Copper binding dynamics and olfactory impairment in fathead minnows (Pimephales promelas)

Copper-Induced Chemosensory Impairment is Reversed by a Short Depuration Period in Northern Clearwater Crayfish (Faxonius propinquus)

Crayfish rely on their chemosensory system for many essential behaviours including finding food, finding mates, and to recognize individuals. Copper can impair chemosensation in crayfish at low concentrations; however, it is not clear if the effect is ameliorated once copper is removed. To better understand the effect of and recovery from copper exposure in crayfish, we exposed Northern clearwater crayfish (Faxonius propinquus) to 31.3 [Formula: see text] copper for 24 h and measured the response of the crayfish to a food cue. The crayfish were then placed into clean water to depurate for an 24 h. The results demonstrated that the crayfish did not respond to a food cue if they had been exposed to copper, but showed a full response after a 24 h recovery period without copper. Higher concentrations of copper have shown a much longer-term effect in rusty crayfish (Faxonius rustics), indicating there is a concentration where the copper is causing longer-term damage instead of just impairing chemosensation. These results highlight the fact that even though contaminants like copper can have profound effects at low concentrations, by removing the contaminants the effect can be ameliorated.

Bioavailability and Toxicity Models of Copper to Freshwater Life: The State of Regulatory Science

Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness-based single-linear regression equations, water-effect ratios (WERs), biotic ligand models (BLMs), and multiple-linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness-based versus MLR-based criteria equations. The WER approach was shown to be inherently highly biased. The hardness-based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site-specific testing would be needed to determine reliable Cu criteria for such settings. The hardness-based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness-criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR-based USEPA-style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;42:2529-2563. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Avoidance behaviour and toxicological impact of sunscreens in the teleost Chelon auratus

There is increasing evidence that sunscreen, more specifically the organic ultra-violet filters (O-UVFs), are toxic for aquatic organisms. In the present study, we simulated an environmental sunscreen exposure on the teleost fish, Chelon auratus. The first objective was to assess their spatial avoidance of environmental concentrations of sunscreen products (i.e. a few μg.L-1 of O-UVFs). Our results showed that the fish did not avoid the contaminated area. Therefore, the second objective was to evaluate the toxicological impacts of such pollutants after 35 days exposure to concentrations of a few μg.L-1 of O-UVFs. At the individual level, O-UVFs increased the hepatosomatic index which could suggest pathological alterations of the liver or the initiation of the detoxification processes. At the cellular level, a significant increase of malondialdehyde was measured in the muscle of fish exposed to O-UVFs which suggests a failure of antioxidant defences and/or an excess of reactive oxygen species.

Toxicity mechanisms and bioavailability of copper to fish based on an adverse outcome pathway analysis

Copper (Cu) exists in a variety of forms in different aquatic environments, and affects their bioavailability. In this study we provide a systematic review on toxicity of Cu which focuses on identifying evidence in the mechanisms of Cu toxicity, and apply an adverse outcome pathway (AOP) analysis to identify multiple potential mechanisms and their interactions of Cu toxicity to fish. This analysis process included the mechanisms of behavior toxicant, oxidative toxicant, ion regulation disruption toxicity, as well as endocrine disruption toxicity. It was found that at low levels of Cu exposure, swimming, avoid predators, locating prey and other sensory functions will be impaired, and the organism will suffer from metabolic alkalosis and respiratory acidosis following the inhibition of the carbonic anhydrase active. The main pathway of acute toxicity of Cu to fish is the inhibition of the Na⁺/K⁺-ATPase enzyme, and lead to reduced intracellular sodium absorption, as well as Cu-induced increased cell permeability, in turn resulting in increased sodium ion loss, leading to cardiovascular collapse and respiratory insufficiency. The endocrine disruption toxicity of Cu to fish caused growth inhibition and reproductive reduction. In addition, there are several key pathways of Cu toxicity that are affected by hardness (e.g., Ca²⁺) and intracellular DOC concentrations, including inhibiting Cu-induction, improving branchial gas exchange, altering membrane transport functions, decreasing Na⁺ loss, and increasing Na⁺ uptake. The results of the AOP analysis will provide a robust framework for future directed research on the mechanisms of Cu toxicity.

Copper Exposure Affects Anti-Predatory Behaviour and Acetylcholinesterase Levels in Culex pipiens (Diptera, Culicidae)

Copper is an essential metal that occurs chronically in the environment and affects the development and physiology of aquatic insects. In excess amounts, it can impair their nervous system and behaviour. We tested the anti-predatory behaviour of Cx. pipiens larvae after seven days exposure with several concentrations of copper up to 500 mg L^-1. We measured responses to non- consumptive (predation cues) and consumptive predation (dragonfly larvae) across two generations. We also tested the accumulated effect of copper on AChE enzyme activity. We exposed half of treated and control larvae to predation cues (water with predator odour and crushed conspecifics) and the other half to water without predation cues. We evaluated total distance moved and velocity. Copper reduced the distance moved and velocity, with stronger effects in the second generation. Copper had no significant effect on larvae eaten by dragonflies. Copper inhibited the AChE enzyme across both generations at 500 µg L^-1. Copper can affect the nervous system directly by inhibiting AChE activity, and possibly also by impairing the olfaction sensors of the larvae, resulting in larval inability to detect predation cues.

Avoidance of copper by fathead minnows (Pimephales promelas) requires an intact olfactory system

Fish can detect and respond to a wide variety of cations in their environment, including copper. Most often fish will avoid copper during behavioural trials; however, fish may also show no response or an attraction response, depending on the concentration(s) used. While it may seem intuitive that the response to copper requires olfaction, there is little direct evidence to support this, and what evidence there is remains incomplete. In order to test if olfaction is required for avoidance of copper by fathead minnows (Pimephales promelas) copper-induced movement was compared between fish with an intact olfactory system and fish with induced anosmia. Fish in a control group or a mock-anosmic group avoided copper (approximately 10 µg/L or 62.7 nM copper sulphate) while anosmic fish did not. The evidence demonstrates that an intact olfactory system is required for copper sensing in fish.

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.

Disturbances to energy metabolism in juvenile lake sturgeon (Acipenser fulvescens) following exposure to niclosamide

Since the 1960s, invasive sea lamprey (Petromyzon marinus) populations in the Laurentian Great Lakes have been controlled by applying two chemicals, 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide, aka. Bayluscide®), to streams infested with larval sea lamprey. These "lampricide" applications primarily rely on TFM, and are often combined with 1-2% niclosamide, which increases treatment effectiveness. Niclosamide is also used alone to treat lentic habitats and in rivers with high discharge. However, little is known about niclosamide's possible adverse physiological effects on non-target organisms. Of particular concern is the lake sturgeon (Acipenser fulvescens), which is threatened throughout the Great Lakes basin where its habitat often overlaps with larval lamprey. Because niclosamide is believed to impair ATP production by uncoupling oxidative phosphorylation, we determined how it altered metabolic processes and acid-base balance in young-of-the-year (YOY) lake sturgeon exposed to their 9-h LC₅₀ of niclosamide (0.11 mg L^-1) for 9 h. Exposure to niclosamide led to decreased brain ATP and glucose reserves, and increased lactate, with no effect on brain glycogen. In contrast, substantial (60%) reductions in glycogen were observed in liver, suggesting that hepatic glycogen reserves were mobilized to meet the brain's glucose requirements when ATP supply was impaired during niclosamide exposure. Disturbances in carcass included reduced phosphocreatine (65-70%), 2- and 4-fold increases in pyruvate and lactate, and a slight metabolic acidosis, characterized by a 0.1 unit decrease in intracellular pH (pHi). Each of these disturbances were corrected within 24 h following depuration in clean (niclosamide-free) water. We conclude that if lake sturgeon survive exposure to niclosamide, they are able to rapidly replenish their energy stores (glycogen, ATP, phosphocreatine) and correct any corresponding metabolic disturbances within 24 h.

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.

Chemosensory Dysfunction Induced by Environmental Pollutants and Its Potential As a Novel Neurotoxicological Indicator: A Review

Air pollution composed of the complex interactions among particular matter, chemicals, and pathogens is an emerging and global environmental issue that closely correlates with a variety of diseases and adverse health effects, especially increasing incidences of neurodegenerative diseases. However, as one of the prevalent health outcomes of air pollution, chemosensory dysfunction has not attracted enough concern until recently. During the COVID-19 pandemic, multiple scientific studies emphasized the plausibly essential roles of the chemosensory system in the airborne transmission airway of viruses into the human body, which can also be utilized by pollutants. In this Review, in addition to summarizing current progress regarding the contributions of traditional air pollutants to chemosensory dysfunction, we highlight the roles of emerging contaminants. We not only sum up clarified mechanisms, such as inflammation and apoptosis but also discuss some not yet completely identified mechanisms, e.g., disruption of olfactory signal transduction. Although the existing evidence is not overwhelming, the chemosensory system is expected to be a useful indicator in neurotoxicology and neural diseases based on accumulating studies that continually excavate the deep link between chemosensory dysfunction and neurodegenerative diseases. Finally, we argue the importance of studies concerning chemosensory dysfunction in understanding the health effects of air pollution and provide comments for some future directions of relevant research.

Olfactory epithelium ontogenesis and function in postembryonic North American Bullfrog (Rana (Lithobates) catesbeiana) tadpoles

During metamorphosis, the olfactory system remodelling in anuran tadpoles — to transition from detecting waterborne odorants to volatile odorants as frogs — is extensive. How the olfactory system transitions from the larval to frog form is poorly understood, particularly in species that become (semi-)terrestrial. We investigated the ontogeny and function of the olfactory epithelium of North American Bullfrog (Rana (Lithobates) catesbeiana Shaw, 1802) tadpoles at various stages of postembryonic development. Changes in sensory components observable at the epithelial surface were examined by scanning electron microscopy. Functionality of the developing epithelium was tested using a neurophysiological technique (electro-olfactography (EOG)), and behaviourally, using a choice maze to assess tadpole response to olfactory stimuli (algae extract, amino acids). The youngest (premetamorphic) tadpoles responded behaviourally to an amino acid mixture despite having underdeveloped olfactory structures (cilia, olfactory knobs) and no EOG response. The consistent appearance of olfactory structures in older (prometamorphic) tadpoles coincided with reliably obtaining EOG responses to olfactory stimuli. However, as tadpoles aged further, and despite indistinguishable differences in sensory components, behavioural- and EOG-based olfactory responses were drastically reduced, most strongly near metamorphic climax. This work demonstrates a more complex relationship between structure and function of the olfactory system during tadpole life history than originally thought.

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⁺.

Copper Concentrations in the Upper Columbia River as a Limiting Factor in White Sturgeon Recruitment and Recovery

Currently there is little natural recruitment of white sturgeon (Acipenser transmontanus) in the Upper Columbia River located in British Columbia, Canada and Washington, USA. This review of life history, physiology, and behavior of white sturgeon, along with data from recent toxicological studies, suggest that trace metals, especially Cu, affect survival and behavior of early life stage fish. Sturgeon free embryos, first feeding embryos, and mixed feeding embryos utilize interstitial spaces between gravel. Although concentrations of Cu in the water column of the Upper Columbia River are typically less than US water quality criteria defined to protect aquatic life, samples at the sediment-water interface were as large as 24 µg/L and exceed the criteria. Toxicological studies reviewed here demonstrate mortality, loss of equilibrium, and immobility at Cu concentrations of 1.5 to <16 µg/L and reduced swimming activity was documented at 0.88 to 7 μg/L. Contaminated invertebrates and slag particles provide other routes of exposure. These additional routes of exposure can cause indirect effects from starvation due to potential lack of prey items and ingestion of contaminated prey or slag particles. The lack of food in stomachs during these critical early life stages may coincide with a threshold "point of no return" at which sturgeon will be unable to survive even if food becomes available following that early time frame. These findings become especially important as work progresses to enhance white sturgeon recruitment in the Upper Columbia River. To date, decisions against including trace metals as a factor in sturgeon recovery have focused on surface-water concentrations and measurements of lethality (LC50) to establish threshold concentrations for sturgeon sensitivity. However, information provided here suggests that measurements from the sediment-water interface and effect concentrations (EC50) be considered with white sturgeon life history characteristics. These data support minimizing Cu exposure risk to enhance a successful white sturgeon recovery effort. Integr Environ Assess Manag 2020;16:378-391. Published 2020. This article is a US Government work and is in the public domain inthe USA.

Toxicity and bioaccumulation of Cadmium, Copper and Zinc in a direct comparison at equitoxic concentrations in common carp (Cyprinus carpio) juveniles

The individual toxicity and bioaccumulation of cadmium, copper and zinc for common carp juveniles was evaluated in a direct comparison in two experimental setups. First, fish were exposed for 10 days to different metal concentrations in order to link metal bioaccumulation to LC₅₀ values (concentration lethal to 50% of the animals) and incipient lethal levels (ILL, concentration where 50% survives indefinitely). Accumulated metals showed a positive dose dependent uptake for cadmium and copper, but not for zinc. Toxicity was in the order cadmium>copper>zinc with 96h LC₅₀ values for cadmium at 0.20±0.16 μM, for copper at 0.77±0.03 μM, and for zinc at 29.89±9.03 μM respectively. For copper, the 96h exposure was sufficient to calculate the incipient lethal level and therefore 96h LC₅₀ and ILL levels were the same, while for cadmium and zinc 5 to 6 days were needed to reach ILL resulting in slightly lower values at 0.16 μM and 28.33 μM respectively. Subsequently, a subacute exposure experiment was conducted, where carp juveniles were exposed to 2 equitoxic concentrations (10% and 50% of LC₅₀ 96 h) of the three metals for 1, 3 and 7 days. Again a significant dose-dependent increase in gill cadmium and copper, but not in zinc, was observed during the 7-day exposure. Copper clearly affected sodium levels in gill tissue, while zinc and cadmium did not significantly alter any of the gill electrolytes. The overall histopathological effects (e.g. hyperemia and hypertrophy) of the metal exposures were mild for most of the alterations. Our study showed that copper an cadmium (but not zinc) showed dose dependent metal accumulation, however this bioaccumulation was only correlated with mortality for cadmium. Metal specific alterations were reduced gill sodium levels in copper exposed fish and oedema of the primary epithelium which typically occurred in both levels of zinc exposure.

Metal Bioavailability Models: Current Status, Lessons Learned, Considerations for Regulatory Use, and the Path Forward

Since the early 2000s, biotic ligand models and related constructs have been a dominant paradigm for risk assessment of aqueous metals in the environment. We critically review 1) the evidence for the mechanistic approach underlying metal bioavailability models; 2) considerations for the use and refinement of bioavailability-based toxicity models; 3) considerations for the incorporation of metal bioavailability models into environmental quality standards; and 4) some consensus recommendations for developing or applying metal bioavailability models. We note that models developed to date have been particularly challenged to accurately incorporate pH effects because they are unique with multiple possible mechanisms. As such, we doubt it is ever appropriate to lump algae/plant and animal bioavailability models; however, it is often reasonable to lump bioavailability models for animals, although aquatic insects may be an exception. Other recommendations include that data generated for model development should consider equilibrium conditions in exposure designs, including food items in combined waterborne-dietary matched chronic exposures. Some potentially important toxicity-modifying factors are currently not represented in bioavailability models and have received insufficient attention in toxicity testing. Temperature is probably of foremost importance; phosphate is likely important in plant and algae models. Acclimation may result in predictions that err on the side of protection. Striking a balance between comprehensive, mechanistically sound models and simplified approaches is a challenge. If empirical bioavailability tools such as multiple-linear regression models and look-up tables are employed in criteria, they should always be informed qualitatively and quantitatively by mechanistic models. If bioavailability models are to be used in environmental regulation, ongoing support and availability for use of the models in the public domain are essential. Environ Toxicol Chem 2019;39:60-84. © 2019 SETAC.

An epithelium is not just an epithelium: Effects of Na, Cl, and pH on olfaction and/or copper-induced olfactory deficits

While the toxic effects of several substances on fish olfaction are well known, studies on how water chemistry affects contaminant-induced olfactory toxicity are rare. In the present study, the effect of water pH or Na concentration on fish olfactory response and Cu-induced olfactory toxicity was investigated. Also, the effects of two sodium salts, NaCl and NaNO₃, on olfaction were studied. Juvenile rainbow trout were exposed to 6 and 32 μg/L Cu, each under five different conditions (pH 9, pH 6.5, 20 or 40 mg/L sodium added, or culture water), for 10 days before characterizing fish olfactory response using electro-olfactography (EOG). The results demonstrated that reducing the pH to 6.5 or adding 20 or 40 mg/L Na impairs the fish response to a standard olfactory cue. None of the water treatments were protective against, or synergic with, the toxic effect of Cu on the olfactory system. Of the two Na salts, NaCl caused significantly higher impairment than NaNO₃. The results of the present study demonstrate that water quality modifies contaminant-induced olfactory toxicity, but differently than what is known for other tissues (i.e. gill).

Comparative effects of cadmium, zinc, arsenic and chromium on olfactory-mediated neurobehavior and gene expression in larval zebrafish (Danio rerio)

Studies have shown that olfactory-mediated behaviors that are critical to survival can be disrupted by exposure to certain metals. Polluted waterways often contain elevated levels of metals, yet only a subset have been characterized for their potential to cause olfactory toxicity. A larval zebrafish behavioral assay was developed to characterize concentration-response curves for zinc (Zn), hexavalent chromium (Cr), and arsenate (As) olfaction inhibition. Cadmium (Cd), an established olfactory toxicant, was used as a positive control. As expected, following a 24-hour exposure to Cd, we observed a reduced response to taurocholic acid (TCA), a substrate for ciliated olfactory sensory neurons (OSNs), thus validating the behavioral assay. Zn exposure similarly decreased the olfactory response toward TCA, (IC₅₀: 36 μg/L and 76 μg/L, for Cd and Zn, respectively). The response towards a secondary odorant L-cysteine (Cys), a substrate for ciliated and microvillous OSNs, was significantly altered by both Cd and Zn exposure, although the response to Cys was not completely removed in Zn treated larvae, suggesting preferential toxicity towards ciliated OSNs. No significant changes in olfactory responses were observed following Cr and As exposures. Exposures to binary mixtures of Cd and Zn indicated that Zn had a protective effect against Cd toxicity at low Zn concentrations. QuantiGene (QDP) RNA analysis revealed Cd to be a potent inducer of metallothionein 2 (mt2) mRNA in zebrafish larvae, and Zn to be a weak mt2 inducer, suggesting a protective role of mt2 in Cd and Zn olfactory injury. By contrast, QDP analysis of eight other genes important in mitigating the effects of oxidative stress suggested an antioxidant response to Cd, but not Zn, As, and Cr suggesting that oxidative stress was not a primary mechanism of Zn-induced olfactory dysfunction. In summary, our study indicates that Zn inhibits zebrafish olfaction at environmental concentrations and may potentially mitigate Cd induced olfactory dysfunction when present in mixtures. The zebrafish behavioral trough assay incorporating the odorants L-cysteine and TCA is an effective assay to assess the effects of metals on olfactory function.

Effects of copper on olfactory, behavioral, and other sublethal responses of saltwater organisms: Are estimated chronic limits using the biotic ligand model protective?

There is concern over whether regulatory criteria for copper (Cu) are protective against chemosensory and behavioral impairment in aquatic organisms. We compiled Cu toxicity data for these and other sublethal endpoints in 35 tests with saltwater organisms and compared the Cu toxicity thresholds with biotic ligand model (BLM)-based estimated chronic limits (ECL values, which are 20% effect concentrations [EC20s] for the embryo-larval life stage of the blue mussel [Mytilus edulis], a saltwater species sensitive to Cu that has historically been used to derive saltwater Cu criteria). Only 8 of the 35 tests had sufficient toxicity and chemistry data to support unequivocal conclusions (i.e., a Cu EC20 or no-observed-effect concentration could be derived, and Cu and dissolved organic carbon [DOC] concentrations were measured [or DOC concentrations could be inferred from the test-water source]). The BLM-based ECL values would have been protective (i.e., the ECL was lower than the toxicity threshold) in 7 of those 8 tests. In the remaining 27 tests, this meta-analysis was limited by several factors, including 1) the Cu toxicity threshold was a "less than" value in 19 tests because only a lowest-observed-effect concentration could be calculated and 2) Cu and/or DOC concentrations often were not measured. In 2 of those 27 tests, the ECL would not have been protective if based only on a conservatively high upper-bound DOC estimate. To facilitate future evaluations of the protectiveness of aquatic life criteria for metals, we urge researchers to measure and report exposure-water chemistry and test-metal concentrations that bracket regulatory criteria. Environ Toxicol Chem 2018;37:1515-1522. © 2018 SETAC.

Protectiveness of Cu water quality criteria against impairment of behavior and chemo/mechanosensory responses: An update

A meta-analysis was conducted of studies that reported behavior and chemo/mechanosensory responses by fish, amphibians, and aquatic invertebrates in Cu-containing waters and also reported sufficient water chemistry for calculation of hardness-based and biotic ligand model (BLM)-based water quality criteria (WQC) for Cu. The calculated WQC concentrations were then compared with the corresponding 20% impairment concentrations (IC20) of Cu for those behavior and chemo/mechanosensory responses. The hardness-based acute and chronic WQC for Cu would not have been protective (i.e., the IC20 would have been lower than the WQC) in 33.6 and 26.2%, respectively, of the 107 combined behavior- and chemo/mechanosensory-response cases that also had adequate water chemistry data for BLM-based WQC calculations (32.7% inconclusive). In comparison, the BLM-based acute and chronic WQC for Cu would not have been protective in only 10.3 and 4.7%, respectively, of the same 107 cases (29.9% inconclusive). To improve evaluations of regulatory effectiveness, researchers conducting aquatic Cu toxicity tests should measure and report complete BLM-input water chemistry and bracket the hardness-based and BLM-based WQC concentrations for Cu that would be applicable in their exposure waters. This meta-analysis demonstrates that, overall, the BLM-based WQC for Cu were considerably more protective than the hardness-based WQC for Cu against impairment of behavior and chemo/mechanosensory responses. Environ Toxicol Chem 2018;37:1260-1279. © 2018 SETAC.

Use of electro-olfactography to measure olfactory acuity in the North American bullfrog (Lithobates (Rana) catesbeiana) tadpole

Olfaction is an important sense for aquatic organisms because it provides information about their surroundings, including nearby food, mates, and predators. Electro-olfactography (EOG) is an electrophysiological technique that measures the response of olfactory tissue to olfactory stimuli, and responses are indicative of olfactory acuity. Previous studies have used this technique on a variety of species including frogs, salamanders, daphniids and, most extensively, fish. In the present study, we introduce a novel modified EOG method for use on Lithobates (Rana) catesbeiana tadpoles. Responses to a number of olfactory stimuli including amino acids, an algal extract (Spirulina), and taurocholic acid were tested, as measured by EOG. Tadpoles exhibited consistent and reliable responses to L-alanine and Spirulina extract. Tadpoles also exhibited concentration-dependent responses to Spirulina extract. These findings indicate that tadpole EOG is a viable electrophysiology technique that can be used in future research to study olfactory physiology and impairment in tadpoles.

Experimentally derived acute and chronic copper Biotic Ligand Models for rainbow trout

We evaluated the effects of varying water chemistry ([Ca²⁺]=0.2-3mM, [Mg²⁺]=0.05-3mM, dissolved organic matter (DOM, natural, from maple leaves)=0.3-10mg of CL^-1, pH=5.0-8.5) on the acute (96-h, unfed fish) and chronic (30-d, fed fish) toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) exposed in flow-through conditions. Acute and chronic Biotic Ligand Models (BLMs) were developed from the obtained toxicity data-sets, using the Visual MINTEQ software. Our results indicate that Cu is predominantly an acute toxicant to rainbow trout, as there were no observable growth effects and the 96-h and 30-d LC50 values were similar, with mortality mostly occurring within the first few days of exposure. Calcium and DOM were greatly protective against both acute and chronic Cu toxicity, but Mg seemed to only protect against chronic toxicity. Additional protection by pH 5.0 in acute exposure and by pH 8.5 in chronic exposure occurred. In the range of conditions tested, the observed 96-h LC50 and 30-d LC20 values varied by a factor of 39 and 27 respectively. The newly developed acute and chronic BLMs explained these variations reasonably well (i.e. within a 2-fold error), except at pH≥8 where the high observed acute toxicity could not be explained, even by considering an equal contribution of CuOH⁺ and Cu²⁺ to the overall Cu toxicity. The 96-h LC50 values of 59% of 90 toxicity tests from 19 independent studies in the literature were reasonably well predicted by the new acute BLM. The LC20 predictions from the new chronic BLM were reasonable for 7 out of 14 toxicity tests from 6 independent chronic studies (with variable exposure durations). The observed deviations from BLM predictions may be due to uncertainties in the water chemistry in these literature studies and/or to differences in fish sensitivity. A residual pH effect was also observed for both the acute and the chronic data-sets, as the ratio of predicted vs. observed LC values generally increased with the pH. Additional mechanistic studies are required to understand the influence of pH, Na, and Mg on Cu toxicity to trout. The present study presents the first experimentally developed chronic Cu BLM for the rainbow trout. To the best of our knowledge, it also presents the first acute Cu BLM that is based on a published data-set for trout. These newly developed BLMs should contribute to improving the risk assessment of Cu to fish in freshwater.

Rainbow trout (Oncorhynchus mykiss) detection, avoidance, and chemosensory effects of oil sands process-affected water

Oil sands process-affected water (OSPW) - a byproduct of the oil sands industry in Northern Alberta, Canada - is currently stored in on-site tailings ponds. The goal of the present study was to investigate the interaction of OSPW with the olfactory system and olfactory-mediated behaviours of fish upon the first encounter with OSPW. The response of rainbow trout (Oncorhynchus mykiss) to different concentrations (0.1, 1, and 10%) of OSPW was studied using a choice maze and electro-olfactography (EOG), respectively. The results of the present study showed that rainbow trout are capable of detecting and avoiding OSPW at a concentration as low as 0.1%. Exposure to 1% OSPW impaired (i.e. reduced sensitivity) the olfactory response of rainbow trout to alarm and food cues within 5 min or less. The results of the present study demonstrated that fish could detect and avoid minute concentrations of OSPW. However, if fish were exposed to OSPW-contaminated water and unable to escape, their olfaction would be impaired.

The role of metals in mammalian olfaction of low molecular weight organosulfur compounds

Covering: up to the end of 2017While suggestions concerning the possible role of metals in olfaction and taste date back 50 years, only recently has it been possible to confirm these proposals with experiments involving individual olfactory receptors (ORs). A detailed discussion of recent experimental results demonstrating the key role of metals in enhancing the response of human and other vertebrate ORs to specific odorants is presented against the backdrop of our knowledge of how the sense of smell functions both at the molecular and whole animal levels. This review emphasizes the role of metals in the detection of low molecular weight thiols, sulfides, and other organosulfur compounds, including those found in strong-smelling animal excretions and plant volatiles, and those used in gas odorization. Alternative theories of olfaction are described, with evidence favoring the modified "shape" theory. The use of quantum mechanical/molecular modeling (QM/MM), site-directed mutagenesis and saturation-transfer-difference (STD) NMR is discussed, providing support for biological studies of mouse and human receptors, MOR244-3 and OR OR2T11, respectively. Copper is bound at the active site of MOR244-3 by cysteine and histidine, while cysteine, histidine and methionine are involved with OR2T11. The binding pockets of these two receptors are found in different locations in the three-dimensional seven transmembrane models. Another recently deorphaned human olfactory receptor, OR2M3, highly selective for a thiol from onions, and a broadly-tuned thiol receptor, OR1A1, are also discussed. Other topics covered include the effects of nanoparticles and heavy metal toxicants on vertebrate and fish ORs, intranasal zinc products and the loss of smell (anosmia).

From the Cover: Cadmium Exposure Differentially Alters Odorant-Driven Behaviors and Expression of Olfactory Receptors in Juvenile Coho Salmon (Oncorhynchus kisutch)

Salmon exposed to waterborne metals can experience olfactory impairment leading to disrupted chemosensation. In the current study, we investigated the effects of cadmium (Cd) on salmon olfactory function by modeling an exposure scenario where juvenile salmon transiently migrate through a polluted waterway. Coho were exposed to environmentally relevant concentrations of waterborne Cd (2 and 30 µg/L) for 48 h and (0.3 and 2 μg/L) for 16 days, followed by a 16-day depuration associated with outmigration. Cadmium exposures inhibited behavioral responses towards L-cysteine and conspecific odorants, with effects persisting following the depuration. Behavioral alterations following the 30 µg/L exposure were associated with increased olfactory epithelial gene expression of metallothionein (mt1a) and heme oxygenase (hmox1); reduced expression of olfactory signal transduction (OST) molecules; and reduced expression of mRNAs encoding major coho odorant receptors (ORs). Salmon OR array analysis indicated that Cd preferentially impacted expression of OST and OR markers for ciliated olfactory sensory neurons (OSNs) relative to microvillus OSNs, suggesting a differential sensitivity of these two major OSN populations. Behavioral alterations on exposure to 0.3 and 2 µg/L Cd were associated with increased mt1a, but not with major histological or OR molecular changes, likely indicating disrupted OST as a major mechanism underlying the behavioral dysfunction at the low-level Cd exposures. Laser-ablation mass spectrometry analysis revealed that the OSN injury and behavioral dysfunction was associated with significant Cd bioaccumulation within the olfactory sensory epithelium. In summary, low-level Cd exposures associated with polluted waterways can induce differential and persistent olfactory dysfunction in juvenile coho salmon.

Effects of Lampricide on Olfaction and Behavior in Young-of-the-Year Lake Sturgeon (Acipenser fulvescens)

The lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), is a primary component to sea lamprey control in the Laurentian Great Lakes. Though the lethal effects of TFM are well-known, the sublethal effects on fishes are virtually unknown. Here we studied the effects of TFM on the olfactory capabilities and behavior of young-of-the-year (YOY) lake sturgeon (Acipenser fulvescens). At ecologically relevant concentrations of TFM there was reduced olfactory response to all three cues (l-alanine, taurocholic acid, food cue) tested, suggesting that TFM inhibits both olfactory sensory neurons tested. Sturgeon exposed to TFM also showed a reduced attraction to the scent of food and reduced consumption of food relative to unexposed fish. Exposed fish were more active than control fish, but with slower acceleration. Fish were able to detect the scent of TFM, but failed to avoid it in behavioral trials. The connection between neurophysiological and behavioral changes, and the commonality of habitats between sturgeon and lamprey ammocoetes, suggests that there may be effects at the ecosystem level in streams that undergo lamprey control treatments.

Cadmium-induced olfactory dysfunction in rainbow trout: Effects of binary and quaternary metal mixtures

A functioning olfactory response is essential for fish to be able to undertake essential behaviors. The majority of work investigating the effects of metals on the olfactory response of fish has focused on single-metal exposures. In this study we exposed rainbow trout to cadmium, copper, nickel, zinc, or a mixture of these four metals at or below the current Canadian Council of Ministers of the Environment guidelines for the protection of aquatic life. Measurement of olfactory acuity using an electro-olfactogram demonstrated that cadmium causes significant impairment of the entire olfactory system, while the other three metals or the mixture of all four metals did not. Binary mixtures with cadmium and each of the other metals demonstrated that nickel and zinc, but not copper, protect against cadmium-induced olfactory dysfunction. Testing was done to determine if the protection from cadmium-induced olfactory dysfunction could be explained by binding competition between cadmium and the other metals at the cell surface, or if the protection could be explained by an up-regulation of an intracellular detoxification pathway, namely metallothionein. This study is the first to measure the effects of binary and quaternary metal mixtures on the olfactory response of fish, something that will aid in future assessments of the effects of metals on the environment.

Quantifying Fish Swimming Behavior in Response to Acute Exposure of Aqueous Copper Using Computer Assisted Video and Digital Image Analysis

Behavioral responses of aquatic organisms to environmental contaminants can be precursors of other effects such as survival, growth, or reproduction. However, these responses may be subtle, and measurement can be challenging. Using juvenile white sturgeon (Acipenser transmontanus) with copper exposures, this paper illustrates techniques used for quantifying behavioral responses using computer assisted video and digital image analysis. In previous studies severe impairments in swimming behavior were observed among early life stage white sturgeon during acute and chronic exposures to copper. Sturgeon behavior was rapidly impaired and to the extent that survival in the field would be jeopardized, as fish would be swept downstream, or readily captured by predators. The objectives of this investigation were to illustrate protocols to quantify swimming activity during a series of acute copper exposures to determine time to effect during early lifestage development, and to understand the significance of these responses relative to survival of these vulnerable early lifestage fish. With mortality being on a time continuum, determining when copper first affects swimming ability helps us to understand the implications for population level effects. The techniques used are readily adaptable to experimental designs with other organisms and stressors.

Recovery of Olfactory Mediated Behaviours of Fish from Metal Contaminated Lakes

Fish mediate many biological processes by olfaction, which can be impaired by contaminants (i.e. metals). While the olfactory recovery of fish from metal contaminated lakes if subsequently cultured in clean water has been shown at the neurophysiological level, the recovery potential of olfactory mediated behaviours remains unknown. To study behavioural recovery of fish from metal contaminated lakes, wild yellow perch (Perca flavescens) were collected from two metal-contaminated lakes (Ramsey and Hannah lakes) in the metal-mining district of Sudbury, ON, Canada and cultured in clean water from a reference lake (Geneva Lake) for another 24 h. Olfactory mediated behaviours of the test organisms were tested using avoidance responses to conspecific skin extract. While olfactory mediated behaviours of fish from Ramsey Lake (low contamination) recovered after 24 h in clean water, recovery could not be observed in fish from Hannah Lake (high contamination). These results demonstrate that the recovery of behavioural deficits of fish from metal contaminated lakes is depending on the habitats' metal concentration.

Analyzing the effectiveness of using branchial NKA activity as a biomarker for assessing waterborne copper toxicity in tilapia (Oreochromis mossambicus): A damage-based modeling approach

Branchial Na(＋)-K(＋)-ATPase (NKA) activity has been suggested as a promising biomarker for assessing metal stress in aquatic organisms. However, studies that systematically show the effectiveness of using NKA activity to detect metal exposure and toxicity at the individual level are limited. In this study, we aimed to determine whether branchial NKA activity mechanistically responds to the accumulation of waterborne copper (Cu) and accounts for observed toxicity over time under environmentally-relevant and aquafarming Cu exposure levels (0.2, 1 and 2 mg L(-1)). Temporal trends in Cu accumulation and the corresponding responses of branchial NKA activity resulting from Cu exposure were investigated in laboratory experiments conducted on juvenile tilapia (Oreochromis mossambicus), a freshwater teleost that shows potential as a bioindicator of real-time and historical metal pollution. We used the process-based damage assessment model (DAM) to inspect the time course of Cu toxicity by integrating the compensation process between Cu-induced inhibition and repair of branchial NKA activity. NKA activity acted as a sensitive biomarker for Cu exposure and accumulation in tilapia, which showed induced impairment of osmoregulation and lethality when they were exposed to environmentally relevant levels (0.2 mg L(-1)), but not to higher exposure levels (1 and 2 mg L(-1)) in aquaculture farms or contaminated aquatic ecosystems. This study highlights the benefits and limitations of using branchial NKA activity as a sensitive biomarker to assess the health status of a fish population and its ecosystem.

Sublethal effects of cadmium on auditory structure and function in fathead minnows (Pimephales promelas)

Aquatic ecosystems are threatened by environmental contaminants, and many heavy metals can influence both the structure and function of sense organs in fishes. The use of these senses is vital to the survival and reproductive success of fish and therefore affects the health of the ecosystem as a whole. The current study examines the effects of cadmium on auditory structure and function in the fathead minnow (Pimephales promelas). In the laboratory, fish were exposed for 96 h to a range of cadmium concentrations and both hearing sensitivity and hair cell morphology were quantified. While hair cell numbers were unaffected, cadmium caused an increase in auditory threshold, with a critical range for toxic effects of cadmium estimated at 2.1-2.9 µg L(-1). Cadmium exposure also caused a decrease in response latency at higher cadmium concentrations. The current study demonstrates the sublethal effects of cadmium on fish sensory function while also pointing to the need for more careful interpretation of cadmium impacts on aquatic populations.

Dietary sodium protects fish against copper-induced olfactory impairment

Exposure to low concentrations of copper impairs olfaction in fish. To determine the transcriptional changes in the olfactory epithelium induced by copper exposure, wild yellow perch (Perca flavescens) were exposed to 20 μg/L of copper for 3 and 24h. A novel yellow perch microarray with 1000 candidate genes was used to measure differential gene transcription in the olfactory epithelium. While three hours of exposure to copper changed the transcription of only one gene, the transcriptions of 70 genes were changed after 24h of exposure to copper. Real-time PCR was utilized to determine the effect of exposure duration on two specific genes of interest, two sub-units of Na/K-ATPase. At 24 and 48 h, Na/K-ATPase transcription was down-regulated by copper at olfactory rosettes. As copper-induced impairment of Na/K-ATPase activity in gills can be ameliorated by increased dietary sodium, rainbow trout (Oncorhynchus mykiss) were used to determine if elevated dietary sodium was also protective against copper-induced olfactory impairment. Measurement of the olfactory response of rainbow trout using electro-olfactography demonstrated that sodium was protective of copper-induced olfactory dysfunction. This work demonstrates that the transcriptions of both subunits of Na/K-ATPase in the olfactory epithelium of fish are affected by Cu exposure, and that dietary Na protects against Cu-induced olfactory dysfunction.

Contaminant-specific targeting of olfactory sensory neuron classes: connecting neuron class impairment with behavioural deficits

The olfactory system of fish comprises several classes of olfactory sensory neurons (OSNs). The odourants L-alanine and taurocholic acid (TCA) specifically activate microvillous or ciliated OSNs, respectively, in fish. We recorded electro-olfactograms (EOG) in fathead minnows (Pimephales promelas; a laboratory-reared model species) and wild yellow perch (Perca flavescens) whose olfactory chambers were perfused with either L-alanine or TCA to determine if OSN classes were differentially vulnerable to contaminants, in this case copper or nickel. Results were consistent in both species and demonstrated that nickel targeted and impaired microvillous OSN function, while copper targeted and impaired ciliated OSN function. This result suggests that contaminant-specific effects observed in model laboratory species extrapolate to wild fish populations. Moreover, fathead minnows exposed to copper failed to perceive a conspecific alarm cue in a choice maze, whereas those exposed to nickel could respond to the same conspecific cue. These results demonstrate that fathead minnows perceive conspecific, damage-released alarm cue by ciliated, but not microvillous, OSNs. Fish living in copper-contaminated environments may be more vulnerable to predation than those in clean lakes owing to targeted effects on ciliated OSNs.

Calcium-dependent behavioural responses to acute copper exposure in Oncorhynchus mykiss

Using rainbow trout Oncorhynchus mykiss, the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre-exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu-contaminated water (ranging from 0 to 454 µg Cu l⁻¹ ) and uncontaminated water in a choice tank, O. mykiss acclimated and tested at low Ca concentration (3 mg Ca l⁻¹ avoided the 10 µg Cu l⁻¹ only. By contrast, O. mykiss acclimated and tested at high Ca concentration (158 mg Ca l⁻¹) avoided all the Cu concentrations ≥37 µg⁻¹. The Cu avoidance was connected with increased spontaneous swimming speed in the Cu-contaminated water. When subjected to inescapable Cu exposure (35 µg Cu l⁻¹), O. mykiss acclimated and tested at low Ca concentration reduced their spontaneous swimming speed, whereas no response was observed in O. mykiss acclimated and tested at high Ca concentration. Collectively, the data support the conclusion that in O. mykiss the behavioural responses to acute Cu exposure are Ca-dependent.

Critical body residues, Michaelis-Menten analysis of bioaccumulation, lethality and behaviour as endpoints of waterborne Ni toxicity in two teleosts

Traditionally, water quality guidelines/criteria are based on lethality tests where results are expressed as a function of waterborne concentrations (e.g. LC50). However, there is growing interest in the use of uptake and binding relationships, such as biotic ligand models (BLM), and in bioaccumulation parameters, such as critical body residue values (e.g. CBR50), to predict metal toxicity in aquatic organisms. Nevertheless, all these approaches only protect species against physiological death (e.g. mortality, failed recruitment), and do not consider ecological death which can occur at much lower concentrations when the animal cannot perform normal behaviours essential for survival. Therefore, we investigated acute (96 h) Ni toxicity in two freshwater fish species, the round goby (Neogobius melanostomus) and rainbow trout (Oncorhynchus mykiss) and compared LC, BLM, and CBR parameters for various organs, as well as behavioural responses (spontaneous activity). In general, round goby were more sensitive. Ni bioaccumulation displayed Michaelis-Menten kinetics in most tissues, and round goby gills had lower Kd (higher binding affinity) but similar Bmax (binding site density) values relative to rainbow trout gills. Round goby also accumulated more Ni than did trout in most tissues at a given exposure concentration. Organ-specific 96 h acute CBR values tended to be higher in round goby but 96 h acute CBR50 and CBR10 values in the gills were very similar in the two species. In contrast, LC50 and LC10 values were significantly higher in rainbow trout. With respect to BLM parameters, gill log KNiBL values for bioaccumulation were higher by 0.4-0.8 log units than the log KNiBL values for toxicity in both species, and both values were higher in goby (more sensitive). Round goby were also more sensitive with respect to the behavioural response, exhibiting a significant decline of 63-75 % in movements per minute at Ni concentrations at and above only 8 % of the LC50 value; trout exhibited no clear behavioural response. Across species, diverse behavioral responses may be more closely related to tissue Ni burdens than to waterborne Ni concentrations. To our knowledge, this is the first study to link Ni bioaccumulation with behavioural endpoints. In future it would be beneficial to expand these analyses to a wider range of species to determine whether Ni bioaccumulation, specifically in the gills, gut and whole fish, may be a good predictor of behavioural changes from metal exposure; which in the wild can lead to ecological death.

Olfactory recovery of wild yellow perch from metal contaminated lakes

Fish depend on their sense of smell for a wide range of vital life processes including finding food, avoiding predators and reproduction. Various contaminants, including metals, can disrupt recognition of chemical information in fish at very low concentrations. Numerous studies have investigated metal effects on fish olfaction under controlled laboratory conditions. However, few have measured olfactory acuity using wild fish in source water. In this study, we used electro-olfactography (EOG) to measure the olfactory acuity of wild yellow perch (Perca flavescens) from a clean lake (Geneva Lake) and two metal contaminated lakes (Ramsey and Hannah lakes) from Sudbury, ON, in their own lake water or in water from the other lakes. The results showed that fish from the clean lake had a greater olfactory acuity than those from metal contaminated lakes when fish were tested in their own lake water. However, when fish from the clean lake were held for 24h in water from each of the two contaminated lakes their olfactory acuity was diminished. On the other hand, fish from the contaminated lakes held for 24h in clean lake water showed a significant olfactory recovery relative to that measured in their native lake water. These results show that although fish from a clean lake demonstrated impaired olfaction after only 24h in metal-contaminated water, fish from metal contaminated lakes showed a rapid olfactory recovery when exposed to clean water for only hours.

Dissolved organic carbon modulates the effects of copper on olfactory-mediated behaviors of chinook salmon

The modulation of Cu effects on olfactory-mediated behaviors by dissolved organic carbon (DOC) and Fe was examined in juvenile chinook salmon. Chinook were exposed to several concentrations of Cu, DOC, and Fe alone or in combination in a flow-through system for either 4 d (acute exposure) or 14 d (subchronic exposure) and tested for their ability to detect and avoid the odorant L-histidine in an avoidance/preference trough assay. In both acute and subchronic exposures, Cu inhibited the ability of fish to detect this amino acid in a concentration-dependent manner, and Cu toxicity (olfactory inhibition) decreased with increasing DOC concentration. In both acute and subchronic experiments including DOC, Cu-induced olfactory inhibition decreased in a linear fashion with increasing DOC concentration, although the modulation was lower in subchronic exposures. The protective effect of DOC on Cu olfactory inhibition was reduced only slightly in the presence of Fe, indicating that other metals can potentially affect the modulation of the olfactory inhibition of Cu through competition for DOC binding sites. The results of the present study clearly show the amelioration by DOC of the effects of Cu on juvenile chinook salmon olfaction at a behavioral level. These data further indicate that DOC concentrations should be considered when evaluating the potential impact of Cu on fish olfaction.

Effects of continuous copper exposure and calcium on the olfactory response of fathead minnows

The current gill-based Biotic Ligand Model (gbBLM) is an acute-toxicity model used to predict site-specific safe copper (Cu) concentrations. Recent effort to develop a chronic BLM has focused on the olfactory epithelium. To further this effort, the current study looked at the effect of varying Cu concentration and exposure duration on Cu-induced olfactory dysfunction, and whether calcium (Ca) protected against Cu-induced impairment as it does at the gill. Fathead minnows (Pimephales promelas) were treated with five Cu concentrations for varying exposure durations in hard and soft water. A neurophysiological technique, electro-olfactography (EOG), was employed to determine the level of olfactory dysfunction. At the low, ecologically relevant Cu concentrations tested there was significant inhibition of EOG function; however, over time there was at least a partial recovery of olfactory function, despite the continuous Cu exposure. Calcium did not appear to protect against Cu-induced olfactory dysfunction; and even alone, Ca appeared to interfere with the olfactory response to the amino acid L-arginine. Safe copper concentrations as predicted by the gbBLM, chemosensory-based BLMs, the USEPA BLM, and hardness-adjustment equations based on the exposure waters were not entirely protective against olfactory dysfunction.

Electroantennogram measurement of the olfactory response of Daphnia spp. and its impairment by waterborne copper

In this study an electroantennogram (EAG) method was developed for use on live daphniids. The EAG response of Daphnia magna and Daphnia pulex to a variety of amino acids was measured. The strongest response measured was elicited by L-arginine and was shown to induce a concentration-dependent response indicating the response is olfactory in nature. Subsequent exposures of D. magna to a low, ecologically-relevant concentration of copper (7.5 μg/L) showed a disruption in EAG function. This study utilizes the development of an EAG method for measuring olfactory acuity of live daphniids and demonstrates that at ecologically-relevant concentrations, the olfactory dysfunction caused by copper can be detected. The EAG technique is a useful tool for investigating the olfactory response of daphniids to odourants at the cellular level and detecting the effects of toxicants on the olfactory acuity of daphniids.

Protectiveness of water quality criteria for copper in western United States waters relative to predicted olfactory responses in juvenile Pacific salmon

Copper (Cu) can impair olfaction in juvenile Pacific salmon (as well as other fishes), thus potentially inhibiting the ability of juveniles to avoid predators or to find food. Because Cu is commonly elevated in stormwater runoff in urban environments, storm events may result in elevated Cu concentrations in salmon-bearing streams. Accordingly, there is concern that existing Cu criteria, which were not derived using data for olfactory-related endpoints, may not be adequately protective of juvenile salmon. However, a modification of the US Environmental Protection Agency (USEPA) biotic ligand model (BLM) for deriving site-specific Cu criteria was recently proposed, which accounted for the sensitivity of olfactory endpoints. The modification was based on olfactory inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to Cu in various combinations of pH, hardness, alkalinity, and dissolved organic carbon (DOC) concentrations. We used that olfactory-based BLM to derive 20% inhibition concentrations (IC20) values for Cu for 133 stream locations in the western United States. The olfactory BLM-based IC20 values were compared to the existing hardness-based Cu criteria and the USEPA's BLM-based Cu criteria for these representative natural waters of the western United States. Of the 133 sampling locations, mean hardness-dependent acute and chronic Cu criteria were below the mean olfactory-based BLM IC20 value in 122 (92%) and 129 (97%) of the waters, respectively (i.e., <20% olfactory impairment would have been predicted at the mean hardness-based Cu criteria concentrations). Waters characterized by a combination of high hardness and very low DOC were most likely to have hardness-based Cu criteria that were higher than the olfactory-based BLM IC20 values, because DOC strongly influences Cu bioavailability in the BLM. In all waters, the USEPA's current BLM-based criteria were below the mean olfactory-based BLM IC20 values, indicating that the USEPA's BLM-based criteria are protective of olfactory impairment in juvenile salmon.

Transcriptional impact of organophosphate and metal mixtures on olfaction: copper dominates the chlorpyrifos-induced response in adult zebrafish

Chemical exposures in fish have been linked to loss of olfaction leading to an inability to detect predators and prey and decreased survival. However, the mechanisms underlying olfactory neurotoxicity are not well characterized, especially in environmental exposures which involve chemical mixtures. We used zebrafish to characterize olfactory transcriptional responses by two model olfactory inhibitors, the pesticide chlorpyrifos (CPF) and mixtures of CPF with the neurotoxic metal copper (Cu). Microarray analysis was performed on RNA from olfactory tissues of zebrafish exposed to CPF alone or to a mixture of CPF and Cu. Gene expression profiles were analyzed using principal component analysis and hierarchical clustering, whereas gene set analysis was used to identify biological themes in the microarray data. Microarray results were confirmed by real-time PCR on genes serving as potential biomarkers of olfactory injury. In addition, we mined our previously published Cu-induced zebrafish olfactory transcriptional response database (Tilton et al., 2008) for the purposes of discriminating pathways of olfaction impacted by either the individual agents or the CPF-Cu mixture transcriptional signatures. CPF exposure altered the expression of gene pathways associated with cellular morphogenesis and odorant binding, but not olfactory signal transduction, a known olfactory pathway for Cu. The mixture profiles shared genes from the Cu and CPF datasets, whereas some genes were altered only by the mixtures. The transcriptional signature of the mixtures was more similar to that in zebrafish exposed to Cu alone than for CPF. In conclusion, exposure to a mixture containing a common environmental metal and pesticide causes a unique transcriptional signature that is heavily influenced by the metal, even when organophosphate predominates.

Relationship between biotic ligand model-based water quality criteria and avoidance and olfactory responses to copper by fish

The U.S. Environmental Protection Agency's (U.S. EPA) water quality criteria for Cu were tested to determine whether they protect fish against neurophysiological impairment. From published studies with rainbow trout (Oncorhynchus mykiss), Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), and fathead minnows (Pimephales promelas), 20% inhibition concentrations (IC20s) were calculated for avoidance of Cu-containing water and for impairment of electroencephalogram (EEG) and electro-olfactogram (EOG) responses to natural odorants in Cu-containing water. Additionally, a Cu-olfactory biotic ligand model (BLM) that fits the coho salmon EOG data was parameterized by changing the sensitivity parameter in the ionoregulatory-based BLM. The IC20s calculated from reported Cu avoidance, EEG, and EOG data and IC20s predicted by the olfactory BLM were compared with acute and chronic Cu criteria calculated using U.S. EPA's BLM 2007 or hardness-adjustment equations. The BLM-based chronic criteria were protective in all 16 exposure water-species combinations used in avoidance and olfaction experiments. Additionally, the BLM-based acute criteria were protective in all 11 exposure water-species combinations in which comparisons could be made with olfactory BLM-predicted IC20s but not in two of the 16 exposure water-species combinations in which comparisons could be made with the reported IC20s (which were < or =8% lower than but did not differ significantly from the BLM-based acute criteria; p > 0.05). In effect, the olfactory BLM factored out the relatively high variability in the reported IC20s. It is concluded that the U.S. EPA's BLM-based water quality criteria for Cu protect against these types of neurophysiological impairment in the six species-endpoint combinations analyzed in this paper. However, the U.S. EPA's hardness-based criteria for Cu sometimes were considerably underprotective and sometimes were much less protective than the BLM-based criteria.