Tritium Effects on Germ Cells and Fertility

摘要

Primordial oocytes in juvenile mice show acute gamma-ray LD sub 50 as low as 6 rad. This provides opportunities for determining dose-response relations at low doses and chronic exposure in the intact animal - conditions of particular interest for hazard evaluation. Examined in this way, exp 3 HOH in body water is found to kill murine oocytes exponentially with dose, the LD sub 50 level for chronic exposure being only 2 mu Ci/ml (delivering 0.4 rad/day). At very low doses and dose rates, where comparisons between tritium and other radiations are of special significance for radiological protection, the RBE of tritium compared with exp 60 Co gamma radiation reaches approximately 3. Effects on murine fertility from tritium-induced oocyte loss have been quantified by reproductive capacity measurements. Chronic low-level exposure has been examined also in three primate species - squirrel, rhesus, and bonnet monkeys. In squirrel monkeys the ovarian germ-cell supply is 99% destroyed by the time of birth from prenatal exposure to body-water levels of exp 3 HOH (administered in maternal drinking water) of only 3 mu Ci/ml, the LD sub 50 level being 0.5 mu Ci/ml (giving 0.1 rad/day), one fourth that in mice. Though not completely ruled out, similar high sensitivity of female germ cells has not been found in macaques; and it probably does not occur in man. The exquisite radiosensitivity of primordial oocytes in mice is apparently due to vulnerability of the plasma membrane (or something of similar geometry and location), not DNA. Evidence for this comes from tritium data as well as neutron studies. Tritium administered as exp 3 HOH, and therefore generally distributed, is much more effective in killing murine oocytes than is tritium administered as exp 3 H-TdR, localized in the nucleus. This situation in the mouse may have implications for estimating radiation genetic risk in the human female. (ERA citation 08:021973)