Mechanism of Thifensulfuron-methyl Transformation in Soil

Abstract

Thifensulfuron-methyl [methyl 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2 thiophenecarboxylate] degrades rapidly in a diverse range of agricultural soils. The transformation rates of thifensulfuron-methyl in two different soils were found to increase with temperature, however, no linear relationship (Arrhenius relation) was found in the range 20−65 °C. Thifensulfuron was the sole transformation product formed at 20 °C during the first week of this study. Different transformation products were formed at the upper levels of the temperature range, corresponding to both chemical and biological processes. Thifensulfuron-methyl was not transformed in a soil suspension with a water/soil ratio of 10. A linear relationship between the half-life and this water/soil ratio was found. The transformation rate increased with 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 were in accordance with an enzymatic deesterification of thifensulfuron-methyl in soils. Keywords: Sulfonylurea herbicide; soil; transformation; metabolite; thifensulfuron-methyl