Adsorption considerations of dichlorvos in farm soils from the pampa plain (Argentina): Kinetics and equilibrium studies

Abstract

In agricultural areas, the soils are the principal environmental fate of phytosanitary products. Here, the kinetics, extension, and strength of the adsorption processes become critical to understanding and predicting the potential pollution risk of water resources. Dichlorvos (DDVP) is an organophosphorous pesticide widely used in agriculture and livestock production systems. In this work, the adsorption behavior of DDVP was evaluated in three agricultural soils from the Pampa Plain (Argentina) with 1.15 (S1), 2.79 (S2), and 3.12 (S3) organic matter content. Sorption and desorption assays of DDVP were performed in batch systems to estimate kinetics and equilibrium parameters. Kinetics results indicated that the adsorption takes place over a long time (nearly 30 hours). Adsorption rate is mainly determined by intraparticle diffusion and follows a pseudo-first-order law. Data from equilibrium studies were satisfactorily fitted to the Freundlich equation, yielding adsorption constants ranging from 21-218 mg(1-1/n) mL(1/n) g-1. Organic carbon content does not fully explain the observed differences. Desorption Freundlich constants were higher than the adsorption ones (120 to 1587 mg(1-1/n)mL(1-1/n)g-1), indicating that the process was irreversible. Thus, from equilibrium data could be stated that DDVP mobility in soils is low. However, kinetics assays showed a long time required for adsorption reaction. In conclusion, in a real scenario, the mobility could be higher than that estimated based only on equilibrium considerations. More studies are necessary to address the relevance of kinetic parameters in leachability events.