Characterization of the clomazone sorption process in four agricultural soils using different kinetic models.

Kinetic studies are important for understanding the parameters and processes involved in the sorption of pesticides to soil. Considering the agricultural and environmental relevance of clomazone, its sorption kinetics was studied in four agricultural soils (Regosol, Planosol, Chernozem and Vertisol) at two concentrations (0.5 and 15 mg L). Different kinetic models were applied to the experimental data. The pseudo-second-order model described the data much better than the hyperbolic and pseudo-first-order models, and the kinetic rate constants indicated concentration-dependent clomazone sorption kinetics. The application of the two-site nonequilibrium model (TSNE) revealed a more time-dependent sorption of the lower clomazone concentration than that of the higher clomazone concentration, and the greatest concentration impact occurred in Regosol. Elovich and intraparticle diffusion models predicted more intensive sorption during the slower second phase and that sorption kinetics is governed more by mass transfer across the boundary layer than by a intraparticle diffusion process at higher clomazone concentration. Intraparticle diffusion is the rate-controlling process in Regosol at lower concentration, while this process and the boundary layer control the sorption kinetics in other soils. Significant correlations between some kinetic parameters and soil properties indicate an impact of the soil texture on the clomazone sorption mechanism, which must be considered in assessing the clomazone leaching behavior.