tM kotk= wet BE nt aentensla ad a el 4.2 ie OT a SOILS All of the fallout radionuclides at Bikini are found in the surface of undisturbed soils. The predominant radionuclides are °°>Fe, ©°co, 2%Sr, 1253p, 137cs and 2°7Bi (Tables 1-5). In the Bravo Crater sediment, 69¢o and 297Bi are the predominant radio- nuclides, although others are present in small quantities. The soils and sediments are the principal reservoirs of radionuclides at Bikini. The concentrations of radionuclides, other than plutonium, in surface soil samples collected in 1969 are given in Table 1. The samples were taken from areas where the highest gamma dose rates were measured and hence are maximum values. Differences in proportions of different radionuclides at the islets sampled are obvious. The unusually low concentrations of 137¢g5 relative to other radionuclides in the Eneman samples result from periodic flooding of the area by tidal water and consequent leaching away of 137¢g (Tables 2 and 3). ; The results of gamma-ray spectrum analyses of the composite and individual samples collected in 1970 are given in Table 4. In general, radionuclide concentrations are lower in bulldozed areas than in undisturbed areas, The exceptions to this generality are not surprising, since the lowest and highest values for individual samples from single transects differ by factors of more than ten. Fallout radionuclides in undisturbed atoll soils remain concentrated at the surface for many years (Held et al., 1965; Welander, 1967). The surface ten centimeters at wellpoint four at Bikini Island were sampled by one-half centimeter increments in 1970, and the samples show a gradient of decreasing radionuclide content with increasing depth (Table 5). Soil samples analyzed for plutonium were generally selected from areas containing the highest concentrations of gamma-emitting radionuclides. Exceptions were samples from the camp area at Bikini I. and along the run- way at Eneu I. The results of the plutonium analyses are given in Table 6; !37’cs concentrations are included in the table because they indicate a correlation between 137¢g and 239,249pu concentrations in samples from Bikini I. The ratios of *29,249py to 238pu approach 2:1 at Eneman I. and are about 15:1 in Bravo Crater sediment. Bikini soils contained no detectable 238pu, although they contained the highest concentrations of *39,249pu of the samples analyzed. 4.3 ORGANISMS The radionuclides are available to the land animals through the vegeta- tion, or other animals, where there is selection of specific radionuclides, or through direct ingestion of soil. Similarly, the marine animals may ingest radionuclides by eating another organism or by ingesting sediments.