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Show Major Findings 13 Some pesticides frequently detected nationally in surface- water samples also are found in the Great Salt Lake Basins Study Unit The types of pesticides in streams are closely linked to pesticide use. Such relations help to explain why some pesticides are found in streams in the Great Salt Lake Basins and across the Nation, while others are not. For example, atrazine, which was detected in 100 percent of the samples collected from the Jordan River, which drains land with mixed cover types, also was commonly detected ( in 88 percent of samples) in 47 rivers across the Nation that drain land with mixed cover types. Similarly, the insecticide diazinon and the herbicide prometon, which were detected in about 90 percent of the samples collected from the urbanized Little Cottonwood Creek near Salt Lake City, were commonly detected in 32 other urban streams across the Nation ( 65 percent for diazinon and 85 percent for prometon). The frequency of detection of several pesticides in the Great Salt Lake Basins differed from that of other streams across the Nation. For example, carbaryl, which was detected in 38 percent of samples collected from the agricultural Cub River, was detected in only 9 percent of samples collected from 78 agricultural streams across the Nation. Simazine was frequently detected nationally ( 61 percent of 154 samples), but was detected in only 17 percent of the samples collected from streams in the Great Salt Lake Basins. Metolachlor was detected infrequently in streams in the Great Salt Lake Basins ( only 5 percent of samples) but was detected in 73 percent of 157 samples collected from other streams across the Nation. Undeveloped Agricultural Urban Mixed DOMINANT STREAM BASIN LAND COVER Figure 20. More pesticides were detected in streams affected by urban land use than in agricultural or undeveloped ( forest/ rangeland) streams. The median total concentration of pesticides measured in water samples from streams representative of undeveloped and agricultural land uses ( 0.004 and 0.041 u, g/ L ( microgram per liter), respectively) was lower than that measured in samples from streams principally affected by urban land and mixed land uses ( 0.095 and 0.077 ug/ L, respectively) ( fig. 21). The concentration of pesticides in surface- water samples from the Study Unit was generally low. Ninety- seven percent of the samples had a total pesticide concentration less than 1 ( ig/ L. The maximum concentration of pesticides ( 6.54 fxg/ L) was measured in a sample collected from an urban site near the mouth of Little Cottonwood Creek during a rainstorm ( see " Urban storm runoff affects stream chemistry and temperature")- Eighteen of 49 pesticides detected in stream samples have guidelines for the protection of aquatic communities. Concentrations of carbaryl, diazinon, and malathion exceeded those guidelines ( in 5, 19, and 4 samples, respectively), indicating the potential for impairment of some portions of the 0.0011- Q Undeveloped Agricultural Urban Mixed DOMINANT STREAM BASIN LAND COVER Figure 21. The highest concentrations of pesticides were measured in samples from urban streams. aquatic community. The implications for aquatic organisms of those pesticides detected that do not have aquatic- life guidelines are unknown. None of the pesticides detected in streams exceeded human- health standards for drinking water; however, the USEPA has established standards for only 23 of the 49 pesticides detected. VOCs are common in urban streams Water samples from two urban streams, Little Cottonwood Creek and the Jordan River, were analyzed for 86 volatile organic compounds ( VOCs), 33 of which were detected. Some likely pathways for VOCs to enter urban streams include ( 1) direct discharge into the stream from accidental spills and industrial or wastewater discharge; ( 2) industrial and vehicle emissions, scavenged from air by precipitation, deposited directly into the stream, or transported in runoff; and ( 3) contaminated ground- water inflow. The number of VOCs detected per sample ranged from 3 to 20. Fuel- related BTEX ( benzene, toluene, ethyl benzene, and xylenes) compounds were the most frequently detected group of compounds in Little Cottonwood Creek. |