Photolytical transformation rates of individual polybrominated diphenyl ethers in technical octabromo diphenyl ether (DE-79).

Polybrominated diphenyl ethers (PBDEs) are of environmental concern due to their persistence, potential to bioaccumulate, and possible toxic effects, especially for the lower brominated homologues. Reductive debromination under UV light has been identified as the main abiotic pathway for PBDE transformation. Although the kinetics and transformation products have been determined for individual PBDE congeners in different matrices, no effort has been made to determine the kinetics of these congeners when technical mixtures are exposed to UV light. We irradiated technical octabromodiphenyl ether (DE-79) in a perdeuterated solvent to determine the photolytic transformation kinetics of native PBDE congeners. Each deuterium that replaced bromine resulted in a shift to higher masses compared to the native congener, which was measured by gas chromatography with electron ionization mass spectrometry in the selected ion monitoring mode (GC/EI-MS-SIM). Tri-, tetra-, and pentabromodiphenyl ether products (BDE 28, BDE 47, BDE 49, BDE 99, BDE 100) could be proportioned to higher brominated precursors as a function of irradiation time. The kinetics of UV-irradiated single PBDE congeners matched well with results of previous studies of single congeners. However, when the same congeners were irradiated in the technical DE-79 mixture, their half-lives were longer by 20-160%. This study indicates that individually irradiated PBDE congeners behave differently than if present as a mixture. This result should be taken into account in models predicting the environmental fate of PBDEs and most likely also the mixtures of other contaminant groups.