INFLUENCE OF DIFFERENT FACTORS ON THE ADSORPTION OF CARBOFURAN (2,3-DIHYDRO-2,2-DIMETHYL-7-BENZOFURANYL-N-METHYL CARBAMATE) ON SOILS

The effects of exchangeable cations (H+ and Na+), autoclaving, organic matter, cationic and anionic surfactants, and temperature on the adso rption of carbofuran on two different types of soils were studied. The adsorption isotherms for all effects/treatments were in close agreeme nt with the Freundlich equation and yielded S-shaped isotherms. The am ount of carbofuran adsorbed in all cases was higher in Jhansi red loam soil than in Pilibhit sandy loam soil and was related to organic matt er content, clay content, CaCO3 content, surface area, and cation-exch ange capacity of the soils. The adsorption on soils from both sites fo llows the order H soil --> Na soil --> natural soil at 25 degrees C -- > autoclaved soil --> soil from which organic matter had been removed --> cationic surfactant --> anionic surfactant --> natural soil at 50 degrees C and was in accordance with Freundlich constant K values and distribution coefficient K-d values. The adsorptive capacity of carbof uran for organic matter and clay content for bath the Jhansi and the P ilibhit soils was also evaluated by calculating K-om and K-c values, a nd it was found that the carbofuran adsorption was better correlated w ith clay content than with Organic matter content of soils. On the bas is of adsorption isotherms, various thermodynamic parameters such as t he thermodynamic equilibrium constant K-o, standard free energy (Delta G degrees) changes, standard ethalpy (Delta H degrees) changes, and s tandard entropy (Delta S degrees) changes have been calculated in orde r to predict the nature of isotherms. (C) 1994 Academic Press, Inc.