Radon is a naturally occurring, radioactive gas formed from the breakdown of uranium in soil, rock, and water. It is imperceptible to human senses—colorless, odorless, and tasteless—making specialized testing equipment essential for detection. Understanding radon is important because it is a significant indoor air quality concern, recognized as a leading cause of lung cancer in non-smokers.
Natural Origins and Environmental Presence
Radon gas originates from the natural radioactive decay of uranium, an element found in varying concentrations within the Earth’s crust. Uranium is present in nearly all types of soil, rock, and water, making radon a ubiquitous part of our natural environment.
The concentration of uranium in the ground, and consequently the amount of radon produced, varies significantly by geographic location. Areas with higher concentrations of uranium in the underlying geology, such as certain granite formations or shale deposits, tend to have a greater potential for elevated radon levels. Once formed, radon gas can move freely through porous soils and fissures in rock. While radon is constantly released from the ground into the atmosphere, it typically dissipates quickly outdoors, posing little risk in open-air environments. Radon can also dissolve into groundwater, particularly in private wells that draw water directly from underground sources.
How Radon Enters and Accumulates Indoors
Radon primarily enters homes from the soil beneath the structure, making ground contact points the most common entry routes. The gas moves through the earth and finds pathways into a building through openings or penetrations in the foundation. Common entry points include cracks in concrete slabs, expansion joints, floor-wall joints, and gaps around utility pipes, sump pumps, and support posts.
Pressure differences between the inside of a building and the surrounding soil are a significant factor in drawing radon indoors. Warm air rises within a home, creating a slight vacuum or lower pressure zone at the lowest levels, a phenomenon known as the stack effect. This pressure differential effectively draws radon gas from the soil into the building. This mechanism explains why basements and crawl spaces, which are in direct contact with the earth, are particularly susceptible to higher radon concentrations.
Once inside, radon can accumulate to dangerous levels, especially in enclosed areas with limited ventilation. Basements and crawl spaces often have less airflow compared to upper floors, allowing the gas to concentrate. While less common, radon can also enter homes through private well water, where the gas can be released into the air during activities like showering or washing dishes. Certain building materials can also emit small amounts of radon, though this is generally a minor contributor compared to soil gas entry.