Fusion Science and Technology / Volume 60 / Number 3 / October 2011 / Pages 1173-1178
Biology / Proceedings of the Ninth International Conference on Tritium Science and Technology
An exposure of human or animals to tritium radiation from nuclear fusion reactor is expected to be a low dose and with low dose-rate. We are focusing on the biological effects of tritiated water (HTO) given at low dose and/or with low dose rate. Hypersensitive assay systems for radiation biological experiments using cultured mammalian cells or transgenic mice have been established and their availability for assessment of biological effects of HTO were tested. A hypersensitive detection system for mutagenesis at Hprt locus was established by using hamster cells carrying a human X-chromosome. The cells present more than 50-fold sensitivity for Hprt-deficient mutation, and this allowed us to detect a significant elevation of mutation frequency by radiations at the dose of less than 0.2 Gy.
Because the reverse dose rate effect has been reported for mutation induction by high LET radiation such as neutrons, we first tested whether the reverse dose rate effects could be seen for HTO (tritium beta-rays) or not. No significant change in mutation frequency by HTO was observed in the range of dose rates between 0.05 cGy/h and 2.0 cGy/h, whereas clear reverse dose rate effects was observed in the case of fission neutrons or carbon beam. The result suggests that the reverse dose rate effect does not apply in the case of mutation induction by HTO. In addition, mutation spectrum in the mutants induced by HTO was similar to those in spontaneously induced mutants, suggesting that exposure to a certain level of HTO could enhance the spontaneous mutagenesis.