Etude du comportement physico-chimique de quelques sulfonylurees dans le sol.

Triasulfuron, a component belonging to the new class of sulfonylurea herbicides, is used in cereal crops to control dicotyledon weeds. Its acid properties (pKa = 4.5) reduced application dosage (15 g of a.i/ha) led us to study its behaviour in the soil, namely the adsorption, availability and chemical persistence phenomena. Results have shown that the adsorption and the availability are conditioned by the soil pH and not by its organic carbon content. The lower pH in the soil, more of the triasulfuron is adsorbed and consequently less available. This component could show a higher leaching potential in the soils with alkaline reaction than in those with acid reaction. The study of the chemical persistence of triasulfuron has required the development of an analytical method. This consists in extracting the active ingredient by shaking the soil samples in acetone. A clean up of the extracts through chromatography, successively on florisil and silicagel columns followed by a liquid:liquid partition at pH 5, leads to its quantification by capillary chromatography. This method is easier, and less expensive than those developed by CIBA and adapted to the metabolite CGA195663 of trisulfuron and to other sulfonylurea like chlorsulfuron and metsulfuron-methyl. Gas chromatography-Mass spectrometry has shown that those components are split on the chromatographic column. Only the aminotriazine part (H2N-R2) is identified. This part constitutes a triasulfuron metabolise, the CGA150829. This method leads to the combined evaluation of the initial molecule and two of its metabolites: CGA 195663 and CGA 150829. This analytical method has been applied to the study of the chemical persistence of triasulfuron under field conditions and controlled laboratory conditions in soils and in soil extracts. Results show that the modification of triasulfuron in not detected in the soil solution. However this splitting could be closely linked to the soil matrix.