Tritium concentration in soybean plants exposed to atmospheric HTO during nighttime and daytime

Abstract

Potted soybean plants were exposed to evaporate HTO for 1 h inside an exposure box at two different growth stage (flowering and podding stage, filling stage) during nighttime and daytime. The concentration of tissue-free water tritium (TFWT) and organically bound tritium (OBT) in leaves and beans was measured at the end of the exposure. The results indicated that the quasi-equilibrium between the TFWT concentrations in the soybean leaves and the HTO concentration of the ambient air moisture required more than 1 h to be reached. The relative TFWT concentrations in the nighttime represent about 1/2 to 2/3 of the concentrations obtained in the day in the leaves compared to about 1/2 to 4/3 in the beans. The relative OBT concentrations under night conditions were about 2/5 to 1/2 of those under day conditions in the leaves, contrary to 1/2–7/10 for the beans. By developing tritium concentration assessment model with a short-term release of atmospheric HTO, we comprehensively considered the plant growth stage and the environmental conditions.