| Studying the behavior of adsorption-desorption of pesticides in soil is an important means to judge the residue and degradation status of pesticides after being used in soil,which has important guiding significance and theoretical value for the comprehensive and accurate evaluation of the ecological and environmental effects of pesticides,the scientific and correct application of pesticides,and the remediation of soil contaminated by pesticides.In order to efficiently,quickly and accurately collect and analyze the data of adsorption and desorption of pesticide imidacloprid?IMI?by soil samples,a new polarographic method for the determination of IMI residues in crops and soil samples was established in this research.On this basis,the adsorption-desorption and migration behavior of IMI in seven regions of China was studied,and the effects of soil physical and chemical properties on the adsorption of IMI were also discussed.This research mainly includes the following three parts:1.Establishment of the polarographic analysis method of IMI:Based on IMI in p H=8.0 disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution?PBS?,a sensitive reduction peak can be generated at the initial potential of-0.40 V and the peak potential around-1.10 V?vs.SCE?.And adding 1.0×10-3 mol/L sodium dodecyl sulfonate?SDS?has a sensitizing effect on its peak current,so a new polarographic method for detecting IMI residues in crops has been established.IMI concentration was linearly related to peak current in the range of 2.0×10-6?2.8×10-5mol/L?0.51?7.15?g/m L?and 2.8×10-5?1.2×10-4 mol/L?7.15?31.70?g/m L?,with a detection limit of 0.102?mol/L?0.026?g/m L?and a standard deviation of 1.30%?1.44%.This method can meet the analysis and detection needs of IMI in soil samples.2.In this work,the adsorption-desorption characteristics and mobility of IMI in different soils are investigated by the equilibrium-oscillation method.By studying the adsorption behavior of soil before and after removing organic matter,the effects of soil physical and chemical properties on soil adsorption were discussed in detail.The results show that the adsorption kinetics of IMI in soils can be explained by Elovich equation,and desorption kinetics accords with quasi-first and quasi-second-order kinetic equations;The isothermals adsorption-desorption characteristics are in the line with Linear and Freundlich model,and the correlation coefficients?R2?are greater than 0.926,but adsorption parameters of the seven soils are different.According to the analysis of the correlation between the physic-chemical properties of the soil and the IMI adsorption constant Kf,it is concluded that the soil organic matter content is the most important factor affecting the soil adsorption of IMI and the R2 reaches0.7877.After the removal of organic matter,cation exchange capacity and the adsorption constant Kf is enhanced,and R2 is increased from 0.0670 to 0.3413.All the isotherms adsorption curves of IMI in seven types of soil are non-linear and their adsorption empirical constant?1/n?is not equal to 1.Among them,the soil from Suining accords with S type whereas the others with L type.The Gibbs free energy of IMI in the seven types of soil are lower than 40 k J/mo L,indicating the adsorption mechanism is physical adsorption.3.The mobility of IMI in soil is studied by soil thin layer method.The results show that mobility is regarded as medium and difficult.It was found that its mobility in soil was negatively correlated with the contents of soil organic matter and clay.When the content of organic matter and clay were both high,IMI migration level was not easy to move,while when the content of organic matter and clay was high and low,IMI migration level was medium. |
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