(Beyond Pesticides, September 8, 2006)
According to the Associated Press (AP), some species of male fish are acquiring female sexual characteristics at unusually high frequencies in the Potomac River and its tributaries, prompting concerns about pollutants that might be causing the problem. Environmentalists have long pointed to pesticides and other endocrine disrupting chemicals as having the potential for wreaking such hormonal chaos. The article reports that in some Potomac tributaries, including the Shenandoah River in Virginia, nearly all of the male smallmouth bass caught in a survey last year by the United States Geological Survey (USGS) were so-called intersex fish, producing immature eggs in their testes. In the Potomac itself, 7 of 13 largemouth bass exhibited female characteristics, including 3 that were producing eggs.
Intersex fish were discovered in the Potomac river shed in 2003 and have also been found in other parts of the country. But the frequency found by the surveys is much higher than what had been found elsewhere, said Vicki Blazer, a USGS fish pathologist. Female fish caught in the survey did not develop any unusual sex traits, though fish of both sexes exhibited lesions and other problems related to pollution, said Ms. Blazer, who coordinated the survey. Gerald LeBlanc, an environmental toxicologist at North Carolina State University, told the AP that the high percentages of intersex fish found in the Potomac survey were surprising. It is not uncommon for such fish to be found in other parts of the country, Mr. LeBlanc said, but at lesser frequencies. Most scientists believe that changes are caused by a combination of endocrine disrupting pollutants and synthetic estrogens, such as pesticides and birth control pills. Endocrine disruptors are a diverse group of several thousands of chemicals that are used in everything from pesticides and flame retardants to cosmetics and pharmaceuticals. Endocrine disruptors may be mistaken for hormones by the body and thus their presence may alter the function of hormones, either blocking their normal action or interfering with how they are made in the body. Since hormones regulate things like growth and body development, there is great potential for damage. In particular, some endocrine disruptors are mistaken for the female hormone estrogen. These estrogen mimics interfere with the reproductive system, causing infertility, malformed sexual organs, and cancer of sensitive organs.
Disturbingly, there are many commonly used pesticides that are known or suspected endocrine disruptors, such as atrazine, 2,4-D, lindane, and permethrin. A recent study found that the commonly used lawn pesticide formulation Round-up, with the active ingredient glyphosate, causes damaging endocrine effects in fetuses. EPA does not currently evaluate or consider the endocrine disrupting properties of pesticides during registration or reregistration.
The environmental effects of these chemicals has been well-established: pseudo-hermaphrodite polar bears with penis-like stumps, panthers with atrophied testicles, hermaphroditic deformities in frogs, and male trout with eggs growing in their testes have all been documented as the probable result of endocrine-disrupting chemicals in the environment. Many scientists believe that wildlife provides early warnings of effects produced by endocrine disruptors, which may as yet be unobserved in humans.