|Home||Archived January 13, 2017||(i)|
The occurrence of pesticides at 13 stream sampling stations in the upper Tennessee River Basin was investigated as part of the U.S. Geological Survey National Water-Quality Assessment Program. These stations, 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 consist predominantly of agricultural and forested land use with minor urban and residential influences. Three of the stations with the largest 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 stream samples were collected at the 13 stations, and a total of 31 different pesticides were detected. Using a common censoring level of 0.01 micrograms per liter, atrazine was detected in 59 percent of the samples, and deethylatrazine (a metabolite of atrazine) was detected in 31 percent of the samples. Metolachlor and simazine were detected in 24 and 17 percent of samples, respectively. Tebuthiuron and prometon, which are commonly used in noncropland areas, were detected in 41 and 6 percent of the samples, respectively. The most frequently detected insecticides were carbaryl (6 percent), diazinon (2 percent), carbofuran (2 percent), and chlorpyrifos (1 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 stations and only two samples represented storm-runoff conditions.
Pesticide detection frequencies for the upper Tennessee River Basin were compared to a summary of pesticide detection frequencies compiled by the U.S. Geological Survey from investigations conducted in 36 study units nationwide from 1992 through 1998. Atrazine, deethylatrazine, and tebuthiuron were detected more frequently 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, urban, or mixed land-use watershed categories. Atrazine and deethylatrazine were detected in about 93 and 90 percent, respectively, of samples collected in the upper Tennessee River Basin (using the laboratory minimum reporting levels for each pesticide) compared to the national average of detection frequencies of about 85 and 69 percent, respectively, for samples collected at stations in predominantly agricultural watersheds. Tebuthiuron was detected in 61 percent of samples in the upper Tennessee River Basin as opposed to about 22 percent in samples from agricultural stations nationwide. Conversely, detection frequencies for the herbicides alachlor and acetochlor were considerably lower in the upper Tennessee River Basin than in samples collected nationwide.
|Home||Archived January 13, 2017|