Scientists from the U.S. Geological Survey (USGS) discovered concentrations of selenium and mercury in the food webs of the Grand Canyon, raising concerns regarding the health and safety of fish and wildlife in the area.

In a study featured in the journal Environmental Toxicology and Chemistry, research ecologist Dr. David Walters and his colleagues at the USGS gathered data from six different sites along the Colorado River, which runs through the Grand Canyon.

They discovered that several creatures in the area, including minnows, fish and invertebrates, had concentrations of selenium and mercury that exceeded the thresholds for dietary toxicity for fish and other wildlife that feed on these aquatic animals.

The findings also showed that average concentrations of mercury in many of the fish specimens would make them unfit for human consumption as well.

According to the National Wildlife Federation (NWF), mercury is considered to be a highly dangerous neurotoxin that severely affects the nervous system of humans and animals alike.

"Selenium can cause various health problems in people, such as the loss of teeth and hair as well as issues with alertness," the Environmental Protection Agency (EPA) said. Some compounds of selenium are also associated with the development of tumors in the liver of humans.

Meanwhile, the levels of mercury in rainbow trout, a species of fish commonly caught by visiting anglers in the Grand Canyon, were found to be below the threshold set by the EPA.

The USGS researchers also did not observe deformities on the fish typically linked to the presence of high mercury levels. It is believed that the toxic levels of selenium appear to protect the fish in the canyon from the adverse effects of toxic mercury.

People who consume fish exposed to selenium and mercury, however, would not be protected from the harmful effects of the toxic substances.

Mining and agricultural runoffs are the most common sources of selenium pollution, but the concentrations found in the Grand Canyon naturally come from the soil itself. The mercury concentrations, on the other hand, are believed to have originated from emissions produced by distant electrical plants that burn coal as well as from other human sources.

The USGS researchers suspect that the mercury pollution is being transported to the area by algae that come from Lake Powell.

Photo: Grand Canyon National Park | Flickr 

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