level suggesting metabolic depletion of this congener or reduced assimilation up the food web. Interestingly, both enantiomers of R-HBCD increased with trophic level but the magnitude of the increase was slightly greater for the (-)R-enantiomer. Further, the EF values for the R-isomer show an increase with trophic level and suggest an enantioselectivity in the bioprocessing of the enantiomers. To our knowledge, this is first report of enantioselectivity of HBCD in a food web.
Acknowledgments Funding for analysis was provided by the Northern Contaminants Program (NCP) of the Department of Indian and Northern Affairs, Canada. Mammal collections were funded
in part by the Nunavut Management Research Board. Thanks to Colin Fuchs, Tim Siferd, and Paul Wilkinson (Freshwater Institute) for sample collection in Frobisher Bay, to the hunters and local hunting and trappers associations for mammal collections, and to the scientists and crew aboard the Greenland Institute of Natural Resources research vessel, Paamiut, for sample collections in Davis Strait.
Supporting Information Available The following tables: Table SI1. Method Detection Limits (ng/g, lipid). Table SI2. Range of concentrations of some BFRs in the food web (ng/g, lipid weight) from the Eastern Arctic. δ15N and % lipid values ((standard error) are also presented. Arithmetic mean values are given in parentheses. Table SI3. Trophic level (TL) and lipid adjusted biomagnification factors (BMFTLs) for some BDEs congeners and Rand γ-HBCD and figures: Figure SI1. Map of the Eastern Arctic sampling sites. Figure SI2. Comparison of concentrations between certified BDE values in NIST beluga SRM (top panel) and Wellington fish SRM (bottom panel) and measurements made by DFO laboratory. Figure SI3. Mean ((standard error) concentrations of R-HBCD (top left), γ-HBCD (top right), BDE-209 (bottom left panel, ng/g) and BDE-47 (bottom right panel), and versus the trophic level relationship ((standard error) for the Eastern Arctic food web. Concentrations were lipid and control corrected. Regression analysis plotted on each panel. Clam purposely omitted from the plot for BDE-47. Figure SI4. Mean ((standard error) concentrations of (-)R-HBCD (top left panel), (+)R-HBCD (top right panel), (-)γ-HBCD (bottom left panel) and (+)γ-HBCD (bottom right panel, ng/g) versus the trophic level relationship ((standard error) for the Eastern Arctic food web. Concentrations were lipid and control corrected. Regression analysis is plotted for each panel. This material is available free of charge via the Internet at http://pubs. acs.org.
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