Oxidative Degradation of BPA Using TiO₂ in Water, and Transition of Estrogenic Activity in the Degradation Pathways

The oxidative degradation behavior of bisphenol A (BPA) using titanium dioxide (TiO₂) in water was investigated. The main purposes were to clarify the relationship with estrogenic activity from the degradation pathways demonstrated by oxidation of BPA in water. Approximately 99% of the BPA decomposed within 300 min, and gas chromatography (GC) mass spectrometry (MS) and liquid chromatography (LC) MS analysis revealed many intermediates during the degradation process. Intermediates by decomposition of BPA, such as hydroxylated-BPA (OH-BPA), carboxylic intermediates, phenolic intermediates, and other intermediates produced by the cleavage of a benzene ring were identified and quantified. Estrogenic activities of the degradation pathways of the BPA in water were assessed by using a constructed yeast two-hybrid assay system for human estrogen receptor α (hERα) and Japanese medaka fish (Oryzias latipes) estrogen receptor α (medERα). Estrogenic activity for hERα and medERα was reduced to less than 20% of the initial activity for BPA after 240 min of UV irradiation. However, estrogenic activity for medERα was increased by 110% from the initial activity for BPA at 60 min of UV irradiation. It was estimated that medERα assay was more sensitive for BPA and the intermediates than was the hERα assay. From these findings, we estimate that the intermediates by the oxidation of BPA have the behaviors of xenoestrogen to the aquatic wildlife in the environment.