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Study: Farming, Population Cause Intersex Fish

Posted on: Friday, 8 February 2008, 11:20 CST

Researchers have found that forms of fish containing both male and female traits appear to be more prevalent in areas with more farming and population density, according to a new study by the U.S. Geological Survey.

Although the cause is unknown, researchers assume that wastewater runoff of polluted chemicals is stimulating estrogen production in the intersex fish. Instances of the abnormality have been recorded over the past decade in areas including the southern Great Lakes, the Potomac River watershed, which includes the Eastern Panhandle in West Virginia, and the Southern California coast.

U.S. Geological Survey researchers found the frequency of male smallmouth bass with immature female eggs in their testes was highest where farming is most intense and where human population density is highest. The study also found the prevalence of the form of intersex, known as testicular oocytes, was greatest just before and during the spring spawning season, according to Associated Press.

The results were published in the current edition of the Journal of Aquatic Animal Health.

Researchers collected smallmouth bass from the Shenandoah River, the South Branch of the Potomac, and the Potomac River basin, said USGS scientist Vicki Blazer, who led the study.

"On the Shenandoah, rates of intersex were highest, ranging from 80-100 percent intersex," Blazer said.

Seventy-five percent of those collected from the Potomac basin had testicular oocytes in the most heavily farmed and populated areas, which dropped to 14 percent to 35 percent in less farmed and developed sites.

Fish collected from the South Branch’s percentages ranged from 47 percent to 77 percent, while increasing along with farming and population, the researchers said.

Certain toxic chemical compounds in industrial and household detergents are said to cause male fish to develop female attributes . Last year, the Sierra Club asked the Environmental Protection Agency to ban the use of these chemical compounds, and additionally asked to discontinue the use of these products in areas where wastewater treatment plants aren't equipped to remove nonylphenol ethoxylates, or NPEs.

The compounds, derived from petroleum, are used mainly in detergents but also in paper manufacturing and flame retardants.

NPEs are more tightly restricted in Canada and Europe than in the United States, which issued water-quality limits for the key ingredient, nonylphenol, or NP, in December 2005.

Detergent manufacturers Procter & Gamble of Cincinnati and Unilever have substituted other chemicals in their products, and Wal-Mart is seeking to phase NPEs out of its stores by rewarding companies that find alternatives, according to Associated Press.

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On the Net:

U.S. Geological Survey

Journal of Aquatic Animal Health

Sierra Club

Environmental Protection Agency

Procter & Gamble

Unilever

Wal-Mart

Source: redOrbit Staff

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