Environ. Sci. Technol. 2007, 41, 3392
Response to Comment on “Partitioning and Bioaccumulation of PBDEs and PCBs in Lake Michigan” We appreciate the chance to respond to the letter submitted by A. Katsoyiannis, and hope that our comments help alleviate any concern or confusion. Partitioning and Bioaccumulation. The bioaccumulation factors (BAFs) reported by Streets et al. (1) were calculated using the most recent fish (2002) and water (2004) data available and are not average BAFs for all sampling years, as implied by the letter-writer. A significant increase in PBDE concentration in lake trout is unlikely to occur in such a short period of time because the lake trout are adults and their body burden is an integrated concentration of contaminants over their lifetime (5-10 years). Thus we feel that our BAF calculations are sound and that it is both appropriate and important to report these BAFs. The variation in fish concentrations between years is likely due to a difference in sampling sites as opposed to a change in concentration over time. Lake trout were collected from one site during even years (2000 and 2002) and a different site during odd years (1999 and 2001). The data reflect this, as even-year fish populations have a different concentration than odd-year fish populations. This is true for other contaminants in these fish (data not provided). There are no significant differences in concentrations of contaminants in fish collected from the same site. Our conclusion that BDE-99 may be debrominated in the Lake Michigan food web is based on the observation that BDE-99 does not behave similarly to other PBDEs or PCBs. The BAF of BDE-99 is much lower than we would expect it to be based on the BAFs of other PBDEs and PCBs, as well as its KOW. The relationship between log BAF and log KOW is well-documented (2, 3). We stand by our use of a log KOW of 7.3 (4). This KOW appeared in a peer-reviewed article, whereas the log KOW cited by the writer (6.8) came from workshop proceedings (5). If BAFs for BDE-99 are calculated for fish from each collection year, it can be seen that the log BAF for 2001 (6.2) is even lower than the reported log BAF for 2002 (6.7). This makes an even more compelling argument for debromination of BDE-99. Furthermore, our argument is not based on the KOW of BDE-99 alone. In the relationship between BAF and KOW, there is a noticeable difference between the composition of a common commercial PBDE mixture (Bromkal 70-5DE) and the congener profile in fish. The ratio of BDE-47/BDE-99 in Bromkal 70-5DE is about 1:1 (6). In contrast, the ratio of BDE-47/BDE-99 in fish from lakes Michigan, Huron, and Ontario is about 5:1 and about 5:3 in Lake Superior. One possible explanation for this difference is that BDE-99 may be debrominated in the food web, reducing its ability to bioaccumulate. A similar trend was seen in salmon from Lake Michigan (7). The writer suggests that our PBDE BAFs are lower than those for PCBs, in contrast to the results of Gustafsson et al. (5). However, a closer look at Tables 2 and 3 in our manuscript indicate that this is not the case (1). Our PBDE BAFs are indeed higher than the PCB BAFs when comparisons are made on a direct congener-to-congener basis. The writer points out that the concentrations of PBDEs in the particulate phase show substantial variation. It should be emphasized that the errors in Table 1 of the manuscript are standard errors rather than standard deviations. Despite the fact that there is high relative error in SPM, variation in absolute error is low because concentrations in the particulate phase are so low. Most of the variation is due to variation in SPM among sites. 3392
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 9, 2007
The writer correctly points out that SPM in eq 1 of our manuscript should be kg/L instead of mg/L. The calculations were made with the proper conversion; the error is a mistake in the way eq 1 was written. We apologize for any confusion. Estimates. Our estimation of dissolved-phase concentrations in the other Great Lakes are both sound and appropriate based on the results of predictions using PCB BAFs. As stated in our manuscript, “When the PCB BAF from Lake Michigan was used with the fish concentrations in other lakes to predict the concentrations of total PCBs in water, the resulting predictions were within a factor of 2 of the measured concentrations in 52 of 63 cases” (1). As shown in Figure 2 of our article, PCBs and PBDEs behave in a similar manner with regard to partitioning in the Great Lakes (1), supporting the hypothesis that the behavior of PCBs can be used to predict the behavior of PBDEs. Our predictions are orderof-magnitude estimates and are not meant to be used in any regulatory context. Rather, they are meant to aid in future sampling efforts by providing a ballpark estimate of an expected concentration range. Surrogate Recoveries. Contrary to what the writer suggests surrogate recoveries are not a measure of extraction efficiency but of analytical procedure post-extraction. One approach of testing extraction efficiency is to spike the media prior to sampling, which was not done in this study. Once surrogates were available, surrogate recoveries ((standard error) from 7 lake trout composites were 85% (8.8%) for BDE77 and 77% (4.4%) for BDE-118 (1). Furthermore, recoveries of the 6 congeners of interest from PBDE procedural spike samples were 102% ( 5% (mean ( standard error) (1). We trust that these remarks provide additional clarification to our paper.
Literature Cited (1) Streets, S. S.; Henderson, S. A.; Stoner, A. D.; Carlson, D. L.; Simcik, M. F.; Swackhamer, D. L. Partitioning and Bioaccumulation of PBDEs and PCBs in Lake Michigan. Environ. Sci. Technol. 2006, 40 (23), 7263-7269. (2) Mackay, D. Correlation of bioconcentration factors. Environ. Sci. Technol. 1982, 16 (5), 274-278. (3) Burreau, S.; Zebuhr, Y.; Broman, D.; Ishaq, R. Biomagnification of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) studied in pike (Esox lucius), perch (Perca fluviatilis) and roach (Rutilus rutilus) from the Baltic Sea. Chemosphere 2004, 55 (7), 1043-1052. (4) Sabljic, A.; Guesten, H.; Hermens, J.; Opperhuizen, A. Modeling octanol/water partition coefficients by molecular topology: chlorinated benzenes and biphenyls. Environ. Toxicol. Chem. 1993, 27, 1394-1402. (5) Gustafsson, K.; Bjork, M.; Burreau, S.; Gilek, M. Bioaccumulation kinetics of brominated flame retardants (polybrominated diphenyl ethers) in blue mussels (Mytilus edulis). Environ. Toxicol. Chem. 1999, 18 (6), 1218-1224. (6) Sjodin, A.; Jakobsson, E.; Kierkegaard, A.; Marsh, G.; Sellstrom, U. Gas chromatographic identification and quantification of polybrominated diphenyl ethers in a commercial product, Bromkal 70-5DE. J. Chromatogr. A 1998, 822 (1), 83-89. (7) Manchester-Neesvig, J. B.; Valters, K.; Sonzogni, W. C. Comparison of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in Lake Michigan salmonids. Environ. Sci. Technol. 2001, 35 (6), 1072-7.
Summer S. Streets, Scott A. Henderson, Amber D. Stoner, Daniel L. Carlson, Matt F. Simcik, and Deborah L. Swackhamer Division of Environmental Health Sciences School of Public Health University of Minnesota MMC 807 420 Delaware Street SE Minneapolis, Minnesota 55455 ES0704885 10.1021/es0704885 CCC: $37.00
2007 American Chemical Society Published on Web 04/04/2007
