Occurrence of Cotton Herbicides and Insecticides in Playa Lakes of the High Plains of West Texas

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Abstract

During the summer of 1997, water samples were collected and analyzed for pesticides from 32 playa lakes of the High Plains that receive drainage from both cotton and corn agriculture in West Texas. The major cotton herbicides detected in the water samples were diuron, fluometuron, metolachlor, norflurazon, and prometryn. Atrazine and propazine, corn and sorghum herbicides, also were routinely detected in samples from the playa lakes. Furthermore, the metabolites of all the herbicides studied were found in the playa-lake samples. In some cases, the concentration of metabolites was equal to or exceeded the concentration of the parent compound. The types of metabolites detected suggested that the parent compounds had been transported to and had undergone degradation in the playa lakes. The types of metabolites and the ratio of metabolites to parent compounds may be useful in indicating the time that the herbicides were transported to the playa lakes. The median concentration of total herbicides was 7.2 micrograms per liter, with the largest total concentrations exceeding 30 micrograms per liter. Organophosphate insecticides were detected in only one water sample. Further work will improve the understanding of the fate of these compounds in the playa lakes area.

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Thurman, E.M., Bastian, K.C., and Mollhagen, Tony, 1999, Occurrence of cotton herbicides and insecticides in playa lakes of the High Plains of West Texas, in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the technical meeting, Charleston, South Carolina, March 8-12, 1999, volume 2 of 3--Contamination of hydrologic systems and related ecosystems: U.S. Geological Survey Water-Resources Investigations Report 99-4018B, p. 227-236.

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