Drinking water gets a drug test.

Byline: Brian Rademaekers

Feb. 27--Federal scientists surveying fish in the Potomac River continue to find smallmouth bass with a freakish quirk: The males are making eggs and sperm.

Researchers suspect that these "intersex" bass are victims of a newly recognized form of pollution: trace amounts of pharmaceuticals and other chemicals flushed down toilets or flowing from farms' animal waste.

Compounds including antibiotics and caffeine drain through sewage systems largely untouched, collect in rivers and streams, and eventually return in tiny amounts to drinking water.

Until recently, those pollutants had been virtually undetectable because the concentrations are so low. But instruments now can identify substances in parts per trillion -- each part equivalent to a grain of sand in an Olympic-size swimming pool -- and scientists are finding traces of man-made chemicals in streams in Chester County and drinking-water supplies in Philadelphia and other cities.