Authorities are investigating how three workers were exposed to radioactive plutonium during environmental restoration work at the Nevada Test Site, the National Nuclear Security Administration said.

Two female workers for the test site's main contractor, National Securities Technologies, received the highest of what NNSA spokesman Kevin Rohrer characterized as "minor radiation exposure" on April 30.

A man received less exposure, Rohrer said. The three were among eight workers in the area, including a health physicist and technicians. All were wearing protective gear, including respirators.

"The exposures are relatively low, but they're high enough that it concerns us," he said.

The workers remained on the job, but the women were not allowed into radiation areas, Rohrer said. For privacy reasons, the names of the eight workers were not released.

A spokeswoman for the contractor, Gillian Silver, said the company was conducting an internal investigation and that the company doesn't have any reason "to believe there were any security or safety considerations here."