2

Rodenticide Active Ingredients 

There are a number of substances that are registered or were previously registered as vertebrate control 

agents. Phosphorus and arsenic trioxide were once registered to control commensal rodents in and around 

homes, but the Agency has cancelled all such products. Strychnine is no longer registered for control of 

commensal rodents and for this reason it has typically been evaluated separately from rodenticide active 

ingredients that are registered for control of commensal rodents. Substances such as red squill and pival 

(and its sodium salts), historically used to control commensal rodents, were not supported for 

reregistration by their registrants. As there were no remaining registered products for them, these 

chemicals were not evaluated in the 1998 Rodenticide Cluster RED or thereafter. This regulatory history 

document addresses the ten rodenticide active ingredients that remain registered for control of commensal 

rodents and they include the following: 

1st Generation Anticoagulants 

The first generation anticoagulant rodenticides (FGARs), such as chlorophacinone, diphacinone, 

diphacinone sodium salt, warfarin, and warfarin sodium salt, disrupt the production in the liver of 

vitamin K dependent blood-clotting factors II (prothrombin), VII, IX, and X. Due to the long half-lives of 

the vitamin K-dependent clotting factors, the anticoagulant effect often does not adversely affect the 

rodent until after several days of ingestion The onset of lengthened prothrombin time (PT) from a toxic 

dose may occur within 24 hours, and reach a maximum in 36-72 hours at a dose much lower than the dose 

that can cause hemorrhage (Reigart J.R. et.al, 1999). The agents also increase permeability of capillaries 

throughout the body, leading to widespread internal hemorrhage. 

 warfarin (and its sodium salt) (PC Code 086002, CAS No. 81-81-2) (sodium salt PC Code 086003 

129-06-6) 

o 1950 - First Registered 

o 1954 - Sodium Salt First Registered 

o 1981 - Registration Standard 

o 1991 - Warfarin and it Sodium Salts RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 diphacinone (and its sodium salt) (PC Code 067701, CAS No. 82-66-6) (sodium salt PC Code 

067705 42721-99-3) 

o 1960 - First Registered 

o 1962 - Sodium Salt First Registered 

o 1998 - Included in Rodenticide Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 



 chlorophacinone (PC Code 067707, CAS No. 3691-35-8) 

o 1971 - First Registered 

o 1998 - Included in Rodenticide Cluster Reregistration Eligibility Decision (RED) 
3

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

2nd Generation Anticoagulants (Also Referred to as Long Acting Anticoagulant Rodenticides 

(LAARs) or “Super Warfarins”)

The second generation anticoagulant rodenticides (SGARs) such as brodifacoum, bromadiolone, 

difenacoum, and difethialone are more acutely toxic than are FGARs and were developed to control 

commensal rodents that are resistant to warfarin and other FGARs. SGARs also are more likely than 

FGARs to be lethal effects to rodents as a consequence of one night’s feeding in a single dose. Like the 

FGARs, SGARs block the formation of the active form of vitamin K, which in turn inhibits the 

production of coagulation factors in the liver. These chemicals block the same binding site that warfarin 

and warfarin sodium block, however, SGARs have much longer half-lives in the body (Batten and Bratt, 

1990). Similar to the first generation anticoagulants, the toxic effects of SGARs usually begin several 

days after ingestion, because of the long half-life of the coagulation factors. 

 brodifacoum (PC Code 112701, CAS No. 56073-10-0) 

o 1979 - First Registered 

o 1998 - Included in Rodenticides Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 bromadiolone (PC Code 112001, CAS No. 28772-56-7) 

o 1980 - First Registered 

o 1998 - Included in Rodenticides Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 difethialone (PC Code 128967, CAS No. 104653-34-1) 

o 1995 - First Registered 

o 1998 - Addressed by but not assessed in Rodenticides Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 difenacoum (PC Code 119901, CAS No. 56073-07-5) 

o 2007 - First Registered 

o 2008 - Included in the RMD 

Non-Anticoagulants (Also Referred to as Acute Rodenticides) 

Bromethalin, causes decreased production of ATP in the cells of the central nervous system by 

uncoupling oxidative phosphorylation in the mitochondria. Low levels of ATP reduce the efficiency of 

the enzyme Na/K ATPase, leading to increased intracellular sodium levels. This in turn draws more water 

into neuronal cells (cerebral edema) and increases intracranial pressure which can be lethal. Symptoms 
4

and signs of cerebral edema include headache, dizziness, nausea, numbness, weakness, loss of 

coordination or balance, altered level of consciousness, respiratory depression, seizures, and death. 

Cholecalciferol increases calcium absorption from food, and mobilizes calcium from bone which leads to 

hypercalcemia (increased calcium levels in blood). Hypercalcemia can cause formation of calcium 

crystals in internal organs such as blood vessels, kidneys, stomach wall and lungs (Chavhan S.G., et.al, 

2011). Abnormal heart conduction and irregular heartbeats can also occur since the heart tissue is 

sensitive to changes in blood calcium levels. Symptoms and signs of cholecalciferol poisoning may 

include fatigue, weakness, nausea, anorexia, headache and irregular heartbeats (Goldfrank et.al, 2010). 

Acute renal tubular injury due to hypercalcemia may cause excessive urination, increased water intake, 

protein in urine and increased blood urea levels. Prolonged hypercalcemia may eventually cause kidney 

failure due to formation of kidney stones and calcium deposition in kidney tissues. 

Zinc phosphide can quickly produce toxic phosphine gas when it comes in contact with acids or water. 

Phosphine is thought to produce toxicity by blocking cytochrome oxidase and, inhibiting oxidative 

phosphorylation which may lead to cell death (Perry H.E., 1998). Most of the tissue damage can occur in 

liver, kidneys and heart. Patients may present with symptoms such as, severe gastrointestinal irritation, 

nausea, vomiting (with fishy odor), chills, tightness of chest, difficulty in breathing and cough (from 

pulmonary edema). Development of the liver failure can cause jaundice and excessive hemorrhage. 

Delirium, convulsions and coma may result from renal tubular damage. Common cause of death is from 

ventricular arrhythmias and shock due to myocardial damage (Reigart J.R., 1999). 

 zinc phosphide (PC Code 088601, CAS No. 1314-84-7) 

o 1947 - First Registered 

o 1982 - Registration Standard 

o 1998 - Zinc Phosphide RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 bromethalin (PC Code 112802, CAS No. 63333-35-7) 

o 1984 - First Registered 

o 1998 - Included in Rodenticides Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 

 cholecalciferol (PC Code 202901, CAS No. 67-97-0) 

o 1984 - First Registered 

o 1998 - Addressed by but not assessed in Rodenticides Cluster RED 

o 2004 - Included in Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: 

A Comparative Approach 

o 2008 - Included in RMD 
5

Additional Background

Pests Targeted by Rodenticides 

The three commensal rodent species that occur in the continental U.S., are the Norway (brown or sewer) 

rat (Rattus norvegicus), the roof (black or ship) rat (Rattus rattus), and the house mouse (Mus musculus). 

These species are of Asian origin and were brought to the Western Hemisphere, probably inadvertently, 

via the activities of humans. The Polynesian (Pacific, kiore) rat (Rattus exulans) occurs in forests, fields, 

and commensally in Hawaii and in various U.S. island territories in the Pacific Ocean. Rodenticides are 

also registered for use against other vertebrate pests including, but not limited to voles, deer mice, whitefooted mice, wood rats, kangaroo rats, pocket gophers, prairie dogs, ground squirrels, and some nonrodents (e.g., moles); however, only products intended for the control of commensal rodents are the 

focus of the Agency’s current action. 

Uses of Rodenticide Bait Products 

Rodenticide baits, along with a variety of habitat modification and other pest management techniques, are 

used to reduce the damage caused by rodents. Rodenticide baits are especially useful for rapidly reducing 

rodent numbers in cases of major infestations. For commensal rodent control, rodenticide baits are best 

used within the context of an integrated pest management (IPM) approach that emphasizes measures such 

as sanitation, exclusion, habitat modification, trapping, coordination at the community level, public health 

education, and legal measures such as the enforcement of sanitation codes. 

Rodenticide baits are used, sometimes as part of community rodent-control programs, in situations where 

major commensal rodent infestations must be reduced rapidly. The baits often are used to control rodents 

which have entered homes and other buildings. They are also used to eliminate rodents that remain after 

buildings have been rodent-proofed. Rodenticide baits are commonly used to manage both indigenous and 

introduced rodents that feed on, contaminate, or cause various types of damage to a wide range of crops 

and farm infrastructure and equipment, as well as to grain and other stored food. 

Registered Use Site Categories for Rodenticides 

Buildings and Transport Vehicles 

Prior to the 2008 RMD, the Agency typically allowed the following sites for commensal rodenticides: in 

and around homes and residential buildings, industrial, commercial, agricultural buildings, and similar 

man-made structures and in transport vehicles. For some products, the Agency allowed additional field 

sites (fence lines, gullies, ditches, railroad rights-of way, garbage dumps). For zinc phosphide products, 

the Agency classified products with such field sites as “Restricted Use Pesticides” over 30 years ago. For 

products subject to the 1998 Rodenticide Cluster RED, the Agency required that products with field sites 

be classified “restricted use,” except for hand, underground applications for control of mole and pocket 

gophers. The RMD implemented this requirement of the 1998 Rodenticide Cluster RED. 

 Agricultural Uses –Prior to the 2008 RMD, rodenticide products that were distinctly for use in 

agricultural settings were not common. Agricultural buildings use site restrictions were typically 

limited to inside of homes and agricultural buildings in “non-urban” areas (i.e. rural and suburban 
6

areas). The urban vs. non-urban use site distinction has been replaced with labeling that permits use 

in and within 50 feet of agricultural building. 

 Homeowner Uses – Prior to the 2008 RMD, rodenticide products that were distinctly for use in 

homes were available, but many registered commensal rodenticide bait products were available in 

container sizes ranging from less than one pound to more than 40 pounds and were labeled for 

industrial and agricultural use sites in addition to use in and around residences. In an effort to 

mitigate risk, the 2008 RMD identified certain risk mitigation measures that the Agency intended to 

require of all rodenticide products sold and marketed to residential consumers. 

 Pest Control Operator (PCO) Uses - Prior to the 2008 RMD, the only rodenticide products that were 

distinctly for PCO use were those classified as “restricted use.” Labels for bromadiolone and 

difethialone products distinguished between “urban” and “non-urban” use sites. In “Urban Areas” the 

labeled use sites were in and around homes, industrial buildings, commercial buildings, public 

buildings, transport vehicles (ships, trains, aircraft), related port or terminal buildings, and in alleys. 

In “Non-Urban Areas” labeled use sites included inside of homes and agricultural buildings. In an 

effort to mitigate risk, the 2008 RMD announced that EPA would require certain limitations on 

sale and distribution designed to further distinguish rodenticide products sold and marketed to 

residential consumers from products intended for commercial, agricultural, and other 

professional users.  This has also led to the registration of rodenticide products that are 

distinctly labeled for use by PCOs only.

Field 

 Field-use rodenticides are rodenticide products labeled for use to control rodents and lagomorphs in 

orchards; rangelands; field crops; non-crop areas, including but not limited to fence lines, gullies, 

ditches, orchards, railroad rights-of way, garbage dumps, landfills, and sites not associated with 

human residences or other buildings. Most field-use rodenticides are registered as restricted use 

products (RUP) and require a Certified Applicator license or be under the direct supervision of a 

certified applicator to purchase and apply.

Efficacy Requirements For Rodenticide Products 

As a general matter, in order to obtain or maintain a registration for a pesticide under FIFRA, an applicant 

or registrant must demonstrate that the pesticide satisfies the statutory standard for registration. Section 

3(c)(5) of FIFRA. 7 U.S.C. 136a(c)(5). That standard requires, among other things, that the pesticide 

performs its intended function without causing “unreasonable adverse effects on the environment.” The 

term “unreasonable adverse effects on the environment” is defined under FIFRA section 2(bb) as “any 

unreasonable risk to man or the environment, taking into account the economic, social, and environmental 

costs and benefits of the use of any pesticide.” 7 U.S.C. 136(bb). 

In addition to the standard registration criteria that all registered pesticides must meet, because 

commensal rodents are pests of public health significance, commensal rodenticide products are required 

to meet the efficacy testing requirements that EPA has established for registration of such products under 

FIFRA. In order to demonstrate the effectiveness of a new rodenticide active ingredient or new 

formulation of an existing active ingredient for controlling commensal rodents, EPA requires (1) acute 

oral toxicity testing with wild-type animals of the targeted species; (2) laboratory efficacy screening of 
7

one or more bait formulations with wild-type animals of the targeted species; (3) indoor and outdoor field 

efficacy trials involving the targeted species in actual use situations in different regions of the U.S.1

 

These tests are not designed to rank the efficacy of the various rodenticide products, but instead to 

establish whether each product meets the registration criteria in regards to the products ability to 

effectively control commensal rodent species. 

For additional information on the efficacy requirements for rodenticide products labeled for use on 

commensal rodent pests, see the paper entitled Efficacy Issues Regarding Control of Commensal Rodents 

in the U.S. Using Registered Rodenticides (W. Jacobs, 10/31/2011) in docket ID EPA-HQ-OPP-2011-

0718.

Regulatory History

Pre-1998

Rodenticide products containing any of a variety of different active ingredients have been Federally 

registered under the FIFRA according to the requirements that were in effect at the times that the 

compounds were registered. Requirements for labeling and data support changed over time, with data 

requirements being intensified by certain amendments to FIFRA. 

The 1972 amendments to FIFRA included the requirement that EPA bring pesticides registered prior to 

the passage of those amendments up to the new standards for registering new pesticides. This process 

became known as “Reregistration.” In its first efforts to reregister pesticides, EPA would produce 

Registration Standard documents that summarized then-existing circumstances regarding product labeling 

and data support and identified deficiencies in both areas that registrants were required to support in order 

to reregister their products. EPA then issued data call-ins (DCIs) which required submission of the 

studies needed to address the “data gaps” noted in Registration Standard documents. Registrants were 

required to provide the missing data if they wanted to retain their products’ registrations. 

During the 1980’s, EPA issued Registration Standards for Warfarin and Zinc Phosphide but not for the 

other then-registered rodenticide chemicals that later were considered in the RMD. EPA also issued a 

Registration Standard for the “first-generation” anticoagulant Fumarin, but all of its products 

subsequently were canceled because their registrants did not support them for reregistration. Although 

these Registration Standards represented EPA’s determinations of what data submissions and label 

changes were necessary to support registration, they did not have the force of law. 

The 1988 amendments to FIFRA added to the Act a new Section 4 which outlined a five-phase process 

for reregistration of pesticide chemicals and products for which the first Federal registration had been 

issued prior to November 1, 1984. As required by the amendments, EPA prepared four lists of active 

ingredients for which reregistration was required. List A included active ingredients (such as warfarin 

and zinc phosphide) for which EPA previously had issued Registration Standards. Lists B, C, and D 

included the pesticides registered prior to November 1, 1984, for which no Registration Standard had 

been issued. Lists B, C, and D were to be populated by active ingredients according to priority, as 

                                                           

1

 General guidance for the design of such studies appears on pages 307-310 of Subdivision G of EPA’s Pesticide 

Assessment Guidelines, Office of Pesticides and Toxic Substances, Washington, DC, 1982. 
8

described in Section 4(c)(1) of FIFRA as amended in 1988. The anticoagulants brodifacoum, 

bromadiolone, chlorophacinone, diphacinone, pindone (pival), and valone (PMP) were placed on List B, 

which was to have the highest priority among Lists B, C, and D. The nerve toxicant, bromethalin was 

also placed on List B. 

The 1988 FIFRA amendments required up-front commitments to the reregistration process by the 

registrants of the active ingredients. Registrants were required to indicate which active ingredients and 

which uses of them they intended to support throughout the entire reregistration process. Unsupported 

chemicals and use patterns were to be dropped. Valone and pindone ultimately were not supported. The 

chemicals that were to be supported went through remaining phases of data submission, data evaluation, 

risk assessment, and risk management which led to the production of reregistration eligibility decisions 

for each active ingredient or each grouping of active ingredients (according to related chemistry and/or 

similarity in primary use patterns). Data needed to complete product reregistrations were required via 

product-specific data call-ins (PDCI’s). 

In June 1991, EPA completed a RED for warfarin and its sodium salt which called in additional data and 

identified the following mitigation measures as necessary in order for products to be eligible for 

reregistration: 

 Continued RUP classification of tracking powder products. 

 A statement regarding teratogenicity, warning of warfarin's potential to cause birth defects, was 

required for tracking powder products and concentrates used to prepare dry baits. 

 To prevent contamination of food and feed, tracking powder products intended for use in 

food/feed handling establishments were to limit placement of powder to concealed, inaccessible 

places. 

 To protect children and non-target animals, tracking powder products were required to bear a 

strong precautionary statement and new restrictions limiting placement of powder to locations not 

accessible to children, pets, domestic animals or non-target wildlife. 

 To protect children and non-target animals, bait product labels were to require the use of tamperresistant bait stations wherever bait placements otherwise would be within the reach of children, 

pets, domestic animals, or nontarget wildlife. 

The bait-protection text prescribed via the Warfarin RED was similar to that later included in Pesticide 

Registration Notice (PR Notice) 94-7, which is discussed in more detail later in this document. 

REDs for zinc phosphide and the Rodenticide Cluster were published in 1998, and these addressed 

reregistration eligibility and labeling requirements for end-use products containing brodifacoum, 

bromadiolone, bromethalin, chlorophacinone, and diphacinone. The provisions of these REDs are 

discussed in detail below. The REDs, like the Registration Standards before them, do not have the force 

of law. . 

As they first were registered after November 1, 1984, cholecalciferol and difethialone were not directly 

subjected to reregistration requirements. However, these chemicals plus warfarin and difethialone were 

subject to the risk mitigation measures in the 1998 Rodenticide Cluster RED. 
9

Apart from reregistration activities, EPA took several specific actions to promote safer use of commensal 

rodenticides. In 1983, EPA issued PR Notice 83-5 which summarized EPA policy regarding the use of 

bait stations and noted that label statements such as “Treated baits should be placed in locations not 

accessible to children, pets, wildlife, and domestic animals, or in tamper-proof bait boxes” had been 

required to be stated on rodenticide labels beginning during the 1960’s. That text was modified over time 

by replacing the word “should” with “must.” EPA chose to highlight this language regarding the use of 

bait stations because the Agency had concluded that “bait protection practices directed by labels usually 

were not being followed.” 

On September 16, 1994, EPA issued PR Notice 94-7 (http://www.epa.gov/PR_Notices/pr94-7.html) to 

update and replace PR Notice 83-5. PR Notice 94-7 replaced the term “tamper-proof,” which was used in 

PR Notice 83-5, with “tamper resistant” and expanded the associated label text to indicate the 

characteristics of tamper-resistant bait stations. PR Notice 94-7 listed criteria for “tamper-resistant bait 

stations” and also defined, for EPA registration purposes, “commensal rodents” to include only, Norway 

rats (Rattus norvegicus), roof rats (Rattus rattus), and house mice (Mus musculus). 

In 1993, EPA consulted with the Fish and Wildlife Service (the Service) under the Endangered Species 

Act on certain uses of rodenticides, and in 1993, as part of that consultation, the Service issued a 

biological opinion finding that a number of rodenticides, including several addressed and analyzed in this 

action, will likely jeopardize a number of animal species. The 1993 jeopardy determinations can be found 

in EPA’s “Comparative Ecological Risk Assessment for Nine Rodenticides” (Erickson and Urban, 

7/2004), available under docket number EPA-HQ-OPP-2006-0955 at www.regulations.gov. 

1998 Rodenticide Cluster and Zinc Phosphide Reregistration Eligibility Decisions

EPA completed REDs for the Rodenticide Cluster (brodifacoum, bromadiolone, chlorophacinone, 

diphacinone and its sodium salt, bromethalin, and pival and its sodium salt) and a separate RED for zinc 

phosphide in July 1998. These decisions included comprehensive reassessments of the required data and 

the use patterns of affected products that were registered at the time that the REDs were issued including 

control of commensal and field rodents, and some non-rodent species controlled by these products in and 

around buildings, in vineyards, orchards, rangelands, and field crops. While the 1998 REDs only 

formally assessed the rodenticide active ingredients brodifacoum, bromethalin, bromadiolone 

chlorophacinone, diphacionone and its sodium salt, and zinc phosphide, the Agency required that the 

same risk mitigation measures be adopted for the registrations of certain other rodenticide active 

ingredients, namely warfarin and its sodium salts, difethialone, cholecalciferol (vitamin D-3), and red 

squill. These mitigation measures also were to be adopted for products made with any future newly 

registered active ingredients that claimed to control commensal rodents. 

EPA concluded in 1998 that then-registered uses for brodifacoum, bromadiolone, chlorophacinone, 

diphacinone and its sodium salt, bromethalin, and zinc phosphide, with additional labeling requirements 

and a number of risk mitigation measures, would not cause unreasonable risks to humans or the 

environment and, therefore, were eligible for reregistration. In 1998, EPA determined that all uses of 

pival and its sodium salts were ineligible for reregistration. Prior to 1998, pival and its sodium salt was 

suspended by the Agency in December 1994 for failure of the sole technical registrant, Bell Laboratories, 

Inc., to respond to the Agency’s Data Call-In Notice (DCI) and submit the required data to support the 
10

continued registration. In 2002, Bell Laboratories, Inc.’s pival and its sodium salt technical registrations 

were canceled for failure to pay registration maintenance fees. 

The 1998 REDs identified ways in which the risk concerns posed from the use of these products could be 

addressed while still maintaining the benefits afforded by their use. Via the 1998 REDs, the Agency put 

forth a two-phased approach to mitigating risk. The first phase called for the following short-term 

mitigation measures: 

 Non-agricultural rodenticide bait products must incorporate indicator dyes that will help identify 

when a child has been exposed. 

 Non-agricultural rodenticide bait products must incorporate a bittering agent that could make the 

bait less palatable to children and therefore reduce the likelihood of consumption. 

 Labels which then allowed placement of rodenticide bait “in and around buildings” were required 

to be amended to “indoors and against the outside walls of buildings.” Rat and mouse bait 

placements were to be allowed “around” buildings only if registrants demonstrated that secondary 

risks to birds and mammals were likely to be minimal. 

 All rodenticide products formulated as tracking powders would remain classified and labeled as 

RUP and tracking powder products were to require additional personal protective equipment 

(PPE). 

 All products labeled for field uses, except for those limited to manual underground baiting, were 

to be reclassified and relabeled RUP. 

The proposed Phase I requirements were never enacted and have been superseded by action taken via the 

RMD. 

The goal of the second phase was to reduce accidental rodenticide exposure to children, pets, and nontarget wildlife in the long term by encouraging the development of exposure/risk reduction technologies. 

A stakeholder group was organized to provide the Agency recommendations on how to significantly 

reduce exposures to rodenticides. This stakeholder group became the Rodenticide Stakeholder’s 

Workgroup (RSW), which included a broad range of stakeholders and government representatives, 

including the Centers for Disease Control (CDC), U.S. Department of Agriculture (USDA), EPA, 

members of the medical community, rodenticide manufacturers, public interest groups, members of the 

general public, and the veterinary community. The 1998 Rodenticide Cluster RED specified that this 

stakeholder group was to be formed within 120 days following the publication of the RED and that the 

group’s recommendations were to be provided to the Agency 9 months after the RED’s publication. To 

further examine the ecological risks associated with rodenticide use, the Agency began 

drafting/conducting a comparative ecological risk assessment for rodenticides in 1999. 

At the time of the 1998 Rodenticide Cluster RED’s publication, EPA became aware of new wildlife 

incident data that suggested that there may be a potential exposure problem involving the active 

ingredient brodifacoum. This data was reviewed by the Agency and considered in the rodenticide 

decisions that followed the 1998 RED. 

1998-2008

1999-2001 - Rodenticide Stakeholder’s Workgroup (RSW) 
11

The RSW was formed in 1999 as a subcommittee under the federally-chartered advisory body, the 

Pesticide Program Dialogue Committee (PPDC), to consider the risks to children of accidental rodenticide 

exposure and potential measures to reduce such exposures. The RSW met five times in 1999, and 

ultimately issued a report recommending that EPA not require, as proscribed in the 1998 RED, the 

indicator dye, as no suitable dye had been identified at that time, and not require the bittering agent, due 

to concerns that it might adversely affect the efficacy of rodenticide baits. The work group recommended 

that EPA allow manufacturers to include bittering agents on a voluntary basis.2

 The Agency adopted the 

RSW’s recommendations, and in November 2001, EPA issued a Federal Register Notice (66 FR 59425) 

announcing that it was amending the two rodenticide REDs to allow reregistration of rodenticide bait 

products without requiring the incorporation of a bittering agent and indicator dye. 

By 2001, many rodenticide registrants voluntarily incorporated a bittering agent into rodenticide products. 

Acceptable efficacy data were submitted to the Agency to support the registrations of rodenticide bait 

products that contain a bittering agent. Consequently, the addition of bittering agents remains at the 

discretion of the registrants of commensal rodenticide baits.

1999-2004 – Comparative Ecological Assessment Developed & Refined

In the 1998 REDS, the Agency concluded that further evaluation of the ecological risks of rodenticides 

was necessary. As part of this work, the Agency conducted a comparative ecological assessment in which 

nine rodenticide3

 active ingredients were evaluated, compared, and ranked among one another in terms of 

potential primary and secondary risks to birds and non-target mammals. The risk conclusions from the 

comparative ecological assessment were based on comparative analysis modeling and multiple lines of 

evidence including acute toxicity, persistence of compounds in body tissues of primary consumers (i.e. 

bait eaters), information from laboratory and pen studies in which poisoned prey were fed to predators or 

scavengers in various amounts for one or more days, data from field trials and operational control 

programs, and wildlife mortality incidents. 

Due to the public interest in rodenticides, the Agency elected to employ the full six-phase public 

participation process for the comparative ecological risk assessment. (The public participation process 

that EPA applies to its reregistration eligibility decisions is described in a May 14, 2004 Federal Register 

Notice (69 FR 26819). Between October 1999 and September 2001, the comparative risk assessment was 

drafted by Agency scientists and it underwent internal and external peer review. During the Phase 1 

comment period that closed in December 2001, the Rodenticide Registrant Task Force (RRTF) raised 

some issues that led to additional technical work by EPA scientists. After that work was completed, the 

preliminary risk assessment was made available for public comment in January 2003. EPA accepted 

public comments on the document through May 30, 2003. Then, the Agency reviewed and responded to 

the public comments and revised the risk assessment based upon those comments. 

                                                           

2

 The RSW also considered requiring that rodenticide baits be sold in ready-to-use tamper-resistant bait stations. At 

that time, however, there were no ready-to use bait stations on the market that had been shown to meet EPA’s 

criteria for tamper-resistance. For that reason, among others, the RSW recommended against requiring tamperresistant bait stations. 

3

 The Comparative Ecological Assessment included the active ingredients brodifacoum, bromadiolone, bromethalin, 

cholecalcierol, chlorophacinone, difethialone, diphacinone, warfarin, and zinc phosphide. 
12

In September 2004, the Agency opened Phase 5 of the public participation process by publishing the 

revised comparative ecological risk assessment, which incorporated new ecological incident data and 

reflected revisions made in response to public comments on the preliminary version of the assessment. 

Along with the revised ecological assessment, EPA also published a document discussing the benefits 

associated with rodenticide products and EPA’s preliminary position on appropriate risk reduction 

options. EPA accepted public comments on those documents through January 2005. All of these 

documents and the associated comments can be found in docket EPA-HQ-OPP-2006-0955 at 

www.regulations.gov. 

2004 – West Harlem Environmental Action (WEACT) & Natural Resources Defense Council (NRDC) 

In November 2004, WEACT and NRDC filed suit in the District Court for the Southern District of New 

York, challenging EPA’s 2001 reversal of its 1998 determination that rodenticide bait products posed an 

unreasonable risk of harm to children unless they contained a bittering agent and an indicator dye. In 

August 2005, the District Court upheld EPA’s 2001 determination that an indicator dye should not be 

required. (380 F.Supp.2d 289 (S.D.N.Y. 2005)) However, the court reversed EPA’s decision to rescind 

the bittering agent requirement, and remanded the decision to EPA for further consideration. The court’s 

decision gave focus to EPA’s ongoing efforts to determine how best to reduce exposure and risks to 

children from rodenticide products. 

2005 – Endangered Species Consultation with U.S. Fish and Wildlife Service (the Service) 

In March 2005, EPA initiated informal consultation under section 7(a) of the Endangered Species Act, 16 

U.S.C. §1536(a), for the nine commensal use rodenticides registered at that time for the purpose of 

obtaining technical assistance in identifying the full suite of listed species that may be affected by the full 

range of uses of these products, and to determine whether further, formal consultation would be necessary 

and if so, to explore possible mitigation relative to specific species that may be affected. Several reported 

incidents have involved Federally listed threatened and endangered species, for example the San Joaquin 

kit fox and Northern spotted owl, in addition to the Bald eagle, which is protected under the Bald and 

Golden Eagle Act. The Service previously issued a biological opinion on eight of the rodenticides in 

1993.4

 The jeopardy determinations in that opinion for the individual compounds primarily recommend 

prohibiting use in habitat occupied by listed species and requiring tamper-resistant bait stations for 

outdoor placements for some uses. The 1993 jeopardy determinations can be found in EPA’s 

“Comparative Ecological Risk Assessment for Nine Rodenticides” (Erickson and Urban, 7/2004), 

available under docket number EPA-HQ-OPP-2006-0955 at www.regulations.gov. 

2007 Proposed Risk Mitigation Decision

On January 17, 2007, EPA published a Proposed Risk Mitigation Decision for the nine commensal use 

rodenticides registered at that time.5

 To minimize children’s exposure to rodenticide products used in 

homes, EPA proposed requiring that all rodenticide bait products available for sale to consumers be 

marketed only in tamper-resistant bait stations with solid bait blocks as the only permissible bait form. 

                                                           

4

 The biological opinion does not include difethialone, which was first registered in 1995, or difenacoum, which was 

first registered in 2007. 

5

 Difenacoum was not included in the Proposed Risk Mitigation Decision because it was not registered at the time 

that the proposed decision was issued. 
13

To mitigate ecological risks, the January 2007 proposal included a requirement to classify all bait 

products containing the SGAR active ingredients brodifacoum, bromadiolone, and difethialone as 

restricted use pesticides, thus making them available for purchase and use only by trained, certified 

pesticide applicators or persons under their direct supervision. These three rodenticides were identified in 

the proposal as posing particularly significant risks to non-target wildlife. 

EPA received more than 700 individual written comments on the January 2007 Proposed Risk Mitigation 

Decision, plus a letter from an advocacy group that was signed by more than 6,000 of the group’s 

members. Individual comments were received from a diverse range of stakeholders, including 

government agencies, city governments, nongovernmental organizations (NGOs), wildlife rehabilitators, 

professional pest control operators, livestock producers, rodenticide registrants, and interested citizens.6

Many comments, including those received from the U.S. Department of Housing and Urban Development 

(HUD), the Centers for Disease Control and Prevention (CDC), several NGOs, and some citizens, 

articulated support for EPA’s proposal. Other comments, particularly those received from citizens or 

NGOs who work with, or advocate for wildlife, argued that the Agency’s risk mitigation proposal did not 

provide sufficient protection for children and/or wildlife. Other comments, mainly those received from 

rodenticide registrants and livestock producers, claimed that the risks posed by use of commensal 

rodenticides did not warrant the proposed mitigation or that the proposed mitigation was overreaching. 

The 2007 Proposed Risk Mitigation Decision, related support documents, all comments received, and the 

Agency’s responses to the comments received can be found at www.regulations.gov under docket number 

EPA-HQ-OPP-2006-0955. Responses to comments related to ecological risk, human health, economic 

analyses, and risk mitigation are addressed in separate documents prepared by the Environmental Fate 

and Effects Division (EFED), the Health Effects Division (HED), the Biological and Economic Analysis 

Division (BEAD), and the Special Review and Reregistration Division (SRRD) (now known as Pesticide 

Re-evaluation Division (PRD)). These documents provided additional detail on the Agency’s rationale 

for this proposed mitigation decision. 

2008 Risk Mitigation Decision for Ten Rodenticides

EPA issued the RMD on May 28 2008. This document was formally published in the Rodenticides 

docket (EPA-HQ-OPP-2006-0955) on June 4, 2008. The RMD was the Agency’s final decision on the 

reregistration eligibility of rodenticide products containing brodifacoum, bromadiolone, bromethalin, 

chlorophacinone, cholecalciferol, difenacoum, difethialone, diphacinone (and its sodium salt), warfarin 

(and its sodium salt), and zinc phosphide. The RMD also 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, 380 F.Supp.2d 289 (S.D.N.Y. 2005). The RMD 

specifically focuses on commensal use rodenticides and identified a variety of mitigation measures 

necessary to prevent rodenticides from causing unreasonable adverse effects to human health and the 

environment. To address unacceptable risk to children, pets, and non-target wildlife, the Agency 

                                                           

6

 EPA initially provided for a 60-day comment period for the Proposed Risk Mitigation Decision. But after receiving 

several requests for a comment period extension, the Agency extended the comment period by another 60 days. The 

comment period closed on May 18, 2007. 
14

announced that it would require a number of mitigation measures for commensal use rodenticide 

products. 

To minimize children’s exposure to rodenticide products used in homes, the Agency would require that 

all rodenticide bait products marketed to general and residential consumers be sold only with tamper 

resistant bait stations, with loose bait (e.g., pellets and meal) as a prohibited bait form. To reduce wildlife 

exposures and ecological risks, the Agency would require sale and distribution limits intended to prevent 

general consumers from purchasing residential use bait products containing four of the ten rodenticides 

that pose the greatest risk to wildlife (the SGARs – brodifacoum, bromadiolone, difenacoum, and 

difethialone). Moreover, tamper-resistant bait stations would be required for all outdoor, above-ground 

uses of commensal use rodenticide products. 

EPA afforded registrants three years time to design and implement the mitigation measures, particularly 

since the development of bait stations was believed to require time to test and gain approval. The RMD 

thus provided that until June 4, 2011, registrants who agreed to cancel or amend their rodenticide 

registrations consistent with the RMD could continue to sell or distribute their (then) registered 

rodenticide products without the risk mitigation measures described in the RMD. EPA asked registrants 

to advise EPA by September 2, 2008, whether they would voluntarily adopt the risk mitigation measures 

described in the RMD. 

2008 to Present: RMD Implementation

By September 2008, EPA had been informed by three registrants that they did not intend to voluntarily 

bring their rodenticide products into compliance with the requirements of the May 2008 risk mitigation 

decision. Reckitt Benckiser Inc. specified that they did not intend to voluntarily amend the registrations 

of any of their rodenticide products. Liphatech Inc. informed the Agency that they planned to voluntarily 

conform some of their products to the RMD, but not all. Woodstream, Inc. also stated that they did not 

intend to comply. However, all Woodstream Inc. registrations that did not conform with the RMD were 

amended to include expiration dates such that the registrations of those products they chose not to 

conform to the RMD expired on June 4, 2011. Spectrum Group, a Division of United industries, initially 

informed the Agency that they would voluntarily cancel their non-conforming rodenticide products only 

to rescind their request for voluntary cancellation prior to the request for cancellation being published in 

the Federal Register (an administrative requirement of the voluntary cancellation process). All other 

registrants informed the EPA that they would amend their commensal rodenticide registrations to 

conform to the RMD, that the RMD did not apply to their rodenticide product(s), or that they were 

requesting voluntary cancellation of their rodenticide product(s) to be effective on or before June 4, 2011. 

Also, since 2008, both Reckitt Benckiser Inc. and Liphatech Inc., have registered homeowner rodenticide 

products that conform to the RMD, although they still refuse to amend certain other products. For a list 

of homeowner rodenticide products that conform to the RMD, see http://www.epa.gov/pesticides/miceand-rats/rodent-bait-station.html. 

2010 Reckitt Benckiser Inc. vs EPA

Following Reckitt Benckiser informing EPA that it did not intend to voluntarily adopt the mitigation 

measures in the RMD, Reckitt Benckiser requested that EPA initiate cancellation proceedings for Reckitt 

Benckiser’s affected rodenticide products. EPA informed Reckitt Benckiser Inc. it intended to take 
15

action, but not at that time. Reckitt Benckiser filed a federal legal complaint in District Court (See, 

Reckitt Benckiser, Inc. v. Jackson, 762 F. Supp. 2d 34, 46 (D.D.C. 2011)). Ultimately, the court 

addressed only “whether EPA has the authority under FIFRA to bring enforcement proceedings for 

misbranding before, or rather than, regulatory cancellation proceedings under FIFRA Section 6 against 

products not voluntarily complying with a reregistration RMD.” On this narrow issue, the court found for 

Reckitt Benckiser. 

Referenced Documents

 Potential Risks of Nine Rodenticides to Birds, and Nontarget Mammals: A Comparative Approach 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2002-0049-0002;oldLink=false 

 Risk Mitigation Decision for Ten Rodenticides 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2006-0955-0764;oldLink=false 

 Rodenticide Cluster Reregistration Eligibility Decision 

http://www.epa.gov/oppsrrd1/reregistration/REDs/2100red.pdf 

 Warfarin and it Sodium Salts Reregistration Eligibility Decision 

http://www.epa.gov/oppsrrd1/REDs/old_reds/warfarin_salt.pdf 

 Zinc Phosphide Reregistration Eligibility Decision 

http://www.epa.gov/oppsrrd1/reregistration/REDs/2100red.pdf