No evidence of increased growth or mortality in fish exposed to oxazepam in semi-natural ecosystems

Temperature variability regulates the interactive effects of warming and pharmaceutical on aquatic ecosystem dynamics

Climate warming and pharmaceutical contaminants have profound impacts on population dynamics and ecological community structure, yet the consequences of their interactive effects remain poorly understood. Here, we explore how climate warming interacts with pharmaceutical-induced boldness change to affect aquatic ecosystems, built on an empirically well-informed food-chain model, consisting of a size-structured fish consumer, a zooplankton prey, and a fish predator. Climate warming is characterized by both daily mean temperature (DMT) and diurnal temperature range (DTR) in our model. Results show that DMT and high levels of species' boldness are the primary drivers of community instability. However, their interactive effects can lead to diverse outcomes: from predator collapse to coexistence with seasonality-driven cycles and coexistence with population interaction-driven cycles. The interactive effects are significantly modulated by daily temperature variability, where moderate DTR counteracts the destabilizing interactive effects by increasing consumer reproduction, while large temperature variability considerably reduces consumer biomass, destabilizing the community at high mean temperatures. Our analyses disentangle the respective roles of DMT, DTR and boldness in mediating the response of aquatic ecosystems to the impacts from pharmaceutical contaminants in the context of climate warming. The interactive effects of the environmental stressors reported here underscore the pressing need for studies aimed at quantifying the cumulative impacts of multiple environmental stressors on aquatic ecosystems.

Combined effects of climate change and BDE-209 dietary exposure on the behavioural response of the white seabream, Diplodus sargus

Decabromodiphenyl-ether (BDE-209) is a persistent organic pollutant ubiquitously found in marine environments worldwide. Even though this emerging chemical contaminant is described as highly toxic, bioaccumulative and biomagnifiable, limited studies have addressed the ecotoxicological implications associated with its exposure in non-target marine organisms, particularly from a behavioural standpoint. Alongside, seawater acidification and warming have been intensifying their impacts on marine ecosystems over the years, compromising species welfare and survival. BDE-209 exposure as well as seawater acidification and warming are known to affect fish behaviour, but information regarding their interactive effects is not available. In this study, long-term effects of BDE-209 contamination, seawater acidification and warming were studied on different behavioural traits of Diplodus sargus juveniles. Our results showed that D. sargus exhibited a marked sensitivity in all the behaviour responses after dietary exposure to BDE-209. Fish exposed to BDE-209 alone revealed lower awareness of a risky situation, increased activity, less time spent within the shoal, and reversed lateralization when compared to fish from the Control treatment. However, when acidification and/or warming were added to the equation, behavioural patterns were overall altered. Fish exposed to acidification alone exhibited increased anxiety, being less active, spending more time within the shoal, while presenting a reversed lateralization. Finally, fish exposed to warming alone were more anxious and spent more time within the shoal compared to those of the Control treatment. These novel findings not only confirm the neurotoxicological attributes of brominated flame retardants (like BDE-209), but also highlight the relevance of accounting for the effects of abiotic variables (e.g. pH and seawater temperature) when investigating the impacts of environmental contaminants on marine life.

Environmental Occurrence and Predicted Pharmacological Risk to Freshwater Fish of over 200 Neuroactive Pharmaceuticals in Widespread Use

There is a growing concern that neuroactive chemicals released into the environment can perturb wildlife behaviour. Among these chemicals, pharmaceuticals such as antidepressants and anxiolytics have been receiving increasing attention, as they are specifically prescribed to modify behavioural responses. Many laboratory studies have demonstrated that some of these compounds can affect various aspects of the behaviour of a range of aquatic organisms; however, these investigations are focused on a very small set of neuroactive pharmaceuticals, and they often consider one compound at a time. In this study, to better understand the environmental and toxicological dimension of the problem, we considered all pharmaceuticals explicitly intended to modulate the central nervous system (CNS), and we hypothesised that these compounds have higher probability of perturbing animal behaviour. Based on this hypothesis, we used the classification of pharmaceuticals provided by the British National Formulary (based on their clinical applications) and identified 210 different CNS-acting pharmaceuticals prescribed in the UK to treat a variety of CNS-related conditions, including mental health and sleep disorders, dementia, epilepsy, nausea, and pain. The analysis of existing databases revealed that 84 of these compounds were already detected in surface waters worldwide. Using a biological read-across approach based on the extrapolation of clinical data, we predicted that the concentration of 32 of these neuroactive pharmaceuticals in surface waters in England may be high enough to elicit pharmacological effects in wild fish. The ecotoxicological effects of the vast majority of these compounds are currently uncharacterised. Overall, these results highlight the importance of addressing this environmental challenge from a mixture toxicology and systems perspective. The knowledge platform developed in the present study can guide future region-specific prioritisation efforts, inform the design of mixture studies, and foster interdisciplinary efforts aimed at identifying novel approaches to predict and interpret the ecological implications of chemical-induced behaviour disruption.

Impacts of Oxazepam on Perch (Perca fluviatilis) Behavior: Fish Familiarized to Lake Conditions Do Not Show Predicted Anti-anxiety Response

A current theory in environmental science states that dissolved anxiolytics (oxazepam) from wastewater effluents can reduce anti-predator behavior in fish with potentially negative impacts on prey fish populations. Here, we hypothesize that European perch (Perca fluviatilis) populations being exposed to oxazepam in situ show reduced anti-predator behavior, which has previously been observed for exposed isolated fish in laboratory studies. We tested our hypothesis by exposing a whole-lake ecosystem, containing both perch (prey) and northern pike (Esox lucius; predator), to oxazepam while tracking fish behavior before and after exposure in the exposed lake as well as in an unexposed nearby lake (control). Oxazepam concentrations in the exposed lake ranged between 11 and 24 μg L^-1, which is >200 times higher than concentrations reported for European rivers. In contrast to our hypothesis, we did not observe an oxazepam-induced reduction in anti-predator behavior, inferred from perch swimming activity, distance to predators, distance to conspecifics, home-range size, and habitat use. In fact, exposure to oxazepam instead stimulated anti-predator behavior (decreased activity, decreased distance to conspecifics, and increased littoral habitat use) when using behavior in the control lake as a reference. Shoal dynamics and temperature changes may have masked modest reductions in anti-predator behavior due to oxazepam. Although we cannot fully resolve the mechanism(s) behind our observations, our results indicate that the effects of oxazepam on perch behavior in a familiar natural ecosystem are negligible in comparison to the effects of other environmental conditions.

Low concentrations of oxazepam induce feeding and molecular changes in Radix balthica juveniles

Psychotropics, especially benzodiazepines, are commonly prescribed worldwide. Poorly eliminated at wastewater treatment plants, they belong to a group of emerging contaminants. Due to their interaction with the GABA_A receptor, they may affect the function of the nervous system of non-target organisms, such as aquatic organisms. The toxicity of oxazepam, a very frequently detected benzodiazepine in continental freshwater, has been largely studied in aquatic vertebrates over the last decade. However, its effects on freshwater non-vertebrates have received much less attention. We aimed to evaluate the long-term effects of oxazepam on the juvenile stage of a freshwater gastropod widespread in Europe, Radix balthica. Juveniles were exposed for a month to environmentally-relevant concentrations of oxazepam found in rivers (0.8 μg/L) and effluents (10 μg/L). Three main physiological functions were studied: feeding, growth, and locomotion. Additionally, gene expression analysis was performed to provide insights into toxicity mechanisms. There was a strong short-term activation of the feeding rate at low concentration, whereas the high dose resulted in long-term inhibition of food intake. A significant decrease in mortality rate was observed in juveniles exposed to the lowest dose. Shell growth and locomotor activity did not appear to be affected by oxazepam. Transcriptomic analysis revealed global over-expression of genes involved in the nervous regulation of the feeding, digestive, and locomotion systems after oxazepam exposure. The molecular analysis also revealed a possible interference of animal manipulation with the molecular effects induced by oxazepam exposure. Overall, these results improve our understanding of the effects of the psychoactive drug oxazepam on an aquatic mollusc gastropod.

Chronic Exposure to Oxazepam Pollution Produces Tolerance to Anxiolytic Effects in Zebrafish (Danio rerio)

Environmental concentrations of the anxiolytic drug oxazepam have been found to disrupt antipredator behaviors of wild fish. Most experiments exposed fish for a week, while evidence from mammals suggests that chronic exposure to therapeutic concentrations of benzodiazepines (such as oxazepam) results in the development of tolerance to the anxiolytic effects. If tolerance can also develop in response to the low concentrations found in the aquatic environment, it could mitigate the negative effects of oxazepam pollution. In the current study, we exposed wild-caught zebrafish to oxazepam (∼7 μg L^-1) for 7 or 28 days and evaluated behavioral and physiological parameters at both time points. Females showed reduced diving responses to conspecific alarm pheromone after 7 days, but not after 28 days, indicating that they had developed tolerance to the anxiolytic effects of the drug. Zebrafish males were not affected by this oxazepam concentration, in line with earlier results. Serotonin turnover (ratio 5-HIAA/5-HT) was reduced in exposed females and males after 28 days, indicating that brain neurochemistry had not normalized. Post-confinement cortisol concentrations and gene expression of corticotropin-releasing hormone (CRH) were not affected by oxazepam. We did not find evidence that chronically exposed fish had altered relative expression of GABA_A receptor subunits, suggesting that some other still unknown mechanism caused the developed tolerance.

Less anxious salmon smolt become easy prey during downstream migration

Hatchery-reared salmon smolt used for supplementary stocking often display poor migration behavior compared to wild smolt, which reduces the success of this management action. Oxazepam, an anxiolytic drug, has been shown to intensify salmon smolt migration in mesocosm experiments, and treatment with this drug has, therefore, been suggested as a management option to improve downstream smolt migration. In this study, we tested this by assessing migration performance of hatchery-reared Atlantic salmon (Salmo salar) smolt along a 21-km long natural river-to-sea migration route in a boreal river in Northern Sweden. Using acoustic telemetry, the migration rate and survival of smolt that had been exposed to oxazepam (200 μg L^-1, N = 20) was monitored and compared with a control group (N = 20) of unexposed smolt. Exposed smolt took significantly longer time to initiate migration after release compared to the control fish, but after that we observed no significant difference in downstream migration speed. However, exposed smolt had considerably higher probability of being predated on compared to control smolt. We attribute these results to increased risk-taking and higher activity in oxazepam-exposed smolt, which in turn increased initial non-directional exploratory behavior and decreased predator vigilance. These results are discussed based on current concerns for ecological implications of behavioral modifications induced by pharmaceutical pollution and climate change. We conclude that exposure to oxazepam is an unsuitable management option to prime migration of reared salmon in natural systems.

Protecting the environment from psychoactive drugs: Problems for regulators illustrated by the possible effects of tramadol on fish behaviour

There is concern that psychoactive drugs present in the aquatic environment could affect the behaviour of fish, and other organisms, adversely. There is considerable experimental support for this concern, although the literature is not consistent. To investigate why, fish were exposed to three concentrations of the synthetic opiate tramadol for 23-24 days, and their anxiolytic behaviour in a novel tank diving test was assessed both before and after exposure. The results were difficult to interpret. The positive control drug, the anti-depressant fluoxetine, produced the expected results: exposed fish explored the novel tank more, and swam more slowly while doing so. An initial statistical analysis of the results provided relatively weak support for the conclusion that both the low and high concentrations of tramadol affected fish behaviour, but no evidence that the intermediate concentration did. To gain further insight, UK and Japanese experts in ecotoxicology were asked for their independent opinions on the data for tramadol. These were highly valuable. For example, about half the experts replied that a low concentration of a chemical can cause effects that higher concentrations do not, although a similar number did not believe this was possible. Based both on the inconclusive effects of tramadol on the behaviour of the fish and the very varied opinions of experts on the correct interpretation of those inconclusive data, it is obvious that more research on the behavioural effects of tramadol, and probably all other psychoactive drugs, on aquatic organisms is required before any meaningful risk assessments can be conducted. The relevance of these findings may apply much more widely than just the environmental risk assessment of psychoactive drugs. They suggest that much more rigorous training of research scientists and regulators is probably required if consensus decisions are to be reached that adequately protect the environment from chemicals.

Cisplatin exposure impairs ionocytes and hair cells in the skin of zebrafish embryos

This study aimed to assess the sublethal effects of a platinum-based compound, cisplatin, using a zebrafish model. Zebrafish embryos were incubated in different concentrations of cisplatin at 0-96 h post-fertilization. Using a non-invasive, scanning ion-selective electrode technique (SIET), we measured the functions of hair cells (Ca²⁺ influx) and ionocytes ([H⁺] gradients). The survival rate, hatching rate, phenotype, body length, whole-body ion (Na⁺, Cl^-, and Ca²⁺) and Pt contents were also determined. The effects of cisplatin on zebrafish embryos were demonstrated as first impairing hair cell function (at 1 μM of cisplatin), the hair cell number, and body ion content of Cl^- (at 10 μM of cisplatin), then decreasing ionocyte acid secretion and overall body ion contents of Na⁺ and Ca²⁺ (at 50 μM of cisplatin). The body length and ionocyte density decreased at 100 μM of cisplatin, and survival decreased at 500 μM of cisplatin. As the cisplatin concentration increased, the accumulation of Pt in fish embryos also increased. These results revealed that hair cells are significantly more susceptible to cisplatin toxicity than ionocytes. By determining the lowest observed effective concentration of cisplatin that caused in vivo functional alterations of zebrafish hair cells and skin ionocytes, this model demonstrated 500-fold greater sensitivity than by detecting changes in survival, for early assessment of the effects of platinum-based chemotherapeutic drugs on fish.

Behavioural effects of psychoactive pharmaceutical exposure on European perch (Perca fluviatilis) in a multi-stressor environment

With the ability to resist biodegradation and exert therapeutic effects at low concentrations, pharmaceutical contaminants have become environmental stressors for wildlife. One such contaminant is the anxiolytic oxazepam, a psychoactive pharmaceutical that is frequently detected in surface waters globally. Despite growing interest in understanding how wildlife respond to anxiolytics, synergistic effects of pharmaceuticals and other abiotic (e.g. temperature) and biotic (e.g. predation risk) stressors remain unclear. Here, using a multi-stressor approach, we investigated effects of 7-day oxazepam exposure (6.5 μg/L) on anxiety-related behaviours in juvenile European perch (Perca fluviatilis). The multi-stressor approach was achieved by exposing perch to oxazepam at two temperatures (10 °C and 18 °C), and at two predation risk regimes-generated using chemical cues from the northern pike (Esox lucius). Our exposures resulted in a successful uptake of the drug from the water, i.e., oxazepam was measured in perch muscle tissue at 50 ± 17 ng/g (mean ± SD). We found significant oxazepam-induced effects on boldness, with 76.7% of the treated fish entering the white background (i.e. 'exposed' area where exposure to presumed risks are higher) within the first 5 min, compared to 66.6% of the control fish. We also found a significant effect of temperature on total time spent freezing (i.e. staying motionless). Specifically, fish in the low temperature treatments (oxazepam, predation) froze for longer than fish in high temperatures. Our multi-stressor study is the first to uncover how anxiety-related behaviours in wild juvenile fish are altered by changes in water temperature and perceived predation risk. Importantly, our findings highlight the need to focus on multiple stressors to improve understanding of how organisms not only survive, but adapt to, human-induced environmental change.