Metrafenone (MF), as a new type of benzophenone fungicide, has been widely used in agriculture and is persistent in the environment. Understanding its photochemical fate is essential for the comprehensive evaluation of its ecological risk. In the present work, we reported a detailed study on the photochemical transformation of MF in aqueous solution under irradiation (at λ > 290 nm using a high pressure mercury lamp). MF was relatively photo-reactive showing a low polychromatic quantum yield of photolysis (1.06 × 10⁻⁴, 20 µM) counterbalanced by a significant light absorption above 290 nm. A series of photoproducts were identified by high resolution mass spectrometry (HR-MS) analysis, and three different pathways, including oxidation of the methyl group, debromination and replacement of bromine by hydroxyl group were proposed. Among them, debromination was identified as the dominating process that could be achieved via homolytic C-Br bond cleavage from singlet and triplet MF, as confirmed by laser flash photolysis (LFP) experiments and density functional theory (DFT) calculations. Toxicity assessment revealed that photochemical degradation reduced the ecotoxicity of MF efficiently. Nitrate ions and humic acid promoted the MF photolysis, while bicarbonate exhibited no effect. Results obtained in this work would increase our understanding on the environmental fate of MF in sunlit surface waters.

Metrafenone（MF）作为一种新型的二苯甲酮类杀菌剂，在农业上应用广泛，在环境中具有持久性。了解其光化学归宿对于综合评价其生态风险至关重要。在目前的工作中，我们详细研究了水溶液中 MF 在辐照下（使用高压汞灯在 λ > 290 nm 处）的光化学转化。MF 具有相对的光反应性，显示出光解的低多色量子产率 (1.06 × 10 ^-4, 20 µM) 被 290 nm 以上的显着光吸收抵消。通过高分辨率质谱（HR-MS）分析鉴定了一系列光产物，并提出了三种不同的途径，包括甲基氧化、脱溴和溴被羟基取代。其中，脱溴被认定为是可以实现的主导过程通过通过激光闪光光解 (LFP) 实验和密度泛函理论 (DFT) 计算证实，单线态和三线态 MF 的均裂 C-Br 键裂解。毒性评估表明，光化学降解有效地降低了MF的生态毒性。硝酸根离子和腐殖酸促进了MF光解，而碳酸氢根没有影响。在这项工作中获得的结果将增加我们对阳光照射地表水中 MF 的环境归宿的理解。