Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

Synthetic chemicals, trace elements, and other contaminants can, in sufficient quantities, harm people as well as fish and other wildlife. Both the frequency of chemical contamination and the degree to which these contaminants exceed applicable standards and guidelines are important in understanding the extent and significance of chemical contamination. The number of contaminants found in streams, groundwater, and the like provides basic information on how widespread these compounds are in the environment. However, the presence of chemical contamination does not necessarily mean that the levels are high enough to cause problems; comparison to standards and guidelines provides a useful reference to help judge the significance of contamination.

There are no standards or guidelines for many contaminants. For example, drinking water standards and guidelines do not exist for 33 of the 76 pesticides analyzed in fresh waters, and there are no aquatic life guidelines for 48 of these 76 pesticides. Current standards and guidelines do not account for mixtures of chemicals and seasonal occurrences of very high concentrations. These gaps increase the importance of information on the occurrence of chemical contaminants. In addition, potential effects on reproductive, nervous, and immune systems, as well as on particularly sensitive people, are not yet well understood.

What Do The Data Show?

Streams. All tested streams averaged one or more contaminants at detectable levels throughout the year; about 80% averaged five or more contaminants at detectable levels. Three-fourths of streams tested had one or more contaminants at levels that exceeded guidelines for the protection of aquatic life; approximately one fourth had concentrations of four or more contaminants that exceeded these guidelines. Thirteen percent had at least one contaminant at levels that exceeded standards or guidelines for the protection of human health. Stream water was tested for pesticides, selected pesticide degradation products, and selected nutrients.

Groundwater. About 90% of groundwater wells tested had an average of one or more contaminants at detectable levels, and 40% had an average of five or more contaminants at detectable levels. About one fourth had contaminants at levels that exceeded human health standards or guidelines. Groundwater was tested for pesticides, selected pesticide degradation products, volatile organic contaminants, trace elements, and selected nutrients.

Stream sediments. Nearly all stream sediments tested had an average of five or more contaminants at detectable levels. About half had one or more contaminants at concentrations exceeding aquatic life guidelines. Stream sediments were tested for organochlorine pesticides, PCBs, PAHs, other industrial contaminants, and trace elements.

Freshwater fish. About half of fish tested had at least five contaminants at detectable levels, and approximately the same number had one or more contaminants at levels that exceeded standards for the protection of wildlife. Data are not available on exceedances of human health standards. Whole fish were tested for organochlorine pesticides, PCBs, and trace elements.

Although not shown on the graphs, all fish tested in the Great Lakes had five or more detected contaminants, and all Great Lakes fish had PCB concentrations that exceeded human health standards. (Great Lakes testing focuses on fish with a high likelihood of such contamination, such as coho salmon and lake trout.)

Coastal sediments. More than 98% of estuary sediments tested had five or more contaminants at detectable levels. During 1999-2000, 42% of estuary sediments tested had contaminants above levels designed to predict "possible adverse effects" on aquatic life for one or more contaminants, and about 7% exceeded the level designed to predict "probable adverse effects." Data for the period from 1990-1997 are not comparable because they did not include the North Atlantic and Pacific Coast estuaries. In addition, the pesticide Dieldrin is no longer included in the suite of contaminants used to predict "possible effects" or "probable effects" (see technical note). For these reason, it is not possible directly to compare the data from the earlier time period to the 1999-2000 time period. Estuary sediments were tested for PCBs, PAHs, pesticides, and trace elements. Data on ocean sediments are not adequate for national reporting.