Iron-55 in Rongelap People, Fish and Soils (Draft) (Partial Duplicate of 43518)

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Since 1965, the distribution of 55Fe in the biosphere h~s . been studied both in the United States and in the Scandinavian countries. Initially, 55Fe concentrations were determined in Alaskan Eskimos, residents of Richland, Washington, and in concentrations in environmental samples “and in residents of Finland (2) and Sweden (3) were reported which generally confirmed .“’the findings of the earlier study. Additional research shows t “that (i) marine organisms and people whose diet is largely seafood contain the highest concentrations of 55-. 55residents of the northern hemisphere have higher Fe body burdens than those of the southern hemisphere (5); and (iii) the 55Fe levels in people reached peak concentrations in 1966 and continue to decrease (6,7). we determined the 55 - Fe body burdens of natives at Rongelap Atoll in the Marshall Islands. Not only is their diet high in seafoods (8), but the atoll received high-level fallout following the detonation of a thermonuclear device at Bikini Atoll in We considered it probable that retention of 55Fe at the atoll from that event, coupled with world-wide fallout from largescale nuclear device testing in 1961-62 could lead to unusual body burdens of this radionuclide in the Rongelapese. The method of separation of “55 Fe was identical to that>- previously described in this journal (1). The counting technique

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was used to detect the 5.9-kev x-ray emitted in of551?e. Pulses from the proportional The detection syste-mwas surrounded by four inches of lead .. shielding and the resultant background counting rate under the 55Fe photopeak was 1.7 counts rein-l. Disintegration rates of 55Fe in the samples were determined by comparison with “55Fe electrodeposited from a standard solution obtained from the National Bureau of Standards. Correction was made for the self: absorption of the X-rays in the electrodeposited iron. Stable iron was determined calorimetrically, using o-phenanthralein as 55were estimated by first measuring the . Fe in blood (4-26 ml) . Total blood volume was estimated using body weight and average blood volumes of 82 ml blood per kg body weight for males and 74 ml blood per kg body weight for females. The iron content of blood was assumed to be 65 per cent of the total body iron. This method of calculating total blood volume is that used by Persson (11) in his estimate of 5’Fe body burdens in Lapps of Northern Sweden. Previous estimates of body burdens from composite blood specimens (1,5) were made assuming that the average total blood volumes of 5 liters and that 60 per cent of the total iron is in the blood.

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burdens agreed within 15 per cent of those calculated using body Table 1 gives the average body burdens of 55Fe in a selected group of Rongelapese sampled in March, 1970, and Figure 1 shows a frequency distribution of the body burdens of males and females. Xron-55 levels in the blood samples permit count rate measurements to + were sufficiently high to 5 per cent at the 95 p~r cent (2~) confidence leve1. Not all donors were weighed in 1970, therefore body weights from previous years were used to compute I total blood volumes. However, weights from previous years “ applied mostly to creases with age, and therefore the younger donors. Since weight generally in55 “some individual estimates of Fe body burdens, “ averages shown in Table 1, are likely to be The niaximumbody burden in the males was 0.85 pCi., while . three females had body burdens greater than this value. “The maximum observed female body burden was 1.0 ~Ci, approximately l/100th of the maximum permissible body burden which has been established for non-occupationally exposed individuals considering the total body as the critical ‘organ (18). Previous measurements of “ 55Fe body burdens during a period of increasing Fe fallout generally showed that Fe’body burdens of females were higher than those of males (4”, 5) . Presumably this is due to higher “tL’””cv-

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..” “rat”esof iron in Xemales than in males, witl~ the result that “ females are more nearly at equilibrium with their environment. ‘As environmental levels of 55Fe decrease; females should, on reflect this change by exhibiting lower Fe body those of males. Figure 1 shows that more female . tended toward values <O.4 Veil while male bodY more normally distributed,about a mean of 0.43 Wi. Regression analysis of age onbody burdens showed a significant.- burdens. This observation is consistent with earlier data from Comparison of the 55Fe’body burdens of peoples of different countries (5) requires knowledge of the turnover rates of in the environment and in humans. Jennings (12) has shown that l the 55”Fe specific activities of salmon taken from the northeast Pacific Ocean ~ecreased eightfold between 1964-1967. Assuming that a first eider reaction governed the removal of 55Fe from layer of the ocean (upper 100.m) he calculated tine and rain waters show decreases, but at lesser rates (6). Xron-55 body burdens of adult males in Richland, Washington, decreased approximately fourfold between 1967 and 1970 (7)~ corresponding to an effective Fe half-life of 1.5 years. If the 55Fe turnover rates of Richland, Washington, residents are

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similar to those of insular populations, we conclude that people from maritime cultures would exhibit similar and perhaps faster (13) of this radionuclide in the marine environment. The highest 55Fe body burdens previously female natives at Bethel, Alaska, during 1966 “bodyburden of eighteen females was 1.1 KCi. year, the average Fe body burden of females measured were in During the same and males at “TokaiMura, Japan, was 0.92 ~Ci and 0.63 ~Ci respectively (5). If Fe in Richland, Washingtonz males and in Tokai-Mura males is comparable, by 1970 the latter group four times lower than those measured in Rongelapese males. Iron-55 body burdens of females at Tokai.-Muramight be expected to be : comparable to those of males for reasons discussed earlier. of the donors of the Rongelap study were subjected to radiation during the accidental contamination of Rongelap 1954. “Because of the high levels of radioactivity at the Atoll, the Rongelap natives we’removed to Majuro Atoll where they resided for three and one-half years. Following exposure in 1954, whole body counting and urinalysis disclosed measurable quantities of internally deposited fallout radi.onuclides. By 1957, however, the only radionuclides present in the Rongelapese in significantly measurable quantities were 65Zn 137 Fe analyses were performed at that time so boclyburclens

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of this radionucl ide are ~lotknown.. Howevey-,based on the levels., tmmli (9) . The Rongelapese returned to the atoll in”mid-July, 195.7. Whole body counting and urinalysis measurements one year later disclosed significant body burdens of several radionuclides, 137c~the most notable being . It is probable that 55Fe body burdens increased similarly. .,. The concentrations of 55Fe in a selected species of fish and in soils are listed in Table 2. Activity in the fish is based on wet weights” for comparison with previous work. Pooled samples were used in the analyses to reduce the effect of withinsample variation. The 55 . Fe vaiues for soil samples collected ~ 1963 at both Kabelle Islet and Rongelap Islet are averages of samples collected at depth increments of 0-1.3 cm and 1.3-2.5 cm. Specific activities are not given for soils since varying ~ounts of pre-1954 plant detritus could significantly alter the 55stable iron content but not the Fe activity. In this instance, activity per unit weight of soil is which occur as”a result of input or a better index of changes : loss than is specific The decrease in adFe’specific activities in Mulloidichthys, ecological half-life of 11 months, identical to that observed. by Jennings (11). Higher specific activities may have occurred

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times, however, estimates based .A~ly on exponential not take into account possible retention and cycling of55Fe within the lagoon, or the time lag between deposition “~d maximum specific activity in the aquatic biota. The increase in specific activity of goatfish liver between ,. iate 1961 and mid 1963 reflects the increased environmental concentrations of Fe resulting from testing nuclear devices in 1961-62. Introduction of this radionuclide to Rongelap Atoll can occur both by atmospheric fallout and by water transport of radioactivity from oceanic regimes. The westwar”d-rnovingNorth Equatorial Current is con~prisedof waters from “northern latitudes where fallout from the 1961-62 tests were maximal (14). Speeds of surface currents in both the California and North Equatorial Currents are sufficiently large to account for tr~sport of . waters from 30-40° N latitude to Rongelap Atoll (15) A the time period 1961-63; similarly, maximum surface deposition of and thus the data of Table 2 probably of ’55Fe in soils sites between 1959-1963 do not clarify sources mentioned ~ove; the change in collected from the same either of the input concentrations are greater than can be accounted for by physical decay. Natural processes which remove Fe from the upper 2.54 cm of soil may preclude its use as a precise collector, and therefore the results are.

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. “u~efulonly to indicate order of magnitude values of Fe soil :concentrations present at the collection time. Unfortunately, it is-not possible to offer a clear argument in’ explanation of the Fe body burdens of the Rongelapese presented here at this time., Samples from 1963 through 1969 would have shed light on the problem, but “none are available 8 for analysis, The possibility of Rongelap lagoon acting as a I intriguing. Removal and retention of both stable Fe and 55Fe “from the North Equatorial Curren~ could lead to high specific activities of the radionuclide in species important ,in the Rongelapese diet. The-fact that livers from mature goatfish contain between 2-3 times as much stable iron per unit wet weight as do livers of mature salmon (4) is consistent with this argument. . “ Marsh”allese in general show a tendency toward anemia (9) and thus may absorb more iron from their diet than do non-anemic individuals. The 55Fe body burdens of the Rongelapese may there-. fore only reflect more complete uptake of iron rather than uptake .of iron of high specific activity. It is clear that further measurements of the specific activities of b3Fe in the diets of the Rongelapese and the effective half-life this radionuclide will be needed to clarify they display for

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H.E. Palmer and T.M. Beasley, Science 149, 431 (1965): T. Jaakkola, in Radioecological Concentration Processes, B. Persson, in Radioecological Concentration Processes, ‘B. Aberg and F.P. Hungate, Eds. (Pergmon, Oxfoid, 1967), i (T-446) (1967). This report contains a brief review of past medical surveys on Ronge\apese natives and a biblio– graphy listing medical reports, radioecological studies, . and graduate theses which deal with work conducted at E.B. Sandell, in Calorimetric Determination of Traces of

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13. E.E. Held, Pacif. Sci. 14, 18 (1960).’ 15. J.P. Tully, in Studies on Oceanography, K. Yoshida, Ed. . 16. The higher specific activity noted in goatfish liver in August 1963 may reflect more nearly the specific activity of waters at Rongelap Atoll than does the sample of March 1963. Livers from immature goatfish were used in the August specimen, while the March sample was obtained from mature fi”sh. Recent measurements of the specific activity of immature and mature goatfish liver collected at Johnston Atoll in 1968 showed that &mature fish livers contained less stable iroh and more 55Fe per unit wet weight than did livers from mature fish. We assume that the immature fish are in the process of . . forming their iron stores and therefore more nearly reflect the environmental specific activities than do the mature fish whose iron stores are already formed. In the latter case, exchange rates may be slow. T.W. Duke and T.R. Rice, in Proceedings of the Gulf and Caribbean Fisheries Institute, J. Higman, Ed. (Univ. of

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and soil samples from Rongelap Atoll. Sample numbers are in parentheses; stable Fe and Fe are expressed 4.04 0.98 4.1Rongelap Islet Liver (20) September 1959 Kabelle Islet Soil (O-2.5 cm) August 1963 0.06 * Saple comt~g times were arranged to determine 55Fe in biological 5 per cent at the 95 per cent confidence level (2@); to + 5-20 per cent at the 67 per cent confidence Stable Fe determination, f 10 per cent at the 67 per cent cofifidence level (if). Acti~itfes are corrected to