Evaluation of the Japanese health risks induced by global fallout tritium

Radioactive tritium (3H) generated by the atmospheric nuclear detonation tests has been circulated in the global environment to cause, through various pathways, low-level world-wide contamination of the environment and potential health risks to human beings. In this study, the dynamic performance of tritium in the global environment was modeled considering its transport with foods/feeds imported from all over the world. The mathematical model was examined by comparing the numerically simulated results with the fallout monitoring data. Main results obtained in this study were as follows: (1) The mathematical model developed in this study can reproduce well the global scale tritium circulation and its concentration in food; (2) The excess fatality rate of Japanese by the dietary intake of tritium is estimated to be on the order of 10(-8) y(-1) at present, which is about two orders of magnitude smaller than that by 90Sr; and (3) About 70% of the Japanese internal radiation dose by tritium is due to drinking water. Farm products, especially imported wheat, are secondly important in the Japanese health risk evaluation; its contribution, however, becomes small if the isotopic exchange effect of tritium is considered.