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The Grand Canyon is Full of Mercury

Researchers find high levels of mercury and selenium in plants and animals along the Colorado River

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The Grand Canyon boasts one of the most breathtaking natural landscapes on Earth, and draws over 4.7 million visitors each year. Now, writes UPI’s Brooks Hays, researchers have discovered something else in the canyon: mercury contamination.

When researchers from the U.S. Geological Survey measured levels of mercury and selenium at six sites along 250 miles of the Colorado River, writes Hays, they found “significant levels of mercury and selenium in plant and animal samples.” In a release, the researchers noted that concentrations of these chemicals “regularly exceeded risk thresholds for fish and wildlife.”

The team recently published their findings in the journal Environmental Toxicology and Chemistry. Mining runoff, algae blooms and coal plants seem to be to blame for the contamination. Researchers tested invertebrates, minnows, and rainbow trout during their study, finding larger concentrations of toxins in small fish.

That’s surprising, says Ted Kennedy, who co-authored the study. In the release, he notes that usually, large rainbow trout have higher concentrations of mercury due to a phenomenon called biomagnification, in which concentrations of contaminants increase in organisms that are higher up the food chain. Kennedy says that the Grand Canyon, which provides limited feeding opportunities for fish, seems to have different biomagnification effects than other ecosystems.

One of the suspected culprits is algae from Lake Powell, which absorbs mercury from the atmosphere and the water, then carries it to the canyon. As scientists continue to study mercury in the lake and the canyon, it’s unclear just how contaminated the Grand Canyon has become — or how to clean up one of America’s most spectacular natural treasures.

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