The Grand Canyon is full of mercury

Grand Canyon
CC BY 2.0 Grand Canyon NPS/flickr

From the ‘Is Nothing Sacred?’ file: Researchers find levels of mercury and selenium exceeding wildlife toxicity thresholds in the beloved national park.

Few places in the Lower 48 appear to be more pristine than the Grand Canyon. It’s breathtaking and remote, in fact, it’s one of the more remote ecosystems in the county. Yet even so, one of our most notable and secluded landscapes can’t escape exposure to toxic chemicals.

The U.S. Geological Survey has published a study in which they reveal startling concentrations of mercury and selenium in the Colorado River food webs of the Grand Canyon. The levels exceed dietary fish and wildlife toxicity thresholds throughout the Colorado River Basin, and selenium concentrations are particularly high.

These risk thresholds signify the concentrations of toxins in food that could be harmful if eaten by fish, wildlife and humans, notes a statement for the study. The findings add fuel to the fire of growing research showing that even remote ecosystems can be victim to contaminants from afar.

“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.

Potential sources of atmospheric mercury being dumped into the Grand Canyon ecosystem include a large regional atmospheric pool – much of it originating outside of the country – but also nearby sources like a coal-burning power plant located near Page, Arizona. The primary source of selenium is runoff associated with irrigation of selenium-rich soils in the upriver watershed.

While they found that mercury and selenium concentrations in minnows and invertebrates exceeded dietary fish and wildlife toxicity thresholds, fortunately mercury levels in rainbow trout were not as alarming. Although the number of samples was relatively low, rainbow trout is the most common species harvested by anglers in the study area and their levels were below the EPA threshold that would trigger advisories for human consumption.

“The good news is that concentrations of mercury in rainbow trout were very low in the popular Glen Canyon sport fishery, and all of the large rainbow trout analyzed from the Grand Canyon were also well below the risk thresholds for humans,” said Dr. Ted Kennedy, USGS researcher and co-author of the study.

Exposure to high levels of selenium and mercury has been linked to lower reproductive success, growth, and survival of fish and wildlife, notes the statement. For now there have been no human consumption advisories for fish caught from the study area, but future studies are planned to assess potential risks to humans that may consume fish from there. From canary in the coalmine to minnow in the canyon.

The Grand Canyon is full of mercury
From the ‘Is Nothing Sacred?’ file: Researchers find levels of mercury and selenium exceeding wildlife toxicity thresholds in the beloved national park.

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