Chemical avoidance responses of fishes

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

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

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.

Wastewater plumes can act as non-physical barriers for migrating silver eel

Non-physical barriers for migrating fish, such as effluent plumes discharged by sewage treatment plants (WWTPs), are hardly considered, and field studies on this topic are very scarce. The encounter with these plumes however may evoke behavioural responses in fish and could delay or (partially) block the migration. In this study, the behavioural responses of 40 acoustically-tagged silver eel (Anguilla anguilla) were monitored in situ, when confronting a WWTP effluent plume during their downstream migration in the canal Eems, the Netherlands. Their behavioural responses and the potential blocking effect of the plume were assessed using a 2D and 3D telemetry design displayed in the waterway, and matched to a modelled and calibrated WWTP effluent plume. When confronted with the WWTP effluent plume during their downstream migration, 22 of the silver eels (59%) showed an avoidance response, varying from lateral diverting to multiple turning in the vicinity of the effluent plume. Nineteen out of these 22 (86%) eventually passed the study site. No silver eel showed attraction to the plume. Delays in migration were from several hours up to several days. Due to the strong variation in discharged volumes and flow velocity of the receiving canal, the WWTP plume did not always flow over the full width of the canal. As a result, numerous migratory windows, where silver eels could pass the WWTP while avoiding direct contact with the plume, remained available in time. When discharge points cannot be avoided, reduced or restricted to areas that are not preferred as fish migration routes, discharge points should be designed such, that the chance is limited that a waterway is (temporarily) impacted over its full width.

Fear generalization and behavioral responses to multiple dangers

Animals often exhibit consistent-individual differences (CIDs) in boldness/fearfulness, typically studied in the context of predation risk. We focus here on fear generalization, where fear of one danger (e.g., predators) is correlated with fear of other dangers (e.g., humans, pathogens, moving vehicles, or fire). We discuss why fear generalization should be ecologically important, and why we expect fear to correlate across disparate dangers. CIDs in fear are well studied for some dangers in some taxa (e.g., human fear of pathogens), but not well studied for most dangers. Fear of some dangers has been found to correlate with general fearfulness, but some cases where we might expect correlated fears (e.g., between fear of humans, familiar predators, and exotic predators) are surprisingly understudied.

Avoidance responses by Danio rerio reveal interactive effects of warming, pesticides and their mixtures

Temperature variations and thermal extremes events caused by climate change can have profound implications for the toxicity of pesticides in aquatic organisms. Using an innovative system (Heterogeneous Multi-Habitat Test System - HeMHAS) that allows the simulation of different scenarios within a spatially heterogeneous landscape, the effects on the habitat selection of Danio rerio fish caused by the pesticides fipronil and 2,4-D were studied as single compounds and in mixture and integrated with air temperature variation (20, 24 and 28 °C). As a result, D. rerio detected and avoided both pesticides at air temperatures of 20 and 24 °C; however, at 28 °C no significant difference was observed in habitat choice by fish. Additionally, when pesticides were mixed in a heterogeneously contaminated landscape, it was observed that D. rerio detected contamination and preferred the clean zone at 20 and 24 °C; however, at 28 °C the potential to escape from the most contaminated areas was impaired. Thus, contamination by both pesticides made the habitat selection behavior of fish at 20 and 24 °C more noticeable. In addition, the association between pesticides and temperature showed negative effects on the response of fish to detect and escape from contaminated environments, suggesting the influence of temperature in altering the ability of the organism to provide an efficient response to stress.

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.

Combined effects of abamectin and temperature on the physiology and behavior of male lizards (Eremias argus): Clarifying adaptation and maladaptation

Chemical pollution and global warming are two major threats to organisms, which can interact to affect the normal activities of living beings. In this study, to explore the effects of abamectin and high temperature on adaptability of lizard, male adult Eremias argus (a native Chinese lizard) were exposed to environmentally relevant concentrations of abamectin (0.02 mg·L^-1 and 2 mg·L^-1) and different temperature (26 °C and 32 °C) for 30 days. The fitness-related behaviors (locomotion, predation, and thermoregulation) of lizards were evaluated. Physiological effects were addressed using biochemical biomarkers related to oxidative stress, detoxification, and neurotransmitter content. The results showed that abamectin could affect the neurotransmitter systems, cause oxidative stress, and alters lizard locomotion and predation-related behaviors of lizards, but lizards up-regulating detoxification metabolic enzymes, exhibiting higher body temperature preference to alleviate the toxicity of abamectin, and compensate the increased energy demand for detoxification and repair damage by increasing food intake. After exposure to high temperature, lizards showed adaptation to high temperature (higher body temperature preference), the thermal compensation mechanisms may involve elevated Hsp70 levels and increased food intake. At the combined effects of abamectin and high temperature, more obvious behavioral disorders and more severe oxidative stress were observed, although lizards avoided the negative effects of overheating and pollutants by seeking thermal shelter and reducing energy expenditure, this may subsequently reduce foraging opportunities and the ability to obtain energy needed for vital physiological functions (i.e., growth, maintenance, and reproduction). From a long-term perspective, these short-term adaptive strategies will be detrimental to individual long-term survival and population sustainability, and may transformed into maladaptation.

Humane acute testing with tadpoles for risk assessment of chemicals: Avoidance instead of lethality

In spite of the sensitivity of amphibians to contamination, data from fish have been commonly used to predict the effects of chemicals on aquatic life stages. However, recent studies have highlighted that toxicity data derived from fish species may not protect all the aquatic life stages of amphibians. For pesticide toxicity assessment (PTA), EFSA has highlighted that more information on lethal toxicity for the aquatic life stages of amphibians is still needed to reduce uncertainties. The current review aims to propose a test with amphibians based on spatial avoidance, as a more humane alternative method to the lethality tests for chemicals. A review of lethal toxicity tests carried out with amphibians in the period between 2018 and 2021 is presented, then we discuss the suitability of using fish toxicity data as a surrogate to predict the effects on more sensitive amphibian groups. The possible differences in sensitivity to chemicals may justify the need to develop further tests with amphibian embryos and larvae in order to reduce uncertainties. A new test is proposed focused on the avoidance behaviour of organisms fleeing from contamination to replace lethal tests. As avoidance indicates the threshold at which organisms will flee from contamination, a reduction in the population density, or its disappearance, at the local scale due to emigration is expected, with ecological consequences analogous to mortality. Avoidance tests provide an ethical advantage over lethal tests as they respect the concepts of the 3 Rs (mainly Refinement), reducing the suffering of the organisms.

Trace metal elements and organic contaminants are differently related to the growth and body condition of wild European sea bass juveniles

Chemical contaminants are one of the causes of the ongoing degradation of coastal and estuarine nurseries, key functional habitats in which the juveniles of many marine species grow. As chemical contaminants can cause a decrease in the energy available and induce defence mechanisms reducing the amount of energy allocated to life history traits, quantifying their effect on the fitness of juvenile fish is key to understand their population-level consequences. However, these effects are primarily estimated experimentally or in the wild but on a limited number of contaminants or congeners that do not reflect the wide variety of chemical contaminants to which juvenile fish are exposed. To address this issue, we measured concentrations of 14 trace metal elements (TMEs) and bioaccumulative organic contaminants (OCs) in European sea bass juveniles (1-year-old) from three major French nurseries (Seine, Loire and Gironde estuaries). We tested the hypotheses that (i) levels and profiles of contaminants differed among studied nurseries, and ii) fish growth and body condition (based on morphometric measurements and muscle C:N ratio) were lower in individuals with higher contaminant concentrations. Multivariate analyses showed that each nursery had distinct contaminant profiles for both TMEs and OCs, confirming the specific contamination of each estuary, and the large array of contaminants accumulated by sea bass juveniles. Increasing concentrations in some TMEs were associated to decreased growth, and TMEs were consistently related to lower fish body condition. The effect of OCs was more difficult to pinpoint possibly due to operational constraints (i.e., analyses on pooled fish) with contrasting results (i.e., higher growth and decreased body condition). Overall, this study shows that chemical contaminants are related to lower fish growth and body condition at an early life stage in the wild, an effect that can have major consequences if sustained in subsequent ages and associated with a decline in survival and/or reproductive success.

Dichlorvos and Paraquat induced avoidance responses in tadpoles (Amietophrynus regularis reuss, 1833) and their contribution to population decline

Pesticides notwithstanding their benefits in agriculture pose threats to non-target fauna such as amphibians. This study examined the avoidance responses of tadpoles of the African common toad, <i>Amietophrynus regularis</i>, exposed to Dichlorvos and Paraquat under a non-forced multi-compartmented exposure system (NFS) and estimated the Population Immediate Decline (PID) by integrating avoidance and lethal responses. The NFS was designed to allow the free movement of tadpoles across six compartments in order to elucidate the ability of aquatic organisms to detect and potentially avoid contaminated environments at will. The tadpoles (n=3 per compartment/concentration; 18 per system) were exposed to gradients of Dichlorvos (0, 0.3, 0.5, 0.7, 1.0 and 2.0 mg/L) and Paraquat (0, 1.0, 5.0, 10.0, 15.0, and 20.0 mg/L) in quadruplicates with their distribution recorded every 20 mins for 3 h. 48 h acute toxicity tests under forced exposure system (FS) was performed using the same range of concentrations. Acute toxicity (48 h) response in the FS tests was dose dependent with LC₅₀ values of 0.79 mg/L and 6.46 mg/L recorded for Dichlorvos and Paraquat, respectively. The mean percentage distribution of tadpoles recorded for Dichlorvos and Paraquat was about 11% and 0% in the highest concentrations (2.0 and 20.0 mg/L) to 58% and 69% in compartments with no contaminants (control), respectively. PID was primarily driven by avoidance responses rather than mortality. These findings are of conservation interest as it elucidates the potential of both pesticides to impair local distribution of amphibians and cause biodiversity loss.

Are habitable clean areas in heterogeneously contaminated landscapes functioning as escape zones for fish populations to alleviate stress?

Environmental contamination is a problem that reduces the quality of ecosystems and may make them unsuitable to accommodate life. As many ecosystems are connected, some organisms avoid the stress from continuous exposure to contaminants by moving towards less disturbed areas. However, the landscapes in which organisms move might vary regarding the concentrations of contaminants, in the form of gradients or patches of contamination. Therefore, although it is expected that organisms prefer clean areas, their sporadic contact with contamination should not be ignored, as the greater the probability of being in contact with contaminated areas, the higher the stress. The aim of this study was to assess how the stress (cortisol levels) of zebrafish (Danio rerio) varies as a consequence of heterogeneity in the chemical composition of the habitats and the presence of uncontaminated areas in this heterogeneous landscape. Zebrafish were exposed to heterogeneous contamination scenarios containing different concentrations of copper along a free-choice multi-compartmented system, in which they were able to flee from the most contaminated areas. Fish escaped from the most contaminated areas with an avoidance by 50% of population (AC₅₀) at concentrations of 41 (copper gradient scenario), 25 (spatially limited contamination scenario) and 69 (highly contaminated scenario) μg/L. Higher cortisol levels were observed in the populations exposed to homogeneously contaminated and highly contaminated (by copper) scenarios (both with no acceptable clean area to flee to). In summary, the uncontaminated areas might be crucial for the spatial dynamics of fish populations in a chemically heterogeneous landscape due to their role as escape zones to alleviate stress.

Interaction of the Olfactory System of Rainbow Trout (Oncorhynchus mykiss) with Diltiazem

Diltiazem is ubiquitously prescribed and has been reported in many effluents and freshwater bodies. Being a calcium channel blocker, diltiazem could disrupt the function of the sensory and central nervous systems. In the present study, using electro-olfactography (EOG), we investigated the interaction of diltiazem with the olfactory sensory neurons (OSNs) of rainbow trout by looking into the detection threshold and effects of immediate (~5 min) and acute (24 h) exposure to diltiazem at 6.6, 66, and 660 µg/L. We also studied the accumulation of the drug in fish plasma and whole body. Brief exposure to diltiazem impaired the OSN response to a chemosensory stimulus in a concentration-dependent manner at 6.6 µg/L and higher, whereas OSNs exposed for 24 h only displayed an impairment at 660 µg/L. Chemical analysis showed that the accumulation of diltiazem in fish plasma and body correlated with the EOG response because it was 10 times higher in the group that displayed a significant impairment (660 µg/L) compared to the other 2 groups (6.6, 66 µg/L). This correlation suggests that the impact of diltiazem on OSNs might partially be through the accumulated molecules in the fish bloodstream. Fish did not detect diltiazem as a sensory stimulus even at concentrations as high as 660 µg/L; thus, fish could potentially swim toward or fail to escape harmful concentrations of diltiazem. Environ Toxicol Chem 2022;41:554-550. © 2020 SETAC.

Effects of Episodic Exposure to High-pH Water on Survival of Atlantic Salmon Eggs and Juveniles: Results from Laboratory and Field Studies

Although effects of acidification on salmonid fish are well studied and documented, effects of episodic high pH have rarely received attention. In the present study, we investigated effects of high-pH events on Atlantic salmon (Salmo salar) using both field and laboratory data. Effects of an episodic high-pH event on juvenile densities in a Norwegian river were studied using data from several electrofishing surveys conducted both before and after the event. Effects of high pH on survival of eggs were studied by exposing eggs to a range of high-pH treatments for different durations. Juvenile densities from the field study showed that the high-pH event had little or no effect on the cohort that had been exposed to pH 9.7-10.3 during the egg stage. This finding was in accordance with the laboratory experiment that showed no excess mortality on eggs until pH was >12. The high-pH event occurred in March during low winter flows, and densities of older juveniles in May were significantly lower in the affected area compared to controls upstream. In June and September the difference was not significant, but there was a clear spatial trend indicating that the event had a negative effect on densities of older juvenile salmon. Environ Toxicol Chem 2022;41:771-780. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Can a mixture of agrochemicals (glyphosate, chlorpyrifos and chlorothalonil) mask the perception of an individual chemical? A hidden trap underlying ecological risk

As aquatic environments associated with conventional agriculture are exposed to various pesticides, it is important to identify any possible interactions that modify their effects when in a mixture. We applied avoidance tests with Danio rerio, exposing juveniles to three relevant current use pesticides: chlorpyrifos (CPF), chlorothalonil (CTL) and glyphosate (Gly), individually and in binary mixtures (CPF-Gly and CTL-Gly). Our goal was to identify the potential of contaminants to trigger the avoidance response in fish and detect any changes to that response resulting from binary mixtures. Avoidance was assessed for three hours using an open gradient system with six levels of increasing concentrations. Fish avoided environmentally relevant concentrations of the three compounds. The avoidance of CPF [AC50 = 7.95 (3.3-36.3) µg/L] and CTL [AC50 = 3.41 (1.2-41.6) µg/L] was evident during the entire period of observation. In the case of Gly, the response changed throughout the experiment: initially (until 100 min) the fish tolerated higher concentrations of the herbicide [AC50 = 52.2 (12.1-2700) µg/L] while during the later period (after 100 min) a clearer avoidance [1.5 (0.8-4.2) µg/L] was observed. The avoidance recorded using CPF and CTL alone was attenuated by the presence of Gly. Applying an additive concentration model, Gly initially acted synergistically with the other two compounds, although this interaction was not observed during the later period. Avoidance gives us an idea of how the distribution of populations may be altered by contamination, our results suggest that in some mixtures this response may be inhibited, at least temporarily, thus masking the ecological risk of the exposure.

Lethal and sublethal effects in Pink salmon (Oncorhynchus gorbuscha) following exposure to five aquaculture chemotherapeutants

Early life stages of Pink salmon (Oncorhynchus gorbuscha) are at risk of exposure to the active ingredients of chemotherapeutant formulations (hydrogen peroxide [HP], azamethiphos [AZ], emamectin benzoate [EB], cypermethrin [CP] and deltamethrin [DM]) used to control sea lice in salmon aquaculture. LC50 values (95% confidence intervals) for acute 48-h water exposures in order of least to most toxic to seawater-adapted pink salmon fry were: HP (227 [138-418] mg/L), EB (1090 [676-2006] µg/L), AZ (80 [52-161] µg/L), CP (5.1 [3.0-10.5] µg/L), and DM (980 [640-1800] ng/L), and in subchronic 10-d lethality sediment exposure tests: EB (2065 [1384-3720] µg/kg), CP (97 [58-190] µg/kg), and DM (1035 [640-2000] ng/kg). Alterations in behaviour varied between chemicals; no chemical attracted pink salmon fry; fish avoided HP to a limited extent at 50 mg/L), as well as EB (300 µg/L), and AZ (50 µg/L). Significant concentration-dependent decreases in olfactory responsiveness to food extract were seen following AZ, CP and DM exposures that occurred at lower concentrations with longer exposure periods (10 µg/L, 0.5 µg/L and 100 ng/L thresholds at 7 d). Following 10-d sediment exposures, olfaction was only affected by CP exposure at 50 µg/kg. Significant decreases in swimming performance (Ucrit) occured for HP, AZ, CP and DM at concentrations as low as 100 mg/L, 10 µg/L, 2 µg/L and 200 ng/L, respectively. This study provides comprehensive data on the lethal and sublethal effects of aquaculture chemotherapeutant exposure in early life stage pink salmon.

The behavioural response of European seabass (Dicentrarchus labrax) to chlorinated seawater effluents

Seawater chlorination is widely used for coastal, marine industries for the prevention of fouling. Using a choice chamber system, we investigated the influence of chlorinated seawater at typical concentrations occurring near chlorinated cooling water discharges, on the behaviour of juvenile seabass (Dicentrachus labrax). These studies showed that there was evidence of an effect of chlorination, with models predicting 22% fewer fish present in the chlorine dosed chamber compared to the undosed chamber in all control runs (mean number of fish in the dosed chamber in all control runs was 2.23 in comparison to 1.74 when chlorine was present). These data suggest that when food is available D. labrax will enter areas that are at mean chlorination levels of 0.04 mg l^-1, which are typical close to the discharge of power station cooling water but are more likely to move away once the food supply is reduced.

Why the Stall? Using metabolomics to define the lack of upstream movement of invasive bigheaded carp in the Illinois River

Bigheaded Carp have spread throughout the Mississippi River basin since the 1970s. Little has stopped the spread as carp have the ability to pass through locks and dams, and they are currently approaching the Great Lakes. However, the location of the leading edge in the Illinois River has stalled for over a decade, even though there is no barrier preventing further advancement towards the Great Lakes. Defining why carp are not moving towards the Great Lakes is important for predicting why they might advance in the future. The aim of this study was to test the hypothesis that anthropogenic contaminants in the Illinois River may be playing a role in preventing further upstream movement of Bigheaded Carp. Ninety three livers were collected from carp at several locations between May and October of 2018. Liver samples were analyzed using gas chromatography-mass spectrometry in a targeted metabolite profiling approach. Livers from carp at the leading edge had differences in energy use and metabolism, and suppression of protective mechanisms relative to downstream fish; differences were consistent across time. This body of work provides evidence that water quality is linked to carp movement in the Illinois River. As water quality in this region continues to improve, consideration of this impact on carp spread is essential to protect the Great Lakes.

Sub-Lethal Peak Exposure to Insecticides Triggers Olfaction-Mediated Avoidance in Zebrafish Larvae

In agricultural areas, insecticides inevitably reach water bodies via leaching or run-off. While designed to be neurotoxic to insects, insecticides have adverse effects on a multitude of organisms due to the high conservation of the nervous system among phyla. To estimate the ecological effects of insecticides, it is important to investigate their impact on non-target organisms such as fish. Using zebrafish as the model, we investigated how different classes of insecticides influence fish behavior and uncovered neuronal underpinnings of the associated behavioral changes, providing an unprecedented insight into the perception of these chemicals by fish. We observed that zebrafish larvae avoid diazinon and imidacloprid while showing no response to other insecticides with the same mode of action. Moreover, ablation of olfaction abolished the aversive responses, indicating that fish smelled the insecticides. Assessment of neuronal activity in 289 brain regions showed that hypothalamic areas involved in stress response were among the regions with the largest changes, indicating that the observed behavioral response resembles reactions to stimuli that threaten homeostasis, such as changes in water chemistry. Our results contribute to the understanding of the environmental impact of insecticide exposure and can help refine acute toxicity assessment.

Environmental Hazards of Boron and Vanadium Nanoparticles in the Terrestrial Ecosystem-A Case Study with Enchytraeus crypticus

From the start of the 21st century, nanoecotoxicological research has been growing in fast steps due to the need to evaluate the safety of the increasing use of engineered nanomaterials. Boron (B) and vanadium (V) nanoparticles (NPs) generated by anthropogenic activities are subsequently released in the environment; therefore, organisms can be continuously exposed to these NPs for short or long periods. However, the short and long-term effects of BNPs and VNPs on soil organisms are unknown. This work aimed to recognize and describe their potential toxicological effects on the model species Enchytraeus crypticus, assessing survival and reproduction, through a longer-term exposure (56 days (d)-OECD test extension of 28 d), and avoidance behavior, through a short-term exposure (48 hours (h)). After 28 d, BNPs did not induce a significant effect on E. crypticus survival, whereas they decreased the organisms' reproduction at 500 mg/kg. From 10 to 500 mg/kg, VNPs decreased the E. crypticus survival and/or reproduction. After 56 d, 100 to 500 mg/kg BNPs and 50 to 500 mg/kg VNPs, decreased the reproduction output of E. crypticus. The estimated Effect Concentrations (EC_x) based on reproduction, for BNPs, were lower at 56 d compared with 28 d; for VNPs, an opposite pattern was found: EC_x 28 d < EC_x 56 d. BNPs did not induce an avoidance behavior, but organisms avoided the soil contaminated with 10 mg VNPs/kg. The tested NPs showed different E. crypticus apical effects at 28 d from the ones detected at 56 d, dependent on the type of NPs (B vs. V). In general, VNPs showed to be more toxic than BNPs. However, the effects of VNPs were alleviated during the time of exposure, contrarily to BNPs (which became more toxic with extended duration). The present study adds important information about NPs toxicity with ecological significance (at the population level). Including long-term effects, the obtained results contributes to the improvement of NPs risk assessment.

Assessment of Advanced Oxidation Processes Using Zebrafish in a Non-Forced Exposure System: A Proof of Concept

Water bodies and aquatic ecosystems are threatened by discharges of industrial waters. Ecotoxicological effects of components occurring in untreated and treated wastewaters are often not considered. The use of a linear, multi-compartmented, non-forced, static system constructed with PET bottles is proposed for the quality assessment of treated waters, to deal with such limitations. Two synthetic waters, one simulating wastewater from the textile industry and the other one simulating wastewater from the cassava starch industry, were prepared and treated by homogeneous Fenton process and heterogeneous photocatalysis, respectively. Untreated and treated synthetic waters and their dilutions were placed into compartments of the non-forced exposure system, in which zebrafish (Danio rerio), the indicator organism, could select the environment of its preference. Basic physical–chemical and chemical parameters of untreated and treated synthetic waters were measured. The preference and avoidance responses allowed verification of whether or not the quality of the water was improved due to the treatment. The results of these assays can be a complement to conventional parameters of water quality.

Approaches to Test the Neurotoxicity of Environmental Contaminants in the Zebrafish Model: From Behavior to Molecular Mechanisms

The occurrence of neuroactive chemicals in the aquatic environment is on the rise and poses a potential threat to aquatic biota of currently unpredictable outcome. In particular, subtle changes caused by these chemicals to an organism's sensation or behavior are difficult to tackle with current test systems that focus on rodents or with in vitro test systems that omit whole-animal responses. In recent years, the zebrafish (Danio rerio) has become a popular model organism for toxicological studies and testing strategies, such as the standardized use of zebrafish early life stages in the Organisation for Economic Co-operation and Development's guideline 236. In terms of neurotoxicity, the zebrafish provides a powerful model to investigate changes to the nervous system from several different angles, offering the ability to tackle the mechanisms of action of chemicals in detail. The mechanistic understanding gained through the analysis of this model species provides a good basic knowledge of how neuroactive chemicals might interact with a teleost nervous system. Such information can help infer potential effects occurring to other species exposed to neuroactive chemicals in their aquatic environment and predicting potential risks of a chemical for the aquatic ecosystem. In the present article, we highlight approaches ranging from behavioral to structural, functional, and molecular analysis of the larval zebrafish nervous system, providing a holistic view of potential neurotoxic outcomes. Environ Toxicol Chem 2021;40:989-1006. © 2020 SETAC.

Zebrafish (Danio rerio) behavioural response to an odorant mixture containing attracting and repelling odorants

Odorants guide essential activities such as foraging and fleeing predators. Studies usually examine behavioural and physiological effects of individual odorants, while animals in the environment are exposed to multiple stimuli simultaneously. In this study, we exposed zebrafish to a mixture of attraction-evoking and aversion-evoking amino acids, and behavioural responses were observed. Attraction to l-alanine and avoidance to l-cysteine were observed, and so these amino acids were used to make the mixture (zebrafish also avoided l-serine, but this was weaker than with l-cysteine exposures). When exposed to the mixture, fish responded with avoidance, which suggests that aversion-evoking stimuli outweigh attraction-evoking stimuli. Attraction towards the mixture was seen only when the concentration of l-cysteine was decreased from 0.1 to 0.001 mM. Olfactory ablation surgery confirmed that the behaviours were olfactory-mediated. Overall, this study demonstrated that odorant stimuli that repel outweigh stimuli that attract until their concentration decreases by as much as 100-fold.

The environmental risks of pharmaceuticals beyond traditional toxic effects: Chemical differences that can repel or entrap aquatic organisms

The aim of the present study was to assess the risks of four different pharmaceutical active compounds (PhACs; diazepam, metformin, omeprazole and simvastatin). Acute and chronic toxicities were studied using the bacterium Aliivibrio fischeri and the microalgae Pseudokirchneriella subcapitata; while the repellency and attractiveness were assessed by avoidance tests with juvenile Cypirinus carpio using a multi-compartmented exposure system. Omeprazole was found to be an acutely toxic drug (EC₅₀: 0.015 mg/L), while the other PhACs, except simvastatin, showed some chronic toxicity. Regarding avoidance, simvastatin and omeprazole induced an escape response for 50% of the fish population at 0.032 and 0.144 mg/L, respectively; contrarily, diazepam was attractive, even at lethal concentrations, representing a dangerous trap for organisms. The toxicity of the PhACs seemed not to be directly related to their repellency; and the mode of action seems to determine the repellency or attractiveness of the chemicals. Contamination by PhACs is of concern due to the environmental disturbance they might cause, either due to their acute and chronic toxicity (at the individual level), repellency (at the ecosystem level: loss of local biodiversity) or attraction to potentially lethal levels.

Not Only Toxic but Repellent: What Can Organisms' Responses Tell Us about Contamination and What Are the Ecological Consequences When They Flee from an Environment?

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.

Predicting zebrafish spatial avoidance triggered by discharges of dairy wastewater: An experimental approach based on self-purification in a model river

Wastewater discharges from dairy industries can cause a range of harmful effects in aquatic ecosystems, including a decline in biodiversity due to species evasion. Therefore, it is important to know the purification potential of rivers for the removal of pollutants released in dairy wastewater (DWW). The hypothesis adopted in this work was that the release of DWW into stretches of the Ribeirão dos Pombos River (São Paulo State, Brazil) might trigger an avoidance response, resulting in fish migrating to other regions, with the response being greater when the self-cleaning potential of the river is smaller. Therefore, the goals of the present study were to: (i) investigate how land use and seasonality of the rainfall regime influence the quality of the water in different areas of the river (P1: river source; P2: urban region; P3: rural region); (ii) assess the potential of the river to purify DWW; and (iii) evaluate the potential toxicity and repellency of DWW to the freshwater fish Danio rerio, using acute toxicity (mortality) and non-forced avoidance tests, respectively. P1 was shown to be the most preserved area. The chemical composition of the river varied seasonally, with higher concentrations of Cl^- and SO₄^2- at P3 during the rainy period. The river purification potential for DWW was higher at P2, due to greater microbiological activity (associated with higher BOD). The DWW was more acutely toxic in water from P2. The avoidance response was strongly determined by the concentration of DWW, especially for water from P2. The high capacity for self-cleaning at P2 did not seem sufficient to maintain the stability of the ecosystem. Finally, the non-forced exposure system proved to be a suitable approach that can assist in predicting how contaminants may affect the spatial distributions of organisms.

Repellency and mortality effects of sunscreens on the shrimp Palaemon varians: Toxicity dependent on exposure method

Contamination by sunscreens has become a serious environmental problem due to the increasing use of these products in coastal regions. Their complex chemical composition supposes an input of different chemical compounds capable of producing toxic effects and repelling organisms. The aim of the current study was to experimentally check the repellency of three commercial sunscreens [A (lotion), B (gel) and C (milk spray)] by assessing the escape (displacement towards areas with lower sunscreen levels) of the estuarine shrimp Palaemon varians exposed (4 h) to a gradient (0-300 mg/L) of the sunscreens in a heterogeneous non-forced exposure scenario. Additionally, mortality and immobility (72 h) were checked in a traditional forced exposure scenario. Considering that the toxicity of sunscreens is a little controversial regarding their chemical availability in the medium, two different methods of sunscreen solubilisation were tested: complete homogenization and direct immersion. Very low mortality was observed in the highest concentration of sunscreens A and C applied by direct immersion; however, for sunscreen B, the main effect was the loss of motility when homogenization was applied. Repellency was evidenced for two sunscreens (A and B) applied by direct immersion. The homogenization in the medium seemed to lower the degree of repellency of the sunscreens, probably linked to the higher viscosity in the medium, preventing the motility of shrimps. By integrating both short-term responses (avoidance and mortality/immobility), the PID (population immediate decline) calculated showed that avoidance might be the main factor responsible for the reduction of the population at the local scale.

Development of Carbon Dioxide Barriers to Deter Invasive Fishes: Insights and Lessons Learned from Bigheaded Carp

Invasive species are a threat to biodiversity in freshwater. Removing an aquatic invasive species following arrival is almost impossible, and preventing introduction is a more viable management option. Bigheaded carp are an invasive fish spreading throughout the Midwestern United States and are threatening to enter the Great Lakes. This review outlines the development of carbon dioxide gas (CO2) as a non-physical barrier that can be used to deter the movement of fish and prevent further spread. Carbon dioxide gas could be used as a deterrent either to cause avoidance (i.e., fish swim away from zones of high CO2), or by inducing equilibrium loss due to the anesthetic properties of CO2 (i.e., tolerance). The development of CO2 as a fish deterrent started with controlled laboratory experiments demonstrating stress and avoidance, and then progressed to larger field applications demonstrating avoidance at scales that approach real-world scenarios. In addition, factors that influence the effectiveness of CO2 as a fish barrier are discussed, outlining conditions that could make CO2 less effective in the field; these factors that influence efficacy would be of interest to managers using CO2 to target other fish species, or those using other non-physical barriers for fish.

Sublethal effects of contaminants on marine habitat-forming species: a review and meta-analysis

Contaminants may affect ecosystem functioning by reducing the fitness of organisms and these impacts may cascade through ecosystems, particularly if the sensitive organisms are also habitat‐forming species. Understanding how sub‐lethal effects of toxicants can affect the quality and functions of biogenic habitats is critical if we are to establish effective guidelines for protecting ecosystems. We carried out a global systematic review and meta‐analysis critically evaluating contaminant effects on properties of habitat‐formers linked to ecosystem functioning. We reviewed a total of 95 publications. However, 40% of publications initially captured by the literature search were identified as having flaws in experimental design and ~11% did not present results in an appropriate way and thus were excluded from the quantitative meta‐analysis. We quantitatively reviewed 410 studies from 46 publications, of which 313 (~76%) were on plants and seaweeds, that is macro‐algae, saltmarsh plants and seagrasses, 58 (~14%) studied corals and 39 (~10%) looked at toxicant impacts on bivalves, with 70% of those on mussels and the remaining studies on oysters. Response variables analysed were photosynthetic efficiency, amount of chlorophyll a (as a proxy for primary production) and growth of plants, seaweeds and corals as well as leaf area of plants. We also analysed filtration, growth and respiration rates of bivalves. Our meta‐analysis found that chemical contaminants have a significant negative impact on most of the analysed functional variables, with the exception of the amount of chlorophyll a. Metals were the most widely harmful type of contaminant, significantly decreasing photosynthetic efficiency of kelps, leaf area of saltmarsh plants, growth of fucoids, corals and saltmarsh plants and the filtration rates of bivalves. Organic contaminants decreased the photosynthetic efficiency of seagrass, but had no significant effects on bivalve filtration. We did not find significant effects of polycyclic aromatic hydrocarbons on any of the analysed functional variables or habitat‐forming taxa, but this could be due to the low number of studies available. A meta‐regression revealed that relationships between concentrations of metal contaminants and the magnitude of functional responses varied with the type of metal and habitat‐former. Increasing concentrations of contaminants significantly increased the negative effects on the photosynthetic efficiency of habitat‐formers. There was, however, no apparent relationship between ecologically relevant concentrations of metals and effect sizes of photosynthetic efficiency of corals and seaweeds. A qualitative analysis of all relevant studies found slightly different patterns when compared to our quantitative analysis, emphasising the need for studies to meet critical inclusion criteria for meta‐analyses. Our study highlights links between effects of contaminants at lower levels of organisation (i.e. at the biochemical and/or physiological level of individuals) and ecological, large‐scale impacts, through effects on habitat‐forming species. Contaminants can clearly reduce the functioning of many habitat‐forming marine species. We therefore recommend the adoption of routine measures of functional endpoints in monitoring and conservation programs to complement structural measures.

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⁺.

Effects of Amorphous Silica Nanopowders on the Avoidance Behavior of Five Soil Species-A Screening Study

Silica nanoparticles (SiO2NPs) are one of the most used in commercial products and biomedical tools, however, their environmental effects have not been fully described. Although negative effects of SiO2NPs on the behavior of freshwater invertebrates have been reported, the knowledge is limited, especially the effect of nanopowders in terrestrial organisms. Accordingly, the aim of the present study is to understand the effects of SiO2NPs on the avoidance behavior of five soil species, whose niche may differ thus contributing to differential harmful SiO2NPs effects. Hence, avoidance assays testing SiO2NPs concentrations of 0, 10, 100, 250, 500 and 1000 mg/kg were performed with Enchytraeus crypticus, Folsomia candida, Tenebrio molitor, Porcellionides pruinosus and Eisenia fetida. SiO2NPs induced different behavioral effects, depending on the invertebrate ecology/habitat, exposure route and physiology. T. molitor, P. pruinosus and F. candida did not avoid contaminated soil; however, E. crypticus and E. fetida significantly avoided SiO2NPs spiked soil. Since these terrestrial worms (oligochaetes) live mostly burrowed in the soil, this can provide greater opportunity for SiO2NPs' uptake. On the other hand, the other tested organisms mainly living on the upper part of the soil did not avoid the SiO2NPs spiked soil. The avoidance data obtained here also highlight the need for further studies to understand whether (or not) the detected behavioral responses are linked to either neurotransmission processes or sensorial aspects of the biological models.

Do you smell the danger? Effects of three commonly used pesticides on the olfactory-mediated antipredator response of zebrafish (Danio rerio)

Fish are warned about the presence of predators via an alarm cue released from the skin of injured conspecifics. The detection of this odor inherently initiates an antipredator response, which increases the chance of survival for the individual. In the present study, we assessed the effect of three commonly used pesticides on the antipredator response of zebrafish (Danio rerio). For this, we analyzed the behavioral response of zebrafish to a conspecific skin extract following 24 h of exposure to the respective contaminants. Results demonstrate that fish exposed to 20 μg/L of the organophosphate insecticide chlorpyrifos significantly reduced bottom-dwelling and freezing behavior, suggesting an impairment of the antipredator response. For the urea-herbicide linuron and the pyrethroid insecticide permethrin, no statistically significant effects could be detected. However, linuron-exposed fish appeared to respond in an altered manner to the skin extract; some individuals failed to perform the inherent behaviors such as erratic movements and instead merely increased their velocity. Furthermore, we determined whether zebrafish would avoid the pesticides in a choice maze. While fish avoided permethrin, they behaved indifferently to chlorpyrifos and linuron. The study demonstrates that pesticides may alter the olfactory-mediated antipredator response of zebrafish in distinct ways, revealing that particularly fish exposed to chlorpyrifos may be more prone to predation.

Does the previous exposure to copper alter the pattern of avoidance by zebrafish in a copper gradient scenario? Hypothesis of time-delayed avoidance due to pre-acclimation

The traditional ecotoxicity assays (forced exposure) tend to use organisms that are cultured under controlled conditions or that come from undisturbed ecosystems, with no (or negligible) previous contact with contamination. The same occurs in the non-forced approach, in which organisms are exposed to a contamination gradient and can move between different concentrations choosing the less toxic one. Considering that organisms inhabiting contaminated ecosystems tend to be gradually exposed to contamination, an abrupt exposure from uncontaminated conditions to a contaminated environment might present two problems: lack of ecological relevance to a scenario where the contamination occurs gradually and a magnification of the toxicity due to the sudden change in the environmental conditions. Therefore, a key question should be addressed: might a previous exposure to contamination reduce the organisms' perception of the danger of a contaminant (hypothesis of time-delayed avoidance due to pre-acclimation-TDADP), altering their avoidance response pattern? We tested the avoidance of zebrafish (Danio rerio: ±2 months old) populations when exposed to a copper gradient (0-400 μg/L). The populations differed according to the period (24 h and 7 and 30 days) in which they were acclimated to copper (ca. 400 μg/L). The avoidance in the 2 h experiments changed as a consequence of the acclimation period. In the population that was not previously acclimated, 40% of the fish moved to the less contaminated compartment and only 6.7% stayed in the most contaminated one; for the other populations those values were, respectively, 31 and 11% (24 h-acclimation), 28 and 26% (7 day-acclimation) and 19 and 27% (30 day-acclimation). An abrupt exposure to a contaminant might overestimate the response if this is analyzed in the short-term. When the avoidance tests were prolonged to 24 h, the avoidance tended to reach similar values to those of the non-acclimated population, thus supporting our TDADP hypothesis.

Forage fish and polycyclic aromatic compounds in the Fort McMurray oil sands area: Body burden comparisons with environmental distributions and consumption guidelines

The Fort McMurray region in northeastern Alberta (Canada) is rich in natural sources of polycyclic aromatic compounds (PACs) from exposed bitumen beds; anthropogenic sources are being released with increased oil sands industry expansion. Here we report on investigations of PACs (47 compounds) in three species of forage fish collected during the 2012-2013 Joint Oil Sands Monitoring Program (JOSMP) fish health investigations and compare results with PAC data for sediment and water collected under JOSMP and earlier programs. PAC concentrations in sediments varied three orders in magnitude and were highest at downstream tributary mouths, which flowed through the exposed McMurray Formation, and along reaches of the Athabasca River where the formation was exposed. PAC concentrations in water were less variable but with higher concentrations near exposed bitumen beds. Forage fish exhibited the weakest spatial gradients in ΣPACs concentration, which averaged 102 ± 32 ng/g in trout-perch from the Athabasca River, 125 ± 22 ng/g in lake chub from the Ells River, and 278 ± 267 ng/g in slimy sculpin from the Steepbank, Firebag, and Dunkirk Rivers. Low-molecular weight compounds, particularly naphthalenes and fluorenes, dominated fish PACs. Phenanthrenes occurred in greater percent composition in fish caught in areas where PAC concentrations in sediments were higher due to the proximity of bitumen sources than in other areas. Dibenzothiophene, a major component of bitumen PAC, was a minor component of fish ΣPACs. Forage fish PAC concentrations were below fish consumption guidelines established by the European Commission (2011) and for the reopening of the commercial fisheries closed by the Deepwater Horizon oil spill. PAC concentrations in forage fish were similar to concentrations observed in many other studies (fish market surveys, estuaries, and marine waters) and lower than in fish sampled from highly impacted areas (near refineries, harbors, and other industrialized areas).

Risk of triclosan based on avoidance by the shrimp Palaemon varians in a heterogeneous contamination scenario: How sensitive is this approach?

As the exposure of organisms to contaminants can provoke harmful effects, some organisms try to avoid a continuous exposure by using different strategies. The aim of the current study was to assess the ability of the shrimp Palaemon varians to detect a triclosan gradient and escape to less contaminated areas. Two multi-compartmented exposure systems (the linear system and the HeMHAS-Heterogeneous Multi-Habitat Assay System) were used and then results were compared. Finally, it was aimed how sensitive the avoidance response is by comparing it with other endpoints through a sensitivity profile by biological groups and the species sensitive distribution. The distribution of the shrimps along the triclosan gradient was dependent on the concentrations, not exceeding 3% for 54 μg/L in the linear system and 7% for 81 μg/L in the HeMHAS; 25% of organisms preferred the compartment with the lowest concentrations in both systems. Half of the population seems to avoid concentrations around 40-50 μg/L. The triclosan concentration that might start (threshold) to trigger an important avoidance (around 20%) was estimated to be of 18 μg/L. The profile of sensitivity to triclosan showed that avoidance by shrimps was less sensitive than microalgae growth and avoidance by guppy; however, it might occur even at concentrations considered safe for more than 95% of the species. In summary, (i) the HeMHAS proved to be a suitable system to simulate heterogeneous contamination scenarios, (ii) triclosan triggered the avoidance response in P. varians, and (iii) the avoidance was very sensitive compared to other ecotoxicological responses.

Current knowledge of seepage from oil sands tailings ponds and its environmental influence in northeastern Alberta

Seepage of oil sand process-affected waters (OSPW) from tailings ponds into surface waters is a common concern in the minable oil sands region of northeast Alberta. Research on seepage has been extensive, but few comprehensive treatments evaluating all aspects relevant to the phenomenon are available. In this work, the current information relevant for understanding the state of seepage from tailings ponds was reviewed. The information suggests the infiltration of OSPW into groundwater occurs near some ponds. OSPW may also be present in sediments beneath the Athabasca River adjacent to one pond, but there are no clear observations of OSPW in the river water. Similarly, most water samples from tributaries also show no evidence of OSPW, but these observations are limited by the lack of systematic, systemic, and repeated surveys, missing baseline data, standard analytical approaches, and reference materials. Waters naturally influenced by bitumen, discharge of saline groundwaters, and dilution also potentially affect the consolidation of information and certainty of any conclusions. Despite these challenges, some data suggest OSPW may be present in two tributaries of the Athabasca River adjacent to tailings ponds: McLean Creek and Lower Beaver River. Irrespective of the possible source(s), constituents of OSPW often affect organisms exposed in laboratories, but research in all but one study suggests the concentrations of organics in the surface water bodies assessed are below the standard toxicological effect thresholds for these compounds. In contrast, many samples of groundwater, irrespective of source, likely affect biota. Biomonitoring of surface waters suggests generic responses to stressors, but the influence of natural phenomena and occasionally nutrient enrichment are often suggested by data. In summary, valuable research has been done on seepage. The data suggest infiltration into groundwater is common, seepage into surface waters is not, and anthropogenic biological impacts are not likely.

Avoidance behaviour of the shrimp Palaemon varians regarding a contaminant gradient of galaxolide and tonalide in seawater

The musk fragrances galaxolide (HHCB) and tonalide (AHTN) are compounds of emerging concern that have been found in various environmental compartments. The present study addressed the ability of HHCB and AHTN to elicit the avoidance response in the estuarine shrimp Palaemon varians and to predict the population immediate decline (PID) of P. varians when exposed to HHCB and AHTN by integrating both avoidance (non-forced exposure) and lethality (forced exposure) responses. The avoidance response was tested in a non-forced multi-compartmented static system, in which the shrimps could move freely among the compartments with different concentrations. The shrimps (n = 3 shrimps per compartment/concentration; 18 shrimps per system) were exposed to a gradient (0, 0.005, 0.05, 0.5, 5 and 50 μg/L) of both substances and their positions were checked at every 20 min for a 3 h period. The results from 24-h forced exposure showed no dose-response relationship and the highest percentage mortality was 17% for HHCB at 0.005 and 0.5 μg/L. In the 3-h non-forced exposure to a gradient of HHCB and AHTN, significant concentration-dependent spatial avoidance was observed for both substances. The shrimps avoided the lowest concentration of HHCB and AHTN (0.005 μg/L) by 15% and 16%. The avoidance increased significantly (p < 0.005) to a 61% and 57%, respectively, for the highest concentration (50 μg/L). The population immediate decline was driven by the avoidance behaviour of the shrimps rather than mortality. These results indicated that the aversiveness of HHCB and AHTN might have serious consequences for habitat selection processes by organisms.

Shedding light on the effects of hydraulic fracturing flowback and produced water on phototactic behavior in Daphnia magna

The effluent produced during hydraulic fracturing (i.e. flowback and produced water; FPW), is a complex hyper-saline solution that is known to negatively impact the survival and the fitness of the water flea Daphnia magna, but to date effects on behavior are unstudied. In the current study, the effects of FPW on phototactic behavior of D. magna were examined. Exposure of naïve animals to FPW resulted in a dose-dependent increase in the speed of appearance of daphnids in the illuminated zone of the test apparatus (i.e. a faster positive phototaxis response). A similar dose-dependent response was observed in a test solution where the salt content of FPW was recreated in the absence of other components, suggesting that the effect was largely driven by salinity. The effect of FPW was significant when the raw FPW sample was diluted to 20% of its initial strength, while the effect of salt-matched solution was significant at a 10% dilution. A distinct effect was observed following FPW pre-exposure. After a 24 h pre-exposure to 1.5% FPW, Daphnia displayed a significantly inhibited positive phototaxis response when examined in control water, relative to control animals that were not pre-exposed to FPW. This effect was not observed in salinity pre-exposed animals, however these daphnids displayed a significantly reduced phototactic response when tested in saline waters, indicating a loss of the positive phototaxis seen in naïve organisms. These data indicate that FPW can induce perturbations in the behavior of aquatic invertebrates, an effect that may influence processes such as feeding and predation rates.

Habitat selection response of the freshwater shrimp Atyaephyra desmarestii experimentally exposed to heterogeneous copper contamination scenarios

In contaminated aquatic ecosystems, it is expected that organisms suffer some effects caused by the contaminants. However, for mobile organisms inhabiting heterogeneously contaminated ecosystems, the continuous exposure to contaminants can be avoided by moving to less contaminated habitats. The present study evaluated the habitat selection of the freshwater shrimp Atyaephyra desmarestii experimentally exposed to different copper concentrations to verify whether the heterogeneous contamination distribution and the connectivity between habitats with different copper levels could generate a random population distribution similar to metapopulation. The experiments were performed in the HeMHAS (Heterogeneous Multi-Habitat Assay System), a non-forced multi-compartmented exposure system, in which it is possible to simulate the distribution of contaminants in a linear gradient or as patches of contamination. Copper was used to simulate a linear contamination gradient (26 to 105 μg/L Cu) and two patchy scenarios with three contamination levels [reference zone (R: 26 ± 7 μg/L Cu), mixing zone (M: 61 ± 2 μg/L Cu) and disturbed zone (D: 101 ± 12 μg/L Cu)], with two mixing zones or one central mixing zone in a heterogeneous scenario. In the copper gradient scenario, a clear trend of shrimps (59.6 ± 8.0% of the population) moving to the reference zones and an avoidance of 66.7 ± 11.1% of the most contaminated zone were observed. For the patchy scenarios, a random distribution of organisms (34, 36 and 30% for R, M and D zones, respectively) was observed in the scenario with one mixing zone; on the other hand, a slight preference for the reference zones (44.9 ± 4.8%) was evidenced in the scenario with two mixing zones. As shrimps are able to select less contaminated areas, it is highly important to preserve clean zones in heterogeneously contaminated environments, such as the arrangement in meta-ecosystems, as the less- or uncontaminated zones might represent less stressful areas to protect populations against continuous contamination exposure.

Oil sands process-affected water impairs the olfactory system of rainbow trout (Oncorhynchus mykiss)

Oil sands process-affected water (OSPW), a byproduct of the extraction of bitumen in the surface mining of oil sands, is currently stored in massive on-site tailings ponds. Determining the potential effects of OSPW on aquatic ecosystems is of main concern to oil sands companies and legislators concerned about the reclamation of mining sites. In the present study, the interaction of OSPW with the chemosensory system of rainbow trout was studied. Using an electro-olfactography (EOG) technique, a 24 h inhibition curve was established and concentrations that inhibit the olfactory system by 20% and 80% (IC20 and IC80) were estimated at 3% and 22% OSPW, respectively. To study the interaction of exposure time and concentration along with the mechanism of the toxic effects, rainbow trout were exposed to 3% and 22% OSPW for 2, 24, and 96 h. An EOG investigation of olfactory sensitivity demonstrated a positive interaction between exposure time and concentration of OSPW concentration, because an increase in either or both elevated the inhibitory effect. To investigate whether or not structural damage of the olfactory epithelium could account for the observed inhibitory effects of OSPW on fish olfaction, the ultrastructure of the olfactory epithelium of exposed fish was investigated using scanning electron microscopy (SEM) and light microscopy (LM). The SEM micrographs showed no changes in the structure of the olfactory epithelium. The light micrographs revealed an increase in the number of mucous cells in 22% OSPW. The results of the present study demonstrated that exposure to OSPW impairs the olfactory system of rainbow trout and its effects increase gradually with increasing exposure time. The present study demonstrated that structural epithelial damage did not contribute to the inhibitory effects of OSPW on the olfactory system.

Spatial avoidance as a response to contamination by aquatic organisms in nonforced, multicompartmented exposure systems: A complementary approach to the behavioral response

The idea that the hazard of contaminants is exclusively related to their toxic effects does not consider the fact that some organisms can avoid contamination, preventing toxicity. Although inferences about avoidance are made in most behavioral ecotoxicology studies, assessment of the real spatial displacement (organisms moving toward another habitat to escape contamination) is difficult due to the type of exposure (confined and mandatory) used in the bioassays: a forced exposure approach. A complementary approach using nonforced exposure systems to assess how contaminants affect the spatial distribution of organisms in a bicompartmented (toxic or nontoxic) environment has long been described. Recently, this nonforced approach has been developed to include a multi compartmented system in which different samples can be simultaneously tested. The aim of the present review was to describe the importance of the nonforced, multicompartmented exposure approach to simulate a gradient or patches of contamination, to describe the 2 main exposure systems, and to highlight the ecological relevance of including spatial avoidance and habitat preference in ecotoxicological studies. The multicompartmentalization of the system makes it possible to simulate more complex scenarios and therefore include new ecological concepts in bioassays. We also contrasted spatial avoidance in the nonforced exposure systems with the behavioral endpoints measured under other exposure systems. Finally, we showed that the nonforced, multicompartmented exposure approach makes it possible 1) to improve environmental risk assessments by adding the dispersion pattern of organisms in a multihabitat scenario, and 2) to integrate ecological concepts such as recolonization of recovering habitats, loss of habitat connectivity, habitat fragmentation, and contamination-driven metapopulation, which have received limited attention in ecotoxicological studies. Environ Toxicol Chem 2019;38:312-320. © 2018 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).

Swimming performance of a freshwater fish during exposure to high carbon dioxide

Deterring the spread of invasive fishes is a challenge for managers, and bigheaded carp (including bighead and silver carp, Hypophthalmichthys spp.) are invasive fish that have spread throughout large portions of the Mississippi River basin and threaten to invade the Great Lakes' ecosystem. Studies have shown that elevated levels of carbon dioxide gas (CO₂) have the ability to act as a nonphysical fish barrier, but little work has been done on the efficacy of CO₂ to deter fish movement in flowing water. An annular swim flume was used to measure U_burst and sprint duration of the model species largemouth bass (Micropterus salmoides) across a range of pCO₂ levels (< 400 μatm [ambient]; 10,000 μatm; 50,000 μatm; and 100,000 μatm). This species was tested as a proxy because of the likelihood of a similar CO₂ response being produced, as well as constraints in obtaining and housing appropriately sized Asian carp. A significant decrease in U_burst swimming occurred when exposed to 100,000 μatm. No effects on sprint duration were detected. In both swimming tests, 15% of fish lost equilibrium when exposed to 50,000 μatm pCO₂, while 50% of fish lost equilibrium when exposed to 100,000 μatm. Together, results define target levels for managers to impede the spread of largemouth bass and potentially other invasive freshwater fishes, helping guide policy to conserve aquatic ecosystems.

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.

Stress-driven emigration in complex field scenarios of habitat disturbance: The heterogeneous multi-habitat assay system (HeMHAS)

Lines of evidence used in ecological risk assessment (ERA) are essentially three: chemistry, biology and ecotoxicology. Until now, the fundamental assumption made when measuring ecological risks is that organisms are forcedly exposed to stressors. However, when organisms can avoid disturbed habitats by escaping to less stressful areas, the assumption that exposure is mandatory to pose risk may not match field disturbance scenarios. A non-forced exposure approach using a linear free-choice multi-compartmented system has been proposed previously as a complementary tool to assess the effects on organisms' spatial avoidance/preference responses. Yet, the linearity of the latter system limits avoidance measurements to one spatial dimension. A novel, heterogeneous multi-habitat assay system (HeMHAS) consisting of 18 connected circular compartments (3 compartments on a vertical axis in each one of 6 zones on a longitudinal axis; a 2D system) is put forward here to be used in heterogeneous-habitat selection studies, as it makes it possible to assess the ability of organisms to detect contamination and other stressors and select more favorable habitats. In the present study, the avoidance to copper by zebrafish (Danio rerio) was tested after exposing organisms to a copper gradient in the HeMHAS and compared with that in the linear system. Avoidance occurred for all copper concentrations: 43% in the lowest (21 μg·L^-1) to 72% in the highest (221 μg·L^-1). Results obtained within the HeMHAS (AC₅₀: 60 μg·L^-1) were statistically (p = 0.72) similar to avoidance of copper by D. rerio in the linear non-forced system (AC₅₀: 89 μg·L^-1). In summary, the simulation of a copper gradient in the HeMHAS (2D system) allowed to assess the potential repellency of copper to zebrafish and to corroborate the ability of organisms to detect and avoid potentially toxic concentrations.

Nucleobase-containing compounds evoke behavioural, olfactory, and transcriptional responses in model fishes

The sensory system of animals detects a massive and unknown array of chemical cues that evoke a diversity of physiological and behavioural responses. One group of nitrogen-containing carbon ring chemicals—nucleobases—are thought to be involved in numerous behaviours yet have received little attention. We took a top-down approach to examine responses evoked by nucleobases at behavioural, tissue, and gene expression levels. Fish generally avoided nucleobases, and this behaviour, when observed, was driven by purines but not pyrimidines. At the tissue level, olfactory neuron generator potential responses tended to be concentration specific and robust at concentrations lower than amino acid detection ranges. In terms of gene expression, more than 2000 genes were significantly upregulated following nucleobase exposure, some of which were expected (e.g., genes involved in purine binding) and some of which were not (e.g., tubulin-related genes). Humanized RNA pathway analysis showed that we had exposed the animal to a nucleobase. Our data indicate that responses to nucleobase-containing compounds may be highly structure based and are evident from changes in behaviour to mRNA expression. Many of these responses were surprising, and all provide numerous routes for further research endeavour.

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.

Fish can smell trace metals at environmentally relevant concentrations in freshwater

The objective of the present study was to investigate the ability of the olfactory system of rainbow trout (Oncorhynchus mykiss) to detect three trace metals, cadmium (Cd), copper (Cu), and nickel (Ni), using electro-olfactography (EOG). The olfactory response to all three metals was measured at either 10^-6 M or at a concentration established by Alberta Environment and Parks (AEP) as the criterion for the protection of aquatic life. Results of the present study demonstrated that the olfactory system of rainbow trout can detect all three metals (i.e. Cd, Cu, and Ni) in water at environmentally relevant concentrations. These results provide physiological evidence for a role of the olfactory system in fish behavioural responses (as shown in previous studies) when they encounter metal contaminated waters.

A novel approach to assessing environmental disturbance based on habitat selection by zebra fish as a model organism

Aquatic ecotoxicity assays used to assess ecological risk assume that organisms living in a contaminated habitat are forcedly exposed to the contamination. This assumption neglects the ability of organisms to detect and avoid contamination by moving towards less disturbed habitats, as long as connectivity exists. In fluvial systems, many environmental parameters vary spatially and thus condition organisms' habitat selection. We assessed the preference of zebra fish (Danio rerio) when exposed to water samples from two western Ecuadorian rivers with apparently distinct disturbance levels: Pescadillo River (highly disturbed) and Oro River (moderately disturbed). Using a non-forced exposure system in which water samples from each river were arranged according to their spatial sequence in the field and connected to allow individuals to move freely among samples, we assayed habitat selection by D. rerio to assess environmental disturbance in the two rivers. Fish exposed to Pescadillo River samples preferred downstream samples near the confluence zone with the Oro River. Fish exposed to Oro River samples preferred upstream waters. When exposed to samples from both rivers simultaneously, fish exhibited the same pattern of habitat selection by preferring the Oro River samples. Given that the rivers are connected, preference for the Oro River enabled us to predict a depression in fish populations in the Pescadillo River. Although these findings indicate higher disturbance levels in the Pescadillo River, none of the physical-chemical variables measured was significantly correlated with the preference pattern towards the Oro River. Non-linear spatial patterns of habitat preference suggest that other environmental parameters like urban or agricultural contaminants play an important role in the model organism's habitat selection in these rivers. The non-forced exposure system represents a habitat selection-based approach that can serve as a valuable tool to unravel the factors that dictate organisms' spatial distribution in connected ecosystems.