A sensory system at the interface between urban stormwater runoff and salmon survival

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.

Acute Toxicity of Copper to Three Species of Pacific Salmon Fry in Water with Low Hardness and Low Dissolved Organic Carbon

Proposed development of a mine within Alaska's Bristol Bay watershed (USA) has raised concerns about the potential impact of copper (Cu) on Pacific salmon (Oncorhynchus spp.). We conducted 96-h flow-through bioassays using low-hardness and low dissolved organic carbon water to determine the acute lethal toxicity of Cu to sockeye (Oncorhynchus nerka), Chinook (Oncorhynchus tshawytscha), and coho salmon (Oncorhynchus kisutch) fry. We aimed to determine Cu toxicity under field-relevant water quality conditions and to assess three methods of calculating ambient Cu criteria: the biotic ligand model (BLM), a multiple linear regression model endorsed by the US Environmental Protection Agency, and the hardness-based model currently used by the State of Alaska. The criteria generated by all models were below 20% lethal Cu concentrations by factors ranging from 2.2 to 54.3, indicating that all criteria would be protective against mortality. The multiple linear regression-based criteria were the most conservative and were comparable to BLM-based criteria. The median lethal concentrations (LC50s) for sockeye, Chinook, and coho were 35.2, 23.9, and 6.3 µg Cu/L, respectively. We also used the BLM to predict LC50s for each species. Model predictions differed from empirical LC50s by factors of 0.7 for sockeye and Chinook salmon, and 1.1 for coho salmon. These differences fell within the acceptable range of ±2, indicating the model's accuracy. We calculated critical lethal Cu accumulation values for each species to account for differing water chemistry in each bioassay; the present study revealed that coho salmon were most sensitive to Cu, followed by sockeye and Chinook salmon. Our findings underscore the importance of considering site- and species-specific factors when modeling Cu toxicity. The empirical data we present may enhance Cu risk assessments for Pacific salmon. Environ Toxicol Chem 2023;42:2440-2452. © 2023 SETAC.

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.

Improvement of heavy metal removal from urban runoff using modified pervious concrete

Heavy metals are one of the major chemical pollutant groups in urban runoff. The application of porous concrete is a potential alternative to conventional runoff management systems with the ability to remove heavy metals. Hence, a thorough understanding of the heavy metal removal mechanisms and constraints of conventional porous concrete opens a path for the development of effective modifications. This review critically discusses the major contributors in ordinary porous concrete which supports heavy metal removal. The effects of initial concentration, contact time and competing ions on heavy metal removal using porous concrete are also discussed. Additionally, the effect of decalcification, atmospheric carbonation, acid influent on heavy metal removal is reviewed. The major drawback of porous concrete is the high pH (>8.5) of the effluent water, decalcification of the porous concrete and leaching of adsorbed pollutants. Overall, the addition of adsorbent materials to the porous concrete increases removal efficiencies (7% - 65% increase) without neutralizing the effluent pH. Meanwhile, the addition of Reduced Graphene Oxide is successful in reducing the leachability of the removed heavy metals. The addition of pozzolanic materials can lower the effluent pH while maintaining similar removal efficiencies to unmodified porous concrete. Therefore, developing a novel method of neutralizing the effluent pH must be prioritized in future studies. Additionally, the toxicity that can occur due to the abrasion of modified porous concrete requires study in future research. Further, advanced characterization methods should be used in future studies to understand the mechanisms of removal via the modified porous concrete materials.

Response of Olfactory Sensory Neurons to Mercury Ions in Zebrafish: An Immunohistochemical Study

Olfactory sensory neurons (OSNs) of fish belong to three main types: ciliated olfactory sensory neurons (cOSNs), microvillous olfactory sensory neurons (mOSNs), and crypt cells. Mercury is a toxic metal harmful for olfaction. We exposed the olfactory epithelium of zebrafish to three sublethal Hg2+ concentrations. Molecular markers specific for the different types of OSNs were immunohistochemically detected. Image analysis of treated sections enabled counting of marked cells and measurement of staining optical density indicative of the response of OSNs to Hg2+ exposure. The three types of OSNs reacted to mercury in a different way. Image analysis revealed that mOSNs are more susceptible to Hg2+ exposure than cOSNs and crypt cell density decreases. Moreover, while the ratio between sensory/nonsensory epithelium areas is unchanged, epithelium thickness drops, and dividing cells increase in the basal layer of the olfactory epithelium. Cell death but also reduction of apical processes and marker expression could account for changes in OSN immunostaining. Also, the differential results between dorsal and ventral halves of the olfactory rosette could derive from different water flows inside the olfactory chamber or different subpopulations in OSNs.

Interaction of copper with titanium dioxide nanoparticles induced hematological and biochemical effects in Clarias gariepinus

The increasing demand for engineered nanomaterials induces potential harmful impact into aquatic ecosystems and is a great concern for freshwater biodiversity. The present study showed that enhancing toxic property of titanium dioxide nanoparticles (TiO₂ NPs) with copper (Cu) was responsible for the disruption of hormonal, hematological, and biochemical activities, in Clarias gariepinus. The study revealed that C. gariepinus intravenously injected with safe concentrations of TiO₂ NPs (3μg g) and Cu (2.5 μg g) alone and binary mixtures (TiO₂ NPs (3μg g) + Cu (2.5μg g)) for a period of 96h remarkably changed hormonal activities and hematological and biochemical indices of the fish. Our findings indicated that both chemicals accumulated in vital organs (the brain, serum, heart, gonad, liver, gills, serum, and kidney) and the presence of TiO₂ NPs enhanced the bioavailability of copper. Fish exposed to TiO₂ NPs alone significantly increased thyroxine (T₄) and further decreased triidothyronine (T₃). In addition, the binary mixtures showed antagonistic effects on both hormones. The hematological indices (WBC, RBC, HGt, MCV, MCH, MCHC, and Hct) were altered in all treatment groups. Decrease in WBC, RBC, HGt, Hct, and MCV were observed. Furthermore, the co-exposure further decreased WBC (60.28%), RBC (47.10%), HGt (75.99%), Hct (25.34%), and MCV (16.18%), in contrast, MCH and MCHC increased by of 2 folds, respectively. Metabolic enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) showed significant (p<0.05) increase, with additive effect in co-exposure. However, the alkaline phosphatase (ALP) activity decreased significantly in co-exposure. Significant (p<0.05) decrease of antioxidants, superoxide dismutase (SOD), glutathione transferase (GST), catalase (CAT), and metallothionein (Met) was observed in all the treatments with additive effect of 64.9%, 30.77%, and 91.31% in SOD, GST, and CAT, respectively. However, there was an increase in lipid peroxidation (MDA) in all treated fish. The results indicate that combined mixture influences the accumulation, hormonal, hematological, and biochemical factors which could affect the health of the fish.

Anthropogenic factors associated with contaminants of emerging concern detected in inland Minnesota lakes (Phase II)

Contaminants of emerging concern (CECs) include a variety of pharmaceuticals, personal care products, and hormones commonly detected in surface waters. Human activities, such as wastewater treatment and discharge, contribute to the distribution of CECs in water, but other sources and pathways are less frequently examined. This study aimed to identify anthropogenic activities and environmental characteristics associated with the presence of CECs, previously determined to be of high priority for further research and mitigation, in rural inland lakes in northeastern Minnesota, United States. The setting for this study consisted of 21 lakes located within both the Grand Portage Indian Reservation and the 1854 Ceded Territory, where subsistence hunting and fishing are important to the cultural heritage of the indigenous community. We used data pertaining to numbers of buildings, healthcare facilities, wastewater treatment plants, impervious surfaces, and wetlands within defined areas surrounding the lakes as potential predictors of the detection of high priority CECs in water, sediment, and fish. Separate models were run for each contaminant detected in each sample media. We used least absolute shrinkage and selection operator (LASSO) models to account for both predictor selection and parameter estimation for CEC detection. Across contaminants and sample media, the percentage of impervious surface was consistently positively associated with CEC detection. Number of buildings in the surrounding area was often negatively associated with CEC detection, though nonsignificant. Surrounding population, presence of wastewater treatment facilities, and percentage of wetlands in surrounding areas were positively, but inconsistently, associated with CECs, while catchment area and healthcare centers were generally not associated. The results of this study highlight human activities and environmental characteristics associated with CEC presence in a rural area, informing future work regarding specific sources and transport pathways. We also demonstrate the utility of LASSO modeling in the identification of these important relationships.

Effects of polystyrene nanoplastics on Ctenopharyngodon idella (grass carp) after individual and combined exposure with zinc oxide nanoparticles

The toxicity of polystyrene nanoparticles (PS NPs) and ZnO nanoparticles (ZnO NPs), in combination is poorly known. Thus, the aim of the current study was to evaluate the effects of PS NPs (760 μg/L) on Ctenopharyngodon idella exposed to it, both in separate and in combination with ZnO NPs (760 μg/L), based on behavioral, biochemical and genotoxic biomarkers. Current data have indicated that PS NPs, for a short exposure period (3 days), both in separate and in combination with nanoparticles, have affected animals' response to the mirror test. On the other hand, all treatments have equally induced C. idella inactivity towards alarm substances and DNA damage. There was increased oxidative stress, mainly in groups exposed to PS NPs (in combination, or not, with nanoparticles); although increased, the evaluated antioxidant levels did not appear to be enough to inhibit the effects of treatment-induced production of free radicals. Together, these results are likely co-responsible for the observed changes. The current study did not observe antagonistic, synergistic or additive effect on animals exposed to the combination between PS NPs and ZnO NPs; however, this outcome should not discourage the performance of similar studies focused on assessing the (eco)toxicity of pollutant mixtures comprising nanomaterials.

Urban stormwater and crude oil injury pathways converge on the developing heart of a shore-spawning marine forage fish

Understanding how aquatic organisms respond to complex chemical mixtures remains one of the foremost challenges in modern ecotoxicology. Although oil spills are typically high-profile disasters that release hundreds or thousands of chemicals into the environment, there is growing evidence for a common adverse outcome pathway (AOP) for the vulnerable embryos and larvae of fish species that spawn in oiled habitats. Molecular initiating events involve the disruption of excitation-contraction coupling in individual cardiomyocytes, which then dysregulate the form and function of the embryonic heart. Phenanthrenes and other three-ring (tricyclic) polycyclic aromatic hydrocarbons (PAHs) are key drivers for this developmental cardiotoxicity and are also relatively enriched in land-based urban runoff. Similar to oil spills, stormwater discharged from roadways and other high-traffic impervious surfaces contains myriad contaminants, many of which are uncharacterized in terms of their chemical identity and toxicity to aquatic organisms. Nevertheless, given the exceptional sensitivity of the developing heart to tricyclic PAHs and the ubiquitous presence of these compounds in road runoff, cardiotoxicity may also be a dominant aspect of the stormwater-induced injury phenotype in fish early life stages. Here we assessed the effects of traffic-related runoff on the embryos and early larvae of Pacific herring (Clupea pallasii), a marine forage fish that spawns along the coastline of western North America. We used the well-characterized central features of the oil toxicity AOP for herring embryos as benchmarks for a detailed analysis of embryolarval cardiotoxicity across a dilution gradient ranging from 12 to 50% stormwater diluted in clean seawater. These injury indicators included measures of circulatory function, ventricular area, heart chamber looping, and the contractility of both the atrium and the ventricle. We also determined tissue concentrations of phenanthrenes and other PAHs in herring embryos. We find that tricyclic PAHs are readily bioavailable during cardiogenesis, and that stormwater-induced toxicity is in many respects indistinguishable from canonical crude oil toxicity. Given the chemical complexity of urban runoff, non-tricyclic PAH-mediated mechanisms of developmental toxicity in fish remain likely. However, from the standpoint of managing wild herring populations, our results suggest that stormwater-driven threats to individual survival (both near-term and delayed mortality) can be understood from decades of past research on crude oil toxicity. Moreover, Pacific herring embryos are promising sentinels for water quality monitoring in nearshore marine habitats, as in situand sensitive indicators of both toxic runoff and the effectiveness of pollution reduction efforts such as green stormwater infrastructure.

Act now before its too late: Copper exposure drives chemo-ecology of predator-prey dynamics of freshwater common spiny loach, Lepidocephalichthys thermalis (Valenciennes, 1846)

Due to the extensive use of copper (Cu) in various commercial products, its existence in aquatic bodies (freshwater and marine) is not unusual. Cu is well known for its effect on the olfactory physiology of fish. However, there are limited studies on the effect of Cu on important ecological functions in fish (predator-prey dynamics) that are primarily influenced by olfaction. In a series of experiments, we studied the effect of Cu exposure on the chemoreceptive behavior of the prey fish, Lepidocephalichthys thermalis. Prey fishes were exposed to an environmentally relevant concentration (5 μg/L) of Cu for 3 h and the anti-predator responses against native (Channa gachua) and alien predatory fish (tilapia) were quantified using an ethological assay. Cu exposed prey fishes did not recognize the native predator and had a lower survival rate than control (unexposed) fishes in predation trials. Cu exposed prey fishes have failed to learn associatively to detect a non-native predator resulting in higher mortality in prey population in direct encounters with tilapia. However, such a lack of predator recognition was found to be short-term and the treated prey fishes recovered anti-predator responses within 72 h. In addition, Cu inactivated the alarm cue which acts as a signal for the presence of predators and ensures associative learning and therefore it was considered to be an 'info-disruptor' in the present study. These outcomes together demonstrate that even at low concentration, Cu influences ecological decisions and survival against predators. Owing to the ubiquitous occurrence of Cu in water bodies, the present investigation will contribute to the knowledge of how environmental stressors alter the crucial ecological decisions of prey individuals in aquatic ecosystems. In addition, we suggest that freshwater reservoirs containing high levels of Cu could be unsuitable for the long-term survival of prey fishes and freshwater biodiversity.

Banded tetra (Astyanax aeneus) as bioindicator of trace metals in aquatic ecosystems of the Yucatan Peninsula, Mexico: Experimental biomarkers validation and wild populations biomonitoring

Bioindicator organisms are important tools in environmental monitoring studies. Understanding this, the overall goal of the present study was to evaluate the sensitivity and viability of the native fish species Banded tetra, (Astyanax aeneus; Günther, 1860), widely spread in the aquatic ecosystems of the Yucatan Peninsula in Mexico, as a bioindicator organism. In order to do this, we performed a bioassay at sublethal concentrations using copper (CuSO₄) to experimentally evaluate and validate the relationship between the trace metals and oxidative stress biomarkers response [(catalase (CAT), lipoperoxidation content (LPO)], detoxification [(glutathione S-transferase (GST), metallothionein content (MT)] and neurotoxicity (AChE) in muscle of A. aeneus. Results showed changes in biomarkers after 96 h: Catalase activity (CAT) was significantly higher above 1.5 and 2 mg/L (154.35 and 172.50% increase, respectively); lipid peroxidation contents (TBARS), GST activity, and MT content were very similar to CAT activity at 1.5 and 2 mg/L of Cu. In terms of neurotoxicity, AChE activity was significantly inhibited at 0.1 mg/L (64%; p < 0.001) and 0.5 mg/L (44%; p < 0.001) of Cu. Based on the bioassay results, we performed a trace metal monitoring campaign in muscle of A. aeneus caught in 15 sites with different anthropogenic activities, during the summer of 2017, to establish a baseline of trace metals pollution in the state of Campeche. A. aeneus showed the highest trace metal accumulation in the following order: Al > Fe > Mn > Zn > Cu > Hg > Cr > Pb > Cd > V > As, while sites were arrange as follows: Xnoha lagoon > Palizada River > Candelaria River > Ululmal > Maravillas > López Mateos. PCA showed a cluster between biomarkers (GST, CAT, TBARS, and MT) and concentration of metals (Cd, Cu, Fe, Zn, Hg and Cr). Conversely, AChE inhibition was not related to a specific metal, but highest inhibitions (>50%) were present in those sites with intensive agricultural practices. These results determined that, based on its physiological response and trace metal bioaccumulation, Astyanax aeneus can be considered a good bioindicator for evaluating the presence of trace metals in tropical aquatic systems of the Yucatan Peninsula.

Quantifying the elemental composition of mosses in western Washington USA

Major and trace element deposition across western Washington, USA was assessed in 2016 and 2017 by analyzing tissue metal concentrations in the epiphytic mosses Isothecium stoloniferum (Bridel) and Kindbergia praelonga (Hedw.) Ochyra. We used an intensive, vertically stratified sampling approach in Acer macrophyllum canopies in the Hoh Rainforest on the Olympic Peninsula, WA and in Seattle, WA to collect 214 samples of I. stoloniferum. An extensive, ground-based sampling approach was used across an urban-to-wildland gradient to collect 59 K. praelonga samples. Intensive samples were collected four times (April, July, and October of 2016 and in January 2017) and extensive samples three times (April, July, and October 2016) to assess seasonal differences in metal concentrations across sampling locations. A total of 273 moss samples were analyzed for Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Sr, Ti, and Zn concentrations. Elevated concentrations of these elements were found in moss samples from both intensive and extensive sampling efforts across all seasons. Sampling location for both intensive and extensive sampling efforts was found to be a significant factor in determining moss metal concentrations. Metal deposition in and around Seattle appears to be derived from the regional transportation sector and other industrial sources. Ten I. stoloniferum samples from Seattle and the Hoh Rainforest were analyzed for Pb and Sr isotope ratios to help differentiate between natural and industrial-based emission sources. Hoh Rainforest Pb isotopes appear to be explained by a mixture of long-range Asian Pb influences and natural Pb sources, whereas Seattle Pb isotopes appear driven by industrial and road dust sources.

Promising Practices for Alternatives Assessment: Lessons from a Case Study of Copper-Free Antifouling Coatings

Alternatives assessment (AA) is intended to identify safer and more sustainable approaches for managing chemicals used in industrial applications and consumer products and to avoid the adoption of regrettable substitutions. In the United States, the state of Washington prescribes a science-based approach for conducting an AA that meets regulatory requirements. This paper provides an overview of the approach, based on the Interstate Chemicals Clearinghouse (IC2) AA Guide, and illustrates its application to the examination of suitable alternatives to Cu-based antifouling coatings commonly used for recreational boats in the Pacific Northwest. Legislation has been passed in Washington State that will ban the use of certain Cu-based products in both freshwater and marine environments. The AA approach was used to identify and evaluate several alternatives to Cu-based antifouling boat paint products. Five promising practices that AA practitioners should consider when using the IC2 AA Guide in similar assessments of alternatives to industrial practices and consumer products include actively engaging stakeholders, enhancing the decision framework using a selection guide approach, scoping alternatives broadly, optimizing ingredient transparency, and identifying data gaps that could interfere with substitution efforts. The role AA plays in driving consumer product and similar technology innovations and its implications for the future are discussed. Environ Assess Manag 2019;00:1-13. © 2019 SETAC.

Damsels in Distress: Oil Exposure Modifies Behavior and Olfaction in Bicolor Damselfish (Stegastes partitus)

In fishes, olfactory cues evoke behavioral responses that are crucial to survival; however, the receptors, olfactory sensory neurons, are directly exposed to the environment and are susceptible to damage from aquatic contaminants. In 2010, 4.9 million barrels of crude oil were released into the northern Gulf of Mexico from the Deepwater Horizon disaster, exposing marine organisms to this environmental contaminant. We examined the ability of bicolor damselfish (Stegastes partitus), exposed to the water accommodated fraction (WAF) of crude oil, to respond to chemical alarm cue (CAC) using a two-channel flume. Control bicolor damselfish avoided CAC in the flume choice test, whereas WAF-exposed conspecifics did not. This lack of avoidance persisted following 8 days of control water conditions. We then examined the physiological response to CAC, brine shrimp rinse, bile salt, and amino acid cues using the electro-olfactogram (EOG) technique and found that WAF-exposed bicolor damselfish were less likely to detect CAC as an olfactory cue but showed no difference in EOG amplitude or duration compared to controls. These data indicate that a sublethal WAF exposure directly modifies detection and avoidance of CAC beyond the exposure period and may suggest reduced predator avoidance behavior in oil-exposed fish in the wild.

Transcriptional Basis of Copper-Induced Olfactory Impairment in the Sea Lamprey, a Primitive Invasive Fish

Olfaction mediates behaviors necessary for survival and reproduction in fishes. Anthropogenic inputs of contaminants into aquatic environments, specifically copper, are known to disrupt a broad range of olfactory-mediated behaviors and can cause long-lasting damage even at low concentrations that have profound impacts on the biology of aquatic organisms. The sea lamprey (Petromyzon marinus) is a primitive fish species invasive to the North American Great Lakes that relies on olfaction to navigate during natal homing and in mate choice during reproduction. To investigate effects of copper on sea lamprey olfaction and the potential for maintenance of olfactory function during copper exposure, we exposed juvenile sea lamprey to environmentally ecologically relevant copper concentrations (0, 5, 10 and 30 µg/L) for 24 hr and characterized gene transcription response in olfactory tissue (i.e., peripheral olfactory organ and olfactory bulb) and forebrain using whole transcriptome sequencing. Copper exposure induced a pattern of positive dose-dependent transcriptional response. Expression changes primarily reflected up-regulation of genes involved in apoptosis and wound healing. Unlike higher vertebrates, genes specifically related to the olfactory senses of the sea lamprey, e.g., olfactory receptors, exhibited little transcriptional response to copper exposure, suggesting the mechanism of copper-induced olfactory impairment is through necrosis of the olfactory bulb and not copper-selective inhibition of olfactory receptors. Fully two-thirds of the differentially expressed genes at higher doses of copper have no known function and thus represent important candidates for further study of the responses to copper-induced olfactory injury. Our results shed light on the evolution of vertebrate olfactory repair mechanisms and have important implications for the conservation and management of both invasive and native populations of lamprey.

Elevated CO2 impairs olfactory-mediated neural and behavioral responses and gene expression in ocean-phase coho salmon (Oncorhynchus kisutch)

Elevated concentrations of CO₂ in seawater can disrupt numerous sensory systems in marine fish. This is of particular concern for Pacific salmon because they rely on olfaction during all aspects of their life including during their homing migrations from the ocean back to their natal streams. We investigated the effects of elevated seawater CO₂ on coho salmon (Oncorhynchus kisutch) olfactory-mediated behavior, neural signaling, and gene expression within the peripheral and central olfactory system. Ocean-phase coho salmon were exposed to three levels of CO₂ , ranging from those currently found in ambient marine water to projected future levels. Juvenile coho salmon exposed to elevated CO₂ levels for 2 weeks no longer avoided a skin extract odor that elicited avoidance responses in coho salmon maintained in ambient CO₂ seawater. Exposure to these elevated CO₂ levels did not alter odor signaling in the olfactory epithelium, but did induce significant changes in signaling within the olfactory bulb. RNA-Seq analysis of olfactory tissues revealed extensive disruption in expression of genes involved in neuronal signaling within the olfactory bulb of salmon exposed to elevated CO₂ , with lesser impacts on gene expression in the olfactory rosettes. The disruption in olfactory bulb gene pathways included genes associated with GABA signaling and maintenance of ion balance within bulbar neurons. Our results indicate that ocean-phase coho salmon exposed to elevated CO₂ can experience significant behavioral impairments likely driven by alteration in higher-order neural signal processing within the olfactory bulb. Our study demonstrates that anadromous fish such as salmon may share a sensitivity to rising CO₂ levels with obligate marine species suggesting a more wide-scale ecological impact of ocean acidification.

Copper toxicity in Bristol Bay headwaters: Part 2-Olfactory inhibition in low-hardness water

We investigated the olfactory toxicity of copper (Cu) to rainbow trout in low-hardness (27 mg/L as CaCO₃ ) water formulated in the laboratory over a 120-h period using a flow-through design. The fish's response to an alarm cue (e.g., reduction in activity) was recorded to determine the exposure concentrations and durations that inhibited olfactory detection of the cue after 3, 24, 48, and 96 h of Cu exposure and after 24 h of clean water recovery following the 96-h exposure period. Exposures were conducted with a range of Cu concentrations from 0.13 (control) to 7.14 μg Cu/L (dissolved Cu). We observed a dose-dependent response in olfactory inhibition with a 20% reduction in the probability of responding to the alarm cue, relative to controls, at 2.7 and 2.4 μg Cu/L after 24 or 96 h of exposure, respectively. Olfactory inhibition manifested between 3 and 24 h of exposure. Our 24- and 96-h 20% olfactory inhibition estimates fell between the criteria derived using the biotic ligand model (BLM; criterion maximum concentration [CMC] and criterion continuous concentration [CCC] values were 0.63 and 0.39 μg Cu/L, respectively) and water hardness-based criteria (CMC and CCC values were 3.9 and 2.9 μg Cu/L, respectively). Therefore, the hardness-based criteria do not appear to be protective and the BLM-derived criteria do appear to be protective against Cu-induced olfactory inhibition given our test water chemistry. Neither the hardness-based criteria nor the BLM-derived criteria appear to be protective against our estimated Cu behavioral avoidance response concentrations at 24- and 96-h exposures (0.54 and 0.50 μg Cu/L, respectively). Environ Toxicol Chem 2019;38:198-209. © 2018 SETAC.

Differential nickel-induced responses of olfactory sensory neuron populations in zebrafish

The olfactory epithelium of fish includes three main types of olfactory sensory neurons (OSNs). Whereas ciliated (cOSNs) and microvillous olfactory sensory neurons (mOSNs) are common to all vertebrates, a third, smaller group, the crypt cells, is exclusive for fish. Dissolved pollutants reach OSNs, thus resulting in impairment of the olfactory function with possible neurobehavioral damages, and nickel represents a diffuse olfactory toxicant. We studied the effects of three sublethal Ni²⁺ concentrations on the different OSN populations of zebrafish that is a widely used biological model. We applied image analysis with cell count and quantification of histochemically-detected markers of the different types of OSNs. The present study shows clear evidence of a differential responses of OSN populations to treatments. Densitometric values for G_{α olf}, a marker of cOSNs, decreased compared to control and showed a concentration-dependent effect in the ventral half of the olfactory rosette. The densitometric analysis of TRPC2, a marker of mOSNs, revealed a statistically significant reduction compared to control, smaller than the decrease for G_{α olf} and without concentration-dependent effects. After exposure, olfactory epithelium stained with anti-calretinin, a marker of c- and mOSNs, revealed a decrease in thickness while the sensory area appeared unchanged. The thickness reduction together with increased densitometric values for HuC/D, a marker of mature and immature neurons, suggests that the decrements in G_{α olf} and TRPC2 immunostaining may depend on cell death. However, reductions in the number of apical processes and of antigen expression could be a further explanation. We hypothesize that cOSNs are more sensitive than mOSNs to Ni²⁺ exposure. Difference between subpopulations of OSNs or differences in water flux throughout the olfactory cavity could account for the greater susceptibility of the OSNs located in the ventral half of the olfactory rosette. Cell count of anti-TrkA immunopositive cells reveals that Ni²⁺ exposure does not affect crypt cells. The results of this immunohistochemical study are not in line with those obtained by electro-olfactogram.

Spatial and temporal variations of nutrition in representative river networks in Southwest China

To control pollutants in rivers, we need to have an understanding of the spatial and temporal variations on nutrients and environmental processes in complex river networks. In this study, 177 sampling sites were located in Jinjiang River in 2017, 15 monitoring stations in Jinjiang River from 2011 to 2016 were also collected. According to the data from the monitoring station, the total phosphorus (TP) and total nitrogen (TN) were the dominant contaminants. By analyzing historical water quality data and up-to-date information about the nutrient concentrations, the secondary canals of the Jinjiang River system, most of which were black and odorous, were much more seriously polluted than the main channel and tributaries. Correlation analysis indicated that the NH₃, CODcr, TN, and TP had similar sources (R²_NH3-CODcr = 0.572, R²_NH3-TN = 0.543, R²_NH3-TP = 0.537, p < 0.01). The vertical banks of urban rivers and the inadequate and poorly maintained pipe network systems promote deterioration of water quality in these secondary canals. Overall, our results suggest that the river water quality could be improved if the municipal pipe network systems were better maintained and if the vertical banks were transformed into vegetated buffer strips. This study will support initiatives to improve the water quality and function of the river network ecosystem.

Effect of Deepwater Horizon Crude Oil Water Accommodated Fraction on Olfactory Function in the Atlantic Stingray, Hypanus sabinus

The Deepwater Horizon oil spill was the largest accidental marine oil spill in history, releasing nearly 5 million barrels of crude oil. Crude oil causes both lethal and sublethal effects on marine organisms, and sensory systems have the potential to be strongly affected. Marine fishes rely upon the effective functioning of their sensory systems for detection of prey, mates, and predators. However, despite the obvious importance of sensory systems, the impact of crude oil exposure upon sensory function remains largely unexplored. Here we show that olfactory organ responses to amino acids are significantly depressed in oil exposed stingrays. We found that the response magnitude of the electro-olfactogram (EOG) to 1 mM amino acids decreased by an average of 45.8% after 48 h of exposure to an oil concentration replicating that measured in coastal areas. Additionally, in oil exposed individuals, the EOG response onset was significantly slower, and the clearing time was protracted. This study is the first to employ an electrophysiological assay to demonstrate crude oil impairment of the olfactory system in a marine fish. We show that stingrays inhabiting an area impacted by an oil spill experience reduced olfactory function, which would detrimentally impact fitness, could lead to premature death, and could cause additional cascading effects through lower trophic levels.

Differential copper-induced death and regeneration of olfactory sensory neuron populations and neurobehavioral function in larval zebrafish

Fish rely heavily on their sense of smell to maintain behaviors essential for survival, such as predator detection and avoidance, prey selection, social behavior, imprinting, and homing to natal streams and spawning sites. Due to its direct contact with the outside environment, the peripheral olfactory system of fish is particularly susceptible to dissolved contaminants. In particular, environmental exposures to copper (Cu) can cause a rapid loss of olfactory function. In this study, confocal imaging of double-transgenic zebrafish larvae with differentially labeled ciliated and microvillous olfactory sensory neurons (OSNs) were used to examine cell death and regeneration following Cu exposure. Changes in cell morphologies were observed at varying degrees within both ciliated and microvillous OSNs, including the presence of round dense cell bodies, cell loss and fragmentation, retraction or loss of axons, disorganized cell arrangements, and loss of cells and fluorescence signal intensity, which are all indicators of cell death after Cu exposure. A marked loss of ciliated OSNs relative to microvillous OSNs occurred after exposure to low Cu concentrations for 3 h, with some regeneration observed after 72 h. At higher Cu concentrations and 24-h exposures, ciliated and microvillous OSNs were damaged with increased severity of injury with longer Cu exposures. Interestingly, microvillous, but not ciliated OSNs, regenerated rapidly within the 72-h time period of recovery after death from Cu exposure, suggesting that microvillous OSNs may be replaced in lieu of ciliated OSNs. An increase in bromodeoxyuridine labeling was observed 24 h after Cu-induced OSN death, suggesting that increased proliferation of the olfactory stem cells replaced the damaged OSNs. Olfactory behavioral analyses supported our imaging studies and revealed both initial loss and restoration of olfactory function after Cu exposures. In summary, our studies indicate that following zebrafish OSN damage by Cu, regeneration of microvillous OSNs may occur exceeding ciliated OSNs, likely via increased proliferation of the cellular reservoir of neuronal OSC precursors. Transgenic zebrafish are a valuable tool to study metal olfactory injury and recovery and to characterize sensitive olfactory neuron populations in fish exposed to environmental pollutants.

Delayed effects and complex life cycles: How the larval aquatic environment influences terrestrial performance and survival

Species with complex life cycles are susceptible to environmental stressors across life stages, but the carryover and latent effects between stages remain understudied. For species with biphasic life histories, such as pond-breeding amphibians, delayed effects of aquatic conditions can influence terrestrial juveniles and adults directly or indirectly, usually mediated through fitness correlates such as body size. We collected adult southern toads (Anaxyrus terrestris) from 2 source populations-a natural reference wetland and a metal-contaminated industrial wetland-and exposed their offspring to 2 aquatic stressors (a metal contaminant, copper [Cu], and a dragonfly predator cue) in outdoor mesocosms (n = 24). We then reared metamorphs in terraria for 5 mo to examine delayed effects of early life stage environmental conditions on juvenile performance, growth, and survival. Larval exposure to Cu, as well as having parents from a contaminated wetland, resulted in smaller size at metamorphosis-a response later negated by compensatory growth. Although Cu exposure and parental source did not affect larval survival, we observed latent effects of these stressors on juvenile survival, with elevated Cu conditions and metal-contaminated parents reducing postmetamorphic survival. Parental source and larval Cu exposure affected performance at metamorphosis through carryover effects on body size but, 1 mo later, latent effects of parental source and larval predator exposure directly (i.e., not via body size) influenced performance. The carryover and latent effects of parental source population and aquatic Cu level on postmetamorphic survival and juvenile performance highlight the importance of conducting studies across life stages and generations. Environ Toxicol Chem 2018;37:2660-2669. © 2018 SETAC.

Responses of biomarkers in Atlantic salmon (Salmo salar) following exposure to environmentally relevant concentrations of complex metal mixture (Zn, Cu, Ni, Cr, Pb, Cd). Part II

The aim of this research was to assess interactions between metals at low exposure concentrations (Maximum-Permissible-Concentrations accepted for the inland waters in EU) and to assess possible influence of background exposure (10-times reduced concentration of a single metal) on toxicological significance of selected biomarkers in Salmo salar after treatment with metal mixture (Zn - 0.1, Cu - 0.01, Ni - 0.01, Cr - 0.01, Pb - 0.005 and Cd - 0.005 mg/L). The tissue-specific bioaccumulation, genotoxicity and cytotoxicity responses (erythrocytic nuclear abnormalities assay) in peripheral blood, kidneys, gills and liver erythrocytes of fish to metal mixtures were assessed after 14 days treatment. Treatment with primary mixture (MIX) or two variants of this mixture (Cr↓ (10 times reduced Cr⁶⁺ concentration) and Cu↓ (10 times reduced Cu²⁺ concentration)) induced the strongest responses in genotoxicity and cytotoxicity endpoints. Exposure to these mixtures highly affected Zn, Cu and Cd bioaccumulation in liver tissue. The highest amount of Ni accumulated was measured after Cd↓ treatment in all tissues. Treatments with reduced concentration of non-essential metal resulted in an increased accumulation of Pb, Ni, or Cd; treatments with reduced concentration of essential metal resulted in a reduced accumulation of certain metals (especially Cd and Pb) in tissues compared between treatments. Glucose content in blood and behavioural endpoints were evaluated after short-term exposure to metal mixtures (MIX, Cr↓, Cu↓). Significant increase in blood glucose concentration was measured after all treatments. These metal mixtures elicit significant behavioural alterations in fish. Consequently, this research revealed a significant influence of background exposure considering mixture toxicity.

Contribution of particulate matter in storm runoff to organic phosphorus loads in urban rivers

To help us control pollution caused by urban runoff, we need to understand how particulate matter in storm runoff contributes to the total pollutant load. In this study, we collected samples from ten sites along on the banks of an urban river during five rainfall events. We determined the grain size and phosphorus (P) forms in the particulate matter to assess how much P there was in storm runoff. The results showed that the particles were mostly medium-sized, and particles with a diameter of less than 850 μm but greater than 150 μm accounted for 50% of the total particulate matter. The average particulate P concentration, at 298.7 mg/kg, was high and was mostly organic P (Po), which had an average concentration of 134.64 mg/kg. The concentrations of the different P forms varied with particle size. The main fraction in the large-sized grains was acid-extractable inorganic P (Pi), while Po and alkalinity-extractable Pi dominated in medium- and small-sized particles. Overall, our results illustrate that, by enhancing the control of particulate matter in storm runoff, P, and in particular Po, inputs to urban rivers can be reduced.

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.

Historical legacies of river pollution reconstructed from fish scales

Many rivers have been impacted by heavy metal pollution in the past but the long-term legacies on biodiversity are difficult to estimate. The River Ulla (NW Spain) was impacted by tailings from a copper mine during the 1970-1980s but absence of baseline values and lack of subsequent monitoring have prevented a full impact assessment. We used archived fish scales of Atlantic salmon to reconstruct levels of historical copper pollution and its effects on salmon fitness. Copper bioaccumulation significantly increased over baseline values during the operation of the mine, reaching sublethal levels for salmon survival. Juvenile growth and relative population abundance decreased during mining, but no such effects were observed in a neighbouring river unaffected by mining. Our results indicate that historical copper exposure has probably compromised the fitness of this Atlantic salmon population to the present day, and that fish scales are suitable biomarkers of past river pollution.

Reuse water: Exposure duration, seasonality and treatment affect tissue responses in a model fish

Partially remediated gray (reuse) water will likely find increasing use in a variety of applications owing to the increasing scarcity of freshwater. We aimed to determine if a model fish, the goldfish, could sense reuse water using olfaction (smell), and if 30min or 7d (acute) and 60d (sub-chronic) exposures would affect their olfactory responses to natural odorants. We examined olfaction as previous studies have found that numerous chemicals can impair the olfactory sense, which is critical to carrying out numerous life-sustaining behaviors from feeding to mating. We also examined if fish olfactory and liver tissues would mount a response in terms of biotransformation enzyme gene expression, and whether treatment of reuse water with UV/H₂O₂ ameliorated adverse effects following reuse water exposure. We found that fish olfactory tissue responded to reuse water as it would to a natural odorant and that UV/H₂O₂ treatment had no influence on this. With acute exposures, olfactory impairment was apparent regardless of water type (e.g. responses of 23-55% of control), but in sub-chronic exposures, only the untreated reuse water caused olfactory impairment. The exposure of fish to reuse water increased the expression of one enzyme (CYP1A; >2.5-6.5 fold change) and reuse water treatment with UV/H₂O₂ reversed the effect. There was a seasonal effect that was likely due to changes in water quality (60d summer exposure impaired olfaction whereas spring and fall exposures did not). Overall, the data suggest that reuse water may be detected by olfaction, impair olfactory responses in fish receiving unavoidable exposures, and that exposure duration and season are important factors to consider regarding adverse effects.

Differential response of olfactory sensory neuron populations to copper ion exposure in zebrafish

The peripheral olfactory system of fish is in direct contact with the external aqueous environment, so dissolved contaminants can easily impair sensory functions and cause neurobehavioral injuries. The olfactory epithelium of fish is arranged in lamellae forming a rosette in the olfactory cavity and contains three main types of olfactory sensory neurons (OSNs): ciliated (cOSNs) and microvillous olfactory sensory neurons (mOSNs), common to all vertebrates, and a third minor group of olfactory neurons, crypt cells, absent in tetrapods. Since copper is a ubiquitously diffusing olfactory toxicant and a spreading contaminant in urban runoff, we investigated the effect of low copper concentration on the three different OSNs in the olfactory epithelium of zebrafish, a model system widely used in biological research. Image analysis was applied for morphometry and quantification of immunohistochemically detected OSNs. Copper exposure resulted in an evident decrease in olfactory epithelium thickness. Moreover, after exposure, the lamellae of the dorsal and ventral halves of the olfactory rosettes showed a different increase in their sensory areas, suggesting a lateral migration of new cells into non-sensory regions. The results of the present study provide clear evidence of a differential response of the three neural cell populations of zebrafish olfactory mucosa after 96h of exposure to copper ions at the sublethal concentration of 30μgL^-1. Densitometric values of cONS, immunostained with anti-G _αolf, decreased of about 60% compared to the control. When the fish were transferred to water without copper addition and examined after 3, 10 and 30days, we observed a partial restoration of anti-G _αolf staining intensity to normal condition. The recovery of cOSNs appeared sustained by neuronal proliferation, quantified with anti-PCNA immunostaining, in particular in the early days after exposure. The densitometric analysis applied to mOSNs, immunostained with anti-TRPC2, revealed a statistically significant decrease of about 30% compared to the control. For cOSNs and mOSNs, the decrement in staining intensity may be indicative of cell death, but reduction in antigen expression may not be excluded. In the post-exposure period of 1 month we did not find recovery of mOSNs. We hypothesize that cOSNs are more sensitive than mOSNs to copper treatment, but also more prompted to tissue repair. Anti-TrkA-immunopositive crypt cells appeared not to be affected by copper exposure since statistical analysis excluded any significant difference between the control and treated fish. Comparative studies on OSNs would greatly enhance our understanding of the mechanisms of olfaction.

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.

Smell no evil: Copper disrupts the alarm chemical response in a diadromous fish, Galaxias maculatus

Fish, at all life stages, utilize olfactory information in the decision-making processes essential to survival. Olfaction is a sensitive sensory process, and toxicants within urban aquatic environments can have destructive or depreciating effects. In the present study, the authors exposed Galaxias maculatus, a native fish commonly found in urban waterways throughout southeastern Australia, to 1 of 5 ecologically relevant copper (II) chloride concentrations (<1 μg/L, 1 μg/L, 6 μg/L, 8 μg/L, 18 μg/L) for 16 h. After exposure, the authors tested the response of individual fish to 1 of 3 stimuli: a conspecific skin extract containing a stress-inducing alarm chemical odor, a conspecific odor, and distilled water as a control. Stress responses were quantified through behavioral assays. The authors found evidence for distinct changes in behavioral response with increasing copper concentration and a marked difference in response between control fish and fish exposed to the alarm chemical odor. Copper, even at relatively low concentrations, can have a significant effect on the stress response behavior shown by G. maculatus. Environ Toxicol Chem 2016;35:2209-2214. © 2016 SETAC.

Effects of metal and predator stressors in larval southern toads (Anaxyrus terrestris)

Natural and anthropogenic stressors typically do not occur in isolation; therefore, understanding ecological risk of contaminant exposure should account for potential interactions of multiple stressors. Realistically, common contaminants can also occur chronically in the environment. Because parental exposure to stressors may cause transgenerational effects on offspring, affecting their ability to cope with the same or novel environmental stressors, the exposure histories of generations preceding that being tested should be considered. To examine multiple stressor and parental exposure effects we employed a 2 × 2 × 2 factorial design in outdoor 1000-L mesocosms (n = 24). Larval southern toads (Anaxyrus terrestris), bred from parents collected from reference and metal-contaminated sites, were exposed to two levels of both an anthropogenic (copper-0, 30 µg/L Cu) and natural (predator cue - present/absent) stressor and reared to metamorphosis. Toads from the metal-contaminated parental source population were smaller at metamorphosis and had delayed development; i.e., a prolonged larval period. Similarly, larval Cu exposure also reduced size at metamorphosis and prolonged the larval period. We, additionally, observed a significant interaction between larval Cu and predator-cue exposure on larval period, wherein delayed emergence was only present in the 30-µg/L Cu treatments in the absence of predator cues. The presence of parental effects as well as an interaction between aquatic stressors on commonly measured endpoints highlight the importance of conducting multistressor studies across generations to obtain data that are more relevant to field conditions in order to determine population-level effects of contaminant exposure.

Copper at low levels impairs memory of adult zebrafish (Danio rerio) and affects swimming performance of larvae

Metal contamination at low levels is an important issue because it usually produces health and environmental effects, either positive or deleterious. Contamination of surface waters with copper (Cu) is a worldwide event, usually originated by mining, agricultural, industrial, commercial, and residential activities. Water quality criteria for Cu are variable among countries but allowed limits are generally in the μg/L range, which can disrupt several functions in the early life-stages of fish species. Behavioral and biochemical alterations after Cu exposure have also been described at concentrations close to the allowed limits. Aiming to search for the effects of Cu in the range of the allowed limits, larvae and adult zebrafish (Danio rerio) were exposed to different concentrations of dissolved Cu (nominally: 0, 5, 9, 20 and 60μg/L; measured: 0.4, 5.7, 7.2 16.6 and 42.3μg/L, respectively) for 96h. Larvae swimming and body length, and adult behavior and biochemical biomarkers (activity of glutathione-related enzymes in gills, muscle, and brain) were assessed after Cu exposure. Several effects were observed in fish exposed to 9μg/L nominal Cu, including increased larvae swimming distance and velocity, abolishment of adult inhibitory avoidance memory, and decreased glutathione S-transferase (GST) activity in gills of adult fish. At the highest Cu concentration tested (nominally: 60μg/L), body length of larvae, spatial memory of adults, and gill GST activity were decreased. Social behavior (aggressiveness and conspecific interaction), and glutathione reductase (GR) activity were not affected in adult zebrafish. Exposure to Cu, at concentrations close to the water quality criteria for this metal in fresh water, was able to alter larvae swimming performance and to induce detrimental effects on the behavior of adult zebrafish, thus indicating the need for further studies to reevaluate the currently allowed limits for Cu in fresh water.

Chemical avoidance responses of fishes

The hydrosphere is a repository for all of our waste and mistakes, be they sewage, garbage, process-affected waters, runoff, and gases. For fish living in environments receiving undesirable inputs, moving away seems an obvious way to avoid harm. While this should occur, there are numerous examples where it will not. The inability to avoid harmful environments may lead to sensory impairments that in turn limit the ability to avoid other dangers or locate benefits. For avoidance to occur, the danger must first be perceived, which may not happen if the fish is 'blinded' in some capacity. Second, the danger must be recognized for what it is, which may also not happen if the fish is cognitively confused or impaired. Third, it is possible that the fish may not be able to leave the area, or worse, learns to prefer a toxic environment. Concerning generating regulations around avoidance, there are two possibilities: that an avoidance threshold be used to set guidelines for effluent release with the intention of driving fishes away; the second is to set a contaminant concentration that would not affect the avoidance or attraction responses to other cues. With the complexities of the modern world in which we release diverse pollutants, from light to municipal effluents full of 1000s of chemicals, to the diversity present in ecosystems, it is impossible to have avoidance data on every stimulus-species combination. Nevertheless, we may be able to use existing avoidance response data to predict the likelihood of avoidance of untested stimuli. Where we cannot, this review includes a framework that can be used to direct new research. This review is intended to collate existing avoidance response data, provide a framework for making decisions in the absence of data, and suggest studies that would facilitate the prediction of risk to fish health in environments receiving intentional and unintentional human-based chemical inputs.

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.

Confirmation of Stormwater Bioretention Treatment Effectiveness Using Molecular Indicators of Cardiovascular Toxicity in Developing Fish

Urban stormwater runoff is a globally significant threat to the ecological integrity of aquatic habitats. Green stormwater infrastructure methods such as bioretention are increasingly used to improve water quality by filtering chemical contaminants that may be harmful to fish and other species. Ubiquitous examples of toxics in runoff from highways and other impervious surfaces include polycyclic aromatic hydrocarbons (PAHs). Certain PAHs are known to cause functional and structural defects in developing fish hearts. Therefore, abnormal heart development in fish can be a sensitive measure of clean water technology effectiveness. Here we use the zebrafish experimental model to assess the effects of untreated runoff on the expression of genes that are classically responsive to contaminant exposures, as well as heart-related genes that may underpin the familiar cardiotoxicity phenotype. Further, we assess the effectiveness of soil bioretention for treating runoff, as measured by prevention of both visible cardiac toxicity and corresponding gene regulation. We find that contaminants in the dissolved phase of runoff (e.g., PAHs) are cardiotoxic and that soil bioretention protects against these harmful effects. Molecular markers were more sensitive than visible toxicity indicators, and several cardiac-related genes show promise as novel tools for evaluating the effectiveness of evolving stormwater mitigation strategies.

Methods for evaluating the pollution impact of urban wet weather discharges on biocenosis: A review

Rainwater becomes loaded with a large number of pollutants when in contact with the atmosphere and urban surfaces. These pollutants (such as metals, pesticides, PAHs, PCBs) reduce the quality of water bodies. As it is now acknowledged that physico-chemical analyses alone are insufficient for identifying an ecological impact, these analyses are frequently completed or replaced by impact studies communities living in freshwater ecosystems (requiring biological indices), ecotoxicological studies, etc. Thus, different monitoring strategies have been developed over recent decades aimed at evaluating the impact of the pollution brought by urban wet weather discharges on the biocenosis of receiving aquatic ecosystems. The purpose of this review is to establish a synthetic and critical view of these different methods used, to define their advantages and disadvantages, and to provide recommendations for futures researches. Although studies on aquatic communities are used efficiently, notably on benthic macroinvertebrates, they are difficult to interpret. In addition, despite the fact that certain bioassays lack representativeness, the literature at present appears meagre regarding ecotoxicological studies conducted in situ. However, new tools for studying urban wet weather discharges have emerged, namely biosensors. The advantages of biosensors are that they allow monitoring the impact of discharges in situ and continuously. However, only one study on this subject has been identified so far, making it necessary to perform further research in this direction.

Present knowledge and perspectives on the role of copper in brake materials and related environmental issues: A critical assessment

This critical review presents several aspects related to the use of copper as a main component in brake pads in road vehicles. The compositions of these materials are attracting increasing interest and concern due to the relative contribution of wear products to particulate matter emissions in the environment as a result of braking action even though there has been a reduction in exhaust products from internal combustion engines. We review the data on the main wear mechanisms in brake systems and highlight the positive role of copper. However, similar to other heavy metal emissions, even the release of copper into the atmosphere may have important environmental and health effects. Thus, several replacement strategies are being pursued, and the positive and negative features will be critically reviewed. Additionally, the future perspectives in materials development will be discussed.

Coho salmon spawner mortality in western US urban watersheds: bioinfiltration prevents lethal storm water impacts

Adult coho salmon Oncorhynchus kisutch return each autumn to freshwater spawning habitats throughout western North America. The migration coincides with increasing seasonal rainfall, which in turn increases storm water run-off, particularly in urban watersheds with extensive impervious land cover. Previous field assessments in urban stream networks have shown that adult coho are dying prematurely at high rates (>50%). Despite significant management concerns for the long-term conservation of threatened wild coho populations, a causal role for toxic run-off in the mortality syndrome has not been demonstrated.We exposed otherwise healthy coho spawners to: (i) artificial storm water containing mixtures of metals and petroleum hydrocarbons, at or above concentrations previously measured in urban run-off; (ii) undiluted storm water collected from a high traffic volume urban arterial road (i.e. highway run-off); and (iii) highway run-off that was first pre-treated via bioinfiltration through experimental soil columns to remove pollutants.We find that mixtures of metals and petroleum hydrocarbons - conventional toxic constituents in urban storm water - are not sufficient to cause the spawner mortality syndrome. By contrast, untreated highway run-off collected during nine distinct storm events was universally lethal to adult coho relative to unexposed controls. Lastly, the mortality syndrome was prevented when highway run-off was pretreated by soil infiltration, a conventional green storm water infrastructure technology.Our results are the first direct evidence that: (i) toxic run-off is killing adult coho in urban watersheds, and (ii) inexpensive mitigation measures can improve water quality and promote salmon survival. Synthesis and applications. Coho salmon, an iconic species with exceptional economic and cultural significance, are an ecological sentinel for the harmful effects of untreated urban run-off. Wild coho populations cannot withstand the high rates of mortality that are now regularly occurring in urban spawning habitats. Green storm water infrastructure or similar pollution prevention methods should be incorporated to the maximal extent practicable, at the watershed scale, for all future development and redevelopment projects, particularly those involving transportation infrastructure.

Fine-scale chemical exposure differs in point and nonpoint source plumes

Increasing influxes of anthropogenic chemicals into aquatic ecosystems has led to growing global concern surrounding human and ecosystem health. As more freshwater systems are deemed not potable or usable for agricultural purposes, more attention is being paid to remediation and mitigation efforts. Predicting and preventing the impacts of the chemical inputs first requires a thorough understanding of the spatio-temporal distribution of chemical plumes in natural habitats. Plume dispersion is intimately tied to fluid mechanics; therefore, alterations in the way that chemical plumes are introduced to habitats can have profound effects on chemical distribution. Such alterations can subsequently alter the exposure to which organisms are subjected. This study examined the influence of point versus nonpoint sources in structuring the distribution of chemicals in a simulated flowing freshwater habitat. The fine-scale (molecular) spatio-temporal distribution of chemicals was measured in situ using an electrochemical detector. Molecular concentration at varying distance and height from the source was quantified using dopamine coupled with an electrochemical detection system. The fine-scale distribution of chemical plumes from point and nonpoint sources showed significant differences in how organisms will be exposed to chemicals. Overall, this study characterized plumes from nonpoint sources as having significantly longer peak lengths and rise times as well as greater peak heights and maximum slopes than plumes from point sources, thus providing a significantly different exposure paradigm. This quantification of how chemicals move differently throughout a fluid medium when introduced from point and nonpoint sources allows a greater understanding of how chemical plumes can potentially affect aquatic ecosystems.

Sublethal copper toxicity impairs chemical orientation in the crayfish, Orconectes rusticus

Before reaching concentrations that are high enough to cause mortality, elevated levels of chemical pollution can significantly alter a keystone indicator species' ability to extract sensory information. To organisms that rely on chemical signals to make crucial ecological decisions, increased amounts of a pollutant may impact chemoreceptive abilities by altering the perception of the sensory landscape or impairing the functioning of sensory organs. Heavy metal pollutants entering an aquatic ecosystem are of increasing concern due to discernible effects on chemoreception in many ecologically and economically important species. In order to determine the effects of sublethal copper toxicity on chemically mediated behavior, male and female rusty crayfish, Orconectes rusticus, were exposed to ecologically relevant concentrations of copper (4.5, 45, and 450 µg/l) for 120 h. Following exposure, crayfish were allowed to orient toward a food odor stimulus. During orientation trials, select crayfish oriented under a point or nonpoint source copper background pollutant at the same concentration as the exposure period. Orientation trials were videotaped and analyzed using EthoVision XT 8.5 (Noldus Information Technology, The Netherlands) for differences in overall success in locating the food source and orienting parameters. Significant differences were found in the overall orientation ability of O. rusticus to locate an odor source when previously exposed to copper in combination with a source of pollution in the background of orientation trials. Crayfish exposed to copper in any capacity during the experiment (regardless of concentration or background during trials) showed slower walking speeds toward the source, decreased turning angles, increased heading angles toward the source, and decreased upstream heading angles. Results from this experiment support that copper impairs the ability of crayfish to detect, process, and/or respond appropriately to chemosensory information in order to successfully localize a food odor source.

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.

Impaired behavioural response to alarm substance in rainbow trout exposed to copper nanoparticles

To date, studies of the toxicity of engineered nanoparticles (NPs) in fish have not fully considered effects on olfactory-mediated behaviours, despite their ecological importance. In this study the effects of copper NPs (Cu NPs) on the anti-predator behavioural responses of juvenile rainbow trout (Oncorhynchus mykiss) to trout alarm substance was investigated. Individual fish were exposed for 12h to a control (no added Cu), 50μgl(-1) of Cu as Cu NPs, or 50μgl(-1) Cu as CuSO4, after which fish behaviours were analyzed in 10min periods before and after the addition of the alarm substance stimulus. The response of control fish to deionised water (negative control, no alarm substance stimulus) was also analyzed. The alarm substance elicited a behavioural response in the control fish characterized by an immediate freeze response and the slower resumption of swimming activity compared to negative controls exposed to the sham deionised water stimuli. In fish exposed to Cu NPs, the behavioural response to alarm substance was eliminated, with no significant difference in behaviours compared to negative controls. In comparison, exposure to 50μgl(-1) Cu as CuSO4 decreased, but did not eliminate the response of fish to alarm substance, which indicated a significantly greater effect of Cu NPs on olfactory mediated behaviours than of the equivalent concentration of Cu as CuSO4. Measurement of total Cu concentrations in the tissues of fish demonstrated no significant accumulation of Cu from any treatment in gill, liver or brain, confirming the effects of Cu NPs, and to a lesser extent CuSO4, on behavioural responses were mostly associated with the interaction of the materials with the external surfaces of the fish. Scanning electron microscopy revealed that Cu as CuSO4 caused a pronounced depletion of ciliated sensory and non-sensory cells in the olfactory rosette surrounding the midline raphe, whereas Cu NPs had no impact on the structure of the rosette. However, exposure to Cu NPs caused a significant increase in the ratio of oxidized to reduced glutathione in brains of fish, indicating some systemic oxidative stress that was not observed in either controls or fish exposed to CuSO4. Overall, the study showed that the olfactory mediated behaviours of fish were potentially more sensitive to Cu NPs than CuSO4 and NPs elicited effects via a mechanism that is distinct from that of the metal salt.

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.