Bisphenol risk in fish exposed to a contamination gradient: Triggering of spatial avoidance

A multi-evidence approach in an Amazonian river based on land use, water quality, histopathological effects and habitat selection behavior in fish

The Amazon rivers constitute the largest river basin in the world, with a high level of biodiversity. The Tocantins River is one of the most important rivers in this region, which has been impacted by different land uses. The objective of this study was to carry out a multi-evidence analysis focusing on the water quality of the Tocantins River, close to the municipality of Marabá-PA. We analyzed forest cover and water quality and, using the model organism Danio rerio, performed toxicity tests for histopathological effects, as well as the habitat selection approach by exposing fish to different river water samples in a multi-compartment device. The results showed that the studied area has already lost almost 30% of its forests in recent decades. Regarding water quality, the upstream (C1) and downstream (C5) points are the least impacted. On the other hand, the other points (C2-C4), closer to the city, greater input of pollutants was detected. Fish exposed to water samples from the most impacted sites showed several oedemas and hyperplastic cells in the gills. Regarding habitat selection behavior, there was a marked avoidance by samples with the highest contamination load. The results of this study lead to the understanding of the potential negative effects of human activities on local Amazonian biodiversity, since the potential toxicity of the environment, in conjunction with changes in the habitat selection process, could lead to a decline in populations of aquatic organisms, altering the environmental balance.

Behavioural, developmental and biochemical effects in zebrafish caused by ibuprofen, irgarol and terbuthylazine

The increasing use of chemicals and their release into aquatic ecosystems are harming aquatic biota. Despite extensive ecotoxicological research, many environmental pollutants' ecological effects are still unknown. This study examined the spatial avoidance, behavioural and biochemical impacts of ibuprofen, irgarol, and terbuthylazine on the early life stages of zebrafish (Danio rerio) under a range of ecologically relevant concentrations (0-500 μg/L). Embryos were exposed following the OECD guideline "fish embryo toxicity test" complemented with biochemical assessment of AChE activity and behavioural analyses (swimming activity) using the video tracking system Zebrabox. Moreover, spatial avoidance was assessed by exposing 120 hpf-old larvae of D. rerio to a gradient of each chemical, by using the heterogeneous multi-habitat assay system (HeMHAS). The results obtained revealed that the 3 compounds delayed hatching at concentrations of 50 and 500 μg/L for both ibuprofen and irgarol and 500 μg/L for terbuthylazine. Moreover, all chemicals elicited a dose-dependent depression of movement (swimming distance) with LOEC values of 5, 500 and 50 μg/L for ibuprofen, irgarol and terbuthylazine, respectively. Zebrafish larvae avoided the three chemicals studied, with 4 h-AC50 values for ibuprofen, irgarol, and terbuthylazine of 64.32, 79.86, and 131.04 μg/L, respectively. The results of the HeMHAS assay suggest that larvae may early on avoid (just after 4 h of exposure) concentrations of the three chemicals that may later induce, apical and biochemical effects. Findings from this study make clear some advantages of using HeMHAS in ecotoxicology as it is: ecologically relevant (by simulating a chemically heterogeneous environmental scenario), sensitive (the perception of chemicals and the avoidance can occur at concentrations lower than those producing lethal or sublethal effects) and more humane and refined approach (organisms are not mandatorily exposed to concentrations that can produce individual toxicity).

Concentrations of bisphenols and phthalate esters in the muscle of Mediterranean striped dolphins (Stenella coeruleoalba)

Bisphenols (BPs) and phthalate esters (PAEs) are important compounds for the plastics industry, also called "everywhere chemicals" due to their ubiquity in daily use products. Both chemical groups are well-known environmental contaminants, whose presence has been reported in all environmental compartments, and whose effects, mainly associated to endocrine disruption, are detrimental to living organisms. Cetaceans, due to their long life-span, low reproduction rate and high position in the trophic web, are especially vulnerable to the effects of contaminants. However, little is known about BP and PAE concentrations in cetacean tissues, their potential relation to individual biological variables, or their trends over time. Here, the concentration of 10 BPs and 13 PAEs was assessed in the muscle of 30 striped dolphins (Stenella coeruleoalba) stranded along the Spanish Catalan coast (NW Mediterranean) between 1990 and 2018. Six BP and 6 PAE compounds were detected, of which only 4,4'-(cyclohexane-1,1-diyl)diphenol (BPZ) was detected in all the samples, at the highest concentration (mean 16.06 μg g-1 lipid weight). Sex or reproductive condition were largely uninfluential on concentrations: only dimethylphthalate (DMP) concentrations were significantly higher in immature individuals than in adults, and the overall PAE concentrations were significantly higher in males than in females. Temporal variations were only detected in bis(4-hydroxyphenyl)ethane (BPE), diethylphthalate (DEP) and dimethylphthalate (DMP), whose concentrations were lower, and 9,9-Bis(4-hydroxyphenyl)fluorene (BPFL), which were higher, respectively, in samples taken between 2014 and 2018, probably reflecting shifts in the production and use of these chemicals. These results provide the first assessment of concentrations of several BP and PAE compounds in the muscle of an odontocete cetacean.

Occurrence, distribution, and ecological risk of bisphenol analogues in marine ecosystem of urbanized coast and estuary

Bisphenol analogues are prevalent globally because of rampant usage and imprecise processing techniques, prompting alerts about environmental and health hazards. The method employed in this study by solid phase extraction (SPE) and liquid chromatography-tandem quadrupole mass spectrometer (LC-MS/MS) for both quantification and qualitative analysis of the bisphenol compounds in the surface water samples. The coastal and estuarine surface water of Port Dickson and Lukut ranges from 1.32 ng/L to 1890.51 ng/L of bisphenol analogues. BPF mean concentration at 1143.88 ng/L is the highest, followed by BPA and BPS at 59.01 ng/L and 10.96 ng/L, respectively. Based on RQm for bisphenol analogues, the highest for BPF at 2.49 (RQ > 1, high risk), followed by BPS at 0.12 (0.1 < RQ < 1, medium risk) and BPA at 0.09 (0.1 < RQ < 1, medium risk). The presence and current risk of bisphenols analogues should alert the possible water quality degradation soon.

Stable magnetic CoZn/N-doped polyhedron with self-generating carbon nanotubes for highly efficient removal of bisphenols from complex wastewaters

Bisphenols have extensively been found in various environmental matrices and caused public concerns due to their endocrine-disrupting potential. Herein, we developed a ZIF-67@ZIF-8-derived CoZn/nitrogen-doped carbon (CoZn/NC) as a robust adsorbent for bisphenols in wastewaters. The self-generating carbon nanotubes and the open metal sites provided sufficient adsorption sites. The Co component endowed the derivative with strong magnetism facilitating its separation from water. CoZn/NC exhibited exceeding water stability in pH 3 - 12 solution and withstood water up to 15 days. The great applicability of CoZn/NC was validated with 16 real wastewaters from different sources (recoveries exceeding 97.9%). Fast adsorption kinetics were observed with removal efficiencies above 96.5% within 1 min. The adsorption isotherms were well fitted with the Langmuir model, with adsorption capacities of 222, 200, 193, and 321 mg g^-1 for bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, respectively. Variations in external conditions, including pH 3 - 9, humic acid (50 mg L^-1), and NaCl (0.1 mol L^-1), had negligible impacts on the adsorption process. The characterizations and density functional theory computation demonstrated that electrostatic, hydrophobic, π - π, and cation- π interactions are the driving forces in this system. The as-prepared CoZn/NC exhibits great promise in real wastewater treatment.

A Mini-review of the Toxicity of Pollutants to Fish Under Different Salinities

In recent years, with the development of the global economy, water pollution has increased. Pollutants migrate, accumulate, and diffuse in aquatic environments. Most of the pollutants eventually enter aquatic organisms. The accumulation of pollutants affects the development and reproduction of organisms, and many pollutants have teratogenic, carcinogenic, and/or mutagenic effects. Aquatic organisms in estuaries and coastal areas are under pressure due to both salinity and pollutants. Among them, salinity, as an environmental factor, may affect the behavior of pollutants in the aquatic environment, causing changes in their toxic effects on fishes. Salinity also directly affects the growth and development of fishes. Therefore, this paper focuses on metals and organic pollutants and discusses the toxic effects of pollutants on fish under different salinities. This research is of great significance to environmental protection and ecological risk assessment of aquatic environments.

Acute toxicity of Bisphenol A (BPA) to tropical marine and estuarine species from different trophic groups

BPA is chemical pollutant of very high concern due to its toxicity to the environment and risks for human health. Environmental concern consists in BPA entrance into aquatic ecosystems due to acute and chronic toxicity to invertebrates and vertebrates. This study aimed to determine acute BPA toxicity to tropical estuarine-marine species of four trophic levels and integrate BPA toxicity values using species sensitivity distribution (SSD) analysis. Our hypothesis is that BPA toxicity increases towards higher trophic levels. Microalga (Tetraselmis sp.), zooplanktonic grazer (Artemia salina), deposit-feeder invertebrate (Heleobia australis), and omnivorous fish (Poecilia vivipara) were chosen as experimental models. Tetraselmis sp. showed the highest BPA tolerance, without a concentration-dependent response. Species sensitivity have increased from A. salina (LC_50,96h = 107.2 mg L^-1), followed by H. australis (LC_50,96h = 11.53.5 mg L^-1), to P. vivipara (LC_50,96h = 3.5 mg L^-1). Despite the toxicity hierarchy towards trophic levels, which partially supported our hypothesis, SSD did not evidence a clear pattern among estuarine-marine trophic groups. Our study disclosed the sensitivity of not yet investigated species to BPA and, in an integrative way, highlighted BPA toxic effects at different trophic levels. Although estimated acute hazardous concentration (HC5 = 1.18 mg L^-1) for estuarine and marine species was higher than environmentally relevant concentrations, sublethal adverse effects induced by BPA exposure may lead to unbalances in population levels and consequently affect the ecological functioning of tropical coastal systems.

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

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

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

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

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

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

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

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

Occurrence, trophic transfer, and health risk assessment of bisphenol analogues in seafood from the Persian Gulf

The presence of chemicals in marine organisms is an important issue for human health due to the growing rate of seafood consumption. Potential exposure to seven bisphenol analogues through seafood consumption was investigated in some popular seafood from the Persian Gulf. Bisphenols were analyzed by gas chromatography-mass spectrometry. Bisphenol A (BPA) and bisphenol B (BPB) were the first and second most common bisphenols in the studied samples, respectively. The highest levels of BPA (mean 13.58 ± 5.70 μg/kg.dw) and BPB (mean 10.30 ± 7.98 μg/kg.dw) were found in E.coioides species. Bisphenol F and bisphenol AF were detected only in P. armatus and L. klunzingeri, respectively. Trophic transfer investigation demonstrated that BPA and BPB were biomagnified in the studied organisms through their diet. The eco-toxicity and estrogenic risk assessment indicated that seafood consumption does not pose a health threat to consumers. However, routine monitoring of bisphenols in seafood seems to be necessary to ensure food safety.

Multiple biomarkers response in a Neotropical fish exposed to paralytic shellfish toxins (PSTs)

The Alagados Reservoir (Southern Brazil) is used as water supply, and since 2002 there have been reports with a presence of cyanobacterial blooms and cyanotoxins. In order to assess the water quality and the ecological integrity of the reservoir, we evaluated biochemical, genotoxic and osmoregulatory biomarkers in the freshwater cichlid fish (Geophagus brasiliensis) that were exposed to PSTs. The fish were sampled in the Alagados Reservoir in February 2016 (Summer) and were divided in three groups: 1) Reservoir group (RES): fish were collected immediately after sampling; 2) Depuration group (DEP): fish were submitted to the depuration experiment for 90 days in the laboratory; and 3) Reproduction group (REP): fish were kept in the laboratory until the fertilization and the chemical analyses were performed on the offspring (F1 generation). In the RES and DEP the blood, brain, muscle, liver and gills were collected for biochemical, genotoxic and osmoregulatory biomarkers analysis. Our results showed that the fish from the Alagados Reservoir (RES) presented oxidative stress and DNA damage; and after 90 days (DEP), the antioxidant system and DNA damage were recovered. Although PSTs were considered a risk to the ecological integrity of this water body; PSTs concentrations were not found in the tissues of the F1 generation. In addition, the biomarkers used were useful tools to evaluate the effects of environment contamination. Therefore, it is necessary to develop new technologies and monitoring programs in order to reduce cyanobaterial blooms, cyanotoxins and human activities that cause the contamination in aquatic environments.

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

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

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

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

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

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

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

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

Avoidance response by shrimps to a copper gradient: Does high population density prevent avoidance of contamination?

Bioassays using the nonforced exposure approach have been shown to be a relevant tool that might complement the traditional ecotoxicological risk assessment. Because the nonforced exposure approach is based on spatial displacement of organisms and the consequent habitat selection processes, the population density might play an important role in the decision to avoid or prefer an ecosystem. Therefore, the aim of the present study was to assess if the avoidance response to contamination, measured in a nonforced exposure system, is density-dependent and how determinant contamination could be for the habitat-selection process in comparison with the population density. The freshwater shrimp Atyaephyra desmarestii was exposed to a copper gradient in a nonforced exposure system formed by 7 interconnected compartments (total volume 600 mL), which contained different copper concentrations. The density treatments used were 3, 5, and 10 organisms per compartment, corresponding to 0.5, 0.8, and 1.7 organisms per 100 mL, respectively. Clearly, the avoidance response to copper was more intense in the population with the lower density: the highest population density showed the lowest avoidance. The concentrations that triggered an avoidance of 50% of the population were 47, 134, and 163 μg L^-1 . In summary, it was observed that shrimps were able to detect and avoid potentially toxic copper concentrations but that the avoidance response was affected by population density. Environ Toxicol Chem 2018;37:3095-3101. © 2018 SETAC.

Influence of interspecific interactions on avoidance response to contamination

An increasing number of studies have shown the ability of organisms to escape from toxic effects due to contamination, by moving spatially towards less contaminated habitats. However, this issue has been investigated in monospecific scenarios, without considering possible interactions between species during the contamination avoidance process. It is widely known that the spatial distribution of one species can be affected by another one, in different ways. Therefore, the main question addressed in the present study was as follows: Might interspecific interaction between the freshwater fish Danio rerio (zebrafish) and Poecilia reticulata (guppy) change their behavior patterns in terms of avoidance in the presence of a copper gradient? Zebrafish and guppies exposed to a copper gradient were tested for avoidance responses in a free-choice, non-forced, static, multi-compartmented exposure system, using two distinct approaches: (1) monospecific tests, in which only one species was exposed to the copper gradient, at two different population densities; and (2) multispecific tests, in which both species were tested simultaneously. In the control (with no copper) monospecific tests, both species were randomly distributed; however, in the control multispecific test, P. reticulata tended to aggregate. In the monospecific tests with a copper gradient, both species avoided copper in a similar way, with AC₅₀ (concentration triggering avoidance in 50% of the exposed population) values between 15 and 18 μg·L^-1, irrespective of the population density. However, in the multispecific tests, P. reticulata displaced D. rerio to previously avoided copper levels, consequently increasing the AC₅₀ of D. rerio to 75 μg·L^-1. This study shows the importance of understanding the interactions among species in contaminated areas, and the way that one species can prevent the avoidance behavior of another.