Male fish carrying eggs - intersex fish - have been found in Pennsylvania's Susquehanna, Delaware and Ohio river basins, a sign that the water may be tainted with chemicals, according to the U.S. Geological Survey.
The research found that two fish species, smallmouth bass and white sucker, were exhibiting the effects of exposure to endocrine-disrupting chemicals. Intersex characteristics caused by hormones and hormone-mimicking compounds include immature eggs in male fish, the USGS said.
"The sources of estrogenic chemicals are most likely complex mixtures from both agricultural sources, such as animal wastes, pesticides and herbicides, and human sources from wastewater treatment plant effluent and other sewage discharges," Vicki Blazer, a research fish biologist and lead author of a study, said in a statement.
Blazer told the Los Angeles Times on Wednesday that any of these chemicals could affect humans, particularly those that come from human excretion and have hormones from things such as birth control. However, she said, the real danger for the fish is that they spend all of their time in the water and are continuously saturated in them.
The fish had to have been born with these defects, she said.
Estrogenic chemicals disrupt the endocrine system, which regulates the release of hormones like estrogen and testosterone. This interferes with the fish's ability to reproduce.
Blazer and colleagues collected fish from 16 sites in the Susquehanna, Delaware and Ohio river basins. Intersex males were found at every site where smallmouth bass were collected, and the severity of their condition was generally worse in places just downstream from wastewater treatment plants, the researchers found.
Bass seem to be especially prone to becoming intersex when exposed to estrogenic compounds, Blazer and colleagues said in the study.
The researchers also sampled white suckers and redhorse suckers. Redhorse suckers didn't have any intersex characteristics, but the team found an egg cell precursor, or stem cells that could potentially develop into eggs, in the blood of some white suckers.
The most common hormone found in water and soil samples was estrone, a potent endocrine-disrupting chemical often found in sewage from wastewater plants and the manure of animals such as cows, chickens and pigs, the researchers said.
"We weren't expecting the issue to be as widespread as it was," Blazer said. "The number of fish affected and the severity was surprising."
Northern Virginia Rep. James P. Moran, a Democrat, issued a statement and called the findings "troubling" and "yet another example of the adverse effects on water pollution in this country and another reminder that lawmakers need to take chemical waste regulation more seriously."
"We need to be conscious of the substances flowing into our water sources," Moran said. "Our rivers and the wildlife living there are among our country's most precious resources. It's a shame to see them deteriorated at the hands of irresponsible human behavior."
Blazer said reducing the use of pharmaceutical drugs and personal care products, such as fragrances, could help with the issue. She also said upgrading wastewater plant technology and fencing rivers so animals, such as cows, won't excrete directly into the water would help.