Radiocontamination of the environment and its effects on the mother and fetus: I—Classification of fission products and neutron-activated elements according to their rate of placental transfer

Abstract

Intra-uterine irradiation of the fetus can be an important factor in the pathogenesis of embryopathies. Fetal irradiation occurs either by direct action of electromagnetic radiations on both mother and fetus, or by internal contamination of the mother, followed by systemic distribution of the radiocontaminant and subsequent placental transfer and fetal uptake. Fission products or activated elements can be divided into different categories, according to their respective rate of placental transfer: there is free transfer for natural metabolites and probably for inert gases and perhaps some discrimination for the periodic relatives of natural metabolites. The colloidal forms of rare earths do not cross the placenta. A large proportion of fission products is constituted by non-metabolites, whose metabolic fate and placental transfer are unknown. Fetal uptake of fission products is presently limited, especially the variation of tissular concentration in function of the age of the embryo. There is no evidence that, for a given radiocontaminant, embryo and fetus have the same critical organs as adult tissues. The damaging effect of the radiocontaminant in embryonic tissues is probably different from that produced by the same amount of radioactive element in adult tissue, due to the difference in radiosensitivity and also to the different metabolic profile of the cells. The study of the effects of radiocontaminants on fetus is an urgent problem, in view of the impending development of peaceful uses of nuclear energy. An indirect method of approach is the determination of the retention of radiocontaminants by human placentas, obtained from deliveries in different geographic areas of the world. Cesium-137 is the first contaminant of interest; in placentas obtained from normal deliveries of the Montreal area, preliminary measurement indicated a retention of Cs 137 in the placentas similar to that calculated from the total-body burden obtained in the literature. No determination was made on placentas of inhabitants of Canadian northern regions. Further studies are needed in this direction, chiefly a world-wide determination of placental retention of Cs 137, related to the dietary habits and chiefly to the degree of radiocontamination of the geographic area where the placentas were obtained.