Coal ash, the waste generated by coal-fired power plants, is already known to contain environmental contaminants such as selenium, cadmium and arsenic. Now, researchers at Duke say it may also be radioactive.

“Radiation is another set of contaminants that needs to be considered when we are trying to weigh the impact of coal ash in the environment,” says Avner Vengosh, a professor of geochemistry and water quality at Duke’s Nicholas School of the Environment.

Vengosh and a team of researchers found radium isotopes and lead-210 in coal ash at levels five times higher than in normal soil.

He says this could pose a human health hazard if coal ash is not properly handled. Dry ashes can be easily inhaled. Wet coal ash can leak into ponds and rivers as happened in 2014 when tens of thousands of tons spilled into the Dan River.

The Environmental Protection Agency is set to begin regulating coal ash next month, but those regulations don’t yet include monitoring of radioactive materials. Vengosh says that needs to change.

“I think that naturally occurring radioactive materials should be part of an overall monitoring procedure to make sure that those contaminants that occur in coal ash indeed remain in coal ash, and not transferred or mobilized into drinking water or waterways around coal ash ponds or landfills.”

Duke Energy is preparing to move 20 million tons of coal ash from across the state to sites in Chatham and Lee Counties. Vengosh says he’d like to see increased transparency and monitoring to make sure that process is completed safely.

“The common sense answer is first, that all information is transparent and available, and second, that there is independent monitoring of what’s going on,” says Vengosh. “So I think if those two conditions are met, that we do know what’s happened and we can actually report that, then I would feel more secure about this process.”

More broadly, he notes that the energy industry as a whole is largely exempt from the Clean Water Act, leaving scientists in the dark when it comes to monitoring water quality and pollution.

“It’s a much larger issue of lack of regulation and lack of monitoring, and I think that kind of legacy is resulting in us waking up one day and seeing we have an issue or a problem someplace.”

The study was published September 2 in the journal Environmental Science and Technology.