Effects of nano-SiO2 on the adsorption of chiral metalaxyl to agricultural soils

- Adsorption of rac-metalaxyl on soil is enhanced by the addition of nano-SiO2.
- SiO2 changed nonenantioselective adsorption isotherm from Henry to Freundlich.
- SiO2 loses its adsorption capacity after entering soil and the decrease is soil dependent.
- Competitive adsorption, different dispersion behavior leads its decreased adsorption.
- Interactions between SiO2 and soil particles is quantified by EDLVO calculation.

The application of nanotechnology in agriculture, pesticide delivery and other related fields increases the occurrence of engineered nanoparticles (ENPs) in soil. Since ENPs have larger surface areas and normally a high adsorption capacity for organic pollutants, they are thought to influence the transport of pesticides in soils and thereafter influence the uptake and transformation of pesticides. The adsorption pattern of racemic-metalaxyl on agricultural soils including kinetics and isotherms changed in the presence of nano-SiO2. The adsorption of racemic-metalaxyl on agricultural soil was not enantioselective, in either the presence or the absence of SiO2. The adsorption of racemic-metalaxyl on SiO2 decreased to some extent in soil-SiO2 mixture, and the absolute decrease was dependent on soil properties. The decreased adsorption of metalaxyl on SiO2 in soil-SiO2 mixture arose from the competitive adsorption of soil-dissolved organic matter and the different dispersion and aggregation behaviors of SiO2 in the presence of soil. Interactions between SiO2 and soil particles also contributed to the decreased adsorption of metalaxyl on SiO2, and the interactions were analyzed by extended Derjaguin-Landau-Verwey-Overbeek theory. The results showed that the presence of nano-particles in soils could decrease the mobility of pesticides in soils and that this effect varied with different soil compositions.

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