Radium-226 transfer factor from soils to crops and its simple estimation method using uranium and barium concentrations

Radium-226 (226Ra) should be assessed to determine the safety of geological disposal of high-level radioactive and transuranic wastes. Among the environmental transfer parameters that have been used in mathematical models for the environmental safety assessment, soil-to-plant transfer factor (Fv) is of importance; it is defined as the plant/soil concentration ratio. Reported Fv data for 226Ra are still limited due to the low concentration of 226Ra in plants in the natural environment. In this study, we collected Fv of 226Ra (Fv-Ra) for crops and then applied a statistical approach to estimate Fv-Ra instead of directly measuring the radionuclide. We found high correlations between 226Ra and U concentrations in soils (because 226Ra is a progeny in the 238U series), and between 226Ra and Ba concentrations in plants (because they are chemically similar in plant uptake). Using U in soil and Ba in plant values, we could estimate Fv-Ra with good accuracy; the difference between estimated and measured Fv-Ra values was a factor of 1.2 on average for crops. The method could estimate Fv-Ra for the soil-to-plant systems where 226Ra and Ba concentrations in soil are within the normal range, e.g. 8–100 Bq kg−1-dry for 226Ra and 84–960 mg kg−1-dry for Ba.