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

Radium-226 ((226)Ra) 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 (F(v)) is of importance; it is defined as the plant/soil concentration ratio. Reported F(v) data for (226)Ra are still limited due to the low concentration of (226)Ra in plants in the natural environment. In this study, we collected F(v) of (226)Ra (F(v)-Ra) for crops and then applied a statistical approach to estimate F(v)-Ra instead of directly measuring the radionuclide. We found high correlations between (226)Ra and U concentrations in soils (because (226)Ra is a progeny in the (238)U series), and between (226)Ra 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 F(v)-Ra with good accuracy; the difference between estimated and measured F(v)-Ra values was a factor of 1.2 on average for crops. The method could estimate F(v)-Ra for the soil-to-plant systems where (226)Ra and Ba concentrations in soil are within the normal range, e.g. 8-100 Bq kg(-1)-dry for (226)Ra and 84-960 mg kg(-1)-dry for Ba.