Centimeter 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 mm I'"'l'"" ,,,,!,,,,I,,,,I,,"l'"'l'"'l""l""i'"'l'"', 1 2 3 4 5 Inches lllll,.O.°.+o,,,,+,,,,,+ ,, LllLIg IIII1_IIIII'---4Ilut"-=-+ , HF'. q,to al--1 , _ BNL-60261 Assessment of Plutonium Exposures in Rongelap and Utirik Populations by Fission Track Analysis of Urine" L.C. Sun, A.R. Moorthy, E. Kaplan, J.W. Baum, and C.B. Meinhold Radiological Sciences Division, Department of Advanced Technology, Brookhaven National Laboratory, Upton, NY I1973 ABSTRACT A nuclear device, code-named Bravo, detonated at Bikini Atoll at 6:45 a.m. on 1 March 1954, unexpectedly released a large amount of radioactivity. Over 40 years after this incident, the study of its impact on the radiological health and environmental safety of the residents of Rongelap and Utirik Atolls continues. In 1987, researchers at Brookhaven National Laboratory established a fission track analysis (FTA) method tbr low-level "--_gPuurinalysis. Two years later, a new shipboard protocol was developed for collecting 24-h radiologically clean urine samples. The purpose of this paper is to update information on the FTA method for measuring low-levels of plutonium, and to summarize results on the distribution of-_gPu in the populations of Rongelap and Utirik between 1981-1991. Plutonium detection levels (99% confidence level) in these samples were 2-3 _Bq, which is equ'valent to 0.2-0.3 mSv effective dose equivalent (EDE) to age 70 tbr Marshallese. The latest 1991 FTA data indicate average EDE of 0.62 mSv and 1.6 mSv fbr the people of Rongelap and Utirik, respectively, which both are the highest values since 1988. KEYWORDS Fission Track Analysis; Marshall Islands; Plutonium urinalysis; Bravo Exposures. INTRODUCTION On the morning of 1 March (U.S. time, i.e., 28 February for the Central Pacific), 1954, a thermonuclear device (code named Bravo) was detonated at Namu Island, Bikini Atoll, the Republic of the Marshall Islands (RMI) (Committee on Natural Resources of the U.S. House of Representatives, 1994). There was an unexpectedly large weapon-yield and, consequently, a large area of coral reef was contaminated and destroyed. The fallout cloud dropped radioactive ashes over an area approximately 350 km long and 30 to 65 km wide (Cronkite and Bond, 1956). Bravo's radioactive ashes contaminated Rongelap Atoll and Utirik Atoll so that the ambient radiation levels rose dramatically in many islands in the northern RMI (Tipton and Meinbaum, 1981; Robison et al., 1982). The Rongelap and Utirik atolls are about 100 and 275 nautical miles (185 and 500 km) east of Bikini • This work was supported by the U.S. DOE under contract #DE-ACO2-76CHO0016 and prepared for the International Symposium on Plutonium in the Environment, Ottawa, Canada, July 6-8, 1994. ..... " atoll. Two hundred and ninety people were exposed directly to fallout and, subsequently, evacuated from their homes: there were 239 Marshallese (AEC, 1956), 28 Americans (Phillips, 1982), and 23 Japanese fishermen (Kumotori et al., 1980). A comprehensive report on the radiation injuries to the Marshallese and Americans was published by the Atomic Energy Commission (1956). This report stated that within four days after the Bravo detonation, all residents (64 Rongelapese and 157 from Utirik) were relocated by the U.S. government to other atolls in the southern Republic of the Marshall Islands. Individual exposures estimated from external fallout radiation were 1.75 Gy in the Rongelap Atoll and 0.14 Gy in the Utirik Atoll (Sondhaus et al., 1956). The people of Utirik and Rongelap were returned to their homelands three months, and three years later, respectively. In 1985, the Rongelap people chose to move to Mejatto Island in Kwajalein Atoll because of their concern about additional exposure to fallout radiation, including plutonium (Noshkin et al., 1979; Kohn, 1989). The Rongelap people are waiting for further scientific confirmation on radiological conditions before returning to the atoll. Since 1954, the Medical Department t)f Brt)t)khaven National Laboratory (BNL) has been evaluating the radiation dose and providing medical care tt) all the people of the northern RMI (Cohn et al., 1956, Conard et al., 1956; Conard et al., 1975; Conard, 1992; Adams et al., 1989). In 1974, the BNL Radiological Safety Program was initiated, then under the Safety and Environmental Protection Division, and at present, within the Department of Advanced Technology (Greenhouse and Miltenberger, 1977; Greenhouse et al., 1980; Miltenberger et al., 1981; Lessard et al., 1984; Sun et al., 1992). The current BNL Marshall Island radiologicai monitoring and bioassay sampling program, named "Radiation Protection Marshall Islands (RPMI)," is funded by the U.S. Department of Energy Office of Health. The objectives of RPMI are to determine the radionuclides now present in the body of the Marshallese people and to assess the dose they received. Plutonium is perceived as the major radiological concern because it has a half-life of 24,065 years, remains in the body long after intake, and, at the levels of interest, can only be detected in urine and feces. Following an intensive investigation, BNL determined that the levels of plutonium in the Marshallese' urine samples were so low that the available methods for quantifying _gPu were inadequate. In 1987, a fission track analysis (FTA) rnethod was developed by Moorthy (Moorthy et al., 1988) and used for plutonium urinalysis for the Marshallese; all the plutonium data discussed in this paper were obtained using this method. The few data reported by Lessard et al., (1984) are not included in this assessment because the samples are suspected of being contaminated. This paper focuses on the collection experiences and results t'rom the bioassay missions conducted in RMI in September 1988, July 1989, February 1991, and June 1991. MATERIALS AND METHODS Fi_si0n Track Analysis fFTA) Procedures The FTA procedure is a four-step process (Moorthy et al., 1988). It begins with (1) wet-ashing the sample, reducing it to a white, inorganic form. Then, (2) this white powder undergoes a series of chemical separations to recover plutonium and to remove uranium. The removal of naturally occurring uranium is essential because the -__U isotope fission cross-section is comparable to that ofZ_gPu (Bansal et al., 1992). Next, (3) an aliquot of each sample is placed on a quartz slide, dried, and then exposed to a total of 10tt thermal neutrons to induce fission. When fission occurs, about 90% of the energy yield from fission events appears as kinetic energy of the fission fragments. The energetic fragments damage the quartz surface, leaving etchable tracks. Finally, (4) after etching the quartz slides with a solution t_f hydrotlut_ric acid, the damaged sites are t_bserved as tracks (Fig. 1) and counted under a microscope with 160 x ma,31zfication. Each quartz slide has spaces for three samples, so that 30 FTA measurements can be obtained from the 10 slides that constitute one batch. These 30 measurements are divided as illustrated in Fig. 2. One sample space is reserved for flux monitoring (FM) measurenaents. The neutron flux monitor is made of a constant known "-_'_Puactivity used to monitor neutron exposure during irradiation in the reactor and to provide a comparison between separate irradiations. Each of the remaining two spaces has an evaporated aliquot of a chemically processed sample, either a urine-blank, a urine spike (Sp), or a urine sample (numbered from 1 to 10 see Fig 2 - 1 to 10). The results from the urine blank give a level on the total FTA system's noise, while the spiked samples constitute calibration check points for interpreting the data. Among the 30 measurements in a batch, 10 are urine samples, 10 are performance evaluation monitors, and 10 are neutron flux monitors. Of the ten performance evaluation measurements, five (two blanks and three spiked samples) are used as described, four are duplicate urine samples processed in another batch, which evaluate the consistency between two batches, and the last one is a second aliquot from one of the 10 urine samples currently being processed which evaluates the overall reprt_ducibility of results. Hence• the precision anti reliability of FTA measurements can be assessed from the readings of the neutron flux monitors and the results of the performance evaluations. A group of 10 slides is irradiated in the Brookhaven Medical or High Flux Beam reactor. Quality control (QC) between two batches are illustrated in Fig. 3. Fig. 3 shows an arrangement of a group of 10 slides; eight of the slides are from a current batch, and two are from the previous batch. The term "batch" is used for all ten quartz slides resulting from the chemical separation preparations; they are shared within the dotted box in Fig 2. The term "group" is for those ten quartz slides arranged for neutron irradiation; they are shown within a dotted box in Fig. 3. Therefore, every irradiated group of slides has two slides identical to the last two slides from the previous irradiated group. The time for processing a batch of 30 samples is about 30 days. FTA Calibration and Sensitivity Before 1 January 1989, urine blanks were drawn from a composite urine sample collected from one BNL employee with no known occupational or accidental exposure to plutonium. Later, urine blanks were taken from a composite synthetic urine solutitm prepared according to a formula from Battelle Memorial Institute (MacLeilan et al., 1988). The :'a°Puspikes were at six different concentration levels (3.7 to 36.7 p.Bq per sample) in 1987, and five different c¢_ncentrations (3.7 to 18.4/zBq per sample) in 1989. Table 1 (a and b) summarizes the tt_tal nurnher (n), the mean (u,), and the standard deviation (tr) of all 1987, 1989, and 1991 blank and spike samples are summarized in Table l(a) and l(b), 0 "9 Figure 1.