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A Larger, More Brominated Version of Polybrominated Diphenyl Ether (PBDE) Flame Retardants Found to Degrade Under UV Light

2013-08-27

A recent study by Environment Canada research scientist Dr. Robert Letcher demonstrated that Tetradecabromodiphenoxybenzene (TDBDPB) can undergo stepwise reductive debromination when exposed to ultra-violet or natural sunlight radiation and when dissolved in the solvents tetrahydrofuran, methanol, or n-hexane.

When irradiated with light of different energies, including natural light, the current-use flame retardant tetradecabromodiphenoxybenzene sequentially looses bromine atoms to become degradation products that could be more bioavailable and bioaccumulative in biota including in wildlife © Robert Letcher

When irradiated with light of different energies, including natural light, the current-use flame retardant tetradecabromodiphenoxybenzene sequentially looses bromine atoms to become degradation products that could be more bioavailable and bioaccumulative in biota including in wildlife © Robert Letcher

TDBDPB contains 14 bromine atoms and is the major component of commercial flame retardant mixtures such as the recently phased out SAYTEX 120. Highly brominated flame retardant compounds such as TDBDPB and decabromodiphenyl ether (BDE-209) have relatively low bioavailability, but in some cases have been shown to be of environmental concern.

The degradation of TDBDPB was examined under exposure to a variety of UV light wavelengths. UV-A had the least effect with a half-life longer than an hour, UV-C produced a half-life just over a minute, and UV-B had the greatest effect with a halflife under a minute. Natural sunlight was also examined which gave a half-life around 5 minutes. TDBDPB and BDE-209 degraded at similar rates in n-hexane and under sunlight conditions. Technical TDBDPB powder exposed to UV-B and -C radiation also produced less brominated products, although the rate was much slower compared to when in solution.

Exposure of TDBDPB solutions to natural sunlight generated a number of polybrominated diphenoxybenzene (PBDPB) photolysis products, among which the PBDPBs containing four to seven bromine atoms were the most frequently observed and estimated to be most concentrated.

Based on the TDBDPB half-lives, the study’s findings showed that the amount of UV radiation needed to break carbon – bromine bonds was strongest with UV-B and UV-C, weakest with UV-A.

This study has potential relevance to additional reports of several polybrominated diphenoxybenzene contaminants containing four to seven bromine atoms found in Great Lakes herring gull eggs, which may be linked to a TDBDPB flame retardant source via photolytic degradation to more bioavailable and persistent debromination products.

D. Chen, R.J. Letcher, L.T. Gauthier, S.G. Chu. 2013. Tetradecabromodiphenoxybenzene flame retardant undergoes photolytic debromination. Environmental Science and Technology. 47:1373-1380.

Contact: Dr. Robert Letcher (613) 998-6696, Ecotoxicology and Wildlife Health Division, Wildlife and Landscape Science Directorate