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WSU Past Studies in Radiochemistry and Dosimetry

Dumit, Sara. Development of a new compartmental model for plutonium decorporation therapy. Ph.D. dissertation. Washington State University, July 2018.

Individuals with significant intakes of plutonium (Pu) are typically treated with chelating agents. The trisodium salt form of calcium diethylenetriaminepentaacetate (Ca-DTPA) is a decorporation drug that forms stable complexes with plutonium in-vivo, enhancing its excretion. Since plutonium biokinetics is affected by its complexation with this drug, standard biokinetic models cannot be used to estimate plutonium intake. Prior to this work, only ad hoc solutions were available for modeling plutonium biokinetics during and after chelation therapy. In this study, a new model composed of two linked structures describing the distinct kinetics of the intravenously injected Ca-DTPA and the in-vivo formed Pu-DTPA chelate, was developed, parameterized, and validated. Chelation is assumed to take place in the blood and the extracellular fluids (ECF), including the ECF surrounding the liver, skeleton and soft tissues, portraying a fast and slow kinetics. United States Transuranium and Uranium Registries (USTUR) whole-body donor (Case 0212) was exposed to plutonium via wound and treated extensively with Ca-DTPA. Urine measurements and post-mortem plutonium activities in the liver and the skeleton from Case 0212 were used for model development and initial validation, respectively. The model was implemented in SAAM IIĀ® software with the Leggett et al. (2005) plutonium systemic model, the International Commission on Radiological Protection (ICRP) Publication 100 human alimentary tract model, and the National Council on Radiation Protection and Measurements’ Report 156 wound model. The Coordinated Network for Radiation Dosimetry (CONRAD) approach to decorporation modeling was applied by using a chelation constant describing the kinetics of the in-vivo chelation reaction. The model structure was tested with the ICRP Publication 67 and the Luciani and Polig plutonium systemic models. The model’s fitting of urine and autopsy data was compared to the CONRAD model and its optimized version, resulting in both improved goodness-of-fit to the bioassay data, and more accurate predictions of post-mortem plutonium retention. The model was further validated using USTUR Case 0269, who inhaled soluble plutonium and was treated with different chelating agents. The model developed in this work simultaneously fits the chelation affected and non-affected urinary excretion data and predicts autopsy data in major deposition sites.

Elliston, James T. The distribution of uranium in human tissues. Ph.D. dissertation. Washington State University, August 2001.

The environmental intake of uranium has been determined in the tissues of a whole human body donor to the United States Transuranium and Uranium Registries (Case 0425) using a newly developed recovery corrected kinetic phosphorescence analysis method which combines alpha spectrometry with kinetic phosphorescence analysis. This case had an occupational exposure to plutonium and americium but no known occupational exposure to uranium. The distribution for uranium from this investigation was compared to previous studies of natural uranium in human tissues, to the current International Commission on Radiological Protection models, and to the distributions of plutonium and americium in the same tissues of this case. The differences in the distributions of U, 239+240Pu, and 241Am lend validity to the different assumed biokinetic distributions of U, 239+240Pu, and 241Am in human tissues. Recovery corrected KPA showed improved precision and accuracy for the low level determination of U compared to direct KPA and offers an optimized method for the determination of low levels of U in human tissues especially when the original sample solutions are very dilute or have matrix problems. The hypothesis that served as the basis for this research was that the current ICRP model does not accurately depict the distribution of uranium in the human body. This research shows that the skeletal system from USTUR Case 0425 has a non-uniform distribution for the concentrations of U and conflicts with ICRP 23 (1975) ICRP 30 (1979); Harley and Fisenne (1990); Fisenne et al., (1988); and Igarashi et al., (1987).

Glover, Samuel E. Distribution of thorium and other trace elements in human tissues. Ph.D. dissertation. Washington State University, May 1998.

Thorium from environmental intake has been determined in the tissues of a whole body donor to the United States Transuranium and Uranium Registries (Case 0212) using pre-concentration neutron activation analysis method developed for these analyses. This case had occupational exposure to plutonium an americium but no known occupational exposure to thorium. Distribution data for thorium from this work is compared to previous studies of natural and colloidal thorium in human tissues and to the distribution of plutonium and americium in the same tissues of this case. Three methods were developed and evaluated including: sulfate based electrodeposition of thorium and other actinides; tracer corrected, pre-concentration neutron activation analysis; and combined alpha spectrometry pre-concentration neutron activation analysis for determination of isotopic thorium. Select trace elements (e.g. cadmium, chromium, an zinc) were also determined in some of these same tissues by instrumental neutron activation analysis.

Love, Suzanne F. An investigation of specific problems with the determination of plutonium isotopic ratios in environmental and biological samples. Ph.D. dissertation. Washington State University, 1997.

Two projects were investigated in the course of this study. The first was to determine whether reported differences in the behavior of 238Pu and 239+240Pu could be observed in a laboratory situation and if so, to determine the mechanism(s). Soil samples were obtained from Rocky Flats Plant (RFP) and four islands in Bikini Atoll. The 238Pu/239+240Pu ratio was determined during column extractions, sequential bath extractions, and soil particle size studies to monitor the behavior of 238Pu and 239+240Pu. The first conclusion was that the RFP soil indicated no differences in the behavior of 238Pu and 239+240Pu. Even though previous reports had indicted differences in the isotopes at this site, this study suggested that these could be explained by analytical and statistical uncertainties in the data. For three of the soils from Bikini Atoll, 238Pu was found to be more easily extracted from the soil than 239+240Pu. Furthermore, it was found that 238Pu was enriched in the finer particles size fraction of the soil which explained its enhanced extraction. The second project involved the development of a combined alpha spectrometry and fission track method for the determination of the 240Pu/239Pu ratio in human tissues. Dissolved tissues of occupationally exposed workers who were registrants of the United States Transuranium and Uranium Registries were obtained. In this study, Pu was purified and isolated from Am, U and Th, after the addition of 238Pu as a radiotracer. After electrodeposition onto vanadium planchets, the 239+240Pu activity was determined by alpha spectrometry. A fission track method was developed to determine 239Pu in the presence of 238Pu and 240Pu, using the WSU Triga III reactor and Lexan TM polycarbonate track detectors. Combining the two techniques allowed the determination of the 240Pu/239Pu ratios. The method provided an alternative to mass spectrometry, which is currently the routine method used for 240Pu/239Pu determinations.

Medley, Duane W. An investigation of the simulated twenty-four hour protocol for uranium in urine by kinetic phosphorescence analysis. M.S. thesis. University of Washington, 1992.

Bioassays are the primary means of detecting the nature and quantity of internally-deposited radionuclides in exposed workers. The National Council on Radiation Protection and Measurements (NCRP), in its guidance document on bioassay procedures, defines bioassay as, the determination of the kind, quantity, location, and/or retention of radionuclides in the body by direct (in vivo) or by in vitro analysis of material excreted or removed from the body. This definition is widely accepted by the nuclear industry.

The principal bioassay method used for internal deposition of uranium is in vitro analysis of urine. If internal deposition of uranium occurs, uranalysis is used to detect and quantify the dosimetric consequences to workers. The NCRP states that, Analysis…for materials such as uranium excreted in the urine may provide a useful assessment of the existing systemic burden.

Taken from the beginning of thesis.

Moody, Cheryl A. Investigation of the extraction chromatographic behavior of thorium, uranium, plutonium and americium in soft tissues. M.S. thesis. Washington State University, December 1996.

An extraction chromatographic method for the pre-concentration and separation for Th, U, Pu and Am in human soft tissues has been developed. For method development, known amounts of bovine liver and lung tissues were ashed at 120˚ C, muffled at 450˚ C, and then chemically wet ashed in HNO3/H2O2. An aliquot of the dissolved sample was taken, and then radioactive isotopic tracers (242Pu, 243Am, 232U and/or 229Th) were added to each sample to measure the efficiency of separation.

Because of the complex matrix of soft tissue samples, it was necessary to pre-concentrate the actinides prior to elemental separation d determination of Th, U, Pu and Am. The actinides were simultaneously pre-concentrated utilizing the extraction chromatographic TRU® resin. Following the pre-concentration of actinides from prepared tissue samples, each desired actinide was i9ndividually separated using extraction chromatographic resins. The TEVA® and TRU® resin columns were in a tandem configuration. Actinide isotopes were then determined by alpha spectrometry following electrodeposition.

To validate the TRU® resin pre-concentration method combined with the TEVA®/TRU® resins separation method, several different samples were analyzed, including blank samples, QA/QC samples, and human tissue samples previously analyzed in the United States Transuranium and Uranium Registries (USTUR). These method validation results, as well as the bovine liver and lung tissue results, are discussed. Concluding remarks and topics for further investigation are included.

Nielsen, Christopher E. An analysis of the microdistribution and long-term retention of 239Pu(NO3)4 in the respiratory tracts of an exposed plutonium worker and experimental beagles. M.S. thesis. Washington State University, 2012.

The long-term retention of inhaled soluble forms of plutonium raises concerns as to the potential health effects in persons working in nuclear energy or the nuclear weapons program. The distributions of long-term retained inhaled plutonium-nitrate [239Pu(NO3)4] deposited in the lungs of an accidentally exposed Hanford worker and in the lungs of experimentally exposed beagle dogs with varying initial lung depositions were determined. Autoradiographs of selected histological lung, lymph node, trachea, and nasal turbinate tissue sections were made to determine the location of plutonium within the tissues. A variety of specific stains were used to detect apoptosis and connective tissue generation. These studies showed that fibrotic scar tissue effectively encapsulated the plutonium and prevented its clearance from the body or translocation to other tissues. Alpha activity from deposited plutonium in the human case was observed primarily along the sub-pleural regions and strongly associated with the deposition of a carbon material, thought to be cigarette residue. No alpha activity was seen in the tracheobronchial lymph nodes of the exposed human. However, high activity levels in the tracheobronchial lymph nodes of the beagle dogs indicated they were more effective in clearing deposited plutonium from the lung tissues to the tracheobronchial lymph nodes. In both the human and beagle dogs, the appearance of bound plutonium was inconsistent with current biokinetic models for soluble forms of plutonium. The presence of sequestered plutonium in the beagle dogs suggested similar retention in the human case may not have been totally from cigarette smoking. The findings presented here provide additional support for a need to revise the lung model and include a bound plutonium fraction occurring after inhalation of plutonium nitrate, qualitatively not unlike that occurring after inhalation of insoluble plutonium oxide particles which also have been reported as being sequestered in pulmonary scar tissue. This bound fraction will have a marked effect on the dose to the lungs and the potential increase in cancer risk. It is suggested that the observation of long term retention of inhaled soluble plutonium nitrate in lungs be reflected in biokinetic models for radiation protection purposes.

Qu, Hongguo. Actinide CU resin study in actinide determination in human tissue. M.S. thesis. Washington State University, December 1996.

The use of Actinide-CU(R) resin (EIChroM Industries) as a pre-concentration step in the determination of human tissues has been investigated. Conditions for the use of Actinide-CU(R) resin for pre-concentrating actinides of Am and Pu in bone tissue and the typical soft tissues liver and lung have been determined. Determination of 242Pu and 241Am in the eluate from the column by liquid scintillation counting (LSC) indicate that the retention of Am and Pu in these tissue solutions by the A-CU column and the elution from the resin is quantitative. Incomplete decomposition of the Actinide-diphosphonate complexes (Am and Pu) from A-CU column causes poor recoveries in the electrodeposition step in routine alpha spectrometry analysis. This problem was solved by using 30% H2O2 and concentrated HNO3 with NaVO3 to oxidatively decompose the complexes. The pre-concentrated Pu plus Am fraction is then separated using ion exchange (AG1-X4 resin) to separate and purify the Pu fraction and solvent extraction (DDCP) followed by AG MP-1 column or extraction chromatography (TRU®) to separate and purify Am fraction. An average recovery of Pu of 84% and an average recovery of Am 89% were obtained using this method, determined by alpha spectrometry. The results indicate that the A-CU resin can be used in combination with other chemical procedures in the USTUR Radiochemical Program. A set of USTUR verified human bone tissue and human soft tissues were used to establish the validate method. Results obtained from this work show no significant differences to the verified values (1 standard deviation). Thus, from this study, it was found that: the Actinide-CU resin is effective for preconcentrating actinides in sample solutions of human tissues.

Hunacek, Mickey M. An evaluation of risk coefficients for thorotrast patients based on the dosimetry information from two whole body donors. M.S. thesis. Washington State University, December 1994.

No abstract available.

Marshall, Elaine T. Distribution of uranium in two whole body donors. M.S. thesis. Washington State University, 1994.

Most of the human biokinetic data for uranium have been obtained by studying individual tissues on autopsy, rather than the tissues of an entire organ system or even a whole body. The intent of this study was to supplement the existing data base by examining the uranium concentrations in tissues and organs of two whole body donors to the United States Transuranium and Uranium Registries (USTUR).

The donated tissues were analyzed at Los Alamos National Laboratory using a relatively new technique, kinetic phosphorescence analysis (KPA), which relies on the luminescent properties of the uranyl ion, rather than the radioactive decay of the long-lived uranium isotopes. This project report includes a comparison of the available analytical techniques to illustrate the reasons for choosing the KPA technique to analyze the tissues.

Uranium concentrations in the skeleton appear to be a function of bone composition, taking into account the fractions of cortical and trabecular bone. Overall geometric mean skeletal concentrations were calculated to be 4.84 ± 2.79 ng g-1 for USTUR Case 0213 and 5.75 ± 3.19 ng g-1 for USTUR Case 0242. With several assumptions, the skeletal uranium burdens were estimated to be 41,500 ng for USTUR Case 0213 and 55,900 ng for USTUR Case 0242.

Soft tissues had a much greater variability in uranium concentration. The variability in skin tissue samples was attributed primarily to the presence of extrinsic contamination that had been naturally incorporated into the tissue. For the other tissues, the differences in concentration were attributed to differences in health, lifestyle, and metabolics. The lung tissue concentrations of Case 0242 at 1.3 ng g-1 are somewhat elevated above that from the International Commission on Radiological Protection (ICRP) Publication 23 data and are about 5 times greater than the overall geometric mean for soft tissue for this donor. The tracheobronchial lymph node concentrations for Case 0213 and Case 0242, at 22.8 ng g-1 and 65.7 ng g-1 respectively, are significantly above those expected from the ICRP Publication 23 data. The observations together indicate that inhalation is an important route of intake in non-occupational exposures. The concentrations in the kidney for both individuals, at 0.94 ng g-1 and 0.97 ng g-1 respectively, were markedly less than those expected from the ICRP Publication 23 model. With similar assumptions as those made to estimate the skeletal uranium burden, the soft tissue uranium burden was estimated. The soft tissue uranium burden for USTUR Case 0213 was approximately 28,000 ng and that of USTUR Case 0242 was 16,600 ng.

Summing skeletal and soft tissue uranium burdens, the total quantity of uranium in the body can be assessed. The total body burden of uranium in USTUR Case 0213 was found to be 69,500 ng and that for USTUR Case 0242 was 72,500 ng. In spite of the individual tissue variations, when the tissue weights for Reference Man were used, the overall estimated body burdens of uranium in USTUR Case 0213 (~96,000 ng) and in USTUR Case 0242 (~74,000 ng) agree reasonably well with that of Reference Man at 90,000 ng.

Although the majority of this study was dedicated to the analysis of the data obtained via the KPA technique from the two whole body donors, some time was devoted to investigating the present models for describing uranium distribution and the applicable retention functions as presented in International Commission on Radiological Protection (ICRP) Publications 23 and 30. This project report also includes the results of a survey of the literature undertaken to identify and evaluate related studies that have been performed since the ICRP models were published. The results of the present analysis were compared, where possible, to published results as well as the ICRP retention functions.