Movement of Dichlorvos in Farm Soils: Batch and Column Studies.

Abstract Soils are the principal environmental fate of pesticides in agricultural areas. Thus, the kinetics, extension, and strength of the adsorption process become critical. Dichlorvos (DDVP) is an organophosphorous pesticide that is used both in agriculture and livestock production. Sorption/desorption assays of DDVP in two agricultural soils (with different textural characteristics) from Pampa Plain (Argentina) were performed in both batch and column systems. From batch studies, kinetics and sorption/desorption equilibrium parameters were estimated. Our results showed that the maxima adsorption is reached after 30 h of time of contact and followed a pseudo-first-order rate. Adsorption/desorption data were well fitted to the Freundlich model obtaining high adsorption constants of 90 mg(1-1/n) mL(1/n) g-1 and 21 mg(1-1/n) mL(1/n) g-1 for the clay loam and sandy loam soil, respectively. The isotherms were non-linear in both cases and the desorption process was unfavourable. Also, positive hysteresis was present for the sandy loam soil. From column studies, breakthrough curves were used to evaluate the mobility of DDVP in the soils at 1, 10, and 50 mg L-1 of DDVP. Eluted profiles were asymmetrical as well they presented retardation effects that were in connection with the results in batch conditions. Non-equilibrium sorption was stated for the DDVP movement through columns. Thus, high mobility was observed for DDVP in both soils despite their textural differences.