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    Monitoring risk from contaminant mixtures in stormwater with water quality measurements, bioassays, and bioassessment
    (University of Waterloo, 2025-11-20) Izma, Gab
    Urban stormwater management ponds (SWPs) are increasingly valued not only for their role in mitigating runoff but also for the biodiversity they support in densely developed environments. However, these systems receive complex contaminant mixtures from urban runoff, including pesticides, pharmaceuticals, industrial chemicals, and metals. These pollutants can accumulate in biologically active compartments like biofilms, posing risks that are not always captured by traditional water-based monitoring. My thesis investigates the nature, accumulation, and ecological effects of contaminants in SWPs using a combination of chemical, biological, and toxicological approaches. The objectives of my research were to: (1) characterize pesticide contamination in SWPs using water, biofilm, and passive samplers; (2) quantify pesticide accumulation in biofilms and identify influencing factors; (3) assess the toxicity of contaminated biofilms through dietary exposure; (4) survey the broader suite of urban contaminants in SWPs to develop a stormwater contaminant signature; and (5) examine relationships between environmental conditions and aquatic community composition. In Chapter 2, I surveyed 21 SWPs in Brampton, Ontario for pesticide contamination. I compared three monitoring approaches across the ponds - time-integrated water sampling, biofilm cultured on artificial substrates, and organic-diffusive gradients in thin films (o-DGT) passive samplers - finding that o-DGTs had the highest pesticide detection rates. However, issues with reproducibility in passive sampler data highlighted the challenges of using them for quantitative risk assessment. Despite generally low concentrations in water and biofilm samples, the widespread detection of diverse pesticide classes across all three matrices emphasized the chronic, mixture-based exposures in these ponds and informed recommendations for future monitoring strategies. In Chapter 3, I further investigated the use of biofilms as a sensitive and ecologically relevant matrix for contaminant monitoring. Examining a wider set of pesticide analytes, I found that over half of the pesticides detected in biofilm samples were not detected in water, suggesting that conventional sampling approaches may overlook important alternative exposure routes. Calculated bioconcentration factors (BCFs) varied widely and were not well explained by pesticide properties or water quality variables, pointing to the complexity of contaminant uptake mechanisms. To test the potential toxicity of these contaminated biofilm samples, in Chapter 4 I conducted a series of dietary exposure assays with two invertebrate grazers. Mayfly nymphs (Neocloeon triangulifer) and juvenile freshwater snails (Planorbella pilsbryi) fed with contaminated biofilms from the SWPs showed reduced survival and growth compared to controls. Although the test results did not always correlate with measured pesticide levels, these results support the ecological relevance of biofilm-mediated exposure and suggest the presence of additional stressors not captured in targeted chemical analyses. I further expanded the chemical scope in Chapter 5 by analyzing over 700 unique urban contaminants across water, biofilm, and o-DGT samples. In total, 200 organic compounds were detected, including personal care products and traffic-related pollutants, as well as persistent elevated levels of fecal indicators and chloride. From these data, I developed the Urban Stormwater Contaminant Signature (USCS): a proposed list of common, environmentally relevant compounds to guide future monitoring and toxicity testing in urban aquatic systems. Finally, in Chapter 6 I examine how environmental variables shape aquatic community composition. Diatom and macroinvertebrate assemblages sampled from the SWPs were dominated by pollution-tolerant taxa, with diatoms responding primarily to water quality (e.g., nutrients, chloride, herbicides) and macroinvertebrates more sensitive to habitat features associated with pond naturalization. Landscape-scale metrics (e.g., impervious cover) calculated from buffer zones had limited predictive power, suggesting that local conditions and upstream drainage characteristics play a stronger role in shaping biological communities. This research highlights the need to expand contaminant monitoring in stormwater systems beyond conventional water sampling, incorporating matrices like biofilm and tools such as passive samplers to better reflect the complexities of exposures in urban environments. The detection of numerous unmonitored or rarely assessed compounds suggests that current regulatory frameworks may underestimate the complexity and risk of urban chemical mixtures. Recognizing stormwater ponds as both infrastructure and ecosystems calls for more ecologically grounded approaches to design, management, and risk assessment; ones that support biodiversity alongside water quality improvement and flood protection.
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    Development of Functional Binders and Li2S@Carbon Nanocomposites for High-Performance Lithium Sulfide Batteries
    (University of Waterloo, 2025-11-20) Huang, Zhe
    Lithium sulfide (Li2S) is a promising cathode material for lithium-sulfur batteries (LSBs) owing to its high theoretical capacity (1166 mA h g-1) and potential for safer, scalable battery architectures. In contrast to sulfur cathode, Li2S enables direct pairing with commercial anode materials, avoiding the safety risks of lithium metal. Despite these merits, practical application of Li2S is challenged by its hygroscopic nature, which forms insulating LiOH/Li2O surface layers that cause a large first-charge overpotential; its high melting point (~938 °C), which prevents melt infiltration into carbon frameworks; sluggish redox kinetics; severe polysulfide dissolution; poor conductivity. Addressing these challenges requires integrated advances in binder design, electrode engineering, and cathode nanostructuring. The large first-charge overpotential due to the insulating LiOH/Li2O surface layer in Li2S-LSBs hinders activation and induces irreversible side reactions. Chapter 3 proposes mitigating the activation barrier by exploiting the reaction between polyvinylidene fluoride (PVDF) binder and LiOH/Li2O through dehydrofluorination. The overpotential was successfully reduced from 3.74 V with 30 min slurry grinding to 2.75 V by extending slurry stirring to 48 h. However, PVDF was also found to react with Li2S itself, partially consuming active material and lowering discharge capacity. Overall, this study provides mechanistic insights into the origin of Li2S activation overpotential and demonstrates the dual role of conventional PVDF binders, where slurry processing with PVDF can effectively reduce the first-charge barrier, while also highlighting the limitations of PVDF as a binder for Li2S electrodes. Since PVDF proved unsuitable for Li2S electrodes, Chapter 4 investigates alternative binders capable of enhancing the electrochemical performance of Li2S-LSBs. A binder based on a zinc acetate triethanolamine (Zn(OAc)2·TEA) complex was developed, which not only provides strong polysulfide-trapping ability but also exhibits redox catalytic activity, leading to markedly improved capacity, rate capability, and cycling stability compared with PVDF. To further reinforce electrode integrity and improve dispersion stability, polyethylenimine (PEI) was incorporated to form a Zn(OAc)2·TEA/PEI hybrid binder. Electrochemical testing showed that Li2S cathodes employing Zn(OAc)2·TEA/PEI with 10 wt.% PEI achieved superior rate performance, high discharge capacity, and excellent long-term cycling stability. An additional advantage of these binders is their fluorine-free composition, which aligns with sustainability goals and complying with emerging regulations, including EU restrictions on per- and polyfluoroalkyl substances (PFAS). In Chapter 5, an efficient precursor solution infiltration-decomposition strategy was invented to synthesize Li2S@Carbon nanocomposites under mild conditions, overcoming the challenges of Li2S’s high melting point, poor solubility, and the large particle size of commercial Li2S. In this approach, Li2S was first reacted with carbon disulfide (CS2) in ethanol at ambient temperature to form a highly soluble lithium trithiocarbonate (Li2CS3) precursor, which was readily infiltrated into mesoporous Super P carbon (SP). Subsequent thermal decomposition of Li2CS3@SP at 400 °C produced Li2S@SP-400 nanocomposites with a Li2S:SP mass ratio of 60:40, containing finely dispersed Li2S particles (~11 nm) uniformly confined within the Super P matrix. Electrochemical testing demonstrated that these nanocomposites delivered a high discharge capacity of 821 mA h g-1 (Li2S) at 0.1 C, equivalent to 1190 mA h g-1 (S), and exhibited superior rate capability and cycling stability compared to commercial Li2S, non-infiltrated Li2S nanoparticles, and melt-infiltrated sulfur composites (S@SP). The thermal decomposition of Li2CS3 precursor releases a large amount of CS2 gas (~62 wt.% of the precursor), which creates internal voids and limits the in-pore Li2S loading. To address this, Chapter 6 builds upon precursor infiltration-decomposition method with a multi-cycle strategy, enabling higher Li2S content and in-pore loading. Using mesoporous Super P as the conductive host and Li2CS3 as the precursor, repeated infiltration-decomposition cycles progressively increased the pore filling factor (FF) and in-pore Li2S loading (IPL), from FF = 38% and IPL = 30% for Li2S@SP-1 (one cycle) to FF = 91% and IPL = 73% for Li2S@SP-5 (five cycles), while also raising the overall Li2S content to 70 wt.%. Direct structural evidence from XRD and SEM confirmed reduced crystallite size, suppressed external deposition, and uniform Li2S distribution in the optimized Li2S@SP-5. Electrochemical tests demonstrated that Li2S@SP-5 delivered an initial discharge capacity of 807 mA h g-1 (Li2S) at 0.1 C, 598 mA h g-1 (Li2S) in the first cycle at 1.0 C, and retained 376 mA h g-1 (Li2S) after 500 cycles at 1.0 C. To construct high-performance cathodes, the functional binder from Chapter 4 was combined with the high in-pore loading Li2S@SP from Chapter 6. This attempt failed because Zn(OAc)2·TEA/PEI-based binders exhibited limitations with highly reactive nanoscale Li2S, resulting in diminished binding effectiveness. Chapter 7 therefore introduces a series of polyethylenimine-epoxy resin (PEI-ER) binders, where high-molecular-weight PEI anchors and catalyzes polysulfides while epoxy crosslinking reinforces mechanical stability, making this strategy particularly effective for stabilizing nanoscale Li2S composites. The in-situ crosslinking method further improved processing by removing the short crosslinking time window and enabling uniform networks without altering Li2S@SP morphology. Electrochemical tests showed the optimized in-situ crosslinked PEI-ER1:1 binder achieved 928 mA h g-1 at 0.05 C, 688 mA h g-1 in the first cycle at 0.5 C and retained 325 mA h g-1 after 1000 cycles at 0.5 C with stable Coulombic efficiency. SEM confirmed its compact structure, establishing in-situ PEI-ER crosslinking as a robust binder strategy for nanoscale, high-loading Li2S cathodes. Chapter 8 serves as the culmination of these research projects, combining the optimized Li2S@Carbon cathodes from Chapter 6 and functional binders developed from Chapter 7 with commercial Si/C anodes to successfully assemble and evaluate lithium-anode-free full cells, with PVP used as a baseline comparison, thereby demonstrating their practical feasibility. The in-situ crosslinked PEI-ER1:1-based full cell batteries delivered 670 mA h g-1 at 0.1 C and retained 304 mA h g-1 after 100 cycles (~45% retention), outperforming PVP-based full cell batteries (582 to 250 mA h g-1, ~43%). At 0.5 C, the in-situ crosslinked PEI-ER1:1-based full cell batteries achieved 564 mA h g-1 after activation and maintained 377 mA h g-1 after 500 cycles (66.8% retention), while the PVP counterparts fell from 573 to 176 mA h g-1 (30.7%). These results underscore the binder’s role in stabilizing cathodes and mark the successful assembly of lithium-free-anode Li2S full cells with commercial Si/C anodes. In summary, this thesis addresses the critical challenges of Li2S cathodes, including the large first-charge overpotential, the drawback of PVDF consuming Li2S, the large particle size of commercial Li2S, the high melting point and poor solubility that hinder conventional Li2S@Carbon composite fabrication, and the limitations of binders when applied to nanoscale Li2S, each identified in the process of resolving the preceding issue. By systematically investigating these problems, this thesis advances functional binder design, exploits precursor chemistry, and engineers nanostructured composites, concluding with the successful demonstration of lithium-anode-free full cell batteries. Further improvements could be achieved by employing more efficient carbon hosts with tailored structures, developing high-loading electrodes, integrating solid-state electrolytes to mitigate polysulfide dissolution, and incorporating catalytic components to accelerate Li2S redox kinetics, thereby pushing Li2S-LSBs closer to practical, high-energy-density applications.
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    Validating & Measuring Influenza Vaccine Effectiveness among and against Cardiovascular Hospitalization
    (University of Waterloo, 2025-11-19) Amoud, Razan
    Background: Influenza is a viral respiratory infection that causes serious health outcomes such as hospitalization and death and represents an important public health burden globally. Vaccination is one of the most effective interventions to prevent influenza and its complications. Although administrative databases such as pharmacy billing claims are used to measure influenza vaccination status, little is known of the validity of these databases in Ontario. Patients with cardiovascular disease (CVD) may have an altered immune response, despite being at a higher risk of influenza complications. It is not known if the Vaccine Effectiveness (VE) in this population is comparable to the general population. Further, there is a lack of research in Canada evaluating influenza vaccine effectiveness against cardiovascular outcomes, particularly using robust study designs such as the test-negative design. Three interrelated studies were carried out. First, a validation study was completed to examine the accuracy of the combination of Ontario’s administrative data from pharmacy and physician billing claims in identifying an individual’s vaccination status. The second study assessed the influenza VE against laboratory-confirmed influenza among older adults hospitalized with CVD conditions in Ontario and examined sex and age group as potential effect modifiers in the association between influenza vaccination and laboratory-confirmed influenza. The third study measured influenza VE against acute CVD outcomes using the Test-Negative Design (TND) for the first time among older adults in Ontario who were hospitalized within three days of their influenza testing. Methods: In the first study, I validated the combined physician and pharmacy billing claims within administrative databases using the linked reference standard of self-report data from the Canadian Community Health Survey (CCHS). This study estimated sensitivity, specificity, Positive Predictive Value (PPV), and Negative Predictive Value (NPV), with 95% Confidence Intervals (CI) of the estimates. In the second study, I used the TND to measure influenza VE against laboratory-confirmed influenza. The analysis included both crude and adjusted estimates accounting for potential confounders (sex, age group, neighbourhood income quintile, rurality, number of outpatient visits, beta-blocker medication use, statin medication use, receiving home care services, and influenza testing relative to the peak month of the season, and year of influenza season). In addition, I assessed effect modification of sex and age group on influenza VE by using two different methods: introducing interaction terms into the model and stratification. In the third study, I examined influenza VE against acute CVD outcomes, also using the TND. The exposure of interest was vaccination status, cases were those hospitalized for myocardial infarction, unstable angina, or stroke and testing positive for influenza, and controls were those hospitalized for a non-cardiovascular event and testing negative for influenza. Both crude and adjusted VE were estimated. Sensitivity analyses were performed to test the robustness of the findings by varying inclusion criteria, outcome definitions, and statistical adjustments. Results: In the first study, the CCHS identified 43% as vaccinated across the two survey cycles of 2013 and 2014. The sensitivity for the combined pharmacy and physician billing codes was 60.1% (95% CI 59.3%–61.0%), specificity was 98.5% (95% CI 98.3%–98.7%), PPV was 96.7% (95% CI 96.3%–97.1%) and NPV was 76.9% (95% CI 76.4%–77.5%). The second study included 1,159 patients, and almost half were vaccinated. Among vaccinated patients, 14% tested positive for influenza compared to 20% of unvaccinated patients.. Crude and adjusted VE were 32% [95% CI, 8–50%] and 43% [95% CI 20%–60%], respectively. Neither inclusion of interaction terms separately in the full model, nor stratification by sex or age group, revealed any evidence of effect modification. The third study included 33,710 hospitalized individuals who tested positive for influenza and had a CVD event (cases) or tested negative and did not have a CVD event (controls). There were 18,519 vaccinated individuals (55%). Among vaccinated patients, 0.4% tested positive for influenza and were hospitalized for a cardiovascular event, compared to 0.8% of unvaccinated patients. The adjusted influenza VE against cardiovascular outcomes was 43% [95% CI 25%–58%; p-value =0.0001]. Conclusion: Compared to past studies with only physician billing claims, the validation study provided improved performance measures of sensitivity, specificity, PPV and NPV values in the combined physician and pharmacy billing claims in identifying individual vaccination status in Ontario. The second study estimated influenza VE against laboratory confirmed infection and supports that influenza VE among older adults with CVD hospitalization is comparable to the general population. Also, no significant effect modification in VE was observed by the patient’s sex, or age. These findings suggest that the protective effect of the influenza vaccine against laboratory-confirmed influenza is consistent across key demographic and clinical subgroups within this high-risk population. The third study found that the influenza vaccine provides a significant protective effect against CVD outcomes. The global findings of this thesis emphasize the validity of administrative databases at estimating population-level vaccination rates and show the importance of influenza vaccination as an effective strategy to reduce both influenza hospitalization and CVD events. This unique research equips healthcare providers and policy makers with relevant findings to support their campaigns and recommendations on influenza VE, particularly in relation to CVD outcomes.
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    Turing Instability of a Closed Nutrient-Phytoplankton-Zooplankton Model with Nutrient Recycling
    (University of Waterloo, 2025-11-19) Xu, Xiangye
    We investigate Turing instability in a closed Nutrient–Phytoplankton–Zooplankton (NPZ) ecosystem that incorporates delayed nutrient recycling, formulated as a reaction–diffusion system. Although spatial diffusion typically enhances system stability, our study focuses on how differing diffusion rates among species can destabilize steady states and lead to the emergence of spatial patterns. To explore this, we first perform a linear stability analysis to identify the conditions under which Turing instability arises. These theoretical predictions are then validated through numerical simulations. Our study progresses systematically: beginning with a two-species model, extending to a threespecies system, and finally to a four species NPZD model. This stepwise framework provides both conceptual insight and quantitative understanding of how diffusion influences instabilities, offering a comprehensive perspective on pattern formation in multi-species plankton ecosystems.
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    Mitigating Hardware Trojan Risks in the Global IC Supply Chain: Pre- and Post-Silicon Detection Approaches
    (University of Waterloo, 2025-11-19) Pintur, Michael
    The integrity of modern systems is critically dependent on trust in the underlying hardware, yet complex Integrated Circuit (IC) supply chains introduce numerous vulnerabilities for malicious insertions. This thesis confronts the challenge of IC trust by examining two distinct detection methodologies, illuminating the fundamental trade-offs inherent in practical hardware verification under black-box conditions. The first contribution targets Trojan detection in Third Party Intellectual Property (3PIP) by adapting power-based side-channel fuzzing with Field-Programmable Gate Arrays (FPGAs). This investigation confirms that dynamic power analysis serves as an effective oracle for identifying the activation of a Trojan, creating a statistically significant side-channel anomaly. However, the work also demonstrates that random fuzzing is an impractical search strategy for discovering the low-probability trigger required for activation, highlighting a significant barrier to its widespread adoption. To overcome the limitations of methods requiring dynamic Trojan activation, this work explores static, on-chip sensing using Ring Oscillator Networks (RONs). This research addresses a gap in prior work by characterizing RON behaviour on a modern 28nm process and subsequently developing a statistical framework to distinguish malicious modifications from normal process variations. The proposed approach was validated against a benchmark hardware Trojan and successfully classified all Trojan-free and Trojan-infected devices. These results confirm that RON-based detection remains effective on 28nm process technology and demonstrate the robustness of the developed anomaly detection algorithm. By juxtaposing a dynamic, trigger-based detection method with a static, reference-based approach, this thesis illuminates the fundamental trade-offs inherent in hardware trust verification. The findings reveal a practical difference between the high specificity of dynamic analysis and the broad applicability of static verification. This research concludes that while physical side-channels are powerful tools, future progress will depend on developing solutions that effectively balance these competing demands, for a more comprehensive security strategy in the IC supply chain.