Modelling pesticides residues

This work is a contribution to the development of a specific method to assess the presence of residues in agricultural commodities. The following objectives are formulated: to identify and describe main processes in environment — plant exchanges, to build of a model to assess the residue concentration at harvest in agricultural commodities, to understand the functioning of the modelled system, to characterise pesticides used in field crops and identify optimisation potentials in phytosanitary measures. The frame for the methodological developments corresponds to the procedure for the evaluation of the toxicity provided for the Life Cycle Impact Assessment methodology and for the method Impact 2002+. In chapter 2, the methodological procedure for the assessment of human toxicity potential is introduced. First the factors of fate and exposure are described, including the notion of harvest fraction, the amount of substance found in harvest per unit of substance emitted initially in the system, the main result of the present study. Then the effect factors and the framework for impact evaluation are introduced. Chapter 3 describes the principles accounted for the building of the fate model. Wheat crop and a restricted list of substances are chosen for these methodological developments. The model is composed by compartments describing the environment and the plant. Its functioning is based on initial amounts of substance in the source compartments, on transfer rates linking the compartments and on a dynamic evolution as a function of time between the treatment and the harvest. Air, soil and formulation deposit on plant are the primer compartments receiving the treated substance. Each transport is described by a transfer rate accounting for the process and for the equilibrium partitioning between the two exchanging compartments. Degradation of substance and plant growth are additional processes considered. Each compartment is described by a linear differential equation for the variation of mass accumulating and dissipating. Their assembly builds the model solved as a function of time. This exact resolution is complemented by additional tools to better understand the system functioning and to provide further approximations of the results: the system is simplified into subsystems describing the source and the receiving plant compartment and analytically solved using interpretable equations. Chapter 4 describes and discusses all transport and dissipation processes determining the fate of the substance in the limits of the system. The recent publications concerning the understanding and the modelling of pesticide transfer from formulation deposit on plant through the cuticular membranes give new possibilities to model pesticide fate and to better account for the direct applications on the plant. In chapter 5, the core model is first applied and its functioning analysed. The low availability and partly unsatisfying quality of data for pesticides description