Received for review March 6, 2006. Revised manuscript received June 15, 2006. Accepted June 16, 2006. This research was supported through a grant (RR00-9) from the California Rice Research Board.

Abstract:

The degradation of penoxsulam {2-(2,2-difluoroethoxy)-N-5,8-dimethoxy[1,2,4]triazolo[1,5-C]pyrimidin-2-yl-6-(trifluoromethyl)benzene-sulfonamide} was studied in flasks simulating flooded rice field conditions using four representative rice field soils from the Sacramento Valley. Degradation half-lives (t_1/2 values) ranged between 2 and 13 days. Increased degradation rates were observed in flask systems with steeper redox gradients between the flooded soil layer and the overlaying water. Two transient metabolites were identified that were temporarily formed in amounts exceeding 5% of the total initial mass of penoxsulam. The results of high-performance liquid chromatography/¹⁴C radiodetection studies indicate that the degradation of the triazolopyrimidine system and its substituents is the main pathway of microbial transformation processes. Microbial activity, as measured by dehydrogenase activity, was not affected by penoxsulam concentrations corresponding to the proposed maximum annual use rate of 40 g active ingredient/ha.

Keywords: Anaerobic transformation; paddy incubation conditions; environmental fate; Granite; triazolopyrimidine sulfonamide; acetolactate synthase inhibitor; metabolic activity

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