Photodegradation pathways of nonabrominated diphenyl ethers, 2-ethylhexyltetrabromobenzoate and di(2-ethylhexyl)tetrabromophthalate: identifying potential markers of photodegradation.
Photodegradation kinetics of several polybrominated diphenyl ethers (PBDEs), particularly decabromodiphenyl ether (BDE 209), have been reported in various matrixes, demonstrating that it photodegrades primarily via debromination. However, it has been difficult to determine the primary pathways by which bromine is cleaved from BDE 209 to form nona- and octabrominated congeners. In this study, photodegradation of the three nonaBDE congeners (i.e., BDE 206, 207, and 208) was examined individually in three different solvents exposed to natural sunlight and then analyzed to identify the primary degradation products. Rapid degradation of nonaBDEs (half-lives ranging from 4.25 to 12.78 min) was observed coincident with formation of octa- and heptabrominated PBDEs. BDE 207 photodegraded most rapidly while BDE 206 photodegraded the slowest. The photodegradation pathways of each nonaBDE congener were consistent among the different solvent matrixes tested; however, mass balances were found to vary with the type of solvent used in the experiment (recovery ranging from 76 to 95%). The octabrominated congener, BDE 202, and the ratio of BDE197 to BDE 201,were identified as congeners that may serve as environmental markers of photolytic debromination of decaBDE. Additional photodegradation studies were conducted with two new brominated flame retardants used in replacements for pentaBDE mixtures: 2-ethylhexyltetrabromobenzoate (TBB) and di(2-ethylhexyl)-tetrabromophthalate (TBPH). Both TBB and TBPH underwent photolysis more slowly than nonaBDEs (half-lives ranging from 85.70 to 220.17 min) and primarily formed debrominated products.
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