Many contaminants found in nation's streams, but few drinking-water standards exceeded, USGS report shows

June 28, 1999

In a look at water-quality conditions of 20 of the country's largest and most important river basins, the U.S. Geological Survey announced today (June 28, 1999) that streams in areas with significant agricultural or urban development almost always contain complex mixtures of nutrients and pesticides.

The complex nature of those chemical mixtures and the lack of current human and aquatic health criteria to determine risk of exposure, make addressing these issues a top national priority.

Secretary of the Interior Bruce Babbitt said, "Over the last two decades, our nation has made great progress in improving water quality and, yet, as the USGS report points out, major challenges remain in protecting our aquatic resources.

"The widespread occurrence of pesticides and nutrients in water documented in the USGS report underscores the need to devote more attention to the quality of our waterways and the life that depends on them," Babbitt said.

The good news is that concentrations of individual pesticides in samples from wells and as annual averages in streams were almost always lower than current U.S. Environmental Protection Agency drinking-water standards and guidelines.

The USGS assessment results suggest that aquatic life may be more at risk than humans from these contaminants. More than one-half of agricultural and urban streams sampled had concentrations of at least one pesticide that exceeded a guideline for the protection of aquatic life.

The potential risk to people and to aquatic life can only be partially addressed, based on available standards and guidelines. The health picture is made more complex by the lack of standards or guidelines for many pesticides and their "breakdown" products or metabolites. Adding to the complexity is the fact that existing standards and guidelines were developed for individual chemicals and do not take into account exposure to mixtures of chemicals and seasonal pulses of high concentrations.

USGS analysis of almost every stream sample and about one-half of the well samples detected the presence of two or more pesticides. The ability of the USGS to "detect" these chemicals in water samples does not automatically translate into impacts on human or aquatic health. (The level of accuracy demanded by the USGS to assess the effects on water quality is a minute amount -- sometimes parts per trillion -- that is well below the threshold used for setting standards and guidelines.)

In addition, potential effects on reproductive, nervous and immune systems, as well as on chemically sensitive individuals, are not yet well understood. For example, some of the most frequently detected pesticides are suspected endocrine disrupters that have potential to affect reproduction or development of aquatic organisms or wildlife by interfering with natural hormones.

"Despite considerable progress in the four decades since Rachel Carson warned the nation of the risks posed by environmental contaminants, a large range of nutrients and other contaminants continue to enter our waterways, said Mark Schaefer, deputy assistant secretary for water and science at the Interior Department, in commenting on the report.

"The President's Clean Water Action Plan lays out a blueprint for addressing the nation's water-quality problems," Schaefer said. "The challenge is to find ways to work cooperatively to reduce urban and agricultural contaminants on a watershed-by-watershed basis.

Schaefer pointed to the report's implication that understanding patterns of contamination in relation to land use, pesticide use and the natural characteristics of hydrologic systems can help reduce the amounts of pesticides that reach streams and ground water. Of the urban streams studied by the USGS, nearly every one had concentrations of insecticides that exceed guidelines for protection of aquatic life, which shows this is not just an agricultural problem.

Turning to nutrients, the USGS report said that nitrate generally does not pose a health risk for people whose drinking water comes from streams or from aquifers (water-bearing rock formations) buried relatively deep beneath the land.

Protection of human health is more difficult in rural agricultural areas where shallow ground water is used for domestic water supply. High levels of nitrate in shallow ground water also may serve as an "early warning" of possible future contamination of older underlying ground water, which is a common source for public water supply.

Looking at the aquatic environment, concentrations of nitrogen and phosphorus commonly exceed levels that can contribute to excessive growth of algae and other nuisance plants in streams. Such growth can clog water intake pipes and filters and interfere with recreational activities, such as fishing, swimming and boating. The subsequent decay of the algae can result in foul odors, bad taste in drinking water and low dissolved oxygen in aquatic habitats -- oxygen that is necessary for fish and other aquatic life to survive.
The USGS report is based on analysis of data collected from 20 major river basins and aquifer systems across the country. The report, The Quality of Our Nation's Waters--Nutrients and Pesticides, published as USGS Circular 1225 is available on the World Wide Web as downloadable portable document files (PDF) at: or in printed form (single copies of the report are at no cost) from: Branch of Information Services, P.O. Box 25286, Denver, CO 80225, or by fax request to: 303-202-4693. Please specify USGS report C-1225.

As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation, economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy and mineral resources.

This press release and in-depth information about USGS programs may be found on the USGS home page: To receive the latest USGS news releases automatically by email, send a request to Specify the listserver(s) of interest from the following names: water-pr: geologic-hazards-pr; biological-pr; mapping-pr; products-pr; lecture-pr. In the body of the message write: subscribe (name of listserver) (your name). Example: subscribe water-pr joe smith.

(Note to Editors: See attached "highlights" for further information on the USGS water- quality report.)

Selected highlights and implications of the USGS water-quality report:

* IT'S ALL RELATIVE--The types and relative levels of concentrations of nutrients and pesticides found in streams and ground water are closely linked to land use and the chemicals applied in each setting. Some of the highest concentrations of nitrogen and herbicides, including those most heavily used (such as atrazine, metolachlor, alachlor and cyanazine) were detected in USGS samples collected from streams and shallow ground water in agricultural areas. Some of the highest concentrations of phosphorus and insecticides (including diazinon, carbaryl and malathion) were found in urban streams.

* LINGERING LEGACY--The mixtures of contaminants found in the USGS study include chemicals that are no longer in use, such as DDT, which was banned in the early 1970's. These persistent insecticides still are found at elevated levels in fish and streambed sediment in many urban and agricultural streams across the Nation. But there is good news in that there has been a national reduction in concentrations of these organochrlorine insecticides (DDT, dieldren and chlordane) in whole fish. Concentrations of DDT in sediments also have decreased, as indicated in sediment-core samples from urban and agricultural reservoirs and lakes.

* TIMING IS EVERYTHING--Seasonal patterns in water quality of streams emerged in most basins in the USGS study. The patterns reflect many factors, but mainly the timing and amount of chemical use. Other influences are the frequency and magnitude of runoff from rainstorms or snowmelt. Specific land-management practices, such as irrigation and tile drainage also affect water quality. Concentrations of nutrients and pesticides are highest during runoff following chemical applications. The seasonal nature of these factors dictate the timing of elevated concentrations in drinking-water sources and aquatic habitats and serve as a guide in developing water management strategies.

* LAY OF THE LAND MATTERS--Local geography and natural features, including topography, geology, soils, hydrology and climate, affect the occurrence of nutrients and pesticides in water. Add the influence of land-management practices like tile drainage, irrigation and conservation strategies, and it matters a great deal as to where you are in the country as to what the impacts are on water quality, the USGS report said.

US Geological Survey

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