Ketoprofen products induced photosensitization of sulfonamide antibiotics: The cocktail effects of pharmaceutical mixtures on their photodegradation.

Indirect photolysis induced by naturally occurring sensitizers constitutes an important pathway accounting for the transformation and fate of many recalcitrant micropollutants in sunlit surface waters. However, the photochemical transformation of micropollutants by photosensitizing pharmaceuticals has been less investigated. In this study, we demonstrated that the non-steroidal anti-inflammatory drug ketoprofen (KTF) and its photoproducts, 3-acetylbenzophenone (AcBP) and 3-ethylbenzophenone (EtBP), could sensitize the photodegradation of coexisting sulfonamide antibiotics, e.g., sulfamethoxazole (SMX), under artificial 365 nm ultraviolet (UV) and sunlight irradiation. Key reactive species including triplet excited state and singlet oxygen (O) responsible for photosensitization were identified by laser flash photolysis (LFP) and electron paramagnetic resonance (EPR) techniques, respectively. High-resolution mass spectrometry (HRMS) and structure-related reactivity analyses revealed that the sensitized photolysis of SMX occurred mainly through single electron transfer. The rate constants of sulfonamides sensitized by AcBP photolysis followed the order of sulfisoxazole (SIX)＞sulfathiazole (STZ)＞SMX＞sulfamethizole (SMT). Exposure to sunlight also enhanced the photolysis of SMX in the presence of KTF or AcBP, and water matrix had limited impact on such process. Overall, our results reveal the feasibility and mechanistic aspects of photosensitization of coexisting contaminants by pharmaceuticals (or their photoproducts) and provide new insights into the cocktail effects of pharmaceutical mixtures on their photochemical behaviors in aqueous environment.