© Page 168 not all organisms at Rongelap £) Radioecology but that the levels at which they occur are extremely low and so escape detection. Passing from the soil to the soil solution, the term being used here to mean leachates collected in the field from lysimeters, strontius-90, cesiua-137, and antimony 135 are the principal nu- clides found, although Rul06-Rn106, cerium-144, and europium-155 are also detectable (Cole et al., vertebrates containing zinc-65 are known to be consumed by fish found to contain zinc-65, but, in general, no definite sources of zinc-65 are known to exist five years after fallout. It is possible that there is concentration of undetectable levels from the sea water or algae. The possibility that most of the zinc-65 radioactivity in fish is residual appears to be ruled out by the fact that young fish contain relatively high levels. 1961). Here differences exist with respect to soil type in that the leachates from immature soil, consisting almost exclusively of parent material, contained only antimony-125 and strontium-90. tain a wider spectrum of radionuclides than do the fish. These are manganese-54, cobalt-57,60, zinc- difference. only invertebrates in which strontium-90 has been There is to us no evident explanation for this The ground water probably contains these nuclides since their movement has been detected in leachates to depths of 30 inches, but the levels are so low in ground water that special techniques would have to be developed to detect then. The land plants contain principally cesium-137 and strontium-90. Manganese-54 and zinc-65 have been found in plants from the more heavily contaminated islets but are present in relatively insignificant amounts. In general, cesium-137 accounts for 90 per cent or more of the radioactivity in the land plants and strontium-90 for the remainder. This is unlike the situation usually found on continental soils and is a consequence of the low The marine invertebrates taken as a whole con- 65, strontium-90, cerium-144, and probably europiua155. The corais contain cobalt-60 and are the consistently detected. From limited data available thus far it appears that these nuclides were deposited in the skeletal material soon after fallout and have remained localized in portions of the coral colony actively growing at that time. The clams contain mostly zinc-65. cobalt-57 and cobalt- 60. Weiss and Shipman (1957) originally reported the concentration of cobalt-60 in the kidney of Tridacnid clams collected at Rongelap in 1956. Animals such as the sea cucumber (Holothuria, Stichopus) and spider snail (Lambis, Strombus), which ingest large amounts of om se nots, contain ruthenium-106, cerium-144, and probably europiusa-155. Of several species of algae sampled in 1959 cesium-137 by plants (Walker et al., 1961), and affect the distribution of cesium-137 within the the only radionuclides detected were ruthenius-106, cerium-144 and europium-155. In general, the levels of radioactivity in the algae are lower than in the fish or invertebrates. plant species and plant parts with respect to the relative amounts of cesium-137 and strontium. For 57,60, zinc-65, zirconium-95, ruthenium-106, and potassium content of Rongelap soil. Amendments of potassium to Rongelap soil reduce the uptake of plant. There are, of course, differences between example, copra contains very little strontium-90 as compared with Pandanus fruit, and the basal leaves of various plants contain more strontium-90 relative to cesium-137 than do the terminal leaves. This variation is related to differences in mobility between cesium and potassium, and strontium and calciuna. The rats contain cesium-137 and strontiun-90, reflecting the radionuclides present in the plants on which they feed, The coconut crab and the land The plankton contain manganese-54, cobalt- cerium-144, but all in minute amounts. In 1959 plankton samples collected by pumping a total of two and a half million gallons of water were pooled for gamma-ray spectrum analysis and were found to contain only enough of these nuclides for qualitative analysis without resorting to chemical separations. Further analysis has been deferred until other studies with the individual samples can be completed. The lagoon sediments contain strontius-90, hermit crab (Coenobita rlatus) contain the same nuclides but concentrate strontium-90, as has been ruthenium-106, cerium-144, and europium-155. The radioactivity is associated mainly with the fines and is concentrated in the top two to four inches, dropping off rapidly with depth. The occurrence of radionuclides in man at Radionuclides other than naturally occurring potassium~-40 were not detected in sea water al- reported for Coenobita from Eniwetok Atoll (Held, Rongelap has been summarized by Cohn et al. (1960). In 1958 these nuclides were cesium-137 and strontium-90 coming form the food plants, and zinc-65 coming to man from marine products. The birds, which feed almost exclusively on marine organisms, contain primarily zinc-65and occasionally small amounts of manganese~-54 and cobalt-60. Strontium-90 is also found in small amounts in bird bone and may reflect direct uptake from the ingestion of soil, although there is no direct evidence that this occurs. Radionuclides in fish are limited to manganese- 54, cobalt-60, and zinc-65, the latter being predominant. On a dry-weight basis for a sample of goatfish (Mulloidichthys samoensis) testes have the highest levels, e ver, gastrointestinal tract, and eyes are lower by about an order of magnitude, and the muscle and bone lower by still another order of magnitude. If the total amount of radio- activity by tissue is considered, then bone is tne principal depository of zine-65 (Joyner, 1961, personal] communication). The sources of zinc-65 for fish are open to question. In some instances in- though larger samples and more sensitive techniques undoubtedly would have revealed their presence. In sum, on land the present distribution of long-lived fission products, strontium-90 and cesium-137, can be expected to remain very such as it is now. The levels of radioactivity will be reduced primarily by physical decay of the radic- nuclides so long as other factors such as changed agricultural practices or a catastrophic storm do not occur. In the lagoon, the levels of radioactivity will decline more rapidly than on land because of the presence of shorter-lived radionuclides, with the exception of strontium-90. The latter does not enter the marine food web to any significant extent and may remain as a label useful in evaluating the long-term effects of physical forces in the lagoon. SUMMARY The qualitative distribution of radionuclides at Rongelap Atoli 2s determined approximately five