Studies of mutagenesis caused by low dose rate tritium radiation using a novel hyper-sensitive detection system

A novel hyper-sensitive detection system was developed to detect Hprt-deficient mutations using Hprt deficient hamster fibroblast cells which carry a normal human X-chromosome. The system has been found to be 100-fold more sensitive for detecting mutations than the conventional system which uses an internal Hprt gene. The mutation frequency induced by 1 Gy of tritium radiation at different dose rates (0.9, 0.4, 0.04, and 0.018 Gy/h) was measured. No significant differences in mutation frequencies were observed within the range of dose rates used, suggesting that if a reverse dose-rate effect exists, it may not be observable with tritium radiation at dose rates over 0.018 Gy/h. Interestingly, molecular analysis of the Hprt locus in Hprt-deficient mutants induced by tritium showed that deletion sizes observed in the hamster cell's human X-chromosome under these conditions are much smaller in cells exposed at 0.04 (and 0.018 Gy/h) than in cells exposed at 0.9 Gy/h. This phenomenon seems to be specific for tritium radiation because it was not apparent after exposure to gamma-rays. The novel hyper-sensitive detection system used here is useful for analysis of the mutagenic effects of low doses of tritium radiation delivered at low dose rates.