What Is Radon?
By Daniel SmokeDirector of Operations
About one in fifteen U.S. homes is estimated to sit at or above the EPA action level of 4 pCi/L. And because radon is colorless, odorless, and tasteless, testing is the only way to know whether yours is one of them. Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil, rock, and water. The EPA estimates it is the second leading cause of lung cancer in the United States, responsible for approximately 21,000 deaths annually.
How Radon Is Produced
Radon is formed as part of the natural radioactive decay chain of uranium, which is present in trace amounts in soil and rock throughout the world. Uranium decays to radium, which decays to radon gas (radon-222). Radon itself then decays into a series of short-lived radioactive particles called radon progeny or radon daughters. It is these progeny, polonium-218 and polonium-214, that pose the greatest lung cancer risk when inhaled. They attach to airborne particles and lung tissue.
How Radon Enters Buildings
Radon gas migrates from soil into buildings through any opening in the foundation or floor: cracks in concrete slabs and foundation walls, gaps around service pipes and conduits, exposed soil in crawlspaces, sump pits, construction joints, and porous concrete block walls. The driving force is typically a pressure differential. Buildings tend to be at slightly lower pressure than the surrounding soil, drawing soil gases inward. This effect is stronger in cold weather when homes are heated and tightly sealed.
Where Radon Levels Are Highest
Radon levels vary significantly by geography, geology, building construction, and occupant behavior. High radon levels have been found in every state and in a wide range of building types. The EPA publishes radon zone maps that identify counties with higher predicted average indoor radon levels. But these are generalizations. Levels vary considerably from house to house within the same neighborhood. Buildings with basements or slabs-on-grade in direct contact with soil typically have higher radon levels than buildings with crawlspaces or those built over well-ventilated foundations.
Why Radon Is Dangerous
When radon gas is inhaled, most of it is exhaled without causing harm. The danger comes from its radioactive decay products, which attach to airborne particles that can be deposited in the lungs. These particles emit alpha radiation directly into sensitive lung tissue, damaging DNA and increasing the risk of lung cancer over time. The risk is dose-dependent. The higher the radon level and the longer the exposure, the greater the risk. Smokers exposed to elevated radon have dramatically higher lung cancer risk than either non-smokers or non-exposed smokers.
The EPA Action Level
The EPA recommends taking action to reduce radon levels when the average annual concentration is at or above 4 picocuries per liter (pCi/L). The EPA also recommends considering mitigation for levels between 2 and 4 pCi/L. The average indoor radon level in U.S. homes is approximately 1.3 pCi/L; the average outdoor level is about 0.4 pCi/L.
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