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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

MEMORANDUM Date 12/09/2015

Subject: Registration Review –Preliminary Problem Formulation for Ecological Risk and 

Environmental Fate, Endangered Species, and Drinking Water Assessments for

Diphacinone and Diphacinone Sodium Salt

PC Codes: Diphacinone 067701

Diphacinone Sodium Salt 067705

DP Barcode: 426286

To: Christina Motilall, Chemical Review Manager

Neil Anderson, Branch Chief

Risk Management and Implementation Branch 1

Pesticide Re-evaluation Division (PRD)

From: Christine Hartless, Ph.D., Wildlife Biologist

James Lin, Ph.D., Environmental Engineer

Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs

Through: Melissa Panger, Ph.D., Senior Advisor

Ron Parker, Senior Environmental Engineer

Elyssa Arnold, Risk Assessment Process Leader

Brian Anderson, Branch Chief

Environmental Risk Branch 2

Environmental Fate and Effects Division

Office of Pesticide Programs

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the registration review of the rodenticides

diphacinone (PC Code 067701) and diaphacinone sodium salt (PC Code 067705). 

The problem formulation draws on information from both open literature and studies submitted 

by the technical registrants in response to data requirements. This document is intended to 

provide an overview of what is currently known regarding the environmental fate and ecological 

effects associated with diphacinone and its sodium salt and outlines uncertainties regarding 

attributes of the parent compound and its transformation products. It describes the preliminary 

ecological risk hypothesis and the processes that will be used during the completion of drinking 
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water and ecological risk assessments in support of registration review. This document also 

recommends studies that should be included in a data call-in (DCI) to address uncertainties 

surrounding the environmental fate and potential ecological effects of diphacinone and 

diphacinone sodium salt.
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Preliminary Problem Formulation for the Environmental 

Fate and Ecological Risk, Endangered Species, and Drinking 

Water Assessments in Support of the Registration Review of 

Diphacinone and Diphacinone Sodium Salt

Diphacinone

2-(diphenylacetyl)indan-1,3-dione

(CAS 82-66-6)

(PC Code 067701)

Diphacinone sodium salt

2-(diphenylacetyl)indan-1,3-dione, sodium

(CAS 42721-99-3)

(PC Code 067705)

Environmental Risk Branch II

Environmental Fate and Effects Division

Christine Hartless, Ph.D., Wildlife Biologist

James Lin, Ph.D. Environmental Engineer

Reviewed by:

Melissa Panger, Ph.D., Senior Advisor

Ron Parker, Senior Environmental Engineer

Elyssa Arnold, Risk Assessment Process Leader

Brian Anderson, Branch Chief

U. S. Environmental Protection Agency

Office of Pesticide Programs

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

December 9, 2015
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Table of Contents

1 EXECUTIVE SUMMARY..................................................................................................................................5

2 INTRODUCTION ............................................................................................................................................5

3 USE CHARACTERIZATION ..............................................................................................................................6

4 CONCLUSIONS FROM PREVIOUS RISK ASSESSMENTS.................................................................................. 10

4.1 ENDANGERED SPECIES ASSESSMENTS .....................................................................................................................10

4.2 REREGISTRATION ELIGIBILITY DECISION...................................................................................................................10

4.3 NEW USE ASSESSMENTS......................................................................................................................................11

4.4 DRINKING WATER ASSESSMENT .............................................................................................................................12

5 ENVIRONMENTAL FATE AND TRANSPORT .................................................................................................. 12

5.1 TRANSPORT AND MOBILITY ..................................................................................................................................12

5.2 DEGRADATION...................................................................................................................................................13

5.3 TRANSFORMATION PRODUCTS ..............................................................................................................................14

6 RECEPTORS ................................................................................................................................................. 15

6.1 TOXICITY SUMMARY ...........................................................................................................................................15

6.2 SECONDARY TOXICITY..........................................................................................................................................17

6.3 INCIDENT DATABASE REVIEW................................................................................................................................21

7 EXPOSURE PATHWAYS OF CONCERN.......................................................................................................... 21

8 ANALYSIS PLAN........................................................................................................................................... 22

8.1 STRESSORS OF CONCERN......................................................................................................................................22

8.2 MEASURES OF EXPOSURE.....................................................................................................................................22

8.3 MEASURES OF EFFECT .........................................................................................................................................30

9 ENDANGERED SPECIES ASSESSMENT .......................................................................................................... 30

10 ENDOCRINE DISRUPTOR SCREENING PROGRAM......................................................................................... 30

11 PRELIMINARY IDENTIFICATION OF DATA GAPS........................................................................................... 31

11.1 FATE ...........................................................................................................................................................31

11.2 EFFECTS.......................................................................................................................................................31

12 REFERENCES ............................................................................................................................................... 35

APPENDIX A: LABEL USE INFORMATION FOR DIPHACINONE AND DIPHACINONE SODIUM SALT BASED ON BEADS 

SUMMARY REPORT.............................................................................................................................................. 46

APPENDIX B: SUMMARY OF ECOTOXICITY DATA FOR DIPHACINONE................................................................... 48

APPENDIX C. SCREENING LEVEL MODELS TO EVALUATE POTENTIAL IMPORTANCE OF DRINKING WATER AND 

INHALATION EXPOSURE PATHWAYS.................................................................................................................... 50

APPENDIX D. WILDLIFE MORTALITY INCIDENTS ATTRIBUTED TO USE OF DIPHACINONE..................................... 53
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1 Executive summary

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation for the ecological risk, environmental fate, endangered species, and drinking water 

assessments to be conducted as part of the registration review of diphacinone (PC code 067701) 

and diphacinone sodium salt (PC code 067705). Diphacinone sodium salt easily and quickly 

converts to diphacinone by hydrolysis in the environment. Therefore, all environmental fate and 

toxicity data for diphacinone (067701) will be bridged to diphacinone sodium salt (067705). 

For this registration review, the stressor of concern for drinking water, terrestrial organisms, and 

aquatic organisms is diphacinone (067701) only. For clarity throughout this Problem 

Formulation, “diphacinone (067701)” will be used to refer specifically to 2-

(diphenylacetyl)indan-1,3-dione, “diphacinone sodium salt (067705)” will be used to refer

specifically to 2-(diphenylacetyl)indan-1,3-dione, sodium, and “diphacinone” will be used to 

refer collectively to diphacinone (067701) and/or diphacinone sodium salt (067705). 

The problem formulation describes the methods planned to be used during the completion of 

drinking water and ecological risk assessments in support of registration review and provides an 

overview of the environmental fate, ecological effects, and potential risks associated with the use 

of diphacinone as well as uncertainties unique to risk assessment of diphacinone. This document 

also identifies additional studies that would be beneficial to the conduct of an ecological risk 

assessment. 

Data requested to address ecological effect uncertainties are:

 Avian acute oral toxicity test (850.2100), one passerine species

 Avian reproduction toxicity (850.2300), for two species

 Prenatal Developmental Toxicity Study (870.3700) or Reproduction and Fertility Effects 

Study (870.3800), one species

 Earthworm Subchronic Toxicity Test (850.3100), one species

 Data evaluating toxicity and/or bioaccumulation of diphacinone in terrestrial 

invertebrates

No additional data are requested for the environmental fate assessment at this time.

2 Introduction

Diphacinone (067701) and its sodium salt (067705) are indandione anticoagulant rodenticides

and are classified as first-generation anticoagulants. Anticoagulants are vitamin-K antagonists 

that disrupt normal blood-clotting mechanisms and induce capillary damage. They uncouple

oxidative phosphorylation depressing hepatic synthesis of prothrombin and clotting factors VII, 

IX and X and cause direct damage to capillary permeability. Typically, death is delayed for four 

to ten or more days after a lethal dose is ingested, and animals may continue to feed and move 

about until shortly before death. Death results from hemorrhage, and exposed animals may 

exhibit behavior that may make them more susceptible to predation (Cox and Smith, 1992). This 

may result in secondary exposure to predatory animals. Some of the consumed diphacinone will 
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be excreted or metabolized by animals that have eaten bait, but some is sequestered in various 

body tissues for days or weeks. 

The anticoagulant rodenticides registered in the United States have been grouped into "firstgeneration" (warfarin, chlorophacinone, diphacinone) and "second-generation" (brodifacoum, 

difenacoum, bromadiolone, difethialone) compounds. Although there is overlap in their 

metabolic and toxicological properties, second-generation anticoagulants tend to be more acutely 

toxic than are the first-generation anticoagulants, and they are retained longer in body tissues.

The greater potency and duration of action of long-acting anticoagulant rodenticides is attributed 

to their: (i) greater affinity for vitamin K(1)-2,3-epoxide reductase; (ii) ability to disrupt the 

vitamin K(1)-epoxide cycle at more than one point; (iii) hepatic accumulation; and (iv) unusually 

long biological half-lives due to high lipid solubility and enterohepatic circulation (Watt et al.

2005).

EFED evaluated the most recent ecological risk assessments for diphacinone in association with 

the updated toxicity, exposure, and usage information to determine if sufficient data are available 

and if further updates are needed to support registration review. In addition, EFED considered 

the latest Agency science policies and risk assessment methodologies. Any additional relevant 

data that become available at the time of the registration review will be incorporated into the 

assessment. The structure of diphacinone and its sodium salt, as well as the chemical names and 

other identifiers can be found in the chemical identity table in Section 5 of this document. 

3 Use Characterization

Table 1 summarizes the use patterns and bait concentrations for given groups of target species. 

Details for individual products are not included; however, this table provides characterization for 

the expected use patterns of diphacinone (067701) and diphacinone salt (067705). In addition to 

the Section 3 labels summarized in Table 1, there are currently eight Section 24C labels for 

diphacinone (067701): 

 target species of Norway rats, roof rats, wood rats, deer mice, California and montane 

voles, California ground squirrels, chipmunks, black tailed jackrabbits, and muskrats in 

California; 

 Norway and black rats in Alaska;

 wood rats in Arizona;

 small Indian mongoose (Herpestes auropunctatus), roof rats, Norway rats, Polynesian 

rats (R. exulans), and house mice (Mus musculus) in Hawaii; 

 Columbian ground squirrel (Spermophilus columbianus) and Richardson's ground 

squirrel (S. richardsoni) in Montana; and

 a 0.01% diphacinone bait for California Ground Squirrels (Spermophilus beecheyi), 

Belding's Ground Squirrels (S. beldingi), deer mice (Peromyuscus spp.), and house mice 

in California. 

Since there is no national level usage data for this chemical, no Screening Level Usage Analysis 

(SLUA) is available for diphacinone (067701) or diphacinone sodium salt (067705). Appendix 

A lists the maximum use patterns for the labeled use sites for diphacinone (067701) and for 
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diphacinone sodium salt (067705). The table is based on the “EFED Table 1 Report,” which is a 

part of the Label Use Report Package created by BEAD in support of Registration Review 

(USEPA, 2015). Prior to the registration review assessment, the label review will be updated.
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Table 1. Overview of Section 3 Labels for Diphacinone(067701) and Diphacinone sodium salt (067705)

Target Species % a.i. Bait form General Use Pattern Use Sites Maximum application rate and reapplication interval

Diphacinone

House mouse (Mus 

musculus), Roof rat 

(Rattus rattus), Cotton 

rats (Sigmodon hispidus), 

Eastern harvest mouse 

(Reithrodontomys 

humuli), Golden mouse 

(Ochrotomys nuttalli), 

Polynesian rat (Rattus 

exulans), and/or Meadow 

vole (Microtus 

pennsylvanicus). 

0.005

Bait block, 

pellet, treated 

grain, place 

pack

Use indoors and within 100 

feet of man-made 

structures. Must use bait 

station for outdoor above 

ground use or when 

children or non-target 

mammals or birds can 

access the bait. Some 

labels restrict use indoors; 

some restrict to within 50 

feet of man-made structure.

Indoor and within 

100 feet or within 

50 feet of manmade structures 

(residential, 

commercial, 

agricultural, 

industrial, public 

buildings,

ships/boats)

Refill/replace bait boxes as needed. 

House mouse, Norway 

rat, and Roof rat 

0.2 Tracking 

powder

Use indoors or in rat 

burrows leading indoors.

Indoor or in rat 

burrow leading 

indoors.

Repeat if burrows are reopened. Maintain 

powder in treated areas for at least 20 days.

0.1

Concentrate to 

be mixed in 

bait. Resulting 

concentration of 

diphacinone in 

final bait is 

0.005%.

Use in and within 100 feet 

of man-made structures. 

Must use bait station for 

outdoor above ground use 

or when children or nontarget mammals or birds 

can access the bait.

Indoor and within 

100 feet of manmade structures.

Maintain bait station for 10 (rat) or 15 

(mouse) days. Can establish permanent station 

if pest pressure continues.

Pocket gopher (Geomys 

spp. and Thomomys spp.) 

and/or moles (Scalopus 

aguaticus, Condylura 

cristata, and Scapanus

spp.) 0.005 Pellet or treated 

grain

Applied underground to 

burrow system by hand or 

by mechanical burrow 

builder

Agricultural crop 

and non-crop areas, 

orchards, 

rangeland, forest, 

ornamental turf, 

golf courses, crop 

borders, parks.

Not specified.

Meadow voles (Microtus 

pennsylvanicus) and pine 

voles (M. pinetorum)

Bait station, hand 

broadcast, mechanical 

ground broadcast, aerial 

broadcast

Commercial 

nurseries, dormant 

fruit tree orchards

Broadcast application – apply 10 lbs. 

product/acre with 2nd application one month 

later, if needed. For some labeled sites, max 

application rate of 20 lbs 

product/acre/application.
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Table 1. Overview of Section 3 Labels for Diphacinone(067701) and Diphacinone sodium salt (067705)

Target Species % a.i. Bait form General Use Pattern Use Sites Maximum application rate and reapplication interval

For California ground 

squirrel (Spermophilus 

beechyi) and/or 

Townsend ground squirrel 

(Urocitellus townsendii)

Bait station, hand 

broadcast, or mechanical 

ground broadcast

around buildings, 

in noncrop areas 

(such as a long 

levees and ditch 

banks, along fence

lines), in rangeland 

and pasture land, 

and in crop areas

(such as dormant 

orchards), parks, 

golf courses

Bait station: 2-4 lbs bait/station. Bait to be 

available for at least 30 days or till feeding 

stops. Broadcast 70 gms product near burrow. 

Re-apply every 2-3 days for 3-4 total 

applications.

Black tailed prairie dog 

(Cynomys ludovicianus)

Place 1/4 cup bait at least 6 

inches into each burrow

Rangeland and 

adjacent non-crop 

areas

If needed, may make second application 

several weeks or months later. 

Norway rats, roof rats,

Polynesian rats, house 

mice or other types of 

invasive rodents for 

control or eradication. For 

conservation purposes on 

islands, grounded vessels 

or vessels in peril of 

grounding. 

0.005 Pellet

Bait stations, burrow 

baiting, canopy bailing or 

aerial and ground 

broadcast application 

techniques.

Conservation 

reserve lands, 

forest, ships, boats, 

shipholds. 

Bait station: Maintain an uninterrupted 

supply of fresh bait for at least 15 days or until 

signs of rodent activity cease. Where a 

continuous source of infestation is present, 

permanent bait stations may be used.

Burrow baiting- place 85 to 113 g bait in 

each burrow; maintain bait for at least 15 days 

or till rodent activity stops. 

Canopy baiting: 113-200 gm bait in bag per 

placement, no mention of retreatment. 

Broadcast: 10 – 12.5 lbs bait/acre with 

second application 5-7 days later. Or single 

application at max of 20 lbs product/acre. 

Diphacinone sodium salt (067705)

House mouse, Norway 

rat, and Roof rat 0.106%

Liquid 

concentrate to 

be mixed in 

water. Resulting 

concentration of 

diphacinone in 

final bait is 

0.005%.

Put liquid solution in bait 

boxes. For indoor use only. 

For use inside of 

industrial, 

commercial, 

agricultural, and 

public buildings, 

and similar manmade structures.

Can establish permanent bait stations if 

necessary. 
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4 Conclusions from Previous Risk Assessments

The Agency has conducted previous ecological risk assessments on diphacinone that serve as a 

basis for this problem formulation. They are briefly summarized below. 

4.1 Endangered Species Assessments

An endangered species risk assessment was completed for diphacinone (067701) in 2011 

(USEPA 2011) to address potential risk to the Salt marsh harvest mouse (SMHM) 

(Reithrodontomys raviventris), San Joaquin Kit Fox (SJKF) (Vulpes macrotis mutica), Alameda 

Whipsnake (AW) (Masticophis lateralis euryxanthus), and California Tiger Salamander (CTS) 

(Ambystoma californiense) for which diphacinone was alleged to be of concern in a complaint 

made by the Center for Biological Diversity against United States Environmental Protection 

Agency on May 30, 2007 (Case No: 07-2794-JCS). Based on the best available information, the 

Agency made a “May Affect, and Likely to Adversely Affect” determination for the SMHM, 

SJKF, AW, and CTS from all uses of diphacinone. Additionally, the Agency determined that 

there was the potential for modification of designated critical habitat for the AW and CTS from 

the use of diphacinone.

4.2 Reregistration Eligibility Decision 

The Reregistration Eligibility Decision (RED) for diphacinone was published in 1998 as part of 

the rodenticide cluster (USEPA, 1998b). The RED found that all uses of diphacinone except for 

field rodenticide uses involving baits with diphacinone concentrations greater than 0.005% were 

eligible for reregistration. In addition, the RED found that all rodenticides must incorporate an 

indicator dye and a bittering agent. Both these measures were intended to help reduce human 

exposure. Other mitigation measures included improved label language regarding placement of 

bait stations around buildings, submission of information on poisonings, restricted use 

classification of tracking powders and baits, and the formation of a stakeholder group to 

investigate safer use technologies. 

“Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative 

Approach” (USEPA 2004b) evaluated primary and secondary exposure of diphacinone, 

among other rodenticides, to birds and mammals. This assessment determined that the 

greatest risk of diphacinone use to non-target animals is via primary and secondary exposure 

to mammals. Risk associated with primary and secondary exposure to birds, however, was 

also of concern. These elements provide the general framework for this assessment and are 

supported through the calculation of RQs in this assessment. The study also specified a 

number of factors contributing to uncertainty in assessing anticoagulant rodenticides. Those 

factors that contributed the most uncertainty were: (1) missing data, including acute, 

chronic, and secondary toxicity as well as data regarding retention of some active 

ingredients in the liver, blood, and other body tissues; (2) the variable quality and quantity of 

existing data on metabolism and retention times in rodents and non-target species; (3) 

specific use information by formulation, including typical amounts applied by use site, 

seasonally, and annually; distances applied from buildings; amounts used in rural versus 
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urban areas; use by Certified Applicators versus homeowners and other non-certified 

applicators; and other such relevant information; (4) information on the number and species 

of birds and non-target mammals frequenting baited areas and the likelihood of their finding 

and consuming bait or poisoned primary consumers in the various use areas; (5) methods to 

determine liver concentration(s) and total body burdens of rodenticide that would 

corroborate death or even if such a cause-effect relationship is appropriate (e.g., the 

“threshold of toxicity” concentration); (6) not accounting for the impacts of sub-lethal 

effects on reproduction and non-target mortality (e.g., clotting abnormalities, hemorrhaging, 

stress factors including environmental stressors, such as adverse weather conditions, food 

shortages, and predation); (7) not accounting for bioaccumulation of repeated sub-lethal 

exposures to bait or poisoned rodents utilized as food by predators and scavengers; and (8) 

lack of incident reporting. While all of these uncertainties remain, the level of uncertainty 

has been reduced through the use of additional data submitted by the registrant or available 

in the scientific literature. 

In 2008, EPA released the Risk Mitigation Decision for Ten Rodenticides (RMD) (EPA 2008, 

Docket ID EPA-HQ-OPP-2006-0955). Diphacinone products were included in the list of ten 

rodenticides addressed in this document. The focus of this decision was:

1) To minimize children’s exposure to rodenticide products used in homes by requiring 

that all rodenticide bait products marketed to general and residential consumers be 

sold only with bait stations, with loose bait (e.g., pellets and meal) as a prohibited bait 

form. 

2) To reduce wildlife exposures and ecological risks, by requiring sale and distribution 

limits intended to prevent general consumers from purchasing residential use bait 

products containing four of the ten rodenticides that pose the greatest risk to wildlife 

(the second generation anticoagulants – brodifacoum, bromadiolone, difenacoum, and 

difethialone). Moreover, bait stations will be required for all outdoor, above-ground 

uses of these second generation anticoagulants.

EPA 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 rodenticides subject to the 

Notice of Intent to Cancel (NOIC) (brodifacoum, difethialone, warfarin and bromethalin) and for 

two rodenticides that are likely alternatives (i.e., active ingredients included in products with 

RMD-compliant registrations for commensal rodent control, specifically, chlorophacinone and 

diphacinone (067701); bromethalin has both compliant and non-compliant registrations). To 

support the NOIC, EPA conducted an extensive assessment of the potential for primary and 

secondary effects of the rodenticides under evaluation. This work was brought before the Science

Advisory Panel (SAP) in 2011 for review; meeting materials are available under docket number 

EPA-HQ-OPP-2011-0718. 

4.3 New Use Assessments

The two most recent Section 3 New Use assessments were:
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 proposed use of diphacinone (067701)on black-tailed prairie dogs (BTPD, Cynomys 

ludovicianus) (DP Barcode D403356, completed in 2012)

 proposed label amendment for diphacinone (067701) to add California ground squirrel 

(CGS, Spermophilus beechyi) as a target species and to expand the treatment area (both 

geographically and use sites) for voles (DP Barcode D426928, completed in 2015) 

These risk assessments suggested that diphacinone (067701) presents a risk to both endangered 

and non-endangered species of terrestrial animals, including mammals, birds, terrestrial-phase 

amphibians, reptiles, and invertebrates. There was a potential for direct effects to listed terrestrial 

animals (vertebrates and invertebrates) through consumption of bait or prey that have eaten bait. 

Consequently, there is a potential concern for indirect effects upon the listed organisms due to 

decreased prey availability and habitat modification (for individuals that use the BTPD or CGS

burrows). Risks to aquatic organisms, as well as to aquatic plants, were not expected for these

proposed uses of diphacinone (067701). Toxicity data are not available for aquatic or terrestrial 

plants; however, exposure, and thus risk, is expected to be low. 

As stated in the Section 3 assessments, the only available environmental fate data from studies 

for diphacinone (067701) are 1) physicochemical properties, 2) hydrolysis, 3) aerobic soil 

metabolism, and 4) aged column leaching. However, because of the specific results of studies 

and because the specific use and application rates for diphacinone, relative to established endpoint toxicities, is low, EFED can satisfactorily evaluate/screen limits of potential environmental 

concentrations and ecological effects without additional environmental fate data. In these

assessments for the proposed use of diphacinone (067701), EFED concluded that studies with a 

potential to add high value to the risk assessment were:

 Field Testing for Terrestrial Wildlife (850.2500),

 Acute Passerine Study (850.2100), and

 Avian Reproduction Study (850.2300), two species.

4.4 Drinking water assessment

The previous assessments concluded that due to the application amounts and methods, and the low 

water solubility of diphacinone, the exposure of surface water or ground water is expected to be 

negligible. No drinking water assessment has been conducted.

5 Environmental Fate and Transport 

5.1 Transport and Mobility

Due to a relative low vapor pressure of approximately 1 x 10-8 Torr and a Henry’s Law constant 

of approximately 2 x 10-10 atm-m3/mole, the volatilization of diphacinone (067701) is not expected 

to be a significant route of dissipation. Since there is no accepted guideline study for adsorption, 

an empirical approach to correlate the octanol to water partitioning ratio (Pow or Kow) and the 

soil organic matter to water sorption coefficient (Koc). The relationships (Sawhney 1989), 

assuming soil organic matter is typically about 58% carbon [i.e., organic carbon (oc) = organic 
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matter (om)/1.72)], are 

log (Kom) = 0.904 log (Pow) - 0.779 (n = 12, r-squared = 0.989)

log (Koc) = 0.904 log (Pow) - 0.779 + log 1.72

Another empirical relationship given in a technical guidance document supported by the 

European Community (Directive 93/67/EEC) to calculate Koc from Pow is:

log Koc = 0.52 log (Pow) + 1.02

Log Pow for diphacinone (067701) is 4.27 (based on Kow of 20,000). Thus, from the first 

relationship, log Koc = 3.32 and Koc is roughly 2100; from the second, log Koc = 3.24 and Koc 

is roughly 1700. These similar Koc values indicate diphacinone (067701) to be slightly mobile. 

When combined with a low water solubility of 0.3 mg/L, the potential to contaminate ground 

water is small.

There is no available bioconcentration study at this time. However, judging from the 

diphacinone (067701) octanol-to-water partitioning ratio (Kow) of approximately 20,000, there 

is a potential for bioconcentration. 

5.2 Degradation

Diphacinone (067701) was stable against simple hydrolysis at pH 7 and 9. At pH 5, hydrolysis 

proceeded with an extrapolated half-life of approximately 44 days. Products of hydrolysis were 

not satisfactorily identified or quantified. However, since the apparent hydrolysis was 

appreciable only at acidic pH, the hydrolytic degradation will not be important in the natural pH 

range. 

Laboratory aerobic soil metabolism data are from a single sandy loam soil from North Dakota. 

The mean half-life of diphacinone (067701) in this soil was 30 days (average of 28 and 32 days) 

from studies done at two different radiolabeled positions. A major soil metabolite (> 10% of 

dose) was diphenylglycolic acid which peaked at a maximum of approximately 20-25% of the 

initial dose around one month after treatment. This metabolite then remained at a relatively 

constant concentration until the end of the 3.5 month study. This study also indicated that the 

major metabolite, diphenylglycolic acid, was somewhat resistant to further metabolism.

The chemical properties and environmental fate parameters are summarized in Table 3. 
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Table 3. Chemical Properties and Environmental Fate Parameters of Diphacinone

(067701)

Parameter Value Source

Selected Physical/Chemical Parameters

Molecular mass (molecular formula) 340.48 g/mol (C23H16O3 ) calculated

Vapor pressure 1 x 10-8torr DP268619, 2000

Aqueous solubility 0.3 mg/L http://extoxnet.orst.edu/pi

ps/diphacin.htm

Henry’s Law Constant 2 x10-10 atm-m3/mol DP268619, 2000

Octanol-to-water partition coefficient (KOW) 20,000 DP268619, 2000

Persistence in Water

Hydrolysis half-life Stable in pH 7 and 9,

44 days (pH 5) MRID 43582401

Aqueous photolysis half-life Stable DP268619, 2000

Persistence in Soil

Aerobic soil metabolism half-life 28.3 days and 31.7 days MRID 42035001 – a 

single sandy loam soil

Mobility

Adsorption coefficients (KOC) 1700 mL/g 

2100 mL/g 

based on the empirical 

approaches

(Note: DP214197, 1997, require to submit (1) hydrolysis, and (2) Leaching - Adsorption/Desorption study).

5.3 Transformation Products

Chemical names and structures of diphacinone and its environmental transformation products are 

listed in Table 4. A major degradate of diphacinone is diphenylglycolic acid. Acute oral toxicity 

of diphenylglycolic acid to the mouse is LD50 = 2000 mg/kg-bw1. This major degradate detected 

in the aerobic soil metabolism study, diphenylglycolic acid, comprised up to 25% of the applied 

material about a month after application. This degradate appears to be persistent, but its mobility is 

unknown. Because diphacinone is formulated in pelleted bait or weather-resistant rodenticide 

products and primarily used in bait application, it is probable that contact of this degradate with 

soil and water will be minimal. Furthermore, because risk to the assessed species is expected to 

result from direct consumption of bait products or from consumption of prey which directly 

consumed the bait, the formation of degradation products in the soil and water is not of major 

concern in this assessment. Risk from the diphenylglycolic acid degradate will not be quantified

in the risk assessment.

 

1 See reference at: http://toxnet.nlm.nih.gov/cgi-bin/sis/search2/r?dbs+hsdb:@term+@DOCNO+7709
15

Table 4. Diphacinone and Its Environmental Transformation Products

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type MRID

Maximum 

%AR 

(day)

Final 

%AR 

(study 

length)

PARENT

Diphacinone

(067701)

2-(diphenylacetyl)

indan-1,3-dione

Diphacinone

sodium salt 

(067705)

2-(diphenylacetyl)

indan-1,3-dione, 

sodium

TRANSFORMATION PRODUCTS

Diphenylglycolic 

acid

diphenylglycolic 

acid

Aerobic 

soil 42035001 24.5(30 days)

16.3

(105 days)

Carbon dioxide Carbon dioxide

O O

Aerobic 

soil 42035001 37.3(105 days)

37.3

(105 days)

6 Receptors

6.1 Toxicity Summary

Table 5 provides a summary of the taxonomic groups and the surrogate species tested to 

characterize the potential acute and chronic ecological effects of diphacinone. All toxicity data 

were derived using diphacinone (067701); however, these data are bridged to diphacinone 

sodium salt (067705). In addition, the table provides a preliminary overview of the potential 

acute toxicity of diphacinone by providing the acute toxicity classifications. No ecotoxicity data 
16

are available for any degradates of diphacinone. All available toxicity data are summarized in 

Appendix B.

Diphacinone is highly toxic to slightly toxic to birds on an acute oral basis, moderately toxic to 

birds on a subacute dietary exposure basis, and very highly toxic to mammals on an acute oral 

exposure basis. Studies evaluating chronic toxicity of diphacinone to birds and mammals have 

not been submitted to the Agency. In addition, data on the toxicity of diphacinone to terrestrial 

invertebrates and terrestrial plants have not been submitted to the Agency. 

Brooks et al. (1998) evaluated oral and dermal toxicity of diphacinone to Brown Tree Snakes 

(Boiga irregularis). Acute oral exposure to diphacinone resulted in LD50s of 20.75 mg/kg-bw 

with a slope of 4.23 (ethanol used as a carrier) and 32.21 mg/kg with a slope of 5.0 (propylene 

glycol used as a carrier). All snakes were observed for seven days; all mortalities occurred 

within 24 hrs of diphacinone administration. At necropsy, there was no evidence of 

hemorrhaging, suggesting diphacinone has an alternative mode of action in snakes. No 

mortalities occurred following dermal application of diphacinone.

Technical grade diphacinone is classified as moderately toxic to freshwater fish and invertebrates 

on an acute exposure basis. Acute estuarine/marine fish and invertebrate data as well as chronic 

exposure effect data to diphacinone for fish and invertebrates have not been submitted to the 

Agency. In addition, no toxicity data for aquatic plants were submitted to the Agency.

Table 5. Most Sensitive Test Species Evaluated for Assessing Potential Ecological Effects 

of Diphacinone1.

Taxonomic 

Group

Study 

Type Tested Species Toxicity Endpoint

Acute Toxicity 

Classification/

NOAEC most 

sensitive 

endpoint(s)

MRID and 

Classification

Birds2

Acute oral

(primary 

bait 

consumer)

Northern 

bobwhite

Colinus 

virginianus

LD50 = 1630 mg a.i./kgbw

Slope = na

Slightly toxic.

Mortalities 

occurred ≤5 days 

after gavage, 

observed 30 days

42245201

Acceptable

Acute oral

(secondary 

consumer)

American 

kestrel (Falco 

sparverius)

LD50 = 98.6 mg a.i./kgbw

Slope = 6.69

Highly toxic. 

7-day study; 

mortalities 

occurred 8-47 hrs 

after dosing

Rattner et al.

2011

Supplemental/ 

Quantitative

Dietary

Mallard duck

(Anas 

platyrhynchos)

LC50 = 906 mg a.i./kgdiet

Slope = 0.5

Moderately toxic.

25-day test, most 

mortalities from 

3-8 days, all 

mortalities less 

than 16 days

42408802 

(Acceptable)

Chronic No data

Reptile

Acute oral 

(single 

dose)

Brown tree 

snake (Boiga 

irregularis)

LD50 = 20.75 mg 

a.i./kg-bw

Slope = 4.2

Highly toxic.

7-day study; 

mortalities 

occurred within 

Brooks et al.

1998. 

Supplemental, 

quantitative.
17

Table 5. Most Sensitive Test Species Evaluated for Assessing Potential Ecological Effects 

of Diphacinone1.

Taxonomic 

Group

Study 

Type Tested Species Toxicity Endpoint

Acute Toxicity 

Classification/

NOAEC most 

sensitive 

endpoint(s)

MRID and 

Classification

24 hrs of dosing

Mammals

Acute oral 

(single 

dose)

Laboratory Rat 

(male), Rattus 

norvegicus

LD50 = 1.9 mg a.i./kgbw

Slope = na

Very highly toxic. 

14-day study, 

mortalities from 

days 2-9

05002272 

supplemental

Dietary 

(5-day 

exposure)

Laboratory Rat

LC50 = 2.08 mg a.i./kgdiet

Slope = 4.2

Very highly toxic. 

Observed 14 

days, mortalities 

days 4-12

Teeters 1981 

(TNM 75)4

(Supplemental)

Chronic No data

Terrestrial 

invertebrates

Acute 

contact No data

Freshwater 

fish3

Acute

Rainbow trout 

(Oncorhynchus 

mykiss) 

96-hr LC50 = 2.6 mg 

a.i./L

moderately toxic 432495025

(Acceptable)

Chronic No data

Freshwater 

invertebrates

Acute

Water flea 

(Daphnia

magna)

48-hr EC50 = 1.8 mg 

a.i./L 

moderately toxic 42282201 

(Acceptable)

Chronic No data

Estuarine/

marine fish

Acute and 

Chronic No data

Estuarine/

marine 

invertebrates

Acute and 

Chronic No data

Terrestrial 

plants

Seedling 

emergence

No data

Vegetative 

vigor No data

Aquatic 

plants and 

algae

Vascular No data

Non-vascular No data

1 Unless otherwise noted, toxicity data were derived using diphacinone (067701); however, these data are bridged 

to diphacinone sodium salt (067705).

2 Birds represent surrogates for terrestrial-phase amphibians and reptiles.

3 Freshwater fish are used as surrogates for aquatic-phase amphibians.

4 Teeters, W.R. (1981) Diphacinone technical: Toxicity to Laboratory Rat: Test No. 75. (U.S. Environmental 

Protection Agency, Pesticides Regulation Div., Agricultural Research Center, Animal Biology Laboratory, 

unpublished report.)

5Study was conducted using technical diphacinone sodium salt (067705); however, the LC50 is reported as 

concentration of diphacinone (067701) in water.

6.2 Secondary Toxicity

Secondary toxicity was evaluated in the laboratory setting by exposing carnivorous birds and 

mammals through the dietary route. Test animals were fed diphacinone in whole or ground 
18

carcasses, which were usually those of rats or mice, or in fortified meat. Most prey animals were 

fed treated bait, although some were dosed orally. Mortality was included as a measurement 

endpoint in all studies. Some studies also reported signs of toxicosis (e.g., bleeding, prolonged 

blood-coagulation time, abnormal behavior, or regurgitation) in surviving test animals. Although 

exposure scenarios, test species, and the number of test animals varied among the studies, 

collectively these studies provide useful information to characterize secondary hazards from 

short-term exposure. Though these types of secondary exposure studies provide information on 

the potential effects from diphacinone exposure that may occur under field conditions, it is often 

not possible to quantify the level of exposure (rodenticide residues in primary consumers or food 

consumption by secondary consumers) or the sensitivity of the exposed animals to the 

rodenticide.

Nine percent mortality was recorded in three secondary bird exposure studies that involved 34 

individual birds from five species (Table 6). Test species were barn owls, great horned owls, 

saw-whet owls (Aegolius acadicus), golden eagles, and American crows (Corvus 

brachyrhynchos). Thirteen (42%) of the survivors displayed some signs of toxicity. In three 

secondary mammal exposure studies, 19 (58%) of 33 test mammals died after feeding on rodents 

fed diphacinone, liver tissue from owls fed diphacinone, or fortified meat. Species affected 

included mink (Mustela vison), mongoose, ermine, deer mice, rats, and dogs (Table 7). 
19

Table 6. Observed Effects of Diphacinone (067701) on Birds Consuming Contaminated Carcasses

Secondary 

species Prey offered to birds No. prey offered daily per bird

No. days birds 

exposed

No. birds 

exposed

No. birds 

dead

No. survivors 

with signs of 

diphacinone 

toxicitya

Reference

(MRID)

Great horned 

owl

Mice fed choice of 

0.01% bait or 

untreated food for 10 

days

2 5 3 2 1 (ct)

Mendenhall and 

Pank 1980

MRID # 

46750931

Saw-whet owl

Mice fed choice of 

0.01% bait or 

untreated food for 10 

days

2 5 1 1 No survivors

Mendenhall and 

Pank 1980

MRID # 

46750931

Barn owl

Mice fed choice of 

0.01% bait or 

untreated food for 10 

days

Ad libitum 10 2 0 0

Mendenhall and 

Pank 1980

MRID #

46750931

American 

crow

Rats fed 0.005% bait 

until death

1

1-2

b

1

6

10

11

0

0

0

5 (eb/ct)

Massey et al.

1997

Golden eagle Meat laced at 2.7 mg 

a.i./kg 454 g 510

4

3

0

0

4 (eb/ct)

3 (eb/ct)c

Savarie.et al.

1979

MRID# 

00079312

a

eb = external bleeding; ih = internal hematoma; bl = bleeding (unspecified); ct = increased blood coagulation time; nr = not reported

b offered 1 rat per crow for 5 days and 2 rats per crow on day 6

c general weakness of all eagles was observed after 5 days
20

Table 7. Observed Effects of Diphacinone (067701) on Mammals Consuming Contaminated Carcasses

Secondary 

species

Prey offered to 

mammals

No. prey offered 

daily per 

mammal

No. days 

mammals 

exposed

No. 

mammals 

exposed

No. 

mammals 

dead

No. survivors 

with signs of 

diphacinone 

toxicitya

Reference

(MRID)

Mink

Nutria fed 0.01% 

carrot bait for up to 10 

days

Ad libitum 5-18 3 3 no survivors Evans and Ward 

1967 b

Mongoose Rats fed 0.005% bait 

for 5 days 1

1

3

5

6

7

8

10

1

1

2

1

1

1

1

0

1

2

1

1

1

1

nr

no survivors

no survivors

no survivors

no survivors

no survivors

no survivors Pank and Hirata 

1976

Ermine MRID# 2467 Deer mice fed 0.01% 

bait for 10 days 2 5 2 1 nr

Striped skunk Deer mice fed 0.01% 

bait for 10 days 2 5 5 0 nr

Deer mouse

Liver from 

diphacinone poisoned 

owls

1 g daily 7 4 1 3 (ct)

Rat Meat containing 0.5 

mg a.i./kg Ad libitum 6 8 4 nr

Savarie et al.

1979

Dog 

(domestic)

Nutria fed 0.01% 

carrot bait for up to 10 

days

Ad libitum 6-10 3 3 no survivors Evans and Ward 

1967b

a

eb = external bleeding; ih = internal hematoma; bl = bleeding (unspecified); ct = increased blood coagulation time; nr = not reported

b Cited in US EPA (2004b) Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative Approach
Page 21 of 60

6.3 Incident Database Review

A thorough review and analysis of available incident reports for all registered

anticoagulant rodenticides was completed in 2013, and a summary of the 24 diphacinone 

wildlife incidents reported with a certainty of possible, probably, or highly probable is 

included in Appendix D. This means that, at a minimum, there was supporting evidence 

(e.g., hemorrhaging) and/or residue data to indicate that the wildlife involved in the 

incident was adversely affected by exposure to an anticoagulant rodenticide and/or an 

independent wildlife specialist, based on findings of a necropsy examination and 

toxicological analysis, identified an anticoagulant rodenticide as the cause of death in the 

incident report. The summary of incident reports will be updated at the time of the 

Registration Review.

The reported avian species include a granivorous pigeon and carnivore/scavenger birds 

that include the snowy owl, great horned owl, turkey vulture, bald eagle, red-tailed hawk, 

and Cooper’s hawk. The reported mammalian species include herbivorous and 

granivorous deer, rabbits, squirrels, and kangaroo rat. Omnivorous mammals such as a 

raccoon and feral pig and carnivores including the San Joaquin kit fox, coyote, bobcat, 

and mountain lion were also cited in the reported incidents. The types of species 

involved in the reported incidents indicate that non-target species are likely being 

exposed via direct ingestion of the bait or through secondary exposure (i.e., ingesting a 

contaminated prey item). 

Although most of the reported wildlife incidents involve animals found dead, there are 

several rodenticide incidents that involve incapacitated animals (most of which died after 

being found). They demonstrate that animals exposed to rodenticides may be 

incapacitated in ways that would almost certainly make them more vulnerable to 

predators and accidental deaths (e.g., car or window strikes). If an animal dies due to 

predation or an accident, their death may not necessarily be attributed to a pesticide, even 

if it is a contributing factor.

7 Exposure Pathways of Concern

The environmental fate properties and use patterns of diphacinone indicate that nontarget consumption of bait, consumption of individuals that have consumed bait, and 

runoff represent potential transport mechanisms of diphacinone to aquatic and terrestrial 

organisms. 

Drinking water and inhalation exposure pathways were screened using the SIP 

(Screening Imbibition Program) and STIR (Screening Tool for Inhalation Risk) screening 

methods SIP and STIR are described in detail at: http://www2.epa.gov/pesticidescience-and-assessing-pesticide-risks/models-pesticide-risk-assessment#terrestrial . The 

drinking water pathway was found not to be an exposure pathway of potential concern for 

acute and chronic risks to mammals as well as chronic risks to birds due to low solubility 

of diphacinone. The inhalation exposure pathway was found not to be an exposure 
Page 22 of 60

pathway of concern for birds due to the low volatility of diphacinone. SIP and STIR 

results are presented in Appendix C.

8 Analysis Plan

8.1 Stressors of Concern

8.1.1 Ecological Risk 

Diphacinone sodium salt (067705) easily and quickly converts to diphacinone (067701) 

by hydrolysis in the environment. Therefore, all environmental fate and toxicity data for 

diphacinone (067701) will be bridged to diphacinone sodium salt (067705). Fate and 

toxicity data are not available for diphacinone sodium salt (067705). Collectively, these 

chemicals will be referred to as diphacinone, and one common risk assessment will be 

conducted.

Diphacinone has two major degradates: diphenylglycolic acid and carbon dioxide. Acute 

oral toxicity of diphenylglycolic acid to the mouse is LD50 = 2000 mg/kg-bw2. For the 

outdoor uses of diphacinone, it is formulated in pelleted bait or weather-resistant 

rodenticide products, it is probable that contact of this degradate with soil and water will be 

minimal. Furthermore, because risk is expected to result from direct consumption of bait 

products or from consumption of prey which directly consumed the bait, the formation of 

degradation products in the soil and water is not a major concern in this assessment. Risk 

from the diphenylglycolic acid degradate was, therefore, not quantified.

8.1.2 Drinking Water 

The previous assessments concluded that due to the application amounts and methods and 

low water solubility of diaphacinone, surface water or ground water contamination with 

diphacinone is unlikely. No drinking water assessment will be needed.

8.2 Measures of Exposure 

In this assessment, transport of diphacinone through runoff to water bodies is considered 

in deriving quantitative estimates of diphacinone. With a vapor pressure of 1.0 x 10-8torr

and a calculated Henry’s Law constant 2 x 10-10 atm∙m3∙mol-1for diphacinone (067701), 

volatilization and atmospheric transport are unlikely. 

For this registration review, it will be assumed that terrestrial animals could be exposed 

to diphacinone through two pathways. Animals may directly consume bait (primary 

 

2 See reference at: http://toxnet.nlm.nih.gov/cgi-bin/sis/search2/r?dbs+hsdb:@term+@DOCNO+7709
Page 23 of 60

consumption), or animals may consume contaminated carcasses either killed or 

scavenged by the consumer (secondary consumption). Both approaches and the expected 

exposure levels are detailed below. It is important to note that these methods are different 

from those typically used in EFED risk assessments.

8.2.1 Estimating Aquatic Exposure

Aquatic exposure due to runoff will be estimated using the Tier 1 GENEEC model and 

input parameters provided in Table 8. GENEEC is a metamodel of the Tier 2 models 

PRZM and EXAMS and is hard-wired to a single, high exposure scenario which is 

intended to be protective of aquatic environments for all crops on a national basis. While 

the specific scenario built into GENEEC is a 10 ha field draining into a 1 ha pond, 2 

meters deep, with no outlet, this scenario is intended to serve as a surrogate for a wide 

variety of small vulnerable water bodies that occur near the top of watersheds. These 

include prairie potholes, swamps, bogs, and other wetlands, playa lakes, and zero and 

first-order streams. 

Table 8. Diphacinone Input Values (GENEEC) for Aquatic Exposures 

Parameter Value Comment

Solubility 0.3 mg/L http://extoxnet.orst.edu/pips/diphacin.htm

Hydrolysis Stable at pH 7 and 9 MRID 43582401

Photolysis in Water Stable DP268619 (2000)

Photodegradation on Soil Stable Conservation assumption

Aerobic Soil Degradation 90 days (half-life) 30 days in single soil study (MRID 

42035001)– adjusted to 90 days (3X) 

for model input 

Aerobic Aquatic Degradation 180 days (half-life) 2X aerobic soil value

Koc 1700 L/kg Based on empirical approach in Section 

5.1.

Incorporation Depth 0.0 inches All labels for broadcast application do 

not allow for incorporation.

Application Rate 0.0136 lb ai/ac Highest labeled application rate appears 

on the SLN, CA78046: “Use a 

mechanical seed spreader calibrated to 

evenly spread 2 oz of bait to cover 40 to 

50 square feet near active burrows or 

runways. Retreat every other day for 3 to 

4 applications.” Most labels that permit 

broadcast application restrict the 

maximum single application rate to 10 

lbs product/acre (0.0005 lbs a.i./acre). 

Number of Apps. 4

Application Interval 2 days
Page 24 of 60

The GENEEC results based on the input values of Table 8 are presented below:

The estimated environmental concentrations (EECs) are 0.731 μg/L, 0.685 μg/L, and 

0.607 μg/L, respectively for the peak concentration, 21-day average concentration, and 

60-day average concentration. Considering the low water solubility of 0.3 mg/L, these 

EECs are only in the range of about 0.2% of solubility; therefore, the likelihood of 

aquatic impacts from the exposure viewpoint is insignificant.

8.2.2 Estimating Primary Terrestrial Exposure

EFED’s exposure assessment for the rodenticides differs from that for most other 

pesticides. For a rodenticide, the bait itself is the potential food item of concern. Thus, 

the amount of active ingredient in the formulated bait is used as an estimated 

environmental concentration (EEC). This information is used to estimate the amount of 

grain bait that birds and mammals of various sizes need to consume to obtain a dose 

expected to be lethal to 50% of the individuals in the population (i.e., LD50 dose). 

Estimates of food-ingestion rates (g dry matter per day) are determined from established 

allometric equations presented in the Wildlife Exposure Factors Handbook (USEPA 

1993). The concentration of diphacinone in grain bait is also used to estimate dietary 

exposure (mg a.i. per kg in bait). 

8.2.2.1 Expected Diphacinone Accumulation through a Single Feeding 

on Bait 

Exposure through bait consumption will be calculated using two methodologies. For the 

first method, diphacinone exposure is calculated as mg a.i./kg-bwt, where kg-bwt is the 

kilograms of the consuming individual for three standard weight classes of passeriforms 

and rodents. Exposure (food dry weight consumption) estimates were derived using 

allometric equations from USEPA (1993). The allometric equations for passeriform birds 

 RUN No. 1 FOR Diphacinone ON Rodent * INPUT VALUES * 

 --------------------------------------------------------------------

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP

 ONE(MULT) INTERVAL Koc (PPB ) (%DRIFT) (FT) (IN)

 --------------------------------------------------------------------

 0.014( 0.055) 4 2 1700.0 300.0 GRANUL( 0.0) 0.0 0.0

 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 

 --------------------------------------------------------------------

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED

 (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND) 

 --------------------------------------------------------------------

 90.00 2 0.00 0.00- 0.00 180.00 180.00

 GENERIC EECs (IN NANOGRAMS/LITER (PPTr)) Version 2.0 Aug 1, 2001

 --------------------------------------------------------------------

 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY

 GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC

 --------------------------------------------------------------------

 731.10 723.89 684.96 606.70 555.46
Page 25 of 60

and rodent mammals were used as these would best approximate those individuals with 

high potential for consuming grain and they would give the most conservative exposure 

estimates. Food dry weight was converted to wet weight assuming the bait contained 10% 

water, similar to the assumption that seeds for wildlife consumption contain 10% water 

(USEPA 1993). Formulas for calculation of dose estimates are provided in Table 9, and 

diphacinone exposure estimates (on a dose basis) are provided in Table 10. 

Table 9 Formulas for Calculation of Daily Diphacinone Intake based on Consumption of 

Bait.

Passeriform bird food intake (g, dry weight): FI (g dry-wt/day) = 0.398 * Wt(g)0.850

Rodent mammal food intake (g, dry weight): FI (g dry-wt/day) = 0.621 * Wt(g)0.564

Food intake (g, wet weight): FI (g wet-wt/day) = FI (g dry-wt/day) / 0.90

Diphacinone intake (mg a.i./kg-bwt/day) = FI (g wet-wt/day) * mg a.i./kg-bait / Wt(g)

Where: Wt(g) = weight (in grams) of the bird or mammal consumer

mg a.i./kg-bait = 50 or 100 depending on diphacinone concentration in bait

Table 10. Expected Daily Diphacinone Intake for Default Bird and Mammal Weights

based on Consumption of Bait.

Weight 

(g)

Food intake 

(g drywt/day)

Food intake 

(g wetwt/day)

Diphacinone intake (mg a.i./kg-bwt/day)

Bait concentration = 

50 mg a.i./kg-bait

Bait concentration = 

100 mg a.i./kg-bait

Passeriform 

Birds*

20 5.1 5.6 14.1 28.2

100 19.9 22.2 11.1 22.2

1000 141.2 156.9 7.8 15.6

Rodent 

Mammals

15 2.9 3.2 10.6 21.2

35 4.6 5.1 7.3 14.6

1000 30.6 34.0 1.7 3.4

*surrogate for reptiles and terrestrial-phase amphibians

8.2.2.2 Expected Diphacinone Accumulation through Multiple Feedings 

on Bait 

Available data on the retention times of diphacinone in animal tissues are provided in 

Table 11. Yu et al. (1982) studied the metabolism and disposition of diphacinone in rats 

and mice. Rats given a single oral dose of radiolabeled diphacinone at either 0.18 or 0.4 

mg a.i./kg, about 70% of the dose was eliminated in feces and 10% in urine within 8 
Page 26 of 60

days, whereas about 20% of the dose was retained in body tissues. Mice given a single 

dose of 0.6 mg a.i./kg eliminated most diphacinone within 4 days, and only 30% was 

retained in body tissues. In another study, cattle that received a single injection of 1 mg 

a.i./kg had almost constant residue concentrations in liver and kidney at 30, 60, and 90 

days after dosing (Bullard et al. 1976). Crowell et al. (2013) evaluated heptatic half-life 

of diphacinone in red deer, pigs, and cattle. The diphacinone half-life in red deer and pigs 

(6 and 12.4 days, respectively) was similar to much of the earlier data. The estimated 

half-life of diphacinone in cattle livers was much longer (similar to the cattle data 

obtained by Bullard et al. (1976). These data demonstrate that there is high species 

variation in elimination rates of diphacinone in mammalian livers. 

Diaz and Whitacre (1976) orally dosed rats with diphacinone (0.32 mg a.i./kg/day) for 

one or two days. Rats dosed for one day were sacrificed at 48 hours, and rats dosed for

two consecutive days were sacrificed 72 hours after the second dose. In rats dosed once

and sacrificed after 48 hours, about 5% of the dose was excreted in feces and urine, 61% 

was retained in body tissues, and 34% was not recovered. Intestines, liver, and hide/tail 

had the highest percentages of diphacinone with 22, 19, and 11%, respectively. In rats 

dosed twice, 45% of the total dose was excreted, 25% was retained in body tissues, and 

30% was not recovered. The body tissues retaining the most diphacinone at 96 hours 

were the hide/tail, liver, intestine, and blood (percentage of diphacinone ranged from 4 to 

6.5%). 

Table 11. Retention of Diphacinone in Liver

Species Dose (mg a.i./kg) # doses Liver retention (days) Reference (MRID)

Pig 12.5 (oral) 3 or 5 Half-life = 5.43 days Fisher 2006

Pig 1.5 (oral) 1 Half-life = 12.4 days Crowell et al. 2013

Rat 1.5 (oral) 1 Half-life = 3 days Fisher et al. 2003 

(48190801)

Rat 0.18 or 0.4 (oral) 1

20% of dose in body tissues at 8 days, 

highest concentrations in liver 

(1.4 and 1.0 mg a.i./kg-liver, 

respectively)

Yu et al. 1982

Mouse 0.6 (oral) 1

30% of dose in body tissues at 4 days, 

highest concentrations in liver 

(0.6 mg/kg-liver)

Yu et al. 1982

Cattle 1.0 (injection) 1 Half-life > 90 days Bullard et al. 1976

Cattle 1.5 (oral) 1

Trial 1: Initial (day 0 to 30): 9.4 days:

Terminal (day 30 onwards): 25.2 days

Trial 2: Initial(day 0 to 30): 4.1 days;

Terminal (day 30 onwards): 35.4 days

Crowell et al. 2013

Red deer 1.5 (oral) 1 Half-life = 6 days Crowell et al. 2013

As indicated previously, diphacinone typically causes mortality several days after 

ingestion, which may allow target animals consume bait for several days before dying. 

This can lead to doses that far exceed the lethal dose. A compound that accumulates in 

body tissues may pose greater risk to primary and secondary consumers, especially if 

repeated sublethal exposure results in the accumulation of a lethal dose or if additional 
Page 27 of 60

exposures occur before the lethal dose has taken its effect (i.e., leading to a dose that is 

beyond what is sufficient to cause mortality). 

Cumulative rodenticide doses for animals consuming bait for six consecutive days were 

also calculated using formulae in Table 12. This analysis will assume that 100% of the 

daily diet of the animals is represented by the rodenticide bait and that they eliminate the 

diphacinone with a half-life of 12.4 days based on the highest definitive liver half-life 

value (Table 11). In the formula, the variable “C” represents the concentration of the 

pesticide in the bait. The elimination rate constant (k) was calculated using the estimated 

diphacinone half-life (t1/2 = 12.4 days), and food intake (FI) was calculated according to 

the allometric equation for each taxonomic group (Table 12). The resulting cumulative 

body burden concentrations of diphacinone are presented in Table 13. 

Table 12. Formulas for Calculation of Diphacinone Body Burden based on 

Consumption of Bait for Six Consecutive Days.

D D e FI C

k

t t

* *  ( 1) 





  1/ 2

k  ln 2 t

Table 13. Calculated diphacinone body burden in avian and mammalian consumers of 

bait after six days of exposure 

Body weight 

(g)

Bait concentration = 50 mg a.i./kg-bait Bait concentration = 100 mg a.i./kg-bait

Passerine Generic Bird Passerine Generic Bird

20 73.7 66.1 175.4 132.2

100 57.9 37.7 115.8 75.4

1000 41.0 16.9 82.0 33.8

Rodent Generic Mammal Rodent Generic Mammal

15 55.3 42.1 110.6 84.2

35 38.2 36.2 76.4 72.4

1000 8.9 19.9 17.8 39.8

8.2.2.3 Expected Diphacinone Exposure based on Bait Concentration

The second exposure method for primary consumption of bait results in a diet 

concentration of 50 or 100 mg a.i./kg-bait (concentrations of diphacinone as packaged in 

bait).

8.2.3 Estimating Secondary Terrestrial Exposure

Secondary exposure analysis (from consumption of contaminated individuals) requires

consideration of residues in tissues of target and non-target organisms that are commonly 

consumed by predators and scavengers. Moreover, it is important to know how long the 

residue persists in body tissues. Residue concentrations for non-target animals fed 

chlorophacinone were submitted by the registrant and are available in open literature. 

Design and methodology vary among studies, adding unknown variability to the results 

and analysis. Pending development of additional methods and testing requirements for 
Page 28 of 60

such studies, these tests provide the best data available. 

The determination of diphacinone intake for individuals consuming diphacinone 

poisoned animals or carcasses is calculated in a manner similar to the approach for 

individuals consuming bait (Section 3.3.1). Empirical residue data will be used instead of 

bait concentration of diphacinone (Table 14). Diphacinone body burdens in deceased 

field and laboratory studies were determined in mammals, after exposure to diphacinone 

bait. Data from four studies were available in which deceased ground squirrels were 

collected from treated fields and analyzed for diphacinone residues. For all studies, it was 

assumed the concentrations were reported using wet weights of the mammals. Mean 

concentrations ranged from 0.9 to 1.4 mg a.i./kg-bw, with reported individual values 

ranging from 0.48 to 3.4 mg a.i./kg-bw. Field collected data are subject to a number of 

uncertainties including, but not limited to: 

 possible partial decomposition of bodies in field, 

 collection may miss carcasses with highest body burdens, and

 collection may miss individuals that were rapidly predated, died off site, or died 

underground.

Because of the lack of data on diphacinone residues in birds, amphibians, and reptiles, it 

was assumed the mammal body burden data would be relevant for all the evaluated 

taxonomic groups. Due to the uncertainties regarding adequate sampling to capture the 

full distribution of carcass residue values, the maximum reported individual value, 3.4 

mg a.i./kg-carcass, will be used for this assessment. 

Table 14. Measured Residue Levels of Diphacinone in Field Exposed California Ground 

Squirrels

Mg a.i./kg 

bait

Sample 

size Days exposed

Mean whole-carcass 

residue in mg a.i /kgcarcass (range)Reference

50 10 unknown 1.4 (0.6-3.4) Baroch 1994a

MRID# 43534601

50 7 unknown 0.9 (0.48-1.89) Baroch 1994b

MRID# 43534602

100 10 unknown 1.4 (0.6-2.6) Baroch 1994a

MRID# 43534601

50 and 100a 76 unknown 0.98 Goodall et al. 2002

MRID# 46117303

a

the study did not allow for distinguishing among squirrels exposed to 50 mg a.i./kg and 100 mg a.i./kg baits

Diphacinone exposure through carcass consumption is calculated as mg a.i./kg-bwt, 

where kg-bwt is the kilograms of the consuming individual for three weight classes of 

birds and mammals. For this analysis, bird weight classes of 100, 1000, and 5000 g 

individuals and mammal weight classes of 50, 1000, and 3000 g individuals were used to 

better represent the larger size of carnivores and scavengers relative to the full range of 

bird and mammal weights. The measured maximum body burden in the prey was then 

used to estimate rodenticide exposure in the secondary consumer using the general food 

intake allometric equations described in Section 3.1 above. Secondary consumers were 
Page 29 of 60

assumed to be mammals weighing 50g, 1000g, or 3000g, or birds weighing 100g, 1000g, 

or 5000g. For example, American kestrels range from 100-150g, red-tailed hawks range 

from 900-1000g and bald eagles range from 4000-5000g (Dunning 1984). Exposure 

(food dry weight consumption) estimates were derived using the generic bird and 

mammal allometric equations from (EPA 1993). Food dry weight was converted to wet 

weight assuming the consumed prey/carcass contained 68% water (USEPA 1993). 

Formulas for calculation of dose estimates are provided in Table 15, and diphacinone 

exposure estimates (on a dose basis) are provided in Table 16. Secondary consumers that 

were snakes were assumed to consume prey equivalent to their body weight in a single 

feeding; however, feedings would not occur on a daily basis (King, 2002). 

Table 15. Formulas for Calculation of Daily Diphacinone Intake for Birds and 

Mammals based on Consumption of Carcasses.

Bird food intake (g, dry weight): FI (g dry-wt/day) = 0.648 * Wt(g)0.651

Mammal food intake (g, dry weight): FI (g dry-wt/day) = 0.235 * Wt(g)0.822

Food intake (g, wet weight): FI (g wet-wt/day) = FI (g dry-wt/day) / 0.32

Diphacinone intake (mg a.i./kg-bwt/day) = FI (g wet-wt/day) * 3.4 mg a.i./kg-carcass 

/ Wt(g)

Where: Wt(g) = weight (in grams) of the bird or mammal consumer

Table 16. Expected Daily Diphacinone Intakes for Carnivorous Birds, Snakes, and 

Mammals based on Consumption of Contaminated Carcasses

Weight (g) Food intake 

(g dry-wt/day)

Food intake 

(g wet-wt/day)

Diphacinone intake 

(mg a.i./kg-bwt/day)1

Birds* 100 13.0 40.6 1.38

1000 58.2 181.7 0.62

5000 165.8 518.1 0.35

Snake** 50 16 50 3.4

250 80 250 3.4

500 160 500 3.4

Mammals 50 5.9 18.3 1.24

1000 68.7 214.7 0.73

3000 169.5 529.8 0.60

*surrogate for reptiles and terrestrial-phase amphibians

**Snakes are capable of eating the equivalent of their body weight in one meal; however, they will not consume 

that quantity of food on a daily basis.

1 See Table 15 for derivation.

The second exposure method for consumption of contaminated carcasses results in a 

carcass concentration of 3.4 mg a.i./kg-carcass (maximum measured concentration of 

diphacinone in carcasses). 
Page 30 of 60

8.2.4 Estimating Additional Environmental Exposures

Screening level calculations suggest that the drinking water pathway and inhalation 

pathways will not pose significant risks to birds and mammals (Appendix C). If 

additional information indicates there may be concerns, these pathways will be reevaluated at the time of the risk assessment. 

No monitoring data in surface water, in groundwater or in air were found from the USGS 

NAWQA program (http://water.usgs.gov/nawqa), the California Department of Pesticide 

Regulation CDPR (http://www.cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm) or from the 

USEPA STORET program. Water monitoring programs such as these generally monitor for 

agricultural pesticides and typically do not include analysis for rodenticides such as 

diphacinone. If water monitoring data are identified at the time the risk assessment is 

conducted, these data will be used for additional exposure characterization.

8.3 Measures of Effect 

Toxicity data presented in Section 6 of this problem formulation will be used to calculate 

risk quotients. Any additional information submitted by the registrant or found in the 

open literature prior to conduct of the risk assessment will also be considered. The open 

literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) 

(USEPA, 2007c), which employs a literature search engine for locating chemical toxicity 

data for aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of 

data can also provide insight into the direct and indirect effects of pesticides on biotic 

communities from loss of species that are sensitive to the chemicals and from changes in 

structure and functional characteristics of the affected communities.

9 Endangered Species Assessment

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), 

the Agency will evaluate risks to federally threatened and/or endangered (listed) species 

from registered uses of pesticides in registration review. The process for evaluating 

potential risks to listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm.

10 Endocrine Disruptor Screening Program

Diphacinone was not included in the first group or the second group of chemicals issued 

an order to conduct Tier 1 EDSP testing. For additional information the EDSP program, 

visit http://www2.epa.gov/endocrine-disruption . 
Page 31 of 60

11 Preliminary Identification of Data Gaps 

11.1 Fate

The environmental fate database for diphacinone is not complete (Table 17). However, 

due to the low water solubility of diphacinone (0.3 mg/L) and the relatively low aquatic 

toxicity, a data gap was not identified as these data are not necessary for risk assessment 

at this time.

Table 17. Available environmental fate data for diphacinone and remaining data gaps.

158

Guideline

(OPPTS)

Description MRID Classification

Are data 

needed for risk 

assessment?

Comments

835.1240

(163-1)

Adsorption/Desorption MRID 43582402 supplemental no

Data have not been 

submitted to fulfill this 

guideline. A data gap was 

not identified as these data 

are not necessary for risk 

assessment at this time.

835.2120

(161-1)

Hydrolysis MRID 43582401 supplemental no

835.2240

(161-2)

Photodegradation in water None NA no

835.2410

(161-3)

Photodegradation on soil None NA no

835.4100

(162-1)

Aerobic soil metabolism MRID 42035001 acceptable no

835.4200

(162-2)

Anaerobic soil metabolism None NA no

835.4300

(162-4)

Aerobic Aquatic 

Metabolism

None NA no

835.4400

(162-3)

Anaerobic Aquatic 

Metabolism

None NA no 

835.6100

(164-1)

Terrestrial Field 

Dissipation

None NA no

850.1730

(165-4)

Fish Bioconcentration 

Factor

None NA no

11.2 Effects

Tables 18 and 19 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are 

needed in order to support risk assessment. 

Inadequate data are available to further characterize the differential toxicity among bird 

species. In addition, there is evidence of different or multiple modes-of-action of 

diphacinone in different taxa. These differences were evidenced by the large variation in 

the LD50 between the bobwhite quail and the American kestrel and by the high mortality 

rates in the brown tree snake when no hemorrhaging was present upon necropsy (Section 

4.1). Additional toxicity data on a wider range of species or data exploring mode-ofaction would be beneficial to better understand the natural variation and to improve 
Page 32 of 60

confidence in the assessment of risk to non-target species. 

No data are available to assess the effects of long-term, low-dose exposure of 

diphacinone on avian reproduction (OCSPP 850.2300) or survival. Avian reproduction 

data are available for another registered indandione anticoagulant rodenticide, 

chlorophacinone. Mallard ducks exposed to dietary chlorophacinone for five days had an 

LC50 = 172 mg/kg-diet (MRID 41513103); however, nine of 16 (56%) adult females died 

exhibiting symptoms of anticoagulant poisoning during the avian reproduction study 

eating a diet containing only 0.96 mg a.i./kg-diet (MRID 489904002). EFED

recommends that additional data on effects of long-term low-dose exposure of 

diphacinone to birds through extended exposure dietary studies and avian reproduction 

studies be requested. 

No data for diphacinone are available to assess the effects of long-term, low-dose 

exposure on mammalian reproduction. Guidelines that would address this data gap are

the Prenatal Developmental Toxicity Study (870.3700) or Reproduction and Fertility 

Effects Study (870.3800). Neither of these studied have been submitted to the Agency for 

diphacinone. Given the observed effects in the reproductive studies reviewed for avian 

effects of chlorophacinone (bobwhite quail and mallards, discussed above) and 

mammalian effects of chlorophacinone (laboratory rat, MRID 43349501, and New 

Zealand white rabbit, MRID 43570801), the Agency is requesting data to evaluate 

reproductive effects of low doses of diphacinone on mammals. These data are important 

to determine exposure levels of diphacinone that would affect non-target mammals. 

No data are available to assess of the toxicity of diphacinone to terrestrial invertebrates. 

EFED does not have concerns for diphacinone exposure to insect pollinators such as bees 

and butterflies, as expected exposures would be low. Diphacinone is not applied as a 

spray and is not expected to be systemic; therefore, expected exposure on plants, 

including flowers, would be low. Insect pollinators would not be expected to feed on live 

animals or carcasses that may have been contaminated with diphacinone. Diphacinone 

exposure to terrestrial invertebrates may occur if individuals feed on the bait, feed on live 

animals contaminated with diphacinone residues, or feed on carcasses with diphacinone 

residues. No terrestrial invertebrate incidents have been reported for diphacinone.

The earthworm LC50 values for bromadiolone, a second generation rodenticide, at 24 h 

and 48 h were 145.70 μg/cm2and 25.03 μg/cm2, respectively, and at 14 d and 28 d were 

449.958 mg/kg-soil and 105.593 mg/kg-soil, respectively (Liu et al. 2015). Incidences of 

terrestrial invertebrates consuming bait containing an anti-coagulant rodenticide and 

subsequently excreting it have been documented (Fisher et al. 2007; Hernandez-Moreno 

et al. 2013). Toxicity of diphacinone to terrestrial invertebrates is unknown; however, 

there is evidence to suggest that toxicity may occur and that the exposure pathway for 

secondary exposure is complete. EFED is not requesting the full suite of pollinator 

protection studies as outlined in recent guidance (http://www2.epa.gov/pollinatorprotection/pollinator-risk-assessment-guidance). However, EFED does request an 

earthworm toxicity study for diphacinone and any additional existing data that 

demonstrate toxicity, or lack of toxicity, to diphacinone for terrestrial invertebrates. 
Page 33 of 60

EFED does not recommend requesting terrestrial plant, aquatic plant, chronic fish, or 

chronic aquatic invertebrate toxicity data at this time as these data would not be expected 

to change the conclusions of this risk assessment. There remains uncertainty in the level 

of risk for each of these taxonomic groups given the missing data; however, the expected 

exposures will be relatively low:

 Terrestrial plants - No data are available to assess of the toxicity of diphacinone 

to terrestrial plants; however, exposure to plants is also expected to be low since 

there is no spray application and the material is applied as a formulated bait or a 

treated grain. Diphacinone binds strongly to organic material (i.e., the formulated 

bait or grain) and little is expected to be available for runoff or leaching. No plant 

incidents have been reported for diphacinone.

 Aquatic plants – No data are available to assess the toxicity of diphacinone to 

aquatic plants; however, aquatic exposure is also expected to be low since there is 

no spray application and the material is applied as a formulated bait or a treated 

grain. Diphacinone binds strongly to organic material (i.e., the formulated bait or 

grain) and little is expected to be available for runoff or leaching. No aquatic 

incidents have been reported for diphacinone.

 Chronic fish and aquatic invertebrates – No data are available to assess the 

chronic toxicity of diphacinone to fish and aquatic invertebrates; however, aquatic 

exposure is expected to be low since there is no spray application and the material 

is applied as a formulated bait or a treated grain. Diphacinone is moderately 

acutely toxic to fish and invertebrates, and chronic effects would not be 

unexpected. However, diphacinone binds strongly to organic material (i.e., the 

formulated bait or grain) and little is expected to be available for runoff or 

leaching for the current uses. No aquatic incidents have been reported for 

diphacinone.

Table 18. Available ecological effects data for terrestrial organisms exposed to diphacinone

and remaining data gaps. 

OCSPP 

Guideline Data Requirement Submitted Studies (MRID)

Study 

Classification

Are data 

needed for 

risk

assessment?

Current Additional Data 

Need

850.2100 Avian oral toxicity 42245201 acceptable Yes Data are requested for avian 

acute oral with passerine

Rattner et al 

2010

supplemental

00128411 supplemental

Rattner et al 

2011

supplemental

850.2200 Avian dietary toxicity 42408801 acceptable No --

42408802 acceptable

850.2300 Avian reproduction (None) (N/A) Yes Data are requested for avian 

reproduction toxicity testing 

for two species. 
Page 34 of 60

Table 18. Available ecological effects data for terrestrial organisms exposed to diphacinone

and remaining data gaps. 

OCSPP 

Guideline Data Requirement Submitted Studies (MRID)

Study 

Classification

Are data 

needed for 

risk

assessment?

Current Additional Data 

Need

Non-guideline Avian inhalation (None) (N/A) No Data have not been 

submitted to fulfill this 

guideline. A data gap was 

not identified as these data 

are not necessary for risk 

assessment at this time.

850.3020 Honey bee acute contact 

toxicity

(None) (N/A) No Data are requested to assess 

risk to terrestrial 

invertebrates. Registrant may 

submit toxicity data for other 

terrestrial invertebrate 

species to address this data 

gap.

850.3030 Honey bee residue on 

foliage

(None) (N/A) No Data have not been 

submitted to fulfill these

guidelines. Data gaps were

not identified as these data 

are not necessary for risk 

assessment at this time.

OECD TG 

213

Acute oral toxicity to 

adult honey bees

(None) (N/A) No

OECD TG 

237

Acute oral toxicity to 

larval honey bees

(None) (N/A) No

Non-guideline Chronic oral toxicity to 

adult honey bees

(None) (N/A) No

Non-guideline Chronic oral toxicity to 

larval honey bees

(None) (N/A) No

Non-guideline Field trial of residues in 

pollen and nectar

(None) (N/A) No

OECD 

Guidance 75

Semi-field testing for 

pollinator

(None) (N/A) No

850.3040 Field testing for 

pollinator

(None) (N/A) No

850.3100 Earthworm Subchronic 

Toxicity Test 

(None) (N/A) Yes Data are requested for 

earthworm toxicity.

850.4100 Seedling Emergence and 

Seedling Growth

(None) (N/A) No Data have not been 

submitted to fulfill this 

guideline. A data gap was 

not identified as these data 

are not necessary for risk 

assessment at this time.

850.4150 Vegetative Vigor (None) (N/A) No
Page 35 of 60

12 References 

Open Literature

Brooks, J.E., Savarie, P.J. and J.J. Johnston. 1998. The oral and dermal toxicity of selected chemicals to 

Brown Tree snakes (Boiga irregularis). Wildlife Research 25:427-435.

Bullard, R.W., R.D. Thompson, G. Holguin. 1976. Diphenadione residues in tissues of cattle. Journal of 

Agricultural and Food Chemistry. 24:261-263.

Cox , P. and R.H. Smith. 1992. Rodenticide ecotoxicology: pre-lethal effects of anticoagulants on rat 

behavior. Proc. Vertebr. Pest Conf. 15:165-170.

Table 19. Available ecological effects data for aquatic organisms exposed to diphacinone

and remaining data gaps. 

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need

850.1010 Freshwater 

invertebrate 

acute toxicity

42282201* Currently under 

re-evaluation

No --

850.1025

850.1035

850.1045

850.1055 

Saltwater 

invertebrate 

acute toxicity 

(None) (N/A) No Data have not been submitted to 

fulfill this guideline. A data gap 

was not identified as these data are 

not necessary for risk assessment 

at this time.

850.1075 Freshwater fish 

acute toxicity 

43249501** Acceptable No --

43249502** Acceptable

850.1075 Saltwater fish 

acute toxicity 

(None) (N/A) No Data have not been submitted to 

fulfill this guideline. A data gap 

was not identified as these data are 

not necessary for risk assessment 

at this time.

850.1300 Freshwater 

invertebrate 

life cycle 

(None) (N/A) No

850.1350 Saltwater 

invertebrates 

life cycle 

(None) (N/A) No

850.1400 Freshwater fish 

early-life stage

(None) (N/A) No

850.1400 Saltwater fish 

early-life stage 

(None) (N/A) No

850.1500 Fish life cycle (None) (N/A) No

850.4400 Aquatic plant 

Toxicity Test 

using Lemna spp.

(None) (N/A) No

850.4500 Algal toxicity (None) (N/A) No

850.4550 Cyanobacteria (None) (N/A) No

* Study being re-evaluated and may be re-classified as precipitate was observed in all test concentrations

** Studies conducted using diphacinone sodium salt (067705); toxicity values reported as diphacinone (067701)
Page 36 of 60

Crowell, M, C Eason, S Hix, K Broome, A Fairweather, E Moltchanova, J Ross and E Murphy. 2013. First 

generation anticoagulant rodenticide persistence in large mammals and implications for wildlife 

management. New Zealand Journal of Zoology,

http://dx.doi.org/10.1080/03014223.2012.746234

Diaz, L.I. and D.M. Whitacre. 1976. Excretion and retention of 14C-diphacinone in rats. Unpubl. report, 

submitted by Velsicol Chemical Corporation. 8 pp. (MRID: 106901)

Dunning, J. B., Jr. 1984. Body weights of 686 species of North American birds. Monograph Number 1. 

Western Bird Banding Association, Cave Creek, Arizona, USA

Fisher P 2006. Persistence of residual diphacinone concentrations in pig tissues following sublethal 

exposure. DOC Research & Development Series 249. Wellington, New Zealand, DOC. 19 p.

Fisher P, O’Connor C, Wright G, Eason CT 2003. Persistence of four anticoagulant rodenticides in the 

livers of laboratory rats. DOC Science Internal Series 139. Wellington, New Zealand, DOC. 19 p. MRID# 

48190801

Fisher, P., Spurr, E., Ogilvie, S., and Eason, C. 2007. Bait consumption and residual concentrations of 

diphacinone in the Wellington tree weta (Hemideina crassidens) (Orthoptera: Anostostomatidae). New 

Zealand Journal of Ecology 31(1): 104-110.

Hernandez-Moreno, D., de la Casa-Resino, I., Lopez-Beceiro, A., Fidalgo, L., Soler, F., Perez-Lopez, M. 

2013. Secondary poisoning of non-target animals in an Ornithological Zoo in Galicia (NW Spain) with 

anticoagulant rodenticides: a case report. Veterinarni Medicina, 58, 2013: (10): 553–559.

King, R.B. 2002. Predicted and observed maximum prey size – snake size allometry. Functional Ecology 

16: 766–772.

Massey, G., L. Valutis, and J. Marzluff. 1997. Secondary poisoning effects of diphacinone on Hawaiian 

crows: a study using American crows as surrogates. Unpubl. report, U. S. Fish and Wildlife Service, Pacific 

Islands Office. 12 pp.

Mendenhall, V.M. and L.F. Pank. 1980. Secondary poisoning of owls by anticoagulant rodenticides. Wildl. 

Soc. Bull. 8:311-315. MRID#s 46750931, 40077202, 00094694

Rattner, BA, KE Horak, SE Warner, DD Day, CU Meteyer, SF Volker, JD Eisemann, JJ Johnson. 2011. 

Acute toxicity, histopathology, and coagulopathy in American kestrels (Falco sparverius) following 

administration of the rodenticide diphacinone. Environmental Toxicology and Chemistry, Vol. 30, No. 5, 

pp. 1213–1222.

Sawhney, B. L. and Brown, K., Editors. 1989. Reactions and Movement of Organic Chemicals in Soils. 

SSSA Special Publication Number 22. Soil Science Society of America, Inc. Madison, WI. 

Savarie, P.J. and R.K. LaVoie. 1979. Secondary toxicity hazards of the anticoagulant brodifacoum to 

American kestrels (Falco sparverius). Unpubl. report, Denver Wildlife Research Center. 24 pp. MRID# 

80244, 00079312

U.S. Environmental Protection Agency. 1993. Wildlife Exposure Factors Handbook. Office of Research 

and Development. December. EPA/600/R-93/187

U.S. Environmental Protection Agency. 1998a. Guidelines for Ecological Risk Assessment. United States 

Environmental Protection Agency (USEPA). Risk Assessment Forum. Office of Research and 
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Development. Available at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12460 (Accessed June 19, 

2009).

U.S. Environmental Protection Agency.1998b. Reregistration Eligibility Decision (RED): Rodenticide 

Cluster. July 1998. EPA 738-R-98-007.

U.S. Environmental Protection Agency. 2004a. Overview of the Ecological Risk Assessment Process in the 

Office of Pesticide Programs. US EPA Office of Pesticide Programs, Environmental Fate and Effects 

Division.

U.S. Environmental Protection Agency. 2004b. Potential Risks of Nine Rodenticides to Birds and 

Nontarget Mammals: a Comparative Approach. July 2004. US EPA Office of Pesticide Programs, 

Environmental Fate and Effects Division.

U.S. Environmental Protection Agency. 2011. Risks of Diphacinone Use to the Federally Threatened 

Alameda Whipsnake (Masticophis lateralis euryxanthus), California Tiger Salamander (Ambystoma 

californiense), and the Federally Endangered Salt Marsh Harvest Mouse, California Tiger Salamander 

(Ambystoma californiense) Sonoma County Distinct Population Segment and Santa Barbara County 

Distinct Population Segment, and San Joaquin Kit Fox (Vulpes macrotis mutica). US EPA Office of 

Pesticide Programs, Environmental Fate and Effects Division. June 21, 2011.

Watt, B.E., A.T. Proudfoot, S.M. Bradberry, and J.A. Vale. 2005. Anticoagulant rodenticides. Toxicol. 

Rev. 24(4):259-269.Yu, C.C., Y.H. Atallah, and D.M. Whitacre. 1982. Metabolism and disposition of 

diphacinone in rats and mice. Drug Metabolism and Disposition 10:645-648.

Environmental Fate Data Submitted To Support Registration for PC Code 067701

Guideline: 161-1 Hydrolysis

-------------------------------------------------------------------------------------

MRID: 95000 Atallah, Y.H.; Diaz, L.I.; McGhee, M.E.; et al. (1977) Aqueous Hydrolysis of Diphacinone: 

Report 408398, No. 3. (Un- published study received Feb 17, 1981 under 876-EX-35; submitted by 

Velsicol Chemical Corp., Chicago, Ill.; CDL:244385-A) 

MRID: 127706 Velsicol Chemical Corp. (1978) Chemical & Physical Properties: (Diphacinone). 

(Compilation; unpublished study received Aug 21, 1978 under 876-EX-36; CDL:234817-A) 

MRID: 127709 Diaz, L.; Schwemmer, B.; Atallah, Y.; et al. (1976) Photolysis of 14C-diphacinone in 

Aqueous Solution: Report 40839, No. 5. (Un- published study received Aug 21, 1978 under 876-EX-36; 

submitted by Velsicol Chemical Corp., Chicago, IL; CDL:234819-D) 

MRID: 134837 Velsicol Chemical, Corp. (1978) Chemical & Physical Properties: ?Diphacinone|. 

(Compilation; unpublished study received Jul 12, 1978 under 876-EX-35; CDL:234419-A) 

MRID: 134840 Yu, C.; Atallah, Y.; Whitacre, D. (1976) Partition Coefficients for Diphacinone, VEL5026, VEl-4207, VEL-4283 and Leptophos: Project No. 408398; Report No. 2. (Unpublished study 

received Jul 12, 1978 under 876-EX-35; submitted by Velsicol Chemical Corp., Chi- cago, IL; 

CDL:234423-D) 

MRID: 136281 Atallah, Y.; Diaz, L.; McGee, M.; et al. (1977) Aqueous Hydrolysis of Diphacinone: 

Project No. 408398; Report No. 3. (Unpublished study received Jul 12, 1978 under 876-EX-35; submitted 

by Velsi- col Chemical, Corp., Chicago, IL; CDL:234423-E) 

MRID: 43582401 Riekena, C. (1995) Hydrolysis of Technical Diphacinone (2-(Diphenylacetyl)-1Hindene-1,3(2H)-dione): Lab Project Number: BEL/0894/C143. Unpublished study prepared by Bell Labs, 

Inc. 40 p. 
Page 38 of 60

MRID: 92049010 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00095000. Diphacinone -

Hydrolysis Study: Project No. 408398. Prepared by Velsicol Chemical Corp. 18 p. 

Guideline: 161-2 Photodegradation-water

-------------------------------------------------------------------------------------

MRID: 92049011 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00127709. Diphacinone -

Photodegradation in Water Study: Project No. 408398. Prepared by Velsicol Chemical Corp. 22 p. 

Guideline: 162-1 Aerobic soil metabolism

-------------------------------------------------------------------------------------

MRID: 128415 Atallah, Y.; Diaz, L.; Yu, C.; et al. (1978) Soil Degradation of the Rodenticide 

Diphacinone: Report 408398, No. 6. (Unpublished study received Aug 21, 1978 under 876-EX-36; 

submitted by Velsi- col Chemical Corp., Chicago, IL; CDL:234819-E) 

MRID: 42035001 Nomura, N.; Hilton, H. (1979) The Metabolism of (Carbon 14)-Diphacinone to Carbon 

Dioxide in Two Hawaiian Sugarcane Soils under Aerobic Conditions. Unpublished study prepared by 

Hawaiian Sugar Planters. 27 p. 

MRID: 44260501 Riekena, C. (1997) Aerobic Soil Metabolism of (carbon 14)-Diphacinone: (Final 

Report): Lab Project Number: 42430: BEL/0497/C192. Unpublished study prepared by Bell Labs, Inc. 116 

p. 

MRID: 92049012 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00128415. Diphacinone -

Aerobic Soil Metabolism Study: Project No. 408398-6. Prepared by Velsicol Chemical Corp. 22 p. 

Guideline: 162-2 Anaerobic soil metabolism

-------------------------------------------------------------------------------------

MRID: 92049013 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00128415. Diphacinone -

Anaerobic Soil Metabolism Study: Project 408398-6. Prepared by Velsicol Chemical Corp. 24 p. 

Guideline: 163-1 Leach/adsorp/desorption

-------------------------------------------------------------------------------------

MRID: 127711 Weber, J. (19??) Leachability of Atrazine, Buthidazole, Bromacil, Diuron, Diphacinone, 

and Prometon through a Lakeland Sand. (Unpublished study received Aug 21, 1978 under 876-EX-36; 

prepared by North Carolina State Univ., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:234819-

G) 

MRID: 127712 Nomura, N. (1978) Adsorption and Mobility of VEL 5026-14C in Five Hawaiian 

Sugarcane Soils. (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Hawaiian 

Sugar Planters' As- soc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL: 234819-H) 

MRID: 127713 Weber, J. (19??) Adsorption and Characterization of Diphacinone and Prometon on 

Lakeland Sand, Alamance Silt Loam, Ca-Montmorillonite, and Acidic Soil Organic Matter. (Unpublished 

study received Aug 21, 1978 under 876-EX-36; prepared by North Carolina State Univ., submitted by 

Velsicol Chemical Corp., Chicago, IL; CDL:234819-I) 

MRID: 134841 Weber, J.; Swain, L. (19??) Report to ...: Leachability of Atzrazine, Buthiazole, Bromacil, 

Diuron, Diphacinone and Prometon through a Lakeland Sand. (Unpublished study received Jul 12, 1978 

under 876-EX-35; prepared by N.C. State Univ., submitted by Velsicol Chemical, Corp., Chicago, IL; 

CDL:234423-I) 

MRID: 134842 Nomura, N. (1978) Adsorption and Mobility of VEL 5026-14C in Five Hawaiian 

Sugarcane Soils. (Unpublished study received Jul 12, 1978 under 876-EX-35; prepared by Hawaiian Sugar 

Planters' Assoc., submitted by Vesicol Chemical, Corp., Chicago. IL; CDL: 234423-J) 
Page 39 of 60

MRID: 134843 Weber, J.; Swain, L. (19??) Report to ...: Adsorption and Characterization of Diphacinone 

and Prometon on Lakeland Sand, Alamance Silt Loam, Ca-montmorillonite and Acidic Soil Organic Matter. (Unpublished study received Jul 12, 1978 under 876-EX-35; prepared by N.C. State Univ., submitted 

by Velsicol Chemical, Corp., Chicago, IL; CDL:234423-K) 

MRID: 43565801 Riekena, C. (1995) Leaching Through Soil of Technical Diphacinone (2-

(Diphenylacetyl)-1H-indene-1,2(2H)-dione): Lab Project Number: BEL/1194/C146. Unpublished study 

prepared by Bell Labs, Inc. 28 p. 

MRID: 43582402 Riekena, C. (1995) Leaching Through Soil of Technical Diphacinone (2-

(Diphenylacetyl)-1H-indene-1,3(2H)-dione): Lab Project Number: BEL/1194/C146. Unpublished study 

prepared by Bell Labs, Inc. 28 p. 

MRID: 92049014 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00127711. Leaching Study: 

?Diphacinone|. Prepared by North Carolina State University. 19 p. 

MRID: 92049015 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00127712. Diphacinone -

Leaching/Adsorption Study. Prepared by Hawaiian Sugar Planters Assn. 28 p. 

MRID: 92049016 Prasad, S. (1990) Haco, Co Phase 3 Summary of MRID 00127713. Diphacinone -

Adsorption Study. Prepared by North Carolina State University. 26 p. 

Guideline: 165-0 Accumulation Studies -- General

-------------------------------------------------------------------------------------

MRID: 127715 Ells, S. (1976) Kinetics of Aged Diphacinone in a Model Aquatic Ecosystem. 

(Unpublished study received Aug 21, 1978 under 876- EX-36; prepared by EG & G, Bionomics, submitted 

by Velsicol Chemical Corp., Chicago, IL; CDL:234819-K) 

Ecological Toxicity Data Submitted To Support Registration for PC Code 067701

Guideline: 71-1 Avian Single Dose Oral Toxicity

-------------------------------------------------------------------------------------

MRID: 73753 Fink, R (1976) Final Report: Acute Oral LD I50^--Mallard Duck: Project No. 107-122. 

(Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Truslow Farms, Inc., submitted 

by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-O) 

MRID: 106914 Calo, C. (1975) Letter sent to R. Ostrowski dated Jul 28, 1975: Acute toxicity studies--

Ramik mouse bait. (Unpublished study received Jun 28, 1977 under 876-124; submitted by Velsicol 

Chemical Corp., Chicago, IL; CDL:231295-AP) 

MRID: 128411 Fink, R. (1976) Acute Oral LD50--Mallard Duck--Technical Diphacinone: Project No. 

107-122. Final rept. (Unpublished study received Jul 12, 1978 under 876-EX-35; prepared by Truslow 

Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:234422-K) 

MRID: 42245201 Campbell, S.; Hoxter, K.; Smith, G. (1991) Diphacinone Technical: An Acute Oral 

Toxicity Study with the Northern Bobwhite: Lab Project Number: 284-103. Unpublished study prepared 

by Wildlife International Ltd. 24 p. 

Guideline: 71-2 Avian Dietary Toxicity

-------------------------------------------------------------------------------------

MRID: 73751 Fink, R. (1976) Final Report: Eight-Day Dietary LCI50^--Mallard Duck: Project No. 107-

121. (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Truslow Farms, Inc., 

submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-K) 
Page 40 of 60

MRID: 73752 Fink, R. (1976) Final Report: Eight-Day Dietary LCI50^--Bobwhite Quail: Project No. 107-

120. (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-N) 

MRID: 79639 Fink, R. (1975) Final Report: Eight-Day Dietary LCI50^--Bobwhite Quail: Project No. 107-

117. (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-G) 

MRID: 88743 Fink, R. (1975) Final Report: Eight-Day Dietary LCI50^--Mallard Duck: Project No. 107-

118. (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-H) 

MRID: 107432 Fink, R. (1976) Final Report: Eight-day Dietary LC50--Bobwhite Quail: ?Technical 

Diphacinone|: Project No. 107-120. (Unpub- lished study received May 12, 1976 under 876-124; prepared 

by Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:225250-A) 

MRID: 127697 Fink, R. (1975) Eight-day Dietary LC50: Bobwhite Quail: Diphaci- none: Project No. 107-

117. Final rept. (Unpublished study re- ceived Oct 29, 1975 under 876-184; prepared by Truslow Farms, 

Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL: 222349-A) 

MRID: 127698 Fink, R. (1975) Eight-day Dietary LC50: Mallard Duck: Diphacinone: Project No. 107-

118. Final rept. (Unpublished study received Oct 29, 1975 under 876-184; prepared by Truslow Farms, 

Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:222350-A) 

MRID: 128412 Fink, R. (1976) Eight-day Dietary LC50--Bobwhite Quail--Technical Diphacinone: Project 

No. 107-120. Final rept. (Unpublished study received Jul 12, 1978 under 876-EX-35; prepared by 

Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:234422-N) 

MRID: 128413 Fink, R. (1976) Eight-day Dietary LC50--Mallard Duck--Technical Diphacinone: Project 

No. 107-121. Final rept. (Unpublished study received Jul 12, 1978 under 876-EX-35; prepared by 

Truslow Farms, Inc., submitted by Velsicol Chemical Corp., Chicago, IL; CDL:234422-O) 

MRID: 42408801 Long, R.; Foster, J.; Hoxter, K. et al. (1992) Diphacinone Technical: A Dietary LC50 

Study with the Northern Bobwhite: Lab Project Number: 284-101A. Unpublished study prepared by Bell 

Labs, Inc. 32 p. 

MRID: 42408802 Long, R.; Foster, J.; Hoxter, K. et al. (1992) Diphacinone Technical: A Dietary LC50 

Study with the Mallard: Lab Project Number: 284-102B. Unpublished study prepared by Wildlife Intl. 36 

p. 

Guideline: 71-3 Wild mammal toxicity

-------------------------------------------------------------------------------------

MRID: 2467 Pank, L.F.; Hirata, D.N. (1976) Primary and Secondary Toxicity of Anticoagulant 

Rodenticides: Job Completion Report: Work Unit DF-103.7. (Unpublished study received on unknown 

date under unknown admin. no.; prepared by U.S. Fish and Wildlife Service, Denver Wildlife Research 

Center, Wildlife Damage Research Station, submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL: 

230307-B) 

MRID: 2468 U.S. Fish and Wildlife Service, Denver Wildlife Research Center (1973) Vertebrate Damage 

Control Research: 1973 Annual Report. By Denver Wildlife Research Center and U.S. Agency for International Development, Office of Agriculture and Fisheries. Den- ver, Colo.: U.S. Fish and Wildlife Service. 

(Available from: U.S. Fish and Wildlife Service, Denver Wildlife Research Center, Denver, CO; pp. 23-25 

only; also~In~unpublished submission re- ceived on unknown date under unknown admin. no.; submitted 

by Velsicol Chemical Corp., Chicago, Ill.; CDL:230307-D) 
Page 41 of 60

Guideline: 71-5 Simulated or Actual Field Testing

-------------------------------------------------------------------------------------

MRID: 45855101 Salmon, T.; Whisson, D.; Gorenzel, W. (2001) Field Efficacy Studies Comparing 

0.005% and 0.01% Diphacinone and Chlorophacinone Baits for Controlling California Ground Squirrels 

(Spermophilus beecheyi): Final Report: Lab Project Number: 00-0471: 29: 30. Unpublished study 

prepared by University of California, Davis. 131 p. 

MRID: 46911901 Mach, J. (2006) Secondary Hazard Study Using Diphacinone-Killed Rodents Fed to 

Domestic Ferrets (Mustela putorius furo): Final Report. Project Number: 05038, 06002. Unpublished 

study prepared by Genesis Laboratories, Inc. 32 p.

MRID: 48373002 Ingenloff, K.; Soniat, M. (2011) Exposure of Kaput Field Rodent Bait B to Northern 

Bobwhite Quail (Colinus virginianus). Project Number: 10004. Unpublished study prepared by Genesis 

Laboratories, Inc. 44 p.

MRID: 48373005 Poche, D. (2011) Exposure of Kaput Field Rodent Bait B to Mallard Ducks (Anas 

platyrhynchos). Project Number: 10003. Unpublished study prepared by Genesis Laboratories, Inc. 47 p.

Guideline: 72-1 Acute Toxicity to Freshwater Fish

-------------------------------------------------------------------------------------

MRID: 60603 Bentley, R.E. (1975) Acute Toxicity of Ramik Mouse Bait to Bluegill (Lepomis 

macrochirus), Rainbow Trout (Salmo gairdneri), and Channel Catfish (Ictalurus punctatus). (Unpublished 

study received Aug 21, 1978 under 876-EX-36; prepared by Bionomics, EG&G, submitted by Velsicol 

Chemical Corp., Chicago, Ill.; CDL:234818-E) 

MRID: 60607 Bentley, R.E. (1975) Acute Toxicity of Diphacinone Technical to Bluegill (~Lepomis 

macrochirus~), Channel Catfish (~Ictalurus punctatus~), and Rainbow Trout (~Salmo gairdneri~). 

(Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by EG&G, Bionomics, submitted 

by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-L) 

MRID: 127699 Bentley, R. (1975) Acute Toxicity of Ramik Mouse Bait to Bluegill (Lepomis 

macrochirus), Rainbow Trout (Salmo gairdneri), and Channel Catfish (Ictalurus punctatus). (Unpublished 

study re- ceived Oct 29, 1975 under 876-184; prepared by Bionomics, EG & G, submitted by Velsicol 

Chemical Corp., Chicago, IL; CDL; 222352-A) 

MRID: 92049005 Kelley, J. (1990) Haco Co. Phase 3 Summary of MRID 00060607. Acute Toxicity of 

Diphacinone Technical to Bluegill, Channel Catfish, and Rainbow Trout. Prepared by EG&G, Bionomics. 

17 p. 

Guideline: 72-2 Acute Toxicity to Freshwater Invertebrates

-------------------------------------------------------------------------------------

MRID: 42282201 Putt, A. (1992) Diphacinone Technical: Acute Toxicity to Daphnids (Daphnia magna) 

under Flow-through Conditions: Lab Project Number: 91-9-3938: 12455. 1290. 6100. 115: 90-10A. 

Unpublished study prepared by Springborn Labs, Inc. 66 p. 

Guideline: 72-3 Acute Toxicity to Estuarine/Marine Organisms

-------------------------------------------------------------------------------------

MRID: 60604 Heitmuller, T. (1975) Acute Toxicity of Ramik to Pink Shrimp (Penaeus duorarum) and 

Fiddler Crabs (Uca pugilator). (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by 

Bionomics--EG&G, Inc., submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-F) 

MRID: 60608 Heitmuller, T. (1975) Acute Toxicity of Diphacinone to Pink Shrimp (~Penaeus duorarum~) 

and Fiddler Crabs (~Uca pugilator~). (Unpublished study received Aug 21, 1978 under 876-EX-36; prepared by Bionomics--EG&G, Inc., submitted by Velsicol Chemical Corp., Chicago, Ill.; CDL:234818-M) 

Guideline: 96-5 Avian toxicants
Page 42 of 60

-------------------------------------------------------------------------------------

MRID: 41375801 Keith, J.; Hirata, D.; Espy, D.; et al. (1990) Field Evaluation of 0.00025% Diphacinone 

Bait for Mongoose Control in Hawaii: Final Report: Lab Project Number: QA-16. Unpublished study 

prepared by Denver Wildlife Research Center. 52 p. 

Guideline: 96-12 Rodenticides on farms and rangelands

-------------------------------------------------------------------------------------

MRID: 41375801 Keith, J.; Hirata, D.; Espy, D.; et al. (1990) Field Evaluation of 0.00025% Diphacinone 

Bait for Mongoose Control in Hawaii: Final Report: Lab Project Number: QA-16. Unpublished study 

prepared by Denver Wildlife Research Center. 52 p. 

MRID: 43805001 Marsh, R.; Howard, W. (1975) A Field Evaluation of Ramik for Ground Squirrel 

Control, March 7, 1975: Lab Project Number: UR-95-01. Unpublished study prepared by Hacco, Inc. 14 

p. 

MRID: 43805002 Marsh, R.; Howard, W. (1976) Report on the Laboratory Efficacy of Ramik for 

Belding's Ground Squirrel: Lab Project Number: UR-95-03. Unpublished study prepared by Hacco, Inc. 8 

p. 

MRID: 44453703 Hacco, Inc. (1997) Field Efficacy of Diphacinone Grain Baits: Lab Project Number: UR 

97-01. Unpublished study. 10 p. 

MRID: 45855101 Salmon, T.; Whisson, D.; Gorenzel, W. (2001) Field Efficacy Studies Comparing 

0.005% and 0.01% Diphacinone and Chlorophacinone Baits for Controlling California Ground Squirrels 

(Spermophilus beecheyi): Final Report: Lab Project Number: 00-0471: 29: 30. Unpublished study 

prepared by University of California, Davis. 131 p. 

MRID: 45855102 VerCauteren, K.; Pipas, M.; Bourassa, J. (2002) A Camera and Hook System for 

Viewing and Retrieving Rodent Carcasses From Burrows: (Diphacinone and Chlorophacinone Baits): Lab 

Project Number: QA-879. Unpublished study prepared by National Wildlife Research Center. 29 p. 

(OPPTS 850.2500) 

MRID: 46117301 Salmon, T.; Whisson, D.; Gorenzel, W. (2001) Field Efficacy Studies Comparing 

0.005% and 0.01% Diphacinone and Chlorophacinone Baits for Controlling California Ground Squirrels 

(Spermophilus beecheyi). Unpublished study prepared by University of California, Davis. 61 p.

MRID: 46117302 VerCauteren, K.; Pipas, M.; Bourassa, J. (2002) A Camera and Hook System for 

Viewing and Retrieving Rodent Carcasses from Burrows. Unpublished study prepared by U.S. Dept. of 

Agriculture, APHIS, ADC. 22 p.

MRID: 46117303 Goodall, M.; Primus, T.; Johnston, J. (2002) Determination of Cholorphacinone (sic) 

and Diphacinone Residues in California Ground Squirrels and Non-Target Animals. Unpublished study 

prepared by U.S. Dept. of Agriculture, APHIS, ADC. 19 p.

MRID: 46271501 Baroch, J.; Malkov, V. (2004) Field Efficacy of Kaput Pocket Gopher Bait (0.005% 

Diphacinone) for the Control of the Plains Pocket Gopher (Geomys bursarius): Amended Final Report. 

Project Number: 02011. Unpublished study prepared by Genesis Laboratories, Inc. 118 p.

MRID: 46749601 Spurr, E.; Lindsey, G.; Perry, C.; et. al. (2003) Effectiveness of Hand-Broadcast 

Application of Baits Containing 0.005% Diphacinone in Reducing Rat Populations in Hawaiian Forests: 

Final Report. Project Number: QA/02A. Unpublished study prepared by U.S. Geological Survey. 224 p.

MRID: 46749602 Spurr, E.; Foote, D.; Perry, C.; et. al. (2003) Efficacy of Aerial Broadcast Application of 

Baits Containing 0.005% Diphacinone in Reducing Rat Populations in Hawaiian Forests: Final Report. 

Project Number: QA/02B. Unpublished study prepared by U.S. Geological Survey. 191 p.
Page 43 of 60

MRID: 46966511 Borchert, J. (2006) Rock Squirrel Simulated Field Study Using Field Rodent Bait: 30-

Day Test (Spermophilus variegates) of Kaput Field Rodent Bait B. Project Number: 05010. Unpublished 

study prepared by Genesis Laboratories Inc. 89 p.

MRID: 47114204 Borchert, J. (2005) Field Efficacy of Petersen Field Rodent Bait (0.005% Diphacinone) 

for Controlling Black-Tailed Prairie Dogs (Cynomys ludovicianus): Final Report. Project Number: 06014. 

Unpublished study prepared by Genesis Laboratories, Inc. 145 p.

MRID: 47185301 Dunlevy, P.; Scharf, L. (2007) Eradication of Norway Rats Using Ramik Green in the 

Bay of Islands, Adak Island, Alaska: Interim Report. Unpublished study prepared by Alaska Maritime 

National Wildlife Refuge. 52 p.

MRID: 47226201 Bruening, J. (2007) Field Efficacy of Kaput-D Prairie Dog Bait for Controlling BlackTailed Prairie Dogs (Cynomys ludovicianus). Project Number: N07004. Unpublished study prepared by 

Genesis Laboratories, Inc. 108 p.

MRID: 47430701 Bruening, J. (2008) Field Efficacy of Kaput-D Combo Bait (EPA Reg. No. 72500-11) 

for Controlling Black-Tailed Prairie Dogs (Cynomys ludovicianus). Project Number: 07021, 

GL/138261/41/3/1. Unpublished study prepared by Genesis Laboratories, Inc. 117 p.

MRID: 48551901 Symmes, C. (2010) Field Efficacy of Field Rodent Bait B (Kaput-D Combo Bait) for 

Controlling Wyoming Ground Squirrels (Spermophilus elegans). Project Number: 10001. Unpublished 

study prepared by Genesis Laboratories, Inc. 150p.

MRID: 49244501 Benton, S. (2013) Comparative Field Palatability of Two Formulations of Kaput Field 

Rodent Bait B Using California Ground Squirrels (Spermophilus beechey). Project Number: N13008. 

Unpublished study prepared by Genesis Laboratories, Inc. 35p.

MRID: 49502601 Baldwin, R. (2014) Field Efficacy of 0.005% Diphacinone Pellets for Control of 

California Ground Squirrels via Bait Station Application. Project Number: BEL/0613/BE831. 

Unpublished study prepared by University of California Kearney Agricultural Center. 127p.

MRID: 49543001 Baldwin, R. (2015) Field Efficacy of 0.005% Diphacinone Pellets for Control of 

California Ground Squirrels via Spot Treatment Application. Project Number: BEL/0614/BE873. 

Unpublished study prepared by University of California, Davis. 112p.

Guideline: 96-17 Mammalian predacides

-------------------------------------------------------------------------------------

MRID: 40565501 Keith, J.; Hirata, D. (1987) Determination of an Acute, Oral LD50 for Diphacinone 

against Mongooses (Herpestes auropunctatus): Mongoose Project (963). Unpublished study prepared by 

Denver Wildlife Research Center. 6 p. 

MRID: 40565502 Keith, J.; Hirata, D. (1986) Laboratory Trials To Determine Minimum Levels of 

Diphacinone in Bait that are Lethal to Mongooses (Herpestes auropunctatus): Mongoose Project (963). 

Unpublished study prepared by Denver Wildlife Research Center. 21 p. 

MRID: 40565503 Keith, J.; Hirata, D. (1987) Laboratory Trial To Determine Mortality of Mongooses 

(Herpestes auropunctatus) Fed 0.00025% Diphacinone Bait: Mongoose Project (963). Unpublished study 

prepared by Denver Wildlife Research Center. 6 p. 

MRID: 40565504 Keith, J.; Espy, D.; Hirata, D. (1987) Small Field Efficacy Trials using Diphacinone 

Bait against Mongooses (Herpestes auropunctatus): Mongoose Project (963). Unpublished study prepared 

by Denver Wildlife Research Center. 8 p. 

Guideline: 810.3300 Treatments to control pests of humans and pets

-------------------------------------------------------------------------------------
Page 44 of 60

MRID: 46966510 Borchert, J. (2006) Field Efficacy of Field Rodent Bait for Controlling Black-Tailed 

Prairie Dogs (Cynomys ludovicianus) of Kaput Field Rodent Bait B. Project Number: 05009. Unpublished 

study prepared by Genesis Laboratories, Inc. 141 p.

MRID: 46966512 Borchert, J. (2006) Field Efficacy Data of Field Rodent Bait B: California Ground 

Squirrels (Spermophilus beecheyi) and Fleas of Kaput Field Rodent Bait B . Project Number: 05019. 

Unpublished study prepared by Genesis Laboratories, Inc. 371 p.

MRID: 47603301 Poche, R. (2008) Determining the Blood Titer Levels and the Effectiveness of Kaput 

Field Rodent Bait B Against Oropsylla spp. Fleas on Black-Tailed Prairie Dogs (Cynomys Ludovicianus). 

Project Number: 08015, 138261/41/3/1, 82/66/6/9. Unpublished study prepared by Genesis Laboratories, 

Inc. 123 p.

MRID: 47633201 Poche, R. (2008) Determining the Blood Titer Levels and the Effectiveness of Kaput 

Field Rodent Bait B Against Oropsylla spp. Fleas on Black-Tailed Prairie Dogs (Cynomys ludovicianus): 

Final Report. Project Number: 08015A1, 08015. Unpublished study prepared by Genesis Laboratories, 

Inc. 6 p.

MRID: 47858501 Ellis, C. (2009) Novel Commensal Rodent Pellet #2: Determining the Blood Titer 

Levels and the Effectiveness of Scimetrics Ltd. Corp., Kaput Combo Baits Against Xanopsylla cheopis 

Fleas on Laboratory Norway Rats (Rattus norvegicus). Project Number: 09002. Unpublished study 

prepared by Genesis Laboratories, Inc. 268 p.

Guideline: 850.2500 Field testing for terrestrial wildlife

-------------------------------------------------------------------------------------

MRID: 45855101 Salmon, T.; Whisson, D.; Gorenzel, W. (2001) Field Efficacy Studies Comparing 

0.005% and 0.01% Diphacinone and Chlorophacinone Baits for Controlling California Ground Squirrels 

(Spermophilus beecheyi): Final Report: Lab Project Number: 00-0471: 29: 30. Unpublished study 

prepared by University of California, Davis. 131 p. 

MRID: 45855102 VerCauteren, K.; Pipas, M.; Bourassa, J. (2002) A Camera and Hook System for 

Viewing and Retrieving Rodent Carcasses From Burrows: (Diphacinone and Chlorophacinone Baits): Lab 

Project Number: QA-879. Unpublished study prepared by National Wildlife Research Center. 29 p. 

(OPPTS 850.2500) 

MRID: 46117301 Salmon, T.; Whisson, D.; Gorenzel, W. (2001) Field Efficacy Studies Comparing 

0.005% and 0.01% Diphacinone and Chlorophacinone Baits for Controlling California Ground Squirrels 

(Spermophilus beecheyi). Unpublished study prepared by University of California, Davis. 61 p.

MRID: 46117302 VerCauteren, K.; Pipas, M.; Bourassa, J. (2002) A Camera and Hook System for 

Viewing and Retrieving Rodent Carcasses from Burrows. Unpublished study prepared by U.S. Dept. of 

Agriculture, APHIS, ADC. 22 p.

MRID: 46117303 Goodall, M.; Primus, T.; Johnston, J. (2002) Determination of Cholorphacinone (sic) 

and Diphacinone Residues in California Ground Squirrels and Non-Target Animals. Unpublished study 

prepared by U.S. Dept. of Agriculture, APHIS, ADC. 19 p.
Page 45 of 60

Ecological Toxicity Data Submitted To Support Registration for PC Code 067705

72-1 Acute Toxicity to Freshwater Fish

-------------------------------------------------------------------------------------

MRID: 43249501 Machado, M. (1994) Diphacinone, Sodium Salt--Prolonged Acute Toxicity to Bluegill 

Sunfish (Lepomis macrochirus) under Flow-Through Conditions: Amended Final Report: Lab Project 

Number: 94/3/5191: 12455/1193/6105/195. Unpublished study prepared by Springborn Laboratories, Inc. 

84 p. 

MRID: 43249502 Machado, M. (1994) Diphacinone, Sodium Salt--Prolonged Acute Toxicity to Rainbow 

Trout (Salmo gairdneri) under Flow-Through Conditions: Final Report: Lab Project Number: 94/3/5216: 

12455/1193/6106/195. Unpublished study prepared by Springborn Laboratories, Inc. 83 p.
Page 46 of 60

Appendix A: Label Use Information for diphacinone and 

diphacinone sodium salt based on BEADs summary 

report

Use

Single Max 

Application 

Rate

Max 

App.

Rate per 

Year

Min Retreatment 

Interval 

(days)

Max # of 

Apps.

Per Year

(or Crop 

Cycle)

Application 

Methods

Diphacinone

Agricultural Crops / Soils

(Unspecified)

0.0000126

lb / burrow NS

14 3

Ground

Bait Treatment,

Spot Treatment

0.003 lb / 

bait station(s) NS NS

Agricultural Fallow/ Idleland 

/ Conservation Reserve 0.0003 lb / bait 

station(s) or

0.005 lb /ac

NS NS NS

Agricultural /Farm Structures 

/ Buildings and Equipment NS NS NS

Agricultural Uncultivated

Areas

0.0003 lb / bait 

stations NS NS NS

Ground

Bait Treatment

Airports / Landing Fields

0.0001 lb / 

placement or 

0.00000219 lb / 

bait station(s)

NS NS NS

Animal Burrows, Harborages 

or Dens Of Plague Reservoir 

Hosts

Automobiles, Taxis, 

Limousines, Recreational 

Vehicles, & Tires

Commercial Transportation

Vehicles (All or Unspecified)

Commercial / Institutional /

Industrial Premises /

Equipment (Indoor)

Commercial / Institutional / 

Industrial Floors

Commercial / Institutional / 

Industrial Premises /

Equipment (Outdoor)

0.0003 lb / 

placement

Christmas Tree Plantations 0.001 lb / ac Aerial, Ground 

Broadcast

Fencerows / Hedgerows 0.0002 lb / bait 

station(s)

Ground

Bait Treatment

Food Processing Plant NonFood Handling Areas 0.0001 lb / 

placement NS NS NS

Ground

Bait Treatment

Food Processing Plant

Premises (Non-Food 

Contact)

Forest Planting

(Reforestation Programs)

0.001 lb / ac Ground

Bait Treatment, 
Page 47 of 60

(Tree Farms, Tree

Plantations, etc.)

Broadcast

Forest Trees (All or

Unspecified)

0.0000126 lb / 

burrow NS 14 3

Ground

Bait Treatment

Golf Course Turf

Household / Domestic

Dwellings Indoor Premises

Household / Domestic

Dwellings Outdoor Premises

0.0001 lb / 

placement

Nonagricultural Outdoor NS NS NS

Buildings / Structures

0.0002 lb / bait 

station(s)

Nonagricultural Right-ofWay / Fencerows /

Hedgerows

0.0136 lb / ac

Nonagricultural Uncultivated

Areas / Soils 0.001 lb / ac

NS

NS

1

Aerial, Ground, 

Broadcast,

Nursery Stock Bait Treatment

NS

Orchards (Unspecified)

Ornamental and/or Shade 

Trees 0.00002188 lb / 

bag

Ground

Bait Treatment

Ornamental Woody Shrubs

and Vines

Ornamental Lawns and Turf 0.0000126 lb / 

burrow 14 3

Pastures 0.0136 lb /ac NS 4

Public Buildings / Structures

(Vert. Pest Control)

0.0001 lb / 

placement NS NS

Railroad Boxcars

Rangeland 0.0136 lb /ac 14 4 Ground

Bait Treatment,

Spot Treatment Recreational Areas

0.0000126 lb / 

burrow 14 4

Refuse / Solid Waste Sites

(Outdoor)

0.0001 lb / 

placement

NS NS

Ground

Bait Treatment

Right-of-Way (Railroad)

Ships and Boats

Streams / Rivers /Channeled

Water

Swamps /Marshes / Wetlands 

/ Stagnant Water

0.0003 lb / bait 

station(s)

Wide Area / General Indoor

Treatment 0.0001 lb / 

placement Wide Area / General Outdoor

Treatment (Public Health 

Use)

Diphacinone Sodium Salt

Agricultural /Farm Structures 

/ Buildings and Equipment 0.0001 lb / 

bait station(s) NS NS NS

Ground

Bait 

Application

(Bait/Liquid)

Commercial / Institutional / 

Industrial Premises / 

Equipment (Indoor)

NS = not specified
Page 48 of 60

Appendix B: Summary of Ecotoxicity Data for 

Diphacinone

Table B-1. Freshwater Fish Acute Toxicity of Diphacinone

Species % a.i. 96-hourLC50

(mg a.i./L) 

Toxicity 

Category

MRID No. Study Classification

Bluegill sunfish, 

(Lepomis macrochirus)

95.8 7.5 Moderately toxic 43249501 Acceptable

Rainbow trout,

(Onchorhynchus 

mykiss)

95.8 2.6 Moderately toxic 43249502 Acceptable

Table B-2. Freshwater Invertebrate Acute Toxicity of Diphacinone

Species % a.i. 48-hourEC50

(mg/L) 

Toxicity 

Category

MRID No. Study Classification

Water flea 

(Daphnia magna)

98.7 1.8 Moderately toxic 42282201 Acceptable

Table B-3: Avian Acute Toxicity to Diphacinone 

Species % A.I. Toxicity Endpoint Toxicity 

Classification

MRID Status

Acute Single Oral Dose

Bobwhite quail 

(Colinus 

virginianus)

96.9 LD50 = 1630 mg 

a.i./kg-bw Slightly toxic

42245201 Supplemental

Bobwhite quail n.a.

LD50 = 2014 mg 

a.i./kg-bw

Practically nontoxic

Rattner et al 2010 Supplemental 

(Quantitative)

Mallard duck 

(Anas 

platyrhynchos)

n.a.

LD50 = 3158 mg 

a.i./kg-bw

Practically nontoxic

00128411

American kestrel 99.2 LD50 = 98.6 mg 

a.i./kg-bw

Moderately 

toxic

Rattner et al 2011 Supplemental 

(Quantitative)

Acute Dietary

Bobwhite quail 96.9

LC50 > 5000 mg 

a.i./kg-diet

Practically nontoxic

42408801 Acceptable

Mallard duck 96.9

LC50 =906 mg a.i./kgdiet

Moderately 

toxic

42408802 Acceptable
Page 49 of 60

Table B-4: Mammalian Acute Toxicity to Diphacinone

Test Type % A.I. Toxicity Endpoint Toxicity 

Classification MRID Status

Acute oral (gavage) single dose

Laboratory rat

(males only)

Rattus norvegicus

tech LD50 = 1.9 mg a.i./kg-bw Very highly 

toxic

Byers 1978

Ecotox Ref # 

J69367

supplemental

Laboratory rat

tech LD50 = 2.46 mg a.i./kg-bw Very highly 

toxic

00060605 qualititative 1

Pine vole

LD50 = 57.7 mg a.i./kg-bw Moderately 

toxic Byers 1978

Ecotox Ref # 

J69367 Meadow vole qualitative LD50 = 14 mg a.i./kg-bw Highly toxic

Pine vole 

LD50 = 102 mg a.i./kg-bw Moderately 

toxic

coyote

LD50 = 0.6 mg a.i./kg-bw Very highly 

toxic

Savarie et al.

1979

00079312,

qualitative

mongoose

LD50 = 0.18 mg a.i./kg-bw Very highly 

toxic

40565501 supplemental

Cats and dogs

LD50 ranged from 0.88 to 15 

mg a.i./kg-bw

Very highly 

toxic to 

Highly toxic

LiphaTech, 

Inc, 1997 qualitative

Acute Dietary

Laboratory Rat 99.9

LC50 = 2.08 mg a.i./kg-diet Very highly 

toxic. 

Teeters 1981 

(TNM 75)2

Supplemental

Laboratory Rat 99.9

LC50 = 2.54 mg a.i./kg-diet Very highly 

toxic. 

Teeters 1981 

(TNM 51)2

Supplemental

1 HED or RD DER not located, upon EFED review data presumed to meet ‘qualitatitive’ classification

2 Teeters, W.R.(1981) Diphacinone technical: Toxicity to Laboratory Rat. (U.S. Environmental Protection Agency, 

Pesticides Regulation Div., Agricultural Research Center, Animal Biology Laboratory, unpublished report.)
Page 50 of 60

Appendix C. Screening Level Models to Evaluate 

Potential Importance of Drinking Water and Inhalation 

Exposure Pathways
Page 51 of 60

SIP (Screening Imbibition Program, v1.0) Inputs and Conclusions

Table 1. Inputs

Parameter Value

Chemical name diphacinone

Solubility (in water at 25oC; mg/L) 0.3

Mammalian LD50 (mg/kg-bw) 1.9

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg-bw)

Mammalian test species laboratory rat

Body weight (g) of "other" mammalian species

Avian LD50 (mg/kg-bw) 1630

Avian test species northern bobwhite quail

Body weight (g) of "other" avian species

Mineau scaling factor 1.15

Mallard NOAEC (mg/kg-diet) 0

Bobwhite quail NOAEC (mg/kg-diet) 0

NOAEC (mg/kg-diet) for other bird species 0

Body weight (g) of other avian species

NOAEC (mg/kg-diet) for 2nd other bird species 0

Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 0.0516 0.0516

Adjusted toxicity value (mg/kg-bw) 1.4614 0.0000

Ratio of exposure to toxicity 0.0353 0.0000

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Due to insufficient data, risk 

cannot be precluded

Table 3. Avian Results

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 0.2430 0.2430

Adjusted toxicity value (mg/kg-bw) 1174.3001 0.0000

Ratio of exposure to acute toxicity 0.0002 0.0000

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Due to insufficient data, risk 

cannot be precluded

 **Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when 

aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to 

a total exposure that has potential for effects to non-target animals.
Page 52 of 60

Welcome to the EFED Screening Tool for Inhalation Risk

This tool is designed to provide the risk assessor with a rapid method for determining the potential

significance of the inhalation exposure route to birds and mammals in a risk assessment.

Input

Application and Chemical Information

Enter Chemical Name diphacinone

Enter Chemical Use rodenticide

Is the Application a Spray? (enter y or n) n

If Spray What Type (enter ground or air) ground

Enter Chemical Molecular Weight (g/mole) 340.38

Enter Chemical Vapor Pressure (mmHg) 1.00E-08

Enter Application Rate (lb a.i./acre) 0.005

Toxicity Properties

Bird

Enter Lowest Bird Oral LD50 (mg/kg bw) 1630

Enter Mineau Scaling Factor 1.15

Enter Tested Bird Weight (kg) 0.178

Mammal

Enter Lowest Rat Oral LD50 (mg/kg bw) 1.9

Enter Lowest Rat Inhalation LC50 (mg/L) 0.0006

Duration of Rat Inhalation Study (hrs) 4

Enter Rat Weight (kg) 0.35

Output

Results Avian (0.020 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 1.83E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.30E-05

Adjusted Inhalation LD50 2.87E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 8.02E-06 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) not applicable

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 not applicable not applicable

Results Mammalian (0.015 kg )

Maximum Vapor Concentration in Air at Saturation (mg/m3) 1.83E-04

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.89E-05

Adjusted Inhalation LD50 3.57E-02

Ratio of Vapor Dose to Adjusted Inhalation LD50 8.10E-04 Exposure not Likely Significant

Maximum Post-treatment Spray Inhalation Dose (mg/kg) not applicable

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 not applicable not applicable
Page 53 of 60

Appendix D. Wildlife Mortality Incidents Attributed to 

Use of Diphacinone

The table below is based on the Summary Table that was included in Docket ID EPAHQ-OPP-2011-0718 (“Risks of Non-Compliant Rodenticides to Nontarget Wildlife -

Appendix D - Wildlife Mortality Incidents”; Document ID EPA-HQ-OPP-2011-0718-

0010). The table was updated to include additional incidents and additional information 

on previously reported incidents that was available to the Agency as of 2013. Any 

additional incidents reported to the Agency after 2013 for diphacinone have not been 

added to the table below. 

For each of the incidents reported below, insufficient information was available to 

ascertain legality of the pesticide use. 
Page 54 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

B000640-001 1987 Probable CA Residential Kit Fox (1)

A San Joaquin kit fox was found dead at a nursery near a 

university where anticoagulant baits had been applied for 

ground squirrel control. Unclotted whole blood was 

present in the abdomen. Several diffuse areas of 

hemorrhages were present in the lungs. The stomach 

contained a few grass stems and some sand. The intestines 

were empty. Diphacinone residues at 0.18 ppm were 

detected by ELISA. 

B000641-001 1986 Highly probable CA Field Raccoon (1), 

Mountain Lion (1)

The California Department of Fish and Game reported this 

incident where a raccoon and mountain lion were found 

dead near a stream. Pooled free blood was found in the 

raccoon, and in the mountain lion there were pinpoint and 

streaked hemorrhages in the small intestine and colon. 

Blood samples were analyzed and the results showed 55 

ppm diphacinone in the raccoon and 45 ppm diphacinone 

in the mountain lion. 

I004768-001 1996 Highly probable NY N/R Deer (1)

A white–tailed deer had been found dead and submitted to 

the Wildlife Pathology Unit. The presence of fairly large 

maggots in the carcass suggests this deer had been dead 

for several weeks. An analysis of the liver detected 

diphacinone residues at 0.2 ppm. 

I004769-001 1996 Highly probable NY Residential Deer (1)

A white-tailed deer was found dead in a residential area 

with hemorrhages appearing like minor bruising and a 

hemorrhagic subcutaneous edema was found in the 

vicinity of the left shoulder and adjoining brisket area. 

The stomach was full of whole corn, vegetation, and 

water. An analysis of the liver detected diphacinone 

residues at 0.93 ppm. 
Page 55 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

B0000-300-84 1997 Highly probable NY Residential Squirrel (1)

A squirrel was found in the yard of a resident. Necropsy 

showed areas of subcutaneous edema and hemorrhage 

found over the ventral thorax and upper abdomen along 

with the right foreleg and on the right side of the head. 

The stomach contents were normal in appearance and 

odor. An analysis of the liver detected diphacinone 

residues at 2.0 ppm. 

I006306-013 1998 Highly probable NY N/R Snowy Owl (1)

A snowy owl was found dead and an analysis of its liver 

detected diphacinone residues. There were no residue 

numbers provided with the report. 

I007107-007 1997 Possible NY N/R Turkey vulture (1)

This incident is one of the incidents reported on the 

consolidated report for the year 1997 submitted by 

California Department of Fish and Game. After an 

analysis the Pesticide Investigation Unit determined the 

loss of the turkey vulture was due to diphacinone 

poisoning.

I005417-004 1989 Possible CA N/R Rabbits (12)

Twelve rabbits were found dead after a hand application of 

sodium monofluoroacetate. Necropsies of two showed 

severe bleeding. A kidney from each of two rabbits was 

analyzed for sodium monofluoroacetate but the finding 

was negative. Subsequently it was learned that 

diphacinone had been used in the area, and the symptoms 

found in the rabbits were in accord with what would be 

expected from diphacinone. No anticoagulant residues 

were detected in the blood, but it is possible that an 

anticoagulant in the blood metabolized before death. No 

analyses of liver samples were conducted.
Page 56 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

I007107-014 1997 Highly probable CA N/R Coyote (1)

The carcass of a yearling female coyote was recovered 

from the Santa Monica Mountains on October 9, 1997. 

Diphacinone was detected in the liver at 1.3 ppm, 0.1 ppm 

in the blood collected from the thoracic cavity and 0.16 

ppm in the stomach contents. Brodifacoum was identified 

in the liver at 0.083 ppm. Free blood was present in the 

body cavities.

I007488-004 1998 Highly probable VA Residential Squirrel (2)

Two grey squirrels were found dead and collected by the 

Virginia Department of Game and Inland Fisheries. The 

stomach and small intestine of the first squirrel contained 

abundant unclotted blood mixed with a scant amount of 

tan granular material. The small intestine for the second 

squirrel contained a smaller amount of unclotted blood. 

The thoracic cavities of both squirrels were filled with 

unclotted blood. Liver analysis detected bromadiolone 

and diphacinone residues in pooled liver samples from 

both squirrels at 4.94 for bromadiolone and 3.41 ppm for 

diphacinone.

I009270-001 1999 Probable NY Residential Hawk (1)

A red-tailed hawk was found moribund in a residential 

area. Small fish, appearing to be sardines were in the 

stomach. The bird was very anemic and lacked blood 

volume. An analysis of the liver detected diphacinone 

residues at 0.34 ppm. 

I011518-001 2000 Possible NY Residential Squirrel (1)

A grey squirrel was found dead in a residential yard. 

There was a hemorrhage over the right orbit of the eye. 

The stomach contained a finely ground material. A small 

area of subcutaneous hemorrhage was present over the 

dorsal thorax. Blunt impact trauma was the immediate 

cause of death, but diphacinone residues detected at 1.02 

ppm may have been contributing.
Page 57 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

I013810-006 1993 Probable NY N/R Snowy Owl (1)

This incident is part of the Contaminant Exposure and 

Effects – Terrestrial Vertebrates (CEE-TV) Database, 

Version 3.3, October 2002 report. A snowy owl was 

found dead and its liver showed traces of diphacinone that 

were suspected as the cause of death.

I014884-018 2003 Possible CA N/R Pigeon (1)

The California Department of Fish and Game report of 

wildlife incidents involving pesticides for calendar years 

2002 and 2003 identified an incident with a pigeon having 

diphacinone and brodifacoum levels detected in its tissues. 

No chemical residue values were provided.

I019839-001 2008 Probable GA Residential Squirrel (1)

A homeowner reported that approximately eight squirrels 

have been found dead in her yard and in the adjacent 

neighbor’s yard. Diphacinone was detected in the liver of 

a squirrel tested at 3.6 ppm. Severe, acute, multifocal, 

subcutaneous, and intramuscular hemorrhaging was 

present. 
Page 58 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

I019968-001 2008 Possible CA Field Bobcat (1)

In 2008, Department of Fish and Game Office of Spill 

Prevention and Response staff in Santa Cruz responded to 

an incident near a lettuce field near Morro Cojo Slough 

involving several dead Canada geese. Additional geese 

were found dead at the site for several weeks after the 

initial incident report. The total number of dead geese was 

estimated to be 70. In addition, two turkey vultures, a redtailed hawk, a barn owl, and a bobcat were found dead in 

the vicinity. The geese and the predators and scavengers 

showed signs of anticoagulant toxicity. The bobcat was 

the only one that tested positive for diphacinone (0.34 

ppm) - most of the other animals tested, tested positive for 

chlorophacinone.

I022935-001 2011 Highly probable CA Field Bald eagle (1)

A bald eagle was found dead in Kern County, CA in 

2011. The eagle carcass was transported and received by 

California Animal Health & Food Safety Lab on 

1/13/2011. The necropsy showed lesions of hemorrhages 

with unclotted blood in many areas of the body. The 

submitted liver had a trace amount of diphacinone.

I023151-001 2011 Possible CA Urban Hawk (1)

A Cooper’s hawk was found dead in a pool of blood on a 

sidewalk in Berkeley, CA. Toxicology testing detected 

brodifacoum and a trace amount of diphacinone.

I023850-001 2012 Highly probable NY N/R Squirrel (1)

The New York State Department of Environmental 

Conservation on March 28, 2012 received a liver sample 

of a gray squirrel collected in Suffolk County, NY. 

Chemical analysis of the liver sample detected 841 ppb of 

diphacinone. The NY State Wildlife Pathologist 

concluded the gray squirrel was poisoned by the 

rodenticide diphacinone.
Page 59 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

I023914-003 2012 Probable NY Urban Hawk (1)

A red-tailed hawk was submitted by the Urban Park 

Rangers after being found dead at a Manhattan 

intersection. The cranial portion of the oviduct was partly 

coated with clotted hemorrhage. The plumage behind the 

vent was stained with feces. Internally, there a small 

amount of clotted hemorrhage in the posterior abdomen. 

The crop contained bird tissue as did the stomach. There 

was a prolapse of the oviduct. An analysis of the liver 

detected difethialone (0.127 ppm), bromodiolone (0.068 

ppm), diphacinone (0.059 ppm), and brodifacoum (0.046 

ppm). The pathologist concluded that, "... the 

anticoagulant load... could have permitted rapid 

hemorrhage from blood vessels damaged by the prolapse, 

leading to shock".

I024146-001 1994 Highly probable CA N/R Kangaroo rat (1)

A Herman kangaroo rat was found ill near a bait box in 

Merced County, CA in 1994. Diphacinone levels in the 

liver of the exposed Herman kangaroo rat was 3.5 ppm. 

This level is sufficient to indicate lethal non-target 

exposure.

I024152-004 2006 Highly 

Probable CA N/R Coyote (1)

In 2006 in Santa Cruz County, CA a laboratory staff 

reported that a coyote liver was submitted to the Pesticide 

Investigations Unit in order to analyze for anticoagulant 

residues. The liver contained four anticoagulants; 

chlorophacinone (1.13 ppb), coumatetralyl (0.10 ppb), 

diphacinone (1.50 ppb) and warfarin (0.060 ppb). It is 

highly likely that mortality was caused by exposure to 

anticoagulants.
Page 60 of 60

INCIDENT 

NUMBER YEAR CERTAINTYA STATE LAND USE

GENERIC 

SPECIES 

(Number

Individuals)

COMMENTS

I024152-009 2010 Highly probable CA N/R Feral pig (1)

The USDA staff contacted the Pesticides Investigations 

Unit about mammary tissue from a pig that had large 

streaks of a black dye-like material. The tissue was sent 

for analysis and it was confirmed that diphacinone was 

detected at 0.008 ppm.

I024154-012 2011 Possible CA N/R Owl(1)

A great horned owl and a kestrel were submitted for 

necropsy and liver analysis. There was no necropsy 

information available in the report yet an analysis of the 

liver detected brodifacoum concentrations of 0.04 ppm in 

the owl and trace amounts of diphacinone. 

A: Certainty describes the level of certainty that exposure to the given pesticide was the cause or a significant contributing factor of the effects observed in the 

incident.