Radon (Rn-222)

Radon is produced by the radioactive decay of uranium-238, which decays through radium-226 to radon-222 — a naturally occurring chain that has continued since Earth formed [1]. Uranium is present in trace amounts in almost all rocks and soils, but is concentrated in granite, phosphate deposits, and uranium-bearing shales. As radon gas forms underground, it diffuses through soil pores and rock fractures and can accumulate in buildings that sit over radon-emitting geology [2]. The U.S. EPA became aware of residential radon as a major health hazard in 1984 when a nuclear power plant worker named Stanley Watras repeatedly set off radiation detectors on his way INTO work — his home in Pennsylvania had radon levels 700 times the EPA action level [1]. The discovery galvanized a national radon testing program. Radon enters buildings through foundation cracks, pipe penetrations, sump pits, and construction joints [2].

Indoor air in homes with poor foundation sealing is the dominant exposure route — radon accumulates in basements and lower floors where fresh air exchange is lowest [1]. Radon levels vary enormously: the U.S. average is ~1.3 pCi/L, but millions of homes exceed the EPA action level of 4 pCi/L, and some homes in high-radon geology (Iowa, Pennsylvania, Montana, Minnesota) reach 20-100+ pCi/L [2]. Well water from ground sources in high-radon areas contains dissolved radon that is released into air during showering and tap use, though this is a secondary contribution compared to soil entry [1]. Occupational exposure occurs in uranium miners (historically very high doses), underground miners, and cave tour guides [2].

Radon doesn't cause harm as a gas — its decay products (polonium-218, lead-214, bismuth-214, polonium-214) do [1]. These short-lived radioactive progeny attach to airborne particles and, when inhaled, deposit on bronchial epithelium where they emit alpha particles. Alpha radiation is highly ionizing and causes DNA double-strand breaks in lung cells within millimeters of the decay site [2]. The link to lung cancer was confirmed by massive cohort studies of uranium miners; residential radon epidemiology (pooled analyses of over 7,000 lung cancer cases) confirmed the association at levels found in homes [1]. Radon and cigarette smoke act synergistically — a smoker in a high-radon home has roughly 10x the lung cancer risk of a nonsmoker in the same home [2].

Smokers in high-radon homes face by far the greatest risk — the combination multiplies lung cancer risk dramatically [1]. Children's lungs are more sensitive to radiation-induced carcinogenesis due to rapid cell division during development. People who spend significant time in basements or lower floors of high-radon homes receive higher doses [2]. Residents in known high-radon geology (Iowa has the highest average state radon levels) should test as a priority. Underground miners who work in uranium or metal ore mining with inadequate ventilation face occupational exposures [1].

1. Test your home — radon testing is inexpensive ($10-30 for a DIY short-term test kit, available at hardware stores) and takes only 48 hours to 90 days depending on the kit type [1]. 2. If your test result is ≥4 pCi/L (EPA action level), hire a certified radon mitigation contractor — sub-slab depressurization systems (a pipe and fan that draw radon from under the foundation and vent it outdoors) reduce radon by 50-99% in virtually all homes [2]. 3. Mitigation systems cost $800-2,500 and last the life of the home with minimal maintenance. 4. Don't smoke and don't allow smoking in your home — radon and tobacco smoke together are exponentially more dangerous than either alone [1]. 5. Test after any major renovation that affects foundation or floor seals. 6. Retest every 2 years or after significant changes to the home [2].