Adsorption, desorption, and degradation of three pesticides in different soils

Abstract

Adsorption, desorption, and degradation of two herbicides (metolachlor and pendimethalin) and a nematicide (cadusafos) were evaluated under laboratory conditions with six soils (ferralsol, regosol, andosol, fluvisol, and two vertisols), selected in a tropical zone (Martinique, French West Indies) and in the Mediterranean area (Languedoc, South of France). Adsorption parameters were calculated using the Freundlich equation, and desorption parameters were evaluated using a 2-compartment model corresponding to two different energy levels. Degradation rate was calculated with a first order equation. Combining values of Koc and half-life in soil, an estimation of the mobility of these pesticides in the soil was made using GUS (ground water ubiquity score). Consideration of pesticide adsorption and resistance to desorption allowed classification of these three compounds according to their mobility: pendimethalin ferralsol > regosol > andosol > fluvisol. Clay or sand content (and cation exchange capacity) of the soils clearly affected adsorption-desorption parameters. The degradation study in the six soils did not show significant differences, but revealed the influence of temperature. GUS values indicated that pendimethalin could be considered as a non-leacher compound, and that cadusafos and metolachlor exhibit a moderate tendency to leaching.