Study On Residue Dynamics Of Isoprothiolane In Tobacco And Its Adsorption And Photochemical Degradation

Isoprothiolane is a kind of systemic fungicide with widespread application. The determination method of isoprothiolane in tobacco samples was studied in this research. Degradation dynamics and residue of isoprothiolane in tobacco and soil under different natural environments in China, photochemical degradation of that in water and adsorption of that in soil also were analyzed, aiming to provide scientific evidences for environmental remediation, the security evaluation of ecological environment and the reasonable use of isoprothiolane. The main results are summarized as following:The determination method of isoprothiolane residue in tobacco samples by gas chromatography was established. The sensitivity, accuracy and reproducibility of this method are adequate to meet the analysis requirement of pesticide residue. The results showed that:the average recovery of isoprothiolane in tobacco was between96.26%～101.68%, and the variation coefficient was between1.84%～9.16%. The minimum detection of isoprothiolane was1×10-11g and minimum detection concent-ration of that in tobacco was0.01mg/kg.Based on the field tests, the studies on the degradation dynamics of isoprothiolane in tobacco and soil in Changsha and Tuyun were compared, and then the resolution models of isoprothiolane in tobacco and soil were established. The results showed that the degradations of isoprothiolane in tobacco and soil were accorded with the first-order kinetics equation Ct=C0·e-kt. Isoprothiolane degradations in tobacco and soil in Changsha, Hunan and Guizhou were relatively fast and the half-life was4.46～5.01days and5.30-6.29days, respectively. In tobacco and soil of the final residue is not high, after spraying14d, residues in tobacco leaves and soils of isoprothiolane are lower than the set value of MRL1.00mg/kg.The isoprothiolane adsorptions in three different soils were studied. The results showed that:soils had strong adsorptions of isoprothiolane, but which were significantly different from each other due to different physical and chemical properties of soils. Fruendlich equation could be used to describe the adsorption of isoprothiolane in soils with the correlation coefficient of0.9717-0.9835. Isoprothiolane adsorptions in three soils were order as:rice soil from Hangzhou>red soil from Changsha> yellow soil from Guizho. Increasing or decreasing pH value, or increasing temperature, reduced the isoprothiolane absorption in soils.With high-pressure mercury lamp as light source, photochemical degradation of isoprothiolane in buffer solution at different initial concentrations and pH values were tested. The results showed that:the photolysis rate of isoprothiolane under mercury lamp was relatively fast and that under the sun was slow. The pH value of solution affected the photolysis of isoprothiolane significantly, photolysis rate in the solution increased with increase or decrease of pH value.