Possible existence of dose-rate threshold for mutation induction by chronic low-dose-rate gamma-rays.

This article focuses on evaluating the dose-rate effects of low-dose gamma radiation on somatic mutations using a hyper-sensitive cell system (GM06318-10 cells) that detects mutations in the hypoxanthine-phosphoribosyltransferase 1 (HPRT1) gene. The study exposed cells to gamma irradiation at dose-rates of 6.6, 20, and 200 mGy per day until a total dose of 0.2 Gy was reached, finding a tendency for reduced mutant frequency at the lowest dose-rate (6.6 mGy d⁻¹), though not statistically significant. Mutation spectra did not differ between irradiated and control groups at any dose-rate, contrasting with previous findings for tritiated water (HTO) exposure, which showed dose-rate-dependent changes and suggested mechanistic differences between tritium beta-rays and gamma-rays. The results indicate a possible dose-rate threshold below 20 mGy d⁻¹ for gamma-ray-induced mutagenesis, warranting further investigation to clarify underlying mechanisms and implications for low-dose radiation exposure.