PLANT AND SOIL RELATIONSHIPS OF URANIUM AND THORIUM DECAY SERIES RADIONUCLIDES - A REVIEW

The behavior of radionuclides of the uranium (U) and thorium (Th) deca y series in terrestrial systems is of interest because of environmenta l effects of mining and disposal activities related to nuclear power p lant fuels. The soil-plant relationships of U, Th, and polonium (Po), and some other daughter radionuclides, notably radium (Ra-226), are no t well understood. Most studies have been concerned with relative upta ke of these radionuclides by various plant species. Plant concentratio ns have been related to total contents of these radionuclides in the s oil 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 radionu clides and other elements of interest through the food chain as well a s for other purposes, including biogeochemical exploration for U. Litt le information is available on uptake and transport mechanisms of radi onuclides in plants. However, the mechanisms relating to Ca uptake and translocation in plants may be similar to those of some radionuclides , especially Ra-226. Soil chemical reactions of these radionuclides al so 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.