Formation of organically bound deuterium at each growing stage of rice

Atarashi-Andoh, Mariko  ; Kumakura, Yasuharu*; Amano, Hikaru; Fukui, Masami*

Uptake of tritium by food plants is an important pathway in transferring tritium to the human body. Plants take up tritium as the form of water and a part of tritiated water (HTO) is converted to organically bound tritium (OBT). The formation of OBT in plants depends on the growth stage when the contamination occurs. Potted rice plants were exposed to deuterated water vapor, as a substitute for HTO vapor, for 4 h at 5 different times during the grain ripening period to estimate the influence of the growth stage on the formation and retention of organically bound deuterium (OBD) in rice. The plants were grown outside before and after the exposure experiments and were exposed to deuterated water vapor in a laboratory in a small chamber equipped with controllers of temperature, humidity and light intensity.The mass of OBD in grain at harvest showed the highest value when the exposure was carried out in the early stage of the ripening period. When the exposure was carried out after 26 day from the heading, the increase of OBD in the grain was a little.