Evaluation of Soil Adsorption-Desorption Capacity for the Assessment of Pesticide Bioavailability

Adsorption is probably the most important form of interaction between pesticides and the soil, since it governs the amount of active substance available. Understanding of the extent and the mechanisms of adsorption of pesticides is an indispensable premise to any type of evaluation of the efficacy of their active principles and their possible impact on the environment. Laboratory studies of the adsorption and desorption of pesticides enable forecasts to be made of their behaviour in the field when the features of the soils on which they are to be applied are known. Tests can be carried out on whole soils or purified fractions: in the first case, the contribution of each adsorbent phase can only be evaluated by determining the correlations between the extent of adsorption and the chemical and physical properties of the soil. Pesticides can be adsorbed on a soil through variously strong physicochemical bonds. The type and degree of adsorption and also the extent to which it is reversible will depend on the properties of both the soil and the pesticide.