Distribution of Atrazine and Similar NitrogenContaining Herbicides, Lower Kansas River Basin

By John K. Stamer and Ronald B. Zelt

Nonpoint-source contamination of surface

and ground water from agricultural activities is a national issue. Contaminants include pesticides, sediment, nutrients (nitrogen and phosphorus), and fecal bacteria. Of these contaminants, pesticides receive the most attention because they are toxic to aquatic life and are therefore potentially toxic to humans through consumption of contaminated water supplies or fish. Farmers depend on pesticides, including herbicides, to increase crop yields. Herbicides prevent or inhibit the growth of weeds that remove nutrients and moisture needed by the crops. If weeds are harvested with the crop, the value of the harvested crop is less than that of a weed-free crop. Herbicides are applied before planting, or as pre- and post-emergent compounds during or some time after planting. Herbicides often are used in urban areas and in large quantities for nonselective weed control in industrial applications, such as along railroad rights-of-way.

The USGS began a surface-water-quality assessment of the 15,300-square-mile lower Kansas River basin in southeastern Nebraska and northeastern Kansas (fig. 1) in 1986 as part of the National Water-Quality Assessment (NAWQA) program. About 85 percent of the study unit area is agricultural land typical of the midwestern United States; principal crops are corn, sorghum, soybeans, and wheat. The study unit includes the Big Blue and Delaware River basins and smaller tributaries to the 170-mile reach of the Kansas River from Junction City, Kans., to its confluence with the Missouri River at Kansas City, Kans. Three large Federal reservoirs (Tuttle Creek, Perry, and Clinton Lakes) lie within the Kansas part of the study unit. These reservoirs are used for flood control, low-flow augmentation, public-water supplies, and recreation. Most of the surface-water storage in the lower Kansas River basin is held in these three reservoirs, which have a substantial effect on streamflow and water quality in the Kansas River. In the study unit, surface runoff provides much of the water used for public supply, and surface water is the principal source of public supply in the Kansas part of the study unit.

The areal and temporal distribution in surface water of atrazine and similar nitrogencontaining herbicides, such as alachlor, cyanazine, metolachlor, and simazine, are being defined in this study of the lower Kansas River basin. As a group, these compounds are used extensively throughout the study unit; atrazine is used the most. In 1989, an estimated 4.3 million pounds of the active ingredient atrazine were applied to corn and sorghum cropland in the study unit. This amount is about 5 percent of the total amount of atrazine used in the United States during that year.

Analyses by USGS personnel of available data on 458 water samples collected at 20 surface-water sites from 1978 to 1986 by personnel of the Kansas Department of Health and Environment indicated that atrazine, metolachlor, and alachlor were the herbicides most frequently detected in water from the Kansas part of the study unit; the highest concentrations were for atrazine.

Atrazine, unlike metolachlor or alachlor, was detected during each month of the year. Median concentrations of atrazine in water samples collected during June, July, and August of each year from 1978 to 1986 exceeded the Maximum Contaminant Level (MCL) of 3.0 micrograms per liter established by the U.S. Environmental Protection Agency for finished public-water supplies under the Safe Drinking Water Act of 1986.

After the available data were analyzed, USGS personnel measured concentrations of nitrogen-containing herbicides in samples of stream water that were collected during lowflow conditions from summer 1988 to spring 1989 at 61 synoptic-sampling sites in the study unit (fig. 1). During low flow, shallow ground water is the source of most of the flow in unregulated streams. Analyses of these samples indicated that atrazine was the most frequently detected herbicide and had the highest concentration of any pesticide measured in surface water during low flow. In general, the highest concentrations of atrazine were measured in the Big Blue River basin upstream of Tuttle Creek Lake where the largest amounts of atrazine were applied to the land (fig. 1). In July 1988, the median concentration of atrazine in samples from the 61 sites was 2.6 micrograms per liter; 38 percent of the samples had concentrations of atrazine higher than the established MCL of 3.0 micrograms per liter.

Concentrations of atrazine during low flow also fluctuated seasonally; the highest median concentrations occurred in spring and summer and the lowest in fall and winter. Of the 61 sites sampled during low flow, only one site-the outflow of Perry Lake on the Delaware River-had atrazine concentrations

ESTIMATED ATRAZINE APPLICATIONBy county, in pound per square mile, 1989

MISSOURI RIVER

KANSAS

CITY

KANSAS

MISSOURI

higher than the established MCL of 3.0 micrograms per liter during each of the four seasons. Following atrazine, in order of decreasing median concentrations, were the herbicides metolachlor, cyanazine, and simazine; median concentrations of these compounds during low flow ranged from 0.1 to 0.3 microgram per liter.

To define the temporal variability of concentrations of herbicides in the principal streams in the study unit, water samples were collected monthly or more frequently from 12 fixed stations from March 1989 to February 1990 to provide samples that covered the range of expected streamflows. Analyses of these water samples indicate that atrazine was the herbicide most frequently detected in water (95 percent of 178 samples) and that atrazine concentrations fluctuated seasonally from March 1989 to February 1990. The highest concentrations occurred during June and July 1989 when median concentrations exceeded the established MCL of 3.0 micrograms per liter. In August 1989, more than 25 percent of the samples contained atrazine concentrations that exceeded the established MCL. The lowest median concentrations

in response to runoff from croplands where corn and sorghum are grown.

In contrast to unregulated streams, atrazine concentrations measured in water samples from the Delaware River at the outflow of Perry Lake showed no seasonal variability (fig. 2). Concentrations of atrazine gradually decreased from 4.0 micrograms per liter in March 1989 to 1.7 micrograms per liter in February 1990, and concentrations were equal to or higher than 3.0 micrograms per liter from March through mid-August 1989. The volume of water in Perry Lake in relation to its outflow appeared to moderate the seasonal fluctuations in atrazine concentrations from inflowing streams. In contrast, analyses of outflow-water samples from Tuttle Creek Lake on the Big Blue River indicated some seasonal fluctuations in atrazine concentrations because the volume of water in Tuttle Creek Lake is much smaller in relation to its outflow.

Note that March 1989 to February 1990 was a relatively dry period and that higher atrazine concentrations could occur during

wet periods. For example, from April to October 1986, the median concentration of atrazine, 4.4 micrograms per liter, in the Big Blue River downstream from Tuttle Creek Lake was higher than the established MCL. This median concentration was determined from 10 samples, and the maximum concentration was 8.3 micrograms per liter. The Big Blue River often contributes a large percentage of the streamflow in the Kansas River during summer months; therefore, high concentrations of atrazine in the Big Blue River can cause atrazine concentrations in the Kansas River to increase to more than 3.0 micrograms per liter. Public-water supplies for Topeka, Lawrence, and the Kansas City, Kans., metropolitan area are withdrawn from the Kansas River downstream from its confluence with the Big Blue River.

For the March 1989 to February 1990 sampling period, mean concentrations of atrazine at 3 of the 12 fixed stations in the study unit exceeded the established MCL of 3.0 micrograms per liter. One station is on West Fork Big Blue River near Dorchester, Nebr.,

30,000

10,000

1,000

100

0.10

0.10

10

0.01

ATRAZINE CONCENTRATION, IN MICROGRAMS PER LITER

Delaware River

and two stations are on the Delaware River, the drainage area of which lies entirely in Kansas. All three stations are downstream from areas that are predominantly cropland. Upstream of Perry Lake, the sampling station on the Delaware River near Muscotah, Kans., is downstream from two public surface-watersupply intakes and upstream from one intake.

Atrazine concentrations in samples from the outflow of Perry Lake are representative of atrazine concentrations within the lake. Public-water supplies are withdrawn from Perry Lake for two rural water districts and several Federal- and State-owned recreational areas. Water withdrawn from the Delaware River and Perry Lake receives no special treatment to remove atrazine from the finished water, and there is the potential for concentrations of atrazine in these publicwater supplies to exceed the MCL at different times of the year.

Atrazine and similar nitrogen-containing herbicides pose a special problem in publicwater supplies because these compounds are relatively water soluble. Several studies in different States have shown that conventional

water treatment is ineffective for removal of atrazine, alachlor, or similar compounds from the finished water.

The USGS has begun to implement the NAWQA program with 20 additional study units. Results from the assessment were used by the Kansas State Board of Agriculture Technical Advisory Committee (TAC) as the basis for establishing the Delaware River basin in northeastern Kansas as a pesticide management area pesticide management area. This pesticide management area is the first in the Nation that targets reducing the amount of atrazine in runoff that enters inland surface waters. Administration of the pesticide management area includes components of management and conservation practices, education, monitoring, research, enforcement, and evaluation. The USGS is involved with the research and monitoring components of the pesticide management area through the Federal-State cooperative program and will continue to provide information that may be used by the TAC as it considers the establishment of additional pesticide management areas in Kansas.

Aerial photograph of Perry Lake, Kans., showing the dam, outlet of the lake, beach area for swimmers, and recreational