following prenatal or neonatal exposure gradually moves into the bone
matrix during subsequent bone-remodeling processes.
The radiation doses produced in the embryonic stage are assumed to be
relatively homogeneous and represent a small fraction of the doses
received by the pregnant woman when averaged over all tissues. The dose
to the fetus would constitute an even smaller fraction of the maternal dose
to any tissue in which there was specific deposition (Sikov et al., 1992). As
gestation progresses, there is an increase in the relative plutonium
concentration in specific fetal tissues, namely the bone and liver (Sikov et
al., 1992). Although limited information is available, experimental animal
and human data suggest that the average concentration is higher in the fetus
during the second or third trimesters than in soft tissues of the pregnant
woman, exclusive of the liver, yet significantly less than in maternal tissues
of primary deposition, i.e., the bone and liver.
Because placental structures, including the yolk sac, effectively trap
plutonium, progenitor cells of the gametes and hematopoietic lines that
appear initially in the blood islands of the yolk sac are irradiated while they
are primitive stem cells. However, the dose received by the early
embryonic cells and the detriment produced is not currently known.