Transfer factors of radionuclides and stable elementsfrom soil to rice and wheat

Abstract

It is important to obtain local transfer factors (TFs) of long-lived radionuclides for assessment of radioactive waste disposal, because climates, soil types and vegetation can affect TFs. Global fallout ⁹⁰Sr and ¹³⁷Cs are good tracers to obtain the TFs under natural conditions, however, their radioactivity levels in plants are extremely low. To close the gap, analyses of stable isotopes and natural radioisotopes in rice and wheat grains and their associated soils collected throughout Japan were carried out in order to obtain TFs under equilibrium conditions. We focused on rice and wheat, because the consumption of cereals is very high in Japan and other Asian countries. About 40-50 elements such as Cs, Sr, Th and U in plant and soil samples were measured by ICP-MS and ICP-OES. From the data, TFs of stable elements were calculated; among the values, TFs of Cs and Sr for rice and wheat were compared with the TFs of ¹³⁷Cs and ⁹⁰Sr. Using the elements' concentrations data, we proposed a `Reference rice' (brown rice and polished rice) and a `Reference paddy soil' to provide elemental composition data which can serve as reference values in mathematical transfer models and which allows the comparison of data for other crops.