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Chemosphere. 2018 Dec;212:365-375. doi: 10.1016/j.chemosphere.2018.08.031. Epub 2018 Aug 11.

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

Author information

1
School of Environment, Tsinghua University, Beijing, 100084, China.
2
School of Environment, Tsinghua University, Beijing, 100084, China. Electronic address: wjliu@tsinghua.edu.cn.
3
School of Environment, Tsinghua University, Beijing, 100084, China. Electronic address: wsun@tsinghua.edu.cn.

Abstract

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 μM SMX, 0.2 mM PMS, pH0 = 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 (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 MPUV-only 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.

KEYWORDS:

Medium pressure UV (MPUV); Peroxymonosulfate (PMS); Sulfamethoxazole (SMX); Sulfate radical; Toxicity assessment

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