Correspondence/Rebuttal pubs.acs.org/est
Reply to Comment on “Novel Methoxylated Polybrominated Diphenoxybenzene Congeners and Possible Sources in Herring Gull Eggs from the Laurentian Great Lakes of North America”
W
e respond to a commentary submitted by Hardy et al.1 concerning our recent article, “Novel Methoxylated Polybrominated Diphenoxybenzene Congeners and Possible Sources in Herring Gull Eggs from the Laurentian Great Lakes of North America”.2 We thank the authors for their comments, but would like to discuss several aspects that were proposed as we feel some comments by Hardy et al. may mislead readers. We reported the discovery of several novel brominated compounds found in the Great Lakes herring gulls and tentatively identified them as congeners of methoxylated polybrominated diphenoxybenzenes (MeO-PBDPBs).2 We also hypothesized several possible sources/precursors for MeO-PBDPBs, and in particular tetradecabromodiphenoxybenzene (TDBDPB). TDBDPB (CAS No: 58965−66−5) is the major component of SAYTEX 120, a commercial flame retardant product manufactured by Albemarle Corporation.3 Hardy et al. pointed out that our statement “SAYTEX 120 is a currently used BFR” is not accurate, as “SAYTEX 120 was discontinued some time ago, with limited distribution through 2010 and January 2011”. Hardy et al. also stated that “SAYTEX 120 was produced for essentially one North American customer in volumes substantially below those of major-use brominated flame retardants” and “based on this alone, its environmental distribution is expected to be limited”. However, SAYTEX 120 had been manufactured by Albemarle prior to 2003 or earlier according to Weil and Levchik.4 With manufacturing data unfortunately not available to the public, we did not know how much exactly had been produced and hence were unable to assess its environmental distribution. In addition, even though SAYTEX 120 was discontinued as stated by Hardy et al., a very recent web search found that a number of suppliers from around the world (particularly in the Asia) currently are selling TDBDPB or TDBDPB-containing products. Hardy et al. stated that SAYTEX 120 (or TDBDPB) is unlikely to be bioaccumulated or bioconcentrated, due to its high molecular weight and limited water solubility.1 We agree as this is supported by data reported in Howard and Muir,5 where TDBDPB has a high logKow value of 16.89 and a very low bioconcentration factor (BCF) of only 3. Hardy et al. concluded that the “(TDBDPB) molecule is stable and unlikely to undergo environmental biodegradation”. This is a misleading conclusion as Hardy et al. do not cite any reference to corroborate this statement. Moreover, we have completed photodegradation studies and found that TDBDPB can undergo rapid degradation under exposure to UV or natural light condition, and where a number of polybrominated diphenoxybenzene (PBDPB) product compounds are formed with less than 14 bromine atoms.6 In comparison to the wellknown polybrominated diphenyl ethers (PBDEs), and based on logKow values, lesser brominated PBDPB congeners are expected to have greater bioaccumulation potentials than TDBDPB. For example, the analogous BDE209 (CAS No. © 2012 American Chemical Society
001163−19−5) has a logKow of 12.11, whereas BDE47 (CAS No. 5436−43−1) has a logKow of 6.81. Thus, it is highly plausible that TDBDPB degrades in the environment to lesser brominated PBDPBs, and that oxidative metabolism to OHand possibly MeO-PBDPBs can occur in biota exposed to lesser brominated PBDPBs as we have suggested.2 Hardy et al. commented that the comparatively high MeOPBDPB exposure in herring gull eggs from the Channel-Shelter (C−S) Island (Lake Huron) colony was atypical. They argue this point due to the fact that this island is a man-made structure designated as a confined disposal facility (CDF) by the U.S. Army Corps of Engineers.1 We are well aware of this fact. However, as the actual sources of MeO-PBDPBs remain unknown, we stress that it is unclear if there is any link between elevated C−S Island and its function as a CDF, and elevated exposure of gulls breeding at C−S Island to MeO-PBDPBs or their precursors. In addition, we have reported in herring gull eggs that for major flame retardants, such as PBDEs and hexabromocyclododecane (HBCD), the C−S Island colony was not significantly elevated in contrast with other sites across the Great Lakes.7,8 Regardless of the fact that the C−S Island functions as a CDF, the MeO-PBDPB concentration as high as 36.8 ng/g ww in gull eggs suggested substantial bioaccumulation potential for these compounds and/or their precursors in exposed gulls, which is one of the major points proposed in our article. The opinion of Hardy et al. suggested that MeO-PBDPB compounds we reported in herring gull eggs were of natural aquatic origin. The actual source(s) of MeO-PBDPBs in herring gull eggs is currently uncertain, but we considered sources of natural aquatic origin as only as a remote possibility. Natural sources cannot explain the substantially elevated exposure in gull eggs from C−S Island compared to other Great Lakes sites. The spatial distribution pattern among gull colonies2 clearly indicated a point source contamination. In the case of OH- or MeO-PBDEs, although some reported congeners are naturally occurring, mostly ortho substituted congeners such as 6-OH-BDE-47 and 6-MeO-BDE-47, additional OH- or hydroxy-methoxy PBDEs have been demonstrated as metabolites from PBDE exposure.9 Furthermore, in continuing studies on MeO-PBDPBs in herring gulls, we recently observed in retrospective temporal studies, that although other factors may exist, the composition of the diets of gulls from the Great Lakes has been shifting over time to items of terrestrial rather than aquatic origin.10 That is, terrestrial foodstuffs may contribute elevated MeO-PBDPB exposure to gulls and that Br5- versus Br6-MeO-PBDPB congeners may be more abundant in a diet of terrestrial origins. Overall, in light of an extreme lack of relevant information, more research is necessary to address questions Published: February 22, 2012 3589
dx.doi.org/10.1021/es300700x | Environ. Sci. Technol. 2012, 46, 3589−3590
Environmental Science & Technology
Correspondence/Rebuttal
(10) Chen, D.; Letcher, R. J.; Gauthier, L. T.; Chu, S. G.; McCrindle, R. Retrospective temporal trends of methoxylated polybrominated diphenoxybenzenes and dietary isotope tracers in the eggs of herring gulls from the North American Great Lakes. 2012. In preparation.
related to the sources, exposure pathways, environmental behavior and fate of MeO-PBDPBs and precursors. Finally, Hardy et al.1 wanted to correct statements made in an earlier paper8 from the Letcher Group regarding 1,2dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH; CAS No. 3322−93−8) and 1,2,5,6-tetrabromocyclooctane (TBCO; CAS No. 3194−57−8), and marketed by Albermarle as Saytex BCL462 and Saytex BCL-48, respectively. Hardy et al. stated that “Albermarle has discontinued manufacture of both products; BCL-462 years ago and BC-48 was distributed through 2010”. Also, “Neither product was produced in substantial quantities (by Albermarle)”. While this may be true, TBECH (CAS No. 3322−93−8) and TBCO (CAS No. 3194−57−8) containing products are currently manufactured or supplied by numerous companies in China, Taiwan, Europe and/or the United States (http://www.chemexper.com/search/cas/3322938.html).
Da Chen* Robert J. Letcher*
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Wildlife and Landscape Directorate, Science and Technology Branch, Environment Canada, National Wildlife Research Centre, Carleton University, Ottawa, ON, K1A 0H3, Canada, and Department of Chemistry, Carleton University, Ottawa, ON, K1S 5B6, Canada
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (R.J.L.);
[email protected] (D.C.). Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Hardy, M. L.; Hall, T.; Le Van, S. W. Correspondence on the origin of methoxy-polybrominated diphenoxybenzenes in gull eggs in the Great Lakes as reported by Chen et al. Environ. Sci. Technol. 2012, DOI: 10.1021/es300095k. (2) Chen, D.; Letcher, R. J.; Gauthier, L. T.; Chu, S.; McCrindle, R.; Potter, D. Novel methoxylated polybrominated diphenoxybenzene congeners and possible sources in herring gull eggs from the Laurentian Great Lakes of North America. Environ. Sci. Technol. 2011, 45, 9523−9530. (3) Albemarle Corporation. SAYTEX 120 flame retardant. 2008. http://www.hmroyal.com/msds/Saytex%20120.pdf (accessed February 2012). (4) Weil, E. D.; Levchik, S. Current practice and recent commercial developments in flame retardancy of polyamides. J. Fire Sci. 2004, 22, 251−264. (5) Howard, P. H.; Muir, D. C. G. Identifying new persistent and bioaccumulative organics among chemicals in commerce. Environ. Sci. Technol. 2010, 44, 2277−2285. (6) Chen, D.; Letcher, R. J.; Gauthier, L. T.; Chu, S. Photodegradation of tetradecabromodiphenoxybenzene. 2012. In preparation. (7) Gauthier, L. T.; Hebert, C. E.; Weseloh, D. V. C.; Letcher, R. J. Current-use flame retardants in the eggs of herring gulls (Larus argentatus) from the Laurentian Great Lakes. Environ. Sci. Technol. 2007, 41, 4561−4567. (8) Gauthier, L. T.; Potter, D.; Hebert, C. E.; Letcher, R. J. Temporal trends and spatial distribution of non-polybrominated diphenyl ether flame retardants in the eggs of colonial populations of Great Lakes herring gulls. Environ. Sci. Technol. 2009, 43, 312−317. (9) Kelly, B. C.; Ikonomou, M. G.; Blair, J. D.; Gobas, F. A. P. C. Hydroxylated and methoxylated polybrominated diphenyl ethers in a Canadian Arctic marine food web. Environ. Sci. Technol. 2008, 42, 7069−7077. 3590
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