Comparison of 95Zr and 95Nb Distributions in Maternal and Fetal Rabbit Tissues.

The fission products 95Zr and 95Nb form a radioactive “parent-daughter” pair whose metabolic behavior in animals and man is of interest because of their appearance in the environment following the detonation of nuclear devices. Peaks in the concentrations of 95Zr-95Nb on airborne particles were observed during early 1962 and 1963(1), and these nuclides have been identified in food(2) and humans (3,4). The early work of Hamilton and associates (5) and others (6,7) has shown that small but measurable amounts of 95Zr-95Nb can enter the mammalian body via ingestion and inhalation. 95Zr and 95Nb both emit gamma rays, but their energies (0.72–0.76 Mev) are so similar that it is impractical to assay the amounts of each nuclide in a mixture by γ-scintillation spectrometry. This has made it difficult to compare the metabolic behavior of the parent 95Zr to that of the daughter 95Nb, in the carrier-free condition. Sastry et al(8) approached this problem by determining the effective physical half life of γ-activity in tissues obtained from rats following intraperitoneal administration of 95Zr-95Nb. They utilized the fact that the physical half life of 95Zr is 65 days while that of 95Nb is 35, and reported that bone tissue accumulated more 95Zr than 95Nb. However, we have found no published data on the transplacental movement and subsequent disposition of these isotopes between a pregnant animal and its fetus. The purpose of the work now to be reported was to compare the distribution of 95Zr and 95Nb in an adult mammal to that in the growing fetus. Methods. Five pregnant Dutch rabbits, estimated to be within one week of completion of full term, each received an intravenous injection of approximately 50 μc carrier free 95Zr-95Nb as oxalates in normal saline solution.