Influence of Temperature on the Thyroidogenic Effects of Diuron and Its Metabolite 3,4-DCA in Tadpoles of the American Bullfrog (Lithobates catesbeianus)

Prednisone and prednisolone effects on development, blood, biochemical and histopathological markers of Aquarana catesbeianus tadpoles

Synthetic glucocorticoids are often found in surface waters and can cause harmful effects to aquatic organisms such as amphibians. In this work we evaluated the effects of the drugs prednisone (PD) and prednisolone (PL) on developmental, molecular, blood, biochemical and histological markers. Aquarana catesbeianus tadpoles were exposed for 16 days to environmentally relevant concentrations of 0, 0.1, 1 and 10 µg/L of both drugs. PD increased the transcript levels of the enzyme deiodinase III (Dio3), the hormones cortisol and T4 and delayed development. Changes in the thyroid gland occurred after tadpoles were exposed to both drugs, with a reduction in the diameter and number of follicles and an increase/or decrease in area. Also, both drugs caused a decrease in lymphocytes (L) and an increase in neutrophils (N), thrombocytes, the N:L ratio and lobed and notched erythrocytes. Increased activity of the enzymes superoxide dismutase, glutathione S-transferase and glucose 6-phosphate dehydrogenase was observed after exposure to PD. Furthermore, both drugs caused an increase in the activity of the enzymes catalase and glutathione peroxidase. However, only PD caused oxidative stress in exposed tadpoles, evidenced by increased levels of malondialdehyde and carbonyl proteins. Both drugs caused an increase in inflammatory infiltrates, blood cells and melanomacrophages in the liver. Our results indicate that PD was more toxic than PL, affecting development and causing oxidative stress.

The primary neurotoxic factor, Lansamide I, from Clausena lansium fruits and metabolic dysfunction invoked

Wampee (Clausena lansium) is a common fruit in South Asia. The pulp is a tasty food, and the seed is a typical traditional herb in China. However, we identified a primary toxic compound, Lansamide I, by NMR and X-ray diffraction of single-crystal. The compound occurred at 4.17 ± 0.16 mg/kg of dried seed and 0.08 ± 0.01 g/kg of fresh fruit. In our phenotype-based toxicity investigation, the compound caused decreased hatchability of zebrafish eggs, increased malformations such as enlarged yolk sacs and pericardial edema, and delayed body length development. Moreover, the compound also caused nerve cell damage and decreased locomotor activity. The compound caused an increase in peroxidation levels in vivo, with increases in both malondialdehyde and superoxide dismutase levels, but did not interfere with acetylcholinesterase levels. Metabolomic studies found that the compound caused significant up-regulation of 16 metabolites, mainly amino acids and peptides, which were involved in the nucleotide metabolism pathway and the betaine biosynthesis module. The qRT-PCR revealed that the substance interfered with the mRNA expression of tat and dctpp. These discoveries offer fresh perspectives on the toxicity mechanisms and metabolic response to the primary harmful molecules in wampee, which could inform the rational usage of wampee resources.

Sesamin alleviated fluoride - induced thyroid endocrine disruption in zebrafish (Danio rerio)

Previous studies have indicated that fluoride could induce the damage of thyroid. However, the effects of sesamin on thyroid endocrine function in zebrafish exposed to fluoride have not been clarified. This study was designed to investigate the alleviating effects of sesamin on thyroid endocrine disruption in zebrafish induced by fluoride. The results showed that sesamin significantly improved growth performance in adults exposed to fluoride; decreased significantly the mortality rate, increased remarkably the hatching rate and body length, and alleviated the phenomenon of spinal curvature, yolk cyst and pericardial cyst to varying degrees in fluoride-exposed embryos and larvae. Sesamin alleviated remarkably the damage of thyroid tissues in fluoride-exposed adults. Moreover, sesamin obviously reduced oxidative stress and improved the imbalance of thyroid hormones in fluoride-exposed adults or larvae. In addition, sesamin reversed the expression of endocrine-related genes of thyroid in fluoride-exposed adults or larvae. This indicates that sesamin can affects the thyroid tissue structure, hormone levels, and the expression of endocrine-related genes of thyroid, thus alleviating the thyroid endocrine disorder induced by fluoride and improving the growth and development. This study also demonstrates that sesamin can be a promising novel treatment for thyroid endocrine disorder caused by fluoride.

Effects of the herbicide ametryn on development and thyroidogenesis of bullfrog tadpoles (Aquarana catesbeiana) under different temperatures

Thyroid hormones (TH) are essential for the metamorphosis of amphibians and their production can be influenced by environmental stressors, such as temperature fluctuations, and exposure to aquatic pollutants, such as herbicides. In the present study we evaluated the influence of different temperatures (25 and 32 °C) on the effects of the herbicide ametryn (AMT, 0 - control, 10, 50 and 200 ng.L^-1) for 16 days on thyroidogenesis of bullfrog tadpoles. Higher temperature and AMT exposure caused a delay in the development of tadpoles, despite no differences were noted in weight gain and total length of the animals. Levels of triiodothyronine (T3) and thyroxine (T4) were not altered neither by AMT nor by temperature, but the highest temperature caused a decrease in total area and number of follicles in the thyroid gland. Transcript levels of thyroid hormone receptors alpha and beta (TRα and TRβ) and iodothyronine deiodinase 3 (DIO3) were lower at 32 °C, which is consistent with developmental delay at the higher temperature. Tadpoles exposed to 200 ng.L^-1 of AMT at 25 °C also presented delayed development, which was consistent with lower TRα and DIO3 transcript levels. Lower levels of estradiol were noted in tadpoles exposed to AMT at the higher temperature, being also possibly related to a developmental delay. This study demonstrates that higher temperature and AMT exposure impair thyroidgenesis in bullfrog tadpoles, disrupting metamorphosis.

Influence of temperature on the biomarker responses of bullfrog tadpoles (Lithobates catesbeianus) to 2-hydroxyatrazine exposure

The influence of temperature (25 and 32 °C) on the biomarker responses of bullfrog tadpoles (Lithobates catesbeianus) to different concentrations of the atrazine metabolite 2-hydroxyatrazine (2-HA, 0, 10, 50 and 200 ng.L^-1, 16 days), was evaluated. Temperature affected the activities of superoxide dismutase, glutathione S-transferase and acetylcholinesterase. The activities of catalase, glutathione peroxidase, glucose-6-phosphate dehydrogenase and carboxylesterase presented no alterations. Frequencies of micronuclei and nuclear abnormalities were also not altered. 2-HA decreased SOD activity at 25 °C and caused histopathological changes in the liver and the kidney at both temperatures, with the kidney being more affected by the combination of higher temperature and 2-HA exposure, presenting glomerular shrinkage and an increase in Bowman's space. Our results indicate that at environmentally relevant concentrations, 2-HA can cause changes in biomarker responses as well as in the morphology of liver and kidney in L. catesbeianus tadpoles. Temperature has an important influence on biomarker response and histopathological alterations.

Using mesocosms to evaluate the impacts of pasture intensification and pasture-sugarcane conversion on tadpoles in Brazil

This study evaluated the effects of environmental contamination caused by pasture intensification and pasture-sugarcane conversion on oxidative stress, biotransformation, esterase enzymes, and development of Scinax fuscovarious and Physalaemus nattereri. Tadpoles were exposed in mesocosms allocated in three treatments: (1) untreated extensive pasture (EP); (2) intensive-pasture conversion (IP) (2,4-D herbicide + fertilizers); and (3) pasture-sugarcane conversion (SC) (fipronil + 2,4-D + fertilizers). After 7 days of exposure, IP reduced catalase (CAT) and increased malondialdehyde (MDA) levels in P. nattereri, while this treatment decreased glucose-6-phosphate dehydrogenase (G6PDH) and CAT activities in S. fuscovarious. SC decreased CAT, G6PDH, and glutathione S-transferase (GST) activities in P. nattereri. In S. fuscovarius, SC reduced G6PDH, acetylcholinesterase (AChE), and carboxylesterase (CbE) activities. MDA was raised in both tadpole species exposed to SC, evidencing oxidative stress. Integrated biomarker responses showed higher scores in both species exposed to SC. Our results warn that management practices currently applied to sugarcane cultivation in Brazil can negatively impact the functional responses of amphibians at natural systems.

Assessment of multiple biomarkers in Lithobates catesbeianus (Anura: Ranidae) tadpoles exposed to zinc oxide nanoparticles and zinc chloride: integrating morphological and behavioral approaches to ecotoxicology

The ecotoxicological risk to vertebrates posed by zinc oxide nanoparticles (ZnO NPs) is still poorly understood, especially in animals with a biphasic life cycle, which have aquatic and terrestrial phases, such as amphibians. In the present study, we investigated whether acute exposure (7 days) to ZnO NPs and zinc chloride (ZnCl₂) at three environmentally relevant concentrations (0.1, 1.0, and 10 mg L^-1) induces changes in the morphology, chondrocranium, and behavior of the tadpoles of Lithobates catesbeianus (Anura: Ranidae). Tadpoles exposed to both forms of Zn did not undergo any morphological or behavioral changes at the lowest concentrations (0.1 and 1.0 mg L^-1). However, the animals exposed to the highest concentration (10 mg L^-1) lacked oral disc structures, were smaller in size, had a longer tail, and presented changes in the position and coiling of the intestine and malformations of the chondrocranium in comparison with the control group. This indicates that ZnO NPs and ZnCl₂ altered the development of the tadpoles, causing delays in their metamorphosis and even reducing individual fitness. The tadpoles exposed to both forms of Zn at 10 mg L^-1 also had reduced mobility, especially in the presence of conspecifics. Based on these findings, we emphasize the importance of studying morphological, skeletal, and behavioral biomarkers to evaluate the toxic effects of metal-based nanoparticles in amphibians.

Influence of temperature on biomarker responses of bullfrog tadpoles (Lithobates catesbeianus) exposed to the herbicide ametryn

The S-triazine herbicide ametryn (AMT) is relatively low adsorbed in soils and has high solubility in water, thus believed to affect non-target aquatic organisms such as amphibians. Temperature increases can intensify the effects of herbicides, possibly increasing the susceptibility of amphibians to these compounds. The aim of this study was to evaluate the influence of temperature (25 and 32 °C) on the responses of biochemical biomarkers in bullfrog tadpoles (Lithobates catesbeianus) exposed to different concentrations of AMT (0, 10, 50 and 200 ng.L^-1) for a period of 16 days. The antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) and the biotransformation enzyme glutathione S-transferase (GST) had their activity decreased at the highest temperature (32 °C). SOD activity was reduced at 200 ng.L^-1 and 32 °C compared to the control at the same temperature. AMT exposure also decreased the activities of alanine aminotransferase and gamma glutamyl transferase. On the other hand, the activities of acetylcholinesterase, carboxylesterase, alkaline phosphatase, levels of lipid peroxidation and protein carbonyl, as well genotoxic markers (micronucleus and nuclear abnormalities frequencies) were unchanged. The evaluation of integrated biomarker response index (IBR) indicated highest variations at the concentration of 200 ng.L^-1 at 32 °C, suggesting that the combination of high AMT concentrations and temperatures generate more pronounced negative effects to tadpoles.

Hepatic and blood alterations in Lithobates catesbeianus tadpoles exposed to sulfamethoxazole and oxytetracycline

In this study the effects of environmentally realistic concentrations of the antibiotics sulfamethoxazole (SMX) and oxytetracyclyne (OTC) on Lithobates catesbeianus tadpoles were evaluated, through the analyzes of the frequencies of micronucleus and nuclear abnormalities in erythrocytes, alterations in leucocytes, liver histopathology, and changes in hepatic esterase activities and oxidative stress biomarkers. The animals were exposed for 16 days at concentrations of 0 (control), 20, 90 and 460 ng L^-1. No significant difference was found in the frequencies of micronucleus and nuclear abnormalities. The two highest concentrations of SMX and all concentrations of OTC caused a significant increase in the number of lymphocytes. A significant decrease in the number of neutrophils compared to the control group was observed for all concentrations tested of both antibiotics. Also, decrease in the activity of glutathione S-transferase and high histopathological severity scores, indicating liver damage, were found in tadpoles exposed to the two highest concentrations of SMX and all concentrations of OTC. The main changes in the liver histopathology were the presence of inflammatory infiltrate, melanomacrophages, vascular congestion, blood cells and eosinophils. Esterase activities were unchanged. Indeed, the two highest concentrations of OTC caused a reduction in the activities of superoxide dismutase and glucose 6-phosphate dehydrogenase, while the highest concentration inhibited the activity of glutathione peroxidase and increased protein carbonyl levels. These results evidences that environmentally realistic concentrations of SMX and OTC in aquatic environments are capable to significantly disrupt tadpoles' physiology, possibly affecting negatively their survival rate in natural environments.

Parental exposure to propiconazole at environmentally relevant concentrations induces thyroid and metabolism disruption in zebrafish (Danio rerio) offspring: An in vivo, in silico and in vitro study

Propiconazole is used against fungal growth in agriculture and is released into the environment, but is a potential health threat to aquatic organisms. Propiconazole induces a generational effect on zebrafish, although the toxic mechanisms involved have not been described. The aim of this study was to investigate the potential mechanisms of abnormal offspring development after propiconazole exposure in zebrafish parents. Zebrafish were exposed to propiconazole at environmentally realistic concentrations (0.1, 5, and 250 μg/L) for 100 days and their offspring were grown in control solution for further study. Heart rate, hatching rate, and body length of hatched offspring were reduced. An increase in triiodothyronine (T₃) content and the T₃/T₄ (tetraiodothyronine) ratio was observed, indicating disruption of thyroid hormones. Increased protein level of transthyretin (TTR) in vivo was consistent with the in silico molecular docking results and T₄ competitive binding in vitro assay, suggests higher binding affinity between propiconazole and TTR, more than with T₄. Increased expression of genes related to the hypothalamus-pituitary-thyroid (HPT) axis and altered metabolite levels may have affected offspring development. These findings emphasizes that propiconazole, even on indirect exposure, represents health and environmental risk that should not be ignored.

Influence of temperature on growth, development and thyroid metabolism of American bullfrog tadpoles (Lithobates catesbeianus) exposed to the herbicide tebuthiuron

The influence of temperature (25 and 32 °C) on the negative effects of the herbicide tebuthiuron (TBU, 0, 10, 50 and 200 ng.L-1, 16 days) on thyroid function and metamorphosis of Lithobates catesbeianus tadpoles was evaluated. Metamorphosis was accelerated by TBU exposure at 25 ºC, but delayed at 32 ºC with considerable losses of body mass. T3 and T4 levels were not altered. The highest TBU concentrarion at 25 ºC increased TR β and DIO3 transcript levels, which is consistent with development acceleration in tadpoles. At 32 ºC TR β transcript levels were lower than the values recorded at 25 ºC, and those tadpoles exposed to the highest TBU concentration presented increased diameter of thyroid follicles compared to controls at same temperature. This study evidences that TBU at environmentally realistic concentrations is able to disrupt thyroidogenesis in bullfrog tadpoles, impairing their development. These effects are influenced by temperature.

Realistic exposure to fipronil, 2,4-D, vinasse and their mixtures impair larval amphibian physiology

Expansion of sugarcane crops may have contributed to the increased contamination of native habitats in Brazil. Several species of amphibians inhabit ponds formed in flooded farmlands, where pesticide concentrations are usually high. This study evaluated the ecotoxicological effects of the sugarcane pesticides fipronil and 2,4-D, as well as the fertilizer vinasse (isolated and mixed), on physiological responses of Leptodactylus fuscus and Lithobates catesbeianus tadpoles. In situ assays were conducted in mesocosms with concentrations based on the doses recommended by the manufacturer. Vinasse (1.3% dilution) caused 100% tadpoles' mortality immediately after its application. Fipronil and/or 2,4-D altered antioxidant and biotransformation responses, induced neurotoxicity and changed lipid contents in tadpoles. A multivariate approach indicated that the mixture of pesticides induced most of the sublethal effects in both tadpole species, in addition to the isolated fipronil in L. fuscus. Fipronil alone increased glucose-6-phosphate dehydrogenase (G6PDH) activity, decreased acetylcholinesterase (AChE) and total lipid contents, and altered some individual lipid classes (e.g., free fatty acids and acetone-mobile polar lipids) in L. fuscus. The interaction between fipronil and 2,4-D in this species were more evident for lipid contents, although enzymatic alterations in G6PDH, AChE and glutathione-S-transferase (GST) were also observed. In L. catesbeianus, the mixture of pesticides reduced triglycerides and total lipids, as well as increased GST and decreased AChE activities. The detoxifying enzyme carboxylesterase was reduced by 2,4-D (alone or in mixture) in both species. Isolated pesticides also modulated specific lipid classes, suggesting their disruptive action on energy metabolism of tadpoles. Our study showed that fipronil, 2,4-D, and vinasse, individually or mixed, can be harmful to amphibians during their larval phase, causing mortality or impairing their functional responses.

Combined effects of heatwaves and micropollutants on freshwater ecosystems: Towards an integrated assessment of extreme events in multiple stressors research

Freshwater ecosystems are strongly influenced by weather extremes such as heatwaves (HWs), which are predicted to increase in frequency and magnitude in the future. In addition to these climate extremes, the freshwater realm is impacted by the exposure to various classes of chemicals emitted by anthropogenic activities. Currently, there is limited knowledge on how the combined exposure to HWs and chemicals affects the structure and functioning of freshwater ecosystems. Here, we review the available literature describing the single and combined effects of HWs and chemicals on different levels of biological organization, to obtain a holistic view of their potential interactive effects. We only found a few studies (13 out of the 61 studies included in this review) that investigated the biological effects of HWs in combination with chemical pollution. The reported interactive effects of HWs and chemicals varied largely not only within the different trophic levels but also depending on the studied endpoints for populations or individuals. Hence, owing also to the little number of studies available, no consistent interactive effects could be highlighted at any level of biological organization. Moreover, we found an imbalance towards single species and population experiments, with only five studies using a multitrophic approach. This results in a knowledge gap for relevant community and ecosystem level endpoints, which prevents the exploration of important indirect effects that can compromise food web stability. Moreover, this knowledge gap impairs the validity of chemical risk assessments and our ability to protect ecosystems. Finally, we highlight the urgency of integrating extreme events into multiple stressors studies and provide specific recommendations to guide further experimental research in this regard.

Constraints and Opportunities for the Evolution of Metamorphic Organisms in a Changing Climate

We argue that developmental hormones facilitate the evolution of novel phenotypic innovations and timing of life history events by genetic accommodation. Within an individual’s life cycle, metamorphic hormones respond readily to environmental conditions and alter adult phenotypes. Across generations, the many effects of hormones can bias and at times constrain the evolution of traits during metamorphosis; yet, hormonal systems can overcome constraints through shifts in timing of, and acquisition of tissue specific responses to, endocrine regulation. Because of these actions of hormones, metamorphic hormones can shape the evolution of metamorphic organisms. We present a model called a developmental goblet, which provides a visual representation of how metamorphic organisms might evolve. In addition, because developmental hormones often respond to environmental changes, we discuss how endocrine regulation of postembryonic development may impact how organisms evolve in response to climate change. Thus, we propose that developmental hormones may provide a mechanistic link between climate change and organismal adaptation.

Influence of temperature on biomarker responses and histology of the liver of American bullfrog tadpoles (Lithobates catesbeianus, Shaw, 1802) exposed to the herbicide Tebuthiuron

Tebuthiuron (TBU) is a phenylurea herbicide that is extensively used in sugarcane fields. Owing to the low degradation rate, high water solubility, and leaching potential, TBU is believed to have harmful effects on aquatic organisms, such as anuran tadpoles. Contaminant effects can be influenced by temperature since increases in temperature are often associated with increased metabolic reactions. In this study, we evaluated the influence of temperature on the negative effects of TBU in bullfrog tadpoles (Lithobates catesbeianus) through a multi-biomarker approach. Tadpoles were exposed to 0 (control) 10, 50, and 200 ng L^-1 of TBU for 16 days at 25 and 32 °C. TBU increased the transcript levels of genes involved in biotransformation (glutathione S-transferase, GST, and sulfotransferase, SULT) and antioxidant (superoxide dismutase, SOD, and catalase, CAT) enzymes. TBU exposure also increased CAT and glutathione peroxidase (GPx) activities, whereas SOD and carboxylesterase activities were decreased. The highest temperature caused a decrease in the activities of ethoxyresorufin-O-deethylase and SOD but increased the activities of GST, GPx, glucose 6-phosphate dehydrogenase, and acetylcholinesterase. No effects of temperature or TBU exposure were observed in genotoxic markers (frequencies of micronucleous and nuclear abnormalities) or in lipid peroxidation levels. Tadpoles exposed to TBU at all tested concentrations presented a higher index of biomarker responses than that of the control groups. Higher values of severity scores from histological analyses were found in the liver of tadpoles exposed to 50 and 200 ng L^-1 of TBU at 32 °C compared with those of the control group at the same temperature. These results indicate that TBU and temperature increases are able to disturb the metabolic homeostasis of L. catesbeianus tadpoles after 16 days of exposure, causing substantial alterations in biomarker responses and liver morphology.

Global variation in freshwater physico-chemistry and its influence on chemical toxicity in aquatic wildlife

Chemical pollution is one of the major threats to global freshwater biodiversity and will be exacerbated through changes in temperature and rainfall patterns, acid-base chemistry, and reduced freshwater availability due to climate change. In this review we show how physico-chemical features of natural fresh waters, including pH, temperature, oxygen, carbon dioxide, divalent cations, anions, carbonate alkalinity, salinity and dissolved organic matter, can affect the environmental risk to aquatic wildlife of pollutant chemicals. We evidence how these features of freshwater physico-chemistry directly and/or indirectly affect the solubility, speciation, bioavailability and uptake of chemicals [including via alterations in the trans-epithelial electric potential (TEP) across the gills or skin] as well as the internal physiology/biochemistry of the organisms, and hence ultimately toxicity. We also show how toxicity can vary with species and ontogeny. We use a new database of global freshwater chemistry (GLORICH) to demonstrate the huge variability (often >1000-fold) for these physico-chemical variables in natural fresh waters, and hence their importance to ecotoxicology. We emphasise that a better understanding of chemical toxicity and more accurate environmental risk assessment requires greater consideration of the natural water physico-chemistry in which the organisms we seek to protect live.

High temperature stress response is not sexually dimorphic at the whole-body level and is dependent on androgens to induce sex reversal

The understanding of the molecular and endocrine mechanisms behind environmentally-induced sex reversal in fish is of great importance in the context of predicting the potential effects of climate change, especially increasing temperature. Here, we demonstrate the global effects of high temperature on genome-wide transcription in medaka (Oryzias latipes) during early development. Interestingly, data analysis did not show sexual dimorphic changes, demonstrating that thermal stress is not dependent on genotypic sex. Additionally, our results revealed significant changes in several pathways under high temperature, such as stress response from brain, steroid biosynthesis, epigenetic mechanisms, and thyroid hormone biosynthesis, among others. These microarray data raised the question of what the exact molecular and hormonal mechanisms of action are for female-to-male sex reversal under high temperatures in fish. Complementary gene expression analysis revealed that androgen-related genes increase in females (XX) experiencing high water temperature. To test the involvement of androgens in thermal-induced sex reversal, an androgen antagonist was used to treat XX medaka under a high-temperature setup. Data clearly demonstrated failure of female-to-male sex reversal when androgen action is inhibited, corroborating the importance of androgens in environmentally-induced sex reversal.

Tralopyril induces developmental toxicity in zebrafish embryo (Danio rerio) by disrupting the thyroid system and metabolism

Tralopyril, an antifouling biocide, widely used in antifouling systems to prevent underwater equipment from biological contamination, which can pose a potential risk to aquatic organisms and human health. However, there is little information available on the toxicity of tralopyril to aquatic organisms. Herein, zebrafish (Danio rerio) were used to investigate the toxicity mechanisms of tralopyril and a series of developmental indicators, thyroid hormones, gene expression and metabolomics were measured. Results showed that tralopyril significantly decreased the heart-beat and body length of zebrafish embryos-larvae exposed to 4.20 μg/L or higher concentrations of tralopyril and also induced developmental defects including pericardial hemorrhage, spine deformation, pericardial edema, tail malformation and uninflated gas bladder. Tralopyril decreased the thyroid hormone concentrations in embryos and changed the transcriptions of the related genes (TRHR, TSHβ, TSHR, Nkx2.1, Dio1, TRα, TRβ, TTR and UGT1ab). Additionally, metabolomics analysis showed that tralopyril affected the metabolism of amino acids, energy and lipids, which was associated with regulation of thyroid system. Furthermore, this study demonstrated that alterations of endogenous metabolites induced the thyroid endocrine disruption in zebrafish following the tralopyril treatment. Therefore, the results showed that tralopyril can induce adverse developmental effects on zebrafish embryos by disrupting the thyroid system and metabolism.

Agrochemicals disrupt multiple endocrine axes in amphibians

Concern over global amphibian declines and possible links to agrochemical use has led to research on the endocrine disrupting actions of agrochemicals, such as fertilizers, fungicides, insecticides, acaricides, herbicides, metals, and mixtures. Amphibians, like other species, have to partition resources for body maintenance, growth, and reproduction. Recent studies suggest that metabolic impairments induced by endocrine disrupting chemicals, and more particularly agrichemicals, may disrupt physiological constraints associated with these limited resources and could cause deleterious effects on growth and reproduction. Metabolic disruption has hardly been considered for amphibian species following agrichemical exposure. As for metamorphosis, the key thyroid hormone-dependent developmental phase for amphibians, it can either be advanced or delayed by agrichemicals with consequences for juvenile and adult health and survival. While numerous agrichemicals affect anuran sexual development, including sex reversal and intersex in several species, little is known about the mechanisms involved in dysregulation of the sex differentiation processes. Adult anurans display stereotypical male mating calls and female phonotaxis responses leading to successful amplexus and spawning. These are hormone-dependent behaviours at the foundation of reproductive success. Therefore, male vocalizations are highly ecologically-relevant and may be a non-invasive low-cost method for the assessment of endocrine disruption at the population level. While it is clear that agrochemicals disrupt multiple endocrine systems in frogs, very little has been uncovered regarding the molecular and cellular mechanisms at the basis of these actions. This is surprising, given the importance of the frog models to our deep understanding of developmental biology and thyroid hormone action to understand human health. Several agrochemicals were found to have multiple endocrine effects at once (e.g., targeting both the thyroid and gonadal axes); therefore, the assessment of agrochemicals that alter cross-talk between hormonal systems must be further addressed. Given the diversity of life-history traits in Anura, Caudata, and the Gymnophiona, it is essential that studies on endocrine disruption expand to include the lesser known taxa. Research under ecologically-relevant conditions will also be paramount. Closer collaboration between molecular and cellular endocrinologists and ecotoxicologists and ecologists is thus recommended.

Disruptive effects of two organotin pesticides on the thyroid signaling pathway in Xenopus laevis during metamorphosis

Organotin compounds are the ubiquitous environmental pollutants due to their wide industrial and agricultural applications and unexpected releasing into the environment, which show characteristic of endocrine disruptors to interfere with the synthesis, receptor binding or action of endogenous-hormones. Organotin pesticides (OTPs) are used in agriculture and may impact endocrine functions on organisms. Thyroid hormones (THs) play fundamental roles in regulating the basal metabolism and energy balance, while thyroid function can be impaired by environmental contaminants. Therefore, it is crucial to clarify the effects and mechanisms of OTPs on hypothalamus-pituitary-thyroid (HPT) axis. In this study, Xenopus laevis tadpoles at stage 51 were exposed to fentin hydroxide and fenbutatin oxide (0.04, 0.20 and 1.00 μg·L^-1) for 21 days. It was found that both compounds caused inhibitory effects on metamorphic development of tadpoles (e.g., significant decrease in hindlimb length and retarding development). Triiodothyronine (T₃) significantly decreased in tadpoles exposed to 0.20 μg/L and 1.00 μg/L of the two OTPs for 14 days or 21 days. The expressions of TH responsive genes trβ, bteb and dio2 were down-regulated, while tshβ and slc5a5 were up-regulated. Surface plasmon resonance (SPR) binding assays showed that fentin hydroxide had a moderate affinity to recombinant human thyroid hormone receptor β but fenbutatin oxide did not have. Result of the SPR assay was highly consistent with the luciferase reporter gene assays that fentin hydroxide suppressed the relative luciferase activity in the presence of T₃ while fenbutatin oxide did not, demonstrating fentin hydroxide but not fenbutatin oxide displayed an antagonistic activity against T₃-TR complex mediated transcriptional activation. Overall, the findings elucidated the mechanisms induced by OTPs along HPT axis. These results highlighted the adverse influences of organotin pesticides on thyroid hormone- dependent development in vertebrates and the need for more comprehensive investigations of their potential ecological risks.

Effects of 2,4-D-based herbicide (DMA® 806) on sensitivity, respiration rates, energy reserves and behavior of tadpoles

Increased use of sugarcane pesticides and their destination to non-target environments in Brazil has generated concerns related to the conservation of more vulnerable groups, such as amphibians. Besides the high skin permeability, tadpoles are constantly restricted to small and ephemeral ponds, where exposure to high concentrations of pesticides in agricultural areas is inevitable. This study evaluated chronic effects caused by sub-lethal concentrations of 2,4-dichlorophenoxyacetic acid herbicide on energy storage, development, respiration rates, swimming performance and avoidance behavior of bullfrog tadpoles (Lithobates catesbeianus). Firstly, we conducted acute toxicity test (96 h) to estipulate sub-lethal concentrations of 2,4-D and evaluate the sensitivity of three tadpoles' species to this herbicide. Results showed that Leptodactylus fuscus presented the lowest LC₅₀ 96 h, 28.81 mg/L, followed by Physalaemus nattereri (143.08 mg/L) and L. catesbeianus (574.52 mg/L). Chronic exposure to 2,4-D (125, 250 and 500 μg/L) delayed metamorphosis and inhibited the growth of tadpoles at concentrations of 125 μg/L. Effects on biochemical reserves showed that 2,4-D increased total hepatic lipids in tadpoles, although some individual lipid classes (e.g. free fatty acids and triglycerides) were reduced. Protein and carbohydrates contents were also impaired by 2,4-D, suggesting a disruption on energy metabolism of amphibians by the herbicide. In addition to biochemical changes, respiration rates and swimming speed were also decreased after chronic exposure to 2,4-D, and these responses appeared to be correlated with the changes detected in the basic energy content. Avoidance test indicated that tadpoles of L. catesbeinus avoided the presence of 2,4-D, however they were unable to detect increasing gradients of the contaminant. Our data showed that chronic exposure to 2,4-D impaired biochemical, physiological and behavioral aspects of tadpoles, which may compromise their health and make them more vulnerable to environmental stressors in natural systems.

Interactive effects of 3,4-DCA and temperature on the annual killifish Nothobranchius furzeri

Although aquatic organisms are increasingly exposed to pollutants and abnormally high temperatures as a consequence of climate change, interactive effects between those stressors remain poorly assessed. Especially in ectotherms, such as fish, increases in ambient temperature are expected to affect fitness-related traits and physiology. We used the turquoise killifish Nothobranchius furzeri to study the effects of a range of 3,4-dichloroaniline concentrations (0, 50, 100 μg/L) in combination with two temperature conditions (control and control +4 °C) during four months of exposure. As part of an integrated multi-level approach, we quantified effects on classic life history traits (size, maturation time, body mass, fecundity), critical thermal maximum and physiology (energy reserves and stress-associated enzymatic activity). While no interactive effects of 3,4-DCA exposure and increased temperature emerged, our results do show a negative effect of 3,4-DCA on thermal tolerance. This finding is of particular relevance in light of increasing temperatures under climate change. Due to increases in pest species and faster degradation of 3,4-DCA under higher temperatures, increased use of the pesticide is expected under climate change which, in turn, could result in a decreased tolerance of aquatic organisms to high temperatures.

Contaminant and Environmental Influences on Thyroid Hormone Action in Amphibian Metamorphosis

Aquatic and terrestrial environments are increasingly contaminated by anthropogenic sources that include pharmaceuticals, personal care products, and industrial and agricultural chemicals (i. e., pesticides). Many of these substances have the potential to disrupt endocrine function, yet their effect on thyroid hormone (TH) action has garnered relatively little attention. Anuran postembryonic metamorphosis is strictly dependent on TH and perturbation of this process can serve as a sensitive barometer for the detection and mechanistic elucidation of TH disrupting activities of chemical contaminants and their complex mixtures. The ecological threats posed by these contaminants are further exacerbated by changing environmental conditions such as temperature, photoperiod, pond drying, food restriction, and ultraviolet radiation. We review the current knowledge of several chemical and environmental factors that disrupt TH-dependent metamorphosis in amphibian tadpoles as assessed by morphological, thyroid histology, behavioral, and molecular endpoints. Although the molecular mechanisms for TH disruption have yet to be determined for many chemical and environmental factors, several affect TH synthesis, transport or metabolism with subsequent downstream effects. As molecular dysfunction typically precedes phenotypic or histological pathologies, sensitive assays that detect changes in transcript, protein, or metabolite abundance are indispensable for the timely detection of TH disruption. The emergence and application of 'omics techniques-genomics, transcriptomics, proteomics, metabolomics, and epigenomics-on metamorphosing tadpoles are powerful emerging assets for the rapid, proxy assessment of toxicant or environmental damage for all vertebrates including humans. Moreover, these highly informative 'omics techniques will complement morphological, behavioral, and histological assessments, thereby providing a comprehensive understanding of how TH-dependent signal disruption is propagated by environmental contaminants and factors.

Acute exposure of zebrafish embryo (Danio rerio) to flutolanil reveals its developmental mechanism of toxicity via disrupting the thyroid system and metabolism

Flutolanil, an amide fungicide, had been detected frequently in aquatic environments; it is thus potentially a great risk to aquatic organisms and human health. Therefore, we investigated the developmental toxicity and the potential mechanism of thyroid endocrine disruption induced by flutolanil based on ¹H NMR metabolomics analysis using a zebrafish model. Hatching of zebrafish embryo exposed to flutolanil was inhibited at 72 hpf (hour post-fertilization) and survival and body length at 96 hpf. In addition, increased teratogenic effects on embryos were observed, including pericardial edema, spine deformation, and tail malformation. Furthermore, flutolanil induced slower heartbeat and larger pericardial area in the treated groups than control group. Transcription levels of TRH, TSHR, TPO, Dio1, TRα, and UGT1ab were significantly altered after flutolanil exposure. Metabolomics analysis further indicated that flutolanil induced alterations of energy, amino acids, nucleotide, lipids, and fatty acid metabolism. Our study also indicated that flutolanil exposure led to alterations of endogenous metabolites, which induced the thyroid endocrine disruption in zebrafish. Ultimately, embryonic developmental toxicity was caused by flutolanil.

Changes in thyroid status of Menidia beryllina exposed to the antifouling booster irgarol: Impacts of temperature and salinity

The triazine-based herbicide irgarol is widely used in antifouling systems as an algicide and has been detected recently in multiple coastal environments. Studies evaluating sub-lethal responses of fish following exposure to irgarol are limited. Moreover, impacts of climate change on fish endocrinology may also contribute to the sublethal toxicity of irgarol. We assessed the effects of irgarol on thyroid endpoints in juveniles of Menidia beryllina under two different treatments of salinity (10 and 20 ‰) and two temperatures (10 and 20°C). Condition factor coefficients (K) of animals were significantly affected by 0.1 to 10 μg/L of irgarol at the higher temperature. Levels of T3 were changed in whole body homogenates from both temperatures at 10‰ following exposure to 1 to 10 μg/L. T4 levels were altered only at 10°C when animals were treated with 1 to 10 μg/L (10 ‰), and in 0.1 and 10 μg/L (20 ‰). Increased transcripts of deiodinase enzymes at 10 °C may be impacted by salinity and alter thyroid hormone homeostasis. Impact on gene expression of thyroid (α and β) and growth hormone receptors were also determined. Our results highlight the relevance of environmental variable that may impact the ecological risk of irgarol in estuarine systems.

An automated screening method for detecting compounds with goitrogenic activity using transgenic zebrafish embryos

The knowledge on environmentally relevant chemicals that may interfere with thyroid signaling is scarce. Here, we present a method for the screening of goitrogens, compounds that disrupt the thyroid gland function, based on the automatic orientation of zebrafish in a glass capillary and a subsequent imaging of reporter gene fluorescence in the thyroid gland of embryos of the transgenic zebrafish line tg(tg:mCherry). The tg(tg:mCherry) reporter gene indicates a compensatory upregulation of thyroglobulin, the thyroid hormone precursor, in response to inhibition of thyroid hormone synthesis. Fish embryos were exposed to a negative control compound (3,4-dichloroaniline), or a concentration series of known goitrogenic compounds (resorcinol, methimazole, potassium perchlorate, 6-propyl-2-thiouracil, ethylenethiourea, phloroglucinol, pyrazole) with maximum exposure concentration selected based on mortality and/or solubility. Exposure to 3,4-dichloroaniline decreased the fluorescence signal. All goitrogenic compounds exhibited clear concentration-dependent inductions of reporter fluorescence 1.4 to 2.6 fold above control levels. Concentration-response modelling was used to calculate goitrogenic potencies based on EC₅₀ values. The new automated method offers an efficient screening approach for goitrogenic activity.

Thyroid Disruption by Bisphenol S Analogues via Thyroid Hormone Receptor β: in Vitro, in Vivo, and Molecular Dynamics Simulation Study

Bisphenol S (4-hydroxyphenyl sulfone, BPS) is increasingly used as a bisphenol A (BPA) alternative. The global usage of BPS and its analogues (BPSs) resulted in the frequent detection of their residues in multiple environmental media. We investigated their potential endocrine-disrupting effects toward thyroid hormone receptor (TR) β. The molecular interaction of BPSs toward TRβ ligand binding domain (LBD) was probed by fluorescence spectroscopy and molecular dynamics (MD) simulations. BPSs caused the static fluorescence quenching of TRβ LBD. The 100 ns MD simulations revealed that the binding of BPSs caused significant changes in the distance between residue His435 at helix 11(H11) and residue Phe459 at H12 in comparison to no ligand-bound TRβ LBD, indicating relative repositioning of H12. The recombinant two-hybrid yeast assay showed that tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A (TBBPA) have potent antagonistic activity toward TRβ, with an IC₁₀ of 10.1 and 21.1 nM, respectively. BPS and BPA have the antagonistic activity with IC₁₀ of 312 and 884 nM, respectively. BPSs significantly altered the expression level of mRNA of TRβ gene in zebrafish embryos. BPS and TBBPS at environmentally relevant concentrations have antagonistic activity toward TRβ, implying that BPSs are not safe BPA alternatives in many BPA-free products. Future health risk assessments for TR disruption and other adverse effects should focus more on the structure-activity relationship in the design of environmentally benign BPA alternatives.

Insights about the toxic effects of tannery effluent on Lithobates catesbeianus tadpoles

Tannery industries are considered highly polluting due to the large production of polluted wastewater [untreated tannery effluent (UTE)]. Although previous studies have already shown the consequences from fish, birds and mammals' exposure to this pollutant, little is known about its toxicological effect on representatives of class amphibian. Thus, we aim at assessing whether short-term UTE exposure, even at low concentrations (0.2% UTE diluted in water), would be able to induce behavioral, morphological and cyto-genotoxic changes in L. catesbeianus tadpoles. In order to do so, two experimental groups were set (control and tannery effluent) and exposed, or not, to UTE for seven days. A positive control group (cyclophosphamide) was included in the experimental design in order to assess cyto-genotoxicity. Our behavioral results showed that tadpoles exposed to the contaminant presented abnormal responses in the predator-response test; therefore, it evidenced losses in their capacity to recognize chemical olfactory cues of a potential predator. We also searched for changes in mouth length, in dentition, in body length before and after the eyes of animals exposed to UTE. Besides, we observed higher nuclear abnormality frequency in the circulating erythrocytes of tadpoles exposed to the contaminant, as well as in animals belonging to the positive control group. Some of the observed abnormalities were micronuclei, binucleated, notched, kidney-shaped and blebbed cells, multilobulated nuclei, as well as lower mitotic index. Therefore, our data confirm the hypothesis that UTE causes behavioral, morphological and cyto-genotoxic changes in L. catesbeianus tadpoles, fact that opens new perspectives to other investigations about how and which UTE constituents were responsible for the observed effects.

Acute sensitivity of the killifish Nothobranchius furzeri to a combination of temperature and reference toxicants (cadmium, chlorpyrifos and 3,4-dichloroaniline)

Aquatic organisms of inland waters are often subjected to a combination of stressors. Yet, few experiments assess mixed stress effects beyond a select group of standard model organisms. We studied the joint toxicity of reference toxicants and increased temperature on the turquoise killifish, Nothobranchius furzeri, a promising model for ecotoxicological research due to the species' short life cycle and the production of drought-resistant eggs. The acute sensitivity of the larval stage (2dph) to three compounds (cadmium, 3,4-dichloroaniline and chlorpyrifos) was tested in combination with a temperature increase of 4 °C, mimicking global warming. Dose-response relationships were used to calculate 96h-LC₅₀ of 0.28 mg/L (24 °C) and 0.39 mg/L (28 °C) for cadmium, 96h-LC₅₀ of 9.75 mg/L (24 °C) and 6.61 mg/L (28 °C) for 3,4-dichloroaniline and 96h-LC₅₀ of 15.4 μg/L (24 °C) and 14.2 μg/L (28 °C) for chlorpyrifos. After 24 h of exposure, the toxicity of all tested compounds was exacerbated under increased temperature. Furthermore, the interaction effect of cadmium and temperature could be predicted by the stress addition model (SAM). This suggests the applicability of the model for fish and at the same time indicates that the model could be suitable to predict effects of temperature-toxicant interactions.

Impacts of Salinity and Temperature on the Thyroidogenic Effects of the Biocide Diuron in Menidia beryllina

Diuron is a herbicide used in agricultural and urban settings and also as an antifouling agent. Recent studies have indicated sublethal responses of diuron in the endocrine system of fish and amphibians. Given the potential of climate change to also alter fish endocrinology, the combination of environmental stressors with diuron may contribute to its sublethal toxicity. In this study, the effects of temperature and salinity on thyroid targets of diuron were assessed in juveniles of the estuarine fish Menidia beryllina under different conditions of salinity (10 and 20‰) and temperature (10 and 20 °C). Environmentally relevant concentrations of diuron affected the growth, and the higher temperature reduced the condition factor of animals. Increased levels of T3 were observed in fish from all treatments, and at 10 °C, T4 levels were augmented at 10‰ but reduced at 20‰. Increased gene expression of deiodinases at 20‰ in both temperatures suggests the influence of salinity on the regulation of hormone imbalance via deiodination pathway activation. Decreased transcripts of thyroid and growth hormone receptors were also observed following diuron treatment. These results indicate that changes in environmental stressors may have significant impacts on the ecological risk of diuron in estuarine fish.

Isolated and mixed effects of diuron and its metabolites on biotransformation enzymes and oxidative stress response of Nile tilapia (Oreochromis niloticus)

Diuron is one of the most used herbicide in the world, and its field application has been particularly increased in Brazil due to the expansion of sugarcane crops. Diuron has often been detected in freshwater ecosystems and it can be biodegraded into three main metabolites in the environment, the 3,4-dichloroaniline (DCA), 3,4-dichlorophenylurea (DCPU) and 3,4-dichlorophenyl-N-methylurea (DCPMU). Negative effects under aquatic biota are still not well established for diuron, especially when considering its presence in mixture with its different metabolites. In this study, we evaluated the effects of diuron alone or in combination with its metabolites, DCPMU, DCPU and 3,4-DCA on biochemical stress responses and biotransformation activity of the fish Oreochromis niloticus. Results showed that diuron and its metabolites caused significant but dispersed alterations in oxidative stress markers and biotransformation enzymes, except for ethoxyresorufin-O-deethylase (EROD) activity, that presented a dose-dependent increase after exposure to either diuron or its metabolites. Glutathione S-transferase (GST) activity was significant lower in gills after exposure to diuron metabolites, but not diuron. Diuron, DCPMU and DCA also decreased the multixenobiotic resistance (MXR) activity. Lipid peroxidation levels were increased in gill after exposure to all compounds, indicating that the original compound and diuron metabolites can induce oxidative stress in fish. The integration of all biochemical responses by the Integrated Biomarker Response (IBR) model indicated that all compounds caused significant alterations in O. niloticus, but DCPMU caused the higher alterations in both liver and gill. Our findings imply that diuron and its metabolites may impair the physiological response related to biotransformation and antioxidant activity in fish at field concentrations. Such alterations could interfere with the ability of aquatic animals to adapt to environments contaminated by agriculture.

Effects of both cold and heat stresses on the liver of giant spiny frog Quasipaa spinosa: stress response and histological changes

Ambient temperature associated stress can affect the normal physiological functions in ectotherms. To assess the effects of cold or heat stress on amphibians, the giant spiny frogs, Quasipaa spinosa, were acclimated at 22 °C followed by being treated at 5 °C or 30 °C for 0, 3, 6, 12, 24 and 48 h, respectively. Histological alterations, apoptotic index, mitochondrial reactive oxygen species (ROS) generation, antioxidant activity indices and stress-response gene expressions in frog livers were subsequently determined. Results showed that many fat droplets appeared after 12 h of heat stress. Percentage of melanomacrophages centres significantly changed during 48 h at both stress conditions. Furthermore, the mitochondrial ROS levels were elevated in a time-dependent manner up to 6 h and 12 h in the cold and heat stress groups, respectively. The activities of superoxide dismutase, glutathione peroxidase and catalase were successively increased along the cold or heat exposure, and most of their gene expression levels showed similar changes at both stress conditions. Most tested HSP genes were sensitive to temperature exposure, and the expression profiles of most apoptosis-related genes was significantly up-regulated at 3 and 48 h under cold and heat stress, respectively. Apoptotic index at 48 h under cold stress was significantly higher than that under heat stress. Notably, lipid droplets, HSP30, HSP70 and HSP110 might be suitable bioindicators of heat stress. The results of these alterations at physiological, biochemical and molecular levels might contribute to a better understanding of the stress response of Q. spinosa and even amphibians under thermal stresses.

Combined effects of temperature and clomazone (Gamit®) on oxidative stress responses and B-esterase activity of Physalaemus nattereri (Leiuperidae) and Rhinella schneideri (Bufonidae) tadpoles

Temperature is an important factor influencing the toxicity of chemicals in aquatic environments. Neotropical tadpoles experience large temperature fluctuations in their habitats and many species are distributed in areas impacted by agriculture. This study evaluated the effects caused by the exposure to clomazone (Gamit^®) at different temperatures (28, 32 and 36 °C) on biochemical stress responses and esterase activities in Physalaemus nattereri and Rhinella schneideri tadpoles. Results evidenced that temperature modulates the effects of clomazone on biochemical response of tadpoles. Antioxidant enzymes, including catalase, superoxide dismutase (SOD), and glucose-6-phosphate dehydrogenase had their activities increased by clomazone in P. nattereri treated at higher temperatures. The biotransformation enzyme glutathione-S-transferase (GST) was also induced by clomazone at 32 and 36 °C. In R. schneideri, clomazone failed to alter antioxidant enzymes at 28 °C, but SOD and GST were increased by clomazone at higher temperatures after three days. All enzymes had their activities returned to the control levels after eight days in R. schneideri. Lipid peroxidation was induced in both species exposed to clomazone at 32 and 36 °C, but not at 28 °C. Acetylcholinesterase was not sensitive to clomazone and temperature, while most treatments impaired carboxylesterase activity. Integrated biomarker response (IBR) was notably induced by temperature in both species, and a synergic effect of temperature and clomazone was mostly observed after three days of exposure. These findings imply that tadpoles from tropical areas may present differential responses in their physiological mechanism linked to antioxidant defense to deal with temperature fluctuations and agrochemicals presence in their habitats.

Effects of abamectin on bullfrog tadpoles: insights on cytotoxicity

Abamectin is one of the most used pesticides worldwide. However, investigations about its effects on amphibian populations are rare. Thus, the present study sought to investigate possible cytotoxic effects on Lithobates catesbeianus tadpoles exposed to low abamectin concentrations diluted in water. Accordingly, four experimental groups were set: negative control, positive control (cyclophosphamide-40 mL L^-1), abamectin at concentrations 36 μg a.i./L (ABA36 group), and 72 μg a.i./L (ABA72 group), applied as Kraft® 36EC. The micronucleus test was conducted and other nuclear abnormalities in peripheral blood erythrocytes were checked after 24, 48, and 72 h of exposure to the treatments. The total of other nuclear abnormalities was influenced by the treatments, whereas the frequency of micronuclei was influenced by the exposure time. Such frequency was higher in the animals comprising the ABA72 group, which was assessed 72 h after the exposure had begun. The total of other nuclear abnormalities was influenced by the treatments. Animals in the positive control, ABA36, and ABA72 groups showed similar frequency of these abnormalities at 48 and 72 h. However, this frequency was statistically higher than that of animals in their respective negative control groups. Thus, the present study confirmed the hypothesis that the exposure of L. catesbeianus tadpoles to abamectin caused cytotoxic effects on them, although this exposure lasted short and the concentrations were low. It disclosed prospects for variations in the nucleus of erythrocytes circulating in amphibians, a fact that may provide an important/complementary approach for the detection of cytotoxicity caused by abamectin exposure.

The genotoxicity and cytotoxicity of tannery effluent in bullfrog (Lithobates catesbeianus)

Some of the most polluting activities occur in bovine skin processing. Tannery generates effluents containing high concentrations of heavy metals and organic compounds. The phases composing the leather production process generate a large volume of tannery effluents that are often discarded in aquatic environments without any previous treatment. However, the effect these xenobiotics have on adult representatives belonging to the class Amphibia remains unknown. Thus, the aim of the present study is to assess the geno- and cytotoxic effects of tannery effluent on adult male bullfrogs (Lithobates castesbeianus) exposed to it. Accordingly, the animals were divided into the following groups: negative control (tannery effluent-free water), positive control (cyclophosphamide), and effluent (water added with 5% tannery effluent). The animals were euthanized for blood collection, and erythrocyte analyses were conducted after 35 and 90 days of exposure. The micronuclei (MN) frequency and the frequency of other nuclear abnormalities in each of the animals in the experimental groups were assessed in 2000 erythrocytes. According to the present results, the exposure to tannery effluents increased MN frequency as well as other nuclear abnormalities (i.e., lobed nuclei, binucleated cell, kidney-shaped nuclei, notched nuclei, and apoptotic cell) in the erythrocytes of animals in the effluent group and in the positive control group after 35 and 90 exposure days. Thus, the current study corroborated the hypothesis that the tannery effluent has aneugenic and clastogenic potential in adult male bullfrogs (L. castesbeianus). The present study is the first to report such effect.

Influence of temperature on the antioxidant responses and lipid peroxidation of two species of tadpoles (Rhinella schneideri and Physalaemus nattereri) exposed to the herbicide sulfentrazone (Boral 500SC®)

Amphibians can experience large temperature fluctuations in their habitats, especially during the larval stage, when tadpoles are restricted to small and ephemeral ponds. Changes in water temperature can alter development, metabolism and behaviour of cold-blooded animals but also the toxicokinetics of chemicals in the environment. In Brazil, pesticides application is intensified during the rainy season, which is the period of reproduction for many amphibian species. We evaluated here the influence of temperature (28, 32, and 36°C) on the toxicity of the herbicide sulfentrazone (Boral®SC) in tadpoles of Physalaemus nattereri and Rhinella schneideri, by analysis of oxidative stress biomarkers. Exposure of tadpoles to sulfentrazone altered the antioxidant enzymes activities and induced lipid peroxidation with temperature-associated responses. Catalase, superoxide dismutase and glucose-6-phosphate dehydrogenase (G6PDH) were impaired by combined effect of temperature and sulfentrazone in both species. G6PDH was increased in most groups exposed to 36°C. Biotransformation enzyme glutathione-S-transferase had more evident alterations in P. nattereri at higher temperatures and changes in tGSH contents presented different patterns between the species. Lipid peroxidation was particularly induced in tadpoles of P. nattereri. Integrated biomarker response (IBR) index indicated a synergic effect of temperature and sulfentrazone for tadpoles of P. nattereri, while the IBR was mainly influenced by temperature in R. schneideri. Our study showed that temperature modulates biochemical responses in tadpoles exposed to sulfentrazone with a species-specific pattern. These findings imply that the effects of abiotic factors should be taken into account to evaluate the real risks of exposure of amphibians to commonly used pesticides.