Degradation of Thifensulfuron Methyl in Soil:  Role of Microbial Carboxyesterase Activity

Thifensulfuron methyl [methyl 3-[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]-2-thiophenecarboxylate] degrades rapidly in diverse nonsterile agricultural soils. The initial degradation product of thifensulfuron methyl in nonsterile soils is its deesterified derivative, thifensulfuron acid, which is herbicidally inactive. Rapid deesterification of thifensulfuron methyl is eliminated by heat sterilization of soil but only moderately reduced by sterilization with ethylene oxide. Deesterification is inhibited in both nonsterile and ethylene oxide-sterilized soils by iodoacetamide and specific organophosphorus insecticides. Several actinomycetes and bacteria were isolated from soils which could readily deesterify thifensulfuron methyl in pure culture. Cell-free (sterile) culture filtrates of two actinomycetes also catalyzed the deesterification of this herbicide. We conclude that the rapid deesterification of thifensulfuron methyl results, at least in part, from the activity of microbial extracellular carboxyesterase activity. Keywords: Thifensulfuron methyl; sulfonylurea herbicide; soil enzymes; soil carboxyesterase; biodegradation