Intersex fish have been found in the Potomac River in Washington, D.C., where scientists have discovered immature eggs in the sex organs of male smallmouth and largemouth bass.
"It indicates a problem we need to be concerned about," says Vicki Blazer, the fish pathologist at the U.S. Geological Survey, who has studied the problem since 2003, after a large fish kill in the south branch of the Potomac. Blazer first noticed the intersex abnormality in 2004. "We need to try to figure out what's going on."
But so far, scientists have not been unable to pinpoint exactly what contaminants have caused this abnormality. And since the health of a fish indicates the health of the water, environmentalists have asked if the contaminants affecting the fish pose any danger to the millions of people whose tap water comes from the Potomac.
"We know pollution is in the water," says Ed Merrifield, executive director of the Potomac Riverkeeper, an environmental group. "All water runs downhill. If they can't tell us what the problem is, how can they tell us it's not in our water? There may be a danger."
So far, Washington's water utilities say they've found no evidence that tap water taken from the Potomac is unsafe. "There is no indication we have any public health concerns with our finished water," says Charles Murray, the general manger of the Fairfax County Water Authority, which depends on the Potomac River as the water source for half of its 1.4 million northern Virginia customers.
Murray is confident that the barriers and water treatment systems in place can remove a broad range of compounds. "We'd like to know more, but at this point are we concerned that what we have in place is not protecting the public health? No."
The first intersex fish in the area were found three years ago in a West Virginia stream, 200 miles upstream from Washington. After that unusual discovery, scientists set up testing sites all around the region.
According to Blazer, last month's testing at three tributaries that empty into the Potomac found that more than 80 percent of all male smallmouth bass were growing eggs.
"It was certainly surprising," she says. "The south branch of the Potomac is in the rural areas of West Virginia. We tend to think of environmental problems only in urban areas."
The intersex abnormality does not change a fish's appearance. It can be detected only under a microscope.
And while Blazer says she cannot say definitively what is causing the fish to possess both male and female characteristics, she believes the results suggest that the abnormalities stem from "endocrine disrupters" -- which act as a kind of "short" in hormone systems -- in the Potomac River and its tributaries.
Over the last decade, environmentalists have raised concerns over pollutants that mimic hormones; they've caused mutations in several animals, including alligators, polar bears and frogs. Ten years ago, scientists discovered frogs with extra legs, and males with ovaries.
Blazer believes the intersex abnormality cannot be blamed on just one pollutant but on several pollutants acting together. "Many of the chemicals we're finding [that cause this mutation] are something we all use," she says. "They're not just chemicals used by big industry. They're pharmaceuticals, beauty products that everyone uses and discards. They're pesticides and herbicides used in yards."
In 1996, Congress passed the Food Quality Protection Act, which requires the U.S. Environmental Protection Agency to test pesticides and chemicals for their potential to act as endocrine disrupters. But developing the tests was "technically challenging," says Clifford Gabriel, director of the EPA's Office of Science Coordination Policy.
Ten years later, the EPA still hasn't tested any chemical. "It's not a straightforward process," says Gabriel. The agency wants to "make sure we have appropriate tests to make sure we are picking up on possible endocrine disruption."
The EPA expects to be ready with the first tests of potential endocrine disrupters by the end of 2007.
Endocrine disupters are nothing new to water utilities, which have banded together to try to advance the science and learn more about this far-reaching problem.
The four water utilities that depend on the Potomac River for their supply of drinking water want more details on Geological Survey's findings, and what they might mean for people.
"While it's very true the health of the fish indicates the health of the river," says Jeannie Bailey, the public affairs officer at Fairfax County Water Authority, "it doesn't necessarily translate to humans."
Other area utilities echoed Bailey's comments, saying that people should be far less susceptible to the river's pollution than fish are, because of their larger bodies and different hormone systems. And unlike fish, they're not constantly exposed to the water.
But environmentalists don't buy that argument. "No more than I would buy that argument for why mice get tumors," when exposed to certain chemicals, says the Potomac Riverkeeper's Merrifield. " Just because [the fish are] a lot smaller ... those tumors shouldn't be there."
On one point both sides agree: The Geological Survey's findings raise more questions than answers about what causes the abnormalities in the fish, and what possible effects they may have on humans.