The Grand Canyon is Not as Well-Preserved as We Once Thought

Mercury, Selenium found in food webs in the Colorado River

“Although the Grand Canyon segment of the Colorado River features one of the most remote ecosystems in the United States, it is not immune to exposure from toxic chemicals such as mercury.” That’s the opening line of a statement released by the U.S. Geological Survey and it doesn’t get much better from there.

They’re referring to a study that was recently published study in Environmental Toxicology and Chemistry. The study, led by the U.S. Geological Survey, found high concentrations of mercury and selenium in “the Colorado River food webs”, which run through the Grand Canyon. They also mention that these concentrations of chemicals could “be harmful if eaten by fish, wildlife and humans.”

The study, which surveyed six sites along almost 250 miles of the Colorado River, concluded that most of the chemicals were coming from outside of the U.S., by way of air. The selenium, however, is thought to be coming from sources upstream.

“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. 

The types of fish that showed alarming levels of chemicals are minnows and invertebrates. But it’s not all terrible news; the study found “mercury levels in rainbow trout, the most common species harvested by anglers in the study area, were below the EPA threshold that would trigger advisories for human consumption.” Although they do note that the number of rainbow trout sampled was “relatively low.”

There is currently no advisory against human consumption of fish in the area, but they said further studies are planned for the area.

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