The risk of residential radon exposure does indeed vary geographically due to differences in the underlying geology. Radon is a naturally occurring radioactive gas that is produced from the decay of uranium found in soil, rock, and water. Here are some key points about how and why this variation occurs:
Geological Factors
- Uranium-Rich Soils and Rocks: Areas with higher concentrations of uranium in the soil and bedrock are more likely to have elevated radon levels. For example, regions with granite, shale, and phosphate rocks can have higher radon emissions.
- Soil Permeability: Soils that are more permeable (e.g., sandy or gravelly soils) allow radon gas to move more freely and reach the surface, potentially entering homes more easily.
Regional Variations
- United States: The Environmental Protection Agency (EPA) has created a map that divides the country into three radon zones. Zone 1 areas have the highest potential for radon levels above the EPA action level of 4 picocuries per liter (pCi/L), Zone 2 areas have moderate potential, and Zone 3 areas have the lowest potential. High radon zones include parts of the Northeast, Appalachia, the Midwest, and the Northern Plains.
- Europe: Certain areas, such as the Czech Republic, Finland, and Sweden, are known for high radon levels due to their geological conditions.
Local Building Practices and Environmental Factors
- Building Construction: The design and construction of homes can influence radon entry. Homes with basements or those built on slab foundations might have different radon levels due to differences in how radon enters the structure.
- Climate and Weather: Seasonal changes, temperature, and humidity can also impact radon levels in homes. For instance, radon levels can be higher in the winter when homes are sealed tight against the cold.
