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

Page 1

Biology and Medicine DISTRIBUTION OF RADIOACTIWTY 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 by the University of Washington under Contract No. AT(45- 1)540 with the United States Atomic Energy Commission

Page 3

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 area, 50 miles to the west of 300 meters. The plankton water mass extended beyond the survey Eniwetok Atoll, and to a depth of at least contained high levels of Np23g, Mogg - Tc99m, Te132_1132, and u237. Also present in lower amounts were of two samples. Whole fish samples contained essentially the same radioisotopes as the plankton. Shrimp and squid contained high levels of Np239

Page 4

The success of the survey was made possible Walden, USN, Executive Officer, and members of The kind help of Mr. James W. Winchester, by the cooperation 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 The support provided by Task Group 7.1 is hereby recognized.

Page 5

DISTRIBUTION OF RADIOACTIVITY IN SEA WATER AND MARINE ORGANISMS FOLLOWING AN UNDERWATER NUCLEAR DETONATION AT THE ENIWETOK 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 re - sidual 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, covered the four-day period immediately following the Wahoo detonation. The Hydrographic Office of the U S. Navy assigned the USS Rehoboth (AGS-50) to assist the Office of Naval Research in a research

Page 6

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 Office personnel, under the dimade 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 the surface down to 600 feet. The surface measurements 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 scintillation-type probe with a continuous recording device The probe was a modified “well-logging” type provided by Health and Safety Laboratory, New York Operations Office. of these measurements is being prepared for publication by Medical Research Institute.

Page 7

The measurement of radioactivity of the surface water (initial the Laboratory of was conducted with the assistance of personnel from Radiation Biology (University of Washington) and from the Radiation Safety Section of the Los Alamos Scientific under the direction of Maj. Gordon Jacks. The radiobiological survey extended from 10”56’ N Atoll (Fig. 1). The survey included thirty- five plankton four water stations. Eight mid-water trawl collections also were made during the period. Details of these collections describing location, depth of sample, temperature, and depth of thermocline are given in Table 1 and Appendix Tables A, B, and C, and the locations of the stations are shown in Figures 1, 2, and 3. Details of the work aboard ship and the methods of collection were similar to those described by Donaldson et al. and Seymour et al.—— —— MATERIALS AND METHODS Plankton samples were collected with a 1/2-meter plankton net of No. 6 mesh while the ship was drifting at a rate of approximately O. 5 to 1.8 knots per hour. The net, hauled by a 3 / 16-inch wire cable on a

Page 8

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. >artlculate Station no. (meters) OC matter*** Water Total ** Correction factor for self absorption based on K40.

Page 13

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 settle for five minutes in a graduate cylinder, Details of the plankton hauls are given in Appendix Table A. In order to direct the movement of the ship while attempting to delineate 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. 45#), and the total gamma activity of the plankton was determined immediately on the wet sample. Later, at the Eniwetok Marine Biological Laboratory on Parry Island, the gross 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 1-1 /2-inch stainless steel planchet, dried under infrared lamps, and counted aboard ship. The beta-counting equipment consisted

Page 14

of an end-window counter with a 2-inch Anton tube in a 3-inch Anton shield and a Nuclear- Chicago Model 181 scaler. The correction factors for geometry, self-absorption, backscatter, and decay used to convert c/m 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 feet 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

Page 15

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 for beta counting and in pliofilm bags for gamma counting. Radio chemical analyses were made of six samples by ion-exchange techniques. 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 in the water. The filter paper was placed on a 1-1 /2inch stainless steel planchet, 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

Page 18

analyzed in the gamma spectrometer described above. The specific radioisotopes could be identified in a sample when the radioactivity of the isotope was one per cent or more of the total radioactivity of the sample. The fractions were further separated which contained more than one radioisotope by other ion-exchange methods. The anion fractions of were dried, redissolved in separation of the anions of Sb, Sn, Te, and Ru. The separation was done by the modified procedure of Sm Palumbo and Lowman. The anion fractions of samples P th and Reynolds as described by P- 17, were dried and redissolved in concentrated HCL 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

Page 19

lusteroid test tubes. The oxalate fraction of the primary ion- exchange separation of sample P-6 was dried and redissolved 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 SrgO 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 HC1. After cooling, it was passed through contaminants were eluted from acid and 5 per cent ammonium stored for 14 days to allow the reeluted from the column with a cationic resin column and possible the column with O. 5 per cent oxalic citrate at pH 3.5. The column was then *9O daughter to build up. The Y90 was ammonium citrate at pH 3.5 and the The identity of present was calculated from the amount of YgO recovered. YgO was confirmed by determining the decay rate of the

Page 20

Initial radiation survev 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 ship’s 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 target area was 1.5 mr/hr. In the following discussion the average background value has been subtracted Following the detonation, as the ship proceeded from the values 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 ship’s course was changed sharply southward and away from target zero. This point, approximately one mile southeast from target zero, probably represents the limit of the main body of radioactive water at this time ( 1455). The survey was continued in a southwesterly direction and at 1510, when readings of 10 to 30 mr/hr were obtained, the course was changed to a northwesterly one. At 1530, readings of 2 to 8 mr/hr were obtained

Page 21

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 collected 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 suspended in the water accounted target zero. The particulate matter for 6 to 40 per cent of the gross beta activity. llventy- 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

Page 22

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 the 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 …