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 Brookhaven National Laboratory, Upton, New York 11973 Three body burden measurements of the Bikini Island population were conducted from 1974 to 1978 at Bikini Island. During this time, the mean 137CS body burden of the adult Bikini population increased by a factor of 20. This dramatic elevation of the body burden appears to be solely attributable to increased availability of locally grown food ,products, specifically coconuts Ucts. In January 1979, forty-five percent were whole body counted in April 1978 were and coconut plant prodof the individuals that one hundred and forty-five days after the Bikini Island population departed from Bikini Atoll. These results show that the adult 137population mean Cs body burden decreased by a factor of 2.9 between the April 1978 and January 1979 in vivo 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 Rongerik 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 7S). The exposure of individuals to radioactive fallout 6 to 24 hours post detonation of “Bravo” resulted in external total body gamma dose equivalents ranging from 20 to 200 rem (CO 75). This incident initiated the involvementof 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 R. A. Conard and the Brookhaven Medical Team were expanded to include sick call =d body lmrden 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 populati& were conducted by the latter or-

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Bikini Atoll has not been officially turned over to 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 was 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 National Laboratory Radiological Surveillance Program in the Marshall of internally deposited Islands inciuciesthe quantitative assessment 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 multidirectional. 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 seven, 7.6 cm diameter low background magnetically shielded, photomultiplier 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 ? Co and . The current system was calibrated using an Anderson REMCAL phantom (CO 63). Each phantom’s organs in an amount body concentration as defined To verify the activity in the radionucl~de was introduced into the equivalent to the fraction of the total by the ICRP in Publication 2 (ICRY 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 (WBC) (PA65). 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 beldw 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 7 Cs are listed in Table 1 as are t~- ical 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 *5% 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 non-’Bikiniand Bikini residents. Two point sources were used in the QC program. A 137Cs source, which has been used by the BNL medical surveys in previous years, was used to monitor potential changes in system resolution and efficiency as function of time. A second source, a 137c, + 60Co point source, was used for zero and gain determination. Table 2 lists the 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 (1 nCi) 137CS, we can conclude that the detection efficiency of 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. Finally, two Marshallese subjects were counted for quality control purposes. The first person was a recount to determine the expected variability from counting an individual more than once. The replicate count was within 2Z of the initial count. The second Marshallese subject counted was from Rongelap Atoll. This previous Cs result in April 1977 (14 kBq or 371 nCi) (CO 77). The difference of 22% is close to that which would be predicted from the 12% yearly decrease in the Rongelap population. Tables 3 and 4 present a list of adult individuals who were counted in 1974 (CO 75), 1977 (CO 77), 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 general 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 summarize the 137CS 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 (10-15% 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 137Cs data that is presently available. . It presents the mean (X), standard deviation from the mean (~), and range of values reported for the sampled population. The data are segregated by sex and age. Table 8 compares the observed reduction in 137Cs body burdens from April 1978 to January 1979 with the reduction in 137Cs body burden that was expected as a result of relocating the Bikini Population in late August 1978. Values for the biological removal rate constants were obtained from NCRP Report 52 (NCRP 77) and ICRP

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RESULTS AND DISCUSSIONS The whole body counting data indicate that previous estimates of tb.etype of food and amount of various conpor.entsin the 3ikini 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 forg of jekaru (the water sap of the coconut tree), jekomai (a syrup concentrate make from jekaru) and waini (drinking coconuts).’ The matura- /tion time of the coconut tree is 5-7 years. Consequently, one would expect to observe a steady increase in the Cs body burden through 1978 at which time an equilibrium body burden would be reached. Comparison of the observed reduction in the Cs 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 NCR2 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 ‘wher.zew dietary items like pandanus and breadfruit became available for daily consumption. Furthermore, while the population may have been at equilibrium April-September dietary uptake, individuals within the may not have been in equilibrium. This is appareut in the 137Cs body burden data where two individuals showed no 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 explana1. 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 . 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 activity ingestion rate of level does not include the other internally deposited ingestion of Cs had the April 1978 137Cs continued. Tlnisdose equivalent dose equivalent from external radiation or radioactive material. Removal of the Bikini population from Bikini Atoll eliminated the Cs 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., Erookhaven National Laboratory: Medical Department, for his advice and assistance during the initial setup, preliminary operations and transfer of responsibility for bioassay services to our di-

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co 75 Conard, Robert A., et al, Medical Findings in a Marshallese to Radioactive Fallout, BNL 50424 Upton, New York). Population Accidentally Exposed co 77 Personal Communications with S. Cohn, Medical Department Brookhaven National Laboratory. ICRP 59 Recommendations of the International Commission on Radiological protection (ICRP), Publication 2, 1959, Report of C-ittee 11 on 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 Radiological Protection (ICRP), Publication IOA, 1971, Contamination Resulting from Recurrent or Prolonged Uptakes (Pergamon Press, New Estimate of Total Error Associated with a Whole Body Count Result,

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Handbook of Radiation Measurement and Protection, CRC Press Inc.? Cleveland, Ohio (in press). NCRP 77 Recommendations of 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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Sunmary of System Efficiency and MDLS for Field WBC System Nuclide Energy Efficiency XDL Tine

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

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Canparison of Obsened Versus Expected Reduction Factors Expected Reduction Factor for Adult Males (1) Obsemed Reduction Factor for Adult Bikini Males Expected Reduckiou Factor for Adult Females(2) Obsened Reduction Factor for Adult Bikini Females Expected Reduction Factor for Children Ages 5-14(2) Observed Reduction Factor for Children Ages 5-14 (1) Effective half time obtained from ICRP Publication 10A (ICRP 71). (2) Effective half …