| Pesticide application can increase the yield and quality of crops,but excessive application will not only affect the yield and quality of crops,but also lead to excessive pesticide residues and cause environmental and ecological pollution.In this paper,a method for the determination of imidacloprid and its metabolites in cotton leaves and soil was established.The residues and dissipation dynamics of imidacloprid and its metabolites and pyridaben in cotton plants and soils in planting areas of Xinjiang and Shandong were studied.Then,the photodegradation process of imidacloprid in leaves and the adsorption and leaching processes of imidacloprid in soils of the two areas were discussed with the objective to provide basic research data for rational use of pesticides.The main results are as follows:(1)A method for the determination of imidacloprid and its metabolites(5-hydroxy imidacloprid,imidacloprid-olefin,imidacloprid-guanidine,imidacloprid-urea,6-chloronicotinic acid)by high performance liquid chromatography tandem mass spectrometry was established.The pretreatment process of samples was optimized by Qu ECh ERS method.The recoveries of the established method in cotton leaves and soil were 96.74%-118.52% and 95.11%-99.99%,respectively.The relative standard deviations were 5.39%-8.85% and 7.19%-9.25%,respectively.The limits of detection(LOD)were 0.001-0.033 mg/kg and 0.002-0.044 mg/kg,respectively.And the limits of quantification(LOQ)were 0.005-0.056 mg/kg and0.007-0.092 mg/kg,respectively.(2)The dissipation of imidacloprid and pyridaben in cotton leaves and soils conformed to the first order kinetics.The half-lives of imidacloprid in cotton leaves and soil were 1.57-1.63 d and 3.15-3.72 d,respectively.And the half-lives of pyridaben in cotton leaves and soil were 1.90-2.05 d and 3.18-3.25 d,respectively.The above results showed no significant regional differences.(3)The results of the determination of imidacloprid and its metabolites showed that the residual dynamics of imidacloprid and its metabolites in cotton leaves showed a trend of increase-decrease-stabilization and disappeared finally.The detected metabolites imidacloprid-urea,imidacloprid-guanidine and 6-chloronicotinic acid reached the maximum values at 3 d,5 d and 7 d after the spray with the values of 0.480 mg/kg,0.380 mg/kg and 1.17 mg/kg,respectively.(4)The photolysis of imidacloprid in aqueous solution,organic solvent,wax film and cotton leaves were investigated by simulated environmental method.The results showed that the photolysis rate of imidacloprid increased when the initial concentration of imidacloprid decreased.In different p H aqueous solutions,the photolysis rate of imidacloprid was faster under neutral conditions,and slower under acidic and alkaline conditions.In different organic solvents,the photolysis rates ranked the order: cyclohexane >methanol > isopropanol > cyclohexene.The photolysis rate of imidacloprid in extracted wax film was faster than that in carnauba wax film.In the photolysis of imidacloprid in/on leaves,the photolysis rate of imidacloprid on leaf surface layer was the fastest than those in leaf wax layer and leaf mesophyll layer.(5)The adsorption and leaching processes of imidacloprid in different soils were studied by the batch equilibrium method and soil column leaching method.Results showed that the adsorption rate of the soil in Shandong area is higher than that in Xinjiang area because of the high content of organic matter in the soil in Shandong area.After dropping imidacloprid to the leaching soil column,it was found that imidacloprid was mainly concentrated in the 0-15 cm section of the two soil columns,indicating that it was difficult for imidacloprid to migrate downward through the leaching process of the two kinds of soils.After application at the dosage,it was not easy for imidacloprid to pollute groundwater. |
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