Land Crabs and Radioactive Fallout at Eniwetok Atoll

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II HEALTH AND SAFETY UNITED STATES ATOMIC ENERGY COMMISSION LAND CRABS AND RADIOACTIVE FALLOUT AT ENIWETOK ATOLL US DOE ARCHIVES Applied Fisheries Laboratory University of Washington Tech&e1 Dnformetion Service Extension, Oak Ridge, Tenn.

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I This report was prepared as an account of Government sponsored work. Neither the United Sates, nor the Commission, nor any person acting on behalf of the Commission: I A. Makes any warranty or representation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any tnformatlon, apparatus, method, or process disclosed in this report may not fnfrlnge privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any tnformation, apparatus, method, or process disclosed in this report. As used in the above, “person acting on behalf of the Commtssion” includes any employee or contractor of the Commission to the extent that such employee or contractor prepares, handtes or dfstributes, or provides access to, any lnformatlon pursuant to his employment or contract with the Commission. This report has been reproduced directly from the best available copy. Printed in USA. Price $1.25. Available from the Office 0s Technical Services, Department of Commerce, Washington 25, D. C.

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LAND CRABS AND RADI0Ap:'IVEFALLOUT AT ENIWETOK ATOLL Applied Fisheries Laboratory University of Washington WY 27, 1957 DOE ARCHIVES. Operated by the University of Washington under Contract No. AT(45-1)540with the United States Atomic Energy Commission

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The pattern of changing level8 of radloactlvltg is glven for the tissues of land hermit crabs, Coenobita perlatus, from Belle Island, Enlwetok Atoll, during a perl_od of nearly tvo years following the 1954 series of atomic tests. Srgo+ Ygo # and Cs137 vere the principal long-lived fission products found. Srgo levels In the skeleton remained constant throughout the ’ - period of study. The wholehearted cooperation of all members of the staff of the Applied Fisheries Laboratory, who at various times participated ln the collection and preparation of aample8, made this report posslble. Miss Dorothy J. South supplied the result8 of the radloceslum, radiocerlum, and some r af)&ARCHl= strontium determinations. The cooperation of the U. S. Atomic Energy Commlsalon.Divlsion of Biology and Medicine and the Enlvctok Field Office, Task Group 7.1, and Holmes and IVarver greatly facilitated the field collecting.

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Periodic studies of the effects of the atomic testing program on the biota of the Marshall Islands have been made by the staff of the Applied Fisheries Laboratory, University of Enivetok a continuous biological survey was Initiated. In this reF2rt the portion of the survey concerned with the uptake of radionuclidea by the land hermit crab, Coenobita perlatus Edw. T?, is presented. Results of possible ecological and physiological aigniflcance in the movement of strontium and ceaium through the cycle have been obtalned. Strontium-90 concentration In the crab skeleton may be a sensitive index of biologically eptallradloatrontium In the environment. Coenobita 1s an omnivorous scavenger which feeds primarily on land plants and on detrltua washed up on the beaches. It is primarily nocturnal and spends the daylight hours hidden In The crabs were taken from Belle (Bogombogo) Island which lies 2.3 nautical miles southwest of the site of the Mike test of 1952 and the Nectar test of 1954. This island is downwind from the site of these tests. Prior to the Mike test Belle Island had a covering of shrubs, l We are grateful to Dr. C.H. Edmondson, Bernice P. Bishop Museum, Honolulu, Rawail, for identification of the species.

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coconut palma and trees. 14 The IBland was denuded by the blest in lOovember 1952, but by April 1954 had regaLned a heavy growth of shrubs, prlncipslly Sceevola frutescens and Mesaerachmidia argentea. The regrovth was from seedlings and stumps of old plants, A rookery of fairy and noddy terns had also become established. Belle Island was again denuded by the IVectar teat of May 1954 save for stumps and some stripped branches. Dead birds and fish were found in the center of the island as well as along the shorea. about 50 in one pile of debris survived, probably because of the protection of the debris and their habit of quickly wlthdrawlng into their shell when disturbed. It is probable that they withdrew at the first flash of light before the blast reached them. Belle Island regained a lush cover of shrubs by August of 1954, less than three months after the IVectar test, and a fairy tern egg found three months later, ln late November, marked the beginning of a new rookery on the laland. Collection8 were made at approximately dally intervals commencia with the third day following Nectar until the ninth day. Thereafter, the Interval between collections was progressively lengthened to approximately monthly intervals. Three crabs were taken at each collection except that in In one instance, only two were taken. Samples of carapace (exoskeleton), three Instances five, and (“liver”), gut with its content, and gill were removed, either

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from the fresh or frozen specimens, at the Enlvetok Marine Biological Laboratory. The tissues were weighed at the time of dissection and then dried. The packaged dried samples, together with data cards, were sent by air mail to the Applied Fisheries Laboratory, University of WashIngton, for further processing. There the dried samples were ashed at temperatures up to 55J°C on stainless steel counting plates and then counted in an internal gas-flow cou~$_lng chamber. The counts per plate were converted to disintegrations per minute per gram (d/m/g) of wet tissue, a3 of the date of collection, by correcting for sample weight, geometry, backscatter, self-absorption, coincidence and decay. (See WT-616 (UUFL-33) for a more complete discussion of The decay corrections for all tissues except carapace were based on the decay rate of a soil sample collected at Belle Island the day after the Nectar shot. Decay corrections for the carapace were based on the decay rate of 3rgo+Ygo and 5r8g,which constituted virtually 100 per cent of its activity at the time the chemical determlnatlons vere made. The decay correction factors ranged from 1.09 to 12.7. DOE ARCHIVES The variation ln amount of radioactlvlty for each tissue at -- each collection date, although great, (Appendix Table 1) was not great enough to obscure general trends In changes of radioactivity with time or differences in levels of radioactivity The term “activity” as used here means radioactivity per

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“Rate of decline” refers to the rate at which radioactivity is decreasing In a given tissue, organ, or organism In its native Lwels oi activity In the crab tissues three days after the Hectar teat ranged from 5 x lo6 d/m/g In the gut to 7 x 104 d/m/g In the muscle (Figs. 1 and 2). The rate oi decline of activity decreased with time and vas dlffe’rent for each tissue, but Ln general followed the same trend as the decay of mlxed fission products during the first 200 days. Thereafter the rate of decllne for eeuh of the crab tissues approached a constant value vlth a half life In exaess of 20 years. This half’ life Is dependent on factors which include relative abundance and availability of radlonuclides In the food and/ or environment, rate of’ decay of radlonuclides absorbed, biological half’ life and selective uptake of radlonuclldes. Each 0r these, except the rate of’ physical decay, Is in turn dependent on varying envlronmental and physiological conditions. The terms factors. Ecological hali life will be used as the time required for an organism, or Its tissues or organs, in Its native environment to lose 50 per cent of its radloactivlty. When the e%%#cHIVS cal hair life and physical hsir life are equivalent (rate 0r decline= rate of decay), the tissue In question must be at equilibrium with respect to the radioisotopes It contains. For single isotopes an ecologlcal half life greater than the physical

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III III III DAYS AFTER MAY 14, 1954 Fig. 1. Beta-activity in Coenobita gill, muscle, hepatopancreas (“liver”) and gut on successive collection dates. Values in disintegrations per minute per gram wet weight.

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decay of radiostrontium. Values in disintegrations per minute per gram wet weight.

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0r the Isotope. In the converle situation where the ecological halr life Is less than'the phy8lca; half life, a net 1088 of the Isotope Is lndioated. This condition could result from 1088 or the Isotope by the environment, or eco-system, or from 8 phpsiological change In the organism or It8 prima;ryfood 8ource. Such phy8Iologlcal change8 may be transitory or seeaonal. The Increase In radioactivity over proshot levels during carapace than in the row other tiaauea by 8 factor 0r 5 to 10. Maximum post-Nectar levels 0r activity were 100 to 250 timea greater than pre-Mectar level8 in gut, liver, and gill, but only 22 and 26 times greater In muscle and carapace respectively. The lower rate 0r accumulstlon In muscle and carapace would be the material must be absorbed f’rom the gut and vhere borne selection takes.place. The specltlc rate of decline, vi11 be presented Individually for each tissue. probably do not conatltute a 8l@lflCa& proportion 0r the naturally occurring Isotopes. If, for example, a tl88Ue contained 107 d/m/g wet of_!3rg0, .or 5,000 times the maxlmunilevel found in the hermit crab, this would represent only 0.02 mg of strontium, or about 10'5 per cent oi the 88h weight. *he presence of strontium ha8 been reported qu8lltatlvely in crustacea and a quantitative estlmat'eof about one per cent strontium ha8 been

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The carapace was taken aa the sample of exoskeleton, It 1s eaa ily removed, sepatiated from other tissues and washed free of possible external contamination. The radioactivity ln the carapace due to long-lived Isotopes remained approximately constant throughout the period of 537 days counting all of the samples approximately 630 days after the Nectar test (Figs. 2 and 3). Radiochemlcal analysis of 18 samples taken at various times during the collecting period (Table 1 and Appendix Table 2), and three samples taken 35 days before Aectar demonstrated that virtually all of the long-lived activity was 20-gear Qrgo and its The nearly constant level In the carapace (ecological half life= physical decay) Indicates that thla tissue quickly reaches and maintains equilibrium with the available atrontium. GrOSB, Taylor and Watson (1954) report a plateau of retention of Sr90 in rats during continuous feeding at the aame rate, and apparent shifting of the plateau with change in dally dose. 16 DOE ARCHIVES It would be expected that thie relationship alao applies to available calcium which Is metabolically similar to strontium, radiochemical analyses were made was present in amounts too Small (co.2$ of total activity 17) to be determined by the method used. The amount of Sr8g present in the carapace immediately after nectar waa calculated Srom the yielde given by Sullivan la on the 9

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0 Sr go t vso ACTIVITY irag + Srgo DECAY DAYS AFTER MAY 14, 1954 Fig. 3. Radioactivity in Coenobita carapace on successive collection dates compared with the decay of radiostrontium. Values in disintegrations per minute per gram of ash.

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Table 1. Total p-activity and &go+ Ygo ln Coenobita Carapace Determlnetlons made In January and February, 1956. Averages of three samples and their standard errors are given. J) Average of duplicate aliquots of three pooled samples as determined by Dorpthy 3, SOCthj Applied Fksherles

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baals of the $iverage amount of Srgo In the 44 specimens collected during the. first 50 days following Nectar, less the amount present before Nectar. The relative radioactivity of the two isotopes was calculated from their specific activities, A theoretical deca.y curve was then calculated for the combined S-89, sidual from prior tests. Figures 4 and 5 show the actual values superimposed on this theoretical curve. Although there were no specific radiochemical determinations early in the period following Nectar It is reasonable to assume that the exoskeleton has a high degree of selectivity for strontium and that equilibrium must be reached within a few days at most. yhe assumptions are further supported by decay curves which approach the theoretical The relatively low levels of activity at 145 days postNectar are a reflection of a change ln ratio of ash weight to wet weight; Figure 4 represents the beta on an ash weight basis. The change in ratio may be associated with molting, but observations were not made at frequent enough intervals to confirm or deny such an assoclatlon. BOE ARCHIVES Contributions of radiostrontium to the crab skeleton at Belle Island from past tests at Enlwetok and Bikini are’represented In Figure 5. The pre-Mike level is an approxlmatlon since it is based on a single specimen and there was, unfortunately, no were derived by the method outlined above. The Mike teat contributed about twice as much activity as the Nectar test; fallout f’rom

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the pre-Mike tests and the Bikini tests of 1954 together contributed ab.out 5 per cent of the total Srgo activity. 3r9O on the Island is being malntatied at an essentially constant level (decreasing only with vorous hermit crab can be considered callg available strontium. However, in the crab skeleton to that in food physical decay), If the omnlan accurate Index of blologlthe ratio of the strontium items is not known. Judging from the meager data presently available, the radiostrontium content of the crab skelyt& is more than ten times that ln land plants on a wet weight basis and is more than three times .that in soil on a dry weight basis. Isotopes with half lives greater than 20 years contributed nearly all of the activity in muscle tissue 35 days before the. 10 and 1 per cent respectively, of the total activity In muscle tissue collected in February and November, 1955, and analyzed in January and March, 1956. Similar levels, 67, 13, and 1 per cent, were found in coconut crab muscle from Rongelap Atoll (UWFL-43, Table 14). In contrast to. the exoskeleton, muscle tissue had a variable, though generally decreasing, level of long-livewO;E ARCHIVES isotopes throughout the post-Nectar collecting period (Fig. 6). Between 150 and 200 days post-Hectar, the total activity in muscle was dU8 prlmarlly to the long-lived isotopes as evidenced by the Increased ecological half life. The level of total activity in muscle at 172 days (after Nectar) is one-sixth the pretest level, while the level of long-lived isotopes at that a0

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Fig. 6. Counts per minute per gram in Coenobita tissues as of 600 days after May 14, 1954, plotted for each collection

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time la one-eighth that of the pretest level; subsequently there la an increase in activity. BLnce both the total activity and the long-lived activity Increased by approximately equivalent amounts, the increase must be due to an increased net rate of uptake, reflecting a change in the physiology of the crab or a change In the conditions in the environment, leadlng to a greater avallablllty of, ln this case, Cs137 to the crab. The latter possiblllty Is the more easily explained by the observations, The same pattern of decrease in activity followed by 8 rise 1s evldent in the gut and liver of the crab, the leaves …