USGS Identifies Contaminants in Potomac River Possibly Linked to Intersex Fish

(Beyond Pesticides, March 24, 2008)

Scientists at the U.S. Geological Survey (USGS) announced that they have identified ten contaminants, including pesticides, in the Potomac River, which flows through downtown Washington, DC, that could be responsible for the alarming discovery of “intersex fish,” male fish producing eggs. The suspected chemicals include: atrazine, a common herbicide used in agriculture and on lawns that is already linked to sexual abnormalities in frogs; insecticides chlorpyrifos and endosulfan; the herbicide metolachlor; and two chemicals used to add fragrance to perfumes, soaps and other products, tonalide and galaxolide.

To collect the samples, USGS scientists suspended a device intended to serve as a facsimile fish in the Potomac River near the Washington, DC’s Blue Plains sewage plant. The device had a plastic-coated tube, which simulated a fish’s permeable skin, and a layer of simulated fat. According to the Washington Post, the tests on this fake fat revealed a range of potentially worrisome pollutants. Most have been found in other streams around the U.S.

“The types of things we’re finding are the types of things that are associated with everyday life,” David Alvarez, a U.S. Geological Survey research chemist who analyzed samples from the Potomac told the Washington Post. “The contaminants flow into the river from sewer plants and in rainwater washing off of farm fields and suburban lawns. If it’s something we’re using, ultimately it’s going to end up in the water.”

In 2006, USGS discovered in some Potomac tributaries, including the Shenandoah River in Virginia, nearly all of the male smallmouth bass caught 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 rivershed 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 initial survey.

Most scientists have suspected endocrine disruptors and synthetic estrogens, such as pesticides and birth control pills, from the beginning. 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.