Sex-Changing Chemicals Found in Potomac River

Amitabh Avasthi
for National Geographic News
January 22, 2007
Ever since the discovery of gender-bending fish in the Potomac River, scientists have wondered what could be changing the sex of large numbers of fish in the waterway outside Washington, D.C.

They may not have to wonder much longer.

A recent U.S. government study has found large quantities of chemicals in the river and its tributaries—pollutants that are known to cause sex change in animals.

These chemicals, from both residential and industrial sources, may be linked to the unnatural fish, says the U.S. Geological Survey (USGS) report, which was released late last month.

Males With Eggs

The discovery of the abnormal fish "was largely accidental," said Douglas Chambers, a USGS scientist who led the study.

"In 2002 we were looking at stream-water chemistry to understand the large fish die-offs at these sites. It was then that we found smallmouth bass with intersex, a condition where male fish develop premature egg cells."

(See "Male Fish Producing Eggs in Potomac River" [November 3, 2004].)

During a 2003 survey of the Potomac River and the Cacapon River of West Virginia, Chambers and his colleagues found large numbers of intersex fish.

The researchers also found chemicals from pesticides and flame retardants as well as fragrances commonly found in products such as soaps, antiperspirants, and deodorants.

"We analyzed blood plasma of 30 smallmouth bass from six sites," Chambers said. "All the fish contained at least one of the polluting chemicals, including fish that were not intersex."

However, Chambers said, the study has so far not turned up a single case of "imposex"—the condition in which female fish have malformed ovaries or produce sperm.

Hormone Interrupted

Once absorbed by the body, these chemicals—known as endocrine disruptors—interfere with normal bodily functions either by mimicking or blocking the production of hormones.

Experts say endocrine disruptors are found in pesticides, pharmaceuticals, fumigants, and fungicides. Municipal and domestic sewage and wastewater from farms and industries might be routing these chemicals into the water supply.

The presence of such chemicals is not unique to the Potomac. The pollutants have previously been documented in bodies of water in other parts of the United States as well as in Europe.

Scientists have also found reproductive problems in fish and birds in habitats along the U.S. Great Lakes. Similarly, declining alligator populations in Florida's Lake Apopka have been linked to synthetic chemicals that hinder reproduction.

Pollution Cocktail

Chambers says the USGS is analyzing data from last year and is planning to release a more detailed report later this year. The next report will try to make a definitive link between these chemicals and their effects on the environment.

"Currently many of these compounds have not been well researched for their environmental characteristics, how they are taken up by living organisms, and how they can be removed from streams," he added.

Dana Kolpin is a USGS research hydrologist and director of the agency's Emerging Contaminants Project. He reviewed Chambers' study but is not connected with it.

"This is the first step to understanding a very complex issue," Kolpin said.

"We need to understand the cocktail of compounds that are in the environment and whether there are certain bad actors that are causing feminization of males—and what it means for humans [who use this water]."

"It is critical to know where the sources are, how the compounds are being transported, and which ones are being degraded. What happens to them [after they enter the river] is the million-dollar question."

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