Pesticide Uptake Across the Amphibian Dermis Through Soil and Overspray Exposures

Broad-scale pesticide screening finds anticoagulant rodenticide and legacy pesticides in Australian frogs

Pesticide contamination poses a significant threat to non-target wildlife, including amphibians, many of which are already highly threatened. This study assessed the extent of pesticide exposure in dead frogs collected during a mass mortality event across eastern New South Wales, Australia between July 2021 and March 2022. Liver tissue from 77 individual frogs of six species were analysed for >600 legacy and contemporary pesticides, including rodenticides. More than a third (36 %) of the liver samples contained at least one of the following pesticides: brodifacoum, dieldrin, DDE, heptachlor/heptachlor epoxide, fipronil sulfone, and 2-methyl-4-chlorophenoxyacetic acid (MCPA). Brodifacoum, a second-generation anticoagulant rodenticide, was found in four of the six frog species analysed: the eastern banjo frog (Limnodynastes dumerilii), cane toad (Rhinella marina), green tree frog (Litoria caerulea) and Peron's tree frog (Litoria peronii). This is the first report of anticoagulant rodenticide detected in wild amphibians, raising concerns about potential impacts on frogs and extending the list of taxa shown to accumulate rodenticides. Dieldrin, a banned legacy pesticide, was also detected in two species: striped marsh frog (Limnodynastes peronii) and green tree frog (Litoria caerulea). The toxicological effects of these pesticides on frogs are difficult to infer due to limited comparable studies; however, due to the low frequency of detection the presence of these pesticides was not considered a major contributing factor to the mass mortality event. Additional research is needed to investigate the effects of pesticide exposure on amphibians, particularly regarding the impacts of second-generation anticoagulant rodenticides. There is also need for continued monitoring and improved conservation management strategies for the mitigation of the potential threat of pesticide exposure and accumulation in amphibian populations.

Wildlife ecotoxicology of plant protection products: knowns and unknowns about the impacts of currently used pesticides on terrestrial vertebrate biodiversity

Agricultural practices are a major cause of the current loss of biodiversity. Among postwar agricultural intensification practices, the use of plant protection products (PPPs) might be one of the prominent drivers of the loss of wildlife diversity in agroecosystems. A collective scientific assessment was performed upon the request of the French Ministries responsible for the Environment, for Agriculture and for Research to review the impacts of PPPs on biodiversity and ecosystem services based on the scientific literature. While the effects of legacy banned PPPs on ecosystems and the underlying mechanisms are well documented, the impacts of current use pesticides (CUPs) on biodiversity have rarely been reviewed. Here, we provide an overview of the available knowledge related to the impacts of PPPs, including biopesticides, on terrestrial vertebrates (i.e. herptiles, birds including raptors, bats and small and large mammals). We focused essentially on CUPs and on endpoints at the subindividual, individual, population and community levels, which ultimately linked with effects on biodiversity. We address both direct toxic effects and indirect effects related to ecological processes and review the existing knowledge about wildlife exposure to PPPs. The effects of PPPs on ecological functions and ecosystem services are discussed, as are the aggravating or mitigating factors. Finally, a synthesis of knowns and unknowns is provided, and we identify priorities to fill gaps in knowledge and perspectives for research and wildlife conservation.

Mechanistic modelling of amphibian body burdens after dermal uptake of pesticides from soil

Amphibians are currently considered to be covered by pesticide Environmental Risk Assessment schemes by surrogacy assumptions of exposure and susceptibility based on typical laboratory test species such as fish, mammals, and birds. While multiple reviews have shown for this approach to be adequate in the case of aquatic stages, the same cannot be definitively stated for terrestrial stages. Concerns have risen that exposure of amphibians is likely to be highly influenced by dermal absorption, primarily due to the high permeability of their skin and the lack of a protective layer, such as fur or feathers. It is thus hypothesized that dermal uptake could be a significant route of exposure. Consequently, it is necessary to determine the relative importance of different exposure routes that might affect the integrated toxicity outcome for terrestrial amphibian life-stages. Here, a one-compartment Toxicokinetic model was derived and tested using a publicly available dataset containing relevant exposure and uptake information for juvenile anurans exposed to 13 different pesticides. Modelled body burdens were then compared to measured burdens for a total of 815 individuals. Overall, a good concordance between modelled and measured values was observed, with the predicted and measured body burdens differing by a factor of 2 on average (overall R2 of 0.80 and correlation coefficient of 0.89), suggesting good predictivity of the model. Accordingly, the model predicts realistic body burdens for a variety of frog and toad species, and overall, for anurans. As the model includes rehydration (implicit in the evaluated studies) but currently does not account for metabolism, it can be seen as a worst-case assessment. We suggest toxicokinetic models, such as the one here presented, could be used to characterize dermal exposure in amphibians, screen for pesticides of concern, and prioritize risk assessment efforts, whilst reducing the need for de novo vertebrate testing.

Impacts of neonicotinoids on biodiversity: a critical review

Neonicotinoids are the most widely used class of insecticides in the world, but they have raised numerous concerns regarding their effects on biodiversity. Thus, the objective of this work was to do a critical review of the contamination of the environment (soil, water, air, biota) by neonicotinoids (acetamiprid, clothianidin, imidacloprid, thiacloprid, thiamethoxam) and of their impacts on terrestrial and aquatic biodiversity. Neonicotinoids are very frequently detected in soils and in freshwater, and they are also found in the air. They have only been recently monitored in coastal and marine environments, but some studies already reported the presence of imidacloprid and thiamethoxam in transitional or semi-enclosed ecosystems (lagoons, bays, and estuaries). The contamination of the environment leads to the exposure and to the contamination of non-target organisms and to negative effects on biodiversity. Direct impacts of neonicotinoids are mainly reported on terrestrial invertebrates (e.g., pollinators, natural enemies, earthworms) and vertebrates (e.g., birds) and on aquatic invertebrates (e.g., arthropods). Impacts on aquatic vertebrate populations and communities, as well as on microorganisms, are less documented. In addition to their toxicity to directly exposed organisms, neonicotinoid induce indirect effects via trophic cascades as demonstrated in several species (terrestrial and aquatic invertebrates). However, more data are needed to reach firmer conclusions and to get a clearer picture of such indirect effects. Finally, we identified specific knowledge gaps that need to be filled to better understand the effects of neonicotinoids on terrestrial, freshwater, and marine organisms, as well as on ecosystem services associated with these biotas.

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.

Realistic scenarios of pesticide exposure alters multiple biomarkers in BOANA PULCHELLA (ANURA) Adult Frogs

Imazethapyr, a post-emergent herbicide used in worldwide soybean and corn crops, induces genetic and biochemical alterations in aquatic vertebrates. This study examined the relationship between biomarkers at different organization levels and imazethapyr real-life route exposure in Boana pulchella adults. Frogs were exposed to imazethapyr-based formulation Pivot^® H (10.59%) at concentrations representing possible acute routes: field runoff (S1:10 mg.L^-1), exposure after direct foliar application (S2:100 mg.L^-1) and during direct foliar application (S3:1000 mg.L^-1). Post-exposure, endpoints levels were evaluated: organism alterations, biochemical activities and cytogenetic assays. Forty-eight hours post-exposure, antioxidant enzymes decrease, micronuclei induction and DNA damage were observed in all scenarios, while cholinesterase activity increase and body condition reduction were observed in frog-exposed to S3. Ninety-six hours post-exposure, frogs showed glutathione-S-transferase inhibition in S1, micronuclei induction in S2 and S3, and DNA-damage increase in S3. Herbicides routes of exposures in real-life could indicate that authorized applications have a risk to amphibian populations.

Amphibian Dispersal Traits Not Impacted by Triclopyr Exposure during the Juvenile Stage

Exposure to agrochemicals can have lethal and sublethal effects on amphibians. Most toxicology studies only examine exposure during the aquatic larval stage. Survival of the juvenile stage is the most important for population persistence and it is critical to understand the potential impacts of exposure during this life stage. We investigated how short-term exposure to triclopyr, an herbicide commonly used in forestry management, might impact several juvenile traits. To determine if juveniles perceived exposure as an environmental stressor, we measured their release of corticosterone. We also examined dispersal traits by measuring foraging and hopping behavior. We found no evidence that exposure negatively impacted these traits or was a stressor. Our results provide a preliminary assessment of the potential impact of triclopyr on juvenile amphibians, but we recommend additional research on the effects of agrochemicals on juvenile amphibians.

Estimating dermal contact soil exposure for amphibians

Chemical exposure estimation through the dermal route is an underemphasized area of ecological risk assessment for terrestrial animals. Currently, there are efforts to create exposure models to estimate doses from this pathway for use in ecological risk assessment. One significant limitation has been insufficient published data to characterize exposure and to support the selection and parameterization of appropriate models, particularly for amphibians in terrestrial habitats. Recent publications measuring pesticide doses to terrestrial-phase amphibians have begun to rectify this situation. We collated and summarized available measurements of terrestrial amphibian dermal exposure to pesticides from 11 studies in which researchers measured tissue concentrations associated with known pesticide experimental application rates. This data set included tissue concentrations in 11 amphibian species and 14 different pesticides. We then compared the results of two screening exposure models that differed based on surface area scaling approaches as a function of body weight (one based on birds as surrogates for amphibians and another amphibian-specific) to the measured tissue residue concentrations. We define a false-negative rate for each screening model as the proportion of amphibians for which the predicted concentration is less than the observed concentration (i.e., underestimate), contrary to the intent of screening models, which are intended to have a bias for higher exposure concentrations. The screening model that uses birds as surrogates did not have any instances where estimated expected avian doses were less than measured amphibian body burdens. When using the amphibian-specific exposure model that corrected for differences between avian and amphibian surface area, measured concentrations were greater than model estimates for 11.3% of the 1158 comparisons. The database of measured pesticide concentrations in terrestrial amphibians is provided for use in calculating bioconcentration factors and for future amphibian dermal exposure model development. Integr Environ Assess Manag 2023;19:9-16. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Bioaccumulation of pesticides and genotoxicity in anurans from southern Brazil

The expansion of agricultural activities causes habitat loss and fragmentation and the pollution of natural ecosystems through the intense use of pesticides, which may affect the populations of amphibian anurans that inhabit agricultural areas. The present study evaluated the in situ bioaccumulation of pesticides in a population of Leptodactylus luctator that occupies farmland in southern Brazil. We also compared the genotoxicity of L. luctator populations from farmland and forested areas in the same region. We analyzed the micronuclei and nuclear abnormalities of 34 adult anurans, 19 from farmland, and 15 from the forested area. We also assessed the presence of 32 pesticides in liver samples obtained from 18 farmland-dwelling anurans, using chromatographic analysis. We recorded significantly higher rates of nuclear abnormalities in the individuals from the farmland, in comparison with the forest. We detected nine pesticides in the liver samples, of which, deltamethrin was the most common and carbosulfan was recorded at the highest concentrations. The bioaccumulation of pesticides and the higher levels of genotoxic damage found in the anurans from agricultural areas, as observed in the present study, represent a major potential problem for the conservation of these vertebrates, including the decline of their populations and the extinction of species.

Nicosulfuron, a sulfonylurea herbicide, alters embryonic development and oxidative status of hatchlings at environmental concentrations in an amphibian species

The widespread use of agrochemicals for controlling pests and diseases of crops is recognized as a main threat to biodiversity. Sulfonylurea herbicides are being increasingly used and display low levels of degradation in water which suggest that they might affect non-target organisms. In a common garden experiment, eggs of a widespread amphibian (Bufo spinosus) were exposed to sublethal environmentally relevant concentrations of a widely used sulfonylurea herbicide, nicosulfuron, during the whole embryonic development. We assessed development-related traits (i.e., development duration, hatching success, hatchling size and occurrence of malformation) as well as antioxidant markers in response to contamination (i.e., SOD, GPx, catalase, thiols and relevant ratios thereof). We found that sublethal concentrations of nicosulfuron increased embryonic development duration, increased hatchling size and tended to increase malformations. Embryos exposed to nicosulfuron displayed decreased thiols and increased catalase activity suggesting alteration of oxidative status. We did not find any effect of nicosulfuron on SOD and GPx levels. Interestingly, higher catalase activity was linked to higher proportion of malformed individuals, suggesting that exposure to nicosulfuron induced teratogenic effects. Our results suggest that alteration of antioxidant levels might be one physiological mechanism through which nicosulfuron might cause detrimental effects on amphibian embryos. Sublethal effects of pesticides at environmentally relevant concentrations have been overlooked and require further investigations, especially in non-target taxa occurring in agricultural landscapes.

Habitat differences affect the nuclear morphology of the erythrocytes and the hepatic melanin in Leptodactylus fuscus (Anura) in the Brazilian Cerrado savanna

The sensitivity of anuran to the effects of habitat destruction and contamination has led to a preoccupying global decline in their populations. Morphological biomarkers such as micronuclei and other erythrocyte nuclear abnormalities (ENAs), as well as the occurrence of hepatic melanin, can be used to evaluate the effects of habitat impacts. In the present study, these two parameters were combined for the in situ assessment of the effects of soybean cultivation on the grassfrog, Leptodactylus fuscus. Specimens were also collected from a protected area to provide a reference site (non-agricultural environment). The frequency of some of the nuclear abnormalities in the animals from the soybean plantation was much higher than that recorded at the reference site, in particular micronuclei, which were 3.6 times more frequent in the plantation, lobulated nuclei (3.4 times more frequent), and reniform nuclei, which were four times more common than at the reference site. The combined analysis of all the ENAs together also revealed a frequency approximately 1.4 times higher in the animals from the soybean plantation, in comparison with the protected area. Smaller areas of hepatic melanin were observed in the specimens from the soybean plantation. These results provide further evidence of the sensitivity of anurans to habitat impacts and indicate that animals found in soybean plantations are susceptible to systematic alterations of their cells.

Multiple Level Effects of Imazethapyr on Leptodactylus latinasus (Anura) Adult Frogs

Imazethapyr is an herbicide that is used in a variety of crops worldwide, including soybean and corn. The aim of the present study was to evaluate the biomarkers responses of adult Leptodactylus latinasus exposed to the formulation Pivot^® H (10.59% imazethapyr) in the laboratory at concentrations and under conditions that simulate two potential field exposure scenarios: an immersion in field runoff (Scenario 1: 10 mg/L) and a direct exposure to the droplets emitted by spray noozles (Scenario 2: 1000 mg/L). In both scenarios, the experimental procedure involved completely immersing the frogs over a period of 15 s. Different endpoints were evaluated at several ecotoxicological levels 48 and 96 h after the herbicide exposure. These included individual (biometric indices and behavior alterations), histological (liver pigments and lesions), biochemical (catalase, glutathione system and cholinesterase activities) and genotoxic effects (micronuclei induction and nuclear abnormalities). Forty-eight hours after imazethapyr exposure, frogs submitted to Scenario 1 presented an inhibition of liver glutathione-S-transferase activity, whereas histological alterations and increased hepatic cholinesterase levels were observed in frogs exposed under Scenario 2. Ninety-six hours after exposure to the imazethapyr formulation, frogs from the Scenario 1 treatment presented a decrease in liver melanin and hemosiderin, increased hepatic catalase activity and micronuclei induction. For their part, frogs exposed to Scenario 2 presented a decrease in the hepatosomatic index, an increase in liver alterations, melanin reduction and micronuclei induction. The multivariate analysis enables correlations to be made between biomarkers of different organizational level in exposed anurans. Our result indicates that real exposure to imazethapyr formulations under field conditions may pose a risk to Leptodactylus latinasus populations living in the agroecosystems.

Route of exposure influences pesticide body burden and the hepatic metabolome in post-metamorphic leopard frogs

Pesticides are being applied at a greater extent than in the past. Once pesticides enter the ecosystem, many environmental factors can influence their residence time. These interactions can result in processes such as translocation, environmental degradation, and metabolic activation facilitating exposure to target and non-target species. Most anurans start off their life cycle in aquatic environments and then transition into terrestrial habitats. Their time in the aquatic environment is generally short; however, many important developmental stages occur during this tenure. Post-metamorphosis, most species spend many years on land but migrate back to the aquatic environment for breeding. Due to the importance of both the aquatic and terrestrial environments to the life stages of amphibians, we investigated how the route of exposure (i.e., uptake from contaminated soils vs. uptake from contaminated surface water) influences pesticide bioavailability and body burden for four pesticides (bifenthrin (BIF), chlorpyrifos (CPF), glyphosate (GLY), and trifloxystrobin (TFS)) as well as the impact on the hepatic metabolome of adult leopard frogs (Gosner stage 46 with 60-90 days post-metamorphosis). Body burden concentrations for amphibians exposed in water were significantly higher (ANOVA p < 0.0001) compared to amphibians exposed to contaminated soil across all pesticides studied. Out of 80 metabolites that were putatively identified, the majority expressed a higher abundance in amphibians that were exposed in pesticide contaminated water compared to soil. Ultimately, this research will help fill regulatory data gaps, aid in the creation of more accurate amphibian dermal uptake models and inform continued ecological risk assessment efforts.

Dermal Fungicide Exposure at Realistic Field Rates Induces Lethal and Sublethal Effects on Juvenile European Common Frogs (Rana temporaria)

Viticulture is one of the most pesticide-intensive agricultures in Europe, leading to a spatiotemporal overlap of amphibian migration and pesticide applications. Because postmetamorphic, terrestrial amphibian stages are mostly neglected in ecotoxicological studies, we investigated acute effects of viticultural fungicides on juvenile common frogs (Rana temporaria). Tadpoles from an uncontaminated pond were placed in enclosures in 8 ponds with an increasing degree of pesticide contamination in southwest Germany to represent different aquatic exposure backgrounds. After metamorphosis, juveniles were exposed to soil contaminated with 50% of the recommended field rates of the fungicides Folpan^® 80 water dispersible granule (WDG) and Folpan^® 500 suspension concentrate with the same amount of folpet as active ingredient and differing additives. After 48 h, effects on the survival, body mass, and behavior were investigated. No effect of the aquatic exposure background on terrestrial sensitivity could be detected. Acute terrestrial exposure led to mean mortality rates of 14% (13-17%, suspension concentrate) and 60% (17-100%, WDG) and resulted in adverse effects on locomotor activity as well as feeding behavior. Moreover, the results suggest that the toxicity of the 2 tested folpet formulations depends on their additives. Because the identified effects may result in severe impairments and thus in declines of amphibian populations, a more protective risk assessment of pesticides is needed for postmetamorphic amphibians to ensure proper conservation of amphibian populations. Environ Toxicol Chem 2021;40:1289-1297. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Histopathologic and genotoxic effects of deltamethrin on marsh frog, Pelophylax ridibundus (Anura: Ranidae)

It is known that amphibians inhabiting agricultural areas are constantly exposed to chemicals such as insecticides. Deltamethrin, a type II pyrethroid insecticide, is widely used in the world. The present study aimed to investigate the toxic effects of different concentrations (0.625, 1.25, and 2.50 mg/kg body wt) of orally applied deltamethrin to marsh frog (Pelophylax ridibundus) after 96 h of treatment. The histopathological abnormalities in liver, gastrointestinal tract, and kidney tissues were evaluated with quantitative analyses. In liver, increase of melanomacrophagic aggregates, non-homogeneous hepatocyte parenchyma, sinusoidal dilatations, infiltration, vascular epithelial degeneration, central vein degeneration, and congestion were determined in exposed frogs. In gastrointestinal tract, vacuolization, hypertrophy, congestion, infiltration, necrosis, and erosion of the epithelial layer, increasing goblet secretion, degeneration in villi, epithelial disorganization, and edema were observed in high-dose groups. In all experimental groups, glomerular shrinkage, hemorrhage, degeneration, infiltration, increase in Bowman distance, and eosinophilic-stained tubular lumens were detected in kidneys. Histopathological changes were more prominent in 1.25 and 2.50 mg/kg groups than the other groups. To determine the genotoxic effects of deltamethrin, the peripheral blood samples of the frogs were used. The erythrocytic nuclear abnormalities such as micro-nucleus, double-nucleus, kidney-shaped nucleus, notched nucleus, and bud nucleus were determined in the frogs, and the genotoxicity did not show a significant increase between control and low-dose groups, statistically. However, the genotoxic effects increased in medium- and especially high-dose groups. The results of this study showed that acute deltamethrin exposure can lead to histopathologic and genotoxic effects in P. ridibundus.

Avoidance behavior of juvenile common toads (Bufo bufo) in response to surface contamination by different pesticides

Most agricultural soils are expected to be contaminated with agricultural chemicals. As the exposure to pesticides can have adverse effects on non-target organisms, avoiding contaminated areas would be advantageous on an individual level, but could lead to a chemical landscape fragmentation with disadvantages on the metapopulation level. We investigated the avoidance behavior of juvenile common toads (Bufo bufo) in response to seven pesticide formulations commonly used in German vineyards. We used test arenas filled with silica sand and oversprayed half of each with different pesticide formulations. We placed a toad in the middle of an arena, filmed its behavior over 24 hours, calculated the proportion of time a toad spent on the contaminated side and compared it to a random side choice. We found evidence for the avoidance of the folpet formulation Folpan® 500 SC, the metrafenone formulation Vivando® and the glyphosate formulation Taifun® forte at maximum recommended field rates for vine and a trend for avoidance of Wettable Sulphur Stulln (sulphur). No avoidance was observed when testing Folpan® 80 WDG (folpet), Funguran® progress (copper hydroxide), SpinTorTM (spinosad), or 10% of the maximum field rate of any formulation tested. In the choice-tests in which we observed an avoidance, toads also showed higher activity on the contaminated side of the arena. As video analysis with tracking software is not always feasible, we further tested the effect of reducing the sampling interval for manual data analyses. We showed that one data point every 15 or 60 minutes results in a risk of overlooking a weak avoidance behavior, but still allows to verify the absence/presence of an avoidance for six out of seven formulations. Our findings are important for an upcoming pesticide risk assessment for amphibians and could be a template for future standardized tests.

European hares do not avoid newly pesticide-sprayed fields: Overspray as unnoticed pathway of pesticide exposure

Although risk assessments for pesticides involve quantifying exposure routes for animals, little empirical evidence exists on how individuals use areas where pesticides were used. Further, the European Food Safety Authority guidelines for the risk assessment of birds and mammals currently only include direct dietary uptake from exposed plants as important pathway for pesticides, arguing that dermal exposure is generally negligible. Here, we use the European hare (Lepus europaeus) as a model of a farmland specialist to investigate if (1) hares adjust habitat use in response to pesticide spraying, using GPS data, and (2) calculate the pesticide exposure and uptake over different pathways, i.e. foraging uptake versus overspray and subsequent oral grooming, using an agent-based modelling approach. Apart from avoidance of sprayed fields on the spraying day by inactive hares, which was likely caused by the mechanical disturbance rather than the pesticide itself, we found no evidence that hares reduced the use of pesticide-sprayed fields compared to control observations where no pesticides were applied. Our simulation showed that both the proportion of exposed individuals and the pesticide uptake were related to the pathway of exposure (foraging versus overspray/oral grooming), and depended on the age class and the vegetation type. We found that pesticide uptake via overspray/oral grooming might be 7-fold higher compared to foraging and might thus be an important pathway of pesticide exposure in hares. Our findings emphasize that policy makers, specifically the European Food Safety Authority, should incorporate alternative pathways of pesticide exposure for birds and mammals, such as overspray and oral grooming, when conducting environmental risk assessments and take variation in vegetation structure and age-related animal behavior into account, because these factors might affect pesticide exposure. Interactions between pesticide application and vegetation structure may both increase or decrease exposure but can be predicted using a simulation approach.

Potential pesticide exposure during the post-breeding migration of the common toad (Bufo bufo) in a vineyard dominated landscape

Two important drivers of the global amphibian decline are habitat destruction due to an intensification of farming and a related increase of pesticide applications. Recent studies have shown that there might be an underestimated risk of pesticides on terrestrial amphibians. However, there are too few data on the terrestrial habitat use of amphibians in agricultural landscapes to estimate the exposure risk. To fill this knowledge gap, we used telemetry to investigate the post-breeding migration of 51 common toads (Bufo bufo) from a breeding pond in a vineyard-dominated landscape in Southern Palatinate (Germany). We expected most toads to migrate to the nearby Palatinate Forest as a terrestrial habitat. However, only four individuals reached the forest, suggesting that a part of the population is inhabiting the agricultural landscape over large parts of the year. Individuals were also found directly in the vineyards (15% of all relocations), but 23% less often than expected from a random choice and therefore tend to avoid vineyards as terrestrial habitat. To estimate a possible spatial-temporal overlap of toad migration and pesticide application, we combined telemetry data with information about pesticide applications from local wine growers. Seven individuals had a high probability (>75%) of being directly exposed to a pesticide application. Taking spray drift and the half-life values of applied pesticides into account, the number of toads potentially exposed raised to 15 individuals. We estimated that, on a single day up to 24% of the whole breeding population came in contact with pesticides, resulting in a high overall exposure risk. Pesticides can have negative effects on amphibians, and toads try to avoid vineyards as habitats. Therefore, we conclude that a heterogeneous cultural landscape, with buffer strips around ponds, uncultivated patches and migration corridors, might be the best management measure for sustaining amphibians in the agricultural landscape.

Validating buccal swabbing as a minimal-invasive method to detect pesticide exposure in squamate reptiles

The use of enzymatic biomarkers constitutes a widely used approach in ecotoxicology. However, standard sampling procedures are invasive, requiring tissue, organ or blood extraction. This leads to concerns regarding conservation practice, animal welfare and restrictions in study design. New techniques are needed to avoid these problems, but still generate reliable data. Here, we aimed at validating the use of buccal swabs as a reliable method to detect pesticide exposure in reptiles. Common wall lizards (Podarcis muralis) were divided into control, dermal and oral treatment groups and exposed to different pesticide formulations. Subsequently, buccal swabs were taken and enzymatic activity was analyzed. We were able to confirm the suitability of the method to detect effects of pesticide exposure on the enzymatic level. While exposure to the formulation Roundup Ultramax® didn't match when compared to effects previously observed in situ when compared to other glyphosate based formulations, effects could still be detected. This can be seen as a strong indicator that the active ingredient of a formulation may not always be the mian driver for ecotoxicological effectsat the enzymatic level. At the same time, exposure towards the single formulation Vivando® didn't result in any effects. However, individuals residing in agricultural landscapes will mostly be exposed to pesticide mixes containing different formulations. Our results strongly advocate that buccal swabbing is a reliable minimal invasive method to generate samples for detecting effects of pesticide exposure in reptiles. Due to its easy handling, we believe it will provide new opportunities concerning study designs.

An Ecological Assessment of Isaria fumosorosea Applications Compared to a Neonicotinoid Treatment for Regulating Invasive Ficus Whitefly

A pilot study was conducted on a weeping fig, Ficus benjamina shrub hedge in a Florida urban landscape to determine the efficacy of a fungal biopesticide, PFR-97™ which contains blastospores of Isaria fumosorosea, and a neonicotinoid treatment (Admire Pro™) applied against the invasive ficus whitefly pest, Singhiella simplex (Singh). Post treatment, an ecological assessment of the study was conducted by observing the impact of the fungal biopesticide and neonicotinoid treatment on natural enemies, e.g., predators, parasitoids and enzootic fungal pathogens occurring in the whitefly-infested hedge. Both treatments provided a significant reduction in the whitefly population compared to control and were compatible with the natural enemies present. Various natural enemies including fungal entomopathogens were identified associated with the whitefly population infesting the weeping fig hedge. The parasitoids, Encarsia protransvena Viggiani and Amitus bennetti Viggiani & Evans combined parasitized a similar mean number of whitefly nymphs in both treatments and control; however, the number parasitized decreased over time. Natural enzootic fungi isolated from the ficus whitefly nymphs were I. fumosorosea, Purpureocillium lilacinum and Lecanicillium, Aspergillus and Fusarium species. Results from this pilot study suggest there is much potential for using repeated applications of the fungal biopesticide, PFR-97™ as a foliar spray compared to a neonicitionid as a soil drench for managing S. simplex on Ficus species for ≥28 days.

Agrochemical Mixtures and Amphibians: The Combined Effects of Pesticides and Fertilizer on Stress, Acetylcholinesterase Activity, and Bioaccumulation in a Terrestrial Environment

Tank mixtures are popular within the agricultural community because they are time- and cost-effective, but field applications leave nontarget organisms at risk of exposure. We explored the effects of a common herbicide (atrazine and alachlor) and fertilizer (urea) tank mixture on juvenile frog corticosterone stress levels, acetylcholinesterase (AChE) activity, and pesticide bioaccumulation. Single agrochemical or tank mixtures were applied to terrestrial microcosms, and then individual Southern leopard frog (Lithobates sphenocephala) juveniles were added to microcosms for an 8-h exposure. Afterward, frogs were transferred to aquatic microcosms for 1 h to monitor corticosterone prior to euthanasia, brain tissues were excised to evaluate AChE, and tissue homogenates were analyzed for pesticide bioconcentation with gas chromatography-mass spectrometry. Atrazine significantly increased corticosterone in frogs, particularly when combined with alachlor and urea. Atrazine increased AChE and urea decreased AChE, although no interactive effects of chemical combinations were discernible. Relative to their individual treatments, the complete tank mixture with all 3 agrochemicals resulted in 64% greater bioconcentration of atrazine and 54% greater bioconcentration of alachlor in frog tissues. Our results suggest that agrochemical mixtures as well as their active ingredients can lead to altered stress levels and impaired physiological responses in amphibians. An improved understanding of the effects of co-exposure to environmental contaminants in amphibians is important in assessing the ecological risks these compounds pose. Environ Toxicol Chem 2019;9999:1-10. © 2019 SETAC.

Endogenous and exogenous biomarker analysis in terrestrial phase amphibians (Lithobates sphenocephala) following dermal exposure to pesticide mixtures

Pesticide mixtures are frequently co-applied throughout an agricultural growing season to maximize crop yield. Therefore, non-target ecological species (e.g., amphibians) may be exposed to several pesticides at any given time on these agricultural landscapes. The objectives of this study were to quantify body burdens in terrestrial phase amphibians and translate perturbed metabolites to their corresponding biochemical pathways affected by exposure to pesticides as both singlets and in combination. Southern leopard frogs (Lithobates sphenocephala) were exposed either at maximum or 1/10^th maximum application rate to single, double, or triple pesticide mixtures of bifenthrin (insecticide), metolachlor (herbicide), and triadimefon (fungicide). Tissue concentrations demonstrate both facilitated and competitive uptake of pesticides when in mixtures. Metabolomic profiling of amphibian livers identified metabolites of interest for both application rates, however; magnitude of changes varied for the two exposure rates. Exposure to lower concentrations demonstrated down regulation in amino acids, potentially due to their being utilized for glutathione metabolism and/or increased energy demands. Amphibians exposed to the maximum application rate resulted in up regulation of amino acids and other key metabolites likely due to depleted energy resources. Coupling endogenous and exogenous biomarkers of pesticide exposure can be utilized to form vital links in an ecological risk assessment by relating internal dose to pathophysiological outcomes in non-target species.

Risk assessment considerations for plant protection products and terrestrial life-stages of amphibians

Some amphibians occur in agricultural landscapes during certain periods of their life cycle and consequently might be exposed to plant protection products (PPPs). While the sensitivity of aquatic life-stages is considered to be covered by the standard assessment for aquatic organisms (especially fish), the situation is less clear for terrestrial amphibian life-stages. In this paper, considerations are presented on how a risk assessment for PPPs and terrestrial life-stages of amphibians could be conducted. It discusses available information concerning the toxicity of PPPs to terrestrial amphibians, and their potential exposure to PPPs in consideration of aspects of amphibian biology. The emphasis is on avoiding additional vertebrate testing as much as possible by using exposure-driven approaches and by making use of existing vertebrate toxicity data, where appropriate. Options for toxicity testing and risk assessment are presented in a flowchart as a tiered approach, progressing from a non-testing approach, to simple worst-case laboratory testing, to extended laboratory testing, to semi-field enclosure tests and ultimately to full-scale field testing and monitoring. Suggestions are made for triggers to progress to higher tiers. Also, mitigation options to reduce the potential for exposure of terrestrial life-stages of amphibians to PPPs, if a risk were identified, are discussed. Finally, remaining uncertainties and research needs are considered by proposing a way forward (road map) for generating additional information to inform terrestrial amphibian risk assessment.

Blood biomarkers of common toad Rhinella arenarum following chlorpyrifos dermal exposure

Chlorpyrifos (CPF) is a broad spectrum pesticide commonly used for insect control, has great affinity for lipids and is thus a potential for bioaccumulation in aquatic organisms. The aim of this study was to evaluate the toxicity of CPF using the common toad Rhinella arenarum via dermal uptake in plastic bucket to simulate their natural exposition in ponds. R. arenarum toads were exposed individually to solutions containing a nominal concentration of a commercial formulation of CPF insecticide (5 and 10 mg/L). Different enzyme biomarkers (BChE: butyrylcholinesterase, CbE: carboxylesterase, and CAT: catalase) were measured in blood tissue after exposition. The capacity of pyridine-2-aldoxime methochloride (2-PAM) to reverse OP-inhibited plasma BChE and the ratio of heterophils and lymphocytes (H/L) as hematological indicators of stress were also determined. The normal values of plasma B-sterases (BChE and CbE) were highly inhibited (until ≈ 70%) in toads 48 h after exposure to CPF. The results indicate that 2-PAM produced BChE reactivation as well. The activity of CAT was also inducted for dermal exposure at more than double of that in the control toads (CPF; 5 mg/L). H/L ratios did not reveal a significantly increased stress. The study suggests that CPF via dermal uptake induced neurotoxicity and oxidative stress in the common toad R. areanum. Thus, some blood biomarkers employed in our study (i.e. BChE, CbE, 2-PAM, and CAT) might be used as predictors in health and ecological risk assessment of amphibian populations exposed to CPF.

Exploring the amphibian exposome in an agricultural landscape using telemetry and passive sampling

This is the first field study of its kind to combine radio telemetry, passive samplers, and pesticide accumulation in tissues to characterize the amphibian exposome as it relates to pesticides. Understanding how habitat drives exposure in individuals (i.e., their exposome), and how that relates to individual health is critical to managing species in an agricultural landscape where pesticide exposure is likely. We followed 72 northern leopard frogs (Lithobates pipiens) in two agricultural wetlands for insight into where and when individuals are at high risk of pesticide exposure. Novel passive sampling devices (PSDs) were deployed at sites where telemetered frogs were located, then moved to subsequent locations as frogs were radio-tracked. Pesticide concentration in PSDs varied by habitat and was greatest in agricultural fields where frogs were rarely found. Pesticide concentrations in frogs were greatest in spring when frogs were occupying wetlands compared to late summer when frogs occupied terrestrial habitats. Our results indicate that habitat and time of year influence exposure and accumulation of pesticides in amphibians. Our study illustrates the feasibility of quantifying the amphibian exposome to interpret the role of habitat use in pesticide accumulation in frogs to better manage amphibians in agricultural landscapes.

Effect of hydration status on pesticide uptake in anurans following exposure to contaminated soils

In this study, the impact of hydration status on dermal uptake of pesticides in two species of amphibians is examined. Absorption of pesticides in anurans occurs primarily through a highly vascularized dermal seat patch; however, pesticides can also enter through the superficial dermis following exposure. Despite the growing body of literature on dermal exposure in amphibians, little is known on how hydration status influences uptake. Thus, the objective of this study was to investigate the influence of hydration status on absorption of pesticides (atrazine, triadimefon, metolachlor, chlorothalonil, and imidacloprid) in southern leopard frogs (Lithobates sphenocephala) and Fowler's toads (Anaxyrus fowleri). Amphibian treatments included dehydration periods of 0, 2, 4, 6, 8, or 10 h prior to exposure to pesticide-contaminated soils for 8 h. Following exposure, soil and whole-body homogenates were extracted and analyzed by LC-MS/MS. Dehydration time was then regressed against post-exposure concentrations to infer the impact of dehydration on dermal pesticide uptake. Increased dehydration time resulted in significantly lowered pesticide concentrations in both species (F_{6, 293} = 67.66, p = 0.007) for the five pesticides studied. This phenomenon could be due to an energy and/or dilution effect.

Influence of exposure to pesticide mixtures on the metabolomic profile in post-metamorphic green frogs (Lithobates clamitans)

Pesticide use in agricultural areas requires the application of numerous chemicals to control target organisms, leaving non-target organisms at risk. The present study evaluates the hepatic metabolomic profile of one group of non-target organisms, amphibians, after exposure to a single pesticide and pesticide mixtures. Five common-use pesticide active ingredients were used in this study, three herbicides (atrazine, metolachlor and 2,4-d), one insecticide (malathion) and one fungicide (propiconazole). Juvenile green frogs (Lithobates clamitans) were reared for 60-90days post-metamorphosis then exposed to a single pesticide or a combination of pesticides at the labeled application rate on soil. Amphibian livers were excised for metabolomic analysis and pesticides were quantified for whole body homogenates. Based on the current study, metabolomic profiling of livers support both individual and interactive effects where pesticide exposures altered biochemical processes, potentially indicating a different response between active ingredients in pesticide mixtures, among these non-target species. Amphibian metabolomic response is likely dependent on the pesticides present in each mixture and their ability to perturb biochemical networks, thereby confounding efforts with risk assessment.

Using in vitro derived enzymatic reaction rates of metabolism to inform pesticide body burdens in amphibians

Understanding how pesticide exposure to non-target species influences toxicity is necessary to accurately assess the ecological risks these compounds pose. To assess the potential metabolic activation of broad use pesticides in amphibians, in vitro and in vivo metabolic rate constants were derived from toad (Anaxyrus terrestris) livers in experiments measuring the depletion of atrazine (ATZ), triadimefon (TDN), and fipronil (FIP) as well as formation of their metabolites. To determine the predictability of these in vitro derived rate constants, Fowler's toads (Anaxyrus fowleri) were exposed to soil contaminated with each of the pesticides at maximum application rate. Desethyl atrazine (DEA) and deisopropyl atrazine (DIA), both metabolites of ATZ, exhibited similar velocities (V_max) while the K_M constant for DIA was two times higher than DEA. TDN was metabolized into two diastereomers of triadimenol (TDL A and TDL B), where TDL B had a V_max around two times higher than TDL A. The metabolite fipronil sulfone's V_max and K_M were 150 pmol min^-1 mg^-1 and 29 μM, respectively. While intrinsic clearance rates for the pesticides ranged from 0.54 to 38.31 mL min^-1 kg^-1. Thus, gaining knowledge on differences in metabolism of pesticides within amphibians is important in estimating risk to these non-target species since the inherent toxicity of metabolites can differ from the parent compound.

Giant toads (Rhinella marina) living in agricultural areas have altered spermatogenesis

Across diverse taxa, germ cell development is controlled by an intricate cascade of processes that are tightly controlled by the hypothalamic-pituitary-gonadal axis. Endocrine disturbances, such as those induced by endocrine disrupting chemicals (EDCs) can negatively affect spermatogenesis. Here, we investigate whether spermatogenesis is altered in the giant toad, Rhinella marina, living in agricultural areas where EDCs are used relative to suburban areas. We also ask if reductions in spermatogenesis were associated with developmental gonadal abnormalities (intersex) found in the same frogs. We found that toads in agricultural areas exhibited reduced spermatogenesis relative to non-agricultural animals, and that those reductions were not associated with gross gonadal abnormalities. All toads living in agricultural areas had reduced spermatogenesis relative to those living in non-agricultural areas regardless of whether they had gonadal abnormalities originating during development. Similarities in reproductive dysfunction among diverse taxa living in agricultural areas, including humans, suggest that many vertebrate taxa living in agricultural areas around the globe are likely experiencing some level of reproductive dysfunction.

Factors influencing the toxicity of Headline® fungicides to terrestrial stage toads

Amphibians are susceptible to exposure from contaminants via multiple pathways. Pyraclostrobin fungicides have been shown to be toxic to terrestrial amphibians at environmentally relevant concentrations; however, these studies did not account for factors that may influence exposure and effects, such as fungicide formulation, age of the individual, exposure route, and physiological state of the individual. We examined Headline® and Headline AMP® fungicide toxicity to adult Anaxyrus cognatus and Anaxyrus woodhousii by direct overspray, as well as acute toxicity of Headline AMP to juvenile A. cognatus through direct overspray, previously exposed soils, and diet. We also assessed effects of hydration state on fungicide toxicity in juvenile A. cognatus and sublethal effects of fungicide exposure on prey-orientation ability of juvenile A. cognatus. Neither formulation of Headline caused mortality of adult A. cognatus and A. woodhousii at up to 5 times the maximum label rate in North American corn (1052 and 879 mL formulation/ha for Headline AMP and Headline fungicides, respectively, corresponding to 1.52 and 2.2 μg pyraclostrobin/cm² , respectively). Exposures of juvenile A. cognatus to Headline AMP via direct overspray and previously exposed soils (2 types) resulted in median lethal rate (LR50) values of 2.4, 3.34, and 3.61 μg pyraclostrobin/cm² , respectively. Dietary Headline AMP exposure was not toxic, prey-orientations were not influenced by exposure, and effects were similar between dehydrated and hydrated treatments (LR50 = 2.4 and 2.3 μg pyraclostrobin/cm² , respectively). These results, combined with exposure concentrations reported in previous studies, suggest that risk of acute mortality for amphibians in terrestrial environments is low and is dictated by body size and site-specific factors influencing exposure. Environ Toxicol Chem 2017;36:2679-2688. © 2017 SETAC.

Effects of a commonly used glyphosate-based herbicide formulation on early developmental stages of two anuran species

Environmental contamination, especially due to the increasing use of pesticides, is suggested to be one out of six main reasons for the global amphibian decline. Adverse effects of glyphosate-based herbicides on amphibians have been already discussed in several studies with different conclusions, especially regarding sublethal effects at environmentally relevant concentrations. Therefore, we studied the acute toxic effects (mortality, growth, and morphological changes) of the commonly used glyphosate-based herbicide formulation Roundup® UltraMax on early aquatic developmental stages of two anuran species with different larval types (obligate vs. facultative filtrating suspension feeders), the African clawed frog (Xenopus laevis) and the Mediterranean painted frog (Discoglossus pictus). While X. laevis is an established anuran model organism in amphibian toxicological studies, we aim to establish D. pictus as another model for species with facultative filtrating larvae. A special focus of the present study lies on malformations in X. laevis embryos, which were investigated using histological preparations. In general, embryos and larvae of X. laevis reacted more sensitive concerning lethal effects compared to early developmental stages of D. pictus. It was suggested, that especially the different morphology of their filter apparatus and the higher volume of water pumped through the buccopharynx of X. laevis larvae lead to higher exposure to the formulation. The test substance induced similar lethal effects in D. pictus larvae as it does in the teleost standard test organism used in pesticide approval, the rainbow trout (Oncorhynchus mykiss), whereas embryos of both species are apparently more tolerant and, conversely, X. laevis larvae about two times more sensitive. In both species, early larvae always reacted significantly more sensitive than embryos. Exposure to the test substance increased malformation rates in embryos of both species in a concentration-dependent manner, but not at environmentally relevant concentrations. However, the assumed field safety, based on calculated surface water concentrations of the active ingredient (glyphosate), should be validated with realistic field data and buffer strips have to be urgently regarded to any aquatic amphibian habitat.

Soil organic matter content effects on dermal pesticide bioconcentration in American toads (Bufo americanus)

Pesticides have been implicated as a major factor in global amphibian declines and may pose great risk to terrestrial phase amphibians moving to and from breeding ponds on agricultural landscapes. Dermal uptake from soil is known to occur in amphibians, but predicting pesticide availability and bioconcentration across soil types is not well understood. The present study was designed to compare uptake of 5 current-use pesticides (imidacloprid, atrazine, triadimefon, fipronil, and pendimethalin) in American toads (Bufo americanus) from exposure on soils with significant organic matter content differences (14.1% = high organic matter and 3.1% = low organic matter). We placed toads on high- or low-organic matter soil after applying individual current-use pesticides on the soil surface for an 8-h exposure duration. Whole body tissue homogenates and soils were extracted and analyzed using liquid chromatography-mass spectrometry to determine pesticide tissue and soil concentration, as well as bioconcentration factor in toads. Tissue concentrations were greater on the low-organic matter soil than the high-organic matter soil across all pesticides (average ± standard error; 1.23 ± 0.35 ppm and 0.78 ± 0.23 ppm, respectively), and bioconcentration was significantly higher for toads on the low-organic matter soil (analysis of covariance p = 0.002). Soil organic matter is known to play a significant role in the mobility of pesticides and bioavailability to living organisms. Agricultural soils typically have relatively lower organic matter content and serve as a functional habitat for amphibians. The potential for pesticide accumulation in amphibians moving throughout agricultural landscapes may be greater and should be considered in conservation and policy efforts. Environ Toxicol Chem 2016;35:2734-2741. © 2016 SETAC.