Factors Influencing the Biological Fate and Persistence of Radioactive Fall-out

A study was made of the biological fate and persistence of radioactive fall-out relative to the physical characteristics of fall-out contamination, which varied with distance from Ground Zero (GZ). Special attention was given to the type of fall-out contamination on forage plants as representative of the internal emitters available to animals grazing in fall-out-contaminated areas. Data indicated that the activity associated with the plant samples collected from areas within the various fall-out patterns was predominantly the result of external contamination by radioactive fall-out particles less than 44 microns in diameter. The tissue burdens of mixed fission products in animals sampled from fall-out-contaminated environments tended to decrease with distance from GZ in a manner similar to the degree of plant contamination. The relative decrease of total beta radiation in tissues of native animals serially sampled from the same fall-out-contaminated environment in most cases did not markedly deviate from the theoretical beta radioactive decay rate of mixed fission products. In all cases, animals with high activity in the gastrointestinal contents also had relatively high tissue burdens, whereas animals with low activity in the gastrointestinal tract had low tissue burdens.