(CNN) Uranium ore stored at the Grand Canyon National Park museum may have exposed visitors and workers to elevated levels of radiation, according to the park's safety, health and wellness manager.

Elston Stephenson told CNN that he began asking officials from the National Park Service and Department of the Interior last summer to warn workers and tourists they had possibly been exposed to unsafe levels of radiation. After his requests were ignored, he said he sent an email to all park staff at the Grand Canyon on February 4.

"If you were in the Museum Collections Building (bldg 2C) between the year 2000 and June 18, 2018, you were 'exposed' to uranium by OSHA's definition," said the email, which Stephenson provided to CNN.

"Please understand, this doesn't mean that you're somehow contaminated, or that you are going to have health issues. It merely means essentially that there was uranium on the site and you were in its presence. ... And by law we are supposed to tell you."

The National Park Service is investigating what happened and working with the Occupational Safety and Health Administration and the Arizona Department of Health Services, according to the Department of the Interior, which oversees the park service.

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