Submitted to: International Congress of Pesticide Chemistry Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 8/3/1998
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Sorption-desorption of imidacloprid was characterized on soils varying in their physicochemical properties. Sorption coefficients, Kf, ranged from 5 to 18 and the soil OC and CEC gave the higher single correlation coefficients. Sorption iostherm slopes (1/n) ranged from 0.66 to 0.82. Sorption was irreversible, and desorption isotherms slopes decreased with decreasing solution concentrations. Sorption, increased during aging by a factor of 3. Sorption was high on a clay fraction containing a high content of montmorillonite 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 indicated a contribution of the mineral component surfaces of the soil clay in sorption of imidacloprid. Imidacloprid sorbed on montmorillonite and humic acid but not ton iron oxide. Sorption Kd on montmorillonite increased when pH was decreased, suggesting protonation of the imidazol ring. Sorption on binary and ternary associations of the model sorbents also indicated that OC is the most important single component affecting sorption, although there is was a contribution of the mineral surfaces. Sorption-desorption of metabolites imidacloprid-urea, imidacloprid-guanidine, and imidacloprid- guanidine-olefin was determinded. Isotherms slopes (1/n) were less than 1. The order of sorption was imidacloprid-guanidine, more than imidacloprid- guanidine-olefin, more than imidcloprid-urea. Desorption was hysteretic with greatest hysteresis for imidacloprid-guanidine and imidacloprid- guanidine-olefin.