Transfer to the Fetus

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

plutonium crosses the placenta (Okabayashi and Watanabe, 1973). However, placental

and fetal membranes appear to effectively trap a portion of the plutonium that might

otherwise reach the fetus.

The behavior of plutonium in the embryo/fetus changes with the development of the

embryo/fetus (Sikov, 1987; Sikov et al., 1992). Liver and bone surfaces are the principal

sites of plutonium deposition in the embryo/fetus, accounting for approximately 80% of

the deposited plutonium (ICRP 48, 1986). Plutonium that deposits on bone surfaces

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 homo-

geneous 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.

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