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

Abstract

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.