Abstract
The adsorption of carbofuran in aqueous surfactant-free and surfactant (cationic, non-ionic and anionic) solutions of different micellar concentration (½ × CMC, CMC and 2 × CMC) on three different types of Indian soil has been studied using the batch shaking technique. The measured equilibrium adsorption isotherms for the surfactant-free and surfactant/soil/water systems at different critical micellar concentrations were S-shaped and in close agreement to the Freundlich isotherms. Higher adsorption of carbofuran in both systems was observed on silt loam soil followed by loam and sandy soils, and was anticipated by the values obtained for the Freundlich constant, KF, and the partition coefficient, KD. The values of KF and KD obtained also confirmed that the adsorption of carbofuran in aqueous surfactant solutions followed the order cationic > nonionic > anionic at all the CMC values studied. The affinity of carbofuran towards organic matter and the clay content of the soils was evaluated by calculating the Kom and Kc values, when it was found that carbofuran adsorption was better correlated with the clay content than with the organic matter content. The predicted log Kom values were also obtained from the aqueous solubility, 1-octanol/water partition coefficient (Kow), adsorbability index (Al) and first-order molecular connectivity index (1χ) of carbofuran. Use of the aqueous solubility and the 1-octanol/water partition coefficient of carbofuran to predict the adsorption gave values with a considerable error in comparison with those measured experimentally, whereas the use of the absorbability index and first-order molecular connectivity index for carbofuran 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 by carbofuran.