Enhanced desorption of herbicides sorbed on soils by addition of Triton X-100.

A study of the desorption of atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine) and linuron [1-methoxy-1-methyl-3-(3,4-dichlorophenyl)urea] adsorbed on soils with different organic matter (OM) and clay contents was conducted in water and in the presence of the non-ionic surfactant Triton X-100 at different concentrations. The aim was to gain insight into soil characteristics in surfactant-enhanced desorption of herbicides from soils. Adsorption and desorption isotherms in water, in all Triton X-100 solutions for atrazine, and in solutions of 0.75 times the critical micelle concentration (cmc) and 1.50cmc for linuron fit the Freundlich equation. All desorption isotherms showed hysteresis. Hysteresis coefficients decreased for linuron and increased or decreased for atrazine in Triton X-100 solutions. These variations were dependent on surfactant concentration and soil OM and clay contents. In the soil-water-surfactant system desorption of linuron from all soils was always greater than in the soil-water system but for atrazine this only occurred at concentrations higher than 50cmc. For the highest Triton X-100 concentration (100cmc), the desorption of the most hydrophobic herbicide (linuron) was increased more than 18-fold with respect to water in soil with an OM content of 10.3% while the atrazine desorption was increased 3-fold. The effect of Triton X-100 on the desorption of both herbicides was very low in soil with a high clay content. The results indicate the potential use of Triton X-100 to facilitate the desorption of these herbicides from soil to the water-surfactant system. They also contribute to better understanding of the interactions of different molecules and surfaces in the complex soil-herbicide-water surfactant system.