Transfer characteristics of organically bound tritium into plant and foodstuffs

From the significance, with respect to dose, of organically bound tritium (OBT) in diet, ratios (SAR) of the specific activity of OBT to that of tissue free water tritium (TFWT) were investigated for various kinds of foodstuffs. The ratio of Japanese rice and Chinese rice ranged between 0.6 and 0.8 proved that the specific activity of OBT becomes less than unity due to the isotope discrimination in the assimilation process under the steady state condition. The ratio of about unity was also demonstrated for various kinds of world-wide foodstuffs. Very high SAR values reported by Italian studies on food items are therefore discounted. The difference of residence time between OBT and TFWT in plant, and the influence of atmospheric HTO vapor on both TFWT and exchangeable OBT were observed and considered to be the major causes of the variation of SAR value of foodstuffs under the dynamic condition. (author)