Translocation and degradation of pyrazosulfuron‐ethyl in rice soil

Abstract

Pyrazosulfuron-ethyl {ethyl 5-[(4,6-dimethoxypyrimidin-2-ylcarbamoyl)-sulfamoyl]-1-methylpyrazole-4-carboxylate} is a new rice herbicide belonging to the sulfonylurea group. This study reports the translocation of (14)C-pyrazosulfuron-ethyl to rice plants and its degradation in rice-planted and unplanted soil. Pyrazosulfuron-ethyl did not show any appreciable translocation to rice shoots, as (14)C-activity translocated to the aerial portion never exceeded 1% of the initially applied (14)C-activity over a 25 day period. Results suggested that the dissipation of pyrazosulfuron-ethyl from soils followed first-order kinetics with a half-life of 5.5 and 6.9 days in rice-planted and unplanted soils respectively. HPLC analysis of the organic extract of soil samples showed the formation of three metabolites, namely ethyl 5-(aminosulfonyl)-1-methyl-1-H-pyrazole-4-carboxylate, 5-[({[(4,6-dimethoxy-2 pyrimidinyl)-amino]-carbonyl} amino)-sulfonyl]-1-methyl-1H-pyrazole-4-carboxylic acid and 2-amino-4,6-dimethoxy pyrimidine, in both rice-planted and unplanted soils. The study indicates that pyrazosulfuron-ethyl was a short-lived compound in the soil and was degraded relatively faster in rice-planted soil than in unplanted soil. The herbicide did not show any appreciable translocation to rice plants.