Residue Dynamics In Paddy And Photodegradation Of Pymetrozine

Pymetrozine is a novel selective insecticide.The basic structure is pyridine azomethine.It is effective as a powerful anti-feedant against sucking pests such as aphids,tobacco whiteflies and plant hoppers on a wide range of field,fruit and ornamental crops,provoking a feeding stop and subsequent starvation to death. Recently,the US Environmental Protection Agency(EPA) has classified pymetrozine as a "likely" human carcinogen because two types of(liver benign hepatoma and/or carcinoma) tumors occurred in rat and mouse (male or female) in some studies.For food and environment safety,there is a particular need for simple and reliable analysis method for the determination of it.This text research the analytic method of pymetrozine residue in soil,seedlings and paddy water,determined the residue dynamic and ultimately residue of 25% pymetrozine in soil and rice plant,and had a series of research to study the photodegradation of pymetrozine.Soil samples were extracted with v(methanol)/v(water)=8/2 and 1%ammonium hydroxide,then liquid-liquid partition with dichloromethane;Plant samples are extracted with acetonitrile and anhydrous sodium then dissolved the residue in ammonium acetate buffer,at last,liquid-liquid partition with dichloromethane;brown rice and hull samples are extracted as soil samples and cleaned-up phase is the same as plant samples.Agilent1100 HPLC,DIAMONSIL-C₁₈ reverse column and mobile phase V(methanol):V(water)=30:70 were used to analyze.The different fortification levels of soil,rape plant and rape seed are 0.02mg·kg^-1,0.50mg·kg^-1,1.00mg·kg^-1.The average recovery rate of pymetrozine are 82.5%～98.2%,and C.V. are 1.2%～6.3%,respectively.The recovery rates are all exceed 80%and measure up to residual analysis.The LOD(limit of detection) of this method is 0.2ng,and the LOQ(limit of quantification)for sample are 0.0012 mg·kg^-1,0.005 mg·kg^-1,0.003 mg·kg^-1,respectively.Field trial and high-performance liquid chromatography are carried out to study residue dynamics of pymetrozine in soil,seedlings and paddy water.The final residue is in rice and soil also is studied The half-lives of pymetrozine water are 0.19～0.21 days in the paddy field,while,they are 3.5～4.7 days in the paddy soil and 0.51～0.53 days in the paddy seedlings.The degradation rules of pymetrozine in paddy water, soil and seedlings followed the first order chemical reactions dynamics equation.The rice is sprayed one time with 25%pymetrozine WP according to the recommended dosage300g·hm^-2 and high dosage 600g·hm^-2.The final residues of pymetrozine in paddy soil,straw,rice shells and rice are all below the limit of quantification at harvest time.It shows that pymetrozine is a non-persistent pesticide(half-lives<30days).Recommended dosage300g·hm^-2 of 25%pymetrozine WP is suggested to apply in the rice one time.Based on the experimental results,the MRL of pymetrozine in rice grain may be suggested to be 0.02 mg·kg^-1 temporarily after two-year field trial in Jilin.500W mercury lamp is used to study the photodegradation of pymetrozine.Different concentration and pH of pymetrozine are studied in the same temperature and illumination.In addition,the experiment also analyzed the photodegradation dynamic in soil.After analyzing these samples,we get a conclusion: degradation of low concentration pymetrozine is faster than high concentration;low pH is faster than the high pH;degradation of pymetrozine in 500W irradiation is faster than in sun irradiation.The dynamic equation is C=5.7478e^-0.3887t and the T_1/2 is 1.8h.