State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China.
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin, 150090, China.
Water Res. 2017 Jul 1;118:196-207. doi: 10.1016/j.watres.2017.03.054. Epub 2017 Mar 28.
The frequent detection of sulfamethoxazole (SMX) in wastewater and surface waters gives rise of concerns about their ecotoxicological effects and potential risks to induce antibacterial resistant genes. UV/hydrogen peroxide (UV/HO) and UV/persulfate (UV/PDS) advanced oxidation processes have been demonstrated to be effective for the elimination of SMX, but there is still a need for a deeper understanding of product formations. In this study, we identified and compared the transformation products of SMX in UV, UV/HO and UV/PDS processes. Because of the electrophilic nature of SO, the second-order rate constant for the reaction of sulfate radical (SO) with the anionic form of SMX was higher than that with the neutral form, while hydroxyl radical (OH) exhibited comparable reactivity to both forms. The direct photolysis of SMX predominately occurred through cleavage of the NS bond, rearrangement of the isoxazole ring, and hydroxylation mechanisms. Hydroxylation was the dominant pathway for the reaction of OH with SMX. SO favored attack on NH group of SMX to generate a nitro derivative and dimeric products. The presence of bicarbonate in UV/HO inhibited the formation of hydroxylated products, but promoted the formation of the nitro derivative and the dimeric products. In UV/PDS, bicarbonate increased the formation of the nitro derivative and the dimeric products, but decreased the formation of the hydroxylated dimeric products. The different effect of bicarbonate on transformation products in UV/HO vs. UV/PDS suggested that carbonate radical (CO) oxidized SMX through the electron transfer mechanism similar to SO but with less oxidation capacity. Additionally, SO and CO exhibited higher reactivity to the oxazole ring than the isoxazole ring of SMX. Ecotoxicity of transformation products was estimated by ECOSAR program based on the quantitative structure-activity relationship analysis as well as by experiments using Vibrio fischeri, and these results indicated that the oxidation of SO or CO with SMX generated more toxic products than those of OH.
磺胺甲恶唑（SMX）在废水和地表水中频繁被检出，这引起了人们对其生态毒性效应和诱导抗菌抗性基因的潜在风险的关注。UV/过氧化氢（UV/HO）和 UV/过硫酸盐（UV/PDS）高级氧化工艺已被证明可有效去除 SMX，但仍需要更深入地了解其产物的形成。在本研究中，我们鉴定并比较了 SMX 在 UV、UV/HO 和 UV/PDS 工艺中的转化产物。由于 SO 的亲电性，硫酸根自由基（SO）与 SMX 的阴离子形式的反应二级速率常数高于与中性形式的反应二级速率常数，而羟基自由基（OH）与两种形式的反应活性相当。SMX 的直接光解主要通过 NS 键的断裂、异噁唑环的重排和羟化机制发生。OH 与 SMX 的反应以羟化作用为主导途径。SO 优先攻击 SMX 的 NH 基团，生成硝基衍生物和二聚产物。在 UV/HO 中，碳酸氢根的存在抑制了羟化产物的形成，但促进了硝基衍生物和二聚产物的形成。在 UV/PDS 中，碳酸氢根增加了硝基衍生物和二聚产物的形成，但减少了羟化二聚产物的形成。碳酸氢根在 UV/HO 与 UV/PDS 中对转化产物的不同影响表明，碳酸根自由基（CO）通过类似于 SO 的电子转移机制氧化 SMX，但氧化能力较弱。此外，SO 和 CO 对 SMX 的噁唑环的反应活性高于异噁唑环。基于定量结构-活性关系分析的 ECOSAR 程序和利用发光菌 Vibrio fischeri 的实验对转化产物的生态毒性进行了评估，结果表明，SO 或 CO 与 SMX 的氧化生成的毒性产物比 OH 多。
