Transformation of bisphenol AF and bisphenol S by manganese dioxide and effect of iodide

In this work, transformation of bisphenol A (BPA) alternatives bisphenol AF (BPAF) and bisphenol S (BPS) by manganese dioxide (MnO₂) and the effect of iodide (I^-) during these processes were investigated in comparison with BPA for the first time. These three bisphenols showed appreciable reactivity towards MnO₂ with the half-lives of their loss following the order of BPA < BPAF < BPS under similar conditions, and a higher transformation efficiency was generally obtained at a lower pH. The presence of I^- apparently accelerated the transformation of BPAF and BPS by MnO₂ at pH ≤ 7 but negligibly affected BPA transformation over the pH range of 5-9. This discrepancy could be well explained by the relative contribution of hypoiodous acid (HOI) in situ formed from I^- oxidation by MnO₂. Polymers, hydroxylated derivatives, and bond-cleavage products were detected from BPAF and BPS treated by MnO₂, where a series of reactions of BPAF/BPS radicals formed from one-electron oxidation of BPAF/BPS were likely involved, similar to the case of BPA reported in literature. A group of iodinated aromatic products were additionally identified from BPAF/BPS treated by MnO₂ in the presence of I^- (e.g., iodinated BPAF/BPS and iodinated BPAF/BPS dimers), and they could be further transformed. This study suggests that naturally occurring manganese oxides play a significant role in the attenuation of bisphenols released into the environment and the presence of I^- can display a great effect on their transformation.