AbstractLomefloxacin (LOM) is an important antimicrobial drug. It has been detected in aqueous matrices in several countries. Its continuous introduction into the environment is a potential risk to aquatic and terrestrial organisms. The aim of this study was to evaluate the degradation of LOM by photolysis, peroxidation, and peroxidation assisted by ultraviolet radiation; moreover, the residual antimicrobial activity, the toxicity, and the byproducts formed during degradation processes were evaluated. Peroxidation was inefficient for LOM degradation and was not able to reduce antimicrobial activity. Both photolysis and UV/H