Dose Assessment at Bikini Atoll

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Survey Program of Bikini Soil and Gamma-Exposure Rate ......3 Bikini Ground Water Program .............5 External Gama Dose .,.......,,.,.... 12 Drinking Water Pathway .....,..,..,,.. 20 Marine Food Chain ..........,.....,. 21 Dose Summary and Discussion ............... 37 Terrestrial Food Chain ....,.,..,......

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DOSE ASSESSMENT A T BIKINI ATOLL Bikini Atoll is one of two sites i n the northern Marshall Islands that was used by the United States as testing grounds for the nuclear weapons progeneral cleanup began at Bikini Atoll. Subsistence crops, coconut and Pandanus fruit, were planted on Bikini and Eneu Islands, and housing was constructed on Bikini Island. A second phase of housing was planned for the interior of Bikini that external gamma doses inthe interior of the island might be higher than in other parts of the island. Therefore, t o select a second site for housing on the island with minimimum external exposure, a survey of Bikini Atoll was conducted i n June 1975. External gama measurements were made on Bi kf ni and Eneu Islands, and soil and vegetation s samples collected to evaluate the potential doses via terrestrial food chains and inhalation. Estimates of potential dose via the marine food chain were based upon data Six living patterns were evaluated. One was based on living and obtaining all subsistence crops from Bikini Island,another on living on and obtaining all subsistence crops from Eneu Island. Other patterns consisted of various combinations of housing and subsistence crops from the two islands. The terrestrial pathway con tri - but es the greater percentage, extern al gamma exposure contributes the next highest, and inhalation and marine pathways con tri - bute minor fractions of the total whole body and bone marrow doses. The radio nuclides con tri - but ing the major fraction of t h e dose are 'OS, and 137Cs. All living patterns involving Bikini Island exceed federal guidelines for 30-yr population doses. The Eneu Island living pattern leads to doses that are slightly less than federal guidefor Bikini Atoll lead to higher doses than those on the southern collected on previous trips to the atoll.islands at Enewetak Atoll. Purpose of the 1975 Bikini Survey Bikini Atoll is one o f two sites i n were used by the United States as testing the northern Marshall Islands that grounds for the nuclear weapons

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program from 1946 t o 1958. The Bikini people, since their initial relocation to Rongerik Atoll in 1946, have had a continuing desire to return to their homeland; so in the latter part of the 1960's, the first steps toward re habitation of Bikini Atoll were taken. I n 1969 a general cleanup of debris and buildings began a t Bikini Atoll. Concurrently, scrub vegetation was cleared from Bikini and Eneu Islands,the two major reside n - ti al islands of the Bikini people prior to their relocation(see Fig. 1). An agricultural reclamation program was initiated with the planting of coconut trees on Eneu and Bikini. Additional subsistence crops of breadfruit, Pandanus fruit, papaya, and banana were planted on Bikini Island. To facilitate resettlement, 43 houses were constructed on Bikini Island between 1969 and 1974. A second phase of housing w a s planned for the interior of Bikini Island ; ' however, preliminary data indicated that the external gamma dose inthe interior of Bikini Island might be higher than in other parts of the for the location of second phase housing at Bikini Island that would Fig. 1. Map of Bikini Atoll.

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minimize external exposure, a survey of Bikini Atoll was proposed. plans called for aerial surveys to determine external gamma levels on all islands in the atoll along with ground surveys using scintillation counters and thermoluminescent dosimeters Blkini and Eneu Islands, the prime residence islands. In addition, there was to be a rather large scale effort to sample the soil and vegetation to evaluate the potential dose via the terrestrial pathway. It was felt that this was an especially important goal in view of the significance of the contribution of the food chain to the total dose estimated at Enewetak Emphasis was to be placed on For a number of reasons, the scale of the program had to be reduced from that originally planned. Manpower and support were reduced, and the aerial survey was temporally deferred, leaving the entire program of measuring the external dose levels on Bikini and Eneu Islands to be accomplished by reduced effort was toward the external gamma measurements on Bikini and Eneu Islands. Although the sampling of the food chain pathways was less extensive than we had hoped, we maintained a smaller scale program designed to help assess the potential dose via ingestion pathways. The 1975 Bikini survey was conducted with the help of 20 peoThe emphasis of this port of the ERDA Research Vessel, Liktanur, from June 16 through June 2 4 , The basic plans for the 1975 Bikini survey are outlined below. SURVEY PROGRAM OF BIKINI SOIL AND GAMMA EXPOSURE RATE Survey of Gamma-Exposure Rate The program for the measurement of gamma-ray exposure rates conducted on the ground was designed to examine in detail the geographical variability of the exposure rates on Bikini and Eneu Islands, and verify exposure-rates measured during previous visits. Methods and Measurements tor, which consists of a 2.5-cm-diam ratemeter readout was used. The instrument was calibrated with a 1 3 7 C ~ point source in the primary calibration range of the National Environmental Research Center, Las Vegas, Nevada. While the response of this instrument is energy-dependent, our experience at Enewetak showed that this was not a serious limitation because of the dominance of 137Cs in the radiation background on the atoll. tion chamber. The current produced by the radiation-induced ionization within the chamber is measured by a sensitive We also used

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electrometer with a digital readout. The instrument exhibits a flat energy response over all gamma-ray energies of interest to this survey. It is capable of measuring exposure rates from approximately 1 to 200 pR/hr with an accuracy of about 5%. Thus, the data from this instrument were used as a reference for measurements by other Exposure rates at 1 m above the ground were measured with the NaI locations on a 30-m rectangular grid on Bikini Island and at about 120 locations on a 120-m grid on Eneu Island. The ionization chamber was primarily used for measurements within the central section of Bikini Island with additional measurements made at selected areas. Thus, from this program a very comprehensive picture of the gama-ray exposure rates at both islands is available. Thermoluminescent dosimeters (TLDs) provided a third technique for evaluating the external dose. A complete report on the external g m a measurements and resulting dose assessment has been The soil sampling program was designed to identify the primary radionuclides contributing to the external gamma exposure and to determine the geographical distribution of these radionuclides in the soil on Bikini and Eneu Islands of the Bikini Atoll. This sampling program was integrated with previous programs to avoid duplication of effort. The actual number of samples taken and their specific collection sites were determined by expected activity levels, plans, and the number of locations of recent soil samples collected by other Methods and Measurements Two types of soil samples were collected for analysis: a 15-cm deep, and a profile collection based upon sidewall sampling in a trench in which samples of 100-cm2 area were collected at 15-cm-depth increments to a depth of 90 cm. To pian the survey, Bikini Island was divided into the north, central, and south sections along the respective second baseline roads. Eneu was divided by the airstrip into the north and south sections. The approximate numbers of surface and profile samples collected within these sections are given in Table 1. Note that a major fraction of the surface samples were collected within the central section of Bikini Island. This was because of the higher and more variable gammaexposure rates in this area and the fact that a major fraction of the returning Bikinians are likely

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Table 1. Distribution of soil sample locations on Bikini and EneU No. of sample Surf ace Profiles 2 00 4C entr al section South of second 25 2 t o live in this section.A limited number of profile samples were planned in this area because several samples were collected during previous surveys. The north and south sections of Bikini Island and allof Eneu have lower contamination levels; hence, t h e sampling density was lower. Special emphasis, however, was given t o the lagoon side of both islands since homes may also be erected in these The exact soil-sampling locations were determined by ar and m selection process to obtain statistically meaning ful and unbiased results.Special samples were also collected within "hot spot " areas and other areas of special interest. The samples were placed in plastic bags with ident if i - cation tags and prepared for shipment t o LLL where they were processed and analyzed by gama spectroscopy. Sample s were analyzed for 239 > 240pu and by wet chemistry methods a t report on the analytical procedures BIKINI GROUND WATER PROGRAM The ground water program was designed to establish a network of well locations on Bikini and Eneu Islands to assess the ground water quality and to study systematically t h e hydrology and geochemistry of radio nuclides and major and trace elements inthe ' groundwater system. Water movement and residence times were t o be assessed to deduce the transport rates and mechanisms of radio nuclides deposited in the soil zone or taken up by vegetation. Methods and Measurements Pits were dug witha backhoe tothe hard coral layer ; the ground water reservoir surface w0s approximately 2 m below the ground surface. holes were drilled with a ground power auger at selected locations along the center lines of Bikini and Eneu Islands. The auger penetrated the ground water lens to a depth of approximately 1to

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pipe that was extended to the soil minimize impact on the environment. Each hole was cased with slotThe pits were backfilled to The first hole was located near the water was measured with an in situ conductivity probe. Two holes were then drilled on opposite sides of the center hole and the salinity measured wells, filtered, and sampled. Radionuclides, major elements, nutrients, and bacteria were measured at the Lawrence Livermore Laboratory to provide data for water quality. wells were pumped continuously during a day and sampled serially to determine changes in water quality as a function of usage. The salinity of the Water was pumped from the The well network is available for resampling. On subsequent trips to the atoll we plan to assess thoroughly the dynamics of radionuclide cycling in the ground water reservoir and to maintain a surveillance of the water quality. The program operation was fashioned after our Enewetak ground water study, and comparison of the data from both atolls should be especially valuable for predicting the mechanism and rates of cycling of the constituents in ground water at Pacific Bikini and Eneu ground water sampling and analysis has been published. A complete report on the The main thrust of the program was to determine radionuclide concentrations in food species, to correlate these with soil concentrations at various depths, to determine nuclide availability to plants in the coral soils, and to relate the radioactivity in food species to that in indigenous nonfood species that have the potential to serve as indicator species. The unique information that this survey provided is: concentration factors for detectThe relationship between food species and nonfood species at radionuclide concentration in the vegetation, and A data base for assessment of terrestrial food chain transfer of radioactivity from the soil uation following resettlement of Methods and Mea surements The sampling program consisted of the integration of a series of samples of food species with soil profile samples obtained on an ad hoc, available species basis. All food species growing and bearing fruit on Bikini

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were sampled. A broader sampling program based upon the widely available natural species, Messerschmidia and ScaevoZa, was also carried out to determine the intra-island variations in the radioactivity of the vegetation. Soil profiles were obtained from the root zone of each tree that was sampled to determine the concentration of radioactivity in the root3011 environment. Both leaves and fruit were sampled so that leaf-tofruit concentration ratios could be calculated. Nonfood species were sampled in the vicinity of food species to provide information on species variation in radionuclide uptake and to evaluate the use of concentrations in nonfood species when no food products are available for analysis to predict the impact of human intake. This approach was developed in the Enewetak survey because of the paucity of food species on the atoll. The soil sampling results and the concentration and correlation factors developed from the plant-soil data have been published This program along with the ground water program supplies the data base mitment via food chains and rehabitation of the atoll, BIKINI A I R SAMPLING AND RESUSPENSION Because of limited support facilities, manpower, and time and because of other program demands for air sampling equipment resulting from delays in fielding the Bikini survey, no attempt was made to establish an air sampling program during this sunrey. Upon completion of the field survey in June, nearly 1000 samples including soil, vegetation, animals, and water were returned to LLL for processing and analysis. Because of funding problems, the processing of the samples was not begun until late September; processing was completed by early November 1975. Sample processing is discussed in detail in Ref. 3. The time required to analyze these samples was considerable and was incorporated into a priority framework involving other programs, In addition, funding problems prevented analysis of all samples, so time was required to establish priorities for samples that were sent for analysis. As data became available and as assessment activities began, additional samples that were of. particular importance for assessment purposes were identified. When limited additional funding became available in the summer of 1976, second priority samples were sent €or analysis and incorporated into our assessment. Our data bank for the samples that were analyzed was completed in October 1976.

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REPORTING OF RESULTS The results of this survey are present ed in a series of reports, each dealing with a specific area. The reports covering the 1975 Bikini SurEstimates f o r Future Bikini Atoll Inhabitants, Lawrence Livermore Laboratory, Rept. Analytical Program: 1975 Bikini Radiological Survey, Lawrence Livermore Laboratory, Rept. of the Radionuclide Concentrations i n SoiZ and Plants from the 1975 Terrestrial Survey of Bikini and Eneu Islands, Lawrence Livemore Laboratory, Rept. Evaluation of Radiological Quality of the Water on Bikini and Eneu Islands i n 1 9 7 5 : Dose Assessment Based on In it kl Samof Bikini Atoll, Lawrence Livermore Laboratory, Rept. Annual Doses and Body Burdens medieted for Bikini and Eneu Islands, Lawrence Livermore Living Patterns and Diet Bikini and Eneu Islands were the two major …