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.