Study On Osmotic Characteristics Of Soil Contaminated By Long-Term Pesticide Residues

Organochlorine pesticides and inorganic heavy metal pesticides have been widely used in farmland in China.The permeable characteristics of these soils are of great significance to the water transport and contaminant transport of farmland soil,and have an important impact on agricultural production and comprehensive control of pesticide contaminated soil.In this study,the infiltration characteristics of soil contaminated by long-term pesticide residues were studied by using copper sulfate（CuSO4）contaminated soil and trichloroacetic acid（TCA）contaminated soil.Then the influence of seepage behavior on loess permeability was studied by taking the contaminated soil column of pesticide seepage as the research object.Finally,the infiltration mechanism of the two contaminated soils was analyzed from the perspectives of elements,turbidity,minerals and particle surface structure.The research conclusions are as follows:（1）CuSO₄ has no significant effect on the saturated and air-dried moisture content of loess,while TCA increases the saturated and air-dried moisture content of loess due to its strong corrosion and hygroscopicity.The liquid limit and plastic index of loess decreased with the increase of CuSO₄ and TCA contents,and the two pesticides had no obvious effect on the plastic limit of loess.（2）The permeability changes of CuSO₄ contaminated soil are opposite under the two states of water-saturated and water-released air drying,while the permeability changes of TCA contaminated soil are consistent.When the soil is saturated,the permeability of CuSO₄contaminated soil is affected by the double electric layer thickness at the solid-liquid interface.With the increase of CuSO₄ content in loess,the double electric layer thickness becomes thinner,and the loess permeability coefficient decreases linearly.During air drying,the permeability of CuSO₄contaminated soil is affected by salt swelling.With the increase of CuSO₄ content in loess,the loess structure becomes loose and the soil permeability coefficient increases.The permeability of TCA-contaminated soil is affected by TCA corrosion.With the increase of TCA content,the content of Ca CO₃ in loess decreases,and the particles change from the consolidated state to the stacked state.The seepage channels formed by the stacked state increase the permeability coefficient linearly.The permeability of CuSO₄ contaminated soil and TCA contaminated soil is greatly affected by loess dry density.The higher the dry density of loess,the less the influence of the two pesticides on the permeability of loess.（3）When CuSO₄ percolates,most of Cu²⁺is absorbed by the soil 5 cm above the surface,and the infiltration rate of the overlying solution slows down with the increase of the mass fraction of CuSO₄ solution.As a result,the infiltration rate of the overlying solution at 15 cm is greater than the recharge rate of the overlying solution under the action of dead weight.The distribution of soil moisture content at 15 cm decreased first and then increased.（4）When the TCA mass fraction increased from 0.0%to 7.7%,the distribution density of pores with pore size of 0.1-1.0μm in TCA-contaminated soil decreased,the porosity increased from 25.2%to 40.4%,and the average pore size increased from 0.28μm to 0.34μm.TCA has both agglomerative and corrosive properties to loess.2.3%TCA solution is mainly agglomerated,and the average concentration of suspended particles in turbidity solution is 0.2times of that in pure water test.The concentration of suspended particles in turbidity solution decreases,the solution penetrates rapidly,and the permeability of loess is enhanced.7.7%TCA solution is given priority to with corrosion effect,the turbid liquid aerosols on average concentration is 1.6 times of pure water experiment,the settlement of turbid liquid aerosols formed turbidity current infiltration,makes the upper soil formation of 1-3 cm impervious layer,the soil particles generated between needle and flake chloride crystallization further blocked pore infiltration rate and lower solutions,the loess permeability.