Radon is a naturally occurring radioactive gas that forms from the breakdown of uranium found in nearly all soil and rock formations globally. This gas is colorless, odorless, and tasteless, making it undetectable without specialized equipment. While radon exists at very low, harmless levels outdoors, it can accumulate to higher concentrations when trapped inside enclosed spaces like homes.
Health Risks of Radon Exposure
When inhaled, radon gas poses a significant health risk, increasing the chance of developing lung cancer. As radon decays, it releases tiny radioactive particles, radon progeny, which attach to airborne particles. When inhaled, these particles lodge in the lung lining, emitting radiation that damages DNA in lung cells. This damage can lead to cancerous growths.
Radon is the second leading cause of lung cancer in the United States, following cigarette smoking. Scientists estimate that radon exposure contributes to approximately 15,000 to 22,000 lung cancer deaths annually in the U.S. The risk of lung cancer from radon exposure is substantially higher for individuals who smoke compared to non-smokers, due to a synergistic effect. For instance, at a radon level of 4 pCi/L, the lifetime risk of radon-induced lung cancer death for never-smokers is around 7 per 1,000, but for ever-smokers, it rises to about 62 per 1,000. Radon exposure has no immediate symptoms; signs typically appear only when lung cancer symptoms, such as persistent coughing or shortness of breath, begin to manifest.
Identifying Radon in Your Home
Because radon is undetectable by human senses, testing is the only reliable method to determine its presence and concentration in a home. Do-it-yourself test kits are widely available and offer a straightforward way for homeowners to check radon levels. These tests fall into two categories: short-term and long-term.
Short-term tests typically last between two and 90 days, providing quick results. However, due to natural fluctuations influenced by weather and seasonal changes, a single short-term test might not fully represent the home’s average exposure. Long-term tests, measuring over 90 days, provide a more accurate assessment of average annual exposure. Homeowners can also hire a certified radon measurement professional for expert analysis.
Radon levels are commonly measured in picocuries per liter of air (pCi/L) in the U.S. The U.S. Environmental Protection Agency (EPA) recommends taking action if radon levels are 4.0 pCi/L or higher. While levels below 2 pCi/L are considered low, the EPA suggests considering mitigation for levels between 2 pCi/L and 4 pCi/L, as there is no known safe level of exposure. If an initial short-term test is 4.0 pCi/L or higher, a follow-up test is recommended to confirm elevated levels before mitigation.
Sources and Entry Points of Radon Gas
Radon gas originates from the natural decay of uranium, thorium, and radium in soil and rock beneath buildings. Once formed, this gas can migrate upwards through the ground and enter buildings through various openings in the foundation. Common entry points include:
Cracks in concrete floors and walls.
Expansion joints.
Gaps around service pipes, utility lines, or sump pits.
Exposed soil or gravel in crawl spaces.
The “stack effect” or “chimney effect” draws radon into a home. This occurs as warmer indoor air rises and escapes, creating lower air pressure in basements or lower levels. This negative pressure pulls replacement air and radon gas from the surrounding soil into the home through its foundation. Even well water can serve as a source of radon, releasing the gas into the air when the water is used.
Reducing Radon Levels
Reducing elevated radon levels requires specialized expertise; homeowners should engage a qualified radon mitigation contractor. The most effective method for lowering indoor radon is active soil depressurization (ASD), also known as sub-slab depressurization. This system works by creating negative pressure beneath the building’s foundation. A pipe is installed through the foundation, extending into the soil or gravel layer below, and connected to an exterior fan.
The fan continuously draws radon gas from beneath the foundation and vents it safely outdoors, typically above the roofline, preventing it from entering the living space. While sealing cracks and openings in the foundation can be a supplementary measure, it is rarely sufficient on its own to reduce high radon levels effectively. Active soil depressurization systems operate continuously, providing a permanent solution to radon infiltration. After installation, re-test the home to confirm radon levels are reduced to acceptable concentrations.