Response of biomarkers in amphibian larvae to in situ exposures in a fruit-producing region in North Patagonia, Argentina

Biomarkers at the Individual and Biochemical Level: Effects of Pure and Formulated Lambda-Cyhalothrin in Boana pulchella Tadpoles (Duméril and Bibron, 1841)

We compared the effects of lambda-cyhalothrin as the pure active ingredient and as a formulated product (Zero®), on the larval stage of the autochthonous species Boana pulchella. We evaluated ecotoxicological endpoints, behavioral and developmental alterations, and the biochemical detoxifying, neurotoxic, and oxidative stress responses, covering a wide concentration range from environmental to high application levels. Both pyrethroid preparations displayed similar ecotoxicity (median lethal concentration of ~0.5 mg/L), with the lethal effect of Zero® being more pronounced than that of the active ingredient. Sublethal behavioral alterations in natatory activity were observed at 1000 times lower concentrations, indicating the ecological hazard of tadpole exposure to this pyrethroid at environmentally relevant concentrations. Biochemical endpoints in B. pulchella larvae showed significant responses to lambda-cyhalothrin in the ng/L range; these responses were different for the pure or the formulated product, and they were variable at higher concentrations. Principal components analysis confirmed the prevalence of biochemical responses as early endpoints at the lowest lambda-cyhalothrin concentrations; the Integrated Biomarker Response Index proportionally increased with pyrethroid concentration in a similar way for the pure and the formulated products. We conclude that lambda-cyhalothrin is of concern from an environmental perspective, with particular emphasis on autochthonous anuran development. The battery of biochemical biomarkers included in our study showed a consistent integrated biomarker response, indicating that this is a potent tool for monitoring impacts on amphibians. Environ Toxicol Chem 2024;00:1-11. © 2024 SETAC.

Recovery of Ceratophrys ornata tadpoles exposed to environmental concentrations of chlorpyrifos: evaluation of biomarkers of exposure

Chlorpyrifos (CPF) is one of the most widely used insecticides worldwide despite the fact that many authors have warned about its effects in non-target biota. The effects of CPF on anurans are well known, but the process of recovery from these effects after exposure is less explored. The aim of this study was to evaluate the duration of sublethal effects induced by environmental concentrations of CPF on Ceratophrys ornata tadpoles after exposure. The experimental design consisted of an exposure phase (96 h) in which tadpoles were individually exposed to three concentrations of CPF (0, 0.01 and 0.02 mg CPF/L) and a post-exposure phase (72 h) in which exposed tadpoles were transferred to CPF-free media. Individuals that survived the exposure phase to CPF showed neither long-term lethal effects nor long-term swimming alterations and altered prey consumption after being transferred to CPF-free media. No morphological abnormalities were observed either. However, at the end of both phases, tadpoles emitted shorter sounds with a higher dominant frequency than the tadpoles in the control group, i.e., the tadpoles did not recover their normal sounds. Thus, for the first time in this species, we have shown that effects on sounds should be prioritized as biomarkers of exposure, as they not only provide longer detection times after cessation of exposure, but also involve non-destructive methods. The following order of priority could be established for the selection of biomarkers that diagnose the health status of individuals and precede irreversible responses such as mortality: alterations in sounds > swimming alterations > prey consumption.

Hypothesis-driven dragging of transcriptomic data to analyze proven targeted pathways in Rhinella arenarum larvae exposed to organophosphorus pesticides

Transcriptional analysis of the network of transcription regulators and target pathways in exposed organisms may be a hard task when their genome remains unknown. The development of hundreds of qPCR assays, including primer design and normalization of the results with the appropriate housekeeping genes, seems an unreachable task. Alternatively, we took advantage of a whole transcriptome study on Rhinella arenarum larvae exposed to the organophosphorus pesticides azinphos-methyl and chlorpyrifos to evaluate the transcriptional effects on a priori selected groups of genes. This approach allowed us to evaluate the effects on hypothesis-selected pathways such as target esterases, detoxifying enzymes, polyamine metabolism and signaling, and regulatory pathways modulating them. We could then compare the responses at the transcriptional level with previously described effects at the enzymatic or metabolic levels to obtain global insight into toxicity-response mechanisms. The effects of both pesticides on the transcript levels of these pathways could be considered moderate, while chlorpyrifos-induced responses were more potent and earlier than those elicited by azinphos-methyl. Finally, we inferred a prevailing downregulation effect of pesticides on signaling pathways and transcription factor transcripts encoding products that modulate/control the polyamine and antioxidant response pathways. We also tested and selected potential housekeeping genes based on those reported for other species. These results allow us to conduct future confirmatory studies on pesticide modulation of gene expression in toad larvae.

Biochemical and osmoregulatory responses of the African clawed frog experimentally exposed to salt and pesticide

Salinization and pollution are two main environmental stressors leading deterioration to water quality and degradation of aquatic ecosystems. Amphibians are a highly sensitive group of vertebrates to environmental disturbance of aquatic ecosystems. However, studies on the combined effect of salinization and pollution on the physiology of amphibians are limited. In this study, we measured the standard metabolic rate (SMR) and biochemical parameters of adult males of the invasive frog Xenopus laevis after 45 days of exposure to contrasting salinity environments (400 and 150 mOsm NaCl) with either 1.0 μg/L of the organophosphate pesticide chlorpyrifos (CPF) or pesticide-free medium. Our results revealed a decrease in SMR of animals exposed to the pesticide and in the ability to concentrate the plasma in animals exposed simultaneously to both stressors. The lack of ability to increase plasma concentration in animals exposed to both salt water and CPF, suggests that osmoregulatory response is decreased by pesticide exposure. In addition, we found an increase of liver citrate synthase activity in response to salt stress. Likewise, the liver acetylcholinesterase (AChE) activity decreased by 50% in frogs exposed to salt water and CPF and 40% in those exposed only to CPF, which suggest an additive effect of salinity on inhibition of AChE. Finally, oxidative stress increased as shown by the higher lipid peroxidation and concentration of aqueous peroxides found in the group exposed to salt water and pesticide. Thus, our results revealed that X. laevis physiology is compromised by salinization and pesticide exposure to both environmental stressors join.

Assessing the toxic effects of bisphenol A in consumed crayfish Astacus leptodactylus using multi biochemical markers

Bisphenol A (BPA), an endocrine-disrupting chemical (EDC), has strong potential for daily exposure to humans and animals due to its persistence and widespread in the environment, so its effects directly concern public health. Although invertebrates represent important components of aquatic ecosystems and are at significant risk of exposure, there is little information about the biological effects of EDCs in these organisms. Astacus leptodactylus used in this study is one of the most consumed and exported freshwater species in Europe. In this study, the 96-h effect of BPA on A. leptodactylus was examined using various biomarkers. The LC₅₀ value of BPA was determined as 96.45 mg L^-1. After 96 h of exposure to BPA, there were increases in superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione S-transferase (GST), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) activities and levels of malondialdehyde (MDA), and total oxidant status context (TOSC), and there were decreases in the activity of glutathione reductase (GR), carboxylesterase (CaE), acetylcholinesterase (AChE), Na⁺/K⁺ ATPase, Mg²⁺ ATPase, Ca²⁺ ATPase, and total ATPase and the total antioxidant context (TAC). From the results of this study, it can be concluded that BPA has significant toxic effects on A. leptodactylus based on the selected biochemical parameters of antioxidant, cholinergic, detoxification, and metabolic systems in crayfish even at low doses. Thus, it can be said that BPA can seriously threaten the aquatic ecosystem and public health.

Evaluating Multiple Biochemical Markers in Xenopus laevis Tadpoles Exposed to the Pesticides Thiacloprid and Trifloxystrobin in Single and Mixed Forms

Pesticide exposure is thought to be one of the common reasons for the decline in amphibian populations, a phenomenon that is a major threat to global biodiversity. Although the single effects of pesticides on amphibians have been well studied, the effects of mixtures are not well known. The present study aimed to evaluate the acute toxicity of the insecticide thiacloprid and the fungicide trifloxystrobin on early developmental stages of Xenopus laevis using various biochemical markers (glutathione S-transferase, glutathione reductase, acetylcholinesterase, carboxylesterase, glutathione peroxidase, catalase, alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, Na⁺ K⁺ -adenosine triphosphatase [ATPase], Ca²⁺ -ATPase, Mg²⁺ -ATPase, and total ATPase). The median lethal concentrations (LC50s) of thiacloprid and trifloxystrobin were determined to be 3.41 and 0.09 mg a.i. L^-1 , respectively. Tadpoles were exposed to the LC50, LC50/2, LC50/10, LC50/20, LC50/50, and LC50/100 of these pesticides. Both pesticides significantly affected (inhibited/activated) the biomarkers even at low concentrations. The pesticides showed a synergistic effect when applied as a mixture and altered the biomarkers more than when applied individually. In conclusion, we can assume that tadpoles are threatened by these pesticides even at environmentally relevant concentrations. Our findings provide important data to guide management of the ecotoxicological effects of these pesticides on nontarget amphibians.  Environ Toxicol Chem 2021;40:2846-2860. © 2021 SETAC.

In situ exposure of amphibian larvae (Rhinella fernandezae) to assess water quality by means of oxidative stress biomarkers in water bodies with different anthropic influences

In situ bioassays provide valuable information about the environment and offer more realistic results than usual laboratory experiments. The aim of this study was to evaluate the quality of water bodies from the lower Paraná River basin, the second most important in South America, through analysis of physiochemical parameters, metals and pesticides and in situ exposure of Rhinella fernandezae larvae to assess oxidative stress biomarkers. The sites were: S1(Morejón stream, reference); S2, S3(De la Cruz stream upstream and downstream, respectively) and S4(Arrecifes River). In all sites, dissolved oxygen was low, atrazine was detected and Cu was higher than the limit for aquatic life protection. According to the water quality index, S2, S3 and S4 presented bad water quality, while S1 good water quality. Larvae were exposed in situ for 96h in order to analyze: lipid peroxidation(TBARS) as oxidative damage, antioxidant enzymatic (catalase-CAT-, superoxide dismutase-SOD- and glutathione s-transferase-GST-) and non-enzymatic defenses (reduced glutathione-GSH-). Larvae exposed in the most impacted sites (S2, S3 and S4) presented oxidative stress since the levels of TBARS were around 2 times higher than in S1. Also, the other oxidative stress biomarkers were altered in larvae exposed at S2, S3 and S4. These results highlight the importance of analyzing oxidative stress biomarkers during in situ exposures since they are useful tools for documenting the extent of exposure at sublethal levels. The complex pollution of the water bodies affected the exposed larvae, which may jeopardize the native populations.

Evaluation of the acute toxic effect of azoxystrobin on non-target crayfish (Astacus leptodactylus Eschscholtz, 1823) by using oxidative stress enzymes, ATPases and cholinesterase as biomarkers

Azoxystrobin is a broad-spectrum fungicide used worldwide. Since azoxystrobin spreads to large areas, its toxic effects on non-target organisms have aroused interest. In this study, the acute toxicity (96 h) of azoxystrobin on the crayfish (Astacus leptodactylus) was examined by using various biomarkers. The 96 h-LC₅₀ dose (1656 mg L^-) and its three sub-doses (828, 414, 207 mg L^-1) were applied to crayfish. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were increased significantly compared to the control in hepatopancreas, gill and muscle tissues. The activities of acetylcholinesterase (AChE) and glutathione S-transferase (GST) increased, and glutathione reductase (GR) activity decreased significantly in hepatopancreas. Level of reduced glutathione (GSH) decreased significantly. The content of malondialdehyde (MDA) increased in a dose-dependent manner in all azoxystrobin treatments with the exception of the lowest dose (207 mg L^-1)treatment. ATPases (Na⁺/K⁺ -ATPase, Mg²⁺ -ATPase, Ca²⁺ -ATPase, total ATPase) were significantly inhibited in gill and muscle tissues. The results of the present study indicate that azoxystrobin induces oxidative stress, and has adverse effects on activities of AChE and ATPases in crayfish.

The Rhinella arenarum transcriptome: de novo assembly, annotation and gene prediction

The common toad Rhinella arenarum is widely distributed in Argentina, where it is utilised as an autochthonous model in ecotoxicological research and environmental toxicology. However, the lack of a reference genome makes molecular assays and gene expression studies difficult to carry out on this non-model species. To address this issue, we performed a genome-wide transcriptome analysis on R. arenarum larvae through massive RNA sequencing, followed by de novo assembly, annotation, and gene prediction. We obtained 57,407 well-annotated transcripts representing 99.4% of transcriptome completeness (available at http://rhinella.uncoma.edu.ar). We also defined a set of 52,800 high-confidence lncRNA transcripts and demonstrated the reliability of the transcriptome data to perform phylogenetic analysis. Our comprehensive transcriptome analysis of R. arenarum represents a valuable resource to perform functional genomic studies and to identify potential molecular biomarkers in ecotoxicological research.

Joint Probabilistic Analysis of Risk for Aquatic Species and Exceedence Frequency for the Agricultural Use of Chlorpyrifos in the Pampean Region, Argentina

The Pampa Húmeda region in Argentina is characterized by soybean, wheat, and maize production, with intensive application of agrochemicals such as herbicides and insecticides. We used a joint probabilistic approach to analyze the probabilities for environmental chlorpyrifos concentrations measured in the Pampa Húmeda to exceed acute or chronic hazardous concentration for 5% of the species (HC5) values estimated from species sensitivity distributions for aquatic species. Chlorpyrifos concentrations in water ranged from 0.0005 to 10.8 µg/L, with a median of 0.013 µg/L. The HC5 limits were 0.0637 µg/L for acute and 0.0007 µg/L for chronic effects. The probabilities for chlorpyrifos environmental concentrations to exceed the HC5 values ranged from 35% (acute effects) to 96% (chronic effects). Water quality criteria (WQC) for the protection of aquatic life were also frequently exceeded (by 48-87%) for both acute and chronic effects. Together with published threshold limit values from mesocosm studies, these data suggest that macroinvertebrate communities can be severely affected by the reported environmental concentrations of chlorpyrifos. Indeed, changes in the macroinvertebrate assemblage in the Pampa Húmeda have been correlated with chlorpyrifos levels in sediments. Nevertheless, the actual impact needs to be ascertained by assessing the recovery rate of macroinvertebrate populations in this region. Considering the HC5 for chronic effects and the threshold limits for macroinvertebrate community level effects, we propose 0.7 ng/L as a new WQC to effectively protect aquatic life from long-term exposure to chlorpyrifos. Environ Toxicol Chem 2019;38:1748-1755. © 2019 SETAC.

European common frog Rana temporaria (Anura: Ranidae) larvae show subcellular responses under field-relevant Bacillus thuringiensis var. israelensis (Bti) exposure levels

Bacillus thuringiensis var. israelensis (Bti) is presumed to be an environmental friendly agent for the use in either health-related mosquito control or the reduction of nuisance associated with mosquitoes from seasonal wetlands. Amphibians inhabiting these valuable wetlands may be exposed to Bti products several times during their breeding season. Up until now, information regarding effects on the non-targeted group of amphibians has to be considered rather inconsistent. On this account, we evaluated how three repeated exposures to frequently used Bti formulations (VectoBac^®12AS, VectoBac^®WG) in field-relevant rates affect European common frog (Rana temporaria) larvae. In a laboratory approach, we assessed potential effects with regard to enzymatic biomarkers (glutathione-S-transferase (GST), glutathione reductase (GR), acetylcholine esterase (AChE)), development, body condition and survival until the end of metamorphosis. Although survival and time to metamorphosis were not significantly affected, larval development tended to be shortened in the Bti treated water phase. Furthermore, exposure to Bti induced significant increases of GST (37-550%), GR (5-140%) and AChE (38-137%) irrespectively of the applied formulation, indicating detoxification, antioxidant responses as well as an alteration of neuronal activity. GST activity increased twice as much after two repeatedly executed Bti applications within a time period of 6 days. The examination of several biochemical markers is needed to fully evaluate the ecotoxicological risk of Bti for amphibian populations, especially in the context of worldwide amphibian declines. Nevertheless, following the precautionary principle, it may be advisable to implement certain thresholds for application numbers and intervals in order to ensure environmentally friendly mosquito control programs, especially in areas designated for nature conservation.

Modulation of immune and antioxidant responses by azinphos-methyl in the freshwater mussel Diplodon chilensis challenged with Escherichia coli

The aim of the present study was to characterize the immune response-total hemocyte number, cell type proportion, hemocyte viability, lysosomal membrane stability, phagocytic activity, cellular acid and alkaline phosphatase activity, and humoral bacteriolytic and phenoloxidase activity--in Diplodon chilensis exposed to 0.2 mg/L of azinphos-methyl (AZM), using Escherichia coli as immunological and pro-oxidant challenges. In addition, glutathione-S-transferase and lipid peroxidation thiobarbituric acid reactive substances were analyzed in gill tissue. Mussels from an unpolluted site were treated for 3 d as follows: 1) experimental control; 2) solvent effects control (acetone 0.01%); 3) bacterial challenge effects control (E. coli, 5 cells/mL × 10⁴ cells/mL); 4) pesticide effects control (AZM in acetone); 5) control for combined effects of solvent and bacterial challenge; and 6) exposed to AZM, then challenged with E. coli. The results showed increased granulocyte proportion and phagocytic activity. Partial reversion of deleterious effects of E. coli on lysosomal membranes was observed in mussels exposed to AZM and then challenged with E. coli. Total hemocyte number and humoral bacteriolytic activity were increased only by E. coli challenge. Acid phosphatase activity was increased by both E. coli and AZM, whereas the stimulating effect of E. coli on alkaline phosphatase activity was negatively modulated by AZM. Azinphos-methyl inhibited phenoloxidase activity regardless of the E. coli challenge. Gill glutathione-S-transferase activity was increased by E. coli treatment either alone or pretreated with acetone or AZM and by AZM alone. Thiobarbituric acid reactive substance levels were reduced by AZM alone or combined with the E. coli challenge and by acetone followed by the E. coli challenge. Both acetone and AZM seem to be important modulators of immune and antioxidant responses in D. chilensis. Environ Toxicol Chem 2017;36:1785-1794. © 2016 SETAC.

Chronic toxicity of arsenic during Rhinella arenarum embryonic and larval development: Potential biomarkers of oxidative stress and antioxidant response

The Argentinean autochthonous toad Rhinella arenarum was selected to study the chronic toxicity of arsenic (As) and the biochemical responses elicited by exposure to As in water during embryonic and larval development. Significant decreases in the total reactive antioxidant potential and in catalase activity were observed in individuals exposed chronically to sublethal concentrations of As, which is indicative of an oxidative stress situation. However, an antioxidant response was elicited during chronic exposure to As, as evidenced by the increase in endogenous reduced glutathione content and glutathione-related enzymatic activities such as glutathione S-transferase (GST) and glutathione reductase. This protective response might prevent a deeper decline in the antioxidant system and further oxidative damage. Alternatively, it might be linked to As conjugation with reduced glutathione for its excretion. Considering the sustained increase in GST activity and the decrease in the total antioxidant reactive potential observed, the authors propose them as good candidates to be used as biomarkers during As exposure. Interestingly, glutathione reductase activity was inhibited at a very low concentration of As considered safe for aquatic life. Environ Toxicol Chem 2017;36:1614-1621. © 2016 SETAC.

Comparative study of toxicity and biochemical responses induced by sublethal levels of the pesticide azinphosmethyl in two fish species from North-Patagonia, Argentina

Biochemical effects of azinphosmethyl (AZM), an organophosphate pesticide, were determined in gill, brain and muscle tissues of Odontesthes hatcheri and Jenynsia multidentata. The 96-h toxicity was first assessed, estimating lethal concentrations fifty (LC50) of 7 and 30μgL(-1) AZM for O. hatcheri and J. multidentata, respectively. Considering the LC50, sublethal 96-h static exposures were designed for O. hatcheri (0.1-0.5μgL(-1) AZM) and J. multidentata (5-10μgL(-1)AZM) to determine biochemical endpoints. Brain acetylcholinesterase (AchE) was inhibited by AZM in both species, while the buffer enzyme carboxylesterase (CarbE) was not affected in this tissue. Conversely, muscular AchE was not affected but CarbE was augmented by AZM. The enzymes glutathione reductase, glutathione-S-transferase and CarbE were significantly inhibited in O. hatcheri gills but none of them was affected by AZM in J. multidentata gills compared to control. GSH levels were augmented in gills of both species in exposed fish compared to controls and in addition, lipid peroxidation was significantly increased in O. hatcheri gills. Ex vivo histochemical analysis of ROS by fluorescence microscopy was also performed in J. multidentata gills, indicating a significant increase upon exposure to 10μgL(-1) AZM. Principal component analyses (PCA) were applied, both to the species together or separately. The general analysis demonstrated a clear separation of responses in the two species. For O. hatcheri, the variable that explains the major variation in PC1 is gill catalase and brain AchE in PC2. In J. multidentata in turn, the variable that explains the major variation in PC1 is brain AchE and total oxyradical scavenging capacity in PC2. The toxicity data and biomarker responses obtained for both species were compared to environmental concentrations of AZM detected in superficial water from different points in the Alto Valle region and risk quotients (RQ) were calculated. This approach indicated probable acute effects for O. hatcheri in river and irrigation channels (RQ>0.1), while the risk was unacceptable in drainage superficial water (RQ>1). In contrast, J. multidentata showed minimal risk in river or channel water (RQ<0.1) and probable risk in drainage water (RQ=0.75). We conclude that not only the differential susceptibility of both species to AZM is environmentally relevant, but also that the different biomarkers responding in each case underlie particular pathways stressed by this agrochemical.

Comparative assessment of in vitro and in vivo toxicity of azinphos methyl and its commercial formulation

The toxic effects of Gusathion (GUS), which is a commercial organophosphate (OP) pesticide, and also its active ingredient, azinphos methyl (AzM), are evaluated comparatively with in vitro and in vivo studies. Initially, the 96-h LC50 values of AzM and GUS were estimated for two different life stages of Xenopus laevis, embryos, and tadpoles. The actual AzM concentrations in exposure media were monitored by high-performance liquid chromatography. Also, the sub-lethal effects of these compounds to tadpoles were determined 24 h later at exposure concentrations of 0.1 and 1 mg/L using selected biomarker enzymes such as acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione S-transferase (GST), glutathione reductase, lactate dehydrogenase, and aspartate aminotrasferase. Differences in AChE inhibition capacities of AzM and GUS were evaluated under in vitro conditions between frogs and fish in the second part of this study. The AChE activities in a pure electrical eel AChE solution and in brain homogenates of adult Cyprinus carpio, Pelophylax ridibundus, and X. laevis were assayed after in vitro exposure to 0.05, 0.5, 5, and 50 mg/L concentrations of AzM and GUS. According to in vivo studies AChE, CaE and GST are important biomarkers of the effect of OP exposure while CaE may be more effective in short-term, low-concentration exposures. The results of in vitro studies showed that amphibian brain AChEs were relatively more resistant to OP exposure than fish AChEs. The resistance may be the cause of the lower toxicity/lethality of OP compounds to amphibians than to fish.

Biochemical biomarkers of sublethal effects in Rhinella arenarum late gastrula exposed to the organophosphate chlorpyrifos

We determined the biochemical and molecular effects of the organophosphate insecticide chlorpyrifos (CPF) in the late gastrula embryonic stage of the South American toad Rhinella arenarum continuously exposed from fertilization (24 h). Our objective was to evaluate these responses as potential biomarkers at low, sublethal levels of the toxicant. We first established the EC50 for embryo arrest in 21.3 mg/L, with a LOEC of 16 mg/L. At 4 mg/L CPF, some embryos were unable to complete the dorsal lip of the blastopore and the yolk plug became blur, probably because of abnormal cell migration. Acetylcholinesterase activity, the specific biomarker for organophosphates, was unaffected by any of the tested concentrations of CPF (2-14 mg/L). In turn, 2 mg/L CPF increased the reduced glutathione levels and inhibited glutathione-S-transferase activity, suggesting an oxidative stress and antioxidant response. Catalase was induced by CPF exposure at higher concentrations (8 and 14 mg/L). We also studied transcription factor c-Fos as a signaling event related to development in early embryogenesis. Analysis of nuclear c-Fos protein showed two bands, both enhanced in embryos exposed to 2 and 8 mg/L CPF. While nuclear Erk protein was practically unaffected, Mek protein levels were induced by the OP. Transcription factor c-Fos may be then linking oxidative stress with developmental alterations observed due to CPF exposure. These molecular and biochemical responses observed in R. arenarum gastrula at sublethal CPF exposures may replace non-responsive AChE as very early biomarkers in toad gastrula.

Toxicity of the insecticide chlorpyrifos to the South American toad Rhinella arenarum at larval developmental stage

Chlorpyrifos (CPF) is an insecticide widely used for pest control in the fruit-productive region of North Patagonia, Argentina, where it is found in superficial waters. The aim of this study was to establish the toxic effects of CPF in Rhinella arenarum toad larvae as a potentially exposed species. We determined the 96 h-LC50 (1.46 ± 0.27 mg/L), the LOEC (0.81 mg/L, LC10) and NOEC (0.43 mg/L, LC1) for CPF lethality as endpoint. We also analyzed biochemical biomarkers in larvae exposed to sublethal CPF concentrations. The IC50 for cholinesterase was 0.113 ± 0.026 mg/L, one order of magnitude lower than the LC50. Carboxylesterase activity was inhibited, buffering OP toxicity on cholinesterase. Reduced glutathione increased after 24h as an antioxidant response, and decreased at 96 h together with catalase activity, due to oxidative stress. These biochemical effects suggest that environmentally relevant CPF concentrations pose a threat to R. arenarum larvae progression.

Comparative toxicity of methidathion and glyphosate on early life stages of three amphibian species: Pelophylax ridibundus, Pseudepidalea viridis, and Xenopus laevis

The assessments of pesticide toxicity on nontarget organisms have largely been focused on the determination of median lethal concentration (LC50) values using single/laboratory species. Although useful, these studies cannot describe the biochemical mechanisms of toxicity and also cannot explain the effects of pesticides on natural species. In this study, the toxic effects of glyphosate and methidathion were evaluated comparatively on early developmental stages of 3 anurans-2 natural (Pelophylax ridibundus, Pseudepidalea viridis) and 1 laboratory species (Xenopus laevis). The 96-h LC50 values for methidathion and glyphosate were determined as 25.7-19.6 mg active ingredient (AI)/L for P. viridis, 27.4-22.7 mg AI/L for P. ridibundus, and 15.3-5.05 mg AI/L for X. laevis tadpoles. Furthermore, as early signs of intoxication, glutathione S-transferase (GST), acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione reductase, lactate dehydrogenase, and aspartate aminotrasferase were assayed in 4-day-old tadpoles after 96-h pesticide exposure. The GST induction after 3.2mg AI/L methidathion exposure was determined to be 173%, 83%, and 38% of control, and the AChE inhibition for the same dose was determined to be 86%, 96%, and 30% of control for P. ridibundus, P. viridis, and X. laevis, respectively. Unlike the application of methidathion, all enzyme activities showed statistically significant increases on glyphosate exposure compared to controls. However, these increases in enzyme activities were not shown to be parallel with the increase of concentration. The levels of increases of GST and AChE were determined to be 111% and 31% for P. ridibundus, 13% and 51% for P. viridis, and 15% and 36% for X. laevis after 3.2mg AI/L glyphosate exposure, respectively. The findings of the study suggest that the most sensitive species to pesticide exposure is X. laevis. The selected biomarker enzymes AChE, CaE, and GST are useful in understanding the toxic mechanisms of these pesticides in anuran tadpoles as early warning indicators.

Developmental and polyamine metabolism alterations in Rhinella arenarum embryos exposed to the organophosphate chlorpyrifos

Organophosphorus pesticides (OPs) are widely applied in the Alto Valle of Río Negro and Neuquén, Argentina, due to intensive fruit growing. Amphibians are particularly sensitive to environmental pollution, and OPs may transiently accumulate in ponds and channels of the region during their reproductive season. Organophosphorus pesticide exposure may alter amphibian embryonic development and the reproductive success of autochthonous species. In the present study, embryos of the common toad Rhinella arenarum were employed to assess developmental alterations and to study polyamine metabolism, which is essential to normal growth, as a possible target underlying the effects of the OP chlorpyrifos. As the duration of chlorpyrifos exposure increased and embryonic development progressed, the median lethal concentration (LC50) values decreased, and the percentage of malformed embryos increased. Developmental arrest was also observed and several morphological alterations were recorded, such as incomplete and abnormal closure of the neural tube, dorsal curvature of the caudal fin, reduction of body size and caudal fin length, atrophy, and edema. An early decrease in ornithine decarboxylase (ODC) activity and polyamine levels was also observed in embryos exposed to chlorpyrifos. The decrease in polyamine contents in tail bud embryos might be a consequence of the reduction in ODC activity. The alteration of polyamine metabolism occurred before embryonic growth was interrupted and embryonic malformations were observed and may be useful as a biomarker in environmental studies.