Influence of different factors on the adsorption of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl- N-methyl carbamate) on soils

Abstract

The effects of exchangeable cations (H + and Na +), autoclaving, organic matter, cationic and anionic surfactants, and temperature on the adsorption of carbofuran on two different types of soils were studied. The adsorption isotherms for all effects/treatments were in close agreement with the Freundlich equation and yielded S-shaped isotherms. The amount of carbofuran adsorbed in all cases was higher in Jhansi red loam soil than in Pilibhit sandy loam soil and was related to organic matter content, clay content, CaCO 3 content, surface area, and cation-exchange capacity of the soils. The adsorption on soils from both sites follows the order H soil → Na soil → natural soil at 25°C → autoclaved soil → soil from which organic matter had been removed → cationic surfactant → anionic surfactant → natural soil at 50°C and was in accordance with Freundlich constant K values and distribution coefficient K d values. The adsorptive capacity of carbofuran for organic matter and clay content for both the Jhansi and the Pilibhit soils was also evaluated by calculating K om and K c values, and it was found that the carbofuran adsorption was better correlated with clay content than with organic matter content of soils. On the basis of adsorption isotherms, various thermodynamic parameters such as the thermodynamic equilibrium constant K 0, standard free energy ( ΔG°) changes, standard ethalpy ( ΔH°) changes, and standard entropy ( ΔS°) changes have been calculated in order to predict the nature of isotherms.