Radiobiological Studies with Tradescantia at Nuclear Test Detonations

Abstract

The flowering plant Tradescantia has been used at two nuclear test operations as an experimental organism for the biological effect of the ionizing radiations emitted. Blast and thermal effects of the test device have been excluded and are not considered in these experiments. Previous to the earlier of the two operations, there were several uncertainties about what test radiation would do to living tissue. The unique circumstances of test radiation-which is emitted at very high intensity, consists of a mixture of gamma, /3, neutrons, and at radiations, and is distributed over a very wide range of energies-were the reasons for the genuine uncertainties about how much tissue damage would be caused by test radiation. Some of these biological questions, at least previous to the earlier tests, were: (1) Would the test radiation cause any new or novel effects? Probably a negative answer would be given by most of the biologists concerned with these tests. (2) Would a given dose of test radiation and the same dose of radiation given in the laboratory cause equal effect? Expressing this in another way, could instruments which had been found reliable for measurement in the laboratory be accepted as reliable substitutes for biological measurement of test radiation effect? This amounts to asking if the relative biological efficiency of test radiations is the same as these radiations when they are delivered by the usual laboratory sources. It should become apparent in the various test experiments to be described in this symposium that most of the facts and conclusions to be derived, even qualitative ones, depend almost entirely on a correlation between instrumental and biological measurements. The intention was to estimate the test radiation dose on the basis of chromosomal breakage in Tradescantia, and to compare this biological estimate with, among other things, the physical measurements made simultaneously. The method of biological estimate is simply described. The yield of chromosomal aberrations as a function of dose was derived from a series of laboratory control experiments with measured doses of radiation, designed to simulate as closely as possible the anticipated conditions of test exposure. When the yield of aberrations from the test irradiation had been measured, it was a simple matter to solve for the single unknown, test dose, on the basis of the values for aberration-dose relation from the control experiments: these are called biologically estimated dose.