Distribution of Radioactivity in Sea Water and Marine Organisms Following and Underwater Nuclear Detonation at the Eniwetok Test Site in 1958

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Biology and Medicine DISTRIBUTION OF RADIOACTIVITY IN SEA WATER AND MARINE ORGANISMS FOLLOWING AN UNDERWATER NUCLEAR DETONATION AT THE ENIWETOK TEST SITE IN 1958 Laboratory of Radiation Biology University of Washington Operated b:’ the University of Washington under Contra: t NO. AT(45- 1)540 with the United States Atomic Energy Comm ission

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An investigation of the radioactive contamination of the water and marine organisms in and near the Eniwetok Test Site was conducted during May 1958, shortly before and immediately following an underwater nuclear detonation. At the end of three and one-half days the boundaries of the radioactive water mass extended beyond the survey area, 50 miles to the west of Eniwetok AtoLl, and to a depth of at least 300 meters. The plankton contained high levels of of two samples. once in each Whole fish samples contained essentially the same radioisotopes as the plankton. Shrimp and squid contained high levels of Np239

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The success of the survey was made possible by the cooperation Walden, USN, Executive Officer, and members of The kind help of Mr. James W. Winchester, the crew of the Office of Naval Research, is greatly appreciated, as is also the help of the personnel of the U. S. Navy Hydrographic Office: The authors are especially grateful for the assistance of Mr. Blair W. Gibson who spent many hours in the counting room. . The authors also would like to acknowledge the invaluable assistance, advice and information obtained from the following personnel of the U. S. Navy Monitoring Team: Lt. James W. Duckworth, Rad. Tech. Div. NMRI Ralph E. Severence, HM 1, Rad. Tech. Div. NMRI The support provided by Task Group 7.1 is hereby recognized.

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DISTRIBUTION OF RADIOACTIVITY IN SEA WATER AND MARINE ORGANISMS FOLLOWING AN UNDERWATER NUCLEAR DETONATION AT THE ENIWE TOK TEST SITE IN 1958 Studies were made by the United States in 1955 and 1956 and by Japan in 1954 and 1956 to determine the extent of the residual radioactive contamination in the western Pacific Ocean resulting from the nuclear tests at the Eniwetok Test Site. These studies were concerned with radioactive fallout material produced by the detonation of nuclear devices on land or in very shallow water.,, The present investigation was conducted during the 1958 test series (Hardtack) and was designed primarily to determine the uptake of the short- lived isotopes by marine organisms and to outline the mass of radioactive water immediately following the underwater detonation of a The survey was divided into two phases; the first, a predetonation survey, was designed to evaluate the radioactivity contributed by the earlier tests of the series; the second, a post detonation survey, the four-day period immediately following the Wahoo detonation. Navy assigned the USS Rehoboth (AGS-50) to assist the Office of Naval Research in a research

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program related to the Wahoo event. The Atomic Energy Commission supplied part of the funds for the operational cost of the Rehoboth and in return the Rehoboth was made available for use by the University of Washington Laboratory of Radiation Biology, an AEC contractor, for the period May 3, 1958 to May 20, 1958, to conduct a radiobiological Eight U. S. Navy Hydrographic Office personnel, under the direction of Mr. Alfred W. Anderson, made oceanographic surveys during both phases of the investigation and provided the authors with the water samples from four locations for measurement of radioactivity. A radiation monitoring team from the Radiation Technical Division of the Naval Medical Research Institute, under the direction of Lt. J. W Duckworth, measured the radioactivity of water at the surface, at the intake to the ship’s evaporators, and at designated depths from the surface down to 600 feet. The surface measurements were made . with a survey meter and the measurements of the inflow water to the evaporators were made with a specially designed ion- chamber that was fitted around the intake line. For measurements at depth a gamma probe with a continuous recording device was used. The probe was a modified “well-logging” type provided by the AEC Health and Safety Laboratory, New York Operations Office. A report of these measurements is being prepared for publication by the Naval Medical Research Institute.

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The measurement of radioactivity of the surface water (initial radiation survey) was conducted with the assistance of personnel

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. Table 1. Gross beta activity and temperature of the water obtained with Nansen casts. Values expressed in d/m/l in the particulate matter and in the water (filterable portion less K40 at time of collection. Sample Depth Temp. Particulate ** Correction factor for self absorption based on K40.

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bathythermograph (BT) winch, was lowered rapidly to the desired depth, towed at this depth for designated periods varying from 15 to 125 minutes, and then raised rapidly to deck level. Haul depths from the surface to 457 meters were determined by the use of a BT. The volume of the sample was determined volumetrically by allowing the sample to for five minutes in a graduate cylinder. Details of the plankton are given in Appendix Table A. In order to direct the movement of the ship while attempting lineate the mass of radioactive water produced by the Wahoo detonation, a 5-cc portion of plankton samples P-22 to P-35 was filtered through a Millipore filter disc 47 mm in diameter (pore size O. 45K), and the total gamma activity of sample. Later, at Island, the gross the plankton was determined immediately on the wet the Eniwetok Marine Biological Laboratory on Parry beta activity of the sample was determined on the In some samples the plankton were separated into “large” and “small” plankton. The sample was first filtered through a bronze screen 2-3 /4 inches in diameter with a mesh of 99 to the inch (large plankton), and then through a Millipore filter disc with a pore size of For the determination of gross beta activity, a portion of each sample was placed on a 1- l/2-inch stainless steel planchet, dried under infrared lamps, and counted aboard ship. The beta-counting equipment consisted

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and a Nuclear-Chicago Model 181 scaler. The correction factors for geometry, self-absorption, backscatter, and decay used to convert c/n~ to d/m/g of wet tissue at time of collection are included in Appendix The samples for total gamma counting were placed in pliofilm bags trometer with a 2-inch well-type sodium iodide crystal. Samples containing significant amounts of gamma activity were analyzed to determine the energies of the radionuclides present. Samples containing detectable amounts of beta activity were recounted at frequent intervals to determine radioactive decay. Because of the difficulties of weighing samples aboard ship, the weights were determined at the Eniwetok Marine Biological Laboratory. The radiochemical composition of nine samples was determined by A mid-water trawl of the Isaacs-Kidd type with a spread of six fee[l) was used to collect fish and macroplankton from depths of 14 to 365 meters, Trawl hauls were made at speeds of 4 to 5 knots and for periods of 35 to 147 minutes. A deep-sea, steam-powered anchor-winch was used for streaming the trawl with a l/2-inch

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wire cable. The maximum tension obtained during the deepest trawl was approximately 6, 000 pounds as measured by a dynamometer. The average tension while trawling was approximately 3, 500 pounds. Details of each trawl haul are given in Appendix Table B. After the small fish, shrimp, and miscellaneous plankton were separated, portions of each of these were placed on planchets and in pliofilm bags for gamma counting. Radio chemical made of six samples by ion-exchange techniques. for beta counting Four series of water samples, one before and three following the Wahoo detonation, were obtained from casts with Nansen bottles made by personnel of the U. S. Navy Hydrographic Office. The last three series consisted of seven samples obtained from depths of O to 300 meters, whereas the first series consisted of nineteen samples from depths of O to 1, 039 meters. Details of each sample are given in Table 1. Five hundred ml of water were passed through a Millipore filter 47 mm in diameter and with a pore size of O. 45P to collect the particulate matter present inch stainless steel in the water. The filter paper was placed on a 1-1 /2planchet, dried, and dissolved with acetone, then counted for total beta activity. Four ml of saturated sodium carbonate were added to 80 ml of the filtrate, and the carbonate precipitate was collected on a second Millipore filter paper and counted for beta activity. Naturally occurring K40, normally present in sea water to the extent of

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cesium also remains in the filtrate; however, it accounts one per cent of the total disintegration rate at the time of for less than Gamma. radiation survey of surface water The gamma radiation measurements of the surface water immediately following the Wahoo test were obtained with U. S. Navy survey stationed on the bow of the ship. The readings were relayed to the bridge by telephone at frequent intervals and plotted with the positions of the ship during the survey. The ship was maneuvered to follow a 10 mr/hr surface radiation field (Fig. 4). Radio chemical analyses of the samples Radio chemical analyses by ion-exchange techniques were made of sixteen samples including plankton, fish, shrimp, and squid. The samples were wet-ashed with concentrated HN03 and superoxol and dissolved in 0. 2N HCL. The samples were then passed through O. 28 cm2 x topes were eluted with 50 ml of the following reagents: O. 5 per cent OXalit acid and 5 per cent ammonium citrate at pH 3, pH 4, and pH 6.5 . Aliquots of the collected fractions were counted for total gamma activity, and the fractions with significant amounts of gamma radioactivity were *Available from Dow Chemical Co. , Midland, Michigan.

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analyzed in the gamma spectrometer radioisotopes could be identified in a the isotope was one per cent or more described above. The specific sample when the radioactivity of sample. The fractions which contained more total radioactivity of the than one radioisotope were further separated by other ion-exchange methods. were dried, redissolved in O. 1 M oxalic acid, and passed through O. 13 separation of the anions of Sb, Sn, done by the modified pf-ocedure of Palumbo and Lowman. Te, and Ru. The separation was Smith and Reynolds as described by P- 17, were dried and redissolved in concentrated HC1 to separate the . complex radionuclide mixtures, as described by Wish. In these experiments the samples were passed through O. 03 cm2 x 15 cm-columns containing Dowex- 1 (200-400 mesh) and the radionuclides were sequentially removed by using mixtures of hydrofluoric and hydrochloric acids. Because of the corrosive nature of the HF acid, column plugs made of lucite shavings were used and the fractions were collected in

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lusteroid test tubes. The oxalate fraction of the primary ion- exchange separation of sample P-6 was dried and red&solved in concentrated HC1 for the separation of the transition elements, as described by Kraus and Moore. The sample was passed through a O. 28 cm2 x 26-cm column Samples of plankton and a sample of shrimp were analyzed for Sr90 by the ion-exchange method of Kawabata and Held. The ashed sample was first treated with 80 per cent HN03 to remove strontium from the bulk of the sample and from most of the other radioisotopes present. The solution containing the strontium nitrate precipitate was filtered through a glass filter and was then dissolved in hot O. 2N HCI. After cooling, it was passed through a cationic resin column and possible contaminants were eluted from the column with O. 5 per cent oxalic acid and 5 per cent ammonium citrate at pH 3.5. , The column was then stored for 14 days to allow the YgO daughter to build up. The YgO was reeluted from the column with ammonium citrate at pH 3.5 and the amount of Srg O present was calculated from the amount of YgO re covered. The identity of YgO was confirmed by determining the decay rate of the

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Initial radiation survey The Wahoo device was detonated at 1330 on May 16, 1958, and at 1407 hours, the radiation survey to determine the 10 mr/hr limits of the radioactive water mass was started. A summary of the shipts track and the radiation readings in mr/hr recorded during the survey are presented in Figure 4. Immediately before the Wahoo test while the ship was 7, 000 yards south of target zero, the background radiation aboard ship was 2.0 mr/hr. The average background radiation in the iarget area was 1.5 mr/hr. the average background value has been In the following discussion subtracted from the values Following the detonation, as the ship proceeded in a northeasterly direction, it entered a 3 mr/hr field, at which time (1435) it was turned to the west, During the turn, the radiation level increased rapidly to 500 mr/hr (1451) and then dropped rapidly to 5 mr/hr as the

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when the ship was three and one - quarter miles due west of target zero. As the ship continued northward and then circled back (1542) to parallel the course taken earlier, radiation readings of 2 to 20 mr/hr were observed. At the northernmost point of the survey the readings were 2 mr/hr, and at the westernmost point they were 1 mr/hr. This line represents the approximate detectable downwind limits of contamination at this time. At 1618 the initial survey was completed when the ship was approximately 6, 500 yards downwind (WSW) from target zero. The level of radioactivity in the target area during the next fortyeight-hour period decreased to the pre-Wahoo level. The gross beta radioactivity in the pre and post test samples is given in Table 1. The radioactivity in the samples cone cted prior to the Wahoo detonation was limited to the top 39 meters and for the most part was in a soluble form. Five and one-half hours after detonation, radioactivity was present at all depths sampled and the amounts of radioactivity were much higher than those found one and three-quarter miles southwest of target zero. The particulate matter suspended in the water accounted for 6 to 40 per cent of the gross beta activity. ~enty - seven hours after detonation, four miles due west of target zero, the measured amounts of beta radioactivity in the water were approximately the same. At W + 48, at target zero, the greatest

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amount of radioactivity was found in the samples taken below the thermo - The radioactivity measurements of the plankton samples are given in Table 2. A small amount of beta activity found in the first four samples can be attributed to residual contamination from previous tests. - Because of tne thousand-fold increase in radioactivity of plankton sample P-6 collected on May 6, 1958, as compared to those collected previous to this date, it is assumed that this increase in radioactivity was due to the fallout of the Cactus device detonated on the same day. Samples P-7 to P- 12, collected before the Wahoo test, contained radioactivity in lower amounts (Fig. 2). …