Comparison of hematologic effects of internally deposited radium and plutonium in dogs.

Abstract

The expansion of the atomic energy program and the widespread use of heavy radioactive elements in all areas of research have increased the need for data concerning the permissible total body burden of these elements. Current permissible body burdens are based upon data gathered from several sources. For heavy elements, the information on radium toxicity in man obtained from the luminous dial workers, and from individuals exposed to radium therapeutically or accidentally, serves as a base line (1–4). Permissible total body burdens of other heavy radioactive elements, particularly plutonium, have been arrived at by comparing their toxicity with that of radium in mice or rats and then extrapolating to man on the basis of the radium cases. The toxicity of plutonium has also been studied in a relatively small number of dogs. Thus, the permissible body burden of plutonium has been placed at 0.04 μc, while that for radium is 0.1 μc. Some doubt has arisen as to the reliability of the latter figure, since it has been found that some batches of luminous paints contained significant amounts of mesothorium and radiothorium. A study is being made of the comparative effects of plutonium, radium, radiothorium, and mesothorium in adult beagle dogs. By using a species with a relatively long life span and a skeletal growth pattern generally similar to that of man, we hope to contribute more reliable animal data for extrapolation to human beings. The dose levels of the heavy radioelements which we are employing may produce immediate effects such as the acute radiation syndrome and hematologic changes. Be-nign and malignant bone disease, blood dyscrasias, and hepatic and renal disease are among the recognized delayed effects. This report includes the hematologic alterations which are seen during the first year following injection of plutonium and radium. Results on dogs injected with radiothorium and mesothorium will be reported later. Methods Young adult male and female dogs were selected from a healthy pure-bred beagle colony maintained under optimal conditions. At the time of injection the males have an average weight of 10 kg. and the females of 8 kg. Skeletal maturity is verified by means of roentgenographic examination. We employ five dose levels of each radio-element, estimated on a retained basis as follows: 2.5, 0.81, 0.27, 0.086, and 0.014 μc/kg. The injected doses are based on a 90 per cent retention of plutonium and 25 per cent retention of radium. The injected and retained amounts are given in Table I. The lowest dose level (0.014 μc/kg.) is considered to be equivalent to the current human total permissible body burden of radium, and the other doses are developed from it. The scale of five doses was designed to be sufficiently broad to give an accurate answer on a safe total body burden of radium and plutonium for the dog.