The Impact of Bisphenol A on the Anaerobic Sulfur Transformation: Promoting Sulfur Flow and Toxic H₂S Production

Abstract

Bisphenol A (BPA), as a typical leachable additive from microplastics and one of the most productive bulk chemicals, is widely distributed in sediments, sewers, and wastewater treatment plants, where active sulfur cycling takes place. However, the effect of BPA on sulfur transformation, particularly toxic H₂S production, has been previously overlooked. This work found that BPA at environmentally relevant levels (i.e., 50-200 mg/kg total suspended solids, TSS) promoted the release of soluble sulfur compounds and increased H₂S gas production by 14.3-31.9%. The tryptophan-like proteins of microbe extracellular polymeric substances (EPSs) can spontaneously adsorb BPA, which is an enthalpy-driven reaction (Δ<i>H</i> = -513.5 kJ mol^-1, Δ<i>S</i> = -1.60 kJ mol^-1K ^-1, and Δ<i>G</i> = -19.52 kJ mol^-1 at 35 °C). This binding changed the composition and structure of EPSs, which improved the direct electron transfer capacity of EPSs, thereby promoting the bioprocesses of organic sulfur hydrolysis and sulfate reduction. In addition, BPA presence enriched the functional microbes (e.g., <i>Desulfovibrio</i> and <i>Desulfuromonas</i>) responsible for organic sulfur mineralization and inorganic sulfate reduction and increased the abundance of related genes involved in ATP-binding cassette transporters and sulfur metabolism (e.g., <i>Sat</i> and <i>AspB</i>), which promoted anaerobic sulfur transformation. This work deepens our understanding of the interaction between BPA and sulfur transformation occurring in anaerobic environments.