In 1944 Los Alamos National Laboratory (LANL) instituted a program for the collection and analyses of urine samples from individuals working with plutonium. This program has operated continuously for over 60 years. During that time the plutonium bioassay program incorporated advances in urine sample collection, radiochemical separation techniques, alpha-spectroscopy and thermal ionization mass spectrometry measurement techniques as well as cleanroom technology. All of these advances have produced incremental improvements in plutonium detection limits. A chronological description is given of the methodologies used in the plutonium bioassay program at Los Alamos.

We have developed cleanroom compatible techniques for processing bone samples for characterization of their uranium and plutonium content. The bone samples are dried and ashed in quartz crucibles placed inside cleanroom compatible thermal ashing furnaces. The bone ash is dissolved in ultra-pure acids prepared by sub-boiling distillation. The uranium and plutonium in the samples are isolated and purified by ion-exchange chromatography and measured by thermal ionization mass spectrometry. The technique is capable of detecting 74 picograms of 238U and 8 femtograms of 239Pu in 100 mg bone ash samples. If the ash contains larger amounts of uranium and plutonium, the technique can be used to isotopically fingerprint the material to identify potential origins.

The lung dissolution rates for PuO2 were determined using a 100 day in vitro experiment. A very small amount of the PuO2 rapidly dissolved with a half-time of approximately 10 days, while the majority of the material (> 99%) dissolved with a half-time of approximately 5105 days. This dissolution half time is significantly longer than what is recommended by the ICRP, and would result in higher calculated doses for inhalation intakes of PuO2 than those currently estimated by the ICRP 66 human respiratory tract model for radiological protection.

Extensive soil and sediment sampling was conducted along the Colorado Front Range and the plains east of the Front Range at locations believed to only be exposed to global fallout. The average 240Pu/239Pu atom ratio in the samples collected in Colorado was determined to be 0.165±0.008. A limited number of samples were collected at various locations in the Arctic at approximately 70° N latitude. Analyses of these samples predict that the 240Pu/239Pu atom ratio in environmental samples collected at 70° N latitude at locations only containing fallout is 0.183±0.009. These results provide data that help to precisely define the 240Pu/239Pu atom ratios representative of global fallout at the two locations studied.

As a follow up to the initial 1998 intercomparison study, a second study was initiated in 2001 as part of the ongoing evaluation of the capabilities of various ultra-sensitive methods to analyze 239Pu in urine samples. The initial study1 was sponsored by the Department of Energy, Office of International Health Programs to evaluate and validate new technologies that may supersede the existing fission tract analysis (FTA) method for the analysis of 239Pu in urine at the µBq/l level. The ultra-sensitive techniques evaluated in the second study included accelerator mass spectrometry (AMS) by LLNL, thermal ionization mass spectrometry (TIMS) by LANL and FTA by the University of Utah. Only the results for the mass spectrometric methods will be presented. For the second study, the testing levels were approximately 4, 9, 29 and 56 µBq of 239Pu per liter of synthetic urine. Each test sample also contained 240Pu at a 240Pu/239Pu atom ratio of ~0.15 and natural uranium at a concentration of 50 µBq/ml. From the results of the two studies, it can be inferred that the best performance at the µBq level is more laboratory specific than method specific. The second study demonstrated that LANL-TIMS and LLNL-AMS had essentially the same quantification level for both isotopes. Study results for bias and precision and acceptable performance compared to ANSI N13.30 and ANSI N42.22 have been compiled.

This study presents the characterization of Pu-bearing precipitates and the results from uptake studies of Np and Pit on inorganic colloidal particulates in J-13 water from the Yucca Mountain site. Plutonium solubilities determined experimentally at pH values of 6, 7. and 8.5 are about two orders of magnitude higher than those calculated using the existing thermodynamic database indicating the influence of colloidal Pu(IV) species. Solid phase characterization using X-ray diffraction revealed primarily Pu(IV) in all precipitates formed at PH 6 7, and 8.5. The solubility controlling Pu-bearing solids precipitated at ambient temperature consisted of amorphous Pu(OH)4(S) with several Pu-O distances between 2.3 and 2.7 Angstrom that are characteristic for Pu(IV) colloids. High temperature (90 degreesC) increased solid phase crystallinity and produced Pu(IV) solids that contained Pu oxidation state impurities, X-ray absorption spectroscopic studies revealed diminished Pu-O and Pu-Pu distances that were slightly different from those in crystalline PuO2(s). A Pu-O bond of 1.86 Angstrom was identified that is consistent with the plutonyl(V) distance of 1.81 Angstrom in PuO2+ (aq). Hematite, montmorillonite, and silica colloids were used for uptake experiments with Pu-239(V) Lind Np-237(V). The capacity of hematite to sorb Pu significantly exceeded that of montmorillonite and silica. A low desorption rate as indicative of highly stable Pu-hematite colloids, which may facilitate Put transport to the accessible environment. Neptunium uptake on all mineral phases was far less than Pu(V) uptake suggesting that a potential Pu(V)-Pu(IV) reductive sorption process was involved. The temperature effect on Pu solubility and pseudocolloid formation is also discussed. (C) 2002 Published by Elsevier Science Ltd.

Utilization of thermal ionization mass spectrometry as a routine analytical service provided to the Los Alamos National Laboratory Bioassay Program has evolved significantly since its implementation just over three years ago. Converting this unique research tool designed to support nuclear weapons testing to a quasi-production mode for the routine analysis of ~300 urine samples/year for ultra-low levels of plutonium has required resolution of numerous practical issues. These issues include clean-room sample preparation, adequate tracer recovery, customer specified turn-around times, throughput, water and urine blank values, statistical data reduction, and quality control and performance evaluation sample requirements.

Metal tritides with low dissolution rates may have residence times in the lungs which are considerably longer than the biological half-time normally associated with tritium in body water, resulting in long-term irradiation of the lungs by low energy beta particles and bremsstrahlung X rays. Samples of hafnium tritide were placed in a lung simulant fluid to determine approximate lung dissolution rates. Hafnium hydride samples were analysed for particle size distribution with a scanning electron microscope. Lung simulant data indicated a biological dissolution half-time for hafnium tritide on the order of 10(5) d. Hafnium hydride particle sizes ranged between 2 and 10 microns, corresponding to activity median aerodynamic diameters of 5 to 25 microns. Review of in vitro dissolution data, development of a biokinetic model, and determination of secondary limits for 1 micron AMAD particles are presented and discussed.

This study was performed to establish a quality controlled data set about the levels of anthropogenic radionuclide activity in the environment and in selected biota in the Arctic. Between 1993 and 1997 sediment and marine and terrestrial biota samples were collected in Alaska and in the surrounding waters, These samples were analysed at Los Alamos National Laboratory to identify the presence of the anthropogenic radionuclides, Sr-90,Cs-137, (238)pU, Pu239+240, and Am-241. One goal of this study was to determine the amounts and origins of anthropogenic radionuclides present in sediments. The anthropogenic radionuclide content of the sediments was predominantly the result of deposition of global fallout from nuclear explosions. No other sources of anthropogenic radionuclides could be conclusively identified. Biota samples of subsistence and ecological value were analysed for evidence of bioaccumulation of radionuclides. The measurements were combined with food consumption rates based on survey results for populations residing in three north Alaskan communities and on published, age-dependent ingestion coefficients. This action was carried out to estimate the potential radiological impacts from the consumption of traditional animal foods harvested in this region. No plutonium or americium was detected in any of the fauna samples. The results of this study indicate that the committed equivalent doses to adults from Sr-90 and Cs-137 owing to consumption of traditional food sources are consistent with currently accepted estimates of average doses received by adults in North America from atmospheric nuclear weapons testing fallout.

Historical operations at the Los Alamos National Laboratory have contaminated stream sediments with plutonium and other radionuclides. A small portion of these contaminated sediments has been carried by floods into the Rio Grande drainage system, eventually to be trapped by Cochiti Lake located on Pueblo de Cochiti lands approximately 8 km downstream of the Laboratory. In this study, lake bottom sediment samples provided by the Pueblo de Cochiti were analyzed by thermal ionization mass spectrometry to determine plutonium and uranium activity levels and isotopic atom ratios. This specialized analytical method allows us to take isotopic fingerprints of radionuclides found in the sediment and to determine how much plutonium and uranium came from the Laboratory and how much was deposited by worldwide fallout or is natural. Two distinct types of samples were processed: segments of a continuous vertical core of the entire accumulated sediment sequence and other samples from across the lake bottom at the water/sediment interface. Based on measurement of the {sup 240}Pu/{sup 239}Pu atom ratio, Laboratory-derived plutonium is present in eight of nine samples at the core site. On a depth-weighted basis, approximately one-half of the {sup 239}Pu and {sup 240}Pu came from early operations at the Laboratory; the remaining plutonium came from fallout dispersed by above-ground nuclear tests. In contrast to the core site, the samples from the other locations showed little or no evidence of Laboratory-derived plutonium, with more than 90 percent of the plutonium attributable to fallout. The overall amount of plutonium in all the samples is of the same magnitude as other reservoirs in the region. The net increase in plutonium over upstream reservoirs unaffected by Laboratory activities is a maximum of 0.014 pCi/g or 3.5 times. All of the samples reflect natural uranium compositions. Laboratory-derived uranium is not identifiable, presumably because the sediment contains abundant natural uranium that obscures the Laboratory signatures. Although Los Alamos legacy activities have contributed radioactivity to Cochiti Lake, there is no evidence of Laboratory-produced radionuclides entering the food chain or leaching into the water. Additional core samples are expected to be collected by the Pueblo de Cochiti to reduce uncertainty in contaminant inventory and risk estimates.

Surficial sediments in the western Beaufort Sea contained generally high concentrations of arsenic (up to 58 ppm as corrected for grain size), very low amounts of organochlorine compounds and concentrations of total polycyclic aromatic hydrocarbons (PAHs) ranging from ∼160 to 1100 ng/dry weight. Invertebrates contained higher concentrations of total PAHs than fish, with naphthalene being the largest contributor. Diagnostic ratios of various PAH compounds in our samples do not suggest crude oil as the main source of PAHs. Other sources of PAHs to the region include rivers outflow, coastline erosion, oil seeps, diagenesis, and long-range atmospheric transport. Organochlorine contaminants were consistently found in our samples at concentrations generally lower than those found in other parts of the United States. 137Cesium (Cs) was found in measurable amounts in all sediments and biota samples. Isotopic ratios showed that radionuclides originated most likely from global fallout. Compared to other coastal areas off Alaska, the Arctic, and the conterminous United States, Beaufort Sea contamination appears generally low.

Mobile colloids—suspended particles in the submicrometre size range—are known to occur naturally in ground water1, 2 and have the potential to enhance transport of non-soluble contaminants through sorption3. The possible implications of this transport mechanism are of particular concern in the context of radionuclide transport. Significant quantities of the element plutonium have been introduced into the environment as a result of nuclear weapons testing and production, and nuclear power-plant accidents. Moreover, many countries anticipate storing nuclear waste underground. It has been argued that plutonium introduced into the subsurface environment is relatively immobile owing to its low solubility in ground water4 and strong sorption onto rocks5. Nonetheless, colloid-facilitated transport of radionuclides has been implicated in field observations6, 7, but unequivocal evidence of subsurface transport is lacking3, 8, 9. Moreover, colloid filtration models predict transport over a limited distance resulting in a discrepancy between observed and modelled behaviour3. Here we report that the radionuclides observed in groundwater samples from aquifers at the Nevada Test Site, where hundreds of underground nuclear tests were conducted, are associated with the colloidal fraction of the ground water. The 240 Pu/239 Pu isotope ratio of the samples establishes that an underground nuclear test 1.3 km north of the sample site is the origin of the plutonium. We argue that colloidal groundwater migration must have played an important role in transporting the plutonium. Models that either predict limited transport or do not allow for colloid-facilitated transport may thus significantly underestimate the extent of radionuclide migration.

Use of a uranium double spike in analysis of environmental samples showed that a {sup 235}U enrichment of 1% ({sup 235}U/{sup 238}U = 0.00732) can be distinguished from natural ({sup 235}U/{sup 238}U = 0.00725). Experiments performed jointly at Los Alamos National Laboratory (LANL) and Oak Ridge National Laboratory (ORNL) used a carefully calibrated double spike of {sup 233}U and {sup 236}U to obtain much better precision than is possible using conventional analytical techniques. A variety of different sampling media (vegetation and swipes) showed that, provided sufficient care is exercised in choice of sample type, relative standard deviations of less than {+-} 0.5% can be routinely obtained. This ability, unavailable without use of the double spike, has enormous potential significance in the detection of undeclared nuclear facilities.

Solubilities of neptunium and plutonium were studied in J-13 groundwater (ionic strength of about 3.7 mmol; total dissolved carbonate of 2.8 mmol) from the proposed Yucca Mountain Nuclear Waste Repository site, Nevada, at three different temperatures (25, 60, and 90 degrees C) and pH values (6.0 7.0,and 8.5). Experiments were performed from both over- and undersaturation at defined CO2 partial pressures. The solubility of Np-237 from oversaturation ranged from a high of (9.40 +/- 1.22) x 10(-4) M at pH 6.0 and 60 degrees C to a low of (5.50 +/- 1.97) x 10(-6) M at pH 8.5 and 90 degrees C. The analytical results of solubility experiments from undersaturation (temperatures of 25 and 90 degrees C and pH values 6, 7, and 8.5) converged on these values. The Pu-239/240 solubilities ranged from (4.70 +/- 1.13) x 10(-8) M at pH 6.0 and 25 degrees C to (3.62 +/- 1.14) x 10(-9) M at pH 8.5 and 90 degrees C. In general, both neptunium and plutonium solubilities decreased with increasing pH and temperature. Greenish-brown crystalline Np2O5. xH(2)O was identified as the solubility-limiting solid using X-ray diffraction. A mean thermodynamic solubility product for Np2O5. xH(2)O of log K(sp)degrees = 5.2 +/- 0.8 for the reaction Np2O5. xH(2)O + 2 H+ reversible arrow 2NpO(2)(+) + (x+1)H2O at 25 degrees C was calculated. Sparingly soluble Pu(IV) solids, PuO2. xH(2)O and/or amorphous plutonium(IV) hydroxide/colloids, control the solubility of plutonium in J-13 water.

In order to confirm that the redox reaction Np(V) to Np(IV) may occur, studies are being conducted including exposure of Np(V) to solutions of known E{sub h} vs pH, temperature. Analytic results from ongoing solubility experiments from undersaturation, using Np solids formed in previous oversaturation experiments, are reported.

Los Alamos National Laboratory has developed a series of measurement techniques for identification of nuclear signatures by analyzing bulk samples. Two specific applications for isotopic fingerprinting to identify the origin of anthropogenic radioactivity in bulk samples are presented. The first example is the analyses of environmental samples collected in the US Arctic to determine the impact of dumping of radionuclides in this polar region. Analyses of sediment and biota samples indicate that for the areas sampled the anthropogenic radionuclide content of sediments was predominantly the result of the deposition of global fallout. The anthropogenic radionuclide concentrations in fish, birds and mammals were very low. It can be surmised that marine food chains are presently not significantly affected. The second example is isotopic fingerprinting of water and sediment samples from the Rocky Flats Facility (RFP). The largest source of anthropogenic radioactivity presently affecting surface-waters at RFP is the sediments that are currently residing in the holding ponds. One gram of sediment from a holding pond contains approximately 50 times more plutonium than 1 liter of water from the pond. Essentially 100% of the uranium in Ponds A-1 and A-2 originated as depleted uranium. The largest source of radioactivity in the terminal Ponds A-4, B-5 and C-2 was naturally occurring uranium and its decay product radium. The uranium concentrations in the waters collected from the terminal ponds contained 0.05% or less of the interim standard calculated derived concentration guide for uranium in waters available to the public. All of the radioactivity observed in soil, sediment and water samples collected at RFP was naturally occurring, the result of processes at RFP or the result of global fallout. No extraneous anthropogenic alpha, beta or gamma activities were detected. The plutonium concentrations in Pond C-2 appear to vary seasonally.