| Microplastics are emerging contaminants widespread in the soil environment and the interaction between microplastics and organic pollutants is of wide interest.The soil components can regulate the interaction between microplastics and organic pollutants,thus affecting the environmental behavior of microplastics and organic pollutants.However,few studies have focused on the mechanisms by which soil components influence the adsorption of organic pollutants by microplastics.Therefore,in this paper,we conducted a study on the mechanism of the effect of soil components on the adsorption of thiacloprid by microplastics using humic acid,montmorillonite and kaolinite as representative substances of dissolved organic matter and clay minerals,respectively.This study investigated the adsorption behavior of thiacloprid on microplastics in different environments,and further revealed the influence mechanisms of humic acid and clay minerals in the adsorption of thiacloprid on microplastics through performance experiments,spectral analysis,and theoretical calculations.In addition,the effect of microplastic content on the adsorption of thiacloprid in different soil types was investigated,and the correlation between basic properties of soil and thiacloprid adsorption behavior was explored.The main findings are as follows:（1）The adsorption behavior of thiacloprid on three microplastics was studied by batch adsorption experiments,and the properties of microfibers and pure microplastics were compared.The results showed that the adsorption process of thiacloprid on microplastics was a multilayer physical adsorption process,which was mainly controlled by hydrogen bonds and van der Waals forces.The adsorption capacity of thiacloprid on microfibers（CF and FF）was significantly higher than that on pure microplastics（CA）.（2）The effect of humic acid on the adsorption of thiacloprid by microplastics was affected by the concentration of humic acid.10 mg L-1humic acid reduced the adsorption capacity of thiacloprid on CF,FF,and CA by 18.2%,21.2%and 25.3%,respectively.50 mg L-1humic acid could promote the adsorption of thiacloprid on microplastics.Spectral analysis showed that humic acid could form hydrogen bonds and van der Waals forces with both microplastics and thiacloprid,ultimately affecting the adsorption behavior of thiacloprid on microplastics via competitive adsorption and bridging effect.Theoretical calculation results showed that humic acid competed for adsorption sites on microplastics through phenolic-OH and-COOH,thus competing for adsorption sites on microplastics.The-COOH and alcoholic-OH provided bridging sites for microplastics and thiacloprid,thus forming a“microplastics-humic acid-thiacloprid”complex.（3）The effect of clay minerals on the adsorption of thiacloprid by microplastics was affected by the type of clay minerals and microplastics.Montmorillonite and kaolinite promoted the adsorption of thiacloprid on CF and CA,but inhibited the adsorption of thiacloprid on FF.Clay minerals changed the number of effective adsorption sites in the system.Clay minerals could provide adsorption sites for thiacloprid,while occupying adsorption sites on microplastics through van der Waals forces,hydrogen bonds,and polar interactions.Spectral analysis and theoretical calculation showed that thiacloprid was more inclined to be adsorbed on the silica surface of clay minerals,and montmorillonite provided more effective adsorption sites for thiacloprid.Van der Waals forces played a key role in the adsorption of thiacloprid by clay minerals on microplastics.（4）The adsorption behavior of thiacloprid on microplastics in soil was affected by soil components,soil properties and microplastic content.Overall,microplastic content affected the adsorption of thiacloprid in soil.With the increase of microplastic content,the adsorption capacity of thiacloprid in soil increased and the relative contribution of microplastic to thiacloprid adsorption increased.Microplastics provided adsorption sites for thiacloprid and interacted with the soil to change the soil pore structure,thus promoting the adsorption of thiacloprid.The organic carbon,dissolved organic matter and clay minerals content had a weak positive effect on the adsorption capacity of thiacloprid.In conclusion,the soil components were involved in the interaction process between microplastics and thiacloprid,and thus affected the adsorption behavior of thiacloprid on microplastics.The influence mechanism of humic acid and clay minerals on the adsorption of thiacloprid by microplastics was investigated in detail,which will help to elucidate the migration behavior and direction of microplastics and organic pollutants in the environment. |
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