PHOENIX -- Granite countertops have become a status symbol across the country, yet new research suggests some of those countertops could make homeowners ill.

A Rice University physics professor wrote a paper saying that, depending on the minerals present in the granite, the countertops may release radon gas, which is radioactive.

Radon is a naturally occurring gas that uranium emits as it degrades, and it normally makes its way into homes from the soil.

"The EPA says there's no really safe level of radon," said Paul Furman of AJF Engineering. "They're saying that it causes 20,000 lung cancer deaths a year. That's a big number."

Furman has a background in radon detection and remediation, which he uses in his job as a Valley home inspector.

When he inspects homes, Furman said he looks for average radon levels above four pico curies per liter of air; anything higher is unsafe, according to the Environmental Protection Agency.

The EPA admits there is a potential health problem in granite countertops; however, it says it "does not believe sufficient data exist to conclude that the types of granite commonly used in countertops are significantly increasing indoor radon levels."

Nevertheless, Furman said he has not run across a home where granite countertops were the cause of high radon levels. Still, he said this issue could make homeowners more aware of the dangers radon poses.

As a precaution, some experts suggest homeowners make sure their granite countertops are properly sealed every year or two. If homeowners would like to test for radiation levels, they can hire a professional or purchase a home testing kit available at local hardware stores.