Intersex Fish Linked to Human Activity

By Ker Than LiveScience Staff Writer posted: 17 January 2007 12:42 pm ET

Scientists have linked the high incidence of male fish with female characteristics in the Potomac River Basin to hormone-disrupting chemicals found in human products, including pesticides, flame retardants and personal-care products. 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. Scientists have long suspected that a class of man-made chemicals called endocrine disrupter compounds (EDCs) were behind the “intersex,” characteristics, but a new study is the first to confirm the link. EDCs mimic natural hormones and interfere with the endocrine system’s normal functioning. 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. “All samples contained detectable levels of at least one known endocrine-disrupting compound, including samples from fish without intersex,” said Douglas Chambers, a USGS scientist and lead researcher of the study. 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 waste water runoffs. “This study found that some EDCs are nearly ubiquitous in the environment, also being present at sites where fish are not exhibiting intersex conditions,” the researchers write in a new study available on the USGS website. The high number of EDCs discovered is worrisome because studies have shown that these chemicals act additively or synergistically to create a stronger effect, the researchers add. It is still unclear whether endocrine-disruptors pose any threat to humans, but 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.