 |
|
||||||||||
 |
Home | Did You Know?Polonium and PregnancyFetal/Placental Information According to NCRP Report No. 128, Radionuclide Exposure of the Embryo/Fetus (1998), results of human measurements corroborate the pattern seen in animal studies that found that minimal fractions of polonium salts pass into the fetal tissues. Lacassagne and Lattes (1924) reported that the greatest autoradiographic deposition of polonium was found in the chorionic villi of the rabbit placenta at 6 d after intravenous injection. There was a gradation of amounts in various maternal organs but there was practically no polonium in the fetus. Soremark and Hunt (1966) performed whole-body and microscopic autoradiographic studies that included pregnant mice intravenously injected with single doses of 210Po. Substantial activity remained in the blood throughout the 5 d study period; there were substantial concentrations in spleen, liver and lung, but the heaviest labeling was over the kidneys, especially cortex. There was relatively little labeling of the placenta at early times but activity subsequently increased to levels similar to the renal cortex. Polonium associated with the fetus was not seen through 4 d postexposure but low activity was seen at 5d. They reported only slight activity over the fetal sac membranes (amnion presumably) but it appears that there was substantial activity over the visceral yolk sac. Inferential evidence from subsequent experimental studies confirms the placental deposition and lack of appreciable transfer of injected 210Po. In pilot studies using an equilibrium mixture of 210Pb and 210Po in rats, Hackett et al. (1982b) found intense autoradiographic labeling of the placenta, Reichert's membrane, and visceral yolk sac. The intensity of the labeling was much less when they injected freshly separated 210Pb, indicating that the greatest fraction of the autoradiographic label was derived from the polonium component. As noted above, Carpenter et al. (1973) had found high levels of activity in these same structures in their experiments using an equilibrium mixture of lead. The foregoing result suggests that the explanation for their findings is that the labeling was attributable to the 210Po rather than to the 210Pb. Harrison et al. (1991) have reviewed earlier published data and provided results from more recent experiments that determined concentrations in hematopoietic tissues, in particular. In addition to confirming and quantifying deposition in placenta and in fetal membranes, deposition in the embryo/fetus was measured in these studies. These results were used for dose calculations that extended earlier estimates by Stather et al. (1984), and included calculations of dose to hematopoietic elements. Analyses of specimens of Arctic lichens and grass, reindeer and caribou, and postpartum human placentas measured elevated levels of radionuclides, especially 210Po and 210Pb (Holtzman, 1966). This activity results from natural fallout and concentration by the slow-growing grasses and the animals. These results are compatible with other observations in human tissues, where elevated concentrations have been measured in placentas from populations who consumed reindeer and caribou meat (Hill, 1966). This again represented natural fallout radioactivity resulting from 222Rn. There was excellent correlation with 137Cs, which was also produced in the atmosphere by decay of the fission product 137Xe, and illustrated the role of the food chain. Radiation Dose Estimates It may be assumed that there would be minimal transfer to the embryo/fetus of 210Po (or other isotopes) from the body of the pregnant woman and essentially no radiation dose. However, the placenta and membranes would receive some deposition from any polonium in her circulation. Polonium could be formed within the conceptus by decay of radon and its progeny, such as 210Pb and there would be subsequent decay of the 210Po. Get the full report and references at: http://NCRPpublications.org
|
|
|
|||||||||||||||||||||||||||||||
Home | About NCRP | Our Mission | Current Program | News & Events | Publications | Members | Related Organizations |
