Theses/Dissertations - Environmental Science

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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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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    Microplastic pollution in surface waters of urban watersheds in Central Texas, USA : a comparison above and below treated wastewater effluents.
    (2018-11-20) Stovall, Jasmine K., 1992-; Bratton, Susan.
    Microplastics are polymer-based particles ranging in size from 50 µm to 5 mm. The behavior of microplastics within freshwater systems remains understudied. The purposes of this study are to assess microplastic levels in spring-fed and runoff-fed freshwater systems in small, urban watersheds above and below local point-source wastewater effluents, to investigate patterns in microplastic spatial distribution and to evaluate the influence that seasonality and land use may have on microplastic frequency and form. A total of 779 surface water samples of 800-mL were collected across five study locales and analyzed via visual inspection. In total, 1,198 microplastics were found, inclusive of fibers (95.0%) and fragments (5.0%). Approximately 57% of all samples were contaminated with microplastics, on average, ranging from 33.3%-80% per study locale. Overall, significant differences between sample site and sampling interval suggest that seasonality and land use influence microplastic frequency within a system, while spatial locale influences particle color and form.
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    Individual and interactive influences of low dissolved oxygen and calcium channel blockers in inland aquatic systems.
    (2018-08-31) Saari, Gavin N., 1988-; Brooks, Bryan W.
    Understanding and managing influences of multiple stressors represents a major water quality challenge, particularly in urbanizing regions. Because aquatic hazard assessments with chemical and nonchemical stressors can identify the global trends in occurrence and hazards of stressors for the protection of aquatic life, probabilistic aquatic hazard assessments were performed to examine whether water quality guidelines for dissolved oxygen (DO) are protective of aquatic life in inland waters. My analyses indicate that adverse effects of low DO to freshwater invertebrates and fish have been underestimated in inland waters. Additional low DO threshold information, including sublethal toxicity, for additional species such as warm water fish and mollusks across multiple life history stages is necessary to support environmental assessment and management of ecosystem protection goals. Similar techniques were used to examine the occurrence of calcium channel blockers (CCBs), a common class of vasodilators and cardio suppressants, in environmental matrices, and to predict hazards to non-target aquatic organisms in multiple environmental matrices and geographic regions. Whereas environmental occurrence of CCBs in freshwater and effluent have predominantly been reported from North America and Europe, data is lacking from many developing regions around the world and hazards and risks of CCBs to non-target biota remains poorly understood. Therapeutic hazard values (THVs), a comparative pharmacology and toxicology approach, employed during probabilistic hazard assessments with environmental exposure distributions revealed that amlodipine and verapamil in effluent and freshwater exceeded THVs 28% of the time. Diltiazem exceeded minimum human therapeutic thresholds in fish plasma ~18% of the time in surface waters. This approach demonstrated the utility of global assessments to identify specific CCBs and geographic regions where environmental assessments appear necessary. Subsequently, to understand adverse effects of individual and multiple stressors influencing cardiac function (DO, diltiazem, or DO x diltiazem), toxicity studies were performed using a comparative toxicology and pharmacology approach in fathead minnows (Pimephales promelas) across larval and adult life stages. DO x diltiazem toxicity studies with larval fish revealed acute lethality increased with decreasing DO levels and altered burst swimming behavior at DO water quality criteria levels deemed protective of aquatic life. In adult fathead minnows, low DO (3.0 mg DO/L) increased uptake of diltiazem and altered physiological responses (e.g., hematocrit, plasma lactate) at and above human therapeutic plasma levels. Failing to consider low DO influences with chemical exposure during toxicological studies of cardioactive medications and potentially other cardiotoxicants underestimates adverse outcomes in fish.
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    Influences of nutrients and salinity on Prymnesium parvum elicited sublethal toxicity in two common fish models.
    (2018-07-12) Hill, Bridgett N., 1993-; Brooks, Bryan W.
    The magnitude, frequency, and duration of harmful algal blooms (HABs) are increasing worldwide primarily due to climate change and anthropogenic activities. Prymnesium parvum is a euryhaline and eurythermal HAB forming species that has expanded throughout North America resulting in massive fish kills. Previous ecotoxicological work supported an understanding of conditions resulting in HABs and fish kills; however, the primary endpoint selected for these studies was acute mortality. Whether adverse sublethal responses to P. parvum occur in fish are largely unknown. To begin to address this question, fish molecular and biochemical oxidative stress (OS) responses and behavioral alterations in two common fish models were investigated. Varying nutrient and salinity conditions influenced P. parvum related OS and fish behavioral responses of two common fish models, and these responses were heightened by conditions nonoptimal for P. parvum growth. Such sublethal observations present important considerations for future assessment and management of P. parvum.
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    Microplastic ingestion by freshwater and marine fish from the Brazos River basin and Texas nearshore marine waters.
    (2018-07-16) Peters, Colleen Ann, 1990-; Bratton, Susan.
    This dissertation serves as one of the first comprehensive system investigations of microplastic ingestion by freshwater and marine fish from the Brazos River basin and Texas nearshore marine waters. In total, 436 freshwater sunfish were sampled and 45% contained ingested anthropogenic materials, consisting of -macro (4%) and -micro (96%) sized contaminants. Microplastic ingestion was greater within fish collected from urban areas, in comparison to upstream and downstream sites, suggesting that human development (i.e. paved roadways) and local urbanization are two possible factors impacting microplastic ingestion by sunfish. The marine portion of this research (Chapter Four) examined a total of 1,381 fish, inclusive of six species of a shared ecological guild, and 42.2% of stomachs contained microplastic fibers (86.4%), beads (12.9%) and fragments (<1%). Despite a substantial overlap in diet, ordination of ingested prey items clustered samples into distinctive species groupings, reflective of the foraging gradient among species. Grunt displayed the lowest overall frequency of microplastic ingestion and the most distinctive ordination grouping, indicating their selective invertebrate foraging preferences. While all six species had ingested microplastic, the results suggest that grunt, as selective invertebrate foragers, are less likely to ingest microplastic than species which exhibit generalist foraging preferences and methods of prey capture. When comparing microplastic ingestion between freshwater sunfish and marine pinfish, species which serve as ecological analogs between the systems, there was no significant difference in the overall frequency or mean number of microplastics ingested. However, the pinfish stomach content contained microplastic fiber, bead, and fragment morphologies, while the sunfish stomach content only contained microplastic fibers. Pyr-GC/MS analysis classified forty-three of the marine microplastic samples as polyvinyl chloride (34.8%), polyethylene terephthalate (9.3%), nylon (9.3%), silicone (2.3%), and epoxy resin (2.3%). Approximately 42% of samples could not be classified into a specific polymer class, due to a limited formation of pyrolytic products, low product abundance, or a lack of comparative standards. Overall, this dissertation demonstrates that microplastic ingestion is ubiquitous throughout Texas aquatic environments, influenced by species diet and foraging methods, and reflective of local land use patterns and major sources of pollution.