QUALITATIVE DISTRIBUTION OF RADIONUCLIDES AT RONGELAPATOLL niversity of B ashington, Seattle, Washington In March, 1958, a radioecological study of Rongelap Atoil was instituted at the request of the Division of Biology and Medicine, U. 8. Atomic Energy Commission (AEC). This repoft will be con- cerned with generalizations regarding the distribution of radionuclides 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 8C miles to the west. Gamma radiation dose rates at Rongelap or D+# 1 (detonation + one day) ranged from 3.5 roentgens per hour at the southern islets of the atoll to 35 roentgens per hour at the northern islets (Dunning, 1957). Eighty-two natives residing on Rongelap Island, 1n the south, were evac- uated and did not return until June, 1957. At that time the returning population approached 300 in number but since appears to have stabilized at 230. Several radiological and biological surveys, primarily of a monitoring nature, were conducted frum the time of the first contamination until 1958 (Dunning, 1957). During this time the gamma radiation dose rates over land areas declined at approximately the rate predicted for mixed fission products by Miller and web (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 radionuclides 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 Marghall Islands, in the Central Pacific Ocean, at about 1}° It is a typical atoll with a lagoon area of North. 388 square miles and abort 180-foot average depth. The emergent land area is about three square miles and is made up of 6] small islets rangiig in size from a fract-on of an acre to the largest island, Rengelap, which is about four miles long and onehalf mile across at its widest point. There is one smali islet on the western reef and the remaincer are strung along the northern, eastern, and southern reefs. The islets on the nurthern reef are not as well developed as thase to the east and south. The waters of the lagoon are essentially isothermal (Robinson, 1954). The cire.lation, generated by the northeast trade winds, 1S trom east to west at the surface with a return- ing bottom current (Von Arx. 1954). tame fresh water lens. There is, however, some potab!« water in wells at Rongelap and Eniwetok Islets. E. E. HELD Laboratory of Radiation Biology, w) tirely dependent on cisterns as a source of water. Rainfall in this area is comparatively iow and the islets small, so that there is not a well-developed The estimated tor renewal of water in the iagoon ts about 3u days The parent material of both soils and the la- goon bottom is primarily calcium -arbonate origi- cati:<s mainly from coralline algae. corals and furamivifera. There is also some accumulation of eumice drift in the soits whe natives uf the area are Microne-isns. Thed: sgriculture is limited i. variety :f products and the only Significant export is copra About ualf of the food consumed at the vresen. time is tmported. Fish and other marine organisms are eaten but these sources are not exploited as much ¢s they couia be The Kongelapese are almost en- The native style wattle and palm frond build- ings 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. 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, Gygis alba, and the noddy terns, Anous Stolidus an ok tenuirostris. which nest in large numbers on some of the uninhabited islets. The reptiles are represented by skinks, geckos, and a blind snake. Land crabs are common, the most spectacular being Birgus 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 1s a tremendous proliferation of both numbers and variety of organisms on the reefs and in the lagoon. For example, there are over 700 species of fish. Plankton, however, is extremely sparse and as a consequence the 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 organisys, However, under actual field conditions and without benefit of study before the addition of radiation 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 Atoll and has suggested that the primary cause of this condition is radiation. In our opinion, however, 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) have concluded from studies of Drosophila populations at Bikini, Eniwetok. Rongelap- ah 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 cesium-137 and strontium-90 are the principal radionuclides found in the land organisms, while the neutron- induced radionuclides zinc-65, cobalt-60 and manganese~54 are found primarily in the marine organisms. Still detectable in the soil are manganese-54, jdror-55. cobalt-57, cobalt-60, zinc-65, strontium90, zirconium-95, ruthenium-106, antimony~-125, cesium-137, cerium-144, and europium-155, which remain -oncentrated in the upper one to two inches. Wherc higher levels of radionuclides have been present these nuclides have been reported in a wide variety or organisms. It is likely that most of these radionuclides are actually present in most if 167 Reprinted from Radioecology, edited by Schultz and Klement, Reinhold Publishing Corporation and the American Irstitute of Biological Sciences, New York, 1963. SFAeteOTERO? G2ep TURNER 410178