Radioactivity of Invertebrates and Other Organisms at Eniwetok Atoll During 1954-55

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BIOLOGY AND MEDICINE ATOMIC ENERGY COMMISSION OF INVERTEBRATES AND OTHER ORGANISMS AT ENIWETOK ATOLL Technical Information Service Extension, oak Ridge, Term.

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I This report was prepared as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on beha~ of the Commission: A. Makes any warranty or repreeentation, express or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, “person acting on behalf of the Commission” includes any employee or contractor of the Commission to the extent that such employee or contractor

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RADIOACTMTY OF INVERTEBRATES AND OTHER ORGANISMS AT ENIWETOK ATOLL DURING 1954-55 Applied Fisheries Laboratory University of Washington Operated by the University of Washington under Contract No. AT(45-1)540 with the United States Atomic Energy Commission

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The trend in beta radioactivity as measured with methane flow counters over a period of about two years is shown, starting with the 1954 Castle series of nuclear detonations, up to but not including the series Of 1956. The results are presented as graphs each showing the logarithm of the radioactivity of an organism or of a particular tissue of an organism, related to the logarithm of the time after the date of detonation, when nearly all of the radioactivity was assumed to have originated. Invertebrates are considered in greatest detail, and other organisms and materials are included for comparison: island SOil, beach sand, sea water, plankton, algae, land plants, reef fish, birds, and rats. It is proposed for most organisms studied that after a period varying with the organism up to two to four weeks following detonation, a maximum level of radioactivity in the field samples collected is attained, followed by a decline approaching linearity on log-log plots with slopes over the major portion of the two-year period that can be represented as the negative exponent of the time after detonation. These decline slopes varied greatly with different localities and organisms, reaching a maximum of > 3. A few decay rates of individual samples of each organism or material are included for comparison, and these generally were equal to, or less steep than, the declines, suggesting that for some organisms or tissues, the level of radioactivity In the environment decreases more rapidly than oan be accounted for solely by physical decay

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RADIOACTIVITY OF INVERTEBRATES AND OTHER ORGANISMS AT ENIWETOK ATOLL DURING 1954-55 Levels of radioactivity in llving forms have been determined at almost all of the Pacific Proving Ground tests, both immediately before and shortly after the detonations, as well as at occasional relativel great titervals of a year or Tmore later (UWFL-33, 42, and 43 . The present study traces the trends In the beta radioactivity of Invertebrates by means of repeated observations from shortly before the Nectar detonation (May 14, 1954) for a period of nearly two years. For comparison with the invertebrates similar observations on other substances and organisms are included, using some information given more fully in reports by other members of the Applied Fisheries Laboratory who deal with their problems from different points of view. Palumbo (1957) reported on the radioactivity in algae and land plants . Held (1957) studied the trends of radioactivity in the land hermit crab and discovered the preponderance of radiostrontium in the exoskeleton. Welander (1957) described the trends of radioactivlt for the reef fishes of Belle Island. Lowman, fPalumbo, and South 1957) reported the identity of the radioactive non-fission products remaining Zn certain samples collected in 1954-55 and in 1956 as determined in late 1956 and Although the emphasis of the present paper is on invertebrates, certain data from many of the other areas are brought together here In order to compare the trends in levels of radioactivity in a unified form and

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A comparison of the rate at which levels of activity in organisms of the same species change with the passage of time, herein termed decline, with the rate of physical decay, should Indicate changes in availability of the radioactivity to the organism concerned. If decltie is more rapid than decay a reduction of activity in the environment beyond that caused solely by physical decay is suggested, and conversely, a steeper decay than decline suggests either an Lncreese in availability in the environment or an accumulation or concentration of radioactivity by the organism. Equality of decay and decline sug~sta that uptake and excretion of radioisotopes have reached an equilibrium with the environment. It will be shown that cases in which physical decay progressed more rapidly than did the rate of decllne over the same period of time were rare or lacking.

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Radioactivity of common substances and organisms at Eniwetok Atoll was evaluated in two ways, first by concentrated study involving many organisms collected frequently at one Island, Belle, and second, by less lntenslve study at several islands around the atoll in order to elucidate the geographical distribution of the activity. Belle Island (Fig. 1) was the major collecting and observation site, except for rats, for which it was Janet Island. Collections were made on April 15, 1954 at Belle before the Nectar test, almost daily for the week after, and at increasing intervals later. The second aspect of the study, at several islands, involved preNectar collections in April and May, and nine to ten post-Nectar collections, usually expedited by helicopter, at intervals increasing from one to nine months, at which time six islands, Henry, Leroy, AlIce, Olive, Vera, and Bruce were visited. The remaining two islands, Janet and Elmer, were sampled at approximately the same times in comectlon with Fig. 1. Map of Eniwetok Survey meter readings were taken frequently at Belle, but m only about half of the visits to other islands. The Juno meter was used for high (Table 2) levels of activity and the Geiger counter (Nuclear, MX-5) for low levels. Several spti were usually monitored with the instrument one inch from the ground and with the shield both open and closed. Similar readings three feet from the ground were taken less frequently and are For the distributional study on the various islands a handful of Island soil from the top inch, intertidal beach sand, a few milliliters of sea water, algae, and three sea cucumbers were taken. Periodic trips by M-boat around the periphery of the lagoon, a mile or two centrally from the islands, served for sampling sea water, plankton, and pelagic fish by rod and reel. Plankton tows usually lasted from 15 to 30 minutes at from one tO two knots per hour using two l/2-meter nets, fine (No.20 of 173 from either side of the M-boat. Large jellyfish. if present were removed and the samples preserved by adding formalin to make 5%.

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At Belle Island, the invertebrates usually sampled were the killer clam Tridacna, the spider snail Lambls, the land hermit crab Coenobit.a,the black sea cucumber Holothuria atra, and the branching corals Acropora, Porites, Poclllopora, and Heliopora, Fish, and aquatic invertebrates were usually collected along the north or ocean side, algae on the lagoon ana ocean sides, land plants in the central portion, land hermit crabs among the bushes of the north edge, and terns nearby. Rats were obtained centrally on Janet Island. Invertebrates and fish were collected at low tide when possible. Biological specimens were put on ice in insulated containers and transported to the laboratory at Elmer Island for immediate preparation or for freezing until time was available Soil samples were dried and packaged for shipment. Five- !,,,:. milliliter samples of sea water were dried on 1 l/2-inch stainless steel plates and ashed, except that in 1956, 100-milliliter ~.,..”..: samples were used because of the low level of the activity. , ,,.,,,.,.,. Th se were treated with sodium carbonate to remove potassium.‘,,. 4 (K80 contributes about O.6 disintegrations per minute per milliliter), and then filtered, and the precipitate used for counting. Radiocesi.umIs also lost by treatment with sodium Plankton was prepared by filtering and removing as much as 1-2 grams to the 1 l/2-inch counting plates, drying, and ashlng. From occasional poor tows the wet sample weight was as low as Portions usually sampled from the Invertebrates were: from clams, mantle, adductor muscle, gill, kidney, visceral mass, and shell; from spider snails, mantle, muscle of foot, terminal portions of liver and gut, visceral mass, and shell; from the land hermit crab, gill, dlgestlve gland or liver, gut, carapace, and muscle of leg; from sea cucumbers, gonad when sufficiently plentiful, gut and contents, muscle of the body wall, and body wall or integument with or without attached muscle; and from coral the terminal portions of small branches. Shell samples of clams and snails were usually taken from the thin edge to include The term gut as used in this report implies any portion of the digestive tract not more specifically designated and includes Sample size was Influenced somewhat by the nature of the sample and the amount of radioactivity present. When activity was low, larger samples were used. Between 50 and 200 milligrams of ash were usually considered desirable, but weights ranged widely, from less than 10 to more than 1000 milligrams. Shell and gut with sandy content were more lightly Samrled on a wet

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weight basis than soft tissues. Weighed samples of tissues In pliofilm bags were dried overnight at 100° C and sent to the Applied Fisheries Laboratory in Seattle for processing,which was usually accomplished about a month after collecting. In processing, the samples l.npliofilm bags were applied to the plates(l l/2-inch stainless steel, previously weighed), ashed overnight at 500° - 5500 C, slurried with alcohol, and dr!ed. The plated ash received a few drops of Formvar dissolved in ethylene dichloride (up to 1 mg dry equivalent) to affix the ash to the plate. The plates were then weighed, and counted in methane gas-flow counters. Except in the case of’rats, counts were corrected back to date of collection ustig the decay rate of island soil For rats the decay correction was based upon the individual decay rate for each plate. Self-absorption correction factors were based upon land soil collected June 7, 1954 at Edna> the decay curve of which (plate 9170) appears in Figure 5, page 11. Within seven months after Nectar an increase In average energy necessitated a reduction in the self-absorption correction factor for the later counttig. The following tabulation illustrates these changes. Ash weight Self-absorption correction factor for counting in mg/p2ate Before November 1, 1954 After November 1, 1954 Geometry and backscatter for the counters and plates used required a combined correction factor of 1.54. Coincidence correction factors were determined and applied for the counters employed. For the decay curves plate counts were used, corrected only for coincidence. Applying these correction factors gave values in disintegrations per minute per gram (d/m/g) of wet tissue as of the date of collection. Processing techniques are further di~cussed in UWFL-43 and WT-616. Three significant figures were retained throughout the calculations, finally being rounded to two. After plotting d/m/g against time the ordinate was in some ing 1 uc to equal 2.2 x 10 d/m.

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The Nectar test (May 14, 1954) %?8Sused origin except where otherwise indicated, but as the date of earlier shots also con~ributed-radioactivityto the sampleg studied. Especially the Bikini (March 1, 1954) shot contributed greatly to some of the samples. Residual long-lived products from earlier detonations prior to 1954 rendered the curves less steep than they would have been as a result of the 1954 series alOne. The trends of activity as related to time are of two kinds, the physical decay of individual samples, and the rate of change in activity of a certain type of sample at a certain locality. To distinguish it from physical decay, the latter trend will be referred to in this report as decline. Results are shown as graphs of the relationship of logarithm of radioactivity to logarithm of time of collection after detonation. The date of origin used may deviate somewhat from detonation day or the true origin without markedly affecting linearity of the plot over the period of study. The slope 1s changed according to the date of origin selected, but if the same origin is used for both decay and decline, the two may be Hunter and Ballou (1951) show on logarithmic plot the theoretical decay of mixed slow-neutron-- initiated fission products of U-235 over a period from 1 to 1000 days as a slightly curving line with a predominant downward curvature (concave 7below and a general slope varying A similar presentation of the trends of radioactivity observed in the present study facilitates comparison with this curve and within the study itself. In log-log graphs it will be convenient to speak of slopes or rates of decline and decay as becoming more or less steep with the passage of time, and when the terms steepening or leveling are applied to the trends, the log-log – Fig. 2. Mixed fission relationship is implied. A single product decay, gross half life when plotted semiloga- beta. (After Hunter rithmically gives a straight line, and Ballou). while on the same plot a mixture of half lives results h a line of In the declines shown as straight lines on log-log plots possible fluctuations of a cyclic nature attributable to season or other variables are ignored.

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Plan of presentation For each of the ten Primry subjects of investigation (survey meter readings, soil, water, plankton, algae, land plants, invertebrates, fish, birds, and rats), the trends or declines are shown graphically, and in some cases also In tabular form. For all subjects the regressions along with relevant data are brought together in Table 1. Where available the pre-NecWr level appears near the left edge of the decline graph as either a short horizontal bar or wedge. For the straight lines depicting the declines where llnearity appears to prevail, the time span involved is stipulated in Table 1 as well as being shown by the abscissal range of the llnes in the graphs. For conversion between microcurles and disintegrations per minute the following relationship was employed: The log-log regression llne is determined by its slope and y-intercept on day number 1, according to the relationship: where Y 1s the amount of radioactivity at time t tn days after assumed detonation day, and a is the y-intercept expressed in units of radioactivity of the regression line of slope b on day number 1. For example, the second entry in Table 1, survey meter readings at Belle, graphed in Figure 3, involved observations on 16 days over the period 5-540 days after Nectar. The with a correlation of -.971, which is far beyond the 1% level Along with decline data, available decays for as nearly simultaneous periods as possible are presented …