Pyraclostrobin is a fungicide used widely across the world. However, its photolysis pathway and toxic mechanism is unclear. In this study, photolysis and photo-induced toxicity of pyraclostrobin to Vibrio fischeri were determined. The results showed that direct photolysis dominated the degradation of pyraclostrobin. Gas Chromatography-Mass spectrometry and quantum chemical calculation revealed that the pyraclostrobin was firstly photo-degraded into Methyl N-phenyl-carbamate and 1-(4-chlorophenyl)-3-hydroxy-1H-pyrzole, synthetic intermediates of pyraclostrobin, then into aniline, benzoquinone and acids. Toxicity assay showed that bioluminescent inhibition rate to V. fischeri fluctuated with radiation/illumination time and the toxicity curve can be classified into three phases (Phase I: 0-10 min, incline; Phase II: 10-60 min, decline; Phase III: 60-120 min, incline). The up-and-down curve indicates the change of parent compound during the photolysis. Simulation of molecular docking showed that the CDOCKER interaction energy of pyraclostrobin (-44.71) lower than other intermediate products (>-30.00), indicating that the parent compound is more toxic than its intermediates. An increased toxicity observed in the toxicity curve was attributed to the generation of benzoquinone with log1/EC50 of 6.73, which can greatly change structure of target luciferase in Vibrio fischeri. In addition, the addition of radical scavengers can inhibit the bioluminescence of the tested solutions, indicating the involvement of radicals in the transformation of intermediates. This paper reveals that one of photochemical transformation products of pyraclostrobin can cause more toxic than its parent compound to bacteria. Environmental risk assessment should consider not only the parent compound, but also its metabolites.

中文翻译：

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吡菌酯对费氏弧菌的光解和光诱导毒性：途径和毒性机理。

高温菌是一种在世界范围内广泛使用的杀菌剂。但是，其光解途径和毒性机理尚不清楚。在这项研究中，测定了吡菌酯对费氏弧菌的光解和光诱导毒性。结果表明，直接光解作用主导了吡菌酯的降解。气相色谱-质谱法和量子化学计算表明，吡菌胺酯首先被光降解为N-苯基氨基甲酸甲酯和1-（4-氯苯基）-3-羟基-1H-吡唑，吡菌胺酯的合成中间体，然后被降解为苯胺，苯醌和酸。毒性试验表明，对费氏弧菌的生物发光抑制率随辐射/照射时间的变化而变化，毒性曲线可分为三个阶段（第一阶段：0-10分钟，倾斜；第二阶段：10-60分钟，下降；第三阶段） ：60-120分钟，倾斜）。上下曲线表示光解过程中母体化合物的变化。分子对接的模拟表明，吡菌胺酯（-44.71）的CDOCKER相互作用能低于其他中间产物（> -30.00），表明母体化合物比其中间体更具毒性。在毒性曲线中观察到的毒性增加归因于苯醌的生成，log1 / EC50为6.73，它可以极大地改变费氏弧菌中目标荧光素酶的结构。另外，自由基清除剂的添加可以抑制测试溶液的生物发光，表明自由基参与中间体的转化。本文揭示了吡菌胺酯的一种光化学转化产物对细菌的毒性比其母体化合物高。环境风险评估不仅应考虑母体化合物，还应考虑其代谢产物。