Behavioural ecotoxicology, an "early warning" signal to assess environmental quality

17α-Ethinylestradiol exposure disrupts anxiety-like behaviours but not social preference in sea bass larvae (Dicentrarchus labrax)

Endocrine-disrupting chemicals (EDCs) are widespread pollutants known to interfere with hormonal pathways and to disrupt behaviours. Standardised behavioural procedures have been developed in common fish model species to assess the impact of various pollutants on behaviours such as locomotor activity and anxiety-like as well as social behaviours. These procedures need now to be adapted to improve our knowledge on the behavioural effects of EDCs on less studied marine species. In this context, the European sea bass (Dicentrarchus labrax) is emerging as a valuable species representative of the European marine environment. Here, we designed and validated a two-step procedure allowing to sequentially assess anxiety-like behaviours (novel tank test) and social preference (visual social preference test) in sea bass. Thereafter, using this procedure, we evaluated whether social behavioural disruption occurs in 2-month-old larvae after an 8-day exposure to a xenoestrogen, the 17α-ethinylestradiol (EE2 at 0.5 and 50 nM). Our results confirmed previous studies showing that exposure to 50 nM of EE2 induces a significant increase in anxiety-like behaviours in sea bass larvae. On the contrary, social preference seemed unaffected whatever the EE2 concentration, suggesting that social behaviour has more complex mechanical regulations than anxiety.

Does copper contamination change thermotaxis of the soil arthropod Folsomia candida (Collembola)?

Behavioural thermoregulation (thermotaxis) is essential for soil invertebrates to evade thermal extremes in terrestrial environments. Extensive and continuous use of copper (Cu) based products has led to elevated Cu concentration in soils across the globe and in some areas reaching concentrations that are hazardous to soil invertebrates. We hypothesised that environmental stressors, for example, exposure to heavy metals may compromise the adaptive behavioural thermoregulation of organisms, but very little is known of such interactions. In this study, we chose Cu as a model toxicant and investigated the potential effect of Cu-contaminated soils on the behavioural thermoregulation of springtails (Folsomia candida). We measured the distribution of springtails when placed on a temperature gradient ranging from 6 to 46 °C and estimated their thermal preference as an indicator of behavioural thermoregulation. Results showed that within 60 min of being introduced to the thermal gradient, the distribution of springtails was unimodal with slight skewness towards high temperature. Springtails exhibited a consistent preferred temperature range of approximately 21-23 °C across all Cu exposure levels and time points. However, Cu contamination increased the frequency of springtails recorded along the gradient where temperature was above 30 °C. We interpreted this observation as Cu-exposed animals having an elevated risk of entering heat coma and not being able to evade noxious temperatures. We conclude that Cu contamination does not alter the thermal preference of F. candida but compromises their ability to tolerate extreme high temperature. Incorporating behavioural responses into ecotoxicological assessments provides ecologically relevant insights into the impacts of chemical pollution on soil ecosystems.

Behavioral Responses of Imidacloprid-Dosed Farmland Birds to a Simulated Predation Risk

Sublethal exposure to imidacloprid and other neonicotinoid insecticides may affect the neurological functions of birds. As such, behavior may be compromised. Here, we tested experimentally the effects of 1 and 6 mg/kg bw of imidacloprid on the antipredator behavioral responses of the red-legged partridge (Alectoris rufa) to simulated predator threats. Sixty-six partridges were challenged in groups or individually to intra- and interspecific alarm calls, to a raptor silhouette (aerial predation risk), and to a fox model (terrestrial predation risk). Antipredator behaviors were recorded as active (escape, active vigilance) and passive (passive vigilance, crouching, and freezing) responses. Latency in response to the stimuli, percentage of individuals who responded, response duration, speed of active responses, and vocalizations were measured. In experiments with partridges in the group, crouching against simulated predation risk lasted less time in birds treated with 6 mg a.i./kg bw than in control birds. In the experiments with individual partridges, passive vigilance against the intraspecific alarm lasted longer in birds treated with 6 mg a.i./kg bw than in control birds. The observed hyperreactivity to the predatory threat after a sublethal imidacloprid exposure can have consequences on survival under field conditions, where predation is a main driver of population dynamics.

Ecological consequences when organisms avoid a contaminated environment: A study evaluating the toxicity of fipronil

The ability of aquatic organisms to sense the surrounding environment chemically and interpret these signals correctly is crucial to their survival and ecological niche. This study applied the Heterogenous Multi-Habitat Assay System - HeMHAS to evaluate the avoidance potential of Daphnia magna to detect fipronil-contaminated habitats in a connected landscape after a short (48 h), previous, forced exposure to an environmentally relevant concentration of the same insecticide. The swimming of daphnids was also analyzed by recording the total distance covered. D. magna preferred areas with less contamination, although the effect of fipronil on their swimming ability (a decrease) was observed for all the concentrations tested. The application of non-forced multi-compartment exposure methodologies is a recent trend and is ecologically relevant as it is based on how contamination can really produce changes in an organism's habitat selection. Finally, we consider the importance of more non-forced exposure approaches where Stress Ecology can be aggregated to improve systemic understanding of the risk that contaminants pose to aquatic ecosystems from a broader landscape perspective.

A Dangerous Couple: Sequential Effect of Phosphorus Flame-Retardant and Polyurethane Decrease Locomotor Activity in Planarian Girardia tigrina

Understanding the interplay among organophosphorus flame retardants (OPFRs), microplastics, and freshwater organisms is crucial for unravelling the dynamics within freshwater environments and foreseeing the potential impacts of organic pollutants and plastic contamination. For that purpose, the present research assessed the exposure impact of 10 mg L-1 flame-retardant aluminium diethylphosphinate (ALPI), 10 μg mg-1liver microplastics polyurethane (PU), and the combination of ALPI and PU on the freshwater planarian Girardia tigrina. The exposure to both ALPI and PU revealed a sequential effect, i.e., a decrease in locomotor activity, while oxidative stress biomarkers (total glutathione, catalase, glutathione S-transferase, lipid peroxidation) and metabolic responses (cholinesterase activity, electron transport system, and lactate dehydrogenase) remained unaffected. Despite this fact, it was possible to observe that the range of physiological responses in exposed organisms varied, in particular in the cases of the electron transport system, cholinesterase activity, glutathione S-transferase, catalase, and levels of total glutathione and proteins, showing that the energetic costs for detoxification and antioxidant capacity might be causing a lesser amount of energy allocated for the planarian activity. By examining the physiological, behavioural, and ecological responses of planarians to these pollutants, insights can be gained into broader ecosystem-level effects and inform strategies for mitigating environmental risks associated with OPFRs and microplastic pollution in freshwater environments.

Effects on food intake of Gammarus spp. after exposure to PFBA in very low concentrations

Per- and polyfluoroalkyl substances (PFAS) are a group of thousands of highly persistent anthropogenic chemicals widely used in many industries. Therefore, they are, ubiquitously present in various types of environments. Despite their omnipresence, ecotoxicological studies of most PFAS are scarce, and those available often assess the effects of long chain PFAS. In this study, we present the results of an exposure experiment in which wild aquatic amphipod Gammarus spp. was exposed to the short chain perfluorinated substance perfluorobutanoic acid (PFBA) at very low and environmentally relevant concentrations of 0, 10 and 100 ng/L. The exposure lasted for 12 days, and food intake and non-reproductive behavior were analyzed. Exposure to 10 and 100 ng/L PFBA resulted in a lower consumption of food during exposure but no effect on behavior was found.

Exposure to Sublethal Concentrations of Lead (Pb) Affects Ecologically Relevant Behaviors in House Sparrows (Passer domesticus)

Global contamination of environments with lead (Pb) poses threats to many ecosystems and populations. While exposure to Pb is toxic at high concentrations, recent literature has shown that lower concentrations can also cause sublethal, deleterious effects. However, there remains relatively little causal investigation of how exposure to lower concentrations of environmental Pb affects ecologically important behaviors. Behaviors often represent first-line responses of an organism and its internal physiological, molecular, and genetic responses to a changing environment. Hence, better understanding how behaviors are influenced by pollutants such as Pb generates crucial information on how species are coping with the effects of pollution more broadly. To better understand the effects of sublethal Pb on behavior, we chronically exposed adult wild-caught, captive house sparrows (Passer domesticus) to Pb-exposed drinking water and quantified a suite of behavioral outcomes: takeoff flight performance, activity in a novel environment, and in-hand struggling and breathing rate while being handled by an experimenter. Compared to controls (un-exposed drinking water), sparrows exposed to environmentally relevant concentrations of Pb exhibited decreases in takeoff flight performance and reduced movements in a novel environment following 9-10 weeks of exposure. We interpret this suite of results to be consistent with Pb influencing fundamental neuro-muscular abilities, making it more difficult for exposed birds to mount faster movements and activities. It is likely that suppression of takeoff flight and reduced movements would increase the predation risk of similar birds in the wild; hence, we also conclude that the effects we observed could influence fitness outcomes for individuals and populations altering ecological interactions within more naturalistic settings.

Synergistic effects of microplastic and lead trigger physiological and biochemical impairment in a mangrove crab

Microplastics (MP) are vectors for other environmental contaminants, such as metals, being a considerable problem, especially in the aquatic ecosystem. To investigate the combined effects of MP (high density polyethylene) with lead (Pb), we exposed the mangrove fiddler crab Minuca vocator to Pb (50 mg L-1), and MP (25 mg L-1) alone and in mixture, for 5 days. We aimed to determine Pb and MP bioaccumulation, as well as physiological (oxygen consumption and hemolymph osmolality) and biochemical (superoxide dismutase, catalase, glutathione peroxidase, and lipid peroxidation) traits effects. Co-exposure of MP and Pb significantly increased the bioaccumulation of Pb, but reduced MP tissue accumulation. Regarding the physiological traits, increasing osmolality and oxygen consumption rates compared to the control were observed, particularly in the combined Pb and MP exposure. As to biochemical traits, the combination of Pb and MP induced the most significant responses in the enzymatic profile antioxidant enzyme activity. The catalase (CAT), glutathione peroxidase (GPx), and dismutase superoxide (SOD) decreased compared to individual exposure effects; the combination of MP and Pb had a synergistic effect on promoting lipid peroxidation (LPO). The co-exposure of MP and Pb acted synergistically when compared to the effects of the isolated compounds. Due to the increasing MP contamination in mangroves, more severe physiological and biochemical effects can be expected on mangrove crabs exposed to metal contamination.

Understanding the differential impacts of two antidepressants on locomotion of freshwater snails (Lymnaea stagnalis)

There is growing evidence of negative impacts of antidepressants on behavior of aquatic non-target organisms. Accurate environmental risk assessment requires an understanding of whether antidepressants with similar modes of action have consistent negative impacts. Here, we tested the effect of acute exposure to two antidepressants, fluoxetine and venlafaxine (0-50 µg/L), on the behavior of non-target organism, i.e., freshwater pond snail, Lymnaea stagnalis. As compounds interact with chemical cues in the aquatic ecosystems, we also tested whether the effects altered in the presence of bile extract containing 5α-cyprinol sulfate (5α-CPS), a characterized kairomone of a natural predator, common carp (Cyprinus carpio). Behavior was studied using automated tracking and analysis of various locomotion parameters of L. stagnalis. Our results suggest that there are differences in the effects on locomotion upon exposure to venlafaxine and fluoxetine. We found strong evidence for a non-monotonic dose response on venlafaxine exposure, whereas fluoxetine only showed weak evidence of altered locomotion for a specific concentration. Combined exposure to compounds and 5α-CPS reduced the intensity of effects observed in the absence of 5α-CPS, possibly due to reduced bioavailability of the compounds. The results highlight the need for acknowledging different mechanisms of action among antidepressants while investigating their environmental risks. In addition, our results underline the importance of reporting non-significant effects and acknowledging individual variation in behavior for environmental risk assessment.

Ecotoxicological Effects of Potassium Dichromate on the Tadpole Shrimp Triops longicaudatus

The tadpole shrimp Triops longicaudatus is a freshwater crustacean with fast embryonic and larval development, short life cycle, and high fecundity. They are very active swimmers of a reasonable size, easy to spot and record. Such characteristics make it a promising candidate as an experimental model in ecotoxicology to evaluate the effects of aquatic pollutants, particularly using its locomotor behavior as an endpoint. To evaluate the sensitivity of T. longicaudatus and develop endpoints of interest, we conducted exposure experiments with lethal and sub-lethal concentrations of potassium dichromate, a compound known for its ecotoxicological importance and as a hexavalent chromium source. The endpoints evaluated were mortality, growth, sexual maturation, reproductive output, cholinesterase activity and locomotor/swimming behavior. The 96 h median lethal concentration was found to be 65 µg/L. Furthermore, exposure to potassium dichromate at higher concentrations had a significant negative impact on the growth rate of T. longicaudatus in terms of both body mass and length. The time for maturation was also delayed at higher concentrations. In addition, locomotor behavior allowed for the discrimination of all tested chromium concentrations and the control group and from each other, proving to be the most sensitive endpoint. Overall, the data support the potential of T. longicaudatus as a model for ecotoxicity testing, using apical endpoints with impact at the population level; in particular, results suggest that behavior assessments in this species might be useful for detecting hazardous compounds in environmental monitoring of freshwater ecosystems.

Avoidance behaviour of aquatic macroinvertebrates for real-time detection of micropollutant surge in wastewater effluents

Micropollutants are regularly detected at the outlets of wastewater treatment plants (WWTPs). Across urban and industrial WWTPs, monitoring directives only require assessment for a handful of chemicals via sampling methods that fail to capture the temporal variability in micropollutant discharge. In this study, we develop a biotest for real-time on-line monitoring of micropollutant discharge dynamics in WWTPs effluents. The selected biomonitoring device ToxMate uses videotracking of invertebrate movement, which was used to deduce avoidance behaviour of the amphipod Gammarus fossarum. Organism conditioning was set up to induce a state of minimal locomotor activity in basal conditions to maximise avoidance signal sensitivity to micropollutant spikes. We showed that with a standardised protocol, it was possible to minimise both overall movement and sensitivity to physio-chemical variations typical to WWTP effluents, as well as capture the spikes of two micropollutants upon exposure (copper and methomyl). Spikes in avoidance behaviour were consistently seen for the two chemicals, as well as a strong correlation between avoidance intensity and spiked concentration. A two-year effluent monitoring case study also illustrates how this biomonitoring method is suitable for real-time on-site monitoring, and shows a promising non-targeted approach for characterising complex micropollutant discharge variability at WWTP effluents, which today remains poorly understood.

Exposure to Low Concentrations of AMPA Influences Morphology and Decreases Survival During Larval Development in a Widespread Amphibian Species

Glyphosate's primary metabolite, AMPA (aminomethylphosphonic acid), is one of the most widely detected anthropogenic substance in surface waters worldwide. However, ecotoxicological studies on the potential effects of this metabolite at environmental concentrations on wildlife are scarce. Yet, due to its chemical properties, AMPA is likely to affect non-target species. In this study, we investigated sublethal effects of environmental concentrations of AMPA on the larval development of a widespread amphibian species, the spined toad Bufo spinosus. We performed a factorial experiment to study the effect of concentration and the timing of exposure (during embryonic development, larval development or both) to AMPA on the morphology, rate of development and survival of tadpoles. AMPA and timing of exposure interactively affected tadpole size (individuals exposed to AMPA after hatching were transitorily smaller, while individuals exposed to AMPA before hatching were longer), but not duration of development. Most of these effects were linked to exposure during embryonic development. Such effects in individuals exposed during embryonic development solely were long-lasting and persisted until the latest larval stages. Finally, we found that exposure to AMPA after hatching (during the larval stage) increased mortality. Exposure to low environmental concentrations of AMPA could have long-lasting consequences on fitness and population persistence. These findings are especially important to take into account at a time when multiple threats can interact to affect wildlife.

Chronic poly(l-lactide) (PLA)- microplastic ingestion affects social behavior of juvenile European perch (Perca fluviatilis)

Juvenile perch were exposed to 2 % (w/w) poly(l-lactide) (PLA) microplastic particles (90-150 μm) in food pellets, or 2 % (w/w) kaolin particles, and a non-particle control food over 6 months. Chronic ingestion of PLA microplastics significantly affected the social behavior of juvenile perch, evident as a significantly increased reaction to the vision of conspecifics. PLA ingestion did not alter life cycle parameters, or gene expression levels. In addition to reactions to conspecifics, fish that ingested microplastic particles showed tendencies to decrease locomotion, internal schooling distance, and active predator responses. The ingestion of natural particles (kaolin) significantly downregulated the expression of genes related to oxidative stress and androgenesis in the liver of juvenile perch, and we found tendencies to downregulated expression of genes related to xenobiotic response, inflammatory response, and thyroid disruption. The present study demonstrated the importance of natural particle inclusion and the potential behavioral toxicity of one of the commercially available biobased and biodegradable polymers.

Locomotion behavior of juveniles of the freshwater pearl mussel Margaritifera margaritifera: A new non-invasive tool for the evaluation of stress effects

The lack of knowledge about the sensitivity of the endangered freshwater pearl mussel (FWPM) Margaritifera margaritifera to environmental pollution and the rapid decline of its populations in Europe, have led to the need of developing non-destructive experimental protocols in order to assess the impact of such pollution. This species has a complex life cycle and the early life stages are considered the most sensitive. This study deals with the development of a methodology for the assessment of juvenile mussels' locomotor behavior using an automated video tracking system. Different parameters were determined such as the duration of the video recording and light exposure as a stimulus during the experiment. Locomotion behavior pattern of juveniles was assessed in control condition and also following exposure to sodium chloride as a positive control in order to validate the experimental protocol developed in this study. Results showed that juveniles locomotion behavior was stimulated under light exposure. Moreover, exposure to sublethal concentrations of sodium chloride (0.8 and 1.2 g/L) for 24 h was found to decrease juveniles' locomotion by almost three-times, thus validating our experimental methodology. This study allowed to provide a new tool for the assessment of stress condition impacts on the juveniles of the endangered FWPM, highlighting the interest of such non-destructive biomarker of health for protected species. Consequently, this will help in the improvement of our knowledge on M. margaritifera sensitivity to environmental pollution.

Antidepressant pharmaceuticals in aquatic systems, individual-level ecotoxicological effects: growth, survival and behavior

The growing consumption of antidepressant pharmaceuticals has resulted in their widespread occurrence in the environment, particularly in waterways with a typical concentration range from ng L^-1 to μg L^-1. An increasing number of studies have confirmed the ecotoxic potency of antidepressants, not only at high concentrations but also at environmentally relevant levels. The present review covers literature from the last decade on the individual-level ecotoxicological effects of the most commonly used antidepressants, including their impact on behavior, growth, and survival. We focus on the relationship between antidepressants physico-chemical properties and dynamics in the environment. Furthermore, we discuss the advantages of considering behavioral changes as sensitive endpoints in ecotoxicology, as well as some current methodological shortcomings in the field, including low standardization, reproducibility and context-dependency.

Process-oriented impacts of microplastic fibers on behavior and histology of fish

Microplastic pollution has raised global concern for its hazards to biota. To determine the direct impact of microplastics during their contact with fish, we exposed goldfish (Carassius auratus) to 100 and 1000 items/L waterborne microplastic fibers in the short- and long-term. In the presence of 1000 items/L of microplastic fibers, the coughing behavior of fish increased significantly after 2 h of exposure. Predatory behaviors decreased significantly by 53.0% after 45 d of exposure, and the reduction in daily food intake was negatively related to exposure duration in the 1000 items/L group. In addition, microplastic fibers stimulated dynamic mucus secretion across different fish tissues during the different processes evaluated in this study, with 30.0% and 62.9% overall increases in the secretory capacity of mucus cells in the 100 and 1000 items/L groups, respectively. These behavioral and histological alterations were derived from the ventilation, feeding, and swimming processes of goldfish. We regarded these changes as process-oriented impacts, suggesting the effects of microplastics on fish and how fish cope with microplastics.

Pesticide use in banana plantations in Costa Rica - A review of environmental and human exposure, effects and potential risks

Biodiversity is declining on a global scale. Especially tropical ecosystems, containing most of the planetary biodiversity, are at risk. Agricultural monocrop systems contribute to this decline as they replace original habitats and depend on extensive use of synthetic pesticides that impact ecosystems. In this review we use large-scale banana production for export purposes in Costa Rica as an example for pesticide impacts, as it is in production for over a century and uses pesticides extensively for more than fifty years. We summarise the research on pesticide exposure, effects and risks for aquatic and terrestrial environment, as well as for human health. We show that exposure to pesticides is high and relatively well-studied for aquatic systems and humans, but hardly any data are available for the terrestrial compartment including adjacent non target ecosystems such as rainforest fragments. Ecological effects are demonstrated on an organismic level for various aquatic species and processes but are not available at the population and community level. For human health studies exposure evaluation is crucial and recognised effects include various types of cancer and neurobiological dysfunctions particularly in children. With the many synthetic pesticides involved in banana production, the focus on insecticides, revealing highest aquatic risks, and partly herbicides should be extended to fungicides, which are applied aerially over larger areas. The risk assessment and regulation of pesticides so far relies on temperate models and test species and is therefore likely underestimating the risk of pesticide use in tropical ecosystems, with crops such as banana. We highlight further research approaches to improve risk assessment and, in parallel, urge to follow other strategies to reduce pesticides use and especially hazardous substances.

Atrazine contaminated sites and bullfrog tadpoles: evasive trends and biochemical consequences

Atrazine (ATZ) is one of the most used active principles in agricultural systems. This pesticide has the ability to easily accumulate in terrestrial and aquatic environments, causing impacts with chronic adverse effects. Avoidance tests are tests that seek to assess the concentration from which a given organism escapes, that is, migrates to another habitat. They are being used as a modality of innovative and minimally invasive ecotoxicological tests. Our objective was to evaluate the sensitivity and possible toxic effects of ATZ in bullfrog tadpoles (Lithobates catesbeianus), through avoidance tests and oxidative stress analyses. We performed the behavioral avoidance test lasting 12 h, with observations every 60 min in a linear multi-compartment system with seven compartments. Each compartment corresponded to a concentration: negative control, 1, 2, 20, 200, 2000, 20,000 µg L^-1. After the selection of habitat, organisms were forcedly maintained in the chosen concentrations for 48 h and then, metabolic effects were measured assessing the blood plasma amino acid profile and liver protein degradation. We also determined the effective concentrations of ATZ tested at 0 h and 48 h. The results showed that there was an effect of the treatment on the distribution of tadpoles, but not on the hours or on the combined effect (interaction). The biochemical analyses also showed a concentration-dependent relationship which caused significant toxic effects even in a short period of time. In conclusion, these frogs were able to avoid places with high concentrations of ATZ in the first hours of exposure, which suggests that in the natural environment these animals can migrate or avoid areas contaminated by this herbicide; however, depending on the selected concentration, serious biochemical consequences can occur.

Previous stress causes a contrasting response to cadmium toxicity in the aquatic snail Potamopyrgus antipodarum: lethal and behavioral endpoints

In aquatic ecosystems, animals are often exposed to a combination of stressors, including both natural and anthropogenic factors. Combined stressors may have additive or interactive effects on animals, either magnifying or reducing the effects caused by each stressor alone. Therefore, standardized bioassays can lead to overestimations or underestimations of the risk of toxicants if natural stressors are not bear in mind. The inclusion of natural stress in laboratory bioassays may help to extrapolate the laboratory results to ecosystems. This study assesses the effects of successive exposure to two sources of stress (high water conductivity and cadmium toxicity) on the behavior and survival of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca). I conducted a bioassay consisting on exposure to high conductivity (5000 mg NaCl/L, 7 days), followed by exposure to cadmium (0.03, 0.125, and 0.25 mg Cd/L for 7 days) and by a post-exposure period (7 days). Mortality, inactivity, and the time to start activity of active animals were monitored in each animal. In general, cadmium lethality was higher in animals previously undergoing high conductivity than in non-stressed ones. Previously stressed animals showed longer time to start activity, with a noticeable effect at the two highest cadmium concentrations. Animals submitted to the two highest cadmium concentration both, stressed and non-stressed, showed a moderate recovery during the post-exposure period. It is concluded that previous stress caused a worsening of the cadmium toxicity on the aquatic snail Potamopyrgus antipodarum, which is especially noticeable for mortality. However, there was no interactive effect between cadmium and conductivity on snail activity, which may be indicative of recovery after cadmium exposure regardless the previous stress suffered by the snails.

Post-exposure Period as a key Factor to Assess Cadmium Toxicity: Lethal vs. Behavioral Responses

The exposure of animals to pollution in ecosystems is not always chronic. Toxicants can remain in aquatic ecosystems for a short-term. To improve the extrapolation of laboratory results to natural scenarios the inclusion of post-exposure periods is a relevant issue. The present study focuses on the assessment of cadmium toxicity on survival and behavior of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca) during exposure and post-exposure. Animals were exposed for 48 h to cadmium (0.05, 0.14, 0.44 and 1.34 mg Cd/L) and 168 h of post-exposure. During the post-exposure period an increase in mortality in all concentrations was observed. The effects observed during the post-exposure period on the LC50 and EC50 were significant. During the post-exposure, behavior showed a clear recovery in surviving animals exposed to 0.44 mg Cd/L. Animals exposed to 0.05 mg Cd/L did not show differences with control. Therefore, mortality after exposure should be included in the ecotoxicological bioassays for a more realistic estimation of the cadmium effects. To assess the degree of animal recovery after cadmium exposure, behaviour has been shown as an adequate parameter.

Cuttlefish color change as an emerging proxy for ecotoxicology

Lately, behavioral ecotoxicology has flourished because of increasing standardization of analyses of endpoints like movement. However, research tends to focus on a few model species, which limits possibilities of extrapolating and predicting toxicological effects and adverse outcomes at the population and ecosystem level. In this regard, it is recommended to assess critical species-specific behavioral responses in taxa playing key roles in trophic food webs, such as cephalopods. These latter, known as masters of camouflage, display rapid physiological color changes to conceal themselves and adapt to their surrounding environments. The efficiency of this process depends on visual abilities and acuity, information processing, and control of chromatophores dynamics through nervous and hormonal regulation with which many contaminants can interfere. Therefore, the quantitative measurement of color change in cephalopod species could be developed as a powerful endpoint for toxicological risk assessment. Based on a wide body of research having assessed the effect of various environmental stressors (pharmaceutical residues, metals, carbon dioxide, anti-fouling agents) on the camouflage abilities of juvenile common cuttlefish, we discuss the relevance of this species as a toxicological model and address the challenge of color change quantification and standardization through a comparative review of the available measurement techniques.

Behavioral and physiological toxicity thresholds of a freshwater vertebrate (Heteropneustes fossilis) and invertebrate (Branchiura sowerbyi), exposed to zinc oxide nanoparticles (nZnO): A General Unified Threshold model of Survival (GUTS)

The toxic effects of Zinc oxide nanoparticles (nZnO) on Branchiura sowerbyi and Heteropneustes fossilis, was assessed in a 96-hour acute exposure regime using behavioral (including loss-of balance and clumping tendencies) and physiological (mucus secretion and oxygen consumption) endpoints. While the relationship between behavioral, physiological biomarkers, and exposure concentrations was assessed using correlation analysis, nZnO toxicity was further predicted using the General Unified Threshold model for Survival (GUTS). The time-dependent lethal limits for acute nZnO toxicity (LC₅₀) on B. sowerbyi were estimated to be 0.668, 0.588, 0.448, and 0.400 mg/l, respectively, at 24, 48, 72, and 96 h whereas for H. fossilis the LC50 values are 0.954, 0.905, 0.874 and 0.838 mg/l. Threshold effect values i.e., LOEC (Lowest Observed Effect Concentration), NOEC (No Observed Effect Concentration), and MATC (Maximum Acceptable Toxicant Concentration) threshold effect values at 96 h were higher for fish compared to the oligochaete. For B. sowerbyi, the GUTS-SD (stochastic death) model is a better predictor of nanoparticle exposure effects compared to the GUTS-IT (individual tolerance) model, however in the case of H. fossilis, the reverse pattern was observed. Oxygen consumption rate was negatively correlated to mortality under acute exposure duration. The strong negative correlation between mortality and oxygen consumption strongly suggests a metabolic-toxicity pathway for nZnO exposure effects. The higher toxicity threshold values i.e., LOEC, NOEC, and MATC for fish compared to the oligochaete invertebrate indicates greater risks for invertebrates compared to vertebrates, with resultant implications for local habitat trophic relationships.

Differing behavioral changes in crayfish and bluegill under short- and long-chain PFAS exposures: Field study in Northern Michigan, USA

The emergent contaminant family, per- and poly-fluorinated alkyl substances (PFAS) has gained research attention due to their widespread detection and stability within the environment. Despite the growing amount of research on perfluorooctanesulfonic acid (PFOS) and perfluoro-n-octanoic acid (PFOA) in aquatic organisms, investigations detailing behavioral and physiological effects of aquatic organisms exposed to a mixture of PFAS analytes in the wild have been limited. The objective of this study was to evaluate the potential behavioral and histological effects of environmental exposure to PFAS compounds within multiple trophic levels of aquatic ecosystems. The current study investigates effects of environmentally relevant PFAS concentration exposures in crayfish (Faxonius immunis, F. rusticus, F. virilis) and bluegill (Lepomis macrochirus) sourced from four water bodies in Northern Michigan. Antipredator response and foraging behavioral assays were used to investigate potential effects on crayfish; a swimming speed behavioral assay and liver and gill histology analysis were used to investigate potential effects on fish. Linear mixed model and multiple regression analyses resulted in significant relationships between tissue accumulation levels of long chain PFAS compounds and crayfish foraging and fish critical swimming speed responses. Crayfish foraging decreased and fish critical swim speeds increased with PFAS exposure which may lead to energetic and population concerns. Antipredator response in crayfish and liver and gill histology in fish were not significantly related to PFAS tissue or water concentrations. The sensitivity of crayfish and bluegill behavior contributes to the growing body of research regarding the differential toxicity of short-chain and long-chain PFAS compounds. The sensitivity of some aquatic organism behaviors to PFAS accumulated in tissue may have implications for PFAS transfer and alterations to ecosystem functioning; based on the results of this field study, further laboratory research is recommended to further evaluate these relationships.

Assessing the potential chronic, sublethal and lethal ecotoxicity of land-applying biosolids on Folsomia candida and Lumbricus terrestris

The ecotoxicity of biosolids has been studied extensively using single-compound toxicity testing and 'spiking' studies; however, little knowledge exists on the ecotoxicity of biosolids as they are land-applied in the Canadian context. The purpose of this study is to elucidate the chronic, sub-lethal (i.e., behavioural), and lethal impacts of land- applying biosolids on the environmentally relevant Folsomia candida (springtails) and Lumbricus terrestris (earthworms) and concomitantly ascertain whether the use of biosolids for nutrient amendment is a sustainable practice. This study is part of a larger multi-compartment programme which includes terrestrial plants and aquatic arthropods. After a review of existing government protocols and research, the current study suggests new environmentally relevant bioassays as to elucidate the true nature of the potential ecotoxicity of land-applying biosolids, within a laboratory context. Specifically, protocols were developed (e.g., shoebox bioassays for L. terrestris sub-lethal testing) or modified (e.g., using Evans' boxes (Evans 1947) for chronic and sub-lethal testing on L. terrestris). Subsequently, two biosolids were tested on springtails and earthworms using avoidance and reproductive bioassay endpoints, at application rates that represent standard (8 tonnes ha^-1) and worst-case scenarios (22 tonnes ha^-1). Results indicated no effect of biosolids at the environmentally relevant concentration; the worst-case scenario exhibited a positive significantly significant relationship (indicating preference for treatment conditions). We suggest that further assessment of the potential ecotoxicological impact of biosolids employ (i) environmentally relevant organisms, (ii) appropriate bioassays including the use of whole-organism endpoints, and (iii) multi-kingdom testing (e.g., Kingdom Plantae, Animalia) to comprehensively elucidate answers. Lastly, in situ (field assays) are strongly encouraged for future studies.

RNA-seq reveals potential gene biomarkers in fathead minnows (Pimephales promelas) for exposure to treated wastewater effluent

Discharged wastewater treatment plant (WWTP) effluent greatly contributes to the generation of complex mixtures of contaminants of emerging concern (CECs) in aquatic environments which often contain neuropharmaceuticals and other emerging contaminants that may impact neurological function. However, there is a paucity of knowledge on the neurological impacts of these exposures to aquatic organisms. In this study, caged fathead minnows (Pimephales promelas) were exposed in situ in a temperate-region effluent-dominated stream (i.e., Muddy Creek) in Coralville, Iowa, USA upstream and downstream of a WWTP effluent outfall. The pharmaceutical composition of Muddy Creek was recently characterized by our team and revealed many compounds there were at a low microgram to high nanogram per liter concentration. Total RNA sequencing analysis on brain tissues revealed 280 gene isoforms that were significantly differentially expressed in male fish and 293 gene isoforms in female fish between the upstream and downstream site. Only 66 (13%) of such gene isoforms overlapped amongst male and female fish, demonstrating sex-dependent impacts on neuronal gene expression. By using a systems biology approach paired with functional enrichment analyses, we identified several potential novel gene biomarkers for treated effluent exposure that could be used to expand monitoring of environmental effects with respect to complex CEC mixtures. Lastly, when comparing the results of this study to those that relied on a single-compound approach, there was relatively little overlap in terms of gene-specific effects. This discovery brings into question the application of single-compound exposures in accurately characterizing environmental risks of complex mixtures and for gene biomarker identification.

Same sensitivity with shorter exposure: behavior as an appropriate parameter to assess metal toxicity

The exposure of animals to toxicants may cause a depletion in the energy uptake, which compromises reproduction and growth. Although both parameters are ecologically relevant, they usually need long-term bioassays. This is a handicap for the availability of toxicological data for environmental risk assessment. Short-term bioassays conducted with environmental concentrations, and using relevant ecological parameters sensitive to short-term exposures, such as behavior, could be a good alternative. Therefore, to include this parameter in the risk assessment procedures, it is relevant the comparison of its sensitivity with that of growth and reproduction bioassays. The study aim was the assessment of differences between endpoints based on mortality, behaviour, reproduction, and growth for the toxicity of metals on aquatic animals. We used the ECOTOX database to gather data to construct chemical toxicity distribution (CTD) curves. The mean concentrations, the mean exposure time, and the ratio between the mean concentration and the exposure time were compared among endpoints. Our results showed that behavioral, growth, and reproduction bioassays presented similar sensitivity. The shortest exposure was found in behavioral and reproduction bioassays. In general, the amount of toxicant used per time was lower in growth and reproduction bioassays than in behavioral and mortality bioassays. We can conclude that, for metal toxicity, behavioral bioassays are less time-consuming than growth bioassays. As the sensitivity of behavior was similar to that of growth and reproduction, this endpoint could be a better alternative to longer bioassays.

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

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

Fish Behavior as a Neural Proxy to Reveal Physiological States

Behaviors are the integrative outcomes of the nervous system, which senses and responds to the internal physiological status and external stimuli. Teleosts are aquatic organisms which are more easily affected by the surrounding environment compared to terrestrial animals. To date, behavioral tests have been widely used to assess potential environmental risks using fish as model animals. In this review, we summarized recent studies regarding the effects of internal and external stimuli on fish behaviors. We concluded that behaviors reflect environmental and physiological changes, which have possible implications for environmental and physiological assessments.

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.

Response of marine amphipods to sediment variables (Chabahar Bay- Iran): A step toward localizing amphipod-based bioindices

Chabahar Bay will undergo industrial and coastal pressures according to the government plan to develop the Makran coasts. Therefore, knowing its biological community as well as their possible interactions with environmental variables, before and after coastal development, is important. The amphipod community structure and their response to the structural and contaminant parameters of the sediment include: granulometry, total organic matter (TOM) overloading, heavy metal contamination based on the Pollution Load Index (PLI) and polycyclic aromatic hydrocarbons (PAHs) during post monsoon season of 2017 were investigated from 19 stations. Traditional diversity and taxonomic distinctness indices were calculated. Multivariate analysis revealed the main role of sediment grain size and depth in shaping amphipod community structure. Consequently, two specific ecological niches were determined: species that prefer non-muddy substrates; and those dwelling in muddy or muddy sandy biotopes. No correlation was found between the Shannon diversity (H'), the average taxonomic distinctness indices (Δ+) together and both with contamination parameters. The Δ+ funnel plot well separated under-stressed stations from the healthy ones. The presence of only Ampelisca congeners in under-stressed stations revealed the tolerant nature as well as species-specific response of the genus to anthropogenic impacts. Considerable tolerant response (P > 0.05, r² = 0.4) of A. zamboangae to PAHs; A. persicus to TOM were observed. High concentration of nickel (Ni) in the studied area already stated due to erosion of ophiolite units from Makran Mountains. The significant correlation of the recently described Iranian species A. lowryi with Ni assumes that it is a native species that is well adapted to the geological conditions of the seabed. Instead Urothoe platydactyla can be considered as early warning signal for PAHs, TOM, Ni and cadmium (Cd) contamination particularly for non-muddy substrates. Our findings help to localize common biotic indices (e.g. AMBI, BENTIX, and BOPA) for studied area through correctly assignment of amphipods to the sensitive/tolerant ecological groups. Finally, we state that in the current situation of Chabahar Bay, in which no special industrial complexes have been established, any sediment-disrupting activity (i.e. sedimentation, dredging, trawling) affects its amphipod communities more than chemical pollutants.

Zeolitic Imidazolate Framework-8 Nanoparticles Exhibit More Severe Toxicity to the Embryo/Larvae of Zebrafish (Danio rerio) When Co-Exposed with Cetylpyridinium Chloride

The combined application of nanoparticles and surfactants has attracted tremendous attention in basic research and industry. However, knowledge of their combined toxicity remains scarce. In this study, we exposed zebrafish embryos to cetylpyridinium chloride (CPC, a cationic surfactant, at 0 and 20 μg/L), zeolitic imidazolate framework nanoparticles (ZIF-NPs, at 0, 30, and 60 mg/L), and their mixtures until 120 h post-fertilization (hpf). Within the used concentration range, both single and combined exposures exhibited limited effects on the survival and hatching of zebrafish. However, the combined exposure of ZIF-NPs and CPC caused more severe effects on the heart rate at both 48 and 72 hpf. The combined exposure also induced significant hyperactivity (i.e., increasing the average swimming velocity) and oxidative stress in zebrafish larvae (at 120 hpf), although all single exposure treatments exhibited limited impacts. Furthermore, the level of reactive oxygen species (or malondialdehyde) exhibited a significantly positive correlation with the heart rate (or average swimming velocity) of zebrafish, suggesting that oxidative stress plays a role in mediating the combined toxicity of CPC and ZIF-NPs to zebrafish. Our findings suggest that the interaction of CPC and ZIF-NPs should not be ignored when assessing the potential risks of their mixtures.

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.

Behavioural changes and flight response of a mosquito (Culicidae) and an earthworm (Lumbricidae), respectively, after exposure to imidacloprid

A major point of concern in ecotoxicology is the effects of pesticides on nontarget organisms. This can impact the ecological role played by certain beneficial species in nature. Regarding neonicotinoid insecticides such as imidacloprid (IMI), several measures, including limited trade, restrictive use, and ban have been implemented in Europe and the USA but not globally. The goal of our study was to evaluate the potential risk of this still widely used agrochemical on the behaviour of mosquito larvae (Culicidae) and the escape behaviour of earthworms (Lumbricidae). Changes in breathing, swimming and resting were recorded in mosquitoes postexposure to 0, 1 and 2 mg IMI/L for 10 min. Earthworms were topically exposed in water for 2 minutes to 0, 5, 10 and 20 mg IMI/L. The escape behaviour (initial escape distance and speed) of the earthworms were recorded. In culicids, resting particularly was significantly increased by the exposure to imidacloprid (p < 0.05). In earthworms, the initial escape distance was statistically longer (p < 0.05) when fleeing from the 5 mg IMI/L solution than the solutions with the two highest concentrations. The worms exposed to the 5 mg IMI/L reacted faster than those exposed to the higher concentrations, which explained the long distance covered in the same amount of time. These results point to the relatively quick onset of the neurotoxic effects of imidacloprid, crippling earthworms and altering the buoyancy of mosquito larvae. The ecological consequences of these findings on the completion of life cycles and the survival of these species in nature are yet to be established.

Behavioral Variables to Assess the Toxicity of Unionized Ammonia in Aquatic Snails: Integrating Movement and Feeding Parameters

Behavioral endpoints are important parameters to assess the effects of toxicants on aquatic animals. These endpoints are useful in ecotoxicology because several toxicants modify the animal behavior, which may cause adverse effects at higher levels of ecological organization. However, for the development of new bioassays and for including the behavior in ecotoxicological risk assessment, the comparison of sensitivity between different behavioral endpoints is necessary. Additionally, some toxicants remain in aquatic environments for a few hours or days, which may lead to animal recovery after toxicant exposure. Our study aimed to assess the effect of unionized ammonia on the movement and feeding behaviors of the aquatic gastropod Potamopyrgus antipodarum (Tateidae, Mollusca) and its recovery after exposure. Four treatments were used: a control and three nominal concentrations of unionized ammonia (0.25, 0.5 and 1 mg N-NH₃/L). Each treatment was replicated eight times, with six animals in each replicate. Animals were exposed to unionized ammonia for 48 h (exposure period) and, subsequently, to control water for 144 h (post-exposure period). Two movement variables were monitored without food and five feeding behavioral variables were monitored in the presence of food. Some of the feeding behavioral variables showed higher sensitivity (LOEC = 0.25-0.5 mg N-NH₃/L) than the movement behavior variables monitored without food (LOEC = 1 mg N-NH₃/L). After exposure to unionized ammonia, animals showed a recovery of most behavioral endpoints. The inclusion of post-exposure period and feeding behaviors in bioassays may make studies more realistic, which is crucial for a proper ecotoxicological risk assessment.

Fluoxetine-induced neurotoxicity at environmentally relevant concentrations in adult zebrafish Danio rerio

Fluoxetine (FLX) exerts its therapeutic effect by inhibiting the presynaptic reuptake of the neurotransmitter serotonin. Nonetheless, at high concentrations of this drug, adverse effects occur in the brain of exposed organisms. Bearing this into account, the objective of this study was to evaluate the neurotoxic effects of the fluoxetine through the evaluation of behavior (Novel tank test), determination of oxidative stress, and determination of acetylcholinesterase (AChE) activity in adult zebrafish Danio rerio. For this purpose, Danio rerio adults were exposed to three environmentally relevant concentrations (5, 10, 16ngL^-1) of FLX for 96h. Our results demonstrate fish presented a significant disruption in their behavior, as they remained long-lasting time frozen at the top of the tank. Since we observed a significant reduction of AChE activity in the brain of fish, we believe the above described anxiety-like state is the result of this enzyme impairment. Moreover, as FLX-exposed fish showed a significant increase in the levels of oxidative damage biomarkers, we suggest this AChE disruption is associated with the oxidative stress response fish exhibited. Based on our findings, we believe the environmentally relevant concentration of FLX alters the redox status of the brain, impairing this way the behavior of fish and making them more vulnerable to predation.

Effects of subchronic exposure to environmentally relevant concentrations of a commercial fluridone formulation on fathead minnows (Pimephales promelas)

Invasive aquatic plants are a widespread problem in United States' waterways, and aquatic herbicide treatments are a common tool used in their management. Fluridone is an active ingredient in aquatic herbicides used globally to control aquatic plants. In order to be effective, fluridone requires a long contact time with plants resulting in extended exposure to non-target organisms. While there has been limited studies exploring the effects of fluridone on non-target aquatic organisms, the effects of subchronic commercial fluridone exposure at concentrations representative of operational use rates for plant management on fish are poorly understood. Therefore, we conducted a series of three exposure experiments using environmentally relevant concentrations on different life stages of the fathead minnow (Pimephales promelas). We exposed fathead minnows to a commercial fluridone formulation, Spritflo®, at environmentally relevant concentrations of 0.00, 3.00, 12.00, 25.00, and 100.00 μg/L. Exposure times included subchronic periods up to 35 days and a trans-generation exposure of 65 days, which is a likely residence time of fluridone when applied for plant management. Following 30 days of fluridone exposure, adult male fish had an increased presence of nuptial tubercules, an indicator of endocrine disruption, and an enlarged liver compared to the control. Additionally, we conducted larval fish behavior experiments and found fluridone exposure negatively affected prey capture ability, locomotion, and position preference. Our findings suggest fluridone treatment concentrations used in aquatic plant management do not directly cause mortality in fathead minnows, though sub-lethal effects observed could cause a decline in biological fitness and pose potential ecological implications.

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.

Avobenzone and nanoplastics affect the development of zebrafish nervous system and retinal system and inhibit their locomotor behavior

The use of cosmetics is growing with each passing day, arousing widespread attention to their ingredients. Avobenzone (AVO) and nanoplastics (NPs) are typical ingredients in cosmetics, which coexist in the aquatic environment and have a combined effect on aquatic organisms. In this study, the accumulation of AVO and NPs in zebrafish larvae and effects on gene expression and enzymatic activity related to nervous functions, and locomotor behavior were investigated. AVO and NPs accumulated continuously in zebrafish, and the combined exposure enhanced AVO accumulation. After recovery, the accumulated concentrations of AVO and NPs in zebrafish remained unchanged, suggesting that AVO and NPs could not be eliminated in 72 h. The genes regulated nervous system development were affected mainly by AVO exposure, while the genes regulated retinal system development were affected by NPs exposure. Single and combined exposures of AVO and NPs affected the activities of acetylcholinesterase and antioxidant enzymes in zebrafish, and superoxide dismutase activity could not return to normal level after 72 h of recovery period. The locomotor activity of zebrafish larvae was significantly inhibited by AVO and NPs, which might be related to the alterations in functions of nervous system development and retinal system development as well as the interference of neurotransmitter system and antioxidant system.

Acute exposure of embryo, larvae and adults of Danio rerio to fipronil commercial formulation reveals effects on development and motor control

The insecticide fipronil, one of the main pesticides used in Brazil, is often detected in natural aquatic environments, and causes neuronal hyperexcitation by inhibiting GABAergic neurotransmission, leading to putative alterations in behaviour and development. This work sought to analyse the toxicity of formulated Regent^® 800WG (80% fipronil) on development (fish embryo toxicity test, FET), morphology, and swimming behaviour of larvae and adults of zebrafish (Danio rerio). FET was performed following OECD236 guidelines at concentrations ranging from 0.002 to 1600 μg.L^-1 of formulated Regent^® 800WG. Adults were exposed to 0.2, 2 and 20 μg.L^-1 of the product for 24 and 96 h, and were submitted to the light-dark, novel tank and swimming endurance tests No lethal parameters were observed in larvae, but in concentrations above 400 µg.L^-1, there was shortening of the body axis and decreased swimming behavior. In adults, exposure to the pesticide did not lead to changes in free swimming parameters. However, a marked decrease of swimming endurance was observed at all experimental treatments, although probably not in consequence of energetic depletion, since baseline blood glucose levels and condition factor were similar at all conditions. Furthermore, zebrafish adults did not show their natural preference for the dark environment. The pesticide likely has anxiolytic effects on zebrafish, as well as a compromising effect on locomotor control, illustrating that behavioural changes, which could affect activities on the natural environment, such as escape and predation, may occur even in environmentally relevant concentrations of this pollutant.

Sub-lethal exposure to malaria vector control pesticides causes alterations in liver metabolomics and behaviour of the African clawed frog (Xenopus laevis)

In this study we explore the sub-lethal effects of two malaria vector control pesticides, deltamethrin and dichlorodiphenyltrichloroethane (DDT), on Xenopus laevis by incorporating different levels of biological organisation. Pesticide accumulation in frog tissue was measured alongside liver metabolomics and individual swimming behaviour to assess whether changes presented at these different levels, and if such changes could be linked between levels. Results showed evidence of concentration dependent accumulation of DDT and its metabolites, but no measurable accumulation of deltamethrin in adult X. laevis after 96 h of exposure. Both DDT and deltamethrin were shown to cause alterations in the liver metabolome of X. laevis. We also showed that some of these changes can be enhanced in exposure to a mixture of these two pesticides. Initial behavioural responses recorded directly after exposure were seen in the form of decreased activity, less alterations between mobility states, and less time spent at the water surface. This response persisted after 96 h of exposure to a mixture of the two pesticides. This study shows that sub-lethal exposure to pesticides can alter the biochemical homeostasis of frogs with the potential to cascade onto behavioural and ecological levels in mixture exposure scenarios.

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.

Sub-lethal effects of soil multiple contamination on the avoidance behaviour of Eisenia fetida

Natural ecosystems are frequently exposed to complex mixtures of different chemicals. However, the environmental risk assessment is mainly based on data from individual substances. In this study, the individual and combined effects on the terrestrial earthworm E. fetida exposed to the anionic surfactant sodium lauryl ether sulphate (SLES) and the pesticides chlorpyrifos (CPF) and imidacloprid (IMI) were investigated, by using the avoidance behaviour as endpoint. Earthworms were exposed to a soil artificially contaminated with five sub-lethal concentrations of each contaminant, both as single substances and in combination of binary and ternary mixtures. Overall results showed that IMI provoked the highest avoidance effect on earthworms, with a concentration value that induced an avoidance rate of 50% of treated organisms (AC50) of 1.30 mg/kg, followed by CPF (AC50 75.26 mg/kg) and SLES (AC50 139.67 mg/kg). The application of the Combination Index (CI) method, indicated that a deviation from the additive response occurred for most of the tested chemical mixtures, leading to synergistic or antagonistic avoidance responses. Synergistic effects were produced by the exposure to the two lowest concentrations of the CPF+IMI mixture, and by the highest concentrations of SLES+CPF and SLES+CPF+IMI mixtures. On the contrary, antagonistic effects were observed at the lowest concentrations of the binary mixtures containing the SLES and at almost all the tested concentrations of the SLES+CPF+IMI mixture (with the exception of the highest tested concentration). These results show that the avoidance test is suitable to assess the detrimental effects exerted on earthworms by chemical mixtures in soil ecosystems and the use of behavioural endpoints can increase the ecological significance of environmental risk assessment procedures.

Locomotor behavior of Neocaridina palmata: a study with leachates from UV-weathered microplastics

Weathering of plastics leads to the formation of increasingly smaller particles with the release of chemical compounds. The latter occurs with currently unknown environmental impacts. Leachate-induced effects of weathered microplastics (MPs) are therefore of increasing concern. To investigate the toxicity of the chemical mixtures from such plastics, we exposed the freshwater shrimp Neocaridina palmata to enriched leachates from unweathered and artificially weathered (UV-A/B light) MPs (≤1 mm) from recycled low-density polyethylene (LDPE-R) pellets and from a biodegradable, not fully bio-based starch blend (SB) foil. We analyzed the individual locomotor activity (moved distance and frozen events) on day 1, 3, 7 and 14 of exposure to five leachate concentrations equivalent to 0.40–15.6 g MPs L⁻¹, representing the upper scale of MPs that have been found in the environment. The median moved distance did not change as a function of concentration, except for the unweathered SB treatment on day 14 that indicated hyperactivity with increasing concentrations. Significant impacts were solely detected for few concentrations and exposure days. Generally, no consistent trend was observed across the experiments. We further assessed the baseline toxicity of the samples in the Microtox assay and detected high bioluminescence inhibitions of the bacterium Aliivibrio fischeri. This study demonstrates that neither the recycled nor the biodegradable material are without impacts on test parameters and therefore cannot be seen as safe alternative for conventional plastics regarding the toxicity. However, the observed in vitro toxicity did not result in substantial effects on the behavior of shrimps. Overall, we assume that the two endpoints examined in the atyid shrimp N. palmata were not sensitive to chemicals leaching from plastics or that effects on the in vivo level affect other toxic endpoints which were not considered in this study.

Planarian behavioural endpoints in ecotoxicology: A case study evaluating mercury and salinity effects

Freshwater planarians can be useful for the evaluation of contaminant stress on behavioral endpoints. In this work, we studied the sensitivity of the freshwater planarian Girardia tigrina in response to two model stressors (Hg and NaCl) by evaluating mortality, feeding rate and locomotion. A simple feeding assay with G. tigrina was devised, and an automated tracking system was used to evaluate locomotion. The estimated 96 h LC₅₀s were 176.8 μg L^-1 of Hg and 6.79 g L^-1 of NaCl. Acute effects of Hg also included the disintegration of tissues, and loss of pigmentation. Acute effects of NaCl included motionlessness and rupture of the tegument. Hg and NaCl sub-lethal exposures caused feeding inhibition and locomotion impairment. This study demonstrates the usefulness of planarians for ecotoxicological research and that sensitive behavioral endpoints can evaluate the sub-lethal impacts of stressors to freshwater invertebrates.

Advances in real-time monitoring of water quality using automated analysis of animal behaviour

Monitoring of freshwater quality and its potential sudden contamination is integral to human health, sustainable economic development and prediction of pollutant impact on aquatic ecosystems. Although there have been significant advances in technologies for automated sampling and continuous analysis of water physicochemical parameters, the current capabilities for real-time warning against rapidly developing unknown mixtures of chemical hazards are still limited. Conventional chemical analysis systems are not suitable for assessing unknown mixtures of chemicals as well as additive and/or synergetic effects on biological systems. From the perspective of neurotoxicology the acute exposures to chemical agents that affect nervous system and can enter the freshwater supplies accidentally or as a result of deliberate action, can only be reliably assessed using appropriate functional biological models. In this regard real-time biological early warning systems (BEWS), that can continuously monitor behavioural and/or physiological parameters of suitable aquatic bioindicator species, have been historically proposed to fill the gap and supplement conventional water quality test strategies. Alterations in sub-lethal neuro-behavioural traits have been proven as very sensitive and physiologically relevant endpoints that can provide highly integrative water quality sensing capabilities. Although BEWS are commonly regarded as non-specific and lacking both quantitative and qualitative detection capabilities, their advantages, if properly designed and implemented, lie in continuous sensing and early-warning information about sudden alteration in water quality parameters. In this work we review the future prospects of real-time biological early warning systems as well as recent developments that are anchored in historical successes and practical deployment examples. We concentrate on technologies utilizing analysis of behavioural and physiological endpoints of animal bioindicators and highlight the existing challenges, barriers to future development and demonstrate how recent advances in inexpensive electronics and multidisciplinary bioengineering can help revitalize the BEWS field.

Effects of pristine microplastics and nanoplastics on soil invertebrates: A systematic review and meta-analysis of available data

In laboratory studies, microplastics and/or nanoplastics (MPs/NPs) have been shown to cause a variety of ecotoxicological effects on soil invertebrates. Existing data on the effects of these plastic debris on biological functions and physiological systems, showed a great variability among studies. Thus, how soil invertebrates respond to different types, shapes, sizes and concentrations of pristine MPs/NPs remains to be further characterized. The present work is an up-to-date review on quantitative and qualitative data on the effects of pristine MPs/NPs on soil invertebrates in laboratory conditions. Research priorities are also discussed. Out of a total of 1061 biological endpoints investigated in 56 studies, 49% were significantly affected after exposed to pristine MPs/NPs. The polymers with chloro and phenyl groups had more negative impacts on soil invertebrates than other polymers. Most studies used earthworm and nematode species as model organisms. For nematodes, the impact of MPs/NPs seemed to be concentration-dependent and higher concentrations of pristine MPs/NPs appeared to have more adverse impacts on biological functions and physiological systems, but this trend was not confirmed in earthworms. Meta-analysis revealed that pristine MP/NP concentrations higher than 1 g kg^-1 (in soil) may decrease growth and survival of earthworms, while a concentration higher than 1 μg L^-1 (in water) may affect nematode reproductive fitness.

Acclimation effect on fish behavioural characteristics: determination of appropriate acclimation period for different species

In the present study, the authors investigated the effect of acclimation duration (up to 4 h) on behavioural characteristics of taxonomically and functionally different fish species, i.e., the migratory rheophilic salmonids rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar), and the non-migratory eurytopic European perch (Perca fluviatilis) and three-spined stickleback (Gasterosteus aculeatus). Specifically, the authors explored fish behavioural patterns based on specific endpoints (average, maximum and angular velocity) during the acclimation period, and determined the acclimation period suitable for the tested fish species. The performed behavioural data analysis showed that the minimum time needed to adjust fish activity to a more stable (baseline) level should be at least 2 h for O. mykiss and S. salar and 1 h for G. aculeatus. Nonetheless, P. fluviatilis behaviour did not show significant changes during the 4 h acclimation. The results of this study revealed that the effect of the acclimation duration on such rheophilic species as O. mykiss and S. salar was greater than that on the eurytopic species P. fluviatilis and G. aculeatus, indicating that acclimation period is important in managing fish stress before behavioural observations. For all species, the highest variability was found in the endpoint of maximum velocity, and the lowest in that of angular velocity. This study showed that before starting actual toxicity testing experiments, it is important to determine an appropriate, species-specific acclimation period.

Double-edged sword: Fluoxetine and ibuprofen as development jeopardizers and apoptosis' inducers in common toad, Bufo bufo, tadpoles

Nowadays the presence of pharmaceuticals in the environment is a real problem. Ending up in aquatic environments they negatively affect non-target organisms. Considering the limited studies on the negative effects of pharmaceuticals in amphibians, a better understanding of the mechanisms underlying the sub-lethal effects of drug mixtures in wildlife is an urgent call. Representing particularly vulnerable organisms currently at risk of extinction, amphibians are perfect non-target organisms to explore the consequences of pharmaceuticals during sensitive life-stages. To address this existing research gap, the effects of two drugs, the antidepressant fluoxetine and the anti-inflammatory ibuprofen, as well as their combination has been studied. Tadpoles of Bufo bufo were exposed for seven days to two environmentally realistic concentrations of fluoxetine, ibuprofen and their mixture. The development, behavior and erythron profile were then evaluated as endpoints of exposure response. Both drugs negatively affected tadpoles' growth and development by significantly delayed their time to metamorphosis and reduced body weight. Behaviors were also impaired with a significant increase of unresponsiveness to different stimuli. Mutagenic analysis of blood revealed a significant increase in the frequency of cellular and nuclear abnormalities. Given the complexity of systems and functions affected, our work confirms the toxicological potential of fluoxetine and ibuprofen in B. bufo tadpoles by emphasizing their role as tadpole development delayers and erythrocyte apoptosis-inducers. To our knowledge, this is the first study trying to elucidate the potentially toxic effects of a mixture of an antidepressant with a non-steroidal anti-inflammatory drug using bullfrog tadpole as model organism. Both drugs interacted in impairing development and fitness in tadpoles, which might affect long-term species perpetuation and population dynamic. More in-depth research is needed to elucidate the nature of interaction and molecular mechanisms of mixed pharmaceutical compounds on non-targeted organisms.

Applications of advanced neuro-behavioral analysis strategies in aquatic ecotoxicology

Despite mounting evidence of pleiotropic ecological risks, the understanding of the eco-neurotoxic impact of most industrially relevant chemicals is still very limited. In particularly the acute and chronic exposures to industrial pollutants on nervous systems and thus potential alterations in ecological fitness remain profoundly understudied. Since the behavioral phenotype is the highest-level and functional manifestation of integrated neurological functions, the alterations in neuro-behavioral traits have been postulated as very sensitive and physiologically integrative endpoints to assess eco-neurotoxicological risks associated with industrial pollutants. Due to a considerable backlog of risk assessments of existing and new production chemicals there is a need for a paradigm shift from high cost, low throughput ecotoxicity test models to next generation systems amenable to higher throughput. In this review we concentrate on emerging aspects of laboratory-based neuro-behavioral phenotyping approaches that can be amenable for rapid prioritizing pipelines. We outline the importance of development and applications of innovative neuro-behavioral assays utilizing small aquatic biological indicators and demonstrate emerging concepts of high-throughput chemo-behavioral phenotyping. We also discuss new analytical approaches to effectively and rapidly evaluate the impact of pollutants on higher behavioral functions such as sensory-motor assays, decision-making and cognitive behaviors using innovative model organisms. Finally, we provide a snapshot of most recent analytical approaches that can be applied to elucidate mechanistic rationale that underlie the observed neuro-behavioral alterations upon exposure to pollutants. This review is intended to outline the emerging opportunities for innovative multidisciplinary research and highlight the existing challenges as well barriers to future development.

Size-dependent adverse effects of microplastics on intestinal microbiota and metabolic homeostasis in the marine medaka (Oryzias melastigma)

Microplastic (MP) is an emerging environmental pollutant and exposure to MPs has been associated with numerous adverse health outcomes in both wild and laboratory animals. The toxicity of MPs depends on concentration, exposure time, chemical composition and size distribution, but the impacts of particle size remain inconclusive yet. In this study, adult marine medaka (Oryzias melastigma) were exposed to different size of polystyrene MPs (PS-MPs) with concentration of 10 mg/L for 60 days and the growth performance, lipid metabolism, immune parameters and gut microbiome were determined. Results indicated that particle size is a dominant factor causing lipid metabolism disorders and hepatic toxicity in PS-MPs-exposed fish. The bodyweight, adipocyte size and hepatic lipid contents were significantly increased in 200 μm PS-MPs-exposed fish, while 2 and 10 μm PS-MPs-exposed fish exhibited liver injury principally manifested asthepresence oflittlefibrosis and inflammation. Given that larger particles could not enter the circulatory system, the impacts of PS-MPs on intestinal microbial biota homeostasis were further investigated. The results not only showed the characterization of gut microbial communities in Oryzias melastigma, but also indicated that microbial diversity and composition were altered in gut of fish exposed to PS-MPs, in particular 200 μm PS-MPs. The differentially abundant bacterial taxa in PS-MPs-exposed fish mainly belonged to the phylum Verrucomicrobia, Firmicutes and Fusobacteria. And furthermore, increased abundance of Verrucomicrobia and Firmicutes/Bacteroidetes ratio and decreased Fusobacteria were correlated with the increased bodyweight. Intestinal microbiome should play a critical role in regulating host lipid metabolism in fish exposed to lager size of PS-MPs.