Persistence of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, and nicosulfuron in farm dugouts (ponds).

Cessna, A.J., Donald, D.B., Bailey, J., and Waiser, M.J. (2015). "Persistence of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, and nicosulfuron in farm dugouts (ponds).", Journal of Environmental Quality, 44(6), pp. 1948-1955. doi : 10.2134/jeq2014.11.0503  Access to full text

Abstract

Sulfonylurea herbicides are applied at relatively low rates (3–40 g ha−1) to control weeds in a variety of crops grown in the prairie pothole region of south–central Canada. Because of their high phytotoxicity and the likelihood of their transport in surface runoff, there is concern about impacts of sulfonylurea herbicides to wetland ecosystems embedded in agricultural landscapes. In a previous study, dissipation half-lives (DT50 values) were determined for three sulfonylurea herbicides (thifensulfuron-methyl, ethametsulfuron-methyl, and metsulfuron-methyl), each possessing a hydrolyzable methyl ester linkage. In the current study, persistence of three sulfonylurea herbicides without a methyl ester linkage was determined in prairie farm dugouts (ponds). The dugouts were fortified with environmentally relevant concentrations (3.3–6.5 μg L−1) of either sulfosulfuron, rimsulfuron, or nicosulfuron. The order of persistence of these herbicides in dugout water from May and June to November and December was nicosulfuron > sulfosulfuron > rimsulfuron, with DT50 values of 75, 44, and 10 d, respectively. The lack of a methyl ester linkage in these herbicides did not significantly affect their overall persistence relative to those with the ester linkage. In all three dugouts, the decrease in herbicide mass in the water column from water loss via hydrological discharge to groundwater was minimal. The relatively long persistence of these herbicides in the water column of the dugouts reflects the stability of the sulfonylurea linkage to hydrolysis in weakly alkaline waters and indicates not only that microbial and photolytic degradation were low but also that there was little partitioning into sediments. Core Ideas: • Farm dugouts were fortified at environmentally relevant concentrations. • Herbicides did not contain a methyl ester moiety, so no ester hydrolysis. • Herbicide and chloride ion concentrations were monitored from spring until ice cover. • Chloride ion concentrations were used to normalize herbicide concentrations. • Chloride ion mass was used to determine herbicide loss via hydrologic discharge.

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