MODEL OF 210PB AND PO-210 PLACENTAL-TRANSFER TO FETAL BONE

Because of the paucity of actual measurements, a theoretical model has been developed that predicts the in utero activity levels of Po-210 i ngrowing from Pb-210. Experimental data have shown that the placental transfer of lead takes place, but precludes the transfer of significan t amounts of polonium. Bone volume seekers with long half-lives that c an substitute for calcium, such as Pb-210, are assumed to have similar specific activities, per g Ca, in fetal bone as they have in maternal bone. The dependence of the ingrowth of Po-210 from Pb-210 with gesta tional age was calculated with the input of experimental data on the m ass of stable lead and calcium in the fetal skeleton and the whole bod y. It is predicted that the P-210/Pb-210 activity ratio is approximate ly 0.25 in the bone of the third-trimester fetus. The verification of the assumptions made in this hypothetical model regarding the placenta l transfer and fetal uptake of natural long-lived radionuclides must a wait the results of future measurements.