Intersex Fish Linked to Human Activity

This story was updated at 4:04 pm EST.

High amounts of hormone-disrupting chemicals have been found in several spots along the Potomac River Basin, as well as in the blood of male fish with female sex characteristics living in the river’s water, according to a new study.

Researchers have traced the chemicals back to several man-made products, including pesticides, flame retardants and personal care products such as perfume, cologne and antibacterial hand washing soap.

In 2003, scientists began finding egg cell precursors, called oocytes, on the testes of male smallmouth bass living in the river. Researchers suspected the reproductive anomalies were due to disruptions in the fishes’ endocrine system, which controls the release of certain hormones—such as estrogen and testosterone—and helps to regulate many sexual and reproductive characteristics in organisms.

One primary suspect has been a class of man-made chemicals called endocrine disrupter compounds (EDCs). These chemicals mimic natural hormones and interfere with the endocrine system’s normal functioning. The new study, available on the U.S. Geological Survey website, confirms that EDCs are prevalent in the Potomac River’s water.

“We’re finding some of the compounds that are either are known or suspected endocrine disrupter compounds widely in the environment,” said Douglas Chambers, a USGS scientist and lead researcher of the study. “We’re seeing them both in places where we see intersex fish and where we have not found intersex fish. Some of the compounds are nearly ubiquitous in the environment.”

However, scientists have yet to establish a definitive link between EDCs and intersex characteristics in fish, Chambers said.

“Part of the missing picture right now is we don’t have all of the age data for the fish which is an important determination of length of exposure to some of these compounds,” he explained.

The researchers analyzed samples of 30 smallmouth bass from eight sites along the river, including male and female fish with normal sex organs and intersex males.

The researchers found traces of many known or suspected endocrine-disrupting chemicals found in the fishes’ blood. EDCs and antibiotics were also found in water from various sources, including fish hatcheries, poultry-processing plants and city water runoffs.

The high number of EDCs discovered is worrisome because studies have shown that these chemicals combine synergistically to create a stronger disruptive effect in some animals.

Whether endocrine-disruptors pose any threat to humans, however, is still not known. “There’s not any clear evidence at this moment,” Chambers told LiveScience. “We’re seeing yearly worldwide reports about declines in human male sperm counts and some other sorts of indicators, but whether there is a linkage between the compounds and these effects is just unknown at this time.”

High intersex occurrence in aquatic species has been documented at other locations in the U.S. and Europe. Industrial pollutants have also been linked to developmental abnormalities in other animals as well, including alligators, frogs and polar bears.

• Sewage and Intersex Fish
• Pollution Blamed for Intersex Fish
• Potomac 'Intersex' Fish Worry Scientists
• Study: Polar Bear Genitals are Shrinking