DEGRADATION OF THIFENSULFURON METHYL IN SOIL - ROLE OF MICROBIAL CARBOXYESTERASE ACTIVITY

Thifensulfuron methyl [methyl ]carbonyl]amino]-sulfonyl]-2-thiopheneca rboxylate] degrades rapidly in diverse nonsterile agricultural soils. The initial degradation product of thifensulfuron methyl in nonsterile sails is its deesterified derivative, thifensulfuron acid, which is h erbicidally inactive. Rapid deesterification of thifensulfuron methyl is eliminated by heat sterilization of soil but only moderately reduce d by sterilization with ethylene oxide. Deesterification is inhibited in both nonsterile and ethylene oxide-sterilized soils by iodoacetamid e and specific organophosphorus insecticides. Several actinomycetes an d bacteria were isolated from soils which could readily deesterify thi fensulfuron methyl in pure culture. Cell-free (sterile) culture filtra tes of two actinomycetes also catalyzed the deesterification of this h erbicide. We conclude that the rapid deesterification of thifensulfuro n methyl results, at least in part, from the activity of microbial ext racellular carboxyesterase activity.