Dosimetric Results for the Bikini Population

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DOSIMETRIC RESULTS FOR THE BIKINI POPULATION Safety and Environmental Protection Division Brookhaven National Laboratory Upton, New York 11973 During the mid 1940 ' s through 1958, the United States conducted high yield weapons tests at Bikini and Enewetak Atolls, These areas were contaminated with fallout from the tests.A restoration program, concentrating on the main residence islands of Bikini and Eneu Islands at Bikini Atoll, began i n 1969. Approximately thirty Trust Territory residents including some former Bikini Atoll inhabitants participated in the initial cleanup and redevelopment of the Atoll. During subsequent years,the Bikini population increased to some 140 individuals at the time of their departure in August 1978. Between 1969 and 1974, scrub vegetation on Bikini and Eneu Islands was cleared and indigenous food crops were planted. These crops consisted mainly of coconut, pandanus and breadfruit trees but included a garden development where squash,papaya, bananas and other crops were grown (RO 77). During the maturation interval for most of the tree crops (5-7 years),the majority of the food consumed on Bikini Island was imported by Trust Territory supply vessels. AS the local vegetation developed,the diet became less restricted to imported foods so that by 1978, the diet contained substantial quan zi -

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Bio as sy and external exposure monitoring programs were initiated for Bikini Island residents in anticipation of the changing dietary situation, and with the realization that it was essential to do personnel monitoring on those individuals living on Bikini Island. Extensive external radiation monitoring was performed in 1975 through the joint efforts of Brookhaven National Laboratory and Lawrence Livermore Laboratory. Data were collected using an en v iron - mental ionization chamber to quantify exposure rates,portable NaI scintillation survey meters t o map the external radiation fields,a portable gamma spectroscopy system to define the major energy components of the external field and to determine energy dependence corre c - tion factors for the ion chamber, and L iF thermo luminescent dosimeter s to measure long term integral exposures.External exposure estimates were developed based on these measurements and a n assumed living pattern (GU 76, GR 79). Urine samples for radio nuclide bio as say were collected during BNL medical field trips to Bikini between 1970 and 1976 (CO 75, unpublished results).This program was reinstated by BNL Safety and Environmental Protection Division in 1978 with systematic 24 hour urine collections from all adult Bikini an s.Urine bio as say results were used to calculate ''5,- and 137cs- 137mBa body burdens and resultant radiation dose equivalents for all Bikini an s from whom a satisfactory urine sample was obtained. Whole body counting was performed i n 1974 and 1977 by the BNL Medical Department (CO75, CO 77), and the program continued in 1978

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Environmental Protection Division along with counting of former Bikini Island residents tor Majuro Islands, Majuro Atoll, and on radio nuclide body burdens was accomplished with a trailer - mounted shadow - shield whole body counter. Dose commitments were calculated from the measured body burdens for many persons residing at Bikini Island during the years 1969 through 1978. In addition to retrospective dose equivalents, whole body counting and bio as sy techniques provided the database from which dose equivalent commitments were calculated. These calculations,to - get her with external radiation measurements,provided a complete as - ses s ment of dose to the Bikini population from chronic exposure to im - port ant fallout radio nuclides in their home atoll environment. In the following tables,the dose equivalent during the residency interval and dose equivalent : commitments to bone, bone marrow and the total body a represented. The mean for the dose equivalent and dose equivalent commitment was determined from individual data points which represent a wide distribution of residence intervals. The mean value corresponds to the mean residence interval(years)for the population described.Residence intervals were determined through verbal interrogation of participants in the personnel

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Tables1 and 2represent the bone and bone marrow mean doses and ranges in mRem which were the result of ingesting 9oSr-90Y during the residency interval. These data were derived from measured urine activity concentrations during the uptake period.Constant conti nu - o us ingestion of activity was assumed inthe models used to calculate the dose equivalents and dose equivalent commitments. Table3depicts the external dose equivalent resulting from liv - ing on Bikini Island. The dose equivalent during the residency inter - val varies for subgroups within the population according to the assumed living patterns elected.Since these values were obtained from ion chamber measurements and hypothetical living patterns, no range of results has been provided.In this report, one Roentgen i s assumed equal to one Rem. Table4presents the average whole body doses due to the in ges - tion of I3’Cs. Data were derived from whole body counting measurments made in1974, 1977 and 1978. Constant continuous uptake of Cs in the diet was not assumed. For these calculations,the uptake period was divided into three intervals during which the137C ~ activity ingestion rate for a given interval remained constant,but increased stepwise with time to account for observed increases in Table5 summarizes the total body dose equivalent during the residency period from internal137Cs and man-made external radiation, and the total body dose equivalent commitment upon departure from Bikini Atoll in August 1978.A standard deviation for these quant i -

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ties of approximately ? 40% ofthe mean was observed in adult subgroups.Internal dose equivalent distributions in figures one through three were constructed by first calculating mean daily act iv - it y ingestion rates for different subgroups of the Bikini Island population based on the individual measurement data from which Tables 1, 2 , and 4 were derived.Secondly,these mean activity ingestion rates and individual residence inter al values we used as input data to mathematical models applied to inhabitants who did not participate in our personnel monitoring programs. gimes for the uptake,retention and excretion of internally deposited radio nuclides.Finally,dos i metric models which allow for constant continuous uptake of 'OS, and stepwise increasing uptake for 137Cs The models describe various rewere chosen to determine the internal dose equivalent and do see qui va - lent commitment for all inhabitants. Thus for residence periods between the years 1969 and 1978,these figures evince a maximally exposed person receiving a whole body dose equivalent and commitment o f 3rem, and a population average dose equivalent and commitment of1.2 rem from man-made radioactivity on Bikini Island. Safety and Environmental Brookhaven National Laboratory

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CO 75 Conard, Robert, A., et al., 1975, A Twenty Year Review of Medical Findings in a Marshallese Population Accidentally Ex posed to Radioactive Fallout, BNL 50424 (Brookhaven National Laboratory, Upton, New York). CO 77 Personal Communications with S. Cohn, Medical Department, Brookhaven Nat iona 1 Laboratory. External Exposure Measurements at Bikini Atoll, BNL 51003 (Brookhaven National Laboratory, Upton, New York). External Dose Estimates €or Future Bikini Atoll Inhabitants, Whole Body Counting Results from 1974 to 1979 for Bikini Island Residendents, Health Physics Journal, in press. "Dose Assessment at Bikini Atoll: UCRL-51879, Part 5, (Lawrence Livermore Laboratory, California).

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List OE Table 'Titles Table 1: 9"Sr-9uY Bone Do sim eC ric Averages for Bikini aris Table3 : Uteriid1 Totdl Uady Dos i metric Average for Bikini an s Sources for E'oniier Bikini Residents

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List of Figure Cdp t ions Figure 1: Total Male dnd Fondle Distribution of Dose Equivalent (During dnd Post Residence) or Residence Interval for Figure2 : Total Male Distribution of Dose Equivalent(During and Post He s it le rlc e) or Residence Interval for Inhabitants of Bikini lsldiid, Bikini Atoll Residence)or Residence Interval for Inhabitants of Bikini

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Fig. I . TOTAL MALE AND FEMALE DISTRIBUTION OF DOSE EQUIVALENT (DURING AND POST RESIDENCE ) OR RESIDENCE INTERVAL FOR INHABITANTS OF BIKINI ISLAND, BIKINI ATOLL

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R AD IAT ION 1000 2000 3000 0 1000 2000 3000- 0 DOSE EQUIVALENT (mRem) DOSE EQUIVALENT (mRem) Fig. 2. TOTAL MALE DISTRIBUTION OF DOSE EQUIVALENT (DURING AND POST RESIDENCE) OR RESIDENCE INTERVAL FOR

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RAD IAT I ON R AD IAT ION AND POST RESIDENCE) OR RESiDENCF INTERVAL. FOR INHABITANTS 3 F BIKINI IS LARD. 31KIM' ATOLL