Taeies Eade PCR eM ge7 | 1 Louris (Vou. 91 MFP Ode eee 1964] MARTIN : RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION 305 on plants during a period of three weeks following contamination was parallel to the beta decay of < 44» fallout particles.* Under favorable conditions, some of the water soluble material deposited on leaves maybe assimilated byfoliar absorption. Russell et al. (1955, 1959) and Russell and Possingham (1959) reporting on fallout studies made in Australia and in the United Kingdom, have indicated that considerable l toot l quantities of water soluble fission products may be retained by foliar ab- Sr sorption. Since there have been no direct observations of foliar absorption of fallout originating from detonations at the Nevada Test Site (Romney et al. 1962) we may suppose that foliar absorption is probably more significant in humid grassland or pasture regions than in arid grassland or desert-shrub regions. 3. Animals. The possible modesof fission product ingestion by herbivores are: (a) ingestion of fallout contaminated plants, (b) ingestion of fallout Lt td mil Table 8. dverage beta activity in tissues of jack rabbits serially collected from an area contaminated by fallout from the Nevada Test Site* (80 miles from Ground Zero). _——_— — o =o Time of Collection, Days after Contamination 2 3 10 220 Baekground** Average beta activity extrapolated to time of sampling and expressed as npe/g fresh tissue Lung Caecum Liver Kidney Muscle Bone 116 61 21 1 1 16,500 4,350 606 . 6 7 817 67 3 1 2 1 990 21 55 18 385 639 3 1 3 2 376 10 103 60 * After: Lindberg et al. (1959). ** Based on animals eollected before contamination. oS 8 i9 20 k rabbits colFrom Larson ield studies ntaminated of activity from the pelt during preening, (c) accidental ingestion of contaminated soil while digging or feeding, and (d) swallowing of material cleared from the lungs and nasopharynx. Duringthe first few weeks after fallout, the correlation between the activity of plants and that of the gut contents of herbivores is usually quite close, and the other three possible modes of ingestion are probably of minor significance. The maximum concentration of mixed fission products in the tissues of herbivores living in fallout contaminated environments occurs usually within a few days after fallout. The total body burden of internal beta emitters then decreases (Figure 7) in proportion to the decreased activity of forage plants, and this may approximate the rate of mixedfission product decay. * Studies completed after this paper was written (Martin 1963, 1964) have shown that the effective half-lives of radionuclides on fallout-contaminated plants are significantly shorter than their respective radioactive half-lives, and losses in excess of radioactive decay have been attributed primarily to wind action,