An upper bound on uranium-mining radon contributions to regional environmental ²¹⁰Pb inventories

Radon releases from uranium-mining legacies are commonly evaluated in relation to inhalation exposure. Here, the separate question is whether the ²¹⁰Pb produced from sustained legacy releases could perturb the inventories used to date and interpret soils, sediments, peat and other environmental archives. This paper bounds that possibility and tests the natural-meteoric provenance assumption underlying regional excess-²¹⁰Pb interpretation. Because decay-chain mass balance conserves atoms rather than activity, conversion from a 3.8-day radionuclide to a 22.3-year radionuclide reduces the associated activity source term by λ₂₁₀/λ₂₂₂ ≈ 4.7 × 10^-4. For a documented remediation-era source scale of 10¹⁴ Bq y^-1, even complete capture of all generated ²¹⁰Pb over 10⁶ km² would yield only about 0.05 Bq m^-2 y^-1, compared with a contextual natural deposition range of 50-200 Bq m^-2 y^-1. A complementary source-ratio diagnostic indicates that individual legacies contribute about 10^-4 of the natural radon source within representative continental footprints, while the largest historical district aggregates contribute about 10^-3-10^-2. Documented legacy releases are therefore unlikely to perturb regional-mean ²¹⁰Pb deposition or the inventories derived from it detectably. Localized source-receptor episodes cannot be excluded, but particulate and erosion-mediated inputs from ²²⁶Ra-bearing residues are the more plausible pathways at facility and catchment scales and may warrant explicit consideration and targeted, pathway-based monitoring.