WASHINGTON — Pollution experts pressed a congressional panel Thursday for a new national approach that monitors the country's waters more broadly for the presence and impact of hundreds of recently detected contaminants from pharmaceuticals to fire retardants.

Rep. Eddie Bernice Johnson, D-Texas, chairwoman of the House Subcommittee on Water Resources and Environment, opened her panel's hearing with a warning. A former nurse, Johnson said the presence of these contaminants makes her "question just how safe our waters actually are — especially to human health over the long term."

Equipped with more refined tests, researchers in recent years have discovered the existence of a complex brew of unregulated contaminants beyond conventional industrial and agricultural pollutants. These low-concentration, emerging contaminants include discarded and excreted pharmaceuticals, vitamins and cosmetics, as well as some pesticides and industrial compounds.

Risks are poorly understood, though there is evidence that pharmaceuticals and hormone-like compounds can harm aquatic life. Preliminary research indicates that some waterborne drugs also may promote antibiotic-resistant germs and impair the workings of human cells in the laboratory.

Some experts testified to the panel that the Clean Water Act, which aims to clean up pollution in rivers and streams, may not be equal to the task for a host of newly recognized pollutants occurring in complex mixtures.

Environmental researcher Peter L. deFur of Virginia Commonwealth University suggested the Clean Water Act could be reshaped to "require monitoring and reporting of all chemicals in discharges, regardless of the identity and chemical nature." A limited number of pollutants are monitored now.

David P. Littell, Maine's commissioner of Environmental Protection, said "it is more effective to prevent substances of high concern from entering the waste stream" than relying on the chemical-by-chemical water quality standards.

Drugs have raised special concerns, because they are designed to affect the human body at low concentrations and because their use and presence in waterways is so widespread. In a continuing investigation, The Associated Press has reported that at least 46 million Americans are supplied with drinking water that has tested positive for traces of pharmaceuticals. The stories, which began appearing in March, have prompted a national flurry of water testing and federal and local hearings like the one convened by Johnson.

Pharmaceuticals in water are blamed mostly on unmetabolized drugs excreted by humans and animals, then flushed into sewage systems connected to streams and rivers. However, the AP reported earlier this week that hospitals and long-term care centers intentionally discard an estimated 250 million pounds a year of unused pharmaceuticals and tainted packaging — and much of those drugs also go directly down drains toward water supplies.

In an interview before the hearing, subcommittee member U.S. Rep. Candice Miller, R-Mich., said the Environmental Protection Agency ought to impose controls on healthcare facilities that dump unused pharmaceuticals down the drain. "I think we should step up and make sure this is not happening," said Miller.

But she put forward a less ambitious bill in July. If adopted, it would only require the EPA to assemble a task force to craft recommendations for safer disposal of unused pharmaceuticals. The EPA is already following its own approach with a study of whether such restrictions are needed.

A separate bill proposed by Rep. Carolyn McCarthy, D-N.Y., would make the EPA further study pharmaceuticals and personal care products in the water; how better to monitor them and their risks; and how to clean them up.

Non-voting Delegate Eleanor Holmes Norton, D-Washington, D.C., pleaded for more government action. Decrying the existence of male fish that develop eggs in their sex organs, a situation blamed on hormone-like contaminants, she wondered aloud "how much we need to know before it occurs to us that something needs to be done."

Ben Grumbles, the EPA's top water official, balked at any immediate, sweeping upgrade of water standards. He told the panel more research and evaluation are needed now.

However, in an interview later, he said critics are correct to question whether the existing regulatory mechanism can handle the complex mixtures being detected in waters.

"It may be that there needs to be a more effective way to deal with the mixtures," he added.