Iron-55 in Rongelap People, Fish and Soils (Health Physics Pergamon Press 1972, Vol. 22 (March), PP. 245-250, Printed in Northern Ireland)

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Health Pl~~ics Pergamon Press 1972. Vol. 22 (March), pp. 24~–250. Printed in Northern Ireland IRON-55 IN RONGELAP PEOPLE, FISH AND SOILS Laboratory of Radiation Ecology, College of Fisheries, University of Washington, 407871 Lfedical Department, Brookhaven National Laboratory, Upton, L. I., New York (Receiued 5 Februqy 1971; in revised form 12 April 1971) & Abstract—The 5sFe body burdens for 60 residents of Ron3e1ap Atoll are reported. The measured burdens are approximately 3 times higher than those of a similar number of residents from ‘1’okai-mura, Japan. Since previous mcasuremeuts in 1966 revealed substantial 55Febody burdcus in Japanese residents, the current RonSciapcse 55Fe body burdens pose interesting SIISCE 1965, the distribution of 55Fe in the biosphere has been studied both in the United States and in the Scandinavian countries. in Alaskan Eskimos, residents of Richland, Washington, and in representative foodstuffs of environmental samples and in residents of generally confirmed the findings of the earlier study. Additional research shows that (i) marine organisms and people whose diet is largely seafood contain the highest concenhemisphere have higher 55Fe body burdens than those of tbe southern hemisphere; 15} and (iii) the 551e levels in people reached peak concentrations in 1966 and continue to decrease.t~, 7) JA.AKKOX.A(8)has recently presented an excellent summary of the measurements of 55Fe in Finnish Lapps which includes a valuable ]k7e determined the 55Fe body burdens of nalives at Rongelap Atoll in the Nfarshall Islands. Our interest in this particular population derives from two important considerations. I~irst, the R ongelapese are a maritime culture, and tllcy derive a large por[ion of their diet from the sea.(g) Prominent in this diet arc (he Estimates of fish consumption vary, but daily intakes between 75–1 50 g appear reasonable. There are no apparent qualitative differences in the diets of males or females. Thus, the determination of 55[;e in this population is of interest for comparison with other maritime cultures. Second, Rongelap Atoll received high-level fallout following the detonation of a thermonuclear device at Bikini Atoll in 1954.(10) We considered it probable that retention of 55Fe at the atoll from that event, coupled with input from world wide fallout from large-scale nuclear device testing in 1961–1962 might lead to elevated concentrations of 55Fe in marine species in the Rongelapese diet and therefore unusual body burdens of this radionuclide in METHODS AND TECHNIQUES The method of separation of55Fe was identical to that previously described. (lJ The counting technique was changed slightly; a gas filled coincidence Ivith an umbrella of nine Geiger– hliillcr tllbes was used to detect the 5.9-kcV X-ray emitted in the electron capture decay of 55~:c. Pulses from the proportional counter analyzer. The cktcction system was surrounded by 4 in. of lead shielding and the resultant background counting rate under the

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246 IRON-55 IN RONGELAP PEOPLE, FISH AND SOILS Disintegration rates of 55Fe in the samples were cleposited from a standard solution obtained from the National Bureau of Standards. Correction was made fo; the self-absorption of the X-rays in the electrodeposited iron. Stable iron was determined calorimetrically, using OBody burdens were estimated by first measuring the 551e in a known volume of blood (4– 26 ml). Total blood volume was estimated using body weight and average blood volumes of 82 ml blood pm- kg body weight for males and 74 ml Mood per kg body weight for females. The iron content of blood was assumed to be 65 % of the total body iron. This method of calculating total blood volume is that used by PERSSON~12Jin his estimate of 55Fc body burdens in Lapps of N’orthern Sweden. Previous estimates of body burdens from composite blood specimens {l, 5, were made assuming that the average total blood volume was 51. and that 60% of the total iron is in the blood. Using this method with the Rongelap data, the average calculated using body weights. Table 1 gives the average body burdens of 55Fe in the group of Rongelapese sampled in March 1970, and Fig. 1 shows a frequency distribution of the body burdens of males and females. The Rongelapese which were included in this study consisted entirely of those individuals who were subjected to external radiation in 1954. Iron-55 levels in the blood samples were sufllciently high to permit count rate fidence level. Not all donors were weighed in 1970, therefore body weights from previous years ~vere used to compute total blood volumes. However, vwights from previous years applied mostly to younger donors. Since weight generally increases with age, some individual estimates of 55Fe body burdens, and therefore the averages sb.o~ws in Table 1, are likely to be The maximum body burden in the males was 0.85 pCi, while 3 females had body burdens greater than this value. The maximum observed female body burden was 1.0 pCi, Table 1. A wrage 55Fe body burdens of Rongelape~e FIG. 1. Frequency distribution of 3:17e body burdens in Ronge]ap males and females. Body burdens h~vc b[c!l gr’oupcd into classe;. Example: 3 Rongelap males had 55Fc body burdens between 0.10-0.20

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approximately 1/1 OOth of the maximum permissible body burden which has been estabviduals considering the total body as the critical organ. (13) Previous measurements of 55Fe body burdens during a period of increasing 55Fe fallout generally showed that 55Fe body burdens of females were higher than those of males. {t’s) Presumably this is due to higher turnover rates of iron in females than in males, with the result that females are more nearly at equilibrium with their environment. As environmental levels of 55Fe decrease, females should, on the aver%% reflect this change by exhibiting lower 55Fe body burdens than those of males. Figure 1 shows that more female body burdens tended toward values <0.4 pCi, while male body burdens were more normally distributed, about a mean of 0.43 pCi. Regression analysis of age on body burdens showed a significant correlation (P < 0.001); older individuals had higher asFe body burdens. Table ~ shows a tabulation of the average 65Fe body of males and females by age groups. The number of samples per age group is admittedly small yet the general increase of 551?e body burden with age appears qualitatively consistent with earlier data obtained by analyzing blood from Seattle, Washington males in 1966. Comparison of the aSFe body burdens of edge of the turnover rates of 55Fe in the environment and in

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248 IRON-55 IN RONGELAP PEOPLE, FISH AND SOILS Table 3. Iron-!i5 content in goatjsh (Mulloidichthy~, sp.) and soil samplesfrom Rongela} Atoll. Number of fish liuers contributing to single, pooled sample ana~zed are in parentheses,; ~table Fe and 55Feare expressed per kilogram of wet tissue or per kilogram d~ soil . Rongelap islet Liver (20) September 1959 4.04 0.98 4.1 Kabelle islet Liver (7) September 1961 0.68 0.76 0.9 Rongelap islet Liver ( 10) March 1963 1.40 1.15 1.2 Kabelle islet Liver (71) August 1963 2.49 0.37 6.7 Kabelle islet Soil (O-2.5 cm) August 1959 0.24 Kabelle islet Soil (O-2.5 cm) August 1963 0.06 Rongelap islet Soil (O-2.5 cm) March 1959 0.05 Rongelap islet Soil (O-2.5 cm) August 1963 0.006 Fe determination, + 10~0 at the 67~0 confidence level (la). Activities are corrected to collection 65Fe body burdens were probably small. {la) The Rongelapese returned to the atoll in mid-July 1957. Whole body counting and urinalysis measurements one year later disclosed increased body burdens of several radionuclidcs, the most notable being 137CS. It is probable that 65Fe body burdens increased similarly. The concentrations of55Fe in a selected species of fish and in the calcareous soils are listed in Table 3. Activity in the fish is based on wet weights for comparison with previous work. The amount of sample that was available for analysis was small and therefore it was necessary to combine individual samples. This prevents an estimate of the range of 55Fe concentrations which occur between fish, i.e. the within sample variation. The number in parenthesis in Table 2 for the biological samples indicates the number of fishes which contributed to the pooled, single sample analyzed. The 55Fe values for soil samples collectcci in 1963 at both Kabclle Islet and RongcIap Islet arc averagm of samples collected at depth increments of O–1.3 and 1.3–2.5 cm. Specific activities are not given for soils since varying amounts of pre-1 954 plant detritus could significantly alter the stable iron content but not the 55Fe activity. In this instance, activity per unit weight of soil is a better index of changes which occur as a result of input or loss than is specific activity. The decrease in s5Fe specific activities in tween 1959–1 961 corresponds to an ecological half-life of 11 months, identical to that observed by JE~NIINGS.(14) Higher specific activities may have occurred at earlier times; however, estimates based only on exponential loss would not take into account possible retention and cycling of 55Fe within the Iagoon, or the time lag between deposition and maximum specific activity in the aquatic biota. The increase in specific activity of goatfish liver between late 1961 and mid 1963 reflects the increased environmental concentrations of 6sFe resulting from testing nuclear devices in 1961 –1 962. Introduction of this radionuclide to Rongclap Atoll can occur both by atmospheric fallout and by water transport of radioactivity from oceanic regimes. The ~restward-moving from northern latitudes where fallout from the

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196 1–1962 tests were maximal. Speeds of surface currents in both the California and North Equatorial Currents are sufficiently large to account for transport of waters from 30 to 40”N latitude to Rongelap Atoll(17) in the time period 196 1–1 963; similarly, maximum surface deposition of 55Fe occurred in 1963,{16) and thus the data ofTable 2 probably reflect contributions from both sources. The higher specific activi[y 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 fish. Recent measurements of the specific activity of immature and mature goatfish liver collected at Johnston Atoll in 1968 showed that immature fish livers contained less stable iron 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 ir<,n stores and therefore more nearly reflect the environmental specific activities than do tl]c mature fish whose iron stores are already formed. In the latter case, exchange rates may Our measurements of 55Fe in soils collected from the same sites between 1959–1 963 do not clarif}r either of the input sources mentioned above; the changes in concentrations arc greater dlan can be accounted for by physical decay. Natural processes which remove 55Fc fl-oi~l tile upper 2.54 cm of soil may preclude its use as a precise collector, and therefore the results arc useful only to indicate order ofrna,gnitucfe ralues of 55Fe soil concentrations present at the collecUnfortunately it is not possible to offer a clear argument- in explanation of the 55Fe body burdens of the Rongelapese presented here, at this time. Samples from 1963 through 1969 would have shed light on the problem, hut none arc available for analysis. In a speculative vein, several explanations can be advanced. First, the possibility of Rongelap lagoon actinx as a nutrient and trace-element “trap” sinlilar to estuaries is intriguing. Removal and retention within the lagoon of both stable iron could lead to high specific activities of 551’c in species important in the Rongelapese diet. The fact that livers fkom mature goatfish contain between 2–3 times as much stable iron per unit ~vet weight as do livers of mature salmonf4J is consistent with this argument. Second, JENNsuggested that large amounts of 55Fe were introduced into the northern hemisphere as tropospheric fallout during the 1961–1 962 test series and that deposition may have occurred in rather narrow latitudinal bands (maximum input at that subsequent stratospheric deposition of 55Fe from these tests was similar to that observed for port of 55Fe from these high latitudes by major ocean current systems feeding the North Equatorial Current (in addition to biological and physico-chernical factors) will deplete northern waters of this radionuclide. As discussed earlier, transit time for these waters from high latitudes to Rongelap Atoll is measured in vcar, and if is therefore possible that the higher ~~Fc body burdens in the Rongclapese reflects a “lag” time between the 5sFe specific activities of Lk-orthern Pacific and Southern Pacific Ocean biota due to this transport. Finally it is possible that the high 55Fe Rongelapcse body burdens relative to the Japanese donors results from a combination of dietary intake and uptake and re~rntion differences for iron between the two groups sampled. L’nfortunately precise dietary information for both groups is lacking and little is knowm about the 55Fe specific activities of the foods eaten by both groups. The Rongelapcsc do not suffer from iron deficiency anemia, SC) enhanccci uptake of iron from the diet is probably inconsequential. It is clear that further measurements of the specific activities of 65Fe in Ibe diets of the Rongelapese and other maritinw cultures and the effective half-life they display for this radionuclide will be needed to clarify the questions raised her-c. pro,. idcd helpful discussions during preparation of tile manuscript. Supported by AEC under Contract

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250 IRON-55 IN RONGELAP PEOPLE, FISH AND SOILS 2. T. JAAKXOLA, in: Radioecological Concentration 3. B. PERSSON, in: Radioecological Concentration pp. 253-258, Pergamon Press, Oxford (1967). Northwest Lab. Rep. 1051, Part 2, pp. 73-74 Rep. 50029 (’I’-446) (1967). This report contains a brief review of past medical surveys on Rongelapese natives and a bibliography listing medical reports, radioecological studies, and graduate theses which deal with work conducted at Rongelap Atoll. science, New York (1959). 13. International Commission for Radiological Protection, Recommendations: Report 2, Permissible Dole for Interna[ Radiatwn, Pergamon Gulf and Caribbean Fisheries Institute (Edited by