Evaluation of effect of Surfactants on the Movement of Synthetic Pyrethroids in Soils using a Soil Thin-layer Chromatography Technique

The effect of different critical micelle concentrations (1/2 CMC, at CMC and 2 x CMC) of surfactants, cetyl trimethyl ammonium bromide (cationic), sodium dodecyl sulphate (anionic) and Tween’20’ (nonionic) on the movement of synthetic pyrethroids (cypermethrin, deltamethrin and fenvalerate) in soils by using a soil thin - layer chromatographic technique is reported. The penetrability K increased by decreasing the plate angle and followed the order: sandy loam>loam>silt loam soil. The penetrability K also decreased in surfactant free and surfactant ammended soils, when developed in aqueous surfactant solutions of soil followed by loam and silt loam soils. On the basis of R_f values, the movement of pyrethroids followed the order: fenvalerate > cypermethrin > deltamethrin, both in surfactant ammended and surfactant free soils, when developed in distilled water and aqueous surfactant solutions of different CMCs. The movement was directly proportional to the aqueous solubilities, and inversely to the polarities of pyrethroids. Adsorption of pyrethroids on soils, chemical nature of the surfactants and their concentrations in terms of critical micelle concentrations (CMCs) in soils and eluents influenced the movement.