Effect of natural aquatic humic substances on the photodegradation of bisphenol A

Abstract

The photochemical degradation of bisphenol A (BPA) was studied in the presence of natural humic sub stances from different origins under simulated solar irradiation. BPA underwent insignificant direct photolysis in neutral water, but rapid photosensitized degradation in four humic substances solutions via pseudo-first-order reaction occurred. The photodegradation rate of BPA was insensitive to the different initial BPA concentrations and was inhibited in aerated solution compared with the deoxygenated medium. The reactive oxygen species (ROS) such as ?·OH and ¹O₂ produced from excitation of humic substances under irradiation was determined from the quenching kinetic experiment using molecular probe. The five main intermediate photoproducts of BPA in Nordic lake fulvic acid (NOFA) were tentatively identified using gas chromatography/mass spectrometer (GC/MS). Based on the identification of ROS and the analysis of photoproduct formation, the possible phototransformation pathways of BPA were proposed, involving the direct photolysis due to the energy transfer from the triplet state humic substance (³HS^*) to BPA molecules and hydroxyl radical addition and oxidation as well.

Keywords

bisphenol A, humic acid, fulvic acid, reactive oxygen species, hydroxyl radical, singlet oxygen