Toxicity of waterborne Copper in premetamorphic tadpoles of Lithobates catesbeianus (Shaw, 1802)

Nuclear abnormalities and DNA damage indicate different genotoxic stress responses of marsh frogs (Pelophylax ridibundus, Pallas 1771) to industrial and agricultural water pollution in South Bulgaria

Amphibians are continuously exposed to pollutants and anthropogenic stressors in their natural habitats, representing a significant challenge to their survival. This study aimed to quantify the extent of DNA damage caused by chronic industrial and agrochemical surface water pollution in wild populations of the marsh frog (Pelophylax ridibundus). The observed genotoxic effects on the marsh frog DNA, manifesting as abnormalities in erythrocyte nuclei, micronuclei, and DNA strand breaks, demonstrate a clear cause-and-effect relationship with surface water parameters, heavy metals, metalloids, and pesticides. The most prevalent nuclear abnormalities observed were notched and blebbed nuclei and nuclear buds, indicative of chromosomal instability. The significant correlation between cadmium, lead, and copper contamination and the increased frequency of DNA breakage in the marsh frogs from the industrial site indicates that heavy metal contamination has a higher genotoxic potential than pesticide contamination. These findings underscore the vulnerability of amphibians inhabiting heavy metal-contaminated wetlands to genotoxic stress due to their lower tolerance to environmental genotoxins. Therefore, using in situ assays to detect erythrocyte nuclear abnormalities and DNA damage in P. ridibundus could serve as a reliable indicator of environmental quality and provide early detection of anthropogenic pollution.

Toxicity comparison and risk assessment of two chlorinated organophosphate flame retardants (TCEP and TCPP) on Polypedates megacephalus tadpoles

Tris(2-chloroethyl) phosphate (TCEP) and tris(1‑chloro-2-propyl) phosphate (TCPP) are widely used as chlorinated organophosphate flame retardants (OPFRs) due to their fire-resistance capabilities. However, their extensive use has led to their permeation and pollution in aquatic environments. Using amphibians, which are non-model organisms, to test the toxic effects of OPFRs is relatively uncommon. This study examined the acute and chronic toxicity differences between TCEP and TCPP on Polypedates megacephalus tadpoles and evaluated the potential ecological risks to tadpoles in different aquatic environments using the risk quotient (RQ). In acute toxicity assay, the tadpole survival rates decreased with increased exposure time and concentrations, with TCEP exhibiting higher LC50 values than TCPP, at 305.5 mg/L and 70 mg/L, respectively. In the chronic assay, prolonged exposure to 300 μg/L of both substances resulted in similar adverse effects on tadpole growth, metamorphosis, and hepatic antioxidant function. Based on RQ values, most aquatic environments did not pose an ecological risk to tadpoles. However, the analysis showed that wastewater presented higher risks than rivers and drinking water, and TCPP posed a higher potential risk than TCEP in all examined aquatic environments. These findings provide empirical evidence to comprehend the toxicological effects of OPFRs on aquatic organisms and to assess the safety of aquatic environments.

Ecotoxicity assessment of triphenyl phosphate (TPhP) exposure in Hoplobatrachus rugulosus tadpoles

Triphenyl phosphate (TPhP), a widely used aromatic organophosphate flame retardant, is known to accumulate in organisms through water, air, and soil, consequently, causing toxicity. This study is the first to evaluate the acute and sub-chronic toxicities of TPhP to amphibians. In the acute toxicity analysis, the 96-h median lethal concentration (LC₅₀) for GS35 Hoplobatrachus rugulosus tadpoles was 2.893 mg/L, and the 10% effect concentration (EC₁₀) was 289 μg/L. After two weeks of exposure to low TPhP concentrations, the survival and metamorphosis rates of H. rugulosus tadpoles decreased, and the metamorphosis time was prolonged as the TPhP concentration increased. The threshold concentration that affected tadpole survival and metamorphosis time was 50 μg/L and 100 μg/L, respectively. No significant differences were observed in the condition factor and hepatic somatic index of the tadpole after metamorphosis; however, tadpole body mass and TPhP concentration were negatively correlated. Further, TPhP inhibited the expressions of Cu-Zn sod and cat, thereby reducing the activities of superoxide dismutase and catalase in the tadpole liver. The threshold for affecting gene expression and enzymatic activity was 100 μg/L. These findings provide significant insights on the stress ecology of aquatic organisms.

Effects of lithium and selenium in the tail muscle of American bullfrog tadpoles (Lithobates catesbeianus) during premetamorphosis

The amphibian populations have faced a drastic decline over the past decades. This decline has been associated with the presence of contaminants in the environment, among other environmental stressors. The present study tested the responses following the exposure to lithium (2.5 mg L^-1) and selenium (10μg L^-1), both isolated and as a mixture, on the metabolic status of the tail muscle of premetamorphic American bullfrog (Lithobates catesbeianus) through the assessment of the total protein content, mobilization of glucose and triglycerides, and the activity of lactate dehydrogenase (LDH). The exposure followed a 21-day assay with two sampling periods (on the 7th and 21st day after the onset of exposure) to evaluate the effects over time. The group exposed to the mixture presented a statistically decreased LDH activity (P < 0.05) in both sampling periods. The presence of selenium elicited a statistically significant increase (P < 0.05) in the glucose mobilization after 7 days of exposure. After 21 days, the animals exposed to selenium presented levels of glucose mobilization comparable to the control group. The mobilization of glucose and triglycerides remained similar to the control group for the animals exposed to lithium and to the mixture in both periods of sampling (P > 0.05). The total protein content did not show any statistical difference in the treated groups throughout the experiment (P > 0.05). The presented results highlight the importance of the assessment of mixtures that can occur in the environment, since the combination of contaminants may elicit distinct toxicity compared with the effects triggered by the chemicals isolated.

Cytogenotoxicity evaluation of a heavy metal mixture, detected in a polluted urban wetland: Micronucleus and comet induction in the Indian green frog (Euphlyctis hexadactylus) erythrocytes and the Allium cepa bioassay

Heavy metal contamination in wetland ecosystems is a serious environmental and health concern. This study evaluated the cytogenotoxicity of a previously evidenced heavy metal contamination (Cd, Cr, Cu, Pb and Zn ∼5 ppm each) in a polluted urban wetland, the Bellanwila-Attidiya sanctuary (BAS) in Sri Lanka, using a battery of cytogenotoxic assays. Micronucleus and comet assays evaluated the genotoxicity in erythrocytes of a common amphibian, the Indian green frog (Euphlyctis hexadactylus), under natural metal exposure in the wetland, and in vitro exposure, respectively.The Allium cepa bioassay assessed the cytogenotoxicity of the heavy metal mixture and of the individual metals, under laboratory exposure. Although in vivo natural exposure showed no significant induction of micronuclei in frog erythrocytes (P > 0.1), a significant and dose dependent elevation of comets was evident with in vitro exposure to the metal mixture (P < 0.001). Field controls did not show significant impacts in the A. cepa bioassay, whereas individual exposure to heavy metals reported lower effects than their combined exposure under laboratory conditions; Pb²⁺was the most toxic metal, with the highest mitotic inhibition (Pb²⁺>Cd²⁺>Zn²⁺>Cr⁶ >Cu²⁺), mutagenic potential as evaluated in the percentage incidence of chromosomal aberrations (Pb²⁺> Zn²⁺> Cu²⁺> Cr⁶⁺> Cd²⁺) and cytotoxicity evaluated by the incidence of cell apoptosis and necrosis (Pb²⁺>Cr⁶⁺>Cu²⁺>Cd²⁺>Zn²⁺). Thus, the test battery of micronucleus, comet and A. cepa assays that reveal differential aspects of cytogenotoxicity may serve as a valuable tool in environmental monitoring, primarily to screen for complex environmental mixtures of heavy metals that may impact ecological health.

Cytotoxicity and mutagenicity of the waters of the Marrecas River (Paraná, Brazil) to bullfrogs (Lithobates catesbeianus)

Animals have a long history of assessing ecosystem responses to environmental disturbances, and amphibians stand out for presenting themselves as good animal model and bioindicators of environmental quality. The main purpose of the present work was to investigate the cellular effects of contamination of waters of the Marrecas River, located in the southwest of the state of Paraná, Brazil. Therefore, the objective of the present study was to investigate and monitor the cytotoxic and mutagenic effect, with bullfrog tadpoles, and to discuss these effects with land use along this hydrographic basin. Mutagenic effects were determined by micronucleus assay, and cytotoxicity by other nuclear changes, such as segmented cells, binucleated cells, cells with buds and reniform cells. Water samples were obtained at nine sites along the Marrecas River, covering areas with rural and urban hydrological contribution. For each site, four samples were collected, along the years 2017 and 2018, encompassing the four seasons (summer, autumn, winter, and spring). The results showed mutagenic and cytotoxic effect in four sampling sites, and only cytotoxic effect in other four sites. These effects may be due, possibly, to the use of different agrochemicals across the hydrographic basin region, which have predominant hydrological contributions from crops. Data of this study indicate the presence of cytotoxic and mutagenic contaminants in the waters of the Marrecas River, which can generate environmental problems on the river fauna/flora, and can also affect the local population health.

Micronucleus test in tadpole erythrocytes: Trends in studies and new paths

The micronucleus test has been applied for more than three decades in tadpoles, generating an early warning of environmental quality. In this study, we reviewed 48 articles on the micronucleus test in tadpoles, published between 1987 and 2018. The findings reveal that pesticides have been the main topic discussed in the induction of micronucleus and other nuclear abnormalities in anuran larvae to the detriment of the widespread use of compounds used in agriculture. In addition to pesticides, a number of other xenobiotic agents have been targeted for genotoxic damage, such as heavy metals, radiation and wastewater. An appeal is reported to environmental contaminants, which when released naturally into the environment or because of human activities may contaminate aquatic habitats, threatening populations of tadpoles that depend on these environments for their survival. Larvae can bioaccumulate these contaminants that cause progressive impacts, ranging from DNA damage to metamorphosis delays, as well as malformations. We found that Argentina is the main driving force for the application of this test in anuran larvae along with Brazil. Different erythrocyte malformations have been reported for the erythrocyte nuclear abnormalities test, binucleated cells, nuclear buds, notched, lobed, reniform, nuclear bebbled, anucleated, picnotic and apoptotic cells are the most cited. In summary, the presence of chemical or physical agents, along with other disturbances of the habitat, can have a significant impact on the life history of the species, contributing to the decline of anuran populations.

Evaluation of the sensitivity of Microhyla fissipes tadpoles to aqueous cadmium

Cadmium (Cd) exposure is harmful to amphibians in natural environments and the Cd concentration is a key parameter in water monitoring. Cd pollution has been a severe issue in the Yangtze River and its southern reaches in recent years. Acute toxicity assays were employed to determine the tolerance limits of Cd for Microhyla fissipes tadpoles and five different concentrations of Cd (0, 50, 100, 200 and 300 μg/L) were involved to detect its chronic effects on metamorphosis, growth, locomotion, genotoxicity and enzymatic activities of M. fissipes tadpoles. The results showed that the 24-h and 48-h LC₅₀ values of Cd on M. fissipes tadpoles were 2591.3 μg/L and 1567.9 μg/L, respectively, and the presumable non-lethal concentration obtained was 172.2 μg/L. During the 70-day chronic toxicity assays, Cd showed negative impacts on survival, growth, metamorphosis and the frequency of erythrocytes nuclear abnormality of M. fissipes tadpoles. However, the Cd exposure caused the increased body size and condition of tadpoles at complete metamorphosis (GS46). The tadpoles exposed to 200 μg/L of Cd exhibited degraded locomotor performance at GS46. Weight increments of tadpoles were inhibited at Day 14 and massive deaths were observed over the next 14 days. The enzymatic activities of tadpoles experienced a shock response stage (GS30-GS35) and a complete recovery stage (GS36-GS41) in all treatments. However, the enzymatic activities (except alkaline phosphatase) of tadpoles at GS46 increased after Cd exposure, especially at high concentrations. In summary, Cd is a threat to M. fissipes tadpoles as that causes reduced fitness.

Assessment of environmental quality of water bodies next to agricultural areas of Buenos Aires province (Argentina) by means of ecotoxicological studies with Rhinella arenarum

Little is known about the effects of polluted water bodies from Buenos Aires Province on the development of native fauna. Ecotoxicological quality of water bodies from agricultural sites was evaluated by means of standardized laboratory bioassays with embryos and larvae of the native amphibian Rhinella arenarum. The organisms were acutely and chronically exposed to surface water samples from streams of Arrecifes (A), Pergamino (P) and Salto (S) districts that represent the most important agricultural core from the region. Lethal, sublethal and genotoxic effects were assessed. Water sample from (A) caused chronic toxicity (LC₅₀:45.35%) in embryos, followed by (S) and the water sample from (P) was not toxic. In larvae, an inversion of the toxicity pattern was found. Thus, the 504 h-LC₅₀s were 28.12%, 39% and 61% for (S), (P) and (A), respectively. A stage-dependent sensitivity was registered, being larvae more affected than embryos. Significant genotoxic effects, estimated by micronucleus test were observed in the larvae exposed to water samples from all sites. The present study warns about environmental degradation of surface waters next to agricultural areas of Buenos Aires Province. This fact jeopardizes R. arenarum populations in this area.

Blood cell responses and metallothionein in the liver, kidney and muscles of bullfrog tadpoles, Lithobates catesbeianus, following exposure to different metals

The hematological parameters and metallothionein (MT) levels in the liver, kidney and muscles were measured in bullfrog tadpoles, Lithobates catesbeianus, following exposures to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) alone or in combination (1:1 and 1:1:1) for 2 and 16 days. Metal accumulation occurred in all organs, with the highest values found in the kidney, followed by the muscles and liver. After exposure to isolated metals, the accumulation was in the following order: Cd > Zn > Cu in the liver and muscles and Cd > Cu > Zn in the kidney. Exposure to combined metals (Zn + Cu, Zn + Cd, Cu + Cd and Zn + Cu + Cd) revealed complex responses, such as metal accumulation increased or decreased over the exposure periods, suggesting possible competion at the uptake sites and/or metabolization and elimination processes in each organ. The MT concentration increased in the organs of tadpoles following metal exposure alone, mainly in the liver, for both periods. After the combined exposures, the MT levels were higher in the liver and muscles at 16 days, suggesting that the interaction between metals was additive, and the level was decreased in the kidney after 2 and 16 days of exposure. The whole blood hemoglobin content (Hb), red blood cell count (RBCs) and mean corpuscular hemoglobin (MCH) differed from the control groups after 2 and 16 days of exposure, showing changes in the improvement of oxygen transport. The number of lymphocytes increased, and the levels of neutrophils, eosinophils, basophils and monocytes were reduced after exposure to the metals. The changes in blood cells suggested that tadpoles have a mechanism to improve oxygen transport probably because of the increased oxygen demand and a general reduction in defense cells. The exposure of L. catesbeianus to metals during the larval phase can generate long-term dysfunction to a degree, which could lead to alterations in their health status.

Active biomonitoring of mussels Mytilus galloprovincialis with integrated use of micronucleus assay and physiological indices to assess harbor pollution

The mussels Mytilus galloprovincialis collected from a noncontaminated site (Chaib Rasso) were transplanted during one, three and six months at Ghazaouet harbor (GH), areas with a strong gradient of pollution. The micronucleus test (MN) was selected to monitor the impact of contamination, along with physiological indexes (condition index CI and organo-somatic indexes RI and GSI). The results show a negative correlation of MN variation in gill cells with CI but a positive correlation with transplantation duration. However, a significant correlation was found between the indexes. Moreover, the findings indicate that MN in the hemolymph and gills of transplanted mussels for one, three and six months at GH are significantly higher than those of the reference site. However, no significant differences were noted between the three transplants at the two organs. Monitoring the physiological status of mussels, in parallel with the biomarker measurements, is useful in assessing the impact of contaminants.

Acute and chronic sensitivity, avoidance behavior and sensitive life stages of bullfrog tadpoles exposed to the biopesticide abamectin

As compared to other aquatic organism groups, relatively few studies have been conducted so far evaluating the toxicity of pesticides to amphibians. This may at least partly be due to the fact that regulations for registering pesticides usually do not require testing amphibians. The sensitivity of amphibians is generally considered to be covered by that based on toxicity tests with other aquatic organisms (e.g. fish) although the impact of a pesticide on amphibians may be very different. In the present study, acute and chronic laboratory tests were conducted to evaluate the acute and chronic toxicity of abamectin (as Vertimec(®) 18EC) to bullfrog (Lithobates catesbeianus) tadpoles. Acute tests were conducted at two tadpole stages (Gosner stage 21G and 25G) and avoidance tests were also conducted with stage Gosner stage 21G tadpoles. Calculated acute toxicity values were greater than those reported for standard fish test species, hence supporting the use of fish toxicity data as surrogates for amphibians in acute risk assessments. Given the limited number and extent of available amphibian toxicity studies, however, research needs to increase our understanding of pesticide toxicity to amphibians are discussed.

Effects of Cutrine-Plus® algaecide and predators on wood frog (Lithobates sylvaticus) tadpole survival and growth

Copper contamination is increasing in many aquatic ecosystems. One mode by which copper can be introduced into aquatic ecosystems is as an algaecide, such as Cutrine-Plus®. Using a mesocosm experiment, we examined the effects of Cutrine-Plus® on wood frog (Lithobates sylvaticus) tadpoles. In addition, we examined how the presence of a nonnative predator the Western mosquitofish (Gambusia affinis) may interact with exposure to Cutrine-Plus®. Exposure to our low and high Cutrine-Plus® treatments had a strong negative effect on the wood frog tadpoles, and survivorship was greatly decreased in the low treatment, and no tadpoles survived in the high treatment. Additionally, the tadpoles that survived the low treatment were significantly smaller than those in the control treatment. Mosquitofish had no effect on the survivorship or growth of wood frog tadpoles, and mosquitofish presence did not have a significant interaction with the Cutrine-Plus® treatments. Cutrine-Plus® clearly had a negative effect on wood frog tadpoles at the concentrations used in our experiment, which were at and below the label-recommended dosages, suggesting that the use of Cutrine-Plus® in natural ponds may have negative consequences for wood frog populations and possibly other amphibians.

Flurochloridone-based herbicides induced genotoxicity effects on Rhinella arenarum tadpoles (Anura: Bufonidae)

Acute toxicity and genotoxicity of the flurochloridone (FLC)-containing commercial formulation herbicides Twin Pack Gold(®) (25 percent a.i.) and Rainbow(®) (25 percent a.i.) were evaluated on Rhinella arenarum (Anura: Bufonidae) tadpoles exposed under laboratory conditions. Lethal effect was evaluated as end point for lethality, whereas frequency of micronuclei (MN) and single cell gel electrophoresis (SCGE) were employed as end points for genotoxicity. Lethality studies revealed equivalent LC-5096 h values of 2.96 and 2.85 mg/L for Twin Pack Gold(®) and Rainbow(®), respectively. Twin Pack Gold(®) did not induce DNA damage at the chromosomal level, whereas Rainbow(®) increased the frequency of MN only when the lowest concentration (0.71 mg/L) was used. However, all concentrations of Twin Pack Gold(®) and Rainbow(®) increased the frequencies of primary DNA lesions estimated by alkaline SCGE. This study represents the first evidence of the acute toxic and genotoxic effects exerted by two FLC-based commercial formulations, Twin Pack Gold(®) and Rainbow(®), on tadpoles of an amphibian species native to Argentina under laboratory conditions. Finally, our findings highlight the importance of minimizing the impacts on nontarget living species exposed to agrochemicals.

Copper-driven avoidance and mortality in temperate and tropical tadpoles

Amphibians have experienced an accentuated population decline in the whole world due to many factors, one of them being anthropogenic contamination. The present study aimed to assess the potential effect of copper, as a worldwide and reference contaminant, on the immediate decline of exposed population due to avoidance and mortality responses in tadpoles of three species of amphibians across climatic zones: a South American species, Leptodactylus latrans, a North American species, Lithobates catesbeianus, and a European species, Pelophylax perezi. A non-forced exposure system with a copper gradient along seven compartments through which organisms could freely move was used to assess the ability of tadpoles to detect and avoid copper contamination. All species were able to avoid copper at a concentration as low as 100 μg L(-1). At the lowest (sublethal) concentrations (up to 200 μg L(-1)) avoidance played an exclusive role for the population decline, whereas at the highest concentrations (> 450 μg L(-1)) mortality was the response determining population decline. The median concentrations causing exposed population immediate decline were 93, 106 and 180 μg L(-1) for Le. latrans, Li. catesbeianus and P. perezi, respectively. Contaminants might, therefore, act as environmental disruptors both by generating low-quality habitats and by triggering avoidance of tadpoles, which could be an important response contributing to dispersion patterns, susceptibility to future stressors and decline of amphibian populations (together with mortality).

Use of Lithobates catesbeianus tadpoles in a multiple biomarker approach for the assessment of water quality of the Reconquista River (Argentina)

The water quality of the Reconquista River (Argentina) water was monitored between 2009 and 2010 by means of a multiparametric approach. This periurban river is affected by agricultural, urban, and industrial discharges. Water samples were collected at a dam located in the headwaters and at 18 km downstream (M). Physicochemical profile and two water-quality indices (WQIs) were determined. Laboratory bioassays were performed by exposing Lithobates catesbeianus tadpoles to environmental samples for 96 h and determining the following parameters: (1) brain: acetylcholinesterase (AChE) activity; (2) gill: catalase and glutathione-S-transferase (GST) activities and glutathione (GSH) content; (3) liver: CAT and GST activities, superoxide dismutase, lipid peroxidation, and GSH content; (4) condition factor and hepatosomatic index; and (5) genotoxicity [micronucleus (MN) test in erythrocytes]. Physicochemical profile and WQIs corresponded with extensive pollution in M. Important temporal and spatial variability in biomarkers of tadpoles exposed to samples was found. Multivariate analyses showed that AChE in brain, MN frequency, liver and gill GST activities, and GSH content were key biomarkers.

Effects of copper, zinc and dragonfly kairomone on growth rate and induced morphology of Bufo arabicus tadpoles

It is well documented that many amphibian species can detect chemical signals from predatory invertebrates and subsequently develop alternate phenotypes that are protective against predation. The effects of metallic pollutants on the development of predator-induced morphology have not previously been reported. Tadpoles of the Arabian toad Bufo arabicus were exposed for 20 days to copper (0, 10 or 100 μg/L), zinc (0, 10 or 100 μg/L) and kairomones of larval dragonflies (Crocothemis erythrea 1 dragonfly/12 L) in a fully crossed design. The effects of these treatments of growth and body shape were measured. Measured copper concentrations after 24 h were 4.25 μg/L±1.30 (10 μg/L nominal) and 34.9 μg/L±2.15 (100 μg/L nominal). Measured zinc concentrations were 3.04 μg/L±0.1 (10 μg/L nominal) and 26.3 μg/L±12.3 (100 μg/L nominal). Tadpoles exposed to 34.9 μg/L copper were significantly lighter and had a shorter body length than other groups. There was no direct effect of zinc on growth or tadpole shape. Tadpoles exposed to dragonfly kairomones were heavier, wider and had deeper bodies when viewed laterally and had longer tails but overall length was not affected. At 4.25 μg/L copper differences between the control and predator-exposed phenotypes increased but at 34.9 μg/L the phenotypes converged, indicating that copper may inhibit the induced response.