Production Mechanism of Hydroxylated PCBs by Oxidative Degradation of Selected PCBs Using TiO2 in Water and Estrogenic Activity of Their Intermediates

Abstract

The oxidative photodegradation behaviors of selected polychlorinated biphenyls (PCBs) [2,3,3',4'-tetraCB (BZ number: CB56), 2,3',4',5-tetraCB (CB70), and 3,4,4',5-tetraCB (CB81: coplanar PCB)] using titanium dioxide (TiO2) in water were investigated. The main purposes were to clarify the structural relation between the original PCBs and the intermediates derived by TiO2 oxidation and to evaluate the estrogenic activity in the treated PCBs during the oxidative reactions. Approximately 90% of the three tetraCBs decomposed within 120 min. Intermediates by decomposition of three tetraCBs, such as some OH-tetraCBs and OH-triCBs, carboxylic intermediates, phenolic intermediates, and other intermediates produced by the cleavage of a benzene ring were identified and quantified. In the degradation pathways, the produced amounts of OH-tetraCB and OH-triCB increased within 60 min of irradiation time. Estrogenic activities of the intermediates from the three tetraCBs in water were assessed by using a yeast two-hybrid assay system for human estrogen receptor alpha (hERalpha). The maximal estrogenic activities were induced by the solutions of decomposed CB81 with irradiation time at 60 min. We found that the solutions at an irradiation time of 60-120 min contained several 4-OH-tetraCBs and 4-OH-triCBs substituted with OH and Cl at para- and para'-positions. It is presumed that the chemical structures of the 4-OH-PCBs are similar to that of 17beta-estradiol (beta-E2); these intermediates present strong estrogenic activities. Moreover, we learned that there is a high possibility of conversion from some low toxic PCBs congeners to strong estrogenic OH-PCBs.