The Northern Marshall Islands Radiological Survey; a Quality Control Program for Radiochemical Analyses

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I ne lwortnern Marshall Islands Radiological Survey: A Quality Control Program for

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This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or imphed, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government thereof, and shall not be used for advertising or product endorsement purposes. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore sational Laboratory under Contract W-7405-Eng-48.

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The Northern Marshall Islands Radiological Survey: A Quality Control Program for Manuscript date: August 2983 LAWRENCE LIVERMORE NATIONAL LABORATORY University of California . Livermore, California . 94550 * Oregon State University, College of Oceanography Available from: National Technical Information Service l U.S. Department of Commerce 5285 Port Royal Road l Springfield, VA 22161 l $7.00 per copy l (Microfiche $4.50 )

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Preparation of Standards and Duplicates .................. Preparation of Standards ....................... Terrestrial Animal Standard ..................... Marine Organism Standard .................... Certification of Standards ...................... Preparation of Duplicates ...................... Terrestrial Animal Duplicates ................... Marine Organism Duplicates .................... Marine Sediment Duplicates .................... Evaluation of Data ........................... Terrestrial Animal Analyses ..................... Marine Sample Analyses ....................... Appendix. Quality Control Results for Duplicate Pairs Plotted Against Each Other ........................

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THE NORTHERN MARSHALL ISLANDS RADIOLOGICAL SURVEY: A QUALITY CONTROL PROGRAM FOR RADIOCHEMICAL ANALYSES More than 16,000 radiochemical analyses were performed on about 5,400 samples of soils, vegetation, animals, fish, invertebrates, and water to establish amounts of 9oSr, 137Cs, 241 Am, and plutonium isotopes in the Northern Marshall Islands. Three laboratories were contracted by Lawrence Livermore National Laboratory to perform the radiochemical analyses: Environmental Analysis Laboratory (EAL), Richmond, California; Eberline Instrument Corporation (EIC), Albuquerque, New Mexico; and Laboratory of Radiation Ecology (LRE), University of Washington, Seattle, Washington. The analytical precision and accuracy were monitored by regularly including duplicate samples and natural matrix standards in each group of about 100 samples analyzed. Based on the duplicates and standards, over 83% of the radiochemical analyses in this survey were acceptable--97% of the analyses by EAL, 45% of the analyses by EIC, and 98% of the analyses by LRE. The Northern Marshall Islands Radiological Survey (NMIRS) was a large-scale effort to collect soil, vegetation, animal, fish, invertebrate, and water samples and assess the radiation dose from the ingestion and inhalation pathway and external environments of 12 atolls and 2 islands in the Northern Marshall Islands. The Lawrence Livermore National Laboratory (LLNL) was responsible for this effort, including the collection and processing of the various samples.’ Overall, about 5,400 samples were collected and over 16,000 radiochemical analyses were performed to establish the amounts of specific radionuclides in the soils, vegetation, animals, fish, invertebrates, and water. For such an extensive analytical program, no one laboratory had the capability to analyze all the samples in a reasonable time. Accordingly, three laboratories were contracted to perform the required Any analytical program depends on the quality of the measurements being made. Most laboratories spend a certain part of their effort to establish the accuracy and reproducability of their analytical work. Blind interlaboratory comparisons such as the Department of Energy (DOE) intercalibration exercise2 and analysis of natural matrix

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standards such as those available from the National Bureau of Standards and from the International Atomic Energy Agency are two methods by which the quality of a laboratory’s work can be shown. In a large-scale survey such as the Northern Marshall Islands program where samples are analyzed by several laboratories, it is all the more important to assess the validity of the data by regularly having the participating For this program we have selected three criteria for the analytical reliability of the (I) The first criterion places limits of acceptability on counting errors. Because radioactive decay is a statistical process, sufficient counts must be collected to provide a level of confidence that the number reported is a true measure of the radioactivity of the sample. Until this criterion is met it is difficult, if not impossible, to evaluate the data for the remaining two criteria. Consequently, we established a set of acceptable counting errors (Table 1). The requirements were scaled to the total radioactivity of the sample, which is the product of the amount of sample available and its specific activity (activity per unit weight of sample). Compliance could be easily checked by the individual analyst because it is based on information available to him: the measured specific activity and weight of the sample received. This criterion was developed prior to initiation of the NMIRS field-sample collection program to estimate the amount of samples required by any competent contractor to measure worldwide fallout. Samples of sufficient size with higher activity were thus well above the limits of detection of the contracting laboratories. This was done to avoid reporting machine limits that give only upper limits to the concentrations of the samples and thus will overestimate the amount of radioactivity actually present in the environment when these limits are used as real values. This is not an uncommon practice when assessing environmental data. (2) The second criterion required that the laboratories reproduce their results on replicate analyses. A set of blind duplicate samples was included with each group of roughly 100 samples (called DCD for the accompanying Delivery Control Document) and results of the pair of analyses were considered acceptable if they agreed within twice the measurement accuracy required in Table 1. Satisfactory performance on duplicates required acceptability on 80% of all duplicate pairs included in each DCD. Duplicate samples were prepared and distributed by LLNL.

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Table 1. Allowable counting errors according to the total activity in the sample received by the contracting laboratories. (3) The third criterion required that the laboratories accurately determine the radionuclide concentrations of blind standards. Although all three of the criteria are important, perhaps this is the most significant because it includes accuracy of measurement as well as precision (reproducibility); any systematic errors in the measurement would appear. Responsibility for preparing,

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standardizing, and distributing the standard samples was assigned to Western Oregon State College (WOSC). In this way the primary responsibility for evaluating the analytical integrity of the data was vested in a disinterested In some cases, small variances from these criteria were allowed to facilitate processing the data, but the deviations were never great enough to compromise the integrity of the data. Specifically, the error requirements shown in Table 1 were relaxed by 20% for some of the early DCDs to accomodate problems some of the contractors had in reducing counting errors. For example, for samples where a 10% relative standard deviation was required, a 12% relative standard deviation was allowed. Another variance was in the number of duplicates and standards that had to be in compliance. In general, for a DCD to be considered acceptable, 80% of the duplicate pairs and 100% of the standards had to be in compliance with the QC criteria. When the number of duplicate pairs did not permit exactly 80% compliance (for example, 3 of 4 pairs would give 75% compliance), a fraction of duplicates in compliance slightly less than but near 80% was still considered to be acceptable. Less than 100% compliance on standards was allowed occasionally if the radiochemical analysis on the standard was near the accepted activity and if the laboratory had established a record of accurate radiochemical analysis on other subsamples of the standard in question. Laboratories .participating in the radiochemical analyses of samples from the NMIRS were Environmental Analysis Laboratory (EAL), Richmond, California; Eberline Instrument Corporation (EIC), Albuquerque, New Mexico; and Laboratory of Radiation Ecology (LRE), University of Washington, Seattle, Washington. spectrometry), 241 Pu (mass spectrometry and liquid scintillation counting), ,and 241Am (alpha pulse-height analysis). There were 16,282 analyses, including the duplicate and standard samples of the QC program , requested of the three participating laboratories. The largest fraction of the analyses was performed by EAL: 65.6% (42.3% terrestrial and 23.3% marine). Slightly over one-fourth of the analyses, 2X5%, was performed by EIC. The balance, 8.996, was analyzed by LRE. Table 2 summarizes the duplicate and standard analyses associated with the 15,745 analyses of soil, vegetation, terrestrial animal, marine organisms, and marine sediment

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Table 2. Summary of the duplicate and standard analyses evaluated for each participating laboratory as part of the quality control program for the Northern Marshall Islands a Environmental Analysis Laboratory. b Eberline Instrument Corporation. ’ Laboratory of Radiation Ecology.

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evaluated as part of the NMIRS QC program. The 537 water analyses were evaluated and accepted separatelye Of the 15,745 analyses evaluated herein, 12.5% were associated with the QC program. On an individual laboratory basis, QC program analyses accounted for 12.7% of EAL’s, 1 I % of EIC’s, and 15.6% of LRE’s evaluated analyses. PREPARATION OF STANDARDS AND DUPLICATES PREPARATION OF STANDARDS The samples from the survey included soil and marine sediments, plant material, marine tissue, and terrestrial animal tissue, and we prepared standards of each of the four natural matrixes. Because the purpose of the standards was to substantiate the analyses of other environmental samples, the character of the standards matched that of the samples as closely as possible. The radioactivity in .the standards was from the natural environment and not merely added to the samples from a solution in which the chemical forms of radioactivity might be quite different from those in the samples. Consequently, each standard was prepared from material collected directly from the environment. Environmental samples of vegetation and marine or terrestrial animal tissues generally did not have enough radioactivity to serve as adequate standards. These samples were spiked with environmentally labeled radioactive algae--the same algae used by Volchok and Feiner at the DOE Environmental Measurements Laboratory (EML) to prepare standards for the DOE intercalibration exercise.2 The soil standard was collected at the Marshall Islands and a large sample was shipped to LLNL where it was dried and ball milled. It was then shipped to WOSC where it was sieved and the entire sample was blended in a large twin-cone blender. The homogenized soil was canned and labeled to conform to the style of samples prepared at LLNL. This standard was also used for the marine sediment standard. To prepare the vegetation commercial potato flakes, blended standard, we added a known amount of algae to it in a twin-cone blender, and then it was canned and

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Terrestrial Animal Standard A large sample of beef was dried and ashed at LLNL and shipped to WOSC. The ash was spiked with a known amount of algae, blended, and reashed at 4OOOC. The reashed beef was blended in a small twin-cone blender, canned, and labeled. Marine Organism Standard A large fish sample was collected and ashed at LLNL and then shipped to WOK. The ashed sample was spiked with a known amount of algae, blended, and then reashed at 4OOOC. The reashed sample was then blended in a small twin-cone blender, canned, and CERTIFICATION OF STANDARDS The first step in certifying the standards was to show that the methods used to prepare the samples produced a homogeneous sample. Because the vegetation standard was the first prepared, the greatest attention was given to it. Homogeneity was first tested by measuring 137 Cs in a random selection of ten aliquots of the standard by nondestructive analysis on a Ge(Li) gamma-ray spectrometer. Because the samples were not in the counting geometry normally used by WOSC, only relative activities were measured. As shown in Table 3, there was excellent agreement among the ten samples. Similarly, the 2.6% relative standard deviation of 10 measurements of 137Cs done radiochemically and the 4.7% relative standard deviation of 16 measurements of 239+240 Pu (Table 4) provide evidence that the procedures used to prepare the samples produced a homogeneous sample. Because the marine and terrestrial animal standards were prepared in the same manner as the vegetation standard by adding algae and blending, their homogeneity is likewise established. In the course of this survey, the homogeneity of the vegetation and animal samples was confirmed by one of the participating laboratories (EAL). Because the soil standard had no added radioactivity, it was a slightly different case, but the 5.4% standard deviation about the mean of ten 239+240Pu analyses shows that it was likewise homogeneous (Table 5). Moreover, many analyses by the participating laboratories have further confirmed its homogeneity. Certified activities of the standards were established in two ways. First, the radioactivity of the algae used to spike samples of vegetation, fish, and beef had been measured at EML, and because it was used to prepare samples for the DOE

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Table 3. The ’ 37Cs measured by gamma-ray spectrometry in a random selection of vegetation standard samples. a Only relative counts were measured because samples were not in the counting geometry we normally used. Table 4. Radionuclides measured in vegetation standard samples. All analyses done radiochemically except as noted. NOTE: Numbers of replicates are in parentheses. a Western Oregon State College, Oregon State University. b Environmental Measurements Laboratory. d Lawrence Livermore National Laboratory.

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Table 5. Radionuclides measured in soil standard samples. All analyses done radiochemically except as noted. NOTE: Numbers of replicates are in parentheses. Western Oregon State College, Oregon State University. Environmental Measurements Laboratory. Measured by gamma-ray spectrometry. Lawrence Livermore National Laboratory. intercalibration exercise, the measurements were well corroborated. These known additions of radioactivity were used to establish the expected radioactivity. Second, all the standards except the terrestrial animal standard were analyzed radiochemically. The results of these analyses are shown in Tables 4-6. The laboratories at WOSC and Oregon State University (OSU) have collaborated for several years and their results are combined. Corroborating analyses were performed by EML and LLNL. The radiochemical methods at WOSC and OSU have been demonstrated for the measurement of 1 37cs, 239+240pu 3 and 241 Am (see Ref. 41, and the measurements of those three radionuclides were taken as the certified values. Because the WOSC, OSU measurement of 90 Sr had not been demonstrated, we used the analyses of EML to certify the 9oSr As Tables 4-6 show. 1 excellent agreement was found for all radionuclides. In Table 7 we present only the expected values for the terrestrial animal standard because it was prepared by the same method as the vegetation and marine organism standards by adding known amounts of the radionuclides. Consequently, no radiochemical analyses were required. We are confident that the certified activities, or expected values in the case of the terrestrial animal standard, are correct within the tolerance quoted in Tables 4-7. This has been further demonstrated by the high degree …