Toxicology

A significant portion (15-20%) of mercury (Hg) in the Arctic Ocean is believed to originate from Arctic rivers, such as the Mackenzie River watershed in the NWT. Recent (2005- 2020) Hg monitoring data of freshwater and fish tissue and environmental model outputs were compiled and used to develop a Bayesian Network Relative Risk model (BN-RRM), a probabilistic model capable of analyzing causal relationships. The objectives of the model were to estimate the risk posed to fish health and the subsequent dietary Hg-exposure to humans; to compare the relative risks between regions of the watershed; and to identify the influential Hg sources. The output of the BN-RRMs differed significantly throughout the watershed, with atmospheric Hg deposition and soil erosion Hg release consistently flagged as important explanatory variables. Analysis of the endpoint uncertainties revealed gaps in knowledge and in Hg datasets, which should be the focus of study for future monitoring programs.

Author Keywords: Aquatic Ecosystems, Arctic, Bayesian Network, Mercury, Risk Assessment, Toxicology

The detection of ciguatoxins (CTXs) in biological samples is challenging due to their low concentrations, the presence of various congeners, and the absence of standardized methods. This study uses high resolution mass spectrometry (HRMS) with P-CTX-3B as a reference standard. The protonated molecules ([M+H]+) were most prevalent, especially when acetonitrile/water was utilized, providing enhanced sensitivity. Optimized collision energies of 15 eV for protonated molecules and flow rates of 10 µl/min enhance sensitivity and peak intensities, respectively. Acetonitrile/water (ACN/H2O) is recommended as the primary solvent for HRMS method, an aspect underexplored in existing literature. The detection of CTX-3B in fish tissue samples proved to be challenging, caused by variations in ion peak intensities and matrix effects, requiring a deeper exploration of the impact of complex matrices on CTX detection. The study emphasizes the need for a reliable internal standard to mitigate these effects and highlights the ongoing challenge of developing a rapid, simple, and sensitive detection method. The study's specific focus on the P-CTX-3B analogue significantly contributes to methodology development for this congener, serving as a foundational step in understanding and detecting CTX. Despite notable progress, the study acknowledges the absence of an ideal assay, outlining key challenges for future research on ciguatera analysis. It underscores the continuous necessity for method reevaluation, testing, and the broader goal of establishing a more clarified and rugged method for the identification of CTX in fish.

Author Keywords: Analytical Chemistry, Ciguatera Fish Poisoning, Ciguatoxin, High-Resolution Mass Spectrometry, Optimization, P-CTX-3B

Macrophytes play an important role in aquatic ecosystems, and thus are integral to ecological risk assessments of environmental contaminants. In this dissertation, I address gaps in the assessments of contaminant fate and effects in macrophytes, with focus on glyphosate herbicide use for invasive plant control. First, I evaluated the suitability of Typha as future standard test species to represent emergent macrophytes in risk assessments. I concluded that Typha is ecologically relevant, straight-forward to grow, and its sensitivity can be assessed with various morphological and physiological endpoints. Second, I assessed effects from glyphosate (Roundup WeatherMAX® formulation) spray drift exposure on emergent non-target macrophytes. I performed toxicity tests with five taxa, Phragmites australis, Typha × glauca, Typha latifolia, Ammannia robusta, and Sida hermaphrodita, which in Canada collectively represent invasive, native, and endangered species. I found significant differences in glyphosate sensitivity among genera, and all species' growth was adversely affected at concentrations as low as 0.1% (0.54 g/L), much below the currently used rate (5%, 27 g/L). Third, I assessed the potential for glyphosate accumulation in and release from treated plant tissues. I found that P. australis and T. × glauca accumulate glyphosate following spray treatment, and that accumulated glyphosate can leach out of treated plant tissues upon their submergence in water. Finally, I assessed effects of released glyphosate on non-target macrophytes. I found that P. australis and T. × glauca leachate containing glyphosate residues can stimulate the germination and seedling growth of T. latifolia, but can exert an inhibiting effect on A. robusta, although leachate without glyphosate caused similar responses in both plants. Additionally, I found no negative effects in A. robusta when exposed to glyphosate residues in surface water, or when grown with rhizosphere contact to an invasive plant that was wicked (touched) with glyphosate. My results show that non-target macrophytes can be at risk from glyphosate spray for invasive plant control, but risks can be mitigated through informed ecosystem management activities, such as targeted wick-applications or removing plant litter. Integrating contaminant fate and effect assessments with emergent macrophytes into ecological risk assessments can support the protection of diverse macrophyte communities.

Author Keywords: Ecosystem management, Ecotoxicology, Glyphosate, Herbicide, Invasive plant, Species at risk

This study investigated the role of the JNK signaling pathway in cadmium-treated mouse embryo forelimb bud cells in vitro. Primary cultures of forelimb bud cells harvested at day 11 of gestation were pre-treated with JNK inhibitor SP600125, and incubated with or without CdCl2 for 15, 30, 60, 120 minutes and 24, 48 hours or 5 days. Endpoints of toxicity were measured through cell differentiation by Alcian Blue Assay and phosphorylation of JNK proteins by Western blot. The results demonstrated that, in the cell differentiation assay, inhibiting JNK activation by 20 μM SP600125 causes an enhanced toxic effect in limb cells and inhibits cell differentiation, whereas 2 μM decreases differentiated nodule numbers under both cadmium stress and normal conditions. In conclusion, the JNK pathway has an essential role in the differentiation processes of limb bud cells in normal growth conditions.

Author Keywords: Cadmium, Cell Signaling, JNK, Limbs, Mouse Embryo, Teratology

Silver nanoparticles (AgNP) released into aquatic environments could threaten natural bacterial communities and ecosystem services they provide. We examined natural lake bacterioplankton communities' responses to different exposures (pulse vs chronic) and types (citrate and PVP) of AgNPs at realistic environmental conditions using a mesocosm study at the Experimental Lakes Area. An in situ bioassay examined interactions between AgNPs and phosphorus loading. Bacterial communities exposed to high AgNP concentrations regardless of exposure or capping agent type accumulated silver. We observed increases in community production during additions of polyvinylpyrrolidone (PVP) -capped AgNPs and that site and nutrient-specific conditions are important to AgNPs toxicology in aquatic systems. Toxicological effects of AgNP are attenuated in natural conditions and differ from results from laboratory studies of AgNP toxicity. Our results demonstrate more studies are needed to fully assess the risk posed by these novel chemicals to the environment. This work could be useful in forming risk assessment policies which are largely based on lab studies and typically demonstrate strong toxic effects.

Author Keywords: bacterial production, bacterioplankton communities, ecological stoichiometry, Experimental Lakes Area, mesocosms, silver nanoparticles

The main goal of this thesis was to assess the potential impacts of discharges of treated effluent from a small facultative sewage lagoon serving approximately 300 residents of the Mississaugas of the Credit First Nation to freshwater mussel populations in Boston Creek, a small tributary of the lower Grand River. The current resident mussel populations inhabiting Boston Creek were assessed using semi-qualitative visual surveying methods. In addition to various population level observations, other possible point and non-point influences on water quality in Boston Creek were identified. Following this, Lasmigona costata mussels were deployed as biomonitoring organisms alongside passive samplers during the October 2017 lagoon discharge period. Time weighted average (TWA) concentrations of select Contaminants of Emerging Concern (CECs) and Polycyclic Aromatic Hydrocarbons (PAHs) were estimated from levels of these compounds accumulated on passive samplers to understand the influence of wastewater on water quality in Boston Creek. Finally, mussel tissues were analyzed for various biomarkers of exposure to contaminants. Population surveys indicated that Boston Creek supports a plentiful and diverse community of freshwater mussels and may be a refuge for the Species of Special Concern, Villosa iris. Passive sampling revealed that most PAHs measured were present at concentrations below detection limits, while CECs were typically detected at relatively low concentrations (ng/L) directly downstream of the lagoon discharge. Biomarker responses detected in Lasmigona costata generally could not be attributed to exposure to the lagoon effluent but these data may indicate response to other point and non-point sources of pollution that could be affecting resident freshwater mussel populations in Boston Creek. The mussels surveyed in Boston Creek may be displaying community level effects of exposure to other sources of pollution in the area. The results of this thesis will help in establishing water quality guidelines in the lower Grand River watershed that will assist in the recovery strategy for freshwater mussel species at risk in Ontario.

Author Keywords: Biomarkers, Biomonitoring, CECs, First Nations, Freshwater Mussels, SAR