A confluence of contaminants: streams' organic mix may pose environmental risk.

Three years of work by U.S. government scientists have identified at least 82 drugs, hormones, and other organic compounds that pollute national waterways. The individual contaminants, ranging from insect repellents to cattle antibiotics, appear at low concentrations. An independent study, however, indicates that the combined effects of such chemicals may spell trouble.

Taken together, the findings are "quite disturbing," says Ana M. Soto, an endocrinologist at Tuffs University School of Medicine in Boston.

Past research has documented drugs, pesticides, and other contaminants in wastewaters in Europe (SN: 3/21/98, p. 187) and Canada (SN: 4/1/00, p. 212). The new study by the U.S. Geological Survey (USGS) is the first to thoroughly examine these substances in U.S. waterways. Earlier reports from the data had already indicated that several organic compounds turn up in drinking water (SN: 11/3/01, p. 285).

Researchers led by Dana W. Kolpin of the USGS laboratory in Iowa City, Iowa, took water samples from 139 streams in 30 states during 1999 and 2000. They mainly surveyed sites downstream of industrial plants, sewage-treatment facilities, or wastewater-emitting livestock farms.

The researchers tested each sample for up to 95 different organic compounds found in pharmaceuticals and household chemicals. They found at least one of the chemicals on their hit list in 80 percent of the waterways, with an average of 7, and a maximum of 38, contaminants per stream.

The three most abundant types of organic contaminants were steroids, ingredients of plastics, and compounds from detergents. An insect repellent, DEET, appeared in 74 percent of the samples. The researchers also found fire retardants, antibiotics, birth-control drugs, and caffeine, they report in the March 15 Environmental Science and Technology.

The USGS wastewater assessment "is the best to date" in terms of comprehensiveness, says Christian G. Daughton of the Environmental Protection Agency's National Exposure Research Laboratory in Las Vegas. Still, he notes, the researchers looked for "just a subset of all the chemicals that could be present."

Most of the chemicals appear in concentrations of just a few parts per billion, amounts that haven't been identified as hazardous to human health. For 68 of the 82 compounds found, however, no limits for tolerable exposures have been set and reliable data on their health effects are lacking.

The discovery of 22 types of antibiotics in the streams is especially worrisome because their presence could increase bacteria's antibiotic resistance, says Thomas A. Ternes of the Institute for Water Research and Water Technology in Wiesbaden, Germany.

Soto is also concerned because 33 of the contaminants have known or suspected hormonal effects. Previous studies have suggested a link between deformities in fish and sex steroids entering streams after livestock consumed them in feed and then excreted them (SN: 1/5/02, p. 10).

At the highest of the concentrations reported in the new study, estrogens such as nonylphenol and estradiol have strong, long-term effects on fish and other aquatic organisms, says Ternes.

Contaminants may be especially potent when they appear in combination, says Andreas Kortenkamp, a toxicologist at the University of London. In independent research reported in an upcoming Environmental Science and Technology, he and two colleagues detail the biological effects of a mixture of eight estrogenic chemicals.

The researchers created a blend in which none of the chemicals alone was concentrated enough to affect estrogen-sensitive molecules on yeast cells. The mixture, however, did trigger a response.

Kortenkamp's finding demonstrates that "estrogens act additively even when the dose of each compound in the mixture is apparently negligible," says Soto.

Organic contaminants other than hormones could behave the same way, says Daughton. As future drugs are added to the nation's medicine chest, and thereby its waters, he says, it's imperative that scientists understand how they interact to affect the environment and human health.

Further monitoring of contaminants' prevalence in the environment would flag compounds that merit research, but the USGS may not get the chance to follow through. The latest budget from the Bush administration would eliminate the program that conducted the study.