Ten Pesticides—Atra
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Pesticide concentrations at all fixed sites ranged often applied to powerline and road rights-of-way, was from 0.001 to 2.0 µg/L (table 4). Ten pesticides—atra- detected at a substantially higher frequency at Copper zine, bromacil, dichlorprop, 2,6-diethylaniline, meto- Creek than at the Nolichucky River or Big Limestone lachlor, metribuzin, simazine, carbaryl, carbofuran, Creek. Detection frequencies for Big Limestone Creek and diazinon—were detected in water samples at con- and the Nolichucky River near Lowland were similar centrations greater than 0.10 µg/L (table 4). In 47 of for atrazine, deethylatrazine, metolachlor, napropam- the 362 water samples collected at the fixed sites, one ide, and carbofuran (fig. 4). The most noticeable dif- or more pesticides were detected at a concentration ference between these two sites was that metribuzin, greater than 0.10 µg/L. Concentrations of atrazine an herbicide used to control a large number of grasses exceeded 0.10 µg/L in 37 samples, and concentrations and broadleaf weeds on a variety of agricultural crops of metolachlor exceeded 0.10 µg/L in 11 samples. (potatoes, soybeans, and winter wheat), was detected Seven water samples had concentrations of one or in 17 percent of the samples at the Nolichucky River more pesticides exceeding 0.50 µg/L, and only four near Lowland but was not detected at Big Limestone samples had concentrations of one or more pesticides Creek. Big Limestone Creek is a tributary to the Noli- that exceeded 1.0 µg/L. chucky River, and both drain the same general agricul- Differences in pesticide occurrence among the turally dominated area; however, the Big Limestone three agricultural sites (Big Limestone Creek, Copper Creek Basin contains a higher percentage of agricul- Creek, and Nolichucky River) were related to the vari- tural land use (both pasture and cropland) than the ety of land uses and pesticide application within each remainder of the Nolichucky River Basin. Agricultural 2 basin. Among the agricultural sites, more pesticides land accounts for only about 39 percent (650 mi ) of (22) were detected in samples from the Nolichucky the drainage upstream of the Nolichucky River site; River near Lowland than from the other agricultural however, most of the area adjacent to or directly sites (fig. 4). Similarly, more pesticides also were upstream from the sampling site is predominantly detected in samples from Big Limestone Creek (17) agricultural. than at Copper Creek (11) probably because of a Detection frequencies of pesticides at the three greater percentage of agricultural land use and a agricultural sites generally characterize pesticide greater variety of crops grown in the Big Limestone detection at all fixed sites; however, some noticeable Creek Basin. Tebuthiuron, a noncropland herbicide differences were observed (fig. 4). At the agricultural 14 Seasonal and Spatial Variability of Pesticides in Streams of the Upper Tennessee River Basin, 1996-99 sites, 27 different pesticides were detected. Detection Comparisons of Detection Frequencies in the frequencies at Big Limestone Creek near Limestone Upper Tennessee River Basin with Detection and the Nolichucky River near Lowland were particu- Frequencies Across the Nation larly high when compared to the detection frequencies at the other fixed sites for the pesticides (atrazine and Pesticide detection frequencies for the UTEN metolachlor), which are commonly used for agricul- were compared to a national summary of pesticide ture in the UTEN. Detection frequencies of pesticides detections compiled by the USGS from NAWQA stud- in water samples at the Nolichucky River site more ies that were completed in 36 of the Nation’s major closely resembled detection frequencies at the other 10 hydrologic basins from 1992 to 1998 and that included fixed sites probably because of a greater degree of analyses of about 2,500 samples collected at 115 fixed mixed land use in the Nolichucky River Basin. Detec- sites. Pesticide detection frequencies in the UTEN tion frequencies of pesticides for Copper Creek, how- were compared to the national averages for stream ever, varied considerably from the other sites, sites with agricultural drainages as well as for sites particularly for some of the more commonly detected with drainages of mixed land use. pesticides such as metolachlor, simazine, and prome- Atrazine, deethylatrazine, tebuthiuron, and ton (fig. 4). Tebuthiuron was detected more frequently napropamide were detected in streams of agricultural at Copper Creek than at the other agricultural sites, drainages in the UTEN more frequently than at agri- perhaps as a result of road construction and weed con- cultural sites included in the national summary of pes- trol on roadway rights-of-way upstream of the sam- ticide detections (fig. 5). Atrazine and deethylatrazine pling site. At Copper Creek, 11 pesticides were were detected in 99 and 98 percent of samples in the detected in 51 samples; however, only 4 pesticides UTEN compared to the national average for agricul- were detected in more than 2 samples (less than 4 per- tural sites of 85 and 69 percent, respectively. Tebuthiu- cent of samples). ron was detected in 62 percent of samples in the Of the 47 pesticides that were analyzed in all UTEN compared to the average of 22 percent for agri- samples (using the GC/MS method), 7 pesticides cultural sites nationwide. The detection frequency for detected at the fixed sites were not detected at any of napropamide in the UTEN slightly exceeded the the sites included in the spatial analysis. Conversely, national average for agricultural indicator sites (6.2 only one pesticide (terbacil) was detected at a spatial- and 5.6 percent, respectively). Pesticides that were analysis site that was not detected in samples collected detected considerably less frequently in the UTEN at the fixed sites. streams than at the nationwide agricultural sites Pesticides in Streams of the Upper Tennessee River Basin 15 included alachlor, acetochlor, carbofuran, diazinon, the samples collected at UTEN sites had concentra- metolachlor, metribuzin, prometon, and simazine. tions of one or more pesticides that exceeded the Atrazine, deethylatrazine, metolachlor, tebuthiu- chronic aquatic-life criteria (fig. 6), and the exceed- ron, and napropamide were detected more frequently ances were for atrazine, diazinon, carbaryl, and lin- at mixed land-use sites in the UTEN than at mixed dane. land-use sites included in the national summary of Total pesticide concentrations were computed pesticide detections (fig. 5). Atrazine and deethylatra- by summing the concentrations of the detectable pesti- zine were detected in 94 and 95 percent of samples cides (above the MRL) for each sample in order to from mixed land-use sites in the UTEN compared to account for the presence of multiple pesticides. Total the national average for mixed land-use sites of 83 and pesticide concentrations for samples collected at the 68 percent, respectively. For mixed land-use sites, fixed sites in the UTEN ranged from less than metolachlor was detected in 84 percent of samples in 0.001 µg/L at Clear Creek at Lilly Bridge near Lanc- the UTEN compared to 74 percent nationwide; and ing, Tenn., to 3.15 µg/L for a sample with eight pesti- tebuthiuron was detected in 61 percent of samples in cide detections collected at Nolichucky River near the UTEN compared to the average of 34 percent for Lowland, Tenn. The effects of pesticide mixtures on mixed land-use sites nationwide. Detection frequency biota and human health are unknown; however, this is for napropamide in the UTEN slightly exceeded the an area of active research, and the U.S. EPA is consid- national average for mixed land-use sites (fig. 5). ering establishing health standards for combinations of Comparison of detection frequencies at sites with pesticides (U.S. Environmental Protection Agency, mixed land-use drainages in the UTEN with national 1994). averages reveal results similar to the agricultural sites with the exception of metolachlor, which was detected more frequently in the UTEN. SEASONAL AND SPATIAL VARIABILITY OF PESTICIDES IN STREAMS OF THE UPPER TENNESSEE RIVER BASIN Water-Quality Standards Pesticide occurrence and concentrations varied The U.S. EPA has established water-quality seasonally and spatially in the UTEN and were closely standards and guidelines that specify thresholds of associated with land use and time of application. Peak concentrations of certain chemicals that have adverse concentrations of pesticides generally were detected effects on human health, aquatic organisms, and wild- during the spring and immediately following pesticide life. Although the maximum contaminant levels application. However, low levels (concentrations gen- (MCL) and lifetime health advisory levels (HAL) erally less than 0.10 µg/L) of pesticides were detected established by the U.S. EPA (2000) pertain to finished throughout the year at the fixed sites in the UTEN. drinking water supplied by a community water system, Seasonal variability was evident for several pes- values are provided with which ambient concentra- ticides at the 13 fixed sites. Monthly sampling for pes- tions can be compared. MCLs or HALs have been ticides at fixed sites was conducted to characterize the established for 21 of the 31 pesticides and metabolites seasonal variation of pesticides in streams in the detected at sites in the UTEN study (table 4). Aquatic- UTEN. Peak concentrations occurred during the grow- life criteria have been established for the