The biological half-time of radioactive Cs in poikilothermic and homeothermic animals.

Literature data for the half-time of Cs in one-, two-, and three-compartment models have been collated and regressed to yield general descriptions of clearance for homeotherms (warm-blooded animals) and poikilotherms (cold-blooded animals) of different sizes. Cesium half-times increase with body weight and are longer in poikilotherms than in homeotherms. These trends and the values of the associated regression coefficients imply that Cs clearance is a function of metabolic rate. The patterns are especially visible in analyses of the larger compartments, perhaps because the curve splitting required to analyze smaller, more rapidly cleared pools is necessarily subjective. The route by which acutely contaminated animals receive their Cs also influences clearance. Inhaled Cs appears to be retained longer than injected Cs, which is in turn retained longer than ingested Cs. This suggests that Cs is discriminated against in biological transfers, so that Cs dust remains in the lungs whereas Cs in the food is less readily absorbed. These patterns of Cs clearance suggest that large animals, poikilotherms, and animals contaminated by inhalation or injection may receive a greater dose.