Accelerated degradation of antibiotics via UV irradiation in the presence of chlorite: roles of reactive species, degradation pathways, and toxicity

This study compares the degradation kinetics and mechanisms of two typical antibiotics, levofloxacin (LEV) and metronidazole (MNZ), which exhibit distinct reactivities toward reactive species, using UV/chlorite (ClO 2 − ) process. Compared to direct UV photolysis, the introduction of ClO 2 − significantly enhanced the degradation efficiency at neutral pH, increasing that of LEV and MNZ from 59.6% and 22.6% to 93.3% and 41.1%, respectively. LEV and MNZ showed distinct degradation pathways due to structural differences. At pH 7, LEV degradation was driven mainly by RCS (47.6%) > UV (37.2%) > •OH (15.2%), while MNZ degradation followed UV (50.0%) > •OH (39.0%) > RCS (11.0%). As the concentration of ClO 2 − increased, the k obs of LEV rose continuously, whereas that of MNZ exhibited a distinct optimum. The effect of a coexisting substance on LEV and MNZ degradation depended on its species. The transformation of LEV involved decarboxylation, hydroxylation, demethylation, piperazine/quinolone ring cleavage, and chlorination, whereas MNZ degradation primarily proceeded via hydroxylation and N-ethanol group loss/oxidation. While E. coli toxicity tests showed that UV/ClO 2 − significantly reduced LEV toxicity, it slightly increased that of MNZ. This effective antibiotic-degrading technology exhibits compound-specific, pH-dependent mechanisms, necessitating optimization to manage transformation product toxicity for ecological safety.