Environmental behaviour of tritium and assessment of public absorption dose tritium

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(1)The low dose effects of tritiated water (HTO) on mouse lymphocyte DNA (in vitro irradiation) were determined by the comet assay using ICR male mouse of 20 to 23 weeks old. After lymphocytes were exposed to 17-50mGy of HTO, the lymphocytes embedded agarose gel slides were washed and cell lysis treatment was conducted before electrophoresis. The individual comets on stained slides after electrophoresis were analyzed using imaging software. No significant DNA damages were observed.(2)Among the chemical forms of tritium released in the environment, tritiated water has a large contribution to the dose. Heavy water (D_2O) vapor release experiments were carried out in a greenhouse using D_2O as a substitute for HTO and uptake and loss kinetics of D_2O in leaves and formation, translocation and retention of organically bound deuterium (OBD) in bean of soy bean were investigated using different growth process of soybean. Rate constants of D_2 uptake in leaves in the daytime and nighttime release, rate constants and the half time of D_2O loss in leaves after release were determined. After D_2O release, OBD concentration in bean increased gradually until 3-4 days after the exposure and then decreased with time due to metabolic consumption in bean.(3)An exposure condition of tritium radiation from nuclear fusion reactor could be a long-term exposure with low dose rate. The biological effects of low dose rate radiation are not clear because any suitable detection system has not been established. To examine the low dose rate effect of tritium, a hypersensitive mutation detection system using hamster cells carrying a human X-chromosome was established. The mutation induction by tritiated water at dose rate between 0.18 and 44 cGy/h was tested. The mutation frequency seemed to be slightly increased at lower dose rate.