Effects of water quality on palladium-induced olfactory toxicity and bioaccumulation in rainbow trout (Oncorhynchus mykiss).

Through emission processes, palladium (Pd) particulates from industrial sources are introduced into a range of ecosystems including freshwater environments. Despite this, research on Pd-induced bioaccumulation, uptake, and toxicity is limited for freshwater fishes. Unlike other metals, there are currently no regulations or protective guidelines to limit Pd release into aquatic systems, indicating a global absence of measures addressing its environmental impact. To assess the olfactory toxicity potential of Pd, the present study aimed to explore Pd accumulation in olfactory tissues, olfactory disruption, and oxidative stress in rainbow trout (Oncorhynchus mykiss) following waterborne Pd exposure. Olfactory sensitivity, measured by electro-olfactography, demonstrated that Pd inhibits multiple pathways of the olfactory system following 96 h of Pd exposure. In this study, the concentrations of Pd for inhibition of olfactory function by 20% (2.5 µg/L; IC20) and 50% (19 µg/L; IC50) were established. Rainbow trout were then exposed to IC20 and IC50 Pd concentrations in combination with varying exposure conditions, as changes in water quality alter the toxicity of metals. Independent to Pd, increased water hardness resulted in decreased olfactory perception owing to ion competition at the olfactory epithelium. No other environmental parameter in this study significantly influenced Pd-induced olfactory toxicity. Membrane-associated Pd was measured at the olfactory rosette and gill following exposure; however, this accumulation did not translate to oxidative stress as measured by the production of malondialdehyde. Our data suggest that Pd is toxic to rainbow trout via waterborne contamination near field-measured levels. This study further demonstrated Pd bioavailability and uptake at water-adjacent tissues, adding to our collective understanding of the toxicological profile of Pd. Taken together, our results provide novel insights into the olfactory toxicity in fish following Pd exposure. Integr Environ Assess Manag 2024;00:1-13. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Daphnia magna digestive activity is differentially altered when exposed to equally turbid waters caused by either suspended sediment or suspended microplastics.

Turbidity can be a result of suspended natural particles, such as sediment, or anthropogenic particles such as microplastics. This study assessed whether Daphnia magna, a pelagic filter feeder known to ingest suspended particles, have an altered response to equally turbid environments caused by the presence of either suspended bentonite or suspended polyethylene microplastics. Compared to controls, daphnids exposed to suspended bentonite maintained their feeding efficiency and increased their digestive activity, as measured by mandibular movement, peristalsis, and expulsion, to pass bentonite through the digestive tract. The same effects were not seen in microplastic-exposed individuals, in which feeding efficiency was decreased and only peristaltic movement was increased but without a coordinated increase in expulsion, suggesting that microplastics do not have the same ability as bentonite to pass through the digestive tract. This study highlights the need to discern the identities of particulates contributing to turbid environments as different particles, even of the same size, can have different effects on filter feeders, which inherently ingest suspended particles.

The Combined Effect of Copper Nanoparticles and Microplastics on Transcripts Involved in Oxidative Stress Pathway in Rainbow Trout (Oncorhynchus Mykiss) Hepatocytes.

Copper nanoparticles (CuNPs) and microplastics (MPs) are two emerging contaminants of freshwater systems. Despite their co-occurrence in many water bodies, the combined effects of CuNPs and MPs on aquatic organisms are not well-investigated. In this study, primary cultures of rainbow trout hepatocytes were exposed to dissolved Cu, CuNPs, MPs, or a combination of MPs and CuNPs for 48 h, and the transcript abundances of oxidative stress-related genes were investigated. Exposure to CuNPs or dissolved Cu resulted in a significant increase in the transcript abundances of two antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD). Exposure to CuNPs also led to an upregulation in the expression of Na+/K+ ATPase alpha 1 subunit (ATP1A1). Microplastics alone or in combination with CuNPs did not have a significant effect on abundances of the target gene transcripts. Overall, our findings suggested acute exposure to CuNPs or dissolved ions may induce oxidative stress in hepatocytes, and the Cu-induced effect on target gene transcripts was not associated with MPs.

In vitro characterization of cadmium transport across the gastro-intestinal membrane of the fathead minnow (Pimephales promelas) in the presence and absence of microplastics.

There is concern that microplastics can act as a vector for cadmium through adsorption and desorption of free-ionic cadmium. Little is known about the uptake of cadmium following ingestion of cadmium-microplastic complexes. This study used an in vitro gut sac technique to investigate the translocation of cadmium across the gut barrier of fathead minnows following the simulated ingestion of cadmium, microplastics, or their complexed mixture. Microplastics did not cross the gut membrane, nor did microplastics alter the rate of cadmium translocation, which was estimated to be 1.2 ± 0.04 ng Cd / hour. Less cadmium translocated when cadmium-microplastic complexes were injected than the equivalent dose of only cadmium, indicating that the presence of microplastics was protective of dietary cadmium uptake. This work highlights the importance of considering dietary uptake and the role of microplastics acting as a vector for cadmium in aquatic environments and stresses the need to understand how environmental (digestive or ambient) characteristics govern cadmium-microplastic interactions.

Effects of Exposure to Cadmium, Microplastics, and Their Mixture on Survival, Growth, Feeding, and Life History of Daphnia magna.

There is concern that microplastics can act as a vector for cadmium (Cd), altering the bioavailability and subsequent toxicity of Cd to ecologically important species such as Daphnia magna. The toxicity of Cd to D. magna has been well described; however, what is not known, and what the present study addresses, was how the addition of polyethylene microplastic altered Cd toxicity. Using high-throughput feeding assays and size assessments, the present study quantified effects of exposure to Cd, microplastic, or their mixture on daphnids from neonate to adult. Exposure to Cd inhibited feeding efficiency, while exposure to microplastic inhibited growth rates of juveniles. Daphnia magna coexposed to Cd and microplastic showed significant decreases in both feeding and prereproductive growth rate. There were no differences in life-history traits across any treatments. The alterations of feeding and growth while maintaining reproductive endpoints (time to first brood, reproductive frequency, the number of neonates released at each reproductive event, and the size of neonates produced) might be the result of a shift in energy allocation away from somatic growth, allowing individuals to maintain reproductive output despite lower nutritional reserves. Our findings suggest that cocontamination of microplastic and Cd has additive effects on feeding and growth rates, resulting in a greater energy allocation shift. Environ Toxicol Chem 2023;42:1401-1408. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Single and combined effects of cadmium, microplastics, and their mixture on whole-body serotonin and feeding behaviour following chronic exposure and subsequent recovery in the freshwater leech, Nephelopsis obscura.

Microplastics and metals are contaminants detected in many freshwater systems globally. Interactions of microplastics with other contaminants including cadmium poses potential threats to the health of aquatic organisms including Nephelopsis obscura, a predatory leech species that is widespread and serves important ecological and economic roles. The feeding biology of N. obscura has been well-described, including that serotonin regulates feeding behaviour. Further, exposure to cadmium has been found to cause decrease whole-body concentrations of serotonin. The influence that microplastic contamination and co-contamination of cadmium and microplastics has on N. obscura is unknown. The present study had three objectives: (1) to determine if water or sediment contaminated with cadmium, microplastics, or their mixture resulted in greater cadmium uptake by N. obscura, (2) to assess effects of chronic (21-day) exposure of N. obscura to waterborne cadmium, microplastics, and their mixture on bioaccumulation of cadmium, concentrations of serotonin, and feeding behaviour (latency to feeding, time spent feeding, and distance moved), and (3) to reassess the bioaccumulation of cadmium, concentrations of serotonin, and feeding behaviour following transfer to an uncontaminated environment for a one-week recovery period. This study revealed that access to and presence of sediment is protective against cadmium uptake and that cadmium is more readily accumulated from waterborne sources, even in environments where both sediment and surface water are contaminated. After 21-days of exposure to waterborne cadmium, microplastics, and their mixture, accumulation of cadmium, decreased concentrations of serotonin, and impaired feeding behaviours were greatest in leeches from the co-exposures compared to leeches from either single contaminant exposure group. Finally, after one week of depuration and recovery in freshwater following the 21-day exposures, concentrations of serotonin and feeding behaviour were restored in individuals from the microplastic exposure; however, cadmium-exposed individuals continued to show decreased concentrations of serotonin and behavioural deficits. The co-exposure of leeches to cadmium and microplastics resulted in additive effects to serotonin synthesis and feeding behaviour; however, this study demonstrated that leeches were able to recover from microplastic toxicity within a week whereas cadmium toxicity persisted.

A proposed reporting framework for microplastic-metal mixtures research, with emphasis on environmental considerations known to influence metals.

In recent years, there has been an increase in research to understand the consequences of microplastic contamination. A subset of this research assesses the interaction of microplastics with metals and the subsequent effects of the resulting microplastic-metal complexes in freshwater environments. While our understanding of how microplastics behave in freshwater remains largely unknown, our knowledge of metal behavior in those same environments is well-established. The behavior (partitioning, speciation, bioavailability) of metals is highly dependent on environmental characteristics, including water quality variables such as hardness, pH, and dissolved organic matter. This study reveals that despite our understanding of metal behavior, there is little consideration for these influential factors in the current body of microplastic-metal research. Multiple instances highlighted throughout this study show that even when similar plastic, metal, and biota are utilized, there are conflicting observations as to whether the mixture is toxic; we stress that without adequate reporting of environmental conditions, these contradictions are likely to persist without explanation. Through justification of water quality characteristics known to influence metal behavior, this study proposes a framework of reporting requirements for all future microplastic-metal research.

Impact of Copper Nanoparticles and Copper Ions on Transcripts Involved in Neural Repair Mechanisms in Rainbow Trout Olfactory Mucosa.

Olfactory mucosa is well known for its lifelong ability for regeneration. Regeneration of neurons and regrowth of severed axons are the most common neural repair mechanisms in olfactory mucosa. Nonetheless, exposure to neurotoxic contaminants, such as copper nanoparticles (CuNPs) and copper ions (Cu2+), may alter the reparative capacity of olfactory mucosa. Here, using RNA-sequencing, we investigated the molecular basis of neural repair mechanisms that were affected by CuNPs and Cu2+ in rainbow trout olfactory mucosa. The transcript profile of olfactory mucosa suggested that regeneration of neurons was inhibited by CuNPs. Exposure to CuNPs reduced the transcript abundances of pro-inflammatory proteins which are required to initiate neuroregeneration. Moreover, the transcript of genes encoding regeneration promoters, including canonical Wnt/ß-catenin signaling proteins and developmental transcription factors, were downregulated in the CuNP-treated fish. The mRNA levels of genes regulating axonal regrowth, including the growth-promoting signals secreted from olfactory ensheathing cells, were mainly increased in the CuNP treatment. However, the reduced transcript abundances of a few cell adhesion molecules and neural polarity genes may restrict axonogenesis in the CuNP-exposed olfactory mucosa. In the Cu2+-treated olfactory mucosa, both neural repair strategies were initiated at the transcript level. The stimulation of repair mechanisms can lead to the recovery of Cu2+-induced olfactory dysfunction. These results indicated CuNPs and Cu2+ differentially affected the neural repair mechanism in olfactory mucosa. Exposure to CuNP had greater effects on the expression of genes involved in olfactory repair mechanisms relative to Cu2+ and dysregulated the transcripts associated with stem cell proliferation and neural reconstitution.

Comparison of transcriptome responses of the liver, tail fin, and olfactory epithelium of Rana [Lithobates] catesbeiana tadpoles disrupted by thyroid hormones and estrogen.

Thyroid hormones (THs) are important developmental regulators in vertebrates, including during the metamorphosis of a tadpole into a frog. Metamorphosis is a post-embryonic developmental period initiated by TH production in the tadpole thyroid gland. The two main bioactive forms of TH are L-thyroxine (T4) and 3,5,3'-triiodothyronine (T3); these hormones have overlapping but distinct mechanisms of action. Premetamorphic tadpoles are highly responsive to TH and can be induced to metamorphose through exogenous TH exposure, making them an important model for both the study of vertebrate TH signaling and endocrine disrupting chemicals (EDCs). It is important to differentiate TH-mediated responses from estrogenic responses in premetamorphic tadpoles when assessing dysregulation by EDCs as crosstalk between the two endocrine systems is well-documented. Herein, we compare the RNA-sequencing-derived transcriptomic profiles of three TH-responsive tissues (liver, olfactory epithelium, and tail fin) in premetamorphic bullfrog (Rana [Lithobates] catesbeiana) tadpoles exposed to T3, T4, and estradiol (E2). These profiles were generated using the latest available genome assembly for the species. The data indicate that there is a clear distinction, and little overlap, between the transcriptomic responses elicited by E2 and the THs. In contrast, within the THs, the T3- and T4-induced transcriptomic profiles generally show considerable overlap; however, the degree of overlap is highly tissue-dependent, illustrating the importance of distinguishing the two THs and the affected signaling pathways within the target tissue type when evaluating hormone active agents. The data herein also show that E2 and TH treatment can uniquely induce significant changes in expression of their respective "classic" bioindicator transcripts vtg (E2) and thra, thrb, and thibz (THs). However, care must be taken in the interpretation of increased vep or esr1 transcripts as a change in transcript levels can be induced by THs rather than solely E2.

Invertebrate metal accumulation and toxicity from sediments affected by the Mount Polley mine disaster.

On August 4, 2014, a tailings dam failed at the Mount Polley copper and gold mine near Likely, British Columbia, Canada, releasing approximately 25 M m[Formula: see text] of contaminated water and solid tailings material into Polley and Quesnel lakes. Water, sediment, freshwater scuds (Hyalella azteca), and mayfly larvae (Ephemeroptera) were collected during the summer of 2018 from Polley Lake, affected and unaffected sites in Quesnel Lake, and both mine-contaminated and clean far-field sites as references. Analytical results indicated that invertebrates from sites affected by the tailings breach had elevated metal concentrations relative to those from non-affected or reference sites. We conducted a controlled laboratory exposure to determine if laboratory-reared Hyalella azteca metal concentrations were related to field-collected water or sediments from the same sites as the field study. Half of the replicates prevented amphipods from directly contacting sediments (water-only exposure), while the other half allowed them direct access (sediment and water exposure). Whole-body Cu concentration was highest in Hyalella exposed to substrate from the most contaminated sites as well as in treatments where they were allowed direct access to sediments. Hyalella having direct access to metal-contaminated sediments showed reduced survival and growth relative to those in reference or control treatments. These results suggest that metals from the fine sediments associated with the Mount Polley mine disaster are bioavailable and potentially toxic to epibenthic invertebrates, even several years after the initial breach.

Recovery of rainbow trout olfactory function following exposure to copper nanoparticles and copper ions.

In response to environmental information received by olfactory sensory neurons (OSNs), fish display different behaviors that are crucial for reproduction and survival. Damage to OSNs from direct exposure to environmental contaminants can disrupt fish olfaction. Copper nanoparticles (CuNPs) are neurotoxic contaminants which can impair fish olfactory function. However, it is uncertain if CuNP-induced olfactory dysfunction is reversible. Here, we compared the recovery of rainbow trout olfactory mucosa after being exposed to CuNPs or dissolved copper (Cu2+). Following a 96 h exposure to CuNPs or Cu2+, recovery was tested 14 min and 7 days after exposure using electro-olfactography (EOG). Results indicated the 14 min recovery period was not sufficient to improve the olfactory sensitivity in either Cu treatment. After 7 days of transition to clean water, olfactory mucosa was able to recover from Cu2+-induced dysfunction, while no recovery was observed in the CuNP-exposed OSNs. This olfactory dysfunction in the CuNP treatment was observed when no Cu was significantly accumulated in the olfactory mucosa after the recovery period. The transcript abundances of a subset of genes involved in olfactory signal transduction (OST) were downregulated in the CuNP-exposed fish after the 7-day recovery period. These results revealed that odorant reception through OST cascade remained impaired over the recovery period in the CuNP-treated OSNs. The ion regulation gene transcripts were not dysregulated in either Cu treatment, which suggests that neural ion balance was not affected following the recovery period. Collectively, our findings revealed the CuNP-induced olfactory dysfunction was irreversible after the 7-day recovery period. Given the importance of olfaction in crucial aspects of fish life, it is likely that the CuNP-induced impairment of odorant reception pose risks to the survival of fish.

Effect of copper nanoparticles and copper ions on the architecture of rainbow trout olfactory mucosa.

Olfactory epithelial cells are in direct contact with myriad environmental contaminants which may consequently disrupt their structure and function. Copper ions (Cu2+) and copper nanoparticles (CuNPs) are two types of olfactory neurotoxicants. However, their effects on the structure of olfactory epithelium are largely uninvestigated. The density of olfactory goblet cells in CuNP- and Cu2+ - exposed rainbow trout was assessed using light microscopy throughout time. In both copper (Cu) treatments, the number of goblet cells increased initially over the 24 h exposure and then recovered to normal throughout the 96 h exposure. These data suggested the 96 h exposure to Cu contaminants interfered with protective barrier provided by goblet cells. Nonetheless, lamellar and epithelial thickness of olfactory rosette did not change in the Cu-exposed fish. The gene transcript profile of olfactory mucosa studied by RNA-seq indicated Cu2+ and CuNPs differentially targeted the molecular composition of cell junctions. In the Cu2+ treatment, reduced mRNA abundances of tight junctions, adherens junction, desmosomes and hemidesmosomes, suggest that Cu2+-exposed olfactory mucosal cells had weak junctional complexes. In the CuNP treatment, on the other hand, the transcript abundances of cell junction compositions, except adherens junction, were upregulated. Transcripts associated with gap junctional channels were increased in both Cu treatments. The elevated transcript levels of gap junctions in both Cu treatments suggested that the demand for intercellular communication was increased in the Cu-exposed olfactory mucosa. Overall, our findings suggested that Cu2+ induced greater adverse effects on the molecular composition of olfactory cell junctions relative to CuNPs. Impairment of junctional complexes may disrupt the structural integrity of olfactory mucosa.

The Role of Behavioral Ecotoxicology in Environmental Protection.

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.

Mechanism of copper nanoparticle toxicity in rainbow trout olfactory mucosa.

Chemosensory perception is crucial for fish reproduction and survival. Direct contact of olfactory neuroepithelium to the surrounding environment makes it vulnerable to contaminants in aquatic ecosystems. Copper nanoparticles (CuNPs), which are increasingly used in commercial and domestic applications due their exceptional properties, can impair fish olfactory function. However, the molecular events underlying olfactory toxicity of CuNPs are largely unexplored. Our results suggested that CuNPs were bioavailable to olfactory mucosal cells. Using RNA-seq, we compared the effect of CuNPs and copper ions (Cu2+) on gene transcript profiles of rainbow trout (Oncorhynchus mykiss) olfactory mucosa. The narrow overlap in differential gene expression between the CuNP- and Cu2+-exposed fish revealed that these two contaminants exert their effects through distinct mechanisms. We propose a transcript-based conceptual model that shows that olfactory signal transduction, calcium homeostasis, and synaptic vesicular signaling were affected by CuNPs in the olfactory sensory neurons (OSNs). Neuroregenerative pathways were also impaired by CuNPs. In contrast, Cu2+ did not induce toxicity pathways and rather upregulated regeneration pathways. Both Cu treatments reduced immune system pathway transcripts. However, suppression of transcripts that were associated with inflammatory signaling was only observed with CuNPs. Neither oxidative stress nor apoptosis were triggered by Cu2+ or CuNPs in mucosal cells. Dysregulation of transcripts that regulate function, maintenance, and reestablishment of damaged olfactory mucosa represents critical mechanisms of toxicity of CuNPs. The loss of olfaction by CuNPs may impact survival of rainbow trout and impose an ecological risk to fish populations in contaminated environments.

Sensitivity of Amphibians to Copper.

Amphibian populations are declining globally. Major drivers of these global declines are known. However, the contribution of these major drivers to population declines varies by the presence or absence and the interactive effect of drivers, thus creating local challenges for conservation of populations. Studies have determined that environmental contaminants contribute to amphibian population declines. However, there is a disagreement over the use of amphibians as sentinel species in ecotoxicological testing rather than the traditional taxa used, fish and invertebrates. Reviews of ecotoxicological studies have demonstrated that amphibians are generally less sensitive than fish and invertebrates to different groups of contaminants. Nonetheless, because of the distinct nature and mechanism of toxicity of various contaminants, it is necessary to study contaminants individually to be able to come to any conclusion on the relative sensitivity of amphibians. Copper is one of the most studied environmental contaminants. We conducted a literature review of Cu toxicity to amphibians and the relative sensitivity of amphibians to other aquatic animals. The available data suggest that although amphibians may be tolerant of acute Cu exposure, they are relatively sensitive to chronic exposure (i.e., 100-fold greater sensitivity to chronic compared to acute exposure). In addition, ecologically relevant endpoints specific to amphibians (e.g., duration of metamorphosis and behavior) are shown to provide a better understanding of their sensitivity compared to traditional endpoints (e.g., survival and growth). Our current knowledge on amphibian sensitivity is far from complete. Considering the current status of this globally threatened class of animals, it is necessary to fill the knowledge gaps regarding their sensitivity to individual contaminants, beginning with Cu. Environ Toxicol Chem 2021;40:1810-1821. © 2021 SETAC.

Molecular profiles of naphthenic acid fraction compounds from mine lease wetlands in the Athabasca Oil Sands Region.

Naphthenic acid fraction compounds (NAFCs) are a toxicologically relevant component of oil sands process-affected materials (OSPM). For the first time, we report on differences in the concentrations and distribution of NAFCs from wetlands on an Athabasca oil sands mine site with varied histories of solid and liquid OSPM input. Sampling locations included natural and naturalized reference wetlands, a reclaimed tailings pond, wetlands supplemented with OSPM, opportunistic wetlands, and tailings ponds. Samples were prepared using solid-phase extraction, and analyzed by high-resolution Orbitrap mass spectrometry; NAFC concentrations and characteristics were evaluated for all locations. The NAFCs from tailings ponds were dominated by O3-NAFCs and classical naphthenic acids (NAs; i.e., O2 species) with double bond equivalences of 3 and 4. Reference wetlands had no dominant species, and relatively little NAFC content. The heteroatomic species in opportunistic wetlands were dominated by highly-oxidized NAFC species, where Σ [O3:O6] species constituted 55-75% of the assignable spectrum and 3-4% NAs; in tailings ponds NAs constituted 47-51%. A relatively young (4-year-old) wetland built on a former tailings pond had NAFC concentrations between 65 and 80 mg/L, and NAs constituted 47% of the assignable spectrum. There was thus little apparent oxidation of NAFCs at this young wetland. The composition of NAFCs from one wetland (≥15 years old) supplemented with OSPM contained a greater proportion of oxidized species than tailings, suggesting NAFC transformation therein. These data suggest that while NAFCs are persistent in some wetlands, there is preliminary evidence for oxidation in mature wetlands.

Toxicity of Weathered Sediment-Bound Dilbit to Early Life Stages of Zebrafish (Danio rerio).

Due to high viscosity, bitumen extracted from the Alberta oil sands is diluted with natural gas condensates to form diluted bitumen (dilbit) to facilitate transport through pipelines. Dilbit that is spilled into or near a waterbody is subject to environmental weathering processes such as evaporation and interaction with sediments. This is the first study that assessed the toxicity of weathered sediment-bound dilbit (WSD) to fish early life stages. Exposure of zebrafish (Danio rerio) embryos to water-soluble fractions (WSFs) or water-accommodated fractions (WAFs) of WSD from 30 min to 120 h postfertilization resulted in pericardial edema, yolk sac edema, and incidences of uninflated swim bladder. The presence of oil-mineral aggregates (OMAs) in the WAFs greatly increased toxicity, despite all fractions having similar concentrations of dissolved polycyclic aromatic hydrocarbons (PAHs). There were greater cyp1a mRNA abundances in larvae exposed to WAFs, suggesting that there were differences in bioavailability of PAHs between fractions. However, there was little evidence that embryotoxicity was caused by oxidative stress. Results suggest that evaporation and sediment interaction do not completely attenuate toxicity of dilbit to zebrafish early life stages, and OMAs in exposures exacerbate toxicity.

The Single and Combined Effects of Wildfire Runoff and Sediment-Bound Copper on the Freshwater Amphipod Hyalella azteca.

The frequency of wildfire is expected to increase with time as a function of climate change. Recent studies in our laboratory have demonstrated that pyrogenic polycyclic aromatic hydrocarbons can cause greater-than-additive effects in Hyalella azteca in the presence of low concentrations of Cu. We hypothesized that freshwater animals inhabiting Cu-contaminated sites, such as those in the vicinity of Cu mines, may be vulnerable to nonadditive toxicity from contaminants released by wildfires. To investigate the interaction between Cu and water conditioned by burnt wood ash (fire extract), we exposed H. azteca for 14 d to binary mixtures of 225 mg/kg Cu-enriched artificial sediment (225 mg Cu/kg) and a fire extract dilution series (12.5, 25, 50, 75, and 100%). All binary mixtures of Cu-enriched sediment and fire extract resulted in complete mortality with the exception of Cu-enriched sediment + 12.5% fire extract. The combination of Cu-enriched sediment with 12.5% fire extract had a more-than-additive effect on survival and tissue Cu concentration, but there was no reduction in growth or acetylcholinesterase activity compared to the 225 mg/kg Cu-contaminated sediment or fire extract control, respectively. Acetylcholinesterase activity was significantly reduced in amphipods exposed to fire extract, but the presence of Cu did not exacerbate this effect. The results suggest that Cu-contaminated water bodies that receive runoff from wildfires are at risk of enhanced toxicity. Environ Toxicol Chem 2020;39:1988-1997. © 2020 SETAC.

Rainbow trout (Oncorhynchus mykiss) chemosensory detection of and reactions to copper nanoparticles and copper ions.

Copper is known to interfere with fish olfaction. Although the chemosensory detection and olfactory toxicity of copper ions (Cu2+) has been heavily studied in fish, the olfactory-driven detection of copper nanoparticles (CuNPs)-a rapidly emerging contaminant to aquatic systems-remains largely unknown. This study aimed to investigate the olfactory response of rainbow trout to equitoxic concentrations of CuNPs or Cu2+ using electro-olfactography (EOG, a neurophysiological technique) and olfactory-mediated behavioural assay. In the first experiment, the concentration of contaminants known to impair olfaction by 20% over 24 h (EOG-based 24-h IC20s of 220 and 3.5 µg/L for CuNPs and Cu2+, respectively) were tested as olfactory stimuli using both neurophysiological and behavioural assays. In the second experiment, to determine whether the presence of CuNPs or Cu2+ can affect the ability of fish to perceive a social cue (taurocholic acid (TCA)), fish were acutely exposed to one form of Cu-contaminants (approximately 15 min). Following exposure, olfactory sensitivity was measured by EOG and olfactory-mediated behaviour within a choice maze was recorded in the presence of TCA. Results of neurophysiological and behavioural experiments demonstrate that rainbow trout can detect and avoid the IC20 of CuNPs. The IC20 of Cu2+ was below the olfactory detection threshold of rainbow trout, as such, fish did not avoid Cu2+. The high sensitivity of behavioural endpoints revealed a lack of aversion response to TCA in CuNP-exposed fish, despite this change not being present utilizing EOG. The reduced response to TCA during the brief exposure to CuNPs may be a result of either olfactory fatigue or blockage of olfactory sensory neurons (OSNs) by CuNPs. The observed behavioural interference caused by CuNP exposure may indicate that CuNPs have the ability to interfere with other behaviours potentially affecting fitness and survival. Our findings also revealed the differential response of OSNs to CuNPs and Cu2+.

Contrary to Marine Environments, Common Microplastics in Freshwater Systems May Not Emit Dimethyl Sulfide: An Important Infochemical.

The ingestion of microplastics by marine species has been at least partially attributed to plastics emitting a dimethyl sulfide signature when exposed to marine conditions. Dimethyl sulfide, a member of the volatile organic sulfur compounds group, is an infochemical that many species rely on to locate and identify prey while foraging. Microplastic ingestion is also observed in freshwater systems; however, this study shows that the same dimethyl sulfide signature is not obtained by three common types of plastic (high-density polyethylene, low-density polyethylene, and polystyrene) in freshwater systems, suggesting that there may be an alternate mechanism driving plastic ingestion by freshwater species.