Report, Qualitative Distribution of Radionuclides at Rongelap (Reprinted from Radioecology)

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In Ha’rch, 1958, a radioeculoglcal study of Rongelap Attiil was Instituted attbe request of the tion of r~dlonuclides at the atoll in the fall of 1959, >ome five years after contamination with Ro~qelaP Atoll was accidentally contaminated on March 1, 1954, with radioactive fallout from a ther-.[>nuclear device detonated at Bikini Atoll some 80 ml~~s to the west. Gamma radiation dose rates from 3.5 roentgens per hour .it the southern islets of the atoll to 35 roentgens per hour at the nor:hsiding on Rongela,> Island, In the south. were evacuated 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 anu ~ioiogical surveys, prlmarlly of a monitoring nature, were conducted 1958 (Dunning, 1957). trurlng th~s time the gamma radiatlo!~ dose rates over land areas declined at approximately the rate pre~llcted for mixed fission in gamma dose rate were uhserved In 1956 and 1958, However, the totel contribution of raaionuclldes & [Ion of one per cent of the amount from the 1954 Rongelap Atoll is located in the Marshall Islands, in the Central Pacif.c Ocean, at about 11° North, It is a typical atoll with a lagoon area of .l$j~ square miles and about ltiO-fcot overage depth The enxrgent land ~rea is about three square miles and is made IIp of 6i small islets rangl,ig in size from a fract c;n of an acre t<> the largest :sland, Rcnge .ip, whlct? is about four miles long and onehalf ::Lle across at i:s widest point. t’here is one small islet on the western reef and the remaincttr are strung along the northern, eastern. and southern reefs. The islets on the nurthern reef are not as well developed as t.hose to [he ea;[ and south. The waters of the lagoon are ~’.ltltion, generated by the northeast tr:lde winds, ing bottom currect (Von Arx. 1954). The estimated The parent material oi both so~is and the lar,.Jtil ma:nly from coralline algae, corals and tirely dependent on cisterns as a source of water. Rainfall in this area is comparatively low and the islets small, so that there is not a well-devel~ped fresh water lens. There is, however, some potab”: water In wells at Rongelap and Eniwetok Islets. The native style wattle and palm frond buildings have been replaced by plywood and :iluminum structures built to Rongelapese specifications by the .WC, Sanitation habits have been altered by the advent of pit toilets.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 numbers on some =e~abited islets. The reptiles are represented by skink.s, geckos, and a bIind snake. Land crabs are common, the most spectacular being Bir us latro, and individuals. The most severe Dest armears to be the beetle, Brontispa SP., which atta;ks the 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 organisms, However, under actuaI 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 .sIscific 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 q ore 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 Droso hila populations at Bikini, Eniwetok, Rongel&ontaminated atolls that while there is evidence of genetic changes caused by radiatl;~ ot~{ factors mask the radiation effects. it is not likely that such questions will be ;esolve:i without controlled experimentation ~ith the species involved, under varying conditions, and with an eye toward the possibility of synergistic effects. Approximately five years after fallout the tium-9fi are the principal radionuclides found in the land organisms. while the neutron-induced arc ‘ound primarily in the marine organisms. Still detectable in the soil are manganese-54, remain concentrated in the upper one to two inches. Wfterc hl;ner levels of radionuclides have been present these nuclides have been reported in a wide varietj or organlsrns. It is llkcly that most of these radlonuclides are actually present in most if Reprinted from Rudioeco[ogy, edited by Schultz and Kkment. Reinhold Publishing

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not all organisms at ROngelap but that the levels at which they oCCUr are eXtremely low and so escape Passing from the soil to the soil solution, the term being used here to mean leachates collected in the field from lysimeters, strontium-90, and europium-155 are also detectable (Cole et al., 1961). Here differences exist with respect to soil type in that the leachates from immature soil, consisting almost exclusivelyof parent material, There 1s 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 them. The land plants contain principally cesium-137 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 potassium content of Rongelap soil. Amendments of, potassium to Rongelap soil reduce the uptake of cesium-137 by plants (Walker et al., 1961), and affect the distribution of ceeium-137 within the plant. There are, of course, differences between plant species and plant parts with respect to the relative amounts of cesium-137 and strontium. For 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 reflecting the radionuclides present in the plants on which they feed, The coconut crab and the land hermit crab (Coenobita perlatus) contain the same nuclides but concentrate strontium-90, as has been The occurrence of radionuclides in man at 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-65 and 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 manganesedominant. On a drv-wei=ht basis for a samnle of highest levels, the iver, gastrointestinal tract, and eyes are lower by about-an order of magnitude, and the quscle and bone lower by still another order of magnitude. If the total amount of radioactivity by tissue is considered, then bone Is tne fish are open to question. In some instances invertebrates 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 tbe fact that young fish contain relatively high levels. The marine invertebrates taken as a whole contain a wider spectrum of radionuclides than do the 155. The corals contain cobalt-60 and are the only invertebrates in which strontium-90 has been 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 60. Weiss and Shipman (1957) originally reported the concentration of cobalt-60 in the kidney of Tridacnid clams collected at RonuelaD in 1956. Animals such as the sea cucumber-(Eoiothuria, Sticho us) and spider snail (Lambis, Of several species of algae sampled in 1959 the only radionuclides detected were ruthenium-106, levels of radioactivity in the aigae are lower than in the fish or invertebrates. cerium-144, but all in minute amounts. 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 nuclidea 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 strontium-90, radioactivity is associated mainly with the fines and is concentrated in the top two to four inches, dropping off rapidly with depth. Radionuclides other than naturally occurring potassium-40 were not detected in sea water although larger samples and more sensitive techniques undoubtedly would have revealed their presence. In SUB, on land the present distribution of cesium-137, can be expected to remain very much as it is now. The levels of radioactivity will be reduced primarily by physical decay of the radicnuclides 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 tbe 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. The qualitative distribution of radionuclides at Rongelap Atoll JS determined approximately five

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,, Qualitative Distribution of Radionuclidea Page 169 f years after contamination by fallout from a thermonuclear device indicates distinct differences between the terrestrial andmsrine environments. The levels of radioactivity are low, the concentrations being less than the maximum permissible concentration for radionuclides in food or drinking water of nan. Of the wide spectrum of radionuclides concentrated in the surface layers of the soil, stroncipal nuclides entering into the soil solution. The prlncipai nuclides in the land plants and planteating animals SUCh as coconut crabs and the indigenous rats are CeSiUm-i37 and, to a lesser degree, strontium90. Bottom sediments contain nuclides in the lagoon water have not been detected but are probably present in minute amounts. Planktonic organisms contein traces of manganese-54, and cerium-144. The principal nuclide found in the marine algae is cerium-144. In the marine invertebrates cobalt-60 and zinc-65 occur most cwnly. Corals and coralline algae contain some strontium90, while the fish and sea birds are found to contain mostly zinc-65. The presence of zinc-65, tives reflects a diet of both marine and terresThis work was jn?rformed under contract number mission and the University of Washington. Radioisotopes and environmental circumstances: The Internal radioactive contamination of al Pacific island community exposod to local fallout. of the teneion lysimster in coral atoll and glacial till soils. Soil sCi. 25: 321-325.— of certain areaa in thePacific Ocean fm nuclear Government Printing Office, Washington, D.C. 60 fallout on plants. Atoll Raeearch Bulletin No. Seld, E.E. 1960. bmd crabs and fiseion products at Eniwetok Atoll. Pacific Sci. ~(l): 18-27. photon pulse rate of fiseion prnducte from elow Robineon, U.K. 1954. Sea temperature in tbe Ssrabsll C.L. lfard, 19S7. Oenetic studiee of irradiated natural populations of Droeo hlla. Arx, V.S. 1954. Circulation eyeteme of Bikini lnd Radiocesium in plants grown on Rongelap Atoll soile. In Recent Advances in &tan centration by killer clme of cobalt-60 from