EPA Radon Zone 1
Radon is the #2 cause of lung cancer in the United States after tobacco — and the #1 cause among people who have never smoked. EPA designates counties into three zones based on predicted indoor radon levels. Zone 1 counties are predicted to average above the 4 pCi/L action level. Here's how those zones line up with where Americans are actually being diagnosed with — and dying from — lung cancer.
Sources: EPA Map of Radon Zones (402-R-93-071) · CDC US Cancer Statistics 2017–2021 · NCI State Cancer Profiles · WHO Handbook on Indoor Radon · Darby et al., BMJ 2005 (16% increase in lung cancer risk per 100 Bq/m³ long-term exposure).
The overlay
Each dot is a state. X-axis is the average indoor radon level (pCi/L); Y-axis is lung cancer mortality (per 100k, age-adjusted). Bubble size is the share of tested homes above the 4 pCi/L action level. The cluster of red Zone 1 dots in the upper-right is the signal — high radon and high lung mortality run together — but tobacco prevalence and the radon–smoking synergy do most of the lifting at the very top.
Bubble size = share of tested homes ≥ 4 pCi/L. Iowa, Pennsylvania, and Colorado sit furthest right; Kentucky, West Virginia, and Tennessee sit highest on the mortality axis — the Appalachian Zone 1 corridor where high radon meets the country's heaviest smoking burden.
Zone 1 leaderboard
Within Zone 1, lung mortality varies almost 3× — from Colorado and New Mexico at ~26 per 100k to Kentucky at ~57. The gap is driven mainly by adult smoking prevalence and screening coverage, which interact multiplicatively with radon exposure. A smoker living in a high-radon home faces a roughly 25× higher lung cancer risk than a never-smoker in a low-radon home.
Source: NCI State Cancer Profiles 2017–2021 (lung & bronchus, age-adjusted, both sexes). EPA zone classification: 402-R-93-071.
Zone-level summary
Averaged across the states in each zone, lung mortality rises monotonically with the predicted radon level — but the slope is modest at the zone level because tobacco swamps the geological signal. Radon's contribution is clearest in never-smokers and in lifetime non-smokers exposed in childhood.
Average across states in each EPA zone (n = 19, 8, 5). Indoor radon avg (pCi/L) per zone: 1 5.2 · 2 2.7 · 3 1.3.
Findings
Pooled European, North American, and Chinese residential studies (Darby 2005; Krewski 2005; Lubin 2004) all show lung cancer risk rising linearly with cumulative radon — with no safe threshold. Each 100 Bq/m³ (~2.7 pCi/L) of long-term residential exposure raises lung cancer risk by ~16%.
Radon and tobacco interact multiplicatively. A lifelong never-smoker faces ~0.4% lifetime radon-attributable lung cancer risk at 4 pCi/L; a current smoker at the same exposure faces ~10%. WHO estimates 3–14% of all lung cancers are radon-attributable depending on national smoking patterns.
Radon emanates from uranium-bearing bedrock — granite, shale, phosphate, and glacial till. Iowa sits on glacial till loaded with uranium-rich material; Appalachia sits on Devonian black shale; Colorado's Front Range is granite. Zone 1 follows the geology, then the housing stock (basement homes trap more radon) amplifies it.
Sub-slab depressurization systems cost ~$800–$1,500 and reliably drop indoor radon below 2 pCi/L. EPA estimates universal US mitigation in Zone 1 homes would prevent ~5,000 lung cancer deaths per year. Testing is the bottleneck: <25% of US homes have ever been tested.
The lung is still developing through adolescence, and the latency from exposure to cancer is 15–40 years. Children growing up in Zone 1 basements accumulate the highest lifetime dose. Mitigating before the teen years yields the largest absolute risk reduction.
Recent cohort analyses (Turner 2012; Barbosa-Lorenzo 2016) report modest associations between residential radon and chronic lymphocytic leukemia and possibly skin basal-cell carcinoma. Evidence is still developing; lung cancer remains the dominant, well-established outcome.
Bottom line
A short-term test kit costs ~$15 at any hardware store. Long-term kits (3–12 months) cost ~$30 and give a much more accurate picture. State radon programs often subsidize or supply kits free.
EPA recommends mitigating at ≥4 pCi/L and considering mitigation at 2–4 pCi/L. WHO's reference level is 100 Bq/m³ (~2.7 pCi/L). Aim as low as reasonably achievable, especially in homes with children or smokers.
A $1,200 sub-slab system reducing exposure from 8 → 1 pCi/L cuts a non-smoker's lifetime lung cancer risk by roughly 1 percentage point — comparable to the absolute benefit of low-dose CT screening in eligible smokers.
The single largest reduction in radon-attributable risk comes from not smoking. Combined with mitigation, quitting collapses the 25× synergistic risk back toward the never-smoker baseline within ~10–15 years.
Radon testing is one of the items on the personal screening checklist.