天然酚类抗氧化剂对果蔬表面二噻农杀菌剂光化学转化的影响及其机理研究

Photochemical transformation of pesticide at the surface of fruits and vegetables is one of the hot spots in the area of environmental chemistry. However, it is still difficult to elucidate the mechanism on their photochemical transformation at the surface of plants because of the complex components in plants and uncertain environmental factors. Enlightened by our former research results that the concentrations of natural phenolic antioxidants in Chinese waxberry fruits, branches, and leaves were significantly affected by the treatment of dithianon fungicides, we are plan to study the effects of two typical natural phenolic antioxidants including of caffeic acid and quercetin on the photochemical transformation of dithianon at the surface of waxberry plants. The objectives of this study are to: (i) characterize the structures of photochemical-transformed products and identify the free radicals during the photochemical reaction by using the analytical techniques such as high-performance liquid chromatography coupled with high-resolution mass spectrometry and laser flash photolysis spectrometry; (ii) examine the pathways and kinetics of dithianon photodegradation in the presence of phenolic antioxidants; (iii) elucidate the mechanism on effects of phenolic antioxidants on the photochemical transformation of dithianon; and (iv) provide the new evidences for clarification of dithianon photodegradation and its residue control at the surface of plants. In this proposal, the new way is to be put forward for research on pesticide photodegradation. It could further promote the crossing and blending of environmental chemistry, food science, and pesticide science, and has the great theoretic significance and potential value for practical application.

果蔬表面农药光化学转化是环境化学领域的研究热点之一，但由于受环境介质中复杂变量因子和植株受体内各种成份的影响，农药在果蔬表面光转化机理的阐明至今仍是一个难题。本项目在我们前期发现二噻农杀菌剂影响杨梅果肉和枝叶中酚类抗氧化剂含量的启发下，研究两种典型的天然酚类抗氧化剂咖啡酸和槲皮素对杨梅植株表面二噻农光化学转化的影响，利用高效液相色谱-高分辨质谱和激光闪光光解光谱等技术，通过光解产物结构表征和光化学反应自由基检测，推测二噻农在酚类抗氧化剂存在条件下光化学转化途径和反应动力学，解析天然酚类抗氧化剂对二噻农光化学转化的作用机制，为果蔬表面二噻农光解机理的阐明及其残留控制提供新的科学依据。本研究为农药光降解研究领域提出了崭新的研究思路，并能促进环境化学、食品科学及农药学的学科交叉融合，具有较好的理论意义和潜在的应用价值。

随着各种农药在现代农业生产中的广泛应用，果蔬的产量日益提高，但由于残留农药造成的环境污染和食品安全也成为当今世界亟待解决的重要问题之一。果蔬表面农药光化学转化也逐渐成为环境化学领域的研究热点之一，但由于受环境介质中复杂变量因子和植株受体内各种成份的影响，农药在果蔬表面光转化机理的阐明至今仍是一个难题。本项目主要研究典型的环境组分及植物中酚类抗氧化剂对杨梅植株表面二噻农农药光化学转化的影响，通过光解产物结构表征和光化学反应自由基检测，推测二噻农在典型环境组分及酚类抗氧化剂存在条件下光化学转化途径和反应动力学，解析二噻农在植物表面光化学转化机制。在国家自然科学基金项目的支持下， 建立了以色谱-质谱为主的二噻农、咖啡酸、槲皮素或其光化学反应后的稳态产物等的分析方法；研究了二噻农杀菌剂在室内杨梅植株表面的光化学转化以及光源、光照时间等因子的影响，采用色谱-质谱分离鉴定二噻农在植株表面不同阶段光降解产物，初步推测二噻农在作物表面光化学转化途径及其动力学；研究了典型环境组分如硝酸根、Fe(III)、富里酸(FA)及酚类抗氧化剂咖啡酸、槲皮素对二噻农光化学转化的影响； 考察了咖啡酸或槲皮素与二噻农的浓度比、光源、溶剂环境等因子的影响。实验结果表明：二噻农的光降解符合一级反应动力学；二噻农在汞灯光照下比氙灯光照下更易发生光降解，且光降解速率随着灯功率的增加而增加；酚类物质能促进二噻农光降解但在不同光源下有所差异；抑制试验表明，FA通过产生的FA*促进二噻农的光降解，而硝酸根和Fe(III)通过产生羟基自由基促进二噻农光降解; 通过降解产物表征发现二噻农光照后先降解为 4,9-二氧基-2,3,4,9-四氢萘[2,3-b]噻吩-2,3-二腈，再水解为1,4-二氢萘-1,4-二醇和2-巯基顺丁烯二腈或者再光解为苯乙酮。

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