The Tissue Distribution and Excretion of Cesium-137 following Inhalation-preliminary Data for Rats. Lf-4.

Data were obtained for the distribution-excretion pattern of cesium in rats over a period of 102 days following inhalation exposure. Three groups of 20 rats each were exposed to aerosols generated from solutions of "carrier' free", 1 and 8 per cent cesium chloride which contained cesium-137 as a tracer. Urine and feces of all rats were collected daily until sacrifice, and the time-tissue distribution patterns were determined after death. All measurements were ma.de by gamma counting with sodium iodide crystals. Cesium chloride, being extremely soluble, was absorbed rapidly from the lungs and the digestive tract and the amount initially deposited in lung was reduced to less than 1 per cent during the first post-exposure day. The initial deposition in the lung was dependent on the aerosol particle size which was varied by the addition of the cesium chloride "carrier"; more lung deposition occurred with the smallest particle sizes. After the first day, the skeletal muscle and skin contained the largest amounts of this fission product but several organs such as lung and kidney had approximately the same concentrations. Because of lack of significant amounts of radioactivity at the later sacrifice times, no definite decision could be made regarding the choice of one "critical" organ for greatest radiation effect. 137 Total excretion of Cs displayed an early rapid phase followed by two successively slower phases, presumably the entire pattern being fit by an exponential function. These three phases, obtained from the whole body retention curve, can be resolved into half-lives of approximately .6, 7.0 and 18.7 days. The importance of interspecies comparison in obtaining parameters for estimating hazards to man is discussed, using cesium metabolism as an example.