New findings suggest despite the fact that the Grand Canyon segment of the Colorado River is one of the most untouched ecosystems in the United States; it is still contaminated with toxic chemicals such as mercury.
A recent study led by the U.S. Geological Survey discovered the concentrations of mercury and selenium in Colorado River food webs of the Grand Canyon National Park generally exceeded the exceeded risk thresholds for fish and wildlife. These findings mean local food eaten by humans and animals alike could have harmful effects.
"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.
To make their findings, the researchers looked at food webs at six sites along nearly 250 miles of the Colorado River downstream from Glen Canyon Dam in the summer of 2008. The results revealed mercury and selenium concentrations in minnows and invertebrates exceeded dietary fish and wildlife toxicity thresholds. The researchers noted the number of these samples were relatively low, and concentrations in highly-fished rainbow trout proved to be below EPA thresholds for consumption.
