Male Bass Across Region Found to Be Bearing Eggs

Blazer said water tests in the upper Potomac have detected low levels of a few known endocrine disruptors. But she said none of them has been pinpointed as a cause for the intersex condition, and the problem might be several pollutants acting in combination.

Also unclear is the effect on the Potomac's bass population. There have been several bad spawning years in the past decade, scientists said, and several large die-offs of smallmouth bass in the Shenandoah in recent years. But neither has been conclusively linked to the intersex problem.

Even less understood -- both in the Potomac and around the world -- is how these pollutants affect human health.

In 1996, Congress required the U.S. Environmental Protection Agency to help answer that question by developing a screening program to identify which chemicals are endocrine disruptors. Ten years later, the agency hasn't tested a single chemical, officials said.

Environmental groups have accused the EPA of proceeding too slowly. Agency officials have defended their efforts by saying the research has been more complex than expected.

"I would have hoped it would have been faster, but this is a very difficult program," said Clifford Gabriel, director of the EPA's Office of Science Coordination and Policy. "We want to make sure we get the science right."

In the area, at least four drinking-water utilities -- the Washington Aqueduct, Fairfax Water, the Frederick County authority and the Washington Suburban Sanitary Commission, which serves Montgomery and Prince George's counties -- take water from the Potomac. That has prompted some environmentalists to worry about problems in tap water, in light of the intersex problems in fish.

"If they can't tell us what the problem is," said Ed Merrifield, executive director of a group called Potomac Riverkeeper, "then how can they tell us that they've taken it out of the water?"

At the four utilities, officials said they felt confident that the Potomac water was being filtered and cleaned well enough that it posed no health risk from endocrine disruptors. But Charles M. Murray, general manager at Fairfax Water, said he wanted more certainty about those pollutants and their effects.

"The question is: Are we analyzing for the right things?" said Murray, whose utility serves a large swath of Northern Virginia and gets about half of its water from the Potomac.