Endosulfan acute toxicity in Bufo bufo gills: ultrastructural changes and nitric oxide synthase localization

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

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

Gill Junction Injury and Microbial Disorders Induced by Microcystin-Leucine Arginine in Lithobates catesbeianus Tadpoles

Microcystin-LR (MC-LR) is widely present in waters around the world, but its potential toxic effects and mechanisms on amphibian gills remain unknown. In the present study, tadpoles (Lithobates catesbeianus) were exposed to environmentally realistic concentrations of 0.5, 2 μg/L MC-LR, and 0 μg/L MC-LR (Control) for 30 days with the objective to unveil the impairment of gill health. The lysozyme was downregulated, while pattern recognition receptors and complement and adaptive immune processes were upregulated and the ability of gill supernatant to inhibit pathogenic bacteria decreased in the 0.5 and 2 μg/L MC-LR groups. The transcriptions of epithelial barrier components (e.g., CLDN1) were significantly decreased in MC-LR-exposed gills, while the gill content of lipopolysaccharide (LPS) endotoxins and the transcriptions of downstream responsive genes (e.g., TLR4 and NF-κB) were concurrently increased. In addition, the number of eosinophils and the expression of pro-inflammatory cytokines (e.g., IL-1β and TNF-α) were increased. These results imply that exposure of tadpoles to low environmentally concentrations of MC-LR leads to inflammation, increased permeability, and a reduced ability to inhibit pathogenic bacteria. The epithelial cells of inner gill filaments increased and transcriptions of hypoxic stress genes (e.g., HIF-1α, FLT1, and SERPINE1) were upregulated within the exposed group. As a consequence, exposure to MC-LR may lead to hypoxic stress. MC-LR exposure also drove gill microbiota to a dysbiosis. The relative abundance of Elizabethkingia was positively correlated with content of LPS and transcriptions of NF-κB and TNF-α. Overall, this study presents the first evidence about the pronounced impacts of MC-LR exposure on gills of amphibians, highlighting the susceptibility of early developing tadpoles to the environmental risks of MC-LR.

Imperative role of electron microscopy in toxicity assessment: A review

Electron microscope (EM) was developed in 1931 and since then microscopical examination of both the biological and non-biological samples has been revolutionized. Modifications in electron microscopy techniques, such as scanning EM and transmission EM, have widened their applicability in the various sectors such as understanding of drug toxicity, development of mechanism, criminal site investigation, and characterization of the nano-molecule. The present review summarizes its role in important aspects such as toxicity assessment and disease diagnosis in special reference to SARS-COV2. In the biological system, EM studies have elucidated the impact of toxicants at the ultra-structural level in various tissue in conformity to physiological alterations. Thus, EM can be concluded as an important tool in toxicity assessment and disease prognosis.

Evaluation of the potential teratogenic and toxic effect of the herbicide 2,4-D (DMA® 806) in bullfrog embryos and tadpoles (Lithobates catesbeianus)

The objective of this work was to evaluate the potential teratogenic and toxic effect of the herbicide 2,4-D (DMA® 806) on bullfrog embryos and tadpoles (Lithobates catesbeianus). We used the FETAX (Frog Embryo Teratogenesis Assay Xenopus) assay for embryos, and for tadpoles, we used acute (96 h) and chronic (49 days) toxicity tests and evaluated aspects of healthiness, hematology, and histopathology. The LC_50-144h (Median Lethal Concentration), EC_50-144h (Median Effective Concentration), MCIG (Minimum Concentration to Inhibit Growth) and TI (Teratogenic Index) for embryos were 792 mg/L, 593 mg/L, 150 mg/L of 2,4-D (DMA) and 1.34, respectively. For tadpoles, the LC_50-96h was 700 mg/L of 2,4-D (DMA) and chronic test indicated an inflammatory process and erythrocytosis (with possible polycythemia), with consequent reduction of the spleen. This demonstrates physiological stress probably due to dehydration, which can be proven by the gill tufts widening intercellular space and gill tuft fusions. We also found injuries to the kidneys and skin of the animals even in the lowest concentration tested. Our results indicated that this pesticide is minimally teratogenic and has a low toxicity on L. catesbeianus embryos and tadpoles, but it can inhibit embryo growth in concentrations lower than those tested in this study. We hypothesized that the herbicide 2,4-D (DMA® 806) may be a respiratory allergen for L. catesbeianus tadpoles and recommend precautionary measures for prolonged exposure of aquatic organisms to this pesticide.

Chronic exposures to fungicide pyrimethanil: multi-organ effects on Italian tree frog (Hyla intermedia)

Amphibian habitats are easily contaminated by several pollutants, and in agricultural landscapes the likely exposure scenario is represented by pesticides. Many of these substances are known or suspected to act as endocrine disrupting chemicals (EDCs). The goal of the present study was to assess the effects of pyrimethanil, a common-used but also overlooked fungicide, on liver, kidney and gonadal differentiation of Hyla intermedia. Through a multi-organ evaluation, we demonstrated that a long term exposure to two environmentally relevant concentrations of pyrimethanil (5 and 50 µg/L) elicits a range of toxic responses. First we showed that pyrimethanil induces underdevelopment of ovaries and interferes with normal sexual differentiation, thus revealing the endocrine disruption potential of this fungicide. Moreover we revealed that all considered organs are seriously affected by this fungicide and both necrosis and apoptosis contribute to the histological response. This is the first report on the effects of pyrimethanil on gonads, liver and kidney histology of a non-model species and it demonstrates that the hazardous properties of this fungicide can result from several pathological processes affecting different key compartments of amphibian.

Effect of acute salinity stress on ion homeostasis, Na+/K+-ATPase and histological structure in sea cucumber Apostichopus japonicus

Background

Sea cucumbers (Apostichopus japonicus) are an imperiled fauna exposed to a variety of environmental condition such as salinity and studies are urgently needed to assess their effects to guide aquaculture efforts. The effects of acute salinity stress on coelomic fluid osmotic pressure, ion concentrations, the activity of Na⁺/K⁺-ATPase in respiratory trees and the histological variations were measured to evaluate the salinity tolerance of sea cucumbers.

Results

Significant correlations in osmotic pressure were observed between coelomic fluid and ambient environmental salinity. In coelomic fluid, Na⁺ concentration was observed fluctuated during salinity 18 psu and the inflection point presented at the 6 h. The Na⁺/K⁺-ATPase activity in respiratory trees indicated the “U-shaped” fluctuant change and the change trend was opposite with the Na⁺ concentration. The ions (K⁺, Cl⁻) concentration decreased and showed the same tendency at salinity 40 psu with salinity 18 psu. The total coelomocytes counts and phagocytosis of coelomic fluid Na⁺/K⁺-ATPase activity indicated fluctuating changes under different salinity stress. Histological variation revealed a negative relation between decreasing salt concentration and tissue integrity. Tissue damages were significantly observed in intestines, muscles and tube feet under low salinity environment (18, 23 and 27 psu). The connective tissue in intestines of A. japonicus exposed to 18 and 23 psu damaged and partly separated from the mucosal epithelium. The significant variations occurred in tube feet, which presented the swelling in connective tissue and a fracture in longitudinal muscles under low salinity (18 psu). The morphological change of tube feet showed the shrinkage of connective tissue under high salinity (40 psu). The amount of infusoria in the respiratory trees decreased or even disappeared in salinity treatment groups (18 and 23 psu).

Conclusion

The results inferred that osmoconformity and ionoregulation were seen in sea cucumbers, which contributed to understand the salinity regulatory mechanisms of A. japonicus under acute salinity stress.

Toxicity of atrazine, glyphosate, and quinclorac in bullfrog tadpoles exposed to concentrations below legal limits

This work sought to ascertain survival and possible changes in levels of glycogen, triglycerides, total lipids, cholesterol, protein, and lipid peroxidation in gills, liver, and muscle of bullfrog tadpoles (Lithobates catesbeianus) exposed to low concentrations of atrazine (2.5 μg L(-1)), glyphosate (18 μg L(-1)), and quinclorac (0.025 μg L(-1)) at laboratorial conditions. Tadpoles showed a reduction of glycogen and triglyceride in all organs and an increase in lipid peroxidation (LPO) compared with control animals. Total lipid in gills and muscle increased in exposure to atrazine, and gills alone in exposure to glyphosate, but decreased in gills, liver, and muscle after quinclorac. Cholesterol increased in gills and liver after atrazine, in gills and muscle after glyphosate, and decreased in liver after quinclorac. Total protein in gills decreased after exposure to all herbicides, increased in muscle after atrazine, and in liver and muscle after quinclorac. These findings show that at concentrations of these herbicides tested can lead to an increase in energy expenditure to maintain homeostasis and survival of these animals despite the increase in lipid peroxidation levels in all organs analyzed. Responses observed can be one of the factors responsible for the decline in the number of amphibians around the world.

Differential uptake of endosulfan in the South American toad under sublethal exposure

Agroecosystems are usually polluted with a wide variety of contaminants with pesticides being very frequently detected. Endosulfan, an organochlorine pesticide, has been shown to cause both lethal and sublethal effects on aquatic organisms such as amphibians and especially on its early developmental stages. In this context, the aim of this study was to evaluate the uptake of environmentally relevant concentrations of endosulfan and its correlation with differential sensitivity in the early development stages of the common South American toad, Rhinella arenarum. Embryos and larvae were exposed to sublethal concentrations of endosulfan for several periods of exposures. According to the developmental stage at which they were exposed, the uptake rate was different. Bioconcentration factors (BCFs) for embryos significantly decreased with exposure time and concentration (p < 0.05) reaching a BCF of ≤1679 for embryos at 96 h of exposure to 0.001 mg endosulfan L(-1). BCFs for larvae significantly increased with exposure time (p < 0.05) obtaining a maximum of 40 at 504 h. In our previous study, we reported that embryos were less sensitive to the effects of endosulfan than larvae, which is in line with the main tendency of embryos to bioconcentrate endosulfan as observed in this study.

Effects of low dose endosulfan exposure on brain neurotransmitter levels in the African clawed frog Xenopus laevis

Understanding the impact of pesticides in amphibians is of growing concern to assess the causes of their decline. Among pesticides, endosulfan belongs to one of the potential sources of danger because of its wide use and known effects, particularly neurotoxic, on a variety of organisms. However, the effect of endosulfan was not yet evaluated on amphibians at levels encompassing simultaneously brain neurotransmitters and behavioural endpoints. In this context, tadpoles of the African clawed frog Xenopus laevis were submitted to four treatments during 27 d: one control, one ethanol control, and two low environmental concentrations of endosulfan (0.1 and 1 μg L(-1)). Endosulfan induced a significant increase of brain serotonin level at both concentrations and a significant increase of brain dopamine and GABA levels at the lower exposure but acetylcholinesterase activity was not modified by the treatment. The gene coding for the GABA transporter 1 was up-regulated in endosulfan contaminated tadpoles while the expression of other genes coding for the neurotransmitter receptors or for the enzymes involved in their metabolic pathways was not significantly modified by endosulfan exposure. Endosulfan also affected foraging, and locomotion in links with the results of the physiological assays, but no effects were seen on growth. These results show that low environmental concentrations of endosulfan can induce adverse responses in X. laevis tadpoles. At a broader perspective, this suggests that more research using and linking multiple markers should be used to understand the complex mode of action of pollutants.

Endosulfan induces COX-2 expression via NADPH oxidase and the ROS, MAPK, and Akt pathways

Endosulfan (1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenebismet-hylene) is correlated with endocrine disruption, reproductive, and immune dysfunctions. Recently, endosulfan was shown to have an effect on inflammatory pathways, but its influence on cyclooxygenase-2(COX-2) expression is unclear. This study investigated the effects of COX-2 and molecular mechanisms by endosulfan in murine macrophage RAW 264.7 cells. Endosulfan significantly induced COX-2 protein and mRNA levels, as well as COX-2 promoter-driven luciferase activity and the production of prostaglandin E2, a major COX-2 metabolite. Transfection experiments with several human COX-2 promoter constructs revealed that endosulfan activated NF-κB, C/EBP, AP-1, and CREB. Moreover, Akt and mitogen-activated protein kinases (MAPK) were significantly activated by endosulfan. Moreover, endosulfan increased production of the ROS and the ROS-producing NAPDH-oxidase (NOX) family oxidases, NOX2, and NOX3. Endosulfan-induced Akt/MAPK pathways and COX-2 expression were attenuated by DPI, a specific NOX inhibitor, and the ROS scavenger N-acetylcysteine. These results demonstrate that endosulfan induces COX-2 expression via NADPH oxidase, ROS, and Akt/MAPK pathways. These findings provide further insight into the signal transduction pathways involved in the inflammatory effects of endosulfan.

Concentration, distribution, and human health risk assessment of endosulfan from a manufacturing facility in Huai'an, China

Endosulfan concentrations and its distribution in air, soil, sediment and foodstuffs in the area surrounding a production facility in Huai'an, China were investigated because of its threats to the environment and human health. Air concentrations for endosulfan Ι, endosulfan II and endosulfan sulfate measured in this study were several orders of magnitude higher than those reported previously for this region. Surface soil concentration ranges of endosulfan I, endosulfan II, and endosulfan sulfate were greater than in sediment. Endosulfan II was the greatest contributor to total endosulfan concentrations in both surface sediment and soil followed by endosulfan sulfate and endosulfan Ι. However, a different concentration profile was observed in fish and crop samples, with endosulfan sulfate having the highest concentration followed by endosulfan I and endosulfan II. The concentration of Σendosulfans (endosulfans Ι and II) in soil decreased rapidly with increasing distance from the plant by a factor of 10 within 45 km. Trace amounts of Σendosulfans were observed in deep soil layers which implied that these compounds are transported through the leaching of pore water in soil. This demonstrated that emissions from the manufacturing facility can lead to ground water contamination in the area near the plant. A screening level human health risk assessment of Σendosulfans based on the worst-case scenario was performed for people living in the vicinity of the manufacturing facility. The hazard indices were at least 2 orders of magnitude of <1, indicating no adverse health effects are likely to occur at current exposure levels, and the risk to human health is generally acceptable.

Toxicity of endosulfan on embryo-larval development of the South American toad Rhinella arenarum

Endosulfan is a widely used pesticide despite its extreme toxicity to a variety of taxa and its worldwide ban. The aim of the present study was to evaluate the acute and chronic toxicity of endosulfan on the embryonic-larval development of the common South American toad Rhinella arenarum. The results showed that lethal and sublethal effects increased with concentration and exposure time. The sensitivity to endosulfan increased during the larval period, the complete operculum stage (S.25) being the most sensitive (504-h median lethal concentration [LC50] = 0.01 mg endosulfan/L; 10% lethal concentration [LC10] = 0.004 mg endosulfan/L). Endosulfan exposure caused morphological abnormalities such as general underdevelopment, edema, gill malformations, and cellular dissociation as well as neurotoxicity. Our results also showed that larvae exposed to concentrations of 0.005 mg endosulfan/L and 0.01 mg endosulfan/L completed metamorphosis earlier than controls, but with underdevelopment. The 240-h teratogenic index was 6.13, implying a high risk for embryos to be malformed in the absence of significant embryonic lethality. Because the hazard quotients for chronic exposure were over 1, the level of concern value and toxicity endpoints obtained in the present study for R. arenarum occurred at concentrations lower than the levels of endosulfan reported in the environment, this pesticide should be considered a potential risk for this species.

Toxicity of endosulfan to tadpoles of Fejervarya spp. (Anura: Dicroglossidae): mortality and morphological deformities

The acute toxicity of endosulfan to the tadpoles of three coexisting species of the anuran genus Fejervarya revealed 96 h LC50 values of 46.715, 6.596, and 3.015 μg l(-1) for Fejervarya sp.1, F. teraiensis and Fejervarya sp.2, respectively. Toxicity of endosulfan was also tested at the sublethal concentrations of 5 and 0.5, and 0.3 and 0.03 μg l(-1) (c 10 and 1% of their respective 96 h LC50 values) in Fejervarya sp.1 and Fejervarya sp.2, and 0.35 and 0.18 μg l(-1) (c 5 and 2.5% of 96 h LC50) in F. teraiensis. Endosulfan was observed to cause mortality at concentrations as low as c 1, 2.5 and 10% of their respective 96 h LC50 values in Fejervarya sp.2, F. teraiensis, and Fejervarya sp.1. Such vulnerabilities are likely to have implications for the survival of natural populations of these co-existing species as well as other anurans present in the study area where pesticide use is relatively high in the tea plantations. Morphological deformities caused by endosulfan comprised failure to develop one or both forelimb in Fejervarya sp.1 and F. teraiensis, stunted hindlimb growth in Fejervarya sp.1, and axial malformation in Fejervarya sp.1 and Fejervarya sp.2. Fore- and hind-limb deformities were likely to have occurred due to the impairment of thyroid metabolism by endosulfan. These effects illustrate the threat that continued endosulfan use poses to natural populations of anuran amphibians.

Exposure and post-exposure effects of endosulfan on Bufo bufo tadpoles: morpho-histological and ultrastructural study on epidermis and iNOS localization

Endosulfan is a persistent organic pollutant (POP) that has lethal and sublethal effects on non-target organisms, including amphibians. In a laboratory study, we investigated direct and post-exposure effects of endosulfan on Bufo bufo tadpoles. For this purpose we exposed the tadpoles to a single short-term contamination event (96 h) at an environmentally-realistic concentration (200 μg endosulfan/L). This was followed by a recovery period of 10 days when the experimental animals were kept in pesticide-free water. The endpoints were assessed in terms of mortality, incidence of deformity, effects on behavior, and the morpho-functional features of the epidermis. We found that a short-term exposure to the tested concentration of endosulfan did not cause mortality but induced severe sublethal effects, such as hyperactivity, convulsions, and axis malformations. Following relocation to a pesticide-free environment, we noted two types of response within the experimental sample, in terms of morphological and behavioral traits. Moreover, by using both ultrastructural and a morpho-functional approach, we found that a short-term exposure to endosulfan negatively affected the amphibian epidermis. We also observed several histo-pathological alterations: increased mucous secretion, an increase in intercellular spaces and extensive cell degeneration, together with the induction of an inducible isoform of nitric oxide synthase (iNOS). Following the post-exposure period, we found large areas of epidermis in which degeneration phenomena were moderate or absent, as well as a further increase in iNOS immunoreactivity. Thus, after 10 days in a free-pesticide environment, the larval epidermis was able to partially replace elements that had been compromised due to a physiological and/or a pathological response to the pesticide. These results highlight the need for both exposure and post-exposure experiments, when attempting to assess pollutant effects.

Lethal and sublethal effects of three insecticides on two developmental stages of Xenopus laevis and comparison with other amphibians

It has been suggested that Xenopus laevis is less sensitive than other amphibians to some chemicals, and therefore, that the Frog Embryo Teratogenesis Assay-Xenopus (FETAX) may have limited use in risk assessments for other amphibians. However, comparisons are based mostly on results of FETAX, which emphasizes embryos. Larval X. laevis may be more sensitive to chemicals than embryos and may serve as a better life stage in risk assessments. The present study was conducted to determine the lethal and sublethal effects of 3 insecticides (malathion, endosulfan, and α-cypermethrin) on X. laevis embryos and larvae and to compare toxicity of X. laevis with that of other amphibians. All 3 insecticides have different modes of action, and they caused mortality, malformations, and growth inhibition in both developmental stages. Compared with embryos, larvae were more sensitive to endosulfan and α-cypermethrin but not to malathion. Xenopus laevis larvae had low sensitivity to endosulfan, median sensitivity to malathion, and high sensitivity to α-cypermethrin/cypermethrin relative to other larval amphibians. Our results suggest that X. laevis larvae may generate more protective toxicity estimates in risk assessments than embryos. Xenopus laevis may have limited use in evaluating risk of organochlorine insecticides to other amphibians but may provide useful toxicity thresholds for pyrethroid and perhaps organophosphorus insecticides.

Effects of salinity stress on Bufo balearicus and Bufo bufo tadpoles: Tolerance, morphological gill alterations and Na(+)/K(+)-ATPase localization

Freshwater habitats are globally threatened by human-induced secondary salinization. Amphibians are generally poorly adapted to survive in saline environments. We experimentally investigated the effects of chronic exposure to various salinities (5%, 10%, 15%, 20%, 25%, 30% and 35% seawater, SW) on survival, larval growth and metamorphosis of tadpoles from two amphibian populations belonging to two species: the green toad Bufo balearicus and the common toad Bufo bufo. In addition, gill morphology of tadpoles of both species after acute exposure to hypertonic conditions (20%, 25%, and 30% SW) was examined by light and electron microscopy. Tadpoles experienced 100% mortality above 20% SW in B. balearicus while above 15% SW in B. bufo. We detected also sublethal effects of salinity stress on growth and metamorphosis. B. bufo cannot withstand chronic exposure to salinity above 5% SW, tadpoles grew slower and were significantly smaller than those in control at metamorphosis. B. balearicus tolerated salinity up to 20% SW without apparent effects during larval development, but starting from 15% SW tadpoles metamorphosed later and at a smaller size compared with control. We also revealed a negative relation between increasing salt concentration and gill integrity. The main modifications were increased mucous secretion, detachment of external layer, alteration of epithelial surface, degeneration phenomena, appearance of residual bodies, and macrophage immigration. These morphological alterations of gill epithelium can interfere with respiratory function and both osmotic and acid-base regulation. Significant variations in branchial Na(+)/K(+)-ATPase activity were also observed between two species; moreover an increase in enzyme activity was evident in response to SW exposure. Epithelial responses to increasing salt concentration were different in the populations belonging to two species: the intensity of histological and ultrastructural pathology in B. bufo was greater and we noticed the appearance in exposed samples of the tubular vesicle cells (TVCs). Taken together, our results demonstrated that increased salinity of freshwater may give cause for concern and must be considered a stressor for amphibians as well as other pollutants.

Toxicity effect of dichlorvos on loach (Misgurnus anguillicaudatus) assessed by micronucleus test, hepatase activity analysis and comet assay

Pesticides and other chemicals at environmental concentrations often have detrimental effects. Many aquatic species are particularly threatened because of their susceptibility and also because water environment are often polluted. This study preliminarily evaluated the toxicity effect of dichlorvos (DDVP) on loach ( Misgurnus anguillicaudatus) using the methods of micronucleus (MN) test, hepatase activity and comet assay. The tested results showed that indeed very little DDVP had strong toxicity effect on loach and its 50% lethal concentration (LC50) at 24 h, 48 h and 96 h was 8.38 μg l−1, 7.168 μg l−1 and 6.411 μg l−1, respectively; The glutamic-pyruvic transaminase (GPT) and glutamic–oxalacetic transaminase (GOT) activity of loach liver decreased; meanwhile, the GPT and GOT activity of loach serum, the MN rate (‰) and three comet parameters of tested fish increased with the increase in the treatment concentration and treatment time of DDVP, and there was significant difference between control group and each treatment group ( p < 0.05). These results suggested that DDVP residues might become toxic chemical contaminant in environment and would threaten aquatic and other organisms.

Endosulfan effects on Rana dalmatina tadpoles: quantitative developmental and behavioural analysis

Endosulfan is an organochlorine pesticide that was recently labeled as a persistent organic pollutant, but it is still widely employed, particularly in developing countries. The goal of this study is to evaluate the acute (LC(50)) and chronic effects (developmental and behavioural traits) of this insecticide on Rana dalmatina tadpoles after exposure to ecologically relevant concentrations (0.005, 0.01, and 0.05 mg/L) by applying video-tracking techniques to evaluate the quantitative effect of endosulfan on amphibian behavioural patterns. The 96 h LC(50) value was 0.074 mg endosulfan/L. Tadpoles chronically exposed to 0.01 and 0.05 mg endosulfan/L underwent high mortality rate, decreased larval growth, delayed development, and increased incidence of malformations, and they did not reach metamorphosis by the end of the experiment. Moreover, tadpoles exposed to these concentrations exhibited several abnormalities in swimming patterns, such as shorter distance moved, swirling, resting, and unusual use of space. The exposure to 0.005 mg endosulfan/L did not cause any significant effects on behaviour, larval growth, or development, but we observed a significant decrease in both survival and time to metamorphosis. We showed that developmental abnormalities are dose-dependent and that the pesticide effects could differ depending on the endosulfan concentration and the species tested. We also validated the hypothesis that behavioural analysis, along with the use of new analytical methods, could be a useful tool in amphibian ecotoxicological studies.

Effects of a sublethal pesticide exposure on locomotor behavior: a video-tracking analysis in larval amphibians

Organochlorine pesticides such as endosulfan have been shown to have both lethal and sublethal effects on amphibians. In this context, behavioral endpoints have proved their usefulness in evidencing impacts of such chemicals at environmental concentrations that do not necessarily cause mortality. The recent development of video-tracking technologies now offers the possibility of accurately quantifying locomotor behaviors. However, these techniques have not yet been applied to evaluating the toxicity of pesticides in amphibians. We therefore aimed at determining the potential toxicity of endosulfan on endpoints associated with locomotion after short-term environmental endosulfan exposure in Rana temporaria tadpoles and at using these data as warning systems for survival alterations after a longer exposure. To this end, we analyzed video-tracks of 64 tadpoles (two pesticide treatments: 5 and 50 μg L(-1), one control and one solvent-control) with Ethovision XT 7 software. The highest endosulfan concentration had a significant effect on all four behavioral endpoints. Contaminated tadpoles traveled shorter distances, swam less often, at a lower mean speed, and occupied a less peripherical position than control tadpoles. The lowest endosulfan concentration had similar but lower effects, and did not affect mean speed during swimming. Survival was reduced only after a long-term exposure to endosulfan and was associated with short-term behavioral dysfunctions. These results show that endosulfan strongly affects the behavioral repertory of amphibian tadpoles, but in different ways depending on concentration, thus suggesting that the pesticide has complex modes of action. Given the importance of locomotion and space use in tadpole success in their aquatic environment, these results confirm the toxic action of endosulfan. By highlighting effects before mortality markers, video-tracking systems also show their potential as sentinels of sublethal effects of pesticides.

Using sets of behavioral biomarkers to assess short-term effects of pesticide: a study case with endosulfan on frog tadpoles

Pesticides and other chemicals often have detrimental effects at environmental concentrations. Many amphibian species are particularly threatened because of their susceptibility but also because wetlands are often polluted. Behavioral assessments of toxicity have the advantage of showing sublethal effects but quantitative measures at varied scales of integrations are rarely considered together. In this study, we aimed at showing that these behavioral endpoints could be differently affected across time and concentrations, and be biomarkers of toxicity. To this end, we tested the effects of an organochlorine pesticide (endosulfan) on amphibians during a standard 96 h test. We evaluated possible lag effects in continuing the analyses after removal of the pesticide. The study was based on 240 tadpoles (4 pesticide treatments: 0.4, 3, 22, and 282 μg/l, 1 control and 1 solvent-control). Abnormal behaviors such as lying and swirling rapidly were exhibited only in the presence of the pesticide. Essential functions such as breathing and feeding were deeply affected by the pesticide: contaminated tadpoles breathed and fed less than control tadpoles. They also moved less and occupied a more central position in the aquariums in the presence of the pesticide. A higher mortality was only found at the highest concentration. These results suggest that endosulfan is toxic to amphibians at environmental concentrations. Behavioral markers showed potential as early warning systems. They should thus be used in complement to other markers to detect sublethal effects only a few days after application of the pesticide and at concentrations where mortality does not occur.

Acute and chronic effects of endosulfan on the haemato-immunological and histopathological responses of a threatened freshwater fish, spotted murrel, Channa punctatus

Two experiments, one short-term and one long-term, were conducted to elucidate the acute and chronic effects, respectively, of endosulfan exposure on the haemato-immunological and histopathological responses of Channa puncatatus. In the short-term study, fish were exposed to sublethal endosulfan (8.1 μg l(-1)) for 12, 24, 36, 48, 72 and 96 h. In the long-term study, fish were fed with normal diet and simultaneously either exposed to endosulfan (1.2 μg l(-1)) for 90 days or not. Results showed that the ascorbic acid levels in both the liver and the muscle decreased significantly (P < 0.05) by acute and chronic endosulfan exposure. The haemoglobin (Hb) level reduced significantly (P < 0.05) by 15.5% within 12 h of acute endosulfan exposure, further decreased by 25.8% after 24 h of exposure, however, thereafter the values increased and at the end of 72 h returned to normal levels. Almost similar trend was observed for the erythrocyte (RBC) count. The WBC count and the nitroblue tetrazolium (NBT) value showed a general increasing trend with increase in the duration of acute endosulfan exposure. The chronic exposure of C. punctatus to endosulfan significantly (P < 0.05) lowered the Hb level, RBC and WBC counts, NBT reduction value and the plasma parameters such as plasma protein, albumin (A) and globulin (G) compared with that of the control (except for A/G ratio). Endosulfan exposure also severely altered the liver histological structure. Overall results indicated that both short-term acute and long-term chronic endosulfan exposure had a significant impact on the haemato-immunological parameters and tissue histopathology of C. punctatus.

Phylogeny meets ecotoxicology: evolutionary patterns of sensitivity to a common insecticide

Pesticides commonly occur in aquatic systems and pose a substantial challenge to the conservation of many taxa. Ecotoxicology has traditionally met this challenge by focusing on short-term, single-species tests and conducting risk assessments based on the most sensitive species tested. Rarely have ecotoxicology data been examined from an evolutionary perspective, and to our knowledge, there has never been a phylogenetic analysis of sensitivity, despite the fact that doing so would provide insights into patterns of sensitivity among species and identify which clades are the most sensitive to a particular pesticide. We examined phylogenetic patterns of pesticide sensitivity in amphibians, a group of conservation concern owing to global population declines. Using the insecticide endosulfan, we combined previously published results across seven species of tadpoles and added eight additional species from the families Bufonidae, Hylidae, and Ranidae. We found significant phylogenetic signal in the sensitivity to the insecticide and in the existence of time lag effects on tadpole mortality. Bufonids were less sensitive than hylids, which were less sensitive than the ranids. Moreover, mortality time lags were common in ranids, occasional in hylids, and rare in bufonids. These results highlight the importance of an evolutionary perspective and offer important insights for conservation.

Current-use pesticide transport to Costa Rica's high-altitude tropical cloud forest

To gain insight into the atmospheric transport and deposition of organic contaminants in high-altitude forests in the humid tropics, pesticides were analyzed in air, water, and soil samples from Costa Rica. Passive samplers deployed across the country revealed annually averaged air concentrations of chlorothalonil, endosulfan, and pendimethalin that were higher in areas with intensive agricultural activities than in more remote areas. Atmospheric concentrations were particularly high in the intensively cultivated central valley. Only endosulfan and its degradation products were found in soils sampled along an altitudinal transect on the northern side of Volcano Turrialba, which is facing heavily cultivated coastal plains. Consistent with calculations of cold trapping in tropical mountains, concentrations of endosulfan sulfate increased with altitude. Pesticide levels in lake, creek, fog, and arboreal water samples from high-elevation cloud forests were generally below 10 ng · L(-1). Endosulfan sulfate was the most abundant pesticide in water, with concentrations ranging from 0.4 to 9.4 ng · L(-1). Its levels were highest in water sampled from bromeliads. Levels of total endosulfan in water are much lower than the reported median lethal concentration (LC50) value for acute toxicity of α-endosulfan to tadpoles. Although this suggests that the presence of pesticide might not have a direct impact on amphibian populations, the possibility of effects of chronic exposure to a mixture of substances cannot be excluded. Fog was relatively enriched in some of the analyzed pesticides, such as dacthal and chlorothalonil, and may constitute an important deposition pathway to high-altitude tropical cloud forest.

Toxicity of chlorpyrifos to larval Rana dalmatina: acute and chronic effects on survival, development, growth and gill apparatus

Chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)phosphorothioate] is a widely used non-systemic organophosphorus insecticide frequently detected in surface waters around the world. The goal of this study is to evaluate the acute and chronic effects of this insecticide on Rana dalmatina tadpoles. To assess the sensitivity of this species, the LC50 value (i.e. the concentration at which 50% of tadpoles die) was determined after 96 h. Our results showed that 5.174 mg L(-1) chlorpyrifos caused 50% mortality in tadpoles at Gosner stage 25. Chronic toxicity tests were also conducted to evaluate the sublethal effects of chlorpyrifos; tadpoles were exposed to three ecologically relevant concentrations (0.025, 0.05 and 0.1 mg L(-1)) in static renewal tests from Gosner stage 25 (tadpoles shortly after hatching) until completed metamorphosis (Gosner stage 46). No significant reduction was observed in survival, larval growth (mass), snout-vent length, stage development or number metamorphosed. In contrast, chlorpyrifos exhibited significant chronic toxic effects on larval development, manifested as the appearance of abnormalities, including tail flexure, skeletal and muscle defects in later stages of development in tadpoles exposed to all tested concentrations. We also evaluated the chronic effects of chlorpyrifos on gill morphology and ultrastructure. Tadpoles were sacrificed after 8 days and 30 days of exposure. Observations by both scanning (SEM) and transmission electron microscopy (TEM) showed considerable morphological and ultrastructural changes. The main gill effects recorded were mucous secretion, epithelium detachment and a degeneration phenomenon. Comparing these results with our previous findings, we demonstrate that the first effect of chlorpyrifos on R. dalmatina is gill alteration, thus supporting the role of a morphological approach in toxicological studies.

Oxidative stress in macrophages from spleen of Nile tilapia (Oreochromis niloticus) exposed to sublethal concentration of endosulfan

Endosulfan is a widely used insecticide with immunosuppressive or immunopotentiating effects which alters the immune response of fish. The effects of the acute exposure to endosulfan on a series of parameters of the innate immune response (IIR) of Nile tilapia (Oreochromis niloticus) were investigated-phagocytosis, production of oxygen reactive species, lipoperoxidation as well as spleen cell viability, relative spleen weight and splenocyte concentration-to fully document the effects of this pesticide on Nile tilapia. Juvenile Nile tilapia were exposed in vivo and for 96h to each one of nine concentrations of endosulfan in order to determine the pesticide's acute toxicity level and calculate the lethal concentration of endosulfan to these organisms (LC(50)=12,795ppb). Functional assays showed that endosulfan, at a level equivalent to (1)/(2)LC(50), altered some parameters of the spleen macrophages of Nile tilapia. Phagocytosis, production of oxygen reactive species, and lipoperoxidation increased significantly in exposed fish. Spleen cell viability and relative spleen weight were lower in exposed organisms compared to non-exposed ones, without reaching statistical significance. Splenocyte concentration was not altered in the present experimental conditions. Thus, in vivo exposure (7ppb) of juvenile organisms stimulated the phagocytic activity up to significant oxidative stress levels as indicated by the increased lipid peroxidation in plasma. It can be concluded that short exposure to low concentration of endosulfan stimulated macrophage activity but that there was no significant reduction in the structural parameters of the IIR.

Environmentally relevant concentrations of endosulfan impair development, metamorphosis and behaviour in Bufo bufo tadpoles

Endosulfan is a widely used organochlorine pesticide with well-documented neurotoxic effects in both humans and laboratory animals (mammals and fish). Neurotoxicity has been implied also in amphibians after short-term exposure to endosulfan. Little is known about effects of chronic exposure of endosulfan in amphibians. Previously, we examined the short-term toxicity of endosulfan in common toad (Bufo bufo) tadpoles and determined the LC50 value to 0.43 mg/L. In the present study, we investigated the effects of endosulfan on B. bufo tadpoles after chronic exposure to ecologically relevant concentrations. Tadpoles were exposed in a static renewal test, from shortly after hatching (Gosner stage 25) to completed metamorphosis, to 0.01, 0.05 and 0.1mg endosulfan/L (nominal). The exposure period lasted 43-52 days. Mortality, larval growth (mass), development (reached Gosner stage at various times and deformities presence), metamorphosis and behaviour (swimming activity) were monitored regularly over the entire course of larval development. Our results show that 0.05 and 0.1mg endosulfan/L caused impaired behaviour, prolonged time to metamorphosis, increased incidences of mouth and skeletal malformations as well as mortality, and reduced body weight (observed also at 0.01 mg/L) in B. bufo tadpoles. Behavioural effects occurred at exposure day 4, before any other effects occurred, indicating a neurotoxic effect. Endosulfan levels found in groundwater and surface water range from 0.1 to 100 microg/L and after extraordinary runoff events, concentrations exceed 0.5 mg/L in surface water. Our results indicate that endosulfan may negatively affect wild frog populations in agricultural areas.