Mercury And Other Toxins Contaminate Grand Canyon Segment Of Colorado River

Research shows that in spite of the fact that the Grand Canyon of the Colorado River is among the "most untouched ecosystems" in the United States, it still shows worrying levels of pollution with toxins such as mercury.

A U.S. Geological Survey showed that mercury and selenium are concentrated in Colorado River.

The food webs of the Grand Canyon National Park contain more than the exceeded risk thresholds for fish and wildlife, which mean that consuming local food could be harmful.

"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 David Walters, USGS research ecologist and lead author of the study, according to hngn.

Studying the food webs at six sites along 250 miles of the Colorado River downstream from Glen Canyon Dam in 2008, scientists found that there were mercury and selenium concentrations in minnows and invertebrates that were more than dietary fish and wildlife toxicity thresholds.

"We also found some surprising patterns of mercury in rainbow trout in the Grand Canyon. Biomagnification usually leads to large fish having higher concentrations of mercury than small fish. But we found the opposite pattern, where small, [three]-inch rainbow trout in the Grand Canyon had higher concentrations than the larger rainbow trout that anglers target. This inverted pattern likely has something to do with the novel food web structure that has developed in Grand Canyon," said Ted Kennedy, USGS researcher and co-author of the study.

Most of the sources of the toxins are found in remote ecosystems in the U.S. and include airborne transport that come from outside. The downstream transport from upstream sources also introduce contaminants such as mercury into the food webs.

The selenium-rich soil due to irrigation in the upper Colorado River basin made its way down to the Colorado River in the Grand Canyon.

The contamination has led to reduced growth and reproductive rates in fish as well as exposed humans to health risks.

The findings were published in a recent edition of the journal Environmental Toxicology and Chemistry.