Effect of Tween80 and β-cyclodextrin on the distribution of herbicide mefenacet in soil-water system

The effect of two solubilizers, Tween80 and beta-cyclodextrin (BCD) on the distribution of herbicide mefenacet (MF) in soil-water system was investigated. The results indicated that in the absence of Tween80 and BCD, the adsorption of MF on the natural soils fitted well with the Freundlich model and the K-f values were positively related to organic carbon content in the soils. The K-oc values were in the ranges of 52.7-606.6 L kg(-1). Desorption of MF from the soils was irreversible and positive hysteresis was observed in all the cases. In addition, it was found that the solubility of MF in aqueous phase could be enhanced greatly in the presence of Tween80 and BCD. The adsorption isotherms of Tween80 were fitted well with the linear Langmuir sorption model, and that of BCD fitted well with linear adsorption model. Moreover, it was also observed that the presence of proper concentration of Tween80 and BCD can enhance the transfer of MF from soil phase to aqueous phase. Although BCD presented more adsorption loss than Tween80, a carbon-normalized model suggested the adsorbed BCD had a weaker affinity for MF than the adsorbed Tween80, and experiment results showed the BCD could be a more effective solvent for desorption of MF compared with Tween80. The present study indicated that Tween80 and BCD had great potential in the area of ex situ enhanced soil remediation especially that based on full dynamic mixed model. (C) 2010 Elsevier B.V. All rights reserved.