Effect Of Alginic Acid And Its Derivatives On The Adsorption And Migration Behavior Of Pesticides In Soil

The formation and stability of soil aggregates play an important role in the adsorption and migration of pesticides.Affected by extreme environments and unreasonable farming and fertilization methods,in some areas,soil aggregates have been destroyed,affecting the safety of crop yields.Therefore,it is very important to repair the soil structure and reduce the migration of pesticides.Sodium alginate（Alg）is a natural pollution-free polysaccharide that is easy to gelate to form a three-dimensional gel network structure.It has strong adsorption and can be used to promote the formation of soil aggregates and enhance the adsorption behavior of pesticides.In this paper,octylamine bond and tetrastyrene group were introduced into the side chain of sodium alginate by using four-component Ugi condensation reaction with high efficiency and high subutilization rate,amphiphilic sodium alginate derivatives（Ugi-Alg,Ugi）and sodium alginate derivatives with aggregation induced luminescence（Alg-TPVA）were obtained,respectively.The effects of sodium alginate and its derivatives on the adsorption and migration of pesticides in tropical soil were studied by using their gel properties,amphiphilicity and aggregation induced luminescence properties.The effects of calcium alginate（Ca-Alg）and amphiphilic calcium alginate（Ca-Ugi）on the adsorption and migration of pesticides in soil were studied by using the gel properties and amphiphilicity of sodium alginate and its derivatives.Different from small molecular surfactants,acetamiprid in the presence of sodium alginate and its derivatives satisfies the linear adsorption model in soil.500 mg/L of Alg,Ugi,Ca-Alg and Ca-Ugi,the adsorption coefficients of acetamiprid on soil were 3.42 g/L,4.58 g/L,4.34 g/L and 4.72 g/L,respectively.Ca-Ugi gave acetamiprid a mobility of about 20%.The effect of sodium alginate and its derivatives on the environmental behavior of pesticides in soil needs further study.（3）To clarify the correlation between soil microstructure and environmental behavior of pesticides in soil,the effects of sodium alginate and its derivatives on the formation of soil aggregation and on the adsorption and migration of pesticides in soil were studied by using their hydrogel properties and amphiphilicity.It was found that the three-dimensional hydrogel structure of both Ca-Alg and Ca-Ugi could promote the formation of soil aggregation.Moreover,the hydrophobic association between octylamine chain of Ca-Ugi and soil organic matter can significantly improve the formation of soil aggregation.Under the action of hydrogel,with the increase of soil aggregate stability ADI value,the adsorption capacity of acetamiprid on soil increased and slowed down its migration.Compared with hydrophilic Ca-Alg,the hydrophobic association of acetamiprid and the octyamine chain of Ca-Ugi effectively improved the adsorption of acetamiprid on soil and reduced the leaching rate of acetamiprid.（4）In order to further reveal the influence mechanism of sodium alginate and its derivatives on soil microstructure,the effects of sodium alginate and its derivatives on the dispersion-aggregation behavior of mineral soil particles were studied by their visualizing the hydrogel properties and aggregation induced luminescence properties.Confocal laser scanning microscope results showed that Alg-TPVA with green fluorescence was distributed on the mineral soil surface,and the mineral soil aggregation with the cross linking of Alg-TPVA under the action of calcium ions.At this time,the green fluorescence was evenly distributed on the mineral soil surface.When three-dimensional hydrogel of Ca-Alg-TPVA was added to mineral soil,it was observed that mineral soil could be directionally aggregated under the network capture,and the green fluorescence distribution of the hydrogel was relatively concentrated.The potential on the surface of kaolinite was further compressed by the cross-linking of Alg-TPVA on mineral soil surface with Ca²⁺,indicating that gelation properties compress colloidal potential more strongly than ions and resulting in loose and porous mineral soil aggregation.However,under the trapping effect of gel network,the bulk density of mineral soil is higher.Unlike kaolinite,hydration of bentonite enhances the interlayer spacing of bentonite particles,the electrostatic repulsion of bentonite by Alg-TPVA was weakened.This dispersal-aggregation behavior provides a new idea for the application of Marine biomass resources in soil.