Effect of lifetime intake of organically bound tritium and tritiated water on the oocytes of rats.

Rats were continuously exposed to constant activity of tritium in drinking water (HTO group) or to tritium organically bound in food (T-food group) in the period from conception of F1 generation through maturity. Female offspring were killed at the age of 21 and 71 days and the oocytes in their ovaries were counted. Mean dose rates absorbed in the ovaries were for the HTO groups 7.25 +/- 0.37 and 14.73 +/- 0.79 mGy/day and for the T-food group 4.84 +/- 0.25 mGy/day. Reduction in the oocyte number in the ovaries of females exposed to tritiated food was bigger than in the ovaries of females exposed to tritiated water. The dependence of the survival of small oocytes on the dose rate and the corresponding total accumulated dose had an exponential character. The damaging effect of tritium was for the period from conception to 21 days of age bigger than from 21 to 71 days of age. Of all stages of oocyte development, the highest sensitivity to tritium irradiation was observed in small oocytes and oocytes with one complete layer of follicle cells. As a result, relative number of growing and large oocytes increased.