A small fraction of Pu is assimilated from soil by native and cultured plants, TABLE 5 Concentrations of 738py* ranged from 0.002 to 0.05 pCi g-! in native vegetation. Concentration ratios based on soil containing 25 to 150 pCi go! of Pu ranged from 10-3 to 10-5 for herbaceous and woody species. Native species iricluded both annuals and perennials, Plutonium was assimilated by vegetable crops planted in a field plot on the floodplain where the soil Pu contained 63 + 0.4 (S.E.) pci gol. Concentrations of 735Pu in foliage of three different species ranged from 0.1 to 0.3 pCi gn). Concentrations of Pu in edible tissue (0.003 to 0.04 pCi g-) of the vegetable crops were lower by approximately 1 to 2 orders of magnitude. Most CR values for vegetable foliage were approximately 10-3, while the CR values for fruits were on the order of 107" or less. Both Pu concentrations and CR values of native and cultivated species exhibit high variability. Coefficients of variation (CV) are greater than 50% and frequently exceed 100% (Dahiman et al., 1976). Differences in Pu among species within foliage and fruit data sets were not preat. Therefore, individual observations were pooled within the respective data sets, and a "t" test showed that the Pu concentration of foliage (N=35) was significantly different (p < 0,01, df 64, Fe5.15) from that of fruits (N=31). Before Pu in vegetation can be attributed to uptake by the root pathway, it is necessary to demonstrate that results are not an artifact of surface contamination. From four different kinds of information, it appears that surface contamination ig not the source of Pu in vegetation at the ORNL floodplain site. (1) Deposition of Pu from either global fallout or from local sources is insufficient to yield the concentrations observed in native species or RATIOS" OF INDIGENOUS AND ANTHROPOGENIC ACTINIDES IN SOIL AND VEGETATION OF THE OAK RIDGE FLOODPLAIN Soil U Th Pu 1.0 2.1 16.3 Vegetation Bushbean 1.0 0.50 3.3 Soybean 1.0 0,66 3.1 Millet 1.0 0.20 0.15 "Ratios in terms of ug g7', ug g°! and dpm for U, Th, and Pu respectively normalized to 1.0 for U (Bondietti and Sweeton, 1977). cultivars from the floodplain (7 x 10°" pci g-! from combined deposition** vs. 1 x 107! pci g-! observed. (2) Vegetation samples were washed and rinsed in a sonic bath before they were processed for analysis. Microscopic examination of washed leaves showed no soil particles or debris on the surfaces following the cleaning treatment. (3) Different ratios of U, Th, and Pu in soil and in vegetation suggest that surface contamination ia not the main source of Pu observed in plant tissue (Table 5). The ratios of these elements would be the same in both soil and vegetation if surface contamination were the source of the elements. Element ratios are commonly used by geochemists in differentiating the environmental behavior of elements. When the ratios differ between soil and vegetation, as observed in this case, the evidence suggests a metabolic mechanism rather than surface contamination, (4) Ambient airborne Pu is not detectable in the canopy of the species sampled. *Includes 24%pu, **Accumulation of Pu in vegetation (P) from fallout and local Oak Ridge sources is calculated from = AxVxetxr x 1o7" -3 pci x fCiv" -1 _ gy x 10°" pct g-!; where A is air concentration (0.016 fCi m7}, Table 1), V¥V is deposition velocity (0.01 m sec7!), t is time interval of accumulation (150 days or 13 x 108 sec), vr is fraction of Pu deposited on vegetation that is retained at end of growing season (0.1), and M is density of foliage (300 g m-2), 314 315