"Heavy Metals Polluting Colorado River In Grand Canyon National Park"

"As far away from society as you might seem while floating on the Colorado River through Grand Canyon National Park in Arizona, or hiking along its shorelines, heavy metals are polluting the river in concentrations that could pose a health risk.

According to a U.S. Geological Survey study just published in Environmental Toxicology and Chemistry, concentrations of mercury and selenium in the river's food web 'regularly exceed risk thresholds for fish and wildlife. These risk thresholds indicate the concentrations of toxins in food that could be harmful if eaten by fish, wildlife and humans.'

“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."

National Parks Traveler had the story August 20, 2015.