The soil degradation of the herbicide florasulam

The route and rate of degradation of florasulam, a low-rate triazolopyrimidine sulfonanilide herbicide, was investigated in six soil types under aerobic conditions at 20 or 25 °C. Degradation products were isolated and identified by mass spectroscopy. Florasulam was rapidly degraded by microbial action with an average half-life of 2.4 days (range 0.7 to 4.5 days). The first step in the degradation pathway involved conversion of the methoxy group on the triazolopyrimidine ring to a hydroxy group to form N-(2,6-difluorophenyl)-8-fluoro-5-hydroxy[1,2,4]triazolo[1,5-c]pyrimidine-2-sulfonamide. This metabolite degraded, with a half-life of 10 to 61 days, via partial breakdown of the triazolopyrimidine ring to form N-(2,6-difluorophenyl)-5-aminosulfonyl-1H-1,2,4-triazole-3-carboxylic acid. This was followed by cleavage of the sulfonamide bridge to form 5-(aminosulfonyl)-1H-1,2,4-triazole-3-carboxylic acid. Other degradation processes involved decarboxylation of the carboxylic acid metabolites and mineralisation to form carbon dioxide and non-extractable residues.