Predicting uranium and radium availability and plant uptake from soil properties

Considerable interest in the behaviour of the natural radionuclides uranium and thorium and their daughter radionuclides in the terrestrial environment was shown in the past years. Interest in behaviour of these elements in soils and plants is linked with the potential health and environmental effects from uranium mining and (geological) disposal activities. Enhanced levels of naturally occurring radionuclides (NOR) in the environment may also be associated with industrial activities extracting and processing materials containing NOR. Further, the dominant radionuclide in geological disposal is U and its daughter 226Ra may contribute to the human dose at long times. There is, however, limited information on how soil physico-chemical characteristics and processes in the root environment affect U and Ra availability and uptake. The present study explores the dominant soil factors ruling U and Ra mobility and availability to plants and intends to quantify the effect. Eighteen soils collected under pasture (9 soils for radium) were selected such that they covered a wide range for those parameters hypothesized as being potentially important in determining U or Ra sorption. Ryegrass was grown as test plant on 238U spiked soils and ryegrass and clover on the 226Ra spiked soils.