Rodent Control Pesticide Safety Review
Rodenticides are used to control rodent pests that can cause significant damage to property, crops, and food supplies as well as spread diseases, posing a serious risk to public health. Rodenticides are used in residential, agricultural, and non-agricultural settings to control a variety of pests including house mice, Norway rats, roof rats, moles, voles, pocket gophers, prairie dogs, ground squirrels, feral hogs, and mongooses.
Eleven rodenticide active ingredients can be divided into three categories:
- First-generation anticoagulants: warfarin, chlorophacinone, and diphacinone.
- Second-generation anticoagulants: brodifacoum, bromadiolone, difenacoum, and difethialone.
- Non-anticoagulants: bromethalin, cholecalciferol, strychnine and zinc phosphide.
All the anticoagulants interfere with blood clotting, and death can result from excessive bleeding. Second-generation anticoagulants are especially hazardous for several reasons. They are highly toxic, and they persist a long time in body tissues. The second-generation anticoagulants are more likely to be toxic in a single feeding than earlier products, but since time-to-death is several days, rodents can feed multiple times before death, leading to carcasses containing residues that may be many times the lethal dose. Predators or scavengers that feed on poisoned rodents may consume enough to be harm.
The non-anticoagulants have differing ways of affecting pests:
- Bromethalin is a nerve toxicant that causes respiratory distress.
- Cholecalciferol is vitamin D3, which in small dosages is needed for good health in most mammals, but in massive doses is toxic, especially to rodents.
- Strychnine is a neurotoxin that acts as an antagonist of glycine receptors, resulting in uncontrollable muscle contractions. A lethal dose can cause convulsions that lead to rapid asphyxiation and death.
- Zinc phosphide causes liberation of toxic phosphine gas in the stomach.
To minimize the possibility of children and pets being exposed to mouse and rat poisons, EPA requires consumer products:
- Be sold with bait stations that securely contain the poison.
- More protective bait stations that offer resistant to tampering by children, pets, and/or to weathering are available and required for applications made around children, pets, or outdoors.
- Contain block or paste poison bait. Loose bait forms are no longer permitted.
Rodenticide manufacturers may no longer sell consumer products:
- With more than one pound of poison.
- Containing four pesticides that pose the greatest risk to non-target wildlife (called second generation anticoagulants – brodifacoum, bromadiolone, difenacoum, and difethialone). Baits containing these poisons may still be used in homes by pest control professionals.
Non-target wildlife and pets can also be poisoned if they eat rodents that have consumed certain poisons.
In 2008, EPA issued a risk mitigation decision (RMD) for 10 rodenticides that represented the Agency’s final decision on the reregistration eligibility of rodenticide products at that time and constituted the Agency’s final action in response to the remand order in West Harlem Environmental Action and Natural Resources Defense Council v. U.S. Environmental Protection Agency. The 2008 RMD included mitigation measures to reduce risks to human health and non-target organisms. For example, EPA implemented minimum packaging size requirements for products on the consumer market (must be in packages one pound or less), prohibited products intended for general consumers (i.e., homeowners or residential consumers) from containing second-generation anticoagulant rodenticides (SGARs), and required tamper- and weather-resistant bait stations for outdoor, above-ground placements where children, pets, and wildlife may be present. Read about cancellation of products that do not meet the stricter standards.
In November 2022, EPA issued proposed interim decisions (PIDs) for 11 rodenticides undergoing registration review. EPA is proposing mitigation measures to protect human health and mitigate ecological risk to non-target organisms, including potential effects on federally listed endangered and threatened (i.e., listed) species. The PIDs cover three first generation anticoagulant rodenticides (FGARs), four SGARs and four non-anticoagulant rodenticides. Strychnine (the 11th rodenticide) was not part of the 2008 RMD but is now included as part of EPA’s registration review of the rodenticide group.
These PIDs propose additional mitigation measures based on findings in the 2020 draft human health and ecological risk assessments (DRAs) and feedback submitted during the DRAs’ public comment period. These mitigation measures are intended to reduce exposure to non-target organisms, such as mammals and birds that may inadvertently consume rodenticides through their prey or animals that may have consumed the rodenticide directly. EPA is proposing:
- Classifying all SGARs, strychnine and zinc phosphide products as restricted use pesticides (RUPs).
- Classifying as RUPs all FGAR, bromethalin and cholecalciferol products sold in packages larger than one pound. By limiting the sale and use of these products to people trained and certified to use them, this proposed mitigation measure is expected to limit exposure non-target organisms.
- FGARs, bromethalin and cholecalciferol sold in packages of less than one pound to still be available for use by consumers.
In addition, EPA is proposing the following to help ensure proper use:
- Requiring additional personal protective equipment (PPE) for occupational handlers using products that are loose formulations;
- Prohibiting refillable bait stations for consumer-sized products and prohibiting consumer-sized zinc phosphide products;
- Prohibiting spot and broadcast application of some rodenticide products in turf, lawns, parks, golf courses, campsites and other recreation areas;
- Restricting the method, timing and location of spot, broadcast and below-ground applications of chlorophacinone and diphacinone in cropped areas, rangeland and pastureland;
- Post-application search, collection and disposal of carcasses of target pests or non-target animals, cleanup of bait moved from its original placement location, and reporting of dead and dying non-target organisms; and
- Requiring registrants to develop, implement and maintain rodenticide stewardship plans that include development of education and outreach materials intended for product users and make these plans available on their websites.
The PIDs are now available for public comment in their respective pesticide registration review dockets at www.regulations.gov for 75 days. See the Federal Register notice for more information. After the PIDs, the next step in the registration review process is issuing an interim decision.
Additional Endangered Species Mitigations
In support of EPA’s broader efforts to meet its obligations under the Endangered Species Act (ESA), EPA also identified mitigation measures in these PIDs to reduce exposures to three listed species and one critical habitat, which are serving as pilots for these measures. This work furthers the goals outlined in EPA’s April 2022 ESA Workplan to provide practical and timely protections from pesticides for listed species.
The ESA workplan described how EPA is developing early mitigation for a subset of species where EPA predicts a likelihood of a jeopardy or adverse modification finding for one or more of the registration review pilot pesticides if mitigation is not undertaken. One of these pilots is for rodenticides, which will focus on addressing effects to mammals and birds that consume rodenticide bait (primary consumers) and to birds, mammals and reptiles that consume primary consumers (secondary consumers).
As part of its registration review ESA pilot for the rodenticides, EPA evaluated their potential effects on individuals and populations of Stephens’ kangaroo rat, Attwater’s prairie chicken, and the California condor and its designated critical habitat. EPA’s draft evaluation determined that rodenticide use is “likely to adversely affect” these three species but predicted the proposed mitigations will protect them from likely “jeopardy” (i.e., potential impacts to the survival of listed species) and “adverse modification” of critical habitat. A “likely to adversely affect” determination means EPA reasonably expects that at least one individual animal of any of the three species may be exposed to one or more of the rodenticides at a sufficient level to have an adverse effect.
EPA’s draft likelihood of jeopardy and adverse modification predictions examine effects of the rodenticides at the species scale (i.e., the population as opposed to an individual of a species). While EPA has made predictions about the likelihood of jeopardy and adverse modification, the U.S. Fish and Wildlife Service (USFWS) is responsible for making the actual jeopardy/adverse modification findings for these species and has the sole authority to do so.
EPA chose these three listed species because they represent species that may be affected by rodenticides through different routes of exposure (e.g., primary consumption (Stephens’ kangaroo rat, Attwater’s prairie chicken) and secondary consumption (California condor).
To focus the mitigations where they are most needed while retaining options for rodenticide users, the proposed mitigation measures for the three listed species would be targeted in specific geographic areas most relevant to the species. The PIDs include proposed mitigation measures to be included on the Bulletins Live! Two website for the species and the critical habitat of the California Condor.
The draft evaluation for the three species and one critical habitat and associated mitigation measures are pilots for other listed species that may be similarly exposed and affected by rodenticides. In developing and applying mitigation measures for these species, EPA recognized that not all rodenticides have the same effects.
In addition to describing the pilot and the mitigation measures for the selected species, the PIDs also describe EPA’s plans for expanding those mitigation measures to the other approximately 90 listed species potentially affected by rodenticides. This plan, when finalized, will be known as the Rodenticide Strategy the Agency described in its November 2022 update to its ESA Workplan.
EPA also intends to make effects determinations for all listed species available in a draft biological evaluation (BE), which the Agency anticipates making available for public comment in November 2023. The BEs will contain EPA’s draft analysis of the potential effects of the rodenticides on listed species and their designated critical habitats and will identify mitigation measures for these species and critical habitats to avoid or minimize exposure from the rodenticides (Rodenticide Strategy). EPA expects to complete the final BE for the rodenticides in November 2024.
If EPA’s final BE continues to find that rodenticide use is likely to adversely affect listed species or adversely modify their critical habitats, then EPA will initiate formal consultation and share its findings with USFWS, which will use the information in EPA’s BE to inform its biological opinions. If the USFWS determines in its final biological opinions that additional mitigations are necessary to address any jeopardy or adverse modification determination, or to address any incidental take, then EPA will work to ensure that any necessary registration or labeling changes are made.