Sunlight-mediated environmental risks of tinidazole in seawater: A neglected ocular toxicity of photolysis mixtures.

Tinidazole (TNZ), a common nitroimidazole antibiotic, is pervasive in aquatic ecosystems, posing potential threats to marine organisms. The environmental fate of TNZ, particularly under solar irradiation, and the associated secondary risks are not well characterized. Herein, the photochemical reactivity of TNZ and four other typical nitroimidazoles (i.e., metronidazole, ornidazole, dimetridazole, and secnidazole) were quantified for multiple photoreactive species. The photolysis products of these nitroimidazoles were identified under solar irradiation, from which the reaction pathways were tentatively proposed. Furthermore, the photo-induced toxicity evolution mechanisms of TNZ were investigated by comparing phenotypic, transcriptomic, and metabolomic changes in marine medaka embryos (Oryzias melastigma) after exposure to TNZ and its photo-irradiated mixtures. Our results indicated that the photo-irradiated TNZ enhanced visual toxicity to marine medaka embryos compared to the parent compound. The photolysis mixtures induced embryonic ocular malformation and significantly affected the expression of the associated genes with the initiation/termination of the phototransduction cascade, leading to metabolite changes related to visual impairment. This work reported the first comprehensive assessment of the photolysis-mediated environmental fate and secondary risks of TNZ in seawater. The findings highlighted the necessity of including complex photolysis mixtures under solar irradiation in future chemical risk assessments of marine environments.