Plant Accumulation of Natural Radionuclides as Affected by Substrate Contaminated with Uranium-Mill Tailings

Environmental concern due to plant accumulation of natural radionuclides is a major concern in uranium mining areas. To evaluate the risk associated with the transfer of radionuclides to edible plants, the uptake of ²³⁸U, ²²⁶Ra, and ²¹⁰Pb by Chinese cabbage (Brassica rapa L. subsp. pekinensis (Lour.) Hanelt) grown in soils contaminated with uranium-mill tailings (UMT) was investigated. Test plants were grown under controlled conditions in substrate composed of soil and UMT in different ratios. Activity concentrations of ²³⁸U, ²²⁶Ra, and ²¹⁰Pb in substrate, leaves, and roots were measured and the concentration ratios determined. Soil characteristics were determined, since they directly affect bioavailability of radionuclides. Concentration ratios of ²³⁸U, ²²⁶Ra, and ²¹⁰Pb in leaves varied from 0.001 to 0.006, 0.024 to 0.172, and 0.004 to 0.011, respectively, and in roots from 0.020 to 0.126, 0.015 to 0.241, and 0.033 to 1.460, respectively. Concentrations of ²³⁸U, ²²⁶Ra, and ²¹⁰Pb in leaves and roots were found to correlate with the amount of ²³⁸U, ²²⁶Ra, and ²¹⁰Pb in the substrate. A higher amount of ²²⁶Ra accumulated in aboveground parts (57–877 Bq kg^?1 d. m. for leaves) compared to ²³⁸U (0.6–4.7 Bq kg^?1 d. m. for leaves) and ²¹⁰Pb (8–53 Bq kg^?1 d. m. for leaves), which were mainly stored in the roots. The relationships between the amount of radionuclides in plants and soil characteristics and their role in radionuclide uptake are discussed and critically evaluated.