Male Bass Across Region Found to Be Bearing Eggs
Wednesday, September 6, 2006
Abnormally developed fish, possessing both male and female characteristics, have been discovered in the Potomac River in the District and in tributaries across the region, federal scientists say -- raising alarms that the river is tainted by pollution that drives hormone systems haywire.
The fish, smallmouth and largemouth bass, are naturally males but for some reason are developing immature eggs inside their sex organs. Their discovery at such widely spread sites, including one just upstream from the Woodrow Wilson Bridge, seems to show that the Potomac's problem with "intersex" fish extends far beyond the West Virginia stream where they were first found in 2003.
The cause of the abnormalities is unknown, but scientists suspect a class of waterborne contaminants that can confuse animals' growth and reproductive systems. These pollutants are poorly understood, however, leaving many observers with questions about what the problems in fish mean for the Potomac and the millions of people who take their tap water from it.
"I don't know, and I don't think anybody knows, the answer to that question right now: Is the effect in the fish transferable to humans?" said Thomas Jacobus, general manager of the Washington Aqueduct, which processes Potomac water to provide drinking water for residents of the District, Arlington County and Falls Church.
Jacobus, like others at area utilities, said there was no evidence that tap water taken from the Potomac was unsafe to drink. They said humans should be far less susceptible to the river's pollution than fish, because people are not exposed constantly to the water, our hormone systems work differently, and our larger bodies should require higher doses of any pollutant to cause problems. As research on the fish continues, other scientists across the region are trying to determine whether Potomac water or mud can affect human cells. This research, including tests at West Virginia University that examine whether cells react as if estrogen or estrogen mimics are present, has not reached any solid conclusions.
The first intersex fish in this area were found three years ago in the South Branch of the Potomac, a tributary more than 200 miles upstream from Washington. In 2004, more abnormal bass were discovered in a section of the upper Potomac near Sharpsburg, Md.
Following up, last fall federal and state researchers caught smallmouth bass in the Shenandoah River in Virginia and in the Monocacy River and Conococheague Creek in Maryland. All three tributaries eventually empty into the Potomac. At the site on the Potomac itself in the District, there are no smallmouth bass, so the researchers examined largemouth bass.
The results were striking, according to Vicki S. Blazer, a fish pathologist with the U.S. Geological Survey. More than 80 percent of all the male smallmouth bass they found were growing eggs, including all of the fish caught at four of the seven survey sites. The intersex condition doesn't change the fish's outward appearance but can be detected under a microscope.
At the site in Washington, seven of 13 male largemouth bass showed some kind of unusual feminine characteristic. Six of the seven fish tested positive for a protein used to produce eggs, and three of the seven contained eggs, Blazer said.
Taken together, Blazer said, the results on both bass species seemed to indicate that the Potomac watershed has a problem with "endocrine disruptors," contaminants that interfere with nature's chemical signaling. In this case, she said, the contaminants might have turned on bodily processes that normally are only active in female fish.
"What we're seeing now is that it's definitely not a problem just in the South Branch," she said. "There is this sort of widespread endocrine disruption in the Potomac, but we don't know still what are the causes."
Pollutants that mimic hormones have emerged as a worldwide concern in the past decade, blamed for problems in animals as diverse as alligators, minnows and polar bears. Although scientists say the research is in its infancy, they have identified a large array of pollutants that might affect animals, including human estrogen from processed sewage, animal estrogen from farm manure, some pesticides and additives to soap.