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Man-Made Chemicals May Put Strain on Fish
To investigate, scientists from the Geological Survey, the U.S. Fish and Wildlife Service and the Maryland Department of Natural Resources began taking samples of water in 2005 and 2006.
In the river near the District's Blue Plains sewage plant, scientists suspended a device intended to serve as a facsimile fish. The device had a plastic-coated tube, which simulated a fish's permeable skin, and a layer of simulated fat.
"We're trying to see what the fish sees," Alvarez said.
They saw a lot. The tests on this fake fat revealed a range of potentially worrisome pollutants. Most have been found in other streams around the United States, scientists said, adding that the pollutants are of special concern in the Washington area because of the intersex fish.
The discoveries included trace amounts of atrazine, a herbicide commonly used on farm fields. The EPA has put the herbicide on a list of chemicals to be tested for hormone-mimicking effects. Some scientific studies have already linked atrazine to sexual abnormalities in frogs and fish.
"There's a weight of evidence that something's going on here," said Nancy Golden, a wildlife toxicologist with the Fish and Wildlife Service, who said she was summarizing a common view, not her own conclusion.
A company that makes atrazine, the agribusiness Syngenta in Basel, Switzerland, has insisted that the chemical presents no undue risks if used properly.
Also found in the Potomac were the insecticides chlorpyrifos and endosulfan and the herbicide metolachlor. All three are on the EPA's list of chemicals to be tested for hormone-mimicking effects. Researchers said the chemicals, as well as atrazine, might have washed off suburban lawns in the Washington area or farm fields farther upstream.
Other chemicals were apparently added, unknowingly, by urban residents in the course of daily life. These included two chemicals used to add fragrance to perfumes, soaps and other products: tonalide, and galaxolide. The chemicals, when washed down drains, can pass through sewage treatment systems and into rivers.
Geological Survey researcher Vicki S. Blazer said that some evidence suggested all of the chemicals could interfere with hormones.
The research study did not look for traces of pharmaceuticals, but a separate round of federal testing has found traces of six pharmaceuticals in local drinking water taken from the Potomac.
Researchers said this new set of results marked a big step toward finding the reason for the Potomac's gender-confused fish, though it did not solve the case.
"We're beginning to narrow down some of the . . . possible chemical causes," Blazer said. "Now we have a better idea of what's there."
The repercussions for human health are also unclear. At the Washington Aqueduct, the agency that turns river water into tap water for the District, Arlington County, Falls Church and parts of Fairfax County, the treatment process is not designed to remove the chemicals.
The agency's general manager, Thomas P. Jacobus, said tests on "finished" water showed trace levels of both atrazine and metolachlor last year. He said, however, that the levels of the chemicals were so low they did not seem to pose a danger.
Ed Merrifield, executive director of the environmental group Potomac Riverkeepers, said he still wants more information about the impact of the pollutants.
"None of these chemicals should be in our water," he said.