The transfer factors (TFs) of uranium (U), thorium (Th), radium (Ra) and lead (Pb) from soil to agricultural products were determined in order to estimate the internal radiation dose to the human body through ingestion. Samples of rice, potato, onion, cabbage, mandarin orange, spinach, apple and soil were collected from various districts in Japan. After appropriate pretreatment of the samples, concentrations in the sample solutions were measured by ICP-MS (for U, Th and Pb) and liquid scintillation counter (for Ra). It was recognized that TFs were 4.9×10-6 (apple) and 3.6×10-4 (spinach) for U, 2.8×10-6 (apple) and 2.3×10-4 (spinach) for Th, and 4.0×10-3 (hulled rice), 7.0×10-5 (onion) and 5.0×10-3 (hulled rice) for Pb. The TF of Ra, however, was not determined due to detection limitations. TF values obtained in the present study range from the same order of magnitude to 1/100 compared to the data in TRS364 as reported by IAEA. It was revealed that the internal radiation dose caused by the intake of uranium series radioactive nuclides through agricultural food ingestion was 16μSv/y, where Pb was the most contributory nuclide.
