Washington — Radon, an invisible and odorless radioactive gas, remains the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths annually, according to federal health agencies . While the risk is preventable, recent modeling indicates that approximately 14.3% of the U.S. population—or 42.8 million residents—is exposed to radon concentrations at or above the Environmental Protection Agency’s action level of 4 picocuries per liter (pCi/L) .
The U.S. Environmental Protection Agency (EPA) and the U.S. Surgeon General identify radon as the primary cause of lung cancer among nonsmokers and the second leading cause overall . The gas naturally originates from the decay of uranium in soil, rock, and water, entering buildings through foundation cracks and sump systems . Because exposure is inhalation-based and cumulative, health officials emphasize that any home can harbor elevated levels, regardless of geographic location or building age .
Geological surveys conducted by the U.S. Geological Survey (USGS) in coordination with the EPA have mapped radon potential across the country, though federal agencies caution that these zones are intended as a general guide for targeting testing rather than a substitute for individual home measurements . According to the USGS, elevated radon levels have been measured in every designated radon zone, underscoring the necessity of testing rather than relying solely on geographic risk maps .
Exposure Disparities and Risk Concentrations
A peer-reviewed study published in Environmental Science & Technology provides refined estimates of population-level exposure by analyzing distributional data rather than relying on average concentrations . The research estimates that while 14.3% of Americans exceed the EPA action level, approximately 2.1%—or 6.2 million people—are exposed to concentrations exceeding 10 pCi/L, a level associated with significantly heightened carcinogenic risk . The study notes that the South, despite having the lowest proportion of exceedances among regions, accounts for the second-largest absolute number of exposed individuals due to its large population size .
The EPA maintains that the action level of 4 pCi/L is not a safety threshold but a point at which remediation is recommended to reduce risk . The agency advises that homeowners consider mitigation for levels between 2 and 4 pCi/L as well . For context, the average indoor radon level in the U.S. is approximately 1.3 pCi/L, while outdoor levels average 0.4 pCi/L .
Federal Guidance and Mitigation Efficacy
The U.S. Surgeon General and the CDC recommend that all homes be tested for radon, regardless of location . Testing is available through inexpensive short-term kits or certified professionals. If elevated levels are confirmed, qualified contractors can install mitigation systems—typically sub-slab depressurization—which the EPA states can reduce indoor radon concentrations by up to 99% .
The CDC’s Environmental Health Tracking Network aggregates radon testing data from laboratories and state programs to identify areas with low testing rates but high potential risk, aiming to direct public health resources toward communities with the greatest need .
References
- American Chemical Society. “The proportions of ZCTAs with fitted screening-floor radon concentrations exceeding the EPA action level…” Environmental Science & Technology. [https://pubs.acs.org/esthag/article-pdf/doi/10.1021/acs.est.6c01333/67961162/acs.est.6c01333.pdf]
- Centers for Disease Control and Prevention. “Why Should I Raise Awareness About Radon?” [https://www.cdc.gov/radon/php/guidance/]
- Centers for Disease Control and Prevention. “Radon Testing.” [https://www.cdc.gov/environmental-health-tracking/php/data-research/radon-testing.html]
- U.S. Geological Survey. “Geologic Radon Potential Map of the United States.” [https://data.usgs.gov/datacatalog/data/USGS:687e988bd4be027f6b8de54d]
- U.S. Environmental Protection Agency. “Test, Fix, Save a Life: EPA Region 7 Encourages Home Testing During National Radon Action Month.” [https://www.epa.gov/newsreleases/test-fix-save-life-epa-region-7-encourages-home-testing-during-national-radon]
- Centers for Disease Control and Prevention. “CDC-NCEH-EHNexus-RADON-Adela-Salame-Alfie.” [https://www.cdc.gov/eh-nexus/media/podcasts/transcripts/CDC-NCEH-EHNexus-RADON-Adela-Salame-Alfie-p.pdf]
- U.S. Environmental Protection Agency. “Basic Radon Facts.” [https://archive.epa.gov/ecoambassadors/web/pdf/radonfactsheet.pdf]
- TRICARE Newsroom. “January Is National Radon Action Month: Learn To Manage Risk.” [https://newsroom.tricare.mil/News/Defense-Health-Agency-News/Article/4023571/january-is-national-radon-action-month-learn-to-manage-risk]
- ScienceBase (USGS). “Geologic Radon Potential Map of the United States.” [https://www.sciencebase.gov/catalog/item/687e988bd4be027f6b8de54d]
