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Anaerobic transformation of a technical brominated diphenyl ether mixture by super‐reduced vitamin B12 and dicyanocobinamide

The anaerobic transformation of the technical octabromo diphenyl ether mixture, DE‐79, was investigated by incubation with two super‐reduced corrinoids, dicyanocobinamide and cyanocobalamin (vitamin B12). The transformation produced 33 brominated diphenyl ethers (BDEs), 23 of which could be assigned to known structures. Within 1 d, the hepta‐ to nona‐BDEs in DE‐79 were almost quantitatively transformed with dicyanocobinamide to lower‐brominated homologs. Along with the decrease of high‐brominated congeners, concentrations of some tetra‐ to hexabromo congeners initially increased, followed by a decreasing or constant concentration during longer incubations. Super‐reduced cyanocobalamin also was able to transform BDE congeners of DE‐79. Whereas the transformation rates of hepta‐ to nona‐BDEs of DE‐79 by both corrinoids were comparable, tri‐ to hexa‐BDEs were susceptible to further transformation by super‐reduced cyanocobalamin. Incubation of DE‐79 with either corrinoid produced significant amounts of BDE 49. Because this congener is found in small quantities in both penta‐ and octabromo technical BDE mixtures, it may be a suitable indicator for reductive debromination of higher‐brominated BDEs. Isolated BDE 196 was incubated as well with super‐reduced dicyanocobalamine. After 1 d, 13 BDEs could be detected, with BDE 153, BDE 100, and BDE 99 dominating. After 7 d, only tetra‐BDEs or lower‐brominated BDEs were detectable. It could be shown that reductive debromination by super‐reduced corrinoids is a possible source for lower‐brominated BDEs (i.e., BDE 47, BDE 99, BDE 153, and BDE 154). The patterns observed with our bench‐scale study design demonstrate that anaerobic transformation in the presence of reducing agents can help to explain the occurrence of environmentally relevant BDE congeners (e.g., BDE 47, BDE 99, and BDE 153).