Submitted to: World Congress of Soil Science
Publication Type: Proceedings
Publication Acceptance Date: 8/20/1998
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Sorption-desorption of the new insecticide imidacloprid was characterized on ten soils varying in their physicochemical properties. Sorption coefficients Kf and the soil OC and CEC gave the higher single correlation coefficients. Desorption hysteresis was greater at low soil solution concentrations. Sorption-desorption of metabolites imidacloprid-urea, imidacloprid-guanidine, and imidacloprid-olefin was determined in three soils. Isotherm slopes (1/n) were less than 1. Sorption decreased in the order imidacloprid-guanidine (Kfoc, 3200), imidacloprid-guanidine-olefin (Kfoc, 2740), imidacloprid (Kfoc, 412), imidcloprid-urea (Kfoc, 203), in the 3 soils. Desorption was hysteretic with greatest hysteresis for imidacloprid-guanidine and imidacloprid-guanidine-olefin. Sorption, as indicated by Kd values, increased during incubation or aging by a factor of 3. Sorption was high on a clay fraction containing a 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 substantially 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 montmorillonite and humic acid but not on iron oxide. Sorption Kd on montmorillonite increased from 15 to 180 when pH was decreased from 3.5 to 1.0, suggesting protonation of the -NH group 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.