USGS Reports Majority of U.S. Fresh Water Contaminated with Pesticides

(Beyond Pesticides, June 9, 2004)

A new nationwide study of streams and groundwater by the U.S. Geological Survey (USGS) finds that a majority of the nation’s fresh water sources, particularly in agricultural and urban development areas, are contaminated with low concentrations of chemicals.

The USGS study found pesticides in 94 percent of all the water samples and in 90 percent of fish samples, according to a May 22 article in Science News. In urban areas, insecticides such as diazinon and malathion which are commonly used on lawns and gardens were found in nearly all of the streams that were sampled. Streams in agricultural areas were more likely to contain herbicides-especially atrazine, metolachlor alachlor, and cyanazine.

While the report conceded that such widespread contamination is cause for concern it highlighted that the concentrations found were well below the U.S. Environmental Protection Agency’s (EPA) recommended limits in most places, writes Science News. However, USGS Chief Hydrologist Robert Hirsch added that, “Concentrations of contaminants in water samples from wells were almost always lower than current EPA drinking-water standards and guidelines. However, the possible risk to people and to aquatic life can only be partially addressed because of the lack of criteria for many chemicals and their degradation or ‘breakdown’ products. In addition, criteria were developed for individual chemicals and do not take into account exposure to mixtures or seasonal high pulses in concentrations.” EPA also does not collect adequate information to determine the impacts on human health and the environment of constant low-level exposure to pesticides over time.

A recent study of synthetic pyrethroid accumulations in creek sediments at levels toxic to freshwater bottom dwellers (often used as quality indicators) further calls into question the sufficiency of some of EPA’s contamination limits. (See Beyond Pesticides Daily News story.)

The data, which is considered the most comprehensive yet, was gathered by more than 400 scientists over a 10 year period under the auspices of the National Water-Quality Assessment program. Using the collections from thousands of rivers, aquifers, wells, fish, and sediments across the country, scientists analyzed as many as 11 million samples for more than 600 chemicals.

The report also added weight to the problem of containing pesticidal contamination. Various insecticides usually associated with rural agricultural areas surprised researchers by showing up in urban water sources, the study found. “We didn’t expect to see such a difference,” says Timothy L. Miller, chief of the USGS Office of Water Quality. According to Science News, Miller speculates that insecticides are being applied more extravagantly to lawns and golf courses than to croplands.

Of the 51 areas studied in the first phase of the program, the USGS has already launched a second round of studies in 42 areas to determine trends, fill critical gaps, and increase understanding of natural and human factors that affect water quality.

Free copies of the NAWQA reports are available from 1-888-ASK-USGS, by fax 303-202-4693 or online at For an overview, go to