4.
Measurements on Humans

The measurement of the kind, quantity, location, and retention of radionuclides in the body (often called bioassay) is accomplished either by direct means or by indirect means. With direct, or in vivo, bioassay, a radiation detector (or system of detectors) outside the body is used as a whole-body or partial-body counter to identify and estimate the body burden or organ burdens of radionuclides. This method can be used for radionuclides that emit radiation that is sufficiently penetrating to be detected outside the body, such as penetrating gamma rays associated with cesium-137, potassium-40 and cobalt-60. Indirect, or in vitro, methods involve the collection and analysis of samples that are excreted, secreted, or removed from the body (such as urine, feces, breath, hair, and perspiration) and infer the body burden or organ burdens through use of a metabolic model. In vitro methods, commonly urinalysis, must be used for radionuclides whose emissions cannot be readily detected outside the body, such as plutonium and strontium.

Bioassay measurements have both historical and prospective relevance to the Marshall Islands situation. Historical measurements provide information on the uptake of radionuclides from past habitation on the islands, provide data on the metabolic behavior of the relevant radionuclides in these populations, and provide a basis for testing models that are used to estimate intake and radionuclide burdens from environmental data. A contemporary bioassay program would establish preresettlement baselines on the people expecting to return to Rongelap. A bioassay program for the Rongelap people after resettlement will provide a means for tracking dose from future radionuclide intake.

Bioassay measurements on Rongelap residents have been performed by BNL personnel as part of a medical examination program after the nuclear-test series in the Pacific (Lessard et al., 1984; Miltenberger et al., 1980; Sun et al., 1992b). Whole-body counting, with emphasis on cesium-137, has been conducted since 1958. From the studies conducted by BNL during the Rongelap resettlement from 1957 to 1985 the whole-body measurements were instrumental in providing information on the build-up of radionuclide burdens. For the first few years after resettlement the body-burdens of cesium-137 and strontium-90 increased, reached an equilibrium with the environment, and then began a gradual decline. The body-burdens of cesium-137 were found to reach their peak in 1965 at about 23% of the maximum permissible lifetime values for world populations (Conard, 1992). In the early 1980s, BNL began investigating urine-bioassay methods suitable for detecting plutonium-239 and 240 in the Marshallese. Early attempts using a Photon Electron Rejection Alpha Particle Liquid Scintillation (PERALS) technique were unsuccessful owing to high readings contributed from naturally occurring concentrations of polonium-210. These findings prompted the development of the fission-track analysis (FTA) method to obtain better sensitivity by removing the polonium interference. Unfortunately the early PERALS and FTA results, which were released without adequate QA, may have contributed to the people of Rongelap deciding to leave their



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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands 4. Measurements on Humans The measurement of the kind, quantity, location, and retention of radionuclides in the body (often called bioassay) is accomplished either by direct means or by indirect means. With direct, or in vivo, bioassay, a radiation detector (or system of detectors) outside the body is used as a whole-body or partial-body counter to identify and estimate the body burden or organ burdens of radionuclides. This method can be used for radionuclides that emit radiation that is sufficiently penetrating to be detected outside the body, such as penetrating gamma rays associated with cesium-137, potassium-40 and cobalt-60. Indirect, or in vitro, methods involve the collection and analysis of samples that are excreted, secreted, or removed from the body (such as urine, feces, breath, hair, and perspiration) and infer the body burden or organ burdens through use of a metabolic model. In vitro methods, commonly urinalysis, must be used for radionuclides whose emissions cannot be readily detected outside the body, such as plutonium and strontium. Bioassay measurements have both historical and prospective relevance to the Marshall Islands situation. Historical measurements provide information on the uptake of radionuclides from past habitation on the islands, provide data on the metabolic behavior of the relevant radionuclides in these populations, and provide a basis for testing models that are used to estimate intake and radionuclide burdens from environmental data. A contemporary bioassay program would establish preresettlement baselines on the people expecting to return to Rongelap. A bioassay program for the Rongelap people after resettlement will provide a means for tracking dose from future radionuclide intake. Bioassay measurements on Rongelap residents have been performed by BNL personnel as part of a medical examination program after the nuclear-test series in the Pacific (Lessard et al., 1984; Miltenberger et al., 1980; Sun et al., 1992b). Whole-body counting, with emphasis on cesium-137, has been conducted since 1958. From the studies conducted by BNL during the Rongelap resettlement from 1957 to 1985 the whole-body measurements were instrumental in providing information on the build-up of radionuclide burdens. For the first few years after resettlement the body-burdens of cesium-137 and strontium-90 increased, reached an equilibrium with the environment, and then began a gradual decline. The body-burdens of cesium-137 were found to reach their peak in 1965 at about 23% of the maximum permissible lifetime values for world populations (Conard, 1992). In the early 1980s, BNL began investigating urine-bioassay methods suitable for detecting plutonium-239 and 240 in the Marshallese. Early attempts using a Photon Electron Rejection Alpha Particle Liquid Scintillation (PERALS) technique were unsuccessful owing to high readings contributed from naturally occurring concentrations of polonium-210. These findings prompted the development of the fission-track analysis (FTA) method to obtain better sensitivity by removing the polonium interference. Unfortunately the early PERALS and FTA results, which were released without adequate QA, may have contributed to the people of Rongelap deciding to leave their

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands homeland for Mejatto in 1985 (Sun et al., 1992c). Whole-body Counting Review of Activities Detailed information on the whole-body counting (WBC) system, its use, and the associated quality-assurance (QA) program was given to all members of the committee in a notebook entitled Operating and QA Procedures Documents for the Radiological Dose Assessment Project. In addition, the current Marshall Island Radiological Safety Program at BNL was reviewed by several members of this committee during a site visit on May 28, 1992. That visit provided the opportunity to review much of this material and to see an operating WBC system similar to the two currently used on the ship, Offshore Venture, during sampling trips to the Marshall Islands. The committee was also provided copies of a report dated April 23, 1990, prepared by an independent BNL scientific review committee. The report was attached to a letter dated May 2, 1990, from Roscoe L. Hall, chairman of the review committee, to Walter Kato, chairman of the BNL Department of Nuclear Energy. The review committee reported that "the whole-body counting procedures used for estimating total body burdens of cesium-137, potassium-40 and cobalt-60 were within acceptable guidelines of technical excellence and conformed to recognized standards set for making accurate measurements of these radionuclides in vivo." Recent bioassay missions to the Marshall Islands were conducted during July 1989, February 1991, and June 1992. The general approach during those missions was to measure baseline cesium-137 body burdens in populations from Enewetok, Rongelap, and Utirik Atolls. Table 4-1 shows the numbers of persons (volunteers) that were counted who were residents, or former residents, of those locations during the 1989 and 1991 missions and the population average dose rates from ingested cesium-137 based on those measurements; the uncertainties in doses shown as 1 standard deviation (L. C. Sun, Personal communication, 1994) Each person was counted for 15 min. Because two different chair-oriented counting systems were used, part of the QA program involved recounts of some persons in the same chair and cross-counts of some persons in both chairs. There was no statistically significant difference between original counts and recounts at the 97% confidence level or between original counts and cross-counts at the 99% confidence level; hence, the precision obtained in these measurements was judged to be high. On the basis of information provided on the counting and standardizing procedures and on the QA program, the committee believes that the program is technically sound and capable of producing consistent, reproducible, and high-quality WBC measurements of Marshall Island residents. Two aspects of dose-assessment strategy that will need to be addressed are who should be counted and how often counts should be made. The MOU for the Rongelap Resettlement Project bears directly on those aspects. A primary condition for determination to initiate resettlement is (Article II, Section 2) "that the calculated maximum whole-body radiation dose equivalent to the maximally exposed resident shall not exceed 100 millirem (mrem)/year above natural background, based upon a local food only diet." Also, the MOU

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands Table 4-1. Numbers of Persons Residents and Former Residents of Several Locations Who Volunteered for Whole-Body Counting and the Population Averages of Cesium-137 Annual Dose Rates Determineda   Number Persons Counted Cesium-137 Population Average Annual Dose Rateb   1989 1991 1989 1991 Enewetok 216 311 11 ± 3 (1.1 ±0.3) 22 ± 4 (2.2 ± 0.4) Rongelap (Mejatto) 258 427 3 ± 2 (0.3 ± 0.2) 2 ± 2 (0.2±0.2) Utirik 414 272 39 ± 2 (3.9± 0.2) 35 ± 3 (3.5 ± 0.3) Others 28 41       — —     Totals 916 1,051     a Data presented in an unpublished Brookhaven National Laboratory internal report (Sun et al., 1992c); based on measured WBC distribution medians from cesium-137. b Dose rates expressed in units of μSv/y (mrem/y); uncertainties are 1 standard deviation. states (Article II, Section 11) that ''the parties ... recognize the need for continual radiological monitoring both of returned citizens and of the Rongelap Atoll environment upon resettlement." As will be seen later, cesium-137 will continue to be the major contributor to dose; therefore WBC should be the primary means of providing continued radiological monitoring. The emphasis of the BNL program has been on population-related values. However, with the emphasis given the maximally exposed resident in the MOU, changes in the future direction of the WBC program might be required. It appears that the BNL program, has so far emphasized how many people to count, rather than whom to count and how often to count them. There has been no plan to follow a defined group of individuals with prescribed characteristics of age distribution, life style, or diet; instead, only volunteers have been counted. Because the makeup of the volunteer group has been different in each sampling trip, it is difficult to interpret increases or decreases in average cesium-137 body burdens measured in the sampled population from one sampling trip to another and it's particularly difficult to obtain and maintain individual records that will be needed to evaluate future trends. The BNL staff has considered an effort to locate records for persons who have undergone multiple whole-body counts. Although this effort might provide some additional information, the long time between counts is a critical shortcoming. All WBC is now currently done on the ship Offshore Venture and can be done only when the ship is available for BNL use. Other organizations, such as LLNL, use the ship, and seasonal weather conditions also affect the schedule. According to BNL personnel, plans call for one sampling trip per year and half the planned survey done each year, for instance, Rongelap and Utirik is sampled one year and

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands Enewetok and Bikini (Kili) the next year. On this schedule, the Rongelap people will be counted every 2 y; this is an inappropriate schedule for trying to follow possible intakes of cesium-137 which has an effective biological half-time of about 100 d. Recommendations The Committee offers the following recommendations for the WBC program: Until experience dictates otherwise, the program should ensure that every member of the resettled population receives a whole-body count annually. This will aid in providing assurance that the conditions of the MOU are being met by determining actual body burdens and thereby providing the data necessary to evaluate the dose to the maximally exposed resident. Adopt the approach of following a defined Rongelap subpopulation during different seasons to obtain a better temporal definition of cesium-137 uptake and loss before and after resettlement. Summarize the data on persons who have participated in the historical WBC program over the long term. This will aid in identifying a core study group for the future. It would also provide insight into the initial rapid increase observed in cesium-137 body burdens in the "average adult" from 11 nCi in 1957 to 730 nCi in 1958 and the increase from 170 to 280 nCi during 1979-1982. Develop the facilities or logistical capability for regular, more frequent counting of the study group. There are two possible approaches. One would be to use another ship that could be dedicated most of the time to WBC activities; this option might not be feasible, because of the substantial costs involved. Another approach is to establish facilities at selected locations so that WBC instrumentation could be quickly installed, used, and moved to the next location; this option seems possible on the basis of experience in maintaining WBC facilities in remote areas (Hanson, 1982; Hanson et al., 1964), although some logistical aspects would have to be addressed, including staffing, electrical power, water, air conditioning; and continued participation of the study group. Centralized, land-based WBC facilities on three atolls in the Marshall Islands (or however many locations are deemed necessary for the DOE mission) would have several advantages over the current ship-based practice: weather conditions would be less constraining, more adults would be available without the 24-h confinement to the ship now required, sampling could include more frequent recounts of people (as recommended above); and greater mobility and flexibility of WBC capability could be integrated with dietary and life style phenomena to provide measurements at critical times indicated by that information. Give greater representation to adolescent females in the WBC program. In 1983 dose rates calculated for cesium-137 in young females (59 mrem/y) were nearly twice those calculated for adult males and females (32 mrem/y). Adolescent females had cesium-137 body

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands burdens exceeding those of both adult males and adult females during the measurement years 1981-1984 and 1989. Urinalysis for Plutonium According to the dosimetry estimates made by Robison et al. (1993), the primary contributors to the annual effective radiation dose for persons on Rongelap Island would be the external dose from cesium-137 in the soil and the internal dose from cesium-137 in food. Together, those two sources account for about 95% of the annual radiation dose. The inhalation and ingestion of plutonium-239 and plutonium-240 account for about 1% of the calculated annual effective dose, as does the inhalation and ingestion of americium-241. Although plutonium-239 and plutonium-240 are expected to be minor contributors to the annual effective radiation dose, plutonium is a concern of the Rongelap people and soil concentration limits are included in the MOU. A logical follow-up to assure the limits are not exceeded is to determine the extent to which plutonium-239 and plutonium-240 have been deposited in the bodies of Rongelap residents after resettlement and verify that plutonium-239 and plutonium-240 are in fact minor contributors to dose. As discussed above, WBC is a useful tool for measuring internal burdens of radionuclides that emit radiations, x-and γ-rays, that can escape from the body and be measured by external detectors. However, WBC is not useful for measuring low-level internal deposition of alpha-emitting radionuclides such as plutonium-239 and plutonium-240 because of the very short range of the emitted alpha radiation (about 40 μm in unit-density tissue). Therefore, an in vitro bioassay test, such as urinalysis, is generally used to detect and estimate the magnitude of internal deposition of plutonium and other alpha-emitting radionuclides. The usefulness of urinalysis for assessing possible uptakes of plutonium after resettlement depends on the expected magnitude of internal deposition, the fraction of the internal burden excreted per day, the sensitivity of the analytical radiochemical method used, and other factors. Urinary excretion of plutonium by resettled Rongelap persons will consist of a baseline long-term excretion from any residual systemic burdens acquired from previous exposure, a baseline component consisting of prompt and long-term excretion from the general worldwide environmental contamination, and the potential prompt-excretion component (plus, eventually, the long-term excretion) from any intake associated with resettlement. Pertinent questions regarding long term follow-up of a population that has potential for ingestion of plutonium then are these: What is the expected baseline excretion for these people? What new contribution is likely to be expected from local sources, and can it be detected in the presence of the preexisting component? What excretion corresponds to a "significant" increment of intake, and can it be detected in the presence of the pre-existing component? Sensitivity Requirements When absorbed from the gastrointestinal tract after ingestion or from the respiratory tract after inhalation, plutonium enters the blood and is deposited primarily in the liver and skeleton where it is retained for biological half-lives of 20 and 50 y, respectively. A small fraction (about 1%) of the amount that enters the blood is excreted in the urine during the first day after

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands absorption. Later urinary excretion of plutonium from this absorption decreases rapidly because of the prolonged retention of plutonium in the liver and skeleton, eventually approaching excretion of about 2 x 10−5 of the systemic burden per day. Knowledge of these rates is important when interpreting the analytical results for plutonium in urine. Because of worldwide fallout of plutonium due to atmospheric testing of nuclear weapons, it is likely that residents of the northern hemisphere have sufficient systemic burdens of plutonium to produce daily urinary plutonium excretion rates of around 2-4 μBq (54-108 aCi; aCi = attocurie = 10−15 Ci) (Boecker et al., 1991). The urinary excretion of plutonium by Marshall Islands residents has been measured recently with a very sensitive fission-track analytical technique that is claimed to detect plutonium-239 concentrations as low as 2 μBq (54 aCi) per 24-h urine sample (Sun et al., 1992b; Sun, private communication, BNL briefing, 1992). In their estimates, Sun et al. assume an excretion of 1-2 μBq (27-54 aCi) per 24-h urine sample from adults as a result of global weapons fallout. Of the 67 Rongelap urine samples assayed in 1989, 16 were above 2 μBq (54 aCi) for a 24-h sample; the highest was 6 μBq (162 aCi). Values of this magnitude are the background levels against which the results of future urinalysis must be distinguished to follow any possible future uptakes of plutonium after resettlement. After resettlement, exposures might occur as a result of ingestion of plutonium in food or soil or inhalation of plutonium resuspended into air from the soil. Such exposures would be expected to be primarily low-level, chronic exposures. Two approaches can be considered for analysis of plutonium in Rongelap residents exposed under these conditions: the very sensitive fission-track process now being used by BNL staff and the much less sensitive alpha spectrometric process currently used to detect and assess possible occupational exposures to plutonium. Considerable day-to-day fluctuations occur in urinary excretion of plutonium and these fluctuations in the background excretion rates can interfere with the detection of a very small increases in the level in plutonium due to chronic intakes after resettlement. For purposes of discussion, assume that urinary excretion must increase by 4 μBq (108 aCi) for it to be detected above the existing background excretion level. With the long-term urinary excretion factor of 2 x 10−5 of the systemic burden per day, such an excretion would correspond to a systemic plutonium burden of about 0.2 Bq (5.4 pCi). With an approximate dose-conversion factor of 27 μSv of annual effective dose from 1 Bq of systemically deposited plutonium (0.1 mrem/pCi), a systemic burden of 0.2 Bq (5.4 pCi) would result in an annual effective dose of 5 μSv (0.5 mrem). Those conditions suggest that the fission-track analytical process could be used for long-term urinalysis to follow the possible systemic deposition of plutonium from low-level chronic exposures that would contribute a small fraction to the total dose likely from radionuclide contamination. If the fission-track analytical method is used for that purpose, it is important to understand possible problems with its use. It is still a new method with which little operational experience is available as described later. The method is extremely sensitive, and fluctuations in the observed daily excretion rate can be quite large for a variety of reasons including temporarily larger excretions from very recent intakes. These fluctuations could be misleading in interpretation. As an alternate approach, one might consider the use of the alpha-spectrometry method.

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands However, the detection sensitivity is about 1/40 that of the fission-track method, and the minimum detectable systemic burden would be about 7 Bq (189 pCi). Such an internal burden of plutonium would result in an annual effective dose of about 0.2 mSv (20 mrem), or 1/5 the annual limit specified in the MOU. This method, therefore, is insufficiently sensitive and does not provide a useful alternative to the more sensitive fission-track analytical process. Review of Activities A program of urinalysis of the Marshallese, in addition to the WBC program, is being conducted by BNL. In this committee's review of BNL activities, it observed problems in the methods, partly because of the attocurie-level sensitivity they are attempting to achieve (Moorthy et al., 1992). Because the rate of excretion of systemic plutonium is so small, the procedure for its analysis must have high sensitivity. The BNL procedure, which is based on fission-track counting, consists of many steps and is very time-consuming. To avoid contamination by uranium, whose 235 isotope produces fission-tracks that would be interpreted as being caused by plutonium, elaborate reagent-purification and container-cleaning procedures are necessary. Separation and purification of plutonium are accomplished by anion exchange. Because of great changes in volumes and concentrations of the solutions, two anion-exchange steps are used, the second with distilled acids and carefully washed containers to exclude uranium. The purified plutonium fractions are mounted on quartz slides that have been exhaustively washed, and they are sent to a reactor for neutron irradiation, after which the number of fission tracks on each slide is carefully determined. The results are used to calculate the amount of plutonium-239 present. The sensitivity of the method is estimated to be around 2 mBq (54 aCi). As anticipated, the complex nature of the plutonium analysis resulted in the development of an extensive radioanalytic procedure. During the review of the procedure supplied to committee members as a BNL internal report there were a number of questions raised. The documented BNL procedures given the committee contained errors that could lead to improper chemical operations that could invalidate the final results, and it did not, in some steps, describe what is actually done. For example, in two cases there was confusion between nitrate and nitrite ions, one being specified when the other is required. Sodium nitrite is used to convert all plutonium to the tetravalent state so that it will sorb on an anion-exchange column; if sodium nitrate were used instead, some of the plutonium would not be converted and would pass through the anion-exchange column unsorbed, leading to a low value for the final plutonium content. Plutonium is also subject to hydrolysis that forms colloidal species that tend to sorb onto container walls, but there are ways to prevent this, such as keeping solution pH low and using Teflon containers. At one point, the BNL procedure called for dilution with water, which can cause localized areas of high pH that can lead to hydrolysis; dilute acid should be used for this dilution. Containers are said to be exhaustively washed to remove uranium contamination, but they are not specified as made of Teflon. The need to exclude uranium is indeed important, but equally so is the need to avoid plutonium loss by sorption. These possibly contradictory requirements might require a compromise, but at least the factors influencing the choice of an optimum container should be addressed. The conditions leading to plutonium retention by the container are not limited to

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands hydrolysis. Evaporating a plutonium solution—even in concentrated acid—to total dryness can cause the residue to become overheated and bake onto the container bottom; complete redissolution is then difficult. Despite that problem, the BNL procedure provided in an internal report called for evaporation to dryness. Another question that needs further verification is whether the higher content of plutonium-240 in fallout than in weapons-grade plutonium, has been taken into account in the calculations. Although there have been informal assurances that this correction has been made, the matter needs further documentation. The BNL recipe for synthetic urine provided to the Committee includes creatine instead of creatinine, even though the latter is the normal component of urine. In conversations with BNL staff, it was indicated that they were currently using neither. The omission is important because creatinine, a potential complexing agent, could have a significant effect on the behavior of plutonium. When the committee discussed the shortcomings cited above with BNL personnel, they stated that they were not adhering strictly to the procedure provided, that the procedure was being updated, and that the committee's concerns were unwarranted. The new procedure was under development and was expected to be implemented in June 1993. In February 1994, the committee was provided a preliminary draft of an updated version of the chemical procedures (Kaplan, personal communication, 1994). The ''marked-up" draft procedures suggest that many of the points raised in the critique of the original procedures have been recognized. Whether application of the new procedures is eminent is, however, unknown. It is important that the new procedures be properly reviewed and documented prior to their being implemented in the routine laboratory setting. The primary recommendation of the committee is that, in an analytic procedure as complex as that used in the analysis of trace quantities of plutonium in urine, there must be careful oversight, review, and testing to assure optimum precision and accuracy of the assay. Efforts should also be intensified to develop alternative techniques, such as mass spectroscopy, that may have the necessary sensitivity, but a higher degree of accuracy and precision. The QA program, under which the plutonium analyses were conducted by BNL personnel consisted almost entirely of the use of in-house-prepared blind samples in synthetic urine. This program needs improvement. As part of this program, sample exchange was instituted with the University of Utah (Singh, personal communication, 1993), but apparently only two samples have been run by both laboratories to date. The results on the two samples were encouraging: the two laboratories' values agreed to within 25% in both cases, with one laboratory reporting a higher value for one sample and the other a higher value for the other sample. Nevertheless, two samples constitute far too small a population from which to draw a meaningful conclusion. More exchange samples were not run, because of lack of adequate funding at that time, but it was stated that an additional four exchange samples are planned. Results of these exchanges, if they have taken place, have not been available to this committee. In any case, additional sample exchanges are necessary before the validity of the BNL procedure can be properly assessed. The University of Utah is a good choice for this sample exchange, because its procedure is substantially different from the BNL procedure, specifically in the use of a front-end precipitation with rhodizonic acid for preliminary separation of plutonium, the use of hydrochloric acid rather than nitric acid solutions in the anion-exchange steps, and the use of polycarbonate rather than quartz slides to mount the samples for neutron-irradiation. The claimed sensitivity of the Utah procedure is about 1.5 μBq (40 aCi).

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Radiological Assessments for Resettlement of Rongelap in the Republic of the Marshall Islands Conclusions and Recommendations For measurement of plutonium in urine, to ensure that plutonium remains a negligible contribution to dose, an extremely sensitive method will be required to detect likely intakes. The fission-track method currently being used (and apparently undergoing further refinement) appears to have sufficient sensitivity to provide the needed assurances, but its accuracy and precision is presently unproven. Careful attention is needed to ensure that problems inherent in the chemical-separation procedures and in the urine-collection protocol are resolved and understood. The committee feels that an active program of interlaboratory comparison should be undertaken to document the accuracy and precision of the techniques being implemented for routine plutonium analysis. In addition, problems encountered in interpreting measurements of plutonium in urine need to be carefully documented and understood before any program is initiated for routine monitoring of plutonium intake.

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