Study On Residue Dynamics Of Lambda-cyhalothrin In Cabbage And Its Adsorption And Photochemical Degradation

Lambda-cyhalothrin is a kind of insecticide that is used most widely in agriculture. In order to use it rationally, and comprehensively evaluate the effects of it on environment and provide scientific basis for environmental remediation, the residue analytical method, the dynamic degradation in cabbage and soil, the adsorption and photochemical degradation of Lambda-cyhalothrin were studied in this paper. The main conclusions obtained were listed as follows:An analytical method for determination of Lambda-cyhalothrin residue in cabbage by gas chromatography has been established. The analytical method of sensitivity, precision, accuracy and repeatability satisfy the essential rules of pesticide residue determination. The results show that the average recovery of Lambda-cyhalothrin in cabbage was in range of 91.34%-94.39%, and the coefficient of variation was in range of 3.05%-9.79%. The minimum detectable quality of Lambda-cyhalothrin was 1.7×10-12g. The minimum detectable concentration of Lambda-cyhalothrinin cabbage is 0.01mg/kg.A field experiment was conducted to reveal dynamic degradation of Lambda-cyhalothrin in cabbage and soil distributed in Changsha, Guangzhou, Hangzhou and Yangzhou. The degradation models of Lambda-cyhalothrin in cabbage and soil were established. The results showed that the kinetic reaction equation of degradation of Lambda-cyhalothrin in cabbage and soil was fitted as Ct=C0·e-kt. Lambda-cyhalothrin dissipated rapidly in cabbage and soil. The half-life of Lambda-cyhalothrin in cabbage and soil were 5.53d-7.37d and 3.09d-7.15d respectively.Absorption of Lambda-cyhalothrin in three different soils was studied. The results showed that:soils had strong adsorption for Lambda-cyhalothrin, which varied with properties of the soil tested. The isotherm data were fitted to Freundlich equation, the correlative coefficient was in range of 0.9797-0.9934.The adsorption benefit from the reduction of PH and the changes are apparent at PH 5 to 9.Under the HPML, The photochemical degradation of Lambda-cyhalothrin in different concentration and different pH value buffer solutions were studied. The results showed that:the higher the concentration of Lambda-cyhalothrin is, the slower the degradation rate will be.The photochemical degradation rate of Lambda-cyhalothrin increased with the raising of pH, and changing in the order of pH9> pH7>pH5.