Acute toxicity tests and meta-analysis identify gaps in tropical ecotoxicology for amphibians

The toxicity and health risk of chlorothalonil to non-target animals and humans: A systematic review

Chlorothalonil (CTL), an organochloride fungicide applied for decades worldwide, has been found to be present in various matrixes and even accumulates in humans or other mammals through the food chain. Its high residue and diffusion in the environment have severely affected food security and public health. More and more research has considered CTL as a possible toxin to environmental non-target organisms, via influencing multiple systems such as metabolic, developmental, endocrine, genetic, and reproductive pathways. Aquatic organisms and amphibians are the most vulnerable species to CTL exposure, especially during the early period of development. Under experimental conditions, CTL can also have toxic effects on rodents and other non-target organisms. As for humans, CTL exposure is most often reported to be relevant to allergic reactions to the skin and eyes. We hope that this review will improve our understanding of the hazards and risks that CTL poses to non-target organisms and find a strategy for rational use.

Pesticide use in banana plantations in Costa Rica - A review of environmental and human exposure, effects and potential risks

Biodiversity is declining on a global scale. Especially tropical ecosystems, containing most of the planetary biodiversity, are at risk. Agricultural monocrop systems contribute to this decline as they replace original habitats and depend on extensive use of synthetic pesticides that impact ecosystems. In this review we use large-scale banana production for export purposes in Costa Rica as an example for pesticide impacts, as it is in production for over a century and uses pesticides extensively for more than fifty years. We summarise the research on pesticide exposure, effects and risks for aquatic and terrestrial environment, as well as for human health. We show that exposure to pesticides is high and relatively well-studied for aquatic systems and humans, but hardly any data are available for the terrestrial compartment including adjacent non target ecosystems such as rainforest fragments. Ecological effects are demonstrated on an organismic level for various aquatic species and processes but are not available at the population and community level. For human health studies exposure evaluation is crucial and recognised effects include various types of cancer and neurobiological dysfunctions particularly in children. With the many synthetic pesticides involved in banana production, the focus on insecticides, revealing highest aquatic risks, and partly herbicides should be extended to fungicides, which are applied aerially over larger areas. The risk assessment and regulation of pesticides so far relies on temperate models and test species and is therefore likely underestimating the risk of pesticide use in tropical ecosystems, with crops such as banana. We highlight further research approaches to improve risk assessment and, in parallel, urge to follow other strategies to reduce pesticides use and especially hazardous substances.

Acute aquatic toxicity of two commonly used fungicides to midwestern amphibian larvae

Fungicide usage has increased globally in response to the rise in fungal pathogens, especially in the agricultural sector. However, research examining the toxicity of fungicides is still limited for many aquatic species. In this study, we examined the acute toxicity of two widely used fungicides, chlorothalonil and pyraclostrobin, on six North American larval amphibian species across multiple families using 96-h LC50 tests. We found that pyraclostrobin was approximately 3.5x more toxic than chlorothalonil; estimated LC50 values ranged from 5-18 µg/L for pyraclostrobin and 15-50 µg/L for chlorothalonil. Comparing across amphibian groups, we found that salamanders were 3x more sensitive to pyraclostrobin than anuran species and equally as sensitive to chlorothalonil. Notably, our estimated LC50 values within the range of the expected environmental concentration for these fungicides suggesting environmental exposures could lead to direct mortality in these species. Given the widespread and increasing usage of fungicides, additional work should be conducted to assess the general risk posed by these chemicals to amphibian and their associated aquatic habitats.

Non-destructive methods to assess health of wild tropical frogs (túngara frogs: Engystomops pustulosus) in Trinidad reveal negative impacts of agricultural land

Amphibians are threatened globally with at least 43% of species declining and the most important stressor being habitat loss or degradation. Amphibians inhabiting highly biodiverse tropical regions are disproportionately threatened; however, the effects of landscape alterations on amphibian health are virtually unknown. In this study, we utilised non-destructive techniques to compare size (weight, snout-vent length [SVL]), body condition, male secondary sexual features (forelimb width, nuptial pad length) and breeding success (egg number, fertility [percentage fertilised eggs], hatching success) in túngara frogs (Engystomops pustulosus) collected from reference (n = 5), suburban (n = 6) and agricultural (n = 4) sites in Trinidad; characterised by presence/absence of crops/houses. All measured endpoints were negatively impacted in frogs collected from agricultural sites. The largest effect was observed for hatching success (2.77-fold lower) and egg number (2.5-fold lower). Less pronounced effects were observed on male frogs (weight: 1.77-fold lower; SVL: 1.18-fold lower; forelimb width: 1.33-fold lower; nuptial pad length: 1.15-fold lower). Our findings demonstrate negative impacts of agricultural sites on túngara frog health, with the number of viable offspring reduced by almost one third. The methods outlined here are technically simple and low-cost and thereby have potential for application to other species in order to investigate the potential impacts of habitat degradation on amphibian health. Furthermore, as these methods are non-destructive, they could be used to investigate the potential contribution of frog size and/or reproductive capability as a causative factor contributing to population declines in threatened species, which is particularly pressing in tropical regions.

Assessment of RNA extraction protocols from cladocerans

The usage of cladocerans as non-model organisms in ecotoxicological and risk assessment studies has intensified in recent years due to their ecological importance in aquatic ecosystems. The molecular assessment such as gene expression analysis has been introduced in ecotoxicological and risk assessment to link the expression of specific genes to a biological process in the cladocerans. The validity and accuracy of gene expression analysis depends on the quantity, quality and integrity of extracted ribonucleic acid (RNA) of the sample. However, the standard methods of RNA extraction from the cladocerans are still lacking. This study evaluates the extraction of RNA from tropical freshwater cladocerans Moina micrura using two methods: the phenol-chloroform extraction method (QIAzol) and a column-based kit (Qiagen Micro Kit). Glycogen was introduced in both approaches to enhance the recovery of extracted RNA and the extracted RNA was characterised using spectrophotometric analysis (NanoDrop), capillary electrophoresis (Bioanalyzer). Then, the extracted RNA was analysed with reverse transcription polymerase chain reaction (RT-PCR) to validate the RNA extraction method towards downstream gene expression analysis. The results indicate that the column-based kit is most suitable for the extraction of RNA from M. micrura, with the quantity (RNA concentration = 26.90 ± 6.89 ng/μl), quality (A260:230 = 1.95 ± 0.15, A280:230 = 1.85 ± 0.09) and integrity (RNA integrity number, RIN = 7.20 ± 0.16). The RT-PCR analysis shows that the method successfully amplified both alpha tubulin and actin gene at 33-35 cycles (i.e. Ct = 32.64 to 33.48). The results demonstrate that the addition of glycogen is only suitable for the phenol-chloroform extraction method. RNA extraction with high and comprehensive quality control assessment will increase the accuracy and reliability of downstream gene expression, thus providing more ecotoxicological data at the molecular biological level on other freshwater zooplankton species.

Widespread Pig Farming Practice Linked to Shifts in Skin Microbiomes and Disease in Pond-Breeding Amphibians

Farming practices may reshape the structure of watersheds, water quality, and the health of aquatic organisms. Nutrient enrichment from agricultural pollution increases disease pressure in many host-pathogen systems, but the mechanisms underlying this pattern are not always resolved. For example, nutrient enrichment should strongly influence pools of aquatic environmental bacteria, which has the potential to alter microbiome composition of aquatic animals and their vulnerability to disease. However, shifts in the host microbiome have received little attention as a link between nutrient enrichment and diseases of aquatic organisms. We examined nutrient enrichment through the widespread practice of integrated pig-fish farming and its effects on microbiome composition of Brazilian amphibians and prevalence of the globally distributed amphibian skin pathogen Batrachochytrium dendrobatidis (Bd). This farming system drove surges in fecal coliform bacteria, disturbing amphibian skin bacterial communities such that hosts recruited higher proportions of Bd-facilitative bacteria and carried higher Bd prevalence. Our results highlight previously overlooked connections between global trends in land use change, microbiome dysbiosis, and wildlife disease. These interactions may be particularly important for disease management in the tropics, a region with both high biodiversity and continually intensifying anthropogenic pressures on aquatic wildlife habitats.

Lethal toxicity of the herbicides acetochlor, ametryn, glyphosate and metribuzin to tropical frog larvae

Despite the high amphibian biodiversity and increasing pesticide use in tropical countries, knowledge on the sensitivity of tropical amphibians to pesticides remains limited. The aim of this study was to evaluate the acute toxicity of the active ingredients of four of the main herbicides used in Brazilian sugarcane production to tadpoles of two tropical frog species: Physalaemus cuvieri and Hypsiboas pardalis. The calculated 96 h-LC50 (median lethal concentration; in mg a.s./L) values for P. cuvieri and H. pardalis were 4.4 and 7.8 (acetochlor); 15 and <10 (ametryn); 115 and 106 (glyphosate); and 85 and 68 (metribuzin), respectively. These toxicity values demonstrated little interspecies variation and the toxicity of the herbicides appeared to be at least partly related with the respective octanol-water coefficient. Published acute toxicity data of fish and amphibians for herbicides were also compiled from the US-EPA ECOTOX database. These data indicated little difference in herbicide sensitivity between tropical amphibians and both non-tropical amphibians and fish. These findings indicate that temperate (fish and amphibian) herbicide toxicity data are also protective for tropical amphibians. Constraints in such extrapolations and indications for future research are discussed.

Fungicides: An Overlooked Pesticide Class?

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the entire growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modeling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

Freshwater neotropical oligochaetes as native test species for the toxicity evaluation of cadmium, mercury and their mixtures

The toxicity of metals, whether isolated or in mixtures, involves changes in biochemical processes as well as in cell membranes, which may lead to deleterious short- and long-term effects on the affected organisms. Among metals, cadmium and mercury stand out due to their abundance in nature, frequent use for industrial activities and biological accumulation, with high levels of residence in trophic chains. Benthic communities are particularly prone to metal pollution since metals usually accumulate in sediments. The aim of this study was to evaluate the acute toxicity of mercury and cadmium, single and in mixture, to two native species of epibenthic oligochaetes: Allonais inaequalis and Dero furcatus. In order to assess the potential of these species as bioindicators, we compared their sensitivity with those of other internationally used species by applying the species sensitivity distribution approach. The 96h-LC₅₀ of cadmium chloride was 627 and 364 μg L^-1 for A. inaequalis and D. furcatus, respectively, evidencing that the latter species is almost twice as sensitive to this metal than A. inaequalis. For mercury chloride, the 96h-LC₅₀ was 129 μg L^-1 for A. inaequalis and 92 μg L^-1 for D. furcatus. The sensitivities of these oligochaetes were superior or similar to that of other frequently used oligochaete test species such as Tubifex tubifex and Lumbriculus variegatus. The metal mixtures had synergism in general (D. furcatus) or at high doses only (A. inaequalis), implying a potentiation of their toxic effects when both metals co-occur in the environment. By comparing the derived toxicity values with concentrations of cadmium and mercury measured in the field, it can be concluded that aquatic organisms are likely to be at risk when exposed to the environmental relevant concentrations of cadmium and mercury here tested, especially when they are both present.

Comparison of Diazinon Toxicity to Temperate and Tropical Freshwater Daphnia Species

The presence of pesticides in water bodies presents unique challenges to the ecosystem and all the life forms. Biological methods have been widely used to examine the toxic effects of various toxicants including pesticides. The present study aims at determining the adverse effects of diazinon, a nonsystemic organophosphate insecticide, on two cladoceran species including the temperate Daphnia magna (D. magna) and the tropical Daphnia lumholtzi (D. lumholtzi). The 48 h LC50 values demonstrated higher toxicity of diazinon for D. lumholtzi at a concentration of 3.41 µg·L−1 compared to D. magna at a concentration of 4.63 µg·L−1. After 14 days of exposure to diazinon, the survival capacity as well as the reproduction potential of the two cladoceran species clearly reduced and their rate of population increase (RPI) decreased at concentrations >0.1 µg·L−1. The present study indicated that the tropical cladoceran (D. lumholtzi) was more sensitive than the temperate D. magna. Therefore, it could be used as an indicator for toxicity assessment in tropical environments. The presence of diazinon in water bodies can be associated with significant risk to aquatic organisms.

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.

A pesticide paradox: fungicides indirectly increase fungal infections

There are many examples where the use of chemicals have had profound unintended consequences, such as fertilizers reducing crop yields (paradox of enrichment) and insecticides increasing insect pests (by reducing natural biocontrol). Recently, the application of agrochemicals, such as agricultural disinfectants and fungicides, has been explored as an approach to curb the pathogenic fungus, Batrachochytrium dendrobatidis (Bd), which is associated with worldwide amphibian declines. However, the long-term, net effects of early-life exposure to these chemicals on amphibian disease risk have not been thoroughly investigated. Using a combination of laboratory experiments and analysis of data from the literature, we explored the effects of fungicide exposure on Bd infections in two frog species. Extremely low concentrations of the fungicides azoxystrobin, chlorothalonil, and mancozeb were directly toxic to Bd in culture. However, estimated environmental concentrations of the fungicides did not reduce Bd on Cuban tree frog (Osteopilus septentrionalis) tadpoles exposed simultaneously to any of these fungicides and Bd, and fungicide exposure actually increased Bd-induced mortality. Additionally, exposure to any of these fungicides as tadpoles resulted in higher Bd abundance and greater Bd-induced mortality when challenged with Bd post-metamorphosis, an average of 71 d after their last fungicide exposure. Analysis of data from the literature revealed that previous exposure to the fungicide itraconazole, which is commonly used to clear Bd infections, made the critically endangered booroolong frog (Litoria booroolongensis) more susceptible to Bd. Finally, a field survey revealed that Bd prevalence was positively associated with concentrations of fungicides in ponds. Although fungicides show promise for controlling Bd, these results suggest that, if fungicides do not completely eliminate Bd or if Bd recolonizes, exposure to fungicides has the potential to do more harm than good. To ensure that fungicide applications have the intended consequence of curbing amphibian declines, researchers must identify which fungicides do not compromise the pathogen resistance mechanisms of amphibians.

Amphibian population genetics in agricultural landscapes: does viniculture drive the population structuring of the European common frog (Rana temporaria)?

Amphibian populations have been declining globally over the past decades. The intensification of agriculture, habitat loss, fragmentation of populations and toxic substances in the environment are considered as driving factors for this decline. Today, about 50% of the area of Germany is used for agriculture and is inhabited by a diverse variety of 20 amphibian species. Of these, 19 are exhibiting declining populations. Due to the protection status of native amphibian species, it is important to evaluate the effect of land use and associated stressors (such as road mortality and pesticide toxicity) on the genetic population structure of amphibians in agricultural landscapes. We investigated the effects of viniculture on the genetic differentiation of European common frog (Rana temporaria) populations in Southern Palatinate (Germany). We analyzed microsatellite data of ten loci from ten breeding pond populations located within viniculture landscape and in the adjacent forest block and compared these results with a previously developed landscape permeability model. We tested for significant correlation of genetic population differentiation and landscape elements, including land use as well as roads and their associated traffic intensity, to explain the genetic structure in the study area. Genetic differentiation among forest populations was significantly lower (median pairwise F_ST = 0.0041 at 5.39 km to 0.0159 at 9.40 km distance) than between viniculture populations (median pairwise F_ST = 0.0215 at 2.34 km to 0.0987 at 2.39 km distance). Our analyses rejected isolation by distance based on roads and associated traffic intensity as the sole explanation of the genetic differentiation and suggest that the viniculture landscape has to be considered as a limiting barrier for R. temporaria migration, partially confirming the isolation of breeding ponds predicted by the landscape permeability model. Therefore, arable land may act as a sink habitat, inhibiting genetic exchange and causing genetic differentiation of pond populations in agricultural areas. In viniculture, pesticides could be a driving factor for the observed genetic impoverishment, since pesticides are more frequently applied than any other management measure and can be highly toxic for terrestrial life stages of amphibians.

Sensitivity of a tropical micro-crustacean (Daphnia lumholtzi) to trace metals tested in natural water of the Mekong River

Metal contamination is one of the major issues to the environment worldwide, yet it is poorly known how exposure to metals affects tropical species. We assessed the sensitivity of a tropical micro-crustacean Daphnia lumholtzi to three trace metals: copper (Cu), zinc (Zn) and nickel (Ni). Both, acute and chronic toxicity tests were conducted with metals dissolved in in situ water collected from two sites in the lower part of the Mekong River. In the acute toxicity test, D. lumholtzi neonates were exposed to Cu (3-30μgL^-1), Zn (50-540μgL^-1) or Ni (46-2356μgL^-1) for 48h. The values of median lethal concentrations (48h-LC₅₀) were 11.57-16.67μg Cu L^-1, 179.3-280.9μg Zn L^-1, and 1026-1516μg Ni L^-1. In the chronic toxicity test, animals were exposed to Cu (3 and 4μgL^-1), Zn (50 and 56μgL^-1), and Ni (six concentrations from 5 to 302μgL^-1) for 21days. The concentrations of 4μg Cu L^-1 and 6μg Ni L^-1 enhanced the body length of D. lumholtzi but 46μg Ni L^-1 and 50μg Zn L^-1 resulted in a strong mortality, reduced the body length, postponed the maturation, and lowered the fecundity. The results tentatively suggest that D. lumholtzi showed a higher sensitivity to metals than related species in the temperate region. The results underscore the importance of including the local species in ecological risk assessment in important tropical ecosystems such as the Mekong River to arrive at a better conservational and management plan and regulatory policy to protect freshwater biodiversity from metal contamination.

Additive effects of mean temperature, temperature variability, and chlorothalonil to red-eyed treefrog (Agalychnis callidryas) larvae

Amphibian populations are declining globally, and multiple anthropogenic stressors, including contamination by pesticides and shifting climates, are driving these declines. Climate change may increase average temperatures or increase temperature variability, either of which may affect the susceptibility of nontarget organisms to contaminants. Eight-day ecotoxicological assays were conducted with red-eyed treefrog (Agalychnis callidryas) larvae to test for additive and interactive effects of exposure to the fungicide chlorothalonil, average temperature, and temperature variability on tadpole growth and survival. Egg masses were collected from seasonal ponds at La Selva Biological Station in Costa Rica, and tadpoles were exposed to a series of chlorothalonil concentrations across a range of ecologically relevant mean temperatures (23.4-27.3 °C) and daily temperature fluctuations (1.1-9.9 °C). Survival was measured each day, and tadpole growth was measured at the end of each trial. Concentrations of chlorothalonil ≥60 µg/L reduced survival, although survival was not affected by mean temperature or daily temperature range, and there were no synergistic interactions between chlorothalonil and temperature regime on survival. Chlorothalonil suppressed tadpole growth at relatively low concentrations (∼15 µg/L). There were impacts of both average temperature and daily temperature range on tadpole growth, although there were no synergistic interactions between temperature regimes and chlorothalonil. The results should inform efforts to manage ecosystems impacted by multiple large-scale anthropogenic stressors as well as methods for the design of ecologically appropriate toxicology trials. Environ Toxicol Chem 2016;35:2998-3004. © 2016 SETAC.

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.

A meta-analysis synthesizing the effects of pesticides on swim speed and activity of aquatic vertebrates

Pesticide contaminants are ubiquitous in aquatic environments and pose a threat to biodiversity. Pesticides also have diverse mechanisms of action that make it difficult to identify impacts on exposed wildlife. Behavioral measures represent an important link between physiological and ecological processes, and are often used to generalize sub-lethal effects of pesticide exposure. In order to bridge the toxicological and behavioral literature, and identify chemical classes that denote the largest threat, we conducted a meta-analysis summarizing the effects of pesticides on swim speed and activity of aquatic vertebrates. We found that exposure to environmentally relevant concentrations of pesticides reduced the swim speed of exposed amphibians and fish by 35%, and reduced overall activity by 72%. There were also differences in the magnitude of this effect across chemical classes, which likely reflect underlying physiological processes. Pyrethroids, carbamates, and organophosphates all produced a large decrease in swim speed, where as phosphonoglycines and triazines showed no overall effect. Pyrethroids, carbamates, organophosphates, organochlorines, and organotins also produced a large decrease in activity, while phosphonoglycines had no overall effect, and triazines had the opposite effect of increasing activity. Our results indicate that even sub-lethal concentrations of pesticides have a strong effect on critical behaviors of aquatic vertebrates, which can affect fitness and alter species interactions. We expect our synthesis can be used to identify chemical classes producing the largest sub-lethal effects for further research and management.

Multifactorial theory applied to the neurotoxicity of paraquat and paraquat-induced mechanisms of developing Parkinson's disease

Laboratory studies involving repeated exposure to paraquat (PQ) in different animal models can induce many of the pathological features of Parkinson's disease (PD), such as the loss of dopaminergic neurons in the nigrostriatal dopamine system. Epidemiological studies identify an increased risk of developing PD in human populations living in areas where PQ exposure is likely to occur and among workers lacking appropriate protective equipment. The mechanisms involved in developing PD may not be due to any single cause, but rather a multifactorial situation may exist where PQ exposure may cause PD in some circumstances. Multifactorial theory is adopted into this review that includes a number of sub-cellular mechanisms to explain the pathogenesis of PD. The theory is placed into an environmental context of chronic low-dose exposure to PQ that consequently acts as an oxidative stress inducer. Oxidative stress and the metabolic processes of PQ-inducing excitotoxicity, α-synuclein aggregate formation, autophagy, alteration of dopamine catabolism, and inactivation of tyrosine hydroxylase are positioned as causes for the loss of dopaminergic cells. The environmental context and biochemistry of PQ in soils, water, and organisms is also reviewed to identify potential routes that can lead to chronic rates of low-dose exposure that would replicate the type of response that is observed in animal models, epidemiological studies, and other types of laboratory investigations involving PQ exposure. The purpose of this review is to synthesize key relations and summarize hypotheses linking PD to PQ exposure by using the multifactorial approach. Recommendations are given to integrate laboratory methods to the environmental context as a means to improve on experimental design. The multifactorial approach is necessary for conducting valid tests of causal relations, for understanding of potential relations between PD and PQ exposure, and may prevent further delay in solving what has proven to be an evasive etiological problem.

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.

Copper and nickel effects on survival and growth of northern leopard frog (Lithobates pipiens) tadpoles in field-collected smelting effluent water

Trace metals can have subtle yet chronic impacts on organisms by inducing physiological stress that reduces their survival or impedes their ability to tolerate additional environmental stressors. The toxicity literature indicates, however, that aquatic organisms react differently to trace metals depending on the environments in which they reside. The objective of the present study was to understand the response of northern leopard frog (Lithobates pipiens) larvae to ionic copper (Cu), nickel (Ni), and their combination within an effluent water collected downstream of a tailings wetland area. Tadpoles were assigned randomly to 1 of 8 Cu concentrations (8-200 μg/L), 7 Ni concentrations (160-1200 μg/L), or 8 Cu and Ni combined concentrations (8:160-200:1200 μg/L) and showed significant differences in survival and life history traits among treatments. In the Cu and Cu and Ni combined treatments, tadpole survival decreased with increased Cu exposure starting at Cu = 160 μg/L and in the Ni treatment, tadpole survival decreased with increased Ni exposure starting at Ni = 650 μg/L. All Cu-exposed treatments induced a growth increase as the concentration increased, whereas the tadpoles showed a significant decrease in growth rate in Ni treatments. These contrasting outcomes suggest a plastic response to trace metals whereby tadpoles allocate energy reserves toward either escaping or coping with stress. Finally, the authors' argue that future studies will benefit from examining the impacts of multiple stressors in aquatic ecosystems to provide better environmental mitigation.

Integrated assessment of biochemical markers in premetamorphic tadpoles of three amphibian species exposed to glyphosate- and methidathion-based pesticides in single and combination forms

In this study, we evaluated the toxic effects of a glyphosate-based herbicide (GBH) and a methidathion-based insecticide (MBI), individually and in combination, on premetamorphic tadpoles of three anuran species: Pelophylax ridibundus, Xenopus laevis, and Bufotes viridis. Based on the determined 96-h LC50 values of each species, the effects of a series of sublethal concentrations of single pesticides and their mixtures after 96-h exposure and also the time-related effects of a high sublethal concentration of each pesticide were evaluated, with determination of changes in selected biomarkers: glutathione S-transferase (GST), glutathione reductase (GR), acetylcholinesterase (AChE), carboxylesterase (CaE), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH). Also, the integrated biomarker response (IBR) was used to assess biomarker responses and quantitatively evaluate toxicological effects. Isozyme differences in CaE inhibition were assessed using native page electrophoresis; results showed that GBH to cause structural changes in the enzyme but not CaE inhibition in P. ridibundus. In general, single MBI and pesticide mixture exposures increased GST activity, while single GBH exposures decreased GST activity in exposed tadpoles. The AChE and CaE activities were inhibited after exposure to all single MBI and pesticide mixtures. Also, higher IBR values and GST, GR, AST, and LDH activities were determined for pesticide mixtures compared with single-pesticide exposure. This situation may be indicative of a synergistic interaction between pesticides and a sign of a more stressful condition.