Assessing dimethoate contamination in temperate and tropical climates: potential use of biomarkers in bioassays with two chironomid species

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

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

Strategies of cellular energy allocation to cope with paraquat-induced oxidative stress: Chironomids vs Planarians and the importance of using different species

Paraquat (PQ) is still used in several countries worldwide as an herbicide for weed control in agricultural production, ponds, reservoirs and irrigation canals. Thus, PQ is frequently found in surface water systems and is potentially toxic to aquatic organisms, since it can cause mitochondrial dysfunction altering in the redox state of cells. This study aimed to investigate the chronic effects of PQ to Chironomus riparius and Girardia tigrina, and compare their physiological strategies to cope with environmental stress. The mean emergence time was the most sensitive endpoint for Chironomids, with the lowest observed effect concentrations (LOEC) being 0.02 for males and 0.1 mg PQ L^-1 for females. Moreover, PQ reduced the body weight of male and female imagoes, with LOECs of 0.5 and 2.5 mg PQ L^-1, respectively. Paraquat also decreased the respiration rate (LOEC = 2.5 mg PQ L^-1) and total glutathione (tGSH) content (LOEC = 0.5 mg PQ L^-1). Thus, the aerobic production of energy was not affected and allowed chironomids to cope with oxidative stress induced by PQ, but with consequent physiological costs in terms of development rates and weight of adults. In planarians, PQ decreased the locomotion and feeding activity, and delayed photoreceptor regeneration (LOECs = 2.5 mg PQ L^-1 for all endpoints). Despite increased aerobic energy production (LOEC = 0.5 mg PQ L^-1), planarians were not able to cope with oxidative stress induced by the highest PQ concentrations, since lipid peroxidation levels were significantly increased (LOEC = 2.5 mg PQ L^-1) concomitantly with a significant decrease of tGSH (LOEC = 2.5 mg PQ L^-1). These results showed that planarians were unable to cope with oxidative stress induced by PQ with consequent impairments of behavior and regeneration despite an increased aerobic energy production.

Steroid androgen 17 alpha methyltestosterone used in fish farming induces biochemical alterations in zebrafish adults

The 17 alpha methyltestosterone (MT) hormone is fed to Oreochromis niloticus larvae in fish farms with the purpose of inducing sex reversal. The aim of this study was to evaluate the toxicity and sub-lethality of MT (99.9% purity) and cMT (a commercial MT with 90% purity) in zebrafish (Danio rerio) adults, where the animals were exposed to concentrations of 0, 4, 23, 139, 833 and 5000 µg/L for 96 hours. Genotoxicity was evaluated by micronucleus test (MN), nuclear abnormalities (NA) and comet assay. A low genotoxic potential of MT was showed, inducing micronucleus, nuclear abnormalities and DNA damage in Danio rerio, depending on the use of MT or cMT, gender and tested concentrations. In the sub-lethality trials, there was a basal difference in the activity of the enzymatic biochemical markers for males and females, while the Glutatione S transferase (GST) activity decreased in all analyzed tissues, and for males the enzymatic activity decreased only in the intestine. Results suggest that MT has a toxic potential to fish because it alters enzymatic metabolic pathways and may pose a risk to the ecosystems.

Seasonal ecotoxicological monitoring of freshwater zooplankton in Bir Mcherga dam (Tunisia)

Dams represent large semi-closed reservoirs of pesticides and various organic and inorganic pollutants from agricultural and human activities, and their monitoring should receive special attention. This study evaluated the environmental health status of Bir Mcherga dam using zooplankton species. The dam has a capacity of 130 Mm³ and its waters are used for irrigation, water drinking supply, and fishery. Copepods and cladocerans (crustaceans) were collected in situ monthly between October and August 2012. Oxidative stress (CAT, MDA), neurotoxicity (AChE), and genotoxicity (micronucleus test) biomarkers were analyzed in two zooplankton species: Acanthocyclops robustus and Diaphanosoma mongolianum. High values of cells with a micronucleus were observed during summer. AChE activities were inhibited during early winter and summer. The high seasonal variability of CAT and MDA levels indicates that zooplankton is continuously exposed to different oxidative stresses. These results suggest that there is an obvious and continuous multi-faceted stress in Bir Mcherga reservoir and, consequently, an urgent monitoring of freshwater environments in Tunisia is needed, particularly those intended for human consumption and irrigation.

Behavior of detoxifying enzymes of Aedes aegypti exposed to girgensohnine alkaloid analog and Cymbopogon flexuosus essential oil

Because mosquito control depend on the use of commercial insecticides and resistance has been described in some of them, there is a need to explore new molecules no resistant. In vivo effects of girgensohnine analog 2-(3,4-dimethoxyphenyl)-2-(piperidin-1-yl)acetonitrile DPPA and Cymbopogon flexuosus essential oil CFEO, on the detoxifying enzymes acetylcholinesterase (AChE), glutathione-S-transferase (GST), nonspecific esterases (α- and β-), mixed function oxidases (MFO) and p-NPA esterases were evaluated on a Rockefeller (Rock) and wild Aedes aegypti population from Santander, Colombia (WSant). The action was tested after 24h of exposure at concentrations of 20.10, 35.18 and 70.35mgL^-1 of DPPA and 18.45, 30.75 and 61.50mgL^-1 of CFEO, respectively. It was found that AChE activity of Rock and WSant was not influenced by the evaluated concentration of DPPA and CFEO (p>0.05), while MFO activity was significantly affected by all CFEO concentrations in WSant (p<0.05). GST, α- and β-esterase activities were affected in Rock exposed at the highest CFEO concentration, this concentration also modified β-esterases activity of WSant. DPPA and CFEO sublethal doses induced inhibition of AChE activity on untreated larvae homogenate from 12 to 20% and 18 to 26%, respectively. For untreated adult homogenate, the inhibition activity raised up to 14 to 27% for DPPA and 26 to 34% for CFEO. Elevated levels of detoxifying enzymes, found when CFEO was evaluated, showed a larval sensitivity not observed by the pure compound suggesting that DPPA, contrary to CFEO, was not recognized, transformed or eliminated by the evaluated detoxifying enzymes.

Sublethal Effects of Insecticide Exposure on Megacopta cribraria (Fabricius) Nymphs: Key Biological Traits and Acetylcholinesterase Activity

Megacopta cribraria F. (Hemiptera: Plataspidae), the kudzu bug, is an invasive insect pest of U.S. soybean. At present, insecticide application is the primary and most effective control option for M. cribraria In this study, the potential effects of sublethal and low-lethal concentrations (LC10 and LC40) of three common insecticides on key biological traits and acetylcholinesterase (AChE) activity of the treated nymphal stage of insect were assessed. The results show that the sublethal concentration of imidacloprid significantly reduced adult emergence rate of M. cribraria A low-lethal concentration of imidacloprid significantly increased nymphal development time, but significantly decreased adult emergence rate and adult longevity. Both sublethal and low-lethal concentrations of acephate caused an increase in nymphal development time and a reduction in adult emergence rate and adult longevity. Fecundity of females was significantly reduced only by exposure to low-lethal concentrations of acephate. Sublethal and low-lethal concentrations of bifenthrin increased nymphal development time, but significantly decreased adult emergence rate. In addition, we found that the AChE activity of M. cribraria was significantly increased only by LC40 imidacloprid, but strongly inhibited by acephate.

Environmental Fate and Toxicology of Dimethoate

The insecticide dimethoate, an organophosphate, was first introduced in 1962 for broad spectrum control of a wide range of insects including mites, flies, aphids, and plant hoppers. It inhibits AChE activity, resulting in nerve damage, which may lead to death. It is considered highly toxic to insects although dimethoate resistance has been observed. Dimethoate has both a low vapor pressure (0.247 mPa) and Henry's law constant (l.42x10(-6) Pa m3/mol), thus volatilization is not a major route of dissipation from either water or moist soils. Photolysis is considered a minor dissipation pathway. However, studies have shown that in the presence of a catalyst, the rate of photolysis does increase. The insecticide has high water solubility (39,800 mg/L) and under alkaline conditions, hydrolysis predominates representing a major degradation pathway. It has a low soil sorption capacity (Koc=20) which varies by soil type and organic matter content. Dimethoate is degraded by microbes under anaerobic conditions and bacterial species have been identified that are capable of using dimethoate as a carbon source. Although many intermediate by-products have been identified by abiotic and biotic processes, the major degradation product is omethoate. Dimethoate has been found to adversely impact many organisms. In plants, photosynthesis and growth are highly impacted, whereas birds exhibit inhibition in brain enzyme activity, thus sublethal effects are apparent. Furthermore, aquatic organisms are expected to be highly impacted via direct exposure, often displaying changes in swimming behavior. Toxicity results include inhibition in growth and more importantly, inhibition of acetylcholinesterase activity.

Sub-lethal toxicity of environmentally relevant concentrations of esfenvalerate to Chironomus riparius

Integrative studies focused on sub-organismal responses to pyrethroid exposure are important to understand life history responses. In this study, the ecotoxicological effects of esfenvalerate (ESF) on Chironomus riparius were assessed using five biochemical biomarkers related to neurophysiological function (acetylcholinesterase) and oxidative stress (catalase; glutathione-S-transferase; total glutathione and lipid peroxidation). In addition, effects on cellular energy allocation were assessed and all results were compared with organismal level responses (larval growth, emergence and sex ratio). Exposure to sub-lethal concentrations of ESF caused the failure of C. riparius antioxidant defenses (inhibition of catalase activity and decreased levels of total glutathione), which was reflected as oxidative damage. C. riparius energy budget was decreased by exposure to ESF due to an increased energy consumption. Life cycle tests showed that exposure to ESF impaired C. riparius developmental rates and increased male:female ratios, thereby confirming its toxicity and potential population level effects at environmentally relevant concentrations.

A multi-platform metabolomics approach demonstrates changes in energy metabolism and the transsulfuration pathway in Chironomus tepperi following exposure to zinc

Measuring biological responses in resident biota is a commonly used approach to monitoring polluted habitats. The challenge is to choose sensitive and, ideally, stressor-specific endpoints that reflect the responses of the ecosystem. Metabolomics is a potentially useful approach for identifying sensitive and consistent responses since it provides a holistic view to understanding the effects of exposure to chemicals upon the physiological functioning of organisms. In this study, we exposed the aquatic non-biting midge, Chironomus tepperi, to two concentrations of zinc chloride and measured global changes in polar metabolite levels using an untargeted gas chromatography-mass spectrometry (GC-MS) analysis and a targeted liquid chromatography-mass spectrometry (LC-MS) analysis of amine-containing metabolites. These data were correlated with changes in the expression of a number of target genes. Zinc exposure resulted in a reduction in levels of intermediates in carbohydrate metabolism (i.e., glucose 6-phosphate, fructose 6-phosphate and disaccharides) and an increase in a number of TCA cycle intermediates. Zinc exposure also resulted in decreases in concentrations of the amine containing metabolites, lanthionine, methionine and cystathionine, and an increase in metallothionein gene expression. Methionine and cystathionine are intermediates in the transsulfuration pathway which is involved in the conversion of methionine to cysteine. These responses provide an understanding of the pathways affected by zinc toxicity, and how these effects are different to other heavy metals such as cadmium and copper. The use of complementary metabolomics analytical approaches was particularly useful for understanding the effects of zinc exposure and importantly, identified a suite of candidate biomarkers of zinc exposure useful for the development of biomonitoring programs.

Additive effects of predator cues and dimethoate on different levels of biological organisation in the non-biting midge Chironomus riparius

The combined effects of a pesticide and predation risk on sublethal endpoints in the midge Chironomus riparius were investigated using a combination of predator-release kairomones from common carp (Cyprinus carpio) and alarm substances from conspecifics together with the pesticide dimethoate. Midge larvae were exposed for 30 days to three sublethal dimethoate concentrations (0.01, 0.1 and 0.25 mg L(-1)) in the presence or absence of predator cues. Sublethal endpoints were analysed at different levels of biological organisation. Available energy reserves, enzyme biomarkers, feeding rate and life history endpoints were investigated. Three endpoints were significantly affected by the two highest dimethoate concentrations, i.e. AChE activity, age at emergence and emergence success, with a significant decrease in response after exposure to 0.25, 0.1 and 0.01 mg L(-1) dimethoate, respectively. Four sublethal endpoints were significantly affected by predator stress: Total protein content, GST activity and biomass decreased only in the presence of the predation risk, while AChE activity further decreased significantly in the presence of predation cues and effects on AChE of combined exposure were additive. From this study we can conclude that sublethal life history characteristics should be included in ecotoxicity testing as well as natural environmental stressors such as predator stress, which might act additively with pollutants on fitness related endpoints.

Cholinesterases and neurotoxicity as highly sensitive biomarkers for an organophosphate insecticide in a freshwater gastropod (Chilina gibbosa) with low sensitivity carboxylesterases

In the Upper Valley of Río Negro and Río Neuquén in Argentina, agriculture represents the second most important economic activity. Azinphos-methyl has been found in water from this region throughout the year at a maximum concentration of 22.48 μg L(-1) during the application period. Toxicological studies on local non-target species have been performed mostly on vertebrates, while mollusks, which could be more sensitive, have not been studied so far. This work aims to characterize cholinesterase (ChE) and carboxilesterase (CE) activities of Chilina gibbosa, a freshwater gastropod native to southern Argentina and Chile. These enzymes, together with neurotoxicity signals, are evaluated herein after as sensitive biomarkers of exposure to azinphos-methyl at environmentally relevant concentrations. Effects of azinphos-methyl on antioxidant defenses: glutathione (GSH), catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST) are also studied in order to complete a set of biomarkers with different sensitivity and specificity, to propose C. gibbosa as a sentinel species. The highest specific activity was obtained with acetylthiocholine as substrate, followed by propionylthiocholine (83% in comparison to acetylthiocholine) and butyrylthiocholine (19%).The lowest Km and the highest efficiency for ChE were obtained with acetylthiocholine. Regarding CEs activities, a higher efficiency was obtained with p-nitrophenyl butyrate than with p-nitrophenyl acetate. Eserine produced significant inhibition of ChE activity (81% with 0.001 mM and 98% with 1mM) while iso-OMPA did not produce any significant effect on ChE. Our results show that C. gibbosa ChE is very sensitive to azinphos-methyl (CI50 0.02 μg L(-1)) while CEs are inhibited at higher concentrations (CI50 1,000 μg L(-1)). CEs have been reported to be more sensitive to OPs than ChEs in most of the aquatic invertebrates protecting the organisms from neurotoxic effects. In contrast, C. gibbosa, has ChE which are much more sensitive to azinphos-methyl than CEs and shows marked signs of neurotoxicity. Regarding antioxidant defenses, GSH levels were significantly increased by 0.02 and 20 μg L(-1) azinphos-methyl (80 and 103%, respectively), CAT activity was increased 85% only at 0.02 μg L(-1) and SOD and GST did not show any significant response. Since ChE activity, neurotoxicity signs, GSH and CAT are sensitive biomarkers of acute exposure to azinphos-methyl at environmental concentrations C. gibbosa could be included as sentinel species in monitoring programs of pesticide hazard in regions of Argentina and Chile.

Different effects of subchronic exposure to low concentrations of the organophosphate insecticide chlorpyrifos in a freshwater gastropod

Chlorpyrifos is an organophosphate insecticide used for pest control on a number of food crops in many parts of the world. In recent years, there has been an important decrease in the number of organisms of Planorbarius corneus. Since the presence of pesticides in the water can be one of the reasons for this decrease, it is very important to study the effect of subchronic exposure to environmental concentrations of pesticides on these organisms. The aim of the present work was to investigate different effects of the subchronic exposure to low concentrations of the organophosphate chlorpyrifos in P. corneus and the possibility to use these as biomarkers. To this end, we have exposed the organisms to 0.4 and 5 μg L(-1) of chlorpyrifos for 14 days and recorded the number of egg masses, the number of eggs per mass, the number of eggs without embryo, the time for hatching, and the % of hatching and survival. We have also determined the activities of cholinesterases, carboxylesterases and glutathione S-transferase in whole organism soft tissue and in the gonads. A 14 days exposure to 0.4 μg L(-1) caused an increase in the number of egg masses without eggs and a decrease in carboxylesterases measured with p-nitrophenyl butyrate. However the exposure to 5 μg L(-1) also caused an increase in the time for hatching, a decrease in the % of hatching and survival and also inhibition of cholinesterases and carboxylesterases with p-nitrophenyl acetate and butyrate. In contrast, the glutathione S-transferase has not been modified with the tested concentrations. We concluded that when P. corneus exposed to chlorpyrifos for 14 days, the CES determined with p-nitrophenyl butyrate proved to be the most sensitive biomarker. However, exposure to environmental concentrations showed a decrease in the reproduction ability which could cause a decrease in the number of organisms of this species.

Dimethoate affects cholinesterases in Folsomia candida and their locomotion--false negative results of an avoidance behaviour test

The main mode of action of organophosphate insecticides is to inhibit acetylcholinesterase (AChE), which causes neuromuscular paralysis leading ultimately to death. The collembolan Folsomia candida is an important and standard test species in ecotoxicology, where effects on avoidance behaviour are assessed. Being related to insects they represent potential targets of insecticides such as the organophosphate dimethoate. In the present study we exposed F. candida to dimethoate having 2 main aims: 1) to assess the ability of F. candida to avoid it, and 2) to assess its effect on the cholinergic synapses to explore the link. For the latter, several sub-steps were needed: a) to characterise the existing ChE types and b) assess ChE activity (via exposure in vitro and in vivo). No avoidance was observed within the tested concentration range (0-0.32-1-3.2-10-32 mg/kg), in fact an apparent "attraction" (more animals on the spiked side) was observed. As expected, there was a significant decrease of AChE activities (AChE being the main ChE type) with an increase of dimethoate dose (IC(50)=1.4 mg/kg). Further, post-exposure video records showed that organisms were still alive in the spiked soil but lacked the locomotion ability (immobilised). The AChE inhibition correlated positively with immobilisation. Hence, this observation also showed that the apparent "attraction" behaviour observed in the avoidance test is rather a direct effect of not being able to escape due to paralysis hence a false-negative avoidance. This can constitute a confounding factor in an avoidance behaviour test and consequent interpretation, which is not accounted for at present.

Single versus combined lethal effects of three agricultural insecticides on larvae of the freshwater insect Chironomus dilutus

Pesticides are currently regulated individually but are present in aquatic systems as mixtures of toxicants. In this study, the lethal effects of three agricultural insecticides--chlorpyrifos, imidacloprid and dimethoate--on Chironomus dilutus larvae were examined. Ninety-six-hour static bioassays were performed using single, binary, and ternary toxicant mixtures. The effects of the binary mixtures were investigated using the MIXTOX model to determine if the mixtures behaved additively, synergistically, or antagonistically. Dimethoate was much less toxic than chlorpyrifos or imidacloprid. Chlorpyrifos and dimethoate were not additive in mixture despite their common mode of action (MOA) and resulted in opposing effects (synergism and antagonism, respectively) when combined with imidacloprid. Synergism was observed in the ternary mixture. These results suggest that current mixture models based on MOA alone may not always be adequate in describing mixture effects, as in the current situation of mixtures with relatively few components. Other factors, such as water solubility, secondary MOA, and mechanisms of toxicity, should also be considered in future investigations of multichemical-mixture effects.

The relationship between total cholinesterase activity and mortality in four butterfly species

The relationship between total cholinesterase activity (TChE) and mortality in four butterfly species (great southern white [Ascia monuste], common buckeye [Junonia coenia], painted lady [Vanessa cardui], and julia butterflies [Dryas julia]) was investigated. Acute contact toxicity studies were conducted to evaluate the response (median lethal dose [LD50] and TChE) of the four species following exposure to the organophosphate insecticide naled. The LD50 for these butterflies ranged from 2.3 to 7.6 µg/g. The average level of TChE inhibition associated with significant mortality ranged from 26 to 67%, depending on the species. The lower bounds of normal TChE activity (2 standard deviations less than the average TChE for reference butterflies) ranged from 8.4 to 12.3 µM/min/g. As a percentage of the average reference TChE activity for the respective species, the lower bounds were similar to the inhibition levels associated with significant mortality, indicating there was little difference between the dose resulting in significant TChE inhibition and that resulting in mortality.

Gene expression responses linked to reproduction effect concentrations (EC 10,20,50,90) of dimethoate, atrazine and carbendazim, in Enchytraeus albidus

Background

Molecular mechanisms of response to pesticides are scarce and information on such responses from soil invertebrates is almost inexistent. Enchytraeus albidus (Oligochaeta) is a standard soil ecotoxicology model species for which effects of many pesticides are known on survival, reproduction and avoidance behaviour. With the recent microarray development additional information can be retrieved on the molecular effects.

Methodology/Principal Findings

Experiments were performed to investigate the transcription responses of E. albidus when exposed to three pesticides – dimethoate (insecticide), atrazine (herbicide) and carbendazim (fungicide) – in a range of concentrations that inhibited reproduction by 10%, 20%, 50% and 90% (EC₁₀, EC₂₀, EC₅₀ and EC₉₀, respectively). The goal of this study was to further identify key biological processes affected by each compound and if dose-related. All three pesticides significantly affected biological processes like translation, regulation of the cell cycle or general response to stress. Intracellular signalling and microtubule-based movement were affected by dimethoate and carbendazim whereas atrazine affected lipid and steroid metabolism (also by dimethoate) or carbohydrate metabolism (also by carbendazim). Response to DNA damage/DNA repair was exclusively affected by carbendazim.

Conclusions

Changes in gene expression were significantly altered after 2 days of exposure in a dose-related manner. The mechanisms of response were comparable with the ones for mammals, suggesting across species conserved modes of action. The present results indicate the potential of using gene expression in risk assessment and the advantage as early markers.

In situ aquatic bioassessment of pesticides applied on rice fields using a microalga and daphnids

This study assessed the effects of episodic contamination on a drainage canal adjacent to an area of intensive rice production (Coimbra, Portugal). Four monitoring periods were considered [i) before herbicide application (day-14), ii) at the first application day (day 0), iii) 3 or 5 and iv) 6days after]. Each one consisted in three complementary evaluation lines: a) physico-chemical analyses, b) whole effluent toxicity (WET) assays with Pseudokirchneriella subcapitata, c) in situ bioassays to assess microalgae (P. subcapitata) growth, and the feeding rate and survival of Daphnia longispina and Daphnia magna. Study sites were located upstream, in a protected wetland (L1), and downstream, in the vicinity of rice fields (L2). Along with the application of agrochemicals, there was a general decrease of the water quality, especially in L2, due to nutrient and herbicide inputs. Herbicide peaks (on days 0, 5 and 6) in L2 water samples were recorded concomitantly or immediately after their application. Regarding the in situ bioassessment, the algae growth decrease from day 0 onwards in L1, whilst in L2 its inhibition was generally coherent with the decline of the water quality. Apparently, WET tests indicated that the limitation of nutrients could be affecting algae growth in L1, however, conclusions should be cautious. The feeding depression of daphnids occurred on days 0 and 5 for D. longispina and only on day 0 for D. magna, while significant reductions on survival were restricted to day 0 for both species. The impairments occurring on day 0 were linked to a potential increased toxicity driven by the ingestion of particle-bound herbicides and suspended particles. The feeding rate of daphnids provided an earlier indication of toxic impairments, though it is prompted the use of complementary endpoints and trophic levels in order to understand the cumulative effects due to various herbicide pulses.

Effects of imidacloprid exposure on Chironomus riparius Meigen larvae: linking acetylcholinesterase activity to behaviour

Imidacloprid (IMI) is an insecticide that interferes with the transmission of stimuli in the nervous system of insects. It is neurotoxic by mimicking nicotine through its binding to the nicotinic acetylcholine receptor. In this work, experiments comprising 96 h exposure followed by 48 h in clean medium were conducted to evaluate the toxicity of IMI to Chironomus riparius and its potential recovery. Behavioural parameters and AChE activity were assessed. After 96 h exposure to IMI, AChE activity, and the behaviour parameters ventilation and locomotion were reduced. There were no signs of recovery after removal to clean water for 48 h. Ventilation behaviour was the most sensitive parameter and the one with the highest correlation to AChE activity. Despite the possibility that IMI might be having an indirect effect on AChE activity, the behavioural endpoint showed a higher sensitivity than the biochemical response itself. This work highlights the importance of linking parameters with ecological relevance at individual level (behavioural parameters) with biochemical responses, to unravel xenobiotics mode of action.

Laboratory measurements of biomarkers and individual performances in Chironomus xanthus to evaluate pesticide contamination of sediments in a river of southeastern Brazil

This study aimed at evaluating biomarkers, individual and population responses in the native Chironomus xanthus to assess the toxicity of pesticide-contaminated sediments from the Monjolinho River (Southeast Brazil). We measured cholinesterase (ChE) and glutathione S-transferase activities (GST), as biomarkers and survival, individual growth and adult emergence, as individual performances. There was no response of the ChE activity and a tendency to decreased GST activity in contaminated sites, but this was generally not statistically significant. Therefore, there was no association of the biomarker responses with exposure to sediment containing pesticides. In contrast, ash free dry mass was significantly increased and male emergence was decreased in C. xanthus exposed to the same sediments. In conclusion, the selected biomarkers were not sensitive and specific enough to detect and anticipate effects of pesticide contamination at the levels measured in the study area. Nevertheless, individual performances alterations pointed to potential pollution problems and possible ecological consequences.

Cholinesterase and glutathione-S-transferase activities in freshwater invertebrates as biomarkers to assess pesticide contamination

Studies investigating the use of biomarkers in pesticide risk assessment have greatly increased in recent years; however, issues concerning the ecological meaning of enzymatic responses have proved controversial. Ideally a good biomarker response should be modulated by the environmental contaminants alone and demonstrate a predictable behavior towards certain types of toxins. As these premises are rarely observed, the present study aims to outline research that has contributed to an understanding of the behavior of two widely used biomarkers, cholinesterase and glutathione-S-transferase, describing environmental and biotic factors that affect their response in freshwater invertebrates. Studies were performed in the main classes of aquatic invertebrates with these biomarkers and conclusions were reached concerning their behavior towards the main classes of pesticides. Links between biomarker responses and conventional endpoints were evaluated so that ecological relevance could be attributed to enzymatic responses. Toxicity of mixtures was investigated, and cases of synergism and antagonism were pointed out as factors changing the expected toxicity of aquatic systems and leading to misinterpretations of biomarker responses. Finally, the use of biomarkers as a tool for biomonitoring and in situ assays was investigated, with discussion of advantages and disadvantages of their use.

Effects of triclosan on zebrafish early-life stages and adults

BACKGROUND, AIM AND SCOPE

The biocide triclosan (TCS) is commonly used in personal care, acrylic, plastic, and textiles products. TCS has been detected in surface water in several countries, and its ecological impact is largely unknown. In this work, the toxicity of TCS in zebrafish (Danio rerio), embryos and adults was studied. Several lethal and sub-lethal endpoints were analysed in organisms exposed to TCS such as mortality, embryo development and behaviour, hatching, micronuclei and biochemical markers (cholinesterase (ChE), glutathione S-transferase (GST) and lactate dehydrogenase (LDH)).

MATERIALS AND METHODS

Embryo/larvae assay followed the OECD guideline on Fish Embryo Toxicity Test. Embryos were exposed at nominal concentrations of 0.1, 0.3, 0.5, 0.7 and 0.9 mg/l of TCS for 6 days and were inspected daily with the help of a stereomicroscopy for mortality, developmental parameters (otolith formation, eye and body pigmentation, somite formation, heart beat, tail circulation, detachment of the tail-bud from the yolk sac) and hatching. A similar test was run to obtain larvae for ChE, GST and LDH analysis. The adult test followed the OECD Guideline TG 203 in semi-static conditions. Adult zebrafish of similar length and age were exposed to nominal concentrations of 0.1, 0.2, 0.3, 0.4 and 0.5 mg/l of TCS for 96 h and were inspected daily for mortality and behaviour alterations. A second test was run to obtain organs for biomarkers analysis: Heads, muscles and gills were isolated and snap-frozen in eppendorfs and used for ChE, LDH and GST determinations, respectively. Adult zebrafish testing also comprised a third test for micronucleus analysis in which the nominal concentrations of 0, 0.175 and 0.350 mg/l were used. Peripheral blood was obtained by cardiac puncture and used for the analysis.

RESULTS

TCS showed acute toxicity for embryo/larvae (96 h LC(50) = 0.42 mg/l) and delayed hatching. Moreover, embryo toxicity was evident: Delay on the otolith formation and eye and body pigmentation were found, and malformations were also evident, including spine malformations, pericardial oedema and undersize. Biomarkers levels were affected: ChE and LDH activity were increased in larvae exposed to 0.25 mg/l, and GST activity was increased in larvae exposed to 0.25 and 0.35 mg/l. TCS also demonstrated acute toxicity to adult zebrafish (96 h LC(50) = 0.34 mg/l). However, TCS did not change biomarkers levels and did not elicit a micronucleus in adults.

DISCUSSIONS

Despite the fact that similar 96 h LC(50) values have been found for D. rerio embryos and adults (0.42 and 0.34 mg/l, respectively), the embryo assay was much more informative, showing important effects at several levels, including teratogenic response, hatching delay and alteration of biomarker levels. TCS does not seem to be genotoxic for adult fish or to interfere with biomarkers levels at the concentrations tested.

CONCLUSIONS

TCS has deleterious effects on zebrafish adults and during early stages, (including embryotoxicity, hatching delay and alterations of biomarkers levels). The range of endpoints used on the embryo test allows an integrated analysis that contributes to a better understanding of the toxicity and mode of action of TCS.

RECOMMENDATIONS AND PERSPECTIVES

Future works should focus on a deeper investigation of TCS modes of action on zebrafish early-life stages. As embryo testing was revealed to be so informative, a refinement of the test could be made, including other endpoints such as different biochemical markers as well as DNA microarrays to assess a gene expression level for the effect of exposure to TCS. In the perspective of risk assessment, these endpoints should be explored in order to assess their usefulness as early warning signs and links should be sought between these short-term tests and effects of long-term exposures as it is observed in more realistic scenarios.

Effects of azinphos-methyl exposure on enzymatic and non-enzymatic antioxidant defenses in Biomphalaria glabrata and Lumbriculus variegatus

Azinphos-methyl is an organophosphate insecticide used for pest control on a number of food crops in many parts of the world. The oligochaete Lumbriculus variegatus and pigmented and non-pigmented specimens of the gastropod Biomphalaria glabrata are freshwater invertebrates that have been recommended for contamination studies. Recently, it has been shown that L. variegatus worms exhibit a higher cholinesterase (ChE) activity and a greater sensitivity to in vivo ChE inhibition by azinphos-methyl than pigmented B. glabrata snails. The aims of the present study were (1) to investigate if, in addition to its anticholinesterase action, azinphos-methyl has also pro-oxidant activity in L. variegatus and B. glabrata, and (2) to examine if species that are highly susceptible to the neurotoxic effects of organophosphates also suffer a greater degree of oxidative stress. Therefore, total glutathione (t-GSH) levels and activities of cholinesterase (ChE), superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glucose 6-phosphate dehydrogenase (G6PDH) were measured in the whole body soft tissue of organisms exposed for 48 and 96 h to a level of azinphos-methyl that produces 50% of inhibition on ChE. Results showed different patterns of antioxidant responses between the gastropods and the oligochaetes, and even between the two phenotypes of gastropods: (1) in exposed L. variegatus t-GSH levels increased and CAT and SOD activities decreased with respect to control organisms, (2) in pigmented gastropods, SOD decreased while CAT transiently diminished, and (3) in non-pigmented gastropods, SOD activity showed a biphasic response. GST and G6PDH were not altered by azinphos-methyl exposure. Of note, t-GSH levels were 4-fold times higher in L. variegatus than in both phenotypes of B. glabrata. This may suggest that GSH could play a more important role in antioxidant defense in L. variegatus than in B. glabrata.