Pharmaceuticals and personal-care products - contaminants that, while being detected worldwide, are unregulated in water - are a growing concern for water-quality experts.
The Pennsylvania intersex fish discoveries have prompted the state Department of Environmental Protection to launch a sampling campaign of several river systems in search of 180 compounds, including endocrine-disrupting chemicals, new pesticides, and old products such as DDT.
The Delaware River Basin Commission and partner researchers also have found caffeine, over-the-counter products such as naproxen and ibuprofen, prescription drugs such as codeine, and antibiotics.
Natural and synthetic hormones rank among the top chemicals in U.S. surface waters for potential ecological harm, a 2012 DRBC report noted.
"We have to be vigilant," said Thomas Fikslin, manager of the commission's monitoring and modeling branch. "It's why we do the monitoring we do, to see first of all what chemicals are there, and then determine potential hazards to human health and aquatic life."
But, he added, "Just because you measure something in high concentration doesn't mean it's a problem." Conversely, "measuring something in a low concentration doesn't mean it's not a problem."
Intersex fish are a problem.
In the latest study, Blazer tested smallmouth bass and suckers in the Ohio, Susquehanna, and Delaware watersheds.
Suckers, which are bottom-feeders, showed few intersex characteristics. But the bass from all sites had immature eggs in their testes.
Blazer found the highest prevalence and severity in the Susquehanna drainage area. But at the Falls Bridge over the Schuylkill near East Falls, 50 percent of the smallmouth bass they caught had intersex characteristics.
Blazer and her colleagues also used a specific strain of yeast to measure estrogenicity in the water. In places with intersex fish, it was higher.
The sources of the estrogenic chemicals, Blazer said, "are likely complex mixtures from both agricultural sources, such as animal wastes, pesticides, and herbicides, and human sources, [such as] waste water treatment plants and other sewage discharges."
In most cases, Blazer said, farmers are not feeding estrogenic compounds; manure simply contains them. In addition, pesticides and herbicides can be estrogenic.
Likewise, humans naturally excrete estrogens, as well as the synthetic estrogens from birth control pills. The latter "tend to be of higher potency," she said, "and are more stable, and hence, last longer in the environment."
Generally, Blazer found that severe intersex characteristics occurred downstream of waste water treatment plants. The Schuylkill has 435. Most facilities are not designed to remove pharmaceuticals that people ingest, then excrete.
Agricultural land use, however, could be the bigger culprit. Overall, both the numbers of intersex fish and immature eggs correspond with the amount of agriculture in the watershed above the collection sites. In upstream areas along the Schuylkill, the percentage of land given over to farming is high.
The study findings, published recently online by the journal Environmental Monitoring and Assessment, were not good news to Tom Davidock, who oversees the Schuylkill Action Network, an educational and outreach program of the Partnership for the Delaware Estuary. He often works with farmers to help them reduce their environmental impacts, and "this is just another one of those messages we'll have to start looking into," he said.
Blazer did not start out looking for intersex fish. When she began working the Potomac, she was investigating fish kills in the watershed. But she soon began finding male fish with immature eggs and a precursor to yolk material.
Similarly, fish kills in the Susquehanna are what attracted the interest of the Pennsylvania DEP. First-year smallmouth bass were getting sick and dying late every summer.
After state officials learned of Blazer's work, they began their own testing program for emerging contaminants in 2013. They are sampling the waters not just of the Susquehanna, but also the Delaware, Allegheny, Juniata, and Youghiogheny Rivers.
Although smallmouth bass are the immediate concern, they may simply be an early indicator of "bigger problems in the river," said Rod Kime, a DEP environmental program manager.
"We're finding concentrations of many of these compounds," Kime said, but he called that "not unusual" in "any place there are people or farms."