Page 1 of 43 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D.C., 20460

PC Code: 119901

DP Barcode: 429384

Date: March 16 , 2016



### MEMORANDUM

Subject: Registration Review

– Preliminary Problem Formulation for Ecological Risk

, Environmental Fate

, and Drinking Water As sessments for Difenacoum

To: Ricardo Jones , Chemical Review Manager

Neil Anderson

, Branch Chief Risk Management and Implementation Branch 1

Pesticide Re

- evaluation Division ( 7508P ) Office of Pesticide Prog rams

From: Nathan Miller, Biologist Andrew Shelby

, Physical S cientist

Environmental Risk Branch 6

Environmental Fate and Effects Division (7507P) Office of Pesticide Programs

Reviewed: Michael Wagman

, Biologist William Eckel, Ph.D., Senior Sci ence Advisor

Monica Wait , RAPL

Environmental Risk Branch 6

Environmental Fate and Effects Division (7507 P ) Office of Pesticide Programs

Through: Mark Corbin

, Branch Chief

Environmental Risk Branch 6

Environmental Fate and Effects Division (750 7 P ) Office of Pesticide Programs

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

formulation for the ecological risk, environmental fate, and drinking water assessment s to be conducted as part of the registratio n r eview of the rodenticide difenacoum

.

The problem formulation draws on information from both open literature and studies submitted by the technical registrants. This document is intended to provide an overview of what is currently known regarding the environmental fate and ecological effects associated withPage 2 of 43 difenacoum and outlines uncertainties regarding attributes of the parent compound and its transformation products . It describes the preliminary ecological risk hypothesis and the processes that wi ll be used during the completion of drinking 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 environmen tal fate and potential ecolog ical effects of difenacoum

.Page 3 of 43 

## Preliminary Problem Formulation for the Environmental Fate and Ecological Risk , Endangered Species

, a nd Drinking

Water Assessment s in Support of the R eg istration Review of

D ifenacoum

Difenacoum

4

- hydroxy

- 3

- [3

- (4

- phenylphenyl)

- 1,2,3,4

- tetrahydronaphthalen

- 1

- yl]chromen

- 2

- one (CAS 56073

- 07

- 5 ) (PC Code 119901 )

Environmental Risk Branch V I Environmental Fate and Effects Division

Nathan Miller

, Biologist Andrew Shelby, Physical Scient ist

Reviewed by: Michael Wagman

, Biologist William Eckel, Ph.D., Senior Science Advisor

Monica Wait , RAPL

Mark Corbin , Branch Chief U. S. Environmental Protection Agency Office of Pesticide Programs 1200 Pennsylvania Ave., NW

Mail Code 7507P Washington, DC 20460Page 4 of 43 Table of Contents

1 Executive summary

................................ ................................ ................................ ................. 5

2 Introduction

................................ ................................ ................................ ............................. 5

3 Use Characterization

................................ ................................ ................................ ............... 6

4 Conclusions from Previous Risk Assessments

................................ ................................ ....... 7

4.1 Endangered Species Assessments

................................ ................................ ........ 7

4.2 Section 3 New Chemical Risk Assessment

................................ .......................... 7

4.3 Comparative Risk Assessment

................................ ................................ ............. 7

4.4 Risk Mitigation Decision and Notice of Intent to Cancel

................................ .... 8

4.5 Drinking Water Assessments

................................ ................................ ............... 8

5 Environmental Fate and Transport

................................ ................................ .......................... 9

5.1 Transformation Products

................................ ................................ .................... 10

6 Receptors

................................ ................................ ................................ ............................... 10

6.1 Toxicity Summ ary

................................ ................................ .............................. 10

6.2 Secondary Toxicity

................................ ................................ ............................ 12

6.3 Incident Database Review

................................ ................................ .................. 15

7 Exposure Pathways of Concern

................................ ................................ ............................ 17

8 Analysis Plan

................................ ................................ ................................ ........................ 17

8.1 Stressors of Concern

................................ ................................ ........................... 17

8.2 Measures of Exposure

................................ ................................ ........................ 17

8.3 Measures of Effect

................................ ................................ ............................. 23

9 Endangered Species Assessment

................................ ................................ .......................... 23

10 Endocrine Disruptor Screening Program

................................ ................................ .............. 24

11 Preliminary Identification of Data Gaps

................................ ................................ ............... 24

11.1 Environmental Fate

................................ ................................ ............................ 24

11.2 Ecological Effects

................................ ................................ .............................. 26

12 References

................................ ................................ ................................ ............................. 31 Appendix A: Difenacoum Fate/Chemistry and Ecotoxictiy Bibliography

................................ ... 3 6 Appendix B. Screening Level Models to Evaluate Potential Importance of Drinking Water and Inhalation Exposure Pathways

................................ ................................ ................................ ...... 42Page 5 of 43 

## 1 Executive summary

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem formulation for the ecological risk, environmental fate, and drinking water assessments to be

condu cted as part of the registration review of difenacoum . The problem formulation describes the methods planned to be used during the completion of the ecological risk assessment in support of registration review and provides an overview of the environmental fate, ecological effects, and potential risks associated with the use of difenacoum as well as uncertainties unique

to risk assessment of difenacoum

. EFED does not anticipate conducting a drinking water

assessment for difenacoum for use in the human healt h risk assessment for reasons that will be

discussed in more detail below. This document also identifies additional studies that would be

beneficial to the conduct of an ecological risk assessment.

Data needs for ecological effects are:

• Avian acute ora l toxicity test (850.2100), one passerine species

• Avian reproduction toxicity (850.2300), for an upland game bird ( e.g., bobwhite quail ( Colinus virginianus )) and waterfowl species ( e.g., mallard duck ( Anas platyrhynchos ))

.

• Earthworm Subchronic Toxicity Te st (850.3100), one specie s ( Eisenia fetida )

The test substance for each of these tests should be technical grade (TGAI). However, g iven that the available data indicate a differential in toxicity between difenacoum’s cis and trans isomers, the above requ ested toxicity studies should track the ratio of these isomers in the tested mixture. At this time, EFED does not anticipate needing to call in any additional environmental fate data

for difenacoum.



## 2 Introduction

Difenacoum is a second generation coumari n anticoagulant rodenticide

. It uncouple s oxidative phosphorylation depressing hepatic synthesis of prothrombin and clotting factors II, VII, IX and

X an d interfering with the vitamin K 1 cycle (Hayes and Laws, 1991).

Anticoagulants are vitamin

- K antagoni sts that disrupt normal blood

- clotting mechanisms and induce capillary damage. 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 res ults 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. Second generation anticoagulant rodenticides, like difenacou m, tend to be

more acutely toxic in a single feeding and persistent in biological tissue than first generation anticoagulant rodenticides (Erikson and Urban, 2004)

.

EFED evaluated the most recent ecological risk assessments for difenacoum in association w ith 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 m ethodologies. The structure ofPage 6 of 43 difenacoum as well as the chemical name and other identifiers can be found in the chemical identity table in Section 5 of this document.



## 3 Use Characterization

T here is no national level usage data for difenacoum ( PC code 1 19901 )

. Table 1 lists the maximum use patterns (application rates, number of reapplications, etc.) for the labeled use sites

for difenacoum

. The table is based on the Label Us ag e Report Package created by the Biological and Economics Analysis Division ( BEA D ) in support of Registration Review (USEPA, 2015).

There ar e currently eight active Section 3 labels for difenacoum , two for technical difenacoum

and six for end

- use products

. Difenac oum is formulated as ready

- to

- use pelleted bait

. The target pests inc lude: Norway rat ( Rattus norvegicus ), house mouse ( Mus musculus ), roof r ats ( Rattus

rattus ), Polynesian r ats ( Rattus exulans ), c otton r ats ( Sigmodon hispidus), eastern harvest m ice ( Reithrodontomys humuli ), golden m ice ( Ochrotomys nuttalli ), meadow v oles ( Microtus pennsylvanicus ), white

- throated w oodrats ( Neotoma albigula ), s outhern plains w oodrats ( Neotoma micropus), and Mexican w oodrats ( Neotoma mexicana )

. C oncentrations in bait are

0.00 5% difenacoum

. All labeled uses carry the follow restrictions:

“ D o not place bait near to or inside of ventilation duct openings. Do not contaminate water, food feed, food or feed handling equipment, milk or meat handling equipment, or any area where there is a possiblility of contaminating food, feed, milk, or meat or surfaces that come in contact with food, feed, milk, or meat. All outdoor placements of this product must be in bait stations. Tamper resistant bait stations must be used for outdoor and indoor placements of this product if children, pets, non

- target mamma ls, or birds may access bait. All placements of this product in USDA

- inspected facilities must be in tamper

- resistant bait stations. Do not broadcast. Wear water

- resistant gloves when handling bait. ”

Table 1. Label Use Information for difenacoum based on BEAD’s summary report

Use Single Max Application Rate Application

Methods

Agricultural/Farm Structures/Buildings and Equipment; Commercial/Institutional/Industrial/Equipment (Indoor); Commercial Transportation Facilities (All or Unspecified) ; Household /Domestic Dwellings Indoor Premises; Household/Domestic Dwellings Outdoor Premises; Public Buildings/Structures (Vert. Pest Control); Refuse/solid waste sites (indoor) 0.000 1 lb/placement Bait station

Food processing plant premises (nonfood contact) 0.000 1 lb/placement Bait station Commercial Transportation Vehicles (All or Unspecified); Wide Area/General Indoor Treatment; Wide Area/General Outdoor Treatment (Public Health use) 0.0001 lb/placement Bait stationPage 7 of 43 

## 4 Conclusions from Previous Risk Assessments

The Agency has conducted previous ecological risk assessments for difenacoum that serve as a basis for this problem formulation. They are briefly summarized below.



### 4.1 Endangered Species Assessments

An endangered species risk assessment for San Fran c isco Bay Species was completed for

difenacoum in 2012 (USEPA 2012 ) to address potential risk to the Salt marsh harvest mouse (SMHM) ( Reithrodontomys raviventris ), Alameda Whipsnake (AW) ( Masticophis lateralis euryxanthus ) and San Joaquin Kit Fox (SJKF) ( Vulpes mac rotis mutica ) for which difenacoum 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 , AW, and SJKF from the uses of difenacoum

. Additionally, the Agency determined that there was the potential for modification of designated

critical habitat for the AW from the use of difenacoum

.



### 4.2 Section 3 New Chemical Risk Assessment

The Section 3 new chemical ecological risk assessment for difenacoum was published in 2007 (USEPA, 2007 ). Difenacoum was conditionally registered in September 2007 in accordance

with F IFRA section 3(c)(7)(C) provided that all difenacoum products are amended to comply with EPA’s Final Risk Mitigation Measures for registered products containing the other second generation anticoagulants, on the same time schedule as those similar rodentic ides.



### 4.3 Comparative Risk Assessment

“Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Co mparative Approach” (USEPA 2004 ) evaluated primary and secondary exposure risks of several

rodenticides to birds and nontarget mammals. This docum ent did not evaluate difenacoum specifically, however it indicated that rodenticide baits are formulated to be lethal to small mammals, and they are not selective to nontarget species. The document stressed that all baits pose a high potential for primary risk to birds and nontarget mammals that eat bait. Avian and mammalian predators and scavengers are said to be at risk f rom feeding on animals poisoned with anticoagulant baits. The 2004 assessment also specified a number of factors contributing to

uncerta inty 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 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

bird s and non

- target mammals frequenting baited areas and the likelihood of their finding andPage 8 of 43 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 woul d 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 abnormalitie s, 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 p redators and scavengers; and (8) lack of incident reporting.



### 4.4 Risk Mitigation Decision and Notice of Intent to Cancel

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

Document ID EPA

- HQ

- OPP

- 2006

- 0955

- 0764 availabl e at www.regulations.gov ). D ifenacoum products were included in the list of ten rodenticides addressed in the 2008 document. The focus

of th e decision was:

1) T o minimize children’s exposure to rodenticide products used in homes by requiring

that all rodenti cide 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

lim its 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

difet hialone). 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 addition al 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 rode nticides that are likely alternatives ( i.e. , active ingredients included in products with

RMD

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

warfarin ; 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 av ailable under docket number EPA

- HQ

OPP

- 2011

- 0718 at www.regulations.gov

.



### 4.5 Drinking W ater A ssessment s

D ifenacoum is applied as a bait in bait stations ; it tends to bind to organic matter, and little is expected to partition or runoff into drinking water s ources; therefore, this route of exposure was

not assessed during reregistration

. D ue to the limited use pattern (bait applications only) and the relatively low environmental exposure of difenacoum , no drinking water assessment isPage 9 of 43 anticipated during regist ration review unless use rate s increase significantly or if a new use is proposed in the future.



## 5 Environmental Fate and Transport

Table 2 summarizes the physicochemical properties of difenacoum based on available data and

model estimates

. Difenacoum is considered hardly mobile to immobile in the environment (based on FAO 2000 mobility classification and estimates from EPISuite v4.1 ) and persistent to all forms of degradation . Volatilization from moist soil surfaces is not expected to be an important rou te of dissipation given an estimated Henry's Law constant of 1.4X10

- 12 atm

m 3 /mole

. Difenacoum is not miscible with water (1.7 mg/L) but is soluble enough for aquatic exposure to occur should it be released in clean water

. However, if released in natural water s
, difenacoum is expected to adsorb to suspended solids and sediment based upon the modeled

K OC

. Volatilization from water surfaces is not expected to be an important route of dissipation based upon this compound's estimated Henry's Law constant . An estimated bioconcentration

factor ( log BCF ) of 3.8 suggests a potential for bioconcentration in aquatic organisms if exposure

were to occur . With respect to abiotic routes of degradation, difenacoum is stable to hydrolysis but degrades rapidly due to aqu eous photolysis with half

- lives less than a day at all environmentally relevant pHs

.

With respect to biotic routes of degradation, difenacoum is persistent with DT 50 s greater than 108 days from registrant submitted studies

. An EU study reports a half

- lif e of 439 days.

Difenacoum end use products are formulated as a mixture of trans and cis isomers. Differential environmental fate data is not available for the separate isomers but the range of the cis isomer is

50% to 80% of difenacoum and the trans isom er is 20% to 50% of difenacoum (EFSA, 2009).

No difenacoum aquatic monitoring data is currently available through NAWQA or California Department of Pesticide Regulation or evident through the open literature. Aquatic exposure is not expected to occur con sidering difenacoum bait is contained in bait stations and not exposed to precipitation. Furthermore, if bait were exposed to precipitation, it is expected that difenacoum would remain adsorbed to the bait considering its high adsorption coefficent.

Tab le 2 . Physical

- chemical Properties of Difenacoum

Study Value and units Source

CAS Number 56073

- 07

- 5 (difenacoum)

151986

- 16

- 2 ( trans isomer)

151986

- 15

- 1 ( cis isomer) PPDB 1
EFSA, 2009 2

SMILES Code O=C \ 1c6c(OC(/O)=C/1C5c2ccccc2CC(c4ccc(c3 ccccc3)cc4 )C5)cccc6 PPDB

Molecular weight 444.52 PPDB

1 http://sitem.herts.ac.uk/aeru/ppdb/en/index.htm

2 https://circabc.europa.eu/sd/a/27fea8d9

- 9eb2

- 4cf9

- b16b

- 263500238206/F inal

- AR

- difenacoumSep09public.pdfPage 10 of 43 Tab le 2 . Physical

- chemical Properties of Difenacoum

Study Value and units Source

Hydrolysis Stable MRID 46750903 Photolysis 3.3 hrs at pH 5 8.1 hrs at pH 7 7.3 hrs at pH 9 PPDB

Solubility 1

. 7 mg/L at pH 7 MRID 46750903 Biodegradation DT50 > 108 days

. t 1/2 = 439 days MRID 46750914

PPDB Organic carbon Partition Coefficient (K
oc ) 4,827,000 mL/g o.c. (MCI method) 46,020 mL/g o.c. (K OW method) EPISuite v4.1

Vapor pressure 6.7*10

- 9 to 5.4*10

- 14 Pa EPISuite v4.1 Henry’s law constant 1.4 X10

- 12 atm

- m 3 /mole EPISuite v4.1

Octanol

- water partiti on coefficient (K
ow ) Log K OW = 7.6 EPISuite v4.1

Difenacoum has the potential to move offsite through food consumption by target species, which travel away from the application site. Other than direct consumption of bait and secondary poisoning, other ro utes of environmental exposure are expected to be minimal. Difenacoum is strongly sor bed to the bait formulation

, and therefore movement of residues by means of leaching through the soil profile to an aquatic environment is not likely . Further, difenacou m is unlikely to volatilize, unlikely to move offsite due to method of application (bait formulation ), and due to the relatively low application rates (maximum of 0.00 01 lb a.i./placement), and unlikely to runoff or leach in substantial quantities

.



### 5.1 Transfo rmation Products

Difenacoum transformation products through abiotic, soil biotic, or sediment biotic degradation have not been identified due to the persistence of difenacoum and because those types of data are lacking.



## 6 Receptors

6.1 Toxicity Summary

Table 3 provides a summary of the taxonomic groups and the surrogate species tested to characterize the potential acute and chronic ecological effects of difenacoum

. In addition, the table provides a preliminary overview of the potential acute toxicity of difenac oum by providing the acute toxicity classifications. No ecotoxicity data are available for any degradates of

difenacoum ( difenacoum has no known major degradates)

.

Difenacoum is moderately toxic to birds on an acute oral basis, very highly toxic to birds on a subacute dietary exposure basis, and very highly toxic to mammals on an acute oral basis. Sublethal effects noted in the acute oral study in live test birds that were euthanized and subsequently subjected to necropsy (MRID 46750922) included hemorrhag ing and lethargy in all

birds while mortality was 40% even at the lowest treatment group of 50 mg/kg bw . Post

- mortemPage 11 of 43 examinations indicated evidence of hemorrhaging and blood clots in the liver and other organs for birds exposed to the ≥0.75 mg/kg treatment diets in the sub

- acute dietary study (MRID 46750926). A submitted study evaluating the chronic toxi city of difenacoum to Japanese quail was found to be unacceptable due to high control mortality and husbandry concerns

.

Several studies were submitted on difenacoum’s (or its cis or trans isomers) effect on a number of mammalian species including the rat ( Rattus norvegicus ), house mouse ( Mus musculus ), rabbit ( Oryctolagus cuniculus ), domestic dog ( Canis lupus familiaris ), domestic cat ( Felis sylvestris

cattus ), sheep ( Ovis aries ), domestic pig ( Suc scrofa ), guinea pig ( Cavia porcellus ) and hamster ( Mesocr icetus auratus ). However, of the mammalian acute oral studies, only the rat studies were determined to be acceptable.

Difenacoum is very highly toxic to mammals on an acute oral exposure basis based on the rat data (male acute oral LD 50 = 1.8 mg/kg

- bw, MRID 46750935)

. Additionally, MRID 46766206 shows

that the cis isomer may be more toxic than the trans isomer and the house mouse may be more sensitive than the rat with male mice exposed to the cis isomer having an LD 50 of 0.45 mg a.i./kg

bw (female mic e exposed to the cis isomer in the same study had an LD 50 of 1.0 mg a.i./kg

- bw)

, while the trans isomer was approximately 2

- 3 times less toxic (male and female LD 50 s of 1.18 and 2.75, respectively) . EFED typically averages the male and female LD 50 values if a difference exists between them. In the risk assessment, male mouse data with the cis isomer will be used for

risk characterization.

No acceptable acute dietary or chronic mammalian data are available for difenacoum. In addition, data on the tox icity of difenacoum to terrestrial invertebrates and terrestrial plants have

not been submitted to the Agency.

Technical grade difenacoum is classified as very highly toxic to freshwater fish and highly toxic

to freshwater invertebrates on an acute expos ure basis based on study

- author reported toxicity

. Acute estuarine/marine fish and invertebrate data as well as chronic exposure effect s data to

difenacoum for fish and invertebrates have not been submitted to the Agency. While no toxicity data for aquati c vascular plants were submitted to the Agency , toxicity data were submitted for a single species of aq uatic nonvascular aquatic plant ( green algae

, Pseudokirchneriella subcapitata ) and indicate that difenacoum is toxic to algae based on study

- author repor ted toxicity.

Table 3 . Most Sensitive Test Species Evaluated for Assessing Potential Ecological Effects of

D ifenacoum

.

Taxonomic Group Study Type Tested Species Toxicity Endpoint (95% CI) Acute Toxicity

Classification/

NOAEC most

sensitive endpoint(s) M RID and

Classification

Birds 1 Acute oral (primary

bait consumer) Colinus virginianus (Northern bobwhite) LD 50 = 67 mg a.i. /kg

bw ( 3.5

— 150.7). Slope

= 1.22 Moderately toxic 46750922
(Acceptable)Page 12 of 43 Table 3 . Most Sensitive Test Species Evaluated for Assessing Potential Ecological Effects of

D ifenacoum

.

Taxonomic Group Study Type Tested Species Toxicity Endpoint (95% CI) Acute Toxicity

Classification/

NOAEC most

sensitive endpoint(s) M RID and

Classification

Dietary Anas platyrhynchos ( Mallard) LC 50 = 14.1 mg a.i. / kg

diet (6.9

— 88.2). Slope

= 1.13 Very highly toxic 46750926 ( Supplemental )

Mammals Acute oral (single dose) Laboratory Rat LD 50 = 1.8 mg a.i. /kg

bw (1.5

— 2.1) Very highly toxic 46750935

46750936 (Acceptable)

Chronic No data

Terrestrial

invertebrat es Acute

contact No data

Freshwater

fish 2 Acute Rainbow trout (Oncorhynchus mykiss) 96

- hr LC 50 0.064 m g a.i. /L Very highly toxic 46750919 ( In

review )

Chronic No data

Freshwater

invertebrates Acute Water flea ( Daphnia magna) 48

- hr LC 50 0.61 mg /L H ighly toxic 46750917 (In review)

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

A quatic plants and algae Vascular No data

Non

vascular Green algae ( P

. subcapitata ) 72

- hr EC 50 0.32 mg/L Not applicable 46750929 (In review)

1 Birds represent surrogates for terrestrial

- phase amphibians and reptiles.

2 Freshwater fish are used as surr ogates for aquatic

- phase amphibians.



### 6.2 Secondary Toxicity

Secondary toxicity is considered exposure to non

- target predatory animals that occurs as a result of their consuming other organisms (including target pests) that have eaten difenacoum treated

bai ts. Seco ndary toxicity can also occur where nestlings and other young animals are fed exposed prey animals. As part of the litigation risk assessment for d ifenacoum for selected species in the San Francisco Bay area

, a summary of available literature on secondary toxicity for both acute and chronic exposures were summarized (EPA, 2012). In the available studies, birds and mammals were exposed to difenacoum in whole or ground carcasses, which were usually those of rats or mice, or in fortified meat. Most prey animals were fed treated bait,Page 13 of 43 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 r egurgitation) 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 for characteri zation of secondary hazards from short

- term exp osure. Though these types of secondary exposure studies provide information on the potential effects

from difenacoum 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.

EPA will update the secondary toxicity analysis for difenacoum at the time of the registration review preliminary risk assessment.

6.2.1 Availa ble Studies for Secondary Toxicity to Birds

Mendenhall and Pank (1980) compared secondary hazards of 6 anticoagulant rodenticides, including difenacoum, to barn owls ( Tyto alba ). For difenacoum, s ix owls were exposed for either 1, 3, 6, or 10 days to rat s fed with bait (50 ppm a.i.). Exposed rats were offered free choice of bait (5 to 13 g daily) or laboratory chow for 10 days; body residues were not

determined. None of the difenacoum

- exposed owls died, but the 3 owls fed for 6 or 10 days hemorrhaged, 1 severely ( Table 4 ).

Table 4

. Adverse Effects of Difenacoum to Barn Owls Exposed To Rats Fed Bait (adapted from Mendenhall and Pank 1980)

Days exposed No. tested/

no. dead Sublethal effects

Observed

Difenacoum (50 ppm) 1

3

6

10 1/0

2/0

1/0

2/0 the 3 owls offered rats for 6 or 10 days survived but all hemorrhaged (1 severely)

Wyll ie (1995) and Newton et al. (1990) reported on toxic effects to barn owls fed mice exposed

to four rodenticides, including difenacoum. The mice were fed bait (no cho ice) for a single day and allowed to die, which took 2 to 11 days. Residues of difenacoum in dead mice were present at greater concentrations in the liver than the rest of the carcass and were estimated to be 10

- 17 μg difenacoum for a whole 35g mouse. De ad mice were then offered to the owls in 3 phases, each phase separated by a recovery period lasting at least 75 days. In phase I, each owl (6 per rodenticide) was offered 3 mice for 1 day only. Surviving owls were offered 6 mice each during

a 3

- day peri od in phase II and 12 mice each during a 6

- day period in phase III. Mortality, evidence of external bleeding, and blood

- coagulation times were monitored. The 6 owls fed

difenacoum

- dosed mice survived with no evidence of external bleeding, and blood

- coagu lation times returned to normal within 5 to 23 days. During phases II and III, both survivors bled fromPage 14 of 43 the mouth, feet, and newly

- grown feathers for up to 30 days, and blood

- coagulation times did not reach normal until 16 to 78 days after treatment.

T he registrant also supplied a report by Gray et al. (1992 ; MRID 46750932 ), similar to the published paper by Gray et al. (1994) cited in EFED’s comparative risk assessment (USEPA, 2004b) . In this study, the authors examined effects in barn owls fed mice t hat were exposed to three rodenticides, including difenacoum. Batches of mice (6 per rodenticide) were fed 50 ppm wax block bait either in weighed amounts of 1.0 g

– 5.0 g for 23 hours or ad libitum for 24 or 48 hours. Representative mice from each batch were selected and analyzed for residues, and mice

contained 0.95

– 5.20 mg/kg of residue depending on the rodenticide (specific data were not provided). Four owls per rodenticide were fed treated mice for 15 days, and the amount of

rodenticide fed to the owls was varied by feeding mice that fed on more or less bait or by feeding them more or fewer mice. Details of the feeding scheme for each owl are not provided. After

the 15

- day treatment period the owls were fed untreated mice and observed for another 15 days

or until deat h. One owl fed difenacoum died. Owls fed difenacoum ate 36

– 128 μg difenacoum per da y, and the owl that died ate 101 μg/day. This owl ate the second highest dose of the four, but had the highest liver residue ( Table 5 ). No other effects were described in the report. Susceptibility and possibly absorption and elimination varied between the owls, and the sample size was very small. The authors concluded that although the toxicity of difenacoum and the other rodenticides was high, the risk resulting from a baiting program was low due to the low incidence of treated mice likely to be present in a pulse

- baiting program using a retrievable wax block bait available intermittently. These conclusions do not necessarily translate directly to the proposed use of difenacoum, however, since the pelleted end

- use product is retrievable and can be used in permanent bait stations.

Table 5: Secondary Toxicity in Barn Owls (from Gray, 1992, 1994)
Residue Concentration (mg/kg)

Survival Status Anticoagulant

consumed

(μg/day) Cumulative consumption (mg/kg owl bw) Liver Fat Muscle

Difenacoum (50 ppm):

Survived (n=3) 36

– 128 1.6

– 5.5 0.06

– 0.14 <0.01 0.01

Died (n=1) 101 3.7 0.25 0.01 0.01

6.2.2 Available studies for Secondary Toxicity to Mammals

Shore et al. (2003) p resent data on residues in polecats ( Mustela putorius ) accidentally killed on roads in England. Livers were analyzed for residues of second

- generation anticoagulant rodenticides, including difenacoum, bromadiolone, flocoumafen, and brodifacoum . This work was an extension of that presented in Shore et al. (1996) and Shore et al. (1999), which were discussed in EFED’s comparative risk assessment ( USEPA, 2004 b ). Of 100 carcasses collected for all three studies between 1992 and 1999, 31 contained residues of at least one second

generation anticoagulant. Difenacoum was the most prevalent compound detected in 26 animals. Four polecats contained residues of multiple anticoagulants: two contained residues ofPage 15 of 43 difenacoum and bromadiolone, and the other two contai ned residues of difenacoum, bromadiolone, and brodifacoum. Among these studies, the authors concluded that the residues resulted from hunting activities of the polecats on nearby farms in winter and that they were probably killed when they dispersed into the landscape at a later time. Since the terminal phase

liver elimination half

- life of most second

- generation anticoagulants in mammals can exceed 100 days, difenacoum and the other compounds can be detected for months after ingestion. Although the samp ling scheme was unlikely to permit the collection of fatally poisoned animals, the maximum liver residue of difenacoum (0.917 ug/g) and bromadiolone (0.23 ug/g) approached that of a polecat that was poisoned by secondary exposure ( Birks 1998, as cited in

S hore et al. 2003) and a stoat that died after feeding on contaminated voles (Grolleau et al. 1989,

as cited in Shore et al. 2003 ), respectively.

McDonald et al. (1998 ) tested for anticoagulant residues in stoats ( Mustela erminea ) and weasels ( Mustela niva lis ) shot or trapped on game farms in England. Nine out of 40 stoats and three out

of 10 weasels contained residues of at least one rodenticide. Difenacoum was not found in any of the animals tested; however, in the area of England in which the study was conducted, coumatetralyl is used more widely, and was the most frequently detected anticoagulant. According to the authors, difenacoum and bromadiolone were the most widely used rodenticides in the rest of England, and these are more toxic than coumatetr alyl. Thus

, the authors concluded that the hazards of secondary poisoning may be more pronounced where difenacoum and bromadiolone anticoagulants are used. This conclusion is supported by the results of Shore et al. (2003).

These studies indicate the widespread occurrence of secondary exposure resulting from rodent control activities. All three species are exclusively carnivorous and would have been very unlikely to consume bait directly. Polecats are known to prey on animals that are targets of

rode nt control programs. However, weasels and stoats feed on these animals much less often, so predators do not necessarily have to forage around buildings in order to be secondarily exposed (McDonald et al. 1998).



### 6.3 Incident Database Review

A summary of the 5 difenacoum wildlife incidents reported in the Environmental Incident Information System (EIIS, version 2.1.1) database, with a certainty classification of “ possible ”

,

“ probabl e” , or “ highly probable ” is included in Table 6

. These classifications mean tha t, at a minimum, there was supporting evidence ( e.g ., hemorrhaging) and/or residue data to indicate

that the wildlife involved in the incident were adversely affected by exposure to an anticoagulant rodenticide and/or an independent wildlife specialist, ba sed on findings of a necropsy examination and toxicological analysis, identified an anticoagulant rodenticide as the cause of death in the incident report. The reported avia n species include carnivore/scavenger birds that

include the bald eagle, red

- tailed hawk , and kite.

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 rod enticides 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 notPage 16 of 43 necessarily be attributed to a pesticide, even if it is a contributing factor. Difenacoum has also not been registered for as long as other second generation anticoagulant rodenticides ( e.g. brodifacoum), which have comparatively greater reporting of incidents associated with the ir use. The lack or low occurrence of reported incidents does not necessarily indicate the actual frequency with which incidents related to the use of difenacoum may occur.

Table 6. Wildlife Mortality Incidents for Difenacoum Reported in the EIIS Data base

Incident

ID Year Legality Certainty State Land Use Generic Species (Number Affected) Comments

I016488

- 005 1999 Undeter

mined Possible UK* N/R Kite

- bird (1) Trace concentrations of

difenacoum and brodifacoum detected in liver samples

I016488

- 009 19 99 Undeter

mined Probable UK* N/R Kite

- bird (1) Brain hemorrhaging was linked

to c oncentrations of difenacoum (0.2 ppm) and brodifacoum (0.04 ppm) detected in liver samples

I016488

- 010 1997

- 1999 Undeter

mined Possible UK * N/R Kite

- bird (9) Five o f nine samples tested were positive for either bromadiolone

or difenacoum or both. Liver residues ranged from 0.05 to 0.40 mg/kg; however, illegal poisoning with either alphachloralose or carbofuran was implicated in four of the

five deaths

I023352

- 001 2 011 Undeter

mined Possible NE Rangeland/

pasture Bald Eagle (1) Less than 0.002 ppm difenacoum detected in liver samples along with less than quantifiable

residues of six other rodenticides. Chlorophacinone was detected at 0.4 ppm.

I024829

- 001 2009 Undet er

mined Highly

Probable NY N/R Red

- tailed

hawk (1) C oncentrations of difenacoum (0.02 ppm), bromadiolone (0.13 ppm), and brodifacoum (0.05 ppm) were detected in liver samples *UK: United Kingdom . I016488

- 05,

- 09,

- 10 are incidents associated with difenaco um’s use that were reported in the open literature ( Carter and Burn, 2000)

.

N/R: Not reported

There were no aggregate incidents reported for difenacoum in the US EPA’s Office of Pesticide Programs Incident Data System as of December 21, 2015. EPA will update this review of reported difenacoum incidents at the time of the registration review preliminary risk assessment.Page 17 of 43 

## 7 Exposure Pathways of Concern

The environmental fate properties and use patterns of difenacoum indicate th at non

- target consumption of b ait and consumption of indi viduals that have consumed bait represent potential transport mechanisms of difenacoum to terr estrial organisms.

Drinking water and inhalation exposure pathways for birds and mammals were screened using the SIP (Screening Imbib ition Program) and STIR (Screening Tool for Inhalation Risk) screening methods SIP and STIR are described in detail at: http://www2.epa.gov/pesticide

science

- and

- assessing

- pesticide

- risks/models

- pesticide

- risk

- assessment# terrestrial

. The drinking

water pa thway was found not to be an exposure pathway of potential concern for acute risks to

birds due to low solubility of difenacoum relative to toxicity

. However, the drinking water pathway is an exposure pathway of potential concern for acute risks to mammals . Chr onic risks

to mammals and birds cannot be excluded because there is insufficient data on chronic toxicity. The inhalation exposure pathway could not be explored using STIR because no mammalian inhalation toxicity data is available. However, inhalati on is not expected to be an exposure pathway of concern for birds or mammals due to the low volatility of difenacoum

. SIP results are presented in Appendix B

.



## 8 Analysis Plan

8.1 S tressors of Concern

8.1.1 Ecological Risk Assessment

For this registration review cas e , t he stressor of ecological concern for terrestrial organisms is the parent compound, difenacoum

.

8.1.2 Drinking Water Assessment

A difenacoum d rinking water assessment for use in the human health risk assessment is not expected to be conducted during r egist ration review because difenacoum b ait s are contained in

bait stations, and therefore not available for runoff

.



### 8.2 Measures of Exposure

A previous risk assessment (USEPA, 2007) modeled aquatic exposure of difenacoum and found that negligible concentrations o f difenacoum could occur in the water column relative to the toxicity to aquatic organisms. Model results indicated a pe ak concentration of 0.143 μg/L in

surface water . This result is driven by difenacoum’s immobility within its bait formulations. The

most sensitive aquatic endpoint is an LC 50 of 64 μg a.i./L for the rainbow trout ( Oncorhynchus mykiss ). This endpoint is more than two orders of magnitude greater than the estimated environmental concentration ( EEC ) . Additionally, outdoor bait is placed in bai t stations and

therefore not available for runoff, and spray drift is not expected for this chemical. For thesePage 18 of 43 reasons, EFED does not expect to conduct a quantitative aquatic ecological risk assessment during registration review.

For the difenacoum regis tration review risk assessment , it will be assumed that terrestrial animals could be exposed in two different pathways. Animals may directly consume bait (primary consumption), or animals may consume contaminated prey either killed or scavenged by the

cons umer (secondary consumption). Both approaches and the expected exposure levels are detailed below. It is important to note that these methods differ from what is typically done in

EFED risk assessments , but they are appropriate for difenacoum based on the use parameters and environmental exposures described previously and consistent with other EFED risk assessments

for rodenticides

.

8.2.1 Estimating Primary Terrestrial Exposure

EFED’s exposure assessment for the rodenticides differs from that for most other p esticides. 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 o f 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. , LD 50 ). Estimates of food

- ingestion rates (g dry matter per day) are determined

from established allomet ric equations presented in the Wildlife Exposure Factors Handbook (USEPA 1993). The concentration of difenacoum in grain bait is also used to estimate initial dietary exposure (mg a.i. per kg in bait) which in turn is used to calculate avian and mammalian dietary RQs.

8.2.1.1 Expected Difenacoum Accumulation through a Single Feeding on

Bait

Exposure through bait consumption will be calculated using two methodologies. For the first method, difenacoum exposure is calculated as mg a.i./kg

- bw , where kg

- bw is the k ilograms 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 a nd 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 7 , and difenacoum exposure estimates (on a dose basis) are provided in Table 8

. Risk quot ients ( RQs ) are generated by dividing these exposure estimates of

difenacoum (mg a.i./kg

- bw ) for a given weight class by the most conservative toxicity endpoint

for the relevant taxa scaling adjusted for the default body weights. RQs using these exposure

estimates will be generated for acute bird and mammal (using LD 50 data) non

- targets.Page 19 of 43 Table 7

. Formulas for Calculation of Daily Difenacoum 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

D ifenacoum intake (mg a.i./kg

- bw /day) = FI (g dry

- wt /day) /bw (in kg)* mg a.i./kg

- bait dry weight * 1kg/1000g

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

mg a.i./kg

- bait = 50 based on difenacoum concentration in registered bait

Table 8

. Expected Daily Difenacoum Intake for Default Bird and Mammal Weights based on Consumption of Bait.

Weight

(g) Food intake (g dry

wt/day) Dif enacoum intake (mg a.i./kg

- bw/day)

Bait concentration =

50 mg a.i./kg

- bait

Passeriform

Birds* 20 5.1 12.8

100 19.9 10

1000 141.2 7.1

Rodent

Mammals 15 2.9 9.7

35 4.6 6.6

1000 30.6 1.5
*surrogate for reptiles and terrestrial

- phase amphibians

8.2.1.2 Expected Difenacoum Accumulation through Multiple Feedings on

Bait

Available data on the retention times for difenacoum are provided in Table 9

. Vandenbroucke et al. (2008) orally dosed groups of mice with 12.88 μg a.i./mouse difenacoum , which is

appr oximately one

- half of the LD 50 dose. Difenacoum was then assayed in liver tissue and blood plasma from euthanized mice at various times up to 21 days after dose administrations. The study authors estimated the elimination half

- life of difenacoum in liver t issue to be 61.8 days and

the half

- life in blood plasma to be 20.4 days.

The discrepancies between the half

- lives estimated in Vandenbroucke et al. (2008) and Bratt (1987) may be a result of different difenacoum elimination rates among species.Page 20 of 43 Table 9 . Retention of Difenacoum in Blood and Liver

Rodenticide Species Dose (mg a.i./kg) # doses Blood t 1/2 a (days) Liver

retention a,b (days) Reference (MRID)

Difenacoum Mouse 12.88 μg/mouse 1 20.4 61.8 (t 1/2 ) Vandenbroucke et al.

, 2008

Difenacoum Rat 1.2 mg /kg 1

-- 118 (t 1/2 ) Bratt , 1987 ( 46750957 )

a t 1/2 for plasma and liver is the elimination half

- life

b liver retention is expressed as either the time period for which residues persist or as the elimination half

- life

As indicated previously, difenacoum i s known to persist in biological tissue. 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 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 2 were also calculated using the formula s i n Table 10 . This analysis assumed that 100% of the daily diet of the animals is represented by the rodenticide bait and that they eliminate the difenacoum with a

half

- life of 118 days based on the highest definitive liver half

- life value ( Table 9 )

. In the formula, D is the dose and D t is the total dose. T he variable “C” represents the concentration of the pesticide in the bait (mg/kg) . The elimination rate constant (k) was calculated using the

estimated difenacoum half

- life (t 1/2 = 118 days), and food inta ke (FI ; mg/kg

- bw/day ) was calculated according to the allometric equation for each taxonomic group ( Table 7 ). The resulting cumulative body burden concentrations of difenacoum are presented in Table 11

. Different half

- life assumptions based on available da ta may be used to further characterize risk in

the registration review risk assessment.

2 Average time to mortality between bait consumption and mortality for first and second generation anticoagulant rodenticides ( risk assessment methodology from USEPA, 2011)

.Page 21 of 43 Table 10. Formulas for Calculation of Difenacoum Body Burden based on Consumption of Bait for Six Consecutive Days

DD tt = � DD nn 6

nn = 1 ∗ ee − kk ( 6

− nn )

where

kk = ln ( 2 ) tt 1 / 2 ⁄

Table 11. Calculated difenacoum 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

Passerine Generic Bird

20 75.1 67.3

100 59.0 38.4

1000 41.7 17.2

Rodent Generic Mammal

15 56.4 42.9

35 39.0 36.9

1000 9.0 20.3

8.2.1.3 Expected Difenacoum Exposure based on Bait Concentration

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

50 mg a.i./kg

- bait (concentrations of difenacoum as packaged in bait). RQs will be calculated using this estimate of dietary concentration and the LC 50 (mg a.i./kg

- diet) available from dietary toxicity studies. RQs using these exposu re estimates will be generated for acute bird and mammal (using LC 50 data) non

- targets.

8.2.2 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 difenacoum are available in open lit erature (Gray et al., 1992, 1994)

. Additionally, a number of laboratory tests using avian and mammalian predators and scavengers are available to assess mortality from secondary exposure resulting from consumption of prey animals that have been exposed to

difenacoum. Design and methodology vary among studies, adding unknown variability to the results and analysis. Pending development of additional methods and testing requirements for such studies, these tests provide the best data available.Page 22 of 43 The determin ation of difenacoum intake by individuals consuming difenacoum poisoned animals or carcasses is calculated in a manner similar to the approach for individuals consuming bait ( Section 8.2 .1 .2 ). Empirical residue data are used instead of bait concentration of difenacoum ( Table 1 1 ). D ifenacoum body burdens in carcasses collected from field and laboratory studies were determined in mammals, after exposure to difenacoum bait. Data are available for a variety

of small

- and medium

- sized mammalian granivores and omnivo res. No data were identified for other exposed taxonomic groups ( e.g., birds and reptiles ). For all studies, it was assumed the concentrations were reported using wet weights of the mammals.

In laboratory studies, mean difenacoum residues in mam malian carcass ranged from 0. 52 to 0.74 mg a.i./kg

- bw and are summarized in Table 12

.

Table 1 2

. Difenacoum Residue Levels in Mammalian Primary Consumers.

mg ai/kg

bait Target species Site Sample size Days exposed Mean whole

carcass residue (mg a.i./kg

- bw) Reference (Ecotox Number)

25 Rat Laboratory 10 per strain 5 S usceptible

strain (TAS)

0.52 ± 0.038 (SE) Atterby et a l. 200 5 (E079379)

Resistant strain

HH

0 .63 ± 0.045 (SE)

Resistant strain

HB

0 .68 ± 0.062 (SE)

25 Rat Laboratory 10 pe r strain 10 Resistant strain

HH

0 .55 ± 0.055 (SE) Atterby et a l. 200 5 (E079379)

Resistant strain

HB

0 .64 ± 0.0 32 (SE)

25 Rat Laboratory 10 20 Resistant strain

HB

0 .74 ± 0.04 (SE) Atterby et a l. 200 5 (E079379)

50 ppm Mouse Gray et a l. 1994

Difenacoum exposure through carcass consumption is calculated as mg a.i./kg

- bw , where kg

- bw is the kilograms of the consuming individual for three weight classes of birds and mammals. For this analysis, bird weight classes of 50, 1000, and 2000 g individu als and mammal weight classes of 50, 1000, and 3000 g individuals are 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 is then used to estimate rodenticide exposure in the secondary consumer using the general food intake allometric equations described in Section 8.2.1 above. Secondary

consumers are assumed to be mammals weighing 50g, 1000g, or 3000g, or birds weighing 100g,Page 2 3 of 43 1000g, or 5000 g. 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 are derived using the generic bird and mammal allometric

eq uations from (EPA 1993). Food dry weight was converted to wet weight assuming the consumed prey/carcass contained 68% water (USEPA 1993).

8.2.3 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 B ). If additional information indicates there may be concerns, these pathways will be re

- evaluated at the time of the registration review risk assessment.

No monitori ng 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 rodenticide s such as difenacoum

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

, th o se 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 informat ion 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, 2007), which employs a

literatu re 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 EPA’s responsibility under the Endangered Species Act (ESA), the Agency wi ll evaluate risks to federally listed threatened and endangered (listed) species from registered uses of pesticides in accordance with the Joint Interim Approaches developed to implement the recommendations of the April 2013 National Academy of Sciences (N AS) report, Assessing Risks to Endangered and Threatened Species from Pesticides

. The NAS report outlines recommendations on specific scientific and technical issues related to the development of pesticide risk assessments that EPA and the Services must conduct in connection with their obligations under the ESA and FIFRA. EPA will address concerns specific to difenacoum in connection with the development of its final registration review decisi on for difenacoum

.Page 24 of 43 In November 2013, EPA, the U.S. Fish and Wildlife Service, National Marine Fisheries (the Services), and USDA released a white paper containing a summary of their joint Interim Approaches for assessing risks to listed species from pes ticides. These Interim Approaches were developed jointly by the agencies in response to the NAS recommendations, and reflect a common approach to risk assessment shared by the agencies as a way of addressing scientific

differences between the EPA and the Services. Details of the joint Interim Approaches are contained in the November 1, 2013 white paper

, Interim Approaches for National

- Level Pesticide Endangered Species Act Assessments Based on the Reco mmendations of the National Academy of Sciences April 2013 Report.

Given that the agencies are continuing to develop and work toward implementation of the Interim Approaches to assess the potential risks of pesticides to listed species and their designa ted critical habitat, this ecological problem formulation supporting the Preliminary Work

Plan for difenacoum does not describe the specific ESA analysis, including effects determinations for specific listed species or designated critical habitat, to be co nducted during registration review. While the agencies continue to develop a common method for ESA analysis, the planned risk assessment for the registration review of difenacoum will describe the level of ESA analysis completed for this particular regist ration review case. This assessment will allow EPA to focus its future evaluations on the types of species where the potential for effects exists, once the scientific methods being developed by the agencies have been fully vetted. Once the agencies have fu lly developed and implemented the scientific methods necessary to complete risk assessments for listed species and their designated critical habitats, these methods will be applied to subsequent analyses of difenacoum as part of completing this registratio n review.



## 10 Endocrine Disruptor Screening Program

Difenacoum 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/endocri ne

- disruption/endocrine

- disruptor

- screening

- program

- edsp

overview

.



## 11 Preliminary Identification of Data Gaps

11.1 Environmental Fate

Since difenacoum’s use patterns and product formulatio ns in bait boxes are not expected to result in exposure to soil, water, or air, many OCSPP 835 environmental fate guideline studies

have not been submitted or are fulfilled in summary form

. If a new use with increased

environmental exposure s is proposed in the future, additional environmental fate guideline studies may be necessary for a better understanding of difenacoum’s persistence and mobility.Page 25 of 43 Table 13

. Available Environmental Fate Data for Difenacoum

.

OCSPP

Guideline Data Requirement Submitted

S tudies (MRID) Study

Classification Are data needed

for risk

assessment? Current Additional Data

Need

835.2120 Hydrolysis 46750910 Unreviewed No None

835.2240 Aqueous photolysis 46750 928 Unreviewed

summary No A guideline study has not

been submitted , but a summary with physical chemical modeling

estimates has been submitted. This summary

fills data needs for the current use pattern given aquatic exposure is not expected.

835.2410 Soil photolysis (None) (N/A) No Data have not been

submitted to fulfill thi s guideline. A data gap was

not identified as these data are not necessary for risk

assessment at this time.

835.4100 Aerobic soil

metabolism 46750928 Unreviewed

summary No A guideline study has not

been submitted , but a data

summary has been

submitted. This summary

fills data needs for the current use pattern given aquatic exposure is not expected.

835.4200 Anaerobic soil

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

submitted to fulfill this guideline. A data gap was

not identified as these data

are no t necessary for risk

assessment at this time.

835.4300 Aerobic aquatic

metabolism (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.

835. 4400 Anaerobic aquatic

metabolism 46750916 Unreviewed No Unreviewed study

conducted under ISO 11734

835.1230

835.1240 Adsorption/ desorption and leaching 46750907

46750908 Unreviewed No Unreviewed studies

conducted under OECD guideline 121 and BBA Part

I V/4

- 2

835.6100 Terrestrial field dissipation (None) (N/A) No Data have not been

submitted to fulfill thisPage 26 of 43 Table 13

. Available Environmental Fate Data for Difenacoum

.

OCSPP

Guideline Data Requirement Submitted

S tudies (MRID) Study

Classification Are data needed

for risk

assessment? Current Additional Data

Need

Storage Stability Study (TFD) (None) (N/ A) No guideline. A data gap was

not identified as these data are not necessary for risk

assessment at this time.

850.1730 Fish

bioconcentration (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.

Environmental Chemistry

Method: Water

850.6100 A nalytical

method in water and independent laboratory

validation (None) (N/A) No

Environmental Chemistry

Method: Soil Analytical

method in soil and independent laboratory

validation (None) (N/A) No



### 11.2 Ecological Effects

Tables 15 and 16 identify submitte d 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.

Currently, i nadequate data are available to further cha racterize the differential toxicity among bird species. In addition, there is evidence of different or multiple modes

- of

- action of

rodenticides in different taxa. Additional toxicity data on a wider range of species or data exploring mode

- of

- action would b e beneficial to better understand the natural variation and to improve 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 difenacoum on avian reproduction (OCSPP 850. 2300) or survival. Avian reproduction data available for another registered anticoagulant rodenticide, chlorophacinone

, highlights the potential for effects from long

- term, low

- dose exposure

. For chlorophacinone, m allard ducks exposed to dietary

concentrat ions for five days had an LC 50 = 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 489904 002). EFED recommends that additional data on effects of long

- term low

- dose exposure of difenacoum to birds through extended exposure dietary studies and avian reproduction studies be requested.

No data are available to assess of the toxicity of difenaco um to terrestrial invertebrates. EFED

does not have concerns for difenacoum exposure to pollinators such as bees and butterflies,Page 27 of 43 because expected exposures would be low. Difenacoum is not applied as a spray; therefore, expected exposure on plants, includ ing flowers, would be low. Pollinators would not be expected to feed on live animals or carcasses that may have been contaminated with difenacoum

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

on live anim als contaminated with difenacoum residues, or feed on carcasses with difenacoum residues. No terrestrial invertebrate incidents have been reported for difenacoum

.

The earthworm LC 50 values for bromadiolone, a second generation rodenticide, at 24 h and 48 h were 145.70 μg/cm 2 and 25.03 μg/cm 2 , 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 s ubsequently excreting it have been documented (Fisher et al. 2007; Hernandez

- Moreno et al. 2013). Toxicity of difenacoum to terrestrial invertebrates is unknown; however, there is evidence to suggest that toxicity may

occur and that the exposure pathway fo r secondary exposure is complete. EFED is not requesting the full suite of pollinator protection studies as outlined in recent guidance , at this time ( http://www2. epa.gov/pollinator

- protection/pollinator

- risk

- assessment

- guidance ). However, EFED does request an earthworm toxicity study for difenacoum and any existing data that demonstrate toxicity, or lack of toxicity, to difenacoum for terrestrial invertebrates.

Given that the available data indicates that the cis isomer is more toxic than the trans isomer, additional toxicity studies that report the ratio of these isomers in the tested material would be helpful.

Although they are technically considered data g aps, EFED does not recommend requesting terrestrial plant, aquatic plant, chronic fish, or chronic aquatic invertebrate toxicity data for

difenacoum at this time since these data would not be expected to change the conclusions of th e registration review ri sk assessment. There remains uncertainty in the level of risk for each of these taxonomic groups given the missing data; however, the expected exposures for the currently registered use pattern s will be relatively low:

• Terrestrial plants

- No data are ava ilable to assess of the toxicity of difenacoum to terrestrial plants; however, exposure to plants is also expected to be low since there is no registered spray application of difenacoum

, and the material is applied as a formulated

bait in bait stations

. Di fenacoum binds strongly to organic material ( i.e. , the formulated bait) and little is expected to be available for runoff or leaching. No plant incidents have been reported for difenacoum

.

• Aquatic plants

– No data are available to assess the toxicity of d ifenacoum to aquatic

vascular plants , and only one study is available for nonvascular aquatic plants which demonstrates toxicity potential ; however, aquatic exposure is also expected to be low

since there are no registered spray or aerial baiting applicati on s
, and the material is applied as a formulated bait in bait stations

. Difenacoum binds strongly to organic material ( i.e. , the formulated bait) and little is expected to be available for runoff or leaching. No aquatic incidents have been reported for dif enacoum

.Page 28 of 43 • Chronic fish and aquatic invertebrates

– No data are available to assess the chronic toxicity of difenacoum to fish and aquatic invertebrates; however, aquatic exposure is expected to be low since there are no registered spray or aerial baiting a pplication s and the material is applied as a formulated bait in bait stations

. Difenacoum is very highly acutely toxic to fish and highly toxic to freshwater invertebrates, and chronic effects would not be unexpected. However, difenacoum binds strongly to organic material ( i.e.

, the formulated bait) and little is expected to be available for runoff or leaching for this proposed use. No aquatic incidents have been reported for difenacoum

.

Table 1 4 . Available ecological effects data for terrestrial organism s exposed to difenacoum 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 46750922 acceptable

Yes Data are requested for

avian acute oral with passerine species

. Due to the delayed toxicity of anticoagulant rodenticides, the observation period for this study should be extended beyond the

standard 850.2100 guideline

recommendation of 14 days ( i.e. it should be long enough to capture

effects of difenacoum poisoning and continue until evidence of toxicity has subsided). The study

should track the ratio of

difenacoum’s cis and

trans isomers in the

tested material. 46750921 acceptable

850.2200 Avian dietar y toxicity 46750926 supplemental

No

-- 46750923 supplemental

46766204 supplemental

850.2300 Avian reproduction 46799101 unacceptable Yes Data are requested for avian reproduction toxicity testing an upland game bird species and a waterfowl

spec ies

. The study

should track the ratio of

difenacoum’s cis and

trans isomers in the

tested materialPage 29 of 43 Table 1 4 . Available ecological effects data for terrestrial organism s exposed to difenacoum 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. T hese data are not necessary for risk

assessment at t his time

850.3020 Honey bee acute contact toxicity (None) (N/A) No E xposures of honey bees

to difenacoum residues are not expected since they are unlikely to feed

on bait blocks and

residues are not expected to be present in pollen and nectar. Therefore, no honey bee data is requested at this time, but data on other invertebrate species may

be useful for risk

assessment

850.3030 Honey bee residue on foliage (None) (N/A) No

Data have not been

submitted to fulfill these guidelines. T hese data

are not nece ssary 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

N on

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 pollinato r (None) (N/A) No

850.3100 Earthworm Subchronic Toxicity

Test (None) (N/A) Yes Data are requested for earthworm toxicity ( Eisenia fetida ) . The study should track the

ratio of difenacoum’s cis

and trans isomers in the

tested material.

850.4100 Seedlin g Emergence and Seedling Growth (None) (N/A) NoPage 30 of 43 Table 1 4 . Available ecological effects data for terrestrial organism s exposed to difenacoum and remaining data gaps.

OCSPP

Guideline Data Requirement Submitted Studies (MRID) Study

Classification Are data

needed for

risk

assessment? Current Additional

Data Need

850.4150 Vegetative Vigor (None) (N/A) No Data have not been

submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

Table 1 5 . Available ecological effects dat a for aquatic organisms exposed to difenacoum 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

inverte brate acute toxicity 4675091 7 In review Submitted

data are in

review Submitted data are in review

4675091 8 In review

850.1025

850.1035

850.1045

850.1055 Saltwater

invertebrate acute toxicity (None) (N/A) No Data have not been submitted

to fulf ill th ese guideline s

. T hese data are not necessary

for risk assessment at this time

850.1075 Freshwater fish acute toxicity 46750919 In review Submitted

data are in

review Submitted data are in review

46750920 In review

850.1075 Saltwater fish

ac ute toxicity (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

850.1300 Freshwater

invertebrate life cycle (None) (N/A) No Data have not been submitted

to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

850.1350 Saltwater

invertebrates life cycle (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

850.1400 Freshwater fish early

- life stage (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

850.1400 Saltwater fish early

- life stage (None) (N/A) No Data have not b een submitted to fulfill this guideline. T hese data are not necessary for riskPage 31 of 43 

## 12 References

Atterby, H., Kerins, G. M., and MacNicoll , A. D. 2005 . Whole

- Carcass Residues of the Rodenticide Difenacoum in Anticoagulant

- Resistant and

- Susceptible Rat Strains (Rattus norvegicus). Environ.Toxicol.Chem. 24: 318

- 323. Ecotox Reference N umber 079379

Bratt, H. 1987. Difenacoum: Elimination from tissues of rats following administration of a single oral dose. Macclesfield, Surrey, Imperial Chemical Industries Ltd, Central Toxicology Laboratory (Report No. CTL/P/1592). EPA MRID 46750957

Bre ckenridge, A.M., S. Cholerton, J.A.D. Hart, B.K. Park, and A.K. Scott. 1985. A study of the relationship between the pharmacokinetics and pharmacodynamics of 4

- hydroxycoumarin anticoagulants, warfarin, difenacoum, and brodifacoum in the rabbit.

British J. Pharmacol. 84: 81.91.

Brorson T., et al. 1982. Environ Toxicol Chem 13: 543

- 52 (1994) (2) Davis PJ, Rizzo JD; Appl

Environ Microbiol 43: 884

- 90.

Carter, I. and A. Burn. 2000. Problems with rodenticides: the threat to red kites and other

wildlife. Brit ish Wildlife. 11(3): 192

- 197

Cox, P. and R. H. Smith. 1992. Rodenticide ecotoxicology: pre

- lethal effects of anticoagulants

on rat behavior. Proc. Vertebr. Pest Conf. 15:165

- 170.

Davis P.J. And J.D. Rizzo. 1982. Microbial transformations of warfarin: s tereoselective reduction by Nocardia corallina and Arthrobacter species. Appl Environ Microbiol 43:

884

- 90. assessment at this time

850.1500 Fish life cycle (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at t his time

850.4400 Aquatic plant Toxicity Test using Lemna

spp. (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this time

850.4500 Algal toxicity 46766205 In review Submitted

data are in

review Submitted data are in review

46750929 In review

850.4550 Cyanobacteria (None) (N/A) No Data have not been submitted to fulfill this guideline. T hese data are not necessary for risk

assessment at this timePage 32 of 43 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

Eason, C.T. and E. Murphy. 2001. Recognising and reducing secondary and tertiary risks associated with brodifacoum. Pages 157

- 163 in J. J. Johnston (ed.), Pesticides and Wildlife. American Chemical Society Symposium Series 771.

EFSA, 2009. Difenacoum: Product

- type 14 (Rodenticides). Directive 98/8/EC concerning the placing of biocidal products on the market. Assessment Report. Annex I

– Finland. September 17, 2009.

Ellington J.J. 1989. Hydrolysis Rate Constants for Enhancing Property

- Reac tivity Relationships,

USEPA/600/3

- 89/063, NTIS No. PB89

- 220479, p. 45.

Erickson, W., Urban, D., 2004. Potential risks of nine rodenticides to birds and nontarget mammals: a comparative approach, Office of Prevention, Pesticides and Toxic

Substances. US EP A, Washington, DC.

Fisher, P., C.O’Connor, G. Wright, and C.T. Eason. 2003. Persistence of four anticoagulant rodenticides in the liver of laboratory rats. Doc Science Internal Series 139. New Zealand Department of Conservation, Wellington, NZ. 19 pp. MRID# 48190801

Food and Agriculture Organization of the United Nations. FAO PESTICIDE DISPOSAL SERIES 8. Assessing soil contamination: A reference Manual. Appendix 2. Parameters of pesticides that influence processes in soil. Editorial Group, FAO Informa tion Division: Rome, 2000, accessed on May 13, 2011 @ http://www.fao.org/DOCREP/003/X2570E/X2570E06.htm#ch8

.

Gore R.C., R.W. Hannah, and S.C. Pattacini . 1971. Infrared and ultravio let spectra of seventy

- six pesticides. J Assoc Off Anal Chem 54: 1040

- 82.

Gray, A., C.V. Eadsforth, and A.J. Dutton. 1992. Toxicity of Second Generation Rodenticides to barn owls. Brighton Crop Protection Conference

– Pest and Diseases, pp. 781

- 786. MRID

No. 46750932

Gray, A., C.V. Eadsforth, A.J. Dutton, and J.A. Vaughan. 1994. The Toxicity of Three Second

Generation Rodenticides to Barn Owls. Pest Management Science. 42:179

— 184.

Hansch C., et al. 1995. Exploring QSAR. Hydrophobic, Electronic, and S teric Constants. ACS Prof Ref Book. Heller SR, consult. ed., Washington, DC: Amer Chem Soc p. 161.

Hartley D, Kidd H, eds. 1983. The Agrochemicals Handbook, Old Woking, Surrey, UK: Royal Soc Chem/Unwin Brothers Ltd, p. A418.Page 33 of 43 Hazardous Substances Data Ban k (HSDB), accessed on June 1st, 2011 @http://toxnet.nlm.nih.gov/cgi

- bin/sis/search/f?./temp/~fBjbzJ:1

Hayes, W. and E. Laws. 1991. Handbook of Pesticide Toxicology. Volume 3. Academic Press Inc. San Diego, California. p. 1301

- 1302.

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.

Howard, P.H., Ed. 1991. Handbook of Environmental F ate and Exposure Data for Organi c Chemicals. Vol. 111: Pesticides. Lewis Publishers, Chelsea, MI.

King, R.B. 2002. Predicted and observed maximum prey size

– snake size allometry. Functional Ecology 16: 766

– 772.

Kolpin D.W. et al. 2002. Pharmaceuticals, Hormones, and Other Wastewater Contaminants in U.S. Streams, 1999

- 2000: A National Reconnaissance. Environ Sci Technol 36: 1202

- 11.

Lee, C.H. 1994. Secondary toxicity of some roden ticides to barn owls. 4th International Conf. Plant Protection in the Tropics, 28

- 31 March, Kuala Lumpur, Malaysia, pp. 161

- 163.

Lyman WJ et al; Handbook of Chemical Property Estimation Methods. Washington, DC: Amer Chem Soc pp. 4

- 9 (1990).

Masuda, B.M., P. Fisher, and I.G. Jamieson. 2014. Anticoagulant rodenticide brodifacoum detected in dead nestlings of an insectivorous passerine. New Zealand Journal of Ecology. V38(1): 110

— 115).

Masuda, B.M., P. Fisher and B. Beaven. 2015. Residue profiles of brodifacoum in coastal marine species following an island rodent eradication. Ecotoxicology and Environmental Safety. 113 (1

- 8).

McDonald, R., S. Harris, G. Turnbull, P. Brown and M. Fletcher. 1998. Anticoagulant Rodenticides in Stoats ( Mustela ermine ) and weasels ( Mustela nivalis ) in England.

Environmental Pollution 103:17

- 23.

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

rodenticides. Wildl. Soc. Bull. 8:311

- 315. MRID No. 46750931

Meylan W.M., and Howard PH. 19 93. Computer estimation of the atmospheric gas

- phase reaction rate of organic compounds with hydroxl radicals and ozone. Chemosphere 26:

2293

- 99.Page 34 of 43 Nagy, K. A

. (1987). Field metabolic rate and food requirement scaling in mammals and birds. Ecol. Monogr. 57 ,111

- 128

Newton, I., I. Wyllie, and P. Freestone. 1990. Rodenticides in British barn owls. Environmental

Pollution 68:101

- 117. MRID No. 46750933.

Phillips, J. 1996. An investigation in the absorption, tissue distribution, and elimination of

Carbon 14 la belled difenacoum following oral administration to rats. Project number: 1552/2, 1555/2/3/96. Unpublished study prepared by TNO BIBRA International Ltd. 69 p. EPA MRID 46766216

Phillips, J. 2002. An investigation into the elimination and tissue distribu tion of the carbon

- 14 labelled stereoisomers of difenacoum following oral administration to rats. Project number: 3175/3/02, 3175. Unpublished study prepared by TNO BIBRA International Ltd. 57 p. EPA MRID 46766215

Shore, R.F., J.D.S. Birks, P. Freeston e, and A.C. Kitchener. 1996. Second

- generation rodenticides and polecats ( Mustela putorius ) in Britain. Environ. Pollution 91:279

- 282.

Shore, R.F., J.D.S. Birks, A. Afsar, C.L. Wienburg, and A.C. Kitchener. 2003. Spatial and temporal analysis of se cond

- generation anticoagulant rodenticide residues in polecats ( Mustela putorius ) from throughout their range in Britain, 1992

- 1999. Environ. Pollution

122:183

- 193.

Telle, H.

- J. 1955. [The use of cumarin

- containing products in rodent control]. Nachrichte nblatt

des deutschen Pflanzenschutzdienstes 4:93

- 99.

Tomlin, C.D.S. (ed.). 1997. The Pesticide Manual

- World Compendium, 11 th ed., British Crop Protection Council, Surrey, England. p. 1270.

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. 1998. Guidelines for Ecological Risk Assessment. United States Environmental Protection Agency (USEPA). Risk Assessment Forum.

Offic e of Research and Development. Available at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12460 (Accessed June 19, 2009).

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

Pe sticide Programs, Environmental Fate and Effects Division.Page 35 of 43 U.S. Environmental Protection Agency. 2007. EFED Risk Assessment for the Proposed Section 3 Registration of Difenacoum for Control of Norway Rats, Roof Rats, and House Mice.

DP Barcode 338315. Off ice of Prevention, Pesticides and Toxic Substances. Washington, D.C. May 24, 2007.

U.S. Environmental Protection Agency. 2011. Risks of Non

- Compliant Rodenticides to Nontarget Wildlife. Background Paper for Science Advisory Panel on Notice of Intent to

Cancel Non

- RMD compliant Rodenticide Products. Environmental Fate and Effects Division, Office of Pesticide Programs, Office of Chemical Safety and Pollution Prevention. Washington D.C. November 1, 2011.

U.S. Envir onmental Protection Agency. 2012

. Risks of Difenacoum Use To the Federally Threatened Alameda Whipsnake ( Masticophis lateralis euryxanthus ), the Federally Endangered Sa lt Marsh Harvest Mouse ( Reithrodontomys raviventris ), and the Federally Endangered San Joaquin Kit Fox ( Vulpes macrotis mutica ). US EPA Office of Pesticide Programs, Environmental Fate and Effects Division. March 2012.

U.S. Environmental Protection Agen cy. 2015. Label Use Information System Report. US EPA Office of Pesticide Programs, Biological and Economic Analysis Division. A pril 2015.

Vandenbroucke, V., A. Bosquet

- Melou, P. De Backer, and S. Croubels. 2008. Pharmacokinetics of eight anticoagulant rodenticides in mice after singe oral administrations. J. vet. Pharmacol. Therap. 31:437

- 445.

Wyllie, I. 1995. Potential seconda ry poisoning of Barn Owls by rodenticides. Pesticide Outlook.

5:19

- 25.Page 36 of 43 

## Appendix A: Difenacoum Fate/Chemistry and Ecotoxictiy Bibliography

161

- 1 Hydrolysis

MRID Citation Reference

46750910 Lewis, C. (1992) Difenacoum: Hydrolysis Study (Final Report). Project Number: 7031, 38/166. Unpublished study prepared by Hazleton Uk. 96 p.

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpub lished study prepared by Woodstream Corp. 15 p.

46766202 Lewis, C. (1992) Difenacoum: Hydrolysis Study: Amendment to Final Report. Project Number: 38/166R, 7031. Unpublished study prepared by Hazleton Uk. 6

p.



### 161

- 2 Photodegradation

- water

MRID Ci tation Reference

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpublished study prepared by Woodstream Corp. 15 p.



### 162

- 1 Aerobic soi l metabolism

MRID Citation Reference

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpublished study prepared by Woodstream Corp. 15 p.



### 16 2

- 4 Aerobic aquatic metab olism

MRID Citation Reference

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpublished study prepared by Wo odstream Corp. 15 p.Page 37 of 43 

### 163

- 1 Leach/adsorp tion /desorption

MRID Citation Reference

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpubl ished study prepared by Woodstream Corp. 15 p.



### 835.1110 Activated sludge sorption isotherm

MRID Citation Reference

46750907 Hogg, A. (2003) Difenacoum: Physico

- Chemical Testing with Difenacoum: Estimation of Adsorption Coefficient. Project Number: 21677, 341765, 4176A. Unpublished study prepared by Inveresk Research International. 47 p.



### 835.1220 Sediment and soil absorption /desorption isotherm

MRID Citation Reference

46750908 Lewis, C. (1992) (Carbon 14)

- Difenacoum: Aged So il Leaching: Final Report. Project Number: 38/168, 7066, P6732D. Unpublished study prepared by Hazleton Uk. 62 p.



### 835.2110 Hydrolysis as a function of pH

MRID Citation Reference

46750910 Lewis, C. (1992) Difenacoum: Hydrolysis Study (Final Report). Project Number: 7031, 38/166. Unpublished study prepared by Hazleton Uk. 96 p.

46766201 Lewis, C. (1992) (Carbon 14)

- Difenacoum: Aged Soil Leaching: Amendment to Final Report. Project Number: 38/168, 7066. Unpublished study prepared by

Hazleton Uk. 7 p.

46766202 Lewis, C. (1992) Difenacoum: Hydrolysis Study: Amendment to Final Report. Project Number: 38/166R, 7031. Unpublished study prepared by Hazleton Uk. 6

p.Page 38 of 43 

### 835.2210 Direct photolysis rate in water by sunlight

MRID Citation Refere nce

509 Hall, B.; Jackson, R.; Priestley, I. (1992) Difenacoum: Photolysis in Buffered Aqueous Solutions. Project Number: 8704, 381614. Unpublished study prepared by Inveresk Research International. 123 p.



### 835.3300 Soil biodegradation

MRID Citation Reference

46750914 Lewis, C. (1992) (Carbon 14)

- Difenacoum: A Study of the Degradation in Two Soils: Final Report. Project Number: 38/167, 6927. Unpublished study prepared by Hazleton Uk. 78 p.

46766203 Lewis, C. (1992) (Carbon 14)

- Dife nacoum: A Study of the Degradation in Two Soils: Amendment to Final Report. Project Number: 38/167R, 6927. Unpublished study prepared by Hazleton Uk. 7 p.



### 835.3400 Anaerobic biodegradability of organic chemicals

MRID Citation Reference

46750 916 Penwell, A. (2004) Difenacoum: Determination of Anaerobic Biodegradability. Project Number: BL7788/B. Unpublished study prepared by Astrazeneca Uk Ltd. 24 p.



### 850.2100 Avian acute oral toxicity test

MRID Citation Reference

46750921 Nol an

- Smith, S. (1997) Difenacoum: Acute Oral Toxicity to Mallard Duck: Final Report. Project Number: 355/39/1007. Unpublished study prepared by Covance Laboratories, Ltd. 60 p.

46750922 Ross, D.; ROberts, N.; Fairley, C. (1980) The Acute Oral Toxicity (LD5 0) of Difenacoum to the Bobwhite Quail. Project Number: ICI/309/WL/8076, CTL/C/932. Unpublished study prepared by Huntingdon Life Sciences, Ltd. 20

p.



### 71

- 2 850.2200 Avian Dietary ToxicityPage 39 of 43 MRID Citation Reference

46750924 Nolan

- Smith, S . (2000) Difenacoum: Acute Dietary Toxicity to Mallard Duck: Final Report. Project Number: CLE/355/40, CLE/355/40/D1141, DF/959/0077. Unpublished study prepared by Covance Laboratories, Ltd. 67 p.

46750925 Ross, D.; Roberts, N.; Fairley, C. (1980) The Su bacute Dietary Toxicity (LC50) of Difenacoum to the Bobwhite Quail. Project Number: 56/79, ICI/305/791197. Unpublished study prepared by Huntingdon Life Sciences, Ltd. 16 p.

46750923 Nolan

- Smith, S. (1998) Difenacoum: Acute Dietary Toxicity to Bobwhite Q uail: Final Report. Project Number: 355/41/1007. Unpublished study prepared by Covance Laboratories, Ltd. 60 p.

46750926 Ross, D.; Roberts, N.; Fairley, C. (1980) The Subacute Dietary Toxicity (LC50) of Difenacoum to the Mallard Duck. Project Number: CTL /C/888, ICI/304/791198. Unpublished study prepared by Huntingdon Life Sciences, Ltd. 19 p.

46766204 Nolan

- Smith, S.; Sharples, R. (2000) Difenacoum: Acute Dietary Toxicity to Ring

- necked Pheasants: Final Report. Project Number: 355/42, 355/42/D1142. Unpu blished study prepared by Covance Laboratories, Ltd. 63

p.



### 850.2300 Avian reproduction test

MRID Citation Reference

46799101 Linder, T. (2006) Avian Reproduction Study with Difenacoum in the Japanese Quail (Coturnix coturnix japonica): Fina l Report. Project Number: 04012. Unpublished study prepared by Genesis Laboratories, Inc. 205 p.



### 71

- 5 Simulated or Actual Field Testing

MRID Citation Reference

40077207 Hoppe, A.; Krambias, A. (1982) The response of captive Chukar par tridge s to the ingredients and anticoagulant poisons used in ro

- dent baits in Cyprus. P.

639

- 646 in Proceedings of a conference on the organization and practice of Vertebrate Pest Control; Aug 30

- Sept 3, 1982, Elvetham Hall, Hampshire, England.



### 850.1075 Fish acute toxicity test, freshwater and marine

MRID Citation ReferencePage 40 of 43 46750919 Wyness, L. (1995) Difenacoum: Acute Toxicity to Oncorhynchus mykiss: Final Report. Project Number: 355/17/1018. Unpublished study prepared by Corning Hazleton (Europ e). 32 p.

46750920 Wyness, L. (1995) Difenacoum: Acute Toxicity to Lepomis macrochirus: Final Report. Project Number: 355/23/1018. Unpublished study prepared by Corning Hazleton (Europe). 32 p.



### 850.1010 Aquatic invertebrate acute toxicity, test, f reshwater daphnids

MRID Citation Reference

46750917 Wyness, L. (1995) Difenacoum: Acute Toxicity to Daphnia magna: Final Report. Project Number: 355/18/1018. Unpublished study prepared by Corning Hazleton (Europe). 38 p.

46750918 Kent, S.; Tapp, J.; Sankey, S.; et. al. (1991) Difenacoum: Acute Toxicity to Daphnia magna. Project Number: BL4314/B, V480/B. Unpublished study prepared by Imperial Chemical Industries, Ltd. 19 p.



### 850.5400 Algal toxicity, Tiers 1 and II

MRID Citation Reference

46750929 Wyness, L. (1995) Difenacoum: Inhibition of Growth to the Alga Selenastrum Capricornutum: Final Report. Project Number: 355/19/1018, 355/19. Unpublished study prepared by Corning Hazleton (Europe). 37 p.

46766205 Smyth, D.; Tapp, J.; Sanke y, S.; et. al. (1991) Difenacoum: Toxicity to the Green Alga: Selenastrum capricornutum. Project Number: V480/A, BL4307/B, FT51/91. Unpublished study prepared by Imperial Chemical Industries, Ltd. 21

p.



### NON Guideline Selections

35806 Mendenhall, V.M.; Pa nk, L.F. (1979) Secondary Poisoning of Owls by Anticoagulant Rodenticides. (U.S. Fish and Wildlife Service, Patuxent and Denver Wildlife Research Centers, unpublished study)

80242 Mendenhall, V.M.; Pank, L.F. (1979) Secondary Poisoning of Owls by

Antico agulant Rodenticides. (U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center; unpublished study; CDL: 245704

- M)

94694

40077202
on DER Mendenhall, V.M.; Pank, L.F. (1980) Secondary poisoning of owls by anticoagulant rodenticides. Wildlife Soc iety Bulletin 8(4):311

- 315. (Also~In~unpublished submission received Feb 7, 1982 under 12455

- 34; submitted by Bell Laboratories, Madison, Wis.; CDL: 246741

- C)Page 41 of 43 46750931 Mendenhall, V.; Pank, L. (1980) Secondary Poisoning of Owls by Anticoagulant

Rodecti cides: (Difenacoum, Bromadiolone, Brodifacoum, Diphacinone, Fumarin, Chlorophacinone). The Wildlife Society Bulletin 8(4): 311

- 315.

46750932 Gray, A.; Eadsforth, C.; Dutton, A.; et. al. (1992) Toxicity of Second Generation Rodenticide to Barn Owls: (Brod ifacoum, Difenacoum, Flocoumafen). Brighton Crop Protection Conference Pests and Diseases: 781

- 786.

46750933 Newton, I.; Wyllie, I.; Freestone, P. (1990) Rodenticides in British Barn Owls: (Difenacoum, Brodifacoum). Environmental Pollution 68: 101

- 117.

46750934 Buckle, A. (2004) Expert Review of Literature on the Ecotoxicology of Difenacoum and Wildlife in the European Union. Unpublished study prepared by Alan Buckle Consulting, Ltd. 239 p.

46750961 Croucher, A. (1998) Analysis of Difenacoum in Rat C arcasses: Validation of a Method and Analysis of Samples: Amended Final Report. Project Number: CLE/355/45/D2140, 355/45, CLE/355/45/02R. Unpublished study prepared by Covance Laboratories, Ltd. 31 p.

46750928 Harrison, E. (2005) Summary of Environmental Fate and Ecological Effects Studies Conducted with Difenacoum, A New Rodenticide Active Ingredient. Unpublished study prepared by Woodstream Corp. 15 p.Page 42 of 43 

## Appendix B. Screening Level Models to Evaluate Potential Importance of Drinking Water and Inhalati on Exposure Pathways

SIP ( Screening Imbibition Program, v1.0) Inputs and Conclusions
Table 1. Inputs

Parameter Value

Chemical name Difenacoum

Solubility (in water at 25 o C; mg/L) 2

Mammalian LD 50 (mg/kg

- bw) 1.8
Mammalian test specie s laboratory rat Body weight (g) of "other" mammalian species

Mammalian NOAEL (mg/kg

- bw)
Mammalian test species Body weight (g) of "other" mammalian species

Avian LD 50 (mg/kg

- bw) 67
Avian test species northern bobwhi te quail Body weight (g) of "other" avian species
Mineau scaling factor 1.15 Mallard NOAEC (mg/kg

- diet)
Bobwhite quail NOAEC (mg/kg

- diet)
NOAEC (mg/kg

- diet) for other bird species
Body weight (g) of other avian species

NOAEC (mg/kg

- diet) for 2nd other bird species Body weight (g) of 2nd other avian species

Table 2. Mammalian Results

Parameter Acute Chronic
Upper bound exposure (mg/kg

- bw) 0.3440 0.3440 Adjusted toxicity value (mg/kg

- bw) 1.3845 0.0000
Ratio of exposure to toxicity 0.2485 0.0000

Conclusion* Exposure through drinking water alone is a

potential concern for

mammals Due to insufficient data, risk cannot be precluded

Table 3. Avian Results

Parameter Acute Chronic
Upper bound ex posure (mg/kg

- bw) 1.6200 1.6200 Adjusted toxicity value (mg/kg

- bw) 48.2688 0.0000
Ratio of exposure to acute toxicity 0.0336 0.0000Page 43 of 43 Conclusion* Drinking water exposure alone is NOT a potential
concern for birds Due to insufficient data, risk cannot be p recluded

*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.