Review of Marshall Islands Fallout Studies (Report)

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Persons who were present on March 1, 1954, at Rongelap Island, Rongelap Atoll, Sifo Island, Ailingnae Atoll, and Utirik Island, Utirik Atoll in the Marshall Islands have been examined by medical specialists to determine if any observable effects occurred as a result of exposure to radioactive fallout from the Pacific weapon test known as Operation Castle BRAVO. Medical specialists have reported short-term effects exhibited over a period of many months and possible long-term effects exhibited over many years. A study was undertaken to reexamine thyroid-absorbed dose estimates for people who were exposed accidentally at Rongelap, Sifo, and Utirik Islands. The study included: 1) reevaluation of radiochemical analysis to relate results from pooled urine to intake, retention, and excretion functions, 2) analysis of neutron irradiation studies of archival soil samples to estimate area1 activities of the iodine isotopes, 3) analysis of source term, weather data, and meteorology functions predicting atmospheric diffusion and fallout deposition to estimate airborne concentrations of the iodine isotopes, and 4) reevaluation of radioactive fallout contaminating a Japanese fishing vessel in the vicinity of Rongelap Island on March 1, 1954, to determine fallout components. The relative location of the exposed people is given as Figure 1. The original estimates of external whole-body dose from the acute exposure were 1.75 gray (175 tad) at Rongelap and 0.14 gray (14 rad) at Utirik (Cr56). The first estimate of thyroid dose from internal emitters in Rongelap people was 100 to 150 rep (Cr56). Thus the first estimate of total thyroid absorbed dose was 2.68 to 3.15 gray (268 to 315 rad) for Rongelap people in general and for internal plus external exposure. In 1964, three teenage girls who were exposed in .1954 underwent surgery for benign thyroid nodules. In 1964, 3 to &year-old child thyroid dose was reexamined by James on the basislgf 1) urine bioassy results and 2) a range _ of values for thyroid burden of I, thyroid mass, and uptake retention functions for iodine (Ja64). In addition two modes of intake were considered, inhalation and ingestion. For 3 to 4-year-old girls the extreme range of thyroid dose from internal emitters was estimated at 2 to 33 gray (200-3300 rad). The most probable total thyroid dose was in the range of 7 to 14 gray (700-1400 rad). The James estimate of most probable total thyroid absorbed dose to the child was 2 to 5 times higher than the estimate reported by Cronkite for Rongelap *people. The value for the James estiamte of total thyroid dose was extrapolated to other ages and to the Utirik people and reported along with medical effects by Conard (Co74). The number of radiation-induced thyroid lesions per million person-rad-years at risk was tabulated by Conard for the Rongelap and Utirik exposed populations. It was clear that the risks of radiation induced benign and cancerous lesions were not comparable between the two atolls for any age grouping. The thyroid cancer risk for the Japanese population exposed at Nagasaki and Hiroshima, as reported by the National Research Council's Committee on the Biological Effects of Ionizing Radiation, was 1.89 excess cases per million person-rad-years of tissue dose (CBEIR80). This parameter was 7.0 at Rongelap and 17.8 at Utirik for the lo-pear and older age grouping

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Variation between atolls in risk of radiation-induced thyroid cancer and the difference when compared to other irradiated groups had become an important scientific and health-related question with the considerable political overtones. Early in 1977, Bond, Borg,;Conard, Cronkite, Greenhouse, Naidu, and Meinhold, all members of Brookhaven National Laboratory (BNL), and Sondhaus, University of California, College of Medicine, initiated a reexamination of the technical issues. In 1978, formal program objectives and funding were supplied to BNL by the Department of Energy's Division of Biological and Environmental Research. In June 1978, the Meteorology Division at Lawrence Livermore National Laboratory was subcontracted to provide a computer simulation of the dispersion, transport, and deposition of fallout from the 1954 atmospheric nuclear test, BRAVO. A subcontract to provide neutron activation analysis of archival soil samples was given to the Radiological Sciences Department, Battelle-Pacific Northwest Laboratory. Soil samples were provided by Seymour, the director of the University of Washington's Laboratory of Radiation Thyroid absorbed dose tabulated here was estimated from results on 131I activity excreted in urine and the specific nuclide composition of BRAVO fallout. Surface and airborne activity, fallout granule size, and exposure rate at times after the detonation were developed for 142 nuclides at Rongelap and Utirik on the basis of the reported nuclide composition on day 26 postdetonation. Over 70 documents were reviewed for information regarding exposure-rate readings, film-badge readings, fallout composition, dose and dose rate, body burdens, urine analyses, gastrointestinal tract contents, bone marrow and thyroid dose estimates, and activity measurements in soil, water, marine life, and land animals. Results from the meteorology study and archival soil study were also reexamined and compared to fallout composition A tabulation of the estimates of thyroid absorbed dose, age at exposure and specific nuclides was done for each location. For an adult male, the om iodine and tellurium nuclides was 7.7 times the ~~~~~~~da~",,"5b',~ed~~e1~~Iat Rongelap , 10 times at Sifo Island and 4.7 times at Utirik Island. James the absorbed dose due to f3fumed the total thyroid absorbed dose was 2.6 times I (Ja64). The factor 2.6 would be appropriate for slightly older fallout than that experienced at Rongelap, Utirik or Sifo Islands. Thryoid absorbed dose was based on ingestion intake. Inhalation $%e and absorption through skin could not be reconciled with measurements I in urine or with external exposure rate measurements. Observations of the range of 137Cs body burdens during protracted exposure (Mi79) and the range associated with the contents of the stomach in cases of sudden death (Ev66) were used to estimate maximum thyroid absorbed dose. Th average internal thyroid dose at Rongelap Island was based on the average 151I activity collected in urine. The contribution to thyroid dose from external sources was estimated from the air exposure created by 142 nuclides which were estimated from results of BRAVO fallout composition. The external dose was similar to original estimates by Sondhaus for oersons exposed at Rongelap and Utirik Islands. The original external dose estimates at these islands, 1.75 gray and 0.14 gray (175 rad and 14 rad) .j were derived from survey instrument readings taken after

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badge data from a nearby military outpost (So55). Our external dose value at Sifo Island, 1.1. gray (110 rad) was greater than the 0.69 gray (69 rad) originally estimated by Sondhaus from post-evacuation surveys of exposure rate. The difference was due to the presence of very short-lived activation and transuranic nuclides which, according to the nuclide composition, must have been present during exposure at Sifo Island. Medical observations concerning thyroid abnormalities have been tabulated along with the new thyroid dose estimated for each person. From these results, the mean cancer risk rate in the exposed population of 251 people was 150 thyroid cancers per million person-gray-years at risk (1.5 f 2.5 thyroid cancers per million person-rad-years at risk). The mean time at risk for thyroid cancer was 19 years. The uncertainity derived for the estimate of risk was based on the standard deviation in adult mean urine activity concentration, the standard deviation in thyroid absorbed dose per unit intake, and the standard deviation in the spontaneous frequency of thyroid lesions in the unexposed comparison group* In order to avoid unwarrented external and internal dose from the deposited radioactivity, the inhabitants of these atolls were relocated out of the affected area. They returned to Utirik in June 1954 and to Rongelap in June 1957. Environmental and personnel radiological monitoring programs were initiated in the mid 1950's by Brookhaven National Laboratory. The objective was to maintain a comprehensive radiological safety program. Post-return body-burden histories and activity-ingestion rate patterns were determined as were estimates of internal committed effective dose equivalent. External exposure rate and living pattern data were also collected. Relationships between body burden or urine activity concentration and a declining continuous intake scenario were developed in order to model retrospective and prospective dose equivalent. The dosimetric conclusions for the protracted exposure are summarized in Table 1 (Le84). exposure of Rongelap andTable 1. Dosimetric conclusions for the protracted Utirik Adults from day of return to 50 years. Committed Effective Committed Effective A decline in the daily activity ingestion rate greater thanIS9at due adioactive decay was value of 3% per year :EorPu was estimated from sparse data. Current studies are aimed at determining the dosimetric impact of Pu. These values for the % per year decline in activity ingestion rate were observed at both atolls and i:< do not account for thleadditional decline due to radioactive decay.

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should not be extrapolated to other fallout exposures and 3) the medical observations quoted are not infallible, that is, a reevaluation of medical results may result in other cancer sites, different classifications for thyroid lesions or additional thyroid lesions. The sources of information were many and varied. Discussions with persons initially involved, eg. Stan Cohn, Vie Bond, and Eugene Cronkite led to documents which have been cited in the reference section. A search for records at DOE headquarters led to the many files currently held by Tom McGraw. Mr. McGraw has acted as a repository for many Atomic Energy Commission documents. Some of these documents related directly to this study and were not easily located anywhere else. An abundance of environmental results have been published by the University of Washington's Laboratory of Radiation Ecology (also known as Applied Fisheries Laboratory). Medical information was published by Brookhaven National Laboratory's Medical Department and dietary information was published by both the Medical Department and the Safety and Environmental Protection Division. Much of the early and detailed observations about the accident were recorded in documents published by the U.S. Naval Radiological Defense Laboratory and by the naval Medical Research Institute. The conclusions of the acute exposure study were that the population mean thyroid absorbed dose at Rongelap was 21 gray (2,100 tad). It was 6.7 gray (670 rad) at Sifo and 2.8 gray (286rad) at Utirik. The overall thyroid cancer risk was in agreement with results published for Japanese exposed at Nagasaki and Hiroshima. The major route for intake of fallout was by direct ingestion. This resulted from outdoor food preparation and consumption practices during the period fallout clouds passed over the islands. FIGWE 1. Relative location of the exposed people.

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BRAVO Cloud Dimensions. The BRAVO device was detonated on a sandspit near Nam Island, Bikini Atoll at 0645 March 1, 1954 (28/2/54 1845 GCT). It was a 17 MT thermonuclear yield. The upper limit to cloud height was 40 km (25 miles). The diameter 10 minutes after the burst was 110 km (70 miles). The fission/fusion ratio was estimated to be 0.47. It was the first in the Castle series of exoeriments. The second shot was 100 KT and occurred 30 days later. The next three shots were 150 KT, 9.5 MT and 10 MT respectively. The 9.5 and 10 MT shots may have contributed some fallout at Rongelap and Utirik, perhaps as mch as a 8% of the surface activity. These later shots occurred after persons were evacuated. Cloud Dlmnsions: Operation CASTS - Shot 1 - Bravo.

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Acute Exposure. In order to estimate acute exposure, meteorology and fallout dispersion models were used to calucate external exposure rate and air activity concentrations. Archival soil measurments were used to calculate surface activity levels of the iodine isotopes. The meteorology results and archival soil results were not used in the final thyroid dose estimate becuase they could not satisfy -the basic criteria that new results 'fit? t be related to previously known facts. Two approaches 1) the estimate of I intake from urine results and 2) the estimate of particle size and nuclide composition by Japanese scientists who examined fallout collected from a Japanese fishing vessel near Rongelap, could both be related to each other and be related to the know facts about fallout arrival and duration, external exposure rate measurements and gross beta measurements. Once the nuclide composition was assessed, the composition was normalized to external exposure rate measurements. Exposure rate histories were constructed for each island. Estimateslgf intake of radioiodines and radiotelluriums were normalized to the I intake estimate which was based on Rongelap urine results and related to external exposure rate. The time and mode of intake were based on diet and living pattern observations. The population mean and individual thyroid absorbed dose were based on the age and location of the exposed people. Age dependent values of thyroid absorbed dose per unit activity intake were obtained from the scientific literature. The final results were internal and external thyroid absorbed dose estimates for 251 exposed people.

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Meteorology. Downwind expsoure rate contours were estimated by several groups (Armed Forces Special Weapons Project, Rand Corporation, Naval Radiological Defense Laboratory) for the BRAVO detonation (Ha79). These contours were based on observations of BRAVO cloud dimensions and hodographs for 3 hours, 6 hours and 9 hours post detonation. These contours do not all agree but are within a factor of two for any specific location at Rongelap and Utirik Atolls. Significant departure in exposure rate contours occurs 32 to 190 km (20 to 120 miles) north of Rongelap Atoll out to a distance of 480 km (300 miles) east of the detonation site. Kendall Peterson estimated downwind exposures using the MATHEW-ADPIC modified code suite (Peal). activity concentrations for 148~~ti998:1y!3~~tef~9~sde~~~oa4E~n~~~~~~~~~ae Atoll and the southeastern part o; Rongilap A;011 in'proximity to Rongelap Island. The computer codes were developed for the Atmospheric Release Advisory Capability of the Department of Energy. They were modified to include a large number of upper-air wind levels which was thought by Peterson to be important. Additional modification included a turbulent wake correction to large granules falling from the stratosphere. Parameters for a tropical atmosphere were incorporated into granule fall velocity calculations. An assumption that the activity per granule increased as the cube of granule radius was made. Further description of the analytical approach has heen given by Peterson (Peal).

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BRAVO fallout patterns based on meteorolocry. This contour of exposure rate was estimated by the Armed Forces Special Weapons Project (AFSWP). The contour was cucumber shaped. Exposure rates were hypothetical values at one hoY r after the shot. The contaminated region was an area of more than 70,000 km (27,000 square miles) extending 50 km (30 miles) upwind and over 540 km (340 miles) downwind. The width of the crosswind direction was variable, the maximum being over 220 km (140 miles).

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Whole-body dose estimates. On iZongerikAtoll, a military outpost, a set of film badges were present and readings were obtained (So55). Monitoring instrument readings and the film badge results led Sondhaus to postulate total gamma exposures, from the tfye fallout began up to the time of evacuation, of 0.027, 0.022 and 0.018 C kg (106, 86 and 70 R) based on three assumed fallout durations of 8, 12 and 16 hours, respectively. One film badge remained outdoors at Rongerik from the time of …