MECHANISM OF THIFENSULFURON-METHYL TRANSFORMATION IN SOIL

Thifensulfuron-methyl [methyl ,3,5-triazin-2-yl)amino]carbonyl]amino]s ulfonyl]-2 thiophenecarboxylate] degrades rapidly in a diverse range o f agricultural soils. The transformation rates of thifensulfuron-methy l in two different soils were found to increase with temperature, howe ver, no linear relationship (Arrhenius relation) was found in the rang e 20-65 degrees C. Thifensulfuron was the sole transformation product formed at 20 degrees C during the first week of this study. Different transformation products were formed at the upper levels of the tempera ture range, corresponding to both chemical and biological processes. T hifensulfuron-methyl was not transformed in a soil suspension with a w ater/soil ratio of 10. A linear relationship between the half-life and this water/soil ratio was found. The transformation rate increased vi ith thifensulfuron-methyl concentration, and the relation between the initial. velocity and the thifensulfuron-methyl concentration was well fitted with the Michaelis-Menten equation. These different results we re in accordance with an enzymatic deesterification of thifensulfuron- methyl in soils.