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USGS Finds Pesticides In Nation's Surface and Ground Water
(Beyond Pesticides, May 26, 2004)
In agricultural and urban areas, the quality of our nation's water resources has been degraded by contaminants such as pesticides, nutrients, and gasoline-related compounds, according to Water Quality in the Nation's Streams and Aquifers-Overview of Selected Findings, 1991-2001 released earlier this month. Based on a series of 51 United States Geological Survey (USGS) reports on the health of major river basins across the country (15 of which were also released earlier this month), the overview states that insecticides such as diazinon and malathion were found in nearly all of the streams that were sampled in urban areas. Streams in agricultural areas were more likely to contain herbicides-especially atrazine, metolachlor, alachlor, and cyanazine.

For more than a decade, USGS hydrologists have looked at three questions related to ground and surface water quality. What are the conditions of our nation's streams and ground water? How is water quality changing over time? And how do natural features and human activities affect the quality of streams? According to the USGS Chief Hydrologist Robert Hirsch, "By evaluating and assessing our nation's water resources, we have a better understanding of water quality and this gives us a comprehensive picture of the long-term health of America's rivers and aquifers. We have analyzed the effects of agricultural, urban, and forest land use practices on water quality, habitat, and biota."

Some specific findings regarding pesticides are highlighted below.

Southwestern Ohio and southeastern Indiana:

  • Atrazine and metolachlor, herbicides that are heavily used on agricultural land, were detected in more than 90% of samples from 5 streams in southwestern Ohio, whereas insecticides (such as diazinon) commonly used by homeowners were frequently detected in an urban stream.
  • In 29 small stream basins that drain areas of various land uses, USGS scientists found that insecticide concentrations increased as the amount of urban land increased.
  • Polychlorinated biphenyls (PCBs) and organochlorine insecticides, such as DDT and chlordane, continue to persist in fish tissue even though their use was canceled or restricted in the 1970s and 1980s. Many of these chemicals were detected at concentrations at or near the maximum concentrations found nationwide by the NAWQA Program.
  • Very low concentrations of one or more pesticides were detected in 63% of the groundwater samples from 96 wells. (None of the concentrations exceeded drinking-water standards or guidelines.)

Karst Areas in the Lower Tennessee River Basin:

  • Fifty-two pesticides (38 herbicides, 11 insecticides, and 3 fungicides) were detected in streams and rivers. (Aquatic-life guidelines were exceeded in less than 3% of the samples.)
  • Although uses of DDT and PCBs were discontinued more than 20 years ago, residues of these compounds continue to be detected in fish tissue throughout the Basin. (Less than 3% of the sites had concentrations that exceeded human health action levels or wildlife guidelines.)
  • Although 35 pesticides were detected in wells and springs sampled in carbonate aquifers, none of the detected pesticides exceeded the USEPA drinking-water standards. Pesticides detected in the ground water reflect differences in land uses. General-use pesticides that are applied along road and power line rights-of-way and in urban areas to control woody vegetation and weeds were detected at similar frequencies in the two carbonate aquifers sampled. Cotton, corn, and soybean production is concentrated in the rolling terraces and floodplains of the Eastern Highland Rim. The underlying aquifer in these areas had higher detection frequencies of agricultural pesticides than areas where pasture land is more prevalent.

Oahu Aquifers:

  • VOCs and pesticides were detected together in more than half of sampled public-supply wells, with one exception.
  • Of some 80 similar USGS studies, Oahu ranked first in the nation in the percentage of wells in which fumigants were detected. Fumigants have long been applied to pineapple fields to combat nematodes (rootworms).
  • Four wells exceeded state standards for the fumigants DBCP and TCP. (Where standards were exceeded, the wells already had been taken out of service or were receiving treatment to remove the contaminants.)
  • Several chemicals in stream water and bottom sediment exceeded guidelines established to protect the health of stream animals and fish-eating wildlife. Sediment concentrations of the pesticides dieldrin, chlordane, and DDT were in the highest 5% of streams sampled nationally by USGS, and similarly high concentrations were present in fish tissue. Dieldrin and chlordane were highest in urban areas where they were used to kill termites, and DDT was highest where it had been used for agriculture.

Hirsch noted 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."

The 51 reports on water quality were conducted since 1991 by the USGS National Water Quality Assessment (NAWQA) program. 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 in the characterization of water-quality conditions, and increase understanding of natural and human factors that affect water quality.

TAKE ACTION: Help protect our nation's water by creating a healthy, pest-resistant lawn without the use of toxic pesticides. Find out how here. Get rid of other pests without hazardous pesticides by going to Beyond Pesticides’ Alternatives Fact Sheets. You can also join the Pesticide-Free Zone Campaign and national network.