Decomposition Of Fenvalerate-Dimethoate In Wheat And Transportation Of Pyrethroids In Soil

Residue of pesticides found in agriculture,products, drinking water and environmental exposure has raised much concern from the general public in recent years. Therefore, a lot of research works were did. These research works mainly include the degeneration mechanism, the half-life in the environment(including atmosphere, soil, plant and fruit and so on), the analytical (extraction,concentration, clean-up and others), transport in soils, residue in the environment and the solution method and so on.Dimethoate and fenvalerate were selected to controling wheat insects in course of enviormentally and harmless wheat production. In this paper, It were studied that the analysis of dimethoate-fenvalerate and the residue dynamics and final residues in different parts of wheat and soil. Under laboratory conditions, the cleanned method and transportation trends of three pyrethroids in three soils were studied too. It would help to formulate safe application standard of dimethoate and fenvalerate in wheat and soil. The results could be summarized as foliowings:1.A method for determination of fenvalerate and dimethoate residues in wheat and soil were reported. The residues of fenvalerate and dimethoate were extracted with acetonitrile,followed fenvalerate by clean up on a silicegel column,and determination by GC.The results showed that the recoveries of the method were 88.79-103.22% with RSD being 0.78%¹2.64%, and the fortified levels of 0.05^lmg kg"1 for the samples. The detectable limit of GC estimated for fenvalerate and dimethoate is 2.9 10 ng and 3.0 10^-2 ng respectively, and the minimum detectable concentration were 0.05mg kg". The accuracy, reappearance and precision of the method well satisfied the essential rules of pesticide residue determination.2.Decomposition of dimethoate in soil and wheat was studied by a two-year field experiment in Nanjing and Beijing. The soil and wheat were treated with pesticide at 3600mL hm^-2.Samples of soil and wheat were analysised at different time, then dimethoate decomposition procedure was corresponding to the mathematic mode:c=c_oe^-kt.The result showed that dimethoate was degraded easily in soil and wheat.3. With sprayed 25% dimethoate-fenvalerate EC on wheat and soil two or three times at recommended dosage and double recommended dosage,at the interval of 28d, the results showed that dimethoate was safe at this recommended dosage, 28d interval by safety assessment. However,about fenvalerate, all the final residues in wheat is higher than the stand of MRL0.2mg kg^-1.4. A method for extracting,clearing off and determining residues of cyhalothrin, escypermethrin,fenvalerate and deltamethrin in soil was reported. The method uses acetonitrile to extract residues of the pesticides in soil samples,followed by clean up with H2SO4, and determination by GC. The results showed that the recoveries of the method were 84.14-105.15% with RSD being 1.24%-5.82%.This method is proved to be easy in operation,and high in sensitivity,reproductivity and selectivity.5.Under laboratory conditions, the transportation trend of three pyrethroids, cyhalothrin, fenvalerate and deltamethrin in He'nan Fluvo-aquic soil, Jiangxi Red soil ,Nanjing Snuff soil were studied, and the trends of these three pyrethroids were also contrasted. The transportation trends of pyrehtroids were investigated by simulating soil columns in laboratory. The results show that these three pyrethroids are all difficult to move in the soil. The abilities of transportation of cyhalothrin, deltamethrin and fenvalerate are enhanced in turn, and the order of soils adsorption of three pyrethroids followed: Jiangxi Red soil> Nanjing Snuff soil>He'nan Fluvo-aquic soil,mainly due to the difference of water-solubility of these three pyrethroids, organic matter content of soils and soil pH.