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QUALITATIVE DISTRIBUTION OF lViDIONUCLIDES AT RONGELAP ATOLL Laboratory of Radiation Biology University of Washington Paper presented for the First Symposim on Radioecolowt Colorado State University, Fort Collins, colorado~
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The qualitative distribution of radionuclides at Rongelap Atoll as determined approximately five years after contamination by fallout from a thermonuclear device indicates distinct differences between the terrestrial and marine environments. The levels of activity are low, the specific activity being less than the maximum permissible concentration for radioisotopes in food or drinking water of man. Of the wide spectrum of radionuclides concentrated in the surface layers of the soil, Sr90, Sb125 and CS137 are the principal isotopes entering into the sofl solution. The principal isotopes in the land plants and planteating animals such as coconut crabs and the indigenous rats are CS137 and to a lesser degree, cJr90. Bottom sediments contain mainly Sr 90 and EU155. The radionuclides in the lagoon water have not been detected but are probably present in minute amounb. most commonly. Corals and coralline algae contain some Sr90, while the fish and sea birds are found to contain mostly Zn65. The presence of Zn 65, CS137 and SrgO in the body of the natives reflects a diet of both marine and terrestrial origin.
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QUALITATIVE DISTRIBUTION OF RADIONUCLIDES AT RONGELAP ATOLL1 Laboratory of Radiation Biology University of Washington In March 1958 a radioecological study of Rongelap Atoll was instituted at the request of the United States Atomic Energy Commission, Division of Biology and Medicine. This report will be concerned with generalizations regarding the distribution of radioisotopes at the atoll in the fall of 1959, some five years after contamination with radioactive fallout. Rongelap Atoll was accidentally contaminated on March 1, 1954, with radioactive fallout from a thermonuclear device detonated at Bikini Atoll some 80 miles to the west. Gamma dose rates at Rongelap on D + from 3.5 r/hr at the southern islets of the atoll to 35 r/hr residing on Rongelap Island, in the south, were evacuated and did not return until Jbne 1957. At that time the returning lTitle in program for the First Symposium on Radioecology is “Qualitative differences in radioisotopes present in plankton, lagoon bottom, and land plants.”
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population approached 300 in number but since appears to have Several radiological and biological surveys, primarily of a monitoring nature, were conducted from the time of the first contamination until 1958 (Dunning, 1957) . During this time the gamma dose rates over land areas declined at approximately the rate predicted for mixed fission products by Miller and Loeb (1958) . Slight rises in gamma dose rate were observed in 1956 and 1958, resulting from tests conducted during these years. However, the total contribution of radioisotopes from these subsequent fallouts amounted to a fraction of one per cent of the amount from the 1954 fallout. Rongelap Atoll is located in the Marshall Islands, in the Central Pacific Ocean, at about 11° North. It is a typical atoll with a lagoon area of 388 square miles and about 180-foot average depth. The emergent land area is about 3 square miles and is made up of 61 small islets ranging in size from a fraction of an acre to the largest island, Rongelap, which is about 4 miles long and 1/2 mile across at its widest point. There is one small islet on the western reef and the remainder are strung along the northern, eastern and southern reefs. The islets on the northern reef are not as well developed as those to the east and south. The waters of the lagoon are
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essentially isothermal (Robinson, 1954) . The circulation, generated by the northeast trade winds, is from east to west at the surface with a returning bottom current (Von Arx, 1954) . The estimated time for renewal of water in the lagoon is about The parent material of both soils and the lagoon bottom is algae, corals and carbonate originating mainly from foraminifera. There is also some of pumice drift in the soils. The natives of the area are Micronesians. Their agriculture is limited in variety of products and the only significant export is copra. About half of the food time is imported. Fish and other marine consumed at the present organisms are eaten but these sources are not exploited as much as they could be. The Rongelapese are almost entirely dependent on cisterns as a scurce of water. Rainfall in this area is comparatively low and the islets small, so that there is not a well developed fresh water lens. There is, however, some potable water in wells at Rongelap and Eniaetok Islets. The native style wattle and palm frond buildings have been replaced by plywood and aluminum structures built to Rongelapese specifications by the AEC. Sanitation habits have been altered by the advent of pit toilets.
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The terrestrial fauna is limited in variety. The only mammal present is the small field rat, Rattus exulans. The most common birds are the fairy tern, Gyqis alba, and the noddy terns, Anous stolidus and ~. tenuirostris, which nest in large numbers on some of the uninhabited islets. The reptiles are by skinks, geckos, and a blind snake. Land crabs the most spectacular being Birqus latro, the coconut or robber crab. Insects are few, both in number of species and individuals. The most severe pest appears to be the beetle, Brontispa sp., which attacks the coconut palm. In contrast to the land areas there is a tremendous proliferation of both numbers and variety of organisms on the reefs the lagmn. For example, there are over 700 species of Plankton, however, is extremely sparse and as a consethe water is so clear that green algae are found growing at depths of 180 feet. Since the question of the effects of radiation on the organisms inevitably arises, it might be well to consider it briefly before going on to the main subject. There is no doubt that the levels of radiation were of sufficient intensity to affect living organisms. However, under actual field conditions and without benefit of study before the addition of radiation
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as an ecological factor, it is difficult to do more than speculate concerning the cause of the specific anomalies observed. Fosberg (1959) has accurately described the poor condition of the plants at the northern islets of Rongelap and has suggested that the primary cause of this condition is radiation. In our opinion, hwever, other factors, particularly edaphic factors, have probably been more important than radiation. The fact that the nitrogen content of the soils of the northern islets is lower than that of the rest of the atoll is at least circumstantial evidence that for some time there have been differences between these areas with respect to plant growth. Stone et al— —“ (1957) has concluded from studies of Drosophila populations at Bikini, Eniwetok, Rongelap and uncontaminated atolls that while there is evidence of genetic changes caused by radiation other factors mask the radiation effects. In short, it is not likely that such questions will be resolved without controlled experimentation with the species involved, under varying conditions, and with an eye toward the possibility of synergistic effects. Approximately five years after fallout the long-lived fission products CS137 and Sr90 are the principal radionuclides found in the land organisms,while the neutron induced radionuclides Zn65, C06* and 14n54 are found primarily in the marine
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remain concentrated in the upper one to two inches. Where higher levels of radionuclides have been present these isotopes have been reported in a wide variety of organisms. It is likely that most of these radionuclides are actually present in most if not all organisms at Rongelap but that the levels at which they occur are extremely low and so escape detection. used here to mean the soil to the soil solution, the term being leachates collected in the field from lysimeand Sb125 are the principal nuclides found, et al., 1961). Here differences exist with respect to soil type in that the leachates from immature soil,consisting almost There is to us no evident explanation for this difference. 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 them. and Zn65 have been found in plants from the more heavily contaminated islands but are present in relatively insignificant
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amounts. In general, CS137 accounts for 90 per cent or more of the radioactivity in the land plants and Sr 90 for the remainder. This is unlike the situation usually found on continental soils and is a consequence of the low potassium content of Rongelap soil. Amendments of potassium to Rongelap press), and affect the distribution of CS137 within the plant. There are, of course, differences between plant species and plant parts with respect to the relative amounts of potassium and strontium. For example, copra contains very little Sr 90 as compared with Pandanus fruit, and the basal leaves of vari90 relative to CS137 than do theous plants contain more Sr terminal leaves. This variation is related to differences nuclides present in the plants on which they feed. The coconut crab and the land hermit crab Coenobita perlatus contain the same isotopes but concentrate Sr 90 ,as has been reported for Coenobita from Eniwetok Atoll ( Held, 1960). The occurrence of radionuclides in man at Rongelap has been summarized by Cohn et al. (1960). In 1958 these nuclides—— were Cs137 and Sr90, coming from the food plants, and Zn65 coming to man from marine products.
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The birds, which feed almost exclusively on marine organisms, contain primarily Zn 65 and occasionally small found in small amounts bone and may reflect direct uptake from the ingestion of soil, although there is no direct evidence that this occurs. Radionuclides in fish are the latter being predominant. sample of goatfish testes have On a dry-weight basis for a the highest levels, the liver, gastro-intestinal 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 radioactivity by tissue is considered then bone is the principal The sources of Zn65 for fish are open to question. In some instances invertebrates containing Zn65 are known to be consumed by fish found to contain Zn65, but, in general, no definite sources of Zn 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 Zn65 activity in fish is residual appears to be ruled out by the fact that young fish contain relatively high levels. The marine invertebrates taken as a whole contain a wider spectrum of radionuclides than do the fish. These are Mn54,
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contain co6° and are the only invertebrates in which Sr 90 has been consistently detected. From limited data available thus far it appears that these isotopes were deposited in the skeletal material soon after fallout and have remained localized in portions of the coral colony actively growing at that and Shipman (1957) originally reported the concentration of C060 in tie kidney of Tridacnid clams collected at Rongelap in 1956. Animals such as the sea cucumber and spider snail,which ingest large amounts of bottom sediments,contain Ru 106, ce144 Of several species of algae sampled in 1959 the only radionuclides detected were Ru In general, the levels of radioactivity in the algae are lower than in the fish Ce144 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 spectrum analysis and were found to contain only enough of these isotopes for qualitative analysis without resorting to chemical separations. Further analysis has been deferred until other studies with the individual samples can be completed.
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the fines and is water although larger samples and undoubtedly would have revealed their presence. land, the present distribution of long-lived The radioactivity is associated mainly with concentrated in the top two to four inches, rapidly with depth. Radioisotopes other than naturally occurring detected in sea In sum, on fission products, Sr90 and CS137, can be expected to remain very much as they are now. The levels of radioactivity will be reduced primarily by physical decay of the radionuclides so long as other factors such as changed agricultural practices tion of Sr90. The latter does not enter the marine food web to any significant extent and may remain as a tag useful in evaluating the long-term effects of physical forces in the lagon. a catastrophic storm do not occur. In the lagoon, the levels radioactivity will decline more rapidly than on land because the presence of shorter-lived radionuclides, with the excep-
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Radioisotopes and environmental circumstances: The internal radioactive contamination of a pacific island community exposed to local fallout. A Symposium on Radioisotopes in the Biosphere. University of the tension lysimeter in coral atoll and glacial till soils. Soil Sci. Dunning, G. M. 1957. Radioactive contamination of certain areas in the Pacific Ocean from nuclear tests. U. S. Atomic Energy Commission report. Washington. fallout on plants. Atoll Research Bulletin, No. 61. National Academy of Sciences-National Research Council. Held, E. E. 1960. Land crabs and fission products at Eniwetok Atoll. Pacific Science, v. 14, No. 1. Miller, C. F., and P. Loeb. 1958. Ionization rate and photon pulse rate of fission products from slow neutron Robinson, M. K. 1954. Sea temperature in the Marshall islands Stone, Wilson S., et al. 1957.—. Genetic studies of irradiated natural populations of Drosophila. University of Texas. 10. Von Arx, W. S. 1954. Circulation systems of Bikini and Rongelap lagoons. U. S. Geological Survey Professional
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Radiocesium in plants grown on Rongelap Atoll soils. Proceedings of the Ninth International Botanical Congress, tration by killer clams of cobalt-60 from radioactive fallout. Science, v.125, No. 695.