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. 

  • African Clawed Frog
    African Clawed Frog. Photo by Brian Gratwicke.
    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.
      • 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

Quinbi Village, Island of Matzu
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.    

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Scientific Studies: 

  • Comparing the effects of three neonicotinoids on embryogenesis of the South African clawed frog Xenopus laevis
    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. ]

  • Pesticides and Parabens Contaminating Aquatic Environment: Acute and Sub-Chronic Toxicity towards Early-Life Stages of Freshwater Fish and Amphibians
    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.]
  • Carryover effects of pesticide exposure and pond drying on performance, behavior, and sex ratios in a pool breeding amphibian

    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.]
  • Diamondback terrapins as indicator species of persistent organic pollutants: Using Barnegat Bay, New Jersey as a case study
    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]