Role of Organic Matter and Sesquioxides in the Adsorption of Pesticides on Soils

The adsorption of methyl parathion, fenitrothion, carbaryl and diuron was studied on five soils (untreated) and compared with the adsorption on same soils after removal of organic matter and sesquioxides. Isotherms were characterized by Freundlich constant (K) and distribution coefficient (K_d). Simple correlation between Kvalues and soil properties showed that adsorption of pesticides are Significantly related to organic matter, except for sumithion where clay content governs the adsorption of untreated soils. Adsorption for the same soils freed from organic matter and free sesquioxides were mainly controlled by clay content. The adsorption of pesticides by untreated and treated soils were essentially surface phenomenon. The adsorption is temperature-dependent and is exothermic in nature.