Research On Degradation Behavior And Distribution Characteristics Of Chlorpyrifos And Metabolites TCP In Dryland Soils

In recent years,with the rapid development of modern agriculture,the amount of pesticide residues in the soil has gradually increased,which has become a long-term pollution source of soil and groundwater pollution.As a broad-spectrum and high-efficiency organophosphate insecticide,chlorpyrifos is widely used in dryland agriculture in China.Soil is the main destination of chlorpyrifos in the environment.The main degradation product of chlorpyrifos in soil is TCP?3,5,6-trichloro-2-pyridinol?,which is more toxic than its parent compound and has a synergistic effect with its parent compound.It is clear that chlorpyrifos and TCP degradation behavior and residue distribution in soil will contribute to the safe application and ecological risk assessment of chlorpyrifos in agricultural production.In this paper,chlorpyrifos was selected as the target pollutant.The common dryland soils in the north?corn soil,soybean soil and wheat soil?were studied.Based on the method of simultaneous detection of chlorpyrifos and TCP in soils,the dynamic changes of chlorpyrifos in soil were studied by laboratory experiment and field experiment.The process was carried out to determine the degradation and transformation of chlorpyrifos in farmland soil and its residue distribution.A method for simultaneously analyzing chlorpyrifos and TCP in soils by oscillatory extraction-high performance liquid chromatography was established.The recovery rates of chlorpyrifos and TCP in the recovery of two different soils?flush and black soil?were80.38%-103.28%and 85.31%-102.56%,respectively,and the coefficients of variation were2.52%-9.28%and 3.63%⁹.76%.?n=3?The chlorpyrifos and TCP degradation in soil under different moisture conditions were studied by pot experiment.After 45 days,the degradation rates of chlorpyrifos under different moisture treatments?20%FC,40%FC,60%FC,80%FC and100%FC,which in turn represent 20%,40%,60%,80%and 100%of the field capacity?were81.57%⁸5.56%,84.38%⁸9.45%,89.44%⁹5.33%,93.54%⁹7.60%,and 85.85%⁹0.80%,respectively.The chlorpyrifos in soils was degraded most rapidly under 80%FC conditions,followed by 60%FC.The degradation rate of chlorpyrifos in soils is significantly correlated with soil organic carbon,soluble organic carbon and microbial biomass carbon.The results of path analysis show that the variation of moieture contents will lead to content changes of organic carbon,soluble organic carbon and microbial biomass carbon,which has great significance to the degradation rate of chlorpyrifos.In the field experiment,the degradation process of chlorpyrifos in soils were well fitted by the first-order kinetic model The degradation rate constant of chlorpyrifos in crop planting soil was 0.0279-0.0882 d^-1,and the half-life was 7.86²4.84 d.The chlorpyrifos and TCP residues in0-10 cm soil layer decreased gradually,and the chlorpyrifos and TCP residues in 10-20 cm soil layer increased gradually with time.The residual distribution of chlorpyrifos and TCP residues in topsoil showed that the amount of chlorpyrifos in deep soil increased gradually with the increase of dose rate.The results of soil ecological risk assessment showed that the short-term and long-term ecological risk values of chlorpyrifos applied in different crop fields at recommended doses were 59.42,74.74,and 75.77,respectively,but they were at low and medium risk.With the increase of application doses,the ecological risk was increased significantly.