School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, PR China.
Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, PR China.
J Hazard Mater. 2024 Dec 5;480:136082. doi: 10.1016/j.jhazmat.2024.136082. Epub 2024 Oct 5.
As a kind of typical lean meat essences and veterinary drugs, ractopamine (RAC) has been frequently detected in agricultural sewage and livestock, posing potential risk to both aquatic ecosystems and human health. Despite its widespread occurrence, the environmental fate of RAC remains unclear. Here, the mechanisms underlying the direct and indirect photodegradation of RAC was investigated under UV light irradiation at wavelengths of 275 and 365 nm, respectively. The effect of pH, initial concentration, and co-existing ions were examined. For direct photodegradation, the quantum yield of RAC increased with increasing pH values. In solutions containing dissolved organic matter (DOM), indirect photodegradation of RAC intensified with increasing pH values, and the initial concentration of DOM accelerated the process. The presence of Cu was found to inhibit both direct and indirect photodegradation of RAC. Electron spin resonance (ESR) spectrometry and quenching experiments revealed that direct photodegradation was primarily attributed to the decomposition of the triplet state of RAC. Both the triplet state of DOM (DOM*) and singlet oxygen contributed to the indirect photodegradation of RAC. LC-MS/MS analysis indicated that oxidation of the phenol group and subsequent decarboxylation were the principal photodegradation processes. The energies of each state of RAC and the active sites of RAC molecules were computed using frontier molecular orbitals and Fukui indices based on density functional theory. Combining the analysis of photoproducts with energy calculation, pathways of the direct and indirect photodegradation of RAC were proposed. These findings unveiled the photochemical behaviors of RAC concerning the removal and attenuation in aquatic environment.
作为一种典型的瘦肉精和兽药，莱克多巴胺（RAC）经常在农业污水和牲畜中被检测到，对水生生态系统和人类健康都构成潜在风险。尽管它广泛存在，但 RAC 的环境归宿仍不清楚。在这里，分别在波长为 275 和 365nm 的紫外光照射下，研究了 RAC 的直接和间接光降解机制。考察了 pH 值、初始浓度和共存离子的影响。对于直接光降解，RAC 的量子产率随 pH 值的增加而增加。在含有溶解有机物（DOM）的溶液中，随着 pH 值的增加，RAC 的间接光降解加剧，DOM 的初始浓度加速了这一过程。发现 Cu 的存在抑制了 RAC 的直接和间接光降解。电子顺磁共振（ESR）光谱和猝灭实验表明，直接光降解主要归因于 RAC 的三重态分解。DOM 的三重态（DOM*）和单线态氧都有助于 RAC 的间接光降解。LC-MS/MS 分析表明，酚基团的氧化和随后的脱羧作用是主要的光降解过程。使用基于密度泛函理论的前线分子轨道和 Fukui 指数计算了 RAC 的各态能量和 RAC 分子的活性位点。结合光产物分析和能量计算，提出了 RAC 的直接和间接光降解途径。这些发现揭示了 RAC 在水生环境中的去除和衰减的光化学行为。
