Exploring the Role of Photolysis in the Aquatic Fate of Antimicrobial Transformation Products: Implications for One Health

Antibiotic transformation products (TPs) are common contaminants in aquatic environments. With emerging concerns about their potential role in antimicrobial resistance (AMR), elucidating the processes governing their aquatic occurrences and behaviors is important. Yet, the environmental fate of these TPs remains largely unknown. In this pilot study, we investigate the photodegradation kinetics of antibiotic TPs across different environmental waters by exposing selected TPs, from various antibiotic families, to environmentally relevant irradiation intensities. N4-Acetylsulfamethoxazole showed the highest tolerance to photolysis across matrices, whereas for TPs like anhydro-erythromycin, clindamycin sulfoxide, and hydroxy-trimethoprim demonstrated, water constituents clearly modulate aquatic degradation through indirect photolysis. Notably, 4-epianhydrotetracycline, erythromycin A enol ether, and hydroxy-metronidazole were highly susceptible to direct photolysis, which was further enhanced via other pathways such as indirect photolysis. Further, existing computational tools were evaluated for their predictive reliability by comparing experimentally derived half-lives with QSAR-based estimates. The results indicate poor correlation between predicted and observed estimates, highlighting the complexity of environmental photodegradation that current molecular descriptors may not fully capture. This study underscores the need for refining predictive models to improve their generalizability. Ultimately, our findings contribute to a better understanding of the antibiotic TP fate and potential role in the emergence and proliferation of AMR.