Earth Notes: The Unseen Indoor Air Pollutant

Dec 2, 2015

After smoking, the second-leading cause of lung cancer is colorless, odorless, tasteless—and can come from right underfoot. Radon is a naturally occurring gas formed from the radioactive decay of radium and uranium. Those elements are present in most soils and rocks, though usually in very small concentrations.


Radon is radioactive. The alpha particles it produces can become attached to dust, smoke or water vapor particles. Inhaled, they can harm sensitive lung tissue and cause cancer.

It’s geology that determines radon levels. On the Colorado Plateau they’re higher than in some other parts of the Southwest, though generally lower than in many other regions farther north. But if you live near a uranium mine or other uranium-rich geologic hot spot, indoor radon gas may become concentrated, especially in basements and crawl spaces.

One hot spot is the Granite Dells area near Prescott, where the world’s highest-ever indoor radon level was measured. The house had a leaky water well pipe casing, which allowed radon to seep up from the uranium-rich granite below.

The problem was quickly solved by venting the sub floor to the outside and sealing the gap between the well casing and floor.

A few simple measures can prevent elevated levels of indoor radon from building up in your home. If you have a forced air conditioning system, make sure return air ducts are airtight, and any cracks in solid floors or around service pipes are properly sealed. Also keep your house well ventilated.