Response and recovery of brain acetylcholinesterase activity in the European eel, Anguilla anguilla, exposed to fenitrothion

Application of fenitrothion on Heteropneustes fossilis causes alteration in morphology of erythrocytes via modifying hematological parameters

In Bangladesh, the extensive use of fenitrothion on crops and in aquaculture ponds inevitably threatens a range of aquaculture species, including fish, owing to stress responses and physiological disturbances. The present study elucidated the potential toxic effects of fenitrothion on the blood biomarkers (haemato-biochemistry and structure of erythrocytes) of stinging catfish (Heteropneustes fossilis), a commercially significant aquaculture species. Fish were exposed to four sub-lethal concentrations (0%, 10%, 20%, and 40% of the 96-h LC50 value) of fenitrothion in triplicate and observed on the 7th, 14th, 21st, and 28th day following exposure. With increasing fenitrothion concentration, blood glucose and white blood cell levels increased significantly; in contrast, hemoglobin, red blood cell, and packed cell volume substantially decreased. However, the mean corpuscular volume and mean corpuscular hemoglobin did not change significantly during the exordial period (0-7 d); although, at a later stage, changes were observed. Frequencies of observed erythrocytic nuclear abnormalities, such as degeneration, bi-nucleus, micronucleus, notch nucleus, and nuclear bridge and erythrocytic cellular abnormalities, such as echinocytes, fusion, elongation, and tear drop morphology increased significantly in a concentration-dependent manner. Differences between the control individuals and those individuals under treatment were considered insignificant for twin cells on the 14th day of exposure. The study showed the pernicious impact of the effects of fenitrothion on H. fossilis through physiological alteration, which is likely to pose challenges for aquaculture production.

Androgenic activation, impairment of the monoaminergic system and altered behavior in zebrafish larvae exposed to environmental concentrations of fenitrothion

Fenitrothion is an organophosphorus insecticide usually found in aquatic ecosystems at concentrations in the range of low ng/L. In this manuscript we show that 24 h exposure to environmental concentrations of fenitrothion, from ng/L to low μg/L, altered basal locomotor activity, visual-motor response and acoustic/vibrational escape response of zebrafish larvae. Furthermore, fenitrothion and expression of gap43a, gfap, atp2b1a, and mbp exhibited a significant non-monotonic concentration-response relationship. Once determined that environmental concentrations of fenitrothion were neurotoxic for zebrafish larvae, a computational analysis identified potential protein targets of this compound. Some of the predictions, including interactions with acetylcholinesterase, monoamine-oxidases and androgen receptor (AR), were experimentally validated. Binding to AR was the most suitable candidate for molecular initiating event, as indicated by both the up-regulation of cyp19a1b and sult2st3 and the non-monotonic relationship found between fenitrothion and the observed responses. Finally, when the integrity of the monoaminergic system was evaluated, altered levels of L-DOPA, DOPAC, HVA and 5-HIAA were found, as well as a significant up-regulation of slc18a2 expression at the lowest concentrations of fenitrothion. These data strongly suggest that concentrations of fenitrothion commonly found in aquatic ecosystems present a significant environmental risk for fish communities.

Oxidative stress markers in fish (Astyanax sp. and Danio rerio) exposed to urban and agricultural effluents in the Brazilian Pampa biome

Aquatic ecosystems are under constant risk due to industrial, agricultural, and urban activities, compromising water quality and preservation of aquatic biota. The assessment of toxicological impacts caused by pollutants to aquatic environment using biomarker measurements in fish can provide reliable data to estimate sublethal effects posed by chemicals in contaminated areas. In this study, fish (Astyanax sp. and Danio rerio) exposed to agricultural and urban effluents at the Vacacaí River, Brazil, were tested for potential signs of aquatic contamination. This river comprehends one of the main watercourses of the Brazilian Pampa, a biome with a large biodiversity that has been neglected in terms of environmental and social-economic development. Sites S1 and S2 were chosen by their proximity to crops and wastewater discharge points, while reference site was located upstream of S1 and S2, in an apparently non-degraded area. Fish muscle and brain tissues were processed for determination of acetylcholinesterase as well as oxidative stress-related biomarkers. The results showed signs of environmental contamination, hallmarked by significant changes in cholinesterase activity, expression of metallothionein, antioxidant enzymes, glutathione levels, and activation of antioxidant/cell stress response signaling pathways in fish exposed to contaminated sites when compared to reference. Based on these results, it is evidenced that urban and agricultural activities are posing risk to the environmental quality of water resources at the studied area. It is also demonstrated that cell stress biomarkers may serve as important tools for biomonitoring and development of risk assessment protocols in the Pampa biome.

Assessment of water pollution in the Brazilian Pampa biome by means of stress biomarkers in tadpoles of the leaf frog Phyllomedusa iheringii (Anura: Hylidae)

The Brazilian Pampa biome is currently under constant threat due to increase of agriculture and improper management of urban effluents. Studies with a focus on the assessment of impacts caused by human activities in this biome are scarce. In the present study, we measured stress-related biomarkers in tadpoles of the leaf frog Phyllomedusa iheringii, an endemic species to the Pampa biome, and tested its suitability as a bioindicator for the assessment of potential aquatic contamination in selected ponds (S1 and S2) nearby agricultural areas in comparison to a reference site. A significant decrease in acetylcholinesterase activity was observed in S2 when compared to S1 and reference. The levels of total-hydroperoxides were increased in S2 site. In parallel, increased activity of the antioxidant enzymes catalase, superoxide dismutase and glutathione S-transferase were observed in S2 when compared to S1 and reference. Further studies are necessary in order to correlate the changes observed here with different chemical stressors in water, as well as to elucidate mechanisms of toxicity induced by pesticides in amphibian species endemic to the Pampa biome. Nevertheless, our study validates Phyllomedusa iheringii as a valuable bioindicator in environmental studies.

Using a multibiomarker approach and behavioural responses to assess the effects of anthracene in Palaemon serratus

Polycyclic aromatic hydrocarbons (PAHs) are recognised as one of the main groups of contaminants that assume more importance in the marine environment, enhancing the need of studies concerning their adverse effects and more efficient and ecologically relevant tools for environmental monitoring purposes. This study aims to apply an integrated approach including several multi-level biological responses (accumulation levels, biochemical responses important for different physiological functions and behavioural alterations) to assess the ecological relevance of the effects induced by sub-lethal concentrations of anthracene (ANT) in Palaemon serratus (common prawn). ANT accumulation was assessed by measuring the levels of ANT-type compounds in prawn digestive gland, muscle and eye; biochemical responses were determined using biomarkers involved in biotransformation, oxidative damage, energy production and neurotransmission processes; and behavioural alterations through swimming performance after 96 h exposure bioassay (ANT:16-1,024 μg/L). The rationale behind this approach is to assess the ecologically relevant effects induced by ANT in prawn, given by the association between behavioural alterations with biochemical responses, in search for more efficient tools for environmental risk assessment. Results show a significant decrease of swimming velocity (LOEC=128 μg/L) along with increased levels of ANT-type compounds in digestive gland (LOEC=128 μg/L), muscle (LOEC=256 μg/L) and eye (LOEC=32 μg/L) in prawn exposed to ANT. Increased activities of glutathione peroxidase (GPx) and catalase (CAT), involved in anti-oxidant defence system, were also observed (LOEC=256 μg/L; 1024μg/L, respectively) in the digestive gland of prawn, induction of oxidative damage in lipids (LPO) also occurred (LOEC=32 μg/L). The inhibition of swimming velocity showed a correlation with some biochemical parameters measured, including the levels of ANT-type compounds in tissues and LPO, and thus these may be considered sensitive and ecologically relevant criteria as well as early warning endpoints for assessing polycyclic aromatic compounds exposure effects on marine organisms.

Effects of waterborne acephate exposure on antioxidant responses and acetylcholinesterase activities in Synechogobius hasta

The present study was conducted to determine the 24, 48, 72, and 96-h median lethal concentration (LC50) of acephate and investigate the antioxidant response and acetylcholinesterase (AChE) activities in liver, gill, and spleen of Synechogobius hasta exposed to 0 (control), 5, and 10 mg/L acephate, at the fixed interval time of 24, 48, 72, and 96 h, respectively. LC50 value was 60.83 mg/L at 24 h, 51.36 mg/L at 48 h, 47.07 mg/L at 72 h and 40.13 mg/L at 96 h, respectively. Dismutase (SOD), catalase (CAT), AChE activities, and malondialdehyde (MDA) levels in these tissues for the control remained stable over the exposure period. However, for the two tested groups, tissue-, dose-, and time-dependent responses of these parameters were observed in S. hasta. In general, hepatic SOD and CAT activities were significantly inhibited at 24 h, activated, and increased at 48 h, but again inhibited from 48 to 96 h in fish exposed to the two tested concentrations. Hepatic MDA levels of fish for the two tested concentration peaked at 48 h, significantly higher than the control. Hepatic AChE activity was inhibited at 24 h, peaked at 48 h, and then declined at 72 h for the two tested groups. For gills, the highest SOD and CAT activities for the two tested groups were observed at 48 h, higher than the control. AChE activities for the two tested groups were significantly inhibited at 24 h, but activated at 48 h. At 96 h, AChE activities among the treatments showed no significant differences. Gill MDA levels at 48 h for the tested groups were significantly higher than the control, but showed no significant differences at 24 and 72 h among the treatments. In spleen, SOD and CAT activities at 48 h for the two tested groups were significantly higher than those in the control, but at 96 h the vice versa was true. Spleenic AChE activities and MDA levels for the two tested groups were inhibited at 24 h, activated at 48 h, and then were again inhibited at 72 h. Based on these observations earlier, the results obtained in our study will have important toxicological implications for waterborne acephate pollution and, meantime, provide the basis for the effective risk assessment of acephate in water environment and appropriate safety recommendations for fish.

Acute effects of deltamethrin on swimming velocity and biomarkers of the common prawn Palaemon serratus

The main purpose of the present study was to investigate the effects of deltamethrin on biomarkers and behavior of Palaemon serratus (common prawn), since this attempt to link different levels of biological organization will allow determining which biomarkers might be ecologically relevant and will be useful to complement the information about the effects of pesticides by using behavioral parameters. Therefore, parameters of liver antioxidant status, energy metabolism and neurotransmission were determined in different tissues of the common prawn and used to assess the effects at sub-individual level, whereas swimming velocity was used to assess the effects at the individual level. It was also investigated if the swimming velocity can be used as an endpoint in ecotoxicology bioassays and if it can be as sensitive as biomarker endpoints. Swimming velocity was significantly reduced in prawns exposed to deltamethrin, showing a lowest observed effect (LOEC) of 0.6 ng L(-1). Eye acetylcholinesterase (AChE) activity was significantly increased in prawns exposed to 0.6, 1.2 and 2.4 ng L(-1) deltamethrin, whereas muscle cholinesterase (ChE) activity was significantly increased in prawns exposed to 19 and 39 ng L(-1). On the other hand, lactate dehydrogenase (LDH) activity was significantly increased in muscle of prawns exposed to 0.6, 1.2, 2.4, 4.9 ng L(-1) deltamethrin, showing that organisms were requiring additional energy, but probably using it for detoxification processes rather than locomotion, since swimming velocity was inhibited. Glutathione S-transferase (GST) activity was significantly increased in the digestive gland of common prawn exposed to 19 and 39 ng L(-1) deltamethrin. Catalase (CAT) activity was significantly increased in digestive gland of prawn exposed to 19 ng L(-1) deltamethrin. However, CAT activity decreased in digestive gland of prawn exposed to 39 ng L(-1), suggesting an antioxidant defense system failure concomitant with high levels of lipid peroxidation. Thus, global results showed that decreased swimming velocity was not associated with cholinesterase inhibition. In fact, the impairment of swimming velocity may be due to allocation of energy for detoxification and antioxidant protection instead of swimming activity. The present study showed that swimming velocity could be used as an ecologically relevant tool and a sensitive endpoint to assess and complement the study of pesticide effects on marine organisms.

Alterations in serum electrolytes, antioxidative enzymes and haematological parameters of Labeo rohita on short-term exposure to sublethal dose of nitrite

An experiment was conducted to study the effects of short-term exposure to sublethal levels of nitrite on electrolyte regulation, antioxidative enzymes and haematological parameters in Labeo rohita juveniles. The fishes were exposed to graded levels of nitrite (0-15 mg l(-1)) for different duration (0, 12, 24, 48 and 96 h). The 96-h LC(50) value for L. rohita (avg. wt, 66.5 ± 0.5 g) was found to be 11.28 mg l(-1). Activities of antioxidative enzymes (catalase and superoxide dismutase), acetylcholine esterase (AChE) and methaemoglobin reductase, serum electrolytes (sodium, potassium and chloride), haematological parameters and blood glucose level significantly varied (P < 0.05) in a dose-dependent manner. With increasing nitrite concentration and exposure period, a progressive reduction in the total erythrocyte count and haemoglobin were observed. With increase in nitrite concentration, a significant (P < 0.05) increase in activities was evidenced in catalase and superoxide dismutase in liver as well as gill, methaemoglobin reductase in blood, while progressive decline in AChE activity in brain was recorded. The serum sodium and chloride content showed a progressive decline, while potassium showed an increasing trend upon increase in nitrite concentration. The serum K(+) and Cl(-) after 96-h exposure demonstrated a linear relationship (Y = 0.221x + 2.542, R (2) = 0.938, P < 0.01 and Y = -5.760x + 129.5, R (2) = 0.952, P < 0.01, respectively) with nitrite concentrations. This study revealed that nitrite exposure causes alteration in all measured tissue enzymes, serum electrolytes and haematological parameters.

Cholinesterase activities and sensitivity to pesticides in different tissues of silver European eel, Anguilla anguilla

Cholinesterase (ChE) activities were characterized in silver European eel, Anguilla anguilla, grown in the brackish lagoon of Comacchio (Italy). All specimens were harvested at the "lavoriero", a traditional eel trapping weir that captures eels while leaving internal waters at the onset of reproductive migration. To our knowledge, no investigation on ChE was reported in silver eels. Therefore a first characterization of enzyme activity in muscle, brain, liver and plasma of silver eel was carried out, in the presence of different substrates, selective inhibitors, and four pesticides representative of the carbamate and organophosphate classes. Brain and white skeletal muscle showed similar ChE activities, 5- and 10-fold higher than those detected in liver and plasma, respectively. Km values of 0.31 and 0.30 mM, and Vmax values of 40.28 and 35.47 nmol min(-1) mg protein(-1) were obtained in brain and muscle ChE, respectively. Acetycholinesterase was the predominant ChE form in all tissues, as concluded by comparing the effects of BW 284c51, iso-OMPA and eserine. ChE activities in brain and muscle were significantly inhibited by in vitro treatment with pesticides, with the following order of potency: carbofuran>carbaryl>chlorpyrifos≥diazinon.

Mechanistic toxicodynamic model for receptor-mediated toxicity of diazoxon, the active metabolite of diazinon, in Daphnia magna

The organothiophosphate diazinon inhibits the target site acetylcholinesterase only after activation to its metabolite diazoxon. Commonly, the toxicity of xenobiotics toward aquatic organisms is expressed as a function of the external concentration and the resulting effect on the individual level after fixed exposure times. This approach does not account for the time dependency of internal processes such as uptake, metabolism, and interaction of the toxicant with the target site. Here, we develop a mechanistic toxicodynamic model for Daphnia magna and diazoxon, which accounts for the inhibition of the internal target site acetylcholinesterase and its link to the observable effect, immobilization, and mortality. The model was parametrized by experiments performed in vitro with the active metabolite diazoxon on enzyme extracts and in vivo with the parent compound diazinon. The mechanism of acetylcholinesterase inhibition was shown to occur irreversibly in two steps via formation of a reversible enzyme-inhibitor complex. The corresponding kinetic parameters revealed a very high sensitivity of acetylcholinesterase from D. magna toward diazoxon, which corresponds well with the high toxicity of diazinon toward this species. Recovery of enzyme activity but no recovery from immobilization was observed after in vivo exposure to diazinon. The toxicodynamic model combining all in vitro and in vivo parameters was successfully applied to describe the time course of immobilization in dependence of acetylcholinesterase activity during exposure to diazinon. The threshold value for enzyme activity below which immobilization set in amounted to 40% of the control activity. Furthermore, the model enabled the prediction of the time-dependent diazoxon concentration directly present at the target site.

Linking behavioural alterations with biomarkers responses in the European seabass Dicentrarchus labrax L. exposed to the organophosphate pesticide fenitrothion

The acute effects of the organophosphate insecticide fenitrothion on Dicentrarchus labrax juveniles were investigated through a bioassay using biomarkers and swimming behaviour as effect criteria. After 96 h of exposure to sub-lethal concentrations of fenitrothion, the swimming velocity and several biomarkers were individually determined, namely: brain acetylcholinesterase (AChE) activity; muscle cholinesterases (ChE), lactate dehydrogenase and isocitrate dehydrogenase activities; liver ethoxyresorufin-O-deethylase (EROD), glutathione S-transferases, glutathione peroxidase, glutathione reductase, catalase and superoxide dismutase (SOD) activities and lipid peroxidation levels (LPO). A significant decrease of the swimming velocity (LOEC = 2 mg l(-1)), an inhibition of both AChE (LOEC = 0.06 mg l(-1)) and ChE activities (LOEC = 0.03 mg l(-1)), and a positive and significant correlation between the swimming velocity and AChE were found in exposed fish, suggesting an influence of the inhibition of these enzymes in the swimming velocity decrease. An increase of EROD activity (LOEC = 1 mg l(-1)), indicating the involvement of this enzyme in fenitrothion biotransformation, and a negative and significant correlation between EROD activity and swimming velocity were also found, suggesting that the two findings may somehow be related. Furthermore, results show a significant induction of SOD (LOEC = 0.13 mg l(-1)) without LPO increase, suggesting that the enzyme is preventing oxidative stress damage. No significant alterations were found in any of the other parameters tested. Thus, exposure of seabass to fenitrothion in the wild at concentrations similar to those tested here may have adverse consequences at population level as neurotransmission and swimming ability are essential for fish performance and survival.

Tissue-specific in vivo inhibition of cholinesterases by the organophosphate fenthion in Oreochromis niloticus

This study was designed to elucidate the effect of the organophosphate fenthion exposure on cholinesterase-specific activities in brain, liver, and kidney tissues of juvenile Oreochromis niloticus, and to define the best indicator tissue to fenthion exposure. The 96-h LC(50) value was determined as 2.27 mg/L and fish were exposed to 20% of this concentration for 24-, 48-, and 96-h. Recovery periods in similar durations were provided to evaluate the ChE activities. AChE and BChE activities were determined spectrophotometrically. The activities of these enzymes were significantly inhibited in all the tissues tested, liver was the most and kidney was the least affected tissues. The inhibition percentages of AChE and BChE were at similar levels in the liver while BChE was more affected in kidney. BChE was not detected in the brain. A significant positive correlation in ChE inhibitions was found among tissues, and the effect of fenthion on ChE activities was tissue specific. In general enzymes activities were not significantly recovered in 96-h recovery period; however, an elevation in AChE inhibition was observed in brain. Based on the data of this study, the liver may be suggested as the best indicator tissue especially for phosphorothioate exposure.

Tissue-specific inhibition and recovery of esterase activities in Lumbricus terrestris experimentally exposed to chlorpyrifos

Exposure and effect assessment of organophosphate (OP) pesticides generally involves the use of cholinesterase (ChE) inhibition. In earthworm, this enzyme activity is often measured in homogenates from the whole organism. Here we examine the tissue-specific response of ChE and carboxylesterase (CE) activities in Lumbricus terrestris experimentally exposed to chlorpyrifos-spiked field soils. Esterases were measured in different gut segments and in the seminal vesicles of earthworms following acute exposure (2 d) to the OP and during 35d of a recovery period. We found that inhibition of both esterase activities was dependent on the tissue. Cholinesterase activity decreased in the pharynx, crop, foregut and seminal vesicles in a concentration-dependent way, whereas CE activity (4-nitrophenyl valerate) was strongly inhibited in these tissues. Gizzard CE activity was not inhibited by the OP, even an increase of enzyme activity was evident during the recovery period. These results suggest that both esterases should be determined jointly in selected tissues of earthworms. Moreover, the high levels of gut CE activity and its inhibition and recovery dynamic following OP exposure suggest that this esterase could play an important role as an enzymatic barrier against OP uptake from the ingested contaminated soil.

The organophosphorous pesticide, fenitrothion, acts as an anti-androgen and alters reproductive behavior of the male three-spined stickleback, Gasterosteus aculeatus

Fenitrothion (FN) is a widely used organophosphorous pesticide that has structural similarities with the clinical anti-androgen flutamide. The potential for FN to act as an anti-androgen (at exposures of 1, 50, and 200 microg FN/l over a 26-day period) was assessed in male three-spined sticklebacks, Gasterosteus aculeatus, by measuring kidney spiggin concentration, nest-building, and courtship behavior. Spiggin is the glue protein that male sticklebacks use to build their nests and is directly controlled by androgens. FN exposure significantly reduced spiggin production as well as nest-building activity. It also adversely affected courtship--especially the 'zigzag dance' and biting behavior of the males. FN thus appears to have anti-androgenic effects on both the physiology and behavior of the male stickleback.

Sublethal Effects of Organophosphate Diazinon on the Brain ofCyprinus Carpio

Effects of diazinon, at different concentrations and exposure times, were investigated in freshwater fish, Cyprinus carpio, to elucidate the possible mode of action on lipid peroxidation together with the inhibitory effect of diazinon on acetylcholinesterase activity and changes in tissue protein levels. Cholinesterase inhibition is considered to be a specific biomarker of exposure to organophosphorus pesticides. Fish were exposed to 0.0036 microg/L, 0.018 microg/L, and 0.036 microg/L (sublethal) concentrations of diazinon for 5, 15, and 30 days, and biochemical measurements were carried out spectrophotometrically. Brain was chosen as an indicator tissue because it is a target system for the organophosphorus action. More than 20% decline in acetylcholinesterase activity relative to mean activity of the controls was observed in the diazinon-exposed groups. Protein content decreased significantly after 15 days of exposure to 0.018 microg/L and 0.036 microg/L diazinon and after 30 days of exposure to 0.036 microg/L. Malondialdehyde level declined markedly compared with the control levels. This study showed that prolonged exposures of C. carpio to diazinon had significant effects on brain acetylcholinesterase activity and that environmentally relevant concentrations of diazinon can significantly inhibit brain acetylcholinesterase activity. Altered protein content was probably due to the high energy demand under pesticide stress or inhibition of de novo enzyme synthesis. The decreased malondialdehyde content may reflect the possibility of better protection against oxidative stress.

Acute toxicity of dichlorvos to Aphanius iberus (Cuvier & Valenciennes, 1846) and its anti-cholinesterase effects on this species

This study evaluates the toxic effects of the organophosphate pesticide (OP) dichlorvos to the endangered Iberian toothcarp (Aphanius iberus). To this end, the lethal toxicity of dichlorvos based on 96h-LC50 bioassays was determined in saline water (50g/L), and in vivo effects of dichlorvos on cholinesterase (ChE) activity were investigated in adult female and male specimens. The 96h-LC50 value determined by probit analysis was 3.17mg/L (95% confidence limits: 1.34-3.97). The characterisation of the ChE using different substrates and specific inhibitors was also carried out in head and muscle tissues. Acetylthiocholine was the substrate preferred by both head and muscle ChE in males and females. Eserine sulphate and BW284C51 significantly inhibited both head and muscle enzyme activity at low concentrations (muM range), and iso-OMPA had no significant effect. These results indicate that in the head and muscle the predominant ChE form is acetylcholinesterase (AChE) for both sexes. The kinetic parameters for ChE activity (Km and Vmax) were similar in both sexes. The 96h-LC50 value obtained for adult specimens of Iberian toothcarp was 3.17mg/L. ChE activity in head and body tissues of both sexes was significantly inhibited in all concentrations tested (0.5, 1, 2 and 4mg/L) after "in vivo" dichlorvos exposure. However, Iberian toothcarp was able to tolerate high concentrations of dichlorvos, and resist high levels of brain and muscle ChE inhibition without mortality. Both ChE inhibition and recovery followed a similar time-course pattern in response to sub-lethal exposure to dichlorvos (1mg/L), and the enzyme activity did not return to control levels after 96h in clean water. The results of this study show that ChE activity is a good biomarker of exposure to OP in the Iberian toothcarp adults.

Muscular and brain cholinesterase sensitivities to azinphos methyl and carbaryl in the juvenile rainbow trout Oncorhynchus mykiss

The organophosphate azinphos methyl (AzMe) and the carbamate carbaryl are the insecticides mostly used in the irrigated valley of Río Negro and Neuquén, Patagonia, Argentina. Juvenile rainbow trout were exposed to AzMe and carbaryl and the sensitivity of skeletal muscular cholinesterase (ChE) and the time course of inhibition and recovery were evaluated. EC50 values demonstrated that AzMe was a stronger in vivo inhibitor of muscular ChE (1.05+/-0.23 microg/L) than carbaryl (270+/-62.23 microg/L). Muscular ChE was significantly less sensitive to both insecticides than brain ChE. EC50 values obtained for muscular ChE were closer than those for brain ChE to the respective pesticide lethal concentrations, pointing out the relevance of the muscular enzyme in determining acute toxicity. The recovery process of ChE activity after carbaryl exposure (500 microg/L) was fast, whereas no significant recovery was observed with AzMe (1 microg/L) after 21 days in uncontaminated media. Brain and muscular ChE were inhibited and showed a significant but not complete recovery after three consecutive 48-h exposures to AzMe (1 microg/L) followed by a recovery period of 7 days. This scheme mimics the periodical application of the insecticides in the region and suggests a certain probability of a sustained ChE inhibition under field conditions, affecting fish development and survival.

Investigation of acute toxicity of fenitrothion on guppies Poecilia reticulata

Fenitrothion, an organophosphothionate insecticide (CAS number: 122-14-5) and potential toxic pollutant contaminating aquatic ecosystems, was investigated in the present study for acute toxicity. Guppy fish (Poecilia reticulata) were selected for the bioassay experiments. The experiments were repeated three times and the 96 h LC(50) was determined for the guppies. The static test method of acute toxicity test was used. The water temperature was regulated at 23 +/- 1 degrees C. In addition, behavioral changes at each fenitrothion concentration were observed for the individual fish. Data obtained from the fenitrothion acute toxicity tests were evaluated using the probit analysis statistical method. The 96 h LC(50) value for guppy was estimated as 3.28 mg l(-1). Values in the range of microg l(-1) and mg l(-1) have been reported for various other fish species.

Arsenic-induced changes in optic tectal histoarchitecture and acetylcholinesterase-acetylcholine profile in Channa punctatus: amelioration by selenium

Fish (Channa punctatus Bloch) were exposed in vivo for 14 days to non-lethal doses of As2O3 (10% LC50 and 5% LC50). Several endpoints related to histoarchitectural and acetylcholine-acetylcholinesterase (ACh-AChE) profile in the optic tectum were evaluated. Histological examination showed aggregated, disorganized and necrotic cells with irregular outlines in the different layers of optic tectum in the As-treated fish. The histopathological changes were more pronounced on day 7 than on other days and the damage was found to recover on day 14. ACh content and AChE activity demonstrated the usual inverse trend. Arsenic treatment was associated with a dose-dependent increase in AChE activity on day 1, a decrease on day 2 and reactivation on day 7, returning to the basal level on day 14. In vitro inhibition kinetics were set up to determine I50 (35 microM) concentration of As2O3. The ameliorative potential of selenium on arsenic-mediated inhibition of AChE revealed a positive role of Se, especially when Se preceded As2O3 treatment, either in vitro or in vivo.

Methylmercury accumulation, histopathology effects, and cholinesterase activity alterations in medaka (Oryzias latipes) following sublethal exposure to methylmercury chloride

A series of specific toxicological effects including bioaccumulation of the pollutant, histological changes and influences on cholinesterase (ChE) activities were examined in the adult Japanese medaka after the exposure to graded sublethal concentrations (40, 20, 10, 5, 2.5ngHg/mL) of methylmercury chloride (MMC). Methylmercury (MeHg) contents in the exposed medaka tissues ranged from 0.03 to 64.4μgHg/g (wet weight, w.w.). High concentrations of MeHg were accumulated in the liver and brain, while the concentrations in muscle and fat were relatively low. A dose-dependent and exposure time-dependent increase of MeHg contents in tissues was observed. Histopathological changes, such as oedema, vacuolization, pyknotic nucleus, telangiectasis, and degenerative sperm, can clearly be observed in the slices from the liver, gill, and male gonad of the exposed medaka. Inhibition of ChE activity was common in the exposed fish's brain, liver, gill, and muscle. The serious intoxication of MMC to medaka was definitely demonstrated herein.

Organophosphorus pollutants (OPP) in aquatic environment at Damietta Governorate, Egypt: implications for monitoring and biomarker responses

The study was carried out from spring 1999 to spring 2001 to monitor the residue levels of organophosphorus pollutants (OPP) in aquatic environment of the drainage canal surrounding a pesticide factory at Damietta Governorate. Water, sediment, and fish samples were collected at six different seasonal periods. OPPs were analyzed by GLC and confirmed using GC-MS. Chlorpyrifos, chlorpyrifos-methyl, malathion, diazinon, pirimiphos-methyl and profenofos were detected in most samples. Chlorpyrifos was dominant in all water and sediment samples. It was ranged from 24.5 to 303.8 and 0.9 to 303.8 ppb in water and sediment samples, respectively. Diazinon level was slightly similar to chlorpyrifos in fish samples. Data based on the grand total concentration of OPP showed that the most polluted samples were collected either at spring 1999 or autumn 2000. They were 675.5 and 303.8 ppb in water samples and 43.0 and 52.2 ppb in fish collected at spring 1999 and autumn 2000, respectively. The obtained results are in parallel to that found in case of cholinesterase activity where the activity of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) was declined at these seasonal period. The activity levels of AChE and BuChE were found to be 77.18% and 59.67% of control at spring 1999 and 78.62% and 85.80% of control, at autumn 2000, respectively. Thus, AChE and BuChE could be used as biomarkers for tracing and biomonitoring OPP pollution.

The effects of environmental pollutants on complex fish behaviour: integrating behavioural and physiological indicators of toxicity

Environmental pollutants such as metals, pesticides, and other organics pose serious risks to many aquatic organisms. Accordingly, a great deal of previous research has characterized physiological mechanisms of toxicity in animals exposed to contaminants. In contrast, effects of contaminants on fish behaviour are less frequently studied. Because behaviour links physiological function with ecological processes, behavioural indicators of toxicity appear ideal for assessing the effects of aquatic pollutants on fish populations. Here we consider the many toxicants that disrupt complex fish behaviours, such as predator avoidance, reproductive, and social behaviours. Toxicant exposure often completely eliminates the performance of behaviours that are essential to fitness and survival in natural ecosystems, frequently after exposures of lesser magnitude than those causing significant mortality. Unfortunately, the behavioural toxicity of many xenobiotics is still unknown, warranting their future study. Physiological effects of toxicants in the literature include disruption of sensory, hormonal, neurological, and metabolic systems, which are likely to have profound implications for many fish behaviours. However, little toxicological research has sought to integrate the behavioural effects of toxicants with physiological processes. Those studies that take this multidisciplinary approach add important insight into possible mechanisms of behavioural alteration. The most commonly observed links with behavioural disruption include cholinesterase (ChE) inhibition, altered brain neurotransmitter levels, sensory deprivation, and impaired gonadal or thyroid hormone levels. Even less frequently studied are the implications of interrelated changes in behaviour and physiology caused by aquatic pollutants for fish populations. We conclude that future integrative, multidisciplinary research is clearly needed to increase the significance and usefulness of behavioural indicators for aquatic toxicology, and aim to highlight specific areas for consideration.

Nitrite toxicity in Indian major carps: sublethal effect on selected enzymes in fingerlings of Catla catla, Labeo rohita and Cirrhinus mrigala

The effects of 96-h sublethal exposure of nitrite (1, 2, 4, 8 and 10.4 mg l(-1)) on selected enzymatic activities in serum and tissues of fingerlings of catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala) were studied for the first time in these species. All three species responded almost identically to nitrite exposure. With increasing nitrite concentration, reduction in activities was observed in acetylcholinesterase (AChE) in brain and liver; alkaline phosphatase (ALP) in serum, brain and gill; and acid phosphatase (ACP) in gill, while progressive increase in alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) activities in brain, gill and serum, and ACP activity in serum and brain was observed. Lactate dehydrogenase (LDH) activity increased in gill, liver, kidney, brain and serum of all three species with increasing nitrite concentration up to 8 mg l(-1) followed by reduction at 10.4 mg l(-1). The study revealed nitrite stress causing alteration in activities of all measured tissue and serum enzymes in the fingerlings, and so stresses the need for proper management of this particular nutrient in water during carp culture.

Acetylcholinesterase inhibition and increased food consumption rate in the zebrafish, Danio rerio, after chronic exposure to parathion

Acetylcholinesterase (AChE) inhibition is widely regarded as a good biomarker of exposure to organophosphorus pesticides (OP). However, less is known about the relationship between AChE inhibition and consequences for growth, reproduction and survival on organisms. Acute toxicity tests with fish have shown that high percentages of AChE inhibition are needed to cause detrimental effects, but not much is known about the consequences of chronic exposure to this group of chemicals for both AChE activity and higher levels of biological organisation. In this study, zebrafish (Danio rerio) were exposed to sublethal concentrations of the OP parathion for 250 days in a flow-through system. Besides AChE activity, a variety of other parameters were measured: whole-body protein and lactate content, consumption rate, survival, growth and reproduction. AChE inhibition was correlated with exposure concentration, but not with exposure time, and was significant above 0.9 microg/l after 144 days and above 4.3 microg/l after 250 days of exposure. Both parathion and the cosolvent dimethylsulfoxide (DMSO) significantly increased food consumption rate of the fish. Survival, growth, reproduction and lactate content were not affected, while protein concentrations showed only minor effects. These findings support the hypothesis that AChE is a very sensitive biomarker for exposure, but not accurately predict higher level adverse effects following long-term exposure to OPs.

Effects of carbofuran, diuron, and nicosulfuron on acetylcholinesterase activity in goldfish (Carassius auratus)

Juvenile goldfish (Carassius auratus) were exposed to three widely used pesticides; carbofuran, diuron, and nicosulfuron. Acetylcholinesterase (AChE) activity and molecular forms of AChE were first characterized in brain and skeletal muscle of unexposed fish. Skeletal muscle had higher AChE activity than brain (306 and 215 nmol/min/mg protein, respectively). In brain, four molecular forms of AChE were found: A12, G4, G2, and G1. In the muscle, three molecular forms were found A12, A8, and G2. AChE activity was then evaluated in both tissues of fish exposed to different concentration of pesticides (5, 50, and 500 microg/L) for 6, 12, 24, and 48 h. In brain, AChE activity was significantly inhibited during all the periods of exposure in response to 50 microg/L (19-28%) and 500 microg/L (85-87%) carbofuran. Such effect was observed in the muscle only at 500 microg/L (86-92%). Carbofuran had no effect on the distribution of molecular forms. Significant inhibitions (9-12%) of brain AChE activity were also observed in response to diuron and nicosulfuron at 500 microg/L during all periods of exposure and for 50 microg/L nicosulfuron after 24 and 48 h. This study pointed out short-term effects of exposure to sublethal concentrations of the three pesticides, ranging among different chemical families, on brain and muscle AChE in goldfish.