Vulnerability of female germ cells in developing mice and monkeys to tritium, gamma rays, and polycyclic aromatic hydrocarbons

During development female germ cells in both mouse and monkey are extremely sensitive to destruction by low-level chronic tritium exposure (via 3HOH in maternal drinking water). Practical significance of this stems from tritium's importance in nuclear energy production and as an environmental pollutant. In mice exposed from conception to 14 days of age, the LD50 level for oocytes is only 2 μCi per mililiter of body water. The present studies indicate that, for female germ cells in squirrel monkeys exposed in utero, the LD50 is even lower, about 0.5 μCi/ml. This striking sensitivity contrasts with reported radioresistance for primate oocytes, chiefly from acute x-irradiation experiments. The discrepancy is reconciled if germ cells in the fetal primate pass through a highly sensitive period of limited duration. In light of other data showing germ-cell loss following repeated semiweekly x-irradiation during late but not during mid gestation, these results indicate that exceedingly high sensitivity occurs probably about the middle of the last trimester, at which time the LD50 for monkey germ cells is, as for that of the mouse, less than 5 rads. Whereas highest radiosensitivity in primates is before birth, in mice it is after birth. To define the period of sensitivity more sharply, we measured oocyte responses to standard gamma-ray exposures in Swiss-Webster mice at various ages and found them to be maximal between days 5 and 19. Polycyclic aromatic hydrocarbons (PAH's), important as pollutants, also can destroy female germ cells effectively