Degradation of Imazosulfuron in Flooded Soils

Abstract

Degradation of imazosulfuron, 1-(2-chloroimidazo [1,2-a]pyridin-3-ylsulfonyl)-3-(4,6- dimethoxypyrimidin-2-yl)urea, in the flooded soils was studied under laboratory conditions using the compounds labeled with 14 C at imidazopyridine and pyrimidine rings. Imazosulfuron showed significant difference in degradation rates between aerobic and anaerobic conditions, and disappeared from the soils with half-lives of approximately 60 and 3 days, respectively. Imazosulfuron was subjected to the cleavage of sulfonylurea bond and monodemethylation to give 2-amino-4,6-dimethoxypyrimidine (ADPM), 2- chloroimidazo [1,2-α] pyridine-3-sulfonamide (IPSN) and 1-(2-chloroimidazo [1,2-α] pyridin-3- ylsulfonyl)-3-(4-hydroxy-6-methoxypyrimidin-2-yl)urea (HMS) as the major degradation products. 14 C- carbon dioxide gradually increased with time accounting for 11.0-48.3% and 1.6-4.4% under aerobic and anaerobic conditions, respectively, for the period of 360 days. In the sterilized soils under aerobic and anaerobic conditions 30 days after the treatment, the degradation rate of imazosulfuron and amounts of degradation products except for HMS were similar to those observed in nonsterilized soils under aerobic conditions 30 days after the treatment. Imazosulfuron in the soils under aerobic conditions gradually disappeared with time by the hydrolysis of the sulfonylurea bond to give ADPM and IPSN, and finally mineralized to carbon dioxide. On the other hand, imazosulfuron under anaerobic conditions was degraded by soil microorganisms, followed by conversion to soil organic matters.