Search

The emerging field of microplastic-metal mixtures toxicity is riddled with contradictory conclusions relating to the uptake, accumulation, and toxicity of the mixture and each constituent. After initially setting out to fill knowledge gaps through several studies with a phylogenetically diverse set of animal models and exposure scenarios, I recognized that this work contradicted other studies in the field. This thesis draws on our developed understanding of metal behaviour and toxicity in an effort to resolve the confusion relating to microplastic-metal mixtures toxicity. Despite the well-established knowledge that water quality characteristics govern the behaviour of metals in freshwater systems, there has not been adequate water quality reporting in the field of microplastic-metal mixtures toxicity. To address the reality that providing a full suite of water quality characterization is not often feasible for each experiment, we created a model to predict which aspects of water quality primarily govern the association of cadmium and polyethylene, a representative microplastic. The model, combined with understanding the bioavailability of metal-microplastic complexes, provides insight into the hazards of metal toxicity in a given system. This model promotes the harmonization across research in the field which can then collectively be used in policy development to protect aquatic life.

The platinum group elements (PGEs) palladium (Pd) and platinum (Pt) are introduced to aquatic ecosystems through emissions processes from industrial applications. Despite this, little is understood about the toxicity of these metals to aquatic organisms, especially fishes. Considering ambient concentrations of PGEs are relatively low in natural systems, the use of sensitive endpoints such as olfaction is ideal in informing the development of ecological guidelines and risk assessments. We can conclude from the present study that Pd is toxic to rainbow trout olfaction near environmentally relevant concentrations, whereas Pt is not. Through the manipulation of water quality parameters, it is clear water hardness plays a role in olfactory acuity. Further investigation on Pd-induced olfactory toxicity demonstrated bioaccumulation of Pd at the olfactory organ, supporting the bioavailability of waterborne Pd. As PGE contamination continues to increase, understanding ecological impacts remains critical to protect aquatic life from these contaminants of emerging concern.

Fish depend on olfaction for reproduction and survival. Here, using molecular to behavioural endpoints, we compared the effect of two neurotoxic contaminants, Cu ions (Cu2+) and copper nanoparticles (CuNPs) on rainbow trout olfaction. Exposure to equitoxic concentrations of Cu2+ and CuNPs resulted in distinct toxicity patterns over time in rainbow trout olfactory mucosa. During continuous exposure to Cu2+, fish olfactory function was partially recovered. However, the olfactory function of CuNP-exposed fish showed a steady decline over time. Gene-transcript profiles of Cu2+-exposed olfactory mucosa showed neural repair mechanisms were upregulated to recover the olfactory dysfunction. In the CuNP treatment, dysregulation of transcripts that regulate function and reestablishment of damaged olfactory mucosa represented key mechanisms of CuNP-induced olfactory toxicity. Moreover, our findings revealed the CuNP-induced olfactory dysfunction was irreversible after the 7-day recovery period. Collectively, CuNPs and Cu2+ exert their effects via separate mechanisms in rainbow trout olfactory mucosa.

For decades, we have known that chemicals affect human and wildlife behavior. Moreover, due to recent technological and computational advances, scientists are now increasingly aware that a wide variety of contaminants and other environmental stressors adversely affect organismal behavior and subsequent ecological outcomes in terrestrial and aquatic ecosystems. There is also a groundswell of concern that regulatory ecotoxicology does not adequately consider behavior, primarily due to a lack of standardized toxicity methods. This has, in turn, led to the exclusion of many behavioral ecotoxicology studies from chemical risk assessments. To improve understanding of the challenges and opportunities for behavioral ecotoxicology within regulatory toxicology/risk assessment, a unique workshop with international representatives from the fields of behavioral ecology, ecotoxicology, regulatory (eco)toxicology, neurotoxicology, test standardization, and risk assessment resulted in the formation of consensus perspectives and recommendations, which promise to serve as a roadmap to advance interfaces among the basic and translational sciences, and regulatory practices.

Bitumen from the Alberta oil sands must be diluted to form diluted bitumen (dilbit) to facilitate transport through pipelines, yet little is known about its effects on aquatic organisms after a spill. Environmental weathering processes such as evaporation and sediment interaction manipulate spilled dilbit, which could affect its fate and toxicity in the environment. However, most studies to date that have characterized effects of dilbit to aquatic organisms have not incorporated weathering. In the present study, zebrafish (Danio rerio) embryos and adult freshwater amphipods (Hyalella azteca) were exposed to weathered sediment-bound dilbit. Sediment-bound dilbit exacerbated adverse effects associated with dilbit exposure due to oil-mineral aggregates directly interacting with amphipods and zebrafish embryos during exposure. As oil sands production expands, it is important to incorporate weathering processes when testing the toxicity of dilbit to aquatic organisms because sediment-bound dilbit can severely affect the health of freshwater fish and invertebrates.

The bioavailability and toxicity of metals to amphipods is influenced by exposure route and co-toxic mechanisms. Metal bioavailability was studied in amphipods at sites affected by the 2014 Mount Polley Mining Corporation tailings impoundment breach. The area around the lake was also subjected to wildfire in 2017. Bioavailability was more correlated with sediment than waterborne metal concentrations with Cu correlating well with distance from the breach. Copper-sediment bioavailability to amphipods in combination with wildfire runoff was studied resulting in non-additive toxicity. Hyalella azteca exposed to Cu-enriched sediment with fire extract (FE) experienced a more-than-additive effect on survival and amphipod whole-body Cu concentration but no significant reduction in growth or acetylcholinesterase activity compared to the Cu-contaminated sediment or FE alone, respectively. The present study highlighted the importance of using biological vectors to assess toxicity, sediment-focused toxicity study following contamination events, and revealed the co-toxic effect of FE and Cu-enriched sediment.

My thesis contributes to a better understanding of the impacts of OSPW on aquatic organisms by investigating its sub-lethal effects on an invertebrate (Daphnia magna) and a vertebrate (rainbow trout) model species. Studies conducted on D. magna demonstrated that OSPW impairs feeding, reduces hemoglobin content, increases oxygen consumption, and reduces growth, reproduction and macronutrient reserves of exposed animals at 1 to 10% concentrations. I also investigated the interaction of OSPW with the chemosensory system of rainbow trout (Oncorhynchus mykiss). I demonstrated that rainbow trout are able to detect and behaviourally avoid low concentrations (0.1%) of OSPW. However, even a short-term (< 5 min) interaction with OSPW reduced olfactory acuity. The toxic effect of OSPW on the fish olfactory system gradually increased with increasing exposure time. Overall, the results of my thesis suggest that untreated OSPW, even at low concentrations (1% OSPW), can affect different aspects of aquatic animals.

The lower Athabasca River basin of northern Alberta, Canada is situated within bitumen-rich deposits, where oil sands development is a common occurrence. A transplant and chronic exposure experiment between sites containing natural bitumen (NB) and natural bitumen-oil sands area of industry (NB-OSA) was conducted using fathead minnows (Pimephales promelas). Reference fish chemosensation and respiration was impaired and lowered, respectively, to levels observed in the fish NB-OSA of industry after having been transplanted to either contaminated sites. Fish previously exposed to contaminants had lower olfactory acuity and respiration rates than reference fish, remaining unchanged after exposure at either site. Fish pre-exposed to contaminats exhibit limited ability to deal with additional stressors compared to reference fish, as observed by the lower survival rates in these bituminous fish populations. This limited stress coping capabilities demonstrate native fish populations do not possess an advantage within the aquatic systems in the basin.

Calcium plays an essential role in olfactory sensory neuron function. Studies with fish have indicated that in addition to being involved in olfactory signalling, calcium is itself an odourant. In this study we used fathead minnows (Pimephales promelas) and employed two different techniques; electro-olfactography (EOG), a neurophysiological technique that measures olfactory acuity at the olfactory epithelium, and a behavioural choice assay using a trough maze. The results demonstrate that calcium and a known odourant L-arginine are cross-adaptive, that calcium induces an EOG response in a concentration-dependent manner, and that calcium induces a strong avoidance behaviour. The behavioural avoidance was also demonstrated to be olfactorydependent. Taken together, the results demonstrate that calcium is a potent odourant for fathead minnows. Being able to smell calcium may represent an ability to sense and avoid areas with significant changes in ionic strength, thereby avoiding physiological stress.

The influences of metal contamination, fish size, season, and region on tissue metabolic capacities and protein concentrations were examined in yellow perch from two metal gradients (Sudbury, Ontario, and Rouyn-Noranda, Qu´ebec, Canada) in two seasons (spring and summer). In general, increased tissue Cu and Cd contamination was associated with lower aerobic capacities, suggesting direct metal inhibition of aerobic enzymes. However, our data also revealed that tissue Ni contamination positively affected aerobic capacities, possibly due to oxidative damage to mitochondrial membranes leading to compensatory increases in the activity of mitochondrial enzymes. Tissue aerobic capacities decreased, but anaerobic capacities increased, with size. Tissue protein concentrations and metabolic capacities were also influenced by season. A novel finding of this study is that size-corrected tissue enzyme activities can differ markedly in yellow perch sampled in the same season in similar lakes, but separated by a few hundred kilometers. Overall, the results from this large dataset support that tissue metabolic capacities are under seasonal and regional influences, but are also affected by metal contamination. Our study indicates that tissue metabolic enzyme activities should be considered as a tool for ecological risk assessment studies aiming at detecting metal stress in wild fish. However, fish should be sampled over a short period, and reference sites should be close to contaminated sites

This review summarizes some of the main findings of our work with the Metals in the Environment Research Network examining seasonal and regional effects on metal accumulation, growth, condition, and physiology in wild yellow perch (Perca flavescens) from 10 lakes comprising two metal contamination gradients in the industrial regions of Sudbury, Ontario and Rouyn-Noranda, Qu´ebec, Canada. The specific objectives of this review are: (1) to propose threshold tissue metal concentrations to discriminate between fish from contaminated and reference sites; (2) to identify factors that can influence metal accumulation and fish condition; and (3) to define an experimental approach for measuring metal effects in wild yellow perch. Using tissue thresholds appeared useful not only for discriminating fish from clean or contaminated environments, but also provided a simple approach to examine metabolic consequences of tissue metal accumulation. Overall, fish from Sudbury grew faster, expressed higher aerobic capacities, and died younger, but also appeared better at limiting accumulation of some metals than Rouyn-Noranda fish. The condition of the latter fish was clearly more affected by metals than Sudbury fish. Finally, our dataset allows us to propose that yellow perch are highly suitable for ecological risk assessment studies of metal effects in wild fish, but that fish size, season, and region must be considered in sampling design and that several reference sites must be studied for meaningful conclusions to be reached.

This study examined relationships among water, sediment, diet, and fish tissue metal (Cd, Cu, Ni, Se, and Zn) concentrations in yellow perch from metal gradients in two regions (Sudbury (S), Ontario, and Rouyn-Noranda (RN), Qu´ebec, Canada) in two seasons (spring and summer). The objectives of this study were (1) to examine the influences of aqueous and dietary metal contamination on yellow perch liver and kidney metal accumulation; (2) to compare the seasonal and regional variations in gut content and tissue metal concentrations along the two gradients studied; and (3) to investigate the potential of metals for tissue accumulation under conditions of life-long chronic exposure. Our results suggest a greater aqueous than dietary influence on tissue metal concentrations for all metals examined except Cd, where the opposite was observed. Metals did not accumulate in older fish, except for Cd that accumulated with age in RN, but not S, fish. Regional, but also metal-specific differences in metal handling capacities are proposed. Fish from neither region appeared capable of regulating tissue Cd concentrations, but fish from both regions regulated Zn tightly. Sudbury fish appeared better at regulating tissue Cu, Ni, and perhaps also Se concentrations than RN fish, suggesting acclimation or selection for metal tolerance. There were several significant seasonal effects on tissue metal concentrations. However, close examination of the dataset does not allow proposing the presence of a season-linked mechanism explaining these variations, precluding a modeling approach and implying that repeat sampling within and among years is required for proper ecological risk assessment.

Wild yellow perch (Perca flavescens) were sampled from five lakes in each of two metal contamination gradients in Sudbury, Ontario, Canada (n = 1324) and Rouyn- Noranda, Qu´ebec, Canada (n = 1125) in the spring and summer of 2002 and 2003, respectively, in order to examine growth patterns, longevity, and the influences of season and region on fish condition. Fish from Rouyn-Noranda began rapid growth at a young age, whereas fish from Sudbury lakes showed slow growth rates between ages 0–3, after which growth rates improved. Fish from contaminated lakes grew faster and died younger than fish from reference lakes in both contamination gradients. Fish from Sudbury had lower condition than in Rouyn-Noranda, higher condition occurred in summer than spring, and fish from contaminated lakes had lower condition than those from cleaner lakes. Tissue Zn concentrations were correlated with fish condition and showed strong temporal stability. However, it is more likely that Zn covariates, such as Cd or Cu (which were more temporally variable) influenced condition, suggesting that long-term, broad-scale processes are more important than short-term, lake-specific processes for establishing growth patterns, longevity, and fish condition in metal-contaminated systems. Results from this study reveal that fish condition must be interpreted in the light of regional, seasonal, and other factors that can potentially influence fish growth patterns. Ecological risk assessments that fail to take these factors into account may draw erroneous conclusions about risk to indigenous populations.

Rainbow trout (Oncorhynchus mykiss) are often used to estimate important biotic ligand model (BLM) parameters, such as metal-binding affinity (log K) and capacity (Bmax). However, rainbow trout do not typically occupy metal-contaminated environments, whereas yellow perch (Perca flavescens) are ubiquitous throughout most of North America. This study demonstrates that dynamic processes that regulate Cu uptake at the gill differ between rainbow trout and yellow perch. Rainbow trout were more sensitive to acute aqueous Cu than yellow perch, and toxicity was exacerbated in soft water relative to similar exposures in hard water. Whole body Na loss rate could account for acute Cu toxicity in both species, as opposed to new Cu uptake rate that was not as predictive. Time course experiments using radiolabelled Cu (64Cu) revealed that branchial Cu uptake was rather variable within the first 12 h of exposure, and appeared to be a function of Cu concentration, water hardness, and fish species. After 12 h, new branchial Cu concentrations stabilized in both species, suggesting that metal exposures used to estimate BLM parameters should be increased in duration from 3 h to 12+ h. In rainbow trout, 71% of the new Cu bound to the gill was exchangeable (i.e., able to either enter the fish or be released back to the water), as opposed to only 48% in yellow perch. This suggests that at equal exposure concentrations, proportionally more branchial Cu can be taken up by rainbow trout than yellow perch, which can then go on to confer toxicity. These qualitative differences in branchial Cu handling between the two species emphasize the need to develop BLM parameters for each species of interest, rather than the current practice of extrapolating BLM results derived from rainbow trout (or other laboratory-reared species) to other species. Data reported here indicate that a one-size-fits-all approach to predictive modeling, mostly based on rainbow trout studies, may not suffice for making pred

Chemosensation is one of the oldest and most important sensory modalities utilized by aquatic animals to provide information about the location of predators, location of prey, sexual status of potential mates, genetic relatedness of kin, and migratory routes, among many other essential processes. The impressive sophistication of chemical communication systems among aquatic animals probably evolved because of the selective pressures exerted by water as a “universal solvent.” Impairment of chemosensation by toxicants at the molecular or cellular level can potentially lead to major perturbations at higher levels of biological organization. We have examined the consequences of metal-impaired chemosensory function in a range of aquatic animals that represents several levels of a typical aquatic ecosystem. In each case, low, environmentally relevant metal concentrations were sufficient to cause chemosensory dysfunction. Because the underlying molecular signal transduction machinery of chemosensory systems demonstrates a high degree of phylogenetic conservation, we speculate that metal-impaired chemosensation among phylogenetically disparate animal groups probably results from a common mechanism of impairment. We propose developing a chronic chemosensory-based biotic ligand model (BLM) that maintains the advantages of the current BLM approach, while simultaneously overcoming known difficulties of the current gill-based approach and increasing the ecological relevance of current BLM predictions.