Amphibians / Reptiles
Impacts of Pesticides on Amphibians
Amphibians can be indirectly exposed to pesticides through runoff from land that has been treated with pesticides, and even through skin contact with contaminated soil. A 2013 study published in PloS ONE found that amphibians are vanishing at a rate of about 3.7 percent each year, which means that they will be absent from half of the habitats they currently occupy in about 20 years.
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University of California, Berkeley researcher Tyrone Hayes, PhD, has found that male frogs with low dose exposure to endocrine (hormone) disrupting pesticides, such as the widely-used herbicide atrazine, experience inhibited growth of the larynx, have lower testosterone levels, and experience hermaphroditic changes.
African Clawed Frog. Photo by Brian Gratwicke. - The hermaphroditic changes range from males turning fully into females, to still being biologically male but having a loss of interest in reproduction and a lack of sperm, and sometimes even to mating with other males instead of females.
- Exposure to atrazine essentially “chemically castrates” amphibians – impeding their ability to mate and reproduce.
- A 2014 study published in Environmental Pollution demonstrated that frogs accumulate measurable body burdens when exposed to soil that has been treated with pesticides such as imidacloprid, atrazine and fipronil.
- In 2013, biologist Jason Rohr, PhD, studied the effects of atrazine on the immune system of amphibians and found that exposure to atrazine lowers immune functioning, leaving frogs susceptible to death from a certain fungal disease, Batrachochytrium dendrobatidis. This fungal disease, commonly known as chytrid fungus, is devastating amphibian populations across the world. Research has shown that the fungus has been in existence for a long time, but our changing world has created an environment that leaves amphibians vulnerable to the disease. As stated above, pesticides can play a large role in creating this vulnerability.
- Researchers in Germanystudied two chemicals commonly used in orchards and on grains, and found a 100% mortality rate when frogs were exposed to doses recommended on the label.
- The fungicide pyraclostrobin killed all of the frogs within an hour when applied at label recommended rates.
- Dimethoate, a toxic systemic insecticide used on everything from asparagus and cherries, to tangerines and wheat, killed 40% of all frogs within a week of application.
- In 2012, University of Pittsburgh researchers have found that the use of the weed killer Roundup, which contains the active ingredient glyphosate, in sub-lethal and environmentally relevant concentrations causes two species of amphibians to change their physiological shape by interfering with the hormones of tadpoles.
[See More Scientific Studies Below]
Economic Cost
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| Quinbi Village, Island of Matzu. Photo by Prince Roy. |
Amphibians provide essential services for human society. They provide food provisioning services to humans and other wildlife, and have shown promise for medical use – secretions from frog skin have been shown to inhibit the transfer and spread of HIV. Some amphibians can inhibit the spread of mosquito-borne diseases through predation. They are prominent in some religions and mythology, providing cultural services. Finally, they are essential to regulating ecosystem structures, through nutrient cycling and the alteration of physical habitats. Unfortunately, it can be difficult to quantify how to put a number value onto ecological services, as there is not enough research to place a definitive economic value on all of these services that amphibians provide.
Litigation & Lawsuits
A federal district court approved a settlement in November 2013 requiring the U.S. Fish and Wildlife Service to better protect California red-legged frogs from seven common pesticides known to be highly toxic to amphibians. The settlement gave the agency two years to prepare biological opinions under the Endangered Species Act (ESA), to analyze pesticide use in and near the frog’s aquatic and upland habitats.
Quick Links
What Can You Do?
- Learn about the Hazards and Alternatives to using lawn pesticides.
- Go Organic – Visit our Eating with a Conscience page to learn why eating organic foods is the right choice.
- Visit our Tools for Change page to learn how to organize your community against pesticide use.
- Sign up for Beyond Pesticides’ Action Alerts to stay up-to-date on the latest petitions and news.
Scientific Studies:
Neonicotinoids (NEOs) are widely used insecticides that are ubiquitous in agricultural use. Since NEOs are found in natural waters as well as in tap water and human urine in regions where NEOs are widely used, NEOs pose a potential hazard to non-target organisms such as animals and humans. Some of the commonly detected NEOs are imidacloprid (IMD), thiamethoxam (TMX), and its metabolite clothianidin (CLO). Although previously published scientific information, including an assessment of the environmental risks, particularly for bees, had resulted in a ban on the outdoor use of these three NEOs in the EU – their use is now only permitted in closed greenhouses – these NEOs continue to be used in agriculture in many other parts of the world. Therefore, a detailed study and comparison of the effects of NEOs on the embryonic development of non-target organisms is needed to further define the risk profiles.
Embryos of the South African clawed frog Xenopus laevis, a well-established aquatic model, were exposed to different concentrations of IMD, TMX, or CLO (0.1–100 mg/L) to study and compare the possible effects of a single contaminant in natural water bodies on early embryogenesis. The results included a reduced body length, a smaller orbital space, impaired cranial cartilage and nerves, and an altered heart structure and function. At the molecular level, NEO exposure partially resulted in an altered expression of tissue-specific factors, which are involved in eye, cranial placode, and heart development.
Our results suggest that the NEOs studied negatively affect the embryonic development of the non-target organism X. laevis. Since pesticides, especially NEOs, pollute the environment worldwide, it is suggested that they are strictly controlled and monitored in the areas where they are used. In addition, the question arises as to whether pesticide metabolites also pose a risk to the environment and need to be investigated further so that they can be taken into account when registering ingredients.
[Flach, H. et al. (2024) Comparing the effects of three neonicotinoids on embryogenesis of the South African clawed frog xenopus laevis, Current Research in Toxicology. Available at: https://www.sciencedirect.com/science/article/pii/S2666027X24000227?via%3Dihub. ]
The human impact on environmental landscapes, such as land use, climate change or pollution, is threatening global biodiversity and ecosystems maintenance. Pesticides like the herbicide glyphosate have garnered considerable attention due to their well-documented harmful effects on non-target species. During application, the active ingredient glyphosate is utilized in various formulations, each containing different additive adjuvants. However, the possible effects of these formulations on amphibians - the group with the highest decline rates among vertebrates - remain largely unknown.
Therefore, the present study investigated the effects of four glyphosate formulations (Glyphosat TF, Durano TF, Helosate 450 TF, Kyleo) on the embryonic development of the model organism Xenopus laevis (South African clawed frog). Embryos at the 2-cell stage were exposed to various concentrations of glyphosate formulations (glyphosate: 0.01–100 mg/L), and mortality as well as sublethal effects on different organs and tissues were analyzed. The results indicated that the formulations had different effects, particularly on the mortality of Xenopus laevis embryos. At sublethal concentrations, the formulations altered the embryos' external appearance, leading to malformations such as reduced eye and head size. In addition, exposure to formulations impaired heart morphology and function, and the expression of heart-specific genes was altered at a molecular level.
Our results confirmed that glyphosate formulations had a stronger effect on Xenopus laevis embryogenesis than pure glyphosate. Therefore, it is crucial to evaluate the active ingredient and the co-formulations independently, as well as the combined, commercially available products, during pesticide risk assessments and renewal procedures of agrochemicals. The severe global decline of amphibians, partly due to herbicide use, highlights the need for strict and efficient monitoring of environmental pesticide loads and application areas.
[Flach, H. et al. (2024) Glyphosate formulations cause mortality and diverse sublethal defects during embryonic development of the amphibian Xenopus laevis, Chemosphere. Available at: https://www.sciencedirect.com/science/article/pii/S0045653524025244.]
Pesticides and personal care products are two very important groups of contaminants posing a threat to the aquatic environment and the organisms living in it.. Therefore, this study aimed to describe the effects of widely used pesticides and parabens on aquatic non-target biota such as fish (using model organisms Danio rerio and Cyprinus carpio) and amphibians (using model organism Xenopus laevis) using a wide range of endpoints. The first part of the experiment was focused on the embryonal toxicity of three widely used pesticides (metazachlor, prochloraz, and 4-chloro-2-methyl phenoxy acetic acid) and three parabens (methylparaben, propylparaben, and butylparaben) with D. rerio, C. carpio, and X. laevis embryos. An emphasis was placed on using mostly sub-lethal concentrations that are partially relevant to the environmental concentrations of the substances studied. In the second part of the study, an embryo-larval toxicity test with C. carpio was carried out with prochloraz using concentrations 0.1, 1, 10, 100, and 1000 µg/L. The results of both parts of the study show that even the low, environmentally relevant concentrations of the chemicals tested are often able to affect the expression of genes that play either a prominent role in detoxification and sex hormone production or indicate cell stress or, in case of prochloraz, to induce genotoxicity.
[Medkova, D., Hollerova, A., Riesova, B., Blahova, J., Hodkovicova, N., Marsalek, P., Doubkova, V., Weiserova, Z., Mares, J., Faldyna, M. and Tichy, F., 2023. Toxics, 11(4), p.333.]
Neonicotinoid pesticides are widely used to combat agricultural and forest pests, yet the extent of their biological effects and synergies with other stressors is not well understood, particularly for species with complex life cycles such as amphibians. While there is extensive research on the impacts of agricultural chemicals on amphibians (particularly larval stage), research on the effects of the new class of widely used neonicotinoid pesticides across life stages is lacking. In this study, we used aquatic mesocosm manipulations and terrestrial locomotor and behavior trials to evaluate demographic, behavioral, and fitness carryover effects of sublethal neonicotinoid pesticide (imidacloprid) exposure and hydroperiod length on the wood frog (Rana sylvatica), a model organism. We found that the interaction of imidacloprid exposure and shorter hydroperiod led to decreased larval survival to metamorphosis (0.54 ± 0.14, compared to control 0.75 ± 0.04). When exposed to their thermal optimum (18°C), individuals exposed to imidacloprid as larvae had higher terrestrial locomotor performance (284.08 ± 28.62 body lengths traveled) but also experienced the largest decreases in performance (147.88 ± 19.27 fewer body lengths traveled) after terrestrial imidacloprid exposure. In a 48-h substrate choice experiment, post-metamorphic frogs did not show behavioral avoidance of imidacloprid-treated substrates. Finally, we observed a skewed juvenile sex ratio from imidacloprid treatments (~10% fewer males compared to control), and we were not able to assign 15.7% of individuals from imidacloprid treatments to either sex due to ambiguous reproductive organ morphology. Our empirical assessment of carryover effects of chemical exposure and pond drying provides insights into the physiological capacity of taxa with complex lifecycles to respond to contaminants experienced at multiple life stages and informs best practices for neonicotinoid pesticide use in forest settings and conservation strategies for pond-breeding amphibians.
[Thompson, C.M., Sweeney, M.R. and Popescu, V.D., 2022. Journal of Zoology.]
There are increased concerns about the thyroidal effects of many anthropogenic substances in the environment. These substances include agricultural pesticides and industrial and pharmaceutical chemicals among others. Their potential thyroidal effects are of serious health and ecological concerns, as thyroid hormones mediate numerous physiological processes, including growth regulation, general metabolism and metamorphosis in metamorphic animals. This study assessed thyroidal activities of Arsenal formulation (Imazapyr) at environmentally relevant concentrations of 0.5, 2.0 and 3.5 mg/L following a Xenopus metamorphosis assay (XEMA). The result shows that the Arsenal formulation significantly delayed the tadpole development, reduced the hind-limb length (HLL) and increased the whole-body mass (WBM) at a concentration of 3.5 mg/L relative to the control exposure. In histopathology, the formulation increased the epithelium height, at all exposure concentrations, but reduced the colloidal area at 0.5 and 2 mg/L, respectively, and the gland area at 2 mg/L relative to the control. Consequently, the Arsenal formulation is thyroid-active at environmentally relevant concentrations and poses a threat to both human and wildlife, especially metamorphic organisms. With this exposure impact, more studies are imperative to further characterise other endocrine-disrupting potential of this formulation.
[Babalola, O.O. and van Wyk, J.H. (2021) Exposure impacts of Imazapyr formulation on larval development and thyroid histology of Xenopus laevis, Environmental Science and Pollution Research. Available at: https://link.springer.com/article/10.1007/s11356-021-14227-4. ]
Concern over global amphibian declines and possible links to agrochemical use has led to research on the endocrine disrupting actions of agrochemicals, such as fertilizers, fungicides, insecticides, acaricides, herbicides, metals, and mixtures. Amphibians, like other species, have to partition resources for body maintenance, growth, and reproduction. Recent studies suggest that metabolic impairments induced by endocrine disrupting chemicals, and more particularly agrichemicals, may disrupt physiological constraints associated with these limited resources and could cause deleterious effects on growth and reproduction. Metabolic disruption has hardly been considered for amphibian species following agrichemical exposure. As for metamorphosis, the key thyroid hormone-dependent developmental phase for amphibians, it can either be advanced or delayed by agrichemicals with consequences for juvenile and adult health and survival. While numerous agrichemicals affect anuran sexual development, including sex reversal and intersex in several species, little is known about the mechanisms involved in dysregulation of the sex differentiation processes. Adult anurans display stereotypical male mating calls and female phonotaxis responses leading to successful amplexus and spawning. These are hormone-dependent behaviours at the foundation of reproductive success. Therefore, male vocalizations are highly ecologically-relevant and may be a non-invasive low-cost method for the assessment of endocrine disruption at the population level. While it is clear that agrochemicals disrupt multiple endocrine systems in frogs, very little has been uncovered regarding the molecular and cellular mechanisms at the basis of these actions. This is surprising, given the importance of the frog models to our deep understanding of developmental biology and thyroid hormone action to understand human health. Several agrochemicals were found to have multiple endocrine effects at once (e.g., targeting both the thyroid and gonadal axes); therefore, the assessment of agrochemicals that alter cross-talk between hormonal systems must be further addressed. Given the diversity of life-history traits in Anura, Caudata, and the Gymnophiona, it is essential that studies on endocrine disruption expand to include the lesser known taxa. Research under ecologically-relevant conditions will also be paramount. Closer collaboration between molecular and cellular endocrinologists and ecotoxicologists and ecologists is thus recommended.
[Trudeau, V. et al. (2020) Agrochemicals disrupt multiple endocrine axes in amphibians, Molecular and Cellular Endocrinology. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0303720720301611. ]
The diamondback terrapin's (Malaclemys terrapin) wide geographic distribution, long life span, occurrence in a variety of habitats within the saltmarsh ecosystem, predatory foraging behavior, and high site fidelity make it a useful indicator species for contaminant monitoring in estuarine ecosystems. In this study fat biopsies and plasma samples were collected from males and females from two sites within Barnegat Bay, New Jersey, as well as tissues from a gravid female and blue mussels (Mytilus edulis), which are terrapin prey. Samples were analyzed for persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), chlorinated pesticides, and methyl-triclosan. Terrapins from the northern site, Spizzle Creek, closest to influences from industrial areas, had higher POP concentrations for both tissues than terrapins from the less impacted Forsythe National Wildlife Refuge. Sex differences were observed with males having higher contaminant concentrations in fat and females in plasma. PCB patterns in terrapin fat and plasma were comparable to other wildlife. Plasma contaminant concentrations significantly and positively correlated with those in fat. This study addresses several aspects of using the terrapin as an indicator species for POP monitoring: site and sex differences, tissue sampling choices, maternal transfer, and biomagnification.
[Basile ER, Avery HW, Bien WF, Keller JM. 2011. Chemosphere. 82(1):137-44]