Washington - Chemicals known to change the sexual characteristics of fish and other animals have been found in West Virginia tributaries of the Potomac River, which runs through Washington, D.C. and surrounding areas, the U.S. Geological Survey said on Wednesday.

An investigation into fish that had both male and female characteristics turned up a range of chemicals including pesticides, flame retardants, and personal-care products, the USGS said.

The Potomac is fed by rivers and streams in Maryland, Virginia and West Virginia.

"We analyzed samples of 30 smallmouth bass from six sites, including male and female fish without intersex and male fish with intersex," said Douglas Chambers, a USGS scientist who led the study.

"All samples contained detectable levels of at least one known endocrine-disrupting compound, including samples from fish without intersex."

Endocrine disrupters affect the animals' hormone systems. They can cause birth defects and sexual abnormalities called intersex in species ranging from frogs to alligators and perhaps humans as well.

"Antibiotics were detected in municipal wastewater, aquaculture, and poultry-processing effluent, with the highest number of antibiotics and the greatest concentrations found in municipal effluent," the USGS wrote in the report, published at http://pubs.usgs.gov/of/2006/1393/.

The USGS said the sexual changes in the fish were discovered by accident in 2003, when scientists were investigating massive fish kills.

"Many potential sources of contaminants discharge to the South Branch of the Potomac and Cacapon Rivers. Chief among these are runoff from agricultural activities, municipal and domestic wastewater effluent (both treated and untreated), industrial wastewater, and gypsy moth control programs using dimilin (diflubenzuron)," the report reads.