Effect of Cosolvent (Acetone) on the Adsorption and Movement of Cypermethrin in Indian Soils

Abstract

The adsorption and movement of cypermethrin in different types of uncontaminated soils in acetone-water mixtures at different f_s values has been studied by batch shake and soil thin-layer chromatographic techniques, respectively. Higher adsorption and a reduced movement of cypermethrin was observed on silt clay loam soil followed by loam and sandy loam soils and was anticipated by the Freundlich adsorption constants K^m and R_f values. The K^m and R_f values also confirmed that the adsorption of cypermethrin decreased while its movement increased with increasing f_s values. The values of the Freundlich constant K^m were used to evaluate the cosolvent theory for describing the adsorption of cypermethrin in acetone–water mixtures. For each soil, the values of the adsorption coefficient K^m decreased in a linear logarithmic fashion as f_s increased, the slopes of the log K^m versus f_s plots being essentially the same for all soils. Thus, the cosolvent effects on adsorption could be expressed by a single parameter (σ_s) which combines the characteristics of the solvent (acetone) and the adsorbate (cypermethrin). For adsorbates with a low solubility in aqueous solutions, the adsorption data from mixed solvents was extrapolated to f_s = 0 to estimate the values of the adsorption constant K_w in the aqueous phase.