The Biological and Geographical Distribution of Tungsten-185 in the Vicinity of the Enewetak Test Site, April - September, 1958

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THE BIOIQGICAL AND GEOGRAPHICAL DISTRIBWION OF W185 IN THE VICINI~ OF Laboratory of Radiation Biology University of Washington Operated by the University of Washington under Contract No. AT(45-1)540 with the United States Atomic Energy COITIITIISSiOn

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Radiochemlcal separations were made by ion-exchange and precipitation techniques and by gamma spectrum analyses to determine the levels of tungsten-185 on selected samples from the Eniwetok and Bikini test site and from the nearby atolls of Rongelap and Ujelang by its half life, maximum beta The isotope was Identified energy and gamma energy. High levels of W185 were found on plant-leaf and soil samples at Belle and Janet Islands (Eniwetok Atoll) and on plankton collected 155 miles northwest of Eniwetok Atoll during August 1958. Lower levels were found at Vera, Keith, and Henry Islands (Eniwetok Atoll), Nan Island (Bikini Atoll), on the plankton near Ujelang and Rongelap Atolls and on samples from the latter atolls. The W185 appeared to occur as surface contamination with the exception of one fish sample taken at Enlwetok Atoll in which the isotope was found in the liver

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The cooperation of all members of the staff of the Laboratory of Radiation Biology and the support of the Division of Biology and Medicine, U. S. Atomic Energy Commission, are hereby acknowledged. Dr. Lauren R. Donaldson and Dr. Edward E. Held supplied the samples from the islands and atolls outside the Eniwetok Test Site. Mr. Ronald Eisler, and Dr. Arthur Welander helped in the collection of the plankton samples Mr. William Tammanyj Holmes and Narver Radiological Safety Division, supplied the bottom sample from the Yellowwood crater. Mrs. Marilyn Christ assisted in the gamma spectrum analyses. Miss Marion Chase edited the final manuscript. The cooperation of staffs of the Enlwetok Field Office, Task Group 7.1, and Holmes and Narver greatly facilitated the field operations.

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F~llowl.ng the 1954 and 1956 tests of nuclear devl.ces at the Erd.wetok Test Site, investigators from both Japan and the United States reported the occurrence of several neutronInduced radioisotopes in marine organisms from that area (Kawabata, 1954; Rinehart et al, 1955; Yamada et al, 1955;—— —— weiss and Shipman, 1956; ~ano et al, 1956; Seymour et al,—. —— 1957). In later analyses of plankton and fish samples for cent to 99 per cent of the total radioactivity of the individual samples. However, these isotopes were present in only trace amounts in soils, land plants, and terrestrial animals from the same general area. In addition to the neutroninduced radioisotopes the following fission products were present in the plankton and fish samples: ~106- ~106, zr95. The investigations on the uptake and retention of radioisotopes by plankton and fish at the Eniwetok and Bikini test site were continued during the period from August 8 to 14, one 1958 atomic test series. In the of three oceanic radiological surveys was made by members of the Laboratory of Radiation Biology to measure the amounts of radioactivity I.nsea water

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and plankton and to identify the principal radioisotopes in the samples. The USS Collett (DD’730)was provided by the U. S. Navy for the work and the survey Included thirty-nine collecting stations spaced on a fifty-mile grid (Fig. 1) in the area addition to the above named radioisotopes, a neutron-induced radioisotope, tungsten-185, not previously found at the test site by the present authors, was detected In high amounts in some of the samples. The gamma peak of W185 was first observed in gamma spectra made aboard the USS Collett on total plankton samples; however, the isotope was not positively identified until chemical separations were made. In this paper the methods used to establish the identity of the nuclldes are described as well as the pattern and other samples. of distribution of the isotope in plankton MATERIALS AND METHODS and chemical properties of w185 were used to identify the isotope. W185 decays principally by the etnlssion of a beta particl~ of an energy of approximately 0.43 MEv . A gamma component (2.4 per cent) with an energy of 0.055 MEV Is also emitted and can be readily identified in the gamma

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Gamma spectra were made from plankton samples aboard the Collett by means of a single-channel fifty-position spectrometer to determine the presence of gamma-emitting radioisotopes other than the expected fission products. Selected samples containing mixtures of gamma emitters were wet ashed, dissolved in acid solution and passed through a cation exchange column for the separation of the radionuelides. The radioisotopes were identified by beta and gamma energies and by the elution fractions in which they were 185 was obtained byfound. Confirmation of the presence of W chemical precipitation techniques, by beta and gamma and by comparison of sample radionuclide separations trol experiments utilizing spikes of W185. Maximum beta energy was determined by mass absorption techniques. The precipitation method of analysis (Kleinberg, 1954) for W185 consisted of two precipitations of tungstlc acid, each followed by the dissolving of the precipitate in concentrated NH40H. The solution was then scavenged with Fe(OH)3> and with molybdenum and bismuth sulfides In the presence of tartarlc acid. Niobium was removed by extraction with chloroform and cupferron and the tungsten reprecipitated as tungstic acid. The gamma spectrum of the final precipitate showed only W185, free from other gamma emitters.

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The radiochemical technique for the separation of the nuclides by means of ion exchange was adapted from the procedure developed by Swartout et al, (1944) and Tompkins et al,.— —— The dried samples were wet ashed with HN03 and H202, evaporated to dryness and redissolved in 0.2N HC1. To check the radiochemical procedures a “control” sample was prepared in which O.O~c of W185 was added to a 300-mg portion of dry Puget Sound fish and then processed in the same manner as the test samples. The samples were filtered and the filtrates were passed through cation resin columns prepared in the following Preparation of the resin column Dowex 50+, a sulfonated polystyrene resin of the cationic type, of mesh size 100 - 200, was washed three times with 6N HC1, rinsed three times with distilled water and twice with dilute HC1. The resin suspension was placed in a glass column 6 mm in diameter and 100 mm in length containing a glass wool plug in a constriction at the base of the tube. Three column volumes of 0.2N HC1 were run through the resin until the eluate was clear and the desired flow rate was obtained. ~ Available from Dow Chemical Co., Midland, Michigan

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was allowed to pass through the column at a ml per minute and then the column was washed Ions not adsorbed to the resin, are designated as the anion fractions. The cations adsorbed to the resin were removed progressively by passing through the column 50 ml of 0.5 per cent oxalic acid followed by 5 per cent citric acid solutions adjusted to pH 3.5, 4.1, 4.6, ~.I, 5.6 and 6,1 with NH40H. The eluates were collected in test tubes and dried for gamma counting. Aliquots were removed for beta counting The resin bed was removed from the cQlumn at the termination of the elution procedure and was ignited. The ash was counted for beta and gamma activity The disintegration rates for the individual isotopes were determined from the beta Gamma survey procedure After the isotope and gamma counts, W185 was identified in the plankton samples, gamma spectra were collected in and around the made from different types of samples Eniwetok Test Site during the interval April 28 to September 17, 1958. identified by the 0.055 MEV gamma peak rates of this isotope as well as those The radiotungsten was and the disintegration of the other gamma

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emi.tters present in the samples were determined from the gamma curves by use of the method of Conally (1956). A three-inch by three-inch NaI (Tl) crystal was used in conjunction with a 256channel analyzer. Tests for the accuracy of the gamma spectrum method were made with standards and with radioactive spikes the disintegration rates of which had been determined from beta counts. Accuracy of i 20 per cent, based on known spike mixtures, tection of any given isotope in the samples was approximately one per cent of the total gamma activity. The determinations of the levels of Ru10~-Ru106 and Ce141-Ce144 are not as accurate as those obtained for the other isotopes because of the overlapping gamma The ratio of Ru103 to Ru106 was calculated in the following mariner. The .624 MEV peak of Ru106 was determined in selected the contribution of the .513 MEV peak from the same calculated. This value was subtracted from the comMEV gamma peak of Ru103 and the .515 MEV peak of RU106 samples, and the remainder was assumed to be contribThe ratio of Ce141 to Ce144 was calculated In a similar way. The 0.08 MEV and 0.03 MEV peaks of Ce144 were determined in selected samples and the contribution of the .134 MEV Ce 144

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peak was calculated. This value was subtracted from the composi-te .134 MEV and .145 MEV peaks in the samples. The remainder was considered to be from Ce141. The values obtained for all isotopes were corrected to the date of collection of the sample. DISCUSSION OF RESULTS Ocean survey samples During the Collett survey (August 8 to 14) gamma spectra. were made on plankton samples. Pronounced peaks at 0.055 M!ZV and smaller peaks at 0.03 MEV, later identified as those from tungsten-185, were observed in some samples but not in others (Fig. 2). When the station positions for those samples contributing the two peaks were plotted on a chart of the area sampled, a pattern of occurrence was observed (Fig. 3). The plankton specimens containing the W185 were taken in three areas. The region containing the highest levels of W185 in.the plankton (19,000,000d/m/g dry weight) centered 155 nautical miles northwest of Enlwetok Atoll, coincided with an area of high total radioactivity, and was about 180 miles In diameter, with a tongue of activity extending to Enlwetok Atoll. The northern and western boundaries of the radioactive area were not determined. A second area, containing lower levels of W185, was approximately 90 nautical miles west and south of Eniwetok and

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Fig. 2. Gamma spectrum curves of plankton samples collected at stations 3, 38 and 39 during the Collett survey.

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included Ujelang Atoll. Plankton from three stations between the latter contaminated body of water and Eniwetok did not exhibit the W185 peaks. The third area where plankton was found to contain W18~ was east and southeast of Bikini Atoll and included Rongelap Atoll. The results oftin-exchange chemical separations for all radioisotopes on four plankton samples, two fish tissue samples, and the gamma curve analyses for eight plankton samples are shown (Table Integration rates of the samples from stations 36 1 and Fig. 3). In Table 1, the displankton are given. h plankton and 3, W185 contributed 60 per cent and 83 per cent respectively of the total radioactivity. These samples did not contain U237 nor was it detected in any plankton sample containing W . In the plankton samples in which W185 was absent, the radioisotopes of the transition elements Co, Fe, and Zn and the fission products Ba140-La140 contributed almost all of the radioactivity. The gamma spectrum analysis for W185 in those plankton samples containing the isotope is shown at the bottom of Table 1. The highest levels of W185 were found in plankton samples from stations 38 and 39. In Table 1, the disintegration rates per ml of plankton

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are given. The amount of W185 based on volume is highest In plankton from station 3 rather than from station 58, which contained the highest level based on dry weight of plankton. The values based on dry weights are probably more accurate than those based on volume because of errors in volume determination and variation in plankton species between samples, which result In different volume to dry weight ratios. During the three-week Interval following the Collett survey, the station at which the highest values for plankton were found had shifted 150 miles westward If this shift represents the movement of the water mass, it is a net advance of 7.3 miles per day and is a close approximation of the known westward movement of the water In this area. At the end of three weeks the center of high activity was again sampled for water and plankton. No W185 was found (Fig. 4). Plankton collected at two stations just north of Ujelang Atoll contained 280,000 c/m/g dry weight of W185. This isotope, which was also detected on soil, plant and animal samples taken at U~elang Atoll, will be discussed later. Plankton samples collected half way between Bikini Atoll and Rongelap Atoll contained 21,000 d/m/g dry weight of W185. The isotope was also found in samples from Nan Island at Bikini and from Rongelap Atoll.

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Gamma spectrum curves of combined plankton samples of the Collett and of the Sllverstein survey which three weeks wi85 was present was conducted later. at a high level in the plankton from the Collett survey but was absent In the plankton from the Silverstein survey. The Collett samples contained steln samples and the gamma curves are not i~ive ~h-e relative gamma activity in the two samples.

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Water samples of approximately 500 ml each taken at O, 25, SO, 100 and 300 meter depths from five stations were pooled on January 13, 1959, filtered through milliPore filters contained particle sizes Isotopes adsorbed to the particle sizes less than filtrates dried. The filter papers papers. The radioisotopes with .4’jjAplus those in solution were found In the filtrate. The results, corrected to date of analysis (January 13, 1959), a majorOn the date of part of the radlotungsten was either In solution or in a

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colloidal dispersion (<0.2v) and was present in the filtrate fraction of the water samples. Zr95-Nb95 was also found at higher levels in the filtrate fraction than on the filter papers but the ratio was not as high as in the case of W185. In an average of the five samples approximately two per cent of the W185 and 30 per cent of the Zr95-Nb95 remained on the The distribution of W185 and Zr95-Nb95 on the filter papers and In the filtrates at the time of analysis probably. does not represent the condition at the time of collection. Some leaching of radioisotopes would have occurred in planktonic organisms which died during the Interval between collection and analysis. A comparison of the distribution of radioactivity in the above samples with that in allquots of the same samples filtered at the date of collection indicates that this may be the case. The data are as follows: Per cent of activity on filter Filtered at date

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The per cent of activity remaining on the filters In those.samples filtered at date of collection (August 8 - 14, 1958) is 5 to 170 times that found in the samples filtered January 13, 1959. Thus a considerable amount of leaching occurred during the intervening period. After W185 was detected and identified in the samples of plankton from the Collett survey, other …