Increased acetylcholinesterase activities in specimens of Sparus auratus exposed to sublethal copper concentrations

Does temperature influence on biomarker responses to copper exposure? The invasive bivalve Limnoperna fortunei (Dunker 1857) as a model

Biomarkers are useful tools for assessing the early warning effects of pollutants. However, their responses can be influenced by confounding factors. In this study, we investigated the influence of temperature on multiple biomarkers in the invasive freshwater bivalve Limnoperna fortunei exposed to copper (Cu). The mussels were exposed to low and high environmental Cu concentrations at two temperatures (15 °C and 25 °C). After 96 h, the oxidative stress, neurotoxicity, and metabolic parameters were assessed. Our results showed that temperature is a key factor influencing biomarker responses in mussels, with higher glutathione S-transferase activity and lower energy reserves at cold temperature. In addition, the effects of Cu were greater at the highest concentration at 15 °C (increased lipid peroxidation and cholinesterase activity). Overall, these findings suggest that cold stress increases the susceptibility of L. fortunei to metal effects and highlight the importance of including temperature in toxicity testing and biomonitoring. In addition, using the invasive bivalve L. fortunei as a model could prove valuable in its role as a sentinel species for other organisms.

Biological monitoring of soil pollution caused by two different zinc species using earthworms

Zinc oxide nanoparticles (ZnO-NPs) are commonly used in both commercial and agricultural sectors. As a result, ZnO-NPs are extensively discharged into soil ecosystems, creating a significant environmental issue. Therefore, it is crucial to assess their influence on the soil ecology to ensure its secure and enduring utilization in the future. The exact degree of toxicity associated with ZnO-NPs and their ionic form is still uncertain. To address the challenges, the study used the soil bioindicator earthworm species Eudrilus eugeniae as an experimental model to evaluate the effects of two zinc species (ZnO-NPs and ZnCl2) at 100, 250, 500, and 750 mg kg-1 and control (0 mg kg-1) in garden soil over 28 days. The investigation also examined the impact of exposure on survival, reproduction, neuro-biomarker, avoidance behavior, and accumulation. The highest avoidance rates were 27.5% for ZnO-NP and 37.5% for ZnCl2 at 750 mg kg-1. ZnCl2 treatment reduced juvenile production by 3.73 ± 1.73, while ZnO-NPs showed 4.67 ± 1.15. At 750 mg kg-1, soils with ZnCl2 (63.3%) demonstrated lower survival rates than those with ZnO-NPs (53.3%), likely because of higher Zn ion levels. After 28 days of exposure, ZnCl2 (536.32 ± 11 mol min-1) activated AChE enzymes more than ZnO-NPs (497.7 ± 59 mol min-1) at the same dose, compared to control (145.88 ± 28 to 149.41 ± 23 mol min-1). Nanoparticles and zinc ions bioaccumulated and reacted negatively with the neurotoxic marker AChE, affecting earthworm reproduction and behavior. However, earthworms exposed to ZnCl2 exhibited less intestinal Zn than those exposed to NPs. The present work contradicts the finding that ZnO-NPs have hazardous effects on soil organisms. The results indicate that earthworm E. eugeniae may significantly affect soil metal uptake from metallic nanoparticles (NPs). This may help design NP soil pollution mitigation strategies. The study offers valuable information for establishing a relationship between the environmental toxicity of ZnO-NPs and soil ecosystems.

Systemic effects of settleable atmospheric particulate matter (SePM) on swamp ghost crab Ucides cordatus

Metallurgical activities are a significant source of settleable atmospheric particulate matter (SePM). The material is exposed to wind action, leading to its deposition throughout terrestrial and aquatic ecosystems, thus promoting contamination by metals and metalloids. However, knowledge of the impacts on biota is scarce. In aquatic coastal zones, evaluating hemolymph in invertebrates makes it possible to have insights into the pre-pathogenic effects and health status of organisms. Our study aimed to evaluate bioaccumulation and the sublethal effects of SePM on the mangrove crab Ucides cordatus by assessing biomarkers of cito-genotoxicity in the hemolymph. Organisms underwent a 30-day experiment with four treatments: control; 0.01 g.L-1, 0.1 g.L-1, 1 g.L-1 of SePM, with hemolymph sampled at 2, 7, 15, and 30 days of exposure to assess lipid peroxidation (LPO), DNA damage (strand break), cholinesterase (ChE) and lysosomal membrane stability (LMS). The results revealed metals' bioaccumulation in soft tissues (Al, Fe+, Fe++, Cu, Zr, Nb) and dose-time-dependent responses for LPO, DNA strand break, ChE, and LMS. Significant correlation was found between LPO and Cu (tissue), reduced LMS and Al and Fe (tissue), and Cu, Zn, Ag, and Bi in water. Hemolymph was related to the toxicokinetic and toxicodynamic of metals and metalloids from SePM in Ucides cordatus. New toxicological evidence was obtained to shed light on the impacts of SePM on the ecological status of coastal zones.

Protective effect of cholecalciferol against cobalt-induced neurotoxicity in rats: ZO-1/iFABP, ChAT/AchE and antioxidant pathways as potential therapeutic targets

Cobalt (Co) toxicity has been reported to produce central nervous system and gastrointestinal abnormalities. This study assessed the therapeutic effect of cholecalciferol (Cho) supplementation against damages caused by sub-acute (14-day) cobalt chloride (CoCl2) exposure in the brain and intestines. Thirty-five male Wistar rats were divided equally into five groups: Group I (control) received no treatment; Group II received oral CoCl2 (100 mg/kg) only; Groups III, IV, and V received 1000, 3000 and 6000 IU/kg of cholecalciferol, respectively by oral gavage, and concurrently with CoCl2. Cobalt-treated rats showed neuronal vacuolation and presence of pyknotic nuclei in the cerebral cortex and hippocampus, depletion of Purkinje cells in the cerebellum, as well as inflammation and congestion in the intestinal mucosa. Cobalt also increased brain and intestinal hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations, while simultaneously reducing glutathione (GSH) content, superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities. Further, CoCl2 induced increases in brain acetylcholinesterase (AchE) activity and serum zonulin (ZO-1) levels. Conversely, Cho administration suppressed CoCl2-induced damages in the brain and intestines by reducing lipid peroxidation and increasing the activities of antioxidant enzymes. Remarkably, Cho produced stimulation of brain choline acetyltransferase (ChAT) and suppression of AchE activity, along with dose-dependent reduction in serum levels of ZO-1, intestinal fatty acid-binding protein (iFABP) and nitric oxide. In conclusion, the protective role of cholecalciferol against cobalt-induced toxicity occurred via modulation of cholinergic, intestinal permeability and antioxidant pathways. The results may prove significant in the context of the role of gut-brain connections in neuroprotection.

Effect of sulfate on the osmoregulatory and physio-biochemical responses of GIFT (Oreochromis niloticus) juveniles reared in potassium-deficient medium saline waters

The inland saline waters were continuously observed to have low potassium concentrations compared to their seawater counterpart of the same salinity. We hypothesize that the toxic effect of sulfate may manifest in low potassium saline (LPSW) waters compared to brackish water of the same salinity. Thus, LC50 trials were performed in GIFT (genetically improved farmed tilapia) fry (0.5 ± 0.02 g) to determine the acute sulfate toxicity in freshwater (FW, 0.5 g L-1), artificial seawater (ASW, 10 g L-1), and LPSW (10 g L-1). The median lethal concentrations (96h LC50) of sulfate ion in FW, LPSW, and ASW for the GIFT were 5.30 g L-1, 2.56 g L-1, and 2.98 g L-1, respectively. A second experiment was conducted for 21 days, exposing fish to a sub-lethal level of sulfate ion (SO42-) concentration (1000 mg L-1, one-fifth of FW LC50) with different types of waters (FW, freshwater, 0.5 g L-1; ASW, artificial seawater, 10 g L-1; LPSW, low potassium saline water, 10 g L-1) with and without sulfate inclusion to constitute the treatments as follows, (FW, FW + SO4, ASW, ASW + SO4, LPSW, LPSW + SO4). The effect of sulfate on GIFT reared in sulfate-rich potassium-deficient medium saline water was evaluated by focusing on the hematological adjustments, stress-induced oxidative damage, and osmoregulatory imbalances. The survival was not altered due to the sulfate concentration and K+ deficiency; however, there were significant changes in branchial NKA (Na+/K+-ATPase) activity and osmolality. The increase in NKA was highest in LPSW treatment, suggesting that internal ionic imbalance was triggered due to an interactive effect of sulfate and K+ deficiency. The cortisol levels showed a pronounced increase due to sulfate inclusion irrespective of K+ deficiency. The antioxidant enzymes, i.e., SOD (superoxide dismutase), catalase, GST (glutathione-S-transferase), and GPX (glutathione peroxidase), reflected a similar pattern of increment in the gills and liver of the LPSW + SO4 groups, suggesting a poor antioxidant status of the exposed group. The hepatic peroxidation status, i.e. TBARS (thiobarbituric acid reactive substances), and the peroxide values were enhanced due to both K+ deficiency and sulfate inclusion, suggesting a possible lipid peroxidation in the liver due to handling the excess sulfate anion concentration. The hematological parameters, including haemoglobin, total erythrocyte count, and hematocrit level, reduced significantly in the LPSW + SO4 group, indicating a reduced blood oxygen capacity due to the sulfate exposure and water potassium deficiency. The hepatic acetylcholine esterase activity was suppressed in all the treatments with sulfate inclusion, while the highest suppression was observed in the LPSW + SO4 group. Thus, it is concluded that sulfate-induced physiological imbalances manifest more in potassium-deficient water, indicating that environmental sulfate is more detrimental to inland saline water than freshwater or brackish water of the same salinity.

Cardiotoxic and neurobehavioral effects of sucralose and acesulfame in Daphnia: Toward understanding ecological impacts of artificial sweeteners

Artificial sweeteners are widely used in food and pharmaceuticals, but their stability and persistence raise concerns about their impact on aquatic life. Although standard toxicity tests do not reveal lethal effects, recent studies suggest a potential neurotoxic mode of action. Using environmentally relevant concentrations, we assessed the effects of sucralose and acesulfame, common sugar substitutes, on Daphnia magna focusing on biochemical (acetylcholinesterase activity; AChE), physiological (heart rate), and behavioural (swimming) endpoints. We found dose-dependent increases in AChE and inhibitory effects on heart rate and behaviour for both substances. Moreover, acesulfame induced a biphasic response in AChE activity, inhibiting it at lower concentrations and stimulating at higher ones. For all endpoints, the EC50 values were lower for acesulfame than for sucralose. Additionally, the relationship between acetylcholinesterase and heart rate differed depending on the substance, suggesting possible differences in the mode of action between sucralose and acesulfame. All observed EC50 values were at μg/l levels, i.e., within the levels reported for wastewater, with adverse effects observed at as low as 0.1 μg acesulfame /l. Our findings emphasise the need to re-evaluate risk assessment thresholds for artificial sweeteners and provide evidence for the neurotoxic effects of artificial sweeteners in the environment, informing international regulatory standards.

Effects of Carbon Nanoparticles and Chromium Combined Exposure in Native (Ruditapes decussatus) and Invasive (Ruditapes philippinarum) Clams

Studies have described the occurrence of nanoparticles (NPs) in aquatic ecosystems, with particular attention to the widely commercialized carbon nanotubes (CNTs). Their presence in the environment raises concerns, especially regarding their toxicity when co-occurring with other pollutants such as metals. In the present study, changes to the metabolic capacity, oxidative, and neurologic status were evaluated in the presence of carboxylated multi-walled CNTs and chromium (Cr(III)) using two of the most ecologically and economically relevant filter feeder organisms: the clam species Ruditapes decussatus and R. philippinarum. Results indicated that although Cr, either alone or in combination with CNTs, was found in a similar concentration level in both species, a species-specific Cr accumulation was observed, with higher values in R. decussatus in comparison with R. philippinarum. Inhibition of antioxidant defenses and neurotoxic effects were detected only in R. philippinarum. The interaction between contaminants seems to have no effect in terms of antioxidant enzyme activities and neuro status. Nevertheless, synergistic activation of responses to both contaminants may have altered the metabolic capacity of bivalves, particularly evident in R. decussatus. While both clams are tolerant to both contaminants (alone and together), they showed a relevant accumulation capacity, which may represent a possible contaminant transfer to humans.

Hazardous effects of road-side soils on the redox and cholinesterasic homeostasis of mound-building termite (Cornitermes cumulans)

For our knowledge, the roadside soils end up being the deposit of various residues discarded by drivers or passengers, plus, that coming from the runoff of rainwater. Basically, we do not know the impacts that this pollution causes on animals which inhabit these environments. Thus, in this study, our objective was to evaluate how the presence of plastic microfibers (MPFs), organic compounds and heavy metals affect the redox and cholinesterase homeostasis of mound-building termite [Cornitermes cumulans (workers) adults]. As a result, we noticed that MPFs were present in all sampled areas, being higher in road area (RA). Regardless of the presence of these pollutants, animals sampled in the RA were those in which we observed greater production of reactive oxygen species (ROS), hydrogen peroxide (H₂O₂) and nitric oxide (NO) (via nitrite), whose higher activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), was not able to counterbalance the oxidative stress suggested by the evaluated biomarkers. Moreover, we observed increase in acetylcholinesterase (AChE) activity in these same animals, which suggests a cholinesterasic effect. Such alterations were positively correlated with the contamination of soil samples by Cd, Pb, Zn, Fe and Cu, as well as with the presence of the 11,10-guaiane-type sesquiterpenoid compound, identified only in the RA. Thus, our unique study reveals that the contamination of roadside soils constitutes an additional environmental stressor to populations of C. cumulans, which reinforces the need for greater attention and further investigation to be given to the pollution of these environments.

Cellular level response of the bivalve Limecola balthica to seawater acidification due to potential CO2 leakage from a sub-seabed storage site in the southern Baltic Sea: TiTank experiment at representative hydrostatic pressure

Understanding of biological responses of marine fauna to seawater acidification due to potential CO₂ leakage from sub-seabed storage sites has improved recently, providing support to CCS environmental risk assessment. Physiological responses of benthic organisms to ambient hypercapnia have been previously investigated but rarely at the cellular level, particularly in areas of less common geochemical and ecological conditions such as brackish water and/or reduced oxygen levels. In this study, CO₂-related responses of oxygen-dependent, antioxidant and detoxification systems as well as markers of neurotoxicity and acid-base balance in the Baltic clam Limecola balthica from the Baltic Sea were quantified in 50-day experiments. Experimental conditions included CO₂ addition producing pH levels of 7.7, 7.0 and 6.3, respectively and hydrostatic pressure 900 kPa, simulating realistic seawater acidities following a CO₂ seepage accident at the potential CO₂-storage site in the Baltic. Reduced pH interfered with most biomarkers studied, and modifications to lactate dehydrogenase and malate dehydrogenase indicate that aerobiosis was a dominant energy production pathway. Hypercapnic stress was most evident in bivalves exposed to moderately acidic seawater environment (pH 7.0), showing a decrease of glutathione peroxidase activity, activation of catalase and suppression of glutathione S-transferase activity likely in response to enhanced free radical production. The clams subjected to pH 7.0 also demonstrated acetylcholinesterase activation that might be linked to prolonged impact of contaminants released from sediment. The most acidified conditions (pH 6.3) stimulated glutathione and malondialdehyde concentration in the bivalve tissue suggesting potential cell damage. Temporal variations of most biomarkers imply that after a 10-to-15-day initial phase of an acute disturbance, the metabolic and antioxidant defence systems recovered their capacities.

Cholinesterases of marine fish: characterization and sensitivity towards specific chemicals

Inhibition of cholinesterases has been frequently used as a biomarker for contamination of aquatic environments, because these enzymes are frequent targets for toxic effects of contaminants, such as insecticides derived from phosphoric and carbamic acids. However, this enzyme is also responsive to other contaminants, including metals. The use of cholinesterase inhibition as effect criterion in ecotoxicology studies requires the previous characterization of the specific enzymatic forms that can be present in the different tissues and/or organs of species. This work characterized the soluble ChEs present in the brain and dorsal muscle of three marine fish species, namely Scomber scombrus, Sardina pilchardus and Chelidonichthys lucerna. Pesticides (chlorpyrifos) and metals (copper sulphate) in vitro assays were conducted to quantify the effects of these contaminants on cholinesterases activity. The results of this study showed that acetylcholinesterase (AChE) was the predominant form present in the brain tissues of the three species and in the muscle tissue of one species (Sardina pilchardus). For Scomber scombrus and Chelidonichthys lucerna, the cholinesterase form present in the muscle tissue evidenced properties between the classic acetylcholinesterase and those of pseudocholinesterase forms. The results for the metal (copper) and pesticide (chlorpyrifos) showed that this species may be suitable for monitoring contaminations for these types of contaminants.

The effect of the use of copper carbonate and copper nanoparticles in the diet of rats on the level of β-amyloid and acetylcholinesterase in selected organs

BACKGROUND

Copper has an important role in nervous system function, as a cofactor of many enzymes and in the synthesis of neurotransmitters. Both the dose and the chemical form of copper can determine the impact of this element on metabolism, the neurological system and the immune system.

AIMS

The aim of the study was to determine whether and in what form the addition of copper changes the level of amyloid beta and acetylcholinesterase level in selected rat tissues.

METHODS

Thirty, healthy, male, albino Wistar rats aged 7 weeks were randomly divided into 3 groups. Three experimental treatments were used to evaluate the effects of different levels and sources of Cu (6.5 mg kg of diet) in the diet: Cu₀ - rats fed a diet without Cu supplementation; Cu_salt - rats fed a diet with CuCO₃ (6.5 mg kg of diet) during two months of feeding; Cu_NPs - rats fed a diet with Cu nanoparticles (6.5 mg kg of diet) during two months of feeding. In blood serum and tissue homogenates there rated the indicators proving the potential neurodegenerative effect and epigenetic DNA damage induced by chemical form of copper or lack of additional copper supplementation in diet were determined. There were analysed: level of acetylcholinesterase, β-amyloid, low-density lipoprotein receptor-related protein 1, apyrimidinic endonuclease, thymidine glycosidase, alkylpurine-DNA-N-glycosylase and glycosylated acetylcholinesterase.

RESULTS

Irrespective of the form of copper added, it was found to increase acetylcholinesterase level in the brain, spleen and liver, as well as in the blood plasma of the rats. Copper in the form of CuCO₃ was found to increase acetylcholinesterase level in the kidneys. The addition of both forms of copper caused a marked increase in the plasma concentration of β-amyloid in comparison with the diet with no added Cu. The addition of both forms of copper caused a marked increase in the plasma concentration of β-amyloid in comparison with the diet with no added Cu.

CONCLUSIONS

A lack of added Cu in the diet of rats reduces the concentration of amyloid-β in the blood, whereas administration of copper, in the form of either CuNPs or CuCO₃, increases the level of this peptide in the blood. The use of copper in the form of CuNPs in the diet of rats does not increase the level of β-amyloid more than the use of the carbonate form of this element. The use of CuNPs or CuCO₃ in the diet of rats increases acetylcholinesterase level in the brain, spleen, liver, and blood. CuNPs in the diet of rats were not found to increase acetylcholinesterase level to a greater extent than Cu⁺² carbonate.

Ecotoxicological responses of Eisenia andrei exposed in field-contaminated soils by sanitary sewage

The disposal of untreated sanitary sewage in the soil has several consequences for human health and leads to environmental risks; thus, it is necessary investigating, monitoring and remediating the affected sites. The aims of the current study are to evaluate ecotoxicological effects on Eisenia andrei earthworms exposed to soil subjected to sources of sanitary sewage discharge and to investigate whether prevention values established by the Brazilian legislation for soil quality, associated with the incidence of chemical substances in it, are satisfactory enough to assure the necessary quality for different organisms. Earthworms' behavior, reproduction, acetylcholinesterase activity, catalase, superoxide dismutase and malondialdehyde levels were evaluated. The reproduction and behavior of earthworms exposed to sanitary sewage were adversely affected. Increased superoxide dismutase and catalase activity acted as antioxidant defense mechanism. Significantly increased lipid peroxidation levels and acetylcholinesterase activity inhibition have indicated lipid peroxidation in cell membrane and neurotransmission changes, respectively. Results have confirmed that sanitary sewage induced oxidative stress in earthworms. In addition, based on biochemical data analysis, the integrated biomarker response (IBR) has evidenced different toxicity levels in earthworms between the investigated points. Finally, results have indicated that effluents released into the soil, without proper treatment, lead to contaminant accumulation due to soil saturation and it can hinder different processes and biological development taking place in the soil. In addition, the current study has shown that physical-chemical analyses alone are not enough to assess soil quality, since it is also requires adopting an ecotoxicological approach. Brazilian legislation focused on soil quality must be revised and new guiding values must be proposed.

Toxic effects of naturally-aged microplastics on zebrafish juveniles: A more realistic approach to plastic pollution in freshwater ecosystems

We aim at evaluating the toxicity of naturally-aged polystyrene microplastics (MPs) in Danio rerio at intermediate development stage. Animal models were stactically exposed to 4 × 10⁴ and 4 × 10⁶ microparticles/m³ for five days - this concentration is environmentally relevant. We evaluated MP's impact on animals' nutritional status and REDOX balance, as well as its potential neuro- and cytotoxic action on them. Initially, MPs did not induce any change in total carbohydrates, triglycerides and total cholesterol levels. MP accumulation was associated with oxidative stress induction, which was inferred by the nitrite and thiobarbituric acid reactive substances levels. Furthermore, we observed that such stress was not counterbalanced by increase in the assessed enzymatic (total glutathione, catalase and superoxide dismutase) and non-enzymatic (total thiols, reduced glutathione and DPPH radical scavenging activity) antioxidants. The association between high acetylcholinesterase activity and numerical changes in neuroblasts distributed on animals' body surface confirmed MP's neurotoxic potential. MP's ability to induce apoptosis and necrosis processes in animals' erythrocytes suggested its cytotoxic action; therefore, the present study is pioneer in providing insight on how MPs can affect young freshwater fish at environmental concentrations. It is essential knowing the magnitude of these pollutants' impact on the ichthyofauna.

The Single and Combined Effects of Wildfire Runoff and Sediment-Bound Copper on the Freshwater Amphipod Hyalella azteca

The frequency of wildfire is expected to increase with time as a function of climate change. Recent studies in our laboratory have demonstrated that pyrogenic polycyclic aromatic hydrocarbons can cause greater-than-additive effects in Hyalella azteca in the presence of low concentrations of Cu. We hypothesized that freshwater animals inhabiting Cu-contaminated sites, such as those in the vicinity of Cu mines, may be vulnerable to nonadditive toxicity from contaminants released by wildfires. To investigate the interaction between Cu and water conditioned by burnt wood ash (fire extract), we exposed H. azteca for 14 d to binary mixtures of 225 mg/kg Cu-enriched artificial sediment (225 mg Cu/kg) and a fire extract dilution series (12.5, 25, 50, 75, and 100%). All binary mixtures of Cu-enriched sediment and fire extract resulted in complete mortality with the exception of Cu-enriched sediment + 12.5% fire extract. The combination of Cu-enriched sediment with 12.5% fire extract had a more-than-additive effect on survival and tissue Cu concentration, but there was no reduction in growth or acetylcholinesterase activity compared to the 225 mg/kg Cu-contaminated sediment or fire extract control, respectively. Acetylcholinesterase activity was significantly reduced in amphipods exposed to fire extract, but the presence of Cu did not exacerbate this effect. The results suggest that Cu-contaminated water bodies that receive runoff from wildfires are at risk of enhanced toxicity. Environ Toxicol Chem 2020;39:1988-1997. © 2020 SETAC.

Biomarkers of the oxidative stress and neurotoxicity in tissues of the bullfrog, Lithobates catesbeianus to assess exposure to metals

Lithobates catesbeianus tadpoles were exposed to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) alone or combined (1:1 and 1:1:1) for 2 and 16 days. Results showed a significant increase in the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities in the liver, kidney and muscle (except for GPx) in the groups exposed to metal either alone or co-exposed after 2 days compared to the control. After 16 days, SOD, CAT and GST activities decreased significantly in the liver and kidney and GPx activity increased in the liver. Reduced glutathione (GSH) increased in the liver and kidney following combined exposure and decreased after 2 days of metal exposure in the muscle. There were significant increases in lipid hydroperoxide (LPO) levels in the liver, kidney and muscle (2 and 16 days), with the highest levels after metal co-exposure. Cholinesterase (ChE) activity increased significantly in the brain after 2 days of exposure but decreased in the brain (16 days) and muscle (2 days) after exposure to metals, alone and combined. The current study highlighted that the antioxidant system of L. catesbeianus was sensitive to metals and specially to the co-exposure of the three metals, despite presenting differences in the response among tissues. In addition, tadpoles were sensitive at both periods of exposure, but in different modes with stress response (activation, up-regulation) at 2 days and oppression (down-regulation) at 16 days.

Chronic Exposure to Low Concentration Lead Chloride-Induced Anxiety and Loss of Aggression and Memory in Zebrafish

Lead and lead-derived compounds have been extensively utilized in industry, and their chronic toxicity towards aquatic animals has not been thoroughly addressed at a behavioral level. In this study, we assessed the risk of exposure to lead at a waterborne environmental concentration in adult zebrafish by behavioral and biochemical analyses. Nine tests, including three-dimension (3D) locomotion, novel tank exploration, mirror biting, predator avoidance, social interaction, shoaling, circadian rhythm locomotor activity, color preference, and a short-term memory test, were performed to assess the behavior of adult zebrafish after the exposure to 50 ppb PbCl₂ for one month. The brain tissues were dissected and subjected to biochemical assays to measure the relative expression of stress biomarkers and neurotransmitters to elucidate the underlying mechanisms for behavioral alterations. The results of the behavioral tests showed that chronic exposure to lead could elevate the stress and anxiety levels characterized by elevated freezing and reduced exploratory behaviors. The chronic exposure to PbCl₂ at a low concentration also induced a sharp reduction of aggressiveness and short-term memory. However, no significant change was found in predator avoidance, social interaction, shoaling, or color preference. The biochemical assays showed elevated cortisol and reduced serotonin and melatonin levels in the brain, thus, altering the behavior of the PbCl₂-exposed zebrafish. In general, this study determined the potential ecotoxicity of long-term lead exposure in adult zebrafish through multiple behavioral assessments. The significant findings were that even at a low concentration, long-term exposure to lead could impair the memory and cause a decrease in the aggressiveness and exploratory activities of zebrafish, which may reduce their survival fitness.

Biochemical responses revealed in an amphibian species after exposure to a forgotten contaminant: An integrated biomarker assessment

Vanadium is a metal whose toxicity towards terrestrial and aquatic species has been under-reported to date.. The biochemical responses of vanadium in amphibian species have not been determined. To establish the effects of vanadium (V) on exposed adult Xenopus laevis, acute and chronic exposures were conducted, and biomarker analyses were performed on liver and muscle tissues from exposed frogs. Biomarkers of exposure, such as acetylcholinesterase (AChE) and metallothioneins (MT), were analysed. Biomarkers of effect were also analysed to determine possible increases in reactive oxygen species (ROS), and the effect of the exposure on the energy balance in the organisms. These included superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), protein carbonyls (PC), malondialdehyde (MDA), and cellular energy allocation (CEA) (energy available, energy consumption, lipids, proteins and glucose). In acute exposures, the energy balances in organisms were distinctly affected, possibly due to insulin mimetic properties of V. In chronic exposures, MT, AChE, SOD, CAT and GSH responses were more pronounced. Although AChE is generally inhibited by pollutant exposure, in this study, it was stimulated. There were significant inhibitions of SOD and CAT, previously observed in frog species. PC levels increased in the highest acute exposure concentration, indicating protein damage. The IBR.v2 revealed the biochemical responses of V more effectively than traditional statistical analysis.

Effect of copper exposure and recovery period in reared Diplodus sargus

The aquaculture growth can be followed by the occurrence of more and new pathogenic agents, since the production leads to higher fish densities in confined areas more appropriate to the appearance and propagation of pathologies. Copper sulfate has been widely used in preventing and controlling fish parasites. The objective of this study is to investigate the effects of copper treatments in the fish tissues (bioaccumulation and histological changes in different organs), mortality and evaluate what happens during the recovery period. White sea bream (Diplodus sargus) were exposed to copper sulfate (0.25 and 0.5 mg L^-1) during 60 days followed with a 75-day recovery period. The results showed that the concentration of copper in fish liver was significantly higher in the 0.5 mg L^-1 treatment than in the 0.25 mg L^-1 treatment. Conversely, copper load in the muscle did not differ significantly between treatments and control. Copper levels in muscle, and especially in liver, increased during copper exposure (up to 60 days). In summary, at higher concentrations copper sulfate treatment (0.5 mg L^-1) might be toxic to fish, which showed histological alterations and copper accumulation in their tissues, mainly in the liver. Nevertheless, individuals returned to their original state after a 75-day recovery period and the tested copper concentrations does not represents risk for food safety.

Effects of copper on larvae of the marbled crab Pachygrapsus marmoratus (Decapoda, Grapsidae): Toxicity test and biochemical marker responses

The importance of trace elements in ecotoxicological investigations is a well-known issue when monitoring polluted areas such as commercial harbors. Copper represents one of the most common metal contaminants, often detected in these areas as it is widely employed in various fields and has many sources of inflow in the marine environment. Pachygrapsus marmoratus is a widespread intertidal crab species that has been extensively studied in ecology, ethology and population genetics. Ecotoxicological studies have also been performed, exclusively on the adult stage. In the present study we investigated the mortality and biochemical (oxidative stress and neurotoxicity) responses of P. marmoratus larvae exposure to environmental relevant concentration of copper. Results showed dose-dependent responses in terms of larval mortality, with a calculated LC₅₀ value of 0.5 mg/L of Cu²⁺. The LC₅₀ concentration was used as the starting point for subsequent biochemical response evaluation. Results also demonstrated dose-dependent activation of antioxidant systems assuming a compensatory antioxidant activity to prevent higher cellular damage when larvae were exposed to the highest concentrations of copper. Moreover, a significant enhancement of neurotransmitter activities was observed, assuming a possible direct interaction of copper with the enzymes or an increase of free copper ion aliquot into the cells.

Toxicity of lead and mancozeb differs in two monophyletic Daphnia species

Lead and mancozeb are two important chemicals used for different human purposes and activities worldwide. Hazard assessment in different areas of the world is carried out with different but phylogenetically similar species, adapted to different climatic conditions, in order to increase relevance. This study evaluated the sensitivity of two monophyletic species, the tropical species Daphnia similis and the temperate species Daphnia magna, to the two chemicals lead and mancozeb. Standard acute and chronic ecotoxicological tests (reproduction and growth), as well as other sublethal measurements such as the intrinsic rate of population increase (r), feeding rate (FR) and O₂ consumption, were recorded along with the analysis of the AChE activity to determine the neurotoxicity of both contaminants. Albeit their similar evolutionary status, D. magna generally presented a lower sensitivity to Pb in comparison to D. similis. Despite the differences in sensitivity, both species presented similar patterns of response under Pb exposure, with diminished reproductive outputs, feeding impairment, reduced O₂ consumption and no effect on AChE activity. Mancozeb decreased the reproduction, rate of population increase and feeding rate, increased the AChE activity in both species and increased O₂ consumption only in D. magna. While D. magna increased O₂ consumption under mancozeb exposure, no effects were observed for D. similis. Thus, species may present different responses and sensitivities to different pollutants, regardless of their phylogeny. Therefore, the use of ecotoxicological assays with native species is crucial for a better ecological risk assessment in contaminated areas.

Biomarkers responses in Manila clam, Ruditapes philippinarum after single and combined exposure to mercury and benzo[a]pyrene

Physiological and biochemical responses in bivalves exposed to pollutants have proved a valuable tool to assess the health of organisms in aquatic ecosystems. The single and combined effects of mercury (Hg²⁺, 2 and 10 μg/L) and benzo[a]pyrene (BaP, 3 μg/L) on physiological and biochemical biomarkers in Manila clam, Ruditapes philippinarum were evaluated. Results showed that significant higher oxygen consumption (OR) and ammonia-N excretion rates (NR) together with significant lower ingestion rates (IR) were observed for the 10 μg/L Hg²⁺ or 3 μg/L BaP treatments compared to controls (P < 0.05). However, clam NR decreased significantly in response to the binary mixtures of 10 μg/L Hg²⁺ and 3 μg/L BaP (P < 0.05). Moreover, the levels of superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferases (GSTs), glutathione (GSH), acetylcholinesterase (AChE) and malondialdehyde (MDA) in the hepatopancreas of clams were induced substantially, whereas glycogen (GLY) contents were suppressed dramatically after Hg²⁺ and BaP exposure. Additionally, the integrated biomarker response (IBR) values measured showed significant increases in combination treatments and they were much higher than that in the Hg²⁺ treatment. This study will provide further information on the defense mechanism in the Manila clam after exposure to marine pollutants and may help evaluate the quality of the aquatic environment.

A blessing in disguise? Natural organic matter reduces the UV light-induced toxicity of nanoparticulate titanium dioxide

Besides their economic value, engineered inorganic nanoparticles (EINPs) may pose a risk for the integrity of ecosystems. Among EINPs, titanium dioxide (nTiO₂) is frequently used and released into surface waters in the μg range. There, nTiO₂ interacts with environmental factors, influencing its potential to cause adverse effects on aquatic life. Although factors like ultra violet (UV) light and natural organic matter (NOM) are considered as ubiquitous, their joint impact on nTiO₂-induced toxicity is poorly understood. This study addressed the acute toxicity of nTiO₂ (P25; 0.00-64.00 mg/L; ~60 nm) at ambient UV light (0.00-5.20 W UVA/m²) and NOM levels (seaweed extract; 0.00-4.00 mg TOC/L), using the immobility of Daphnia magna as response variable. Confirming previous studies, effects caused by nTiO₂ were elevated with increasing UV radiation (up to ~280 fold) and mitigated by higher NOM levels (up to ~12 fold), possibly due to reduced reactive oxygen species (ROS; measured as ^•OH radicals) formation at lower UV intensities. However, contradicting to former studies, nTiO₂-mediated ROS formation was not proportional to increasing NOM levels: lower concentrations (0.04-0.40 mg TOC/L) slightly diminished, whereas a higher concentration (4.00 mg TOC/L) promoted the ROS quantity, irrespective of UV intensity. Measured ROS levels do not fully explain the observed nTiO₂-induced toxicity, whereas increasing acetylcholinesterase and glutathione-S-transferase activities in daphnids (in presence of 8.00 mg/L nTiO₂ and elevated UV intensity) point towards neurotoxic and oxidative stress as a driver for the observed effects. Hence, despite higher ^•OH levels in the treatments where 4.00 mg TOC/L were present, NOM was still capable of reducing nTiO₂-induced stress and ultimately adverse effects in aquatic life.

Effects of cadmium on fecundity and defence ability of Drosophila melanogaster

Cadmium (chemical symbol, Cd) is an extremely common pollutant that poses a toxicity threat to organisms. Therefore, we tested Drosophila melanogaster fecundity, Cd accumulation, and activity of two enzymes following Cd stress and used quantitative real-time polymerase chain reaction (qPCR) to quantify the mRNA expression levels of several genes involved in fecundity and defence. D. melanogaster was placed in a medium containing different concentrations of Cd (13, 26, and 52 mg L^-1), following which, inductively coupled plasma atomic emission spectroscopy showed that Cd accumulation in Drosophila increased with the increase in its dietary intake. We also observed that Cd at these concentrations significantly prolonged the mating latency in females and reduced the number of eggs laid. However, the same Cd concentrations did not affect male fecundity. Acetylcholinesterase activity was only detected at 52 mg L^-1 Cd in both sexes, whereas glutathione S-transferase activity was inhibited at 26 and 52 mg L^-1 Cd in females. The results of qPCR indicated that exposure to 13-52 mg L^-1 Cd affected the expression of reproduction-related genes, including downregulation of enok and upregulation of dally and dpp. The same level of exposure also induced transcriptional responses from three defence-related genes (hsp70, gstd2, and gstd6). Taken together, the results revealed that Cd exposure might negatively affect the expression of genes associated with D. melanogaster reproduction and trigger the transcription of defence-related genes. We suggest that further analyses of fecundity and defence responses may help develop indicators of Cd toxicity and improve our understanding of antitoxin defences.

The bioaccumulation of waterborne zinc in tissues of silver catfish (Rhamdia quelen) and its effect on biochemical parameters

Silver catfish (Rhamdia quelen) is a fish species with neotropical distribution, and is a potential model organism to study polluted environment. The aim of this study is to analyze the response of silver catfish to environmental concentrations of waterborne zinc (Zn) over 96 h. Significant metal accumulation was seen in gill, intestine and liver tissues. No significant accumulation was seen in muscle tissue. Lipid peroxidation increased in the brain, and decreased in the muscle and liver at all levels of exposure. Zinc exposure led to decreased protein carbonyl levels in the brain and increased levels in the liver. The activity of catalase in the liver was reduced for all exposed groups. Glutathione S-transferase activity decreased in the brain at the highest level of exposure and in the liver at all Zn concentrations tested. Non-protein thiols increased in the muscle and in the gills after exposure. Ascorbic acid levels increased in the brain and in the gills. Exposure to Zn also altered the metabolic parameters, causing decreased lactate and ammonia levels in the muscle, and decreased glycogen in the liver. Zinc exposure increased ammonia and amino acid levels in the liver, and increase glycogen and amino acid levels in muscle tissue. Our results demonstrate that exposure to environmentally relevant concentrations of Zn led to accumulation of metals in the tissues of silver catfish, with significant changes in biochemical parameters.

Effect of treated wastewater irrigation in East Central region of Tunisia (Monastir governorate) on the biochemical and transcriptomic response of earthworms Eisenia andrei

Treated wastewater (TWW) reuse for irrigation has become an excellent way to palliate water scarcity in Mediterranean arid regions. However, the toxicological effects of these effluents on the soil's organisms, especially earthworms, have not been well studied as yet. In this paper, earthworms Eisenia andrei were exposed for 7 days and 14 days to five agricultural soils irrigated with TWW for different periods: 1 year, 8 years, and 20 years. In addition, they were also exposed to soil from one reference site sampled from the Ouardenin perimeter in the Monastir Governorate in Tunisia. The effect on earthworms was assessed at the biochemical level by evaluating for catalase (CAT), glutathione-S-transferase (GST), malondialdehyde accumulation (MDA) and acetylcholinesterase inhibition (AChE). On the other hand, genotoxicity and transcriptomic responses were evaluated using micronuclei test (MNT) and gene expression level of CAT and GST. Moreover, metals uptake by earthworms was analyzed. Results showed that CAT and GST activity in the earthworm increased significantly when they were exposed to soils irrigated with TWW for 1, 8 and 20 years. Furthermore, MDA concentration also increased significantly with the increase in exposure period. However, AChE activity decreased and MNi frequency increased in earthworms after 7 and 14 days of exposure to soils irrigated with TWW for more than a year. The gene expression level of CAT and GST showed a significant variability, thus data are discussed in relation to the studied biomarkers (CAT and GST). These data provide new insights into the effect of toxicity of TWW on the soil's macro fauna, which is strongly affected by the trace elements and other organic compounds accumulated in soils after 20 years of TWW irrigation.

Biochemical and transcriptomic response of earthworms Eisenia andrei exposed to soils irrigated with treated wastewater

In order to ensure better use of treated wastewater (TWW), we investigated the effect of three increasing doses of TWW, 10%, 50%, and 100%, on biochemical and transcriptomic statuses of earthworms Eisenia andrei exposed during 7 and 14 days. The effect of TWW on the oxidative status of E. andrei was observed, but this effect was widely dependent on the dilution degree of TWW. Results showed a significant decrease in the catalase (CAT) activity and an increase in the glutathione-S-transferase (GST) activity, and considerable acetylcholinesterase (AChE) inhibition was recorded after 14 days of exposure. Moreover, malondialdehyde (MDA) accumulation was found to be higher in exposed animals compared to control worms. The gene expression level revealed a significant upregulation of target genes (CAT and GST) during experimentation. These data provided new information about the reuse of TWW and its potential toxicity on soil organisms.

Bioaccumulation, cytotoxicity and oxidative stress of the acute exposure selenium in Oreochromis mossambicus

Selenium (Se) is an essential trace-element that becomes toxic when present at high concentrations for aquatic organisms. The knowledge about the mechanism of Se toxicity in freshwater ecosystem is still poorly studied. Thus the aim of the present study was to assess the impact of environmentally relevant concentrations of Se toxicity: 5, 10, 25, 50 and 100 µg/L or water only (control) for periods of 96 hour (h) to test for Se accumulation (gill, liver and brain), its effects on enzymatic and non-enzymatic antioxidant defenses (gill and liver), oxidative stress effects on lipid, protein (gill and liver), DNA (liver) and inhibition of AchE (brain) activity were measured in Mozambique tilapia, Oreochromis mossambicus. Our result showed that Se accumulation was observed in the gill, liver and brain tissues of fish exposed to different concentrations and accumulation varied upon different tissues. Enzymatic (SOD, CAT, GPx and GST) and non-enzymatic (GSH and MT) antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-s-transferase (GST) were significantly increased after 96 h exposure of higher concentrations Se in the gill and liver tissue with the exception of GST activity was significantly inhibited in liver after 96 h exposure of higher concentrations of Se. In contrast, catalase (CAT) activities were inhibited for both tissues of Se exposure at 96 h. Reduced glutathione (GSH) and Metallothionein (MT) levels were increased in the gill and liver tissues after exposure to Se for 96 h. We also observed that Se affected antioxidant defense, increasing oxidative stress indicator of lipid peroxidation (LPO) and protein carbonyl (PCO) in gill and liver tissues of fish exposed to Se for 96 h at the concentration dependent manner. Increased DNA damage scores observed in liver tissue of fish exposed to Se for concentrations dependent manner, indicating potential of Se on fish. We also observed inhibition of acetylcholine esterase (AchE) activity in brain tissue of fish exposed to Se for higher concentrations. The changes in these parameters can be used as suitable biomarkers for monitoring the toxicity of Se in the aquatic environment.

Accumulation, elimination and neuro-oxidative damage under lanthanum exposure in glass eels (Anguilla anguilla)

Rare earth elements (REEs) comprise elements from lanthanum to lutetium that together with yttrium and scandium are emergent contaminants of critical importance for numerous groundbreaking environmental technologies. Transfer to aquatic ecosystems is expected to increase, however, little information is known about their potential impacts in marine biota. Considering the endangered conservation status of the European eel (Anguilla anguilla) and the vulnerability of early fish life stages to contaminants, we exposed glass eels, through water, to an environmentally relevant concentration (120 ng.L^-1) of lanthanum (La) for 7 days (plus 7 days of depuration). The aim was to study the accumulation and elimination of La in eel's body and subsequent quantification of acetylcholinesterase (AchE), lipid peroxidation and antioxidant enzymatic machinery. Accumulation peaked after 72 h-exposure to La, decreasing afterwards, even in continuous exposure. Accumulation was higher in the viscera, followed by the skinless body and ultimately in the head, possibly as a protective mechanism to cope with La neurotoxicity. A significant increase in AChE activity was observed in La-exposed glass eels, suggesting that La³⁺ may inhibit the binding of acetylcholine. A depression in lipid peroxidation was registered under La exposure, possibly indicating that La³⁺ may play physiological activities and functions as a free radical scavenger. Catalase activity was significantly inhibited in La-exposed glass eels after 72 h, indicating that the availability of La may induce physiological impairment. The quantification of Glutathione S-Transferase activity revealed no differences between control and La-exposed organisms. Further investigation is needed towards understanding the biological effects of REEs.

Assessment and monitoring of water quality of the gulf of Morbihan, a littoral ecosystem under high anthropic pressure

This field study is intended to propose a global methodology to assess and monitor the water quality of the gulf of Morbihan, a littoral ecosystem under increasing anthropic pressure. To this end, the Locmariaquer site, where Crassostrea gigas is extensively cultivated, was selected to perform a one-year follow-up of tissular glutathione S-transferase and acetylcholinesterase specific activities in this filter feeder organism. Calculation of an integrated index, corresponding to the ratio of the two enzymes activities, allowed to discriminate from the environmental noise, several clusters which could be representative environmental stress, potentially latent pollution. Moreover, the estrogenic activity was assessed in water samples collected at Locmariaquer and other strategic sites of the gulf. The results evidenced a low estrogenic-disrupting compound contamination of waters. Overall, this methodology produced an accurate outlook of a basal state for the gulf and could be developed in the context of a chronic monitoring of this site.

Cholinesterase characterization of two autochthonous species of Ria de Aveiro (Diopatra neapolitana and Solen marginatus) and comparison of sensitivities towards a series of common contaminants

Biomonitoring of chemical contamination requires the use of well-established and validated tools, including biochemical markers that can be potentially affected by exposure to important environmental toxicants. Cholinesterases (ChEs) are present in a large number of species and have been successfully used for decades to discriminate the environmental presence of specific groups of pollutants. The success of cholinesterase inhibition has been due to their usefulness as a biomarker to address the presence of organophosphate (OP) and carbamate (CB) pesticides. However, its use in ecotoxicology has not been limited to such chemicals, and several other putative classes of contaminants have been implicated in cholinesterasic impairment. Nevertheless, the use of cholinesterases as a monitoring tool requires its full characterization in species to be used as test organisms. This study analyzed and differentiated the various cholinesterase forms present in two autochthonous organisms from the Ria de Aveiro (Portugal) area, namely the polychaete Diopatra neapolitana and the bivalve Solen marginatus, to be used in subsequent monitoring studies. In addition, this study also validated the putative use of the now characterized cholinesterasic forms by analyzing the in vitro effects of common anthropogenic contaminants, such as detergents, pesticides, and metals. The predominant cholinesterasic form found in tissues of D. neapolitana was acetylcholinesterase, while homogenates of S. marginatus were shown to possess an atypical cholinesterasic form, with a marked preference for propionylthiocholine. Cholinesterases from D. neapolitana were generally non-responsive towards the majority of the selected chemicals. On the contrary, strong inhibitory effects were reported for ChEs of S. marginatus following exposure to the selected pesticides.

Effects of Tin on Enzyme Activity in Holothuria grisea (Echinodermata: Holothuroidea)

This study evaluated the effect of tin exposure on enzyme activity in the sea cucumber (Holothuria grisea Selenka, 1867). After exposure to 0 (control), 0.04, 0.08, or 0.12 mg L^-1 tin, we tested the activities of total cholinesterase in longitudinal muscles, acid phosphatase in gonads and the respiratory tree, as well as alkaline phosphatase in the intestines during a 96-h bioassay. Regression analyses showed that all enzyme activities declined with increasing tin concentrations, except for acid phosphatase in the respiratory tree, which were similarly, inhibited at all tin concentrations. These results indicate that H. grisea is a potential bioindicator for seascape habitat monitoring programs, as its biochemical markers show sensitivity to trace elements that can indicate a rise in pollution levels.

Off-site impacts of wildfires on aquatic systems - Biomarker responses of the mosquitofish Gambusia holbrooki

The number of wildfires has markedly increased in Mediterranean Europe, including in Portugal. Wildfires are environmentally concerning, not only due to the loss of biodiversity and forest area, but also as a consequence of environmental contamination by specific compounds including metals and polycyclic aromatic compounds (PAHs). These contaminants, mostly bound to ashes, can reach downstream water bodies, namely through surface runoff, being ultimately dispersed by vast areas and contacting with aquatic biota. Being toxicologically noteworthy, the potential toxic outcomes of the input of such chemicals across the aquatic compartment must be characterized. In this context, the present study used a biomarker-based approach to find early-warning signals of toxicity triggered by the exposure of the mosquitofish, Gambusia holbrooki, to affected aqueous runoff and stream water samples collected from a forest burnt area. The chemical analysis revealed concerning levels of metals and polycyclic aromatic hydrocarbons in both runoff and stream water samples. Biological responses elicited by the collected samples showed the occurrence of pro-oxidative modifications, specifically driven by enzymatic forms involved in the metabolism of glutathione. Despite these effects, no further signs of involvement of metals and PAHs were elicited in terms of neurotoxicity. The overall set of data implicates chemicals resulting from wildfires in clear deleterious effects in exposed fish.

Aluminium sulfate exposure: A set of effects on hydrolases from brain, muscle and digestive tract of juvenile Nile tilapia (Oreochromis niloticus)

Aluminium is a major pollutant due to its constant disposal in aquatic environments through anthropogenic activities. The physiological effects of this metal in fish are still scarce in the literature. This study investigated the in vivo and in vitro effects of aluminium sulfate on the activity of enzymes from Nile tilapia (Oreochromis niloticus): brain acetylcholinesterase (AChE), muscle cholinesterases (AChE-like and BChE-like activities), pepsin, trypsin, chymotrypsin and amylase. Fish were in vivo exposed during 14days when the following experimental groups were assayed: control group (CG), exposure to Al₂(SO₄)₃ at 1μg·mL^-1 (G1) and 3μg·mL^-1 (G3) (concentrations compatible with the use of aluminium sulfate as coagulant in water treatment). In vitro exposure was performed using animals of CG treatment. Both in vivo and in vitro exposure increased cholinesterase activity in relation to controls. The highest cholinesterase activity was observed for muscle BChE-like enzyme in G3. In contrast, the digestive enzymes showed decreased activity in both in vivo and in vitro exposures. The highest inhibitory effect was observed for pepsin activity. The inhibition of serine proteases was also quantitatively analyzed in zymograms using pixel optical densitometry as area under the peaks (AUP) and integrated density (ID). These results suggest that the inhibition of digestive enzymes in combination with activation of cholinesterases in O. niloticus is a set of biochemical effects that evidence the presence of aluminium in the aquatic environment. Moreover, these enzymatic alterations may support further studies on physiological changes in this species with implications for its neurological and digestive metabolisms.

Local salt substitutes "Obu-otoyo" activate acetylcholinesterase and butyrylcholinesterase and induce lipid peroxidation in rat brain

Evidence has shown that ingestion of heavy metals can lead to neurodegenerative diseases. This study aimed to investigate the neurotoxic potential of salt substitutes (Obu-Otoyo); salt A (made by burning palm kernel shaft then soaked in water overnight and the extract from the resulting residue is used as the salt substitute) and salt B (an unrefined salt mined from a local site at Ilobu town, Osun-State, Nigeria) by assessing their effect on some key enzymes linked with neurodegenerative disease [acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities] as well as on malondialdehyde (MDA) content of the rat brain. Salt substitutes were fed to normal rats as dietary inclusion at doses of 0.5 and 1.0% for 30 days. Thereafter, the effect of the salt substitutes on AChE and BChE activities as well as on MDA level in the rat brain was determined. The results revealed that the salt substitutes caused a significant (p<0.05) increase in both AChE and BChE activity and also induced lipid peroxidation in the brain of rats in vivo as well as under in vitro condition in a dose-dependent manner. The effect of the salt substitutes on AChE and BChE activities could be attributed to the presence of some toxic heavy metals. Therefore, the ability of the salt substitutes to induce lipid peroxidation and activate AChE and BChE activities could provide some possible mechanism for their neurotoxic effect.

Early biochemical biomarkers for zinc in silver catfish (Rhamdia quelen) after acute exposure

Contamination of aquatic ecosystems by metals causes various biochemical changes in aquatic organisms, and fish are recognized as indicators of environmental quality. Silver catfish were exposed to six concentrations of zinc (Zn): 1.0, 2.5, 5.0, 7.5, 10.0 and 12.5 mg/L for 96 h to determine the mean lethal concentration (LC50). The value obtained was 8.07 mg/L. In a second experiment, fish were exposed to concentrations of 1.0 or 5.0 mg/L Zn and a control for 96 h. Afterward, the tissues were collected for biochemical analysis. Lipid peroxidation, as indicated by thiobarbituric acid-reactive substance (TBARS), decreased in the liver and brain for all Zn concentrations tested, while in the gills TBARS levels increased at 1.0 mg/L and declined at 5.0 mg/L. Zn increased protein carbonyls in the muscle of silver catfish and decreased it in the other tissues. The enzyme superoxide dismutase increased in both exposed groups. However, catalase did not change. Glutathione S-transferase decreased in the liver and increased in the gills (1.0 mg/L), muscle (5.0 mg/L) and brain (1.0 and 5.0 mg/L). Nonprotein thiols changed only in brain and muscle tissue. Zn exposure inhibited acetylcholinesterase (AChE) activity in the brain at both concentrations tested, but did not change it in muscle. Exposure to Zn inhibited the activity of Na(+)/K(+)-ATPase in the gills and intestine at both concentrations tested. Our results demonstrate that Zn alters biochemical parameters in silver catfish and that some parameters such as AChE and Na(+)/K(+)-ATPase could be considered as early biomarkers of waterborne Zn toxicity.

Response of biochemical biomarkers in the aquatic crustacean Daphnia magna exposed to silver nanoparticles

The proliferation of silver nanoparticle (AgNP) production and use owing to their antimicrobial properties justifies the need to examine the resulting environmental impacts. The discharge of biocidal nanoparticles to water bodies may pose a threat to aquatic species. This study evaluated the effects of citrate-coated AgNPs on the standardized test organism Daphnia magna Straus clone MBP996 by means of biochemical biomarker response. AgNP toxicity was compared against the toxic effect of Ag(+). The toxicity endpoints were calculated based upon measured Ag concentrations in exposure media. For AgNPs, the NOAEC and LOAEC values at 48 h were 5 and 7 μg Ag/L, respectively, while these values were 0.5 and 1 μg Ag/L, respectively, for Ag(+). The EC50 at 48 h was computed to be 12.4 ± 0.6 and 2.6 ± 0.1 μg Ag/L for AgNPs and Ag(+), respectively, with 95 % confidence intervals of 12.1-12.8 and 2.3-2.8 μg Ag/L, respectively. These results indicate significant less toxicity of AgNP compared to free Ag(+) ions. Five biomarkers were evaluated in Daphnia magna neonates after acute exposure to Ag(+) or AgNPs, including glutathione (GSH) level, reactive oxygen species (ROS) content, and catalase (CAT), acetylcholinesterase (AChE), and superoxide dismutase (SOD) activity. AgNPs induced toxicity and oxidative stress responses in D. magna neonates at tenfold higher concentrations than Ag. Biochemical methods revealed a clear increase in AChE activity, decreased ROS level, increased GSH level and CAT activity, but no significant changes in SOD activity. As Ag(+) may dissolve from AgNPs, these two types of Ag could act synergistically and produce a greater toxic response. The observed remarkably high toxicity of AgNPs (in the parts-per-billion range) to crustaceans indicates that these organisms are a vulnerable link in the aquatic food chain with regard to contamination by nanosilver. Graphical Abstract ᅟ.

Bioaccumulation, subcellular distribution, and acute effects of chromium in Japanese medaka (Oryzias latipes)

Chromium (Cr) is an essential element but is toxic to aquatic organisms at elevated concentrations. In the present study, adult Japanese medaka (Oryzias latipes) were exposed to a sublethal hexavalent chromium (Cr(VI)) concentration via dissolved and dietary exposures for 6 d. Various measurements of Cr were made: bioaccumulation in different tissues, subcellular distribution in the liver, effects on antioxidants and acetylcholinesterase (AChE), and Cr-induced lipid peroxidation. The results showed that bioaccumulation increased dramatically in all tested tissues from dissolved exposure but only significantly in the intestine from dietary treatment, implying that dissolved exposure may be predominant for Cr accumulation in medaka. Subcellular distribution revealed that Cr accumulated in the liver was mainly (46%) associated with the heat-stable protein fraction. Among the antioxidants examined, catalase (CAT) responded to dissolved Cr exposure in most tissues whereas superoxide dismutase (SOD) was less responsive. Malondialdehyde concentrations were significantly elevated in most tissues examined in the dissolved Cr-exposed fish, but were only elevated in the liver and intestine in the dietary Cr-exposed fish. The AChE activity in the brain was stimulated by 49% in the dissolved Cr-exposed fish. Reductions in condition factor and gonadosomatic index were also observed. These data help in an understanding of Cr tissue distribution and the acute effects of Cr in Japanese medaka.

Low concentrations of metal mixture exposures have adverse effects on selected biomarkers of Xenopus laevis tadpoles

Polluted ecosystems may contain mixtures of metals, such that the combinations of metals, even in low concentrations, may cause adverse effects. In the present study, we focused on toxic effects of mixtures of selected metals, the LC50 values, and also their safety limit in aquatic systems imposed by the European legislation using a model organism. Xenopus laevis tadpoles were used as test organisms. They were exposed to metals or their combinations due to 96-h LC50 values. Glutathione S-transferase (GST), glutathione reductase (GR), acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione peroxidase (GPx), and catalase (CAT) levels were evaluated. Metallothionein concentrations were also determined. The LC50s for Cd, Pb, and Cu were calculated as 5.81mg AI/L, 123.05mg AI/L, and 0.85mg AI/L, respectively. Low lethality ratios were observed with unary exposure of each metal in lower concentrations. Double or triple combinations of LC50 and LC50/2 concentrations caused 100% lethality with Cd+Cu and Pb+Cd+Cu mixtures, while the Pb+Cu mixture also caused high lethal ratios. The selected enzyme activities were significantly affected by metals or mixtures, and dose-related effects were determined. The metallothionein levels generally increased as related to concentration in unary metals and mixtures. Acceptable limit values of unary metals and mixtures did not significantly change metallothionein levels. The results suggest that oxidative stress-related mechanisms are involved in the toxicity induced by selected metals with combinations of very low concentrations.

Haematological and biochemical parameters and tissue accumulations of cadmium in Oreochromis niloticus exposed to various concentrations of cadmium chloride

Oreochromis niloticus, weighing 36.45 ± 1.12 g were exposed to 10%, 20% and 30% of the LC₅₀ of CdCl₂ which represents treatments (T1)1.68, (T2)3.36 and (T3)5.03 mg/l, respectively, for a period of 10, 20 and 30 days. It was found that, compared to a control group reading of 0.19 ± 0.03 μg/g dry weight, accumulation of Cd in the gills was significantly (p < 0.05) increased in samples ranging between 7.64 ± 0.86 and 61.73 ± 0.82 μg/g dry weight from T1 at 10 days to T3 at 30 days. The accumulation of Cd in the liver, meanwhile, was also observed to significantly increase (p < 0.05) with increasing time and concentrations with results ranging between 3.21 ± 0.12 and 181.61 ± 1.32 compared to the control group results of 0.29 ± 0.04 μg/g dry weight. Although muscles exhibited lower levels of accumulation than the gills and liver they still showed the same pattern of increase compared to the control group, with a significant difference ranging between 0.32 ± 0.02 and 2.16 ± 0.08 compared to the control group results of 0.03 ± 0.001 μg/g dry weight. Also, haematological parameters such as red blood cells (RBCs), haemoglobin (Hb) and haematocrit (Hct) were reduced in fish exposed to Cd at all periods, with significant differences (p < 0.05). Plasma glucose concentration showed a significant increase. Total protein levels of fish showed a significant reduction (p > 0.05) for all exposed treatments. Also, the total lipid level increased significantly as fish were exposed to increasing cadmium concentrations, compared to control fish. Finally, the activities of aspartate aminotransferase (AST IU/l) and alanine aminotransferase (ALT IU/l) showed a significant increase (p < 0.05) with increasing time and concentrations.

Biomarker responses in sunfish species and largemouth bass from the Saluda River, South Carolina

The upstate and Piedmont region of South Carolina is a rapidly urbanizing area as a result of a steadily growing population. This increase in population and development has the potential to negatively impact local aquatic systems like the Saluda River due to increased pollution from runoff, and effluents from industrial and wastewater treatment facilities. During the summer months of 2010, 159 fish from the Centrarchidae family (sunfish species (Lepomis) and largemouth bass - Micropterus salmoides) were collected from 13 sites along the Saluda River. A suite of biomarker assays, including ethoxyresosufin-O-deethylase, bile fluorescence, glutathione S-transferase, thiobarbituric acid reactive substances, bile estrogens, acetylcholinesterase inhibition, metallothionein and tissue metal levels were applied to investigate the impacts of diminished water quality on fish health. Results indicate that fish from the Saluda River are responding to contamination in a site specific manner, with up to four significant biomarker responses in the most impacted sites. Sampling sites in the lower portion of the Saluda watershed are less impacted by pollution than the upper and central sections. The observed biomarker responses can be explained by the proximity of urban areas, point sources and general land use, and demonstrate the applicability of biomarkers in environmental biomonitoring programs.

Effects of chemical and thermal stress on acetylcholinesterase activity in the brain of the bank vole, Myodes glareolus

One of the most important issues in ecotoxicology is better understanding the effects of interactions between chemical pollutants and physical environmental factors on animals. To fill this knowledge gap, changes in the activity of acetylcholinesterase (AChE) in the brain samples of bank voles Myodes (Clethrionomys) glareolus due to temperature effects, and two chemical stressors were studied in a full factorial laboratory experiment (27 treatments). The experiment was divided into three phases: acclimatisation (3 days), intoxication (42 days) and elimination (21 days). During the intoxication phase, animals were orally exposed to different concentrations of either nickel (0, 300 or 800 mg Ni/kg food), chlorpyrifos (CPF) (0, 50 or 350 mg CPF/kg food) or a mixture of both chemicals. During the acclimatisation and elimination phases, the bank voles were given uncontaminated food. The experiment was conducted at three different temperatures (10, 20 or 30 °C), and a 12 h:12 h light:dark regime. The animals were sacrificed at 0, 5, 10, 20, 42, 49 and 63 days after the beginning of the intoxication, and brain samples were obtained for chemical analysis. The nickel accumulation in the brain depended on the level of nickel exposure and on interactions between the temperature and other factors. Nickel exhibited no effect on AChE activity. In contrast, AChE was drastically inhibited by chlorpyrifos and low temperature, but interactions between all factors significantly influenced the enzyme activity during the elimination phase of the experiment. High mortality was observed in the groups exposed to high concentrations of nickel and chlorpyrifos.

Effects of environmentally relevant concentrations of metallic compounds on the flatfish Scophthalmus maximus: biomarkers of neurotoxicity, oxidative stress and metabolism

Flatfish species, such as the turbot (Scophthalmus maximus), are common targets for toxic effects, since they are exposed through the food chain (ingestion of contaminated preys) and are in direct contact with the waterborne contaminant and sediments. Furthermore, these fish species live in close proximity to interstitial water that frequently dissolves high amounts of contaminants, including metals. Despite this significant set of characteristics, the present knowledge concerning flatfish contamination and toxicity by metals is still scarce. To attain the objective of assessing the effects of metals on a flatfish species, S. maximus specimens were chronically exposed to lead, copper and zinc, at ecologically relevant concentrations, and biochemical (oxidative stress: catalase and glutathione S-transferases activities, and lipid peroxidation; neurotoxicity: cholinesterase activity) parameters were assessed on selected tissues (gills and liver). Copper had no significant effects on all tested parameters; lead was causative of significant increases in liver GSTs activities and also in lipoperoxidation of gill tissue; exposure to zinc caused a significant increase in catalase activity of gill tissue. None of the tested metals elicited noteworthy effects in terms of neurotoxicity. The obtained results showed that only the metal lead is of some environmental importance, since it was able to cause deleterious modifications of oxidative nature at relevant concentrations.

Exposure to sublethal concentrations of copper changes biochemistry parameters in silver catfish, Rhamdia quelen, Quoy & Gaimard

The effects of Cu exposure on catalase (CAT) and acetylcholinesterase (AChE) activity, formation of thiobarbituric acid-reactive species (TBARS) and metabolic parameters were evaluated in silver catfish (Rhamdia quelen). The fish were exposed for 45 days to 0, 16 and 29 μg/L Cu. The fish that were exposed to Cu exhibited lower TBARS levels in the muscle and higher TBARS levels in the liver. They also showed lower CAT activity in the liver and lower AChE activity in the brain and muscle. Higher glucose and lactate and lower protein plasma levels were observed in the fish exposed to Cu. The changes in the hepatic metabolic parameters were Cu concentration dependent. In the muscle, lower glycogen and higher lactate levels were observed in the fish exposed to Cu. Alterations in the metabolic parameters showed a preference for the anaerobic pathway of energy production and liver protein catabolism to supply the energy demand.

Cholinesterase activity on Echinogammarus meridionalis (Pinkster) and Atyaephyra desmarestii (Millet): characterisation and in vivo effects of copper and zinc

Metals are released into freshwater ecosystems from natural and anthropogenic sources, compromising their structural and functional equilibrium. As early warning tools, cholinesterases (ChEs) are usually used to assess the effects of organophosphate and carbamate pesticides, but are also known to be inhibited by metals. The objectives of this work were to characterise the activity of ChE present in the amphipod Echinogammarus meridionalis and the shrimp Atyaephyra desmarestii and to evaluate the in vivo effects of the metals copper and zinc in their ChE activity. To achieve this, firstly the activity of ChE forms were characterised using different in vitro assays with substrates and selective inhibitors. Then, the in vivo effects of 48 h exposures to increasing concentrations of copper and zinc on ChE activity were determined. The ChE form present in both species was acetylcholinesterase (AChE) since both revealed preference for the acetylthiocholine iodide substrate, total inhibition with eserine, the inhibitor of ChEs, and with 1,5-bis(4-allyldimethylammoniumphenyl)-pentan-3-one dibromide, the specific inhibitor of AChE, and presented insensitivity to iso-OMPA, a specific inhibitor of butyrylcholinesterase. The activity of ChEs was inhibited by zinc exposures in the amphipod species, but was not affected by copper. Exposure to copper and zinc did not affect ChEs activity in the shrimp at the concentrations tested. This work is a relevant contribution as foundation for the use of AChE in freshwater crustaceans in further studies including biomonitoring campaigns in different contamination scenarios.

Impact of gold nanoparticles on zebrafish exposed to a spiked sediment

Increasing use of metallic nanomaterials is likely to result in release of these particles into aquatic environments; nevertheless it is unclear whether these materials present a hazard to aquatic organisms. The impact of contaminated sediment containing 14-nm gold nanoparticles (AuNPs) was investigated in the zebrafish Danio rerio exposed for 20 days to two concentrations, 16 and 55 µg/g dry weight. AuNPs were released from the sediment to the water column, and during this period the mean concentrations of AuNP in the filtered water fraction were 0.25 ± 0.05 and 0.8 ± 0.1 µg/L, respectively. A similar experiment with ionic gold contamination was simultaneously performed to obtain a positive control. AuNP exposure triggered various effects in fish tissues including modifications of genome composition, shown using a random amplified polymorphic DNA-PCR genotoxicity test. Expression of genes involved in oxidative stress, mitochondrial metabolism, detoxification and DNA repair were also modulated in response to AuNP contamination. Gold altered neurotransmission, since brain acetylcholine esterase activity increased for both tested doses of AuNP but not for ionic gold. Gold accumulation in fish tissues demonstrated the lower bioavailability of AuNP compared to ionic Au, and underlined the higher toxic potential of the nanoparticle form.

Toxicological responses of earthworm (Eisenia fetida) exposed to metal-contaminated soils

The aim of this study was to evaluate the toxicological responses of earthworm (Eisenia fetida) induced by field-contaminated, metal-polluted soils. Biochemical responses and DNA damage of earthworm exposed to two multi-metal-contaminated soils in a steel industry park and a natural reference soil in Zijin Mountain for 2, 7, 14, and 28 days were studied. Results showed that three enzyme activities, including superoxide dismutase (SOD), acetylcholinesterase (AChE), and cellulase, in earthworm in metal-contaminated soils were significantly different from those of the reference soil. Cellulase and AChE were more sensitive than SOD to soil contamination. The Olive tail moment of the comet assay after 2-day exposure increased 56.5 and 552.0 % in two contaminated soils, respectively, compared to the reference soil. Our findings show that cellulase and DNA damage levels can be used as potential biomarkers for exposure of earthworm to metal-polluted soils.

Effects of anthropogenic metallic contamination on cholinesterases of Gambusia holbrooki

Metal contamination causes multiple biological dysfunctions, including impairment of key physiological functions by targeting enzymes. This feature is a matter of concern, since it may imply significant disturbances in energy allocation, behaviour, reproduction, and survival. Inhibition of the cholinesterase (ChE) activity of aquatic organisms by metals has been described, and systematically used in biomonitoring studies as effect criterion of environmental exposure to these compounds. The present paper addresses the feasibility of using ChE inhibition to quantify the adverse acute and chronic effects of metals (copper, zinc, lead, and cadmium) on nervous tissue of Gambusia holbrooki. With the exception of acute exposure to copper, ChE activity was not significantly impaired. The meanings of the reported findings are further discussed, aiming at a more comprehensive use of this biomarker in environmental assessment. Based on the obtained results, the role of ChE inhibition in environmental metal contamination scenarios should be questioned or even discarded.

Toxicity of triphenyltin hydroxide to fish

Triphenyltin (TPhT) is used worldwide in pesticide formulas for agriculture. Toxic effects of this compound to aquatic life have been reported; however, the biochemical response of fish exposed to different concentrations of TPhT hydroxide (TPhTH) was investigated for the first time in this study. The lethal concentration (LC50) of TPhTH to silver catfish, Rhamdia quelen, was calculated from an acute-exposure experiment (96 h). In addition, acethylcholinesterase (AChE) activity in brain and muscle-as well as glucose, glycogen, lactate, total protein, ammonia, and free amino acids in liver and muscle-were evaluated in a chronic-exposure experiment (15-day exposure). Speciation analysis of tin (Sn) was performed in fish tissues at the end of both experiments using gas chromatography coupled to a pulsed-flame photometric detector (GC-PFPD). Concentrations of TPhT, diphenyltin, and monophenyltin (reported as Sn) were lower than limits of quantification (10σ criteria). Waterborne TPhTH concentration used through the experiment was also evaluated by GC-PFPD, and no degradation of this species was observed. The LC50 value for silver catfish juveniles was 9.73 μg L(-1) (as Sn). Decreased brain and muscle AChE activities were observed in fish exposed to TPhTH in relation to unexposed fish (control). Liver glycogen and lactate levels were significantly higher in fish kept at the highest waterborne TPhTH concentration compared with the control. Liver and muscle glucose levels of fish exposed to all TPhTH concentrations were significantly lower than those of control fish. Silver catfish exposed to all TPhTH concentrations showed lower total protein values and higher total free amino acids levels in liver and muscle compared with controls. Total ammonia levels in liver and muscle were significantly higher for the highest TPhTH concentration compared with controls. In conclusion, TPhTH caused metabolic alterations in silver catfish juveniles, and the analyzed parameters can also be used as bioindicators for TPhTH contamination.

In vitro and in vivo inhibition of acetylcholinesterase and carboxylesterase by metals in zebrafish (Danio rerio)

Metals are natural components in ecosystems; however, if these elements are in excess, they can have adverse effects on living organisms. This study analyzes the interference of copper, lead, iron and cadmium in acetylcholinesterase (AChE) and carboxylesterase (CbE) activities in zebrafish. AChE was significantly inhibited in vitro by copper, iron, lead and cadmium at higher concentrations (10 and 20 mmol/L), whereas CbE was inhibited only at a concentration of 20 mmol/L. In vivo, only lead and cadmium were able to cause AChE inhibition at higher concentrations, while iron didn't cause any changes, and copper promoted an increase in AChE activity at a concentration of 0.06 mg/L. CbE activity did not change at any of the times (two and seven days) and concentrations tested, except in the case of copper exposure, which resulted in a decrease in CbE activity. Indeed, iodoacetamide treatment didn't changed AChE neither CbE activities, results which indicate that the metal inhibiting effect is probably not due to its biding to thiol groups close the active site of the enzyme. This outcome reveals that metals are important esterase inhibitors in zebrafish, and should be considered in environmental monitoring studies that use esterase inhibition as exposure biomarkers of organophosphate and carbamate pesticides.