U.S. flag

An official website of the United States government

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

National Research Council (US) Committee on Radiological Safety in the Marshall Islands. Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands. Washington (DC): National Academies Press (US); 1994.

Cover of Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands

Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands.

Show details

Executive Summary

The Committee on Radiological Safety in the Marshall Islands was established by the National Research Council in response to a request from the U.S. Department of Energy (DOE) to assist the department in evaluating radiological conditions on certain atolls in the Republic of the Marshall Islands, especially Rongelap Atoll. The need stems from the provisions of a memorandum of understanding (MOU) established between the Republic of the Marshall Islands and the United States in 1992. That agreement sets out criteria and stipulations pertaining to the resettlement of Rongelap Atoll. The issue of resettlement itself originated in the desire for the people of the Marshall Islands to return to the atolls from which they were evacuated as a consequence of nuclear-weapons testing by the United States during the 1940s and 1950s. The National Research Council was asked to review the scientific studies undertaken by the U. S. Department of Energy to determine if reliable and modem scientific methodology was being used to assess the potential hazard, if any, to persons who might return to live on Rongelap Atoll. A crucial provision of the MOU is that resettlement will occur only if no person returning to Rongelap and subsisting on a native-foods-only diet will receive a calculated annual whole-body radiation dose equivalent of more than 100 mrem above background. The MOU also presents an action level of 17 pCi/g for the concentration of transuranic contamination, i.e., plutonium and americium, in soils below which mitigation will be considered unnecessary.

The assessment of the radiological conditions on Rongelap resulting from the U. S. testing program is narrowed somewhat by the weathering processes and nuclear-decay that has transpired during the 40 years since the atoll was contaminated. At the present time, the isotopes that would contribute significantly to the dose to individuals who might reside on Rongelap are those of strontium-90, cesium-137, plutonium-239, plutonium-240, and americium-241. Of these, cesium-137 accounts for more than 90% of the estimated dose, strontium-90 provides the second most significant contribution at 2-5%, and the transuranic nuclides contribute less that 5% to the total estimated dose.

Resettlement of the northern Marshall Islands is a precedent-setting activity. As far as this committee is aware, the current efforts to resettle the Marshallese are among the first in which a government has undertaken to facilitate and monitor the return of a population that was displaced because of concerns for radiation exposure. The utility of the criteria and procedures used and the resulting protocol might extend well beyond the present situation. The people of Rongelap resettled their homeland in 1957 only to leave again in 1985 ''on the belief that Rongelap was unsafe and that DOE had not told the truth about radiation—either with respect to its contamination of the lands and environment of Rongelap Atoll, or as to its impact upon the people.''1 It is important that the current effort to assess the radiological conditions and their potential impacts on the people of Rongelap avoid the problems of the past.

In its charge to the committee, DOE directed the committee to review and comment on the scientific and technical merit of the processes and procedures used by DOE and its contractors in its evaluation of the radiological conditions on Rongelap and, in short, to determine whether its assessments meet the standards of good science. The committee was asked to give attention specifically to several subjects, including: the appropriateness of application of the International Commission on Radiological Protection's (ICRP) annual radiation dose limits to the dose commitments expected to follow resettlement; the applicability of metabolic and dosimetry models for ingested radioactive materials; the implications of proposed dietary regimens for calculated dose projections; the effect of variations in the native-to-imported food ratio and differences in diet due to sex, age, or individual preference; the methods proposed to reduce exposure to radioactive materials by inhalation or ingestion; the adequacy of follow-up analytical techniques; and the long-term consequences to health of proposed remediation of the environment.

In meeting its charge, the committee had access to reports (both internal, many in draft form, and published) prepared by DOE contractor staff that covered the wide range and varied aspects of the radiological assessments being conducted in the Marshall Islands. In addition, the committee members visited DOE contractor laboratories to observe the procedures and facilities developed and applied in studies of the radiological conditions in the Marshall Islands, conducted numerous discussions with DOE contractor staff and with other scientists actively investigating the conditions in the Marshall Islands, and traveled to the Marshall Islands for a close look at the sites of current radiological studies on Bikini and Rongelap and to observe the conditions on the islands of Mejatto and Ebeye, where many of the previous residents of Rongelap now reside. Discussions were conducted at the National Academy of Sciences facilities in Washington, D.C., and on Mejatto with the leaders of the people of Rongelap who wish to resettle. The committee also was provided with detailed information on the studies being conducted by the Nationwide Radiological Study and the Rongelap Resettlement Project, both of which are under the direction of Dr. S. L. Simon, a health physicist employed by the Republic of the Marshall Islands.

The committee conducted a comperhensive review and evaluation of the data available to it regarding the investigative procedures and models used in the assessment of the potential doses that might be incurred by those individuals who choose to return and live on Rongelap. In many instances the committee had to rely on discussions with the investigators, and unpublished procedures and results provided in internal reports in its investigation; it seems not to have been the tradition of these DOE programs to publish extensively in the peer reviewed literature. Based on its experiences, the committee would recommend that in the future the Department of Energy place greater emphasis on publishing results obtained in its programs in the peer-reviewed literature.

The MOU that was negotiated between the governments of the United States and the Republic of the Marshall Islands includes a rather unusual requirement in its presentation of a radiation dose limit in terms of the dose to the maximally exposed resident. In general, the techniques of radiation dosimetry are not developed for determination of dose to the maximally exposed individual; it is particularly difficult for a population of limited size where the statistical power for determining doses at the extremes of dose distributions is limited. In addition, this population has the potential to gather food from other islands that may have higher radiation burdens, and individuals may "binge" on foods of higher than average radionuclide concentration, e.g., coconut crab. These possibilities make estimates of the dose to the maximally exposed resident highly uncertain. The committee would prefer that the MOU conform to more common radiation protection practices in stating dose limits, however it was not within the charge to the committee to implement or recommend changes to the MOU; these provisions stem from a previously negotiated international agreement. Therefore, assessment of dose estimates and application of dose modeling must be considered within the context of the provisions of the MOU. Although the available data and the standard procedures in radiation protection do not lend themselves to an accurate evaluation of the dose to the maximally exposed resident, the committee presents an assessment of the use of statistics, and of scenarios, in the report in an attempt to address this issue.


The following summarizes the committee's conclusions based on its review of all the material acquired during the course of its deliberations concerning the points enumerated in the committee's charge.


Applicability of ICRP recommendations on annual dose limits. The committee was asked to comment on the ICRP recommendations for general populations as related to the resettlement of Rongelap and other Marshall Islands populations. Because the ICRP recommendations were not developed with the present situation in mind and annual dose limits have already been negotiated for the resettlement of Rongelap and formalized in the MOU, the committee did not feel that it would serve a useful purpose to undertake a detailed discussion of exposure standards. Although the ICRP dose limits applicable to the public were not designed for application to resettlement of previously contaminated land, the ICRP recognizes the use of numerical criteria, action levels as defined in the MOU, as useful tools in decision making. This issue is discussed in Chapter 7.


Environmental sampling and analysis. The programs for systematic environmental sampling and radioassay of soil, vegetation, water, and foodstuffs on Rongelap have been broad in scope and of very high quality. The major focus of these studies has been on the concentrations of cesium in the soil, breadfruit, coconuts, and pandanus and the concentrations of transuranic elements in the soil as the primary radionuclides of interest in this environment. The rigid application of reliable laboratory techniques by the scientists of the Lawrence Livermore National Laboratory (LLNL), a DOE laboratory, has provided a substantial background of information useful in the estimation of potential radiation doses to the resettlement population from exposure to radiation in the environment or through ingestion.


"Hot Spots". The potential for radionuclide hot spots in unsampled regions of the island has been of notable concern to the Rongelap community. However, given the relatively uniform distribution of radionuclides observed in the LLNL grid used to sample soil for radioactivity on Rongelap and the nature of the source contamination, the committee sees little reason to suspect the existence of localized high concentrations of radionuclides (plutonium, cesium, etc.) that would contribute to "hot spots." (The committee has accepted the definition of a "hot spot'' as a local region in which the radionuclide concentration has a value of 10 or more times the mean of the present observations.)


Dietary models. The information obtained from a number of dietary surveys does not appear adequate to provide a reasonable estimate of either current or indigenous diets for the Rongelap community. Based on the available information, however, the committee estimates that a sizeable fraction of the persons on a purely native diet, or any other diet that includes a large intake of coconuts, could exceed the 100-mrem, above normal background, annual dose equivalent limit specified in the MOU. The effects of these uncertainties in the diet models are also discussed in conclusions 6 and 7 below.


Measurements on humans. The whole-body counting system currently used in the Marshall Islands by DOE contractor staff of the Brookhaven National Laboratory (BNL) is practical and reliable for measuring cesium-137 body burdens. To monitor the Rongelap population adequately for whole-body burdens, so that sufficiently accurate information is obtained to assure compliance with the MOU, it will be necessary to follow individuals in the resettlement population systematically for an indefinite period of time. In the environment of Rongelap, strontium-90, plutonium-239, and plutonium-240 are expected to make only a very minor contribution to doses received from the long-term exposure. The accurate measurement of plutonium-239 and plutonium-240 in the urine at the expected very-low levels is extremely difficult, if possible, using current techniques. The problems in accurately measuring and interpreting concentrations of plutonium in urine need to be addressed, improvements documented, and practical considerations and limitations understood in any program that might be set up to monitor plutonium intake.


Dosimetry and its application. Dose estimates have been made by DOE contractor personnel in accordance with accepted methods put forth by the ICRP. External-dose estimates are accurate and sufficiently comprehensive. Internal dose estimates—those related to doses received through inhalation, ingestion, and absorption—are less complete because age-specific estimates are absent. This is not a serious deficiency within the context of the present situation, because estimates for cumulative dose based on the "reference adult" tend to be conservative. In addition, uncertainties introduced by dosimetric techniques are, in general, small relative to those related to dietary information and individual variability.


Uncertainty in dose projections. Two generally accepted methods are used to estimate doses to the maximally exposed individual. One is the probabilistic approach that uses the means and variances of the radiological components used in modeling. The other is the scenario approach, which specifies characteristics of some maximally exposed resident, such as age, sex, residence, and diet. The LLNL dose projections principally used a sophisticated probabilistic approach, but their validity is limited by the small number of samples available for estimating distributions of dietary radionuclide intake and retention. On the basis of using a scenario approach, the present committee estimates that the average individual consuming a local-foods-only diet could receive an annual dose of 92-106 mrem/y, depending on the choice of diet; this estimated range is based on what the committee feels is the most likely combination of local foods and energy intake (see Chapter 5, Table 5-4). Uncertainty in the dose estimate for a particular scenario depends on the uncertainty in environmental sampling data and uncertainty in the dosimetry. Uncertainty in the probabilistic approach also depends on those sources of uncertainty, as well as uncertainty in the dietary intake and in other individual characteristics.


Health effects of remedial actions. The committee believes that the major environmental remedial action now under consideration, the use of potassium fertilizer, would not adversely affect the health of those residing on Rongelap and in fact, to the extent that it increased cultivar yields, would improve the nutrition of the population. Potassium chloride is a fertilizer commonly used in the United States with no known acute or chronic health hazards when used for this purpose. A second, more local remedial action, clearing contaminated soil from the village area, would likewise pose no adverse health effects. The Committee felt that stripping the island of the organic soil to remove contamination in the upper portions of the soil would, however, be unwise owing to the fragile ecology of the island and the long time required for regeneration of the organic topsoil.

Based on the committee's review of the scientific data, the potential radiation doses from the different sources of exposure that might accrue to those who choose to return to live on Rongelap are summarized in Table 1. Here we present dose contributions from two of the several possible diet scenarios that were discussed in the text, namely those provided by the local-plus-imported-available diet (scenario A) presented by Robison et al. (1993), and the local-foods-only diet of Robison et al. (1993), but with the caloric intake adjusted to reflect what the committee feels is a more appropriate energy intake for an active population, i.e., the same calorie intake as obtained for the local-plus-imported-foods diet (scenario C).

Table 1.. Summary of projected Average Radiation Exposures to Rongelap Residents.

Table 1.

Summary of projected Average Radiation Exposures to Rongelap Residents.


On the basis of its review, the committee offers the following recommendations.


Because of the substantial uncertainties in this complex and unprecedented situation, the committee recommends that no categorical assurances be given concerning the MOU requirement that no individual receive a calculated annual radiation dose equivalent of more than 100 mrem above background. Some people returning to Rongelap and subsisting on a local-food-only diet might receive an annual dose in excess of 100 mrem above background if there is no remedial action.


If the citizens of Rongelap decide to accept the uncertainties in dose estimates and return to Rongelap, the Committee endorses two, possibly temporary, remedial actions:

  • The immediate and, as appropriate, continuing application of potassium chloride as a fertilizer to decrease uptake of cesium in foods wherever there are coconut palms or pandanus trees on the island.
  • On resettlement, acceptance of an initial diet in which about half the calories are derived from non-native foods (which might be necessary in any case to support the population while it attempts to re-establish the island's economy).
    These remedial actions can be regarded as temporary measures in the sense that both might be relaxed if monitoring results in appropriate assurance that the dose limits negotiated in the MOU can be met.

To provide reassurance to the people of Rongelap that the limits of the MOU are being met, the committee recommends that, until experience dictates otherwise, every member of the resettled community receive a whole-body count for radionuclide burden and provide a urine sample sufficient for analysis for plutonium before resettlement and each year thereafter. In addition, a cohort of approximately 80 persons (assuming a total resettlement population of approximately 400 people) stratified by age and sex should be examined four times a year in the same fashion to establish seasonal fluctuations, which must be understood if annual doses to the most heavily exposed are to be calculated.


The committee recommends that at the outset, to meet the terms of the MOU, the northern islands of Rongelap and Rongerik Atolls be considered "off limits" for food-gathering. This constraint may be relaxed if the experience of the first several years indicates that the 100-mrem standard would be met even if food-gathering were extended to the northern islands. The environmental sampling program conducted on Rongelap has provided an appropriate background of information for estimating the potential doses for the resettlement of Rongelap Island. The committee recommends that a continued effort be made to characterize the other islands in the atoll that may be used for food gathering in the future. This data is needed to provide detailed estimates of doses that may occur as a consequence of such activities. Such a research effort should be carefully designed with goals established in concert with the needs of the people of the region and in consultation with experts in environmental monitoring and dose assessment. In addition, the committee recommends that environmental monitoring of edible fruits be continued with a focus on determining the biological retention of radionuclides in the environment.


The committee recommends that medical services, with comprehensive medical-record maintenance, be initiated to permit continuing evaluation of the health status of the returning population. This recommendation is not in anticipation of radiogenic illness among those persons, but rather is intended to meet the need for factual information if the community becomes concerned about radiogenic consequences.


The committee recommends that a more formal coordination of the radiological-assessment activities of BNL and LLNL be established than has existed in the past. Similarly, these activities should be coordinated with those of the Scientific Management Team of the Nationwide Radiological Study of the RMI.



Quoted from the testimony of Senator Jeton Anjain, Marshall Islands, on behalf of the people of Rongelap, before the House Committee on Appropriations, Subcommittee on Interior and Related Agencies, The Honorable Sidney R. Yates, Chairman, May 9, 1991.

Copyright 1994 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK236604


Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...