The Role of Behavioral Ecotoxicology in Environmental Protection

Global occurrence and aquatic hazards of antipsychotics in sewage influents, effluent discharges and surface waters

Despite increasing reports of pharmaceuticals in surface waters, aquatic hazard information remains limited for many contaminants, particularly for sublethal, chronic responses plausibly linked to molecular initiation events that are largely conserved across vertebrates. Here, we critically examined available refereed information on the occurrence of 67 antipsychotics in wastewater effluent and surface waters. Because the majority of sewage remains untreated around the world, we also examined occurrence in sewage influents. When sufficient information was available, we developed probabilistic environmental exposure distributions (EEDs) for each compound in each matrix by geographic region. We then performed probabilistic environmental hazard assessments (PEHAs) using therapeutic hazard values (THVs) of each compound, due to limited sublethal aquatic toxicology information for this class of pharmaceuticals. From these PEHAs, we determined predicted exceedances of the respective THVs for each chemical among matrices and regions, noting that THV values of antipsychotic contaminants are typically lower than other classes of human pharmaceuticals. Diverse exceedances were observed, and these aquatic hazards varied by compound, matrix and geographic region. In wastewater effluent discharges and surface waters, sulpiride was the most detected antipsychotic; however, percent exceedances of the THV were minimal (0.6%) for this medication. In contrast, we observed elevated aquatic hazards for chlorpromazine (30.5%), aripiprazole (37.5%), and perphenazine (68.7%) in effluent discharges, and for chlorprothixene (35.4%) and flupentixol (98.8%) in surface waters. Elevated aquatic hazards for relatively understudied antipsychotics were identified, which highlight important data gaps for future environmental chemistry and toxicology research.

Comparative behavioral ecotoxicology of Inland Silverside larvae exposed to pyrethroids across a salinity gradient

Pyrethroids, a class of commonly used insecticides, are frequently detected in aquatic environments, including estuaries. The influence that salinity has on organism physiology and the partitioning of hydrophobic chemicals, such as pyrethroids, has driven interest in how toxicity changes in saltwater compared to freshwater. Early life exposures in fish to pyrethroids cause toxicity at environmentally relevant concentrations, which can alter behavior. Behavior is a highly sensitive endpoint that influences overall organism fitness and can be used to detect toxicity of environmentally relevant concentrations of aquatic pollutants. Inland Silversides (Menidia beryllina), a commonly used euryhaline model fish species, were exposed from 5 days post fertilization (~1-day pre-hatch) for 96 h to six pyrethroids: bifenthrin, cyfluthrin, cyhalothrin, cypermethrin, esfenvalerate and permethrin. Exposures were conducted at three salinities relevant to brackish, estuarine habitat (0.5, 2, and 6 PSU) and across 3 concentrations, either 0.1, 1, 10, and/or 100 ng/L, plus a control. After exposure, Inland Silversides underwent a behavioral assay in which larval fish were subjected to a dark and light cycle stimuli to determine behavioral toxicity. Assessment of total distanced moved and thigmotaxis (wall hugging), used to measure hyper/hypoactivity and anxiety like behavior, respectively, demonstrate that even at the lowest concentration of 0.1 ng/L pyrethroids can induce behavioral changes at all salinities. We found that toxicity decreased as salinity increased for all pyrethroids except permethrin. Additionally, we found evidence to suggest that the relationship between log K_OW and thigmotaxis is altered between the lower and highest salinities.

Exposure, but not timing of exposure, to a sulfonylurea herbicide alters larval development and behaviour in an amphibian species

Environmental contamination is one of the major causes of biodiversity loss. Wetlands are particularly susceptible to contamination and species inhabiting these habitats are subjected to pollutants during sensitive phases of their development. In this study, tadpoles of a widespread amphibian, the spined toad (Bufo spinosus), were exposed to environmental concentrations of nicosulfuron (0 μg/L; 0.15 ± 0.05 μg/L and 0.83 ± 0.04 μg/L), a sulfonylurea herbicide, during different phases of development. Tadpoles were exposed during embryonic (12.98 ± 0.90 days) or larval development (93.74± 0.85 days), or throughout both phases, and we quantified development duration, morphological traits and behavioural features as responses to exposure. Developing tadpoles exposed to nicosulfuron were larger, but with smaller body, and had shorter but wider tail muscles. They were also more active and swam faster than control tadpoles and showed diverging patterns of behavioural complexity. We showed that higher concentrations had greater effects on individuals than lower concentrations, but the timing of nicosulfuron exposure did not influence the metrics studied: Exposure to nicosulfuron triggered similar effects irrespective of the developmental stages at which exposure occurred. These results further indicate that transient exposure (e.g., during embryonic development) can induce long-lasting effects throughout larval development to metamorphosis. Our study confirms that contaminants at environmental concentrations can have strong consequences on non-target organisms. Our results emphasize the need for regulation agencies and policy makers to consider sublethal concentrations of sulfonulyrea herbicides, such as nicosulfuron, as a minimum threshold in their recommendations.

Morphological and behavioral alterations in zebrafish larvae after exposure to contaminated river sediments collected in different weather conditions

Wastewater treatment plants (WWTPs) are the primary source of micropollutants in aquatic ecosystems. Many micropollutants tend to bind to sediments and persist until remobilizion by bioturbation or flood events. Advanced effluent treatment by ozonation has been proven to eliminate most micropollutants. The present study characterizes sediments' toxic potential regarding zebrafish embryo development, which highly complex nervous system is vulnerable to exposure to neurotoxic substances. Furthermore, behavioral changes can be induced even at low pollutant concentrations and do not cause acute toxicity. The study area includes stretches of the main waterbody, the Wurm River (sampling sites W1-W5), and its tributary the Haarbach River (sampling sites H1, and H2) in North-Rhine Westphalia, Germany. Both waterbodies serve as recipients of WWTPs' effluents. The effluent entering the Haarbach River is conventionally treated, while the Wurm River receives ozonated effluent from the Aachen-Soers WWTP. Seven sampling sites up- and downstream of the WWTPs were investigated in June of two subsequent years. The first sampling campaign in 2017 was characterized by prolonged dry weather. The second sampling campaign in 2018 occurred after prolonged rain events and the release of the rainwater overflow basin. Direct exposure of zebrafish embryos to native sediments using the sediment contact test represented an ecologically realistic scenario and showed no acute sublethal effects. Exposure of the zebrafish embryo to freeze-dried sediments representing the ecotoxicological status of sediments during flood events unfolded acute sublethal toxicity. Behavioral studies with zebrafish larvae were an essential part of environmental neurotoxicity testing. Zebrafish larvae exposed to sediments' concentrations causing no acute effects led to behavioral changes signalizing neurotoxic substances in sediments. Polyaromatic hydrocarbons, polychlorinated biphenyls, and nitroaromatic compounds were identified as potential toxicity drivers, whereby the rainwater overflow basin served as a possible source of pollution. Mixture toxicity, effect-directed analysis, and further sediment monitoring are needed.

Effects of Polyurethane Small-Sized Microplastics in the Chironomid, Chironomus riparius: Responses at Organismal and Sub-Organismal Levels

Freshwater provides valuable services and functions to humankind. However, macroinvertebrates that underpin the delivery of many of those ecosystem services and functions are under an additional threat caused by microplastic pollution. Chironomids are one of the most abundant groups of macroinvertebrates in these environments and the most sensitive to microplastics. This investigation addressed the effects of polyurethane (PU-MPs; 7.0-9.0 µm) on the chironomid Chironomus riparius at the organism and sub-organism levels. For this purpose, two assays were carried out: (i) addressing the effects of PU-MPs on C. riparius partial life cycle traits (larval size and emergence parameters) in a 28 d assay considering concentrations up to 750 mg/Kg, and (ii) larvae behaviour (locomotion) as well as the biochemical responses (oxidative damage, aerobic energy production, and energy reserves) in a 10 d assay considering an environmentally relevant concentration with no observed effects on C. riparius previous life history traits (no observed effect concentration; NOEC = (375 mg/kg). Exposure to PU-MPs did not affect C. riparius larval length nor cumulative and time to emergence. Conversely, when exposed to an environmentally relevant concentration for 10 days, contaminated larvae were revealed to be lighter (but not smaller nor less nutritionally affected in terms of energy reserves) and more active when foraging, which was reflected in the activation of their aerobic metabolism when assessing the electron transport chain as a proxy. Notwithstanding, PU-MPs did not originate observable energy costs, either on protein, lipid, or sugar contents on contaminated larvae, which may justify the absence of effects on larval growth and emergence. Therefore, the increased production of energy used for the locomotion and functioning of larvae was at the expense of the fraction of energy that should have been allocated for the weight of the individuals. A long-term exposure involving a multigenerational assessment would bring intel on the potential (cumulative) sub-lethal effects of PU-MPs on C. riparius fitness.

The Amphibian Short-Term Assay: Evaluation of a New Ecotoxicological Method for Amphibians Using Two Organophosphate Pesticides Commonly Found in Nature-Assessment of Biochemical, Morphological, and Life-History Traits

Amphibia is the most threatened class among vertebrates, with >40% of the species threatened with extinction. Pollution is thought to alter amphibian population dynamics. With the growing interest in behavioral ecotoxicology, the neurotoxic organophosphate pesticides are of special concern. Understanding how exposure to neurotoxics leads to behavioral alterations is of crucial importance, and mechanistic endpoints should be included in ecotoxicological methods. In the present study, we tested an 8-day assay to evaluate the toxicity of two organophosphates, diazinon and chlorpyrifos, on Xenopus laevis, that is, on biochemical, morphological, and life-history traits related to locomotion capacities. The method involves measuring biomarkers such as glutathione-S-transferase (GST) and ethoxyresorufin-O-deethylase (EROD; two indicators of the detoxifying system) in the 8-day-old larvae as well as acetylcholinesterase (AChE) activity (involved in the nervous system) in 4-day-old embryos and 8-day-old larvae. Snout-to-vent length and snout-to-tail length of 4-day-old embryos and 8-day larvae were recorded as well as the corresponding growth rate. Fin and tail muscle widths were measured as well for testing changes in tail shape. Both tests showed effects of both organophosphates on AChE activity; however, no changes were observed in GST and EROD. Furthermore, exposure to chlorpyrifos demonstrated impacts on morphological and life-history traits, presaging alteration of locomotor traits. In addition, the results suggest a lower sensitivity to chlorpyrifos of 4-day-old embryos compared to 8-day-old larvae. Tests on other organophosphates are needed to test the validity of this method for the whole organophosphate group. Environ Toxicol Chem 2022;41:2688-2699. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Differential biochemical and behavioral responses induced by cocaine and benzoylecgonine exposure to the red swamp crayfish Procambarus clarkii

Cocaine (COC) and its main metabolite, the benzoylecgonine (BE), are the main illicit drugs measured in aquatic system worldwide, with concentrations up to hundreds of ng/L. Although their current environmental concentrations are low these molecules can induce adverse effects at sub-individual level in non-target organisms. In contrast, the information at individual and behavioral level are still scant. The present study aimed at investigating biochemical and behavioral effects induced by 14-days exposure to environmentally relevant concentrations (50 ng/L and 500 ng/L) of COC and BE towards Procambarus clarkii. At sub-individual level, the activity of antioxidant and detoxifying (superoxide dismutase - SOD, catalase - CAT, glutathione peroxidase - GPx and glutathione S-transferases - GST) enzymes, as well as the levels of lipid peroxidation (LPO), were measured as oxidative stress-related endpoints. We also measured the acetylcholinesterase (AChE) activity to check for neurotoxic effect of COC and BE. At individual level, the modulation of some behavioral tasks (i.e., response to external stimuli, changes in feeding activity and exploration of a new environment) were assessed. Although both COC and BE exposure did not induce an oxidative stress situation, a significant inhibition of AChE activity was noted, resulting in behavioral changes in crayfish exposed to COC only. Crayfish exposed to the higher COC concentration showed an increase in the boldness and a decrease in the feeding activity, suggesting that COC may act according to its psychotropic mode of action.

Disruptions of circadian rhythms, sleep, and stress responses in zebrafish: New infrared-based activity monitoring assays for toxicity assessment

Behavioural disruptions are sensitive indicators of alterations to normal animal physiology and can be used for toxicity assessment. The small vertebrate zebrafish is a leading model organism for toxicological studies. The ability to continuously monitor the toxicity of drugs, pollutants, or environmental changes over several days in zebrafish can have high practical application. Although video-recordings can be used to monitor short-term zebrafish behaviour, it is challenging to videorecord prolonged experiments (e.g. circadian behaviour over several days) because of the darkness periods (nights) and the heavy data storage and image processing requirements. Alternatively, infrared-based activity monitors, widely used in invertebrate models such as drosophila, generate simple and low-storage data and could optimize large-scale prolonged behavioural experiments in zebrafish, thus favouring the implementation of high-throughput testing strategies. Here, we validate the use of a Locomotor Activity Monitor (LAM) to study the behaviour of zebrafish larvae, and we characterize the behavioural phenotypes induced by abnormal light conditions and by the Parkinsonian toxin MPP⁺. When zebrafish were deprived from daily light-cycle synchronization, the LAM detected various circadian disruptions, such as increased activity period, phase shifts, and decreased inter-daily stability. Zebrafish exposed to MPP⁺ (10, 100, 500 μM) showed a concentration-dependent decrease in activity, sleep disruptions, impaired habituation to repetitive startles (visual-motor responses), and a slower recovery to normal activity after the startle-associated stress. These phenotypes evidence the feasibility of using infrared-based LAM to assess multi-parameter behavioural disruptions in zebrafish. The procedures in this study have wide applicability and may yield standard methods for toxicity testing.

Acute toxicity of broflanilide on neurosecretory system and locomotory behavior of zebrafish (Danio rerio)

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC₅₀) of 0.76 mg/L. However, its effect on fish behavior and the underlying mechanisms are still unclear. The present study evaluated the effects of broflanilide on the zebrafish brain over a 96-h exposure by comparing the histopathological changes and relative expression of targeted genes with the behavioral metrics. The results of the toxicity test showed that broflanilide could cause deformities, such as deformation of the operculum and spinal curvature, at 0.6, 0.82 and 1.15 mg/L. Results also showed tissue damage and apoptosis in the cerebellum under 0.27 and 0.6 mg/L exposure. Additionally, broflanilide affected the neurotransmitters, metabolites and transcripts of genes associated with dopamine, gamma-aminobutyric acid expression. and the signaling pathways in zebrafish brains at 0.60 mg/L after 1 h and 96 h of exposure, while the levels of glutamate, glutamate decarboxylase, GABA transaminase, nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) were also inhibited at 0.27 mg/L after 96 h of exposure. The accumulated swimming distance was significantly longer and the average speed was significantly faster than the control at 0.27 and 0.6 mg/L after 1-h of exposure, while these metrics were lowered at 0.6 mg/L after 96 h of exposure. The study results demonstrates that broflanilide affects the zebrafish brain, neurotransmitters and associated fish behaviors. This study also provides deeper insight into the mechanistic understanding of the effects of broflanilide on the zebrafish brain.

Digital Video Acquisition and Optimization Techniques for Effective Animal Tracking in Behavioral Ecotoxicology

Behavioral phenotypic analysis is an emerging and increasingly important toolbox in aquatic ecotoxicology. In this regard digital video recording has recently become a standard in obtaining behavioral data. Subsequent analysis requires applications of specialized software for detecting and reconstructing animal locomotory trajectories as well as extracting quantitative biometric endpoints associated with specific behavioral traits. Despite some profound advantages for behavioral ecotoxicology, there is a notable lack of standardization of procedures and guidelines that would aid in consistently acquiring high-quality digital videos. The latter are fundamental for using animal tracking software successfully and to avoid issues such as identification switching, incorrect interpolation, and low tracking visibility. Achieving an optimized tracking not only saves user time and effort to analyze the results but also provides high-fidelity data with minimal artifacts. In the present study we, for the first time, provide an easily accessible guide on how to set up and optimize digital video acquisition while minimizing pitfalls in obtaining the highest-quality data for subsequent animal tracking. We also discuss straightforward digital video postprocessing techniques that can be employed to further enhance tracking consistency or improve the videos that were acquired in otherwise suboptimal settings. The present study provides an essential guidebook for any aquatic ecotoxicology studies that utilize digital video acquisition systems for evaluation of behavioral endpoints. Environ Toxicol Chem 2022;41:2342-2352. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Elucidating the Differences in Metal Toxicity by Quantitative Adverse Outcome Pathways

Numerous studies have reported that the toxicity differences among metals are widespread; however, little is known about the mechanism of differences in metal toxicity to aquatic organisms due to the lack of quantitative understanding of their adverse outcome pathway. Here, we investigated the effects of Cd and Cu on bioaccumulation, gene expression, physiological responses, and apical effects in zebrafish larvae. RNA sequencing was conducted to provide supplementary mechanistic information for the effects of Cd and Cu exposure. On this basis, we proposed a quantitative adverse outcome pathway (qAOP) suitable for metal risk assessment of aquatic organisms. Our work provides a mechanistic explanation for the differences in metal toxicity where the strong bioaccumulation of Cu enables the newly accumulated Cu to reach the threshold that causes different adverse effects faster than Cd in zebrafish larvae, resulting in a higher toxicity of Cu than that of Cd. Furthermore, we proposed a parameter C_IT/BCF (the ratio of internal threshold concentration and bioaccumulation factor) that helps to understand the toxicity differences by combining the information of bioaccumulation and internal threshold of adverse effects. This work demonstrated that qAOP is an effective quantitative tool for understanding the toxicity mechanism and highlight the importance of toxicokinetics and toxicodynamics at different biological levels in determining the metal toxicity.

High-Throughput Phototactic Ecotoxicity Biotests with Nauplii of Artemia franciscana

Analysis of sensorimotor behavioral responses to stimuli such as light can provide an enhanced relevance during rapid prioritisation of chemical risk. Due to technical limitations, there have been, however, only minimal studies on using invertebrate phototactic behaviors in aquatic ecotoxicity testing. In this work, we demonstrate an innovative, purpose-built analytical system for a high-throughput phototactic biotest with nauplii of euryhaline brine shrimp Artemia franciscana. We also, for the first time, present a novel and dedicated bioinformatic approach that facilitates high-throughput analysis of phototactic behaviors at scale with great fidelity. The nauplii exhibited consistent light-seeking behaviors upon extinguishing a brief programmable light stimulus (5500K, 400 lux) without habituation. A proof-of-concept validation involving the short-term exposure of eggs (24 h) and instar I larval stages (6 h) to sub-lethal concentrations of insecticides organophosphate chlorpyrifos (10 µg/L) and neonicotinoid imidacloprid (50 µg/L) showed perturbation in light seeking behaviors in the absence of or minimal alteration in general mobility. Our preliminary data further support the notion that phototactic bioassays can represent an attractive new avenue in behavioral ecotoxicology because of their potential sensitivity, responsiveness, and low cost.

Sensory-Motor Perturbations in Larval Zebrafish (Danio rerio) Induced by Exposure to Low Levels of Neuroactive Micropollutants during Development

Due to increasing numbers of anthropogenic chemicals with unknown neurotoxic properties, there is an increasing need for a paradigm shift toward rapid and higher throughput behavioral bioassays. In this work, we demonstrate application of a purpose-built high throughput multidimensional behavioral test battery on larval stages of Danio rerio (zebrafish) at 5 days post fertilization (dpf). The automated battery comprised of the established spontaneous swimming (SS), simulated predator response (SPR), larval photomotor response (LPR) assays as well as a new thermotaxis (TX) assay. We applied the novel system to characterize environmentally relevant concentrations of emerging pharmaceutical micropollutants including anticonvulsants (gabapentin: 400 ng/L; carbamazepine: 3000 ng/L), inflammatory drugs (ibuprofen: 9800 ng/L), and antidepressants (fluoxetine: 300 ng/L; venlafaxine: 2200 ng/L). The successful integration of the thermal preference assay into a multidimensional behavioral test battery provided means to reveal ibuprofen-induced perturbations of thermal preference behaviors upon exposure during embryogenesis. Moreover, we discovered that photomotor responses in larval stages of fish are also altered by the as yet understudied anticonvulsant gabapentin. Collectively our results demonstrate the utility of high-throughput multidimensional behavioral ecotoxicity test batteries in prioritizing emerging risks associated with neuroactive drugs that can perturb neurodevelopment. Moreover, we showcase the added value of thermotaxis bioassays for preliminary screening of emerging contaminants.

Frontiers in quantifying wildlife behavioural responses to chemical pollution

Animal behaviour is remarkably sensitive to disruption by chemical pollution, with widespread implications for ecological and evolutionary processes in contaminated wildlife populations. However, conventional approaches applied to study the impacts of chemical pollutants on wildlife behaviour seldom address the complexity of natural environments in which contamination occurs. The aim of this review is to guide the rapidly developing field of behavioural ecotoxicology towards increased environmental realism, ecological complexity, and mechanistic understanding. We identify research areas in ecology that to date have been largely overlooked within behavioural ecotoxicology but which promise to yield valuable insights, including within- and among-individual variation, social networks and collective behaviour, and multi-stressor interactions. Further, we feature methodological and technological innovations that enable the collection of data on pollutant-induced behavioural changes at an unprecedented resolution and scale in the laboratory and the field. In an era of rapid environmental change, there is an urgent need to advance our understanding of the real-world impacts of chemical pollution on wildlife behaviour. This review therefore provides a roadmap of the major outstanding questions in behavioural ecotoxicology and highlights the need for increased cross-talk with other disciplines in order to find the answers.

Identifying Behavioral Response Profiles of Two Common Larval Fish Models to a Salinity Gradient

Salinization of aquatic systems is an emerging global issue projected to increase in magnitude, frequency, and duration with climate change and landscape modifications. To consider influences of salinity on locomotor activity of common fish models, we examined behavioral response profiles of two species, zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), across a gradient of sodium chloride. Following each experiment, behavior was recorded with automated tracking software and then behavioral response variables, including locomotor (e.g., distance traveled, number of movements, duration of movements) and photolocomotor changes, were examined at several speed thresholds (bursting, cruising, freezing) to identify potential salinity responses. Zebrafish responses were significantly (p < 0.05) reduced at the highest treatment level (5.78 g/L) for multiple behavioral endpoints during both dark and light phases; however, fathead minnow responses were more variable and not consistently concentration dependent. Future efforts are needed to understand behavioral response profiles in combination with anthropogenic contaminants and natural toxins across the freshwater to marine continuum, considering salinization of inland waters, sea level rise, and transport of anthropogenic contaminants and algal toxins from inland waters to coastal systems.

Assessment of the Potential Ecotoxicological Effects of Pharmaceuticals in the World's Rivers

During their production, use, and disposal, active pharmaceutical ingredients (APIs) are released into aquatic systems. Because they are biologically active molecules, APIs have the potential to adversely affect nontarget organisms. We used the results of a global monitoring study of 61 APIs alongside available ecotoxicological and pharmacological data to assess the potential ecotoxicological effects of APIs in rivers across the world. Approximately 43.5% (461 sites) of the 1052 sampling locations monitored across 104 countries in a recent global study had concentrations of APIs of concern based on apical, nonapical, and mode of action-related endpoints. Approximately 34.1% of the 137 sampling campaigns had at least one location where concentrations were of ecotoxicological concern. Twenty-three APIs occurred at concentrations exceeding "safe" concentrations, including substances from the antidepressant, antimicrobial, antihistamine, β-blocker, anticonvulsant, antihyperglycemic, antimalarial, antifungal, calcium channel blocker, benzodiazepine, painkiller, progestin, and lifestyle compound classes. At the most polluted sites, effects are predicted on different trophic levels and on different endpoint types. Overall, the results show that API pollution is a global problem that is likely negatively affecting the health of the world's rivers. To meet the United Nations' Sustainable Development Goals, work is urgently needed to tackle the problem and bring concentrations down to an acceptable level. Environ Toxicol Chem 2022;41:2008-2020. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Phototactic behaviour and neurotransmitter profiles in two Daphnia magna clones: Vertical and horizontal responses to fish kairomones and psychotropic drugs

Animal behavioural responses are increasingly being used in environmental risk assessment. Nevertheless, behavioural responses are still hampered by a lack of standardisation. Phototactic behaviour in zooplankton and in particular in Daphnia has often been associated to vertical migration but there is also 'shore-avoidance' horizontal behaviour: Daphnia uses shades along the shore to swim either to or away from the shore and predators. Previously, we develop a vertical oriented behavioural hardware able to reproduce phototactic fish induced depth selection in Daphnia magna, its modulation by fish kairomones and psychotropic drugs and the neurotransmitter profiles associated to those responses. This study aims to test if it is possible to use an horizontal 24 multi-well plate maze set up to assess phototactic fish induced responses in D. magna. The study was conducted using two clones with opposed phototaxis upon exposure to fish kairomones and using psychotropic drugs known to modulate phototaxis. Acrylic strips opaque to visible light but not to the infrared one were used to cover half of the arena of each of the wells of the multi-well plate. Clone P₁32,85 showed positive phototaxis in either the vertical and horizontal set up and negative phototaxis when exposed to fish kairomones or to the muscarinic acetylcholine receptor antagonist's scopolamine and atropine. The opposite behaviour was observed for clone F. Diazepam and pilocarpine ameliorate fish kairomone induced negative phototaxis and picrotoxin increased it only in clone P₁32,85 in the vertical set up. The determination of neurotransmitters showed much greater concentrations of dopamine and of glycine in clone F, which may be relate to its negative phototaxis and its observed lower responsiveness to fish kairomones. The results from this study suggest a simple, fast, and high throughput phototactic behaviour assay for D. magna that can be easily adapted to other species.

Beyond the behavioural phenotype: Uncovering mechanistic foundations in aquatic eco-neurotoxicology

During the last decade, there has been an increase in awareness of how anthropogenic pollution can alter behavioural traits of diverse aquatic organisms. Apart from understanding profound ecological implications, alterations in neuro-behavioural indices have emerged as sensitive and physiologically integrative endpoints in chemical risk assessment. Accordingly, behavioural ecotoxicology and broader eco-neurotoxicology are becoming increasingly popular fields of research that span a plethora of fundamental laboratory experimentations as well as applied field-based studies. Despite mounting interest in aquatic behavioural ecotoxicology studies, there is, however, a considerable paucity in deciphering the mechanistic foundations underlying behavioural alterations upon exposure to pollutants. The behavioural phenotype is indeed the highest-level integrative neurobiological phenomenon, but at its core lie myriads of intertwined biochemical, cellular, and physiological processes. Therefore, the mechanisms that underlie changes in behavioural phenotypes can stem among others from dysregulation of neurotransmitter pathways, electrical signalling, and cell death of discrete cell populations in the central and peripheral nervous systems. They can, however, also be a result of toxicity to sensory organs and even metabolic dysfunctions. In this critical review, we outline why behavioural phenotyping should be the starting point that leads to actual discovery of fundamental mechanisms underlying actions of neurotoxic and neuromodulating contaminants. We highlight potential applications of the currently existing and emerging neurobiology and neurophysiology analytical strategies that should be embraced and more broadly adopted in behavioural ecotoxicology. Such strategies can provide new mechanistic discoveries instead of only observing the end sum phenotypic effects.

The assessment of environmental risk related to the occurrence of pharmaceuticals in bottom sediments of the Odra River estuary (SW Baltic Sea)

The occurrence of 130 pharmaceutically active compounds (PhACs) in sediments collected from 70 sampling sites in the Odra River estuary (SW Baltic Sea) was investigated. The highest concentration levels of the compounds were found in the vicinity of effluent discharge from two main Szczecin wastewater treatment plants: "Pomorzany" and "Zdroje", and nearby the seaport and shipyard. The highest environmental risks (RQ > 1) were observed for pseudoephedrine (RQ = 14.0), clindamycin (RQ = 7.3), nalidixic acid (RQ = 3.8), carbamazepine (RQ = 1.8), fexofenadine (RQ = 1.4), propranolol (RQ = 1.1), and thiabendazole (RQ = 1.1). RQ for each compound varied depending on the sampling sites. High environmental risk was observed in 30 sampling sites for clindamycin, 22 sampling sites for pseudoephedrine, 19 sampling sites for nalidixic acid, 4 sampling sites for carbamazepine, and 3 sampling sites for fexofenadine. The medium environmental risk (0.1 < RQ < 1) was observed for 16 compounds: amisulpride, amitriptyline, amlodipine, atropine, bisoprolol, chlorpromazine, lincomycin, metoprolol, mirtazapine, moclobemide, ofloxacin, oxazepam, tiapride, tolperisone, verapamil, and xylometazoline. Due to the scarcity of toxicological data related to benthic organisms, only an approximate assessment of the environmental risk of PhACs is possible. Nevertheless, the compounds with medium and high risk should be considered as pollutants of high environmental concern whose occurrence in the environment should remain under close scrutiny.

Metal contamination and heat stress impair swimming behavior and acetylcholinesterase activity in embryo-larval stages of the Mediterranean mussel, Mytilus galloprovincialis

Behavioral parameters are increasingly considered sensitive and early bioindicators of toxicity in aquatic organisms. A video-tracking tool was specifically developed to monitor the swimming behaviour of D-larvae of the Mediterranean mussel, Mytilus galloprovincialis, in controlled laboratory conditions. Both maximum and average swimming speeds and trajectories were recorded. We then investigated the impact of copper and silver with or without a moderate rise of temperature on swimming behavior and acetylcholinesterase (AChE) activity of mussel D-larvae and the possible mechanistic link between both biological responses. Our results showed that copper and/or silver exposure, as well as temperature increase, disrupts the swimming behavior of mussel larvae which could compromise their dispersal and survival. In addition, the combined effect of temperature and metals significantly (p < 0.05) increased AChE activity in mussel larvae. Pearson's correlation analysis was performed and results showed that the AChE activity is positively correlated with maximum speeds (r = 0.71, p < 0.01). This study demonstrates the value of behavioral analyzes of aquatic invertebrates as a sensitive and integrate marker of the effects of stressors.

The Influence of the Recording Time in Modelling the Swimming Behaviour of the Freshwater Inbenthic Copepod Bryocamptus pygmaeus

The analysis of copepod behaviour gained an increasing impetus over the past decade thanks to the advent of computer-assisted video analysis tools. Since the automated tracking consists in detecting the animal’s position frame by frame and improving signals corrupted by strong background noise, a crucial role is played by the length of the video recording. The aim of this study is to: (i) assess whether the recording time influences the analysis of a suite of movement descriptive parameters; (ii) understand if the recording time influences the outcome of the statistical analyses when hypotheses on the effect of toxicants/chemicals on the freshwater invertebrate behaviour are tested. We investigated trajectory parameters commonly used in behavioural studies—swimming speed, percentage of activity and trajectory convex hull—derived from the trajectories described by the inbenthic–interstitial freshwater copepod Bryocamptus pygmaeus exposed to a sub-lethal concentration of diclofenac. The analyses presented in this work indicate that the recording time did not influence the outcome of the results for the swimming speed and the percentage of activity. For the trajectory convex hull area, our results showed that a recording session lasting at least 3 min provided robust results. However, further investigations are needed to disentangle the role of concurrent factors, such as the behavioural analysis of multiple individuals simultaneously, whether they are of the same or opposite sex and the implications on sexual behaviour, competition for resources and predation.

Zebrafish Larvae Rapidly Recover from Locomotor Effects and Neuromuscular Alterations Induced by Cholinergic Insecticides

Owing to the importance of acetylcholine as a neurotransmitter, many insecticides target the cholinergic system. Across phyla, cholinergic signaling is essential for many neuro-developmental processes including axonal pathfinding and synaptogenesis. Consequently, early-life exposure to such insecticides can disturb these processes, resulting in an impaired nervous system. One test frequently used to assess developmental neurotoxicity is the zebrafish light-dark transition test, which measures larval locomotion as a response to light changes. However, it is only poorly understood which structural alterations cause insecticide-induced locomotion defects and how persistent these alterations are. Therefore, this study aimed to link locomotion defects with effects on neuromuscular structures, including motorneurons, synapses, and muscles, and to investigate the longevity of the effects. The cholinergic insecticides diazinon and dimethoate (organophosphates), methomyl and pirimicarb (carbamates), and imidacloprid and thiacloprid (neonicotinoids) were used to induce hypoactivity. Our analyses revealed that some insecticides did not alter any of the structures assessed, while others affected axon branching (methomyl, imidacloprid) or muscle integrity (methomyl, thiacloprid). The majority of effects, even structural, were reversible within 24 to 72 h. Overall, we find that both neurodevelopmental and non-neurodevelopmental effects of different longevity can account for the reduced locomotion. These findings provide unprecedented insights into the underpinnings of insecticide-induced hypoactivity.

Predicting the impacts of chemical pollutants on animal groups

Chemical pollution is among the fastest-growing agents of global change. Synthetic chemicals with diverse modes-of-action are being detected in the tissues of wildlife and pervade entire food webs. Although such pollutants can elicit a range of sublethal effects on individual organisms, research on how chemical pollutants affect animal groups is severely lacking. Here we synthesise research from two related, but largely segregated fields - ecotoxicology and behavioural ecology - to examine pathways by which chemical contaminants could disrupt processes that govern the emergence, self-organisation, and collective function of animal groups. Our review provides a roadmap for prioritising the study of chemical pollutants within the context of sociality and highlights important methodological advancements for future research.

Integration of Bioinspired Fibrous Strands with 3D Spheroids for Environmental Hazard Monitoring

Numerous methods have been introduced to produce 3D cell cultures that can reduce the need for animal experimentation. This study presents a unique 3D culture platform that features bioinspired strands of electrospun nanofibers (BSeNs) and aquatic cell lines to compensate for shortcomings in the current cell spheroid generation techniques. The use of BSeNs in 3D zebrafish liver cell cultures is found to improve liver and reproductive functions through spheroid-based in vitro assays such as whole transcriptome sequencing and reproductive toxicity testing, with optimized properties exhibiting results similar to those obtained for fish embryo acute toxicity (FET, OECD TG 236) following exposure to environmental endocrine-disrupting chemicals (17β-Estradiol (E2), 4-hydroxytamoxifen (4-HT), and bisphenol compounds (bisphenol A (BPA) and 9,9-Bis(4-hydroxyphenyl)fluorene (BPFL)). These findings indicate that the beneficial effects of bioinspired materials that closely mimic ECM environments can yield efficient zebrafish cells with intrinsic functions and xenobiotic metabolism similar to those of zebrafish embryos. As a closer analog for the in vivo conditions that are associated with exposure to potentially hazardous chemicals, the straightforward culture model introduced in this study shows promise as an alternative tool that can be used to further eco-environmental assessment.

Internalization, reduced growth, and behavioral effects following exposure to micro and nano tire particles in two estuarine indicator species

Synthetic rubber emissions from automobile tires are common in aquatic ecosystems. To assess potential impacts on exposed organisms, early life stages of the estuarine indicator species Inland Silverside (Menidia beryllina) and mysid shrimp (Americamysis bahia) were exposed to three tire particle (TP) concentrations at micro and nano size fractions (0.0038, 0.0378 and 3.778 mg/L in mass concentrations for micro size particles), and separately to leachate, across a 5-25 PSU salinity gradient. Following exposure, M. beryllina and A. bahia had significantly altered swimming behaviors, such as increased freezing, changes in positioning, and total distance moved, which could lead to an increased risk of predation and foraging challenges in the wild. Growth for both A. bahia and M. beryllina was reduced in a concentration-dependent manner when exposed to micro-TP, whereas M. beryllina also demonstrated reduced growth when exposed to nano-TP (except lowest concentration). TP internalization was dependent on the exposure salinity in both taxa. The presence of adverse effects in M. beryllina and A. bahia indicate that even at current environmental levels of tire-related pollution, which are expected to continue to increase, aquatic ecosystems may be experiencing negative impacts.

Behavioral Impairment in Aquatic Organisms Exposed to Neurotoxic Pollutants

Neuroactive chemicals are compounds that can modulate, at very low concentrations, the normal function of the central nervous systems of an organism through various primary modes of action (MoA) [...]

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.

Two types of microplastics (polystyrene-HBCD and car tire abrasion) affect oxidative stress-related biomarkers in earthworm Eisenia andrei in a time-dependent manner

Microplastics are small plastic fragments that are widely distributed in marine and terrestrial environments. While the soil ecosystem represents a large reservoir for plastic, research so far has focused mainly on the impact on aquatic ecosystems and there is a lack of information on the potentially adverse effects of microplastics on soil biota. Earthworms are key organisms of the soil ecosystem and are due to their crucial role in soil quality and fertility a suitable and popular model organism in soil ecotoxicology. Therefore, the aim of this study was to gain insight into the effects of environmentally relevant concentrations of microplastics on the earthworm Eisenia andrei on multiple levels of biological organization after different exposure periods. Earthworms were exposed to two types of microplastics: (1) polystyrene-HBCD and (2) car tire abrasion in natural soil for 2, 7, 14 and 28d. Acute and chronic toxicity and all subcellular investigations were conducted for all exposure times, avoidance behavior assessed after 48 h and reproduction after 28d. Subcellular endpoints included enzymatic biomarker responses, namely, carboxylesterase, glutathione peroxidase, acetylcholinesterase, glutathione reductase, glutathione S-transferase and catalase activities, as well as fluorescence-based measurements of oxidative stress-related markers and multixenobiotic resistance activity. Multiple biomarkers showed significant changes in activity, but a recovery of most enzymatic activities could be observed after 28d. Overall, only minor effects could be observed on a subcellular level, showing that in this exposure scenario with environmentally relevant concentrations based on German pollution levels the threat to soil biota is minimal. However, in areas with higher concentrations of microplastics in the environment, these results can be interpreted as an early warning signal for more adverse effects. In conclusion, these findings provide new insights regarding the ecotoxicological effects of environmentally relevant concentrations of microplastics on soil organisms.

Noninvasive Electrophysiology: Emerging Prospects in Aquatic Neurotoxicity Testing

The significance of neurotoxicological risks associated with anthropogenic pollution is gaining increasing recognition worldwide. In this regard, perturbations in behavioral traits upon exposure to environmentally relevant concentrations of neurotoxic and neuro-modulating contaminants have been linked to diminished ecological fitness of many aquatic species. Despite an increasing interest in behavioral testing in aquatic ecotoxicology there is, however, a notable gap in understanding of the neurophysiological foundations responsible for the altered behavioral phenotypes. One of the canonical approaches to explain the mechanisms of neuro-behavioral changes is functional analysis of neuronal transmission. In aquatic animals it requires, however, invasive, complex, and time-consuming electrophysiology techniques. In this perspective, we highlight emerging prospects of noninvasive, in situ electrophysiology based on multielectrode arrays (MEAs). This technology has only recently been pioneered for the detection and analysis of transient electrical signals in the central nervous system of small model organisms such as zebrafish. The analysis resembles electroencephalography (EEG) applications and provides an appealing strategy for mechanistic explorative studies as well as routine neurotoxicity risk assessment. We outline the prospective future applications and existing challenges of this emerging analytical strategy that is poised to bring new vistas for aquatic ecotoxicology such as greater mechanistic understanding of eco-neurotoxicity and thus more robust risk assessment protocols.

Structure-to-process design framework for developing safer pesticides

Rational design of pesticides with tunable degradation properties and minimal ecotoxicity is among the grand challenges of green chemistry. While computational approaches have gained traction in predictive toxicology, current methods lack the necessary multifaceted approach and design-vectoring tools needed for system-based chemical development. Here, we report a tiered computational framework, which integrates kinetics and thermodynamics of indirect photodegradation with predictions of ecotoxicity and performance, based on cutoff values in mechanistically derived physicochemical properties and electronic parameters. Extensively validated against experimental data and applied to 700 pesticides on the U.S. Environmental Protection Agency's registry, our simple yet powerful approach can be used to screen existing molecules to identify application-ready candidates with desirable characteristics. By linking structural attributes to process-based outcomes and by quantifying trade-offs in safety, depletion, and performance, our method offers a user-friendly roadmap to rational design of novel pesticides.

A plea for the integration of Green Toxicology in sustainable bioeconomy strategies - Biosurfactants and microgel-based pesticide release systems as examples

A key aspect of the transformation of the economic sector towards a sustainable bioeconomy is the development of environmentally friendly alternatives for hitherto used chemicals, which have negative impacts on environmental health. However, the implementation of an ecotoxicological hazard assessment at early steps of product development to elaborate the most promising candidates of lowest harm is scarce in industry practice. The present article introduces the interdisciplinary proof-of-concept project GreenToxiConomy, which shows the successful application of a Green Toxicology strategy for biosurfactants and a novel microgel-based pesticide release system. Both groups are promising candidates for industrial and agricultural applications and the ecotoxicological characterization is yet missing important information. An iterative substance- and application-oriented bioassay battery for acute and mechanism-specific toxicity within aquatic and terrestrial model species is introduced for both potentially hazardous materials getting into contact with humans and ending up in the environment. By applying in silico QSAR-based models on genotoxicity, endocrine disruption, skin sensitization and acute toxicity to algae, daphnids and fish, individual biosurfactants resulted in deviating toxicity, suggesting a pre-ranking of the compounds. Experimental toxicity assessment will further complement the predicted toxicity to elaborate the most promising candidates in an efficient pre-screening of new substances.

Impact of test chamber design on spontaneous behavioral responses of model crustacean zooplankton Artemia franciscana

The use of small aquatic model organisms to investigate the behavioral effects of chemical exposure is becoming an integral component of aquatic ecotoxicology research and neuroactive drug discovery. Despite the increasing use of invertebrates for behavioral phenotyping in toxicological studies and chemical risk assessments, little is known regarding the potential for environmental factors-such as geometry, size, opacity and depth of test chambers-to modulate common behavioral responses. In this work, we demonstrate that test chamber geometry, size, opacity and depth can affect spontaneous, unstimulated behavioral responses of euryhaline crustacean Artemia franciscana first instar larval stages. We found that in the absence of any obvious directional cues, A. franciscana exhibited a strong innate wall preference behavior. Using different test chamber sizes and geometries, we found both increased wall preference and lowered overall distance traveled by the test shrimp in a smaller chamber with sharper-angled vertices. It was also determined through quantifiable changes in the chambers' color that the A. franciscana early larval stages can perceive, differentiate and react to differences in color or perhaps rather to light transmittance of the test chambers. The interaction between innate edge preference and positive phototaxis could be consistently altered with a novel photic stimulus system. We also observed a strong initial preference for depth in A. franciscana first instar larval stages, which diminished through the acclimatization. We postulate that the impact of test chamber designs on neurobehavioral baseline responses warrants further investigation, in particular considering the increased interest in behavioral eco-neurotoxicology applications.

Chemical characteristics and toxicological effects of leachates from plastics under simulated seawater and fish digest

In recent years, the ecological risks of plastics to marine environments and organisms have attracted increasing attention, especially the leachates from plastics. However, a comprehensive knowledge about the leaching characteristics and subsequent toxicological effects of leachates is still sparse. In this study, 15 different plastic products were immersed in simulated seawater and fish digest for 16 h. The leachates were analyzed through non-target and target analyses and their toxicological signatures were assessed by bioassays. In total, 240 additives were identified from the plastic leachates, among which plasticizers represented the most (16.7%), followed by antioxidants (8.7%) and flame retardants (7.1%). Approximately 40% of plastic leachates exhibited significant inhibitory effects on the bioluminescence using a recombinant luminescent assay. In addition, both the hyperactive and hypoactive behaviors were displayed in the larvae of marine medaka (Oryzias melastigma) exposed to some plastic leachates. In general, the number and amount of identified compounds under simulated fish digest were less than those under simulated seawater. However, the simulated fish digest leachates triggered higher toxicity. Redundancy analysis demonstrated that identified additives did not adequately explain the toxicological effects. Future research should focus on the identification of more additives in the plastic leachates and their potential ecological risks.

Sub-acute exposure to nanoplastics via two-chain trophic transfer: From brine shrimp Artemia franciscana to small yellow croaker Larimichthys polyactis

This study investigated the trophic transfer of nanoplastics in marine food chains. We fed nanoplastic-exposed Artemia franciscana (brine shrimp) to Larimichthys polyactis (small yellow croaker) daily for eight days. Subsequently, the overall health condition, histopathological damage to the liver and digestive tract, and swimming ability of the fish were measured. After the sub-acute exposure to nanoplastics via trophic transfer, the fish showed inhibited growth, severe liver damage, as well as a poorer swimming ability compared to the control. The swimming ability was especially affected, in terms of the overall movement as well as thigmotaxis. The results thus clarified that even an indirect exposure to nanoplastics could induce neurotoxic effects and affect the swimming ability of the fish. As fish are well-known human food resources, the possibility of such trophic transfers affecting higher trophic level organisms, such as humans, cannot be ruled out.

Agricultural surface water, imidacloprid, and chlorantraniliprole result in altered gene expression and receptor activation in Pimephales promelas

The toxicity of single pesticides is likely underestimated when considering complex pesticide mixtures found in agricultural runoff and this is especially true for newer pesticides with little toxicity data on non-target species. The goal of our study was to compare the toxicity of two newer pesticides, imidacloprid (IMI) and chlorantraniliprole (CHL), when an invertebrate and fish were exposed to single compounds, binary mixtures or surface water collected near agricultural fields. A secondary goal was to determine whether changes in select subcellular molecular pathways correspond to the insecticides' mechanisms of activity in aquatic organisms. We conducted acute (96 h) exposures using a dilution series of field water and environmentally relevant concentrations of single and binary mixtures of IMI and CHL. We then evaluated survival, gene expression and the activity of IMI toward the n-acetylcholine receptor (nAChR) and CHL activity toward the ryanodine receptor (RyR). Both IMI and CHL were detected at all sampling locations for May 2019 and September 2019 sampling dates and exposure to field water led to high invertebrate but not fish mortality. Fish exposed to field collected water had significant changes in the relative expression of genes involved with detoxification and neuromuscular function. Exposure of fish to single compounds or binary mixtures of IMI and CHL led to increased relative gene expression of RyR in fish. Furthermore, we found that IMI targets the nAChR in aquatic invertebrates and that CHL can cause overactivation of the RyR in invertebrates and fish. Overall, our finding suggests that IMI and CHL may impact neuromuscular health in fish. Expanding monitoring efforts to include sublethal and molecular assays would allow the detection of subcellular level effects due to complex mixtures present in surface water near agricultural areas.

Transient exposure to sublethal concentrations of a pesticide mixture (chlorpyrifos-difenoconazole) caused different responses in fish species from different trophic levels of the same community

The assessment of early effects caused in biota by sublethal exposure to pesticide mixtures should enhance the realism in the ecological risk assessment for agricultural landscapes. This study aimed to evaluate sub-individual responses in fish, which can be linked with outcomes at higher levels of biological organization and affect their trophic relationships. A multilevel biomarker approach was applied to assess the effects of a 48 h exposure of two freshwater mesoamerican fish species (Parachromis dovii and Poecilia gillii) to a mixture of sublethal concentrations of chlorpyrifos (5 μg/L) and difenoconazole (325 μg/L). Transcriptomic induction of cyp1A and the activities of 7-ethoxy-resorufin-O-distillase (EROD) and glutathione S-transferase (GST) were measured as biotransformation-related biomarkers; cholinesterase activity (ChE) was assessed as a neurotoxicity biomarker; resting metabolic rate (RMR) was measured as a physiological biomarker; and the movement of fish in a dark-light environment as a behavior biomarker. The exposure to the mixture had evident effects on P. gillii, with significant induction of cyp1A transcription, increased EROD activity, ChE inhibition in muscle, and increased permanence in the light side of the dark-light environment. Meanwhile, P. dovii only showed significant induction of cyp1A, without evidence of neurotoxicity or changes in behavior. This study demonstrates that the severity of the effects caused by the exposure to a mixture of pesticides can differ among species from the same trophic chain. The potential impairment of predator-prey relationships is a relevant effect that pesticide pollution can cause and it should be considered for the risk assessment of such contaminants.

Drug pollution & Sustainable Development Goals

The United Nations set "The 2030 Agenda for Sustainable Development," which includes the Sustainable Development Goals (SDGs), a collection of 17 global goals designed to be a "blueprint to achieve a better and more sustainable future for all". Although only mentioned in one of the seventeen goals (goal 3), we argue that drugs in general, and growing drug pollution in particular, affects the SDGs in deeper, not readily apparent ways. So far, the emerging problem of drug pollution has not been sufficiently addressed. Here, we outline and discuss how drug pollution can affect SDGs and even threaten their achievement.

Effects of the antidepressant mirtazapine on the swimming behaviour and gene expression rate of Danio rerio embryos - Is the sedating effect seen in humans also evident for fish?

In the last decade, mirtazapine has become an important antidepressant in clinical use and has also been found at many different environmental sampling sites. Several homologies between the zebrafish Danio rerio and humans, combined with a number of advantages for behavioural and gene expression research using zebrafish embryos, make their use for the analysis of mirtazapine appropriate. The sedative effect of mirtazapine in humans was also found for a specific concentration range in zebrafish embryos (1333.4 μg/L - 2666.9 μg/L). Specifically, 116 hpf old zebrafish embryos showed a reduced swimming distance when exposed to 1334.4 μg/L mirtazapine. Furthermore, changes at the gene regulatory level could be measured (1333.4 μg/L), in particular in the superordinate regulatory systems. For selected transporters of all regulatory systems, an up regulation of the genes by a factor of more than five times could be measured at the highest mirtazapine exposure concentration that was tested. Finally, studies on the protein levels demonstrated an increase in acetylcholinesterase activity for several exposure concentrations (83.3 μg/L and 666.7 μg/L). The physiological changes in zebrafish embryos caused by mirtazapine demonstrate the relevance of these types of studies in aquatic non-target organisms. Such neuroactive substances could pose a potential risk for aquatic organisms below the previously considered concentration threshold for morphological effects.

Dietary Seleno-l-Methionine Causes Alterations in Neurotransmitters, Ultrastructure of the Brain, and Behaviors in Zebrafish (Danio rerio)

Elevated concentrations of dietary selenium (Se) cause abnormalities and extirpation of fish inhabiting in Se-contaminated environments. However, its effect on fish behavior and the underlying mechanisms remain largely unknown. In this study, two-month-old zebrafish (Danio rerio) was fed seleno-l-methionine (Se-Met) at environmentally relevant concentrations (i.e., control (2.61), low (5.43), medium (12.16), and high (34.61) μg Se/g dry weight (dw), respectively, corresponding to the C, L, M, and H treatments) for 60 days. Targeted metabolomics, histopathological, and targeted transcriptional endpoints were compared to behavioral metrics to evaluate the effects of dietary exposure to Se-Met . The results showed that the levels of total Se and malondialdehyde in fish brains were increased in a dose-dependent pattern. Meanwhile, mitochondrial damages and decreased activities of the mitochondria respiratory chain complexes were observed in the neurons at the M and H treatments. In addition, dietary Se-Met affected neurotransmitters, metabolites, and transcripts of the genes associated with the dopamine, serotonin, gamma-aminobutyric acid, acetylcholine, and histamine signaling pathways in zebrafish brains at the H treatments. The total swimming distance and duration in the Novel Arm were lowered in fish from the H treatment. This study has demonstrated that dietary Se-Met affects the ultrastructure of the zebrafish brain, neurotransmitters, and associated fish behaviors and may help enhance adverse outcome pathways for neurotransmitter-behavior key events in zebrafish.

Methamphetamine pollution elicits addiction in wild fish

Illicit drug abuse presents pervasive adverse consequences for human societies around the world. Illicit drug consumption also plays an unexpected role in contamination of aquatic ecosystems that receive wastewater discharges. Here, we show that methamphetamine, considered as one of the most important global health threats, causes addiction and behavior alteration of brown trout Salmo trutta at environmentally relevant concentrations (1 µg l-1). Altered movement behavior and preference for methamphetamine during withdrawal were linked to drug residues in fish brain tissues and accompanied by brain metabolome changes. Our results suggest that emission of illicit drugs into freshwater ecosystems causes addiction in fish and modifies habitat preferences with unexpected adverse consequences of relevance at the individual and population levels. As such, our study identifies transmission of human societal problems to aquatic ecosystems.