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 210 Pb 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- 210 Pb 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 λ 210 /λ 222 ≈ 4.7 × 10 −4 . For a documented remediation-era source scale of 10 14 Bq y −1 , even complete capture of all generated 210 Pb over 10 6 km 2 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 210 Pb deposition or the inventories derived from it detectably. Localized source–receptor episodes cannot be excluded, but particulate and erosion-mediated inputs from 226 Ra-bearing residues are the more plausible pathways at facility and catchment scales and may warrant explicit consideration and targeted, pathway-based monitoring.