Plant and Soil Relationships of Uranium and Thorium Decay Series Radionuclides—A Review

Abstract

The behavior of radionuclides of the uranium (U) and thorium (Th) decay series in terrestrial systems is of interest because of environmental effects of mining and disposal activities related to nuclear power plant fuels. The soft‐plant relationships of U, Th, and polonium (Po), and some other daughter radionuclides, notably radium (226Ra), are not well understood. Most studies have been concerned with relative uptake of these radionuclides by various plant species. Plant concentrations have been related to total contents of these radionuclides in the soil as a plant/soil concentration ratio (CR), even though the fraction of these radionuclides, which may be available to plants, is not well known. These CR values have been used to predict transport of radionuclides and other elements of interest through the food chain as well as for other purposes, including biogeochemical exploration for U. Little information is available on uptake and transport mechanisms of radionuclides in plants. However, the mechanisms relating to Ca uptake and translocation in plants may be similar to those of some radionuclides, especially 226Ra. Soil chemical reactions of these radionuclides also have not been studied as well as those of plant nutrients, although knowledge of the effects of soil pH, soil texture, and organic matter content on uptake, as well as mobility in soil of these radionuclides, has been gained in recent years.

Literature review: Phytoaccumulation of chromium, uranium, and plutonium in plant systems

“…Uranium is chemically toxic to kidneys, and insoluble U compounds are carcinogenic (Department of Energy, 1988). Though U and its daughter elements have not been shown to be essential or beneficial to either plants or animals, many plant species will absorb U and incorporate it into their biomass along with other heavy metals (Mortvedt, 1994;Sims and Kline, 1991;Sheppard et al, 1989;Singh and Narwal, 1984;Narwal et al, 1983;Moffet and Tellier, 1977). This observation suggests the possibility for remediation of Ucontaminated soils through plant uptake.…”

“…Several studies have been conducted on the relationships between plants and soils relevant to radionuclide accumulation by plants (Mortvedt, 1994;Sheppard et al, 1989;Moffett and Tellier, 1977). Plants remove nutrients from the readily exchangeable and soluble fractions of the soil.…”

Soil to plant transfer of 238U, 226Ra and 232Th on a uranium mining-impacted soil from southeastern China

“…Therefore, the knowledge of natural radionuclide concentration levels and their mobility in the environment is of great interest in several scientific fields. It is also important to understand the behavior of natural radionuclides in the environment (e.g., mobility, transfers, translocation), because such information can be used as the associated parameter values for radiological assessments (Mortvedt, 1994;Tome et al, 2003). Migration and accumulation of contaminants (including radionuclides) in the soileplant system is complex, and assessment models commonly utilize a soileplant concentration ratio, referred to as a transfer factor (TF), to estimate the transportation of radionuclides through the food chain.…”

Effects of the mycorrhizal fungus Glomus intraradices on uranium uptake and accumulation by Medicago truncatula L. from uranium-contaminated soil

“…U speciation is closely related to soil properties (especially pH) (Ebbs et al, 1998;Langmuir, 1978;Mortvedt, 1994;) and is one of the key factors influencing U uptake by plants. U is most mobile as U(VI) (Campbell and Biddle, 1977).…”