Bioaccessibility of U, Th and Pb in solid wastes and soils from an abandoned uranium mine

Bioaccessible U, Th, Pb and the ²³⁸U decay products ²¹⁴Pb and ²¹⁰Pb have been determined, using a modified Unified BARGE Method (UBM), in waste solids and soils from an abandoned uranium mine in South West England, UK. Maximum aqua regia extractable concentrations for U, Th and Pb were 16,200, 3.8 and 4750 μg g⁻¹, respectively. ²³⁸U had highest activity concentrations near the mine shaft, where the decay products²¹⁴Pb and ²¹⁰Pb had values of 235 and 180 Bq g⁻¹, respectively. UBM extractions gave mean gastro-intestinal bioaccessibility factors (BAFs) for U and Pb in the waste solids of 0.05 and 0.03, respectively, whereas those for the soils were significantly higher at 0.24 and 0.17. The mean BAFs for the transient radionuclides, ²¹⁴Pb and ²¹⁰Pb, were similar to those for stable Pb implying that the stable and radioactive Pb isotopes were attached to similar sites on the particles. The doses arising from the ingestion of particulate ²¹⁰Pb due to soil pica behaviour were in the range 0.2–65 and < 0.1–6.2 μSv day⁻¹ for a 1-year old child or an adult (>17 years), respectively. The results suggest that the health risk posed by abandoned uranium mines, with waste rock and tailings, throughout the world should take account of the dose due to both bioaccessible radionuclides, as well as their stable counterparts. - Highlights: • Elevated activity concentrations at an abandoned uranium mine. • The bioaccessibility of lead, thorium and uranium using unified in vitro method. • Chemotoxicity and radiotoxicity from the ingestion of solid wastes. • Risk assessments should account for total and bioaccessible radionuclides.