Reaction of tetrabromobisphenol A (TBBPA) with manganese dioxide: kinetics, products, and pathways

Birnessite (delta-MnO2) is a naturally occurring soil and sediment component that has been shown to oxidize organic compounds containing phenolic or aniline moieties. In this study, for the first time we explored the oxidation reaction of tetrabromobisphenol A (TBBPA), the most heavily used brominated flame retardant, with MnO2. TBBPA rapidly dissipated from the reaction solution and the process was accompanied by the dissolution of Mn2+. Dissipation of 50% of TBBPA occurred in less than 5 min in a system (pH 4.5) containing 625 microM MnO2 and 3.50 microM TBBPA at 21 degrees C, and the removal further increased to as high as 90% when the reaction was prolonged to 60 min. Analysis of initial reaction kinetics showed that the reaction orders with respect to TBBPA, MnO2, and H+ were 1.0, 0.8, and 0.25, respectively. Higher initial concentrations of TBBPA and MnO2 both enhanced the reaction. In addition, reaction rates increased as pH decreased. A retarded first-order model was found to closely describe the long-term reaction kinetics (R2 > or = 0.99), from which initial half-lives of TBBPA under different reaction conditions were estimated. A total of 7 reaction products were identified and a tentative reaction scheme was proposed. This study suggests that oxidative transformation of TBBPA by MnO2 may play an important role in the natural attenuation of TBBPA. The reaction may be further optimized for treatment of TBBPA-containing wastewater or remediation of TBBPA-polluted environmental matrices.