Sulfadimethoxine photodegradation in UV-C/H 2 O 2 system: Reaction kinetics, degradation pathways, and toxicity

Sulfonamide antibiotics in water have raised public concern, owing to their stability and capacity to induce microbial resistance. We investigated the degradation efficiencies of photolysis by ultraviolet light and photolysis combined with hydrogen peroxide treatment. Combining ultraviolet light irradiation with hydrogen peroxide treatment was more effective at removing sulfadimethoxine than irradiation alone or UV/persulfate system. We also assessed the effects of hydrogen peroxide concentrations, reaction time, and the composition of the water matrix. The removing efficiency of sulfadimethoxine was negatively affected by high concentrations of hydrogen peroxide and with increasing alkalinity (pH 7.5–9.0). A tentative degradation pathway was proposed, involving the initial one-electron oxidation of sulfadimethoxine by ·OH and further reactions of the formed cation intermediate. We assessed the acute toxicity of the transformation products to Vibrio fischeri, and found that combining ultraviolet light irradiation with hydrogen peroxide treatment exerted lower toxicity to the bacterium than irradiation alone. © 2020 Elsevier Ltd