Toxicity of 241Am and 241Cm after administration at nine days of gestation in the rat

10 μCi/kg body weight of plutonium has been found to be embryocidal, but not teratogenic, when administered to rats after 9 days of gestation. Previous studies suggest that this effect was primarily due to nuclide incorporated in the fetal membranes and, to a lesser extent, in the placenta. Other transuranic elements are distributed similarly to plutonium although there are specific differences. Americium-241 or curium-244 citrate, pH 4.0--4.5, were intravenously injected into rats after 9 days of gestation to compare their prenatal toxicities with that of plutonium and to define their deposition in the fetoplacental unit (FPU) relative to other transuranic elements. In rats killed after 20 days of gestation, it was found that neither nuclide increased the incidence of prenatal mortality or malformations, even at doses up to and including 60 μCi/kg. In rats killed at 1, 3 or 5 days postinjection, a marked avidity of the livers of the dams for 241Am and 244Cm was noted. This presumably led to a shortened half-time in blood and to lower concentrations in the FPU than was observed with most of the transuranic elements studied to date. It thus appears that 241Am and 244Cm are less embryocidal than plutonium and that this is a result of lower concentrations in the placenta and fetal membranes