The Residue And Degradation Of Pymetrozine In Paddy Field And Its Adsorption And Desorption In Soil

Pymetrozine is a heterocyclic pesticides with high efficiency, low toxicity, high selectivity, environmental-friendly features, It not only prevent and treat vegetables, fruit and horticultural crops on the various types of aphids and whiteflies, it can also control of rice leafhoppers, planthoppers class and other pests. There are wettable powder formulations, water dispersible granules agent. U.S. Environmental Protection Agency has seen pymetrozine as a substitute for organophosphorus pesticides. However, some recent study of pymetrozine on mice showed that pymetrozine may cause tumors. In order to evaluate whether it is safe to use in the rice fields, and is hazardous to the environment, the paper has systematically studied the residual degradation of pymetrozine and its effect in the paddy fields of brown rice, the paddy water, soil, rice plant, shell,as well as its soil adsorption and desorption after used. These studies are not only a basis for the work of rice and environmental safety to scientifically use pymetrozine, but also bring down pesticide use and reduce environmental pollution, as well as provide scientific guidance. Mainly be summarized as follows:(1) Through a large number of experiments, a fast, simple and effective high performance liquid chromatography-UV detection method has been established and used in the study of pymetrozine residue in the rice fields. It is also used to determine the residues of pymetrozine in the paddy water and soil, rice straw, rice husk, brown rice.When the concentration was 0.02,0.10,1.00 mg/kg, pymetrozine in different samples,it was measured that the average recovery was 80.20%-98.50%, relative standard deviation was 1.46%～7.55%. The accuracy, precision and sensitivity of this analysis meet the pesticide residue technical requirements. Thus this method can adapt to trial sample analysis and detection in large-scale field.(2) 50% pymetrozine effervescent tablets have been used in the rice fields in Changsha and Hangzhou for two years, the author have studied the degradation dynamics of pymetrozine in the paddy water, soil, rice plants. Experimental results show that:degradation dynamics of pymetrozine are in line with a reaction kinetics model, the results have a high correlation. The average digestion half-lives of pymetrozine were 7.40 d,14.11 d,8.67 d in the paddy water and paddy soil and rice plants.Therefore, pymetrozine is a kind of easy digestion pesticide in the paddy water, soil and rice plants. The final residual results showed that:the 21d after the last time application, pymetrozine residues in unpolished rice did not exceed their MRL value (0.02mg/kg).(3) Studies on the adsorption and adsorption mechanism of pymetrozine in five different soil tested.The results showed the adsorption equilibrium time of pymetrozine was 24 h. Adsorption of pymetrozine in five tested soil can be used to fit Freundlich isotherm equation, and are manifested as physical adsorption process. Pymetrozine in Henan Cinnamon has the strongest adsorption, weakest mobility, while in the alluvial soil in Changsha, the adsorption of pymetrozine is the weakest, the mobility is the strongest. The main influencing factors of soil physical and chemical properties on pymetrozine are soil pH.(4) The desorption condition of pymetrozine has been studied in five different tested soil. The descending for the desorption rate of soil can be observed from the result:Qingdao Cinnamon> Changsha alluvial soil> Yunnan clay loam> Henan cinnamon> Changsha krasnozem, and this has the opposite trend with the soil pH.(5)The addition of surfactant SDBS reduces the adsorption capacity of pymetrozine on soil; when the concentration of SDBS is in the vicinity of the critical micelle concentration, adsorption of pymetrozine on the clay loam reaches the lowest point; when the concentration of SDBS is 500mg/L, adsorption of pymetrozine on the alluvial soil is occasionally higher than the adsorption of pymetrozine on alluvial soil in the antithetical condition; when the concentration of SDBS at 200-500 mg/L,the adsorption trend of pymetrozine on alluvial soil is rising relatively.(6)With the improvement of concentration of bensulfuron methyl,adsorption and desorption capacity of pymetrozine on krasnozem,clay loam and alluvial soil are showing in the trend of declining. The presence of bensulfuron methyl will significantly reduce the residue of pymetrozine in krasnozem,clay loam and alluvial soil.