Endosulfan adsorption on soils in soil-water suspensions containing cationic, non-ionic and anionic surfactants

The adsorption of endosulfan in aqueous surfactant-free and surfactant (cationic, nonionic and anionic) solutions of different critical micelle concentrations (½ x CMC, CMC and 2 x CMC) on three different Indian soils varying in physico-chemical and mineralogical composition has been studied using batch shake technique. The measured equilibrium adsorption isotherms for surfactant-free and surfactant/soil/water systems at different critical micellar concentrations were Sshaped and in close agreement to the Freundlich isotherms. Highest adsorption of endosulfan in both systems was observed on silt loam soil followed by loam and sandy loam soils, and could be anticipated with Freundlich constant, K_F and partition coefficients, K_D values. The obtained values of K_F and K_D also confirmed that the adsorption of endosulfan in aqueous surfactant solutions followed the order cationic > non-ionic > anionic at all the CMCs values studied. The affinity of endosulfan towards organic matter and the clay content of the soils was evaluated by calculating the K_om and K_C values when it was found that endosulfan adsorption was better correlated with the clay content than with the organic matter content. The predicted log K_om values were also calculated by using aqueous solubility, 1-octanol/water partition coefficient (Kow), adsorbability index (AI) and first-order molecular connectivity index (1χ) of endosulfan. Use of 1-octanol/water partition coefficient (Kow) of endosulfan to predict adsorption gave values with considerable error in comparison with those measured experimentally, whereas the use of aqueous solubility, adsorbability index and the first order molecular connectivity index of endosulfan improved the predictions considerably. The results obtained are interesting in that they afford basic data relating to the possible use of surfactants for solving problems of soil contamination posed by endosulfan.