What is Radon?
Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil, rock, and water. It is invisible, odorless, and tasteless. Radon moves up through the ground and into the air, where it can enter homes and buildings through cracks and openings in foundations.
Health Effects
Radon is the second leading cause of lung cancer in the United States, after smoking. The EPA estimates that radon causes approximately 21,000 lung cancer deaths per year. The risk increases with higher radon levels and longer exposure time.
When you breathe in radon, radioactive particles can get trapped in your lungs. Over time, these particles release small bursts of energy that can damage lung tissue and lead to cancer. Smokers exposed to radon have an especially high risk.
Where Does Radon Come From?
Uranium exists naturally in most soils and rocks. As uranium breaks down, it produces radium, which then decays into radon gas. The amount of radon that accumulates indoors depends on:
- Geology — Granite, shale, and phosphate-bearing soils tend to produce more radon
- Soil permeability — Loose, gravelly soils allow radon to move more easily toward the surface
- Home construction — Cracks in foundations, gaps around pipes, and sump pits provide entry points
- Ventilation — Tightly sealed homes with poor ventilation can trap radon at higher concentrations
The EPA Action Level: 4 pCi/L
The EPA has set an action level of 4 picocuries per liter (pCi/L). If your home tests at or above this level, the EPA recommends taking steps to reduce radon. For context:
- Average outdoor air: 0.4 pCi/L
- Average indoor air (US): 1.3 pCi/L
- EPA action level: 4 pCi/L
The EPA also recommends considering mitigation for levels between 2 and 4 pCi/L, since there is no known safe level of radon exposure.
Radon in Water
Radon can also dissolve in groundwater and enter homes through well water. When water containing radon is used for showering or other household purposes, the gas is released into indoor air. Homes with private wells in areas with high radon potential should consider testing their water as well.