Residue And Photolysis Of Protective Fungicide Dithianon

Dithianon was first evaluated in 1992. It was widely used in fruits and nuts as a protective fungicide. Its mode of action is to inhibit spore germination. There had been little research on its behavior in nature environment up to now. By now, in our country, therefore, we haven't had an effective method for analyzing of its residue, and the research on its behavior in nature environment has not yet been performed.In present study we established an analytical method for determining of residue of dithianon by HPLC under optimized conditions, and we investigated the photolytic degradation of dithianon on surface of leaf.Photodecomposition is found to be one of the most important degradation pathways of dithianon occurring in the environment. The process has a direct impact on efficiency and the degradation dynamics of pesticides. Moreover, photolytic products of certain pesticides may also be harmful to environment organisms. In this study, we used different light sources and factors, such as, pH value, solvents and concentration of TiO₂ to investigate the possible photo-degradation pathway of dithianon by using HPLC and LC-MS\MS.The main results were summarized as following:1. The method for determining dithianon residues was established by using HPLC under laboratory conditions. Dithianon was extracted, at the range of 0.05mg/kg-5.0mg/kg, by acetonitrile. The average recoveries and detection limit of the method met the demand for residues analysis. The analytical method was first reported.2. To have investigated photolytic degradation of dithianon on surface of leaf.3. Photolysis of dithianon in laboratory was as following:â‘ 1) In solution of different pH value, the rate of degradation is increased with the pH value.â‘¡Dithianon degradation fast in light. Diffierent light sources resulted in different degradation rate. Dithianon degradation faster in UV light than in xenon lamp.(3) In different concentration of TiO₂, which was in range of Og/L to 2.0g/L, the rate of degradation of dithianon increased fast. But above 2.0g/L, the rate of drgradation increased slowly.4. From information provided by HPLC and LC-MS\MS, the possible photo degradation pathway of dithianon was inferred as following:Photooxidation reaction was occurred under UV 254nm. During the reaction one of the sulfur atoms was departed from the chemical structure to form the unstable intermediate product of 4,9-dioxo-2,3,4,9-tetrahydronaphtho[2,3-b]thioph-ene-2,3-dicarbonitrible (I). I could degraded in two pathways: 1) To be hydrolyzed into 1,4-dihydronaphthalene -1,4 - diol (II) and 2-mercaptomaleonitrile (III) by UV 254nm irradiation; 2) To create acetophenone by photolysis(IV).