Response to "Microbial Reductive Debromination of Polybrominated Diphenyl Ethers (PBDEs)," published in Environmental Science and Technology June 15, 2006

Friday 30 June 2006
This recently published study claims that, in a laboratory setting, some bacteria in the soil can transform Deca-BDE, a commonly used retardant compound, into lower forms of polybrominated diphenyl ethers (PBDEs) that could be harmful to humans.BSEF believes that this study confirms existing research showing that Deca-BDE can degrade anaerobically, but that such degradation does not produce the lower BDE congeners that are being found in the environment. Moreover, the conditions used in the recent study are not environmentally relevant and, therefore, no conclusions regarding Deca-BDE degradation in the environment should be drawn. Specifically, BSEF notes the following issues and concerns: 1. No degradation was found without the solvent trichloroethylene (TCE) being added as a fuel, along with other substrates. Since TCE is not normally present in the environment at high concentrations, the environmental relevance of the study is questionable, i.e., the conditions under which degradation was forced to occur are not likely to be found in the environment. 2. The study is comparable to an inherent biodegradation test, from which one can conclude on the potential, but NOT on the persistency and degradation, of Deca-BDE under actual environmental conditions. For example, under environmental conditions, especially in the case of Deca-BDE, mass transfer limitation could prevent the availability of the compound to microorganisms. In addition, the congeners produced by Deca-BDE debromination were not identified in the study, and therefore an attempt to correlate the results to an actual situation in the environment cannot be made.3. The degradation of Deca-BDE to Octa-BDE congeners is not a new finding. (See Gerecke et al, Anaerobic degradation of decabromodiphenyl ether. Environ. Sci. Technol.357, 2005.) 4. The identification of degradation products was done via gas chromatograph and retention times. As the paper states itself, this approach is prone to co-elutions and cannot properly identify the degradation products that occur. 5. The paper quotes an outdated 2002 study regarding the levels of PBDEs in human milk from Sweden but fails to note that, in fact, the levels in human milk from Sweden have been falling since that time. 6. Concerns about applying Deca-amended sludge to soil have been substantially alleviated by the discovery that, in contrast to laboratory samples, Deca-BDE in actual field samples does not undergo photochemical reductive debromination to lower PBDEs.ConclusionBSEF believes that this paper confirms what is known from previous studies: Deca can degrade anaerobically (as demonstrated by Gerecke et al) but it does not produce the lower BDE congeners that are being found in the environment. The conditions used in the study are not environmentally relevant (presence of TCE, specially trained microbes) and therefore no conclusions should be drawn from the study.