Environ. Sci. Technol. 2007, 41, 417-423
Fate of Higher Brominated PBDEs in Lactating Cows AMELIE KIERKEGAARD,* LILLEMOR ASPLUND, CYNTHIA A. DE WIT, AND MICHAEL S. MCLACHLAN Department of Applied Environmental Science, Stockholm University, SE-106 91 Stockholm, Sweden GARETH O. THOMAS, ANDREW J. SWEETMAN,† AND KEVIN C. JONES† Department of Environmental Science, and Centre for Chemicals Management, Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, U.K.
Dietary intake studies of lower brominated diphenyl ethers (BDEs) have shown that fish and animal products are important vectors of human exposure, but almost no data exist for higher brominated BDEs. Therefore, the fate of hepta- to decaBDEs was studied in lactating cows exposed to a naturally contaminated diet by analyzing feed, feces, and milk samples from a previous mass balance study of PCB. Tissue distribution was studied in one cow slaughtered after the experiment. BDE-209 was the dominant congener in feed, organs, adipose tissues, and feces, but not in milk. In contrast to PCBs and lower brominated BDEs, concentrations of hepta- to decaBDEs in adipose tissue were 9-80 times higher than in milk fat and the difference increased with degree of bromination/log Kow. The congener profiles in adipose tissue and feed differed; BDE-207, BDE-196, BDE-197, and BDE-182 accumulated to a surprisingly greater extent in the fat compared to their isomers, suggesting metabolic debromination of BDE-209 to these BDEs. The results indicate that meat rather than dairy product consumption may be an important human exposure route to higher brominated BDEs.
Introduction Polybrominated diphenyl ethers (PBDEs) belong to the family of additive brominated flame retardants used in a variety of polymer systems and in textiles. Of the three main commercial PBDE mixtures, Penta- and OctaBDE have been banned in Europe since 2004 and production has ceased in North America, but the production and use of DecaBDE continues. DecaBDE contains primarily the fully brominated BDE-209. Scientific reports on PBDEs in the environment have focused on lower brominated BDE congeners. Studies presenting results for BDE-209 are scarce, possibly reflecting the analytical difficulties (1). Due to its hydrophobicity and low vapor pressure, BDE209 absorbs to particles which can undergo long-range transport as seen in deposition samples from the central * Corresponding author phone: +4686747182; fax: +4686747637; e-mail:
[email protected]. † Centre for Chemicals Management. 10.1021/es0619197 CCC: $37.00 Published on Web 12/10/2006
2007 American Chemical Society
Baltic Proper (2). BDE-209 was also the major BDE congener in reference soil samples from a Swedish study, indicating atmospheric deposition as the source (3). BDE-209 has been shown to induce tumors in rats and mice (4) and to cause neurotoxic effects in neonatally exposed mice that worsened with age (5). Despite a short half-life in humans (about 15 days), BDE-209 is detected in blood from workers with no occupational exposure (6), indicating continuous exposure. Food basket analyses have identified fish as the main contributor to the dietary intake of lower brominated BDEs in humans from Europe (e.g., ref 7), whereas a recent survey of U.S. food concluded that meat was the most important source of dietary intake of PBDEs by adults (8). Although the latter investigation included one heptaBDE and BDE-209, the levels varied greatly between samples of the same food group, thus making it difficult to evaluate the origin of higher brominated BDEs in the diet. An important human exposure pathway for PCBs and PCDD/Fs, including the more highly chlorinated congeners, is via atmospheric deposition on plants and uptake in grazing animals with consequent contamination of meat and dairy products (9). This exposure pathway may be important for the higher brominated BDEs. In support of this, BDE-209 has been found in terrestrial avian tissues and eggs (10, 11), in red foxes (12), and in grizzly bears (13). Interestingly, BDE209 was the most abundant BDE congener in grizzly bears feeding on terrestrial food, whereas the lower brominated congeners dominated in grizzly bears consuming salmon. So far, no studies of dairy cows have been done. The aim of the present investigation was therefore to study the digestive tract absorption, tissue distribution, and excretion via milk of PBDEs in cows, based on exposure via “naturally” contaminated feed. Stored samples from a previous mass balance study of PCBs in lactating cows, performed in Devon, U.K. (14), were analyzed for PBDEs. Here we report on the results for the hepta- through decabrominated diphenyl ethers. The mass balance for the tri- to hexaBDEs is reported elsewhere (15).
Materials and Methods Samples. The study was performed over a period of 3 months in an experimental husbandry farm in Devon, a rural area in the southwest England. The experiment was originally designed for a long-term mass balance of PCBs (14). Details of the study design and sample collection and handling are presented in ref 14 and are briefly described below. The cows were kept indoors, and feed consumption and milk production were measured on a daily basis. Both milk and feces were subsampled once a week for 13 weeks from bulked morning and evening samples. The feed consisted of silage (unlimited access), concentrate, and a mineral supplement. The silage was produced on site and stored in tightly covered clamps (a three-sided storage structure). The average consumption of feed and production of milk and feces are summarized in Table S1 in the Supporting Information. For the present study, samples from two cows were analyzed, one of which was slaughtered after the experiment. The 13 weekly samples of feces and milk fat were pooled into five samples, three representing 3 week periods, and two representing 2 week periods. Adipose tissue from six lipid compartments (see the Supporting Information), liver, kidney, heart, and leg muscle were collected from the slaughtered cow. All samples were kept frozen in hexanerinsed glass containers until analysis. Chemicals. Chemicals, including the standards used, are listed in the Supporting Information. VOL. 41, NO. 2, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Sample Preparation and Cleanup. Subsamples of 1-2 g of grass silage, concentrate, and feces were taken for dry weight determinations (105 °C, overnight). The fat content of milk and tissues was determined gravimetrically. Silage. The grass silage was manually cut into 0.5 cm lengths. A subsample of 25 g was frozen with liquid nitrogen and pulverized together with 50 g of anhydrous sodium sulfate in a Waring blender with a dry grinding attachment. The ground silage mixture was transferred to a preextracted thimble, spiked with the surrogate standards overnight, 13C12BDE-183 and 13C12-BDE-209 (Table S2, Supporting Information), and Soxhlet extracted with 450 mL of DCM (8 h). After evaporation the solvent was changed to n-hexane. The extract was further treated with concentrated sulfuric acid and cleaned up on a combined silica (1.5 g, 2% deactivated in sealed glass ampoules) and acidified silica column (2 g, 2:1 silica/sulfuric acid w/w). The PBDEs were eluted with n-hexane (1-6 mL discarded, 6-29 mL collected). Concentrate, Mineral. The feed supplements were ground to a fine powder. A subsample of 10 g was spiked with surrogate standards overnight and extracted in 50 mL test tubes according to the method (original Jensen) described in ref 16. The cleanup was performed as described for silage above. Feces. The pooled sample was homogenized, and 18 g was subsampled for extraction. After the addition of surrogate standards (overnight) the sample was extracted in test tubes with 2-propanol/diethyl ether/n-hexane in a slightly modified version of the method (Jensen modification II) described in ref 16. The combined extract was washed with aqueous potassium hydroxide solution (0.5 M in 0.9% NaCl). The organic phase was subsequently evaporated and treated with concentrated sulfuric acid. Additional cleanup was achieved with acidified silica (1 g) and activated silica (1.5 g) columns. Milk Fat. The samples were pooled to a combined weight of 5.5 g. After the addition of surrogate standards the fat was solvent extracted in test tubes according to the method (original Jensen) in ref 16. The combined solvents were evaporated. The bulk fat dissolved in 15 mL of n-hexane was removed by treatment with potassium hydroxide (15 mL of 1 M KOH in 96% ethanol) for 1 h at 60 °C. After cooling, 15 mL of aqueous 0.9% sodium chloride solution was added, and two phases formed. The organic phase was collected, and the aqueous phase was reextracted with 2 × 5 mL of n-hexane. The total extract was subsequently evaporated and cleaned up as the silage. Organs and Adipose Tissues. Approximately 1 g of adipose tissue and 10 g of the organs were extracted according to the method (original Jensen) in ref 16. In brief, the samples were spiked with surrogate standards, homogenized, and solvent extracted with acetone/n-hexane/diethyl ether. The extracts were further cleaned up with concentrated sulfuric acid and an acidified silica column (1 g). The volumetric standards were added to all sample extracts before GC/MS analysis. The final volume of the extracts was adjusted to 25-100 µL depending on the matrix and detection method. Analysis. Apart from mineral and concentrate, the analysis of hepta- to nonaBDEs was performed using HRMS on a Micromass AutoSpec Ultima MS (EI). DecaBDE was analyzed using LRMS in negative chemical ionization mode (ECNI) on a Finnigan MAT SSQ 7000 MS as this method was more sensitive. The instrumental conditions and a list of the ions monitored are presented in the Supporting Information (Table S3). Quantification. The following PBDE congeners were detected and quantified: BDE-173, BDE-182, BDE-183, BDE184, BDE-191 (heptaBDEs), BDE-196, BDE-197, BDE-203, (octaBDEs), BDE-206, BDE-207, BDE-208 (nonaBDEs), and BDE-209. The identification was based on the relative 418
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retention time versus the surrogate standards differing by less than 0.005 from that of the calibration standards. Coelution could not be excluded for hepta- and octaBDEs. A reference standard of BDE-208 was not commercially available at the time of analysis, and this congener was therefore quantified using the BDE-207 reference standard, assuming it has the same response factor in HRMS, EI. The limit of quantification (LOQ) was established based on 5 times the total amount in the blanks or 5 times the noise. The LOQ differed between the matrices and with sample size and was in the range of 0.4-150 pg/g lipid weight or dry matter. The absolute recoveries of the labeled surrogate standards varied between 61% and 95%. More information on LOQ and recoveries is given in the Supporting Information (Tables S4 and S5). Quality Assurance. All glassware was heated to 450 °C overnight and further rinsed with solvents before use. The extracts were at all times shielded from UV light and from deposition of dust/particles in the laboratory air. GC/MS analysis was performed mixing samples and calibration standards randomly. The samples were quantified with standard solutions using 10 different concentration levels, which were analyzed 1-3 times. Procedural blanks covering the whole procedure were run in parallel with the samples on all extraction occasions. BDE-209 is subject to degradation during extraction/ cleanup as well as in the final analytical detection system. Since the degradation products include lower brominated BDEs that were also analyzed, e.g., the octa- and nonaBDEs, the results were corrected using the isotope-labeled BDE209 surrogate standard as a tracer of BDE-209 degradation (see the Supporting Information). Furthermore, two separate calibration standard series containing BDE-209 and lower brominated BDEs, respectively, were used. While only a small fraction of BDE-209 degraded, up to 50% of the amount of a single nonaBDE originated from this degradation (Table S6, Supporting Information). Silage (two out of three samples), concentrate, and mineral samples were analyzed in duplicate. One feces sample and a control feces sample were also analyzed in duplicate. The difference between duplicates was on average 9-21% calculated as the difference compared to the mean. The largest variability was obtained for BDE-209 (8-33%). The general procedure used for the extraction and cleanup of feces, feed, and biological tissues has been applied with good results regarding both precision and accuracy in interlaboratory exercises (1) and in the EU project “Biological Reference Materials for Organic Contaminants (BROC)” (17).
Results and Discussion Input-Output Balance. Concentrations of hepta- to decaBDEs in the different matrices are presented in Table S7 in the Supporting Information. Deca-, nona-, and octaBDEs were detected in all samples, whereas the heptaBDEs were below the quantification limit in most matrices apart from the adipose tissue. In general, BDE-209 was the dominant congener, including the lower brominated BDEs (15), in all matrices except the milk (Table S7, Supporting Information). A mass balance of higher brominated PBDEs in lactating cows was attempted using silage, concentrate, and mineral as the inputs and feces and milk fat as the outputs, whereby the BDE mass flows were integrated over the 3 month period of the study. Silage was the main contributor to the BDE input. The dominant output route was feces. The milk concentrations were generally low, but although the contribution to the output was less than 1% for BDE-206, BDE208, and BDE-209, the congeners BDE-207, BDE-196, and BDE-197 represented a larger share, up to 41% (see later discussion). Converting the concentrations into chemical mass flows for the five periods gave highly variable input
rates, mainly due to the differing amounts of PBDEs found in the three batches of silage used (Table S8, Supporting Information). The levels of BDE-209 were 20-30 times higher in the second silage batch compared to those in the first and third (Figure S1, Supporting Information). A concurrent increase in the output (milk + feces) was observed in both cows, but the increase was only a factor of 4 (Table S8, Supporting Information). The calculated output widely exceeded the input at the beginning/end of the experiment, while the opposite was true during the middle period. The great variability in the silage concentrations suggests that there was a source of PBDE contamination to the silage. The output via feces would be expected to be closely linked to the dietary intake. The fact that the output via feces varied much less than the intake via diet indicates that the grass silage samples did not capture the contamination in a manner that reflected the cows’ exposure. This conclusion is reinforced by the great discrepancies between the input-output balances during the five intervals of the experiment. The origin of the contamination in the silage is not known. The first and second samples were both from the second grass cut on the farm, but from different clamps. Both samples were analyzed in duplicate on separate occasions, and the sample treatment and storage does not explain the differences. Furthermore, the congener pattern differed between the samples. The first low-level samples had a profile resembling a mixture of technical octa- and decaBDE products, while the second, high-level sample had a much stronger contribution of the decaBDE product, suggesting different sources. The present study design was based on the premise that contaminant exposure would be uniform over time and could be quantified with a small number of samples. The results indicated that this was unfortunately not the case. Therefore, it was not possible to quantitatively assess the mass balance or the dietary absorption. However, the data nevertheless give valuable insights into the behavior of higher brominated PBDEs in cows. Organs and Adipose Tissues. All six adipose tissues representing different lipid compartments in the cow (see the Supporting Information) had similar concentrations and a similar congener profile on a lipid weight basis (Figure 1A, Table S7, Supporting Information). This was also true for PCBs and lower brominated BDEs in the same cows (14, 15). The heart, kidney, liver, and leg muscle had generally lower concentrations than the adipose tissues (Figure 1B). The lowest concentrations were detected in the liver (apart from BDE-197), perhaps indicating that the cow was in a phase of elimination, i.e., the cow was mobilizing PBDEs from the tissues. Contaminants may remobilize more rapidly from well-perfused organs, e.g., the liver, compared to less perfused tissues such as the adipose tissue. This explanation has previously been invoked to explain the distribution of PCDD/ Fs in cows, where an increase in dietary exposure resulted in higher levels in more perfused organs (18). Transfer to Milk. Although the concentrations in feces indicated a peak in exposure in the middle of the sampling period, no or only traces of a corresponding increase in the milk concentrations were seen. Thus, milk levels were not influenced by the changes in uptake but rather reflected the concentrations in the storage compartments within the cow. This is further evidence that the cow was in an elimination phase, perhaps because the PBDE levels in feed during the experiment were low compared to the cows’ historical exposure. Since the rate of elimination via milk was very slow compared to the PBDE inventory in the cows (see below), the milk concentrations would be expected to change only very slowly during an elimination phase. The adipose tissue accounts for about 15% of the live weight of cows (19). Over 90% of the PBDE body burden was contained in the adipose tissue, making this the major
FIGURE 1. (A) Mean concentrations and standard deviations of higher brominated BDEs in adipose tissues (n ) 6). (B) Ratio of the congener concentrations in tissues/organs vs mean adipose tissue concentrations, both in pg/g lipid weight. The congeners are presented in the order of elution from the GC column; / organ level < LOQ (measured values (not LOQ) are plotted).
FIGURE 2. Milk fat/adipose tissue concentration (on a lipid weight basis) ratio of PBDE and PCB congeners vs log Kow (milk and body fat data for higher brominated BDEs from this study, for lower brominated BDEs from ref 15, and for PCB unpublished data (G. O. Thomas)). A complete list of the congeners and log Kow values used are presented in Table S9 in the Supporting Information. contaminant reservoir. The concentrations were 9-80 times higher in the adipose tissue compared to those in the milk fat, with the difference increasing with the degree of bromination. A negative correlation was observed between the milk fat/adipose tissue concentration ratio and the octanol-water partition coefficient (Kow) of the compound (Figure 2). For BDE congeners with log Kow > 7, a progressively smaller fraction was transferred to the milk. This is in contrast to the lower brominated BDE congeners and PCBs, which were present in both milk fat and adipose tissue in similar concentrations in the same experiment (15, 19). A comparable discrimination in the transfer of lipophilic contaminants to milk has been shown for PCBs in arctic mammals such as gray seal (20, 21), harbor seals (22), harp seals (23), as well as in polar bears (24). Studies on milk transfer of brominated substances are limited. However, Fries et al. established a milk fat/adipose tissue ratio of 0.42 for hexabrominated biphenyls in dairy cows over a large VOL. 41, NO. 2, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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concentration range (25). This is in the same range as the two hexaBDEs from this experiment, BDE-154 and BDE-153 (ratios of 0.60 and 0.47, respectively) (15). A contaminant concentration ratio of 1 between different tissues can be expected if the sorption properties of the two tissues are similar and the two phases are close to a partitioning equilibrium. Since both adipose tissue and milk fat consist largely of neutral lipids (triglycerides), it is considered unlikely that minor differences in lipid composition could account for the 9-80 fold differences in BDE concentrations. A more probable explanation is that the adipose tissue and milk were not close to a partitioning (thermodynamic) equilibrium. The Kow dependency of the adipose tissue to milk transfer illustrated in Figure 2 has also been observed for the dietary absorption of lipophilic organic contaminants in a range of organisms (26). Two explanations for this dependency have been proposed. The first states that the transfer of the more lipophilic chemicals is related to their larger size, which makes it difficult for them to pass through the membranes that must be crossed during the transfer process (27). The second explanation is that compounds with high Kow partition to a very low extent into water and, thus, have difficulty passing as freely dissolved molecules through aqueous microenvironments that they encounter during the transfer process (28). Both of these explanations could apply to the transfer of BDEs from the adipose tissue to the milk. Interestingly, the restricted transfer of BDE-209 to milk observed in this study stands in contrast to the high dietary absorption efficiency of BDE-209 reported for seals (29), which would suggest that there are differences in the magnitude or the nature of the factors limiting these two transfer processes. The dominant resistance for adipose tissue to milk transfer may be associated with the redistribution from the adipose tissue to the blood or with the transfer from the blood to the milk in the mammary glands. If the resistance was in the adipose to blood transfer, one would expect lower levels in more perfused tissues than in less perfused tissues. This was observed (see above, Figure 1B), but the difference was small compared to the adipose to milk ratios obtained. For polar bears and gray seals, which also exhibit reduced adipose tissue to milk transfer of more lipophilic contaminants, it has been argued that the primary resistance is located in the mammary glands (20, 30). The largest discrimination in the transfer of hydrophobic pollutants to milk reported so far is among arctic mammals. Generally, they produce high-energy milk with a fat content of up to 50%. The concentrations of hepta- to nonaPCBs were 90% lower in gray seal milk versus blubber (21), whereas in the present study the heptaBDEs were about 90% lower and decaBDE as much as 99% lower in milk compared to the adipose tissues. The fat content of dairy milk is comparatively low (4%), but dairy cows are selectively bred to favor high milk yields. The discrimination of superhydrophobic pollutants is possibly accentuated in mammals with a high throughput of milk fat because the time to equilibrate between the lipid compartments is too short. Biotransformation. The congener profile in the body fat and organs also differed from the profile in the feed (Figure 3A). In the adipose tissues the major congeners in order of abundance were BDE-209 > BDE-207 > BDE-196 > BDE197 > BDE-206, whereas the order in feed was BDE-209 > BDE-206 > BDE-207 > BDE-208 > BDE-196 ) BDE-203 > BDE-197. The ratio of the mean concentration in the adipose tissues (n ) 6) to the mean concentration in silage differed by at least 2 orders of magnitude between the congeners, from 0.9 for BDE-209 to 99 for BDE-197 and up to ∼300 for BDE-182 (Figure 3B). BDE-182 was below the LOQ in the silage samples, whereas comparably high levels were found in the adipose tissue (171 pg/g lipid weight). From the fat to 420
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FIGURE 3. (A) Mean concentrations of higher brominated BDEs in adipose tissue and silage on a lipid weight and dry weight basis, respectively. (B) Ratio of the mean concentration in adipose tissues to the mean concentration in silage; / silage level < LOQ (measured values (not LOQ) are plotted).
silage ratio, the four congeners BDE-207, BDE-196, BDE-197 and possibly BDE-182 were identified as having clearly accumulated to a greater extent in the lipids compared to the feed. There are several possible explanations for the differences in congener profile. It is well-known that BDE-209 undergoes photolytic degradation in the presence of UV light (31). However, the congener profile in the tissues does not resemble the profile achieved after photolytic degradation (31). Furthermore, all samples were kept in darkness during storage and the degradation during extraction/cleanup in the lab was corrected for. Another possibility is that the dietary absorption may differ between congeners. Hexabrominated congeners have a lower dietary absorption than tetrabrominated congeners, and based on studies with other halogenated organics, the dietary absorption can be expected to continue to decrease with increasing degree of bromination (15). However, to date all evidence indicates that dietary absorption of lipophilic organic contaminants is a passive, nonfacilitated process (26), and consequently the differences in absorption rate between isomers of the same homologue group are small. In this experiment the adipose tissues/silage concentration ratios differed by a factor of 8 between the nonaBDEs BDE207 and BDE-208, by a factor of 13 between the octaBDEs BDE-197 and BDE-203, and by a factor of ∼25 between BDE182 and BDE-183. Differences in absorption rates of this magnitude would not be consistent with nonfacilitated absorption. The influence of the degree of bromination on dietary absorption efficiency is more likely represented by the congeners with the lowest ratios within each homologue group (BDE-183, BDE-203, BDE-208, BDE-209) (Figure 3B). Bioformation in the digestive system is another possible explanation. Debromination in the gut of carp was observed
FIGURE 4. Tentative pathway for the metabolic debromination originating from BDE-209 and BDE-206. Solid arrows represent debromination at the meta position, which has been previously reported in other organisms. The dotted arrows represent an optional ortho debromination.
after dietary exposure to BDE-183 and BDE-99 (32). The rumen of a cow hosts large amounts of microorganisms, which hypothetically may degrade the higher BDEs anaerobically. Debromination was recently shown in incubation experiments using sewage sludge as inoculum (33). If there was a significant debromination occurring in the rumen, the congener profile would differ between feces and feed. However, no such difference was observed. The most likely explanation for the differences in congener profiles is reductive debromination after absorption. It has previously been reported in fish (34-37). Successive debromination in rainbow trout favored the formation of early eluting nona-, octa-, and heptaBDEs down to BDE-154 (34). In carp one pentaBDE, three hexaBDEs including BDE-154 and BDE-155, two early eluting heptaBDEs, and one unknown octaBDE were produced. More recently, debromination has also been indicated in workers exposed to decaBDE in the rubber and cable industry (38) and in rats exposed to decaBDE in feed (39, 40). Even though the identity of the major heptaand octaBDEs produced in these investigations remains unknown, the pattern in the cow organs does not match the fish. Although two minor peaks present in the cow samples corresponded to the early eluting octaBDEs formed in the rainbow trout, the major octaBDEs were not the same in the two species. The unknown heptaBDEs formed in the fish do not match the BDE-182 that was indicated to accumulate in the cow either. The interpretation of the debromination pathway is difficult, since accumulation reflects both formation and resistance to further debromination. The favored BDE structure for microbial anaerobic debromination had bromine at the meta and para positions, whereas orthosubstituted congeners were more recalcitrant (33). Likewise, meta debromination of BDE-183 and BDE-99 was reported in carp (32). The BDE congeners with the highest adipose tissue to feed ratio in the cows (BDE-197, BDE-196, and BDE207), as well as BDE-182, all had bromine-free meta and ortho positions. This suggests a pathway that may originate directly from BDE-209 including debromination at both the meta and ortho positions or debromination exclusively at
the meta position with both BDE-209 and BDE-206 as precursors (Figure 4). Implications for Risk Assessment. The origin of the BDE209 contamination in the grass silage is intriguing. The farm did not use sewage sludge to fertilize the grassland in the previous year, and there are no records of sewage sludge having been applied to the land for at least 10 years before the study took place. It is unlikely that differing amounts of soil incorporated into the silage during harvesting of the grass could account for the differences. Flame retarded materials used in the handling of the silage (such as canvas used to cover the silage) may be a possible explanation, but the source remains unknown. The present study shows that cows accumulate higher brominated BDEs, and despite an ongoing debromination, BDE-209 was shown to be the major BDE congener in the cow tissues. Cows exposed to higher brominated BDEs do not transfer these to a large degree to milk but instead accumulate them, particularly BDE-209, in the body fat and meat. The carryover of BDE-209 to the milk was estimated to be less than 0.2% for the two cows in the present investigation (see the Supporting Information). Consequently, for risk assessments of higher brominated BDEs, meat rather than dairy products warrant particular attention. Furthermore, these results call into question the proposal to use bioconcentration factors (BCF) derived from diet-tomilk to also account for diet-to-beef transfer in cattle (41). Finally, the lower brominated congeners produced as a result of debromination may have a higher toxicity than BDE209. For instance, the neurobehavioral changes observed in mice neonatally exposed to BDE-209 were suggested to have been caused by metabolites of BDE-209 (5). This also highlights the necessity of investigating single BDE congeners, since bioformation will otherwise bias the results.
Acknowledgments Professor So¨ren Jensen is gratefully acknowledged for valuable advice in the analytical methods development and Yngve VOL. 41, NO. 2, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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Zebu ¨ hr for assisting with HRMS analysis. The study was financially supported by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS). Funding for the original study was provided by the U.K. Ministry for Agriculture, Fisheries and Food (now DEFRA).
Supporting Information Available Tables of the BDE concentrations and mass flows, estimate of the carryover of BDE-209, and information on the analytical conditions and performance. This material is available free of charge via the Internet at http://pubs.acs.org.
(18)
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Received for review August 10, 2006. Revised manuscript received October 22, 2006. Accepted November 3, 2006. ES0619197
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