Tourists visiting the Grand Canyon's museum collections building have been exposed to radiation for nearly two decades, the Arizona Republic reports. A safety manager for the park says the exposure came from uranium rocks stored in buckets between the year 2000 and 2018.

The containers could have exposed adults to 400 times the health limit, and for children, up to 4,000 times what is considered safe.

The rocks have been removed and an investigation is underway.

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The Arizona Republic quotes an email sent earlier this month by safety, health and wellness manager Elston Stephenson, alleging a cover-up by managers to conceal possible health risks.

"If you were in the Museum Collections Building (2C) between the year 2000 and June 18, 2018, you were 'exposed' to uranium by OSHA's definition," Stephenson wrote, according to the newspaper. "The radiation readings, at first blush, exceeds (sic) the Nuclear Regulatory Commission's safe limits. … Identifying who was exposed, and your exposure level, gets tricky and is our next important task."

Stephenson claimed he asked National Park executives to publicize the risks but was ignored.

A spokesperson for the Grand Canyon told the newspaper a recent test revealed only background radiation, which is normal, and said there is no danger to the public.

"There is no current risk to the park employees or public," Emily Davis said. "The building is open. … The information I have is that the rocks were removed, and there's no danger."