Environ. Sci. Technol. 2007, 41, 3391
Comment on “Partitioning and Bioaccumulation of PBDEs and PCBs in Lake Michigan”
TABLE 1. Estimations of the Concentrations (pg/L) of BDE-99 at the Dissolved Phase of Waters from the Other Great Lakes, Based on the Three Different BAFs and the “per Year” Concentrations of BDE-99 in these Lakes BDE-99
Streets et al. (1) presented bioaccumulation factors (BAFs) for polybrominated diphenyl ethers (PBDEs) and also for polychlorinated biphenyls (PCBs) in an aquatic foodweb. The writer of the present correspondence has some objections about the way these BAFs were calculated and further used. The BAFs were calculated by combination of fish data that were collected during 2000, 2001, and 2002 and water data that were sampled during 2004. This is conceptually inappropriate, especially when big differences are observed among the various sampling years. The authors reported that there were no differences in concentrations between years, but a closer look at the “per year” data of their Table 1 suggests that this is not true. At the data from all the Great Lakes, it can be seen that the concentrations of individual and total PBDEs are substantially lower for the year 2001, comparing to 2000 and 2002 (for example, BDE-99 was ∼5 times higher in 2000 than in 2001). Using annual fish data separately, the log BAF values for BDE-99 are 6.90, 6.17, and 6.69, for the years 2000, 2001, and 2002, respectively. Then, the authors compare the average value they observed (6.7) with a bibliographic log KOW value (7.32) and say the fact that BAF is lower than KOW suggests debromination. If someone chooses as log KOW value the one of 6.81 (2), then it is seen that BAF is higher than KOW the years 2000 and 2002 and lower the year 2001. Therefore, the conclusion about debromination (at least based on the BAF/KOW ratio) is not soundly extracted, both because there has been mismatching between water and fish samples and because the log KOW they used might not be the correct one. Furthermore, the authors assumed that these BAF values are roughly the same also at the other Great Lakes, given the similarity in the foodweb lengths across these lakes, and knowing the concentrations of PBDEs in fish samples, they attempted an estimation of the dissolved-phase concentration of PBDEs in the waters of the other Great Lakes. If there is such variation in BAF values within the same lake, but during different years, how can someone use (even for rough estimations) these values for a different lake? The dissolved-phase water concentrations of BDE-99 for the other Great Lakes were recalculated based on the three different BAFs and the results are presented in Table 1 below. As seen, the estimated water concentrations deriving from the various scenarios are varying up to 35 times. Also the authors mentioned that these estimations have great uncertainty, however the results they propose vary a lot less than the ones estimated here. In all these estimations, many other factors that may differentiate the four lakes are neglected, like the different sources of PBDEs, or different characteristics of the waters that influence partitioning, like the dissolved organic carbon or the suspended particulate matter concentrations (SPM), etc. For the latter, although it can be seen that in Lake Michigan the CSPM is quite constant (0.47 ( 0.02), in some cases the concentrations of PBDEs in SPM are varying a lot, without the respective variation at the concentrations of the dissolved phase. As an example, BDE-100 exhibits ∼10% (1.3 ( 0.15) relative standard deviation at the dissolved phase and ∼60% (0.18 ( 0.11) at the particulate phase. This suggests big variation in its partitioning within the same lake, therefore it is difficult to predict what is going to happen in another lake, just by knowing its concentration in trout. The authors mentioned in many instances also that PBDEs and PCBs have similar behavior due to their similar physicochemical properties. The similar behavior is in general 10.1021/es062919+ CCC: $37.00 Published on Web 04/04/2007
2007 American Chemical Society
log BAF
Superior
Huron
Ontario
CTrout for year
Cwater-dissolved
Cwater-dissolved
Cwater-dissolved
2000 2001 2002 2000 2001 2002 2000 2001 2002
6.67 1.07 3.27 35.83 5.75 17.58 10.82 1.74 5.31
1.64 1.13 1.07 8.79 6.08 5.75 2.65 1.84 1.74
4.28 0.82 1.04 22.99 4.39 5.61 6.94 1.33 1.69
1.7a
1.7a
1.8a
6.9 6.17 6.69
a
Streets et al. (1)
true, but in many papers substantial differences have been observed. Concerning the BAFs, Streets et al. (1) found that PBDE factors are similar to or slightly lower than PCB ones, but Gustafsson et al. (2) reported that PBDE BAFs are 5-8 times higher than the respective of PCBs. Based on the similarity of PCBs with PBDEs, the authors accepted the analytical method they used for the extraction of PBDEs from water, although they did not calculate surrogate recoveries for these compounds (due to a delay in availability of surrogates by the manufacturer). Concerning the recovery efficiencies during the extraction procedure, although the structures of these two classes of chemicals are similar, PBDEs are more polar due to the oxygen atom and the resulting asymmetry about the horizontal axis (3). Significant differences in the recovery efficiencies of these two categories were observed by Song et al. (4), and the fact that the authors did not evaluate the recoveries of PBDEs, but accepted the results because of the acceptable levels of PCBs recoveries, might be a reason for uncertainty in their results. Finally, the authors have given as unit for the suspended particulate matter (eq 1 of their paper) the mg/L, but for the correct calculation of the partition coefficient [KP (L/kg)] this should be Kg/L.
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, 7263-7269. (2) 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. (3) 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, 1072-1077. (4) Song, W.; Ford, J. C.; William, A. L.; Mills, W. J.; Buckley, D. R.; Rockne, K. J. Polybrominated diphenyl ethers in the sediments of the Great Lakes. 1. Lake Superior. Environ. Sci. Technol. 2004, 38, 3286-3293.
Athanasios Katsoyiannis European Commission - Joint Research Center Institute for Health and Consumer Protection Physical and Chemical Exposure Unit Via E. Fermi 1, Ispra (VA), I-21020, Italy E-mail:
[email protected]. ES062919+ VOL. 41, NO. 9, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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