Coupled Abiotic-Biotic Degradation of Bisphenol A

Abstract:

Bisphenol A (BPA) is a ubiquitous environmental contaminant with weak estrogenic activity. BPA is readily biodegradable with oxygen available, but is recalcitrant to microbial degradation under anoxic conditions. However, BPA is susceptible to abiotic transformation under anoxic conditions. To better understand the fate of BPA in anoxic environments, the kinetics of BPA transformation by manganese oxide (d-MnO₂) were investigated. BPA was rapidly transformed by MnO₂ with a pseudo-first-order rate constant of 0.413 min^-1. NMR and LC-MS analyses identified 4-hydroxycumyl alcohol (HCA) as a major intermediate. Up to 64% of the initial amount of BPA was recovered as HCA within 5 min, but the conversion efficiency decreased with time, suggesting that HCA was further degraded by MnO₂. Further experiments confirmed that HCA was also susceptible to transformation by MnO₂, albeit at 5-fold lower rates than BPA transformation. Mass balance approaches suggested that HCA was the major BPA transformation intermediate, but other compounds may also be formed. The abiotic transformation of BPA by MnO₂ was affected by pH, and 10-fold higher transformation rates were observed at pH 4.5 than at pH 10. Compared to BPA, HCA has a lower octanol-water partitioning coefficient (Log K_ow) of 0.76 vs 2.76 for BPA and a higher aqueous solubility of 2.65 g L^-1 vs 0.31 g L^-1 for BPA, suggesting higher mobility of HCA in the environment. Microcosms established with freshwater sediment materials collected from four geographically distinct locations and amended with HCA demonstrated rapid HCA biodegradation under oxic, but not under anoxic conditions. These findings suggest that BPA is not inert under anoxic conditions and abiotic reactions with MnO₂ generate HCA, which has increased mobility and is susceptible to aerobic degradation. Therefore, coupled abiotic-biotic processes can affect the fate and longevity of BPA in terrestrial environments.