Modelling the environmental fate of the polybrominated diphenyl ethers

In response to growing alarm over the occurrence of polybrominated diphenyl ethers (PBDEs) in remote regions, this study considers their physical chemistry, environmental partitioning and considerations regarding potential for long-range atmospheric transport (LRAT). Internally consistent physical-chemical property data are presented for five representative congeners (PBDE-15, -28, -47, -99, -153) and used in a multimedia modelling approach. Results of the Level II model indicate that PBDEs will largely partition to organic carbon in soil and sediment and that their persistence will be strongly influenced by degradation rates in these media that are not well known. TaPL3 model estimates of their characteristic travel distance (CTD) suggest limited LRAT potential. The LRAT is also evaluated qualitatively, in terms of surface-air exchange behaviour. PBDEs are shown to be sensitive to seasonally and diurnally fluctuating temperatures. When vegetation is included in the model, 50% of the total mass of PBDE-47 deposited to vegetation returns to the atmosphere, suggesting that it may migrate through a series of deposition/volatilisation hops. Key data that needs to be identified in this evaluation include a better understanding of air-surface exchange, particularly to foliage, and measurements of degradation rates in soil, sediment and vegetation.