18
Mar
Research Highlights Regulatory Failures in Addressing Risks to Nontarget Organisms from Rodenticides
(Beyond Pesticides, March 18, 2025) The November 2024 press release by the U.S. Environmental Protection Agency (EPA) for its Rodenticide Strategy includes the final biological evaluation (BE) of 11 rodenticides. Prior to the finalization of the BE, Beyond Pesticides commented to EPA’s Office of Pesticide Programs in early 2024, disagreeing with the categorical no effect (NE) determinations for all freshwater and marine fish, aquatic mammals, aquatic amphibians, aquatic reptiles, and aquatic invertebrates. (See related Daily News and Action of the Week.) The latest scientific literature highlights the impacts of rodenticides on nontarget organisms, including aquatic organisms that the agency failed to evaluate due to harm that was, as EPA says, “not reasonably certain to occur.â€
Many rodenticides, intended to target rats, mice, squirrels, nutria, and more, are anticoagulants and stop normal blood clotting. Active ingredients in these pesticides can include bromadiolone, chlorophacinone, difethialone, brodifacoum, and warfarin. Anticoagulant rodenticides (ARs), contrary to the agency’s assertions, can be transported to aquatic ecosystems, including both freshwater and marine environments. As mentioned in Beyond Pesticides’ comments, ARs have been detected in raw and treated wastewater, sewage sludge, estuarine sediments, suspended particulate matter, and liver tissues of sampled fish, demonstrating that the aquatic environment experiences a greater risk of anticoagulant rodenticide exposure than EPA claims.
In a Science of The Total Environment study, the authors find evidence of second-generation anticoagulant rodenticides (SGARs) in frog species. Brodifacoum was found in four of the six frog species analyzed by the researchers, and they share, “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.†SGARs were developed after first-generation anticoagulants created resistance in rodents. These compounds contain properties that “pose greater risks to nontarget species†due to their potency, EPA states.
Prior research, also published in Science of The Total Environment, designates SGARs as “(very) persistent, (very) bioaccumulative, and toxic.†While new research is continuing to emerge regarding rodenticides, the authors highlight the previous lack of focus on aquatic species: “So far, worldwide monitoring of AR residues mainly focused on terrestrial and avian non-target species and their routes of exposure… AR residue screening in aquatic compartments is challenging, and accordingly little is known about direct and indirect exposure routes as well as anticoagulants’ distribution and fate in the aquatic environment.â€
The researchers also share: “Further research should investigate the potential risks and hazards of ARs in the aquatic environment in order to pave the way for scientific-based, targeted, and effective regulatory decisions. Until then, the ecological implications for aquatic organisms as well as fish-eating predators remain largely unknown.†This highlights the many data gaps that call in to question EPA’s ability to declare risks to aquatic organisms as “not reasonably certain to occur.â€
The risk of pesticide exposure to nontarget organisms, including both aquatic and terrestrial wildlife, is often disregarded in regulatory assessments. Wildlife can be adversely affected by pesticides through their direct or indirect application, such as pesticide drift, secondary poisoning, runoff into local water bodies, or groundwater contamination. It is possible that some animals can be sprayed directly, while others consume plants or prey that have been exposed to pesticides.
As documented by Lohr, M. et al., “Anticoagulant rodenticides (ARs) have been detected in non-target wildlife species worldwide… Second generation anticoagulant rodenticides (SGARs) pose a particular threat to scavengers and top-order carnivores because their long half-lives allow for biomagnification and bioaccumulation beyond their intended rodent targets.†In analyzing liver tissues from carnivorous and scavenging mammals, 50% tested positive for the presence of ARs. Multiple samples showed more than one AR compound as well.
“This study is the first to document widespread and pervasive AR exposure in native Australian marsupial carnivores, including those in remote locations away from towns,†the researchers share. They continue: “The frequency and severity of exposure, sometimes from multiple ARs, suggest potential population-level impacts on these threatened species. These findings provide further evidence that ARs should be listed as a key threatening process under state and federal legislation.â€
A similar study, in Environmental Chemistry Letters, reports: “We analyzed residues of eight anticoagulant rodenticides in liver samples of 96 great cormorants, 29 common mergansers, various fish species, and coypu, in different German regions. Results show that hepatic residues of anticoagulant rodenticides were found in almost half of the investigated cormorants and mergansers due to the uptake of contaminated fish from effluent-receiving surface waters.†This highlights the presence of ARs in aquatic organisms that are then transferred through the aquatic food web to predators and adds to the concern about ARs’ propensity for biomagnification and bioaccumulation.
The authors conclude that: “Our biomonitoring study demonstrated that piscivorous avian predators in anthropogenically influenced landscapes are exposed to second-generation anticoagulant rodenticides via their fish prey. Transfer of second-generation active ingredients along the aquatic food chain was thus confirmed. Without doubt, future improvements of regulatory measures concerning biocides will be required to mitigate the yet unknown consequences for aquatic wildlife from the nowadays almost exclusive application of second-generation anticoagulant rodenticides during chemical rodent control.â€
Also documenting secondary exposure to ARs, a study in The Journal of Wildlife Management shows how anticoagulant rodenticides cause “the death of mammalian predators and scavengers directly and indirectly through sublethal effects that reduce fitness.†In quantifying AR exposure in carcasses of 365 urban and suburban coyotes in southern California, the researchers report, “Nearly all urban coyotes (98.1%) were exposed to at least 1 AR, compared to 41.7% of rural coyotes, and most individuals had residues of both first-generation (FGAR) and the more potent second-generation (SGAR) compounds, often at concentrations exceeding thresholds considered lethal in other mammals.â€
The authors also share that the “adults tended to have residues of more compounds and at higher concentrations than juveniles, suggesting repeated and chronic exposure.†They continue, “[S]ome coyotes showed evidence of internal bleeding consistent with AR toxicosis and were in poorer body condition,†raising additional concerns for mechanisms of toxicity. (See more research on ARs and carnivores here and here.)
As Beyond Pesticides notes in a previous Daily News, reliance on toxic rodenticides also poses threats to human health. In 2023, guests at a Pittsburgh, PA extended-stay hotel were evacuated by health officials due to a contamination and poisoning incident caused by an unidentified rodenticide. Officials confirmed that the particular rat poison involved in the incident, when exposed to water, releases the highly toxic phosphine gas. According to the Centers for Disease Control and Prevention (CDC), the gas causes many symptoms, including nausea, vomiting, stomach pain, diarrhea, thirst, muscle pain, difficulty breathing, and the accumulation of fluid in the lungs, with acute and prolonged exposure potentially leading to more severe consequences.
There is a wide body of science highlighting the impacts of pesticides on human health and biodiversity. Many of these effects, however, are not taken into account in risk assessments by EPA and other regulatory agencies. (See more on EPA failures here.) Without fully evaluating the potential for chemicals to impact the health of organisms and the environment, both singularly and in mixtures, advocates are calling for a transformation toward an ecologically sustainable land management system rooted in organic principles.
Safety advocates do not consider the risks of using toxic chemicals in agriculture and land management â€reasonable,†under the legal standard of federal pesticide law, given the availability of a safe and effective alternative. Studies show organic practices lower the environmental impact of agriculture, provide human health benefits, enhance biodiversity, and more.
As Beyond Pesticides reported earlier this year, the current health, biodiversity, and climate crises are the most profound problems humanity has yet encountered and calls for dismantling siloes, integrating knowledge among disciplines and between actions, and committing to changing some of our most basic beliefs and dogmas. This is not an optional process; it is life or death, not only for human civilization but for the environmental processes that sustain it. But we can take beneficial steps across the broad spectrum of human activity as long as we consider their effects on the multiple health and environmental elements that intersect and keep our eyes on the prize of a healthy, abundant, and sustainable planet.
All of this is possible with organic as a holistic solution. To learn more, visit the Gateway on Pesticide Hazards and Safe Pest Management, as well as how to avoid hazardous home, garden, community, and food use pesticides with The Safer Choice. To help support Beyond Pesticides’ mission, become a member today and take action to have your voice heard on governmental actions that are harmful to the health of the environment and all organisms.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Lohr, M. et al. (2025) Widespread detection of second generation anticoagulant rodenticides in Australian native marsupial carnivores, Science of The Total Environment. Available at: https://www.sciencedirect.com/science/article/pii/S004896972500467X.
Regnery, J. et al. (2020) Heavy rainfall provokes anticoagulant rodenticides’ release from baited sewer systems and outdoor surfaces into receiving streams, Science of The Total Environment. Available at: https://www.sciencedirect.com/science/article/pii/S0048969720334252.
Regnery, J. et al. (2024) Rodenticide contamination of cormorants and mergansers feeding on wild fish, Environmental Chemistry Letters. Available at: https://link.springer.com/article/10.1007/s10311-024-01762-y.
Rowley, J. et al. (2024) Broad-scale pesticide screening finds anticoagulant rodenticide and legacy pesticides in Australian frogs, Science of The Total Environment. Available at: https://www.sciencedirect.com/science/article/pii/S004896972402672X.
Stapp, P. et al. (2024) Patterns of exposure of coyotes to anticoagulant rodenticides in California, USA, The Journal of Wildlife Management. Available at: https://wildlife.onlinelibrary.wiley.com/doi/abs/10.1002/jwmg.22696.
