In this study, a hazardous DNA-binding agent, bisphenol A 3,4-quinone (BPAQ), was detected among products of bisphenol A (BPA) photocatalytic degradation. To clarify the mechanism of BPAQ formation, we investigated BPA degradation by TiO2 photocatalysis and UV photolysis at 254 nm in detail. The main focus was given to understanding the roles of OH radicals and photogenerated holes in the evolution of potentially harmful aromatic products. Five new intermediates were identified using an enhanced LC-MS-MS/ToF approach. We found that direct hole oxidation was abundantly responsible for the transformations of BPA into quinone and catechol products. Scavenging of free OH radicals induced a mechanism change and intensified BPAQformation. Direct UV photolysis produced two catechol derivatives with potentially lower endocrine-disrupting activity in comparison to BPA. Both of the processes demonstrated similar efficiencies in BPA elimination. Complete mineralization was achieved only in the case of TiO2 photocatalysis, but accompanied by potentially genotoxic intermediates formed by hole oxidation. (C) 2014 Elsevier B.V. All rights reserved.