Correspondence, Subject: Whole Body Counting Results from 1974 to 1979 for Bikini Island Residents

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WHOLE BODY COUNTING RESULTS FROM 1974 TO 1979 FOR BIKINI ISLAND Laboratory, Upton, New York 11973 Three body burden measurements of the Bikini Island population were conducted from by a factor of 20. 1974 to 1978 at Bikini Island. During this time, burden of the adult Bikini population increased This dramatic elevation of the body burden appears to be solely attributable to increased availability of locally grown food ,products, specifically coconuts and coconut plant products. In January 1979, forty-five percent of the individuals that were whole body counted in April 1978 were recounted approximately one hundred and forty-five days after the Bikini Island population departed from Bikini Atoll. These results show that the adult population mean 137Cs body burden decreased by a factor of 2.9 between the April 1978 and January 1979 in viva measurements.

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Bikini Atoll was one area used by the U.S. government to test nuclear weapons from 1946 to 1958. Prior to commencement of the testing program, all Bikini Atoll inhabitants* were moved first to Bongerik Atoll and then finally to Kili Island. On March 1, 1954 a thermonuclear device, code named Bravo, was detonated at Bikini The radioactive cloud from this test moved eastward depositing fallout on several of the Northern Marshall Island Atolls: Bikini Atoll (all Marshallese inhabitants had been moved), Rongelap with 64 people, Ailingnae with 18 people, Rongerik with 28 people, and Utirik with 157 people. The Japanese fishing boat Fukurju - Maru (Lucky Dragon) with 23 fisherman aboard was also contaminated (CO 75). The exposure of individuals to radioactive fallout 6 to 24 hours post detonation of “Bravo” resulted in external total body gammadose equivalents ranging from .20 to 200 rem (CO 75). This incident initiated the involvment of R. A. Conard et al. who for the past 24 years has been responsible for the ongoing medical surveillance of the’ inhabitants living on the contaminated atolls, those Marshallese who were initially exposed to the fallout and have moved, and to a control Marshallese population. The medical history acquired by R. A. Conard included total body’burden measurements of radioactive material inhaled or ingested by the Marshallese. This work was performed by S. Cohn et al. (CO

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In recent years (1974 to present), the medical services provided by B. A. Conard and the Brookhaven Medical Team were expanded to include sick call and body burden measurements of the returning Bikini population. Body burden measurements were made in 1974 (CO 75) and in 1977 (CO 77). In August 1977, the responsibility for providing body burden measurements was transferred from the Medical Division to the Safety and Environmental Protection Division at Brookhaven National Laboratory. The 1978 and 1979 body burden measurements of the Bikini population were conducted by the latter or-

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Although Bikini Atoll has not been officially turned over to the Bikinisus, a significant number of Xatshallese reside there; and the population has risen steadily since rehabilitation efforts began in 1969-70. The population, numbering about 138 persons in April 1978, consisted of caretakers and agriculturists employed by the Trust Territory, and other Bikini families who found their way back to their atoll via Trust Territory trade ships. At the time this report tias written the Bikini residents had been moved to Kili Island in the southern Marshalls and to Ejit Island, Majuro Atoll, (September 1978).

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The Brookhaven Rational Laboratory Radiological Surveillance Program in the Marshall Islands includes the quantitative assessment of internally deposited radioactive material in the Marshallese. In, this report , the results of four whole body counting measurements on the Bikini population, that were conducted in 1974, 1977, 1978 and 1979 are presented. Because the body burden measurements were performed by two different organizations, the current experimental design included a cross check mechanism to ensure that previous and current results are directly comparable. The approach to the problem was mu1tidirec tional. First, key detection components were duplicated. Second, the systems were calibrated in the same manner (CO 63). Third, the operational procedures and counting geometries similar, and duplicate counts were made on Brookhaven known body burdens to ensure total system comparabilThe detector chosen for field use by both Brookhaven organizations is a 28 cm diameter, 10 cm thick, sodium iodide thallium activated scintillation crystal NaI(T1). It is optically coupled to seven, 7.6 cm diameter low background magnetically shielded, photomul tiplier tubes. In the current system the signal output from each photomultiplier tube is connected in parallel through a summing box with the combined output routed to a preamplifier/amplifier and

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The PHA data is stored on a magnetic discette, and the results may be analyzed either in the field or at BNL using a matrix reduction, minimization of the sum of squares technique (TS 76). Analysis of NaI(Tl) spectra by the matrix reduction technique requires that the computer library contain individual standards for each radionuclide that is expected in the field measurements and that the field measurements and standards be the same geometry. To accomplish this, a review of the previous whole body counting data (CO 75, CO 77) indicated the need, to calibrate for Yc 9:.i 60 Co and 137Cs. The current system was calibrated using an Anderson BEMCAL phantom (CO 63). Each phantom's organs in an amount body concentration as defined To verify the activity in the radionuclide was introduced into the equivalent to the fraction of the total by the fCRP,in Publication 2 (ICRP 59). phantom prior to use as a standard, an aliquot of the phantom solution was counted on a lithium drifted germanium detector which was ,calibrated with NBS standard sources. The phantom was then counted in a shadow shield whole body counter MC) (~4165). The whole body counting system consists of a stationary crystal and stationary bed. The counter detects radioactive material located principally in the thorax, so positioning of the phantom and the in vivo counting subjects must be as similar as possible. To facilitate reproducible counting geometries, each subject and the standard phantom was positioned such that the central

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axis of the crystal intersected the central axis of the body‘about 25 cm below the sternal notch. The distance between the surface of the bed and the bottom of the detector is 32.4 cm. The total system efficiencies for 4oK, 6oCo and 13'Cs are listed in Table 1 as are typical minimum detection limits for these nuclides. The quality control (QC) program consisted of a cross comparison of the radionuclide quantities estimated to be in the phantom volume versus NBS calibration standards. Agreement between these two activity concentrations is within f5X for all radionuclides,. Other quality control mechanisms employed were repetitive counting of secondary point source standards, multiple counts of Brookhaven personnel and the recounting of certain no&Bikini and Bikini residents. Two point sources were used in the QC program. A 137Cs source, which has been used by the BEiLmedical surveys in previous years, was used to monitor potential changes in system resolution and efficiency as function of time. A second source, a 137cs + 6oCo point source, was used for zero and gain determination. Table 2 li'ststhe results of Brookhaven personnel counted in the field and at the Brookhaven Medical Department Whole Body Counter by S. Cohn. The results of this comparison of WBC data support our thesis that the field counting system produces results that are consistent with prior studies and that are accurate measurements of radionuclide body burdens in people. From the 2 sigma counting error on all data and the lack of the field systems's sensitivity to detect

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less than 37 Becquerels detection efficiency of (1 nCi) 137Cs, we can conclude that the the field system is less than that of the whole body counter at the BNL Medical Department. However, once the activity of an individual significantly exceeds the minimum sensitivity of the field system, the agreement between the results from the two systems is within the 2 sigma counting statistic error. This is seen from the body potassium measurements. trol purposes. The first person was a recount to determine the expected variability from counting an individual more than once. The replicate count was within 2% of the Marshallese subject counted was from initial count.. The second Bongelap Atoll. This 291 nCi) compared well with his previous 137Cs result in April 1977 (14 kBq or 371 nCi.1(CO 77). The difference of 22% is close to that which would be predicted from the 12% yearly decrease in the Rongelap Tables 3 and 4 present a list of adult individuals who were counted in 1974 (CO 751, 1977 (CO 771, 1978 and 1979. There is a general increase in the body burdens of adult males from 1974 to 1977 by a factor of 13.3, and from 1977 to 1978 by a factor of 1.8. The genera1 increase for adult females from 1977 to 1978 was slightly higher than that for males over the same period. In most cases, the 1979 data are significantly lower than the 1978 data with an average reduction in the 137Cs body burden by a factor of 2.9.

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Tables 5 and 6 suaunarize the i37Cs body burden data collected in 1978 and 1979 for children. It must be noted that data reported here are uncorrected for height and weight differences between subjects and the phantom. This will have a minimal effect on adult data (10-l% possible error) (MI 76). Body burdens of the children . reported in Tables 5, 6 and 7 have been corrected for geometric differences between adult standard man and the average Marshallese Table 7 summarizes the 137 Cs data that is presently available. _ It presents the mean (551, standard deviation from the mean (a), and range of values reported for the sampled population. The data are segregated by sex and age. Table 8 compares the from April 1978 to January den that was expected as a observed reduc t ibn in “‘Cs body burdens 1979 with the reduction in 137 Cs body burresult of relocating the Bikini Population in late August 1978. Values for the biological removal rate constants were obtained from NCRPReport 52 (NCRP 77) and ICRP

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The ijholebody counting data indicate that previous estimates of the type of food a&amount of various components in the Bikini diet did not adequately describe the dietary patterns that existed between 1974 and 1978. As certain local food crops, coconuts, became available in 1976, they were incorporated into the diet in the form centrate make from jekaru) and waini (drinking coconuts).' The maturation time of the coconut8/ tree is 5-7 years. Consequently, one would expect to observe a steady increase in the 137Cs body burden through 1978 at which time an equilibrium body burden would be reached. Comparison of the observed'reduction in the 137Cs body burden from April 25, 1978 to January 24, 1979 with the expected reduction in the body burdens from September 1, 1978 to January 24, 1979 yields .almost identical results for the adult male and adult female groups as shown in Table 8. This implies that the Bikini population was at equilibrium and that the body burdens on September 1, 1978 were not significantly different than those measured in April 1978. The child data do not agree with the expected value; however, the difference is not beyond the range of half-times listed in NCRP Report 52 (NCRP 77). Although NCRP Report 52 lists a mean half-time for children ages 5 through 15, it does not specify the age distribution of the sample. Most of the Bikini children (9) were in the 5-10 year category; hence, one would. expect the observed reduction factor for this group to be somewhat higher than the expected value.

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the body burdens would not have increased when new dietary items like pandanus and breadfruit became available for daily consumption. Furthermore, while the population may have been at equilibrium with their April-September dietary uptake, individuals within the population may not have been in equilibrium. This is apparent in the adult male 137Cs body burden data where two individuals showed no decline in activity between the April 1978 and January 1979 whole body count. In one case, the individual was present on Bikini for In the second prior to the April 1978 count. This places the approximately 60% of his equilibrium body burden value. case, there seems to be;no clear explanation for the lack of any reduction in the body burden. Several possible explana- . 1. the individual may have lived away from Bikini prior to the April count; hence, equilibrium was not established at the time of 2. the individual changed his diet pattern between April and SeptemThese deviations from the norm do not alter the conclusion that equilibrium or near equilibrium had been reached for the population as a whole for 13'Cs. Indeed, they illustrate variations about a.

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Finally, the data clearly illustrates that at least 19% of the Bikini residents would have received a dose equivalent in excess of 5m Sv (0.5 rem) due to the ingestion of 13’Cs had the April 1978 activity ingestion rate of 137Cs continued. This dose equivalent Level .does not .include the dose equivalent from external radiation or other internally deposited radioactive material. Removal of the Bikini population from Bikini Atoll eliminated the 137Cs source term from the diet and limited the dose equivalent received by this

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We would like to express our sincere appreciation to Stanton H. Cohn, Ph.D., Brookhaven National Laboratory, Medic81 Department, for his advice and assistance during the initial setup, preliminary oper:ations and transfer of responsibility for bioassay services to our di-

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nal Contamination in a Fallout-Exposed Population", Health Phys. 9, co 75 Conard, Robert A., et al, 1975, a Twenty-Year Review of Medical Findings in a Marshallese Population Accidentally Exposed to Radioactive Fallout, BNL 50424 (Brookhaven National Laboratory, Upton, New York). co 77 Personal Communications with S. Cohn, Medical Department Brookhaven National Laboratory. of the International Commission on RadiologPublication 2, 1959, Report of Committee XI ou Permissible Dose for Internal Radiation; (Pergamon Press, New ICRP 65 Recommendations of the International Commission on Radiological Protection (ICRP), Publication 9, 1965, Report on Radiation Protection, (Pergamon Press, New York). ICRP 71 Recommendations of the International Commission on Radiologing from Recurrent or Prolonged Uptakes Estimate of Total Error Associated with a Whole Body Count Result,

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Handbook of .RadiationMeasurement and Protection, CRC Press Inc., NCRP 77 Recouunendationsof the National Council on Radiation Protection and Measurements (NCRP), Report 52, 1977, Cesium-137 from the Environment to Man: Metabolism.and Dose (National Council on Radiation Protection and Measurements, Washington, D.C.) TS 76 TPOS Operations Manual 1976, Tennecomp Systems, Inc., Oak

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Summary of System Efficiency and MDLS for Field WBC System Nuclide Energy Efficiency MDL Time

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Location Potassium grams 137Cs.NCi 3 2. NA- Results reported without counting error 3. Data obtained from personal communications with S. Cohn (CO 77)

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Bikini 1978 and 1979 WBC Remltr of Children AGES 5 - 10

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Bikini 1978 and 1979 WBC Results of Children AGES 11 - 15

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Sunwnary of 137 Cr Body Burdens for Bikini Inhabitants, 1974 to 1979 Resul ta Reeul t

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Counted Results Rerult Counted ND - No Data available …