Photosensitized degradation of bisphenol a by dissolved organic matter

The direct and indirect photolysis of bisphenol A (BPA) was investigated using a solar simulator in the absence and presence of dissolved organic matter (DOM). BPA degradation by direct photolysis was significantly slower than its rate in the presence of DOM. In natural waters, the direct photolytic pathway would be even less important due to light screening effects. Surprisingly, differences in the rate of indirect BPA photolysis were relatively small between DOM samples. Two of the DOM samples represented terrestrial (Suwannee River fulvic acid) and autochthonous (Lake Fryxell) geochemical endmembers. The third DOM (Fulton County, Ohio) was derived from a temperate artificial wetland. We were unable to correlate BPA photoreactivity to the structural components of DOM or its extinction coefficient at 280 nm. The addition of methanol, a hydroxyl radical scavenger, to reaction solutions slowed but did not completely quench the indirect photolysis of BPA. This observation suggests that BPA photodegrades via multiple pathways involving other transients formed by the photolysis of DOM. Competitive experiments using 2,4,6-trimethylphenol also reduce the reaction rate of BPA by DOM and imply that other DOM-derived phototransients (e.g., excited triplet state DOM) are involved in the reaction. The reaction rate coefficients reported under solar-simulated irradiance in the presence of DOM are significantly faster than those reported for the microbial degradation of BPA. Thus, in natural surface waters photosensitized transformation of BPA by dissolved organic matter may be as important as biodegradation.