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The occurrence of pesticides at 13 fixed-interval stream sites in the upper Tennessee River Basin was investigated as part of the U.S. Geological Survey National Water-Quality Assessment Program. These sites, sampled at regular intervals (usually monthly), were located in seven major watersheds of the upper Tennessee River Basin in eastern Tennessee and southwestern Virginia, which consists predominantly of agricultural and forested land use with minor urban and residential influences. Three of the sites with the highest amount of agricultural land use were sampled weekly for 7 months during the 1996 growing season.
The most frequently and heavily used herbicides were among the most frequently detected pesticides in the basin. A total of 367 surface-water samples were collected at the 13 fixed-interval sites, and a total of 31 different pesticide compounds were detected. Atrazine was detected in 93 percent of the samples, and deethylatrazine (a degradation product of atrazine) was detected in 90 percent of the samples. Metolachlor and simazine were detected in 64 and 43 percent of samples, respectively. Tebuthiuron and prometon, which are commonly used in noncropland areas, were detected in 61 and 30 percent of the samples, respectively. The most frequently detected insecticides were diazinon (13 percent), carbaryl (10 percent), and chlorpyrifos (9 percent).
Pesticide concentrations varied seasonally and were related to land use. The highest pesticide concentrations occurred in the agricultural basins in late spring and early summer, generally coinciding with the period of pesticide applications, and with the first substantial storm runoff following pesticide applications. Fifteen of the 31 pesticides detected have criteria established for the protection of aquatic life. Of these 15 pesticides, four pesticides [atrazine (one sample), carbaryl (three samples), diazinon (one sample), and lindane (two samples)] were detected at concentrations that exceeded aquatic-life criteria. These exceedances occurred at only three sampling sites and only two samples represented storm-runoff conditions.
Pesticide detection frequencies for the upper Tennessee River Basin were compared to a summary of pesticide detections compiled by the U.S. Geological Survey from investigations conducted in 20 study units nationwide from 1992 through 1996. Atrazine, deethylatrazine, and tebuthiuron were more frequently detected in the upper Tennessee River Basin study unit in comparison to the national summary of pesticide detections for all sites as well as for sites grouped into agricultural or urban watershed categories. Atrazine and deethylatrazine were detected in about 93 and 90 percent, respectively, of samples in the upper Tennessee River Basin compared to the national average of about 80 and 60 percent, respectively. Tebuthiuron was detected in 61 percent of samples in the upper Tennessee River Basin as opposed to an average of about 20 percent nationwide. Conversely, the herbicides simazine and prometon were detected less frequently in the upper Tennessee River Basin than the national average.
Friday, 13-Apr-01 14:34:11 CST
This abstract can be cited as follows:
Treece, M.W., Jr., 2001, Occurrence of pesticides in the upper Tennessee River Basin, 1995-99 [abs.], in Tennessee Water Resources Symposium, 11th, Burns, Tenn., 2001, Proceedings: Tennessee Section of the American Water Resources Association, p. 2B-28.
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