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Adsorption and Movement of Cypermethrin on Indian Soils Amended with Cationic, Non-Ionic and Anionic Surfactants

Laboratory studies were conducted to determine the adsorption and movement of cypermethrin on surfactant-free (natural) and surfactant-amended soils at different micelle concentrations (below the CMC, at the CMC and above the CMC) using batch equilibrium and soil TLC techniques. The measured equilibrium adsorption isotherms for both surfactant-free and surfactant-amended soils were of type C and in close agreement with the Freundlich isotherm. Higher adsorption of cypermethrin in both types of system was observed on silt loam soil than on sandy loam soil as anticipated by the values obtained for the Freundlich constant, KF, and the partition coefficient, KD. The values of KF and KD confirmed that cypermethrin adsorption on surfactant-amended soils followed the order cationic > non-ionic > anionic under all CMC conditions studied. The KF and KD values also confirmed that cypermethrin adsorption was higher on soils amended with surfactants maintained below the CMC, while lower values of KF and KD confirmed the lower adsorption of cypermethrin on soils amended with both non-ionic and anionic surfactants maintained at or above the CMC value relative to the situation with surfactant-free soils. The higher values of KF and KD showed that the adsorption of cypermethrin increased on soils amended with CTAB when the latter was at or above the CMC value relative to surfactant-free soils. The Rf values obtained from soil TLC studies were inversely proportional to the KF and KD values for both surfactant-free and surfactant-amended soils. The affinity of cypermethrin towards the organic carbon and clay content of the soils was evaluated by calculating the Koc and KD values, when it was found that the affinity of cypermethrin was better correlated with the clay content of the soils than with their organic carbon content. The results obtained are interesting in that they afford basic data resulting to the possible use of surfactants for solving problems of soil contamination posed by cypermethrin.