Quantitative assessment of the radon (222Rn) decay product 210Pb in human toenails as a sensitive measure of personalized long-term radon gas exposure history

Lung cancer mortality can be lowered through early-diagnostic screening of people demonstrating a ≥1.5 % 6-year risk of tumor development. However, many who develop lung cancer are ineligible for screening (∼40 % of Canadian patients) as they have insufficient tobacco smoking history. Tools to assess individual lung cancer risk based on exposure to other prevalent environmental carcinogens such as radon (²²²Rn) gas are lacking. Here, we explore ultrasensitive quantification of the ²²²Rn decay product ²¹⁰Pb in toenails (n = 39) as an indicator of personalized, long-term radon exposure history. Toenail cuttings from adults inhaling elevated indoor radon in their primary house (average radon = 354.9 Bq/m³) over a mean of 26.5y (equating to 427 mSv radiation dose) contained 0.298 femtograms of ²¹⁰Pb per nanogram of stable Pb. By contrast, only 0.075 femtograms ²¹⁰Pb per nanogram Pb were detected in toenails from low radon exposure controls (28.4 Bq/m³ over 22.5y equating to 22.8 mSv) - a 397 % difference. Notably, elevated radon decay products (0.245 femtograms of ²¹⁰Pb per nanogram Pb) persisted in toenails from highly radon-exposed people (545.6 Bq/m³ over 18.5y equating to 283 mSv) who, up to 6 years prior to toenail collection, had mitigated their primary residence to reduce radon (post-mitigation radon = 28.1 Bq/m³). No differences were detected on the basis of sex, age, tobacco smoking history, or ²¹⁰Pb-rich game meat consumption. These data suggest that toenail ²¹⁰Pb/Pb isotope (amount) ratios show promise for evaluating individualized retrospective radon dosimetry history - an approach that may become helpful to assess non-tobacco lung cancer risk in the future.