The Hematological Effects of Ionizing Radiations

Abstract

The objectives of the Health Division of the Plutonium Project were essentially (a) to study the fundamental and comparative biological action of external radiations and internally administered radioactive materials, (b) to apply the findings for the protection of individuals who worked in the Project, and (c) to use the findings generally for the protection of the public which was potentially in danger of exposure to these physical hazards. The hematologic studies2 conducted on the Plutonium Project were divided into four main categories, namely, the effects of acute3 whole-body exposure to externally administered penetrating radiation, the effects of chronic4 whole-body exposure to externally administered penetrating radiations, acute toxicity of parenterally and enterally administered radioactive compounds, and chronic toxicity of parenterally and enterally administered radioactive isotopes. In order to correlate properly studies on the peripheral blood effects with those occurring in the hemopoietic tissue, the animals in the same or parallel experiments were sacrificed at intervals for histologic study. All experiments included an adequate number of controls, and the frequency of sampling depended upon the chronic nature of the experiment. Comparative Effects of Acute Whole-Body Exposure to X-Rays and Fast Neutrons In considering the irradiation of the whole body with penetrating radiations of external origin, those of significance in so far as direct effects on the blood and bloodforming tissue are concerned are x-rays, gamma rays, fast neutrons, and slow neutrons. The beta and alpha rays that originate from radioactive substances can largely be neglected, because penetration in tissue is only a few millimeters in the former and a fraction of a millimeter in the latter. The studies on animals by Raper and Barnes (1), Raper, Zirkle, and Barnes (2), Raper, Henshaw, and Snider (3), and others, have demonstrated that, although beta rays may penetrate the skin, the hematologic effects, if any occur, are minimal and are secondary to other more serious pathological changes. No experiments similar to those of Raper and Zirkle have been performed using alpha rays. Since alpha rays have such shallow penetrability (e.g., those emitted by plutonium or radium will penetrate only about 40μ into the skin), no direct effects and only minimal indirect effects on hemopoietic tissue appear likely. Studies on the effects of acute exposure of animals to a slow neutron flux have been carried out by Zirkle (4a). This slow neutron source, however, was contaminated with fast neutrons, and the effect on the hemopoietic system, as reported by Raper, Henshaw, and Snider (3), is therefore difficult to interpret.