Gaseous Deposition Contributes to the Contamination of Surface Waters by Pesticides Close to Treated Fields. A Process-Based Model Study

The contribution of atmospheric pathways to surface waters contamination by pesticides has been demonstrated. At the local scale, modeling approaches as well as measurements show situations where the contribution of gaseous dry deposition is of the same order or even higher than the drift contribution. The approach presented here consists in estimating the gaseous emissions of pesticides applied in the field, their atmospheric dispersion, and finally their gaseous deposition into aquatic ecosystems at the local scale by running process-based models, that is, the one-dimensional model for pesticide volatilization following application on bare soil (Volt' Air) and the local-scale dispersion and deposition model (FIDES-2D), adapted for pesticides. A significant number of scenarios describes contrasted situations in terms of pedoclimatic conditions (covering 9 years of meteorological data), periods of pesticide application per year, physicochemical properties of the pesticides, and spatial configurations. The identification of the main factors governing gaseous deposition led to the definition of an effective emission factor which explains a large part of the deposition variability. Based on the model outputs, deposition curves are proposed, as a base for a new tool to assess the contribution of gaseous deposition to nontarget ecosystem contamination.