Evaluation of component characteristics of soil-surfactant-herbicide system that affect enhanced desorption of linuron and atrazine preadsorbed by soils

The aim of the present work was to evaluate the surfactant-enhanced desorption of atrazine and linuron preadsorbed by soils and to study the effect of different characteristics of the components of soil-surfactant-herbicide systems on the efficiency of desorption. Two soils with organic matter contents of 3.16% and 7.28% and 11 surfactants, three of them anionic (SDS, LAS, and SDOSS) and 8 of them nonionic (Tween 80, Tween 20, Triton X-100, Triton X-114, Brij 35, Brij 30, Tergitol NP-10, and Tergitol 15S12), at concentrations 1.5 and 10 times the critical micellar concentration (cmc) were used. Adsorption-desorption studies were performed using a batch system, and the Freundlich model was applied to the isotherms except for some cases in which this was not possible. The desorption isotherms of both pesticides in aqueous medium pointed to the existence of hysteresis. The values of the hysteresis coefficients of the adsorption isotherms in water decreased in some cases while in others they increased in the presence of the surfactants, depending on the structure of these and on their concentration in water, on the organic matter content of the soil, and on the K(ow) of the herbicide. Parallel to the decrease in hysteresis, the percentage of herbicide desorption and desorption efficiency coefficient (E; ratio between the percentages of herbicide desorption in the presence of surfactant and those found in aqueous medium) increased. For a 10 cmc surfactant concentration, a linear relationship was seen between the E values and the absolute values of the cmc of the surfactants. Also, for the same surfactant, a linear relationship was seen between log E and the log of the absolute concentrations of surfactant in solution. The results obtained are of practical interest for the choice of surfactants for concrete problems involved in the recovery of pesticide-polluted waters using the surfactant-enhanced desorption pumping technique.