Mechanisms and toxicity evaluation of the degradation of sulfamethoxazole by MPUV/PMS process

In this work, a sulfate radical (SO4)-based advanced oxidation process was applied to the degradation of sulfamethoxazole (SMX). In these experiments, a medium pressure UV (MPUV) lamp was employed to active peroxymonosulfate (PMS). It was found that 98% of SMX was removed by MPUV/PMS at a UV dose of 200 mJ cm(-2) (3.95 M SMX, 0.2 mM PMS, pH(0) = 3.7). Direct MPUV photolysis played a remarkable role in SMX removal by MPUV/PMS process. As for the indirect photolysis, SO4 was the major reactive species under acidic and neutral conditions in MPUV/PMS system, while the hydroxyl radical (center dot OH) became the predominant radical under alkaline conditions. The transformation products (TPs) of SMX that formed in the MPUV-only and MPUV/PMS experiments were identified, and the possible degradation pathways were proposed. Photoisomerization of the isoxazole ring was the major pathway of SMX during MPUVonly process. Hydroxylation/oxidation of the aniline and isoxazole ring was the predominant degradation mechanism of SMX by MPUV/PMS. Toxicity evaluation showed that MPUV/PMS was effective at reducing the antibacterial activity of SMX solutions, while MPUV-only was not. However, some TPs with equivalent or even higher antibacterial activity than SMX were formed during the initial degradation period in MPUV/PMS system. Ecotoxicity of SMX and its TPs was also hypothetically predicted via the ECOSAR program, and the results indicated that some TPs could be more toxic than SMX. (C) 2018 Elsevier Ltd. All rights reserved.