Sorption Thermodynamics of Cypermethrin at High Concentrations on Some Indian Soils

Sorption thermodynamics of cypermethrin on four different type of Indian soils (alluvial, forest, hill and humid) from water/acetone mixtures (fs = 0.666) at 30°C and 50°C has been investigated through sorption isotherms, Freundlich equation, distribution coefficient and thermodynamic parameters. The measured equilibrium sorption isotherm for all soil-cypermethrin combinations were of non-linear Freundlich type and yielded ‘S’ shaped curves for soils at both temperatures. The sorption of cypermethrin was higher on hill silt loam soil followed by forest loam, alluvial sandy loam and humid loam soils and lower at higher temperature. The order of sorption was anticipated with K and Kd values. Comparison of the Freundlich coefficient K-values in relation to soil properties suggests that organic carbon, CaCO3, clay content and surface area are the most important factors affecting cypermethrin sorption. From Freundlich sorption constant K values, the organic carbon partition coefficient Koc and clay content partition coefficient Ko values were evaluated and found that cypermethrin sorption was better correlated with clay content than the organic carbon content. The thermodynamic equilibrium constant (Ko), standard free energy (δG°), ethalpy (δH°) and entropy (δS°) changes were calculated in order to predict the nature of sorption.