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Photodegradation of sulfonamides and their N4-acetylated metabolites in water by simulated sunlight irradiation: kinetics and identification of photoproducts

Once released into the aquatic environment, pharmaceuticals may undergo different degradation processes. Photodegradation for example might be an important elimination process for light sensitive pharmaceuticals, such as antibiotics. In this study the fate of sulfonamides (sulfamethazine, sulfadiazine and sulfamethoxazole) and their N4-acetylated metabolites (N4-acetylsulfadiazine, N4- acetylsulfamethazine and N4- acetylsulfamethoxazole) under simulated sunlight irradiation was investigated. The irradiation resulted in total or almost total degradation (88% to 98%) for pharmaceuticals tested, except for sulfamethazine (52%) during 24 h of irradiation. The photoproducts of all investigated pharmaceuticals have been analyzed using high- performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. Structure elucidation performed from photodegradation products of both, sulfonamides and their N4-acetylated metabolites, clearly showed two major formation pathways. These were cleavage of the sulfonamide bond as well as SO2 extrusion. In total, nine photoproducts were elucidated. Among these photoproducts the tautomers of desulfonated sulfadiazine, sulfamethazine and sulfamethoxazole were also present. Tautomers of sulfadiazine and sulfamethazine have been characterized here for the first time as well as some photoproducts of sulfadiazine, sulfametoxazole and their metabolites N4-acetylsulfadiazine and N4- acetylsulfametoxazole. The obtained results are an important piece in the complex puzzle for assessing the environmental fate of sulfonamides and their metabolites in the environment.

photolysis ; pharmaceuticals ; sulfonamides ; metabolites ; degradation pathways ; aqueous system

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