Rodenticides.  Draft Notice of Intent to Cancel and Denial    11/02/2011   

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ENVIRONMENTAL PROTECTION AGENCY 

[OPP-xxxx; FRL-xxxx] 

Notice of Intent to Cancel and Notice of Denial of Registrations for Certain Rodenticide Bait 

Products 

AGENCY: Environmental Protection Agency 

ACTION: Notice of Intent to Cancel and Notice of Denial. 

SUMMARY: This Notice announces the Agency's intent to cancel the registrations of 20 

rodenticide bait products. EPA has determined that all 20 of these rodenticide products cause 

unreasonable adverse effects on the environment because they are in the form of loose bait or 

bait blocks without bait stations conforming to the standards identified in EPA’s 2008 Risk 

Management Decision (RMD), and are sold for residential consumer use in controlling 

commensal rodents in and around buildings. EPA bases this determination on data and other 

information showing that these products cause unreasonable risks to children, companion and 

domesticated animals, and non-target wildlife. 

Further, EPA has determined that eleven of these 20 rodenticide products also cause 

unreasonable adverse effects on the environment because they contain the active ingredients 

brodifacoum or difethialone and are sold for residential consumer use. EPA bases this 

determination on data and other information showing that these products cause unreasonable 

adverse effects to non-target wildlife. All of the 20 products subject to this Notice are in 

physical forms that cause unreasonable risks, and eleven of these products also cause 

unreasonable risks owing to the combination of their composition and use pattern. EPA is 

therefore issuing this Notice of Intent to Cancel pursuant to section 6(b) of the Federal 

Insecticide, Fungicide and Rodenticide Act (FIFRA). In addition, this Notice announces the 

Agency’s denial of certain pending applications for registration for certain rodenticide bait 

products for the same reasons as the proposed cancellations. Effective the date of final 

cancellation, EPA will not allow further sale or distribution of existing stocks of products subject 

to this Notice. After cancellation, producers, distributors and commercial applicators holding 

existing stocks would also become subject to FIFRA section 6(g) reporting requirements. 

DATES: Requests for a hearing by an affected registrant or applicant must be received by the 

Hearing Clerk at the address given below on or before [insert date 30 days after date of 

publication in the FEDERAL REGISTER], or within 30 days of receipt of this Notice by the 

registrant or applicant, whichever occurs later. Requests for a hearing by any other adversely 

affected party must be received by the Hearing Clerk on or before [insert date 30 days after date 

of publication in the FEDERAL REGISTER]. 

ADDRESSES: Requests for a hearing submitted by U.S. Mail must use the following address: 

U.S. Environmental Protection Agency, Office of Administrative Law Judges, Mail Code 1900L, 

1200 Pennsylvania Ave., NW, Washington, DC 20460. Please note that mail deliveries to 

federal agencies are screened off-site, and this security procedure can delay delivery. Requests 

for hearing submitted by hand or courier must use the following address: U.S. Environmental 

Protection Agency, Office of Administrative Law Judges, Franklin Court, Suite 350, 1099 14th 
   

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St. NW, Washington, DC 20005. 

Additional information supporting this action is available for public inspection from 8 a.m. to 4 

p.m., Monday through Friday, except legal holidays in: [Public Response and Program 

Resources Branch, Field Operations Division (7506C), Office of Pesticide Programs, 

Environmental Protection Agency, Potomac Yard South, 2777 Crystal Drive Arlington, VA.] 

FOR FURTHER INFORMATION, CONTACT: By mail: 

Rusty Wasem, Pesticide Re-evaluation Division (7508W), Office of Pesticide Programs, U.S. 

Environmental Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460. 

Telephone: (703) 305-6979; Email: wasem.russell@epa.gov. 

SUPPLEMENTARY INFORMATION: 

I. Introduction 

This Notice is divided into 12 units. Unit II describes the legal authority for this action. 

Unit III describes the regulatory history leading to today’s notice of intent to cancel and notice of 

intent to deny. Unit IV describes the scope of the intended cancellations. Unit V summarizes 

EPA’s human health and domestic animal concerns with the products subject to this Notice. Unit 

VI discusses ecological exposure and risk of the products subject to this Notice. Unit VII 

examines the benefits of these products and the impact of this proposed cancellation action. Unit 

VIII presents EPA’s conclusions regarding whether the products subject to this Notice meet the 

FIFRA registration criteria. Unit IX discusses disposition of existing product stocks. Unit X 

summarizes the interagency review and review by the FIFRA Scientific Advisory Panel. Unit XI 

outlines the procedures for implementing the actions required by this Notice, as well as the 

procedures for requesting a hearing. Unit XII provides a list of reference documents. 

I. Introduction 

II. Legal Authority 

III. Regulatory History 

IV. Scope of Intended Cancellation and Denials 

V. Risks Associated with Exposure to Rodenticide Products Subject to this Notice 

(Human and Domestic Animals) 

VI. Risks Associated with Exposure to Rodenticide Products Subject to this Notice 

 (Non-Target Wildlife) 

VII. Benefits 

VIII. Conclusions Regarding Whether Subject Rodenticide Products Meet the FIFRA 

Registration Criteria 

IX. Existing Stocks of Cancelled Products 

X. USDA, HHS and SAP Review 

XI. Procedural Matters 

XII. References 
   

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II. Legal Authority 

With minor exceptions not at issue here, as provided in FIFRA section 3(a), a pesticide 

product may not be lawfully sold or distributed in the United States unless and until the product 

is registered by EPA. 7 U.S.C. 136a(a). A pesticide registration is a license allowing a pesticide 

product to be sold, distributed, and used for specified uses in accordance with use instructions, 

precautions, and other terms and conditions established by EPA when it grants the registration. 

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). This standard requires a finding that the risks 

associated with the use of a pesticide are justified by the benefits of such use, when the pesticide 

is used in compliance with the terms and conditions of registration or in accordance with 

commonly recognized practices. See Defenders of Wildlife v. Administrator, EPA, 882 F.2d 

1294, 1298-99 (8th Cir. 1989) (describing FIFRA’s required balancing of risks and benefits). The 

burden of demonstrating that a pesticide product satisfies the statutory criteria for registration is 

at all times on the proponents of the initial or continued registration, and continues as long as the 

registration is in effect. 40 C.F.R. §164.80(b). See also, Industrial Union Dept. v. American 

Petroleum Institute, 448 U.S. 607, 653 n.61 (1980); Stearns Electric Paste v. EPA 461 F.2d 293, 

(7th Cir. 1972); Environmental Defense Fund v. EPA, 510 F. 2d 1292, 1297 (D.C. Cir. 1975)). 

Under FIFRA section 6(b), the Agency may issue a Notice of Intent to Cancel the 

registration of a pesticide product whenever it appears either that: (1) A pesticide or its labeling 

or other material required to be submitted does not comply with FIFRA, or (2) when used in 

accordance with widespread and commonly recognized practice, the pesticide generally causes 

unreasonable adverse effects on the environment. 7 U.S.C. §136d (b). If a hearing is requested by 

an adversely affected person, the final order concerning cancellation of the product is not issued 

until after an administrative hearing. 

In the cancellation hearing, the Agency has the burden of going forward to present an 

affirmative case for cancellation. 40 C.F.R. §164.80(a). However, the ultimate burden of proof is 

on the proponent of the registration. 40 CFR §164.80(b); Industrial Union Dept., 448 U.S. at 653 

n. 61; Stearns Electric Paste v. EPA 461 F.2d 293, (7th Cir. 1972). Once the Agency makes its 

prima facie case that the risks of the product’s continued use fail to meet the FIFRA standard for 

registration, the responsibility to demonstrate that the product meets the FIFRA standard is upon 

the proponents of continued registration. 40 CFR §164.80(b); Dow v Ruckelshaus, 477 F.2d 

1317, 1324 (8th Cir. 1973). 
   

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FIFRA Section 3(c)(6) provides that where EPA determines that an application for 

registration does not meet the registration criteria of section 3(c)(5) for registration, the Agency 

must publish a notice of denial and the reasons therefore. Section 3(c)(6) further provides that 

upon such notification of the denial, the applicant for registration, or other interested person with 

the concurrence of the applicant, shall have the same remedies as provided for in section 6. 

III. Regulatory History 

Many pesticides were originally registered well before EPA came into existence or before 

EPA identified a complete set of data requirements sufficient to allow it to determine whether 

new pesticides met the standard for registration. In 1972, Congress therefore directed EPA to 

assess all existing pesticides to determine whether they would qualify for the new standard of 

registration adopted in the 1972 amendments to FIFRA. This process of assessing existing 

pesticides against current standards is known as “reregistration”. Congress in 1988, established a 

formal five-phase process for EPA to use in conducting a comprehensive review of all products 

registered before 1984 to determine whether these products had satisfied all applicable data 

requirements and the registration criteria of FIFRA section 3(c)(5). See FIFRA section 4(a), 7 

U.S.C. § 136a-1(a). 

EPA began the Section 4 reregistration process for products intended to control 

commensal rodents (i.e., house mice (Mus musculus), Norway rats (Rattus norvegicus), roof rats 

(Rattus rattus)) early in the 1990s. These rodents, probably originating in Central and Southeast 

Asia, have been introduced throughout the world by humans (Corrigan 1997; Chiri 2006). These 

commensal rodents typically live in close association with humans, and are often found in and 

around homes as well as commercial establishments (Timm 1994). 

The active ingredients in rodenticide products intended to control commensal rodents 

have different characteristics, but are commonly described as being of one of three general types: 

First generation anticoagulants (FGARs)(warfarin, chlorophacinone, diphacinone, pival), second 

generation anticoagulants (SGARs)(brodifacoum, bromadiolone), and acute toxins (zinc 

phosphide, bromethalin). 1 In 1991, EPA issued a Reregistration Eligibility Decision (RED) for 

rodenticide products containing the active ingredient warfarin. In July 1998, after making a 

comprehensive reassessment of data relating to the use and effects of the remaining rodenticide 

products subject to reregistration, EPA issued two REDs for seven different active ingredients 

that previously had been registered for rodent control in both agricultural and residential settings. 

63 FR 48729, September 11, 1998. One RED (the “Rodenticide Cluster RED”) contained 

eligibility decisions for the ingredients brodifacoum, bromadiolone, chlorophacinone, 

diphacinone, bromethalin, and pival. EPA also issued a second, stand-alone RED (the “Zinc 

Phosphide RED”) for the ingredient zinc phosphide. In these 1998 REDs, EPA issued FIFRA 

section 4(g)(2)(A) determinations that certain rodenticide products would not be eligible for 

 

1

 Two additional second generation anticoagulants, difethialone and difenacoum, and the acute toxin cholecalciferol, 

were first registered after 1984, and therefore were not subject to reregistration. 
   

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reregistration unless their registrants adopted certain risk mitigation measures to reduce the risks 

they posed to human health and the environment. 

In the REDs, EPA stated it would form a stakeholder group to “discuss means of 

significantly reducing exposures” to children. Reregistration Eligibility Decision for the 

Rodenticide Cluster (July 1998). The stakeholder group was created to “develop workable 

mitigation measures to adequately protect children from accidental rodenticide exposures.” Id.; 

see also Rodenticide Stakeholder Workgroup, Recommendations for Managing Rodenticide 

Exposures to Children in the Home: Subcommittee Report to the Pesticide Program Dialogue 

Committee (PPDC) for consideration by the U.S. Environmental Protection Agency (November 

15, 2000) (“the purpose of the [working group] is to provide advice and recommendations to the 

EPA on a pesticide exposure issue involving children”); Id. The group’s objectives included 

discussing long-term risk reduction measures and “decid[ing] on specific timing and other issues 

associated with bait dyes [and] bittering agents.” Reregistration Eligibility Decision for Zinc 

Phosphide (July 1998). In 1999, EPA formed the Rodenticide Stakeholders Workgroup (RSW) 

as a subcommittee of the federally-chartered advisory group the Pesticide Program Dialogue 

Committee (the “PPDC”).2

 The RSW included members from EPA, the United States Consumer 

Product Safety Commission, the District of Columbia Department of Health, Maryland Public 

Interest Research Group, the California Department of Food and Agriculture, the Children’s 

National Medical Center, the Association of Poison Control Centers, and the National Pest 

Control Association. 

The findings and recommendations of the RSW are contained in the November 15, 2000 

report, Recommendations for Managing Rodenticide Exposures to Children in the Home. EPA 

adopted those recommendations in a 2001 amendment to the REDs. 66 Fed. Reg. 59,425. One 

of the recommendations adopted by EPA was to rescind the 1998 RED determination that 

registrants should add a bitter taste to their rodenticide bait products that would dissuade children 

from eating them. An environmental group successfully challenged the 2001 amendment to the 

RED, and a district court remanded it to EPA. West Harlem Env. Action v. EPA, 380 F. Supp. 2d 

289, 294-295 (S.D.N.Y. 2005). 

Also, 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 developed a comparative 

ecological assessment for nine3

 rodenticide active ingredients. Between October 1999 and 

December 2001, the comparative risk assessment was drafted by Agency scientists, received 

both internal and external peer review as well as review by the Rodenticide Registrant Task 

Force. Based on input from these peer reviews, the comparative risk assessment was revised. 

There were two public comment periods in 2003 and 2004 and the Agency reviewed and 

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

 

2

 The PPDC is the principal stakeholder advisory body to EPA’s Office of Pesticide Programs and was established 

pursuant to the Federal Advisory Committee Act. 

3

 The tenth active ingredient, difenacoum was registered in 2007 and therefore, was not included in the Comparative 

Analysis or the Proposed Risk Mitigation. 
   

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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. 

In January 2007, EPA issued a draft Risk Mitigation Proposal for comment. Based on an 

evaluation of the ecological risks associated with the use of rodenticide bait products containing 

these nine active ingredients, and consideration of the public health and other important benefits 

of the use of rodenticide baits, EPA proposed to classify all bait products containing the active 

ingredients brodifacoum, bromadiolone, and difethialone as restricted use pesticides. Further, to 

decrease the possibility of children’s exposure to rodenticide products used in homes, EPA 

proposed requiring that all rodenticide bait products available for sale to consumers be sold only 

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

EPA took comment on the proposed mitigation for 120 days and received extensive 

comments from a wide range of stakeholders. During this comment period, the Rodenticide 

Registrant Task Force surveyed their constituents in 2007 and reported that in 2004, there were 

105 million bait placements and in 2005, the number had increased to 115 million bait 

placements distributed on the consumer market. Based on anecdotal evidence, EPA believed 

that the majority of products sold on the consumer market contained brodifacoum and 

difethialone. Incident data confirmed that brodifacoum was implicated in a high percentage of 

non-target wildlife incidents. Incident data strengthened EPA’s conclusions that if the lower 

toxicity and less persistent active ingredients replaced the higher toxicity and more persistent 

active ingredients for a portion of this market, there would be significant reduction in the levels 

of exposure to non-target wildlife. Based on restrictions some municipalities place on Restricted 

Use pesticides and concerns about the additional burdens on the poultry, livestock and pest 

control operator industries, and recognizing the importance of SGARs to these industries, EPA 

decided to employ sale and distribution limitations – rather than restricted use classification – to 

minimize the use of second generation anticoagulants in settings where the risks outweigh the 

benefits (i.e., most residential settings). 

On May 28, 2008, in response to the district court’s remand order, EPA issued the “Risk 

Mitigation Decision for Ten Rodenticides” (RMD).4

 The RMD explains EPA’s current section 

4(g)(2)(A) conclusions about the reregistration eligibility of rodenticides containing any of ten 

 

4

 The RMD did not reinstate either the bittering agent or indicator dye requirement for a number of reasons. After 

review of all the available information, EPA concluded that, among other things, neither bittering agents nor 

indicator dyes would provide risk reduction comparable to a bait station requirement, because neither prevents 

exposure. At best, bittering agents might reduce consumption, and indicator dyes might provide a signal of an 

exposure event. 
   

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listed active ingredients. Among other things, EPA stated that rodenticide baits sold to residential 

consumers must be packaged in a bait station designed to prevent children, domestic animals and 

non-target wildlife from being able to come into contact with bait. RMD at 17-18. EPA also 

stated that rodenticides containing “second-generation anticoagulants” pose significant risks to 

wildlife and the environment, and that rodenticides containing those compounds should only be 

sold to pest control professionals and agricultural users—not residential consumers—and then 

only with additional risk mitigation measures. Id. EPA stated that unless a rodenticide product 

incorporates the risk mitigation measures listed in the RMD, it “would present unreasonable risks 

inconsistent with FIFRA” and therefore should not remain registered. RMD at 15. 

The RMD announced EPA’s conclusions about rodenticide safety and signaled EPA’s 

intentions for the future completion of the reregistration process. But it did not change the legal 

status of any rodenticide product, now or in the future. EPA did not cancel or suspend any 

rodenticide registrations at that time, nor did it prohibit the sale of registered rodenticides that did 

not incorporate the specified mitigation measures. Instead, EPA asked registrants to adopt those 

mitigation measures voluntarily. Specifically, EPA asked each registrant to decide by September 

2, 2008, whether it intended to adopt the measures. If the manufacturer agreed to do so, it could 

submit a request for voluntary cancellation of its existing registrations that would not be effective 

until June 4, 2011. RMD at 26. 

By June 4, 2011, most rodenticide registrants had voluntarily amended their registrations 

or replaced them with new registrations meeting the risk mitigation goals of the RMD, thereby 

significantly reducing rodenticide risks. Today, only 20 rodenticide products, produced by three 

registrants (Liphatech, Inc.; Reckitt Benckiser, Inc.; and Spectrum Group Division of United 

Industries Corporation), fail to meet the risk mitigation goals of the RMD. As set forth in this 

Notice, EPA intends to achieve the necessary risk reduction identified in the RMD, by cancelling 

and denying the registrations of rodenticide products that do not include mitigation measures 

sufficient to prevent unreasonable risks to man and the environment. 

 

Certain rodenticide registrants who have disagreed with the Agency’s positions regarding 

rodenticides have challenged aspects of the Agency’s actions in two court cases, however, 

neither case has addressed the merits of the scientific, economic, and policy questions at issue in 

this cancellation proceeding. See generally, Reckitt Benckiser, Inc. v. Jackson, 762 F. Supp. 2d 

34, 46 (D.D.C. 2011)(concerning the scope of EPA’s authority to pursue enforcement action in 

lieu of a cancellation proceeding), and Woodstream Corp. v. Jackson, 1:11-cv-00867-JEB 

(D.D.C filed 5/9/2011)(concerning EPA’s authority to grant or amend registrations on a 

conditional basis). 

IV. Scope of Intended Cancellation and Denials 

For the reasons set forth in Units V, VI, and VII, below, EPA has determined that certain 

registered rodenticide bait products, when used in accordance with widespread and commonly 

recognized practice, generally cause unreasonable adverse effects on humans and the 

environment. Accordingly, EPA is today announcing its intention to cancel the registrations of 
   

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the following pesticide products: 

Table 1. Pesticide Products Subject to this Notice of Intent to Cancel. 

Product 

EPA Reg. 

No. Registrant 

Active 

Ingredient Form 

D-Con Concentrate Kills Rats & Mice 3282-3 

Reckitt Benckiser, 

Inc. Warfarin Powder 

D- Ready Mixed Kills Rats & Mice 3282-4 

Reckitt Benckiser, 

Inc. Warfarin Bait Bits 

D- Mouse Prufe Kills Mice 3282-9 

Reckitt Benckiser, 

Inc. Warfarin Pellets 

D- Pellets Kills Rats & Mice 3282-15 

Reckitt Benckiser, 

Inc. Warfarin Pellets in Place Pack 

Rid-A-Rat Rat & Mouse Killer 8845-39 

Spectrum Group, 

Div. of United 

Industries Corp. Warfarin Meal 

D- Mouse Prufe II 3282-65 

Reckitt Benckiser, 

Inc. Brodifacoum Pellets 

D- Pellets Generation II 3282-66 

Reckitt Benckiser, 

Inc. Brodifacoum Pellets 

D- Bait Pellets II 3282-74 

Reckitt Benckiser, 

Inc. Brodifacoum Pellets in Place Pack 

D- Ready Mixed Generation II 3282-81 

Reckitt Benckiser, 

Inc. Brodifacoum Crushed Pellets 

D- Mouse-Prufe III 3282-85 

Reckitt Benckiser, 

Inc. Difethialone Pellets 

D- Bait Pellets III 3282-86 

Reckitt Benckiser, 

Inc. Difethialone Pellets 

D- II Ready Mix Baitbits III 3282-87 

Reckitt Benckiser, 

Inc. Difethialone Crushed Pellets 

D- Bait Packs III 3282-88 

Reckitt Benckiser, 

Inc. Difethialone Pellets in Place Pack 

Generation Meal Bait Packs 7173-247 Liphatech, Inc. Difethialone Meal 

Difethialone Bait Station 7173-283 Liphatech, Inc. Difethialone 

Block in non-RMD 

conforming station 

Difethialone 6g Paste Pl Pks 7173-285 Liphatech, Inc. Difethialone Paste 

Hot Shot Sudden Death Brand Mouse 

Killer 8845-125 

Spectrum Group, 

Div. of United 

Industries Corp. Bromethalin Pellets in Place Pack 
   

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Table 1. Pesticide Products Subject to this Notice of Intent to Cancel. 

Product 

EPA Reg. 

No. Registrant 

Active 

Ingredient Form 

Hot Shot Sudden Death Brand Rat 

Killer 1 8845-126 

Spectrum Group, 

Div. of United 

Industries Corp. Bromethalin Pellets in Place Pack 

Hot Shot Sudden Death Brand Rat & 

Mouse Killer 8845-127 

Spectrum Group, 

Div. of United 

Industries Corp. Bromethalin Pellets in Place Pack 

Hot Shot Sudden Death Brand Mouse 

Killer Bait Station 8845-128 

Spectrum Group, 

Div. of United 

Industries Corp. Bromethalin Pellets in Place Pack 

For the same reasons, EPA is today announcing its denial of applications for registration 

or amended registration of the following pesticide products: 

 

Table 2. Denied Applications for Registration. 

Product 

EPA Application 

No. Registrant Active Ingredient Deficiency 

D-Con Bait Station 

XV Kills Mice 

3282-RNU Reckitt Benckiser 

Inc. 

Brodifacoum Consumer Oriented 

SGAR Product 

D-Con Bait Station 

XVI Kills Mice 

3282-RNL Reckitt Benckiser 

Inc. 

Brodifacoum Consumer Oriented 

SGAR Product 

Bromethalin 0.01% 

Pellet III 

36488-AN Woodstream Corp. Bromethalin Consumer Oriented 

Product in a Pelleted 

Form and Packaged 

Without a Bait 

Station 

Bromethalin Rat 

and Mouse Block 

III 

36488-AR Woodstream Corp. Bromethalin Consumer Oriented 

Product Packaged 

without a Bait Station 

In the RMD, EPA identified a number of mitigation measures that, if adopted would 

make existing rodenticides eligible for reregistration. With this Notice, EPA proposes to cancel 

the rodenticide products identified above based on two of the most significant mitigation 

measures identified in the RMD: Removing SGARs from residential consumer products, and 

assuring that rodenticide products available to residential consumers are in a form that securely 

fits in included bait stations that meet certain standards. Although the mitigation measures 

identified in the RMD are designed to be used in concert, with each measure contributing 

towards safer outcomes, the prohibition against loose bait and the bait station requirement are 

expected to protect children, domestic animals and non-target wildlife from exposures to 

commensal rodenticides generally, while the exclusion of SGARs from the homeowner market is 

expected to reduce environmental loading of SGARs and thereby reduce secondary poisonings 
   

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among non-target wildlife. As currently labeled and sold, each of the rodenticide products 

identified above cause unreasonable risks to man or the environment owing to their lack of one 

or both of these mitigation measures. Individual products may also fail to meet the FIFRA 

registration criteria for other reasons, however, in order to focus this hearing on the most critical 

risk mitigation issues, the proposed cancellations and the denials are based solely on the presence 

of second generation anticoagulants in products labeled for residential consumer use in 

controlling commensal rodents in and around buildings, or any product formulated as loose baits 

or bait blocks without bait stations that meet the standards of the RMD, or both. 

In this Notice, EPA proposes to cancel the registration of 20 products sold in the general 

consumer market, and denies the applications for registration of four additional products. The 

scope of this action is very narrow. There are adequate alternative products on the consumer 

market and the professional applicators (including public health officials, pest control operators 

(PCOs), and other occupational applicators) and agricultural applicators are not affected by this 

Notice. EPA has expressed concern for more than a decade that children, pets, and non-target 

wildlife are being unnecessarily exposed to rodenticides. Most of the children and pet incident 

concerns are occurring in and around homes, despite mandatory label statements requiring use in 

tamper-resistant (or tamper-proof) bait stations where placements otherwise would be accessible 

to children, domestic animals, and/or non-target wildlife. These incidents can be significantly 

reduced if rodenticide products sold in the general consumer market include bait stations 

designed to prevent children, domestic animals and non-target wildlife from being able to come 

into contact with bait. Further, based on the reported incidents of wildlife exposures to 

rodenticides, EPA has determined that it is appropriate to limit use of products containing the 

more toxic and persistent anticoagulants brodifacoum and difethialone. EPA has determined that 

the risks of use by residential consumers of rodenticides containing brodifacoum and difethialone 

outweigh the benefits of such use. There are over 30 alternative rodenticide products currently 

available in the general consumer market that can provide effective rodent control, that fully 

conform to the RMD, and that meet the safety standards required under FIFRA. In addition, 

residential consumers also have access to mechanical control methods as well as the services of 

PCOs who will continue to have access to a broader range of products. 

The Notice addresses only rodenticides intended to control the rodent species commonly 

referred to as “commensal” rodents: the Norway (brown or sewer) rat (Rattus norvegicus), the 

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

commensal rodents in sewers, in and around commercial buildings, and in connection with 

agricultural and food processing operations, are outside the scope of this Notice, as the only 

products EPA proposes to cancel are those available for residential consumer use. Products 

registered for the control of other types of rodents are also outside the scope of this Notice. 

 

In making the determination that the products subject to this Notice do not meet the 

FIFRA registration criteria, EPA has relied upon the evidence and analyses demonstrating 

significant exposure to humans, particularly to children, domestic animals, and non-target 

wildlife from the use of consumer use rodenticide products which are not protected in bait 

stations that meet the standards of the RMD. In addition, this determination relies upon the 
   

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substantial and well documented risks to non-target wildlife from secondary exposures to the 

active ingredients brodifacoum and difethialone. EPA also considered evidence and analyses 

relating to the benefits of continued use of the rodenticide products identified in this Notice, and 

has determined that, based on the availability of adequate and affordable alternative rodenticide 

products and methods of commensal rodent control, the benefits linked specifically to the 

products identified in this Notice are, at best, minimal. However, given the potential for 

exposure these products pose to children, coupled with risks to domestic animals and wildlife in 

the absence of further mitigation, EPA believes that this cancellation action would be warranted 

even if the anticipated costs of rodent control as a result of this action were somewhat greater 

than EPA has estimated. Accordingly, EPA is issuing this Notice of Intent to Cancel and to 

Deny registrations of the consumer-use commensal rodenticide products listed in above. 

V. Risks Associated with Exposure to Rodenticide Products Subject to this Notice 

(Human and Domestic Animals) 

Hazard Characterization of Rodenticide Products Subject to this Notice 

1.. Effects on Mammals 

Rodenticides are designed to kill mammals, so their effects on humans and non-target 

mammals are qualitatively the same as their effects on target pests, unlike other pesticides such 

as herbicides and certain insecticides where adverse effects on mammals tend to be different in 

nature than their effects on target pests. Rodenticides can be divided into three broad classes in 

terms of their effects: first generation anticoagulants, second generation anticoagulants, and nonanticoagulants. The first- and second generation anticoagulants interfere with blood clotting and 

death results from hemorrhage. For both first generation and second generation anticoagulants, 

primary manifestations include nosebleeds, bleeding gums, hematuria, melena, and extensive 

ecchymoses (bruises). Patients may also have symptoms of anemia, including fatigue and 

dyspnea on exertion. If the poisoning is severe, the patient may progress to shock and death. 

SGARs are generally more toxic and more persistent than FGARs. The non-anticoagulant 

rodenticides work in different ways to cause death. Each of these is discussed below: 

• FGARs, such as chlorophacinone, diphacinone, diphacinone sodium salt, warfarin, and 

warfarin sodium salt, disrupt the production in the liver of vitamin K dependent bloodclotting factors II (prothrombin), VII, IX, and X. Due to the long half-lives of the 

vitamin K-dependent clotting factors, the anticoagulant effect doesn’t occur in 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. It is noted that chlorophacinone, diphacinone, and 

diphacinone sodium salt block different binding sites than those blocked by warfarin and 

warfarin sodium salt. 
   

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• SGARs such as brodifacoum, bromadiolone, difenacoum, and difethialone are more 

acutely toxic than first generation agents and can cause lethal effects to rodents in a 

single dose. Like the first generation anticoagulants these agents 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, second generation anticoagulants have much longer half-lives in 

the body (Batten and Bratt, 1990). Similar to the first generation anticoagulants, the 

toxic effects of these agents usually begin several days after ingestion, because of the 

long half-life of the coagulation factors. 

The non-anticoagulants work in a variety of ways and no single common mechanism exists. 

For example: 

• 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 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 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). 
   

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2. Characterization of acute hazard for four rodenticide active ingredients in products 

subject to this Notice 

 

The products subject to this Notice each contain one of four rodenticide active 

ingredients: warfarin, brodifacoum, difethialone and bromethalin. Warfarin is a FGAR; 

brodifacoum and difethialone are SGARs that are very similar in structure to each other. 

Bromethalin is not an anticoagulant but an uncoupler of oxidative phosphorylation whose effects 

are manifested as neurotoxicity. For each of the anticoagulant rodenticides vitamin K1 is an 

antidote to poisoning, although for the second generation anticoagulants, repeated administration 

over many days or weeks is often necessary. Since there is no specific antidote for bromethalin 

poisoning, clinicians and veterinarians treat the symptoms of bromethalin toxicity. 

Anticoagulant rodenticides block the production of vitamin K which is essential for the 

synthesis of several clotting factors. The first sign of toxicity from poisoning is an increase in 

the time it takes blood to clot (prothrombin time). This is not an effect that would be detected 

immediately because it takes time for the anticoagulants to clear vitamin K-dependent clotting 

factors from the blood, nor is it an effect that would be noticed in a home setting, but rather in a 

medical facility. With a higher dose, symptoms become more noticeable and severe, and include 

easy bruising and bleeding from almost any tissue such as gums, nose, urinary tract, 

gastrointestinal tract, etc. In severe cases, there is massive loss of blood leading to death. 

Bromethalin is not an anticoagulant and there are few symptoms that would be regarded 

as “signature” effects at low doses. At low doses, a poisoned individual might exhibit mental 

confusion or dullness. At higher doses as cerebrospinal pressure increases there may be 

indications of weakness in limb strength and at very high doses, death preceded by general 

paralysis or convulsions. 

 

The acute toxicity of each of the four rodenticides will be discussed briefly below with 

the focus being on acute toxicity values and other relevant parameters reported in the studies. 

Warfarin. The acute oral LD50 for warfarin in rats is reported as 3 mg/kg (males only - Gaines, 

T. B. 1969. Toxicol. Appl. Pharmacol. 14, 515-534, MRID 00049330). Another source indicates 

there is considerable variability in reported rat LD50s for warfarin: “Reported oral LD50 values 

for warfarin in rats vary by a considerable magnitude. Values of 11 mg/kg body weight (Lund, 

1982), 58 mg/kg body weight (Thomson, 1988) and 58 mg/kg (female) and 323 mg/kg (male) 

(Hagan & Radomski, 1953) have been reported.” 

(http://www.inchem.org/documents/ehc/ehc/ehc175.htm). Another study supports a large 

difference between the acute toxicity of warfarin to male and female rats with the LD50 for males 

reported to be between 450 and 680 mg/kg and the LD50 for females reported as between 5 and 

10 mg/kg (MRID 00143093). 

Brodifacoum. The oral (gavage) LD50 of brodifacoum in rats is 0.42 mg/kg in males and 0.56 

mg/kg in females. Signs of toxicity at 0.5 and 0.75 mg/kg included pallor, bleeding from the nose 

and/or rectum and/or other sites. Deaths occurred in the period from 3-8 days after dosing. Post 
   

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mortem examination of those animals that died or were sacrificed in extremis and/or showed 

signs of bleeding, revealed the presence of free or clotted blood in the abdominal and/or thoracic 

cavity. Discoloration or pallor of a number of organs was also observed. These findings are 

consistent with the known anticoagulant activity of brodifacoum. There were no mortalities or 

signs of toxicity in male and female rats at a dose of 0.25 mg/kg (MRID 42687501). The halflife for brodifacoum in liver is very long – up to 350 days (MRID 42007502). 

Difethialone. Difethialone is a SGAR that requires only a single ingestion to be effective. 

Difethialone and brodifacoum are very close to each other structurally, differing only in the 

hetero atom in the coumarin ring. Like brodifacoum, difethialone has a long half-life in the body. 

The estimated half life of difethialone in rat liver from a single oral dose at 0.5 mg/kg is 175 days 

for males and 98 days for females (MRID 42065010). In an acute lethality study, the oral 

(gavage) LD50 of difethialone in rats was 0.55 mg/kg (males) and 0.58 mg/kg ((females) (MRID 

40268903). Animals died in 4-8 days with symptoms of anticoagulant toxicity. There were no 

deaths for either males or females at 0.4 mg/kg indicating a very steep dose response curve. 

There was a second acute lethality study in rats (MRID 40268903) in which 0/10 rats died at 0.4 

mg/kg and 10/10 rats died at 0.8 mg/kg. The two acute studies are consistent with each other 

and support an LD50 value of 0.55 mg/kg for acute lethality of difethialone in rats. 

Bromethalin. Bromethalin (N-methyl-2,4-dinitro-N-[2,4,6-tribromophenyl]-6-[trifluoromethyl] 

benzenamine) is not an anticoagulant but an uncoupler of oxidative phosporylation in which the 

the most apparent manifestation of toxicity involves the central nervous system. It is therefore 

recommended for use against anticoagulant resitant mice and rats. The oral LD50 in rats for 

bromethalin is reported as 3.2 mg/kg (males), 2.1 mg/kg (females) and 2.6 mg/kg (combined 

males and females) (MRID 44775101). Another study (MRID 00241521) lists the for LD50

females as (9.1 mg/kg and the LD50 for males as 10.7 mg/kg). 

EPA routinely characterizes the risk to humans posed by pesticides with uses in or 

around the home. An important part of a residential assessment is consideration of potential 

“incidental oral” exposure. The incidental oral assessment seeks to determine the exposure and 

risks to young children who may ingest pesticide that they would pick up on their hands (hand to 

mouth activity), or would be exposed to by mouthing an object with pesticide residue on it, or 

actually pick up granules of pesticide formulation scattered around the home. 

EPA has developed a quantitative approach to evaluating whether a pesticide poses risks 

to those who might be exposed as a consequence of pesticide uses. Using available toxicity 

data and other information such as physical and chemical properties of the pesticide, and activity 

patterns of potentially exposed persons, EPA estimates a level of exposure that would not cause 

harm (referred to in this analysis as the “exposure level of concern”), and compares that level to 

the amount of exposure people would get as a consequence of pesticide use. If the estimated 

exposure exceeds the exposure level of concern, the use of the pesticide poses risks that may or 

may not be unreasonable, depending on the benefits of the use. 
   

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EPA relies primarily on toxicity studies conducted with laboratory animals to derive 

exposure levels of concern for pesticide active ingredients. First EPA examines all of the 

available hazard studies and identifies the most sensitive toxic effect caused by a pesticide for 

the route and duration of exposure that matches the proposed exposure scenario. For 

rodenticides, EPA is primarily concerned about the hazards of a single instance of oral exposure. 

The only acute oral exposure studies available for the subject rodenticides are acute LD50 studies. 

Acute LD50 studies are not designed to identify sublethal toxic effects, but instead, to determine 

the amount of exposure that will cause death to 50% of the test animals after a single exposure. 

Because most chemicals cause adverse effects at dose levels well below a lethal dose EPA 

typically would base a human health risk assessment on toxicity effects more sensitive than the 

acute LD50. However, in the absence of a more appropriate toxicity data, the acute LD50 studies 

were used as the effect of concern for this assessment. 

To derive an exposure level of concern, EPA typically divides the point of departure (i.e., 

the exposure level that corresponds to the toxic effect of concern, here the acute LD50) by 

appropriate uncertainty factors. The uncertainty factors are intended to account for possible 

differences in sensitivity between humans and laboratory animals, for differences between 

humans, and in this case, to account for the likelihood of sublethal adverse effects. Using these 

uncertainty factors, EPA identifies a level of exposure that, with reasonable certainty, would not 

cause harm to humans because the difference between predicted exposures and the levels that 

cause adverse effects is large enough that no harm would reasonably be expected. It should be 

noted that an exposure at a level above the exposure level of concern may not elicit any 

discernable symptoms, depending on the nature of the effect, the amount of the exposure and the 

sensitivity of the individual person. To address the possibility that the pesticide may generally 

be more toxic to humans than animals and the possibility that variations in human sensitivity 

may be greater than seen in the test animals, the Agency usually applies uncertainty factors of at 

least 100, meaning that in order to be presumed safe, an exposure should be at least 100 times 

lower than the toxicity endpoint. Often EPA applies additional uncertainty factors to account for 

the absence of a “no observed adverse effect level” (NOAEL) and to address other limitations of 

the toxicity database. 

Owing to the paucity of data on sublethal effects of the subject rodenticides, EPA can not 

confidently establish exposure levels of concern for acute human exposure to the subject 

rodenticides. However, if EPA had a complete toxicity database with appropriate studies of 

sublethal effects with clearly established NOAELs, EPA would apply to that endpoint an 

uncertainty factor of at least 100 (i.e., a level of concern 100 times lower than the LOAEL) for 

each active ingredient to account for interspecies and intraspecies variability. If EPA had all the 

same studies, but the study showing the most sensitive toxic effect failed to establish a NOAEL, 

EPA would, in all likelihood, use an uncertainty factor of 1000. In the present case, all of these 

uncertainties are present, and moreover, the acute toxicity effect of concern (death) is severe and 

its relationship to sublethal acute adverse effects is unknown. In view of these uncertainties, 

EPA is unable to say with confidence that there is any finite level of exposure to the subject 

rodenticides that can be considered reasonably likely to cause no harm. Nevertheless, with the 

caveat that this undoubtedly understates the risks of sublethal adverse effects, Table 3 below 
   

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shows the LD50 values for each of the rodenticides and what the exposure level of concern would 

be if EPA applied an uncertainty factor of 1000 to derive a level of concern based on rat LD50s. 

Table 3. Surrogate Exposure Level of Concern 

Rodenticide LD50 

(mg/kg) 

Provisional Uncertainty 

Factor 

Surrogate Exposure Level of 

Concern (mg/kg) 

Warfarin 3 mg/kg 1000 0.003 mg/kg 

Brodifacoum 0.42 mg/kg 1000 0.00042 mg/kg 

Difethialone 0.55 mg/kg 1000 0.00055 mg/kg 

Bromethalin 2.6 mg/kg 1000 0.0026 mg/kg 

After deriving an exposure level of concern, EPA would estimate potential exposure of 

different population groups. As is evident from the incident reports and corroborated by studies 

of children’s behavior, young children will pick up and put small amounts of food-like material 

into their mouths. In the 1998 Rodenticide Cluster RED, EPA had cited poison specialist’s 

estimation that a child weighing 10 kg would consume approximately 5 grams of rodenticide bait 

in one bite (less than a quarter of an ounce). In the current analysis, EPA’s estimate of the 

potential exposure to children eating a single, 5-gram bite of rodenticide bait containing any of 

the active ingredients at issue greatly exceeds possible safe levels, without even considering 

potential sublethal effects. Table 4 below shows how the estimated child exposure from taking 

one bite of rodenticide bait compares to the surrogate exposure levels of concern for each of the 

subject rodenticides. 

Table 4. Surrogate Exposure Level of Concern for 5 gm Rodenticide Bait. 

Rodenticide 

% active 

ingredient in a 

bait product 

Rodenticide ingested 

in a 5 gm bite of bait 

by a 10 kg child 

Surrogate Exposure 

Level of Concern 

(UF = 1000) 

Warfarin 0.025% 0.13 mg/kg 0.003 mg/kg 

Brodifacoum 0.005% 0.025 mg/kg 0.00042 mg/kg 

Difethialone 0.0025% 0.0125 mg/kg 0.00018 mg/kg 

Bromethalin 0.01% 0.05 mg/kg 0.00087 mg/kg 

This quantitative analysis based on animal toxicity data is consistent with information 

from reports of incidents of human poisonings. Children who have accidentally ingested 

quantities of the subject rodenticides have displayed symptoms that are consistent with exposure 

to toxic levels of these compounds. Symptoms for the anticoagulants include hematological 

effects such as bruising, and bleeding from gums, nose and other tissues. Symptoms from 

bromethalin poisoning may include effects on cognition and paralysis. These effects are clearly 

harmful. 

In sum, EPA’s analysis shows that, unless use and exposure patterns are changed, 

children could easily ingest quantities of the subject rodenticides that would contain sufficient 

amounts of active ingredient to exceed levels that EPA would consider safe. Consequently, EPA 
   

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could not conclude that exposure to the subject rodenticides was reasonably certain not to cause 

harm. 

 

The rodenticide active ingredients in products subject to this Notice are designed to kill 

rodents and are known poisons to all mammals, so the number of studies concerning their effects 

in humans is understandably limited. Much of the information on their potential risk to humans 

and domestic animals comes from the numerous reported incidents detailing the frequent 

exposure of children to rodenticides, and the serious consequences (including prolonged 

veterinarian care and death) to companion animals. These incidents are discussed in the next 

sections 

3. Human Incident Data 

EPA generally relies on toxicity studies conducted on animals and exposure information 

based on the pesticide’s use pattern when registering a pesticide. After a pesticide is registered; 

however, human observational data about the effects and exposure of registered pesticides may 

be collected and analyzed. In assessing the risks of products subject to this Notice, EPA 

analyzed human observational data, or incidents, from the following sources: 

• summary data from the American Association of Poison Control Centers (AAPCC), 

• Human incident (poisoning) data from such sources as OPP’s Incident Data System (IDS) 

database, 

• NIOSH Sentinel Event Notification System for Occupational Risks (SENSOR), 

• the Agency-sponsored National Pesticide Information Center (NPIC), 

• California’s Pesticide Incident Surveillance Program (PISP), and 

• Additional review of the open literature. 

Incident information can provide important information about actual real-world 

exposures and risks associated with pesticide products. Incident data are collected 

systematically, but differently, by a number of organizations. The databases used by the Agency 

differ with respect to such issues as coverage, certainty/confidence, fields/parameters reported, 

and usability. These five pesticide incident data sources in combination with additional data 

from the open literature provide useful content and historical perspective. Various other 

comparable sources of data are available (e.g. the Bureau of Labor Statistics, emergency room 

outpatient surveillance, etc.) but are believed to be of limited additional utility and were not 

relied upon for the development of this Notice. Information from all 5 databases and open 

literature is provided in the Rodenticides Tier II: Review of Human Incidents, November 1, 2011 

Memorandum; however, in regard to children’s exposures to household products such as 

rodenticide baits, the AAPCC reports are the most applicable and complete, and are therefore the 

focus of this discussion. By looking across the data sources which were used, the Agency is 

confident that the data are adequate and appropriate for the discerning of trends and patterns in 
   

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incident poisonings associated with the following rodenticides used for commensal rodent 

control in bait form: brodifacoum, bromadiolone, bromethalin, chlorophacinone, cholecalciferol, 

difethialone, diphacinone, diphacinone sodium salt, warfarin, warfarin sodium salt, and zinc 

phosphide. Although these incident reporting databases can provide important information 

regarding the frequency, distribution and severity of adverse effects, they are far from 

comprehensive. EPA estimates that only one quarter of the total number of pesticide poisoning 

incidents are reported to the AAPCC or state counterparts. (Blondell and Spann, 06/03/1999, 

D256673). 

 American Association of Poison Control Centers (AAPCC) 

 

The American Association of Poison Control Centers (AAPCC) is a non-profit, national 

organization founded in 1958 that represents the poison control centers of the United States and 

the interests of poison prevention and treatment of poisoning. All of the calls to a poison control 

center are answered by a medical professional trained to answer questions about poisons. 

Additionally, AAPCC reports provide clearly summarized information on pesticide incidents 

within the context of other poisoning events. AAPCC produces an annual summary report 

giving statistics and information on all the poisonings reported to poison control centers in a 

calendar year. AAPCC ranks the severity of human exposure incidents as follows: 

• Death, 

• Major - symptoms are life-threatening or result in residual disability or disfigurement 

(coma, cardiovascular instability, repeated seizures), 

• Moderate – symptoms are more pronounced, prolonged, or more of a systemic nature 

than minor symptoms with no residual disability. Usually some form or treatment is 

indicated (high fever, disorientation), 

• Minor – symptoms are minimal with no residual disability (skin irritation, drowsiness, 

mild gastrointestinal symptoms), or 

• None – patient developed no symptoms as a result of exposure. 

A. Observed Human Exposures and Resultant Health Effects 

 1. Prevalence 

When looking across human incident data sources, as well as the open literature, 

rodenticides are found to be involved in numerous reported incidents, especially those involving 

children less than 6 years old. While all the sources (IDS, NPIC, PISP, NIOSH SENSOR) 

demonstrated that humans are being exposed to rodenticides, it is most evident in the Agency’s 

examination of the AAPCC rodenticide data from 1999 to 2009. These data showed that an 

average of 17,000 human exposures to rodenticides were reported annually. Approximately 85% 

(i.e., approximately 15,000 per year) of these 17,000 exposures occurred to children under 6 

years old over the 11 year period analyzed. Approximately 16% of all reported exposures to 

pesticides in the AAPCC data are related to rodenticide exposure. Approximately 26% of all 

reported pesticide exposures among children under 6 in the AAPCC data are related to 
   

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rodenticide exposure. Although incident data generally do not specify which products were the 

subject of the reported exposures, very few ,if any, consumer rodenticide products available on 

the market during this timeframe included bait stations intended to prevent children’s exposure. 

While certain AAPCC data are publicly available through 2010, EPA purchased access to 

the raw data and ancillary information for the years 1999 to 2005. More detailed analysis of 

AAPCC raw data from 1999 to 2005 of the children’s exposures to rodenticides, demonstrates 

that approximately 3,686 children less than 6 years old were treated at a health care facility for 

the seven year period analyzed. The analysis also demonstrates that on average for this seven 

year period approximately 128 cases per year (or 1%) of the exposures to children result in a 

medical outcome classified by the AAPCC as minor, moderate or major. Also, of all pesticiderelated cases involving children less than 6 years old from 1999 to 2005, approximately 39% of 

those seen in a health care facility are related to rodenticide exposure and 13% of hospitalization 

cases are related to rodenticide exposure. Fortunately, no deaths to children under 6 years old 

have been reported in these AAPCC data from 1999 to 2010. 

 

 2. Circumstances 

Incidents involving children appear to result primarily from their picking up unprotected 

baits in the home. This may result from failure to follow label directions to keep bait away from 

children, though in some cases, baits might have been moved by rodents from appropriate 

placement locations. In some cases it appears that parents underestimate places their children are 

capable of accessing. In other cases, it appears that these children were visiting a different 

environment (such as grandparents, friends, or neighbor’s) and their parent or guardian was 

unaware that the baits were accessible. Most incidents involving adults appear to be due to 

suicide or malicious intent. Accidental exposures, although rare, occasionally occur for adults. 

Approximately 85% (i.e., approximately 15,000 per year) of the 17,000 AAPCC 

exposures to rodenticides occurred to children under 6 years old over the 11 year period 

analyzed. Rodenticide exposure incidents are more likely to involve children than exposure 

incidents associated with any other category of pesticides (Table 5). Out of all reported 

pesticide-related exposure incidents to children under 6 years old, for all pesticides, 

approximately 26% of the exposures are due to rodenticides. 

Table 5. Ratio of Exposures to Children <6 years old to Number of Single Exposures 

per Pesticide Category in AAPCC from 1999-2009

Pesticide Category % Exposures to Children 

disinfectants 55% 

Fungicides 25% 

Herbicides 26% 

insecticides 41% 

organophosphates 29% 
   

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Table 5. Ratio of Exposures to Children <6 years old to Number of Single Exposures 

per Pesticide Category in AAPCC from 1999-2009

Pesticide Category % Exposures to Children 

other pesticides 65% 

rodenticides 85% 

 3. Resultant effects 

The majority (92%) of the rodenticide exposures reported to AAPCC do not result in 

significant symptoms based on those cases which received follow up to determine medical 

outcome. While exposures to rodenticides generally result in no detected clinical signs in 

children, the Agency believes that the number of non-symptomatic exposure incidents is 

unacceptably high because of the social costs associated with evaluating and treating children 

who might have been exposed. 

 

Nevertheless, severe outcomes from human exposures to rodenticides do occur. Despite 

the relatively low number of symptomatic cases, looking at AAPCC data from 1999-2005, 

rodenticide-related exposures are much more likely to receive medical treatment accounting for 

39% of all pesticide-related cases seen in a health care facility and 13% of all hospitalized cases 

involving children less than 6 years old. From 1999-2005, 894 cases were reported having 

minor, moderate, or major effects (Table 6). For cases reporting moderate or major effects, the 

most common effect reported was hematological, 37% and 55% respectively. These symptoms 

are likely a result from anticoagulant rodenticides’ abilities to interfere with blood clotting and 

are likely the result of rodenticide exposure. 

* the categories are not mutually exclusive (i.e. a person could report both a neurological and renal symptom) 

*there were no reported cardio symptoms. 

Table 6. AAPCC Reported Exposure Symptoms for Symptomatic Children Less Than 6 

Exposed to Rodenticide from 1999-2005 

 Level 

of 

Effect 

 

Total 

Expo

sures 

Reported Exposure Symptoms* 

Neurological Ocular Renal Respiratory Misc. Dermal GI Hematological 

Minor 

effect 727 15 (2%) 17 (2%) 0 20 (3%) 180 (25%) 18 (2%) 277 (38%) 36(5%) 

Moder

ate 

effect 

147 7 (5%) 1 (1%) 4 (3%) 2 (1%) 22 (15%) 8 (5%) 34 (23%) 55 (37%) 

Major 

effect 20 1 (5%) 0 0 2 (10%) 5 (25%) 2 (10%) 4 (20%) 11 (55%) 
   

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4. Effects on Domestic Animals 

 A Hazard to Domestic Animals and EPA’s Approach to Assessing Ongoing 

Health Effects on Pets

Rodenticides have much the same effects on domestic animals as they do on humans and 

on target mammals, as discussed above, although species may differ somewhat in sensitivity. 

EPA generally relies on toxicity studies conducted on animals and exposure information 

relevant to the pesticide’s use pattern when initially registering a pesticide. After a pesticide is 

registered; however, observational data about the effects and exposure of registered pesticides 

may be collected and analyzed. In assessing the risks of products subject to this Notice, pet 

observational data, or incidents, from the following sources were analyzed: 

• Information from the National Animal Poison Control Center (APCC), the Pet Poison 

Helpline, and the open literature. 

• OPP’s Incident Data System (IDS) database, 

• the Agency-sponsored National Pesticide Information Center (NPIC), 

Animal Poison Control Center and Pet Poison Helpline 

The American Society for the Prevention of Cruelty to Animals (ASPCA) Animal Poison 

Control Center (APCC) is a 24 hours a day, 365 days a year resource for animal poison-related 

emergencies. Calls to the APCC are triaged by specially trained veterinary toxicologists. The 

Pet Poison Helpline, another poison reporting center which is available throughout the U.S., 

Canada and the Caribbean, is managed by veterinary specialists who also help triage animal 

poisoning events. The veterinary specialists include board-certified veterinary internal medicine 

emergency critical care specialists, and veterinary toxicologists. 

 OPP Incident Data System (IDS) 

The OPP IDS database of pet exposure information includes reports of alleged incidents from 

various sources, including FIFRA Section 6-(a)-(2) reports from registrants and reports from 

other environmental agencies and individual consumers. The IDS exposure severity types for 

domestic animals, as defined by 40 CFR 159.184, are as follows:

• DA – Death – if the domestic animal died or was euthanized; 

• DB – Major – if the domestic animal exhibited or was alleged to have exhibited 

symptoms which may have been life-threatening or resulted in residual disability; 

• DC – Moderate – if the domestic animal exhibited or was alleged to have exhibited 

symptoms which are more pronounced, more prolonged or of a more systemic nature 

than minor symptoms and included some treatment and return to pre-exposure state; 

• DD – Minor – if the domestic animal was alleged to have exhibited symptoms, but they 
   

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were minimally bothersome and resolved rapidly; 

• DE – Unknown – if symptoms are unknown or not specified.5

National Pesticide Information Center (NPIC) 

NPIC is a cooperative effort between Oregon State University and EPA which is funded 

by EPA to serve as a source of objective, science-based pesticide information and respond to 

inquiries from the public and to incidents. NPIC receives approximately 25,000 calls per year, 

with about 4000 of these being related to pesticide exposure incidents. NPIC collects the 

information about the incidents and records that information in a database. NPIC is a source of 

national incident information; but generally receives fewer reports than IDS. Regardless, NPIC 

can provide an additional source of incident information. Unlike IDS, incidents reported to 

NPIC are assigned a certainty classification, which helps ascertain whether the exposure and 

reported outcome are related. 

B. Ongoing Pet Exposure and Resultant Health Effects

1. Prevalence 

The American Society for the Prevention of Cruelty to Animals (ASPCA) Animal Poison 

Control Center (APCC) website identifies the top ten pet toxins of 2010 based on the number of 

calls received. Out of the approximately 167,000 phone calls about pet exposures they received 

during 2010, rodenticides were listed as the third most frequent reason for calls to the APCC 

(after human medications and insecticides). Another 24-hour hotline, the Pet Poison Helpline, in 

2009 identified rodenticides as the third most common toxin involved in dog poisonings (after 

chocolate and insect bait stations) and the fourth most common toxin involved in cat poisonings 

(after lilies, canine permethrin insecticides and household cleaners). 

Both the IDS and NPIC data indicate that the number of reported incidents of pet 

exposure to rodenticides is increasing over time. However, different rodenticides are associated 

with this increase in the different databases. 

IDS reports that the number of reported pet exposures involving first-generation 

anticoagulants and non-anticoagulant rodenticides was relatively stable from 1999 to 2009, 

whereas reported exposures involving second-generation anticoagulant rodenticides (chiefly 

bromadiolone) increased over time, from approximately 200 per year to approximately 1400 per 

year, primarily in the moderate, minor and unknown outcome categories. The overall upward 

trend may be a result of increased usage or increased reporting, rather than an increase in the 

likelihood that use of a product results in an incident. 

 

5

 Some exposures are classified as “D” in IDS, which is a classification used before 1998 (at which point reporting 

requirements were updated) or used to indicate the severity is undetermined; as the focus of this assessment is on 

incidents occurring in 1999 or later, we assume all “D” exposures are “DE” and have undetermined severity. 
   

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 By contrast, NPIC reports that the number of reported pet exposures involving first- and 

second-generation anticoagulants was relatively stable from 1999 to 2010, whereas reported 

exposures involving non-anticoagulants (chiefly zinc phosphide) increased over time, from 

approximately 5 per year to approximately 180 per year. Although as rodenticide bait, zinc 

phosphide is not registered for commensal rodent control in and around homes. The major 

consumer use for zinc phosphide is outdoors for mole and vole control. 

 2. Circumstances 

From the narrative information available regarding these incidents and the literature 

review, it appears that many pets gain access to baits placed in and around homes. EPA believes 

the main reason these incidents are occurring is because loose baits and bait blocks without petresistant bait stations are being placed in areas accessible to pets.

 3. Resultant effects 

The IDS data reflect that although most incidents appear to result in lower severity 

outcomes, there were a substantial number of fatalities (1209) and major outcomes (565) from 

1999 to 2009. The report lists two times more fatalities than major outcomes; which may be due 

to pet owners being more likely to report fatalities. This indicates that rodenticides cause about 

160 of the severe (death or major effect) domestic animal incidents that are reported every year, 

which EPA believes is likely to significantly underestimate the actual number of incidents. 

The IDS data also allows rodenticide active ingredients to be ranked according to the 

severity of domestic animal incidents reported. Although the data may be influenced by market 

share, focusing on those exposures resulting in severe outcomes provides an indication of the 

hazard of a particular active ingredient. The rodenticide with the highest number of incidents 

ranked DA (death) and DB (major) over the period 1999-2010 was brodifacoum (710 incidents), 

followed by bromadialone (355), bromethalin (292) and diphacinone and its sodium salt (262). 

Together, the second generation anticoagulants brodifacoum and bromadialone accounted for 

60% of the major and fatal domestic animal incidents (DA+DB) attributed to rodenticides. 

Comparing the total number of major and fatal incidents (DA+DB) per active ingredient, 

and as a percentage of total incidents for that same active ingredient provides a way to judge 

whether a particular active ingredient is more or less likely to cause serious adverse effects. For 

example, brodifacoum is involved in about twice as many fatalities as bromadialone, but fewer 

exposures overall (about 70% as many as bromadiolone), suggesting greater potential for an 

exposure resulting in a high severity outcome is greater when exposed to brodifacoum. 
   

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Table 7: IDS - Rodenticides as a Percentage of Severe Outcomes, 1999-2009

Rodenticide Category 

Percentage of Death + Major 

Incidents out of Total Exposure 

Count 

Total Exposure 

Count 

Diphacinone and 

diphacinone, sodium salt 

First-generation 

22% 1,192 

Warfarin and warfarin, 

sodium salt 22% 151 

Chlorophacinone 21% 29 

Brodifacoum 

Secondgeneration 

22% 3,229 

Bromadiolone 8% 4,661 

Difethialone 13% 144 

Difenacoum 27% 11 

Bromethalin 

Nonanticoagulant 

12% 2,460 

Zinc phosphide 18% 258 

Cholecalciferol 23% 209 

VI. Non-Target Wildlife Risks Associated with Exposure to Rodenticide Products Subject 

to This Notice 

This discussion summarizes the ecological risk concerns that form part of the basis of 

EPA’s decision to cancel and deny registrations for the commensal rodent control products 

identified above in this notice. EPA has updated its previous risk assessment findings conducted 

in support of the May 2008 RMD through the application of additional effects and exposure data, 

use of additional exposure modeling, and quantitative risk assessment techniques for the four 

rodenticide active ingredients (brodifacoum, difethialone, warfarin and bromethalin) contained in 

products subject to this Notice and for two rodenticides (chlorophacinone and diphacinone) that 

are potential alternatives to brodifacoum and difethialone in the consumer rodenticide market. 

Rodenticide baits are intended to be lethal to rodents and a few other small mammals, but 

they are not selective to target species. Mammals and birds are vulnerable to adverse effects, 

including mortality, from rodenticides, although different species and individuals may have 

differing sensitivities. Rodenticide exposures and mortalities have been documented for 

mammals and birds that are primary and secondary consumers. 

For the purpose of the ecological risk assessment, primary exposure was defined as nontarget organism consumption of rodenticide treated bait. Use of rodenticide baits around 

structures is likely to result in primary exposures among non-target wildlife. Many factors 

influence which non-target animals might be exposed directly to baits. For instance, birds and 

mammals that are attracted to seeds and grains may consume grain-based rodenticide baits and 

baits in forms similar to seeds and grains. Some non-target animals will readily consume 
   

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rodenticide baits that have a block form. Exposure has been reported for a number of species 

that are primary consumers of bait, including quail, turkeys, squirrels, opossums, raccoons, 

skunks, and deer. 

Secondary consumers were defined in the ecological risk assessment as those animals 

that prey upon or scavenge primary consumers of bait. Rodenticide baits also pose potential 

secondary risks, because predators and scavengers are likely to be attracted to dead or dying rats, 

mice, and poisoned non-target animals. In addition, secondary consumers may also consume 

commensal rodent baits that contain flavorings that might appeal to carnivores and omnivores. 

Secondary exposure has been documented in a number of secondary consumer species including 

larger mammals such as bobcats and foxes, and numerous bird species such as hawks, eagles and 

owls. 

The EPA assessment does not evaluate potential risks to aquatic organisms or plants. 

Exposure to aquatic organisms is assumed to be negligible relative to potential exposures to 

terrestrial animals for commensal rodent control via the evaluated consumer use products given 

that (1) direct application to water is unlikely to occur; (2) spray drift of baits is not expected; (3) 

large, contiguous areas are not expected to be treated; and (4) leaching of rodenticides from baits 

is limited. Direct risk to terrestrial plants was presumed low given the modes of action of the 

evaluated rodenticides. 

EPA is concerned with both the primary and secondary risks to birds and non-target 

mammals from exposure to the commensal rodent control products subject to this notice. This 

concern is based upon consideration of several lines of evidence, including (1) an assessment of 

the risks to non-target animals associated with primary exposure to rodenticides; (2) an 

assessment of the risks of non-target animals through secondary exposure to rodenticides; (3) an 

evaluation of available feeding studies as they relate to secondary exposure risks; and (4) an 

evaluation of reported wildlife incidents as they relate to primary and secondary mortality events 

for non-target species in a variety of land use settings, including urban, suburban, and rural 

settings. Tables 8, 9, 10 and 11 below summarize the results of EPA’s analysis of these lines of 

evidence. 
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Table 8. RQs from the bird risk assessment: primary exposure of passerine birds to bait and secondary expredator/scavenger birds to residues in consumed rodents. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Primary exposure 

to passerines 

Single day dose RQ 

20 19.61* 29.80* 0.23 0.50* 0.07 0.01 

100 22.67* 18.39* 0.14 0.31 0.04 0.01 1000 27.89* 9.22* 0.07 0.16 0.02 <0.01 

Six day dose RQ 

20 117* 168* 1.36* 2.94* 0.40 0.05 

100 135* 104* 0.84* 1.81* 0.25 0.03 1000 166* 52* 0.42 0.91* 0.12 0.01 

Dietary RQ NA 38* 45* 0.40 0.86* 0.89* 0.06 

Secondary exposure to carnivores and scavengers 

House mouse consumption: 3 day accumulation in prey RQ 

100 19.77* 17.09* 0.14 0.30 0.04 0.01 

1000 15.42* 5.42* 0.04 0.09 0.01 <0.01 5000 12.96* 2.43* 0.02 0.04 0.01 <0.01 

Norway rat consumption: 3 day accumulation in prey RQ 

100 5.25* 4.52* 0.04 0.08 0.01 <0.01 

1000 4.08* 1.43* 0.01 0.02 <0.01 <0.01 5000 3.43* 0.64* 0.01 0.01 <0.01 <0.01 

House mouse consumption: 6 day accumulation in prey RQ 

100 39.40* 32.98* 0.27 0.58* 0.08 0.01 

1000 30.74* 10.45* 0.09 0.19 0.02 <0.01 5000 25.84* 4.68* 0.04 0.08 0.01 <0.01 

Norway rat consumption: 6 day accumulation in prey RQ 

100 10.43* 8.73* 0.07 0.15 0.02 <0.01 

1000 8.14* 2.77* 0.02 0.05 0.01 <0.01 5000 6.84* 1.24* 0.01 0.02 <0.01 <0.01 

House mouse consumption: dietary RQ NA 17.81* 2069* 0.19 0.41 0.32 0.02 Norway rat consumption: dietary RQ NA 4.71* 5.48* 0.05 0.11 0.09 <0.01 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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Table 9. Additional lines of evidence from the bird risk assessment. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Primary exposure 

to passerines 

Days to consume sufficient bait to reach the LD50

20 <1 <1 4-5 1-2 16-17 >365 

100 <1 <1 7-8 3-4 30-31 >365 1000 <1 <1 14-15 6-7 117-118 >365 

Grams bait consumed to reach the LD50

20 0.3 0.2 25 10 86 >1800 

100 0.9 1.1 160 80 620 >7300 1000 5 15 2100 990 17000 >52000 

Secondary 

exposure to 

carnivores and 

scavengers 

Number of house mice consumed to reach the LD50: 1 day accum. in 

prey 

100 <1 <1 38 18 130 820 

1000 2 4 540 250 1800 1200 5000 5 27 3400 1600 1200 74000 

Number of Norway rats to consume to reach the LD50: 1 day accum. in 

prey 

100 <1 <1 7 3 23 150 

1000 <1 <1 97 45 330 2100 5000 <1 5 610 280 2100 13000 

Secondary feeding study summary counts (#mortalities/ #tested) 

NA 63/149 ND 2/23 0/112 3/34 

Incident data 

summary 

counts 

primary exposure NA 3 0 1 3 1 secondary exposure NA 164 3 5 3 5  unknown exposure NA 21 0 0 1 0 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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Table 10. RQs from the mammal risk assessment: primary exposure of rodents to bait and secondary expopredator/scavenger mammals to residues in consumed rodents. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Primary exposure to 

rodents 

Single day dose RQ 

15 9.93* 4.30* 8.36* 18.05* 0.82* 1.97* 

35 8.48* 3.67* 7.14* 15.42* 0.70* 1.68* 1000 4.55* 1.97* 3.83* 8.27* 0.38 0.90* 

Six day dose RQ 

15 59* 24* 49* 106* 4.7* 11.6* 

35 51* 21* 42* 90* 4.0* 9.9* 1000 27* 11* 22* 48* 2.1* 5.3* 

Dietary RQ NA 94* ND 57* 123* 44* 22* 

Secondary exposure to carnivores and scavengers 

House mouse consumption: 3 day accumulation in prey RQ 

50 11.10* 4.74* 8.81* 19.03* 0.84* 2.49* 

1000 13.78* 5.88* 10.93* 23.61* 1.04* 3.09* 3000 14.91* 6.37* 11.83* 25.56* 1.12* 3.35* 

Norway rat consumption: 3 day accumulation in prey RQ 

50 2.94* 1.25* 2.33* 5.04* 0.22 0.66* 

1000 3.65* 1.56* 2.89* 6.25* 0.27 0.82* 3000 3.95* 1.68* 3.13* 6.76* 0.30 0.89* 

House mouse consumption: 6 day accumulation in prey RQ 

50 22.13* 9.15* 17.35* 37.48* 1.63* 4.20* 

1000 27.46* 11.35* 21.53* 46.51* 2.02* 5.21* 3000 29.72* 12.28* 23.30* 50.33* 2.18* 5.64* 

Norway rat consumption: 6 day accumulation in prey RQ 

50 5.86* 2.42* 4.59* 9.92* 0.43 1.11* 

1000 7.27* 3.00* 5.70* 12.31* 0.53* 1.38* 3000 7.87* 3.25* 6.17* 13.32* 0.58* 1.49* 

House mouse consumption: dietary RQ NA 44.69* ND 26.64* 57.54* 20.42* 10.11* Norway rat consumption: dietary RQ NA 11.23* ND 7.05* 15.23* 5.41* 2.68* 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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Table 11. Additional lines of evidence from the mammal risk assessment. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Primary exposure 

to rodents 

Days to consume sufficient bait to reach the LD50

15 <1 <1 <1 <1 1-2 <1 

35 <1 <1 <1 <1 1-2 <1 1000 <1 <1 <1 <1 2-3 <1 

Grams bait consumed to reach the LD50

15 0.3 0.7 0.3 0.2 6 1.1 

35 0.5 1.3 0.7 0.3 9 2.1 1000 6.7 16 8.0 3.7 61 25 

Secondary 

exposure to 

carnivores and 

Number of house mice consumed to reach the LD50: 1 day accum. in prey 

50 <1 <1 <1 <1 3 <1 

1000 2 5 3 1 27 8 3000 5 11 6 3 60 18 

Number of Norway rats to consume to reach the LD50: 

1 day accum. in prey 

50 <1 <1 <1 <1 <1 <1 

1000 <1 <1 <1 <1 5 1 3000 <1 2 1 <1 11 3 

Secondary feeding study summary counts (#mortalities/ #tested) 

NA 8/19 ND 9/100 32/55 19/33 

Incident data 

summary 

counts 

primary exposure NA 41 1 2 3 9 secondary exposure NA 22 1 0 1 4  unknown exposure NA 16 0 0 0 0 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
   

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1. EPA’s Deterministic Assessment Approach 

In conducting both the primary and secondary risk assessments, EPA utilized its 

deterministic risk quotient (RQ) method to estimate risk to non-target mammals and birds 

associated with the use of the commensal rodenticides. The RQ is a unitless value that is the 

ratio of exposure to the toxicity endpoint. For example, in the context of acute avian risk 

estimates (e.g., mortality), an RQ of 1 would mean that non-target bird species may be exposed 

in the environment to an amount of the pesticide that results in mortality (specifically, the dose at 

which 50% of the test species died). EPA compares RQs to the Agency’s “levels of concern” 

(LOC) for non-target species. The LOC represents the exposure levels at which, in EPA’s 

judgment, a pesticide has the potential to cause risks of concern to non-target organisms. Thus, 

when the RQ for a pesticide exceeds the LOC for a particular category of non-target species, the 

Agency believes there is a risk of concern for species in that category. In this assessment, risk 

quotients were compared with the acute level of concern that EPA regularly uses in assessing 

risks to non-target species generally (LOC = 0.5). Additional levels of concern may also be 

used to evaluate potential risks to species listed as threatened or endangered (LOC = 0.1); 

however, for simplicity, this analysis only used the LOC of 0.5. Therefore, conclusions made 

with respect to the LOC of 0.5 may not apply to listed species. 

Because this deterministic assessment is intended to serve as a screening tool for identifying 

a potential for adverse effects, it is somewhat limited and conservative by design. As a result, 

EPA does not believe that the RQs derived in this assessment can be used as a precise measure of 

the magnitude of effects that will occur, but rather serve as tools for addressing whether or not a 

chemical poses a risk to assessed animals. As a result, direct comparisons between chemicals on 

the basis of RQs can be misleading. In this assessment, the Agency uses other lines of evidence 

to characterize the relative risks of the rodenticides that are subject to this Notice and the 

alternatives considered here. 

 

2. Primary Exposure and Risk 

a. Methodology 

For the purpose of this assessment, primary exposure is defined as non-target organism 

consumption of rodenticide treated bait. Primary exposure risk is influenced by factors including 

toxicity, toxicokinetics (chemical absorption, distribution and elimination in the body), 

concentration of active ingredient in the bait, and availability of bait for consumption. For each 

of the evaluated chemicals, risk is assessed in several ways: 

• single day dose-based exposure to bait based on allometric equations that allow for 

differentiation among taxa and body size is compared to acute oral LD50 toxicity values; 

• six day dose-based exposure to bait based on metabolism rate in the body and allometric 

equations that allow for differentiation among taxa and body size is compared to acute 

oral LD50 toxicity values; and 
   

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• diet-based exposure based on the concentration of chemical active ingredient in bait in 

comparison to acute dietary LC50 values. 

 Further lines of evidence include an analysis of the number of days of bait consumption 

required to reach the median lethal dose of rodenticide and the amount of bait individuals would 

need to consume in order to accumulate the median lethal dose. 

For the single-day dose-based exposure method, exposure was calculated by dividing the 

dose (in milligrams of active ingredient) by the body weight (in kilograms) of the consuming 

individual for three standard weight classes of birds and mammals. Allometric equations that 

relate food consumption to body weight (Wildlife Exposures Handbook, USEPA 1993) were 

used to determine potential exposures for typical birds and mammals of varying sizes. 

Allometric equations were used for the generic bird and mammal. In addition, allometric 

equations for passeriform birds and rodent mammals were also used as these would best 

approximate those individuals with high potential for consuming bait and they would give 

conservative exposure estimates. Animal exposure was determined based on daily food intake 

rates (dry weight), assuming 100% of their diet consisted of dry bait. It was assumed for this 

assessment that the form of the bait would not influence rate of intake or total intake. 

Weight-adjusted LD50 values for birds and mammals were used as the measure of toxicity 

to non-target species. The toxicity values selected for this assessment for birds were the most 

sensitive LD50 values available for Northern bobwhite quail (Colinus virginianus) or mallard 

duck (Anas platyrhynchos). The toxicity values selected for this assessment for mammals were 

the most sensitive LD50 values available for the Norway rat (Rattus norvegicus). For this 

assessment, EPA used standard bird (bobwhite quail and mallard duck) and mammal (Norway 

rat) test species to estimate weight-adjusted LD50 values for non-target animals. Although there 

are numerous studies addressing the toxicity of one or more rodenticides in a wide variety of 

non-target species, these standard test species are the only ones for which studies are available on 

all of the rodenticides of interest; therefore, only these standard test species allowed for 

comparisons of results among chemicals. However, this method may not be conservative if other 

non-target species are more sensitive to rodenticide exposure. 

Scaling factors were used to modify the available avian and mammalian toxicity data to 

account for differences in sensitivity between animals of different body weights. For example, 

when using the default scaling factor, smaller birds are estimated to be more sensitive compared 

to larger birds. Scaling factors, derived from Mineau et al. (1996) for birds are used in this 

assessment, which is consistent with the Agency’s terrestrial animal risk assessment model TREX v.1.4.1. A chemical-specific scaling factor was available for brodifacoum (0.76) from 

Mineau et al. (1996), and for all other chemicals where such a specific value is unavailable, the 

default scaling factor (1.15) was used to adjust the avian LD50s. Using additional data, Mineau 

et al. (2001) provided an alternative scaling factor for brodifacoum (0.88) and a chemicalspecific scaling factor for chlorophacinone (-0.53). Mammalian weight-adjusted LD50 values 

were calculated using the “body weight 3⁄4” adjustment (USEPA 1995, 2011). EPA’s assessment 

for primary exposure and risk utilized default weight classes of birds (small (20 g), medium (100 
   

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g), and large (1000 g)), and mammals (small (15 g), medium (35 g), and large (1000 g)). These 

are the standard bird and mammal body weights used in EFED risk assessments (T-REX 

documentation (version 1.4.1, December 2008). 

The six day dose-based exposure assessment utilized the same toxicity information 

discussed above, but in this assessment RQs were calculated by estimating body burden based on 

the assumption that bait was consumed exclusively for six days. Body burden concentrations 

(mg a.i./kg-bwt) were based on feeding rates and elimination rates from liver half-life estimates. 

For the diet-based primary exposure assessment, EPA evaluated the concentration of a.i. 

in the bait and the dietary LC50. The LC50 (mg a.i./kg-diet) is obtained from 5-day exposure 

dietary toxicity studies. RQs are calculated as a ratio of a.i. concentration and the LC50. Risk 

results that agree between this method and the multiple day accumulated dose method described 

above provide an enhanced degree of confidence in risk conclusions for a given chemical. 

As noted above, EPA also evaluated further lines of evidence, including an analysis of 

the number of days of bait consumption required to reach the median lethal dose of rodenticide 

and the mass of bait animals would need to consume in order to reach the median lethal dose. 

The first line of evidence involved calculation of the number of days it would take an individual 

non-target bird or mammal (assuming the standard body weights described above) to reach the 

LD50 through consuming 100% of its daily diet as bait. The second line of evidence involved 

calculating the amount of bait that would need to be consumed to be equivalent to the LD50.

These additional lines of evidence represent useful tools for comparing risks among chemicals. 

The greatest concerns for non-target primary risk are with those pesticides for which little 

feeding time or only a small amount of treated material is necessary for mortality to occur. 

Mortality to non-target primary consumers become less likely when consistent feeding or large 

amounts of consumption are necessary over a protracted period of time to cause death. 

b. Risk Characterization 

The risks identified by the determinative analyses and the other lines of evidence for each 

of the rodenticides considered in the EPA assessment are characterized below. Tables 12 and 13 

include the RQs for primary exposures of birds and mammals (respectively) to rodenticides. 

These tables also include the estimated number of days required to reach the LD50 through 100% 

consumption of bait and the amount of bait equivalent to the LD50. 
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Table 12. bird risk assessment: primary exposure of passerine birds to bait. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Risk Quotients 

Single day dose RQ 

20 19.61* 29.80* 0.23 0.50* 0.07 0.01 

100 22.67* 18.39* 0.14 0.31 0.04 0.01 1000 27.89* 9.22* 0.07 0.16 0.02 <0.01 

Six day dose RQ 

20 117* 168* 1.36* 2.94* 0.40 0.05 

100 135* 104* 0.84* 1.81* 0.25 0.03 1000 166* 52* 0.42 0.91* 0.12 0.01 

Dietary RQ NA 38* 45* 0.40 0.86* 0.89* 0.06 

Additional lines of 

evidence 

Days to consume sufficient bait to reach the LD50

20 <1 <1 4-5 1-2 16-17 >365 

100 <1 <1 7-8 3-4 30-31 >365 1000 <1 <1 14-15 6-7 117-118 >365 

Grams bait consumed to reach the LD50

20 0.3 0.2 25 10 86 >1800 

100 0.9 1.1 160 80 620 >7300 1000 5 15 2100 990 17000 >52000 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 Table 13. mammal risk assessment: primary exposure of rodents to bait. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Risk Quotients 

Single day dose RQ 

15 9.93* 4.30* 8.36* 18.05* 0.82* 1.97* 

35 8.48* 3.67* 7.14* 15.42* 0.70* 1.68* 1000 4.55* 1.97* 3.83* 8.27* 0.38 0.90* 

Six day dose RQ 

15 59* 24* 49* 106* 4.7* 11.6* 

35 51* 21* 42* 90* 4.0* 9.9* 1000 27* 11* 22* 48* 2.1* 5.3* 

Dietary RQ NA 94* ND 57* 123* 44* 22* 

Additional lines of 

evidence 

Days to consume sufficient bait to reach the LD50

15 <1 <1 <1 <1 1-2 <1 

35 <1 <1 <1 <1 1-2 <1 1000 <1 <1 <1 <1 2-3 <1 

Grams bait consumed to reach the LD50

15 0.3 0.7 0.3 0.2 6 1.1 

35 0.5 1.3 0.7 0.3 9 2.1 1000 6.7 16 8.0 3.7 61 25 
   

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RQs exceed the LOC for all mammals exposed to brodifacoum and difethialone. By 

design, brodifacoum and difethialone represent a lethal primary risk to non-target small 

mammals that may eat either loose treated bait or utilize a bait station. However, the quantitative 

assessment also demonstrates that bait containing these two rodenticides constitutes a primary 

exposure risk concern for larger mammals as well as all avian size classes – that is, species that 

are plainly not the intended targets of these products. This conclusion is consistent across all 

primary exposure risk analyses performed (single oral dose, six-day accumulated dose, dietary 

concentration and the feeding period- lethality assessment). EPA’s analysis indicates birds and 

mammals could attain a lethal dose (LD50) of either brodifacoum or difethialone upon feeding for 

less than one day on treated bait. The brevity of feeding required to reach a potentially lethal 

exposure represents an increased opportunity (relative to all other rodenticides assessed) for nontarget animals – especially birds -- to chance upon loose treated bait and consume a lethal dose. 

Warfarin, as expected for all rodenticides, also demonstrates a primary exposure risk 

concern to small mammals. The assessment of warfarin also indicates a risk to large mammals 

for all assessment methods employed as well. EPA’s analysis indicates that feeding on treated 

bait for less than a day is sufficient to attain a lethal dose in all evaluated size classes of 

mammals, suggesting a similar opportunity, relative to brodifacoum and difethialone, for nontarget mammals to chance upon treated bait and consume a lethal dose. In contrast to 

brodifacoum and difethialone, warfarin’s primary exposure risk for birds is limited to small 

passeriforms and other medium sized birds. While a single day dose risk assessment suggests 

only a risk to small passeriforms from the highest concentration formulation, accounting for the 

potential for multiple day accumulation on a dose basis expands the concerns to include 

passeriforms and other small and medium sized birds at all formulation concentrations assessed. 

The dietary assessment does not consider body weight as a determinant factor. However, this 

assessment method still predicts a risk concern at the highest formulation concentration. EPA 

estimates that birds would attain a lethal warfarin dose after 1 to 7 days of feeding (0.054% 

warfarin bait) or after 4-15 days of feeding (0.025% warfarin bait). This finding suggests that, 

for birds there is less of an opportunity for consuming a lethal dose of warfarin by chance when 

compared with brodifacoum and difethialone, since it would generally require multiple days of 

feeding on warfarin treated bait to reach a lethal dose in birds. 

For bromethalin, as can be expected for a relatively fast acting compound (target 

mortality occurs 1 to 7 days after initial exposure, Pitt et al. 2011, and registrant submitted 

studies), acute risk concern levels are exceeded for all mammalian size classes feeding on treated 

bait regardless of the assessment method EPA employed. In addition, bromethalin exceeds risk 

concern levels in all assessment methodologies with the exception of the dietary exposure 

methodology. EPA’s analysis indicates that less than a single day’s feeding on bromethalin bait 

is sufficient to attain a lethal dose in birds and mammals, suggesting again like brodifacoum and 

difethialone, that adverse effects to non-target wildlife are likely from primary exposure events 

with treated bait. 

Two anticoagulant alternatives, chlorophacinone and diphacinone, also present primary 

exposure risk concerns for nearly all mammal sizes assessed using all primary exposure 
   

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assessment methods (however, large rodents, greater than 1000 g, consuming chlorophacinone 

bait for one day are not expected to experience risk concerns). EPA’s analysis indicates that <1 

day (diphacinone) and <1 to 3 days (chlorophacinone) of feeding on bait are sufficient to attain 

the median lethal dose in mammals. This is not materially different from the other rodenticides 

with respect to the opportunity for non-target mammals to chance upon and feed lethally on 

treated bait. In contrast to mammals, primary avian risk is below concern levels for these two 

compounds. This may be a limitation in the analysis of primary exposure models terminating at 

six days (i.e., longer exposure periods might provide sufficient exposure to bait for adverse 

accumulation to occur); however, the analysis indicates that, unlike brodifacoum and 

difethialone, a very consistent and protracted feeding period for either diphacinone or 

chlorophacinone is required to attain a lethal dose in birds (i.e., daily feedings over weeks to 

months). 

3. Secondary Exposure and Risk 

The toxicity of each of the rodenticides and a variety of factors concerning their fate and 

effects in biological systems influence their potential for risk to secondary consumers, i.e., nontarget wildlife that may ingest living or dead animals that have consumed rodenticide bait. These 

characteristics can be compared to predict the rodenticides’ relative potential for such secondary 

risk. The elimination rate, potential to accumulate within body tissues, time to death, and 

toxicity to both primary and secondary consumers influence exposure and risk. 

A compound that is rapidly metabolized or excreted from a primary consumer likely 

results in a lesser secondary risk to non-target predators and scavengers than one that 

accumulates with repeated exposure, even if repeated exposure occurs weeks or months after 

initial exposure (Eason and Murphy 2000). Compounds that more rapidly clear from the body 

are less likely to pose secondary risk because the rodenticide is less able to accumulate to a level 

sufficient to affect a secondary consumer. Time to death also influences the potential for 

exposure, since compounds that kill rapidly would prevent the primary consumer from 

continuing to eat bait, thereby consuming a dose that would be toxic to a secondary consumer. 

Rodenticides that are slower to cause death also prolong the period when contaminated (and 

potentially more vulnerable) prey are available to predators. The toxicity of the rodenticide to 

the secondary consumer would also affect the risk of adverse effects that would result from 

exposure. Based on these characteristics, rodenticides that are eliminated more slowly and have 

greater potential to accumulate within body tissues, take longer to kill the primary consumer, and 

have greater toxicity to secondary consumers are expected to present greater secondary risk. 

Below is an evaluation of the elimination and accumulation potential for each of the assessed 

chemicals. 

Accumulation and Elimination 

Information available from residue studies in primary consumers indicates that, of the 

anticoagulants, brodifacoum and difethialone accumulate in body tissues to a greater extent than 

warfarin, chlorophacinone, and diphacinone. Data from these types of studies are not available 
   

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for the neurotoxin, bromethalin, but the duration for primary consumers to feed on bromethalin 

bait and accumulate the rodenticide is limited due to this chemical's rapid mode of action and 

observations that target animals stop feeding after a lethal dose is reached. 

Available toxicokinetic data also indicate that, of the anticoagulants, brodifacoum is more 

persistent in animal tissue than all of the other rodenticides considered in EPA’s assessment. In 

one study, brodifacoum was detected in rat livers up to 200 days post exposure to a single oral 

dose of 0.2 mg a.i./kg (Hawkins et al. 1991), and up to 11.7% was detected in livers of rats after 

104 weeks following a single dose of 0.15 mg a.i./kg (Batten and Bratt 1990). Other studies 

reviewed by the Agency provide further evidence of the long-term retention of brodifacoum in 

body tissues, and half-lives range up to 307.4 days in liver tissue and 91.7 days in plasma 

(Vandenbroucke et al. 2008). The study by Vandenbroucke et al. (2008) suggests that 

difethialone may be much less persistent in the body than brodifacoum, with a liver half-life of 

28.5 days and a plasma half-life of 38.9 days. 

Data available for difethialone suggest that this rodenticide is not as persistent as 

brodifacoum. Vandenbroucke et al. (2008) estimated the elimination half-life in liver as 28.5 

days and the half-life in plasma as 38.9 days. Studies submitted to EPA (Belleville 1986 and 

1991, MRID#s 42065010 and 42065009 respectively) indicate that the half-life of difethialone 

may be several times greater than Vandenbroucke et al (2008). Belleville (1991) calculated a 

half-life for difethialone of 74 days in liver. 

Biological persistence data available for warfarin show variation among the species 

tested; however, most of the information on tissue retention indicates that it is generally less 

persistent in the body than brodifacoum and difethialone. A liver half-life of up to 66.8 days has 

been calculated for warfarin in rats (Vandenbroucke et al. 2008), and other estimates are less 

than this value. Most data indicate that the plasma half-lives are less than 1 day. 

Available data also show that chlorophacinone and diphacinone are more persistent than 

warfarin, but less persistent than brodifacoum and difethialone. Liver and plasma half-lives for 

chlorophacinone are 35.4 days and 11.7 days (Vandenbroucke et al. 2008), respectively and a 

plasma half-life of 0.4 days has also been calculated (Belleville 1981). Half-lives for 

diphacinone have been estimated to be shorter in some species (ranging from 3 – 5.43 days), but 

liver retention times in cattle were determined to be >90 days (Fisher 2006, Fisher et al. 2003, 

Bullard et al. 1976). 

Available data on the non-anticoagulant rodenticide bromethalin suggest that it is rapidly 

eliminated by the body. While there are no data on the elimination half-life of bromethalin in 

liver, a metabolism study conducted in rats indicated a plasma half-life of 5.6 days. 

Due to the lack of available whole-body elimination data for all assessed rodenticides, 

liver half-lives were selected from the range of available data as a conservative representation of 

whole body elimination in animals consuming bait. If liver half-lives were not available, as in 

the case of bromethalin, the blood plasma half-life was used. In order to allow for comparisons 
   

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of half-lives among chemicals, liver half-lives for brodifacoum, difethialone, warfarin, and 

chlorophacinone from the same study (by Vandenbroucke et al. (2011)) were selected. Although 

this approach reduces variability due to differences attributed to laboratories, it is not necessarily 

the most conservative approach that could be undertaken. For instance, the liver half-life value 

for difethialone that was reported by Vandenbroucke (28 days) is lower than provided in other 

studies (74 days from Belleville, 1991). Though a liver half-life value is available for 

diphacinone, it is based on a study on pigs, rather than the rats used in the other studies. There is 

some indication from the available half-life studies that species react to anticoagulant 

rodenticides differently. Therefore, this pig value may overestimate or underestimate the liver 

half-life of rats for this chemical. For bromethalin, there are no available data on the liver halflife, so a blood plasma value is used instead. It is uncertain how a blood plasma half-life would 

differ from the liver half-life for this chemical. The half-lives that were used to estimate doses of 

each rodenticide in non-target and target animals are provided in Table 14. 

Table 14. Elimination half-lives for certain rodenticides based on 

elimination rates from liver. 

Rodenticide Elimination half-life (days) 

Brodifacoum 307.4 

Difethialone 28.5 

Warfarin 66.8 

Chlorophacinone 35.4 

Diphacinone 5.5 

Bromethalin 5.6* 

*Value is based on elimination from blood plasma. 

Potential to Accumulate a Lethal Dose 

The assessed rodenticides typically cause mortality several days after exposure, which 

may allow target rodents to feed for several days upon rodenticide bait before dying. This can 

lead to doses that far exceed the lethal dose. EFED estimated the extent to which an 

accumulated dose may exceed the median lethal dose of target animals. For warfarin, estimated 

doses in target rodents were 4 to 17 times the LD50 at days when mortality was observed in the 

acute oral toxicity study with the rat assuming that bait is continuously being consumed over the 

duration of the simulation. For brodifacoum, difethialone and bromethalin, estimated doses in 

target rodents ranged from 2 to 82 times the LD50. For chlorophacinone and diphacinone, 

estimated doses ranged from 3 to 13 times the LD50. This analysis indicates that target rodents 

continually consuming anticoagulant rodenticide bait may contain doses that are orders of 

magnitude above the levels that are sufficient to cause mortality. This is of particular concern 

for secondary consumers that may prey upon target rodents because they could potentially 

receive elevated doses of rodenticides. Bromethalin is not expected to result in elevated levels in 

target rodents because one effect of bromethalin poisoning is that the animals stop feeding. 
   

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a. Assessment Based on Calculated Residues in Prey 

(i) Methodology 

Exposure for secondary consumers was estimated by calculating the amount of 

rodenticide in target rodents (i.e., house mouse and rat) that represent potential prey. As with the 

primary assessment, EPA’s theoretical secondary risk assessment estimated exposure using 

allometric equations of daily food intake from the Wildlife Exposure Factors Handbook (EPA 

1993). Rodenticide intake based on consumption of bait by the primary consumers (prey) was 

calculated for the house mouse (23 g) and Norway rat (485 g). For this analysis, rodenticide 

accumulation in prey over three different time periods (1, 3 and 6 days) was calculated. These 

time periods were used as representative time periods that target rodents may survive after the 

initial daily dose of a pesticide (based on available toxicity studies) and in order to bracket the 

available data from residue studies submitted to the agency and occurring in open literature. 

Accumulation was determined based on daily food intake rates for the prey, conservatively 

assuming 100% of their diet consisted of dry bait. It was assumed that the form of the bait would 

not influence intake. Based on the assumed weight of the primary consumers, the percent active 

ingredient in the bait, and daily food intake, the concentration within the prey animal at the end 

of a day’s feeding was determined. Accumulation of rodenticide within the prey animal over 

time was calculated using an elimination rate constant based on the liver half-lives for each 

chemical (described above). This analysis is expected to produce a conservative estimate of 

exposure. 

In addition to the theoretical estimates of rodenticides in target rodents representing prey 

of secondary consumers, measured rodenticide concentrations in carcasses of rodents were used 

to represent potential exposure values for secondary consumers. Although this method of 

representing concentrations of rodenticides in prey of secondary consumers would be expected to 

be less conservative than the theoretical analysis described in the previous paragraph, both 

analyses produced similar findings. 

Dose-based exposure to secondary consumers was assessed for mammals weighing 50g, 

1000g, or 3000g, and birds weighing 100g, 1000g, or 5000g. These weights were selected based 

on the range of secondary consumers identified in rodenticide incidents in the Environmental 

Incident Information System (EIIS) database. The generic bird and mammal equations for food 

intake (Wildlife Exposure Factors Handbook) were used to calculate the daily rodenticide intake 

for predator/scavenger birds and mammals consuming house mice and Norway rats exposed to 

rodenticide bait for three or six days. Dose-based RQs were calculated by dividing the dosebased exposure values from the theoretical estimated dose by the adjusted LD50 values. 

In addition, dietary-based RQs were calculated for secondary consumers. This was 

accomplished by dividing the theoretical concentrations of rodenticides in target rodents by the 

LC50 values for birds or mammals. 
   

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Risk Estimation

Based on acute exposure of predator and scavenger birds to rodenticides accumulated in 

prey organisms, RQs for brodifacoum and difethialone exceed the Agency’s acute LOC 

regardless of assessed weight class, prey organism consumed, or accumulation scenario. RQs 

calculated for warfarin, diphacinone, and chlorophacinone do not exceed the acute LOCs for 

birds, except for small predator and scavenger birds consuming prey exposed to the higher 

concentration of warfarin (0.054%) bait for six days. The results for bromethalin fall in between 

the two anticoagulant groups, as bromethalin RQs exceed the acute LOC for all predator and 

scavenger birds consuming small prey animals (i.e., house mice), but do not exceed the acute 

LOC for large predator and scavenger mammals consuming large prey animals (i.e., Norway 

rats). When considering dietary-based exposures of predator and scavenger birds to rodenticides, 

brodifacoum and difethialone RQs exceed the acute LOC, while warfarin, chlorophacinone, 

diphacinone, and bromethalin RQs do not exceed the acute LOC. Secondary bird RQs are 

provided in Table 15. Although warfarin, chlorophacinone, and diphacinone RQs for secondary 

birds do not exceed the acute LOC, there is uncertainty associated with these values. Available 

data suggest that some predatory birds may be substantially more sensitive to diphacinone 

exposure compared to the bobwhite quail and mallard ducks that are the source of the majority of 

the avian toxicity data. If this applicable to all secondary consumers exposed to anticoagulant 

rodenticides, the secondary bird RQs calculated for these chemicals may not be conservative. 

For predator and scavenger mammals exposed to rodenticides accumulated in prey, RQs 

for all assessed chemicals exceed the acute LOC, except for predator and scavenger mammals 

exposed to a three day accumulation of chlorophacinone in large prey animals and small 

predators/scavengers exposed to six day accumulation of chlorophacinone in large prey animals. 

Dietary-based RQs exceed the acute LOC for all assessed rodenticides; however, dietary toxicity 

data in mammals are not available for difethialone or bromethalin so these chemicals could not 

be included in this analysis. Secondary mammalian RQs are provided in Table 16. 
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Table 15. RQs from the bird risk assessment: secondary exposure of predator/scavenger birds to residues consumed rodents. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Secondary exposure to carnivores and scavengers 

House mouse consumption: 3 day accumulation in prey RQ 

100 19.77* 17.09* 0.14 0.30 0.04 0.01 

1000 15.42* 5.42* 0.04 0.09 0.01 <0.01 5000 12.96* 2.43* 0.02 0.04 0.01 <0.01 

Norway rat consumption: 3 day accumulation in prey RQ 

100 5.25* 4.52* 0.04 0.08 0.01 <0.01 

1000 4.08* 1.43* 0.01 0.02 <0.01 <0.01 5000 3.43* 0.64* 0.01 0.01 <0.01 <0.01 

House mouse consumption: 6 day accumulation in prey RQ 

100 39.40* 32.98* 0.27 0.58* 0.08 0.01 

1000 30.74* 10.45* 0.09 0.19 0.02 <0.01 5000 25.84* 4.68* 0.04 0.08 0.01 <0.01 

Norway rat consumption: 6 day accumulation in prey RQ 

100 10.43* 8.73* 0.07 0.15 0.02 <0.01 

1000 8.14* 2.77* 0.02 0.05 0.01 <0.01 5000 6.84* 1.24* 0.01 0.02 <0.01 <0.01 

House mouse consumption: dietary RQ NA 17.81* 2069* 0.19 0.41 0.32 0.02 Norway rat consumption: dietary RQ NA 4.71* 5.48* 0.05 0.11 0.09 <0.01 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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Table 16. RQs from the mammal risk assessment: secondary exposure of predator/scavenger mammals to consumed rodents. 

Body weights (g) 

Brodifacoum Difeth- ialone Warfarin (0.025%) Warfarin (0.054%) Chloro- phacinone Dipha- cinone 

Secondary exposure to carnivores and scavengers 

House mouse consumption: 3 day accumulation in prey RQ 

50 11.10* 4.74* 8.81* 19.03* 0.84* 2.49* 

1000 13.78* 5.88* 10.93* 23.61* 1.04* 3.09* 3000 14.91* 6.37* 11.83* 25.56* 1.12* 3.35* 

Norway rat consumption: 3 day accumulation in prey RQ 

50 2.94* 1.25* 2.33* 5.04* 0.22 0.66* 

1000 3.65* 1.56* 2.89* 6.25* 0.27 0.82* 3000 3.95* 1.68* 3.13* 6.76* 0.30 0.89* 

House mouse consumption: 6 day accumulation in prey RQ 

50 22.13* 9.15* 17.35* 37.48* 1.63* 4.20* 

1000 27.46* 11.35* 21.53* 46.51* 2.02* 5.21* 3000 29.72* 12.28* 23.30* 50.33* 2.18* 5.64* 

Norway rat consumption: 6 day accumulation in prey RQ 

50 5.86* 2.42* 4.59* 9.92* 0.43 1.11* 

1000 7.27* 3.00* 5.70* 12.31* 0.53* 1.38* 3000 7.87* 3.25* 6.17* 13.32* 0.58* 1.49* 

House mouse consumption: dietary RQ NA 44.69* ND 26.64* 57.54* 20.42* 10.11* Norway rat consumption: dietary RQ NA 11.23* ND 7.05* 15.23* 5.41* 2.68* 

NA = not applicable ND = no data * RQ exceeds acute risk LOC = 0.50 
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Whole Carcass Residue Analysis 

As discussed above, EPA also assessed secondary risks by analyzing residues in test 

animals that had consumed contaminated carcasses. This analysis differs from the theoretical 

carcass concentration-based risk assessment in that it makes use of measured residues in 

intoxicated target organisms as a basis for dietary exposure in scavengers and predators. Using 

actual animal concentrations eliminates some uncertainty associated with bait feeding, 

absorption, and elimination rates used in the theoretical assessment. However, alone, this 

method is limited by the types and magnitude of rodenticide exposure in the prey base (i.e., the 

animals intoxicated at the primary exposure level). A concordance of risk conclusions made 

using this method with conclusions based on the theoretical method allow for more confidence in 

the risk conclusions overall; however, if the empirically-based RQs calculated in this section do 

not exceed the LOC, risk cannot necessarily be precluded, especially if the theoretically-based 

RQs do exceed the LOC. 

In field and laboratory studies, rodenticide whole-carcass residues were determined in 

mammals after exposure to bait. Data are available for a variety of small and medium sized 

mammalian granivores and omnivores exposed to brodifacoum, difethialone, warfarin, 

chlorophacinone and diphacinone. No data were identified for bromethalin. As with the 

theoretical assessment, rodenticide exposure through carcass consumption is calculated as mg 

a.i./kg-bw, where kg-bw is the kilograms of the consuming individual for three weight classes of 

birds and mammals as set forth above. Weight-adjusted LD50 values for birds and mammals 

were then used to calculate risk. For toxic response elicited from the dietary exposure route 

extended over several days, exposure is measured as mg a.i. residue/kg-diet. Toxicity is 

measured by the LC50 obtained from the dietary studies (5 days on treated diet) for birds and 

mammals. 

 

The acute LOC was exceeded for secondary exposure risk to birds for brodifacoum and 

difethialone; however, RQs for secondary exposure risk to birds exposed to warfarin did not 

exceed the acute LOC. RQs for secondary exposure risk to birds exposed to chlorophacinone or 

diphacinone on an acute basis did not exceeded the acute LOC. Carnivore/scavenger mammalian 

RQs for brodifacoum and difethialone exceeded the acute LOC. For warfarin, chlorophacinone, 

and diphacinone, RQs did not exceed the acute LOC, as shown in Table 17. 

Table 17. Secondary Acute RQs based on a Single-dose of Rodenticide through 

Consumption of Contaminated Carcasses

Predator Birds Mammals 

Predator Weight 

Class

100 g 1000 g 5000 g 50 g 1000 g 3000 g 

Brodifacoum 6.42* 5.01* 4.21* 3.59* 4.46* 4.83* 

Difethialone 4.64* 1.47* 0.66* 1.41* 1.75* 1.89* 

Warfarin < 0.01 < 0.01 < 0.01 0.26 0.32 0.34 

Chlorophacinone < 0.01 < 0.01 < 0.01 0.07 0.08 0.08 

Diphacinone < 0.01 < 0.01 < 0.01 0.19 0.23 0.25 
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Table 17. Secondary Acute RQs based on a Single-dose of Rodenticide through 

Consumption of Contaminated Carcasses

Predator Birds Mammals 

Bolded (*) RQs exceed acute risk LOC (0.5). 

Avian and mammalian RQs based on dietary studies are provided in Table 18. Carnivore 

and scavenger bird RQs for brodifacoum and difethialone exceeded acute risk LOCs. Warfarin 

RQs for carnivore and scavenger birds did not exceed any LOCs. RQs for birds exposed to 

chlorophacinone and diphacinone in their diet do not exceed acute risk LOCs. For carnivore and 

scavenger mammals, RQs for brodifacoum and warfarin exceed the acute risk LOC. There are 

no available mammalian dietary data for difethialone or bromethalin. For the alternative 

rodenticides with conforming labels, mammalian RQs for chlorophacinone and diphacinone 

exceeded the acute LOC. 

Table 18. Secondary Dietary RQs based on a 5-day Exposure of Rodenticide through 

Consumption of Contaminated Carcasses 

 Birds Mammals 

Brodifacoum 5.25* 13.17* 

Difethialone 5.54* ND 

Warfarin < 0.01 0.67* 

Chlorophacinone 0.02 1.39* 

Diphacinone < 0.01 ND 

ND = no data 

Bolded (*) RQs exceed acute risk LOC (0.5). 

b. Secondary Feeding Studies 

 Secondary feeding studies address a number of uncertainties associated with the 

quantitative dose-based risk estimation methods using theoretical or empirically based prey-base 

concentrations estimates of rodenticide. The feeding studies empirically account for primary 

organism feeding, absorption and elimination uncertainties surrounding the theoretical dosebased assessment. They also account for uncertainties associated with biological availability of 

rodenticide from consumed prey and assumptions of predator/scavenger sensitivity to the 

rodenticide which are present in both of the dose-based risk estimation methods. Concordance 

between risk conclusions between all three methods constitutes enhanced confidence in the 

overall risk conclusions made for predators and scavenging wildlife. 

 

Concerns for secondary risks with brodifacoum are supported by available data from 

secondary toxicity studies showing mortality in 63% of predator/scavenger birds and 42% of 

predator/scavenger mammals fed brodifacoum contaminated target organisms. No secondary 

feeding data are available for difethialone. 
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In the case of warfarin, mammalian secondary feeding studies involving mammal 

predators/scavengers show mixed results and for some species the differences extended to a 

dose-dependent response. No mortalities were observed in raccoons and European ferrets (no 

dose dependency and bait concentrations equal to or higher than levels found in US registered 

products). Other studies showed lethalities in mink, least weasels and dogs, though the results 

often involved few test organisms. Avian secondary feeding studies involved testing of four 

species. In three of the four species tested there was no observed mortality. Interestingly, the 

results from feeding tests do not completely parallel the results of the quantitative secondary risk 

assessment where risks were expected for small birds exposed to prey contaminated with higher 

concentrations of warfarin bait. For example no mortality was observed in the feeding studies 

with black-billed magpies (~170 g bodyweight) while the risk assessment suggests a concern for 

a 100 gram bird. Conversely, mortality results were mixed in larger birds of similar weights 

(death in barn owls but not in tawny owls both ~400-500 g body weight). These discrepancies 

may be indicating that allometric relationships for predicting effects of warfarin toxicity may 

incompletely explain the factors contributing to species sensitivity variability. 

Bromethalin secondary feeding studies are limited to a single case. In that study 

involving domestic dogs fed intoxicated rats there were no mortalities (n=4). The number of 

species tested is limited and so there is insufficient evidence from these data alone to make 

definitive conclusions regarding the accuracy of the secondary quantitative risk assessment 

results. No bird feeding studies were available for bromethalin. 

Chlorophacinone secondary toxicity results include studies with five mammal species. 

Mortality responses were variable and ranged from approximately 50 percent to 100 percent of 

individuals tested. In one single species, European ferret, different studies yielded highly 

variable results, ranging from zero to 100 percent mortality. It should be noted again that all 

these studies involve a low number of test individuals and differences in perceived sensitivity 

may be as much a product of low number of individuals as from real differences in toxic 

response across species. Avian feeding studies with chlorophacinone span 10 species with a 

wide range of bodyweights (170 to 4400 g). In no cases were mortalities observed. This is 

consistent with the secondary risk assessment. 

 Diphacinone secondary feeding data span studies from seven mammal species. The 

effects range from 0 to 100 percent mortality. Of particular note is the study involving actual 

secondary feeding with rats. This is of note because (1) the secondary exposure risk assessment 

used a rat acute toxicity endpoint as a surrogate for predators and scavengers and (2) the assumed 

prey item concentrations in the risk assessment were 10 to 20 times higher than tested in the 

feeding study. The feeding study with rats yielded a 50 percent mortality response under 

conditions of similar toxicity and lower exposure than modeled conditions showing risk. 

Looking back on the quantitative risk results, substituting the modeled diphacinone dietary 

concentrations with the actual concentrations used in the feeding study would still trigger 

secondary acute risk concerns. These results are considered supportive of the secondary risk 

assessment with mammals. Avian feeding studies with diphacinone span five species of varying 

bodyweights. In three species there were no mortalities, consistent with the secondary risk 

assessment results. In the case of two owl species, mortalities were observed contrary to the risk 
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assessment results. As discussed earlier, the toxicity endpoint relied upon in the risk assessment 

may underestimate the sensitivity of raptoral species to this chemical. 

a. Estimation of number of prey animals equal to median lethal dose in secondary animals 

 As evaluated in the secondary exposure risk assessment, residues were estimated and 

observed to reach levels in target organisms that, when consumed by predators and scavengers 

can result in death. When considering those risks among the assessed rodenticides it is important 

to consider the likelihood of predators and scavengers encountering enough intoxicated target 

prey to reach potential lethal doses. Furthering the evaluation of secondary exposure of 

rodenticides are the results of analyses of the number of individual target organisms necessary 

for dietary consumption to achieve a lethal dose in predators and scavengers. The fewer the 

number of intoxicated target organisms necessary to reach a lethal dose, the less efficiently and 

intently a predator or scavenger must locate and consume these organisms to reach lethal body 

burdens. The analysis considered different bodyweights of predator/scavengers consuming 

either rats or mice which have ingested bait for a single day or up to six days. Again, 

compounds that can present a lethal dose to predators and scavengers after consumption of target 

organisms with only a single day of exposure are likely to represent greater opportunities for 

lethal secondary exposure events than those which require multiple days of target organism 

exposure . 

 Analyses were conducted to determine the number of rodenticide-intoxicated target 

organism a predator/scavenger mammal would need to consume in order to trigger lethal 

incidents (Table 19). Based on these analyses, every size predator/scavenger mammal exposed 

to brodifacoum through consumption of rats would only need to consume a fraction of a single 

target organism to reach lethal endpoint exposures, even if the rat fed on brodifacoum bait for 

just one day. Comparing brodifacoum results for predator/scavenger mammals to other assessed 

rodenticides does not reveal a marked difference among the chemicals. Owing to their smaller 

size, consumption of brodifacoum intoxicated mice must be slightly more intensive for the 

predator/scavengers to reach lethal endpoint exposure (<1 to 5 organisms) as compared to rats. 

These results are not atypical of the results for difethialone, warfarin and bromethalin assessed 

rodenticides. However, the amount of brodifacoum that must be consumed to reach lethal 

exposure is substantially lower than diphacinone and chlorophacinone. 

Similar analyses were conducted to determine the target organism numbers necessary to 

trigger lethal incidents in scavenger/predator birds (Table 19). Brodifacoum results show 

consumption of only a fraction of an intoxicated rat, regardless of rat exposure duration, is 

needed to reach lethal endpoint exposures in all bird sizes modeled. These results with 

brodifacoum are similar to results with difethialone, but are greater for the other assessed 

rodenticides, particularly for warfarin. Mouse consumption would have to be higher than rat 

consumption, though not substantially so (<1 to 5 organisms consumed) for brodifacoum. 

Again, these results are comparable to difethialone and slightly lower than bromethalin. 

However, similar analyses conducted with warfarin, chlorophacinone, and diphacinone reveal 

that consumption of intoxicated mice must reach much larger levels to reach lethal exposure 

endpoints. When taken together, these analyses suggests that brodifacoum has a substantially 
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 47 ~ 

 

greater opportunity than these other active ingredients to result in lethal incidents following 

exposure of a predator/scavenger bird to intoxicated target organisms. 

Table 19. Secondary Exposure to Predators and Scavengers: Number of animals 

consumed to reach the LD50 from a 1 day accum. in prey 

Body weights 

(g) 

Brodifacoum Difethialone Warfarin 

(0.025%) 

Warfarin 

(0.054%) 

Chlorophacinon

e 

Diphacinone Brometh

-alin 

Secondary Avian Exposure 

 house 

mice 

100 <1 <1 38 18 130 821 1 

1000 2 4 539 249 1836 11602 16 

5000 5 27 3429 1587 11690 73852 104 

 Norway 

rats 

100 <1 <1 7 3 23 147 <1 

1000 <1 <1 97 45 329 2079 3 

5000 <1 5 614 284 2094 13232 17 

Secondary Mammalian Exposure 

house 

mice 

50 <1 <1 <1 <1 3 <1 <1 

1000 2 5 3 1 27 8 5 

3000 5 11 6 3 60 18 11 

Norway 

rats 

50 <1 <1 <1 <1 <1 <1 <1 

1000 <1 <1 <1 <1 5 1 <1 

3000 <1 2 1 <1 11 3 2 

a. Risk Discussion 

The assessment of secondary exposure risks for wildlife involved a series of assessment 

methodologies that encompassed both theoretical accumulation of rodenticides in a prey base as 

well as empirical measurements of rodenticide residues in prey. This assessment concluded that 

all of the assessed rodenticides pose a risk of mortality to secondary mammals. Some of the 

rodenticides pose a risk to birds. Based on the analysis of the number of prey organisms that 

would have to be consumed in order for predators and scavengers to receive an LD50 dose, the 

following general conclusions can be made: 1) brodifacoum, difethialone, and bromethalin pose 

greater secondary risk than warfarin, chlorophacinone, and diphacinone; however, secondary risk 

from bromethalin is somewhat limited due to the lower likelihood of continuous feeding of prey 

after reaching a lethal threshold, and 2) prey that have accumulated more rodenticide through 

longer exposure periods pose greater secondary risks to predator/scavenger birds and mammals. 

4. Incident Findings Related to Primary & Secondary Risk Analyses 

 The quantitative risk assessment does not evaluate the actual potential for wildlife to 
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 48 ~ 

 

come into contact with treated bait; it simply evaluates the consequences of exposure. To 

determine if any documented adverse effects have been reported, indicating complete exposure 

pathways, EPA looks to available incident and exposure information from a variety of sources, 

including state and local governments and pesticide registrants. The majority of available 

reported incidents for the rodenticides assessed are included in EPA’s Environmental Incident 

Information System (Version 2.1) EIIS. EPA believes these data offer strong support for the 

conclusion that residential use of rodenticides in urban/suburban and rural areas provide 

complete exposure pathways to a variety of wildlife and that primary exposure lethal incidents 

involving non-target wildlife can occur. Table 20 presents the total number of reported incidents 

associated with each of the rodenticides considered in EPA’s assessment. Where possible, EPA 

distinguished between incidents resulting from primary and secondary exposures. 

Table 20. Total Number of Wildlife Incidents by Rodenticide Active Ingredient and 

Exposure Type. Incidents occurred between 1971 and 2011.

Rodenticide 

Active 

Ingredient 

Exposure Type 

Primary Secondary Unknown Total 

Brodifacoum 44 186 37 267 

Birds 

3 

Mammals 

41 

Birds 

164 

Mammals 

22 

Birds 

21 

Mammals 

16 

Birds 

188 

Mammals 

79 

Difethialone 1 4 0 5 

Birds 

 0 

Mammals 

1 

Birds 

3 

Mammals 

1 

Birds 

0 

Mammals 

0 

Birds 

4 

Mammals 

1 

Chlorophacinon

e 

6 4 1 11 

Birds 

3 

Mammals 

3 

Birds 

3 

Mammals 

1 

Birds 

1 

Mammals 

0 

Birds 

7 

Mammals 

4 

Diphacinone 10 9 0 19 

Birds 

1 

Mammals 

9 

Birds 

5 

Mammals 

4 

Birds 

0 

Mammals 

0 

Birds 

6 

Mammals 

13 

Warfarin 3 5 0 8 

Birds 

1 

Mammals 

2 

Birds 

5 

Mammals 

0 

Birds 

0 

Mammals 

0 

Birds 

6 

Mammals 

2 

Bromethalin 1 0 0 1 

Birds 

0 

Mammals 

1 

Birds 

0 

Mammals 

0 

Birds 

0 

Mammals 

0 

Birds 

0 

Mammals 

1 

Totals 65 208 38 311 

Birds 

8 

Mammals 

57 

Birds 

180 

Mammals 

28 

Birds 

22 

Mammals 

16 

Birds 

211 

Mammals 

100 

* Incident counts exclude incidents with certainty levels of “unrelated” and “unlikely,” excludes incidents known to 

be associated with intentional misuse, and excludes incidents associated with other active ingredients. 

 In evaluating EPA’s incident database for rodenticides, it is important to understand 

that incidents that have been reported likely represents only a fraction of the incidents that have 

occurred. Because of the delay between consumption of a lethal dose and death associated with 

the rodenticides considered in this analysis, the discovery of animals killed by these rodenticides 

is typically removed, both spatially and temporally, from the immediate site of rodenticide use. 

As a result, the cause of death generally is not obvious to persons finding animals killed by these 
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rodenticides. Only when the mortality is reported to an authority, typically a state fish and 

wildlife office, and that agency conducts an investigation that diagnoses the cause of death is an 

incident linked to rodenticide exposure. The investigating agency may then take tissue samples 

from the animal, normally from the liver, and have laboratory analyses performed to screen for 

the presence of various rodenticides, as well as various other pesticides. Only when the residue 

analysis finds one or more rodenticides in the tissue of the dead animal does the incident become 

diagnosed as a suspected or confirmed rodenticide incident. Because the linkage between 

wildlife mortalities and exposure to the rodenticides subject to this Notice depends on thorough 

investigations, including residue analysis of tissue samples, incident reporting rates vary greatly 

from state to state and likely depend largely on whether the state has the personnel and resources 

to conduct and report investigations. Only two states, New York and California, have had 

programs that have systematically analyzed and reported wildlife mortality incidents, and thus 

are responsible for the majority of known rodenticide incidents. Many states have never reported 

any wildlife mortality incidents related to rodenticides. Given these considerations, and the fact 

that most dead or dying animals are never seen by humans, EPA believes the vast majority of 

wildlife incidents from exposure to rodenticides go unreported. The general character of the 

reported incidents for each chemical are briefly discussed below. 

Notwithstanding the likely extent of underreporting of wildlife incidents, the available 

data do support the quantitative risk assessment’s conclusion that both primary and secondary 

exposure to brodifacoum poses lethal risk to a variety of sizes of mammals and birds. Incidents 

expected to represent likely primary exposure to brodifacoum, include a range of non-target 

mammalian wildlife mortalities, ranging in size from chipmunks to white-tailed deer, consistent 

with the modeled size classes reported to be at risk. For birds, incidents representing likely 

primary exposure involved species ranging from robins to geese, again consistent with the risk 

model predictions. Incidents representing likely secondary exposure to brodifacoum range from 

foxes to mountain lions, consistent with the modeled size classes reported to be at risk. There 

were 186 total incidents for brodifacoum attributed to secondary exposure. For birds, incidents 

likely involving secondary exposure include a variety of raptors, again consistent with the risk 

model predictions for larger birds. These incidents occurred in urban/suburban and rural habitats. 

In sum, incident data indicate that likely lethal events from both primary and secondary exposure 

to brodifacoum for non-target wildlife can occur in rural, suburban, and urban environments. 

The incident data set for difethialone is much more limited than that for brodifacoum. 

Analysis of the toxicity and retention time of difethialone indicates that it is toxicologically 

similar to brodifacoum, suggesting that the lack of observed incidents for this ingredient could be 

due to the low use or to other factors not related to risk. Nevertheless, one lethal incident 

apparently resulting from direct exposure to difethialone treated bait has been reported, involving 

Key deer in a suburban environment. This incident is consistent with the primary risk 

assessment. There are no reported primary incidents involving difethialone and bird species, 

though one should conclude that this finding, confounded by low use of the chemical, neither 

supports nor refutes the primary risk assessment findings. With regard to secondary exposure 

risk, there is a lethal incident involving predatory birds and mammals. All the available 

difethialone incidents are associated with urban/suburban areas. 
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Warfarin incidents with non-target wildlife generally parallel the findings of the 

quantitative risk assessment for primary exposure to this chemical in that primary exposure 

incidents have been reported and complete exposure pathways are confirmed. Little can be said 

regarding the land use characteristics in areas where incidents were reported, which is likely a 

factor of the age of the incident reports. Incidents of secondary poisonings to non-target 

mammals from warfarin have not been reported; however, reported incidents for birds exposed to 

warfarin include a variety of raptoral species presumed to be secondary consumers. These 

secondary exposure incidents are consistent with the quantitative secondary risk assessment and 

are in partial agreement with the available secondary feeding toxicity studies. Incident data 

indicate that likely lethal events from secondary exposure to warfarin for non-target wildlife can 

occur in rural, suburban and urban environments. 

The incident data set for primary exposure of animals to bromethalin is limited to a 

reported mortality of a chipmunk, and this incident involved a commensal rodent control 

product. This limited information is consistent with a quantitative risk assessment that indicates 

a risk to small mammals exposed to treated bait, yet provides little support for the risk 

assessment predictions for larger mammal. There are no incidents involving bromethalin and 

bird species expected to involve primary exposure to treated bait materials. There may be an 

extenuating issue that explains the absence of reported incidents for this chemical. As discussed 

in the incident section of the ecological risk assessment, bromethalin is not a commonly assayed 

compound when investigating wildlife mortality incidents. The incident data set for bromethalin 

related to secondary exposure of animals is limited to birds. This limited information can neither 

support nor refute the mammalian secondary risk assessment but is consistent with the 

quantitative risk assessment for secondary exposure in birds. 

Chlorophacinone incidents of high certainty involving mammals of likely primary 

exposure to bait are scarce but include reports of mortalities in squirrels (Central Park, New 

York) which would be in agreement with the primary exposure risk assessment predictions for 

small mammals. Larger mammal incidents attributable to primary exposure to this chemical are 

not reported. An incident report with a likely primarily exposed bird (California quail in an 

orchard) suggests the possibility that risk from chlorophacinone from primary exposure to birds 

is greater than indicated in the primary risk assessment. Chlorophacinone incidents of high 

certainty involving mammals and birds of likely secondary exposure are scarce but include 

reports of mortalities in wild felids (bobcats) and raptors (red-tailed hawk). The mammal 

incident is consistent with the secondary risk assessment findings. The bird incident is 

inconsistent with the secondary risk assessment. It may be possible that chlorophacinone mirrors 

diphacinone in terms of the sensitivity of raptors being possibly greater than the test species 

employed in the risk assessment (i.e. a 20 fold increase in sensitivity). If the chlorophacinone 

secondary risk assessment was adjusted for this possible increased sensitivity in raptors the 

secondary risk conclusions would then be consistent with reported incidents for dietary subacute 

portions of the analysis but not for the single oral dose analysis. On balance, secondary 

lethalities to birds may occur but the strength of this prediction for this chemical is limited. 

The diphacinone incident data set for mammals is similar to that for chlorophacinone, in 

that the only incident involves a squirrel in an urban setting (Central Park, New York). Again, as 
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for chlorophacinone, there is a diphacinone incident involving a likely primarily exposed bird 

(turkey), again suggesting a possible greater risk to birds than indicated in the quantitative risk 

assessment. This incident involved birds feeding in the vicinity of a prairie dog town, not a 

commensal rodent control operation. Diphacinone incidents of high certainty involving 

mammals and birds of likely secondary exposure are limited but include reports of mortalities in 

wild canids, mustilids and felids (fox, coyote, raccoon, and mountain lion) and raptors (snowy 

and barred owls, red-tailed hawk). The mammal incidents are consistent with the secondary risk 

assessment findings. The bird incidents are inconsistent with the modeling portions of secondary 

risk assessment but consistent with available feeding studies, especially for owls. If the 

diphacinone secondary risk assessment was adjusted for the possible increased sensitivity in 

raptors the secondary risk conclusions would still yield risk quotients below concern levels. On 

balance secondary lethalities to birds may occur but the strength of this prediction for this 

chemical is limited, though the uncertainty in concluding the possibility of a lethal risk is less 

than for chlorophacinone. 

5. Implications for Risk Mitigation 

The proposed cancellations would limit the availability of brodifacoum and difethialone 

in ways that should limit their use to professional applicators in urban and suburban areas. These 

requirements will reduce the potential for wildlife to encounter these rodenticides since most 

rodenticide placements in and around buildings or other man-made structures are made with 

consumer products. As this assessment concludes, these two rodenticides present greater risk to 

non-target species – primarily to birds – than other commensal rodenticides. While the bait 

station requirement will mitigate primary exposure to birds and larger mammals, secondary 

poisoning remains a concern for wildlife that consume mice and rats. In this regard, 

brodifacoum and difethialone present a greater risk of secondary poisoning when compared to 

other commensal rodenticides. Limiting sales of brodifacoum and difethialone in the consumer 

market will likely cause most consumers to turn to one of the other available rodenticides or to 

use alternative mechanical controls, thereby reducing overall use of and wildlife exposure to 

brodifacoum and difethialone. While the replacement compounds may still present some risk of 

secondary poisoning, EPA believes that risk will be greatly reduced. 

This notice also seeks the cancellation of certain rodenticide products in the absence of 

product changes requiring consumer commensal rodent control products to be sold in or with 

appropriate bait stations and in bait forms that are not readily removable from such stations. 

While labels of these products may currently direct the consumer to use bait stations to limit 

exposure to children and wildlife, it is readily apparent that such restrictions have been 

unsuccessful in preventing harmful exposures. EPA expects that the proposed bait station 

restrictions will reduce the geographic extent of bait dispersal across the landscape. As scattered 

bait may offer an increased opportunity for casual encounter with rodenticides when compared 

with a more focally placed bait station moving to bait stations is likely to result in a reduction of 

encounters of wildlife directly with rodenticides which may be especially significant for 

chemicals such as brodifacoum, difethialone, bromethalin and warfarin where only a few feeding 

episodes are sufficient to cause mortality. Moving to bait stations is also likely to result in a 

reduction of predatory and scavenger wildlife encounters with intoxicated prey species because 
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the number and range of affected prey species should be reduced if less scattered bait is 

available. While loose bait will still be available to professional applicators following this 

action, it is EPA’s belief that professional users (including persons who routinely apply 

pesticides as a minor part of their job, as well as full-time professional pesticide applicators) are 

more likely to choose a method of pest control appropriate for the specific circumstances, more 

likely to appreciate the consequences and liability of pesticide misuse, and are in most cases 

acutely sensitive to the economic consequences of overuse. For these reasons, EPA believes that 

pesticides generally pose less risk when applied by professional users than when applied by the 

general public. In the case of rodenticides containing brodifacoum and difethialone, EPA 

believes that this difference is significant enough to warrant taking steps to limit access to these 

products to professional users. Also, the requirement of bait stations and block or paste 

formulations will reduce the likelihood of indiscriminant spreading of pellets on the ground 

which could lead to primary exposures. 

 In addition to the issue of geographical distribution of rodenticide, the requirement for 

bait stations may further limit access to the bait itself. Bait stations are optimized for the 

commensal rodent body size (mice and rats); larger mammals are physically limited by the 

station portal size preventing them from reaching the bait within. And for predators that may 

feed on a variety of sizes of prey species, narrowing the sizes of affected exposed prey will likely 

reduce the proportion of exposed prey in the total diet and so reduce the overall availability of a 

rodenticide to the predator. In addition, the requirement for bait to be in a form not readily 

removable from the stations will further reduce the opportunity for wildlife to come in contact 

with the enclosed bait. 

 

6. Endangered Species Considerations for Rodenticide Active Ingredients

 The Agency has concluded that the rodenticides subject to this Notice pose a risk to nontarget wildlife. By extension, these chemicals would also pose a risk of direct effects to federally 

listed threatened and endangered species. Further, potential indirect effects to any species 

dependent upon a species that experiences effects from use of rodenticide active ingredients 

cannot be precluded based on the deterministic ecological risk assessment. These findings are 

based solely on EPA’s deterministic assessment and, because they do not take into account such 

factors as whether the species would be expected to be exposed to rodenticide active ingredients, 

do not in themselves constitute “may affect” findings under the Endangered Species Act. EPA 

previously 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. EPA has not in large 

measure implemented recommended measures provided in that 1993 opinion, but in March 2005, 

initiated informal consultation. That informal consultation for the nine rodenticides registered at 

that time was 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, 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 
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 53 ~ 

 

threatened and endangered species, for example the San Joaquin kit fox and northern spotted owl. 

In addition, reported incidents include the bald eagle, which is protected under the Bald and 

Golden Eagle Act. While the action EPA is taking in this Notice will likely serve to reduce risks 

to a number of protected species, this action is not intended to resolve the need for mitigation to 

address federally listed and other protected species. Should EPA determine, as a result of its own 

further assessment, or through consultation with the Service, that additional restrictions on use are 

necessary to address adverse impacts to listed and other protected species or designated critical 

habitat, EPA may initiate other appropriate action to address such impacts. 

VII. Benefits 

EPA examined several potential impacts of the proposed cancellation of the rodenticide 

products identified in this Notice, including: 

• Whether residential consumers can achieve the same level of control over rodent 

infestations. 

• Whether it may take longer for residential consumers to achieve control of their rodent 

problems. 

• Whether the cost of rodent control, including non-monetary costs, may increase. 

Overall, there is no evidence to conclude that cancellation of these products will result in 

the loss of a residential consumer’s ability to control commensal rodents, or increase the time 

required to control commensal rodents. As a result of the proposed cancellation, a majority of 

residential consumers switching from cancelled mouse control products to consumer-use 

rodenticide products that would continue to be available post-cancellation are expected to incur 

incremental costs that range from $2 to $12 per infestation, when switching to rodenticide 

products that conform to the RMD with products for mouse control accounting for about 90% of 

rodent control products sales (Kline, 2006). The largest proportion of affected residential 

consumers (those treating for mouse infestations who currently use loose-form rodenticides) are 

expected to see an average increase in cost of $1.50 to $3.00 per infestation. Residential 

consumers currently using rodenticides for rat control that will continue using rodenticides postmitigation could potentially incur a cost savings or an increase in costs up to $97 per rat 

infestation. Lower cost, mechanical control options are also available, but would entail some 

additional non-monetary costs, such as disposing of dead rodents. The additional cost is 

generally less than 2% of the monthly non-housing income for a family of three at the poverty 

line, and a considerably smaller proportion for the majority of residential consumers. 

The following provides an overview of the methodology used in EPA’s impact 

assessment, targeted pests, the use and advantages of the rodenticide products EPA intends to 

cancel and their alternatives, and expected impacts on households that would be affected by the 

proposed cancellation. 
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A. Methodology 

EPA’s analysis explores the potential impacts incurred by households currently using one 

of three general types of rodenticide baits: block form rodenticides sold without bait stations; 

second generation rodenticides that are in loose form, such as bait bits, pellets, whole grain, 

meal, and powder, and second generation rodenticides sold in bait stations. However, EPA’s 

marketplace survey of prices found no examples of several of the products subject to this Notice, 

and no examples of FGARs in loose form. SGARs with bait stations were found in two forms. 

They may be sold as pre-baited, single-use stations (i.e., a single bait sold with the station, which 

is then discarded), or they may be packaged as a single reusable bait station with multiple bait 

blocks. The latter are intended for multiple use and may be more relevant to consumers with 

chronic problems or who use them as part of an exclusion program. Since the single-use and 

multi-packs seem to have different use patterns, EPA considers them separately. 

 

 To assess the impacts of cancelling these three types of products, EPA identifies the 

target rodents and describes how the products are used. The Agency then identifies available 

alternatives and compares their performance in terms of ability and time to achieve control of an 

infestation. EPA also compares other factors that may be considered advantageous or 

disadvantageous, such ease of use and disposition of carcasses, and compares control costs. 

Finally, EPA draws conclusions about the most likely alternatives that will be used in the 

absence of the cancelled products and the impacts of cancellation. 

B. Uses of rodenticides 

Rodenticides are formulated in baits to make them palatable to rodents. Regardless of 

form (i.e., block, loose, or in stations), baits placement will essentially be the same. Baits need 

to be placed in the areas where the rodents are active, typically in their runway, and about 6 to 10 

feet apart. It is often difficult to determine just how many rodents have invaded a home, but the 

amount of droppings helps to inform whether it is a minor infestation or a major infestation. 

Regardless of the method of control, residential consumers need to continually monitor their 

homes for rodent signs during the course of control operations until signs of rodents are no 

longer detected. All the rodenticides take about 3 to 5 days to kill and all rodents may not feed 

immediately. Thus, a typical control program will last from about a week to 10 days. 

Effective use of rodenticides depends on a number of factors including the size and shape 

of the infested area and the size of the infestation. Use of multiple bait placements will increase 

the likelihood that rodents will find and consume them. To characterize the likely range of use, 

EPA evaluated scenarios for a minor infestation and a major infestation, which would encompass 

lesser and greater areas and numbers of rodents. Based on university agricultural extension 

agencies and government recommendations for homeowners to control rodents, EPA concludes 

that six bait placements (e.g., a block, packet, or baited station) would be needed in the case of a 

minor infestation of rodents, and 12 placements would be needed for a major infestation of 

rodents (CDC 2010; Pierce 1993; Koehler and Kern, 2008; Hovanic et al., 2010; Illinois 

Department of Public Health undated). 
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C. Advantages of second generation anticoagulants 

Many of the rodenticides are anticoagulants, which interfere with the animal’s blood 

clotting abilities, resulting in it hemorrhaging to death. The first generation anticoagulant 

rodenticides used in products currently registered in the U.S. include: warfarin, diphacinone, and 

chlorophacinone. Baits using these active ingredients deliver a lethal dose after multiple small 

feedings, (i.e. if the targeted rodent feeds on them for several nights in a row). Consequently, it is 

important to maintain fresh bait and reduce the availability of other food options for rodents to 

consume a lethal dose. 

Rodenticides known as the second generation anticoagulant rodenticides were developed 

to be effective against rodents resistant to warfarin (Hadler and Shadbolt, 1974; Rowe and 

Bradfield, 1975; Dubock and Kaukeinen, 1978). They include: brodifacoum, bromadiolone, 

difethialone, difenacoum, plus others not registered in the U.S. Most second generation 

anticoagulant bait products are formulated such that rodents that eat enough bait may obtain a 

lethal dose in one night of feeding on these rodenticides. Therefore, second generation 

anticoagulants offer the dual benefits of greater performance against rodent populations that are 

resistant to warfarin , and the potential for delivering a lethal dose in a single night’s feeding. 

This provides an advantage where alternative food sources are ubiquitous, such as agricultural 

and food processing establishments, and outdoor public health and sanitation situations such as 

urban alleys and trash collection areas. In residential settings, food sources for rodents are 

generally limited, making multiple feedings on the bait more likely, and the advantage of 

possibly delivering a lethal dose in a single night’s feeding less important. 

D. Advantages of loose baits and bait blocks without bait stations 

Some rodents may be more willing to eat baits in loose forms, including pellets, grain and 

loose meal. Loose baits come in various sizes and rodents are able to pick them up and eat them 

like a seed or nut. Loose baits can be easier to place in hard to reach areas than bait stations and 

bait blocks. Gnawing is a prominent behavior of commensal rodents, and once they recognize a 

block as food they have no difficulty consuming it. Bait blocks formulated with paraffin, grain 

and other materials were originally developed for use in sewers and other wet and damp areas, 

where they remain the bait form of choice. Studies have shown no consistent differences in 

rodents’ consumption of block, pelleted, or meal formulations. Rodenticide baits must be tested 

for palatability and meet EPA’s bait acceptance criteria in order to be registered. Compared to 

bait blocks in bait stations, bait blocks without bait stations may be marginally easier to place as 

they are smaller in size, and the user does not have to orient a bait station so that its entrance is 

easily accessible to target rodents. However, bait stations offer countervailing benefits, 

including protecting the bait from moisture and dust; providing a protected place for rodents to 

feed, allowing them to feel more secure and consume more bait; keeping non-target species, 

including pets, wildlife, and children away from toxic baits; and allowing bait to be placed in 

otherwise difficult locations given weather or potential hazards to non-target animals. 
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E. Alternatives 

1. Alternative rodenticides 

There are currently more than 30 EPA registered consumer use rodenticide products for 

commensal rodents that conform to the RMD. The RMD-conforming consumer use products are 

listed at http://www.epa.gov/pesticides/mice-and-rats/rodent-bait-station.html. 

These products all meet the efficacy testing requirements that EPA has established for 

registration of rodenticides under FIFRA. In order to demonstrate the effectiveness of a 

rodenticide active ingredient, EPA requires (1) acute oral toxicity testing with wild-type rodents 

of the targeted species; (2) laboratory efficacy screening of one or more bait formulations with 

wild-type rodents 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.6

 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. 

a. Pesticidal alternatives to second generation anticoagulants 

Pesticidal alternatives to second generation anticoagulant active ingredients currently 

available for residential consumers include first-generation anticoagulants (chlorophacinone and 

diphacinone) and a non-anticoagulant, bromethalin. 

There is evidence that rats in certain locations in the U.S. have developed resistance to 

anticoagulants, primarily warfarin. As there has been little screening of commensal rodent 

populations in the U.S. for anticoagulant resistance over the past 30 years, there is little current 

information on the prevalence of resistance to anticoagulants generally, or to specific 

anticoagulants. Claims of anticoagulant resistance in the wild can be difficult to separate from 

ineffective rodent control practices (e.g., Timm, 1994a, Drummond and Rennison 1973). In 

addition, the anticoagulants have different chemistries and therefore, different mechanisms of 

binding with VKO. Consequently resistance to one anticoagulant does not indicate resistance to 

other anticoagulants. However, should rodents, resistant to the anticoagulants available to 

residential consumers, invade a home, products containing a non-anticoagulant, bromethalin, is 

available. Bromethalin causes rodents to cease feeding after a toxic dosage has been ingested, 

limiting the possibility of target rodents bearing more than a lethal dose. It is effective in small 

quantities, results in paralysis, and death usually occurs in about three days (Corrigan 1997). 

b. Rodenticide alternatives to loose baits and blocks without bait stations 

 Upon cancellation of rodenticide products labeled for residential consumer use in 

controlling commensal rodents in and around buildings and formulated as loose baits, or bait 

blocks without bait stations that meet the standards of the RMD, residential consumers will still 

 

6

 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. 
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be able to purchase a variety of registered rodenticides with bait stations that meet the standards 

of the RMD. Bait-stations have been employed in effective urban rodent control projects for 

many years, and have also been used in successful eradications of commensal rodent species 

from offshore islands. For several decades, pesticides registered for use to control commensal 

rodents have had label statements requiring use in tamper-resistant (or tamper-proof) bait stations 

where placements otherwise would be accessible to children, pets, domestic animals, and/or nontarget wildlife. 

Depending upon the species being targeted, the design of the bait station, and the specific 

control situation, bait applied in bait stations may be accepted less readily than bait applied to 

burrows or placed in the open. Some rodents (particularly Norway rats) are wary of any new 

objects in their environments, and may avoid a newly introduced bait station for a period of time, 

about 2 or 3 days. Rodents overcome this neophobia, and will enter a well-placed bait station 

and consume the bait. The shelter and protection of bait that the stations provide ultimately may 

encourage feeding and prolong the attractiveness of the bait. 

2. Mechanical alternatives 

Mechanical control of rodents (e.g., snap traps, glue boards, live trapping) is effective, 

especially for mice and when populations are relatively small. Snap traps have a long history of 

use and are an effective way to control mice and rats. Some advantages of snap traps are they 

are relatively inexpensive, they may be reused, the presence of dead rodents verifies success, and 

there is less of an opportunity for odor from decomposing rodents as compared to rodenticides 

because trapped rodents can be quickly located and disposed of daily. Some disadvantages 

include the time and effort of baiting and setting the traps; once sprung a trap will not work until 

reset; the user must dispose of dead rodents; and rats tend to be more difficult to trap than mice. 

Glue boards have a sticky substance that will catch and hold rodents that run across them. 

Some consumers may like the ease of glue boards, since there are no triggers or baits to set. 

Glue traps may be useful to kill snap trap-wary mice and are sometimes used in conjunction with 

snap traps (Illinois Department of Public Health, undated). Dampness, dust, and even 

temperature extremes will diminish the efficacy of the glue boards (Illinois Department of Public 

Health, undated). Since rodents trapped on glue boards do not die quickly, they can use their 

urine, feces, and fur to escape (Corrigan 1997). Rodents have been observed to use paper, dirt, 

or leaves to essentially create bridges over the sticky surfaces (Corrigan 1997). CDC (2010) 

does not recommend glue boards because often the rodents are not dead, thereby increasing the 

potential for disease transmission or rodent bites. 

 There are live traps available on the market for mice and rats. While some live traps use 

baits to entice rodents to enter, other live traps rely on rodent’s innate curiosity. Several models 

of these traps have holding spaces can hold multiple rodents. CDC (2010) does not recommend 

the use of live traps because of increased exposure to rodents that may harbor diseases. Live 

traps require that consumers find another location to release their rodents. Because of the issues 

of humaneness as well the potential for disease transmissions, some state agencies are beginning 

to regulate the relocation of live trapped animals (Witmer and Jojola 2006). 
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3. Professional alternatives 

 

Many residential consumers routinely rely on PCOs to treat their homes for rodents and 

other pests, even though PCO services are more expensive than do-it-yourself pest control. 

PCOs have access to rodenticide products containing second generation anticoagulants, and to 

bait blocks and loose baits, that are not subject to this Notice and which are expected to remain 

available to PCOs for use in areas not accessible to children, domestic animals and non-target 

wildlife. 

F. Effects of Cancellation on Consumers’ Ability to Control Rodents 

Not all control methods are equal. However, the registered rodenticide bait products 

meet EPA efficacy standards. The FGARs generally require rodents to feed on them for several 

nights to acquire a lethal dose, but so long as palatable bait is available, there is no indication that 

rodents will not feed multiple times. Rodents may be able to obtain a lethal dose with one 

night’s feeding on the SGARs. However rodents take 4 to 7 days to die regardless of which 

anticoagulant they consume. Bromethalin has a different mode of action than the anticoagulants, 

and rodents usually obtain a lethal dose after one feeding, cease feeding, and die after 1-3 days. 

To insure that all rodents have been killed, bait must be left out until all signs of rodents are 

gone. Thus, all rodenticides will be used for about the same period of time and achieve the same 

results. The use of stations has not been shown to adversely affect rodenticide performance. 

Snap traps can perform similarly to the rodenticides. Snap traps take somewhat more 

effort since the consumer must bait them. As with rodenticides, it will generally take several 

days to eliminate an infestation and traps must be set until all signs of rodents are gone. Thus, 

control time is not likely to be substantially different from that of rodenticides. Traps also 

require that the consumer deal with dead rodents, which many may find unpleasant. Thus, while 

the level of control is likely to be similar, there may be non-monetary costs associated with the 

use of these control methods in the absence of the rodenticide products identified in this notice. 

1. Incremental costs of rodent control 

This section summarizes EPA’s analysis comparing control costs of rodenticides that 

would be cancelled to available alternatives. As previously mentioned, product groupings that 

would no longer be available to residential consumers after the proposed cancellation (the 

baseline) include: (1) block form rodenticides, (2) loose form SGARs, (3) single-use SGARs in 

bait stations, and (4) multi-pack SGARs in bait stations. Alternative product groupings that 

would remain available to residential consumers after the proposed cancellations are (1) singleuse FGAR/non-anticoagulant rodenticide blocks in bait stations, (2) multi-pack FGAR/ nonanticoagulant rodenticide blocks in bait stations, (3) traditional snap traps, (4) covered snap traps, 

and (5) glue traps. Prices for electronic and live traps were obtained, but since they are not 

recommended by CDC and there is uncertainty regarding their performance, EPA does not 

evaluate them as alternatives. Additionally, the cost for a PCO to treat an infestation is provided 
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in the analysis, but PCOs will not be affected by the proposed cancellations and thus residential 

consumers using PCOs in the baseline will not be impacted. 

For all mouse and rat control methods, the cost of rodent control in a minor infestation is 

calculated as the price of six placements and the cost of rodent control in a major infestation is 

the price of 12 placements. A single placement represents a single unit of control—i.e., one trap 

or rodenticide placement as determined by the manufacturer—and EPA assumes for purposes of 

this analysis that each placement kills one rodent. 

Overall, EPA expects that incremental costs from having to switch from rodenticide 

products currently available to those that would be available post-mitigation will be small. 

Residential consumers treating for mouse infestations are expected to switch from rodenticides 

that would no longer be available to similar rodenticide products that would be available postmitigation. Incremental costs from this change range from $2 to $12 for mouse control. 

However, loose-form rodenticides account for a majority of rodenticide sales and thus residential 

consumers using such products make up the largest proportion of those that will be impacted by 

the mitigation measures. Therefore, most residential consumers are expected to see an average 

increase in cost of $1.50 in a minor infestation and $3 in a major infestation, or $0.25 per 

placement. With 90% of rodenticides sales being for products that are intended to control mice, 

EPA concludes that a majority of residential consumers currently using rodenticides will be 

facing the impacts described above. 

For residential consumers treating for rat infestations, incremental costs range from a 

potential cost savings to $97 per infestation across all alternatives that would be available postmitigation. As in the case of mouse control, it is expected that most residential consumers are 

currently using loose-form rodenticides and will incur incremental costs ranging from $46 in a 

minor infestation to $92 in a major infestation, or $8 per placement. Only a small proportion of 

residential consumers are expected to incur these costs, however, as rat control products make up 

10% of rodenticide sales and only a portion of those sales are for loose-form rodenticides. 

 Both in the case of mouse and rat control, there are lower cost alternative control methods 

that would be available post-mitigation and result in a cost savings, as well as higher cost 

options. Although switching to alternative methods may result in a cost savings, there may be 

associated non-monetary costs such as having to dispose of rodent carcasses when using traps. 

Therefore, EPA expects that consumers currently relying on rodenticides would likely incur at 

least some incremental costs from complying with the proposed NOIC. EPA does not expect the 

proportion of residential consumers relying on PCOs to change as a result of the proposed 

cancellations, because the proposed cancellations are not expected to affect residential 

consumers’ ability to control rodents. 

2. Socio-Economic Equity Assessment 

Changes in the per-unit cost of rodent control do not completely describe the impacts that 

may arise from the proposed cancellations. To place the estimated incremental cost in context, 

EPA has considered how the proposed cancellations would affect households that are below the 
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poverty-threshold. This concern is not only that such households have less income with which to 

purchase rodent control products, but also that, as according to the U.S. Census Bureau’s 

American Housing Survey (2009), households below the poverty-threshold have a greater 

likelihood of rodent problems. 

To assess the per household impacts of cancellation, EPA compares the incremental 

costs, as presented in the previous section, likely to result from the proposed cancellations to 

household monthly disposable income (i.e., excluding housing costs) at the poverty threshold. 

Monthly income rather than annual income was considered as rodent control costs typically are 

not spread evenly through the year, but are instead episodic and possibly seasonal. As povertythreshold income varies depending on housing size, this analysis considered income for a threeperson household, which is considered the average size household in the United States (U.S. 

Census Bureau, 2005-2009). 

The impact on households at the poverty level from switching from control options that 

would no longer be available under this Notice to similar products that would be available postmitigation was also examined. For mouse control, the average incremental costs for consumers 

switching from non-RMD conforming rodenticide products to rodenticides that they would most 

likely adopt in post-mitigation ranges from a cost savings to 1% of monthly non-housing income 

at the poverty threshold for a minor infestation and up to 2% for a major infestation. For rat 

control, incremental costs for consumers at the poverty-threshold who would no longer be able to 

use non-RMD conforming rodenticide products range from a potential cost savings to 5% of 

their monthly non-housing income in a minor infestation and up to 11% in a major infestation 

 

Again, with a majority of rodenticide sales being for mouse control products, it is 

expected that impacts on most low-income residential consumers will be equivalent to 1% to 2% 

of monthly non-housing income.” 

VIII. Conclusions Regarding Whether Subject Rodenticide Products Meet the FIFRA 

Registration Criteria 

Despite mandatory label statements requiring use in tamper-resistant (or tamper-proof) 

bait stations where placements otherwise would be accessible to children, domestic animals, 

and/or non-target wildlife, each of these groups experience significant rodenticide exposures that 

cause risks of adverse effects. The rodenticide products identified in Unit IV of this Notice 

present significantly greater risks to domestic animals and non-target wildlife than other 

rodenticide products registered for the same uses, owing to various factors. Chief among these 

factors are the presence of the active ingredients brodifacoum and difethialone and/or the 

absence of a bait station conforming to the criteria of the RMD in products registered for general 

consumer use in the control of commensal rodents. The exposures to children and risks to the 

environment caused by the rodenticide products identified in this Notice are unreasonable 

because they are avoidable through the use of alternative products that are effective and 

affordable. 
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A. Cancellation and Denial of Registrations of Rodenticides Containing Brodifacoum and 

Difethialone and Intended for Residential Consumer Use. 

1. Effective alternatives to brodifacoum and difethialone are available. 

1. Alternative rodenticides are effective 

 All active ingredients and all or nearly all bait formulations containing them that are 

registered for use to control commensal rodents have met the applicable criteria for registration 

that EPA has established under FIFRA, including data requirements addressing the effectiveness 

of the products against target rodents. Products containing first generation anticoagulant and 

non-anticoagulant rodenticides have been registered based on reliable studies demonstrating 

satisfactory effectiveness against target rodents. EPA concludes that first generation 

anticoagulant rodenticides, non-anticoagulant rodenticides, and mechanical traps, when used in 

combination with prudent sanitation and exclusion measures, are effective for general consumer 

use for the control of commensal rodents in and around buildings. 

 Although there is some evidence that in some situations first generation anticoagulants 

may be less effective against house mice than brodifacoum and difethialone, first generation 

anticoagulant products nevertheless demonstrate sufficient effectiveness to control target pests. 

However, even if there were particular situations where certain active ingredients might be less 

effective against target rodents, residential consumers would still have access to rodenticide 

products containing alternative active ingredients that can provide effective rodent control. In 

addition, residential consumers could also choose to use traps, or to hire a PCO who would have 

access to a broader range of control methods. 

One advantage of brodifacoum and difethialone over first generation anticoagulants is 

that brodifacoum and difethialone baits offer the possibility of delivering a lethal dose in a single 

night’s feeding. This may be an important advantage in situations such as agricultural and food 

processing facilities, where abundant food sources make it unlikely that rodents will return to a 

bait placement. However, in residential settings, competing food sources typically are more 

limited and can be more easily controlled, therefore the possibility of delivering a lethal dose in 

a single night’s feeding is not essential in order to achieve satisfactory rodent control. 

 

2. Alternative rodenticides are affordable 

Most residential consumers will see no increase in costs as a result of the proposed 

removal of rodenticides containing brodifacoum and difethialone from the residential consumer 

market. The majority of residential consumers use mechanical methods of control, which will 

not be affected by the proposed cancellations. Moreover, residential consumers who rely on 

rodent control services provided by housing management or PCOs will not be affected by the 

proposed cancellations. Products containing brodifacoum, difethialone and other SGARs will 

remain available to PCOs, agricultural users, commercial users, and public health officials, who 

therefore will not experience significant cost increases as a result of cancellation of the 

rodenticide products identified in this Notice. 
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The only users likely to be affected by the proposed cancellations are those residential 

consumers who purchase and use rodenticides for control of commensal rodents in and around 

buildings. These residential consumers are unlikely to experience significant cost increases as a 

consequence of the proposed cancellation of brodifacoum and difethialone products because 

there is currently no significant, consistent difference in the price of rodenticide products based 

on their active ingredients: Consumer use products containing brodifacoum and difethialone are 

not generally priced lower than competing products containing first generation anticoagulants or 

non-anticoagulant rodenticides active ingredients. Differences in price appear to be a function of 

other factors, such as the type of product, packaging and brand. Owing to the registration of 

multiple rodenticide products conforming to the RMD and marketed at prices comparable to 

those of the brodifacoum and difethialone products EPA proposes to cancel, these residential 

consumers are likely to experience negligible increases in cost. 

3. Residential consumer use of brodifacoum and difethialone causes adverse effects to nontarget wildlife and domesticated and companion animals that could be avoided. 

Wildlife monitoring studies (analysis of animals that died from causes unknown or 

unrelated to rodenticide poisoning) show that accumulation of brodifacoum residues is prevalent 

in numerous species of avian and mammalian predators and scavengers. Accumulation of 

difethialone also appears to be fairly prevalent in some areas, especially when considering the 

relatively low usage of this rodenticide in the United States. Species in which widespread 

accumulation of anticoagulant rodenticides in liver tissue has been observed include owls, 

hawks, vultures, mustelids, bobcats, and mountain lions. Notably, rodenticides are detected in 

100% of the great horned owls in central Massachusetts and 100% of mountain lions in southern 

California. Inasmuch as products containing brodifacoum and difethialone are only registered 

for use against commensal rodents in and around buildings and are not registered for field uses or 

use against other rodent species, all non-target wildlife exposures to brodifacoum and 

difethialone are believed to result from commensal rodent products registered for use in and 

around buildings.7

 Cancellation of brodifacoum and difethialone products sold to residential 

consumers is expected to reduce environmental loading of these highly toxic and persistent 

chemicals and thereby reduce secondary poisonings among non-target wildlife. Information 

from multiple lines of evidence (predictions from toxicity and metabolism studies, whole carcass 

residue studies, secondary feeding studies, and wildlife incident reports) indicate that 

brodifacoum and difethialone accumulate in body tissues to a greater extent, and persist for a 

longer time, than warfarin, chlorophacinone, diphacinone, and bromethalin. The high retention 

of brodifacoum and difethialone in the tissue of prey animals, combined with their high toxicity, 

presents significant risks of secondary exposure to non-target predators and scavengers. 

Moreover, the potential for target rodents to consume a lethal dose of brodifacoum or 

difethialone in a single night’s feeding, and then to continue to consume additional bait for 3 to 8 

days, can result in rodents with brodifacoum and difethialone body burdens well in excess of the 

dose lethal to the target pest, and in many cases in excess of the lethal dose for non-target 

 

7

 Minor exceptions are brodifacoum and diphacinone products registered to the U.S.D.A. Animal and Plant Health 

Inspection Service for its use in eliminating non-native rodents from islands where they are disrupting the 

ecosystem. “Field uses” refers to uses in crop land, non-crop areas, ditch banks, river banks, gullies, irrigation 

ditches, railroad tracks, fence lines, buffer strips, garbage dumps, landfills, orchards, and rangelands.
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predators and scavengers. 

Incident data support the quantitative risk assessment’s conclusion that secondary 

exposure to brodifacoum poses lethal risk to predator and scavenger mammals and birds, 

notwithstanding the likely extent of underreporting of wildlife incidents. The incident data set 

for difethialone is much more limited than that for brodifacoum, which is not surprising given 

difethialone’s lower extent of use in the United States. However, analysis of the toxicity and 

retention time of difethialone indicates that its risks to predators and scavengers are more similar 

to brodifacoum than to warfarin, chlorophacinone, diphacinone, and bromethalin, suggesting that 

the lack of observed incidents for this ingredient could be due to the low use or to other factors 

not related to risk. 

 All the rodenticides subject to this Notice present primary poisoning risks to non-target 

vertebrates. Primary poisoning risk for large non-target mammals and for birds can effectively 

be eliminated through the use of tamper resistant bait stations. However, the secondary exposure 

risk to predators and scavengers cannot be adequately addressed through bait stations alone. 

These risks are greater for products containing the second generation anticoagulants brodifacoum 

and difethialone than for the warfarin, chlorophacinone, diphacinone, and bromethalin. 

Brodifacoum and (to a lesser extent) difethialone are widely used by residential consumers, and 

limiting availability of these chemicals in the consumer market will likely cause most consumers 

to buy other rodenticides or to use alternative mechanical controls, thereby reducing use and 

environmental loading of brodifacoum and difethialone – and hence, secondary exposure risks 

to non-target wildlife. While switching to alternative rodenticides will not completely eliminate 

secondary exposure risks, EPA believes that these risks to wildlife will be significantly reduced 

if brodifacoum and difethialone are not available to residential consumers but are limited to the 

professional and agricultural markets. 

 

3. Conclusion. 

 Non-target wildlife exposed to rodenticides containing brodifacoum or difethialone 

experience significant adverse effects. These adverse effects occur despite label statements 

requiring use in tamper-resistant bait stations where placements otherwise would be accessible to 

non-target wildlife. Significant numbers of incidents of secondary rodenticide poisonings of 

non-target wildlife occur in urban and suburban areas, suggesting that residential and 

commercial uses of rodenticides for commensal rodent control pose significant risk to non-target 

wildlife. 

 These adverse effects could be substantially reduced if the quantity of brodifacoum and 

difethialone introduced in to the environment were reduced. While rodenticides containing 

brodifacoum or difethialone offer advantages over other rodenticides, these advantages are 

important in certain use situations and less important in others. EPA has determined that control 

of commensal rodents in and around buildings by residential consumers can be satisfactorily 

accomplished without rodenticides containing either brodifacoum or difethialone. EPA has 

determined that the level of commensal rodent control achieved in and around buildings by 

general consumers can also be achieved using alternative methods that significantly reduce risks 
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to non-target wildlife and domestic animals. These alternatives, including registered rodenticide 

products containing warfarin, chlorophacinone, diphacinone, and bromethalin, and mechanical 

rodent control devices, are available on the market at costs comparable to products containing 

brodifacoum or difethialone, and, when used in combination with prudent sanitation and 

exclusion measures, are effective for general consumer use for the control of commensal rodents 

in and around buildings. 

 Inasmuch as rodenticides containing warfarin, chlorophacinone, diphacinone, and 

bromethalin active ingredients and mechanical rodent control devices are available, effective, 

affordable, and cause significantly less risk to the environment, rodenticide products containing 

brodifacoum or difethialone active ingredients cause risks that are unreasonable. Accordingly, 

EPA proposes to cancel the following rodenticide products registered for general consumer use 

for the control of commensal rodents in and around buildings: 

D- MOUSE PRUFE II, EPA Reg. No. 3282-65 (brodifacoum) 

D- PELLETS GENERATION II, EPA Reg. No. 3282-66 (brodifacoum) 

D- BAIT PELLETS II, EPA Reg. No. 3282-74 (brodifacoum) 

D- READY MIXED GENERATION II, EPA Reg. No. 3282-81 (brodifacoum) 

D- MOUSE-PRUFE III, EPA Reg. No. 3282-85 (difethialone) 

D- BAIT PELLETS III, EPA Reg. No. 3282-86 (difethialone) 

D- II READY MIX BAITBITS III, EPA Reg. No. 3282-87 (difethialone) 

D- BAIT PACKS III, EPA Reg. No. 3282-88 (difethialone) 

GENERATION MEAL BAIT PACKS, EPA Reg. No. 7173-247 (difethialone) 

DIFETHIALONE BAIT STATION, EPA Reg. No. 7173-283 (difethialone) 

DIFETHIALONE 6G PASTE PL PKS, EPA Reg. No. 7173-285 (difethialone)

For the same reasons, EPA denies applications for registration of the following products: 

D-CON BAIT STATION XV KILLS MICE, EPA Application No. 3282-RNU 

(brodifacoum) 

D-CON BAIT STATION XV KILLS MICE, EPA Application No. 3282-RNL 

(brodifacoum) 

B. Cancellation and Denial of Registration of Rodenticides Formulated as Loose Baits, or 

Bait Pastes or Blocks Without Bait Stations That Meet the Standards of the RMD, 

Intended for Residential Consumer Use In Controlling Commensal Rodents In and 

Around Buildings. 

 Rodenticides formulated as loose baits (e.g., grain, granules, pellets, meal), paste or bait 

blocks are directly accessible to children, domestic animals and non-target wildlife, unless they 

are placed where children, domestic animals and non-target wildlife cannot reach them or unless 

they are enclosed in secure bait stations. In practice, it is difficult to place rodenticides where 

children, domestic animals and non-target wildlife cannot reach them. Even if rodenticides are 

initially well placed, rodents often move them to other locations for later consumption, and the 
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new locations may be accessible to children, domestic animals and non-target wildlife. 

 The primary exposures of children, and risks for domestic animals and non-target wildlife 

for rodenticides can be substantially reduced if the bait is contained in a bait station that meets 

the standards of the RMD. The RMD describes four types of bait varying in terms of resistance 

to children, dogs, and weather: 

• Tier 1 - Tamper-Resistant and Weather-Resistant: These bait stations are resistant to 

weather and to tampering by children and dogs. Tier I bait stations meet the tamper 

resistance and weather resistance standards set forth in Pesticide Registration Notice 94-

7, and have also satisfactorily demonstrated the ability to isolate bait from children and 

dogs in laboratory testing conforming to EPA protocols. 

• Tier 2 - Tamper-Resistant (but not weather resistant): Tier 2 bait stations have 

satisfactorily demonstrated the ability to isolate bait from children and dogs in laboratory 

testing conforming to EPA protocols. Tier 2 bait stations have not met weather resistance 

standards; therefore, rodenticide bait products that include Tier 2 bait stations must be 

labeled for indoor use only. 

• Tier 3 – Tamper-Resistant for Children Only: Tier 3 bait stations have satisfactorily 

demonstrated the ability to isolate bait from children in laboratory testing conforming to 

EPA protocols. Tier 3 bait stations have not demonstrated the ability to isolate bait from 

dogs and have not met weather resistance standards; therefore, rodenticide bait products 

that include Tier 3 bait stations must be labeled for indoor use only and to prohibit 

placement where the product is accessible to domestic animals and/or non-target wildlife. 

• Tier 4 - Tamper-Resistance Unknown: Tier 4 bait stations have not been demonstrated to 

meet the testing standards required of the higher tiers, however, a Tier 4 bait station must 

be made of a material of sufficient rigidity such that the station is not easily crushed or 

opened by a child less than 6 years of age, not easily chewed by target rodents, and not 

reasonably anticipated to release rodenticide bait except for bait removed by target 

rodents and minor quantities of crumbs created by target rodents. Rodenticide bait 

products that include Tier 4 bait stations must be labeled for indoor use only and to 

prohibit placement where the product is accessible to children, domestic animals and/or 

non-target wildlife. 

1. Rodenticides in bait stations that meet the standards of the RMD are effective 

alternatives to loose baits and unprotected pastes and blocks. 

Studies have shown no consistent differences in rodents’ consumption of block and 

pelleted or meal formulations. Bait-stations are widely used and effective rodent control has 

been achieved using bait stations in a wide variety of circumstances. Some rodents (particularly 

Norway rats) are wary of any new objects in their environments, and may avoid a newly 

introduced bait station for a period of time, generally about 2 or 3 days. Rodents overcome this 

neophobia, and will enter a well-placed bait station and consume the bait. The shelter and 

protection of bait that the stations provide ultimately may encourage feeding and prolong the 

attractiveness of the bait. 
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2. Rodenticides in bait stations that meet the standards of the RMD are affordable 

alternatives to loose baits and unprotected pastes and blocks. 

Most residential consumers will not be affected by the proposed removal of rodenticides 

formulated as loose baits, paste or blocks without bait stations from the residential consumer 

market. The majority of residential consumers use mechanical methods of control, which will 

not be affected by the proposed cancellations. Residential consumers who use rodent control 

services provided by PCOs will not be affected by the proposed cancellations. Professional users 

(such as PCOs, agricultural users, commercial users, and public health officials) generally have 

access to tamper-resistant bait stations (required by existing rodenticide labels for use outdoors 

and where placements otherwise would be accessible to children, domestic animals, and/or nontarget wildlife) and will continue to have access to many registered rodenticides formulated as 

loose baits, paste or blocks without bait stations, notwithstanding the proposed cancellations. 

Inasmuch as these professional users will not be affected by the cancellations, neither will 

residential consumers who rely on their services. 

The only users likely to be affected by the proposed cancellations are those residential 

consumers who purchase and use rodenticides for control of commensal rodents in and around 

buildings. Most of these residential consumers are likely to experience only modest cost 

increases as a consequence of the proposed cancellation of rodenticide products registered for the 

control of commensal rodents in and around buildings products without bait stations conforming 

to the RMD criteria, because there are multiple alternative rodenticide products conforming to 

the RMD and marketed at prices comparable to those of the products EPA proposes to cancel. 

For residential consumers currently using non-RMD conforming rodenticide products to 

control mice, EPA estimates that incremental costs resulting from the proposed cancellations will 

range from $2 to $12 per infestation. For residential consumers controlling rats 

(approximately10% of the consumer rodenticide market), EPA estimates that incremental costs 

resulting from the proposed cancellations will range from a potential cost savings to $ 97 per 

infestation. EPA has examined the impacts from these incremental costs against monthly nonhousing income for a family at the poverty threshold. For mouse control, incremental costs for 

control of a minor infestation would be less than 1%, and a major infestation would be 

approximately 2%, of monthly non-housing income at the poverty threshold. For rat control, 

incremental costs for control of minor and major infestations would be 5% and 11%, 

respectively, of monthly non-housing income at the poverty threshold. These costs would be a 

significantly lower proportion of income for the majority of residential consumers. Therefore, 

the costs associated with the proposed cancellations are expected to have little impact on 

residential consumers. Moreover, mechanical traps offer effective, lower cost rodent control that 

could result in a cost savings for price-sensitive consumers. 

 

3. Loose baits and unprotected pastes and blocks cause adverse effects to children, nontarget wildlife and domesticated and companion animals that could be avoided. 

Bait stations that conform to the standards of the RMD are designed to prevent children, 
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domestic animals and non-target wildlife from being able to come into contact with rodenticides, 

whereas other product presentations do not adequately reduce exposure and ingestion of 

rodenticides. Use of a bait station that substantially reduces exposure to the bait plainly poses 

less risk than alternatives that allow direct contact with the bait. 

 Numerous incidents of children being exposed to loose baits and unprotected blocks have 

been reported. While most exposures generally result in no clinical harm, the numbers of reports 

of exposed children are troubling. Approximately 85% of the rodenticide exposures reported to 

AAPCC (i.e., approximately 15,000 per year) occurred to children under 6 years old. Incidents 

involving children are predominantly accidental exposures from picking up baits placed on floors 

in the home of a parent or guardian. Approximately 1% of the incidents of children’s exposure 

to rodenticides reported to AAPCC are symptomatic (an average of 128 cases per year). While 

only a small proportion of reported incidents involve clinical harm, EPA believes there are social 

and economic costs that arise from addressing children’s exposures to rodenticides, including 

costs to health care facilities, poison control hotlines, and to the families whose children are 

exposed. 

 Rodenticides appear to be involved in numerous reported domestic animal poisonings, 

which have the potential to result in severe outcomes and/or necessitate veterinary care. In 2010, 

APCC identifies rodenticides as the third most likely cause of pet poisonings and the Pet Poison 

Helpline identifies rodenticides as the third most common toxin involved in dog poisonings and 

the fourth most common toxin involved in cat poisonings. OPP’s IDS identifies two rodenticides 

(brodifacoum and bromadiolone) in the top 20 pesticides most likely associated with a domestic 

animal fatality. OPP’s IDS indicates that in recent years there are about 2000 reported incidents 

per year of domestic animals exposed to rodenticides, many of which result in severe outcomes 

(on average 14% result in death or a major outcome) which may necessitate veterinary care. The 

IDS data indicate that about 160 severe (death or major effect) domestic animal incidents 

attributable to rodenticides will be reported every year, which EPA believes significantly 

underestimates the actual number of incidents. 

 The various lines of evidence evaluated by EPA have led the Agency to conclude that 

risks to non-target wildlife from all the rodenticides addressed in the Notice are significant. 

There is little question that wildlife is being exposed to loose bait products. Incident reports and 

exposure studies make clear that a wide range of mammalian and avian wildlife can come into 

contact with the rodenticides from both primary exposures. EPA’s quantitative assessment and 

the incident data provide evidence that exposure can and does result in mortality to wildlife. 

Although many non-target wildlife species avoid areas of human habitation, significant numbers 

of incidents of both primary and secondary rodenticide poisonings of non-target wildlife occur in 

urban and suburban areas. This suggests that residential and commercial uses of rodenticides for 

commensal rodent control pose significant risk to non-target wildlife. 

Moreover, autopsies and biopsies of predatory and scavenging wildlife consistently show 

accumulation of rodenticide residues in liver tissue of numerous predatory and scavenging 

wildlife species, including owls, eagles, hawks, vultures, mustelids, bobcats, and mountain lions. 

Numerous monitoring studies conducted throughout the United States have found second 
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generation anticoagulants present in over 85% of individuals of one or more species studied. 

The prevalence of second generation anticoagulants in wildlife regardless of location of 

collection indicates that rodenticides used in and around buildings for control of commensal 

rodents (the only lawful uses of second generation anticoagulants) affect predatory and 

scavenging wildlife everywhere. 

Bait stations conforming to the RMD can prevent primary exposures to birds and larger 

mammals that cannot gain access to the bait. While bait stations cannot prevent secondary 

exposures to intoxicated prey, bait stations can ensure that intoxicated birds and larger mammals 

are not available as prey to mammalian and avian scavengers and predators. 

4. Conclusion. 

The rodenticides subject to this Notice are known poisons to all mammals and birds, and 

exposure to these rodenticides is widespread among children, domestic animals, and non-target 

wildlife. If rodenticides formulated as loose baits, or pastes or blocks unprotected by bait 

stations continue to be available in the residential consumer market, these exposures are likely to 

continue. 

 Bait stations conforming to the RMD criteria can significantly reduce rodenticide 

exposures among children, domestic animals, and non-target wildlife, compared to products 

without bait stations conforming to the RMD criteria. EPA has determined that control of 

commensal rodents in and around buildings by residential consumers can be satisfactorily 

accomplished without rodenticides formulated as loose baits, or pastes or blocks unprotected by 

bait stations. Registered rodenticide products that include bait stations that meet the RMD 

criteria are available on the market at costs comparable to the rodenticide products subject to this 

Notice, and, when used in combination with prudent sanitation and exclusion measures, are 

effective for the control of commensal rodents in and around buildings. 

 Inasmuch as rodenticides in bait stations that meet the standards of the RMD are 

available, effective, affordable, and cause significantly less risk to man or the environment, 

rodenticide products intended to control commensal rodents in and around structures and 

marketed for general consumer use cause unreasonable risks unless they include a bait station 

that meets the standards of the RMD. Accordingly, EPA proposes to cancel the following 

rodenticide products registered for the control of commensal rodents in and around buildings 

products without bait stations conforming to the RMD criteria: 

D-CON CONCENTRATE KILLS RATS & MICE, EPA Reg. No. 3282-3 (warfarin) 

D- READY MIXED KILLS RATS & MICE, EPA Reg. No. 3282-4 (warfarin) 

D- MOUSE PRUFE KILLS MICE, EPA Reg. No. 3282-9 (warfarin) 

D- PELLETS KILLS RATS & MICE, EPA Reg. No. 3282-15 (warfarin) 

RID-A-RAT RAT & MOUSE KILLER, EPA Reg. No. 8845-39 (warfarin) 

D- MOUSE PRUFE II, EPA Reg. No. 3282-65 (brodifacoum) 

D- PELLETS GENERATION II, EPA Reg. No. 3282-66 (brodifacoum) 

D- BAIT PELLETS II, EPA Reg. No. 3282-74 (brodifacoum) 
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D- READY MIXED GENERATION II, EPA Reg. No. 3282-81 (brodifacoum) 

D- MOUSE-PRUFE III, EPA Reg. No. 3282-85 (difethialone) 

D- BAIT PELLETS III, EPA Reg. No. 3282-86 (difethialone) 

D- II READY MIX BAITBITS III, EPA Reg. No. 3282-87 (difethialone) 

D- BAIT PACKS III, EPA Reg. No. 3282-88 (difethialone) 

GENERATION MEAL BAIT PACKS, EPA Reg. No. 7173-247 (difethialone) 

DIFETHIALONE BAIT STATION, EPA Reg. No. 7173-283 (difethialone) 

DIFETHIALONE 6G PASTE PL PKS, EPA Reg. No. 7173-285 (difethialone) 

HOT SHOT SUDDEN DEATH BRAND MOUSE KILLER, EPA Reg. No. 8845-125 

(bromethalin) 

HOT SHOT SUDDEN DEATH BRAND RAT KILLER 1, EPA Reg. No. 8845-126 

(bromethalin) 

HOT SHOT SUDDEN DEATH BRAND RAT & MOUSE KILLER, EPA Reg. No. 

8845-127 (bromethalin) 

HOT SHOT SUDDEN DEATH BRAND MOUSE KILLER BAIT STATION, EPA Reg. 

No. 8845-128 (bromethalin)

For the same reasons, EPA denies applications for registration of the following products: 

BROMETHALIN 0.01% PELLET III, EPA Application No. 36488-AN (bromethalin) 

BROMETHALIN RAT AND MOUSE BLOCK III, EPA Application No. 36488-AR 

(bromethalin) 

IX. Existing Stocks of Cancelled Products 

FIFRA section 6(a) allows the Agency to permit the continued sale and use of existing 

stocks of pesticide whose use has been cancelled, to the extent the Administrator determines that 

such sale or use would not be inconsistent with the purposes of this Act. Allowing further sale or 

distribution of the products identified in this Notice would not be consistent with the purposes of 

FIFRA. First and most important, the continued sale and distribution of products cancelled 

pursuant to this Notice result in unreasonable adverse effects on the environment. Second, the 

regulated community has been on notice since May 28, 2008 that the Agency intended that sale 

and distribution of these products by registrants must cease by June 4, 2011. During that period, 

most registrants have amended existing rodenticide products, or registered new rodenticide 

products, that cause significantly less risk to the environment, and these rodenticide products are 

widely available. EPA does not believe it to be consistent with the purposes of FIFRA to 

continue to put registrants who voluntarily brought safer products to the market at a competitive 

disadvantage relative to registrants who declined to improve their products. Accordingly, the 

EPA has determined that the continued sale and distribution of existing stocks of pesticide 

products cancelled pursuant to this notice shall not be permitted. 

Sections 3(c)(2)(B) and 6(e) of FIFRA provide that the question of whether the 

disposition of existing stocks is consistent with the purposes of FIFRA is a subject to be 

determined at any suspension or conditional cancellation hearing under those provisions. 
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Section 6(b) does not contain similar language, and the EPA has determined that the question of 

the disposition of existing stocks is outside the scope of any hearing conducted pursuant to 

FIFRA section 6(b). 

X. USDA, HHS and SAP Review 

When the Agency intends to issue a Notice of Intent to Cancel, FIFRA section 6(b) 

requires that it must furnish a draft of that notice and an analysis of the impact of the proposed 

action on the agricultural economy to the Secretary of the Department of Agriculture (USDA), 

and, when a public health use is affected, to the Secretary for Health and Human Services 

(HHS), for comment at least 60 days prior to issuing the notice. In addition, FIFRA section 

25(d) requires the Agency must within the same time period submit the proposed cancellation 

action to the FIFRA Scientific Advisory Panel (SAP) for comment concerning the impact of the 

proposed action on health and the environment. 

In the event that written comments are received from the USDA, HHS or the SAP within 

30 days of such referral, the Agency must publish those comments and the Agency's response to 

the comments with the cancellation notice. 

[Insert summary of any USDA, HHS and SAP comments] 

XI. Procedural Matters