Oxidative Transformation of Bisphenol a in the Presence of Synthetic Manganese Oxides.

Bisphenol A (BPA) is an endocrine-disrupting compound that is widely used in plastic products and is found in natural waters at concentrations that are considered harmful for aquatic life. BPA is often introduced into the environment by wastewater treatment plant effluent and landfill leachate. Mn(III/IV) oxides are commonly found in near-surface environments and their ability to degrade phenolic contaminants (e.g., BPA) is widely acknowledged. However, the details of this process are still unclear, particularly the quantitative evolution of reduced manganese species on the mineral surface and the effect of these species on BPA oxidation kinetics and mechanism. In this study, we investigated the transformation of the δ-MnO₂ solid phase, a synthetic analog to naturally-occurring Mn(IV) oxides, by quantifying the degradation of BPA and by analyzing the solids using a suite of spectroscopic techniques. During sequential additions of 80 µM BPA to 0.33 g/L δ-MnO₂ at pH 7, the BPA degradation rate exhibits a decrease by a factor of 20 from the first addition of BPA to the twelfth addition of BPA. This change in rate is attributed to the accumulation of Mn(II) and Mn(III) on the δ-MnO₂ surface, which was revealed by analyzing solids sampled throughout sequential additions using extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray Photo Electron Spectroscopy (XPS) other techniques?. The main oxidation product of BPA (i.e., 4-hydroxycumyl alcohol; HCA) was quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Kinetic data also demonstrates the degradation of HCA by the δ-MnO₂ solid phase with a rate constant of 0.361 min^-1, which is 16 times slower than the degradation rate of BPA. Our results demonstrate that degradation of BPA by environmentally relevant Mn(IV) oxides initially proceeds rapidly and the buildup of inorganic products during Mn(IV) reduction may ultimately limit BPA oxidation. Nevertheless, Mn(IV) oxides may provide a means for limiting BPA migration in subsurface environmental systems, and have potential to do the same in drinking water and waste water treatment.