"We ended up identifying a problem that is typical of endocrine disruption, that is, seeing eggs in the testes of sexually mature fish," Chris Ottinger, an immunologist at the Geological Survey's National Fish Health Research Laboratory, said on Thursday. "It was something that warranted further investigation."

These so-called endocrine disrupting chemicals are used widely in industry and in consumer products including pharmaceuticals, cosmetics, perfumes, plastics and even materials used to keep barnacles from clinging to boat bottoms.

Theo Colburn, an environmental health analyst who has specialized in studying the effects of endocrine disruptors, said they work during gestation, and have been linked to feminization of male fish in the Great Lakes, smaller penises in alligators and polar bears, and hermaphroditic whales -- with genitalia of both sexes -- in the St. Lawrence River.

SAFE TO DRINK

Laboratory studies have shown developmental effects from very low doses of hormone disruptors, but it would be technically impossible at present to remove such low concentrations of these compounds from drinking water, Colburn said by telephone from her office in Colorado.

The manager of the water utility that covers a large swath of the Washington area stressed that drinking water is safe.

"As water plant manager, what I know is that there is no evidence pointing to any concentrations of these substances in the water that are having human effects," said Thomas Jacobus, manager of the Washington Aqueduct. "The water is safe to drink."

Jacobus said the water was tested for some endocrine disrupting chemicals, but noted that there are potentially 20,000 of these compounds in existence.

The US Environmental Protection Agency said in a statement that the exact amounts of these chemicals, especially at extremely low doses, in the environment are difficult to determine.

"Little is known about the potential harm posed by trace amounts of PPCPs (pharmaceuticals and personal care products) in drinking water," the agency said in a statement. "Current water treatment processes may remove some PPCPs, but more research is needed to determine how efficiently these compounds are removed by various treatment technologies."