Theses/Dissertations - Environmental Science

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Toward improved in vitro models for human health risk assessment : mechanisms of short-chain per- and polyfluoroalkyl substances (PFAS) toxicity.
(2023-08) Solan, Megan E., 1995-; Lavado, Ramon.
The global prevalence of manufactured chemicals lacking comprehensive toxicological profiles poses a significant challenge. This issue is exemplified by the widespread contamination of per- and polyfluoroalkyl substances (PFAS) worldwide. Despite their extensive use in various consumer products, the persistent and toxic nature of PFAS was not fully understood until after their global dissemination. As scientific knowledge advanced and regulatory bodies took action, short-chain alternatives were introduced to replace problematic precursors. However, these alternatives still lack sufficient toxicity data, emphasizing the need for robust chemical safety assessments. Initiatives to develop rapid and cost-effective solutions that utilize exposure-based strategies, hypothesis-driven tiered systems, and animal-free toxicological testing techniques have evolved in response to these issues. While in vitro high-throughput screening (HTS) methods have shown promise, their integration into the existing chemical risk assessment framework faces obstacles concerning physiological relevance. The overarching objective of this dissertation was to enhance our understanding of the mechanisms underlying the toxicity of short-chain PFAS and to develop improved in vitro models for human health risk assessment. The specific aims of this research are as follows: (1) comprehensively review the current state of in vitro methods employed in assessing human health risks associated with PFAS; (2) compare the cytotoxicity profiles of seven PFAS in six human cell lines; (3) investigate the impact of short-chain PFAS on oxidative stress biomarkers in human liver, kidney, muscle, and microglia cell lines; (4) examine the effects of short-chain PFAS on human cytochrome P450 (CYP450) enzymes; and (5) evaluate the influence of short-chain PFAS on gene expression profiles relevant to toxicity using a liver-on-a-chip model. The findings of this research have the potential to impact decision-making processes related to PFAS, the management of PFAS risks, and the development of alternative PFAS compounds. By shedding light on the toxicity mechanisms and enhancing in vitro models, this dissertation contributes to the advancement of human health risk assessment and aids in the development of safer alternatives to PFAS.
Developing an understanding of behavioral and transcriptional implications for the chiral cyanotoxin anatoxin-a and caffeine in common larval fish models.
(2023-08) Lovin, Lea M., 1994-; Brooks, Bryan W.
Neuroactive compounds are widely and routinely detected aquatic contaminants. With multitudes of chemicals having known and unknown neuroactivity and the sensitivity of early neurodevelopment to contaminant insults, early life stage assays are crucial for understanding hazards of these chemicals to public health and the environment. However, one of the most widely used developmental in vivo assays, the OECD fish embryo toxicity test with zebrafish (Danio rerio), an increasingly common alternative vertebrate model, has been shown to be insensitive to many neuroactive chemicals. Therefore, complimentary approaches such as behavioral and gene expression assays have been used to increase sensitivity, but robust and standardized methods for these endpoints are uncommon. This dissertation primarily focuses on the chiral cyanobacterial neurotoxin anatoxin-a, and considers the neurostimulant caffeine, aiming to elucidate behavioral and transcriptional effects while heeding efficiency of compound and animal use. It further considers environmental relevance, stereospecific effects, species sensitivity, and variability of behavioral assays based on arena size. Specifically, a meta-analysis of the current state of anatoxins research in aquatic systems was performed using environmental exposure distributions (EEDs), and collating bioaccumulation and toxicity data, for which quality was inconsistent. Applying EED information, two alternative vertebrate models, zebrafish and fathead minnows, were exposed to environmentally relevant and higher levels of the commonly studied, synthetic (±) anatoxin-a to compare photolocomotor and gene expression responses, with caffeine as a positive methodological control. Whereas zebrafish were highly insensitive to the racemate, the toxin caused significant hypoactivity and transcriptional changes in fathead minnows. This design was repeated with the naturally produced (+) enantiomer. Mortality was caused by multiple treatment levels in fathead minnows and zebrafish, along with behavioral and gene expression changes, with fathead minnows again being more sensitive to several response variables. To further examine comparative behavioral methods used here and previously, the influence of arena size on behavioral responses of naïve and caffeine exposed zebrafish was investigated to understand inherent variability of the experimental observation arena. This dissertation identified novel anatoxin-a consequences, how effects may be underestimated by studies employing racemic mixtures, and the importance of behavioral methodologies in comparative studies with common fish models.
Impacts of long-range transport of biomass burning on air quality in Texas.
(2023-08) Shrestha, Sujan, 1992-; Sheesley, Rebecca Jacobs.
The objective of this dissertation is to (1) provide a detailed analysis of the concentration, trends, and emission ratios of volatile organic compounds (VOCs) and trace gases in major cities in Texas: San Antonio, and Houston, and (2) investigate the physical and chemical properties of transported biomass burning (BB) smoke and their impact on background air quality in Port Aransas, an industrialized coastal site in Texas. To achieve these objectives, mobile and stationary field experiments were conducted to measure the impact of local emissions and transported pollution on air quality in Texas cities. The inter-site comparison of VOCs and trace gases across the San Antonio metropolitan area revealed significant geospatial and temporal variabilities in emissions and processing within this metropolitan area. Further, VOCs concentrations and emission sources were compared for two growing Texas locations in San Antonio and Houston. The results indicate that Texas cities have complex emission scenarios and that future efforts to mitigate ozone (O3) and particulate matter may require various emission reduction strategies. Two long-range transport BB events (BB1 and BB2) were identified at Port Aransas. Several aerosol- and gas-phase BB tracers were evaluated to identify and characterize these long-range transported BB events in an industrialized location. The aerosol composition and optical properties exhibited good agreement with the BB designation, while acetonitrile and carbon monoxide (CO) trends were less specific for identifying dilute BB plumes. The air pollutant measurements in Texas Commission on Environmental Quality (TCEQ) Continuous Ambient Monitoring (CAMS) and Black and Brown Carbon (BC2)- aerosol optical monitoring networks in Texas revealed potential regional impacts of these transported BB events on urban O3 levels. Overall, this chapter supports implementing an extended network of aerosol optical measurements to identify the influence of BB plumes, especially in cities designated as nonattainment or marginal nonattainment of criteria air pollutants.
Overcoming social, technological, and environmental obstacles in regional-to-global renewable energy transitions.
(2023-08) Garrett, Kayla P., 1997-; McManamay, Ryan.
The endpoints of sustainable development, as they are often understood, are seemingly at odds. For example, the objectives for energy transition, social development, and environmental preservation are, at times, in conflict. This requires a paradigm shift in the way researchers, policy makers, economists, and a myriad of other disciplines approach sustainability. The pursuit of one “good” does not inherently have to circumvent the pursuit of others. Historically, haphazard energy deployment has placed strain on environmental, social, and economic systems. Intentional renewable energy integration is of upmost importance to ensure that these systems embody sustainable interactions. In order to achieve a paradigm shift that enables cooperative systems and does not place sustainability endpoints at odds, we must expand and support opportunities for innovation, adaptation, and education within the overlapping sectors of the Energy – Water – Land Nexus. Within this dissertation, I explore two central themes regarding renewable energy transitions: First, that the socio-technical systems needed to support energy transitions is often lacking based on energyshed literacy, goal setting, and planning efforts. These social obstacles allude to limitation on fully realized renewable energy transitions. Chapters Two and Three unpack these concepts through assessing current progress in energy transitions from a regional spatio-temporal standpoint, and community planning standpoint respectively. The second theme is that renewable energy growth - namely hydropower - and environmental mitigation efforts do not have to be at odds, and in fact, can complement each other. Hydropower is one of the few renewable energy technologies that is not intermittent, but it also has a record of resulting in the highest environmental impact. In using hydropower as a case study, I explore some ways in which renewable energy growth can still be achieved while minimizing ecological footprint. Chapters Four and Five seek to quantify increases from hydropower using environmentally benign approaches – where environmental impact is largely realized at existing dams/hydropower plants – yet hydropower potential remains untapped at both national and global scales. This work aims to highlight opportunities for successful energy transitions rooted in a nexus mindset – where the needs of the people and the planet can exist in cooperation.
Sources and composition of organic aerosol on the North Slope of Alaska.
(December 2022) Moffett, Claire E., 1993-; Sheesley, Rebecca Jacobs.
As the Arctic continues to change and warm rapidly, it is increasingly important to understand the contribution of biogenic sources to Arctic aerosol. Biogenic sources of primary and secondary aerosol in the Arctic will be impacted by climate change, including warming and earlier snow and ice melt, while local emissions and long-range transport can drive changes in anthropogenic aerosol. This dissertation focuses on identifying the contribution of biogenic aerosol to organic carbon (OC) and its seasonal trends through the analysis of aerosol chemical and isotopic composition. Aerosol samples were collected at two sites on the North Slope of Alaska (Utqiaġvik and Oliktok Point) over the summer of 2015 and from June 2016 through August 2017. Organic carbon concentrations correlated well between the sites with high contribution from contemporary sources. Backwards air mass trajectory analysis indicates that source regions are primarily marine in the summertime. Methanesulfonic acid (MSA) was utilized to confirm this marine influence. Secondary organic aerosol confirmed the contribution of terrestrial biogenic sources to organic aerosol at both sites. Strong correlations between ambient temperature and MSA and OC were found during the summer. This study provides a multiyear characterization of organic carbon, highlighting the high biogenic influence and indicating areas of interest for future research.
Reconstruction of carbon and nitrogen stable isotope in baleen whale earplugs.
(December 2022) Mansouri, Farzaneh, 1987-; Usenko, Sascha.; Trumble, Stephen; Fulton, James; Sheesley, Rebecca
Changes in sea surface temperature, pH, and stratification have been reported to alter nutrient availability and resulted in a shift in phytoplankton community composition and size structure as well as ocean biogeochemistry over time. An empirical understanding of changes in the marine ecosystem and the ocean’s biogeochemical cycles through time requires a time-series dataset that spans years to decades. Biological time series datasets provide an unparalleled opportunity to investigate regional and global changes in the marine environment. Baleen whales are long-lived sentinel species and an integral part of the marine ecosystem. Interestingly, baleen whales have earplugs, a keratin-rich matric that is capable of recording and archiving the life history of an individual whale. Combining age estimates with elemental and molecular measurements from individual earplugs results in the reconstruction of chemicals and hormones in baleen whales with six-months resolution dating back 100 years. The objective of this dissertation is to reconstruct lifetime δ13C and δ15N profiles (i.e., birth to death) earplugs and investigate years to decadal changes in the ocean ecosystem and individual foraging and feeding ecology. Reconstructed δ13C and δ15N profiles from baleen whale earplugs (N = 17, n = 950 laminae) in this study provide the first recorded birth to death stable isotope profiles for baleen whales. These longitudinal profiles reveal changes in both individual whale behavior such as possible shifts in foraging location and/or trophic level as well as ecosystem-level changes that could be associated with the Suess effect and/or long-term changes in biogeochemical cycling.
The Texas TGV Proposal: Nexus or Nightmare?
(1994) Stoodley, Scott Howard; Alexander, Sara E.; Baylor University.
This thesis objectively analyzes the current Texas TGV High Speed Rail (HSR) proposal. The purpose is to determine whether or not this proposal is in the best economic and environmental interests of the State of Texas and in the larger picture, the United States. The primary objectives are to analyze current HSR systems throughout the world and to critically evaluate the specifications of the Texas proposal. It will also assess the relative success of the HSR systems that are in operation in reference to current U.S. expenditures on different modes of transportation. The major arguments for and against this proposal will also be evaluated. After a comprehensive review, it is the determination of this thesis that the proposed Texas TGV system is in the best interest of the state and in the larger picture, the United States.
Toxicological response to nanomaterial exposure in in vitro lung cells are determined by cell-type.
(2020-10-08) Lujan, Henry, 1993-; Sayes, Christie M.
Nanotechnology is an advancing field that continually introduces new nano-enabled products into consumer products thereby increasing the risk of nanoparticle exposure to humans and the surrounding environment. The increased rate of nanoparticle exposure to humans requires the field of nanotoxicology to rapidly screen for markers of toxicity after nanomaterial exposure. To properly screen for markers of toxicity, this study aims to address gaps in the in vitro nanotoxicology literature. First, the most common biochemical pathways investigated in the nanotoxicology literature were outlined to build a landscape of the in vitro nanotoxicology literature to find the gaps in the literature. Next, ill-defined cell culture parameters were examined to outline the appropriate methodology required to generate proper cytotoxicological models. Lastly, a suite of microscopy techniques was used to examine novel mechanisms through which aluminum (Al) nanomaterials exert their toxicity. Results showed that no two cell lines are alike as each cell-type exhibits differential baseline characteristics. Furthermore, the cell-type and inherent morphological and biochemical differences between all cells influences the toxicological response to nanomaterials. This research will advance the field of nanotoxicology by highlighting the importance of proper characterization for in vitro cell culture systems and nanoparticle test systems to increase the complexity and impact of conclusions drawn from past, current, and future pulmonary nanotoxicological studies.
The testing and use of a new method to evaluate chronic toxicity in Daphnia magna.
(2022-05-05) Bullard, Marlin, 1981-; Matson, Cole W.
The importance of toxicity testing to the protection of people and the environment cannot be overstated, however in order for the data to be of use it must be both relevant to actual conditions of exposure and conducted in a manner that efficiently uses resources. In this research we examined the effect of the exposure of simulated natural waters upon the toxicity of Silver Nanoparticles in order to ascertain if a change in toxicity would be observed compared to lab water exposure and if this toxicity would change over time. In addition, we evaluated new methods to conduct toxicity testing including a new test that would reduce the duration of a standard toxicity test from 21 days to 10 while still testing the same endpoints.
Nanocarriers for infectious disease control : physical, chemical and biological effects.
(2022-01-13) Ameh, Thelma, 1992-; Sayes, Christie M.
Engineered nanomaterials with distinct physicochemical properties have found vast applications in consumer, industrial and pharmaceutical industries. Zerovalent metal nanoparticles such as silver and copper nanoparticles synthesized with specific surface properties can be utilized as non-traditional antimicrobial agents to address the problem of antimicrobial resistance in clinical settings. The characterization of nanoparticles as therapeutic agents or as drug delivery agents is an important component of the drug discovery pipeline. Silver and copper nanoparticles were synthesized via the chemical reduction method with specific surface stabilizing agents. Particle characterization via dynamic light scattering, transmission electron microscopy and spectroscopy confirmed the formation of stable surface stabilized silver and copper nanoparticles with distinct physicochemical characteristics such as unique nanoparticle surface charge. These nanoparticle constructs were tested for antibacterial efficacy against divergent lineages of bacteria species, Escherichia coli, Staphylococcus aureus, and Sphingobacterium multivorum using standardized microbiological assays. These nanoparticles were effective antibacterial agents against the experimental bacteria species, showing a dose dependent antibacterial effect. Antibacterial properties of these nanoparticles were as a result of surface stabilizing agents, surface charge, dose and interactions between bacteria and nanoparticles. Taken alone, bacteria species identity showed minimal effect on antibacterial response to nanoparticle exposure, thus suggesting that the antibacterial mechanism targets highly conserved anatomical and physiological characteristics in the bacterial tree of life. The nanoparticles also demonstrate antibacterial properties at low doses which is suitable for clinical applications. The role of induced generation of reactive oxygen species (ROS) in mammalian and bacteria cells after exposure to the surface stabilized silver and copper nanoparticles was probed. Low toxicity to BEAS-2B human bronchial epithelia cells was observed while nanoparticles induced high levels of ROS in Escherichia coli. Induced ROS showed a positive correlation to bacteria growth inhibition. Metal ion poisoning and nanoparticle effect were shown to drive induced ROS production in varying degrees in both cell types. Further safety and efficacy studies of nanoparticle exposures via in vitro pharmacokinetic models are needed in order to broaden the knowledge perspectives on their use in biomedical applications.
The importance of scale : bioaccumulation of contaminants of emerging concern by bivalves.
(2022-04-01) Burket, S. Rebekah, 1986-; Brooks, Bryan W.
Increasing urbanization presents unique challenges to sustainable environmental quality, particularly in urbanizing arid and semi-arid regions of the United States (U.S.). In urban areas, municipal wastewater treatment plants discharge treated effluent directly to streams, and total stream flow is often dominated by or dependent on wastewater effluent. As a result, contaminants of emerging concern (CECs), which are present in wastewater effluent, are discharged directly to the receiving streams. This has led to a rapidly developing literature for environmental assessment and management of various down-the-drain contaminants. However, most environmental methods focus on measuring pharmaceuticals in water, sediments and fish. A large data gap exists for accumulation of CECs, including pharmaceuticals and personal care products (PPCPs), in bivalves. Filling this data gap is important because bivalves are valued both ecologically and economically; Bivalves are known to improve water quality via their capacity to filter particulate matter from the water column, and bivalve aquaculture operations support local economies and serve as an additional source of food. To capitalize on available suspended particulate matter, these aquaculture platforms are often located in wastewater treatment plant discharge areas, potentially exposing the bivalves to contaminants that can accumulate in their tissue. The results in this dissertation have filled several data gaps related to bioaccumulation of PPCPs by bivalves. First, results from a pilot study in Hong Kong showed that bivalves from both large-scale and small-scale aquaculture operations accumulated low levels of CECs. Second, results from a field-study in an effluent-dependent stream indicated that bivalves accumulated several different types of pharmaceuticals, in some cases reaching steady-state after 8 days exposure, and spatial differences were observed for some compounds, with highest observed concentrations for antidepressants. Third, results from an outdoor mesocosm experiment highlighted different uptake patterns for bivalves during the first 7 days of exposure to treated wastewater, and indicated that bivalves accumulated a greater number of pharmaceuticals when compared to fish in the same streams. Finally, results from a laboratory study highlighted different uptake and elimination patterns for two commonly detected pharmaceuticals.
Metabolism and mechanistic toxicity of environmental pollutants in fish models : integrating in vitro and in vivo systems for ecotoxicological studies.
(2021-09-15) Franco, Marco E., 1991-; Lavado, Ramon.
The presence of legacy and emerging contaminants in the aquatic environment represents a significant threat to aquatic biota, often leading to significant declines of biodiversity. This issue is further aggravated by the influence of abiotic environmental factors, such as climate change, which could potentially modify organisms’ exposure and responses to pollution. Historically, ecotoxicological studies have relied on the use of live animals and endpoints such as mortality, growth, and reproduction to determine whether exposed organisms and populations are at risk. However, these approaches are often hindered by cost, ethic, and scientific limitations, making them unable to provide a thorough representation of exposure conditions and resulting adverse effects. Recently, significant research efforts have highlighted the need to understand pollutant-driven alterations at different levels of biological organization. In this context, new approach methodologies (NAMs), such as in vitro systems, have emerged as robust bioanalytical tools to mechanistically describe chemical-organism interactions, predict potential adverse effects from exposure, and support comprehensive assessments of risk, while reducing animal use. The scope of this dissertation relies on the applicability of NAMs, specifically cell-based bioassays, and their integration with more traditional approaches (e.g. in vivo systems) to address research gaps associated with the biotransformation of legacy compounds by fish populations with different exposure history, the endocrine disruption potential of wastewater effluents, and the description of mechanistic toxicity of natural and anthropogenic pollutants, while considering the influence of different environmental stressors. This work demonstrated that descriptions of adverse effects from exposure to pollutants are significantly facilitated by in vitro systems, but that overall characteristics of the species and areas of interest must be accounted for when selecting appropriate cell-based models, as their improper selection could significantly mislead observations and subsequent environmental management strategies. The integration of cell-based and whole-animal approaches showed that the sensitivity and specificity of in vitro systems are significant limitations for their implementation, and that their value in ecotoxicological studies relies on their integration with more complex experimentation through weight of evidence (WoE) approaches.
Community needs assessment among the Gujjars in Northern India.
(2002) Dorrell, Janet C.; Alexander, Sara E.; Baylor University.
The perceived needs of the Gujjars of northern India were investigated in the Gurdaspur District of Punjab, India. The purpose of this study was to provide baseline data on the Gujjars who migrate to and from the states of Punjab to Himachal Pradesh by assessing their basic human needs within Johan Holmberg's sustainable development framework. These baseline data were gathered using a Needs Assessment Survey that represents approximately seventy-five Gujjar families who suffer problems of under-representation and social, economic and geographic marginalization. The analysis encompassed in the approach, defined as advocacy anthropology, suggested that the Gujjars do perceive a need for development and advocacy, specifically in the areas of education, land distribution, medical access, freedom from exploitation, political empowerment, and relief from poverty.
A stepwise approach to understanding nanomaterial transformations under situationally relevant conditions.
(2021-04-20) Mulenos George, Marina Rochelle, 1995-; Sayes, Christie M.
Given the increasing use of nanomaterials in various consumer products and industrial processes, it is of the utmost importance to better understand potential mechanisms of adverse effects to ensure human health and safety when developing regulations and standard operating procedure with newly developed materials, like nanomaterials. Nanomaterials are materials with one or more dimensions in the nanoscale range that are produced to advance industrial processes, used as an additive in consumer products, and produce novel drug delivery carriers. Standardized toxicological studies focus on newly produced nanomaterial products before they reach the market; however, most of these studies exclusively investigate pristine engineered nanomaterials. The issue with testing pristine engineered nanomaterials is that most environmental and/or human toxicities are induced after nanomaterials undergo transformations, e.g. release of metal ions. The goal of this dissertation was to conduct a comprehensive study of increasingly complex situationally relevant environments on organic and inorganic nanomaterials to understand important insights into nanomaterial transformations and the associated toxicity after exposures in vitro. Situationally relevant conditions occur when nanomaterials are used in products or processes and interact with the surrounding environment, where they then may undergo transformations. These transformations may include distribution with biomolecules or natural organic matter, lipid membranes in cells, high ionic conditions, or changes in temperature, salt concentration, etc. In this study, important physicochemical characterization methods were established for organic and inorganic nanomaterials. Additionally, these nanomaterials were transformed under simulated conditions and examined in increasingly complex environments. Next, the transformed nanomaterials were incubated with an established in vitro liver model to elucidate the relationship between nanomaterial transformations and the associated toxicity after exposure. Finally, transformed nanomaterials were exposed to an in vitro model for steroidogenic disruption to investigate further into adverse effects nanomaterial transformations may have on human health. Ultimately, the aim of this work is to advance the field of toxicology by improving our understanding of nanomaterial transformation mechanisms and to aid in risk assessment and regulations.
Detailed molecular and isotopic characterization of carbonaceous aerosols to assess air quality issues in urban areas : the San Francisco Bay Area and the Houston metropolitan area.
(2020-07-20) Yoon, Subin, 1989-; Sheesley, Rebecca Jacobs.
The objective of this dissertation is to provide detailed characterization of carbonaceous organic aerosols to better understand major sources of particulate matter (PM) and their atmospheric formation in an oxidizing and highly complex urban atmosphere. For this dissertation, optimized radiocarbon (14C) and source characterization techniques were applied to PM samples from the Houston Metropolitan Area and the San Francisco Bay Area. The San Francisco Bay area study was focused on identifying seasonal trends (winter and non-winter) and sources of elemental carbon (EC). The study required isolation of EC for 14C-based source apportionment. Chemical mass balance model (CMB) of EC and 14C-based total organic carbon (TOC; OC + EC) were also included for comparison of source apportionment methods and different carbonaceous aerosol fractions, respectively. Sources of EC and TOC were similar at most of the sites while a few sites (e.g. San Francisco and Napa) were distinctively more impacted by fossil fuel or contemporary/biomass burning sources. The winter season had significantly larger TOC concentration due to meteorological conditions and changes in emissions (e.g. increased residential wood smoke). Relatively good agreement between the 14C-EC- and CMB-EC- was observed for both seasons. The first and second Houston studies focused on identifying diurnal and temporal trends of aerosols using both fine and coarse PM and contribution of secondary organic carbon during periods of poor air quality (i.e. high ozone and PM), respectively. The largest concentrations of fine EC and BC concentrations occured during the mornings while periods of enhanced TOC was driven by an increase in the fine PM. Interestingly, a relatively large contribution of coarse EC was measured in Houston. Based on the 14C and CMB analysis, Houston’s carbonaceous aerosols are largely from secondary biogenic sources while secondary fossil contribution was highly variable. Furthermore, the poor air quality period in the Houston metropolitan area was driven by favorable meteorological conditions (i.e. Bay Breeze) providing stagnant atmospheric conditions, allowing for accumulation and photooxidation of fossil fuel emissions. Overall, the study results provided up-to-date characterization and source apportionment of less studied carbonaceous aerosols fractions at two major U.S. urban coastal regions.
The effect of hypoxia on the cytotoxicity of diesel exhaust particles and a novel oxygenating therapeutic in four cell lines.
(2020-07-21) Dabi, Amjad, 1990-; Bruce, Erica Dawn.
Hypoxia is characterized by oxygen levels in tissue below 2% and is implicated in many diseases and adverse health outcomes including chronic lung disease, neurodegenerative diseases, and delayed wound-healing. Many solutions for tackling hypoxia to alleviate such conditions have been proposed but all carry significant limitations. This study attempts to characterize a novel oxygenating therapeutic known as Ox66™. Another major human health concern is diesel exhaust particles (DEP), a prominent component of air pollution. This study evaluates the toxicity of DEP, Ox66™, and a mixture of both during both hypoxia and normoxia and in 24- and 48-hour exposures using four cell lines. The effect of hypoxia on cytotoxicity carries implications for the health risk assessment of air pollution in patients suffering from hypoxia-related diseases. Additionally, the effect of Ox66™ on the hypoxia induced changes in DEP exposures as observed in their mixture may provide clues about its efficacy.
Interactive effects of copper oxide nanoparticles and arsenic on rice (O.sativa japonica ’Koshihikari’) plant growth and development.
(2019-05-02) Liu, Jing, 1987-; Cobb, George P.
The emerging applications of nanomaterials (NMs) encompass a wide range of industries, including agriculture (e.g., as fertilizers, pesticides, and biosensors). NMs applied in the crop-field may influence plant growth and uptake of heavy metal(loid)s including arsenic (As). Being ubiquitous in the environment and readily bioavailable in aquatic system, As is taken up by rice plants, causes phytotoxicity and accumulates in rice grains. Classified as a Class I carcinogen and causing many diseases, As in rice grains potentially causes human health effects, particularly for infants who are eating rice to transition from breast milk to solid food, and Asian populations with regular daily rice consumption. Although As in water can be removed dramatically by copper oxide nanoparticles (nCuO) due to their high adsorption capacity for As, the interaction of nCuO and As has not been well elucidated on rice plant growth and As accumulation. This project was the first to investigate the interaction of nCuO and As on rice (Oryza sativa japonica’Koshihikari’) plant growth and development during a life cycle (from seed germination to seed maturation). The effects of nCuO and As were determined, individually and interactively, on rice seed germination and early seedling growth in sand and an artificial soil mixture of clay and topsoil. A greenhouse study on the life cycle growth of rice plants in the artificial soil mixture approximated the real agriculture scenario and identified the nCuO dependent acceleration of heading process of rice plants. Particularly, As accumulation in dehusked rice grains was decreased by nCuO to 128 ng/g, 36% lower than the WHO maximum safe concentration of As in white rice (200 ng/g) for humans. Arsenic distribution and speciation inside the plant growth were also affected by nCuO. Transgenerational effects of nCuO and As were also verified on seed germination and early seedling growth of rice plants in this project. These results contribute to the fundamental database of endpoint effects on rice plants, direct future research about wide-scale application of NMs in crop field as fertilizers or amendments, and provide insightful information to investigate the mechanism of the interaction between nCuO and As on plant growth.
Biological responses from contaminants accumulated in seafood using an in vitro human intestinal and liver co-culture.
(2019-06-10) Sutherland, Grace E., 1995-; Lavado, Ramon.
In vitro bioassays have been useful in predicting mechanisms of toxicity; however, conventional cell-based assays grown in monolayers are unavoidably poor models for human tissues due to the lack of complexity and physiological interplay observed in vivo. To address these limitations, the present study utilizes a combination of human intestinal and hepatic cells in a co-culture model. The purposes of these projects are to evaluate the differences between mono- and co-culture systems related to cytotoxicity and enzyme activity, and apply the co-culture model in the screening of seafood samples collected from the Galveston Bay. It was observed that the co-culture model had greater antioxidant enzyme activity compared to that of the monoculture, suggesting that hepatocytes grown in co-culture may be better suited to facilitate the expression of enzymes in response to xenobiotic metabolism in intestinal cells. This emphasizes the importance of adequate model selection to facilitate assessment of risk.
Influences of spatio-temporal variability during aquatic assessments of ionizable contaminants.
(2019-04-16) Scott, William Casan, 1988-; Brooks, Bryan W.
Urbanization and evolving land-use is challenging water management strategies in semi-arid regions of the United States, where stream flows are often dominated by treated wastewater effluent discharges. Effluent-dominated and dependent surface waters are becoming common in urbanized watersheds, where physical and chemistry factors can influence exposure and toxicity of many down-the-drain chemicals and contaminants of emerging concern (CECs). In these effluent-dominated systems, effective exposure increases when rate of chemical introductions to surface waters exceed chemical degradation rates in receiving systems. In fact, many consumer chemicals (e.g., pharmaceuticals) and other contaminants (e.g., ammonia, algal toxins) are ionizable across surface water pH. Here I examined aquatic biota in tidally influenced urban estuaries, where dynamic salinity and pH gradients may challenge prospective and retrospective risk assessments. In several of these urban systems, the ionizable pharmaceutical diltiazem was initially observed to exceed human therapeutic plasma doses in plasma from several fish species, which indicate risks to aquatic life in these dynamic systems. Dickinson Bayou, an urban estuary influenced by onsite (e.g., septic) and centralized effluent discharges, was then examined, in which influences of tides on spatiotemporal hazards of select ionizable contaminants were identified under conditions not typically included in routine surface water quality assessments. A third study employed the Gulf killifish, a common euryhaline species in the Gulf of Mexico, to define influences of salinity and pH conditions on uptake of representative ionizable weak bases (e.g., diltiazem, diphenhydramine) to fish plasma and body burden. Though pH, but not salinity, altered fish uptake, body burdens of diphenhydramine were elevated at low pH and apparent volumes of distribution were lower than studies with freshwater fish. The fourth chapter of this dissertation examined pH influences on toxicity of Prymnesium parvum, a harmful algal bloom (HAB) species in riverine and transition zones of a moderately saline inland reservoir. Combined with climatological and geological influences, anthropogenic changes in some Texas reservoirs support HAB of this typically estuarine alga, which appears to bloom in response to site-specific water chemistry, including pH and salinity. Observations suggest that fatty acid amides are not responsible for P. parvum related fish kills and identified locations of elevated risks for HABs of this emerging threat to water quality. Findings from these studies collectively, highlight the importance of characterizing site-specific influences on bioaccumulation and toxicity of ionizable contaminants, and integrating such information during prospective and retrospective risk assessments.
Bioaccumulation of contaminants of emerging concern in dynamic ecosystems.
(2018-11-14) Haddad, Samuel Perry, 1990-; Brooks, Bryan W.
The aquatic environment includes complex systems on which society relies to provide ecosystem services and support biodiversity. In recent years, the demand for aquatic-ecosystem commodities has greatly increased due to rapid population growth and industrialization. This burgeoning population stresses the global water cycle in many ways including increased fossil-fuel consumption promoting climate change, altered snowpack decreasing instream flows, multiple cities utilizing the same waterways, and increased nutrient loading due to agricultural expansion. And poorly treated sewage Such alterations to aquatic systems leads to unique exposure scenarios of contaminants of emerging concern such as pharmaceuticals and cyanotoxins. Thus, an understanding of exposure, hazards, and bioaccumulation of contaminants of emerging concern in dynamic aquatic systems in necessary to support sustainable management of aquatic resources. In this dissertation, the first study examined bioaccumulation of diphenhydramine, an ionizable weak base pharmaceutical, across different life stages in an organism that demonstrated ontogenetic diet changes in an urban estuary. The findings of this study demonstrated that ontogenetic dietary shifts do not affect the bioaccumulation of diphenhydramine, but exposure difference in water does. The second study investigated whether ionizable weak base compounds with differing properties demonstrated trophic dilution within the food web of urbanizing rivers receiving runoff from snowmelt. This study observed that multiple ionizable weak base pharmaceuticals trophicly diluted with increasing trophic position and that inhalational uptake was the main driver of bioaccumulation in rainbow trout. The third study examined the spatial and temporal fate and transport of ionizable pharmaceuticals within a dynamic aquatic system that shifted from being influenced by spring snowmelt to effluent-dominated conditions. The findings of the third study reported decreasing concentrations with increasing distance downstream regardless of season and the presence of secondary inputs from onsite waste-water systems. The fourth study developed a novel analytical method and then investigated the bioaccumulation potential of various cyanobacterial toxins in a highly eutrophic Texas reservoir. The fourth study identified several novel methodological approaches to analytically identify cyanotoxins and reported the presence of cyanotoxins in Lake Waco, Texas, USA for the first time. These observations collectively provided novel environmental assessment approaches to support an advanced understanding of bioaccumulation within dynamic aquatic ecosystems.

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