Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/100420

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The neuroinflammatory nexus: glial dysfunction in the pathogenesis and therapeutic targeting of neurodegenerative and neurodevelopmental disorders
(Colorado State University. Libraries, 2025) Risen, Sydney J., author; Moreno, Julie, advisor; Tjalkens, Ronald, committee member; LaRocca, Tom, committee member; Nordgren, Tara, committee member
Chronic neuroinflammation is increasingly recognized as a fundamental driver of both neurodegenerative and neurodevelopmental disorders, linking immune dysregulation, glial dysfunction, and disease progression. In neurodegenerative protein misfolding disorders (NPMDs), including Alzheimer's disease, Parkinson's disease, and prion diseases, sustained microglial and astrocytic activation exacerbates protein aggregation, synaptic dysfunction, and neuronal loss, accelerating cognitive decline. Similarly, in neurodevelopment, aberrant inflammatory signaling during critical windows of brain maturation impairs synaptic formation, alters neurotransmitter systems, and predisposes individuals to long-term cognitive and behavioral deficits. Despite distinct manifestations, both disease categories share a pathological feature: a maladaptive neuroimmune response disrupting neural homeostasis. While neuroinflammation is widely implicated in these disorders, defining its molecular mechanisms, identifying therapeutic targets, and understanding environmental contributions remain critical research needs. This dissertation begins to address these gaps by investigating neuroinflammation as both a therapeutic target in NPMDs and a mechanistic link between environmental exposures and neurodevelopmental disruption. The first investigation evaluates SB_NI_112, a novel brain-penetrant RNA-based therapeutic designed to selectively inhibit NF-κB and NLRP3 inflammasome pathways, key regulators of glial activation and chronic neuroinflammation. Pharmacokinetic and biodistribution studies in small- and large-animal models were first conducted to assess SB_NI_112's CNS penetration and safety. These studies confirmed robust brain bioavailability (~30%) and a favorable safety profile, supporting its viability for therapeutic application. Following these findings, SB_NI_112 was tested in a murine prion disease model, where treatment significantly reduced microglial and astrocytic activation in disease-relevant brain regions, preserved hippocampal neurons, and mitigated neurodegeneration. These neuroprotective effects corresponded with improved cognitive performance in novel object recognition tasks, indicating functional preservation despite ongoing prion pathology. Notably, SB_NI_112 treatment extended survival, reinforcing inflammasome inhibition as a viable therapeutic strategy for NPMDs. These findings provide strong proof-of-concept for targeting neuroinflammatory pathways to slow disease progression and preserve cognitive function in neurodegenerative protein misfolding disorders. The second investigation examines the role of environmental neurotoxicants in triggering neuroinflammation and impairing neurodevelopment. Using a juvenile mouse model, this study demonstrates that chronic low-dose manganese (Mn) exposure (50 mg/kg via drinking water) first alters gut microbiome composition, depleting the relative abundance of beneficial Lactobacillaceae, and increasing the relative abundance of pro-inflammatory Erysipelotrichaceae, contributing to gut-brain axis dysfunction. These microbial shifts coincide with significant gliosis in the enteric nervous system, suggesting early neuroimmune activation at the gut interface. This inflammatory response extends to the brain, where widespread microglial and astrocytic activation is observed alongside disruptions in neurotransmitter production and metabolism, including altered dopamine and serotonin homeostasis. Functionally, these neuroimmune and neurochemical disruptions correspond with changes in behavior, indicating impaired neural processing. The presence of inflammatory lesions in the intestinal lining further implicates gut inflammation as a mediator of Mn-induced neurodevelopmental deficits. These findings highlight the systemic impact of Mn exposure, reinforcing the link between environmental toxins, neuroinflammation, and behavioral dysregulation. Together, these studies further support the growing body of evidence that neuroinflammation is a primary driver of neurological disease rather than a secondary consequence, reinforcing the need for targeted neuroimmune interventions. By examining shared inflammatory features across NPMDs and environmentally induced neurodevelopmental disruptions, this work provides additional insight into how glial dysfunction contributes to neurological pathology. These findings support the continued development of neuroimmune-modulating therapeutics, emphasize early intervention, and highlight the importance of environmental risk mitigation. By bridging molecular, pharmacological, and environmental perspectives, this dissertation contributes to the broader understanding of neuroinflammation in disease progression, challenging traditional distinctions between neurological disorders and providing a foundation for future studies. The implications extend beyond basic science, offering translational potential for clinical intervention, public health strategies, and regulatory policies to reduce the burden of neuroinflammatory disease.
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Investigating the relationship between ionizing radiation and neurodegenerative mortality: addressing issues of bias, data pooling, and effect modification
(Colorado State University. Libraries, 2025) Zbysinski, Tony J., III, author; Neophytou, Andreas, advisor; Rosecrance, John, advisor; Magzamen, Sheryl, committee member; Wilson, Ander, committee member
Background Much of the current understanding of the adverse health effects of ionizing radiation (IR) exposure comes from studies of Japanese atomic bomb survivors who experienced acute, high doses of IR. However, these findings may not be generalizable to populations exposed to chronic low doses of IR such as workers and the general population. The U.S. Million Person Study (MPS) was founded to investigate the effects of chronic low dose IR for improved guidance of radiation safety. To address this gap in knowledge, worker cohort studies have been and continue to be conducted to assess the potential risks associated with chronic low dose IR, including neurodegenerative diseases. These studies aim to improve the understanding of IR dose ranges and risks that underly current radiation safety policy. Recent findings underscore a potential increase in risk of neurodegenerative disease from chronic low dose IR which may be of great concern considering the significant burden of such diseases. However, there are inconsistencies in prior research findings regarding the relationship between chronic low dose IR exposure and neurodegenerative disease. Several factors we focus on that can contribute to these inconsistencies are co-exposures to non-radiological substances, lack of power to investigate specific neurodegenerative disease outcomes, and selection mechanisms like the healthy worker survivor effect (HWSE) and competing events. This dissertation research introduces novel techniques to evaluate and improve the internal and external validity of prior and future occupational studies of IR and neurodegenerative-related mortality. The specific objectives of the present study include assessing the role of co-exposures as effect modifiers and/or confounders, enhancing the understanding of the trade-offs of pooling data diverse cohorts together, and addressing selection mechanism concerns. Methods Our first objective focused on assessing the role of co-exposures in the relationship between IR and neurodegenerative-related mortality among workers at the Fernald Feed Materials Plant, referred to as Fernald, and to investigate neurodegenerative-related mortality risk across different job categories. Individual-level, brain IR dose estimates were used alongside co-exposure data from job exposure matrix application to evaluate potential confounding and effect modification. Co-exposures for this evaluation were selected a-priori based on literature review. Cox proportional hazards regression models were used to observe risk of neurodegenerative-related mortality at 10 milligray (mGy) IR brain dose across different groupings of co-exposure status, while logistic regression models were used to calculate odds of neurodegenerative-related mortality across 9 job categories. In our second objective our goal was to evaluate the implications of data pooling in the context of the relationship between IR exposure and neurodegenerative-related mortality by combining data from the Fernald, Linde Ceramics Plant, hereafter called Linde, and Mallinckrodt Chemical Works (MCW) cohorts. The Linde cohort's data was updated to prepare for merging with Fernald and MCW. Extensive data harmonization, such as collapsing continuous IR exposure measurement into a categorical form, was undertaken. Cox proportional hazards regression was again used in data analysis across three distinctive steps that analyzed different aggregation parts between the cohorts, co-exposures of uranium and silica dusts were evaluated. A meta-analysis was also conducted of these same three cohort's individual studies to qualitatively compare overall analogous estimates to the pooled analysis. Lastly, our third objective employed the parametric g-formula to address selection mechanism concerns of HWSE and competing events. The parametric g-formula estimated the effect of hypothetical interventions on the risk of neurodegenerative-related mortality to evaluate the potential for HWSE by reducing IR exposure in hypothetical intervention scenarios. Expert interviews were conducted and supported with literature review to develop feasible hypothetical intervention endpoints of reducing IR exposure with possible real-world explanations including engineering and administrative controls. To investigate competing events, in one approach we modeled a likely competing event, cardiovascular disease (CVD) mortality, and compared cumulative incidence results to another approach without modeling for CVD mortality. Results Aim 1 findings highlighted that occupational exposure to machining fluids may act as an effect modifier of the relationship between IR and neurodegenerative-related mortality. Workers highly co-exposed to machining fluids showed significantly increased risk of neurodegenerative-related mortality at 10 mGy IR brain dose (HR 1.25, 95% CI 1.11, 1.40) compared to the overall baseline estimate (HR 1.01, 95% CI 0.96, 1.06). Additionally, certain job categories such as store and supply services had elevated odds of neurodegenerative-related mortality compared to administrative workers (OR 2.30, 95% CI 0.97, 4.96). Findings in Aim 2 revealed overall results consistent with Aim 1 of no increased risk of neurodegenerative-related mortality at low/moderate IR category (HR 0.95, 95% CI 0.73, 1.24) and high IR category (HR 1.05, 95% CI 0.80, 1.37). There was no evidence of confounding or effect modification by silica or uranium dusts. The meta-analytic estimate of these same cohort's individual studies had a similar summary estimate null finding compared to the pooled analysis finding for high categorical IR (HR 0.95, 95% CI 0.75, 1.20). Results of Aim 3's application of the parametric g-formula indicated that the HWSE may not be a key factor in the relationship between IR and neurodegenerative-related mortality as cumulative incidence (CI) did not change considerably between the natural course (cumulative incidence, 16.99%), engineering control (17.43%), and administrative control (17.14%) interventions in the application modeling for competing events. When comparing approaches that modeled and did not model for competing events, we did find evidence that CVD mortality acts as a competing event for neurodegenerative-related mortality. Conclusions This dissertation found that occupational co-exposures, such as machining fluids, may modify the relationship between IR and neurodegenerative-related mortality. In a pooled analysis of worker cohorts we encountered significant data harmonization challenges that emphasized the importance of careful selection of data pooling candidates and meta-analyses as an alternative to aggregating data for some research questions. Furthermore, the selection mechanism of HWSE may not be a key factor for IR and neurodegenerative-related mortality in Fernald, but CVD mortality appears to act as a competing event to neurodegenerative-related mortality. These findings offer potential explanations and insights into the inconsistencies in prior research of IR and neurodegenerative-related mortality and highlight the need to consider co-exposures, data aggregation approaches, and selection mechanisms. This research contributes by showing the importance of evaluating the role of co-exposures as effect modifiers, providing insights into the goals of multi-cohort pooling efforts by discussing trade-offs of data pooling versus meta-analytic approaches, and exemplified a relatively innovative and novel method of addressing selection mechanism concerns in the field of occupational radiation epidemiology. Future research should focus on replicating these approaches in different circumstances that may alleviate the limitations of the present investigations to continue the overarching goal of best informing radiation safety policy for the general population and modern workforce.
Open Access
Characterization of the performance of extraction chromatographic resins in high radiation environments
(Colorado State University. Libraries, 2025) Mueller, Rebecca, author; Sudowe, Ralf, advisor; Johnson, Thomas, committee member; Brandl, Alexander, committee member; Borch, Thomas, committee member
The overall goal of this work is to analyze the impacts of ionizing radiation on extraction chromatography resins. This includes analyzing how the retention of a particular radionuclide changes as the resin is exposed to increasing doses of ionizing radiation (0 to 50 kGy). The effects of the system and strength of the aqueous mobile phase are also investigated with batch contact studies carried out on 3M nitric acid, 1M nitric acid, 3M hydrochloric acid, and 1M hydrochloric acid. The changes to the surface functionality of the extraction chromatography resins are investigated via FTIR measurements. Changes in the physical structure of the resins and their fragmentation patterns are investigated via MALDI-TOF-MS (Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry, referenced as MALDI colloquially).
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The influence of reproductive access restrictions on health behaviors, infant mortality, and physician supply
(Colorado State University. Libraries, 2025) DeBie, Kelly Ann, author; Neophytou, Andreas, advisor; Gutilla, Molly, committee member; Keller, Kayleigh, committee member; Peel, Jennifer, committee member; Rojas-Rueda, David, committee member
In the past decade, there has been an increasing focus on restriction or elimination of abortion access in the United States. Of particular importance, the Dobbs v. Jackson Women's Health decision in 2022 overturned Roe v. Wade and eliminated the Constitutionally protected right to abortion. After Roe v. Wade became law in 1973, there was an observed decline in maternal mortality with highest impacts in Black maternal mortality, indicating differential impact of both the restriction and removal of reproductive access. It is hypothesized that removal of access will create many impacts and that those impacts may occur in a differential manner. This dissertation has explored the impacts of limiting reproductive care access on people in the United States. Utilizing a background in health policy, law, ethics, maternal mental health advocacy and doula care, I studied how these laws have impacted populations. Trends in out-of-state abortion seekers were analyzed corresponding with state based restrictions and the repeal of the constitutionally protected right to abortion in the Dobbs decision from 2022. Trends in infant mortality were studied to determine whether they are associated with state-level abortion restrictions in both aggregate data and data which has been disaggregated by race, ethnicity, and cause of death. Physician supply was analyzed to determine if there are changes in the overall supply of physicians as well as within the specialty of obstetricians and gynecologists practicing in impacted states. Reproductive care access is an essential component of healthcare, and it is crucial to understand how changes in state and federal law are impacting people's health and well-being.
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Association between socioeconomic status and PM₂.₅ exposure concentrations in Matlosana, South Africa
(Colorado State University. Libraries, 2025) Russell, Madison, author; Elf, Jessica, advisor; Neophytou, Andreas, committee member; Keller, Kayleigh, committee member
South Africa has the highest absolute burden of HIV in the world, with 7.5 million people living with the virus—equating to a prevalence of 19% (Pillay-van Wyk et al., 2016). Despite the use of antiretroviral therapies, HIV-seropositive individuals remain at a heightened risk for cardiovascular disease compared to their seronegative peers (Paisible et al., 2015; Bavinger et al., 2013; Freiberg et al., 2013). Exposure to fine particulate matter (PM2.5) further compounds this risk, as it is a known driver of cardiopulmonary disease, a leading cause of mortality worldwide. Notably, air pollution is responsible for 20% of cardiovascular disease deaths (Yusuf et al., 2019). Given that household and ambient air pollution contribute significantly to overall PM2.5 exposure—accounting for 5.2% and 2.9% of all global deaths, respectively (Health Effects Institute, 2019)—it is crucial to assess their impact on vulnerable populations. This study is part of a larger, overarching project investigating whether HIV infection modifies the relationship between PM2.5 exposure and both systolic blood pressure and percent predicted FEV₁ (forced expiratory volume), a key indicator of lung function. Specifically, this paper seeks to determine whether individuals living with HIV and/or those experiencing socioeconomic disadvantage experience disproportionate exposure to PM2.5. To characterize this study population, we categorized sociodemographic variables, assessed fuel use behaviors, and developed a weighted asset index. We also examined the distribution of both household and personal PM2.5 exposure across various socioeconomic indicators, utilizing the weighted asset index and fuel use composite scores as proxies for household fuel behaviors and stratifying by HIV status. Additionally, we conducted linear univariate and multivariate models separately for log-transformed personal and household PM2.5 measurements to quantify the impact of each variable on geometric mean PM2.5 concentrations. No significant differences in personal or household 24-hour PM2.5 exposure were observed by HIV status nor education level, sex, employment status, total family income, living situation, subjective financial security, adult hunger, child hunger, weighted asset index category, or cooking fuel type. However, a notable association was found for lighting sources: households using both candles and kerosene for lighting exhibited a 370% (95% CI: 121%, 1130%) higher geometric mean for household PM2.5 concentrations compared to those relying solely on clean (electric) lighting. The multivariate models explained 37% of the variability in household PM2.5 concentrations and 34% of the variability in personal PM2.5 concentrations. Notably, this study categorizes this peri-urban community in Matlosana, providing critical insights into socioeconomic disparities that exist in this population. However, our findings suggest that household and personal PM2.5 exposures are not distributed differently among different socioeconomic conditions nor among HIV status. Future research should explore the broader influence of urbanization and ambient air pollution, which may play a more significant role in shaping long-term health outcomes.
Open Access
Evaluating the impact of a train-the-trainer heat-related illness prevention training program among Colorado agricultural workers
(Colorado State University. Libraries, 2025) Martinez, Yessica, author; Valley, Morgan, advisor; Stallones, Lorann, committee member; Brazile, William, committee member
Agricultural workers are at a high risk for heat-related illnesses due to exposure to extreme environmental conditions. In recent years, regulations for heat stress prevention in agricultural workers have been evolving, leading several states to implement rules that address the increasing risks. Although many efforts have been focused on establishing these strategies, adherence remains insufficient and the evaluation of the effectiveness of heat illness prevention trainings has been limited. The objective of this study was to evaluate the effectiveness of a training strategy focused on preventing heat-related illnesses among agricultural workers in Colorado under a train-the-trainer model adapted from the Western Agricultural Health and Safety Center at the University of California Davis materials in accordance with Colorado State regulations. In spring 2024, five virtual training sessions were held in English and Spanish, allowing 64 trainers to complete the training. During the same season, the trainers then trained over 750 farmworkers in Colorado. Using Kirkpatrick's framework and a series of surveys and focus groups, the evaluation assessed changes in the level of reaction, with trainers reporting high satisfaction with the training. The learning level assessment showed significant improvement in trainers' knowledge and the ability to recognize symptoms, understand the risk of heat stress, and strategies to prevent it. At the behavioral level, trainers and farmworkers reported adopting positive changes in their work practices. Finally, the results showed an increase in risk awareness, the importance of participatory leadership, and greater confidence among trainers and workers in protecting themselves from the risk of heat illness. The findings demonstrated that a strategically structured program adapted to agricultural worker's needs can lead to significant changes in learning, workplace behaviors and overall, a better-established safety culture. These activities not only protect workers' health but may also improve their well-being and productivity in the long term.
Open Access
Application of Fourier-transformed-infrared spectroscopy to quantitate amorphous silica in personal air samples in sugarcane cutters
(Colorado State University. Libraries, 2025) Castro, Colton, author; Schaeffer, Joshua, advisor; Adgate, John, committee member; Chaparro, Jacqueline, committee member
In recent years, chronic kidney disease of unknown origin (CKDu) has risen to an epidemic level in Latin America. Specifically, in agricultural communities of sugarcane cutters, the burden of the disease is unusually high. Several hypotheses exist as to the cause of the disease, focusing on various risk factors, including dehydration, nutrition, and thermal stress. Another important risk factor warranting further research is exposure to particulate matter (PM), given its nephrotoxic potential. PM can be defined as solid or liquid particles present in the environment, often microscopic. Sugarcane workers are exposed to high PM concentrations containing various contaminants, including amorphous silica. In sugarcane, the leaves and other excess plant material contain amorphous silica that can be released into the worker's environment during harvest. Quantitating this amorphous silica and determining if it can play a deleterious role in kidney health has become a priority. Still, amorphous silica is a challenging analyte that requires time- and cost-intensive analysis. A previous pilot project aimed to develop a predictive model using Fourier-Transformed-Infrared Spectroscopy (FTIR) to analyze amorphous silica non-destructively and cost-effectively compared to the currently accepted NIOSH method (e.g., X-ray diffraction). The model was created, and initial concentrations of amorphous silica were determined. During the analysis of samples, the need to ascertain the detection limit of the FTIR method was evident. This project, therefore, further aimed to evaluate and analyze amorphous silica using direct-on-filter FTIR spectroscopy. The point of analysis where several discrepancies occurred (i.e., inconsistency with detecting the peak, loading amounts detected, etc.) was determined to be approximately 500 micrograms before the FTIR began to over or underestimate the absorbance values based on concentration changes. This study is one of the first attempts to use FTIR to non-destructively analyze and quantitate air sampling filters. Additionally, the results will be compared to the current limit of detection values for the FTIR methods employed by NIOSH for their silica analysis tool, further contributing to the literature.
Open Access
Application of ambient dose equivalent estimation models in remediated cedar forests of Kawauchi Village Japan
(Colorado State University. Libraries, 2025) Grabowski, Christian Robert, author; Johnson, Thomas, advisor; Brandl, Alexander, committee member; Borch, Thomas, committee member
Many regions contaminated by the release of radionuclides following the 2011 Fukushima Daiichi Nuclear Power Plant disaster are still being investigated today. The mountainous forest areas surrounding Fukushima prefecture were most affected by fallout radionuclides, primarily radiocesium (Cs134 and Cs137), and remain a focus area for remediation and scientific research. Several models have been developed to estimate ambient dose equivalent rates (H*(10)) using data on the depth distribution of fallout radiocesium in the forest soils. Our hypothesis is that two different models will accurately predict radiation doses within 20% based on soil samples. The hypothesis was tested by applying the two models to a research plot in Kawauchi Village Japan, where forestry remediation such as clear-cutting and litter removal has been conducted. Using soil sampling data for radiocesium at the Kawauchi test site, these models were used to estimate H*(10) and compared to measurements taken using handheld instrumentation. The distribution of radiocesium in soil for each sampling locations at the test site was determined using an exponential expression of vertical distribution. These distribution values were then used in two different models, one estimating H*(10) using conversion coefficients from Bq/m2 to μSv/hr, and the other model estimating H*(10) using a "field of view" approach, estimating a surrounding area's contribution to total H*(10) measured at a central point within the test area. The results from this comparison provide a real-world test of computer model effectiveness. The conclusion was that both models could accurately predict radiation levels based on soil samples within 20% of measured values using field instrumentation but could improve if experimental conditions more closely matched those assumed in the model's design.
Open Access
Creating optically stimulated luminescence 3D printing filament and synthesizing radiosensitive optically stimulate luminescence crystals
(Colorado State University. Libraries, 2025) DeVincenzo, Evan Ross Burson, author; Leary, Del, advisor; Boss, Keara, committee member; Sudowe, Ralph, committee member; Vickery, Kate, committee member
In radiotherapy, radiation oncologists use Megavoltage (MV) photon beams to deliver dose to target areas of a patient due to the MV's skin-sparing characteristics, but if the target area is near the surface of the patient, material referred to as a bolus is added to the patient's surface to provide dose build up and bring the maximum dose delivered close to the patient surface. Boluses are 3D printed to minimize air gaps between the patient and the bolus to deliver the dose accurately. Optically stimulated dosimeters (OSLD) are passive dosimeters that collect dosimetric information and are read later by using a stimulating laser to stimulate luminescence from the dosimeter, while a photomultiplier tube (PMT) measures the intensity of the luminescing light. We theorized that it was possible to combine 3D printing technology with OSLD crystals to make OSLD 3D printing filament so that an oncologist could 3D print a patient-specific bolus for a patient receiving radiotherapy treatment, and this bolus would function as a patient-specific dosimeter, ensuring precise, accurate, and safe delivery of dose- enhancing the overall quality of radiation therapy treatment. The first chapter of this study explores how we incorporated OSLD crystals, Al2O3:C, which has a robust field of study exploring its radiosensitivity, with NinjaFlex TPU, a filament used to 3D print patient specific boluses, to create an OSLD filament for oncologists to use to 3D print a bolus which would read by a commercially available LANDAUER microSTAR reader, a reader that utilizes Pulsed Optically Stimulated Luminescence (POSL) technology. We did this by cutting LANDAUER nanoDots, whose primary component is alpha carbon-doped aluminum oxide, into 1 mm or smaller pieces and cutting clear NinjaFlex TPU 3D printing filament into small, less than 1 mm pieces, mixing both at a ratio of 1:90, adding the mixture to a Filabot EX2 extruder, and extruding the mixture at low speed at 180 degrees Celsius. Afterward, the extruded filament was cut and re-extruded 2 more times, then warmed on a hot plate, compressed between 2 glass microscope slides, and cut into 8 mm diameter dots to create Filament Dot (FD) dosimeters. The FDs' dosimetric properties were tested and compared to LANDAUER Dot (LD) dosimeters, whose primary component is Al2O3:C crystals, using a Precision small animal irradiator (SAI). We found that the FDs' dosimetric characteristics were mostly similar to those of the LDs. This is the first study of this type, and we conclude that the results warrant further exploration into integrating OSLD material into 3D printing filament to 3D print radiosensitive patient boluses and 3D other radiosensitive models. LANDAUER had recalled all their nanoDot dosimeters while we were conducting the first chapter of this study, so we decided to explore new ways to synthesize radiosensitive carbon-doped aluminum oxide crystals that the LANDAUER microSTAR could still read. We developed two methodologies: the Arc Furnace methodology, which utilizes an arc furnace to melt aluminum oxide (Al2O3) crystals with carbon (C) powder, and the Hot Acid methodology, which involves mixing alpha-phase aluminum oxide crystals with carbon powder in nitric acid and boiling the nitric acid off then firing the remaining powder in a muffle furnace. The Arc Furnace (AF), Hot Acid (HA), and unmodified aluminum oxide samples were exposed to 1940 cGy using the Precision Small Animal Irradiator. When read by the microSTAR, we found that the AF samples had the strongest luminescence compared to the unmodified aluminum oxide, and the HA samples had no significant difference compared to the unmodified aluminum oxide. Then, to assess if the samples were more sensitive to low energy x-rays, we exposed the samples to an unfiltered beam from the SAI, and we found that the AF samples had a stronger-than-expected increase in luminescence strength when read by the microSTAR, indicating that the AF samples are acutely sensitive to low energy x-rays. We conclude that the Arc Furnace and Hot Acid methodologies created radiosensitive crystals by which the dose can be measured with the LANDAUER microSTAR, and we conclude further research should be conducted to refine these methods. The first study chapter has shown that we can incorporate OSLD crystals into 3D printing filament and the second chapter explores two methodologies to synthesize the crystals. We conclude that further research should be conducted into the methods to synthesize the crystals and the method to integrate the OSLD into the 3D printing filament. This will lead to new methods to create OSLD filament, which can be 3D printed to make radiosensitive boluses that will improve patient outcomes and 3D printing of other objects that researchers will use in other radiotherapy research.
Open Access
Thermophysical property characterization of binary chloride salts for molten salt reactors
(Colorado State University. Libraries, 2024) Harris, Michaella Skye, author; Sudowe, Ralf, advisor; Brandl, Alexander, committee member; Johnson, Thomas, committee member; Thorsett-Hill, Karen, committee member
Thermophysical properties are of critical importance to the successful demonstration of a molten salt reactor (MSR) as they have the most impact on the design, hydraulic function and neutronic behavior. However, there are limited data regarding complex, multicomponent salt systems and no standardized methodologies. Method development has become vital to produce reliable, experimental data to provide evidence to aid in the licensing of next generation reactor materials. Binary, non-actinide salt systems have become the primary focus as the foundation for supplying experimental data for simulations and validating new methodologies and techniques in measurements. Much research is still needed to fully understand the efficacy and viability of salt systems used for the fuel and coolant loops in the MSR. This dissertation focuses on the development of new methodologies and success and failures therewithin. In addition to providing new and adapted methods and techniques, the effects of outside influences and containments on the salt systems have been uncovered during this process.
Open Access
Chemical separations of a flerovium homolog using macrocyclic extractants
(Colorado State University. Libraries, 2024) Ahrens, Nicole Lynn, author; Sudowe, Ralf, advisor; Brandl, Alexander, committee member; Johnson, Thomas, committee member; Omur-Ozbek, Pinar, committee member
The placement of elements on the Periodic Table is governed by their fundamental chemical properties, maintaining specific trends when they are situated in order of increasing atomic number according to periodic law. When it comes to the heaviest of elements like flerovium (Fl), however, relativistic effects have the potential to alter their chemical behavior relative to lighter elements of the same group. The chemistry of Fl must be studied in order to confirm its placement on the Periodic Table, posing a unique challenge due to its low production cross-sections and short half-life. A chemical system capable of exceptionally fast and selective separations is required to achieve this extreme chemistry task. Such a system can be developed for Fl using its lighter homolog Pb. Two classes of macrocyclic extractants were explored with the aim of developing a chemical separation system for ultimate use in a Fl experiment. Specifically, crown ethers and calixarenes were evaluated as extractants for Pb using extraction chromatography and solvent extraction techniques. In these studies, crown ethers containing both oxygen and sulfur as bridging atoms were found to be ineffective Pb extractants in hydrochloric acid matrices. Unsupported calix[4]arenes also possessing bridging oxygens and sulfurs in various oxidation states were observed to be similarly ineffective but illustrated that the selectivity of calixarenes for Pb can be enhanced by modification of the outer functional groups as well as the bridging atoms. Though not effective as Pb extractants on their own, a significant synergistic effect was observed in EXC studies of a mixed system employing Eichrom Pb resin and a mobile phase containing 4-sulfocalix[4]arene with kinetics suitable for a Fl experiment. A similar SX system was then developed using the same crown ether extractant found on Pb resin with carbon tetrachloride as the organic diluent, but Pb extraction by the system was negligible.
Embargo
Assessment and intervention strategies for agricultural inhalation exposures in occupational and community environments
(Colorado State University. Libraries, 2024) Erlandson, Grant, author; Schaeffer, Joshua, advisor; Magzamen, Sheryl, committee member; Abdo, Zaid, committee member; Martenies, Sheena, committee member
Agriculture represents an industry vital to the U.S. economy, supplying the public with nutritious food and providing millions of workers with employment. Also characterized as one of the most hazardous industries for workers, agricultural environments contain a variety of inhalation hazards capable of impacting the health of workers and adjacent community residents. Agricultural inhalation hazards include airborne organic and inorganic dusts; livestock associated gases, pesticides, bacteria, viruses, and antibiotics. This study will focus on (1) bioaerosol exposures in dairy operations and (2) inorganic dust pesticide exposures from agricultural applications. In dairy environments, workers are regularly exposed to high levels of organic dust (bioaerosols) and their inflammatory constituents (e.g., endotoxin, muramic acid, and β-glucans). Dairy bioaerosol exposure is associated with increased prevalence of respiratory disease (e.g., asthma, rhinitis, and chronic obstructive pulmonary disease) in dairy workers. While bioaerosol exposure in dairy environments has been well characterized in previous research, efforts to identify hygienic interventions that control exposure remain unsuccessful. In crop production agriculture, it is well documented that workers are exposed to high levels of pesticides associated with adverse health outcomes (e.g., respiratory and neurologic diseases). Further, in agricultural adjacent community environments, where lower chronic pesticide exposures are found, there is mounting evidence linking adverse health effects (e.g., adult and iii childhood cancers, neurologic and respiratory diseases, and birth outcomes) in residents to exposure from agricultural pesticide applications. However, weak and sometimes inconsistent associations previously reported highlight the limitations of current community exposure assessment techniques used for pesticides. For specific Aim 1, we pilot tested a novel low-cost nasal rinse intervention to modulate airway inflammation in ten bioaerosol exposed dairy workers. Dairy workers were randomly split into treatment (n = 5) and control (n = 5) groups and administered saline nasal rinses before and after their shift for five consecutive days. Treatment group participants received pre-shift hypertonic saline rinses while the control group received normotonic saline rinses. Both received normotonic rinses post-shift. Pro and anti-inflammatory cytokines were measured from recovered saline rinses. Linear mixed model results indicated treatment group participants experienced significantly higher concentrations of anti- (IL-10) and pro-inflammatory cytokines (IL-6 and IL-8) than the control group (p < 0.02, p <0.04, and p < 0.01 respectively). This study demonstrates the capacity of hypertonic saline nasal rinses to successfully upregulate anti-inflammatory cytokine production. However, conflicting upregulation of pro-inflammatory markers cloud interpretations of efficacy. For Aim 2, we further evaluated the immunomodulatory effects of hypertonic saline rinses vs. normotonic saline rinses longitudinally (2-5 shifts) in 45 bioaerosol exposed dairy workers. However, in this aim, treatment group participants received hypertonic rinses pre- and post-shift and 16S sequencing was added to analyses to capture potential washout effects on microbial diversity. No significant differences were observed between group or day for any of the measured markers or microbiome diversity metrics. Yet, non-significant increases in anti-inflammatory IL-10 concentrations across the study period were observed independent of iv treatment group suggesting the rinse itself may be more impactful than tonicity. This study provided mixed but encouraging results that justify further research on nasal rinses as an intervention in bioaerosol exposed dairy workers. For Aim 3, we evaluated the agreement between three exposure assessment techniques used to estimate residential organophosphate (OP) exposure in agricultural adjacent communities located in the Central Valley of California. OP exposure was estimated from household dust samples, California Pesticide Use Report (CPUR) pesticide use modeling, and urinary DAP metabolites across two sampling campaigns. Simple correlation tests revealed moderate correlations (ρs = 0.46) between household dust and use model exposure estimates. Estimates from urinary DAP metabolites exhibited low to no correlation with the other two estimates. Linear mixed model results also indicated no association between urinary DAP metabolites and household dust or use model estimates. This study illustrates a lack of agreement between community pesticide exposure assessment techniques regularly used in research and motivates the development of more robust assessment techniques.
Embargo
Pathogens, pulmonary function, and the nasal microbiome of dairy workers
(Colorado State University. Libraries, 2024) Seidel, James, author; Schaeffer, Joshua, advisor; Magzamen, Sheryl, committee member; Abdo, Zaid, committee member; Valley, Morgan, committee member
Dairy workers are exposed to bioaerosols that are diverse in both size (0-100 µm in aerodynamic diameter) and inflammatory constituents (e.g. endotoxins, muramic acid, and β-glucans). Bioaerosol exposure at dairies is associated with a higher prevalence of chronic obstructive pulmonary disease (COPD), chronic bronchitis, asthma, respiratory pneumonitis, and asthma-like reductions in pulmonary function. More recently, opportunistic pathogens present at dairies such as the novel influenza D virus (IDV), influenza A (IAV), and livestock-associated Methicillin-resistant Staphylococcus aureus (MRSA) have also been a focus of research, as these pathogens can infect workers and pose a public health risk through community spread. Intrinsic factors such as genetics and childhood exposures likely play a major role in exposure response and respiratory disease pathology, but little research has been focused on the nasal microbiome's role in pathogen exposure and cross-shift changes of pulmonary function. From a longitudinal (2-5 working shifts) cohort of dairy workers in the High Plains Region of the US, this research analyzed pathogens found in the nares of dairy workers via pre- and post-shift nasal lavages. The same nasal lavages underwent targeted 16S rRNA gene sequencing to quantify the bacterial communities that comprise the nasal microbiome. Spirometry was also performed on dairy workers pre- and post-shift to measure cross-shift changes in pulmonary function. Overall, 32.1% (n=237) of nasal lavages tested positive for Methicillin-susceptible Staphylococcus aureus (MSSA), 11.4% tested positive for MRSA, 17.3% for IDV, 2.5% for IAV, and 1.3% for influenzas C virus (ICV). Only 1 of the original 31 participants never tested positive for a pathogen during their workweek. Differences in nasal microbiome characteristics emerged based on pathogen positivity, and differential abundance analysis revealed significant differences in genera based on the positivity of both bacterial and viral pathogens. The dairy workers in this study also experienced decreases in cross-shift pulmonary function. The average decrease in forced expiratory volume in one second (FEV1) over 108 working shift was -74.4 ml, and the average decrease of forced vital capacity (FVC) was -92.5 ml. Significant differences in microbiome characteristics did emerge based on post-shift and cross-shift spirometry performances, and taxonomic differences were noted in participants performing poorly on cross-shift FVC. The nasal microbiomes of workers also underwent community state typing, and participants in CST3 showed the most resilience to cross-shift changes in lung function. This research also investigated the efficacy of a hypertonic saline nasal lavage in improving cross-shift changes in pulmonary function. From a cohort of 44 dairy workers, 22 workers received pre- and post-shift hypertonic saline nasal lavages with an osmotic concentration of 400 milliosmole (mOsm). The 22 participants in the control group received pre- and post-shift normotonic saline (308 mOsm) nasal lavages. Based on constructed mixed linear models, the treatment improved cross-shift outcomes of the forced expiratory flow at 25-75% of the vital capacity (FEF25-75%), but had little effect on FEV1 and FVC. The use of a pre- and post-shift lavage of any osmolarity, however, appeared to reduce the burden of cross-shift pulmonary function decline often experienced by dairy workers. For the first time, this research showed that both viral and bacterial pathogens are present in the nares of US dairy workers. This work also identified the nasal microbiome characteristics that may play a role in pathogen exposure and cross-shift lung function outcomes. The use of a saline nasal lavage as an intervention was also explored, and the intervention appeared to improve cross-shift pulmonary function outcomes.
Open Access
Characterizing stooped posture of agricultural tasks
(Colorado State University. Libraries, 2024) Sanders, Denali, author; Rosecrance, John, advisor; Brazile, Bill, committee member; Hobbs-Murphy, Kayna, committee member
Agricultural field workers worldwide are often required to work in stooped postures during their working tasks. Stooped postures constitute a significant risk factor for the development of musculoskeletal disorders, specifically low back pathologies that cause pain. Chronic low back pain is a devastating disorder that can lead to depression, decreased mobility, lower quality of life, absenteeism from work, and decreased work productivity. Unfortunately, few studies have quantified stooped postures among agricultural workers, which makes it difficult to develop targeted work design improvements. The present study aimed to characterize stooped postures among workers engaged in several common agricultural tasks. Agricultural workers (N=43) were recruited from multiple Colorado farms and represented eight distinct work tasks. Participants wore a biomodule that contained a tri-axial accelerometer (Zephyr BioHarness) on their chests to record and log trunk postures in degrees for approximately two hours during specific work tasks. Data recorded on the sensor module were downloaded and analyzed in a customized RStudio program by participant and task to determine task cycle time, percentage of time spent in three posture categories (<0° to 30°, >30° to <60°, ≥60°), and mean trunk flexion. Stooped posture was defined as a trunk flexion equal to or greater than 60 degrees. The data indicated differences in task cycle time, percentage of time spent in posture categories, and mean trunk flexion across agricultural tasks. The results of the current study provide quantitative data that can help inform the development of targeted interventions aimed at reducing stooped postures in agricultural workers. Additionally, the methods developed in the present study may assist the Colorado Department of Agriculture and farm owners with evaluating the policies established in the Colorado Senate Bill (SB 21-087), which limits stooped postures during agricultural tasks that involve thinning and weeding during crop production.
Open Access
Effects of pH, temperature and competing ions on the adsorption of radiocesium on Prussian blue coated detonation nanodiamonds from aqueous solutions
(Colorado State University. Libraries, 2024) Zaiger, Megan, author; Sudowe, Ralf, advisor; Johnson, Thomas, committee member; Lindsay, James, committee member
The accident at the Fukushima Nuclear Powerplant, in 2011, resulted in the generation of radioactive contaminated water which is currently being stored on site. The Tokyo Electric Power Company (TEPCO), who owns the powerplant has begun treating and releasing the water into the ocean after most of the radioactivity has been removed by the Advanced Liquid Processing System (ALPS). Current techniques for preconcentration of radioisotopes, particularly radiocesium, from ocean waters are very labor and time intensive and often take months. Therefore, efficient, rapid, and reliable methods are needed for the determination of radiocesium in ocean water which represents a critical gap that this work seeks to address. A new technique using Prussian Blue (PB) coated detonation nanodiamonds (DND) to adsorb radiocesium from water samples is being investigated by the research group. The new technique takes hours to preconcentrate the radiocesium instead of months. The current study focuses on the effects of varying pH, temperature, competing ions, and stable cesium (Cs) on adsorption behavior of radiocesium. The results of the study show that high pH will result in a minimal decrease in Cs adsorption, while adsorption increases as pH increases, with the lowest adsorption of 95%. Temperature changes resulted in minimal decreases in Cs adsorption with the lowest adsorption of 98% measured at 4°C. Presence of potassium chloride (KCl), sodium chloride (NaCl), and lithium chloride (LiCl) at concentrations up to 1.0 M had no effect on the uptake of radiocesium showing adsorption of above 97% for all elements. However, adsorption decreased significantly in the presence of rubidium chloride (RbCl) as interferent concentration increased, with the lowest adsorption of 68% recorded for 1.0 M RbCl. The addition of stable Cs to low amounts of Cs-137 (1 Bq) saw high uncertainties and low adsorption reflecting the difficulty to obtain consistent results at very low concentrations. The study has shown promise for the use of DND in environmental settings with a continued need to be able to detect low levels of Cs-137.
Embargo
Community noise exposure from oil and gas drilling operations
(Colorado State University. Libraries, 2024) Stepherson, Phillip, author; Brazile, William, advisor; VanDyke, Michael, advisor; Gutilla, Margaret, committee member
Due to an increase in oil and gas (O&G) extraction activity near residential areas in Colorado, many community members may be at a higher risk of harmful noise exposure. The Colorado Energy and Carbon Management Commission (ECMC) has identified multiple sources of high-volume sound associated with O&G site preparation, drilling, and fracking including engines, mud circulation systems, rig top drives, and ancillary equipment. Acute and chronic exposure to elevated levels of environmental noise has been found to cause adverse health effects such as sleep disturbance, annoyance, cognitive performance decline, heart disease, and self-reported impact to overall wellbeing. While there is existing literature quantifying the extent and consequences of community noise exposure from other environmental sources (e.g., air traffic, road traffic, and railway transportation) there are limited published studies on noise exposure from proximity to O&G extraction sites. Researchers suggest, however, that oil and gas extraction operations may be producing harmful levels of noise. It also appears that the noise produced includes substantial low-frequency noise which can make it difficult to control. In addition, low frequency noise exposure may exacerbate the health effects associated with general noise exposure. To assess community noise exposure, a comprehensive environmental noise survey was performed at a new O&G extraction site in Northern Colorado during the drilling phase of operations. The research team collected noise emission data 24 hours per day over two months that included 1-second measurements of sound-pressure level, 1/3 octave bands, and triggered audio recordings. Based on the noise-monitoring results, it was determined that the noise levels from the drilling activities exceeded ECMC published noise exposure limits and noise thresholds related to adverse health effects. Distance was found to be a crucial factor in establishing compliance and reducing exposure, especially for low frequency noise. Increasing the O&G operations setback from community residences to 2,000 feet, as compared to the previous setback distance of 350 feet, was estimated to reduce noise levels by 15dB, which, while a substantial improvement, was not entirely sufficient to eliminate the risk of health effects or establish compliance with low frequency noise limits. High noise levels were found to occur on days that the rig's hoisting mechanism and/or drill were likely in use.
Open Access
Neutron fluence in a Howitzer drum and construction of a water moderated neutron irradiator
(Colorado State University. Libraries, 2024) Diaz Ruiz, Anilu S., author; Sudowe, Ralf, advisor; Johnson, Thomas, committee member; Fisher, Gwen, committee member
The Department of Environmental and Radiological Health Sciences at Colorado State University is utilizing a variety of irradiators to study the effects of ionizing on materials and tissue. Two of these are neutron irradiators based on 1 Ci and 5 Ci plutonium/beryllium (PuBe) sources, respectively. Neutron activation analysis is utilized to measure the neutron fluence at various positions in a Neutron Howitzer containing the 5 Ci source and a water tank containing the 1 Ci source. By determining the neutron flux in both systems, neutron irradiation at different intensities will become available for future research at Colorado State University. Additionally, both the drum and tank will be excellent teaching tools as they demonstrate neutron moderation, neutron shielding, material activation, and fluence measuring. Manufactured by the Nuclear-Chicago Corporation, the Model NH-3 Neutron Howitzer Drum is constructed in such a fashion that the PuBe neutron source can be moved in and out of irradiation position. In the irradiation position, two samples may be exposed to neutrons from the source by placing them in one of two horizontal ports in the drum. Both drum and ports are shielded with paraffin, which allows moderation of the neutron flux to thermal energies. In the experimental study, multiple metal foils were activated in the drum by irradiating them up to the point of measurable activity. Using a High Purity Germanium (HPGe) detector, the activity of the foils is quantified. The results of the measurements were used to calculate the neutron fluence using known neutron capture cross-sections. The calculated neutron fluence was then compared to the neutron fluence determined through a computational model of the drum using the Monte-Carlo N-Particle transport code (MCNP). Using the principles and methods practiced on the Howitzer drum, a water moderated neutron tank was constructed as a secondary neutron irradiator. The compared experimental and modeled neutron fluence spectrum in the drum were used to derive an effective model for total neutron fluence with respect to spacing from the inner end of the sample channel (x) of y = 69759e-0.17x and thermal neutron fluence of y = 12035e-0.176x.
Open Access
Association between exposure to cadmium and lead during gestation and adverse birth outcomes in the household air pollution intervention network (HAPIN) trial
(Colorado State University. Libraries, 2024) Alhassan, Mohamed Adnan, author; Peel, Jennifer, advisor; Clark, Maggie, committee member; Keller, Kayleigh, committee member; Neophytou, Andreas, committee member
Low- and middle-income countries (LMICs) are particularly vulnerable to the adverse effects of metal exposure. These countries' rapid industrialization coupled with population growth, result in substantial environmental exposures, which many governments have limited capacity to formally regulate. Even when regulations exist, many governments have a limited capacity to enforce those regulations. Additionally, LMICs bear a disproportionate burden of adverse birth outcomes, including low birth weight and preterm birth, which carry long-term health implications such as increased risk of chronic diseases, developmental delays, and mortality. Several studies have examined the association between metals and adverse birth outcomes such as low birth weight and preterm births. Specifically, despite the low number of studies, cadmium has been consistently linked to lower birth weights, smaller sizes for gestational age, and reduced head circumference. However, the association between lead exposure and birth outcomes shows inconsistent results. This inconsistency in findings, along with the low number of studies overall, especially in LMICs, regarding lead has prompted further investigation in our current study. Here we utilized data from the Household Air Pollution Intervention Network (HAPIN) trial, a randomized controlled trial conducted in rural areas of Guatemala, Peru, Rwanda, and India. The HAPIN trial evaluated the impact of replacing biomass stoves with liquefied petroleum gas stoves on various health outcomes, including infant birth weight among 3200 participants. The participants in the current analysis included pregnant women with a live singleton birth with exposure and birth data (n=2396). Maternal exposure to cadmium and lead were evaluated by analyzing dried blood spots using inductively coupled mass spectrometry. Blood spots were collected at baseline (9 - <20 weeks gestational age) and 32-36 weeks gestational age; we also evaluated the average of these two measurements. Birth weight was measured using a digital infant scale, with low birth weight defined as <2500 grams, and gestational age at birth was determined using screening data and ultrasonography, with preterm birth defined as <37 weeks. We utilized linear regression for birth weight and gestational age, logistic regression for dichotomous low birth weight, and Cox proportional hazards model for preterm birth. The models accounted for infant sex, maternal age, nulliparity, body mass index, maternal hemoglobin, mother's dietary diversity, food insecurity, tobacco smoking in the household, and study arm. We assessed effect modification by study location, sex, and study arm by including an interaction term. In sensitivity analyses, we included study location, household assets, maternal education in the models; replaced values below the limits of detection (LOD) with LOD/√2, and evaluated metal concentrations standardized by potassium levels. We also excluded maternal hemoglobin from the main model. The mean birth weight was 3,020 (standard deviation [SD]=445.5) grams, and 10.3% of all births were classified as low birth weight. The mean gestational age was 39.5 weeks (SD=1.7 weeks), and 5.2% of the births were preterm. The median lead concentration across the time points was 1.4 μg/dL (IQR: 0.9 – 2.2 μg/dL), and the median cadmium concentration was 1.0 ng/mL (IQR: 0.7 – 1.4 ng/mL), values comparable to those found in other studies. Overall, the results did not indicate a consistent or strong association between lead or cadmium and adverse birth outcomes. Baseline cadmium levels showed a modest increase in the odds ratio for low birth weight (OR per IQR increase: 1.2, 95% CI: 0.97 to 1.47). Sensitivity analyses closely aligned with the main findings. All the results for effect modification did not indicate differences in the strata. The study found a suggestive, but inconsistent evidence between exposure to cadmium and low birth weight. This study has some limitations. There is potential for non-differential measurement error due to the hematocrit effect, which alters the estimated spot volume based on participants' hematocrit levels. A sensitivity analysis using potassium standardized metal concentrations partially addressed this, but individual hematocrit variability can still bias the observed association towards the null, with a moderate magnitude. The probability of the bias is moderate. The chromatographic effect, which can cause variations in concentration due to the interaction between blood and the analyte with the filter paper, was also partially addressed using internal standards, blanks, calibration samples, quality controls, and reference materials. This potential bias is of low probability and magnitude, biasing the observed association toward the null. Confounding bias was considered a concern due to incomplete adjustment for covariates like seasonal variation, which can affect metal exposure and birth outcomes. Sensitivity analyses supported the main model findings, suggesting a low probability and magnitude of confounding bias, which could bias the observed association towards or away from the null. Despite residual confounding concerns linked to socio-economic indicators like assets and diet diversity, the sensitivity analyses did not deviate from the main model findings, indicating a small probability and magnitude of the bias, which would bias the observed association in either direction. The study had several strengths including a large sample size compared to previous studies, especially those in LMICs and it was conducted in three distinct rural LMIC settings, which, to the best of our knowledge, had not been done before. This study's strength lies in its large sample size of 2,152 participants with complete data, enhancing its statistical robustness and addressing the common issue of small sample sizes and missing data in prior LMIC research. Additionally, its unique examination across three distinct rural LMIC settings provides valuable insights into the regional variations affecting the outcomes studied. Future steps include using whole blood samples instead of dried blood spots (DBS) and measuring exposure at multiple time points, particularly at birth via the umbilical cord, could yield more accurate concentrations. It is also recommended that subsequent studies employ better socio-economic indicators to reduce residual confounding effects. Expanding the geographical scope of the study to include a broader range of urban areas within the HAPIN countries would improve the generalizability of the findings. Additionally, future research should consider analyzing the effects of metal mixtures to better replicate real-world environmental conditions and interactions. The results are generally consistent with existing limited data indicating no evidence of an association between lead and adverse birth outcomes and a potential association between higher cadmium exposure during pregnancy with increased risk of low birth weight.
Open Access
Developing a method to sample potential resuspension of radioactive contaminants near the former Rocky Flats Technical Plant
(Colorado State University. Libraries, 2024) Alcantar, Richard V., author; Sudowe, Ralf, advisor; Johnson, Tom, committee member; Volckens, John, committee member
From 1952 until 1989, the Rocky Flats Technical Plant processed plutonium for use as triggers in nuclear weapons. Throughout the facility's nearly 37 years in operation, several events led to radioactive contamination in areas within and surrounding the site. Since then, multiple cleanup projects have occurred, remediating contamination to acceptable levels. However, an increase in the number, size, and severity of Colorado wildfires in recent years has raised public concern for the potential resuspension of radioactive surface contamination to the now-populous areas surrounding Rocky Flats. Air sampling during specific conditions such as high winds, naturally occurring wildfires, and controlled burns would provide valuable data to determine if resuspension of radioactive contamination may be of concern. Sampling under such circumstances, however, is restricted by situation, permission, and weather. Whereas traditional aerosol sampling collects "total dust" samples to amass particles in the air with equal efficiency, without regard to particle size fraction, the use of a cascade impactor to separate aerosols by size can be utilized to relate how deep varied-sized particles might penetrate the human respiratory tract after inhalation. This would not only indicate the presence of radionuclides but also the deposition location within the human body, an important factor in determining the best dose estimate for the person. This study will compare the efficacy of a 3D-printed cascade impactor in separating particle size fractions to the capability of a commercial Andersen cascade impactor. Methods used in this thesis included radiological analysis with a Mirion LB4200 gas proportional counter. Significant imperfections of a printed prototype indicate that a stage-to-stage comparison between a commercial and a 3D-printed cascade impactor cannot be justified. Additionally, it is unlikely that current technology is capable of printing the exact same impactor with each subsequent print. The determination of a similar decay curve between stages of both impactors in some instances as well as similar trends in activity fraction by filter, however, indicate that a functional 3D-printed cascade impactor is feasible. Individually, each printed cascade impactor would require proper characterization to determine the particle size fraction that each stage captures. The evidence outlined in this study suggests that a functional cascade impactor can be fabricated by 3D printing. Still, additional studies would be necessary to characterize particle size distribution properly.
Open Access
Occupational noise exposure and hearing assessment of hydraulic fracturing workers: quiet versus conventional fleets
(Colorado State University. Libraries, 2024) Blevens, Melissa S., author; Brazile, William, advisor; Tsai, Candace Su-Jung, committee member; Van Dyke, Michael, committee member; Autenrieth, Daniel, committee member; Lipsey, Tiffany, committee member
Oil and gas extraction companies are exempt from implementing hearing conservation programs for their workers according to the Occupational Safety and Health Administration's (OSHA) noise standard. The occupational noise exposure and hearing status of these workers has not been published in scientific literature before the present study, presumably due to this exemption. In this study, area and personal noise exposures and worker hearing acuity were measured at both conventional and quiet hydraulic fracturing fleets, allowing a comparison between the fleets. Quiet fleets refer to the use of engineering controls to decrease noise levels of the pumps while conventional fleets do not employ these measures. In both fleets, the authors conducted personal noise dosimetry, equipment noise measurements, and pure tone audiometry pre- and post-work shift to determine if there were temporary threshold shifts (TTS) in hearing. Based on the personal noise dosimetry results, 42/50 (84%) of the quiet fleet and 34/34 (100%) of the conventional fleet workers sampled were at or over 100% noise dose according to the American Conference of Governmental Industrial Hygienists' (ACGIH) noise Threshold Limit Value (TLV). Based on the OSHA Permissible Exposure Limit (PEL) noise criteria, 9/50 (18%) of the quiet fleet workers and 15/34 (44.1%) of the conventional fleet workers were at or over 100% noise dose. Workers in both fleets experienced TTS, but no significant difference was observed between the types of fleets in relation to TTS. Most equipment of both fleets exceeded 85 decibels, but the pumps of the quiet fleet were ~14 dB lower than those of the conventional fleet. Although the quiet fleet noise controls reduced personal noise exposure, a portion of the quiet fleet workers sampled still faced noise levels that could increase the risk of hearing loss. The researchers suggest the initiation of a hearing conservation program despite OSHA exemption to safeguard worker health and recommend workers involved in certain job tasks employ dual hearing protection based on the exposure monitoring results.