High levels of mercury are contaminating the Grand Canyon

 

It is thought to be one of the most pristine examples of natural beauty in the US, but apparently not even the Grand Canyon is safe from pollution, as new research has found that the food webs near the landmark have been contaminated by mercury (Hg) and selenium (Se).

The study, led by scientists at the US Geological Survey and published in the latest edition of the journal Environmental Toxicity and Chemistry, found that the levels of these metallic elements in the interconnected food chains of the Colorado River frequently exceeded levels considered safe.

“The levels of Hg and Se were relatively high compared to other large river in the US, including those in landscapes more impacted by human activities,” USGS ecologist Dr. David Walters told redOrbit via email. “Concentrations regularly exceeded established risk thresholds provided by the EPA and other that are meant to protect fish and wildlife from exposure to Hg and Se.”

According to Discovery News, Dr. Walters and his colleagues collected data from six different sites along the river as it traveled through the canyon, and discovered that mercury and selenium levels in minnows, invertebrates, and fish exceeded dietary toxicity thresholds for both fish and for fish-eating wildlife.

Risk to humans is ‘relatively low’

Mercury, the website explained, is a neurotoxin that damages the central nervous system in both humans and other types of wildlife. Selenium, on the other hand, can cause people to lose their hair and teeth, experience problems with alertness, or develop tumor levels, the EPA added.

“The good news is that risks to humans from mercury exposure in fish is relatively low. The mercury concentrations in rainbow trout, a popular sport fish, were low in larger individuals that people might eat,” Dr. Walters said. So where did these toxic chemicals come from originally?

“The source of selenium to Grand Canyon is from irrigation of selenium rich soils in the upper Colorado River basin,” he said. “The source of mercury is likely atmospheric deposition of Hg related to human burning of fossil fuels, particularly coal. There is a global pool of anthropogenic mercury, we consists of very distant (Asia) and regional sources.”

Based on the design of their study, he said that the USGS cannot attribute the mercury levels in the area to any particular source, but he noted that this could be the target or future research. He also said that ongoing large-scale conservation is attempting to reduce selenium runoff, and that technological and regulatory efforts are trying to reduce coal-related mercury emissions.

“Even remote places on earth are rarely ‘pristine,’” Dr. Walters noted. “Here, we found that the aquatic ecosystem in Grand Canyon is vulnerable to long-range transport of contaminants that are potentially harmful to fish, wildlife, and humans. Managing exposure risks are a challenge in the Grand Canyon, because sources of contamination occur far beyond the National Park boundaries.”

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(Image credit: Thinkstock)