Antimicrobial activity and acute toxicity of ozonated lomefloxacin solution

Lomefloxacin (LOM) is a synthetic antimicrobial from the fluoroquinolone family (FQ) used as a veterinary and human drug. Once in the environment, LOM may pose a risk to aquatic and terrestrial microorganisms due to its antimicrobial activity. This study evaluated the effect of ozonation of LOM (500 μg L^-1), the residual antimicrobial activity against Escherichia coli and acute toxicity against Vibrio fischeri. In addition, degradation products were investigated by UHPLC-MS/MS and proposed. Ozonation was carried out varying the applied ozone dose from 0 to 54.0 mg L^-1 O₃ and pH values of 3, 7, and 11. Ozonation was most efficient at pH 11 and led to 92.8% abatement of LOM in a 9-min reaction time (54.0 mg L^-1 O₃ applied ozone dose). Ozonation at pH 3 was able to degrade 80.4% of LOM. At pH 7, 74.3% of LOM was degraded. Although the LOM concentration and the antimicrobial activity of the solution dropped as ozone dose increased (antimicrobial activity reduction of 95% at pH 11), toxicity to V. fischeri increased for pH 7 and 11 (i.e., 65% at pH 7 and 75% at pH 11). The reduction in antimicrobial activity may be related to the oxidation of piperazinyl and the quinolone moiety. The formation of intermediates depended on the oxidant (hydroxyl radicals or/and molecular O₃) that acted the most in the process.