ABIOTIC AND BIOTIC DEGRADATION OF BISPHENOLS

Bisphenol A (BPA), as well as its substitutes bisphenol S (BPS) and bisphenol AF (BPAF), are high production volume chemicals and potential endocrine disruptors. The oxidized manganese (Mn) species, soluble Mn(III) and solid Mn(IV) (i.e., MnO₂), are typically generated in Mn-cycling driven by Mn-oxidizing bacteria and Mn-reducing bacteria. MnO₂ is a strong oxidant capable of oxidizing a variety of organic contaminants including bisphenols. Soluble Mn(III) commonly occurs near oxic-anoxic interfaces and is an important environmental oxidant. Mn(III) is also associated with both biogenic and synthesized MnO₂. However, the effect of Mn(III) on the degradation of bisphenols is lacking. Mn-oxidizing bacteria effectively remove BPA through enzymatic reactions, which may also be capable of transforming BPA substitutes. Therefore, the present study conducted a series of experiments to demonstrate how Mn-cycling affects the fate of bisphenols. In addition, soluble Mn(III) was demonstrated to mediate BPA degradation. Mn(III) affected the reactivity of MnO₂ thereby affecting BPA degradation. Comparative studies of MnO₂- versus Mn(III)-mediated BPA degradation revealed the formation of distinct transformation products and mechanistic differences. Notably, soluble Mn(III), but not solid MnO₂, degraded adsorbed BPA, and small-angle neutron scattering experiments revealed that both adsorption and degradation of adsorbed BPA occurred in solid matrix pores. Erythrobacter sp. strain SD21, an Mn-oxidizing bacterium, effectively transformed BPA, and the BPA substitutes BPS and BPAF, in the absence of Mn. Hydroxylated bisphenol transformation products were detected, suggesting that hydroxylation is the initial step for bisphenol transformation. Genomic analysis of strain SD21 identified genes encoding monooxygenases and the inhibition experiment suggested that a monooxygenase was involved in the transformation of BPA, BPS, and BPAF. The findings demonstrate that the fate of bisphenols is closely related to Mn-cycling, with crucial roles of Mn(II)-oxidizing microorganisms implicated in the formation of oxidized Mn species. Active Mn-cycling occurs near oxic-anoxic transition zones and the observation that bisphenols are susceptible to degradation/transformation by oxidized Mn species and Mn(II)-oxidizing bacteria has implications for predicting, and possibly managing, the fate and longevity of bisphenols in environmental systems.