Purpose : To analyse the life-span and pathologies of mice living under a continuous very low-dose γ-irradiation.

Material and methods : We exposed 300 C57Bl/6J female mice, 3 weeks old, to 10 cGy year -1 γ-rays while 300 control mice lived in the same room. Irradiation was delivered continuously by thorium nitrate. We kept all the animals until natural death and performed autopsy.

Results : No difference was observed in life-span (mean life-span ±SE: 805.2 ±9.62 days for controls and 815 ±9.57 days for irradiated mice), weight curves or food intake. At autopsy, cancer was present in 40.9% of controls and 37.9% of irradiated mice. They were mainly represented by lymphomas (23.7 and 24.9%) and histiocytic sarcomas (12.6 and 8.7%, respectively, for controls and irradiated mice). Vascular diseases occurred in 24.1% of controls and 23% of irradiated mice. Infections were present at autopsy in 14.1 and 12.3%, respectively, of controls and irradiated animals. No statistical difference was observed at the end of the experiment for cancer or non-cancer diseases between the two groups.

Conclusion : Continuous 10 cGy year -1 γ-irradiation had no adverse effect on malignant or non-malignant diseases in this strain of mouse.