Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2007
Publication Date: 9/20/2007
Citation: Papiernik, S.K., Yates, S.R., Koskinen, W.C., Barber, B. 2007. Processes Affecting the Dissipation of the Herbicide Isoxaflutole and Its Diketonitrile Metabolite in Agricultural Soils under Field Conditions. Journal of Agricultural and Food Chemistry. 55:8630-8639. Interpretive Summary: Isoxaflutole is a relatively new pre-emergence herbicide used in corn production. Isoxaflutole and its breakdown product, DKN, have been detected in groundwater and surface water in the United States. To develop management practices that reduce threat of water contamination by isoxaflutole and DKN, information is required about the rate at which these herbicides disappear from the soil after they are applied. This study was conducted to measure how quickly these herbicides were degraded in the soil, and to what extent they were transported through the soil under typical field conditions in a moist, cool environment. Half of the applied isoxaflutole+DKN disappeared within 8 to 18 days in each of three soils. Herbicide concentrations in soil 100 days after application were usually undetectable. Little or no transport of herbicide beyond 1 m was observed. Simulation modeling using Hydrus-1D for the loam soil suggested that plant uptake was an important mechanism of dissipation. The results of this research support recommendations that plant uptake be accounted for in pesticide dissipation studies. The results of these studies will help guide additional research to quantify the processes affecting pesticide dissipation under field conditions. These results will be useful to federal and state regulatory agencies and pesticide manufacturers when evaluating pesticide labeling requirements and application restrictions.
Technical Abstract: Isoxaflutole is a relatively new pre-emergence herbicide used in corn production. Isoxaflutole's phytotoxic metabolite (DKN) has been detected in groundwater and surface water. Two-year field dissipation studies were conducted in three soil types in Minnesota to examine the processes affecting the dissipation of the herbicide isoxaflutole and its phytotoxic metabolite (DKN) under relatively cool, wet soil conditions. Plots of cuphea (Cuphea viscosissima x C. lanceolata) were treated with isoxaflutole and potassium bromide, a non-sorbed, non-degraded tracer. Replicate soil cores were collected six times during the growing season to a depth of 1 m, and the bromide or herbicide concentration was measured each of five depth increments. The dissipation half-life (DT50) of isoxaflutole+DKN was 8 to 18 days in each soil. Little or no leaching of bromide or herbicide beyond 1 m was observed, and herbicide concentrations in soil 100 d after application were usually undetectable. Simulation modeling using Hydrus-1D for the loam soil suggested that plant uptake was an important mechanism of dissipation. The results of this research support recommendations that plant uptake be accounted for in pesticide dissipation studies.