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Scientists want to know if Rio Grande contaminants are feminizing the endangered silvery minnow

August 25, 2010, 1:00 am

Evidence of contamination in the Rio Grande has been mounting over the last decade.

In 2003, the state’s Environment Department and Department of Health reported that the majority of human wastewater contained antibiotic residues. In fact, up to 90 percent of pharmaceutical doses pass through humans or animals (such as those at dairies) and many antibiotics are not destroyed or removed by conventional wastewater treatment.

WildEarth Guardians Executive Director John Horning was involved for years in the silvery minnow debate.

In order to determine if poor water quality might be contributing to the decline of the silvery minnow, the Middle Rio Grande Endangered Species Act Collaborative Program had asked the Environment Department’s Surface Water Quality Bureau to monitor the Middle Rio Grande. That report was released last year. Although the most critical issue affecting the fish is the lack of adequate river flows to maintain its habitat, the state did find high levels of E coli in the river, as well as elevated levels of metals such as aluminum, copper and chromium. According to the report, water quality conditions exist that may affect the minnow’s reproduction and respiration, “further stressing the fish and reducing the likelihood for recovery.”

The state regularly monitors water quality in all rivers, surveying stretches on a rotating basis, according to Lynette Guevara, assessment coordinator for the Surface Water Quality Bureau. Currently, of the 370 miles of the Rio Grande surveyed, the state has noted “impairments” on 305 of those miles. These impairments range from aluminum levels and elevated temperatures to PCBs in fish tissues and widespread E coli contamination.    

River contamination such as this is not a new phenomenon—but it is an evolving one.

The federal government began funding monitoring projects to learn how certain chemicals were affecting wildlife—including fish—in the late 1960s and ’70s, following Rachel Carson’s exposure in her book, Silent Spring, of the pesticide DDT’s impact on birds. A Fish and Wildlife Service marine biologist, Carson showed that DDT was causing birds to lay eggs with increasingly thin shells, and that certain bird populations were declining.

“That [monitoring] program lasted into the 1980s, and what they noticed was a lot of what are called ‘legacy’ pesticides decreased in fish—and that’s what folks were hoping to see,” Jo Ellen Hinck, a biologist with the US Geological Survey, who is based out of the Columbia Environmental Research Center in Missouri, says.

Legacy chemicals include DDT, PCBs and mercury, which remain in the environment long after their use is discontinued.

Then, in the early 1990s, the issue of “endocrine disrupters” arose, and scientists realized they needed to do more than just measure the amount of contamination in tissue.

Endocrine disrupters include certain types of herbicides such as atrazine; the plastic compound bisphenol A; cadmium; DDT and other pesticides and insecticides still used today, including malathion; and a family of plasticizers known as phthalates.

These compounds affect the endocrine system, reproduction and fetal development, and scientists have learned that, even in very low doses, they can cause problems.

In the mid-1990s, the USGS began sampling fish in nine US river basins, including the Rio Grande, to learn about environmental contaminants. Only this time, scientists weren’t only measuring the amounts of chemicals or metals found within fish tissue. They also were looking for abnormalities in organs such as the liver, kidney, spleen, ovaries and testes.

“Scientists got better at creating chemicals where you didn’t have the accumulation in fish, and have that food chain accumulation—that led to, like, the thinning of bald eagle eggs,” Hinck says. “Those compounds can still have effects on the fish, but you can’t measure them because they don’t accumulate in the fish.”

What Hinck and her colleagues found was that many male smallmouth and largemouth bass had egg cells in their testes. “Intersex” fish showed up in all but one of the basins they studied—including in the Rio Grande. Endocrine disrupting compounds enter the fish’s body and mimic natural estrogens. (Like humans, fish also produce estrogens and androgens.)

Although Hinck says the Rio Grande results weren’t particularly alarming, taken with the data from the other large rivers studied, there is cause for concern.

“We became concerned with the incidents of ovotestes in male bass because it was becoming so prevalent,” she says. “Ovotestes” are gonads with both testicular and ovarian aspects.

In short, bass are not supposed to have eggs within their testicular tissue.

“Do we know what’s causing it? No,” she says. “But we do know that, if the majority of the fish have it, that seems anomalous to us.” Those findings have led them to take on additional studies, to try and learn what causes the reproductive disorders.
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