A Reconstruction of Chronic Doses for Rongelap and Utirik Residents - 1954 to 1980 (Possible Draft)

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A RECONSTRUCTION OF CHRONIC DOSES FOR RONGELAP AND UTIRIK RESIDENTS - 1954 TO 1980 BROOKHAVEN NATIONAL LABORATORY ASSOCIATED UNIVERSITIES, INC. Under Contract No. DE-AC02-76CHOO016 with the Unite{l States Department of Energy

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AND UTIKIK RESIDENTS - 1954 TO 1980 From June 1946 to August 1958, the U.S. Department of Defense and Atomic Energy Commission conducted nuclear weapons tests in the Northern Marshall Islands. BWVO, an aboveground test in the Castle series, resulted in radioactive fallout contaminating Rongelap and Utirik Atolls. On March 3, 1954, the inhabitants of these atolls were *relocated until radiation exposure rates declined to acceptable levels. Environmental and personnel radiological monitoring programs were begun in the mid-1950ts by Brookhaven National Laboratory to ensure that dose equivalents received or conunitted remained within U.S. Federal Radiation Council Guidelines for members of the general public. Bodyburden and dose equivalent histories along with activity ingestion patterns postreturn are presented. Dosimetric methods, results, and internal dose equivalent distributions for subgroups of the population are also described.

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On March 1, 1954, at Bikini Atoll, BRAVO, the first of six nuclear weapons tests in tl}eCastle series, was detonated. The BRAVO device caused substantial surface con~amination on inhabited atolls within a 2,00C)-square-mile area. The contaminated region was cigar shaped and included Ailinginae, Rongelap, Rongerik, and Utirik Atolls which lay east of ground zero at distances from 60 to 300 miles. The fallout on Rongelap, initially visible at H+6 hours, had thinned out to the extent that it was no longer seen at H+1O hours (G162). On March 3, 1954, the 64 residents of Rongelap Atoll and 18 residents of Sifo Island, Ailinginae Atoll, were evacuated. On March 3 and 4, evacuation of 157 Utirik Atoll residents also took place.* During the first few weeks and at Q least once every year from 1957 to the present, a Brookhaven National Laboratory medical team, organized by the Department of Defense and by the Atomic Energy Commission and its successor organizations, has provided medical examinations to monitor the health of the persons initially affected by the fallout from the nuclear testing program, plus a control population. Reports of their findings are The Utirikese and Rongelapese returned to their home atolls in June 1954 and in June 1957 respectively. The earuer repatriation of Utirik Atoll was based on the Ibw level of external radiation exposure measured after the initial 3-month observation period (March to June 1954). The Utirik population was not examined by a Brookhaven medical team until March, 1957, when 144 people received compcehenslve physical examinations. Following the 1957, medical survey, two men, removed from Utirik for medical reasons, were whole-body counted at Argonne National Laboratory and provided urine samples for radiochemical analysis of 1J7CS. Four persons visited Argonne from Rongelap and, in addition,

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pooled urine sam~les from both atolls were analyzed radiochemically for 137CS and 9oSr. Subsequent Brookhaven National Laboratory expeditions by qembers of the Medical Department and Safety and Environmental Protection Division utilized whole-body counting and radiochemical analysis of urine and blood samples to identify and quantify the radionuclides that were present in the body. The results of these radiological measurements are given in te~s of body-burden in Tables 1 and 2. Throughout this paper the units of quantities are S1 derived and those which are accepted for use with the S1 for the time being. ThUS both the ~urie and the Becquerel may be used as units for the quantity activity. The aforementioned body-burden tables illustrate adult mean values for Rongelap and Utirik. An adult, as classified here, was a person over 16 years of age. The mean body mass in this age interval was 60 kilograms. The observed body mass versus age distribution is shown in Figure 1 for Rongelap residents. The same body q ass versus age distribution was observed at Utirik. Because of the paucity of measurements at Utirik, information on 60C0 $ 65Zn, and 55Fe was in some instances derived from the ratio of adult mean body burdens between Rongelap and Utirik. A mean ratio of 2.6 was observed in body ? Cs after they reached their maximum values. The standard deviation of this ratio was 15%% In the following analysis”, personal body-burden histories and residence intervals, in conjunction with contemporary dosimetric models, are used to estimate internal dose. Dosimetric distributions were constructed from the results and a sunxnary of the derived activity ingestion rates and dose equivalents was provided for various subgroups of the population. Additionally, exposure rate history curves were constructed for each atoll for the period following the

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Ronge lap Body Burden* Adult Males Mult Females Adultn Body Numb er Body Number Body Number Days Post Burden of Burden of Burden of NA = Not available

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Adult Hales Adult Femalen Adults Body Number Body Number Body Numb l r Days Post Burden of Burden of 3urden of Rccurn NA - Not available l = Heasured at Argonne National Laboratory .=

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Fig. 1 Body haa l s a Function of A.@ for Reeldenta of Umgelap Atoll

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BRAVO test. These data, together with appropriate conversion factors and living pattern models, provided an estimate of external dose equivalent. Exponentially declining activity concentrations have been face soil for 137C~ 1291 and 90 9 9 Sr from 1954 to the present on and Utirik Atolls. Declining activity concentrations have also in vegetation at a rate greater than that predicted by radioactive decay. Thus exponential decline in dietary activity was assumed and the following general equations were derived.

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time ~st-onset ot uptake, days, instantaneous fraction of atoms decaying per unit time, day-1 initial atom ingestion rate, atoms day-l, instantaneous fraction of atoms removed from compartment i by compartment i deposition fraction, the number of atoms in compartment i relative to the number compartments at the onset ef declining continuous uptake, -1sul)ject urine excretion rate, i day , fraction from GI tract to blood,* fraction excreted by the urine pathway, instantaneous fraction of atoms removed or added to the atom uptake per unit time, day ‘1, due to factors other than radioactive decay, body burden at the onset of uptake, Bq, the number of disintegrations in all compartments occurring during the uptake interval, Bq days. lution integral. At some variable time, T, defined during a fixed uptake interval, T, the daily activity ingestion rate crossing the gastrointestinal tract to blood is given by

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The whole body retention at any time t-T of the fraction of initial radioactivity inputed at time T is Thus, the instantaneous activity at time t-~ that remains following input during It follows that the instantaneous activity at time t-T that remains following input during T is The solution of the integral yields a general expression that depends on the user defining t. For example, if t is the fixed uptake interval, T, plus an additional fixed post uptake interval, 0, then the body burden at T + 0 is As previously stated, Eq. (2) appl~ed at for the situation’that variable time t was the Rongelap and Utirik, it was uptake interval. Additionally, persons who returned to the atolls in June 1954 and June 1957 did so with an initial body burden, q“. The behavior of this contribution to body burden, q, was embodied in the q“ temu of Eq. (2). A similar model was used to relate

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urine activity concentration to body burden. Equation 3 was obtained by Equations (1) and (2) were used to determine the dietary removal rate constant KE and then the initial daily activity ingestion rate required to produce the measured or derived body burden. Equation (3) was used to determine the number of disintegrations that occurred in the body during the residence interval of an individual living on Rongelap or Utirik Atoll. If the mean residence time in the””diet is much much longer than the residence interval, then constant continuous uptake is achieved. Equations (1) and (2) can be converted to the constant continuous equations by replacing KE with some cases only radioactive decay may remove the nuclide from dietary items; for these cases KE would equal zero. In the case of the former Bikini residents, the maturing of coconut trees during residence on Bikini Atoll caused a continuously increasing dietary uptake of Cs . Thus, KE was found to have a negative value. In the case of Rongelap and Utirik, KE was found to have a posi9 9 9 l This indicated that in addition to radioactive decay, some other removal mechanism decreased the radioactivity in’ dietary items during the residence interval. For the nuclide 55Fe, only one mea-.*.. of ~ was not possible. KE was determined by using Eq. (1) or (2) and the population subgroup body burdens or urine activity concentrations. A portion of these bioassay are illustrated for adult males and females in Figures 2 to 6. Two consecuurine or body-burden data points were used to eliminate the unknown ingesrate from the equation. This method yields n-1 estimates of KE where n was

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0.50 III III III III III III III III iII RONGELAP ADULT MALE t //!% RONGELAP POPULATION EXCRETION RATE 10.40 - DAYS POST RETURN TO RONGELAP Excretion Jhte l t Rongalap Atoll

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the number of da~a points. An average value of KE was assigned for each nuclide, and the results for the Rongelap and Utirik populations are given in Table 3. For the evaluation of KE from Eq. 1 and 2, radiological and physiological parameters were obtained from the open literature (ICRP59, ICRP68, ICRP69, ICRP79, Ki78). A representative sample of these parameters is presented Summary of Dietary Rate Constants (K=, d-l) N.D. = No data sufficient for analysis. The values of KE were similar fo”~males and females and for residents of Rongelap and Utirik. For ‘0Sr on Rongelap a factor of 2 difference between KE values was observed for males and females. The female parameter for Rongelap Atoll compares with that obtained from the Utirik data. A paired t-test of the Rongelap male and female data indicates that the male/female difference was highly probable and therefore not significant. This difference leads to a

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Compartment Compartment Cl Tract Fract ion DepOs~c ion Ramova 1 co Blood Excreted in Decay Fract Lon Rate Constant Transfer Urine Canstant Progeny Satio

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bimodal activity--ingestion rate distribution for 90Sr in the Rongelap populaData for 60Co and 65Zn were not sufficient for analysis for the Utirik Atoll residents. Values for KE observed at males and females and body-burden histories Rongelap were assigned to Utirik for population subgroups were reconstructed using Eq. 1 or 2. Figures 7 and 8 illustrate the derived mean adult body-burdens for all significant nuclides studied on Rongelap and Utirik. This method provides a best fit of the data shown in Figures 2 through 6,’and provides a body-burden history during the early years post-return at Utirik, a time when body-burden measurements were not made. Actual data points are also plotted to demonstrate the fit. l The curves shown for 55Fe in Figures 7 and 8 were obtained equal to zero. This underes~imated the initial body burdens and future ones. Since 55Fe contributed less than 1.0% to the total lent, an arbitrary assignment of KE based on observed values for clides was not attempted. During 1974, another series of blood samples was obtained from Rongelap and Utirik (C075). Analysis for Fe has yet to be reported. A recalculation of Fe body-burden and its impact on early dose equivalent rates will be conducted when the data is made available. A substantial change in dose equivalent is not G be expected. Figure 4 and Figure 6 illustrate the observed adult histories of Sr and 137Cs mean urine activity concentrations. Mean values for adult males or all adults were plotted. Measured values for Cs body burdens were also shown in Figure 7. A much smoother curve was plotted in Figure 7 and it was determined that the collection and analysis technique for urine samples introduced the additional variations. On the basis of this observation for Cs, a smooth body-

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DAYS POST RETURN Fis.7 Composite Nuclide Body Burden History for Adults l t Rongelap Atoll

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burden cume for 90Sr, reconstructed from raw data and Eq. 1, was considered a more accurate his~ory. A detailed presentation of the greater variation in urine bioassay measurements versus direct body-burden measurements can be found Figure 9 illustrates the variation exhibited in the body burden of 5 randomly chosen subjects over the 25-year variations may have had a dramatic impact illustrates the adult male, adult female, burden for the 25-year exposure period, a seen during the years 1958 through 1963. monitoring period. These individual on the mean data. In Figure 2, which and adult population mean Cs body decrease followed by an increase was Although the Castle BRAVO test initially contaminated Rongelap in March 1954, it had been proposed that the Hardtack Phase I series added to this an am%unt of contamination equal to that responsible for the Figure 2 body-burden pattern (c063). Figure 9 suggests that counted in those years had maintained or declined in bodythe others. Several factors could have contributed to this variation from the mean such as departure and return to the atoll, sickness, the dietary contribution of imported foods, etc. Since the mean values are based on small numbers of persons who were chosen at random! it is conceivable that individuals like 881 M influenced the mean body-burdens to a greater degree than recontamination of the inhabited atolls~ The impact of individual body-burden patterns on the true mean value is moot since the body-burdens of all individuals were not monitored consistently in the few cases exhibited in Figure throughout their residence intervals except

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RESULTS AND DISCUSSION Daily Activity Ingestion Rates Daily activity ingestion rates were calculated for dosimetrically significant nuclides post-return. An exponential decline was proposed for the ingestion rate within a population subgroup and initial reference values are given in Figures 10 through 14 (June 1, 1957, was assigned as a Figure 10 demonstrates the differences in ingestion of tion subgroups. This undulating pattern was exhibited return date to Rongelap). nuclides for which sufficient data existed for analysis. Differences in ingestion rates of the stable element at the same geographic location have been shown to occur among members of a population (ICRP 23). Age-dependent diet studies for ingestion of CS for urban Japan have values varying from 11 Vg d for adults to 8.6 pg d for children. Sr in a westerntype diet rose from 600 Vg d for infants to 690 pg d-1 for 5 year olds to 3,600 pg d-1 for 13 year olds and fell to a mean of 1,900 pg d -1 for adults. Zn in the United Kingdom rose from 2 to 40 mg d , the higher value of Zn being observed in adult tea drinkers. Fe ingestion in a western-type diet has a minimum at age 3 and maxima at ages 1 and 20 years. Co is ingested at a rate of 20 pg d for Japanese adults and half thi-amount for children. ‘l%eMarshallese population also exhibits dietary changes as a function of age. The authors of the Marshall Islands Diet …