The promotion effect of phenolic acid compound on the photo-removal of estrogen from water under simulated sunlight irradiation

Phenol and its derivatives have received a great deal of attention due to their ubiquitous existence in surface water and recognized to be the main constituents in humic substance. However, few relevant studies concerned whether and how phenolic acids affect the fate of endocrine disrupting chemicals in surface water. In this study, the effect of 3, 5-dihydroxybenzoic acid (DHBA) on the phototransformation of 17 beta-estradiol (E2) and 17 alpha-ethinylestradiol (EE2) under simulated sunlight were systematically investigated. The results showed that DHBA significantly promoted the photolysis of estrogen mainly by producing triplet-excited state and superoxide anion based on density functional theory calculation and quenching experiments for reactive oxygen species (ROS). Interestingly, the intermediates of DHBA could compete with estrogen for reactive species to reduce the enhancing effect on E2 degradation, indicating that the changes on the structure and functional groups of phenolic compounds in photochemical process could further affect the photolysis of contaminants. Photodegradation pathways of E2 in the presence of DHBA were speculated as hydroxylation, oxidation, and coupling reactions. The study provided new insights for better understanding the effects of phenolic compounds on the natural attenuation of emerging organic contaminants in surface water.