CR values for individual Data are summarized Seed CR values ranged from 197° to 10", Range of mean CR values calculated for ae tivity strata in fallout area, collection sites ranged from 1073 to 109, 22.0 + 0.28 TTR CS3 ** 22.2 + 0.41 TTR CS2 + 0.67 26.0 + 0,76 TTR CS1 Data given are for soybean folia ge. from Romney et al. (1975, 1976). + ue | 5. 5E-4 19 3.9E-2 to 5.3E-2 17.0 + 0.93 1.9 4,3E-4 7.6E-4 +13 21 1.4E-2 to 9,2E-2 11.6 + 0.64 6.3 2. 6E-4 0.57 + 0,36 + 0.33 19 7,.4E-3 to 4.2E-2 16.2 + 0.52 0.19 * 0.03 1, 1E-4 + 0.67 1.1E-2 to 9.4E-2 15.8 + 1.4 9.4 + 0.15 23.5 + 0.73 NTS Area 13 TTR DT 5.8 + 0.15 NTS Area 11D to 1.6E-1 6.0 + 0.08 NTS Area 11C 5.6 + 0,27 21 7.8E-2 to 4.4E-1 7,9 + 0,2 0.97 + 0,72 1.8E-4 1.1E-3 5.2 + 0.12 2,7E-2 to 1, 7E-1 4.1 + 0.18 0.34 + 0.12 1.5E-4 5.3 + 0.17 4,.5E-2 to 3.4E-1 0.35 + 0.13 0.83 + Q.i1 0.17 5.24 0.1 6.5 + 1.3E+2 8.5 + 1.0 7.7 + 0.14 NTS Area 11B Glasshoyse Conditions Soil Pu/Am Plant Pu/Am Pu CR Pu CR™* Field Conditions Plant Pu/Am Soil Pu/Am Soil Source Summary of 239-240, and 241 Am Ratios and Pu CR Values for Ve getation and Soil Under Field Conditions Compared to Root Uptake Experim ent Under Glasshous e Conditions Table 3. CONCLUSIONS Two principal incorporation mechanisms are involved in the vegetationcarrier transport of plutonium in the diet of grazing animals and mankind: (1) superficial entrapment of particulate material with possibilities of foliar absorption of soluble contaminant, and (2) root uptake of the contaminant entering soil. It is important to reduce this transport of plutonium as much as possible. Findings from studies in dusty field environments at NTS indicate that superficial contamination its presently the most important route. However, certain natural cycling and concentration processes are underway which, in terms of the long half-life of plutonium, should gradually increase the importance of the root uptake pathway. We suspect that even now the root uptake pathway has increasing importance relative to superficial contamination in humid ecosystems, except at sites subject to local fallout material from such sources as emission stacks of processing facilities. The aged plutonium fallout areas at NTS will continue to be of value as sites in which to make periodic assessments to detect changes in the cycling and concentration of plutonium in various components of the ecosystem. Because of its greater solubility, Am at these sites may show an earlier indication of such changes. We believe it always will be important to avoid disturbances that will increase resuspension and erosion in plutonium contaminated sites at NTS and elsewhere. In their present natural states we believe that the plutonium contaminated sites at NTS and TTR present no radiological hazard to grazing animals and mankind so long as residence within the fenced exclusion areas is prohibited. ACKNOWLEDGMENTS Work was conducted under Contract E(04-t)} GEN-12 between the United States Energy Research and Development Administration and the University of California. Supplemental support was provided by the Nevada Applied Ecology Group, Bioenvironmental Science Division, USERDA Nevada Operations Office. We are indebted to members of the NAEG management and sample collection, preparation and radiochemical analysis teams for their devoted efforts in support of this work.