Pesticides desorption from agricultural soils by organic amendments.

GONZALEZ MARIANA; MIGLIORANZA KARINA SILVIA BEATRIZ; AIZPUN JULIA ELENA; PEÑA ARANZAZU

Marseille, Francia

Simposio; 11th Symposium on Chemistry and Fate of Modern Pesticides and the 5th European Conference on Pesticides and related organic Miropollutants in the Environment,; 2008

 Desorption of a-endosulfan, endosulfan sulfate, p´p´-DDT, p´p´-DDE and a-cypermethrin from agricultural soils was assessed. Soils with different organic carbon content, particle size distribution, and pesticides levels were taken from two typical Argentinean productive systems. Total pesticide residues in soil were 0.63 mg g-1 dry weight for the naturally contaminated soil and 50 mg g-1 for the artificially contaminated soil, where the five compounds were added at an equal initial concentration. The effect of organic carboxylic acids and synthetic surfactants on pesticides desorption from soil was evaluated using batch experiments. Sodium citrate and sodium oxalate were used at levels that are usually exuded by plant roots (0.05 and 0.1M), while solution of Sodium Dodecyl Sulfate (SDS) and Tween 80) were made at 2 and 10 times their critical micelle concentration (CMC). Results showed that desorption of highly hydrophobic compounds such as p´p´-DDT, p´p´-DDE and a-cypermethrin was effectively enhanced by oxalate at the two studied concentrations. Conversely, no effect of citrate or oxalate was observed for the hydrophilic endosulfan with respect to the control (MilliQ water). The non-ionic surfactant Tween 80 behaved similarly to carboxylic acids, while the anionic SDS enhanced pesticide desorption independently of their hydrophobicity.  At the concentrations employed, desorption by surfactants was ca. 5-10 fold higher than that of carboxylic acids. In the artificially contaminated soil the increase of Tween 80 or SDS concentration from 2 to 10 CMC led to a higher desorption rate, while in the naturally contaminated one this was true only for SDS. Results suggest that organic acids and surfactants could be used for soil remediation. However, if these substances occur in irrigation waters, the solubilization of recalcitrant compounds is feasible and leads to a new challenge to face.