Sensitivity of Amphibians to Copper.

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

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).

Challenges and future prospects for developing Ca and Mg water quality guidelines: a meta-analysis.

Anthropogenic activities have the potential to increase water hardness (Ca + Mg) in receiving waters to toxic concentrations, and thus, water quality guidelines (WQG) for Ca and Mg are warranted. However, Ca can modify Mg toxicity in Ca-poor water and additional interactions with other major ions (Na+, K+, HCO3-/CO32-, SO42- and Cl-) may occur, potentially obscuring the water hardness-effect relationship. In a meta-analysis of toxicological studies, we: (i) evaluate the performance of three WQG derivation methods, and (ii) determine the influence of several variables (acute/chronic data, anions, Ca:Mg ratios, non-geographically relevant species) on the models. We find that the most sensitive species- or species sensitivity distribution (SSD)-based WQG derivation methods greatly overestimate water hardness toxicity, particularly if non-resident species are included. Broad-scale implementation of most sensitive species- or SSD-based WQG is impractical because water hardness varies beyond and within the regional scale. Anion type does not affect water hardness toxicity across species, but the Ca : Mg ratio is toxicologically relevant, underscoring the importance of considering ion ratios when developing major ion WQG. Although data supporting formal water hardness WQG are unavailable, we suggest using a two-component background condition approach that supports simultaneous management of water hardness and Ca : Mg ratio, and WQG that are applicable beyond the regional scale.This article is part of the theme issue 'Salt in freshwaters: causes, ecological consequences and future prospects'.

Dietary sodium protects fish against copper-induced olfactory impairment.

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

Recovery of Olfactory Mediated Behaviours of Fish from Metal Contaminated Lakes.

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

Chemosensory mediated behaviors and gene transcription profiles in wild yellow perch (Perca flavescens) from metal contaminated lakes.

The olfactory system of fish is sensitive to the toxic effects of low concentrations of contaminants. To investigate the effects of long-term metal exposure on olfaction in wild yellow perch (Perca flavescens), fish from one clean (Geneva Lake) and two metal-contaminated lakes (Ramsey and Hannah lakes) were collected in and around the metal-mining district of Sudbury, ON. Two different techniques were used to measure the effects of exposure to environmental contamination: (i) behavioral responses were recorded in response to conspecific skin extract and (ii) gene transcription differences in olfactory rosettes were characterized using a novel, 1000-candidate gene yellow perch microarray. Behavioral assays performed on fish from the clean lake demonstrated avoidance of a conspecific skin extract, while fish from metal contaminated lakes showed no avoidance response. A total of 109 out of the 1000 genes were differentially transcribed among the lakes. Most of the differentially transcribed genes were between the two metal contaminated lakes relative to either of the contaminated lakes and the reference lake. No genes were differentially expressed between Geneva Lake (clean) and Hannah Lake (metal contaminated). These results demonstrated that even though the different populations of fish from both Hannah and Ramey lakes were affected at the behavioral level, the impairment of olfaction was not measurable using gene transcriptional changes in olfactory rosettes.

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.

Olfactory recovery of wild yellow perch from metal contaminated lakes.

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