The Biological and Geographical Distrubition of W185 in the Vicinity of the Eniwetok Test Site, April - September, 1958

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THE BIOMGICAL AND GEOGRAPHICAL DISTRIBUTION OF W185 IN THE VICINITY OF THE ENIWETOK TEST SITE, APRIL - SEP!i’El??ER,1958 BEST COPY AVAIUBLE Laboratory of Radiation Biology University of Washington

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The cooperation of all members of the staff of the Laboratory of Radiation Biology and the support of the Commission, are hereby acknowledged. Dr. Lauren R. Donaldson Dr. Edward E. Held supplied the samples from the islands atolls outside the Eniwetok Test Site. Mr. Ronald Eisler, Timothy Joyner, Mr. William Champion, Mr. James Kimmel, Dr. Arthur Welander helped In the collection of the planksamples. Mr. William Tammany, 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 Office, Task Group 7.1, and Holmes and Narver tated the field operations.

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Radiochemical 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 The isotope was Identified by its half life, maximum beta energy and gamma energy. levels of W185 were found on plant-leaf and soil samples 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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Following the 1954 and 1956 tests of nuclear devices at the Enlwetok 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; ALMUIOet al, 1956; Seymour et al,—— —— 1957). Irilater 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 from the same in soils, land plants, and terrestrial animals general area. In addition to the neutroninduced radioisotopes the following fission products were present in the plankton and fish The investigations on the Isotopes by plankton and fish at uptake and retention of radiothe Eniwetok and Elkini test site were continued during the 1958 atomic test series. In the, period from August 8 to 14, one of three oceanic radiological surveys was made by members of the Laboratory of Radiation Biology to measure the amounts of radioactivity in sea water

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Navy for the and to identify the principal radioisotopes in The USS Collett (DD7>O) was provided by the U. S. work and the survey included thirty-nine collecting stations spaced on a fifty-mile grid (Fig, 1) In the area radioisotope, tungsten-185, not previously found at the test site by the present authors, was detected in high amounts in some of the samples. in gamma spectra made samples; however, the The gamma peak of W185 was first observed aboard the USS Collett on total plankton isotope was not positively identified until chemical separations were made. In this paper the methods used to establish the identity of the nuclides 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 emission of a beta particle of an energy of approximately 0.43 Imv. 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 radionuclides. The radioisotopes were identified by beta and gamma energies and by the elutlon fractions in which they were found. Confirmation of the presence of W185 was obtained by chemical precipitation techniques, by beta and gamma energies and by comparison of sample radionuclide separations with control 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 tungstic acid, each followed by the dissolving of the precipitate in concentrated h~40H. The solution was then scavenged with Fe(OH)3, and with molybdenum and bismuth sulfides in the presence of tartaric acid. Niobium was removed by extraction with chloroform and cupferron and the tungsten reprecipitated as tungstic gamma spectrum of the final precipitate showed only from other gamma emitters.

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The radiochemlcal technique for the separation of the nuclides by means of ion exchange Preparation of samples The dried samples were wet was adapted from the proce- (1944) and Tompkins et al,—— 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 The samples were filtered and the filtrates were cation resin columns prepared in the following the resin column Ihwex 50*, a sulfonated polystyrene resin of the cationlc 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.

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was allowed to pass through the column at a ml per minute and then the column was washed 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, 5.1, 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 column 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 and gamma counts. Gamma survev wocedure After the Isotope W185 was identified in the plankton samples, gamma spectra were made from different types of samples collected in and around the Eniwetok Test Site during the interval April 28 to September 17, 1958, The radiotungsten was identified by the 0.055 MEV gamma peak and the disintegration rates of this isotope as well as those of the other gamma

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emitters 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 l Accuracy of i 20 per cent,based on was obtained for six of the isotopes (W185, present in the samples. The given isotope in the samples known spike mixtures, lowest limit of dewas approximately one per cent of the total gamma activity. The determinations of the levels of Ru103-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 the contribution of the calculated. This value MEV gamma peak of Ru103 was determined in selected .513MEV peak from the same was subtracted from the comand the .515 MEN 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 NW peaks of Ce144 were determined in selected samples and the contribution of the .134 MEV Ce 1 ‘+4‘

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peak was calculated. This value was subtracted from the posite .134 MEV and .145 MEV peaks in the samples. me 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 were made on plankton samples.” Pronounced to 14) gamma spectra peaks at 0.055 MEV 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 a=as. 185 in the planktonThe region containing the highest levels of W (19,000,000 d/m/g dry weight) centered 155 nautical miles northwest of Enlwetok Atoll, coincided with an area of high total radioactivity, and was about 18o 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 approximately 90 nautical tiles west and south of Eniwetok and

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

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included Ujelang Atoll. the latter contaminated Plankton from three stations between body of water and Eniwetok did not The third area where plankton was found to contain W185 was east and southeast of Bikini Atoll and included Rongelap Atoll. The results ofim-exchange chemical separations for all radioisotopes on four plankton samples, two fish tissue samples, and the gamma curve analyses for eight plankton shown (Table 1 and Fig. 3). In Table 1, the disrates of the plankton are given. In plankton samples from stations 36 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-~140 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, ‘Ihehighest 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 38, which contained the highest level based on dry weight of plankton. The values based on dry weights are probably more accurate —— tnan-nose based w vuiume 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 masss it is a net advance of 7.3 miles per day and is a close approximation of the known westward end of three weeks pled for water and movement of the water in this area. At the the center of high activity was again samplankton. NO wI*5 was found (Fig. 4). Plankton collected at two stations just north of Ujelang

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Gamma spectrum curves of combined plankton samples of the Collett and of the Silvcrstein survey which was conducted three weeks later. l?185 was present at a high level in the plankton fro; the Collett survey but was absent in the plankton from th Silverstein survey. The Collett samples cont~ined stein samples and the gamma curves are not iYiZIIFZZive ~e relative gamma activity in the two samples.

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Water samples of approximately 500 ml each taken at O, 25, 50, 100 and 300 meter depths from five stations were,+ pooled on January 13, 1959, filtered through millipore filters (pore size .45v) and the filtrates dried. The filter paPers contained particle sizes greater than .4% plus the radi.o- ‘isotopes adsorbed to the papers. The radioisotopes with particle sizes less than .45~plus those in solution were found in the filtrate. The results, corrected to date of On the date of analysis part of the radiotungsten was either In solution or in a

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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 W . In an average of the five samples approximately two per cent W185 and 30 per cent of the Zr95-Nb95 remained on the The distribution of W185 and Zr95-Nb9~ on the filter 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 tion and analysis. A activity in the above this may be the case. died during the interval between colleccomparison of the distribution of radiosamples with that in aliquots of the at the date of collection indicates that 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, 1.958)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 specimens collected at Eniwetok, Bikini, Rongelap, Ujelang, Utlrlk and Wotho Atolls in the Marshall Islands, Kapfngamarangi Atoll in the Caroline Islands, Tarawa Atoll in the Gilbert Islands, and Kusaie and Ponape Atolls in the Senyavin Islands were examined by gamma spectrometry for the photopeak (0.055 MEV) of W185. The isotope was found only in samples from Enlwetok, Bikini, Rongelap and Ujelang Atolls. Eniwetok Atoll Samples Chemical separations were made on Scaevola leaves from Belle Island by ion-exchange and precipitation methods. In the anions from the ton-exchange column only the peaks of energy represented by W185 and Zr95-Nb95 were observed In the gamma spectra. ~lo3+lo6.~lo3+lo6 were driven off by heat in the ashing process. In the precipitation separation, which is specific for tungsten, only the 0.055 MEV photopeak and the 0.03

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B- Anions from above sample c- Tungsten separation from Gamma spectrum curves of Scaevola leaves …