Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 8/20/1998
Publication Date: N/A
Technical Abstract: Sorption-desorption of imidacloprid was characterized on ten soils varying in their physicochemical properties. Sorption coefficients and the soil OC and CEC gave the higher single correlation coefficients. Sorption was irreversible, and desorption hysteresis coefficients were higher at low soil solution concentrations. Isotherm slopes were less than 1. The order rof sorption was imidacloprid-guanidine, more than imidacloprid- guanidine-olefin, more than imidacloprid, more than imidacloprid-urea. Desorption was hysteretic with greatest hysteresis for imidacloprid- guanidine and imidacloprid-guanidine-olefin. Changes in imidacloprid sorption with aging in three soils was determined. Sorption increased during the incubation period by a factor of 3. The influence of the different components of the clay fraction of five soils, montmorillonite, iron oxide, and humic acid and their binary and ternary associations on sorption was determined. Sorption was high on a clay fraction containing high content of montmorillionite with low laminar charge and high OC content. When OC content of the soil clays was reduced by H2O2, sorption decreased, although Koc increased. The increase in Koc was greater on clays whose surface areas increased after H2O2 treatment. This indicates a contribution of the surfaces of mineral components of the soil clay in sorption of imidacloprid. Imidacloprid sorbed on montmorillionite and humic acid but not on iron oxide. Sorption on montmorillonite increased when pH decreased suggesting protonation of the imidazol ring. Sorption on binary and ternary associations of the model sorbents indicated that OC is the most important single component affecting sorption, although there is a contribution of the mineral surfaces.