Mercury Is Contaminating the Grand Canyon

posted: 08/26/15
by: Patrick J. Kiger for Discovery News
Panoramic of Grand Canyon National Park in Arizona.
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Sadly, even the Grand Canyon, a symbolic landmark of America's natural environment, unfortunately isn't immune to the ravages of pollution.

Concentrations of mercury and selenium in canyon's food webs -- the interconnected food chains in the environment -- regularly exceed levels considered risky for fish and wildlife. Those findings are from a study from the U.S. Geological Survey scientists published in the journal Environmental Toxicity and Chemistry.

"Managing exposure risks in the Grand Canyon will be a challenge, because sources and transport mechanisms of mercury and selenium extend far beyond Grand Canyon boundaries," said Dr. David Walters, USGS research ecologist and lead author of the study.

Researchers collected data from six sites along along the Colorado River, which winds through the Canyon. They found that the mercury and selenium concentrations in minnows, invertebrates and fish exceeded dietary toxicity thresholds set for fish and fish-eating wildlife.

The data also revealed that the average mercury concentrations in many of the fish studied would make them unsafe for humans to eat as well.

As this handout from the National Wildlife Federation details, mercury is a highly potent neurotoxin that adversely affects the central nervous system in both people and wildlife. Selenium can cause a variety of health problems in humans, ranging from hair and tooth loss to problems with alertness, and some selenium compounds are linked to liver tumors in humans, according to the EPA.

There was one bit of good news for anglers who visit the canyon. The mercury levels in rainbow trout, the most common species caught, were below the EPA threshold that would trigger advisories for human consumption. Also, the researchers didn't observe the level of deformities usually associated with high levels of mercury, because high levels of toxic selenium seem to protect fish from the effects of mercury toxicity, according to an article in the Arizona Daily Sun.

Humans who ate the fish, however, wouldn't necessarily be protected from the toxic substances.

While silenium pollution can come from agricultural and mining runoff, at least some of the Grand Canyon's high levels are attributable to high levels naturally found in the soil. The mercury pollution, in contrast, most likely comes from emissions from distant coal-burning electrical plants and other human sources.

However, the scientists believe that much of the mercury is actually being transported by algae from Lake Powell, who make their way into the canyon, the Daily Sun reported.

"The findings of the present study add to a growing body of evidence showing that remote ecosystems are vulnerable to long-range transport and subsequent bioaccumulation of contaminants," the researchers wrote.

This post originally appeared on Discovery News

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