Chemical degradation
Bensulfuron methyl hydrolysed rapidly at pH 5 (DT50 of 11 days) but slowly at pH 7 and 9 at 25 ¡ãC (DT50 >150 days).
Cleavage of the sulfonylurea linkage was the primary hydrolytic degradation pathway, yielding methyl 2-(aminosulfonylmethyl)benzoate and 4,6-dimethoxy-2-aminopyrimidine.
Bensulfuron methyl was stable to direct photolysis in sterile buffer solutions, but degraded rapidly via cleavage of the sulfonylurea Sulfonylureas linkage in natural water under sunlight to methyl 2-(sulfomethyl)benzoate and (4,6-dimethoxypyrimidin2-yl)urea, with a DT50 of 3¨C4 days.
Degradation in soils
In moist field soils, bensulfuron methyl was degraded via chemical hydrolytic degradation and microbial processes, with a DT50 of 3¨C4 weeks.
Compounds 2, 3, and 6 [1H-2,3-benzothiazin-4(3H)-one 2,2-dioxide] and CO2 were detected. Similar degradation products were also generated in flooded aerobic and anaerobic water¨Csediment systems.
Metabolism in plants
Plant metabolism studies were conducted with Indica , Japonica, and Samgang rice cultivars, as well as the weed Cyperus serotinus.The crop selectivity of bensulfuron methyl was due to a slower rate of translocation from roots to shoots in tolerant rice and, more importantly, an increased rate of metabolism in rice vs. weed species. For example, excised rice shoots metabolised bensulfuron methyl with a DT50 of 4¨C6 hours while sensitive broad-leaved and sedge weeds did not appreciably degrade bensulfuron methyl (DT50 >50 hours). A moderately sensitive weed (Echinochloa crus-galli) metabolised bensulfuron methyl at an increased rate (DT50 12 hours).Metabolism appeared to proceed initially through O-demethylation of the pyrimidine ring to yield 8 and the hydrolysis of the parent methyl ester to produce bensulfuron (9). Terminal metabolites included cleavage products 2, 3, 6, and unextractable 14C-residues. Usui et al. observed a similar metabolic profile for bensulfuron methyl in both normal and tolerant carrot suspension-cultured cells to yield 2, 6 and 8 as primary products.Metabolism in animals In mammals (rats and goats), bensulfuron methyl was metabolised and rapidly eliminated. The primary metabolic pathway included hydroxylation and O-demethylation yielding compounds 7 and 8, respectively.
Metabolism in animals
In mammals (rats and goats), bensulfuron methyl was metabolised and rapidly eliminated. The primary metabolic pathway included hydroxylation and O-demethylation yielding compounds 7 and 8, respectively. Compound 10 (5-hydroxy-4,6-dimethyoxy-2-aminopyrimidine),from the cleavage of the sulfonylurea linkage, was also observed as a major metabolite in rats. Cleavage and hydrolysis products such as 2, 3,5, and 6 were observed as minor metabolites. Several minor, uniquemetabolites were also isolated from the chicken excreta. These metabolites were ring-opened products resulting from demethylation,oxidation, decarboxylation, and hydrolysis reactions via an intermediate.No significant bensulfuron methylequivalent residues were detected in the animal tissues, milk and eggs.
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