A Reconstruction of Chronic Dose Eqivalents for Rongelap and Utirik Residents - 1954 to 1980

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plovrrs, makrsanvwarranm,rxptt.ssor Imphrd, or asaumra any Irgal Iiabtlity or re. Nalicrnal Trchnical Information Service

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AND UTIRIK RESIDENTS - 1954 TO 1980 ,.=. From June 1946 to Au~8t 19581 the U.S. Department of Defense lnd Atomic ‘<~~+ Energy Cmission conducted nuclear weapons teocs in the ?lorthem Marshall Islands. BRAVO, an above~round test in the Caatle serieot resulted in radioactive fallout contaminating Rongelap and Utirik Atolls, Onlfsrch 3, 1954, the inhabitants of these atolls were relocated until radiation e%poaure rates declined to acceptable levels. Environmental and personnel radiological monitoring programs were begun in the mid 1950’s by Brookhaveu Natior;al Laboratory to ensure that dose equivalents received or conmitted remained wi~hin U*SO Federal Radiation Council Guidelines for members of the general public. Budy burden and dose equivalent histories along with activity iIWWtiOn pattern~ POS return are presented. Doeimetric methods, resultst end internal dose equiv{ilenc “:; distributions for subgroupe of the population ere also deecribed,

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surface contamination on inhabited atolls withxn a 2$000 square mile lrea. l%. .(;&$ contaminated region was cigar shaped and Included Ailxngmaet Rongelapt Rongerik,’ and Utirik Atolls which lay esat of ground zero at distances from 60 v:v~ thinned’out to the extent that it waa no longer @een at li+10hou>/’{}G162). ; 2 On March 3, 1954, the 64 residents of tingelap Atoll lnd’18 residents of Sifo Island$ Ailinginae.Atollt were evacuated, On March 3 lnd 4, evacuation of 157 Utirik Atoll resideats also took place. Wring the first few weeks and at medical team~ organized by the Department of Defense and by the,Atomic Energy monitor the health of the persons initially lffected by the faliout from rlie n The Utirikese and Rongelapese returned to their ~=e at~lls in June 19 and in June 1957 respectively. The earlier repatriation of’lJtirik Atoll wtiu ~,.Ji:,.;$. based”on the low level of external radiation exposure measured 8fter the i.~litial”;$ 3 qonth observation period (M8rch to June 1954). ?%. ceived comprehensivephysical examinations. Following the 19571 medical ~~lney$f- , ..... two men, removed from Utirik for medical reasonst were whole body counted nt ~.+y; Argonne National Laboratory and provided urine samples for radiochemical nl~al- ~~

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sul~,~i,of these radiolo ical meaeure-nto lre given in terms of body burden in lnd those which are ac,cf W for use with the S2 for the time bein&, Thus b the ~{:ie and the,Becque~’tl,~~y be used l units for the qtmtity’aativity, of a~e. The,,meap body mess in this lge interval was 60 kilogrxme. The obae ,,Becauae of the paucity of measurements lt Uti+cr! inforutiou on burdens between Rongelap and Utirik, A mean ratio of 2.6 waa obeerved standard deviation of this ratio was 1S%. ,..,,, L(t,,’ 1., .Xn the following analysis, personal body burden histo~ies &ti re mate internal dose, Dosimetric distributions were constructed from the results, :, , ,,., and a suusaaryof the derived activity ingestion rates and dose equivalents was provided for various sub$roups of the population. history curves were constructed for each atoll for Additionallyt exposure rece the period following the

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.- Fig, 1 Body Mass as a Function of Age for Residents of Rongelap Atoll

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pattern models, provided an qotimate of exterrUl dosoequivslent, face soil for .... a rate greater thm that predicted by radioactive’decay” laumed and the following

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instantaneous frection of atoms removed from compartment.i by compartments ltkthe onset of declining continuous uptake$ (t=o)~ subject urine excyetion rate, & day-lp ,,-/ instantaneous fraction of ltoms removed or added to the ltom uptake the number of disintegrationsin all compartmentsoccurring’durinfi The developmentof Eqs. (I)j (2), and (3) was baeed on the following col!vo- ~:~~ lution integral. At some variable time, T, defined during a fixed:’uptake ,::,4L interval,T} the daily activity ingestionrate crossing the gastrointestinal ;;;$ tract to blood is given by .-’,

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As previously statedt ~p (Z) applied at for the situation that variable time t was the persons who returned to the ltolls in June 1954 and June 1957 did so vith an ini- ‘i.~ tial body burden, q“. 4 The behevior of this contribution to body burden? ~:i ~, was embodied in the q“ temof Eq. (2). 4

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Equations (1) and (2)uere used to determine the instantaneous fractiol~ of ltoms removed or added to the ltom uptake per unit time? ~? lnd then the initial daily activity ingestion rate required to produce the measured?.or derived body burden. Equation (3) was used Co determine the numlw of’disintegrations on Ftongelap or Utirik Atoll, If the mean reeidencetime in the diet is rmich emch long~r than the resi- j~:~ some cases only radioactive decay may remove the nuclide from/~i$@y. items; these cases ~ wmld equal mro, In the caae of the fo the meturing of coconut tr.e~ during residence on Bikini :~’o’ll~cauoed a con-’ tive value. In the case of) Rongelap and Utirikt KE was found to have a positive ‘}: value for 7 ? Cor and Sr. This indicatedthat in lddition to radioactivedecay, some ocher removal mechanism dpcreas~d,.theratipactivity dietary items during the residence interval. For the nuclide Fe, only olte mea- . I(Ewas determinedby using Eq* (1) or (2) and the populseion subgroup mean ,~iif body burden or urine activityCOnCt?IItrathI. Portion# of these bioaaeay data ‘“:? are illustratedfor adult males and females in Figures 2 to 6, Two consec[ltive “~jj urine or body burden data points were used to eliminate the unknown ingestion

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DAYS POST RETURN I Fig. 3 Mean Adult 65Zn Body Burden History at

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102 DAYS POST RETURN Fig, 4 Nean Adult ‘“sr urine Activity Concentration History at Rongelap Atoll

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RONGELAP ADULT MALE F’ifl.3 Mean Adult Sr Urine Activity Excretion Rate at Rongelap Atoll

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DAYS POST RETURN 6 Mean Adult Male 137Cs Urine Activity Concentration History at Rongelap

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rate from chlf equation. This method yields n-l estimates of KE mere n wan the number of data points. An average value of 1$ was assigned for each n(lclidet and the results for the Bongelap and Utirik populations are given il} Table 3. For the evaluation of ~ from Eq. I and 27 radiological and The VtllUf?R Of KE were similar for males and females and for residentsnf RongelapfindUtirik. For 90Sr on Rongelap a factor of 2 differencebetwe!’1~KE values was observed for males and femalea. The female parameter for fton~f’iap Atoll compares with that obtained from the Utirik data. A paired t-test (1 the Rongelap male ond female data highly probable and therefore not significant. This difference leads to ;!

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Date for 60 Co and 65 Zn wore not aufficiont for analysis for the Utirih Atoll residents. Values for KE observed at Rongelap were aasigned” to Utirik males and females and body burden histories for populationsubgroupswere reconstructedusing Eq. 1 or’2. Figures 7 and 8 illustratethe derived meal] adult body burdens for This method provides a provides a body burden best’fit of the dat? show in Figures 2 through 6, ai)d history during the early years post return at Utirik, o time when body burden measurements were not made. Actual data points are al~o plotted to demonstratethe fit, . The curves shown for 55~e in Figures 7 and 8 were obtained by setting 1(E equal CO zero. This underestimated the initial body burdens and overestimated future ones, Since 55 Fe contributed less than 1.0% to the total dose equiv~ lent, an arbitraryasaignmsmt of KE based on observed values for the other :tlclides was not attempted. obtained from Rongelap and During 1974? another series of blood samples wafi Utirik (C075). Analysis for 55 Fe has yet to be of ‘5 Fe body burden and its impact on early dose equivalentrates will be conducted when the data is made available. A SUhf7(.:!?ltial change in dose equivalent is not to be expected. Figure 4 and Figure 6 illustrate the observed adult histories of St and adults were plotted. Measured values for Figtlre7. A mucl) smoother curve was plotted in valuea for adult males or ,711 body burdens were also show!~in Figure 7 and it was determi~l~(l that the collectionand analysis technique for urine $amplea introduced the :!ddiC)n the basis of this observation for 137

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more accuratehistory, A detailed presentation of the greater variation in radiochemical analysis of urine versus direct body burden meacuraments can be Figure 9 illustrates thp variation exhibited in the body burden of 5 randomly chosen subjectsOVSF(the 2S year monitoring period. These individual variation may have had a d:$patic impact On the’ maan data, In Fi@we 2, which burden for the 25 year expoourc pariod? l decrease followed by ln increaoa wan seen during the years 1958 through 1963, Although the, Castle BRAVOteet initially contaminated Rongelap in March 1954s it had been proposed that the Hardtack Phase I series added to this an’amount of contaminationequal to that responsiblefor the Figure 2 body burden pattern (C063).~ Figure 9 suggests that most individualscounted in those years had body burdeno which remained the snrne differently from the others, Several factors variation from the mean such as departure and dietary contributionof imported foods, etc. could have contributed to thic Since the mean values lre based on small numbers of persons who were chosen at randaa, it is conceivable thiit individuals like 881 M influencedthe mean body burdens to a grester degree than recontaminationof the inhabitedatolls. The impact of the individualbody burden pattern on the true mean value is moot since body burdene of all individuals were not monitored consistentlythroughout their residence intervals excrpt in the few cases exhibited in Figure 9.

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DAYS POST RETURN Fig 9 L[dividualNale and Female Body Burden Histories Randomly Chosen From The Rongelap Atoll Population

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Daily activity ingestionrates were calculated for doaimetrically significant nuclidea post return. An exponential decline was proposed for the inges= tion rate within a population subgroup and initial referencevalue. are given in Figures 10 through 14 (June 1$ 1957? was assigned as a return date to Rongelap). Figure 10 demonstrate the d~fferences in ingestion of 137 Cs for varioue population subgroups, This undulatingpattern wao exhibited by 137 90 nuclidea for ‘whichsufficient data existed for lnalysis, Difference in ingestion ratee of the stable clement ltthe same geographic location have been chown to occur lmong members of l ~opvlation (ICRI’ 231. Age dependentdiet studies for ingestion of Cs for urbap’~ipan have valol?n in the United Kingdm rose from 2 to 40 mg d-l) the higher ~lue of Zn being observed in adult tea drinkers. Fe ingestionin a western type diet has a minimum at age 3 and rnaxha at age. 1 and 20 yeare. Co is ingested at l rate of 20 pg d for Japanese adults and half this amount for children, The tfarohalle~o population also exhibits dietary changes aa a function of lge. The authors of che Marshall Islandsdiet and Living Pattern Study (Na80) obeerved coconut ~fil) being used as a mojor food supplement for infantatand later in adult life efi.1 major source of daily fluid intake. Since coconuts and coconut tree sap providcd the major source of Cs on Bikini Atoll (Le80, Hi80)t the shape of Fig ure 10 was n agreement with the observed diet pattern.

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10 Age and Sex Group Mean Values For Activity Ingestion Rate Referenced TIJMid 1957 for Rongelap Atoll

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Males (D) Adult Females (E) Young Adults on RongelaP - Referenced to June 1957

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Fig, 12 Age and Sex Group Mean Values For Mid 1957 For Rongelap Atoll

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deviation observed for the adult activity inge#&ion rete diatribuof the mean valueP 39% of the mean value for young ldultav 48% for 38% for childrenp and 54% ‘forT’infanta. ) Adolescents lnd infanta versus coconut sap supplements would have contributed to the g?qater variation ob$erved in infants. Adoleacenta and young ldults were the po~lation subgroul)s which have been observed to move frequently between leo~ls. This mobility would those observed in the more @tation8ry population 8ubgrOupqs Figure 12 also exhibited ~ wave pattern; however, a distinct difference l}eRongelap ~esidents and were referencedto June observed for the riistribucionawhich contained difference in &he 90Sr dietary rate constants, illdicntedthat the observed differencebetween both sexes, lgain reflecting f}!{! Data from uri,ne bioassay the male and femmle valuee fol I’E Figure 1. shows the individual data calculated for 137CS for lll buplai~ residentsand is referencedto June 1? 1957. The individualmexk 137Cs daily activity ingestionrate was lpproximately 4 times the population ~an value. twcen roles and females was iadicated. Zhis difference arose from the use ~f veiues for KE listed in Tabl’e3 which were derived from urine data for aule and fenule residentsat RongelapAtoll. Its major impact was on the dooe equival~l!t r~re, not on the total dose equivalent;and its effect wa# to cauae the dose eq!livalent rete for males to rise and decline more rapidly than for finales, was not significant. A t-test was performed for consecutiveurine measurement dato during the 23 year residenceinterval. ‘I%eresults indicate that becau~e

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equivalents were not significant, or rate histories for adults on ‘Rongelap. k curve was’’drawn be’tween’’pointep and the appearanceof an increaa~ng Ca ingestion rate’during’’the’’1960s”indicatedtcd the possibilityof anothercontaminatingevent, ,, The Hardtack Phase Z series was conductedjust prior to the observed increase@ the curve and fallout from the cactus, Yellow Woodt and Hickory experimentsdetonatedat Bikini and Enevutak would have reached $tongelap. However, oevsral observation fail to eupport thv conclusion that recontamination was aignificantt ‘fheee aretas foliowet 1) tll[~ increase in 137Cs ingestionrate waa not in conjunctionwith ah’inc’rkaseof 65Zn; however, since 65Zn is an activationproduct it may have not been produrcl in the same proportions. 2) The peak 137 Cs body burden at Utirik occurred nearly three years after the initiatingevent? Caetle BWVO, while the peflk bo:lv burden at hngelap followedsix years after the potentiallycontaminatingexp~riments of the Hardtack series in 1958. 3) The activity ingeetionrate at Utirih demonstrateda continuously declining pattern vereue the humped pattern observed at Rongelap, This occurredeven though there wae an equal external exposure rate history followingthe Hardtack series as measured by the U.S. Public Heal(l) Service on both Rongelapand Utirik (Un59). 4) The peak expoeure rate on Rongelop followingthe Hardtack series was 10,000 times less than the peak ex~Jusure rate followirlgBRAVO. These facts suggest that the Hardtack series was Tloi a m<ljorfactor influencingthe Rongelap body burden patterns. Thus it is postu]atcd that b~dy burden variationswere caused by travel away from the at”ll

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uous uptake model was used. .:~!,. 15 equilibriumdose equivalent rate to the total body per unit body The approximatenature of the estimatewa& due to the lssumption that the radioactiveatoms were distributedamong the body tissues as they would be fol-= lowing constant continuousuptake for periods of time much greater than the m~at] residence time for the total body. In the case of 90Sr, 86% assumed . These assumptionswere not used in the estimate of equivalent. In adclition,since mean adult body burdens were the total dose of 1.2 was needed to adjust for difference in body mass relative to a 70 ki~ff’- grnm adult. Table 5 lists values of I which were determined from information given in ICRP59 anticorrected for body masa differences.

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per Unit Body Burden Figure 15 illustratesthe relative contributionto the Gmpaite dr)sc elide. For the average Rongelap adult? the residence interval be8in$ JUTW 1) 1957; however, many adults were reported to have resettledduring the ne(! 3 to : 6 nmnths (Co80b). The compositedose equivalent rate indicatqd that a h~t~~)d maximum …