The environmental fate of biomass associated polybrominated diphenyl ethers

The widespread use of polybrominated diphenyl ethers (PBDEs) inevitably leads to their occurrence in the atmosphere, soil, and sediment. Biomass, especially dry branches and fallen leaves, may act a large reservoir for PBDEs through atmospheric deposition or soil bioaccumulation. Thus, clarifying the sunlight-induced transformation behaviors of PBDEs on biomass is highly significant for our understanding on its natural self-purification process. In this work, the degradation kinetics and mechanisms of two common PBDEs congeners, decabromodiphenyl ether (BDE-209) and 2,2',4,4'-tetrabromodiphenyl ether (BDE-47), on biomass were systematically studied under natural and simulated sunlight irradiation conditions. The highest photodegradation rate constant of BDE-209 and BDE-47 was observed on sour cherry (SC) and zoysia matrella (ZM), respectively, which was related to their larger light receiving area and poor crystallinity. Due to the higher apparent quantum efficiency, BDE-209 degrades faster than BDE-47 (0.063-0.223 vs 0.006-0.026 h^-1). The sunlight self-purification cycle of BDE-209 and BDE-47 on biomass were 6 and 14 days, respectively, with the corresponding sunlight contribution in the range of 0.12-0.51 ng mW^-1. Products analysis by GC-MS and HPLC-MS/MS revealed that the main reactions involved in the photodegradation of BDE-209 and BDE-47 on biomass were debromination, hydroxylation, cyclization, and C-O bond breaking reaction. Especially, it was firstly proposed that hydroxyl H in lignin from biomass participated in the formation of primary products, which were rationalized by density functional theory (DFT) calculations and control experiments.