|
(098) Retention and Mobility of Isoxaflutole and Its Derivatives in Soil. Beltran, Estelle1, Fenet, Hélène1, Roig, Maxime1, Cooper, Jean François1, Coste, Camille Michel2, 1 2 ABSTRACT- Isoxaflutole (IFT) is a new herbicide developed by Aventis and used on maize. In water, plants and soil IFT is rapidly converted into a diketonitrile derivative (DKN), which is the active principle of the herbicide. Further degradation of DKN into an inactive benzoic acid derivative (BA) has also been reported. Adsorption-desorption studies of the three molecules taken separately were conducted in nine soils varying in physical and chemical properties, using a batch equilibration method. Concentrations ranged from 1 to 50 mg l-1 ; after four hours of contact the supernatant was removed. For the highest concentration studied, the supernatant was replaced with 5 ml 0.01M CaCl2 and four further desorptions were carried out in succession. The adsorption isotherms fitted the Freundlich model. The Freundlich adsorption coefficient Kfa was always higher for IFT than for its derivatives, and increased as a function of organic matter content. The soil pH had an effect on the rate of the chemical degradation of IFT into DKN during the adsorption-desorption experiments. Because the active principle is weakly retained on the soil surface, it seemed interesting to correlate the retention process with mobility under plain field conditions. A plot of 170 m2 was treated with Merlin® formulation at a dose corresponding to 141.2 g of IFT per ha and soil was regularly sampled at 0-10 cm and 10-20 cm depths. The degradation of IFT into DKN appeared to occur rapidly in the 0-10 cm layer, following first order kinetics. After strong rainfall, the conversion IFT/DKN increased and both molecules migrated to the 10-20 cm layer. Because of the low quantity of IFT applied, the derivative BA could be detected but not quantified. Key words: Isoxaflutole, Adsorption-Desorption, Freundlich, Mobility |
