Soil-to-plant transfers of uranium series radionuclides in natural and contaminated settings

¹ ECOMatters Inc., PO Box 430, Pinawa, Manitoba, Canada, R0E 1L0 e-mail: sheppard@ecomatters.com
² Canadian Nuclear Safety Commission, 280 Slater Street, PO Box 1046, Station B, Ottawa, Ontario, Canada, K1P 5S9

Abstract

Uranium and related decay-chain radionuclides remain important subjects of study for a number of reasons. Uranium has the potential to be chemically toxic near mining and processing facilities, and the decay-chain radionuclides can contribute substantially to radiation dose. Establishing an air quality standard for U in Canada has also been tentatively based on its accumulation and toxicity in soil. This paper summarizes two studies. The first investigated the mobility in soil, uptake by plants and ecotoxicity of U near a U refining facility. Because of the presence of co-contaminants, a large number of other elements were measured to fully characterize the samples. In general, the soil solid/liquid partition coefficients, Kd, for U were high enough that leaching is not a dominant process. Plant/soil concentration ratios (CRs) were not consistently different compared to background sites. The second study measured plant/soil CRs for ²¹⁰Pb, ²¹⁰Po, ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³⁰Th, ²³²Th and ²³⁸U on a series of sites across Canada, with emphasis on background sites with possible human food-chain connections. Secular equilibrium was rarely observed, especially in plants.