198 undisturbed arcas for a period of years, al least within the distances studied thus far. The aseesament of fallout on natural areas, therefore, is expressed in terms of activity per unit area. Fallout contamination of soil is determined fram samples taken from cither one square foot or one quarter square foot areas depending upon the objectives of the experiment. Soils data may seem out of place in a symposium on biological material. However, it will be shown that the biological fate of radioactive fallout is dependent to a large extent not upon total fallout deposited in an area but wpon some fraction of the total. Soil sampling provides us with a method of characterizing the total fallout against which data we can compare the biologically significant fraction of homb debris. This latter point is exemplified in Figure 1 which compares the amount of fallout from a 10,000 $3 tooo : \o0o : St 3 $ o3 ~ , EE . 2 € ¥ Tota sou, : é Plant ee ior f « a ~ . z z 44 U SON, FRACTION) r * 20 40 0 C7 0 DISTANCE FROM GROUND ZERO LUKEST single detonation on soil as compared to the amount offallouton plant material as a function of the distanceof the sampling site from Ground Zerg one dav following contamination, It will be noted that activity per unit weight of dried plant material compares quile favorably with theactivity contained inthe less than 44-micron particle size fraction of soil as opposed to otal . soil contamination. Nate also that the degree of plant contamination in this particular case appears to increase, or, conservatively, to stay the sameover (he major portion of the 80 miles distance studied. The significance of these observations are two-fold. First, animals grazing in these fallout areas and feeding upon bi, trappedbythe plantacting as a selective fallout collector. 10 0 Ficurn 1-~The relative degree of radioactive fallout con- tamination. on soils and plants resulting fram a single detonation expressed a8 a functionof the distance of the sampling site from Ground Zero (1. “i i wae these forage plants will not be ingesting gross fallout but rather a specific fraction (the less than 44-micron size group) which has been | Second, since the degree of plant contamination tends to remain the same over a very great distance the internal dose to animals grazing these areas will also be similar and the potential hazard similar over a great portion of . i ACTIVE FALL-OUT F ATE, PERSISTENCE OF RADIO SHORT TERM BIOLOGICAL THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIRLD the fallout pattern. Figure 2 shows a special preparation de- veloped for the study of the characteristics of fallout material contaminating plants. In the field, plant leaves are carefully placed on gummedpaper and backed with blotter material and dried. In the laboratory, an autoradiogram is made which serves as a map for the location of specific particles on the plant leaves. Detailed analysis of many of these preparations support the conclusion that the less than 44micron diameter fallout particles are the principal source of radioactivity in forage material samples within a period of weeks following fallout contamination. It has not been possible to distinguish between external contamination and metabolized fission products in range plants. Experiments in which soil flats have been exposed to fallout and subsequently cultivated in the greenhouse do show that fission products (particularly Sr) are biologically available from fallout and will be accumulated in the plant parts [2]. Figure 3 is a photographof the dried peltof a Mare Fork To DphsareLene Peck tar yn . oh ; i : ‘ | | al 1 ation and the i i by leaves & ha wing the leaf prepar retention fallout particle study of0 & Fiaure 2.—A preparation for preparation to X-ray film [1]. the of exposure m vom diogra ng ee autora resulti heee t area andof kangaroo rat, sampledfrom a fallou from a one-half the autoradiogram resulting film. This hour exposure of the pelt to X-ray ely 12 miles animal was collected approximat after fallout. from Ground Zero about 24 hours minationis Althoughthe degree of fallout conta that we have startling, it is interesting to note burns or damfound no indication of radiation ted from these, age in the plants or rodents collec burns resulting or more distant, areas. Beta verified, howfrom fafioutparticles have been within 20 ever, oh livestock and deer grazing | miles of Ground Zero. ts, it is In regard to metabolizedfission produc of the physioloindeed fortunate that, in terms animals, relagical requirements of plants and biological signifitively few isotopes are of reat cance. However, whether the biological haz- of radioiodine or ards are interpreted in terms ic isotope, radiostrontium or some other specif n prod- other fissio the fact remains that many in tissues for a ucts are apparenUly present t contaminalimited period as aresult, of fallou rule of radiation. As long as the fundamental rily biology remains “that radiation is prima lion ms”, then we a destructive force in living syste of this material are committed to learning more ever its ” what that we must “learn to live with, . lf-life. biological inte oe relationship between the fallout to time, and persistence of radioactive ial within the location of the biological mater ior of the isothe fallout pattern, and the behav cular fission prodtopie precursors of the parti re- which nets under concern are parameters anything quire special consideration and defy ut phenomeput an arbitrary divisionof the fallo term effects. noninto short term and long