Transfer of Polonium to the Embryo and Foetus of Rat and Guinea Pig

Transfer of 210Po to the foetus measured 3 days after administration in rat and 7 days later in guinea pig increased with increasing gestational age to about 0·1% injected activity per rat foetus at birth and 0·6% per guinea pig foetus on day 57, corresponding to whole-body foetus:mother concentration ratios of about 0·1:1 in both species. The greatest concentrations of 210Po were measured in the rat yolk sac during its haemopoietic stage, an order of magnitude greater than concentrations in the placenta and two orders of magnitude greater than foetal concentrations. The results obtained have been used to estimate in utero doses to haemopoietic tissues, taking account of transfer to the blastocyst/egg cylinder, yolk sac, liver and bone marrow. The concentration ratios relative to maternal liver for these tissues were taken to be 1, 3, 0·1 and 0·05 respectively and were applied to periods of human gestation of 0–2·5, 2·5–6, 6–12 and 12–38 weeks respectively. For chronic maternal intake by ingestion of 210P...