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Available data on pesticides in streams, streambed sediment, and ground water from Federal, state, and local agencies are reviewed for part of the Upper Mississippi River Basin study unit of the National Water-Quality Assessment Program. The analysis focuses on a smaller study area encompassing 19,500 square miles that includes the Upper Mississippi River Basin from Lake Pepin upstream to sampling stations on the Mississippi River near Royalton, Minnesota, and the Minnesota River near Jordan, Minnesota, and the entire drainage basins of the St. Croix, Vermillion, and Cannon Rivers. Assessment is generally restricted to two groups of pesticides the most frequently detected herbicides and organochlorine insecticides although pesticides rarely or never detected are noted. Herbicides, including alachlor, atrazine, cyanazine, or metolachlor, were detected in every stream sampled except the Kettle River. Streams draining row-crop areas had the most herbicide detections. Atrazine was the most widely detected herbicide, with detections in all streams sampled except the Kettle River. Concentrations of atrazine, metolachlor, and cyanazine were greatest in July and detectable most of the year at very low (parts-per-trillion) concentrations. The herbicides EPTC and trifluralin were never detected, although they were used in amounts equal to or greater than those detected, reflecting the fact that some herbicides are less persistent than others. A small urban stream draining part of the Lake Harriet Watershed in Minneapolis, Minnesota, contained substantial concentrations of pesticides as well. Eighty-five percent of runoff events sampled in this entirely urbanized watershed had detections of herbicides commonly used for residential purposes, and 43 percent of the events had detections of alachlor, atrazine, cyanazine, or metolachlor herbicides used predominantly for agriculture. Pesticide concentrations in urban runoff remained well above detection limits throughout the summer, indicating repeated applications of pesticides. Selected organochlorine insecticides, banned since the 1970's, still were detected in recent streambed-sediment samples. Three insecticides, 4,4'-DDT, heptachlor, and lindane, and their metabolites account for almost two-thirds of the organochlorine insecticides detected. Organochlorine insecticides were detected more frequently in streambed sediment than in streamwater. Detections in both phases were most frequent within or downstream of the Twin Cities metropolitan area, indicating that most of these insecticides originated from the Twin Cities metropolitan area. The most frequently detected herbicides in ground water were the same as those frequently detected in streams. Most detections were found in the sand and gravel aquifers underlying agricultural areas, including the Anoka Sand Plain and Bonanza Valley. Atrazine, deethylatrazine, and deisopropylatrazine were detected most frequently. Detection frequencies of atrazine were extremely variable among the various agencies, ranging from 0 to 66.7 percent, probably as a result of different sampling purposes, well locations, and detection levels. Atrazine and atrazine metabolites were the only pesticides detected in bedrock aquifers, with detections found mainly in the agriculture-dominated southeastern part of the study area where bedrock commonly outcrops near the surface. Thus, most detections of herbicides in ground water were found in environmental settings where ground water is vulnerable to contamination. Atrazine was the only pesticide that equaled or exceeded a maximum contaminant level (of 3.0 micrograms per liter) for drinking water. Two stream samples from a small urban watershed in Minneapolis had atrazine concentrations of 3.6 and 3.8 micrograms per liter, and one ground-water sample had a concentration of 3.0 micrograms per liter. Trace concentrations (less than 0.06 micrograms per liter) of the organochlorine insecticides chlordane, dieldrin, endrin, and heptachlor exceeded chronic freshwater-quality criteria in stream samples from the Mississippi, Minnesota, St. Croix, and Vemillion Rivers in 1981 and 1990. INTRODUCTION In 1991, the USGS began full implementation of the NAWQA. Major activities of the NAWQA take place within a set of hydrologic systems called study units. Study units comprise diverse hydrologic systems of river basins, aquifer systems, or both. The Upper Mississippi River Basin NAWQA study unit, which encompasses an area of about 47,000 mi2, includes the entire drainage area of the Mississippi River Basin upstream from the outlet of Lake Pepin (fig. 1). The study unit includes areas of rich agricultural lands, forests, wetlands, prairies, and a major urban area. Water quality of the Upper Mississippi River, which contains the headwaters of the largest river in the Nation, is of concern due to reliance on streamwater for water users, for a source of drinking water by major municipalities in the basin, and for good quality water to maintain the health of regional aquatic ecosystems. Ground water is the principal source of potable water to smaller municipalities and domestic water systems in the study unit. Ground water in unconfined sand and gravel aquifers of glacial and alluvial origins is particularly susceptible to degradation from human activities at the land surface. Ground water in these sand and gravel aquifers and in adjoining bedrock aquifers is typically hydraulically connected to rivers throughout the study unit. These features make the Upper Mississippi River Basin study unit an essential component of a comprehensive national assessment of water quality. The first phase of investigation in the study unit, lasting from 1994-99, is focused principally on the effects of the seven-county TCMA on water quality and aquatic ecosystems. As a result, this retrospective analysis focuses on a smaller study area, encompassing 19,500 mi of the eastern portion of the Upper Mississippi River Basin study unit (fig. 1). This study area includes the part of the Upper Mississippi River Basin from Lake Pepin upstream to sampling stations on the Mississippi River near Royalton, Minnesota, and the Minnesota River near Jordan, Minnesota, where longterm water-quality data are available, and the entire drainage basin of the St. Croix River. Most of the TCMA, with a population of about 2,290,000, is included in the south-central part of the study area. Pesticides are used throughout the Upper Mississippi River Basin study unit especially in agricultural and urban areas. Once applied, a small percentage of pesticides often enter streams in runoff (Thurman and others, 1992), in ground-water discharge (Squillace and others, 1993), in atmospheric deposition from aerosols and rainfall (Buser, 1990; Majewski and Capel, 1995), and in ground water through infiltration. Pesticides in streams and ground water are a concern because low concentrations of these compounds can have toxic, mutagenic, or carcinogenic effects in aquatic biota and humans (U.S. Environmental Protection Agency, 1994; Patlak, 1996). Very low concentrations of many pesticides in water are suspected of, or are known to, disrupt the endocrine systems of animals and humans, thereby interfering with their hormonal, sexual, and reproductive viabilities (Colborn and Clement, 1992). Purpose and Scope This report describes the presence and distribution of the most frequently detected pesticides in streams, streambed sediment, and ground water in the study area from 1974-94. Summaries are presented for selected pesticides in stream, streambed-sediment, and groundwater samples collected by the MCES, MDA, MDH, MPCA, USAGE, USGS, and WDNR, applying to periods for which the most data were available. This report also summarizes estimated quantities of the most used herbicides and insecticides for agriculture in the Upper Mississippi River Basin study unit and describes possible relations between the pesticide use and the presence of these pesticides in streams and ground water. This report focuses on synthetic-organic herbicides and insecticides because these pesticides are of concern to environmental and human health (Nowell and Resek, 1994). Furthermore, synthetic-organic pesticides can be distinguished from other sources in the environment because they are used exclusively as pesticides, unlike inorganic pesticides such as copper or arsenic. Insecticides and nematicides collectively are referred to as insecticides in this report. Many pesticides used in the study unit were either not analyzed or not detected in water or in sediment. This report focuses on the most frequently analyzed and detected herbicides, insecticides, and related metabolites and isomers in water and streambed sediment. For brevity, metabolites and isomers of pesticides also are referred to as pesticides. Assessment is restricted to two groups of pesticides the most frequently detected herbicides and most frequently detected insecticides. The most frequently detected herbicides for streams and ground water include atrazine, deethylatrazine, deisopropylatrazine, alachlor, cyanazine, metolachlor, and simazine. The most frequently detected insecticides for streams and streambed sediment include aldrin, chlordane, 4,4'-DDT, 4,4'-DDD, 4,4'-DDE, dieldrin, endrin, y-HCH (or lindane), aand 5-HCH, heptachlor, heptachlor epoxide, and toxaphene. Fungicides are not included because fungicides were rarely analyzed and were not detected in analyses of samples compiled for this report.

water-resources investigations report

Water-quality assessment of part of the upper Mississippi River Basin, Minnesota and Wisconsin — Pesticides in streams, streambed sediment, and ground water, 1974-94