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

Toxicity assessment of a tebuconazole-based fungicide on the embryo-larval development of the common south American toad Rhinella arenarum

Agrochemicals cause diverse effects on aquatic communities, and amphibian species are particularly threatened due the high susceptibility to contamination. Present study evaluates the toxicity of a widely used fungicide tebuconazole (Trigal®) by the assessment of mortality and developmental alterations at acute, subchronic, and chronic exposure during the embryo-larval development of the South American toad Rhinella arenarum. Also, the sensitivity of the different embryonic stages was evaluated with 24-h pulse exposure treatments. The results demonstrated that larvae were more sensitive than embryos at acute exposure (LC50-24 and 96 h = 74.62, 31.92 mg/L and 24.27, 16.81 mg/L for embryos and larvae, respectively). Nevertheless, embryos toxicity increased significantly achieving a sensitivity very similar to larvae at chronic exposure (LC50-168 and 504 h = 13.31, 4.35 mg/L and 14.47, 6.83 mg/L for embryos and larvae, respectively). Embryos exhibited several sublethal effects from 5 mg/L at 96 h onwards, such as delayed development, reduce body size, edemas, tail/axial flexures, weakness, and absence of movements. The teratogenic index at 96 h was 10.13, indicating the severe teratogenic potential of the fungicide. 24-h pulse exposure treatments showed an increased sensitivity in intermediate stages as S.11, S.18, S20, and S.23 (NOEC-96 h = 100, 200, 75, and 20 mg/L, respectively), while stage S.25 was the most sensitive to the fungicide (NOEC-96 h = 5 mg/L). About metamorphic process, tebuconazole caused an acceleration of metamorphosis at the lowest concentration (0.001 mg/L), but also an increase in mortality and in addition, significant differences in the weight in all treatments. The results obtained throughout this work indicate that tebuconazole cause several adverse effects in Rhinella arenarum embryo-larval development.

The Use of Multiple Biomarkers to Assess the Health of Anuran Amphibians in the Brazilian Cerrado Savanna: An Ecotoxicological Approach

Changes in the natural landscape and the indiscriminate use of pesticides can have a major impact on aquatic environments and have contributed to the worldwide decline of amphibian populations. In the present study, we sampled tadpoles of three anuran amphibians (Boana albopunctata, Physalaemus cuvieri, and Dendropsophus minutus) from ponds in six different agricultural landscapes of the Brazilian Cerrado savanna and evaluated whether and to what extent genotoxic and mutagenic damage was related to land use (the amount of forest and agricultural remnants, and related physicochemical factors) and the presence of pesticides in the water of the study ponds. We also evaluated the hepatotoxicity in P. cuvieri, which was the most abundant species at five of the six sampling points. Clomazone and atrazine were the most common pesticides found in the ponds. The B. albopunctata and P. cuvieri tadpoles presented similar patterns of DNA damage among the sampling points. The least DNA damage was found in the D. minutus tadpoles, although this species was present in only one of the study ponds. More binucleated and anucleated cells were observed in B. albopunctata, but there was no significant variation among species in terms of the number of micronuclei or other erythrocytic nuclear abnormalities. Land use and physicochemical factors did not explain the variation in the DNA damage observed in the three anurans. The hepatotoxicity analyses of P. cuvieri revealed the presence of a series of alterations, including the enlargement of the sinusoids, vacuolization of the hepatocytes, the infiltration of inflammatory cells, hepatic steatosis, and dilation of the blood vessels. The interaction between physicochemical factors and the biomarkers analyzed in the present study is complex. In particular, it will be important to better elucidate which factors are contributing, either directly or indirectly, to the decline of anuran amphibian populations, especially in threatened biomes, such as the Brazilian Cerrado. In this case, we would encourage further in situ studies that assess the ecotoxicology of the landscape, together with the systematic monitoring of aquatic environments, to guarantee the long-term integrity of amphibian populations, and those of other organisms that play an essential functional role in the ecosystem. Environ Toxicol Chem 2023;42:2422-2439. © 2023 SETAC.

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

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

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.

Exposure, but not timing of exposure, to a sulfonylurea herbicide alters larval development and behaviour in an amphibian species

Environmental contamination is one of the major causes of biodiversity loss. Wetlands are particularly susceptible to contamination and species inhabiting these habitats are subjected to pollutants during sensitive phases of their development. In this study, tadpoles of a widespread amphibian, the spined toad (Bufo spinosus), were exposed to environmental concentrations of nicosulfuron (0 μg/L; 0.15 ± 0.05 μg/L and 0.83 ± 0.04 μg/L), a sulfonylurea herbicide, during different phases of development. Tadpoles were exposed during embryonic (12.98 ± 0.90 days) or larval development (93.74± 0.85 days), or throughout both phases, and we quantified development duration, morphological traits and behavioural features as responses to exposure. Developing tadpoles exposed to nicosulfuron were larger, but with smaller body, and had shorter but wider tail muscles. They were also more active and swam faster than control tadpoles and showed diverging patterns of behavioural complexity. We showed that higher concentrations had greater effects on individuals than lower concentrations, but the timing of nicosulfuron exposure did not influence the metrics studied: Exposure to nicosulfuron triggered similar effects irrespective of the developmental stages at which exposure occurred. These results further indicate that transient exposure (e.g., during embryonic development) can induce long-lasting effects throughout larval development to metamorphosis. Our study confirms that contaminants at environmental concentrations can have strong consequences on non-target organisms. Our results emphasize the need for regulation agencies and policy makers to consider sublethal concentrations of sulfonulyrea herbicides, such as nicosulfuron, as a minimum threshold in their recommendations.

Latitude-Induced and Behaviorally Thermoregulated Variations in Upper Thermal Tolerance of Two Anuran Species

Although thermal tolerance along geographical gradients gives an insight into species' response to climate change, current studies on thermal tolerance are strongly skewed towards global-scale patterns. As a result, intraspecific variations are often assumed to be constant, despite a lack of evidence. To understand population-specific responses to thermal stress, we investigated the presence of intraspecific variations in the critical thermal maximum (CTmax) of tadpoles in two anuran species, Rana uenoi and Bufo sachalinensis. The study was conducted across a five-degree latitudinal gradient in the Republic of Korea. We exposed the tadpoles to increasing temperatures and recorded the CTmax for 270 R. uenoi individuals from 11 sites, collected in rice paddies, and for 240 B. sachalinensis individuals from ten sites, collected in reservoirs. We also recorded the swimming performance and behavior of the tadpoles when placed in an experimental apparatus during CTmax measurements. We then used linear regressions to determine the relationship between abiotic factors and CTmax. In R. uenoi, we found a positive relationship between latitude and CTmax, but the tadpoles did not display specific thermoregulatory behaviors. In B. sachalinensis, none of the abiotic factors such as climate and geographic coordinates were related to CTmax, but we detected a tendency to swim close to the water surface when water temperature was increasing. For R. uenoi, we tentatively relate the CTmax variability across the latitudinal gradient to a physiological adaptive response associated with habitat characteristics that are assumed to be fluctuating, as the species inhabits small water bodies prone to drying out. In the case of B. sachalinensis, the behavior observed may be linked to oxygen depletion and thermoregulation, as it may buffer temperature changes in the absence of physiological adjustment. These findings suggest that intra-specific variations in CTmax are greater than generally accounted for, and thermal conditions of natural environments are important for understanding thermal tolerance in ectothermic species. Our results highlight that species' specific responses to climate warmings need to be studied to better protect species against climate change.

Effects of the insecticide β-endosulfan on tadpoles of Isthmohyla pseudopuma (Anura: Hylidae)

Conventional agriculture uses pesticides intensively. Once pesticides are released into the environment, they can be toxic to non-target organisms. Exposure of amphibians to pesticides can be lethal and affect their growth, development and behavior. β-endosulfan is a persistent organochlorine that has been detected in environmental samples within protected sites in Costa Rica, far from agricultural areas. The aim of this study was to evaluate the lethal and sublethal effects, as well as changes in three biomarkers (Cholinesterase activity [ChE], glutathione S-transferase activity [GST] and lipid peroxidation [LPO]) in tadpoles of Isthmohyla pseudopuma exposed to β-endosulfan. A 96-h acute test (20, 40, 60, 80, 100 and 200 µg/L) was performed in order to calculate the median lethal concentration (LC₅₀), while effects on growth and development were assessed during a 4-weeks chronic test (10, 20, 30 and 50 µg/L). In addition, we measured the aforementioned biomarkers in tadpoles exposed to concentrations below the LC₅₀. The 96-h LC₅₀ for this species was 123.6 µg/L. We found no evidence of β-endosulfan influencing any of the three biomarkers evaluated. At 50 µg/L, both length and total weight of tadpoles decreased with respect to the control. Also, at 30 and 50 µg/L we observed that individuals showed a slower development. Therefore, we demonstrated that at sublethal concentrations, β-endosulfan negatively affects I. pseudopuma at early stages causing tadpoles to develop slower and smaller than normal.

Different time patterns of the presence of red-eared slider influence the ontogeny dynamics of common frog tadpoles

The coexistence of species in a given community depends on the set of species involved and the timing of their interactions. Many native communities are increasingly forced to face both direct and indirect pressures from new alien predators, which, in extreme cases, can lead to the extinction of prey populations. In this study, we examine the dynamics of the ontogeny of common frog (Rana temporaria) tadpoles under different time patterns of an alien predator-the red-eared slider (Trachemys scripta elegans) presence. We found that the tadpoles had a longer larval period and were smaller in size at metamorphosis and lower in body mass when the predator was present in early development than when the tadpoles developed without a predator. The early presence of a predator conspicuously reduced the growth increments of the tadpoles at early development. After the removal of the predator, growth accelerated above the level measured under the conditions of both the late predator and no predator. However, these growth rates did not exceed the growth rates of equally sized tadpoles in the other treatments and therefore were not sufficient to compensate for the growth slowdown in the first part of development. The presence of a predator in late tadpole development influenced neither the time to metamorphosis nor size/body mass at metamorphosis. In conclusion, the predator had the effect on metamorphosis traits only if it was present in the early development of tadpoles.

Acute, chronic and neurotoxic effects of dimethoate pesticide on Rhinella arenarum throughout the development

Among the factors implicated in amphibian global decline, agrochemicals have been gaining increasing attention. In order to evaluate the toxicity of a dimethoate-based insecticide on the early development of an autochthonous amphibian, Rhinella arenarum, continuous and 24 h pulse exposure bioassays were carried out. Lethal and sublethal effects, neurotoxicity and the ecological risk were assessed. Results demonstrate that larvae were more sensitive than embryos with 504 h-LC50 of 12.82 and 16.38 mg L^-1, respectively. 24 h pulse experiments showed a high toxicity increment at early embryonic stages, while the sensitivity at later stages was high and constant. Dimethoate caused teratogenesis and several sublethal effects as morphological and behavioral alterations but also disruption in the metamorphic process. About neurotoxicity, dimethoate inhibited the activity of butyrylcholinesterase at 0.5 and 1 mg L^-1 exposed larvae. The results obtained in this study as the risk assessment revealed that dimethoate represents a hazard on Rhinella arenarum survival and development but also a potential risk for the continuity of the populations of this species in agroecosystems.

Effect of multiple stressors and population decline of frogs

The ongoing decline in anuran populations is linked primarily to the effects of stressor agents such as pathogens, pesticides, alterations of natural landscapes, and the introduction of exotic species. Most studies that have evaluated the effects of these stressors have focused on a single component, which is the opposite of the reality of most natural environments, where anuran populations tend to suffer the influence of multiple agents simultaneously. Studies of the effects of the interaction between these components are extremely important, given that one agent may potentialize (synergistic effect) or weaken another (antagonistic effect) or, in some cases, have a neutral effect. The present study is based on the scientometric analysis of three bibliographic databases (ISI Web of Science, Scopus, and PubMed), which identified 1376 papers that reported on the global decline of anuran populations, although only 172 of these studies focused on the interactive effects of environmental stressors. Synergistic effects were the most frequent type of interaction, followed by antagonistic effects, and a small number of studies that found no clear interaction between the stressors. Pathogens and pesticides were the classes of stressor studied most frequently, while climate-pathogen and pathogen-pesticide interactions were the combinations that featured in the largest number of studies. Overall, we would recommend a more systematic focus on the dynamics of the interactions among the stressors that impact anuran populations, in particular for the elaboration of conservation programs, given that these agents tend to have complex combined effects.

Influence of octylphenol on gene expression of gonadotropins and their receptors, testicular structure and mating behavior of male Rana chensinensis

In the present study, responses of the Chinese brown frog (Rana chensinensis) to exposure to different doses and duration of Octyphenol (OP) which degraded from alkylphenol ethoxylates (APEs) were characterized during the adult periods. The effects of OP on growth, development and reproduction and the expression of genes in gonad were investigated. The expression levels of fshβ, lhβ, fshr and lhr had significant differences as the exposure time increased. The pathological and morphological changes were also observed in the OP treatments. Furthermore, the number of TUNEL positive cells and the TUNEL index was elevated after exposed to OP. Besides that, OP treatment could influence its mating behavior and reduce the fertilization rates. Taken together, these results indicated that OP disrupt sex steroid signaling, normal development of spermatogenesis, courtship behavior of male frogs and decline fertilization rate in R. chensinensis.

Exposure impacts of Imazapyr formulation on larval development and thyroid histology of Xenopus laevis

There are increased concerns about the thyroidal effects of many anthropogenic substances in the environment. These substances include agricultural pesticides and industrial and pharmaceutical chemicals among others. Their potential thyroidal effects are of serious health and ecological concerns, as thyroid hormones mediate numerous physiological processes, including growth regulation, general metabolism and metamorphosis in metamorphic animals. This study assessed thyroidal activities of Arsenal formulation (Imazapyr) at environmentally relevant concentrations of 0.5, 2.0 and 3.5 mg/L following a Xenopus metamorphosis assay (XEMA). The result shows that the Arsenal formulation significantly delayed the tadpole development, reduced the hind-limb length (HLL) and increased the whole-body mass (WBM) at a concentration of 3.5 mg/L relative to the control exposure. In histopathology, the formulation increased the epithelium height, at all exposure concentrations, but reduced the colloidal area at 0.5 and 2 mg/L, respectively, and the gland area at 2 mg/L relative to the control. Consequently, the Arsenal formulation is thyroid-active at environmentally relevant concentrations and poses a threat to both human and wildlife, especially metamorphic organisms. With this exposure impact, more studies are imperative to further characterise other endocrine-disrupting potential of this formulation, while future applications should be reduced or restricted to less risk environment, if it cannot be stopped from sensitive aquatic systems.

Disruptive effects of chlorpyrifos on predator-prey interactions of Ceratophrys ornata tadpoles: Consequences at the population level using computational modeling

Large-scale ecotoxicological studies have technical and ethical limitations, both related to the need to expose large numbers of individuals to potentially harmful compounds. The computational modeling is a complementary useful and predictive tool that overcomes these limitations. Considering the increasing interest in the effects of pesticides on behavioral traits, the aim of this study was to evaluate the effects of chlorpyrifos (CPF) on intra- and inter-specific interactions of anuran tadpoles, complementing traditional ecotoxicological tools with a theoretical analysis verified by computational simulations. Experiments were developed under two consecutive phases: a first phase of exposure (treated and control group), and a second phase of interactions. The second phase consisted of evaluating the effects of CPF on intra- and inter-specific interactions of exposed C. ornata (Co) tadpoles acting as predators and unexposed Rhinella fernandezae (Rf) tadpoles acting as prey (Experiment I), under different predator-prey proportions (0/10 = 0Co-10Rf, 2/8, 4/6, 6/4, 8/2, 10/0). Also, intraspecific interactions of three Co tadpoles under different conditions of exposure were evaluated (Experiment II: 3 exposed Co, 2 exposed Co/1 non-exposed, 1 exposed Co/2 non-exposed). During the exposure phase, chlorpyrifos induced significant mortality from 48 h (48 h: p < 0.05, 72 h-96 h: p < 0.001), irregular swimming, tail flexure, and the presence of subcutaneous air. Also, it induced effects on the sounds emitted after 96 h of exposure, registering a smaller number of pulses and higher dominant frequencies, and altered intra- and inter-specific interactions. During the interaction phase, the larvae continued to show sound effects, however, the antipredator mechanism continued to be operating and efficient. Finally, it was possible to model the behavior of the larvae under the effects of chlorpyrifos. We conclude that experimental data and computational modeling matched. Therefore, computational simulation is a valuable ecotoxicological tool that provides new information and allows prediction of natural processes.

Persistent pesticides: effects of endosulfan at the molecular level on the aquatic invertebrate Chironomus riparius

Although banned in multiple areas, due to its persistence in the environment, endosulfan constitutes a significant environmental concern. In this work, fourth instar Chironomus riparius larvae were exposed at environmentally relevant endosulfan concentrations of 0.1, 1, and 10 μg/L for 24 h to analyze the possible effects of this acaricide on gene expression and enzymatic activity. Transcriptional changes were studied through the implementation of a real-time polymerase chain reaction array with 42 genes related to several metabolic pathways (endocrine system, detoxification response, stress response, DNA reparation, and immune system). Moreover, glutathione-S-transferase (GST), phenoloxidase (PO), and acetylcholinesterase (AChE) activities were assessed. The five pathways were differentially altered by endosulfan exposure with significant changes in the E93, Dis, MAPR, Met, InR, GSTd3, GSTt3, MRP1, hsp70, hsp40, hsp24, ATM, PARP, Proph, and Def genes. Besides, all of the measured enzymatic activities were modified, with increased activity of GST, followed by PO and AChE. In summary, the results reflected the effects provoked in C. riparius at molecular level despite the absence of lethality. These data raise concerns about the strong alteration on different metabolic routes despite the low concentrations used. Therefore, new risk assessment strategies should consider include the effects at the sub-organismal level as endpoints in addition to the classical ecologically relevant parameters (such as survival). This endeavor will facilitate a comprehensive evaluation of toxicants in the environment.

Genotoxic and melanic alterations in Lithobates catesbeianus (anura) tadpoles exposed to fipronil insecticide

The aim of this study was to evaluate the genotoxic and morphological systemic effects of both an acute and a chronic exposure of bullfrog tadpoles to fipronil. Lithobates catesbeianus tadpoles had morphological biomarkers (skin, liver, and blood) analyzed at Gosner stages 36-38, when exposed to four different concentrations of Regent® 800 WG (80% fipronil): 0.00 (control), 0.04, 0.08, 0.4 mg/L, and four experimental times: 4, 8, 12, and 16 days. Body darkness responded directly to the treatment and exposure time. There was a treatment-dependent decrease in darkness of heads and tails. In relation to the biometric analysis, fipronil induced a decrease in the individual weight and liver mass at the end of the experiments, whereas the hepatosomatic index did not vary according to the treatment. For the exposed animals and for the control group, the area of hepatic melanin increased as exposure time increased. Fipronil has genotoxic effects on L. catesbeianus tadpoles even after short exposure times (e.g., 4 and 8 days), and the main nuclear abnormality is in the anucleate cells. A relevant correlation was observed between genotoxic biomarkers and cutaneous and internal melanin. The frequency of nuclear abnormalities is inversely correlated both with the hepatic melanin area and with the cutaneous melanin of animals. Fipronil has distinct systemic effects on tadpoles based on its concentration, as well as on its exposure time. Such alterations (pigmentation level and rate of erythrocyte abnormality) result in morphological and physiological effects, which may compromise the behavior and survival of the anurans.

Lethal and sublethal effects of the natural and healthy spinosad-based formulation Tracer™ on tadpoles of two neotropical species

This paper presents the first acute toxicity data of the natural insecticide spinosad in amphibians. The sensitivity of two neotropical sympatric anuran species, Boana pulchella and Rhinella arenarum, to spinosad-based formulation Tracer™ was evaluated. Lethal effects are reported in tadpoles of B. pulchella stage 25 between 2.81 and 35.44 mg spinosad/L, while for the same concentration range no lethal effects were detected in tadpoles of R. arenarum of the same stage. In addition, Tracer™ produced sublethal effects at the individual level on the swimming activity, morphology (growth and presence of abnormalities), and development of B. pulchella from 2.81 to 5.78 mg spinosad/L, while in R. arenarum effects were only detected in the swimming activity and growth from 2.78 and 6.22 mg/L, respectively. At the biochemical level, Tracer™ produced inhibition of different enzymatic activities, among them, catalase activity at 2.81 mg spinosad/L, glutathione S- transferase activity from 2.81 to 2.98 mg spinosad/L, and acetylcholinesterase activity at 2.81 mg spinosad/L. These findings allow us to conclude that B. pulchella is more sensitive than R. arenarum to spinosad-based formulation Tracer™. The effects demonstrated here are not consistent with those expected since spinosad is supposed to be an environmental healthy alternative. This paper provides useful and necessary information to implement regulations on the use of new compounds entering the market and its associated risks.

The effect of urban morphological characteristics on the spatial variation of PM2.5 air quality in downtown Nanjing

The effects of the urban morphological characteristics on the spatial variation of near-surface PM_2.5 air quality were examined. Unlike previous studies, we performed the analyses in real urban environments using continuous observations covering the whole scale of urban densities typically found in cities. We included data from 31 measurement stations divided into 8 different wind sectors with individually defined morphological characteristics leading to highly varying urban characteristics. The urban morphological characteristics explained up to 73% of the variance in normalized PM_2.5 concentrations in street canyons, indicating that the spatial variation of the near-surface PM_2.5 air quality was mostly defined by the characteristics studied. The fraction of urban trees nearby the stations was found to be the most important urban morphological characteristic in explaining the PM_2.5 air quality, followed by the height-normalized roughness length as the second important parameter. An increase in the fraction of trees within 50 m of the stations from 25 percentile to 75 percentile (i.e. by the interquartile range, IQR) increased the normalized PM_2.5 concentration by up to 24% in the street canyons. In open areas, an increase in the trees by the IQR actually decreased the normalized PM_2.5 by 6% during the pre-COVID period. An increase in the height-normalized roughness length by the IQR increased the normalized PM_2.5 by 9% in the street canyons. The results obtained in this study can help urban planners to identify the key urban characteristics affecting the near-surface PM_2.5 air quality and also help researchers to evaluate how representative the existing measurement stations are compared to other parts of the cities.

The most important characteristics in terms of the PM_2.5 concentrations were the fraction of trees and the height-normalized roughness length. The study was performed using continuous observations covering the whole scale of urban densities.

Agrochemicals with estrogenic endocrine disrupting properties: Lessons Learned?

Many agrochemicals have endocrine disrupting properties. A subset of these chemicals is characterized as "estrogenic". In this review, we describe several distinct ways that chemicals used in crop production can affect estrogen signaling. Using three agrochemicals as examples (DDT, endosulfan, and atrazine), we illustrate how screening tests such as the US EPA's EDSP Tier 1 assays can be used as a first-pass approach to evaluate agrochemicals for endocrine activity. We then apply the "Key Characteristics" approach to illustrate how chemicals like DDT can be evaluated, together with the World Health Organization's definition of an endocrine disruptor, to identify data gaps. We conclude by describing important issues that must be addressed in the evaluation and regulation of hormonally active agrochemicals including mixture effects, efforts to reduce vertebrate animal use, chemical prioritization, and improvements in hazard, exposure, and risk assessments.

Sensitivity of Boana pulchella (Anura: Hylidae) Tadpoles to Environmentally Relevant Concentrations of Chlorpyrifos: Effects at the Individual and Biochemical Levels

We report sublethal effects of environmentally relevant concentrations of chlorpyrifos at the individual (swimming alterations) and biochemical (esterase activities and antioxidant enzymes) levels in the Montevideo tree frog Boana pulchella larvae. The 50% lethal concentration at 96 h (LC50-96h) for chlorpyrifos in stage-29 B. pulchella tadpoles was 0.98 mg/L, which was close to the 65th percentile of published anuran species sensitivity. In B. pulchella, chlorpyrifos disrupted biochemical processes: tadpoles showed a significant inhibition of esterase activity and a significant induction of antioxidant enzymes, indicating a response to an environmental challenge causing oxidative stress. Using principal components analysis, we could associate chlorpyrifos reduction in esterase activity with swimming alterations at 0.5 mg/L of the toxicant. The biochemical biomarkers reported in the present study respond at levels 20 times lower than the LC50-96h and were associated with a biologically important response-swimming behavior. The link of responses across different levels of biological organization was demonstrated. The species is suitable as a model for ecotoxicological studies at different levels, including the individual and biochemical levels, and may be considered a good reference organism in environmental control programs. Environ Toxicol Chem 2020;39:834-841. © 2020 SETAC.

The impact of elevated temperature and CO2 on growth, physiological and immune responses of Polypedates cruciger (common hourglass tree frog)

BACKGROUND

Amphibians are one of the most susceptible groups to climate change as their development occurs in aquatic environments or in microhabitats with high humidity. Accordingly, our primary objective was to investigate the chronic physiological responses seen in early larval to adult stages of Polypedates cruciger (Common hourglass tree frog) to future climate change based on continuous exposure to elevated temperature and elevated CO2 -induced low water pH. Free-swimming and free-feeding tadpoles were observed until metamorphosis under four experimental treatments; two elevated temperatures, one elevated CO2 (reduced pH) and a control maintained at ambient temperature (29 °C ± 1 °C) and CO2 (pH = 7). Elevated temperature treatments were maintained at 32 °C ± 0.5 °C and 34 °C ± 0.5 °C to represent respectively, the future climate scenarios RCP2.6 (Representative Concentration Pathway 2.6, the 'base-case' scenario) and RCP8.5 ('business-as-usual' scenario) according to the 5th Assessment Report of the IPCC. Elevated CO2 treatment was maintained within the pH range of 5.5-5.6 representing the range expected between RCP8.5 and RCP2.6.

RESULTS

Compared to the control, elevated CO2 accelerated phenological progression of tadpoles through Gosner stages, thus resulting in lower body size at metamorphosis. Both elevated temperatures significantly delayed the development and reduced the growth of tadpoles. 100% mortality was observed in 34 °C treatment before metamorphosis (before Gosner stage 36) while all the tadpoles died after metamorphosis (at Gosner stage 46) in 32 °C treatment. Elevated CO2 increased tadpole activity, in terms of their swimming speed, while both of the elevated temperatures reduced it compared to the control. Catalase activity increased at elevated CO2. Ammonia excretion by tadpoles was decreased by elevated CO2, but increased under temperature elevation. Both Elevated CO2 and temperature treatments reduced the white blood cell count and its percentage of thrombocytes. Percentages of lymphocytes, monocytes and neutrophils were increased at 32 °C, while lymphocyte percentage and lysozyme activity were increased at elevated CO2. Several deformities were observed in tadpoles at elevated temperature and CO2.

CONCLUSIONS

Elevated temperatures and reduced pH due to elevated CO2, being major features of climate change, increase the vulnerability of amphibians, who are already one of the most threatened vertebrate groups. Based on our observations on the model amphibian species P. cruciger, increased vulnerability to climate change occurs by reducing their growth, body size and motility while also reducing their immunity and inducing physical deformities. These impacts are highly-likely to reduce the foraging, competitive and reproductive capabilities in their natural habitats. We conclude further that even the 'best-case' scenario of future climate change can impose significant physiological impacts that could threaten amphibian populations on broader spatial and temporal scales.

GRAPHICAL ABSTRACT

An imazethapyr-based herbicide formulation induces genotoxic, biochemical, and individual organizational effects in Leptodactylus latinasus tadpoles (Anura: Leptodactylidae)

Genotoxic, biochemical, and individual organizational effects on Leptodactylus latinasus tadpoles were evaluated after exposure to an imazethapyr (IMZT)-based commercial herbicide formulation, Pivot® H (10.59% IMZT). A determination of the value of the lethal concentration (LC50) was determined as a toxicological endpoint. Alterations in animal behavior and morphological abnormalities as well as cholinesterase (ChE), catalase (CAT), and glutathione S-transferase (GST) activities were employed as individual sublethal endpoints. Micronuclei frequencies (MNs), binucleated cells (BNs), blebbed nuclei (BLs), lobed nuclei (LBs), notched nuclei (NTs), erythroplastids (EPs), and evaluation of DNA strand breaks were employed as genotoxic endpoints. All biomarkers were evaluated after 48 and 96 h of exposure to concentrations of IMZT within 0.07-4.89 mg/L. LC50_96h values of 1.01 and 0.29 mg/L IMZT were obtained for Gosner stages 25 and 36, respectively. Irregular swimming, diamond body shape, and decreased frequency of keratodonts were detected at both sampling times. Results showed that IMZT increased GST activity and MN frequency at 48 and 96 h of exposure. Other nuclear abnormalities were also observed in the circulating erythrocytes of tadpoles, i.e., NT and BL values after 48 h, and LN, BL, and EP values after 96 h. Finally, results showed that IMZT within 0.07-0.22 mg/L increased the genetic damage index in tadpoles exposed for both exposure times (48 and 96 h). This study is the first to report the sublethal biochemical effects of IMZT in anurans and is also the first report using L. latinasus tadpoles as a bioindicator for ecotoxicological studies.

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.

Endosulfan toxicity in Nile tilapia (Oreochromis niloticus) and the use of lycopene as an ameliorative agent

OBJECTIVES

Endosulfan is a broad-spectrum organochlorine insecticide that has been commercially in use for decades to control insect pests and has been found to pollute the aquatic environment. The current study was carried out to investigate the toxic effects of endosulfan, an organochlorine pesticide, on Nile tilapia (Oreochromis niloticus), a freshwater fish, and the alleviating effects of lycopene on the induced toxicity.

METHODS

Four treatment groups of fish were investigated (3 replicates of 15 fish for each group): (1) a control group, (2) a group exposed to endosulfan, (3) a group that was fed on a basal diet supplemented with lycopene, and (4) a group that was fed on a basal diet supplemented with lycopene and exposed to endosulfan. The experiment was carried out over a 4-week period.

RESULTS

Endosulfan negatively affected liver function, including liver enzymes and plasma proteins. Endosulfan affected blood parameters of fish and reduced the counts of red blood cells (RBCs) and white blood cells (WBCs), as well as affected immunological parameters. Endosulfan caused oxidative stress, as it decreased the values of antioxidants catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), and glutathione (GSH), and increased the level of lipid peroxide malondialdehyde (MDA). Additionally, endosulfan increased cytochrome P450 (CYP450) levels, while it decreased glutathione S-transferase (GST) mRNA transcript levels and distorted the normal histological structure of the liver, gills, and spleen of affected fish. Conversely, lycopene partially restored the aforementioned parameters when administered concomitantly with endosulfan.

CONCLUSION

The results showed the beneficial effects of supplementing fish diets with lycopene as a natural antioxidant for ameliorating the toxicity caused by endosulfan.

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.

Native amphibian larvae exhibit higher upper thermal limits but lower performance than their introduced predator Gambusia affinis

Information on the thermal limits and physiology of ectothermic amphibians is crucial to our understanding of their ecology in the natural environment, particularly with predicted global changes in climate. We documented the thermal limits of larvae of three amphibian species native to Hong Kong, and their introduced, invasive predator, the mosquitofish (Gambusia affinis). We then used larvae of the brown tree frog Polypedates megacephalus as a model amphibian to further investigate growth, oxygen consumption rate and heat shock protein expression with changes in thermal regime. We found that G. affinis was the most tolerant of low temperatures but also the least tolerant of high temperatures. Despite the higher thermal tolerance of the amphibian larvae, further investigation on P. megacephalus demonstrated that optimal temperatures for physiological performance fall within a range of 18.0-21.6 °C, which is far lower than its upper thermal limit, implying that thermal stress occurs during part of the larval stage under natural environmental conditions. This could mean a reduction in their capacity to deal with other stressors such as pollution and predators, and that G. affinis may have an advantage over native amphibians.

Mortality of embryos, developmental disorders and changes in biochemical parameters in marsh frog (Rana ridibunda) tadpoles exposed to the water-soluble fraction of Kazakhstan crude oil and O-Xylene

The effects of different concentrations of water-soluble fraction of crude oil (WSFO) from the Zhanazhol oil field (Aktobe region, Kazakhstan) and compared to o-xylene, prevalent in this oil, on growth and development of marsh frog (Rana ridibunda) were assessed. In subchronic experiments (7 d), a dose-related increase in mortality and incidence of deformities in embryos were observed. In chronic experiments (60 d; starting from the Gosner stage 26), a dose-dependent decrease in body weight, size and developmental delay by 3-4 stages were also detected. In addition, the content of lipid hyperoxide (LHO) and malondialdehyde (MDA), as well as activities of superoxide dismutase (SOD) and catalase (CAT) enzymes in liver of the tadpoles were determined at the end of chronic experiment. Exposure to 0.5 mg/L or 1.5 mg/L WSFO elevated the content of LHO by 76% and 86%, and MDA by 47% and 58% but decreased SOD activity by 26% and 49%, and CAT by 35% and 46%, respectively. A less pronounced adverse effect was found after chronic exposure to the same concentrations of o-xylene. In tadpole liver exposed to o-xylene levels of LHO was increased by 40% and 51%, MDA by 11% and 29%, while the activity of SOD was lowered by 18% and 41%, and CAT - by 13% and 37% in the 0.5 mg/L and 1.5 mg/L treatment groups, respectively. Data demonstrated the embryotoxic and teratogenic effects attributed to WSFO and o-xylene exposure which may involve oxidative stress mechanisms.

Balancing biodiversity outcomes and pollution management in urban stormwater treatment wetlands

Wetlands are increasingly being constructed to mitigate the effects of urban stormwater, such as altered hydrological regimes and reduced water quality, on downstream aquatic ecosystems. While the primary purpose of these wetlands is to manage stormwater, they also attract animals whose growth, survival and breeding (i.e. 'fitness') may be compromised. Such deleterious effects will be exacerbated if animals are caught in 'ecological traps', mistakenly preferring wetlands with unsuitable environmental conditions. Alternatively, wetlands that offer suitable habitat conditions for animals could be beneficial, especially in fragmented urban landscapes. Consequently, a thorough understanding of the potential ecological impacts of stormwater treatment wetlands is critical for managing unintended consequences to urban biodiversity. To help facilitate this understanding, we draw upon findings from a four-year research program conducted in the city of Melbourne in south-eastern Australia as a case study. First, we summarise our research demonstrating that some stormwater wetlands can be ecological traps for native frogs and fish in the study region, whilst others likely provide important habitat in areas where few natural waterbodies remain. We use our work to highlight that while stormwater wetlands can be ecological traps, their effects can be properly managed. We propose the need for a better understanding of the ecological consequences of changes to wetland quality and their population-level impacts across the landscape. We hope that this study will generate discussions about how to most effectively manage constructed wetlands in urban landscapes and more research for a better understanding of the issues and opportunities regarding potential ecological traps.

Effects of low doses Trichlorfon exposure on Rana chensinensis tadpoles

Trichlorfon is an organophosphate insecticide widely used in aquaculture and agriculture. Little is known about the effects of long-term of low doses trichlorfon exposure on amphibians. In this study, we investigated the effects of low doses trichlorfon on Rana chensinensis tadpoles after exposure to 0.01, 0.1, and 1.0 mg/L trichlorfon for 2 and 4 weeks. Survival, growth, development and mortality were monitored regularly over the course of exposure. The results showed that trichlorfon led to a decrease in tadpole survival. Reductions in growth and disruptions to the development of tadpoles were observed in trichlorfon treatments. Morphological abnormalities of affected tadpoles included axial flexures, skeletal malformations and lateral kinks. Trichlorfon increased the frequency of micronucleus (MN) formation in circulating erythrocytes of tadpoles exposed for 2 weeks to 0.1 and 1.0 mg/L trichlorfon. At all concentrations, an enhanced frequency of MN formation was observed in tadpoles exposed for 4 weeks. Exposure to trichlorfon induced other nuclear abnormalities such as lobed and notched nuclei only in tadpoles exposed to 1.0 mg/L trichlorfon for 4 weeks. In addition, exposure to trichlorfon within the 0.01-1.0 mg/L range increased the genetic damage index in hepatic tissues in all treatments. Apoptosis-associated DNA fragmentation in hepatic tissues occurred in a weak ladder-like pattern. This study presents evidence of low doses trichlorfon effects on amphibians, highlighting the properties of this organophosphate insecticide that jeopardize nontarget species exposed to trichlorfon.

Monitoring the morphological integrity of neotropical anurans

Amphibians are considered to be excellent bioindicators to their morphophysiological characteristics and life cycle. In this context, the present study investigated the morphological integrity of anuran larvae collected in preserved environments in the Emas National Park, in the municipality of Mineiros (Goiás state, Brazil), and in environments representative of the agricultural matrix of the Rio Verde region, also in Goiás, where there is a long history of the use of agricultural pesticides. Samples of water from temporary ponds, permanent dams, and veredas were analyzed for the presence of pesticides and, especially atrazine (5350 μg/L), found at significantly higher concentrations in the agricultural matrix. We observed a high percentage (approximately 10%) of morphological malformations including alterations of the fins in Boana albopunctatus and Scinax fuscovarius; alteration in oral structures in B. albopunctatus, Dematonotus muelleri, Physalaemus centralis, Physalaemus cuvieri, and Leptodactylus fuscus mainly in the tadpoles collected in the agricultural environment in comparison with those from the protected area (3.5%; P < 0.0001, χ² 31.75). However, changes in the eyes, mouth, intestines, and nostrils, as well as amelia were observed only in the agricultural environment. The vast majority of the observed malformations were associated with the tail and oral disc, which suggests that these anatomical parameters may be used as sensitive morphological biomarkers. Given these findings, we reinforce that areas of agricultural land may have a deleterious effect on the morphological integrity of the tadpoles and consequently, on their development, and that these features may be used as indicators of environmental quality and health.

Contaminant mixtures interact to impair predator-avoidance behaviours and survival in a larval amphibian

Global declines in amphibian populations are a significant conservation concern, and environmental contamination is likely a contributing driver. Although direct toxicity may be partly responsible, contaminants are often present at sub-lethal concentrations in the wild. Behavioural end-points are becoming an increasingly useful method to estimate the impact of contaminants, particularly if the behavioural responses manifest to affect individual fitness (i.e. survival, growth, or reproduction). In the wild, most animals are affected by multiple stressors, and determining how these interact to affect behaviour is critical for understanding the ecological implications of contaminant exposure. Here, we examined the individual and interactive effect of the heavy metal copper and the insecticide imidacloprid on mortality rates and anti-predator behaviours of spotted marsh frog (Limnodynastes tasmaniensis) tadpoles. This common species frequently occupies and breeds in contaminated stormwater and agricultural wetlands, where copper and imidacloprid are often present. These contaminants may alter behaviour via physiological and neurological pathways, as well as affecting how tadpoles respond to chemical cues. Tadpoles suffered unexpectedly high mortality rates when exposed to imidacloprid concentrations well below published LC50 concentrations. Only unexposed tadpoles significantly avoided predator cues. Copper and imidacloprid reduced swimming speed and distance, and escape responses, while increasing erratic swimming. We observed an interactive effect of imidacloprid and copper on erratic swimming, but in general imidacloprid and copper did not act synergistically. Our results suggest that as contaminants enter waterbodies, tadpoles will suffer considerable direct mortality, reduced foraging capacity, and increased susceptibility to predation. Our results provide the first evidence of imidacloprid affecting amphibian behaviour, and highlight both the adverse effects of copper and imidacloprid, and the importance of exploring the effect of multiple contaminants simultaneously.

Comparative Early Life Stage Toxicity of the African Clawed Frog, Xenopus laevis Following Exposure to Selected Herbicide Formulations Applied to Eradicate Alien Plants in South Africa

The rise in pesticides application has increased the need for better understanding of their ecological impacts. The global amphibian declines, for example, have been positively correlated with pesticides use. The differential susceptibility in the developmental stages of amphibians to chemical substances are still largely unknown. We examined the 96-h differential toxicity responses of embryos, premetamorphic and transitional larval stage of Xenopus laevis, to six formulated aquatic herbicide products containing the active ingredients of diquat dibromide (Midstream), glufosinate ammonium (Basta), imazapyr (Arsenal), and three glyphosate formulations (Roundup, Kilo Max, and Environ Glyphosate). The results showed the premetamorphic stage as the most sensitive to the herbicides toxicity. This study confirmed that the developmental stage at which amphibian are exposed to contaminants is critical to their survival and that the chemical contamination hypothesis of the global decline of amphibians should continue to be considered. This establishment of the premetamorphic larval as sensitive toxicity representative for all developmental stages of X. laevis means that this stage could be used more extensively in pesticides toxicity assessments.

Scientific Opinion on the state of the science on pesticide risk assessment for amphibians and reptiles

Following a request from EFSA, the Panel on Plant Protection Products and their Residues developed an opinion on the science to support the potential development of a risk assessment scheme of plant protection products for amphibians and reptiles. The coverage of the risk to amphibians and reptiles by current risk assessments for other vertebrate groups was investigated. Available test methods and exposure models were reviewed with regard to their applicability to amphibians and reptiles. Proposals were made for specific protection goals aiming to protect important ecosystem services and taking into consideration the regulatory framework and existing protection goals for other vertebrates. Uncertainties, knowledge gaps and research needs were highlighted.

Micronucleus cytome assay in the differential assessment of cytotoxicity and genotoxicity of cadmium and lead in Amietophrynus regularis

Amphibians are increasingly being used as bio-indicator of contamination in ecosystems due to their sensitivity to xenobiotics in the environment. Cadmium and lead compounds, ubiquitous mutagens and carcinogens, are capable of eliciting genome instability in adult toads which may enhance amphibian decline. Micronucleus cytome (MN-cyt) assay, a comprehensive cytogenetic test for the assessment of genome instability induced by xenobiotics in organisms, was utilized in the differential cytogenotoxic evaluation of Cd and Pb in adult Amietophrynus regularis. A. regularis was exposed to six concentrations (8 - 512 mg/L) of the metal solutions to determine 96 h acute toxicity. Four toads per group were exposed to five sub-lethal concentrations (5 - 75 %) of the 96 h LC50 of the metals for 14 days. At post exposure, bone marrow and peripheral erythrocytes were collected for MN-cyt analysis. The metals induced differential concentration and time-dependent increase in mortality with 96 h LC50 of 36.36 mg/L (Cd) and 112.06 mg/L (Pb). No observable effective concentrations (NOEC); Cd=8 and Pb=32 (mg/L) and Lowest observable effective concentrations (LOEC); Cd=16 and Pb=64 (mg/L) were recorded for the metals. Derived toxicity factor (TF) showed that Cd was 3.08 times more toxic to the toads than Pb. The metal solutions induced significant (p<0.05) increase in frequencies of MN, binucleated, nuclear bud, notch, lobe, vacuolated erythrocytes, apoptosis and necrosis compared to the negative control. Cd elicited 1.42 and 3.26 folds increase in MN and NAs respectively, than Pb. MN-cyt assay is a suitable cytogenetic tool for assessing genome instability in A. regularis. Increased genetic instability induced by Cd and Pb may be associated with genetic related syndromes; neoplasms, reproductive dysfunctions and mortality. This suggests threat to amphibian health and may enhance population decline.

Lethal and sublethal effects of the pirimicarb-based formulation Aficida® on Boana pulchella (Duméril and Bibron, 1841) tadpoles (Anura, Hylidae)

Acute lethal and sublethal toxicity of the pirimicarb-based commercial formulation Aficida^® were evaluated on Boana pulchella tadpoles. Whereas mortality was used as end point for lethality, frequency of micronuclei and other nuclear abnormalities as well as alterations in the frequency of erythroblasts in circulating blood as biomarkers for genotoxicity and cytotoxicity, respectively. Swimming, growth, developmental and morphological abnormalities were also employed as sublethal end points. Results show that the species is within the 13th percentile of the distribution of acute sensitivity of species to pirimicarb for aquatic vertebrates. Results revealed values of 23.78 and 101.45mg/L pirimicarb as LC50_96h for GS25 and GS36 tadpoles, respectively. The most evident effects were related with the swimming activity with NOEC and LOEC values within the 0.005-0.39mg/L pirimicarb concentration range. Aficida^® induced DNA damage at the chromosomal level by increasing micronuclei frequency and other nuclear abnormalities, i.e., lobbed and notched nuclei and binucleated cells. Cellular cytotoxicity was found after Aficida^® treatment. The presence of abdominal oedemas in exposed organisms and thus flotation response of organisms could be proposed as a new sensitive exposure parameter. The multiple end point assessment approach used allowed a complete understanding the multi level of effects occurring by exposure to pirimicarb, at least in B. pulchella.

Influence of DEHP on thyroid, sex steroid-related genes and gonadal differentiation in Rana chensinensis tadpoles

In the present study, responses of the Chinese brown frog (Rana chensinensis) to exposure to di-2-ethylhexyl phthalate (DEHP), a common plasticizer, during the larval period were characterized. The effects of DEHP on metamorphosis rate, thyroid hormone, thyroid histology and the expression of genes involved in the steroid hormone synthesis in gonad were investigated. Metamorphosis rate and 50 percent of the tadpoles to reach Gosner stage 42 (T_0.5 ) were significantly slower in all DEHP groups. The thyroid glands of the tadpoles exposed to DEHP clearly exhibited colloid depletion. In addition, decreased concentrations of T4 and T3 were observed in the tadpoles exposed to DEHP. Moreover, the highest DEHP exposure (10 µmol/L DEHP) showed increased ratio of females significantly. Also, up-regulation significantly of transcripts of cytochrome P450 aromatase (CYP19) gene was detected in male tadpoles exposed to DEHP. The present results indicate that this increase in estrogens could lead to female-biased sex ratio in DEHP exposure group. Taken together, the present study indicates that DEHP disrupt thyroid hormone and sex steroid signaling in R. chensinensis tadpoles. Our present observations support evidence of a crosstalk between TH and sex steroids in gonad differentiation.

A combined NMR- and HPLC-MS/MS-based metabolomics to evaluate the metabolic perturbations and subacute toxic effects of endosulfan on mice

Endosulfan is the newly persistent organic pollutants (POPs) added to the Stockholm Convention as its widespread use, persistence, bioaccumulation, long-range transport, endocrine disruption, and toxicity related to various adverse effects. In the present study, male mice were administrated endosulfan at 0, 0.5, and 3.5 mg/kg by gavage for 2 weeks. ¹H-NMR-based urinary metabolomics, HPLC-MS/MS-based targeted serum metabolomics, clinical analysis, and histopathology techniques were employed to evaluate the metabolic perturbations of subacute endosulfan exposure. Endosulfan exposures resulted in weight loss, liver inflammation and necrosis, and alterations in serum amino acids and urine metabolomics. Based on altered metabolites, several significantly perturbed pathways were identified including glycine, serine, and threonine metabolism; TCA cycle; pyruvate metabolism; glycolysis or gluconeogenesis; glycerophospholipid metabolism; and glyoxylate and dicarboxylate metabolism. Such pathways were highly related to amino acid metabolism, energy metabolism, and lipid metabolism. In addition, metabolomic results also demonstrated that gut microbiota was remarkably altered after endosulfan exposure. These observations may provide novel insight into revealing the potential toxic mechanism and evaluating the health risk of endosulfan exposure at metabolomic level.

Effects of a glyphosate-based herbicide and predation threat on the behaviour of agile frog tadpoles

The widespread application of pesticides emphasises the importance of understanding the impacts of these chemicals on natural communities. The most commonly applied broad-spectrum herbicides in the world are glyphosate-based herbicides, which have been suggested to induce significant behavioural changes in non-target organisms even at low environmental concentrations. To scrutinize the behavioural effects of herbicide-exposure we exposed agile frog (Rana dalmatina) tadpoles in an outdoor mesocosm experiment to three concentrations of a glyphosate-based herbicide (0, 2 and 6.5mg acid equivalent (a.e.) / L). To assess whether anti-predator behaviour is affected by the pesticide, we combined all levels of herbicide-exposure with three predator treatments (no predator, caged Aeshna cyanea dragonfly larvae or Lissotriton vulgaris newt adults) in a full factorial design. We observed hiding, activity, proximity to the predator cage and vertical position of tadpoles. We found that at the higher herbicide concentration tadpoles decreased their activity and more tadpoles were hiding, and at least at the lower concentration their vertical position was closer to the water surface than in tadpoles of the control treatment. Tadpoles also decreased their activity in the presence of dragonfly larvae, but did not hide more in response to either predator, nor did tadpoles avoid predators spatially. Further, exposure to the herbicide did not significantly influence behavioural responses to predation threat. Our study documents a definite influence of glyphosate-based herbicides on the behaviour of agile frog tadpoles and indicates that some of these changes are similar to those induced by dangerous predators. This may suggest that the underlying physiological mechanisms or the adaptive value of behavioural changes may similar.

Effect on the growth and development and induction of abnormalities by a glyphosate commercial formulation and its active ingredient during two developmental stages of the South-American Creole frog, Leptodactylus latrans

We evaluated the acute lethal and sublethal effects of technical-grade glyphosate (GLY) and the GLY-based commercial formulation Roundup ULTRA MAX® (RU) on two Gosner stages (Gss) 25 and 36 of the South-American Creole frog, Leptodactylus latrans. Bioassays were performed following standardized methods within a wide range of concentrations (0.0007-9.62 mg of acid equivalents per liter-a.e./L-of RU and 3-300 mg/L of GLY). The endpoints evaluated were mortality, swimming activity, growth, development, and the presence of morphologic abnormalities, especially in the mouthparts. No lethal effects were observed on larvae exposed to GLY during either Gs-25 or Gs-36. The concentrations inducing 50 % lethality in RU-exposed larvae at different exposure times and Gss ranged from 3.26 to 9.61 mg a.e./L. Swimming activity was affected by only RU. Effects on growth and development and the induction of morphologic abnormalities-like oral abnormalities and edema-were observed after exposure to either GLY or RU. Gs-25 was the most sensitive stage to both forms of the herbicide. The commercial formulation was much more toxic than the active ingredient on all the endpoints assessed. Effects on growth, development, and the induction of morphologic abnormalities observed in the range of environmental concentrations reported for agroecosystems of Argentina constitute an alert to the potential detrimental effects of the herbicide that could be affecting the fitness and survival of anurans in agroecosystems.

Acute, chronic and biochemical effects of chlorothalonil on Agalychnis callidryas, Isthmohyla pseudopuma and Smilisca baudinii tadpoles

Declines of amphibian populations have been a worldwide issue of concern for the scientific community during the last several decades. Efforts are being carried out to elucidate factors related to this phenomenon. Among these factors, pathogens, climate change, and environmental pollution have been suggested as possible causes. Regarding environmental pollutants, some pesticides are persistent in the environment and capable of being transported long distances from their release point. In Costa Rica, some pesticides have been detected in protected areas, at locations where amphibian populations have declined. Information about toxicity of pesticides used in Costa Rican agriculture to amphibians is still scarce, particularly for native species.Toxicity tests with chlorothalonil, a fungicide intensively used in Costa Rica, were carried out exposing tadpoles of three Costa Rican native species: Agalychnis callidryas, Isthmohyla pseudopuma, and Smilisca baudinii in order to evaluate acute and chronic toxicity as well as the biomarkers cholinesterase activity (ChE), glutathione-S transferase activity (GST), and lipid peroxidation (LPO).96-h LC₅₀: 26.6 (18.9-35.8) μg/L to A. callidryas, 25.5 (21.3-29.7) μg/L to I pseudopuma and 32.3 (26.3-39.7) μg/L to S. baudinii were determined for chlorothalonil. These three species of anurans are among the most sensitive to chlorothalonil according to the literature. Besides, GST was induced in S. baudinii after exposure to sub-lethal concentrations of chlorothalonil while evisceration occurred in S. baudinii and A. callidryas tadpoles exposed to lethal concentrations of the fungicide. Chronic exposure to sub-lethal concentrations accelerated development in S. baudinii and caused lesions in tail of S. baudinii and I. pseudopuma tadpoles. Our results demonstrate that chlorothalonil is highly toxic to native amphibian species and that low concentrations can cause biochemical responses related to phase II of biotransformation and effects on development.

Evolution determines how global warming and pesticide exposure will shape predator-prey interactions with vector mosquitoes

How evolution may mitigate the effects of global warming and pesticide exposure on predator-prey interactions is directly relevant for vector control. Using a space-for-time substitution approach, we addressed how 4°C warming and exposure to the pesticide endosulfan shape the predation on Culex pipiens mosquitoes by damselfly predators from replicated low- and high-latitude populations. Although warming was only lethal for the mosquitoes, it reduced predation rates on these prey. Possibly, under warming escape speeds of the mosquitoes increased more than the attack efficiency of the predators. Endosulfan imposed mortality and induced behavioral changes (including increased filtering and thrashing and a positional shift away from the bottom) in mosquito larvae. Although the pesticide was only lethal for the mosquitoes, it reduced predation rates by the low-latitude predators. This can be explained by the combination of the evolution of a faster life history and associated higher vulnerabilities to the pesticide (in terms of growth rate and lowered foraging activity) in the low-latitude predators and pesticide-induced survival selection in the mosquitoes. Our results suggest that predation rates on mosquitoes at the high latitude will be reduced under warming unless predators evolve toward the current low-latitude phenotype or low-latitude predators move poleward.

Effects of long-term exposure to two fungicides, pyrimethanil and tebuconazole, on survival and life history traits of Italian tree frog (Hyla intermedia)

Over the last few years, the hazards associated with the extensive use of fungicides have become an issue of great concern but, at present, the effects of these substances on amphibians remain poorly understood. The goal of the present study was to assess the effects of two commonly used fungicides, tebuconazole and pyrimethanil, on Italian Tree Frog (Hyla intermedia), a species frequently found in agricultural areas. Tadpoles were exposed to fungicides from developmental Gosner stage 25 (GS 25) to completion of metamorphosis (GS 46) and the whole exposure period lasted 78 days. For both tested fungicides we used two concentrations (5 and 50μg/L) that are comparable to those detected in surface waters, near agricultural fields. A variety of sublethal effects-on growth, development, behavior, and physiology-may be used for evaluating alterations induced by pollutants in amphibians. We estimated whether pyrimethanil and tebuconazole exposure impacted on H. intermedia life history traits. For this purpose, survival, growth, development, initiation of metamorphosis, success and size at metamorphosis, time to metamorphosis, and frequency of morphological abnormalities were evaluated. We showed, for all considered endpoints, that the exposure to tebuconazole exerts more harmful effects on H. intermedia than does exposure to pyrimethanil. Before the onset of metamorphic climax we showed, for both fungicides, that the low concentrations (5μg/L) induced significantly greater effects than the higher ones (50μg/L) on survival and deformity incidence. During the metamorphic climax, a complete reversal of this nonlinear trend takes place, and the percentage of animals initiating metamorphosis was reduced in fungicide-exposed groups in a concentration-dependent manner. Furthermore, a strong correlation emerged between fungicide exposure and the incidence of morphological abnormalities such as tail malformations, scoliosis, edema, mouth and limb deformities. Exposure to tested fungicides also caused a reduction in developmental rates just prior to the onset of metamorphic climax, which translated to a significant delay in timing of metamorphosis. We detected a drastic decrease in the success at metamorphosis in all exposed groups, compared to control group (86.25%). In fact, the percentage of survived larvae to GS 46, in the high and low concentrations, respectively, was only 22.5% and 36.25% in tebuconazole-exposed groups and 43.75% (50μg/L) and 56.25% (5μg/L) in pyrimethanil-exposed groups. Our findings underscore the hazardous properties of these two fungicides for non-target species in the context of ecotoxicological risk assessment. No published studies have addressed the long-term effects of tebuconazole and pyrimethanil on amphibians. To date, this is one of only a few studies documenting the effects of fungicide exposure over the whole larval development.

Toxic and genotoxic effects of the imazethapyr-based herbicide formulation Pivot H® on montevideo tree frog Hypsiboas pulchellus tadpoles (Anura, Hylidae)

Acute lethal and sublethal toxicity of the imidazolinone imazethapyr (IMZT)-based commercial formulation herbicide Pivot H® (10.59% IMZT) was evaluated on Hypsiboas pulchellus tadpoles. Whereas mortality was used as the end point for lethality, frequency of micronuclei (MNs) and other nuclear abnormalities as well as DNA single-strand breaks evaluated by the single cell gel electrophoresis assay were employed to test genotoxicity. Behavioral, growth, developmental, and morphological abnormalities were also employed as sublethal end points. Mortality studies revealed equivalent LC50 (96h) values of 1.49mg/L (confidence limit, 1.09-1.63) and 1.55mg/L (confidence limit, 1.51-1.60) IMZT for Gosner stage (GS) 25 and GS36, respectively. Behavioral changes, i.e., irregular swimming and immobility, as well as a decreased frequency of keratodonts were observed. The herbicide increased the frequency of MNs in circulating erythrocytes of tadpoles exposed for 48h to the highest concentration assayed (1.17mg/L). However, regardless of the concentration of the herbicide assayed, an enhanced frequency of MNs was observed in tadpoles exposed for 96h. The herbicide was able to induce other nuclear abnormalities, i.e., blebbed and notched nuclei, only when tadpoles were exposed for 96h. In addition, we observed that exposure to IMZT within the 0.39-1.17mg/L range increased the genetic damage index in treatments lasting for both 48 and 96h. This study represents the first evidence of acute lethal and sublethal effects exerted by IMZT on amphibians. Finally, our findings highlight the properties of this herbicide that jeopardize nontarget living species exposed to IMZT.

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

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

Larval performance and oviposition habitat selection of the tree frog, Hyla savignyi, in response to conspecific larval density

Amphibians breeding in temporary pools may experience strong intraspecific density-dependent effects in the form of larval competition and oviposition site selection. These potential effects are untested for the tree frog, Hyla savignyi, an anuran species of conservation concern in Israel. We conducted an outdoor mesocosm experiment to examine how intraspecific larval density may affect larval performance and oviposition habitat selection in H. savignyi. We added ecologically relevant densities of 0, 10, or 40 early-stage tadpoles into mesocosms (plastic tubs) containing 20 L of water. Each density was replicated with four tubs. Time to and size at metamorphosis were not significantly affected by initial H. savignyi density. However, strong intraspecific competitive effects were observed in the form of reduced size at metamorphosis at the high density. We also found that gravid H. savignyi females reduce future intraspecific competition for their progeny by choosing to oviposit in mesocosms with no, or low, densities of H. savignyi tadpoles. Thus, intraspecific competition in this anuran species appears to be an important factor at ecologically relevant densities; larval competition increases with increasing densities and may be avoided by gravid females assessing breeding habitat quality in the form of conspecific tadpole density or mass.