Dose Assessment Activities in the Republic of the Marshall Islands

Paper DOSE ASSESSMENT ACTIVITIES IN THE REPUBLIC NIARSHM.,L ISLANDS ~. L. Sit-non and J. C’. Graham* INTRODUCTION OF THE Ab.wracl-Dose assessments. both ret respective and prospective. comprise one important function of a radiological study commissioned by the Republic of the Nlarshall Islands (RMI) government in late 1989. Estimating past or future exposure requires the synthesis of information from historical data, results from a recently completed field monitoring program. laboratory measurements. and some experimental studies. klost of the activities in the RRH to date have emphasized a pragmatic rather than theoretical approach. In particular, most of the recent effort has been expended on conducting an independent radiological monitoring program to determine the degree of deposition and the geographical extent of weapons test fallout over the nation. Contamination levels on 707c of the land mass of the hlarshall Islands were unknown prior to 1994. The environmental radioactivity data play an integral role in both retrospect} e and prospective assessments. Orre recent use of dose assessment has been to interpret environmental measurements of radioactivity into annual doses that might be expected at every atoll. A second use for dose assessment has been to determine compliance with a dose action level for the rehabitation of Rongelap Island. Careful examination of exposure pathways relevant to the island lifestyle has been necessary to accommodate these purposes, Examples of specific issues studied include defining traditional island diets as well as current da) variations. sources of drinking water, uses of tropicid plants including those consumed for food and for medicinal purposes. the nature and microvariability of plutonium particles in the soil and unusual pathways of exposure, e.g.. that which might be associated with cooking and washing outdoors and inadvertent soil ingestion. A study on tbe prevalence of thyroid disease is also being conducted and the geographic pattern of disease may be useful as a bioindicator of the geographic pattern of exposure to radioiodine. Finally. an examination is underway of gummed film, fixed-instrument, and aerial survey data accumulated during the 1950’s by the Health and Safety Laboratory of the U.S. AEC. This article gives an overview of these marry different activities and a summary of recent dose assessments. Health Phys. 71(4):438456: 1996 Key words: ‘“”G dose assessment; exposure. radiation: fallout; * Nationwide Radiological Stud!. P.C). Box IWJ8, Majrro. Misrshall Islands, 96960. ( Munuscnp: received N Julj 1994: rel,i.wd IY JutIc 1995; accepred 15 May 1996. (KI 7-9078/96/$3.00/0 1 CopvrighI @ 1996 Health Physics Sine!} 438 Bikini and Enewettik Atolls in the Repubhc of tk Marshall Islands (RM1 ) were the sites of the L“.j. atom): weapons testing program in [he Pacific from 1v-M–I 95> The .Marshall Islands have been the subject o: r~diolo~ical Investigation and dose assessment for w\ eral decade>. yet prior to 1994. the nation in its enurety hac ne\er been systematical]! evaluated. In the pa.~:year, [h: RM1 completed its own comprehensive evaluation of th< radiological conditions of its islands (Simon ad Grahan: 1994. 1995b) and addressed specific dose msessrnen[ issues as part of the Nationwide Radiolo+al Stud! (NW’RS. see Simon et al. 1993a for an oven-ww). The stud! was administered by the RM1 government and employed and consulted with scientists from the United States as well as other countries. The stud! ~vas conducted independently of the U.S. Departmen[ of Energ! (DOE), although the DOE still maintains en\ircmmental and health surveillance activities in limited arms of tht nation as mandated under Public Law 99-239 (U.S Congress 1986). The independence of the NWTM was an important political issue within the RM1: satisfying tht need for independence led to critical review. rather thm simple acceptance. of previous radiological che evaluations (Greenhouse et d]. 1977: Bair et al. 19S2: Lessard et al. 1985: Robision et al. 1982a. b; Rotmion and Phillips 1989). All previous evaluations of land contamination and possible radiation doses applied only to the more northern atolls; the NWRS was specifically designed to evaluate the entire nation. A comprehensive radiological evaluation and assessment of potential doses for the entire nation had beer needed for many years as evidenced by continuin~ queries of Marshallese concerning possible contamination of the many atolls and allegations of heahh effect> Dose assessment activities as a component of the NWRS fulfills a specific political role and public senxe, hence these activities are more than an academic exercise or J process of enlarging the database on health risks follov ing radiation exposure. Almost every adult citizen of the Marshall Island> knokvs of the atomic weapons testing program conducted four decades ago. Most citizens believe that a variety or ailments, thyroid diseases in particular. are a result of the U.S. testing program. Public understanding 01 radiatior. Reproduced permi.ssi.on from from the the journal. Health Health Physics Physj. cs with Society .......................................................... ,$ -,,,..-.J ............. 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Dose assessment activities currently underway emphasize recognizing impomm[ pathways of exposure. comparing and supplementing recent radiological data with historical data. and efforts at modeling traditional. contemporary and expected future lifestyles for various locations across the nation. In the viewpoint discussed here. dose assessment can pertain to past, present day. or future exposures. It is the objecti\e of this paper to cite numerous previous reports of’ radiological evaluations and dose assessments, to describe in detail some of the considerations for ongoing and future assessments. and to briefly present some recent dose assessment findings, i ;tl one BACKGROUND Needs for radiological assessment The need for dose assessments in the Marshall Islands was suggested by Public Law 99-239 (U.S. Congress 1986, Section 177. Article VIII): “(a) The Northern Marshall Islands Radiological Survey’ and related environmental studies conducted by the Governmentof the United States represent the best effort of that Government accurately to evaluate and describe radiological conditions in the Marshall Islands; and (b) the Northern Marshall Islands Radiological survey and related environmental studies ha\e been made available to the Government of the Marshall Islands and can be used for the evaluation of the food chain and environment and estimating radiation-related health consequences of’ residing in the Northern Marshall Islands after 1978.” These statements make clear that the estimation of radiation-related health consequences. at least in the northern Marshall Islands, was of interest at the time P.L. 99-239 was written in the mid- 1980’s. The estimation of the number of expected radiation-related health consequence normally uses the collective radiation dose: dose assessment is, therefore, a necessary activity. However. P.L. 99-239 does not describe in any detail how past or present health conditions can be related to radiation exposure before 1978. Presumably, it was believed that all radiation related health effects had already been documented and that these conditions had occurred exclusively among the exposed Ron.gelap and Utrik ‘ The Northern Marsholl Islands Radiological Survey was an aerial survey and ground sampling radiological monitoring program of 11 atolls and 2 islands carried out in 1978 for the U.S. DOE by Its contractors: Lawrence Liverrnore .Sauona] Laboratory and EG&G Energy Measurements Group. Flndmgs of the Northern Marshal Islands Radiological Survey can be found in EG&G ( 1981); Robison et al. (1981 ): Roblson et al. ( 1982a]: and Bair eI al. (1982), for at, long m :11[) \ ,.~r m{ m after exposure (Shore 1992: Wor3g e[ al. 1%? 1. these assumptions ma! not be \alid. The rationale for the design trf the Northern 31arshtill Islands Survey was gilen in EG&G ( 1981 ““The presen[ survey col’et-cd those ~tolls known t~l haie received direct fallout from the BRAi’O e~’ent. ccmducted in March 1954 at Bikini Atoll. In addition. several atolls and islands which might ha~>ebeen a[ the fringes of the BRAVO ftillout were also sun e} cd,.. Because of the absence of documentation [o conclu~i\ e]? support which atolls had received fallout. the de>lgn of that study remained unconvincing to the hlarshall I>lands Government. An inspection of historical data \alldated the concern that the Northern hfarshall Islands Sumey did not utilize all possible information to determine those atolls that may ha~’e received fallout. For example. important data were collected by the Health and Stifety Laboratory (HASL, now the LT.S. DOE Environmental Measurements Laboratory ) during the 1950. s at KwajaIein Atoll. These data (Harley et al. 1960) are summarized here in a time-sequence plot of deposition during the years 1954 through 1958 (Fig. 2). As can be seen in Fig. ~. there were at least three periods when deposition occurred at Kwajalein Atoll at about 100X the background level. Kwajalein is a large atoll south of the region monitored in the Northern Marshall Island> Survey. The months in which the major weapons tests took place in the Marshall Islands are noted on the figure: the precise agreement of the data peaks and the test dates is revealing. Seventeen tests were conducted of a size of one-megaton explosive yield or larger. and the dates of all 17 coincided with the peaks of deposition al K\\ajalein. Kwajaiein Atoll has been a site of a slzeable population for many years: the 1958 census of the Marshall Islands indicates that 9% (– 1.300 people I of the Marshallese population lived there at that time. The need for dose assessment outside of the region co\ered by the Northern Marshall Islands Survey is apparent from reviewing the HASL data: this conclusion echoes the concern expressed by the population at locations across the entire Marshall Islands nation. The historical evidence was of significant importance to the design of the NWRS monitoring and dose assessment program. The Northern hhrshall islands Survey had monitored only 30’% of the land area of the nation. The implications of detectable radioacti\”lty in Kwajalein immediately following the large tes[s provided some rationale for conducting a nationwide monitoring program and partly established the need for independent dose assessments. Several other populated atolls are close by to Kwajtdein Atoll (Fig, 1). and it is possible that thev received at least an equal level of deposition. Whether significant amounts of short-lived radioiodines reached population IJ(f!!, I,(1I k , . .,.)t..1 I: x [ I ],(3, b v ~(r . tlR.4\’O I 1: Jll . I - R()\IH) , I I \!T D.AKOT:\Il q ML + Y.. WKEF. , 135 \ll SECT,\R (I ;Ifl FIRIl 3\!7 +KL):\114\l: q ),, - z ~= ,x, IL c 10”--- 10(’ , DATE Fig. 2. Monthly gummed film monimnng 1960. summarized by author), resul(s (“’’Sr. Bq m -‘) at Kwajalein AIoII (dail} d~t~ values from HASL-93 sites across the RMI depended on the direction of the fallout clouds and the time interval between the explosion~_and the arrival of the fallout. Although the amount ‘ of 1-’ Cs deposited at most of the atolls in the mid- and southern Marshall Islands is relatively 10W.calculations of fission yields indicate that the amount of 131 produced i is about 700 times the amount of ]3TCS.Moreover. local fhllout deposition usually occurred within 48 h of the detonation (Breslin 1955 ); this short transit time implies that radioiodines would be pm-t of the radionuclide mix[ure and could have led to exposure of residents’ thyroid. Assessment goals The goals of the NWRS contemplated various types and uses of dose assessment (Simon et al. 1993a). In particular, the original objectives of the NWRS included “(I ). . . to reassess the radiological conditions of Bikini, Eneiretak, Rongelap and Utirik Atolls. . . performing dose computations (retrospective or prospective) in some cases and engaging in other relevant investigations to better understand any risk involved in inhabiting these atolls. (2) To provide advice to the RMI government and to the .Nuclear Claims Tribunal [the organization responsible tor dispensing compensation] for damages of effects likely associated with the derived radiatmn exposure levels and concerning health conditions which are related to radiation: also to assist in the determination of exposure and risk for individuals where appropriate or possible.” I I Compensation program Radiological assessment in the Marshall Islands plays another very special role: that of providing data and, in some cases. e\idence for an ongoing radiation exposure compensation program. The compensation program is administered by the Nuclear Claims Tribunal (NCT), a judicial body \J hose charge is to “render final determination upon: (a) claims past. present and future of the Government. the citizens and nations of the Republic for loss or damage to person or property which are based on. arises out of, or are ]n any way related to the Nuclear Testing Program. . ‘“(R311 1987). The NCT became a reality following passage of the Marshall Islands Tribunal Act in late 1987. In August 1991. certain medical conditions were used to establish “a list of medical conditions which are irrebuttably presumed to be the result of the Nuclear Testing Program,”’ These conditions included solid tumors of most organs (e.g.. breast. colon, liver, ovary. pancreas, stomach. bladder. thyroid J as well as leukemia, Iymphoma, beta bums. and acute radiation sickness. For eligibility, the claimants must be Marshallese and have been present in the Marshall Islands at any time during the testing period of 1946–1958. For the conditions listed, a dose assessment is not needed. However. other categories of possible claims include damage to or loss of land and other medical conditions not covered by the presumptive list. To properly evaluate the likelihood that those conditions were radiogenic in origin, a credible dose assessment is of considerable importance. Oclctwr 11)90. \’oluIII. - \umk - - Population description One use of dose assessments is I() estimak number-> ot e~pwted health consequences among a population, The u>u:il dosimetric quantity O! in[erest for such purp{ms i~ (he collective dose equi\alen[ S (lCRP 1977) or the c{}liecti\e etYecti\e &Me (lCRP 1992 ). Regardless ot the detincd quwttity that is used. the important twk is lt) dctem~lnc estimates (~t (w~an CIOSCS. hich cun he w \\el~h[ed with tissue weighting t’tict(m and r~ldi:l[l[>rl quall[) t’tictors. o\er the distribution (J1 p(~pulation ages wtd sexes. A description of the popu]a[ion is fundamental 10 reconstruction of collectit’e dose e\en though the number of observable health effects arnony a population is not reliably predictable. The population size us ii function of time and Iocatlon is required to estimate the collec[i~’e close for predicting health consequences. In the case of (he Mw-shal] Islands, the population is distributed among man> difterent locations. The population size in the Marshall Islands and the population distribution among atolls htis changed dramatically since the period of nuclear testin~ ui[h a pronounced migration to the established popu]at]on centers in Kwajalein tind Majuro. The change in size and location of the population is depicted in Fig. 3 (RMI 1990), Not represented in this figure are the (WO main Marshallese population centers on Kwujalein and Mojuro Atoll>. These two locations. representing the first and second most heavily populated centers. experienced annwd ~rowth rates of over 4VC and W. respectively, during the 1980’s. In absolute terms. the popultition size of K\~ajalein and Majuro has changed from 1.284 and 3.415 to over 9,300 and near 20.000. respectively. during the interval from 1958 to 1988. .4 tew atoll~ r,.i\e bec~~rne reinh~blted during the past three decade.. Nhilt t}rners h~\e been ubandoned. F(>rexample. Biklr: wos e\ ~~uatecl in 1946. and pw-tiall> rein habited in 19-2: the p(lpulution V,as again rerno~ed bed) burdens of 1‘7CS b! the U.S. in 197S whirl increased ?()-fold due to con\urnpllon of contaminated foods (McCraw IQ-Y: Miltenberger e[ d. 1979). Toda!. rno~t ot’ the Bikini ;~}mmun~r\ Ii\cs on Kili Island in the st~ttth pa-t of’ the n~tion thl~ugh part (~t’the communit! AIc)II, Rongelap was resides on Ejit Islmd in Ilaluro e\acuated about 5(J h at’ter thj BRAtTO test in 1954 and then reinhtibitul in 195-: the people of that communitv abundoned their home atoll (as well as Ailingin~e and Rongerik) in 1985. M a result of fear engendered in the community follo\~ ]ng the releme ot’ a DOE report (U.S. DOE 1982) in 19!2. This report indicated t’(~rthe first time that contamination le\ ei\ on part of Rongelap Atoll were equivtilent [( those on Bikini Island. In 1971. ii limited number or people relnhabited Enewetak only to leave in 1977 due [(~poor [t~(}dsupply. Since then. the Enewemk people ha\e \pw-adicall> moved between Ujelang tind Erie\\ etak. The nomwlic existence of those who were displticed. direc[l} or indirectly. by evems related to the nucle~r testing program. is not their preferred li~estyle. The los~ of homeland for these people. either for reasons of true safety or due to their fear, has resulted in a dlmrnished sense of community and loss of culturul continult). Most of the location. ut which the people of Enewetak. Bikini. and Rongelap lived did not provide any substantial exposure and. thus, generally reduced the o}’era]l risk to the communlt} as compared to their home atoll. However. for the purpose of estimating collective .Ii, C(l 31, 1() ()” the dll Th 1s1 th~ [e< yc rc I (1 GI fat we N( kn tif li( t:ll Ut ra i 2000 1500 [, !~ I !. II 1{ ! I 2000 1500 II ., ., m ~. 1000 m’ d { 1000 Ta> Bi} 500 500 — 0 0 — Fig. 3. Majuro popultitmn (Mtijuro sizes ior the atolls ot’ [he Mwshall Atoll) and Ebeye (Kwajalein Islands In ] 9S4, 1958. and 19~~ The main population centers of Atoll) are nor shown (see text for rncr: lnformatton ), *I L’(111 exposure. the task is made considerably more complei h!’ the number Of other locations to }vhich indiyidua]. ma) ha\e moved. Time and size distribution of tests Prior [o December 1993. the yields of 45 of 66 tests conducted in the RMI were still classified data. The 1larshal] Islands Go~ernment requested these data in 1992. and. in late 1993. U.S. Secretarv of Energy Hazel ()’ Leary. through tin “Openness lnit~ativc.” announced Ihe yields of the remaining 45 tests (U.S. DOE 1993a. bl. Table 1 shows the annual totiil explosive yield during the years of atomic testing in the Marshall Islands. The exploslve yield of the largest test in the Marshall Islands was 15 MT equivalent TNT. Seventeen tests in the RM1 were of a yield greater than I MT each: these tests contributed about 95% of the total yield, The early years of the testing program, 1946 through 1951, were relati\’ely inactive in terms of proportion of the total yield ( 1.07 X IOh tons TNT). Information concerning the island Ioca[ions of the tests. on-site meteorology, deposition patterns, etc., are contained in DNA ( 1979), an extraction of information from the classified DASA 1251 series of reports (Morgenthau et al. n.d. ). Some of the history of the testing era can be found in different forms in Hines ( 1962), Deines et al. ( 1991 ). and Schultz and Schultz ( 1994). Global fallout Itis widely known that there are varying levels of fallout radioactivity at locations worldwide as a result of weapons tests conducted by the U.S. and other nations. Northern hemispheric locations near the equator are known to have a minimum deposition of fallout radioactivity (Machta et al. 1956; Eisenbud 1987) while locations at mid-latitudes received greater amounts. Global fallout has been deposited within each hemisphere somewhat differently, but it is usually correlated with local rainfall rates as well as latitude. Substantial variation of global fallout over the area of the Marshall Islands might be expected because of the wide range of latitude over which the islands are located and as a result of strong rainfall gradient across the nati(~n. Southern atoll locations receit e appr(~ximatel> 30{)to 430 cm 01 rainfull annually: northern atolls recei]c cwt>lderably less. on the order of IW)-1 75 cm wrnuall\ (XO.\.A 1989u. b). Estimates of glob~il fallout 1‘;CS f& each atoll ha~e been made by hlc Eivan and Simon+ using a predictive model based on Itititude and annual raint~ll rates. the mode] ha\inS been calibrated with publi~hed deposition data (HASL 1977: Larsen 1985) from a \’ariety of’locations in the mid-Pacific region that are outside the RMI. Although deposition general]> increases with increasing latitude in the northern hemisphere. annual rainfall rates across the archipelago var> in the opposite direction. thus neg~Ii\ely compensating for the a latitudinal increase. Predic[ed values of’ global fallout deposition are close to uniiorm across the Marshtill Islands. Predicted deposition t dues of 117CSfrom global fallout vary between 400”and 800 Bq m 2 for tht atoll~ of the Marshall Islands. JVhile global fallout does not substantially contribute to the dose commitment for individuals. it does contribute to the collective dose. More important!. estimating the expected level of ~lobal fallout at each atoll assists in determining which atolls did not likely recei~e locally produced fallout. The estimate of global fallout is also used to determine the fraction of the tottil fallout radioactivity measured at each location that can be attributed to the weapons testing program in the RMI. EXPOSURE PATHWAYS AND RELATED DOSIMETRIC CONSIDERATIONS The recognition of relevant exposure pathways is vital IY important for producing credible dose assessment;, Assessments for inhabitants of the Marshall Islands are unique compared to U.S. scenarios for severtil reasons. First, there are dietary components and minor pa[hways that are normally not of concern. Second. the relative importance of different exposure pathways has substantially changed during the decades since the nuclear tests were conducted. Various issues of exposure pathways and dosimetric considerations are discussed here. Diet One of the most dramatic alterations within the Marshallese culture over the past four decades has been acceptance of dietary changes, including the introduction of prepared and packaged food items. The degree ot acceptance of these changes and the availability of westernized goods varies among atoll communities within the Marshall Islands. Some communities remain today more isolated from such changes because of their remoteness from frequent shipping traffic or because of their low level of economic development that precludes them from purchasing expensive prepared foods. - McEwan. A.C. Caesium- 137 Depsmon from global fatlout in Lheklarsbull Islands. 1992. > Simon. S.L. Comparison of recent 1‘7CS measuremer-m with prethctmn of a global-fallout deposition model and historical dxr. 1993 Table 1. Distribution of test yields among years and between Bikini and Enewetaktest sites Yew 1946 19-M 1951 Percent 0!’ [WA yield* 0.04% ().I % 0.3% t952 10.2” 45.0% 19.4% 1954 1956 t958 Bikini Enewetak 24,9% 71.8% 28.2Tc * Tolal yield equalled 1.07 X Ios Ions TNT: Bikim and Enewetak test sttet combmed. I Those communities direct]! affected by [he nuclear testing program ha\e received \arious t!’pes of compensation OYCTthe yews that has resulted in dramatic changes to diet. F(w example. the communities of Enewetak (sometimes resident on Ujelang Atoll). Bikini (now resident on Kili Island and Ejit Island. Majuro Atoll ~. Rongelap (now resident on Me@to Island and Ebc!e Island. Kwajalein Atoll and Maiuro Atoll). and LJtirik. receive U. S.D.A. surplus foods that are almost entire]) canned except for packaged rice, The distribution of these foods began before the Compact of Free Association (U.S. Congress 1986) was signed into law in 1986 and will continue at least through fiscal year 1996. The food program. intended to only provide supplementary sustenance, provides food to 2,875 persons with a total annual expenditure of about $0.5 million. These communities also receive quarterly compensation payments since the initiation of the Compact. Thus, the two communities having received the greatest individual exposures, i.e.. Rongelap and Utirik. and the two communities whose land was most heavily contaminated, i.e., Bikini and Enewetak. have experienced significant change from traditional dietary patterns. Attempts at retrospective assessments for the years following the BRAJ’O incident. therefore, must take account of these changes over time. The lifestyles of the people of Enewetak, Bikini. and Rongelap have not yet stabilized because of uncertainties about the location of their future home life. Their lifestyles. therefore, will continue to change in concert with decisions they make concerning rehabitation of their traditional homelands. Present day and prospective assessments for these communities. therefore, must rely either on assumptions concerning expected future dietary practices. or they must use a traditional dietary description to determine dose commitments for those people who might choose, or who find it necessary, to return to traditiomd diets. Experiences in developing nations sometimes indicate that the younger population tends not to revert to traditional dietary patterns if newly introduced foods are maintained in sufficient supply through more than a single generation. Thus, the determination of present and future exposure based on traditional dietary patterns is argued by some not to be of importance today. Howe\’er, critics of prospective dose assessments that are based on a traditional diet may not have considered that the availability of compensation money and food supplementation programs may end within the immediate future. Thus, these communities may be forced for economic reasons to revert to more traditional means of sustenance. Thus, dose assessment based on a traditional diet may have continued relevance for certain segments of the Marshall Islands population. in particular for those most directly affected by the atomic testing program, The degree to which local food is used in the diet is to some degree a function of location: imported food shipments arrive more regularly and in greater quantity to communities that produce more copra (dried mature coconut meat) for resale and which are more accessible due to safe reef’conditions. Seasonal \aria[ions in diet are also a part of the yearly c\cle as man) adult ,Marshallese prefer breadfruit and oth~r local frul[. when a\ailable. Variations in diet can also be linked [o meteorological eventi. in particular those of disaster proportions. e.g.. typhoons. Fo]lotving typhoon>. communities ma) depend entirel! on what little local food is a\ailable because of’ dela!s in the arrival of disaster rellci. Similar]}. once disaster aid reaches communities and [he small mnounts of locally grown food are depleted. [he diet ma! consist entirely of imported food for many months. During these periods. Marshallese al other atoll, frequently send locally produced fruit or fish to their extended f~mllies as part of a relief effort, These various t) pes of e~ents add considerably to the difficult) in modeling long term food sources either for the purpose of indii idual or collective dose assessments, Food plants A small variety of plants are used traditionally in the ~Marshall Islands for sources of food. In particular, the coconut palm (Cocos n~{cifera L. ) IS a versatile tree bearing nuts that are consumed in numerous different forms. Commonly drunk for body fluid replenishment, the young “drinking coconut”’ or ni (n~ ). provides a clear slightly sweet liquid. Inside the drinking coconut is a soft, gelatinous layer called me~e (me’ dii). normally scooped out with one’s fingernail and eaten. Other stages and forms of the coconut used for food are the coconut cream—the thick milk obtained from the fully mature coconut called dren in waini: hard coconut meat or }vaini (why’ n~)—the thick coconut meat from the mature coconu[, usually made into shavings and combined with rice or other foods; the coconut embryo or iu (yii)-a sweet spongy material obtained from the center of a sprouted coconut; jekero (jek’ a roo)-the liquid sap of the coconut tree collected from the severed end of a coconul palm branch: jekmai (jek’ ma yil—a thickened version ofjekero produced by boiling. used as syrup; and jekmun in (jem’ a ung)—an alcoholic drink made by fermenting the jekero. The coconut husk is sometimes sucked to gain access to the interfibrous water; /ienawle (ken’ a we) has been reported’ to be mostly commonly consumed by women in the early stages of pregnancy. Concentrations of cesium tend to increase with the age of the coconut and the density of the food product, with }t’aini having a considerably higher concentration than rri. Coconuts are common in virtually every location of the Marshall Islands; over 60Yc of the land area is covered by forests of coconut palms (R.MI 1991). Other locally grown fruits that are not cultivated but normally picked wild are Pandanus ( Pundanus ,jischeriant{s. Marshallese: bob), papaya (Carica papaya L. F.. Marshal lese: keinahbu), breadfruit (A rzocarpl(,s inci.sws, Marshallese: ma), including the presemed product b)t’iro (breadfruit mixed with arrowroot and jekero. wrapped in breadfruit leaves and baked). In some locations. limes ‘ Personal communication from Randy Thomas, Rongelap, Republic of the Marshall Islrmds, citizen of fru & car me va Bq bol (S Se 1s Na M fis a t as sp me tio 19 Jap ran hu we sta to the oc lev grow m’ild as w’ell as a small ~’arlet! of bananas (pimm ). dw latter normally requiring planting and a minimal amount of care. In some communities. common twieties ~~t watermelon and pumpkins tire grown in gardens. Except for the production of tam. a marsh plant used for :] variety of food preparations and medicine. organized .luriculture is not comrnonlj practiced in the Marshall l~lands. Used more in decades past. the Polynesitin Arrow( mak’ mek ]. r~mt ( Tamw le[jt~ff)/JtJff/loifle.s ) or mdmd tended to produce tubers. then harvested. u M commonly leached in a lengthy process to remove bitterness and fina!ly formed into a starchy material that provided the basic carbohydrate dietary component. Md.wliik was a versatile food product and could be kept for long periods of time. A common ndrion across the RM1 toda! is that arrowroot does not grow’ well or in some cases has ceased to exist as a result of a[omic bomb radiation. Observations on the propagation of this belief were discussed by Spenneman ( 1992): he concluded that the decrease in availability of arrowroot is a b>’-product—not of radiation exposure but of the diminishing need to use. and thus to cultivate. the food crop, Commercial availability of flour and rice have contributed to the decline in the cultivation and usage of arrowroot. The potential for uptake of ]37CS is similar in most fruiting plants though differences in uptake are apparent. In particular, the Pandanus accumulates cesium to a higher degree than other fruiting plants though root crops can also accumulate significant cesium. Recent measurements of ‘37CS from Rongelap Island gave average values of 200 Bq kg-’ for medc. 20 Bq kg-] for ni, 900 Bq kg-’ for makmfik (dry weight), 1,000 Bq kg-’ for bob (dry weight), and 470 Bq kg-] for mu (dry weight) (Simon and Graham 1995a). Seafood Fish are an important part of the traditional Marshall Islands diet (see for example Chakravarti and Held 1963; Naidu et al. 1981). Questions are commonly asked in the Marshall Islands about the possible contamination of fish, both in the present and in the past tense. Providing a true comprehensive answer to this question is difficult as from 250 species (Myers 1989) to over 800 fish species (Randell and Randell 1978) have been documented in the waters of the Marshall Islands. Possibly the first scare over radioactive contamination of fish took place following the BRAVO test in 1954. Eisenbud ( 1990) describes a “Tuna Panic” in Japan. and, although he notes it to have been unwarranted, he acknowledged the difficulty in monitoring hundreds of tons of individual fish for contamination as well as the problem of determining a contamination standard for acceptance or rejection of fish. The idea that pelagic tish are freely moving brings to mind two important. but different, possibilities. First, the opportunities for pelagic fish to inhabit a variety of oceanic locations. including those having received low levels of fallout, would tend to reduce the likelihood of high Concen[ra[ions in fish flesh from occurnn:. Thl. same phenomenon. ho\ve\>er. raises local concern because there remains a finite possibiiitv of ti~h bnngln~ contamination from areas near the test si[e~ to more distan[ locations. A related concern is that man] types <>( locally produced food. including fish, ha~re hecn shippe~i for decades h} families to remote family members {~n h other island$. This (Ici(M’food distribution network IX near]! impossible to model because of the lack t~t documentation. Even so. the possibility of sending contaminated fish from one location to another remain> .1 smull but finite possibility. For retrospective assessments. several nuclides ma} be important, For example. the concentration of 55Fe ([~~ = 2.7 y) was determined in people and fish from Rongeltip Atoll (Beasley et al. 1972). 55Fe \vas one ,Jf three radionuclides present in significant quantitw~ (along with 1T7CSand “(’Sr) 3 y after exposure in 195-. Measurements of 5sFe concentrations in liver of goatthh sampled from Rongelap Atoll over the years 195L~ through 1963 showed steadily decreasing concentrations with a representative value of 2 X 10S By kg -1 (\\ et weight). In the area of the northern Marshall islands, representative concentrations of 1S7CSin reef fish are 0.6 By kg-] wet weight (decay corrected from 1982 dat~) (Robison 1982a: Noshkin et al. 198 lb). Fortunately. both reef and pelagic fish generally provide d relativel} uncontaminated source of food today. regardless of location. Plutonium concentrations were reported in fish from et al. 1979) to determine Kwaja]ein Atoll (Noshkin whether fish collected there were substantially higher in activity than as expected from global fallou[ as had been earlier reported (U.S. DOE 1973). Noshkin et al. ( 1979) concluded that concentrations of ‘3Y”240PU the flesh of in fish from Kwajalein were of the order I X 10-~ Bq k~- ‘ (vet weight) as was expected based on global fallout alone. Food collection Food is often collected by community members from a number of islands other than where the community resides. In some cases, Marshallese will visit other atolls for the purpose of collecting food, e.g., Taka is used as a “pantry” for food resources for the people of Utirik (Thomas et al. 1989) even though it received approximately equal deposition as Utrik. There is also significant concern about radioactive contamination of certain foods (e.g., coconuts and coconut crabs ) at Rongerik Atoll (Thomas et al. 1989), a pantry atoll owned by the people of Rongelap. Rongerik Atoll received approximately equal deposition as Rongelap Island (Simon and Graham 1994). Realistic radiological assessments must determine locations from which fcmds are derived. the quantities and types of foods involved. and the location of specific radionuclide concentrauons. 4-M Heal[h Phys!c\ Ocmber 1996. VOiume 71, Number .! I ! Ikledicinal plants A variety of plants are used traditionally for medicinal purposes in the Marshallese culture. but the species. prepora[ion methods. and dosages are not well documented. Whistler ( 1992) h~s reported extensively on the variety. uses, and preparation methods of medicinal plants on other islands in Pol\’nesia ond although some of the some plants used there are the same as in the RM1. there is a paucity of written Information about their use in Mtirshall Islands culture. .4 systematic study of ]“CA concentrations in five species o\’er the geographic rmge of the Marshall Islands Mas conducted by Duffy ( 1994) as part of the NWRS acti~ities. Sampling and radiologictil analysis of these nati\ e vegetation species used in traditional Marshallese medicine was earned out to complement the assessment of potential exposure via ingestion of foods. The uptake potential of these plants across the environment of Ihe RMI has not been studied in the past and, although the ingestion of these plants likely makes up a small pm-t of the plant material and radioactivity consumed b} llarshallese, the dose contribution of this pathway uas previously unexplored. Species and plant parts included in the st,tdy by Duffy were the fruit and Iea\es of Morinda cilri’olia and the leaves of Tournefbrtia argenlea. Scaevola taccada. Triumfetta procurnbens. and Pol>podiurn seolopendra. Plant concentrations generally decreased from north to south, with values of 1.400 Bq kg–’ (dry weight) representative of the northern atolls. decreasing to 1 Bq kg- 1 at the southern atolls. Some difference in uptake between species was noted: however, for dose assessments, the most important factor is the recognition of the pathway and obtaining some credible estimates of intake rates. Duffy determined the dose commitment per me: tM l e dilcirlad ildllll irui!l i([m alfl er ]rmki]nf: :slloim a:$,u;m p t n /G1 ila :s regardi [1 tiw amou nit of ]pl t Wfxj! i ]rlItx: prepwal[iton. g m l ‘he frfxluency of usage. hI[mJe :r,,,. w i<;~[i]I ql]]lt[:Iurlccq-t.ai:rl ad IIk Iy varies b Wve he more urltm i I:n nizedl po pu IIali loIrl c)~ the c(muew ;a114~ the mcm: tmdll~cln;d (u(:lrTIrr]lLlulil[i(ss )r(; ote am 11s. m rainwater catchment system: this system collected approximately 200 million gallons In 1989 (Rlll 1990). Most famijies. particularly those outside of llajuro. collec[ rainwater in a concrete or fiberglass cistern \ia home roof collection and gutter drfiinage systems. Fe\\ open clstems exist today: howeter. many v cre apparently used in past decades. Retrospective dose assessments must consider the possibilities of drinking water containing radloacti~ t contamination as a result of rainout from direct (dn 1 fallout deposition into open catchments or from wa{er collection on contaminated roofs that fed into catchments. The contribution of radioiodine in drinkrng water to the exposure of the Rongelapese followin~ BRAVO was considered by Lessard et al. ( 1985). On]> 23 cm of water were reported in each of eight catchments on Rorrgeiap Island during the days foliowing BRAVO (Sharp and Chapman 1957). The IOU water ie\eis did not tend to concentrate activity according to Lesstid el al. ( 1985): they assumed 20% soiubiiity of iodine r’rom the fallout particies and 50% to 80% of the particies to haie settled out of the iiquid phase. @e~tictlls, ;Ijq; some[irrles rwsed about the pOSSibl C contamination of cistern water collected from roofs that may have been contaminated from resuspended dust. Although the soil/roof/water catchment pathwa> could only contribute a very smaii increment of exposure compared to that from Iocaily grown frui~. further reviews of such possibilities are stiii needed for a trul~ comprehensive evaluation. Present day assessments generally do not need to consider contamination of ground water because of the iow concentrations. The concentrations of radioactivity were reported I]y R.ohison et, al, ( 19823) for inortlmm lMimh241U Islands Iocat.ions (also sw Ikosh,,ki,n et Ial, values for l~’;’C:$lll w’eHl-wamr on 198 II a): currenl i ( I 131[] IF{.rm lap 1:5, IEX: Iand,, for e wmnplc, am on uiworder(It )’, k.2‘-‘r I(decay corrtx:tf:d from 1982]. (D(]tlcerl[.rll[l(]rlsor f :!?IW4(IIUam appmxi rrmteI:y a fact (or of 1O(I imx:r. f; a large } i r I 1 $j~~l(~l]l~lj~;ll(~~[: Idj;IItIfxj t 01 pkanlt Ulpllklk ]~jjylt,ic:! iIII ~C)i CI] [II(: ij$,);];[](:is j r wil,l],i]:lti]lt!?.~plukl]IC on f< RIIEd [ f ffrcm !Jl,B detritus of (corals ;aml Mkr m]axinbf: lifit,,and wa,s by (Gmjeil and Walka 1!Y92 anld ) iater :Wd)ihizd pliants, Aow 11~ impro’vrti in quaiit ‘y by l.ht! lhuiMUp Ot’ Ol,rf!iil niC df!lnilus. Deltai]s of soi [ cl(:v(i:i(:)~)rrl(tllt hw been described by IOISerg ilJMi C;molll ( 1’965) ard r[lir~t:rult:)j?iciii ;nd b a I:iescIrj Id i pl[i ass fi(;aliorls ,Ix!f;]rl discussed h!, Mor ‘IT il Ivc ; cIrll i J :yi ]ril n ( II W])),,IN([II S(I ‘ rwraII m nIt 11s:sii~lll fi lCiilr]It oww- in I);];$,tf:(jl c)iI [:lIIJIIII[J ~~~[ (:(])rl[llr](~lllt[~l S,IO~ ~ ,of I 1:s,,IJ1(: f~l(II 1 I c[]]ra[] irlf~ narl ‘y lc(:)l!r]l[)l!lt:l.c I)/ clcmi,rmted by c:dciwn so] I II]{: cartmr ate with m :y:IIIIfX IIIII m cm-k)(IIr] ;ate as a s (xc) II I[jijIr-y COIT)~)OIlf?.ll,it . ‘1’hc HIOI’M; (Z)t:cl.lrr+erl(;(:: of minerals, ~W[il!js, il;mn of’ upl[ak Id in pmWcurlar,leads to mlat nveiy higih iewls Iridi(xic [i V(: ‘1 ’7(3. i]mplicatirms of a IIow pomwu m ‘] ‘Tlw en virlrmmeIU &W!rnp:wl.ar~tfor creal.irlfythe pot (enl[i for i al high exphos lures to humans to occur vviwrt;ver dmmtia] j ~ 3 .. a;rnm n ls, I:)1, II ‘7(~-,$ ,Jk,(;r[: ,[jltpulsited. ‘Tim t],l;)~)c)rtl.llllil[!t :for nnil t ]l~~alion ,(]If c7esium upuiw in plillrllk Iex 1s1s. ilmwwer, wi Ith ltillc applicat ]Iorlof ~}[ll[;]:;:s)iljtlyl t :.1 (. !,, ~ c 11 a Sr 1) n [C :1rlltl:llll~llti([)lrl l The wahal ion of idhoht i m I;lrl:\ mrnplf; x issue kEIMIU!N! Of close cm h a pamic2]l- k r)lLIITll?!N1’lUS [ :)1~)~ !51 Of \/;[l~l 81[ jl(1 [1 :S Ithl 211 Te ([l u ,:ps l],r(~ di,O:rlsr]le]rl MI(: 111 I ?~ I:r) [ o jI i]l c vi !rorl ‘t;], (cm be It!mx:w [W ]rc d ;ard kc a u :$,(C data ijr ‘t mod ci I:d 0 luijrtilrlrrls ii[rl: mmmd I y d iffic IIIl.‘t I[llk)lai 0 rl. I[ksc s][[ @ 21S ~1[1~i]llf! Ida[l ‘W llllrl~)Cl~[iIl[llC(: C)f f%~tl:l.!l kl]RCE . . i n h;3LL3 mn k [ ml t o u jr] 13 IC d Y xam In I :ng {h I: ‘do 5It c 10nv tx.. S,ia II h; [ cm I(S v IEl ‘-11 q ilrk.led or il gesld J for ]Imlporl:m[ n radionuclkles and the likely amownl of racbrctivi(y int~e (Bq d– ‘J possible via inhalation as compared to ingestion. For 1 7CS and i 311, the ingestion and inhalation dose conversion factors are nearly equal (Eckerman et al. 1988), thus differences in intake between the pathways result mainly from the differences in density of air and roods and the total volume inhaled compared to the mass retake of foods. For ‘3’’Pu, the inhalation dose conversion tactor is several hundred times greater than for ingestion. In a retrospective evaluation of thyroid exposure to tie inhabitants of Rongeiap in 1954, Lessard et al. (1985) concluded that inhalation could not account for the I estimated intake of 131 and that if it were assumed to, lethal exposures of external radiation would have been sustained. Neither was resuspension deemed as a reasonable alternative to ingestion. An evaluation of present day inhalation dose by Robison et al. ( 1982b) indicates that although inhalation is a major source of exposure to transuranic radionuclides, both the inhalation pathway and the transuranics will contribute only a minor portion of the total dose predicted over the next several decades. In evaluating current and future inhalation dose commitments, it is necessary to know both the respirable fraction of the soil m well as the specific activity associated with that fraction. Robison et al. ( 1982b ) reported respirable fractions of 19–24% at Bikini Atoll. Although those data do not specify the specific activity as a function of the respirable size fraction, an enhancement factor (EF, particle. Previously NCRP [ 1975) concluded that particulate p]lulonIIum) irl ItheIun: 1 I;m jyw,h:r krmrd I.him the wrtw unrt of p Iutmum more utnilforml:!’ dlstltilltll[elJ c am] Ii rc ils n([)[,y(e l;Icar It t, Ih tI[)l.lf!hlt ‘thf? IIllrljg!. Howf!ver. d ihovv the abmoi u t(j anrlou n t o [ p] won 1uml th t ev i I:lthx I art il Iks c mri ght Ix inhlId vam If~,w IIt III )tkpresle]nu: 01 InoI~rp i]qltltl(~ I. ‘l~h :s, $~)i is iI.LM;L] js f1]rl.h(;r,connplic ZII,IMI b!{ ‘[k oH l :si me d isltrilm [ii(]In of’ soi 1 pmic Ies m whit h 1. he lradioac [II ~ ~acltwd. i1y ]ma:y k a[[t A]lhwrglr nrrml. ef[dmce indica!t;sl that inh:datwn of t]riil!$~ll]r~in i~~1 rl ‘the h! ~Lr$](LI !Mlands i :s,2 small, rxmWi13uWr [] i t P1‘1 u11 I ( IcI idto Wtd close,, wmnc (c wrol spec ilfi Csslhcm lx (con:sl iar. Ik IOpclrl ir titxi g Irl of houses i Irl Ih a Clrd. In ‘ptlkld ]\&]Jr~,]tl:l]]l ] ‘SI;311)([IS ;~(?)rl(:lr;][lll ]~)ll]r~n’[)11[(~~, j/ ‘[l~~l)l~]>f!~l(jl~~l!i~lill of matwial to ‘enter }mrrtwsas we]I as Ik ;;ic:(:l)rnll~l:l[iflrl dust with much the same radioactivity concentrations as found out-of-doors. host Marshallese houses, particularly those on less urbanized islands, typically do not have furniture: inhabitants sit and sleep on the floor. Moreover. windows are placed at ground level so as to promote ventilation while sleeping on the floor. Other pathways Other lifestyle am-ibutes of Marshallese will likely affect the relative importance of minor pathways. In particular. the closeIy related activities of food preparation, cooking, washing dishes and storing dishes out-ofdoors all provide possible means of transporting radioactive contamination [o humans. Food preparation may take on many forms including catching fish, drying fish in the sun (no’imally on the roof of a house). cooking over an open fire, baking m a fire pit. boiling water in open pots, etc. Food is often consumed outdoors, particularly in the less urbanized Islands. In the past. such practices would have been common nationwide. Dishes are also washed outdoors, typically not far from the site of the fire pit or kerosene stove. Dishes are usually dried outdoors and sometimes stored there. For the purpose of long-term assessments. the dietary behaviors of animals that are eaten should be considered. Pigs and chickens are commonly left loose on many islands to forage for food in the undeveloped i I u. Heiil[h Ph>\]c\ Oc[otrer 1996. Volume ~ 1. >umtx~ part~ of the island: food for pigs includes coconuts fallen from trees. plant roots. insects in [he soil. and scraps from human meals. Pigs. in particular. can ingest relati\’el\ large amounts of soil while foraging. Thus. the transport Of soil radioactivity to humans vi~ consumption of pig tlesh and edible organs requires consideration. Pig flesh from Ron~elap Island was recent]) analyzed for 13TCS concentration as part of a study of the safety of Rongelap for iuture residents. Representati~e values of pig Ilesh vere 400 Bq kg-i (dry weight) ‘37CS. The coconut crab (Birgus Iafro ) was recognized as accumulating significant amounts O! 137CSti-om studies on Rongelap following the BRAVO fallout incident. Chakravarti and Held ( 1960) reported concentrations in 195h of 500 disintegrations rnin - ‘ g ‘—that is equivaIem to nearly 1 X 104 Bq kg’ ‘ (dry weight). This value is only slightly higher, after accounting for radioactive decay. than recent measurements that are of the order of 350 [o 1.000 Bq kg--]. The diet of the coconut crab is mainly coconut meat; thus, the crab flesh can be in equilibrium with. or somewhat greater than. the concentration of ‘37CS in coconut meat. The coconut crab is a unique food that must be considered in assessments: the crab ISconsidered a delicacy by Marshall Islanders and is often eaten in large numbers when available. A recent report in the RMI (Crawford 1992), however, lists the coconut crab as endangered because they are relatively easy to catch and are very slow growing. Lessard et al. ( 1985) discussed living conditions in the context of determining thyroid dose to Rongelapese exposed to BRAVO fallout. They concluded that ingestion was by far the most important route of intake for the Rongelapese exposed to BRAVO fallout and that this route included contamination from hands, plates, and eating utensils. DOSE ASSESSMENT METHODOLOGY AND DATA Historical radiological data Comprehensive radiological data were collected and reported by HASL from the 1952 Operation IVY (Breslin and Cassidy 1955) and the 1954 Operation CASTLE (Eisenbud 1953). Operations IVY and CASTLE provided 10% and 4570, respectively, of the total explosive yield of the testing program conducted in the RMI. Three types of monitoring data were collected by HASL: ( I ) fixed-instrument exposure-rate measurements using stationary meters placed at numerous atolls, (2) measuremerms from aerial surveys immediately followirtg many tests using a scinlilkmtmter that cmdd nrleastwe over [tine of ‘7.2 X 1(1”-”7 ‘?.2 x lo--z C kg”-] s-], and (3) to range !rtlt!iWllWllfMS from gurllmled film placed at a !Kwajalein Am]]. a central atoll location in the archipelago. The gummed film station, one of lmorc t“an 100 monitors placed worldwide, collected fallout for 24 h. after which the film was changed and sent. to I-l..ASI.. analysis, ‘l-he for fixecl-instmrnents provided exposure-rate data in the form of strip chart recordings. The owput from those ha> possibl} [he greatest \alue for retrospective dose assessment becau.e they indicate unequivocal]) u’hethcr local fallout am\ed at the atoll. [he time of arrival of the fallout. and [he deca} -rate. The elapsed time from detonation to deposition and the duration of fallout are important par~meters tor determining the possible exposure [o the rapidly changing radionuclide mixture. Other typei of rele\ant historical data were reported by Sharp and Chapmtin I 1957) who recorded a detailed description of the Rongeiap community, the status of their food and water supplle>. and e\ents that took place following the BRAVO te.:. Sharp md Chapman also included in their report the evacuation and decontamination procedure. and the film bad~e readings and exposure-rate readings from the bodies of Marshallese and U.S. weatherman stauoned on close-by Rongerik Atoll. Information on fallom transit time to Rongelap an Rongerik can also be dedumd from Sharp and Chapman ( 1957): they reported the onset or’ visible fallout a[ approximatel~ 1.400-1 .-l:~) h (the test was conducted al 0645 local time. DN.A 1979) and that the ATN/3a Recording Doslmeter at Rongerik went off scale (at 7.2 X ]0-3 c kg-’s-’) at approximately H + 6 h and 48 min (i.e., 1,333 h). It is difficult to determine if these observations are entirely consistent. Uncertainty in times of fallout arrival are important because of the rapid rate of change of radionuclide mixture soon after the detonation. Some level of interpretation is often required when using historical data. Similarly, the duration of fallout at Rongelap has required considerable interpretation; that uncertainty was described by Lessard et al. (1985). instruments C d d ~ I t [ 1 Contemporary radiological data The essential ingredlen[ to dose assessments. retrospective or prospective. is a comprehensive database of location-specific radiological measurements and specific activities in soil and foods. Several suneys of Bikini and Enewetak have been conducted over the past several decades as part of U.S. sponsored cleanup or evaluation programs; however, in 1978, the U.S. Department of Energy sponsored an aerial gamma spectromemy survey of the atolls of the Northern Marshall Islands (EG&G 1981 ) supplemented with ilmited ground sampling. Verification of those data and collection of new radiological information on the rest of the atolls of the RMI was the primary task of the NWRS. In that study, extensive in-.sifu gamma spectrorneu-ic mem.wernents (9 1 m lmighl) were comhctd for the purpose of clfmmirtin,g soil ~~id inventories of prima cmlining radiont.w]ides. e.g.. ‘~~cs, ~“1 Am,, and @Co. ,All 29 atolls and 5 reef islamds of the Marshall k.iands were monitored at an average i,n-.riru sampling tiensity of 10 gamma :nleasutremertts per kmz. in the Natmnwide Radiolog~cal Study, external exposure-rate estimates and calculations of amal inventory (Bq m’-”z) used established in-siru spectrorrtetry methodology (see Beck et al. 19’72: Beck 1980; Heifer ;an M II1Ie]r 11’988 ‘1’hIt con ‘w: ion 01 extem ~ale xpo$l m d II. m m US(?d(~til.;l fl’O~~l J[iC’(1’lt) alldl l?ilt’t!UJ.~ ( 1198611 a~ld l[CRIF] CIOW ~19V), ‘The (eni~m+n]nnerltd nneasurmwrtls were supplemented menl.s eah;l of and b? laboratory gamma soil ml sptxtmmetry l(ill(:renncnts measun:of 5 cm wCm-d12ep WI+:lCC pd-iks samples (0-3 and cm) Wtalvzl.. for . + soil inventories IIn transumnic radioactivity. lEnvirok7mwml lhe natkmw%k counl-rates study varied over four orders of magniIucte: the lowest values (< 500 E@ m ‘! 1370) were measured m the southern Marshall Islands, and the highest \A.res (> .5 X 105 Bq m-~ 137CS) were at. Bikini, Enew’etak, and )longelap Atolls. These variotts d:ita have recently been made available (Simon and Graham 1994, 19W5bI) [U(]llnsillIic]rtllti d ~Ij]rls Extensive ,spatj:id vaurii:ltiow Ro]ngelap island was conclucr.edin I992 land 1’993l(Simon and Cirilhann 1995a) for determining ccmlplhncc with a dose action level (lR.MI/ RALGC)VDOM301 1992). ‘The demands of that stud) highlighted the need for techniques thal could contribute to interpretation and extrapolation of data. In particular. geostatistical variogram modeling (see for example Cressie 1991) was used to deduce the spatial dependence of the in-siru gamma spectromewic measurement data and to predict values (krigiI~g) at locations intermediate in location to those sampled. Attempts at applying conventional geostatis[ical analysis techniques to the Rongelap monitoring data have pointed out needs for innovation—in particular, the need for non-Gattssian distributional assumptions (Diggle et al. 1995). Though not a panacea for insufficient data, geostatistical modeling may improve the reliability of environmental contamination estimates that are made by simple linear interpo}atiorr or other algebraic weighting procedures. Use of geostatistical analysis to increase the spatial resolution of the local radionuclide inlwntory particularly improves the capability of calculating spatially averaged exposure-rates. Spatial variations in the radionuclide inventory in different sections of Rongelap Island have been documented (EG&G 1981; Simon and Graham 1995a). A variety of assumptions, therefore, were recently considered for the size of the portion of island that residents might frequently use for the purposes of collecting food (SMT 1995). Environmental radioactivity and exposurerates were spatially averaged for the purpose of simulating the exposure that island residents might acquire during food collection activities on various sized parcels of land (e.g.. 200, 500, and 1,000 m). These “radii of utilization” were judged to be relevant to the lifestyle of past or future Rongelap Island residents since nearly all food collecting is conducted by walking. The effect of increasing the radii of utilization is to narrow the distribution of exposure-rate values around the mean value and to reduce the dispersion of predicted doses. monitoring of ccmlernpomrj: radloiogicil rrl(t:i!;lll:{:rrlclrlt) in !mxpecli~ e assessment is generdl!, a stralghtit’orwnrd task: Itlc main difficlll[\, us de[erm[nlrlg M!!evant td]eKaln de!~criptkms fm future ~;jhat~itanrs). Jlosl prtwious as.ws~ ]nenu, for inhabitants of the !vlar!lhdll Islar](is ltil~’~ med dleu~ descript]om published b) >fiidu et JI. ( 198 I ) or unpublished di,et.ary infolntnatic)rrpro~ icled b): The Microne~im Legal Services Corpora[icn (see Roblson et al. 1‘)S2a. lb). A comprehensive anal:, sis of the chemic~l composition of the Rongelapew diel, w:as reported t~) Chakravarti and Held ( 1963) although most models apparently hale nol used those dar.:1.Ilecentij. E@narn et al. ~1994) reported ,a summary of a dietary survey of the Rongeiap community. resident since 1!)85 in Kwajalein Atoll The objective of that stud~ was to determine the di stribut ion of caloric intakes. pri~rnariy amol~g the adult I population, and to translate thos: CIata info a set (If s ;alt rn al ive die M of local food !l, “13tme die[ary ~deernpe liol~s wert: subN:quen[]y approved I?vlhc lFton~elap cOlr]lmunity WI represent their average e~ting h:d)its cmmm[]y ~amiM they wwulld Iilve (III l?orl@q2 under more ‘traditional living ccmdil,ions. These resulls provide a unique solu~ion to deterrnimmon of wadlcionai diet. one of the ma]rt problems of dose reconstructions [o island idlabitant~, Notwithstanding that there is great uncertainty in applying the dietary results to an) s~ngle individual. the dam can be used to describe both the curre[~t diet, which is mainly composed of imporred foods, and various opuons for more traditional eating habits. It is expected that this dieKary description can be reviewed by other communities in the Mm-shall Islands so that amendments relevant to individual commtmiues can be made, if necessary. IDiwal r!; dwta The ulse d Deposition of individual radionuclides A method of calculating concentrations of individual radionuc]ides on the ground following fallout deposiuon was published by Flicks ( ]982). The use of Hicks ( 1981 ) NTS data made possible dose reconstructions in and church 1986; Anspaugh et al. Ne~ada (Anspaugh 1990: Beck and Anspaugh 1990) and in Utah (Simon et al. 1990; Stevens et al. 1990: Stevens et al. 1992). Calculational results of relative external gamma radiation exposure-rates and related radionuclide ground deposition specifically for Pacific tests \vas published by Hicks ( 1984) for the events MIKE (Operation IVY): BRAVO, RO.MEO, and YANKEE ((lpemtion CASTLE); and ZL-NI, TEWA (Operation REDMTNG). Measurements of external exposure-rate (e.g., from Eisenbud 1953) can be used, for example, to determine the local concentration of the rad~oiodines. The reported exposure-rate needs to be first corrected to 12 h post demnation using the exposure-t-me decay data of Hicks ( 1984); the concentration of each radioiodine can then be determined at the time of fallout ,arrival (or any other reference time) using Hicks’ normalized deposition factors. Measurements of beta-activity on gummed film ie.g.. Harley et al. 1960) can also be used to determine i local en~ironmcn[ 0( wch ;3[011 ~IT)JIIIII} soi i ) can pomibiy Ot iodine Conlrlbme in relation to dhe undt?rs,t;jndlrlg [o other fisslorl Iot [he I]e]naf.lor Scajing Some attempts at $cali]lg ex.pcmre h:}’ clnan~es in distance tron-r the test sites have been made in order to ~implif) a~$e~~ment CidcubI[lOll~ ff)r O[her ]CJCdtbnS. Such methods, often used in “’ecologic”’ epidemiologic] studies. are normally a poor surrogate to location specific data. For example, simple estimation of thyroid dose for various atolls could be attempted by scaling downward the thyroid doses estimated at Rongelap by Lessard et al. [ 1985}. Scaling factors could ei[her be the ratio of respect~~e distances to the two atolls or r-a~ioof exposw-erates. Such methods likely yield poor results for at least tu’c)reasons First, the mixture of short-lived radioiodines is intimately related to the transit time of the fallout cloud and the dynamics of decay are not linear. Exposure-rate decreases at early times much faster than the total radioiodine concentration in air. Second, the relative importance of the exposure-pathways may change with location because of local differences in lifestyle (e.g., degree of urbanization, etc.), but, more importantly, because of possible differences in the particle size distribution of local fallout. Finally, a factor frequently overlooked was that the Marshallese community of Rongelap and Ailinginae and the U.S. weathermen on Rongerik. for which detailed thyroid dose assessments have been made (Lessard et al. 1985; Klemm et al. 1986: Goetz et al. 1987), were evacuated relatively soon after the initial exposures Scaling thyroid doses from the Rongelapese to other communities. therefore, cannot be done with certainty, mainly because other communities (e.~., Likiep. Ailuk. Mejit, etc. ) were not evacuated and subjected to decontamination, as were the Rongelapese. Althou~h deposition was significantly lower at other locations. no efforts were made to mmlmize contamination of food, water, or eating utensils. Nieasurement of 1291 The availability of fallout times-of-arrival from the HASL fixed-instrument monitors enables the estimation of local concentrations of mdioiodines immediately following deposition. For some locations and some events, there is little or poor historical data. In those cases, interpretation of other types of information may be necess~. In particular. the mewurement of ]’91 in the *T’he U.S. weatieman were evacuated from Rongenk M two 28 groups, at 3 I h and 36 h post shot. Sixteen Marshallese on kmgelap were evacumed by plane at 51 h pmI sho[: another 48 were evacuated at the same ume by ship. Elgh[een Marshidlese. [temporarily resident produc[.. ‘7”1deposited in the origintited :is F’aci$’ic region would i)tiie newsnril\ ~lotxd or loca] we~pons [cslt falloul: n;) other reyuonal source exis!ed. Thtls. [he gt?ograph]c pat!,em 0[ (‘()] deposition (tibme a regional background VUIUC) tiy be m used to mcertain tht: :~eosgraphic pat[ern of’ local, F~lloIiI and can be used to confirm the partern o!’ deposition SUg!gMUXl by [k memurernen(s ~9t’ ~yCs, 1 1‘?’)ltneinsured :in koi1 from a \ ariety of Iocalions within the U.S. has been sho\vn to remmn within the top 10 cm (Ii3rauer and Streb~n 198.2) (or severtil decades. Soil samples in 5 cm depth increments \vere obtained at locations across the Morshall Islands for the purpose of ‘c”] measurement. At this time. preparations of” soil samples have begun using a caustic fusion prepamtion rnethod~J followed b\ measurement b\ accelerator-based mass spectrome[ry t-see Kilius et til, ~992). Geographic pattern of thyroid disease prevalence as an imlieator of exposure Thyroid disease. both benign and malignant, is known to be caused by. among other things. exposure to ionizing radiation. In particular. the glands in the young are more radiosensitive to both disorders (Shore 1992; Wong et al. 1993). The occurrence of thyroid disease among the exposed Rongeltip population has been well documented (see t’or example. Robbins and Adams 1989). The geographic pattern of prevalence rates has also been used as a surrogate indicator of exposure. For example, thyroid nodular disease was investigated and reported by Hamilton et al. ( 1987): they found the prevalence to be in excess of that expected among a non-exposed population and to decrease with increasing distance from Bikini. They concluded that fallout radioiodine exposure was more widespread than previously believed in the Marshall Islands and that it was the likely cause of those neoplasrns. In the work of Hamilton et al. ( 1987), the prevalence rates of thyroid nodular disease in the Marshallese population nationwide were interpreted as a bioindicator of the possible exposure of the population. There are, of course. numerous difficulties in attempting to estimate the population exposure from prevalence rate data. In particular. the stochastic nature of disease occurrence is particularly apparent in small populations. In an effort to verify the conclusions of Hamilton et al. ( 1987), and to further attempt to understand the radiological health effects over the entire Marshall Islands nation, a nationwide thyroid examination program using both palpation and high resolution ultrasound was begun in early ]993. At the time of this writing. over 6,500 Marshallese. including 4.000 over the age of 30 y, have been examined for thyroid abnormalities. Preliminary results (Simon et al. 1993b) indicate that the prevalence of nodules is at least as high as reported by T Persomd commumcatmn. 199-$. L, Killus. Isorrace, Inc.. Toronto. I I 1 cm Sifo Island in Ailinginae Atoll were evacuated at 54 h posi sbrsl (Sharp and Chapman 1957 ). I I Hamilton el id. ( 1987) wd that th!roid cwtcer also .lppcar> to be in excess. Further stud! is underway for the FUITMW Of making more definitive conclusions concerning [he rates of disewe. Dose reconsmuction for Nlar+alkw alite at the time of Ihe utornic tests is necessarj I(I Merrnine the likelihood that those cases w-e trulv a !C,,UI[ raditit ion exposure. Of FINDINGS This puper briefly presents two of’ the most recent rewll~ of dose assessment activities in the Marshall Idand>: ( I ) summarizing the current radiological condi[mll.s at each atoll in terms of dose and (2) determining compliance of the radiological conditions at Rongelap t~i[h a dose action level for the purpose of prokiding (~uidance on resettlement. .The primary measurements from the NWRS were :]rcal Inventories (Bq m ‘) of 1~7Cs in soil and specific ;lc[i\]tles (Bq kg- ]) in a variety of native foods. These Incaiurernent data ha~’e been coupled with the Rongelab}l Dignan et al. ( 1994) and used !lc,c dietary description thut simulate the variabilt! i[ochastic dose calcula~ions \ {lt a number of parameters including plant uptake. .~:itial variation of exposure-rates over an island. and caloric intake rates among the population. Fig. -$ shows m example of the variation in predicted dose equivalent (external plus internal from ingestion of foods only) as u of 137CS (as measured function of net ill-.silu count-rate \vith a 4070 HPGe detector at 1 m height). The linear relationship superimposed upon the predicted values give the approximate median \ ~iue of the predicted dose m u function o!’ coun[-r~te: [he dispersion of the points around the line ]. lndica~l\e of the uncertain} of the median dose. The linear relationship between i}~-.ri~l~ measured count-rates und lnmrntil do.c was extended to Jll locations of’ the hlar~hall Isiands as means t(} Interpret Into estimates Of dose. The en\ ’ironmenttil count-rates predicted dose \aiues permln to unidentified indii’iduals at each atoll that might adhere to the general dietary description of the assessment scenario. The locationspecific environmental count-rates provided the scaling factor for each location. Lmts of dose. though not widely understood in a technical sense. can be compared among atolls and with ]ntematitrnd guidelines. As an example. Fig, 5 presents present day median estimates of external plus Internal dose (~’ia ingestion of food products onl} I from :‘- Cs on the islands of Bikini Atoll, These particular calculations assume a diet of 75%Iocal food and 25cc imported food (e.g.. rice). h should be noted here that onl) one of the islands in Fig, 5 is actually inhabited today tEneu island). Moreover, many of the other island> do no[ >upport sufficient food bearing plan[s to sustain a popula[lon, The assessment calculations in this figure are on]} intended as a tool to interpret environmental concentrations at each locations into a single consistent unit useful for comparison purposes by the Marshallese communities and government. A second important application of a dose assessment in the Marshall Llands was to satisfy requirements of a 2, 2 mSvy -1 =m” m (es”’) Value 0.124 27.713 0.905 q l. f-;- Chisq 1,5 “.”. . Ilaa F1 ..$ . :. q O . . “~ 1 . 0“5 — 0.5 () ~--–- c1 Net In-situ count rate from ‘3:CS (C s“]) mSv y ‘ ) as a furmion of net Fig. 4. Dose equlvislent-rtite (exlerntd + ]ngest]on. m-siiu count-rate (c s - ‘ ) from ‘“0, determined from numerical slmulmons of local food dtet. \, ? {? ; 1 > .. t ) > 1 ; I 1 1 ., ) I .. I ;! ......................................................... ............................................................. .................................... ...7 .. ;! .-,---~>, .................................................. ............................................... . “1 ~~11 rn W v = m “ {‘c :3 ) .................. ....... ............... .... \/’,:tl 11(; Ill o 1124 27.;?13 ICr-lmq .......... ....... ............. ......... ,..—. ,, i, (, ‘ ,p! II ,,,, -. >. w) .1, 13 om5 L !~“’’’’F’’’’”ll ,,,::,:::,::,,:,:,: -:=,:x::,,:,,, t,::::::-::,: , ,,,1 ,,’0 1--1L .7! .... ,,J,, ‘$. .,”, - . , (), j ..;.. ‘ .&hl’ r r‘ ii::’!. .*.” ,)~’ ; (, jjjpy’(’:l)’” “ !, ,,-’’””’ ---- 4 ~,.j,,:‘[)- '---"---------"--"-i;-----------""-"--------4---"--------"------N{:t in-situ count mu: from !~,” .. ,(.J ((: ;’) d ml in-$,ifu C(W4r11-Hk (1: 5”’) ihwll ‘ 3‘(~!,. 0 Fig. & Dose ,ch:hc rmimxi cqu Ivaknl-ralc f{mltfmd si m d al ims + II rlgml[icm. rn!$v y”- ‘ ]1 as a Iimc[iorl trx117n Inmlf:]ial of IIlrxd food [iiICL tkal~h 11<’-y .: .............. ..... ,Ph};w. (JcIOW: ] ,)!)6. ‘f (II LJ171? [ “~ ?~llmhi?l ~ --------------------------------------------------------------:-r..:, :; )0(. . ... .. :<: :, 01 :: :: .. :: . ..: . i I‘994). Robison et al. ( IIW-l I and ‘Th(me ( 19951. The rcsuitpresxntfxl !i hew fare lhe t’orrn 0} a cumulal[iI’e in pcpuialion [dkrribwim ot’ pmjcckcl (hes for adull women. :innmlg tm of 10 I[his ex:imp]e (IFus. 6). tlhe tari:morl of Idose~j the ]pop u 1illl i [m Irnmil 111 rt:llects the spatial ~haria I:! l:(:lnl~lrilli]l[iti[)n on R.cM7yelI:ip Island. the \wnaticm Cii U(lti C illtakc ]rn,ationaYId ;J ]rnat~treumd~rsti~r]dirig ~ofIifestjlle ;i[ttrnbu[e!>. (Mab:iw :rnm[ include lomt ion- :Ipecific ‘l-he r:diohgical raddqkal informa[iorr-----both current daui and data obtairted durin~~ d3e l,cstinj~ period ;orle needed. ]GortLl]nalte I :Y. 13(MII types of IIn format IIoIn me ov ail I10be for man:! I sir)gle msl ]mpomaut conceptual requiremem for conduct in~~l:tilid a:;wssrrmnts is ]reccrgn izing imrporAr[empfs 10 quanlity usual or 1:1~11 exposure ~i3tkiWiij’S unusi~al exposure pattlways remain as {con~enti~)l-1:~ is~ll~~ ommnf :slcicntisl, pracl.icirtg risk asses.5mne17t. (he Ikssorl s lem-nea repeatedly in Marsho]l Islands studies has been to rely on II(]c:dexpertise to pro’~’icle ]nformaticm irnjpormnt to acquiirnng an ulndcrstmdirr: of pathways. 1’40Ikxmer ir~forrnatio]n can be produced than that provided by d]e popillaticm whose quality of life is under examinatnrm. locatiom ‘l-he ,Ii plant ttptakc, and the vdria [ion of L‘,tlcdlaliom, -’ ‘\‘cd rates rmIglhl ilndikm Ihm about ,35% of t Iht: v(rmnc]7 y “-”‘ 1 ITLSV AL response-surface h ii model W;ISJlimxl 10 Natdardized sensilivi Ky artalvsii. TM partial aid regression correlalicm coefl”icnanls 01 the )rnodel out variables hpw arta]- vsis indicated that 80% of the ~umtior] in closes wm due m the variation in envhmnmerrtal count-rate unci caloric intake fii[es Fmlherrrtore. the analysi \ indici~td tha[ 927c of the variation in doses could be accounted for by imlilcling the wiriat-ion in plan[:soi]l cortcemtralticmratuos tor (he local food products ]ekeru, ccsmnut cream. arid pmtclantts. CONCLUSI(9NS Both retrospective and prospective dose assessments [’or iuhabilants of tlw ~\darsha]l lsktnds necevsaril} cwtcompass traditional dose assessment modeling techniques as well as relevant data for the erlvirommmtal and and ci-dtimd setting of the island nation. III the pcdntncal social corwext of the l’vlarshall Islands, specifying reievaru values for diet and lifestyle parameters for each atoll community as well as [he age and sex dist.ribiuion are key m credible assessments. Utilizing recent environmental radiological meitsurements arid an evaluation of \mrious dietary ah.ermihave been conducted retives, prospective assessments cently for two different purposes. First, the annual dose from external exposure and ingestion of lCICillfoods has been propted for all islands of the RMI m :i means to present a uniform and relatively easily understood metric that can be compared among locations and with intemati,onal guidelines. Representative findings are presented for Bikini Atoll. Second, a prospective assessment for the Island has betm condim.ed using popi~latiori of Ikmge]ap both traditional and current day diets. This exercise has provided irtformiathri useful for determiin]mg compliance action level an4i for advising with an agreed UPOII &se members on issues of safety and reseulecommunity rnertt. Dose reconstruction, on the other hand, has been extremely limited for ?vlarsha]lese. Data requirements for radiological dose for dose reconstruction as opposed to present day dose assessment are more severe because of the rapid rate-of-change of the radiomrclide mixture with time immediately after the test. Some historical tktm are available, however, for these purposes. Future dose reconstruction efforts will be for the purpose of radioepidemiicrlogica] analysis of the participams in a mt[imtwide thyroid disease study. Dose assessment activities have highlighted the need for a co]~iprehensive database of radiological irtfor- Ack/t~~tt/edgnlc,/lr,\----’rhls work was supporrcd by the Repub~Ic of the Marsha]l islands Natmrrwide R;IdIokr~!Ical Study. The autbon are mdehted 1{1 the Government of’ the R!t![ for the opportunil y [0 know il~ people and !0 he of service in matters ot ractiallon protection. Sevemt people crm!ritwted 10 the coi]ection ot (he da(ir ai pwt O( Ibe ‘N’\VRS, includun~! Su!;an llutly and Andrew lBanron. She!la CIornn and Andy Etorchert conducted radwehermstry wadyses. Peler CrIlver provided an .adminislrmive l~nk In the R,Ytl go!,ernrmtmt ami Ihe MIms,ury of l%mIgn AftaIrs Many Marshallew men :iwsled with ihe fieid work and in the t)peration of ihe Itikrcrmlrwy. Includlng ikmdy Thomas, Ake Jorm, T0117 Schrnick. Alex Noah, and Rosen Jorhw il. Members of the t?.ongelap cornmun~ty now re$ichnf! on fVfeJittlu Island have been pii{iem in waiting for sIudy resuhs and have been generous in crffering assusl.ante. Tbe late Senaux Je(on AnJam was instrumental m organizing the Rongclap Resettlement Project and the Mayor of Rongelap, B~lliet Fdrnond has assisted In the mhmmstmtion of the Prcqect. Many wienl.ists have wmke d ‘It]lry m umferslmsd the lnfcstyle and rdinlogica] protection questions relevant w the people of the Marshall Islands. Their work is cited hem. In p,~]~tlliir, }+enry Kclm’s wit and wisdom provided guidance for deterrmirrlng the obymhves mrd the starting pcum for the recent Rangelap !@vettlt!ment Projeci. Harry Pe[ttngitl of the L1. Department of Energv assisted In obtaimrg S mtorrnatwr corwemlng the f~eapons Iests zs well as provided Ioglsl]tcal support numerous times to the Rrrngelap Resettlement Prolecl. Wllilam Rolmwrn of Lawrence I.I vmrrrore Laboratory assi$ted in rrumerou~, cooperanve aclivi~ies with [he NWRS. Harold Beck anti Kevin Miller of he Envmmnrmwl Measurements Laboratory were especially helpful ~n Ibe area of rra-situ spectrome[ry The (J.S. Deprmrment of the Intermr supported the work of the Rongelap Resel[iemerrl project. Several Rhli Gtsvemtmeru offic~als have supported the work of the NWRS, in pamcular Mimster of Health and Environment. ‘~nn~ K!jmer and CIscar ck%rurn m his pmvucns capacity as Chief Secretary and now as, Ctramrnan of the Nuclear Clanns Tribunal. IK.Fujimtrri, 1“. Takahastm 11, Umomo, K, T&aya and others from the Second Department of Surgery of Totroku Umversity Schoot of Medicine (Sendui. Japan) conducted thyroid exammatlorrs !n sopport of the Natloo. wide Thyroid Study conducted by NWR5. The Scientif_rc Adviso~ Panel to the N’WRS (K. F. Bavet’stock. A. C. McEwan, K. R. Trott, K. Sankaranaryman mrd H. G. Paretzke) has prowded gu!dsmce and crverwght for the past 4.5 years. K. F, Baverwcck and A. C. tvlcEwwr also were mstrumen&d m the Rongelap Resettlement Project and K. R, Trott m the Eheye and hkyuro Thyroid Study. Apprcciahon M also extended to Ru!a Escher for provichng edilor’ial ms)stance and greatly needed moral support. Finiilly, this work is de(ilcfiled [o Men-i] Eiscrthud. HIS intefniy. Im!h scientific and personal. foresight and sense of priori[y are an mspmtirm. Hi$ pioneering efforts with HASL during the era of nuclear testing served to save the lives of !he Fiortgenk weather observers and )vhrshallese people resiciing on Rongclfip. These contributions have generally gone unrmucmf. .+T4 HealthPhys]lc. REFERKNCJE:S Ck((lher 1996, 1, olun7:: T I, INurnber .4 l+~smry A)soc]ales !khoo]l : IIw 1. Jncorpor:iled. The H is[oric !flonurose A f rlspiNj2h R..; Churchl. ]3 ~tf,”.}31![()[1C;]] .,[]~r)~[(:~ of 1... from ex(efi:l] gexposurr an(icoll(:c[i!e c~kmtil ye~pmure te~tin~~ ;II lhe ]~ic\z(i;l “TCS,[ ~i[r. ] “re\[ $~r~~f ~l]r~l]gh ! Fdardtack 11. 1958. f-lealtlr Pirys .51 S.5-.51: 19815. A17spaugh. l_ R.: Ricker, YE.. ifl~ack.!i C.: Grrw>m:ln.F, R.: Wheeler. D. L.: Church. B. N’.: Qulnrr. t’. E. Histoticai M]rnales of exkrmid : exposure and collective ewmal y lexp(l!jldrl:from [esttng at Ihe Newki ‘l-esl .SIk. 16, ‘r~s~ Series:ifter k{ard[aclill, 59:525 --!i32;, 1990. 1958. an(i Sumnmy, He;dtlhPhys. Biilr, W. J,: H~611~.J, W.: B. W WXhboUZ, B. U. IVfelclen radiation ilo ailin ko ituion ilo rnajol. ko rar eu.di i!o 1978 (The .Mk:anilng of l?adiat~on for Tho!)e .-ltolls in the Nor~hem Pmtofthe Mtirsl~all Islartds TIMI were Survqv:d rn 19%3) Wdtingmn,DC: (J,:S, De~]fiflmt:r]tolZr]erg):l)()~BMf 1052, 1!)82. J3easltvy,‘r. 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