Interactions of extracellular polymeric substances with ferrihydrite and subsequent 17α-ethinylestradiol photodegradation: Impact of Fe(III)-EPS complexes formation.

Microbial-derived extracellular polymeric substances (EPS) and iron minerals are ubiquitous in aquatic environments, and they can influence the fate of organic micropollutants such as 17α-ethinylestradiol (EE2). However, the interactions between EPS and iron minerals, and their influence on EE2 photodegradation, are seldom addressed in the literature. This study explored the effects of EPS derived from different aerobic or anaerobic microbials on the reductive dissolution of ferrihydrite (Fhy) and subsequent EE2 photodegradation, with emphasis on the impact of Fe-EPS complexes formation. In the dark, EPS could promote the reductive dissolution of Fhy via ligand-metal charge transfer, accompanied by Fe(III)-EPS complexes formation. Irradiation could further enhance such a dissolution process. Dissolved iron could accelerate the photolysis of protein and humic substances, triggering Maillard-like reactions that form the unsaturated medium- or high-molecular-weight polymers. The aerobic-EPS containing more proteins and humic substances photodegraded EE2 more effectively than anaerobic-EPS, with the triplet excited state playing a crucial role. In contrast, Fhy inhibited EPS-mediated EE2 photodegradation via light-shielding effect or photosensitizers oxidative decomposition. The information obtained in this research would contribute to the understanding of photochemistry involving EPS, iron minerals, and steroid estrogens, providing new insights into their environmental behavior.