Production Of Hydroxylated Polybrominated Diphenyl Ethers (OH-PBDEs) From Bromophenols By Manganese Dioxide

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are of significant concern because of their enhanced toxicological effects compared to PBDEs. Research to date has attributed the origin of OH-PBDEs to biological metabolism of PBDEs and natural production in the environment. However, it is unclear how OH-PBDEs are formed naturally. In this study, we explored the formation of OH-PBDEs via the oxidative transformation of simple bromophenols (BPs, e.g.,4-BP,2,4-DBP, and2,4,6-TBP) by birnessite (δ-MnO2). Results showed that OH-PBDEs were readily produced by δ-MnO2with BPs as precursors. For example, oxidation of2,4-DBP by δ-MnO2yielded2’-OH-BDE-68and2’,5’-OH-BDE-25. Other OH-PBDEs, such as6-OH-BDE-13,2’,5’-OH-BDE-3,4’-OH-BDE-121, and2’,5’-OH-BDE-69, were detected from the reaction with4-BP and2,4,6-TBP. The formation of OH-PBDEs was likely resulted from the oxidative coupling of bromophenoxy radicals. Mild acidic conditions enhanced while coexisting cations (e.g., Na, Mg, and Ca) suppressed the transformation. Given the ubiquity of BPs and δ-MnO2, oxidation of BPs by δ-MnO2and other metal oxides is likely an abiotic route for the formation of OH-PBDEs in the environment.