Page 1 of 183 

## Risk s of Non

- Compliant Rodenticides to Nontarget Wildlife

Background Paper for Science Advisory Panel on
Notice of Intent to Cancel Non

- RMD compliant Rodenticide Products



### November 1, 2011

United States Environmental Protection Agency

Office of Chemical Safety and Pollution Prevention
Office of Pesticides Programs

Environmental Fate and Effect Division

Prepared by:

Brian Anderson, Shannon Borges, Kristina Garber, Christine Hartless, Justin Housenger

, Nicholas Mastrota

, Edward Odenkirchen, Elizabeth Riley, Michael WagmanPage 2 of 183 

## Table of Contents

i. Executive Summary

................................ ................................ ................................ ................. 4

1 Background

................................ ................................ ................................ ............................ 14

2 Analysis Plan

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

2.1 Active Ingre dients Assessed

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

2.2 Product Labels under Evaluation

................................ ................................ ................... 18

2.3 Modes of Action

................................ ................................ ................................ ............. 27

2.4 Conceptu al Model of Exposure

................................ ................................ ...................... 28

2.5 Taxonomic Groups Potentially at Risk

................................ ................................ .......... 29

2.6 Measures of Exposure

................................ ................................ ................................ .... 30

2.7 Measures of Toxicity

................................ ................................ ................................ ...... 31

2.8 Meas ures of Risk

................................ ................................ ................................ ............ 32

3 Toxicity, Accumulation, and Elimination of the Evaluated Rodenticides

............................ 34

3.1 Avian and Mammalian Toxicity

................................ ................................ .................... 34

3.2 Elimination of Rodenticides

................................ ................................ ........................... 50

3.3 Estimated Accumulation of Dose over Time

................................ ................................ . 61

3.4 Measured Rodenticide Residues

................................ ................................ .................... 67

4 Primary Exposure and Risk

................................ ................................ ................................ ... 73

4.1 Risks based on the Acute Oral LD 50

................................ ................................ .............. 73

4.2 Risks based on the acute dietary LC 50

................................ ................................ ............ 83

4.3 Uncertainties

................................ ................................ ................................ ................... 85

4.4 Summary of Rodenticide Risks to Bait

- consuming Birds and Mammals

...................... 85

5 Secondary Exposure and Risk

................................ ................................ ............................... 87

5.1 Rodenticide Ingestion through Consumption of Contaminated Carcasses

- Theoretical Analysis

................................ ................................ ................................ ................................ ..... 88

5.2 Rodenticide Ingestion through Consumption of Contaminated Carcasses

- Residue Analysis

................................ ................................ ................................ ................................ ..... 98

5.3 Secondary Exposure Studies

................................ ................................ ........................ 102

5.4 Uncertainties

................................ ................................ ................................ ................. 115

5.5 Discussion of Risks of Rodenticides to Secondary Birds and Mammals

.................... 117

6 Wildlife Incidents

................................ ................................ ................................ ................ 120Page 3 of 183 6.1 Mortality Incidents

................................ ................................ ................................ ....... 120

6.2 Open Literature Evaluations

................................ ................................ ......................... 136

6.3 Exposure Incidents

................................ ................................ ................................ ....... 140

7 Synthe sis of Conclusions

................................ ................................ ................................ ..... 153

7.1 Primary Exposure Risk Conclusions

................................ ................................ ............ 161

7.2 Secondary Exposure Risk Conclusions

................................ ................................ ........ 165

8 References

................................ ................................ ................................ ........................... 171Page 4 of 183 

### i. Executive Summary

A. Background

EPA has update d its previous risk assessment findings conducted in support of the May 2008

RMD through the application of additional effects and exposure data, use of additional exposure modeling, and quantitative risk assessment techniques for the four rodenticides subject to the

NOIC (brodifacoum, difethialone, warfarin and bromethalin) and for t wo rodenticides that are likely alternatives (i.e., active ingredients included in products with RMD

- compliant registrations for commensal rodent control

, specifically, chlorophacinone and diphacinone ; bromethalin has both compliant and non

- compliant registrations )

.

Rodenticide baits are intended to be lethal to rodents and a few other small mammals, but they are not selective to target species. M ammal and bird specie s are vulnerable to adverse effects
from rodenticides if exposed

. Exposure to no n

- target wildlife has been documented in urban, suburban, and rural areas, exposure to does not appear to be limited to isolated incidents, and

r odenticide exposures and mortalities have been documented for mammals and birds that are primary and secondary consumers.

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

- target organism consumption of rodenticide treated bait. Use of rodenticide baits around structures is likely to result in primary exposures among non

- target wildlife. Many factors influence which nontarget animals might be exposed directly to baits . For instance, birds and mammals that are attracted to seeds and grains may consume grain

- based rodenticide baits and baits in forms similar to seeds and grains. Some non

- ta rget animals will likely readily consume rodenticide baits that have a
block form. Exposure has been reported for a number of species that are primary consumers of bait, including various species of birds and squirrels, opossums, raccoons, skunks, and deer.

Secondary consumers are defined as those animals that prey upon or scavenge primary
consumers of bait

. Rodenticide baits also pose s potential secondary risks, because predators and scavengers are likely to be attracted to dead or dying rats, mice, and poisoned non

- target animals. In addition, secondary consumers may also consume commensal rodent baits that contain flavorings that might appeal to carnivores and omnivores. E xposure has been documented in a
number of secondary consumer species inclu d ing larger mammals such as bobcats and foxes, and numerous bird species such as hawks, eagles and owls.

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

- target mammals from exposure to the commensal rodent control products subj ect to t his notice. This concern is
based up on consideration of several lines of evidence , including (1) a n assessment of the risks to

non

- target animals associated with primary exposure to rodenticides ; (2 ) a n assessment of thePage 5 of 183 risks of non

- target animals through secondary exposure to rodenticides; (3) an evaluation of available feeding studies as they relate to secondary exposure risks; and (4) an evaluation of reported wildlife incident s as they relate to primary and secondary mortality events fo r non

target species in a variety of land use settings, inc l uding urban, suburban, and rural settings

.

The risk assessment involved calculation of RQs based on estimates of exposure and toxicity. RQs were compared to the acute level of concern (LOC), w hich is 0.5. An RQ that exceeds the LOC of 0.5 is considered to pose a risk of concern for non

- listed species

. The RQ analysis was supplemented with additional characterization that evaluates the potential for effects to occur

, including an estimate of t he amount of bait (and duration of feeding) required to consume the
median lethal dose, number of prey items required to be consumed to reach the median lethal dose, and a characterization of the uptake and elimination properties of the rodenticides includ ed
in this assessment.

B. Primary Exposure Methods

Risk of rodenticide exposures to primary consumers is influenced by several factors

, including toxicity, toxicokinetics (chemical absorption, distribution and elimination in the body),
concentration of ac tive ingredient in the bait, and availability of bait for consumption. For each of the evaluated chemicals, risk is assessed in several ways:

**•** single day dose

- based exposure to bait based on allometric equations for food intake that

allow for differentiation of dose according to body size is compared to weight adjusted

acute oral LD 50 toxicity values;

**•** multiple day dose

- based exposure to bait based on food intake allometric equations and

metabolism that allow for differentiation o f dose according to body size and elimination

of the chemical over time is compared to weight adjusted acute oral LD 50 toxicity values;

and

**•** Dietary exposure (concentration of chemical active ingredient in bait) is compared to acute dietary LC50 values.

Fu rther lines of evidence include an analysis of the number of days of bait consumption required
to accumulate a median lethal dose of rodenticide and the grams of bait individuals would need

to c onsume in order to accumulate that median lethal dose. An eva luation of required feeding period and the required amount of treated material necessary for consumption to result in exposures of lethal concern is a useful comparative tool among chemicals. Chemicals that require little feeding time or small amounts of treated material to reach the median lethal dose likely represent a greater opportunity for lethal incidents (and thus pose a greater risk) as compared to compounds that would need consistent feeding or large amounts of consumption over protracted periods of time.Page 6 of 183 C. Secondary Exposure Methods

S econdary risk potential was assessed using several lines of evidence

, including:

**•** RQ analysis based on theoretical and empirical residue levels in prey ;

o As with the primary exposure analysis, an analysis was conducted assuming target mammals fed on rodenticide bait for single or multiple days.

**•** Accumulation and elimination characteristics ;

**•** Results from secondary feeding studies ;

**•** Estimation of the number o f organisms required to consume the equivalent of the median lethal dose for a predator or scavenger ;

**•** Incident data

Time to death also influences the potential for exposure, since compounds that kill rapidly would prevent the primary consumer from continuing to eat bait, thereby consuming a dose that would be toxic to a secondary consumer. Rodenticides that are slower to cause death also prolong the period when contaminated (and potentially more vulnerable) prey are available to predators. The toxicity of the rodenticide to the secondary consumer would also affect the risk of adverse effects that would result from expo sure. Based on these characteristics, rodenticides that are eliminated more slowly and have greater potential to accumulate within body tissues, take longer to kill the primary consumer, and have greater toxicity to secondary consumers are expected to pre sent greater secondary risk.

D. I ncident Findings Related to Primary & Secondary Risk Analyse s

The quantitative risk assessment assumes that exposure is occurring under a set of conservative assumptions. It does not evaluate the actual potential for wildl ife to come into contact with treated bait; it simply evaluates the consequences of exposure. EPA uses available incident and exposure information from a variety of sources, including state and local governments and pesticide registrants. The majority of available reported incidents for the rodenticides assessed
are included in EPA’s Environmental Incident Information System (Version 2.1) EIIS. EPA believes these data offer strong support for the conclusion that residential and commercial use of
rodentic ides in urban/suburban and rural areas provide complete exposure pathways to a variety of wildlife and that primary and secondary exposure lethal incidents involving non

- target
wildlife can occur.Page 7 of 183 E. Summary of Results

Results of the risk assessment are summarized in the following tables. Conclusions of the assessment are detailed in Section 7 of this assessment and include the following:

**•** Primary Risks

o Primary exposure risk to mammals is above concern levels and is similar across
the assessed rodenti ci des , which is consistent with their use as rodenticides ;

o Prima r y exposure risk to birds is above concern levels for brodifacoum, difethialone, and bromethalin, and less than a single day of feeding could result in a median lethal dose;

o Primary risk to birds is above concern levels for chlorophacinone and warfarin; however, consumption of bait is generally required to occur for greater durations
to result in median lethal doses compared with the apformentioned brodifacoum, difethialone, and bromethalin ;

o No LOCs were exceeded for diphacinone for primary exposure risks to birds

.

**•** Secondary Risks

o Secondary exposure risks to mammals exceeded concern levels for all assessed chemicals under some exposure scenarios. However, a greater opportunity for secondary exposure to result in median lethal doses was estimated to be greater
for brodifacoum and difethialone relative to the other assessed rodenticides.

o Secondary exposure risk to birds is above concern levels for brodifacoum, and
difethialone under all asse ssed scenarios, and consumption of less than a single contaminated prey animal could result in a median lethal dose;

o Secondary exposure risk to birds was lower than concern levels for chlorophacinone and diphacinone under all scenarios evaluated, and less than concern levels for warfarin under all scenarios evaluated except for small scavengers consuming contaminated mice that accumulated 0.054% warfarin bait for 6 days . Multiple contaminated prey items w ere estimated to be required to
result in a median lethal dose for these chemicals . For bromethalin, concern levels were exceeded for secondary exposure. However, the duration for primary
consumers to feed on bromethalin bait and accumulate the rodenticid e is limited due to this chemical's rapid mode of action and observations that target animals stop feeding after a lethal dose is reached . This in turn limits the potential exposure for secondary consumers.Page 8 of 183 Table 2

- 1. Avian RQ analysis: primary exposure o f passerine birds to bait and secondary exposure of carnivore/scavenger birds to residues in consumed rodents.

Body weights (g) Brodif

acoum Difeth

I alone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Single day dose RQ 20 19.61* 29.80* 0.23 0.50* 0.07 0.01 7.76*

100 22.67* 18.39* 0.14 0.31 0.04 0.01 4.76*

1000 27.89* 9.22* 0.07 0.16 0.02 <0.01 2.40*

Six day dose RQ 20 117* 168* 1.36* 2.94* 0.40 0.05 34*

100 135* 104* 0.84* 1.81* 0.25 0.03 21*

1000 166* 52* 0.42 0.91* 0.12 0.01 11*
Dietary RQ NA 38* 45* 0.40 0.86* 0.89* 0.06 0.48Theoreticalsecondary exposure House mouse consumption: 1 day accumulation in prey RQ 100 6.60* 5.84* 0.05 0.10 0.01 <0.01 1.52*

1000 5.15* 1.85* 0.01 0.03 <0.01 <0.01 0.48

5000 4.33* 0.83* 0.01 0.01 <0.01 <0.01 0.22

Norway rat consumption: 1

day accumulation in prey RQ 100 1.75* 1.54* 0.01 0.03 <0.01 <0.01 0.40

1000 1.36* 0.49 <0.01 0.01 <0.01 <0.01 0.13

5000 1.15* 0.22 <0.01 <0.01 <0.01 <0.01 0.06

House mouse consumption: 3 day accumulation in prey RQ 100 19.77* 17.09* 0.14 0.30 0.04 0.01 4.06*

1000 15.42* 5.42* 0.04 0.09 0.01 <0.01 1.29*

5000 12.96* 2.43* 0.02 0.04 0.01 <0.01 0.58*

Norway rat consumption:

3 day accumulation in

prey RQ 100 5.25* 4.52* 0.04 0.08 0.01 <0.01 1.07*

1000 4.08* 1.43* 0.01 0.02 <0.01 <0.01 0.34

5000 3.43* 0.64* 0.01 0.01 <0.01 <0.01 0.15

House mouse consumption: 6 day accumulation in prey RQ 100 39.40* 32.98* 0.27 0.58* 0.08 0.01 NA

1000 30.74* 10.45* 0.09 0.19 0.02 <0.01 NA

5000 25.84* 4.68* 0.04 0.08 0.01 <0.01 NA

Norway rat consumption:

6 day accumulation in prey RQ 100 10.43* 8.73* 0.07 0.15 0.02 <0.01 NA

1000 8.14* 2.77* 0.02 0.05 0.01 <0.01 NA

5000 6.84* 1.24* 0.01 0.02 <0.01 < 0.01 NAPage 9 of 1 83 House mouse consumption: dietary RQ NA 17.81* 2069* 0.19 0.41 0.32 0.02 0.20

Norway rat consumption: dietary RQ NA 4.71* 5.48* 0.05 0.11 0.09 <0.01 0.05EmpiricalSecondaryExposure Single day dose RQ 100 4.42* 4.64* <0.01 <0.01 <0.01 ND

1000 5.01* 1.47* <0.01 <0.01 <0.01 ND

5000 4.21* 0.66* <0.01 <0.01 <0.01 ND
Dietary RQ NA 5.25* 5.54* <0.01 0.02 <0.01 ND NA = not applicable ; ND = no data ; * = RQ exceeds the acute LOC of 0.5Page 10 of 183 Table 2

- 2. Avian Risk Characterization: Additional lines of evidence

Body weights (g) Brodif

acoum Difeth

I alone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Days to consume sufficient bait to reach the LD 50 20 <1 <1 4

- 5 1

- 2 16

- 17 >365 <1

100 <1 <1 7

- 8 3

- 4 30

- 31 >365 <1

1000 <1 <1 14

- 15 6

- 7 117

- 118 >365 <1

Grams bait consumed to reach
the LD 50 20 0.3 0.2 25 10 86 >1800 0.7

100 0.9 1.1 160 80 620 >7300 4.2

1000 5 15 2100 990 17000 >52000 59Secondary exposure Number of house mice consumed to reach the LD50: 1 day accum. in prey 100 <1 <1 38 18 130 821 1

1000 2 4 539 249 1836 11602 16

5000 5 27 3429 1587 11690 73852 104

Number of Norway rats to consume to reach the LD50: 1 day accum. in prey 100 <1 <1 7 3 23 147 <1

1000 <1 <1 97 45 329 2079 3

5000 <1 5 614 284 2094 13232 17
Secondary feeding study summary counts (#mortalities/ #tested) NA 63/149 ND 2/23 0/112 3/34 NDIncident datasummarycounts primary exposure NA 3 0 1 3 1 0

secondary exposure NA 164 3 5 3 5 0

unknown exposure NA 21 0 0 1 0 0

NA = not applicable ND = no dataPage 11 of 183 Table 2

- 3. Mammalian RQ analysis: primary exposure of rodents to bait and secondary exposure of carnivore/scavenger mammals to residues in consumed rodents.

Body weights (g) Brodif

acoum Difeth

I alone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Single day dose RQ 15 9.93* 4.30* 8.36 * 18.05* 0.82 * 1.97 * 5.1*

35 8.48* 3.67* 7.14 * 15.42 * 0.70 * 1.68 * 4.4*

1000 4.55* 1.97* 3.83 * 8.27 * 0.38 0.90 * 2.4*

Six day dose RQ 15 59* 24* 49* 106* 4.7 * 11.6 * 23*

35 51* 21* 42* 90* 4.0 * 9.9 * 19*

1000 27* 11* 22 * 48* 2.1 * 5.3 * 10*

Dietary RQ NA 94* ND 57 * 123* 44* 22 * 18 *Theoretical secondary exposure House mouse consumption: 1 day accumulation in prey RQ 50 3.71* 1.62* 2.97* 6.41* 0.28 0.94* 1.62*

1000 4.60* 2.01* 3.68* 7.95* 0.35 1.16* 2.01*

3000 4.98* 2.17* 3.99* 8.61* 0.38 1.26* 2.17*

Norway rat consumption: 1 day accumulation in prey RQ 50 0.98* 0.43 0.79* 1.70* 0.08 0.25 0.43

1000 1.22* 0.53* 0.97* 2.11* 0.09 0.31 0.53*

3000 1.32* 0.58* 1.05* 2.28* 0.10 0.33 0.58*

House mouse consumption: 3 day accumulation in prey RQ 50 11.10* 4.74* 8.81* 19.03* 0.84* 2.49* 4.31*

1000 13.78* 5.88* 10.93* 23.61* 1.04* 3.09* 3.53*

3000 14.91* 6.37* 11.83* 25.56* 1.12* 3.35* 5.79*

Norway rat consumption: 3 day accumulation in prey RQ 50 2.94* 1.25* 2.33* 5.04* 0.22 0.66* 1.14*

1000 3.65* 1.56* 2.89* 6.25* 0.27 0.82* 1.42*

3000 3.95* 1.68* 3.13* 6.76* 0.30 0.89* 1.53*

House mouse consumption: 6 day accumulation in prey RQ 50 22.13* 9.15* 17.35* 37.48* 1.63* 4.20* NA

1000 27.46* 11.35* 21.53* 46.51* 2.02* 5.21* NA

3000 29.72* 12.28* 23.30* 50.33* 2.18* 5.64* NA

Norway rat consumption: 6 day accumulation in prey RQ 50 5.86* 2.42* 4.59* 9.92* 0.43 1.11* NA

1000 7.27* 3.00* 5.70* 12.31* 0.53* 1.38* NA

3000 7.87* 3.25* 6.17* 13.32* 0.58* 1.49* NAPage 12 of 183 House mouse consumption: dietary RQ NA 44.69* ND 26.64* 57.54* 20.42* 10.11* ND

Norway rat consumption: dietary RQ NA 11.23* ND 7.05* 15.23* 5.41* 2.68* NDEmpiricalsecondaryexposure Single Day RQ 50 3.59* 1.41* 0.26 0.07 0.19 ND

1000 4.46* 1.75* 0.32 0.08 0.23 ND

3000 4.83* 1.89* 0.34 0.08 0.25 ND

Dietary RQ NA 13.17* NA 0.67* 1.39* 0.61* ND

NA = not applicable ; ND = no data ; * = RQ exceeds the acute LOC of 0.5Page 13 of 183 Table 2

- 4. Mammalian Risk Characterization: Additional lines of evidence from the mammal risk assessment.

Body weights (g) Brodif

acoum Difeth

I alone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Days to consume sufficient bait to reach the LD 50 15 <1 <1 <1 <1 1

- 2 <1 <1

35 <1 <1 <1 <1 1

- 2 <1 <1

1000 <1 <1 <1 <1 1

- 2 <1 <1

Grams bait consumed to reach
the LD 50 15 0.3 0.7 0.3 0.2 6 1.1 0.6

35 0.5 1.3 0.7 0.3 9 2.1 1.1

1000 6.7 16 8.0 3.7 61 25 13Secondary exposure Number of house mice consumed to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 3 <1 <1

1000 2 5 3 1 27 8 5

3000 5 11 6 3 60 18 11

Number of Norway rats to consume to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 <1 <1 <1

1000 <1 <1 <1 <1 5 1 <1

3000 <1 2 1 <1 11 3 2
Secondary feeding study summary counts (#mortalities/ #tested) NA 8/19 ND 9/100 32/55 19/33 0/4Incident datasummarycounts primary exposure NA 41 1 2 3 9 1

secondary exposure NA 22 1 0 1 4 0

unknown exposure NA 16 0 0 0 0 0

NA = not applicable ND = no dataPage 14 of 183 

## 1 Background

In order to develop mitigations for risks associated with rodenticides, the Environmental Fate and Effects Division (EFED) of the Office of Pesticide Programs (OPP) completed an ecological risk assessment in 2004 evaluating primary and secondary exposure of birds and mammals to rodenticides. In this context, pri mary exposure relates to animals that directly consume rodenticide bait and secondary exposure relates to animals that prey upon or scavenge animals
that have consumed rodenticide bait. The 2004 assessment ranked the potential primary and secondary risk f or nine rodenticides and determined that brodifacoum and difethialone posed the greatest risks to non

- target birds and mammals, followed by bromadiolone and diphacinone. Zinc phosphide also posed high primary risk to non

- target animals

.

Based on the re sults of the 2004 analysis completed by EFED as well as an assessment completed by OPP’s Health Effects Division (HED), the Agency issued a Risk Mitigation Decision (RMD) for Rodenticides (EPA, 2008). The RMD issued the final reregistration eligibility st atus of rodenticide products that involved commensal rodent control (house mouse, roof rat, and Norway rat) uses in and around buildings and underground manual application to pocket gopher and mole burrows. The two major mitigation components of the RMD w ere to minimize children’s exposure to rodenticide products used in homes and to reduce wildlife exposure and ecological risks of these products. Mitigation measures that may affect ecological risks include requirements to place baits in bait boxes and li miting applications to within 50 feet of a structure. In addition, r egistrants must control distribution of the second generation anticoagulant products so that they are distributed or sold only to agricultural, farm, and tractor stores or directly to Pes t Control Operators (PCO)

, and the products are not sold or distributed to hardware and home improvement stores, grocery stores, convenience stores, drug stores, club stores, big box stores, and other general retailers.

To date, some products containing t he following rodenticide active ingredients have not voluntarily conformed with the provisions of the RMD: brodifacoum, difethialone, warfarin, and bromethalin. Brodifacoum and difethialone products do not conform with the RMD because packaging requirements intended to reduce wide spread homeowner applications have not been implemented. Warfarin and bromethalin non

- conforming products do not comply with the risk mitigation decision because the form of bait has not been changed to forms of bait that are reasonably expected to remain in a bait station (such as blocks). Lack of conformance with the provisions in the RMD has led the Agency to publish a notice of intent to cancel (NOIC) the registrations of the non

- conforming produc ts

. It should be noted that not all products containing the above active ingredients are non

- conforming with the RMD (see Table 2

- 2 and 2

- 3).Page 15 of 183 The purpose of this document is to provide information on the ecological risks associated with
the rodenticide active ingredients in products that are the subject of the NOIC. This document updates previous risk assessment findings through the application of additional effects and exposure data, use of additional exposure modeling, and quantitative risk assessment techniques
for those chemicals /products subject to the NOIC and for rodenticides that are likely replacements for commensal rodent use s ( i.e., those with current conforming registrations for the commensal homeowner uses).

The risk assessment focuses on a number of lines of evidence of ecological risk which are similar to previous assessments, including: (1) a n assessment of the risks of non

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

- target
animals through secondary exposure to rodenticides; (3) an evaluation of available feeding studies as they relate to secondary exposure risks; (4) an evaluation of reported wildlife incident s as they relate to primary and secondary mortality events for non

- target species in a variety of land use settings, inc l uding urban, suburban, and rural settings ; and (5) a discussion of how the
above lines of evidence inform the RMD.



## 2 Analysis Plan

2.1 Active Ingredi ents Assessed

This assessment evaluates the potential risks to non

- target wildlife from exposure to products containing four rodenticide active ingredients, specifically brodifacoum, difethialone, warfarin, and bromethalin, that do not currently conform t o the RMD. In addition, active ingredients with

RMD

- conforming labels for control of commensal rodents, i.e., chlorophacinone and diphacinone, were also evaluated because they are assumed to serve as likely replacements of products with proposed cancellat ions that have overlapping uses

.

All of the assessed chemicals

, except bromethalin

, are anticoagulant rodenticides. Bromethalin is a neurotoxic agent. Brodifacoum and difethialone are commonly referred to as se cond generation anticoagulants whereas warfarin, chlorophacinone, and diphacinone are commonly referred to as first generation anticoagulants. Second generation anticoagulants are generally more toxic and more persistent within an animal. However, as discussed in subsequent sections of this assessment, some properties of some of the first generation anticoagulants are similar to
the second generation anticoagulants . Mode of action of each of the assessed chemicals is
described later in Section 2.

The chemical structur es of these r odenticides and some of their physical/chemical properties are presented in Table 2

- 1

.Table 2

- 1. Structures and Selected Physical and Chemical Properties of Assessed Rodenticides
Chemical Name Structure Selected Properties

Brodifacoum Class: coumarin anticoagulant Molecular formula: C 31 H 23 BrO 3 Molecular weight: 523.4 g/mol Physical state: solid Melting point: 228

- 232 o C Solubility in water: <10 ppm at 20 o C, pH 7

Difethialone Class: coumarin anticoagulant Molecular formula: C 31 H 24 BrO 2 S Molecular weight: 539.5 g/mol Physical state: solid Melting point: 230 o C Solubility in water: 0.39 ppm at 25 o C

Chlorophacinone Class: indandione anticoagulant Molecular formula: C 23 H 14 O 3 Cl Molecular weight: 373.8 g/mol Physical state: solid Melting point: 140 o C Solubility: 20

- 34 ppmPage 17 of 183 Chemical Name Structure Selected Properties Diphacinone Class: indandione anticoagulant Molecular formula: C 23 H 16 O 3 Molecular weight: 340.4 g/mol Physical state: solid Melting point: 141

- 145 o C Solu bility: 17

- 30 ppm in water

Warfarin Class: coumarin anticoagulant Molecular formula: C 19 H 16 O 4 ; C 19 H 15 NaO 4 (sodium salt) Molecular weight: 308.4 g/mol; 330.1 g/mol (sodium salt) Physical state: solid Melting point: 159

- 165 o C Solubility: 0.196 ppm in water at 25 o C

Bromethalin Class: diphenylamine Molecular formula: C 13 H 7 Br3F 3 N 3 O 4 Molecular weight: 578.0 g/mol Physical state: solid Melting point: 148

- 152 o C Solubility in water: 0.00 38 p pm at 25°C

### 2.2 Product Labels under Evaluation

Table 2

- 2 summarize s label and application information for c urrently registered consumer use
rodenticide labels that do not conform to the 2008 RMD

. Table 2

- 3 summarize s label and application information for all currently registered consumer use rodentici de labels that do
conform to the RMD

. The products listed in Table 2

- 2 are the subject of EPA’s proposed
cancellation. In total, t here are four brodifacoum labels, seven difethialone labels, five warfarin labels, and four bromethalin labels that do not con form to the RMD. There are four chlorophacinone labels, 12 diphacinone labels, and 15 bromethalin labels that do conform to the

RMD.

As indicated in Tables 2

- 2 and 2

- 3 , for each chemical, there is variation in the amount of bait to be used at each placement, target species, and description of placement location. Bait form for
the non

- conforming labels is described as powder (to be mixed with bait by consumer), bait bits, pellets, meal, crushed pellets, block, and paste. All conforming products are composed of a bait block(s) and packaged with a bait station. Chlorophacinone labels under consideration are restricted to indoor uses; therefore, primary consumption of chlorophacinone bait by non

domesticated animals is unlikely. Distance between placements varies depending on the target pest. For house mice, placements are usually prescribed to be 8

- 10 feet apart. For Norway and roof rats, placements are typically 15

- 30 feet apart. The amount of bait and active ingredient to be placed at each location varies for the different labels ( Table s 2

- 4 and 2

- 5 ). This variation in placement size will affect the quantity of a.i. at each placement and may affect the likelihood of a

non

- target orga nism finding and consuming a lethal quantity of the rodenticide in a single location at a single feeding.Page 19 of 183 Table 2

- 2. Non

- conforming consumer use labels for rodenticides : summary of label specifications.

Reg. No Name Form % a.i Target species Max app rates Location of placements

B rodifacoum

3282

- 65 D

- CON MOUSE

PRUFE II Pellets 0.005 House

mouse Open tab, Place wedges (1.5 or 3.0 oz each) at 8

- 12 ft intervals if activity not highly localized (does not specify spacing when activity is localized) Indoor only (homes, industrial, commercial, agricultural, public buildings)

3282

- 66 D

- CON PELLETS
GENERATION II Pellets 0.005 Norway rat, roof rat,
house mouse Rats: 4 bait trays (12 oz. bait) per placement maintain for at least 10 days, placements at 15

- 20 ft intervals In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings

3282

- 74 D

- CON BAIT
PELLETS II Pellets (Place pack) 0.005 Norway rat, roof rat,
house mouse Rat: 16 bait packs (16 oz. bait) per placement 15

- 30 ft intervals, maintain for at least 10 days In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings

3282

- 81 D

- CON READY

MIXED
GENERATION II Crushed
Pellet 0.005 Norway rat, roof rat,
house mouse Rats: 4 bait trays (12 oz. bait) per placement maintain for at least 10 days, placements at 15

- 20 ft intervals In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal building s Difethialone

3282

- 85 D

- CON MOUSE

PRUFE III Pellet 0.0025 House

mouse Open tab, Place wedges (1.5 or 3.0 oz) 8

- 12 ft intervals if activity not highly localized ( Label does not specify rate if activity is localized) Indoor only (homes, industrial, commercial, agricultural, public buildings)

3282

- 86 D

- CON BAIT
PELLETS III Pellet 0.0025 Norway rat, roof rat,
house mouse Rats: 4 trays (12 oz. bait) per placement, placements at 15

- 30 ft. intervals. Maintain at least 10 days. URBAN

- In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings
NON

- URBAN

– inside home and agricultural buildings

3282

- 87 D

- CON II

READY MIX
BAITBITS III Crushed pellet 0.0025 Norway rat, roof rat,
house mouse Rats: 4 trays (12 oz. bait) per placement, placements at 15

- 30 ft. intervals. Maintain at least 10 days. URBAN

- In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings
NON

- URBAN

– inside home and agricultural buildingsPage 20 of 183 Table 2

- 2. Non

- conforming consumer use labels for rodenticides : summary of label specifications.

Reg. No Name Form % a.i Target species Max app rates Location of placements

3282

- 88 D

- CON BAIT
PACKS III Pellet (Place pack) 0.0025 Norway rat, roof rat,
house mouse Rat: 1 6 bait packs (16 oz. bait) per placement, 15

- 30 ft intervals, maintain for at least 10 days URBAN

- In and around homes, industrial, commercial, agricultural, public buildings. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings

NON

- URBAN

– inside home and agricultural buildings

7173

- 247 GENERATION

MEAL BAIT
PACKS meal 0.0025 Norway rat, roof rat,
house mouse Rat: 16 bait packs (14 oz bait) per placement, 15

- 30 ft intervals, maintain for at least 10 days URBAN

- In and around homes, industrial, commercial, agricultural, public buildings, food processing facilities and similar man

- made structures. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings. Also use in alleys.
NON

- URBAN

– inside home, agricultural, industrial, and commercial buildings

7173

- 283 DIFETHIALONE
BAIT STATION Block 0.0025 House

mouse Place 0.7 oz. bait stations 8

– 12 ft
apart. Indoor only

– homes, industrial, commercial, agricultural, and public buildings

7173

- 285 DIFETHIALONE
6G PASTE PL
PKS paste 0.0025 Norway rat, roof rat,
house mouse Rats: 75 packs (16 oz. bait) per placement, 15

- 30 ft apart. Maintain at least 10 days. URBAN

- In and around homes, industrial, commercial, agricultural, public buildings, food processing facilities and similar man

- made structures. In transport vehicles (ships, trains, aircraft) and in and around related port or terminal buildings. Also use in alleys.
NON

- URBAN

– inside home, agricultural, ind ustrial, and commercial buildings Warfarin

3282

- 3 D

- CON CONCENTRATE KILLS RATS & MICE Powder 0.3 (Mix 1 part

concentrate with 11 parts bait) results in 0.025% a.i in bait Norway rat, roof rat, house mouse Rats: 16 oz bait per placement, maintain for at least 10 days, no restriction on how much per area In and around homes, industrial buildings, and similar

man

- made structures

3282

- 4 D

- CON READY MIXED KILLS RATS & MICE Bait bits 0.025 Norway rat, roof rat, house mouse Rats: 4 bait trays (16 oz. bait) per placement maintain for at least 10 days, no restriction on how much per

area In and around homes, industrial buildings, and similar

man

- made structuresPage 21 of 183 Table 2

- 2. Non

- conforming consumer use labels for rodenticides : summary of label specifications.

Reg. No Name Form % a.i Target species Max app rates Location of placements

3282

- 9 D

- CON MOUSE

PRUFE KILLS MICE Pellets 0.054 House

mouse Apply one 2oz box at 8

- 12 ft intervals, maintain for at least 15 days In and around homes, industrial buildings, and similar

man

- made structures

3282

- 15 D

- CON PELLETS KILLS RATS & MICE Pellets (Place pack) 0.025 Norway rat, roof rat, house mouse Rats: 4 bait trays (16 oz. bait) per placement maintain for at least 10 days, no restriction on how much per

area In and around homes, industrial buildings, and similar

man

- made structures

8845

- 39 RID

- A

- RAT RAT & MOUSE
KILLER meal 0.025 Norway rat, roof rat, house mouse Rats: 4 bait packets (16 oz. bait) per placement maintain for at least 10 days, no restriction on how much per

area In and around homes, industrial buildings, and similar

man

- made structures

Bromethalin

8845

- 125 HOT SHOT
SUDDEN DEATH
BRAND MOUSE

KILLER Pellet (Place pack) 0.01 House

mouse 2 place packs (1.5 oz bait) if high activity or 1 place pack (0.75 oz bait) per location (8

- 12 ft apart), maintain for 7 days or till all feeding ceases (whichever longer ) In and around homes, industrial and agricultural
buil dings, and similar man

- made structures. Alleys in urban areas, inside transport vehicles (ships, trains, aircraft), and in and around related port or terminal buildings.

8845

- 126 HOT SHOT
SUDDEN DEATH
BRAND RAT

KILLER 1 Pellet (Place pack) 0.01 Norway rat,
roof rat 4 place packs (6.0 oz bait) per placement, placements 15

- 30 ft apart. maintain for 7 days or till all feeding ceases (whichever longer) In and around homes, industrial and agricultural buildings, and similar man

- made structures. Alleys in
urb an areas, inside transport vehicles (ships, trains, aircraft), and in and around related port or terminal buildings.

8845

- 127 HOT SHOT
SUDDEN DEATH
BRAND RAT &
MOUSE KILLER Pellet (PI pack) 0.01 Norway rat, roof rat,
house mouse 8 place packs (6.0 oz bait) per placement, placements 15

- 30 ft apart. maintain for 7 days or till all feeding ceases (whichever longer) In and around homes, industrial and agricultural buildings, and similar man

- made structures. Alleys in urban areas, inside transport v ehicles (ships, trains, aircraft), and in and around related port or terminal buildings.

8845

- 128 HOT SHOT
SUDDEN DEATH
BRAND MOUSE

KILLER BAIT
STATION Pellet (Place pack) 0.01 House

mouse 2 units (1.5 oz bait) per placement, placements are 8

- 12 ft apart, continue placements till activity
ceases. If unit untouched after 3 days, remove or place elsewhere. INDOORS ONLY

– homes, industrial, and agricultural buildingsPage 22 of 183 Table 2

- 3. Conforming consumer use labels for anticoagulants: summary of label specifications.

Reg. No Name Form and
S tation Tier 1 % a.i Target species Max app rates Location

Chlorophacinone

7173

- 287 Chlorophacinone
Bait Station Bait block, Tier

4 0.005 House mouse One 0.7 oz bait station every 8 feet Indoors only.

7173

- 289 Chlorophacinone
Block 0803 Bait
Station Bait block, Tier

4 0.005 House mouse One 0.7 oz bait station every 8 feet Indoors only.

7173

- 293 Chlorophacinone
Refillable Bait
Station Bait block, Tier
3 0.005 House mouse One 0.42 oz bait station every 8 feet Indoors only.

7173

- 295 Chlorophacinone
Block 0803 Bait
Station II Bait block, Tier

4 0.005 House mouse One 0.7 oz bait station every 8 feet Indoor s only.

Diphacinone

3282

- 98 D Con Bait Station X Bait block, Tier 3 0.005 House mouse 1 oz per placement, every 8 feet. Indoors only

3282

- 99 D Con Bait Station
IX Bait block, Tier 3 0.005 House mouse 1 oz per placement, every 8 feet. Indoors only

3282

- 100 D Con Bait Station
XIV Bait block, Tier1 0.005 House mouse 7 oz bait per placement, every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

3282

- 101 D Con Bait Station
XIII Bait block, Tier
1 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

3282

- 102 D Con Bait Station
XI Bait block, Tier
1 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

3282

- 103 D Con Bait Station
XII Bait block, Tier 1 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

12455

- 119 Tomcat Mouse Killer
VI Bait block, Tier 1 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

12455

- 126 Tomcat Mouse Killer
V Bait block, Tier
1 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors and Outdoors ( within 50 feet of buildings )

12455

- 127 Tomcat Mouse Killer
VII Bait block, Tier 3 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors onlyPage 23 of 183 Table 2

- 3. Conforming consumer use labels for anticoagulants: summary of label specifications.

Reg. No Name Form and
S tation Tier 1 % a.i Target species Max app rates Location

12455

- 128 Tomcat Mouse Killer
IX Bait block, Tier
4 0.005 House mouse Place one 1

- oz bait in bait station every 8 feet. Indoors only

12455

- 130 Tomcat Mouse Killer
VIII Bait block, Tier 3 0.005 House mouse Place one 1

- oz bait inside bait station every 8 feet. Indoors only

61282

- 19 Prozap Mouse Maze Kills Mice Bait block, Tier 4 0.005 House mouse Place one 1.0 oz bait station every 8 feet. Indoors only

Bromethalin

3282

- 96 D

- con Hideaway
Bait Shield II Bait block, Tier

3 0.01 House mouse Use one (0.5 oz) bait station every 8 feet. Indoor only

3282

- 97 D

- con Corner Fit
Bait Shield VIII Bait block, Tier
3 0.01 House mouse Use one (0.5 oz) bait station every 8 feet. Indoor only

9688

- 285 Chemisco Disposable Bait
Station Bait block, Tier
3 0.01 House mouse Use one (0.5 oz) bait station every 8 feet. Indoor only.

9688

- 291 Chemisco Refillable
Bait Station Bait block, Tier
3 0.01 House mouse Use one (0.5 oz) bait station every 8 feet. Indoor only.

12455

- 120 Tomcat Mouse Killer

I Bait block, Tier

1 0.01 House mouse Use one bait station (1 oz bait) per placement every 8
feet. Indoors and Outdoors ( within 50 feet of buildings )

12455

- 121 Tomcat Mouse Killer Bait block, Tier

1 0.01 House mouse Use one bait station (1 oz bait) per placement every 8
feet. Indoors and Outdoors ( within 50 feet of buildings )

12455

- 122 Tomcat Rat Killer Bait block, Tier

1 0.01 House mouse , Norway
and roof rat Use one bait station (4 oz) every 15 feet Indoors and outdoors ( within 50 feet of buildings )

12455

- 123 Tomcat Mouse Killer

II Bait block, Tier
3 0.01 House mouse Use one bait station (1 oz) every 8 feet. Indoor only.

12455

- 124 Tomcat Mouse Killer

IV Bait block, Tier

4 0.01 House mouse Use one bait station (1 oz) every 8 feet. Indoor only.

12455

- 125 Tomcat Rat Killer I Bait block, Tier

4 0.01 House mouse , Norway
and roof rat Use one bait station (4 oz) every 8 feet for mice; every
15 feet fo r rats. Indoor only.

12455

- 129 Tomcat Mouse Killer

III Bait block, Tier
3 0.01 House mouse Use one bait station (1 oz) every 8 feet. Indoor only.Page 24 of 183 Table 2

- 3. Conforming consumer use labels for anticoagulants: summary of label specifications.

Reg. No Name Form and
S tation Tier 1 % a.i Target species Max app rates Location

36488

- 51 Bromethalin Mouse
Bait Station Bait block, Tier

4 0.01 House mouse Use one bait station (0.75 oz) every 8 feet. Indoor only.

67517

- 89 Assault Mouse Bait
Station Bait block, Tier

4 0.01 House mouse Use one bait station (0.5 oz) every 8 feet. Indoor only.

67517

- 90 Assault Mouse Bait
Station II Bait block, Tier

2 0.01 House mouse Use one bait station with 1 oz (2 bait blocks) every 8
feet. Indoor only.

67517

- 92 Assault Mouse Bait
Station III Bait block, Tier
3 0.01 House mouse Use one bait station with one bait block (0.5 oz) every 8 feet. Indoor only.

1 Bait station tier descriptions: Tier I Bait Stations: Tamper

- Resistant and Weather

- Resistant. These bait stations are resistant to weather and to tampering by children and dogs . To be used indoors and outdoors (within 50 feet of buildings, defined as structures that possess walls and a r oof). Tier II Bait Stations: Tamper

- Resistant (but not weather resistant). These bait stations are resistant to tampering by children and dogs . To be used indoors only

. Tier III Bait Stations: Tamper

- Resistant for Children Only. These bait stations are res istant to tampering by children . To be used indoors only

. Tier IV Bait Stations: Tamper

- Resistance Unknown. These bait stations must not claim to be tamper resistant

. To be used indoors only and only in areas inaccessible to children and pets

.Page 25 of 183 Table 2

- 4 . Maximum weight of rodenticide bait and active ingredient to be used at each placement for non

- conforming labels

.
Reg. Num. %a.i. oz bait/ placement gms bait/ placement mg a.i / placement

Brodifacoum

3282

- 65 0.005 3 85 4.3

3282

- 66 0.005 12 341 17.0

3282

- 74 0.005 16 454 22.7

3282

- 81 0.005 12 341 17.0

Difethialone

3282

- 85 0.0025 3 85 2.1

3282

- 86 0.0025 12 341 8.5

3282

- 87 0.0025 12 341 8.5

3282

- 88 0.0025 16 454 11.4

7173

- 247 0.0025 14 397 9.9

7173

- 283 0.0025 0.7 20 0.5

7173

- 285 0.0025 16 454 11.4

Warfarin

3282

- 3 0.025 16 454 113.5

3282

- 4 0.025 16 454 113.5

3282

- 9 0.054 2 57 30.6

3282

- 15 0.025 16 454 113.5

3282

- 39 0.025 16 454 113.5

Bromethalin

8845

- 125 0.01 1.5 43 4.3

8845

- 126 0.01 6 170 17.0

8845

- 127 0.01 6 170 17.0

8845

- 128 0.01 1.5 43 4.3Page 26 of 183 Table 2

- 5 . Maximum weight of rodenticide bait and active ingredient to be used at each placement for conforming labels

.
Reg. Num. %a.i. oz bait/ placement gms bait/ placement mg a.i / placement
Chlorophacinone

7173

- 287 0.005 0.7 20 1.0

7173

- 289 0.005 0.7 20 1.0

7173

- 293 0.005 0.42 12 0.6

7173

- 295 0.005 0.7 20 1.0
Diphacinone

3282

- 98 0.005 1 28 1.4

3282

- 99 0.005 1 28 1.4

3282

- 100 0.005 7 199 9.9

3282

- 101 0.005 1 28 1.4

3282

- 102 0.005 1 28 1.4

3282

- 103 0.005 1 28 1.4

12455

- 119 0.005 1 28 1.4

12455

- 126 0.005 1 28 1.4

12455

- 127 0.005 1 28 1.4

12455

- 128 0.005 1 28 1.4

12455

- 130 0.005 1 28 1.4

61282

- 19 0.005 1 28 1.4

Bromethalin

3282

- 96 0.01 0.5 14 1.4

3282

- 97 0.01 0.5 14 1.4

9688

- 285 0.01 0.5 14 1.4

9688

- 291 0.01 0.5 14 1.4

12455

- 120 0.01 1 28 2.8

12455

- 121 0.01 1 28 2.8

12455

- 122 0.01 4 114 11.4

12455

- 123 0.01 1 28 2.8

12455

- 124 0.01 1 28 2.8

12455

- 125 0.01 4 114 11.4

12455

- 129 0.01 1 28 2.8

36488

- 51 0.01 0.75 21 2.1

67517

- 89 0.01 0.5 14 1.4

67517

- 90 0.01 1 28 2.8

67517

- 92 0.01 0.5 14 1.4Page 27 of 183 

### 2.3 Modes of Action

The anticoagulant rodenticides (warfarin, difethialone, chlorophacinone, and diphacinone are anticoagulants that are included in this assessment ) are vitamin

- K antagonists that disrupt normal
blood

- clotting mechanisms and induce capillary damage (Pelfrene 1991). Hadler and B uckle (1992), in their review of the development of anticoagulant rodenticides provide a summary of
the mechanism of action of these compounds :

Within the liver, Vitamin K is utilized to drive the production of blood clotting factors II, VII, IX & X by the gamma

- carboxylation of glutamic acid residues of precursor proteins. Concomitant with this reaction, the active form of vi tamin K, a hydroquinone (KHj), is converted to an inactive 2,3

- epoxide. Some of this is excreted but the majority is reactivated by an epoxide reductase enzyme...All available anticoagulants seem to share the same site of action; they block the epoxide reduc tase enzyme. The recycling of activated vitamin K is therefore stopped and there is insufficient incoming vitamin K to maintain the carboxylation reaction. The production of clotting factors is critically reduced and eventually, when the supply of factor s already present has degraded, the clotting
mechanism fails and hemorrhaging begins.

The anticoagulant rodenticide s have been grouped in previous assessments into "first

- generation" (warfarin, chlorophacinone, diphacinone) and "second

- generation" (brodifacoum, bromadiolone, difethialone) compounds. Although there is overlap in their metabolic and toxicological

proper ties, s econd

- generation anticoagulants tend to be more acutely toxic than are the first

generation anticoagulants, and they are retained longer in body tissues of primary consumers. The greater potency and duration of action of long

- acting anticoagulant ro denticides is attributed to their: (i) greater affinity for vitamin K(1)

- 2,3

- epoxide reductase; (ii) ability to disrupt the vitamin K(1)

- epoxide cycle at more than one point; (iii) hepatic accumulation; and (iv) unusually long biological half

- lives due to high lipid solubility and enterohepatic circulation (Watt et al. 2005). T he terms “ first generation” and “ second generation ” are not used in this risk assessment as generic grouping terms to differentiate anticoagulant rodenticides in any qualitative or

q uantitative manner. Rather

, the assessment evaluates risks to wildlife based on specific toxicity

, exposure, body burden, metabolism, and incident information available for each rodenticide

. However, of the chemicals evaluated in this assessment, warfari n, chlorophacinone, and diphacinone are commonly referred to first generation anticoagulant rodenticides, and brodifacoum and difethialone are commonly referred to second generation anticoagulants.

Bromethalin is a neurotoxicant that causes adverse eff ects and histological changes to the central nervous system. Van Lier and Cherry (1988) determined that acute toxicity is caused by thePage 28 of 183 uncoupling of mitochondrial oxidative phosphorylation. This leads to fluid build

- up and
deme yel ination inside the cent ral nervous system, eventually leading to respiratory failure because of lack of nerve impulse transmission to the lungs. While both bromethalin and the primary metabolite desmethylbromethalin are active in uncoupling oxidative phosphorylation,
the desmet hylbromalin metabolite is much more potent than the parent compound. Therefore, the rapid transformation of bromethalin into desmethylbromethalin in mammals (other than the guinea pig) is largely responsible for the high acute toxicity of this compound in most mammals (Van Lier and Cherry, 1988). A single feeding of bromethalin may be lethal

, with death being delayed for two or three days (Spaulding et al, 1985), although doses in excess of the LD 50 may cause death within 8

- 12 hr (Van Lier and Cherry, 198 8). Further feeding is inhibited after ingestion of a lethal dose, and death typically occurs rapidly, often within 2 days (Spaulding and Spann ing 1988, Hyngstrom et al. 1994)

. In acute oral mammalian studies submitted to the EPA,
death was observed 3

- 7 days after dose administration.

2.4 Conceptual Model of Exposure

The chemicals evaluated in this assessment are used to control commensal rodents. Commensal rodent control in urban and suburban areas may result in exposure to wildlife as demonstrated by the presence of wildlife mortality incidents and survey data indic ating that exposure occurs in
urban and suburban areas in addition to agricultural areas

. In general terms, the exposure pathways for rodenticides are from direct consumption of rodenticide bait (primary exposure) or consumption of animals that have consu med bait by predators or scavengers (secondary exposure).

For primary exposure, the bait itself is the potential food item of concern. Thus, the amount of active ingredient in the formulated bait represents the exposure concentration. This information
is used to estimate the amount of 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 daily food

- ingestion rates are determined from est ablished allometric equations presented in the Wildlife Exposure Factors Handbook (USEPA 1993) for birds and mammals

.

Potential exposure pathways evaluated in this assessment are illustrated in Figure 2

- 1

. Additional details on the exposure analysis ca n be found below

. Exposure pathways illustrated with dotted lines were not evaluated as part of this assessment because exposure was expected to be negligible relative to direct consumption of bait or consumption of contaminated prey or
because methods us ed to quantify such exposures are not available.Page 29 of 183 Stressor

Source

Attribute Change Rodenticide

Placement of Bait

Terrestrial Invertebrates

Individual organisms
Reduced survival Reduced growth Reduced reproduction Habitat Integrity Reduced availability

of cover and nest sites Food Chain
Reduction in prey availability Terrestrial V ertebrates Exposure Media & Receptors Exposure to BaitIngestion IngestionSecondaryexposurePrimaryexposure Plants Uptake

Figure 2

- 1

. Conceptual Model Diagram of Exposure and Effects in Nontarget Species.



### 2.5 Taxonomic Groups Potentially at Risk

The taxonomic groups that are potentially at risk due to the rodenticides considered in this assessment include mammals and birds that are primary (e.g., granivores) and secondary (e.g., predators) consumers of those rodenticides. The Agency’s concern abo ut risks to birds and nontarget mammals is based on several factors, including :

(1) High acute toxicity of these rodenticide baits, which are designed to be lethal to mammals; (2) Risk quotients (RQs) from past assessments that were based on exposure and toxicity data, that exceed Agency levels of concern (LOCs); (3) Empirical data involving mortality of birds and non

- target mammals exposed to rodenticide baits or poisoned prey in laboratory, pen, and field settings; (4) Retention time of residues in body tissues of pri mary consumers; and (5) Numerous reported incidents that indicate exposure and mortalities of numerous non

- target species, including avian and mammalian predators and scavengers.

In addition, p rimary and secondary consumers may be exposed to rodenticides. Baits containing
rodenticides are formulated to be lethal to rodents and other mammals, and they are not selective to target species. Many factors influence which non

- target animals might be exposed to baits, but many birds and mammals are attracted to seeds and grains and are likely to consume grain

- based baits. A few commensal baits also contain flavorizers such as fish, molasses/peanut butter, or apple that mightPage 30 of 183 appeal to carnivo res and omnivores. Rodenticide baits also pose potential secondary risks, because predators and scavengers are likely to be attracted to dead or dying rats, mice, a nd poisoned nontarget animals.

As will be discussed elsewhere in this document

, the record s of incidents involving the rodenticides
considered in this assessment indicate that they have been detected in numerous wildlife species collected from a variety of land use areas including urban, suburban and rural locations. These data
indicate that c omplete exposure pathways exist where wildlife were exposed to rodenticides in areas where commensal rodent control is expected to occur and mortalities resulted

.

This assessment does not evaluate potential risks to aquatic organisms or to plants . Exposure to aquatic organisms is assumed to be negligible relative to potential exposures to terrestrial animals for commensal rodent control given that (1) direct application to water is unlikely to occur; (2) spray drift of baits is not expected; (3) large, contiguous areas are not expected to be treated; and (4) leaching of rodenticides from baits is limited.



### 2.6 Measures of Exposure

EPA’s exposure assessment for rodenticides differs from that used for most other pesticides

, which are often administer ed to treatment sites via sprays, granules, and other diffuse application
methods

. For pesticides applied via sprays, exposure is assessed as a concentration of the pesticide on plants and insects located on the treated field. 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 to represent exposure , which can then be compared directly to dietary toxicity values such as LC50s or NOAECs expressed as mg/kg

- food

. The concentration of active ingredient in bait is
also used along with estimates of food consumption rates to estimate the amount of grain bait that birds and mammals of various sizes need to consume to obtain a dose expected to be lethal
to 50% of the ind ividuals in the population (i.e., LD 50 ). Estimates of food

- ingestion rates (g dry matter per day) are determined from established allometric equations presented in EPA’s Wildlife Exposure Factors Handbook (EPA 1993).

Secondary exposure analysis require s consideration of residues in tissues of target and non

- target organisms that are commonly consum ed by predators and scavengers

. Exposure s of predators to
individual rodenticides were calculated in two ways. First, the theoretical amount of rodenticide
wi thin prey animals was estimated using allometric equations for food intake estimation (U.S. EPA, 1993) assuming prey consumed either a single day’s feeding or repeated feedings for several days. These two values represent low

- end and high

- end theoretical estimations of rodenticide exposures for secondary consumers . In addition, empirical residue concentrations from prey used in secondary feeding studies were used to derive exposure values for the secondary consumers

. Although t hese values do not likely r epresent high

- end exposure valuesPage 31 of 183 because the prey animals used in these studies may have fed on items other than rodenticide bait

, they represent concentrations of rodenticides that have been measured in primary consumers

. The theoretical and empirical c oncentrations of the rodenticides in primary consumers were both used to estimate potential risks to predators and scavengers. Additional details are presented in the secondary exposure analysis section of this assessment.



### 2.7 Measures of Toxicity

Toxicity endpoints are established based on data generated from guideline studies submitted by the registrant, and from open literature studies that meet the criteria for inclusion into the
ECOTOX database. A number of non

- target animal species have been tested for some chemicals
included in this assessment , but the suite of available species tested is not uniform across all the
evaluated rodenticides

. In order to allow for risk estimations to be made across the assessed
chemicals without a bias associate d with differential sensitivities of tested species that vary across the assessed chemicals (i.e., the number and identity of species tested varies for each chemical assessed) , the toxicity data used for RQ calculations were based on OPP’s standard test

sp ecies for which data were available across all the chemicals evaluated (i.e., Norway rat ( Rattus norvegicus ) for mammals and the Northern bobwhite quail ( Colinus virginianus ) or mallard duck (Anas platyrhynchos ) for birds ) . Use of standard species allows for a comparable analysis across the assessed chemicals; however, it may also result in an underestimation of risk in cases where data are available for more sensitive test species

. In cases where more sensitive species have been tested for a particular chemical (e.g., American kestrels ( Falco sparverius ) for diphacinone), the potential impact of using the more sensitive data is evaluated. F or rodenticides where particularly sensitive species are not tested, their absence may repre s ent a source of

uncert ainty that results in a less conservative risk assessment

. It should be noted that in cases where more sensitive toxicity data are available for a chemical (besides the standard test species), assessments conducted by the Agency to support registration, registration review, or litigation for the assessed chemicals will likely utilize the more sensitive data for risk estimation, if available, than was used here. The data for the standard test species were used here to allow for comparisons of risk conclus ions among the chemicals. Last, the assessment only evaluated potential acute exposures and effects. Risk of reproductive effects was not evaluated due to
several factors

, including : paucity of reproduction toxicity data and the desire to evaluate an endp oint that can be compared with available wildlife incidents (i.e., mortality)

. It is possible that reproductive effects may occur at lower exposure levels than exposures associated with mortality. Details on the toxicity data used for this assessment are included in Sections 3 and 4.Page 32 of 183 

### 2.8 Measures of Risk

Risk was evaluated using several lines of evidence. These include, Risk Quotients (RQs) and data used to further characterize risks including pharmacokinetic data, estimation of the amount
of bait required to reach the median lethal dose, estimation of the number of primary consumers that need to be consumed to reach the median lethal dose of secondary consumers, results of feeding studies

, and incident reports. These are described below.

2.8.1 Risk Quot ients (RQs)

Risk from primary exposure (direct consumption of bait) was evaluated by calculating dietary
based and dose

- based risk quotients (RQs). The RQ is a unitless value that is the ratio of exposure to the toxicity endpoint. An RQ of 1 means that the exposure (dose or concentration based) is equal to the selected toxicity value (i.e., LD50 or LC50) . For example, in the context of acute avian risk estimates (e.g., mortality), an RQ of 1 would mean that non

- target bird species may be exposed in the e nvironment to an amount of the pesticide that results in mortality (specifically, the dose at which 50% of the test species died). EPA compares RQ values to the Agency’s “levels of concern” (LOCs) for non

- target species. For this risk assessment, the non

listed species LOC for acute exposures (LOC = 0.5) was used to evaluate RQs. Additional levels of concern may also be used by the Agency in other assessment to evaluate potential risks to listed species (LOC = 0.1); howeve r, for simplicity, this analysis only used the LOC for non

listed species . Therefore, conclusions made with respect to the LOC of 0.5 may not apply to listed species.

For primary consumers of bait, dietary based RQs were calculated by comparing concen tration of active ingredient in bait (exposure value) to LC50 toxicity values (RQ = a.i. concentration in bait / LC50) . Dose

- based RQs were calculated by converting dietary exposure values to an internal dose for various sized animals using allometric equ ations that estimate food consumption as a function of body weight as described further in Section 3. The resulting dose

based exposure values were then compared to LD50s that were also adjusted for body weight of
the assessed animal. (RQ = Dose

- based E EC / Adjusted LD50).

Potential risks from secondary exposure (i.e., exposures of predators and scavengers through consumption of contaminated prey ) were also evaluated on a dose and concentration basis. Risk
was estimated assuming that predator/scaven ger that consumed prey that fed on bait for 1, 3, or 6 days. During this time period, the animals were assumed to eliminate the chemical. Elimination rates in target animals (i.e., Norway rat and house mouse) were based on empirical data describing elimin ation half

- lives in the liver or plasma as described in Section 3

.Page 33 of 183 2.8.2 Additional Risk Characterization

Because this deterministic assessment is intended to serve as a screening tool for identifying a potential for adverse effects, it is somewhat limited and conservative by design. As a result, EPA does not believe that the RQs derived in this assessment can be used as a precise measure of the magnitude of effects that will occur, but rather serve as tools for addressing whether or not a chemical poses a risk to assessed animals. Because of their design, RQs should not be directly compared among chemicals. In this assessment, the Agency uses other lines of evidence to characterize the relative risks of the rodenticides that are the subject of the NOIC and the
alternatives considered here. These lines of evidence include factors intended to describe the opportunity for exposure to occur at median lethal doses:

**•** Amount of bait required to reach median lethal dose in primary consumers

o Amount of bait required to reach the median lethal dose was estimated using allometric equations for food intake assuming an animal consumed 100% of their diet as dry bait. In addition, the time needed to consume a median lethal dose was
also calculated. These factors were use d to compare the opportunity for primary
exposure to occur at lethal doses across the assessed chemicals.

**•** Number of prey required to reach median lethal dose in secondary c onsumers

o The number of prey animals required to achieve a median lethal dose was used as a comparative metric for the opportunity to achieve a lethal dose across the assessed rodenticides. This analysis assumed that the prey animal consumed bait for 1 to 6 days, t hen were consumed by a predator or scavenger. The opportunity for a lethal dose to be consumed by a predator or scavenger was assumed to be greater as the number of animals required to be consumed to reach a lethal dose
decreased.

**•** Secondary feeding stu dies

o Toxicity studies are available where small mammals were fed diets containing one of the rodenticides, and these animals died or were sacrificed. These contaminated carcasses were fed to the birds and mammals ( i.e. , secondary consumers) being evaluat ed in the studies. T hese types of secondary exposure studies provide information on the potential effects from rodenticide exposure that may occur under field conditions ; however, it is often not possible to quantify the level of exposure (rodenticide resi dues in primary consumers or food consumption by secondary consumers) or the sensitiv it y of the exposed animals to
the rodenticide

.Page 34 of 183 **•** Pharmacokinetic data

o The potential for secondary exposure of scavengers and predators to rodenticides was evaluated by considering pharmacokinetic data. Specifically, the relative
elimination half

- lives of the rodenticides considered in this assessment were used to characterize the relative risks based on the persistence of the rodenticides in exposed pr imary consumers. Although not a quantitative measure of risk, it was assumed that the potential for secondary exposure to a rodenticide increases as the
bio

- elimination half life increases.

2.8.3 Incident Reports

Many incidents of wildlife mortality have bee n reported to the Agency for the rodenticides
considered in this assessment. These incidents were evaluated in order to confirm or refute the
conclusions that were based on the deterministic assessment . Incidents were also used to
determine the spatial ov erlap of reported incidents with urban, agricultural, or suburban areas.



## 3 Toxicity , Accumulation, and Elimination of the Evaluated
Rodenticides

3.1 Avian and Mammalian Toxicity

A summary of the available acute ecotoxicity information for the evaluated chemicals ( brodifacoum, difethialone , warfarin, chlorophacinone

, diphacinone , and bromethalin) is provided in Sections 3.1. 1 through 3 .1.4 . Acute toxicity to terrestrial animals is categorized using the classification system shown in Table 3

- 1 (USEPA, 2004 a) . Toxicity categories for all six chemicals are provided in Table 3

- 2

. F or consistency when comparing across chemicals, avian toxicity categories were based on the most sensitive bobwhite quail or mallard duck studies and mammalian toxicity categories w ere based on the most sensitive laboratory rat studies.

When evaluated across chemicals ( Table 3

- 2 ), there is more variability in toxicity to birds than there is in toxicity to mammals. For avian acute oral toxicity, warfarin and diphacinone were
consider ed slightly toxic, while chlorophacinone was considered moderately toxic and brodifacoum, difethialone, and bromethalin were considered very highly toxic. For avian dietary toxicity, the ordering of chemicals based on toxicity category was very similar. Wa rfarin and diphacinone were considered moderately toxic, chlorophacinone and bromethalin were considered highly toxic, and brodifacoum and difethialone were classified as very highly toxic to birds. For mammals, there was much less variation in toxicity ca tegories. All evaluated rodenticides were classified as very highly toxic to mammals based on the acute oral toxicityPage 35 of 183 test. The four chemicals with quantitative toxicity data (brodifacoum, warfarin, chlorophacinone, and diphacinone), were all classified as very highly toxic to mammals on a dietary basis.

Table 3

- 1. Categories of Acute Toxicity for Avian and Mammalian Studies
Toxicity Category Oral LD 50 Dietary LC 50 Very highly toxic < 10 mg/kg < 50 mg/kg

- diet Highly toxic 10

- 50 mg/kg 50

- 500 mg/kg

- diet Moderately toxic 51

- 500 mg/kg 501

- 1000 mg/kg

- diet

Slightly toxic 501

- 2000 mg/kg 1001

- 5000 mg/kg

- diet Practically non

- toxic > 2000 mg/kg > 5000 mg/kg

- dietPage 36 of 183 Table 3

- 2. Acute oral and dietary toxicity values and categories for the evaluated
rodenticides 1

Chemic al Avian Ma mmalian

LD 50 (mg a.i./kg

- bwt) L C 50 (mg a.i./kg

- diet ) LD 50 (mg a.i./kg

- bwt) L C 50 (mg a.i./kg

- diet )

Brodifacoum 0.25 1.33 0.48 0.53

Difethialone 0.30 0.56 0.56 Not available

Warfarin 525 625 3.0 5.4 Chlorophacinone 258 72 6.26 7.2

Diphacinone 1630 906 1.9 4.2

Bromethalin 4.6 210 2.2 Not available

Avian Ma mmalian

Oral Dietary Oral Dietary

Brodifacoum V ery highly toxic V ery highly toxic

V ery highly toxic V ery highly toxic

Difethialone V ery highly toxic V ery highly toxic Not available

Warfarin Slightly toxic Moderately toxic V ery highly toxic Chlorophacinone Moderately toxic Highly toxic V ery highly toxic

Diphacinone Slightly toxic Moderately toxic V ery highly toxic

Bromethalin V ery highly toxic Highly toxic Not available

1 For consistency when comparing across chemicals, avian toxicity values and categories were based on the most sensitive bobwhite quail or mallard duck studies and mammalian toxicity values and categories were based on the most sensitive laboratory rat stud ies.

3.1.1 Avian acute oral toxicity

Table 3

- 3 summarizes the most sensitive avian acute oral (gavage or capsule) toxicity endpoints for either Northern bobwhite quail ( Colinus virginianus ) or mallard duck (Anas platyrhynchos )

, based on an evaluation of both the registrant

- submitted studies and the open literature. When considering these data, brodifacoum and difethialone have the lowest LD 50 values ( i.e ., 0.25 and 0.30 mg a.i. /kg

- bw t , respectively) for the standard test species. The LD 50 for bromethalin is an order of magnitude higher (i.e., LD 50 = 4.6 mg a.i. /kg

- bw t ) and the LD 50 values for chlorophacinone, warfarin, and diphacinone (LD 50 values = 258, 525

, and 1630 mg a.i. /kg

- bw t

, respectively) are three to four orders of magnitude higher than those of brodifacoum and
difethialone. All evaluated chemicals have multiple avian acute oral studies available resulting in a wide range of reported toxicity ( Appendix A ). When considering the two standard avian test species, nei ther the bobwhite quail nor the mallard duck was consistently more sensitive. In most cases, either the bobwhite quail or the mallard duck represented the most sensitive test species.Page 37 of 183 T able 3

- 3 . Avian acute oral studies used for calculating RQs (restricted to mallard duck and bobwhite quail).

Chemical/ Species %
a.i. LD 50 , mg a.i /kg

bwt (95% CI) Probit slope (95% CI) Average body weight, g (day=0) Study length (days) Ti me to mortality (days) MRID and
classification

Brodifacoum
Mallard duck 97.6 0.25 (0.11, 0.40) 3.0 (1.3, 4.7) 1054 28 3

- 23 days; majority of mortality from

7

- 10 days 41563303 Acceptable

Difethialone
Northern bobwhite quail 96 0.30 (0.16, 0.38) 2 5.9 (1.9, 9.9) 196 30 3

- 19 days 406969

- 01 Acceptable

Warfarin
Mallard duck Tech. 525 (336, 689) 1 3.1 (1.6, 4.6) NA, 21

- weeks old 14 < 1 day Accession#
00248782 acceptable

Chlorophac

inone
Northern bobwhite quail 100 258

(168, 360) 2.9

(1.3, 4.4) 203 30 2

- 5 days 41513101 Acceptable

Diphacinone
Northern bobwhite quail 96.9 1630 3 NA 190 21 5

- 9 days 42245201 Supplemental

Bromethalin
Northern bobwhite quail 96. 3 4.6 (3.3

- 6.0) 3.6 (1.6, 5.7) 194 14 1

- 7 days 00086742, acceptable

1 Previous assessments reported the LD 50 = 621 mg a.i /kg

- bwt based on the moving average estimate. Data were

re

- evaluated and the probit model was selected as providing the best fit to the data.

2 Previous assessments reported the LD 50 = 0.26 mg a.i /kg

- bwt. Data were re

- evaluated and the probit model was selected as providing the best fit to the data.

3 Previous assessments reported the LD 50 ≥ 400 mg a.i /kg

- bwt. Data were re

- evaluated and the binomial model provided an adequate fit to the data.

For brodifacoum, the study with the most sensitive endpoint was conducted using mallard duck
and resulted in an LD 50 = 0.25 mg a.i./kg

- bwt ( MRID 41563303 ). A dditional toxicity tests conducted on ring

- necked pheasants ( Phasianus colchicus ) and Japanese quail ( Coturnix c. ja

ponica ) r esulted in LD 50 s of 0.59 and 11.6 mg a.i./kg

- bwt (MRIDs 6351303 and 46351304 ).

For difeth i alone, the study with the most sensitive endpoint was conducted using bobwhite quail
and resulted in an LD 50 = 0.30 mg a.i./kg

- bwt (MRID 40696901)

. O ne additional av ian gavage study was identified; a n LD 50 of 23.4 mg a

. i

. /kg

- bwt was reported for Japanese quail (MRID 42687702, 40268913 ).Page 38 of 183 For warfarin, the study with the most sensitive endpoint was conducted using mallard ducks and
resulted in an LD 50 = 52 5 mg a.i./kg

- bwt (MRID 00 248782) . In addition, toxicity to domestic
chickens ( Gallus domesticus) was e stimated as LD 50 = 942 mg a.i./kg

- bwt ( Bai and
Krishnakumari 1986 ). Toxicity of a material containing 10% warfarin to mallards was reported

as LD 50 = 120 mg a.i./kg

- bwt (MRID 5005716 ). Two studies using bobwhite quail resulted in

non

- definitive LD 50 s of >2000 and >2150 mg a.i./kg

- bwt (MRIDs 156284 and 153369 ).

For chlorophacinone, the study with the most sensitive endpoint was conducted using bobwhite quai l and resulted in an LD 50 = 258 mg a.i./kg

- bwt ( MRID 41513101). One additional avian oral study using bobwhite quail was identified; an LD 50 of 495 mg a.i./kg

- bwt was reported (MRID
00 39233 ).

For diphacinone, the most sensitive endpoint that corresponded to a standard test species (bobwhite quail or mallard duck) was an LD 50 = 1630 mg a.i./kg

- bwt from a bobwhite quail study (MRID 42245201). A second bobwhite quail study was available in the open literature (Rattner et al ., 2010), which reported an LD 50 of 2014 mg a

. i

. /kg

- bwt. In addition, an LD 50 = 3158 mg a

. i

. /kg

- bwt was determined for mallard ducks (MRID 00 128411 ).

Also for diphacinone, an LD 50 of 96.8 mg a

. i

. /kg

- bwt is available for one raptor species (American kestrel, Falco sparverius ) (Rattner et al . 2011). This study suggests that American kestrels may be more sensitive than the standard test species ( i.e., based on the available studies, 17 to 21 times more sensitive than bobwhite quail and 33 times more sensitive than mallard ducks). None of the o ther evaluated rodenticides have data for which an LD 50 for raptors, or, more generally, predatory birds is available. If the sensitivity of the American kestrel to diphacino n e is representative of other species of raptors, this information suggests that r aptors may be more sensitive to diphacinone than either bobwhite quail or mallard duck. The potential for increased sensitivity of raptors to warfarin was observed by Watanabe et al

. (2010), who demonstrated that hydroxylation rates of warfarin in the grea t horned owl ( Bubo virginianus ) and snowy owl ( Bubo scandiacus ) were much less than that observed in mallards, chickens ( Gallus gallus ), and laboratory rats. This study suggests that raptors may metabolize and detoxify warfarin at slower rates compared to mallard ducks. Taken together, these data may indicate that raptors, which represent secondary consumers of rodenticides, are more sensitive to some rodenticides when compared to the standard test species used to derive the RQs calculated in this

assessmen t. This information will be considered later in the assessment when characterizing the risks of anticoagulant rodenticides to secondary consumers.

The most sensitive results for bromethalin were obtained from a bobwhite quail study (MRID 00086742) that pr ovided an LD 50 = 4.6 mg a.i./kg

- bwt. Two additional studies were conducted using bromethalin on bobwhite quail. One study resulted in a definitive LD 50 = 11.0 mg a

. i

. /kg

-Page 39 of 183 bwt ( MRID 00086741 ), and one resulted in a non

- definitive endpoint of LD 50 < 160 mg a

. i

. /kg

bwt as all birds died by day two of the study (van Lier et al . 1980).

F igure 3

- 1 allows for visual comparison in toxicity sensitivities across chemicals and among studies within a chemical. For avian acute oral toxicity, the most sensitive LD 50 valu es were obtained from either Northern bobwhite quail or mallard duck studies (850.2100 recommended guideline species) for all chemicals except diphacinone.

Figure 3

- 1. Avian acute oral LD 50 (mg a.i./kg

- bwt) values for all evaluated chemicals. LD 50 values represented as a range were plotted using a mid

- point value; no other non

- definitive values were included. Only toxicity values obtained using the technical material were included. Circles represent toxicity values used for RQ calculation.

Although mortality is the endpoint of interest for this assessment, sublethal effects observed in the available toxicity studies are worth noting. Sublethal effects observed in the anticoagulant acute oral studies included lethargy, subcutaneous, intramusc ular, and internal hemorrhaging, piloerection, diarrhea, bloody diarrhea, and anorexia. Sublethal effects noted in the bromethalin acute oral studies included clonic convulsions, prostration, salivation, crouched body posture, ataxia, lethargy, diarrhea, a nd loose feces.

3.1.2 Avian dietary toxicity

Table 3

- 4 summarizes the most sensitive avian dietary toxicity endpoints for either bobwhite quail or mallard duck, based on an evaluation of both the registrant

- submitted studies and the open literature. Mallard ducks and northern bobwhite quail were the only species for which the 0.1 1 10 100 1000 10000 LD 50 (mg a.i./kg

- bwt) Warfarin

Chlorophacinone Difethialone

Diphacinone

Bromethalin BrodifacoumPage 40 of 183 acute avian dietary studies were available. As with the acute avian toxicity data discussed above, difethialone and brodifacoum have the most sensitive acute dietary toxicity endpoints f or birds (i.e., LC 50 values = 0.56 and 1.33 mg/kg

- diet, respectively). The LC 50 value for chlorophacinone
is 1

- 2 orders of magnitude higher (LC 50 = 72 mg/kg

- diet). Bromethalin, warfarin and diphacinone have LC 50 values (i.e., 210, 625 and 906 mg/kg

- diet, r espectively) that are 2

- 3 orders of magnitude less sensitive compared to difethialone and brodifacoum. All six chemicals have multiple avian dietary studies available resulting in a range of reported toxicity values ( Appendix A ).

Table 3

- 4 . Avian acute dietary studies used for calculating RQs (restricted to mallard duck and bobwhite quail).

Chemical/ Species % a.i. LC 50 , mg a.i /kg

diet (95% CI) Probit slope (95% CI) Average body weight, g (day=0) Study length (days) T ime to mortality (days) MRID and
classification

Brodifacoum
Northern bobwhite quail 94 1.33 (0, 2.96) 1 NA 22 40 most from days
3

- 10 00124477 acceptable

Difethialone
Northern bobwhite quail 96 0.56 (0.16, 1.9) NA 30 30 2

- 23 days 406969

- 02 Acceptable

Warfarin
Northern bobwhite quail 100 625 NA 33 15 most from days 3

- 7, one

on day 10 00153365, acceptable,

Chlorophac

inone
Northern bobwhite quail 100 72
(32, 129) 1.5

(0.8, 2.2) 22 30 2

- 9 days 41513102 Acceptable

Diphacinone
Mallard duck 96.9 906
(187, 35110) 0.5

(0.2, 0.8) 185 25 most from 3

- 8 days, all less than 16 days 424088

- 02 Acceptable

Bromethalin
Northern bobwhite quail 96.3 210 (150, 310) 3.7 (1.8, 5.6) 20.7 8 1

- 5 days 00086744, Acceptable

1 Moving average; previous assessments used an LC 50 =0.8 based on the probit model. Probit does not fit the data well and predicts the LC 50 will be less than the lowest test concentration (1.0 mg a.i /kg

- diet) which experienced only 20% mortality. Also noted that 12% control mortality in study due to toe and nostril picking.

NA

– not availablePage 41 of 183 For brodifacoum, one bobwhite quail and one mallard duck dietary toxicity study were identified. The resulting L C 50 s of 1.33 and 2.75 mg a

. i

. /kg

- diet were calculated (MRIDs 00124477 and 00124476).

For difethialone, one bobwhite quail and one mallard duck dietary toxicity study were identified. The resulting L C 50 s of 0.56 and 1.4 mg a.i /kg

- diet were calculated , respectively (MRIDs
406969

- 01; 40268912 and 42687703).

For warfarin, the study with the most sensitive endpoint was conducted using bobwhite quail and
resulted in an LC 50 = 625 mg a.i./kg

- bwt (MRID 00 153365) . Three additional bobwhite quail dietary studies were conducted, resulting in LC 50 s ranging from 300 0 to 6690 mg a.i./kg

- diet (MRIDs 117979, 161724, 156283 ). Three mallard d uck studies were reviewed, resulting in
definitive LC 50 values of 890 and 1726 mg a.i./kg

- diet and a non

- definitive LC 50 > 5000 mg a.i./kg

- diet (MRIDs 153366, 157812, 156285 ). Some of the variability in the warfarin toxicity endpoints may be due to impuri ties in technical material and variability between batches (USEPA, 1982).

For chlorophacinone, the study with the most sensitive endpoint was conducted using bobwhite quail and resulted in an LC 50 = 56 mg a.i./kg

- bwt (MRID 41513102 )

. One additional bobwhite quail study had an LC 50 = 242 mg a

. i

. /kg

- diet (MRID 29144 ), and two mallard duck studies had
LC 50 s of 172 and 426 mg a.i./kg

- diet (MRIDs 41513103, 29144). A Japanese quail study conducted using a 0.25% oil concentrate of chlorophacinone resulted i n an LC 50 = 60 mg a

. i

. /kg

diet (MRID 47323201 ).

For diphacinone, one mallard duck and one bobwhite quail dietary toxicity study w ere identified. The resulting LC 50 s were 906 and >5000 mg a.i /kg

- diet (MRIDs 424088

- 02 and 424088

- 01).

For bromethalin, the study with the most sensitive endpoint was conducted using bobwhite quail
and resulted in an LC 50 = 210 mg a.i./kg

- bwt (MRID 00086744). T wo additional bobwhite quail studies were available [LC 50 s > 50 mg a .i /kg

- diet (MRID 00086745 ) and >200 mg a.i /kg

- diet (Ecoref No. 150784)]. A dietary study was also conducted on mallard ducks resulting in an LC 50 = 620 mg a.i /kg

- diet (MRID 00086746).

F igure 3

- 2 allows for visual comparison in toxicity sensitivities across chemicals and among studies within a chemical. For avian acute dietary toxicity, the most sensitive LD 50 ’s were obtained from either Northern bobwhite quail or mallard duck studies (850.2100 re commended guideline species) for all chemicals.Page 42 of 183 Figure 3

- 2

. Avian acute oral LC 50 (mg a.i./kg

- diet ) values for all evaluated chemicals. LC 50 values represented as a range were plotted using a mid

- point value; no other non

- definitive values were included. Only toxicity values obtained using the technical material were included. Circles represent toxicity values used for RQ calcul ation.

3.1.3 Mammalian acute oral toxicity

Table 3

- 5 summarizes the most sensitive laboratory rat acute oral toxicity endpoints, based on an evaluation of both the registrant

- submitted studies and the open literature. Based on these data,
all of the rodenti cides considered in this assessment are very highly toxic to the laboratory rat; however brodifacoum and difethialone are an order of magnitude more toxic when compared to
the other four chemicals. As summarized below and in Appendix A , a ll six chemicals h ave multiple acute oral studies available with different species of mammals. These data indicate a wide range in mammalian sensitivities to acute exposures to these rodenticides. Although the standard mammalian test species (i.e., the laboratory rat) is am ong the most sensitive test species, more conservative endpoints from other species are available for almost all of the rodenticides
considered in this assessment. 0.1 1 10 100 1000 10000 Chlorophacinone

LC 50 (mg a.i./kg

- diet ) Warfarin Difethialone

Diphacinone

Bromethalin BrodifacoumPage 43 of 183 Table 3

- 5 . Mammalian acute gavage studies used for calculating RQs (restricted to

laborat ory rat , Rattus norvegicus ).

Chemical % a.i. LD50,

mg a.i /kg

bwt (95% CI) Probit slope (95% CI) Average body weight, g (day=0) Study length (days) T ime to mortality (days) MRID and
classification

Brodifacoum 96.1 0.48 2 NA 240 15 4

- 9 42687501 Acceptable 3

Difethialone 98.9 0.56 (0.53,0.59) 15 (10, 20) 230 21 4

- 12 40268903

A cceptable 3

Warfarin 1 100 3.0 (2.0, 3.8) NA >175 14 1

- 13 05002272 (Gaines 1960) Supplemental

Chlorophac

inone 100 6.26 (4.68, 8.30) 2.0 (1.4, 2.9) 175 21 4

- 13 41875301 Acceptable 3

Diphacinone 1 100 1.9 (1.4, 2.3) NA >175 14 2

- 9 05002272 (Gaines 1960) Supplemental

Bromethalin Tech 2.2 (2.0, 2.5) 7.2 (4.7, 9.7) 110

- 135 14 1

- 5 00026524 and
00026523

M inimum 3

1 Only male rats were used in this study. LD 50 was estimated by the study author using the Litchfield and Wilcoxon method. Initial rat weights provided as a minimum.

2 Estimated using binomial method. Confidence intervals could not be calculated.

3 Study classifications by Health Effects Division.

For brodifacoum, one study conducted on laboratory rats resulted in an LD 50 = 0.48 mg a.i /kg

bwt (MRID 42687501). Toxicity tests conducted on pine voles and meadow voles resulted in

LD 50 s of 0.42 and 0.82 mg a.i /kg

- bwt ( Byers, 1978 ). The LD 50 for Richards on’s ground squirrel ( Urocitellus richardsonii ), was 0.13 mg a.i /kg

- bwt (Baril and Pallister 1981, as cited in
Matschke et al . 1983). Mink ( Neovison vison) had an LD 50 = 9.2 mg a.i /kg

- bwt (MRID 00080248). LD 50 s reported for domesticated animals included be agle dogs ( Canis lupus familiaris ) with an LD 50 between 0.25 and 1.0 mg a.i /kg

- bwt (MRID 00087134), Dutch rabbit ( Oryctolagus cuniculus ) with an LD 50 = 0.29 mg a.i /kg

- bwt (MRID 00128426), pigs ( Sus scrofa
domesticus ) with an LD 5 0 between 0.5 and 2.0 mg a.i /kg/diet (MRID 00080246), guinea pig ( Cavia porcellus ), at 2.8 mg a.i /kg

- bwt (00087133), cat ( Felis catus ) at LD 50 = 25 mg a.i /kg

- bwt (MRID 00087134), and sheep ( Ovis aries ) at LD 50 >25 mg a.i /kg

- bwt (MRID 00080247).

For difeth i alone, one study conducted on laboratory rats resulted in an LD 50 = 0.56 mg a.i /kg

- bwt (MRID 40268903 ). LD 50 s for laboratory mice, house mouse, roof rats, and Norway (wild) ratsPage 44 of 183 ranged from 0.29 to 1.29 mg a

. i

. /kg

- bwt ( MRID 40268904 and Lorgue 1984, as cited in
Lechevin and Poché 1988). LD 50 s for the hare ( Lepus spp.) and pig were 0.75 and 2

- 3 mg a.i /kg

bwt, respectively (Lorgue 1984 as cited in Lechevin and Poché 1988). Reported LD 50 s for dogs were 4 and 11.8 mg a.i /kg

- bwt (Harling et al, 1986 as cited in LiphaTech, Inc, 1997, and MRID 41442201).

For warfarin, the most sensitive laboratory rat data was an LD 50 = 3.0 mg a.i /kg

- bwt (MRID 05002272). Additional laboratory rat studies resulted in a range of LD 50 values from low values of 8.7 and <10 mg a.i /kg

- bwt to a high value of 512 mg a.i /kg

- bwt. The LD 50 value for the cat was <2.5 mg a.i /kg

- bwt

. Some of the variability in the warfarin toxicity endpoints may be due to impurities in technical material and variability between batches of technical material (USEPA, 1982). Poché and Mach (2001) also suggest that the degradation rate of warfarin in the gastrointestinal tract of rats probably depends on the variation of bacterial species present and
their abundance.

For chlorophacinone , one study conducted on laboratory rats resulted in an LD 50 = 6.26 mg
a.i /kg

- bwt (MRID 41875301 ). The LD 50 for pine vole ( Microtus subterraneus ) was 17.3 mg
a.i /kg

- bwt (Byers, 1978) and the LD 50 for deer mouse was 1.0

- 3.75 mg a.i /kg

- bwt ( Byers, 1978 ). A toxicity test conducted on black

- tailed prairie dogs ( Cy nomys ludovicianus ) resulted in an

LD 50 of 1.94 mg a.i /kg

- bwt (MRID 47333601).

For diphacinone , the most sensitive laboratory rat data reported an LD 50 = 1.9 mg a.i /kg

- bwt (MRID 05002272) . A second laboratory rat study resulted in an LD 50 = 2.46 mg a.i /kg

- bwt (MRID 00060605). Toxicity tests conducted on pine voles and meadow voles ( Microtus pennsylvanicus ) resulted in LD 50 s of 67.7 and 11.7 mg a.i /kg

- bwt (Byers, 1978 ). LD 50 values for dogs and cats ranged from 0.88 to 15 mg a.i /kg

- bwt (LiphaTech, Inc, 1997). LD 50 s for the coyote ( Canus latrans ) and mongoose ( Herpestes spp) were 0.6 and 0 .18 mg a.i /kg

- bwt, respectively (Savarie et al. 1979 and MRID 405655

- 01 ). These data suggest that diphacinone may be more toxic to carnivores than those animals experien cing primary exposure to diphacinone. This increased sensitivity of secondary exposure animals relative to primary exposure animals was also observed in the avian acute oral toxicity studies.

For bromethalin, the study conducted on laboratory rats used f or risk calculation resulted in an

LD 50 = 2.2 mg a.i /kg

- bwt (MRID s 00026524 and 00026523 ). Other laboratory rat studies
resulted in LD 50 = 2.59 mg a.i /kg

- bwt ( MRID 44775101) and LD 50 = 9.1 and 10.7 for females and males, respectively ( MRIDs 00026524 and 00026523). An LD 50 = 6.6 mg a.i /kg

- bwt was identified for roof rats (Jackson et al . 1982). Laboratory mouse studies consisted of bromethalin
administered in a carrier, PEG

- 200

, (LD 50 = 8.1 and 5.3 for females and males, respectively) and
bromethalin administered in a carrier, acacia

, (LD 50 = 28.9 and 35.9 for females and males,Page 45 of 183 respectively) (MRID 00026523). LD 50 values for rabbits, dogs, and cats ranged from 1.9 to 100

mg a.i /kg

- bwt (MRID 00026523).

F igure 3

- 3 allows for visual comparison in toxicity sensitivities across chemicals and among studies within a chemical. For mammalian acute oral toxicity, the most sensitive LD 50 values were from a variety of species; however, risk estimation was conducted using the most sensitive data from laboratory rats for all chemicals.

Figure 3

- 3

. Mammalian acute oral LD 50 (mg a.i./kg

- bwt) values for all evaluated chemicals.

LD 50 values represented as a range were plotted using a mid

- point value; no other non

- definitive values were included. Only toxicity values obtained using the technical material were included. Circles r epresent toxicity values used for RQ calculation.

As discussed previously, although mortality is the endpoint of interest for this assessment, sublethal effects observed in the available toxicity studies are worth noting. Sublethal effects
noted in the a cute oral anticoagulant studies included lethargy, subcutaneous, intramuscular, and internal hemorrhaging, diarrhea, bloody diarrhea, and anorexia. Sublethal effects noted in the bromethalin studies included hypoactivity, tremors, loss of righting reflex, dyspnea, ptosis, diarrhea, and dieresis. Some of these sublethal effects, in particular lethargy and hypoactivity could decrease the fitness of the target animals, thereby increasing the likelihood that the target animals may become prey to secondary preda tors, resulting in an exposure of secondary predators to rodenticides.

3.1.4 Mammalian dietary toxicity

Table 3

- 6 summarizes the most sensitive laboratory rat dietary toxicity endpoints, based on an evaluation of both the registrant

- submitted studies and the open literature. Reliable acute dietary 0.1 1 10 100 1000 Brodifacoum

Difethialone

Warfarin

Chlorophacinone

Diphacinone

Bromethalin

LD 50 (mg a.i./kg

- bwt)Page 46 of 183 toxicity studies are not available to derive RQs for difethialone and bromethalin; however, there
are data availabl e to characterize the dietary toxicity of bromethalin to mammals. When considering available data for brodifacoum, warfarin, chlorophacinone and diphacinone, all of these chemicals are very highly toxic. As with the acute oral toxicity da t a, brodifacoum is an order of magnitude more toxic to mammals on an acute dietary basis. Several chemicals have multiple acute dietary studies available resulting in a range of reported toxicity ( Appendix A ).

Table 3

- 6 . Laboratory rat acute dietary studies used for calcu lating RQs.

Chemical % a.i. LC 50 , mg a.i /kg

diet (95% CI) Probit slope (95% CI) Average body weight, g (day=0) Study length (days) T ime to mortality (days) MRID and
classification

Brodifacoum 1 98 0.53 (0.45

- 0.68) NA 98 14 4

- 14 Teeters 1981 (TNM 110) Supplemental

Difethialone No data

-- -- -- -- --
Warfarin 98 4.41 (3.43

- 5.64) 5.4 (2.8, 8.0) 98 14 3

- 9 Teeters 1981 (TNM 126) Supplemental
Chlorophac

inone 100 1.14 (0.98

- 1.35) 7.2 (3.8, 10.6) 65 14 4

- 9 Teeters 1981 (TNM 117) Supplemental
Diphacinone 99.8 2.08 (1.57, 2.76) 4.2 (2.3, 6.1) 136 14 4

- 12 Teeters 1981 (TNM 75) Supplemental

Bromethalin No quantitative data -- -- -- -- --

1 LC 50 values estimated via the binomial method. Slopes and c onfidence intervals could not be calculated.

For brodifacoum, the dietary LC 50 values for laboratory ra t range from 0.53 to 0.84 mg a.i / kg

diet (Teeters 1981).

For difethialone, no mammalian dietary toxicity data were identified. Since no dietary toxicity data were available, risk estimation based on dietary toxicity for difethialone cannot be
conducted for mammals.

For warfarin, the dietary LC 50 values for laboratory rat range from 4.41 to 6 .03 mg a.i /kg

- diet (Teeters 1981). Mink ( Neovison vison ) had an LC 50 = 11.7 mg a.i /kg

- diet (Aulerich et al

. , 1987)
and black

- tailed prairie dogs had an LC 50 = 97 mg a.i /kg

- diet (Mach et al

. , 2002).

For chlorophacinone, the dietary LC 50 values for laborat ory rat range from 1.14 to 1.26 mg
a.i /kg

- diet (Teeters 1981).Page 47 of 183 For diphacinone, the dietary LC 50 values for laboratory rat range from 2.08 to 2.55 mg a.i /kg

- diet (Teeters 1981).

For bromethalin, the available LC 50 value for laboratory rat was 5.5 mg a.i /kg

- diet (Jackson et
al

. , 1982). Jackson et al . (198 2) also evaluated dietary toxicity to roof rats and house mice, resulting in LC 50 s of 7.2 and 14.1 mg a.i /kg

- diet , respectively

. This open literature paper was classified as qualitative (no control anima ls and no low dose with no mortality, lack of reported methods and summary data) and cannot be used for risk estimation but can be used for risk
characterization.

F igure 3

- 4 allows for visual comparison in toxicity sensitivities across chemicals and among
studies within a chemical. For mammalian acute dietary toxicity, the most sensitive L C 50 value s were obtained from laboratory rat studies. Only two of the evaluated chemicals had data for additional species. Dietary toxicity data were available for mink a nd black

- footed ferrets on diphacinone and for house mice and roof rats for bromethalin.

Figure 3

- 4

. Mammalian acute dietary LC 50 (mg a.i./kg

- diet ) values for all evaluated
chemicals. No data were available for difethialone. LC 50 values represented as a range were plotted using a mid

point value ; no other non

- definitive values were included. Only toxicity values obtained using the technical material were included. Circles represent toxicity values used for RQ calculation. No data were available for RQ calculation
for difethialone or bromethalin. 0.1 1 10 100 1000 Brodifacoum

Difethialone

Warfarin

Chlorophacinone

Diphacinone

Bromethalin

LC 50 (mg a.i./kg

- diet )Page 48 of 183 3.1.5 Uncertai nties in Toxicity Studies

A description of assumptions, uncertainties, strengths, and limitations of the basic ecological risk assessment as conducted by EFED is described in Chapter 6 of the Agency’s Overview Document (USEPA 2004) and include those relat ed to the effects assessment. Additional uncertainties specific to this toxicity endpoints used in this assessment are discussed below.

All available toxicity endpoints are based on administered dose, not the bioavailable dose. For the acute oral studies, the administered dose is the amount of material enters into the test organism’s body ( e.g ., mg a.i./kg

- bwt). The bioavailable portion of this dose refers to the fraction of the total amount of material in contact with a port

- of

- entry ( e.g., lung, gut, ski n) that actually enters the blood. The bioavailability depends on the absorption, distribution, metabolism, and excretion rates of the chemical in the test organism. These factors can depend on factors such as species, maturity of test animals, dietary mat rix, animal health, and properties of the test chemical. For the evaluated rodenticides it is unknown what percentage of the administered dose is bioavailable to the test organism. It is important to note this uncertainty and to ensure that exposure as cal culated for risk estimation is assumed to also be an administered dose.

For many of the toxicity studies, there is uncertainty in the estimated LD 50 or LC 50 value, as the slope of the dose

- response curve appears to be very flat. For example, the mortal ity responses obtained in a dietary warfarin study on mallard ducks were 40, 40, 60, 60, 70% for diet concentrations of 312, 625, 12500, 2500, and 5000 mg a.i./kg

- diet (MRID 153366)

. Based on the mortality percentages, it would be reasonable to conclude that the LC 50 could lie anywhere between 312 and 2500 mg a.i./kg

- diet and possibly as high as 5000 mg a.i /kg

- diet. A n LC 50 = 879 mg a.i./kg

- diet and a slope of 0.7 was estimated based on the probit regression model. This indicates a lack of sensitivity to increasing concentrations of the chemical that may be due to individual variation in sensitivity to warfarin or individual variation in the likelihood that an incident causing internal bleeding (aggressive behavior, bumping into cage, etc.) would occur. In
addition to the flat dose

- response curves, some studies resulted in very steep dose

- response curves, indicating a rapid change in sensitivity to the chemical as dose increased.

Mammalian dietary LC 50 endpoints were not available for risk estimation for difethialone and bromethalin. No acute dietary mammalian studies were identified for difethialone. One bromethalin paper in the open literature (Jackson et al ., 1982) did contain dietary LC 50 data for three mammalian species (laboratory rat, roof rat, and house mouse). Limitations identified in the published article (no reporting of control data, minimal methods and summary data reported) preclude its use for risk estimation; however, these data were of adequate quality for use in the
risk characterization. Although the acute oral data allow for an estimate of toxicity based on a precise one

- time administered dose, the dietary toxicity data are important in characterizing toxicity based on a longer exposure period when the test material is administered in a dietaryPage 49 of 183 matrix. A complete set of toxicity endpoints for both acute oral (LD 50 ) and acute dietary (LC 50 ) toxicity tests would enable comparisons across chemicals and across exposure scenarios.

For some of the assessed chemicals, there was a large range in LD 50 or LC 50 estimates such that the smallest and largest values spanned several orders of magnitude. Review of the available toxicity data suggests the variability occurs within species, across species, across body sizes, and feeding strategies. Based on the large variation in toxic response seen in the laboratory studies, it can be expected that individual response to rodenticide exposure in real product application situations would also vary greatly.

An additional limitation to the toxicity data sets is that predator/scavenger toxicity data are not represented for all chemicals for both birds and mammals. For birds, the available information suggests that raptors may be more sensitive to anticoagulants than the standard toxicity test species. F or dipha cinone, an LD 50 of 96.8 mg a

. i

. /kg

- bwt is available for the American kestrel (Rattner et al . 2011). This study suggests that American kestrels may be more sensitive to diphacinone than the standard test species ( i.e., based on the available studies, 17 to 21 times more sensitive than bobwhite quail and 33 times more sensitive than mallard ducks). In addition,

t he potential for increased sensitivity of raptors to warfarin was observed by Watanabe et al

. (2010), who demonstrated that hydroxylation rates of wa rfarin in the great horned owl ( Bubo virginianus ) and snowy owl ( Bubo scandiacus ) were much less than that observed in mallards, chickens ( Gallus gallus ), and laboratory rats. This study suggests that raptors may metabolize and detoxify warfarin at slower rates compared to mallard ducks. Taken together, these data may indicate that raptors, which represent avian secondary consumers of rodenticides, are more
sensitive to rodenti cides when compared to the standard test species used to derive the RQs
calculated in this assessment. No avian dietary toxicity data (LC 50 ) were available for predatory/scavenger species.

For mammals, laboratory dog, cat, or pig toxicity data are availa ble for several of the evaluated chemicals; however, the confidence in these LD 50 s is limited as the number of individuals and the number of dose levels tested was often very small. These LD 50 s vary in sensitivity to the
tested chemical relative to the mos t sensitive rat data used for risk estimation, suggesting large individual or species variation in sensitivity to the tested rodenticides. For diphacinone, both coyote and mongoose (LD 50 = 0.6 and 0.18 mg a.i./kg

- bwt , respectively ) were more sensitive
than the most sensitive laboratory rats ( LD 50 = 1.9 mg a.i./kg

- bwt)

. For brodifacoum , mink (LD 50 = 9.2 mg a.i./kg

- bwt) were less sensitive than the most sensitive laboratory rats (LD 50 = 0.48 mg a.i./kg

- bwt); however, Ringer and Aulerich ( 1978 ) noted that mink have a very rapid transit rate (approximately 2 hours) of food through the intestinal tract possibly allowing for excretion of
test material bef ore adequate absorption occurs

. A mink dietary toxicity study was available for warfarin (LC 50 = 11.7 mg a.i./kg

- diet); this study also resulted in a lower toxicity to the tested anticoagulant than the most sensitive rat dietary study (LC 50 = 4.4 mg a.i./kg

- diet).Page 50 of 183 

### 3.2 Elimination of Rodenticides

Considerable differences exist in absorption, metaboli sm and excretion of the anticoagulant rodenticides, which may have important consequences for both primary and secondary risk. A compound that is rapidly metabolized or excreted from a primary consumer may result in a lesser risk of mortality than one that bioaccumulates with repeated sublethal exposure, even if repeated exposure occurs weeks or even months after initial exposure (Eason and Murphy 2000). Those compounds more rapidly cleared from the body are less likely to pose such long

- term risk. The
avai lable information indicates that brodifacoum and difethialone are more persistent in animal tissue than warfarin, chlorophacinone and diphacinone. Few data exist for the non

anticoagulants, but based on lack of toxicity in secondary tests, apparently this rodenticide is not retained in toxicologically significant amounts in animal tissues.

Elimination of anticoagulants from the body is sometimes described as rapid ( e.g., Poche 1986, Kaukeinen et al. 2000); however, such characterizations usually refer to the rapid excretion of unbound or unabsorbed material being excreted principally in feces during the first few days after administration. Alternatively, it may refer to the clearance from the blood as compared with
tissue retention. Rather than concentrati ng solely on the amount of anticoagulant excreted, this risk assessment includes a discussion on the material retained in the body after single and multiple exposures. The studies summarized below indicate the differences among these compounds and their po tential to bioaccumulate with repeat exposure.

3.2.1 Elimination of Brodifacoum Available data indicate that brodifacoum is not readily metabolized, and the major route of excretion of unbound compound is through the feces. After absorption, high concentration s circulate in the blood and are rapidly established in the liver and in other tissues. The half

- life of brodifacoum in ranges from 128 to 307.4 days in liver and 6 to 91.7 days in blood plasma in mammals ( Table 3

- 6 ). Elimination from liver is much slower and biphasic, with a very prolonged terminal phase. It is apparent from the studies discussed below that a proportion of any ingested dose of brodifacoum bound in the liver, kidney, or pancreas remains in a stable form for some time and is only very slowly excreted.

Table 3

- 6. Retention of Brodifacoum 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)

Brodifacoum Mouse 6.44 μg/mouse 1 91.7 307.4 (t 1/2 ) Vandenbroucke et al.

2008Page 51 of 183 Brodifacoum Rat 0.02 or 0.15
0.35 1

1 NA 350 c (t 1/2 )
128 d (t 1/2 ) Batten and Bratt 1990 (42007502)

Brodifacoum Rat 0.2 1 NA 282 (t 1/2 ) Hawkins et al. 1991 (42596801)

Brodifacoum Rat 0.25 1 NA 150

- 200 (t 1/2 ) Bratt and Hudson 1979 (00080235)

Brodifacoum Rat 0.06 4 (at weekly intervals) NA 136 (t 1/2 ) Belleville 1991 (42065009)

Brodifacoum Rat 0.35 1 NA 130 (t 1/2 ) Parmar et al. 1987 e

Brodifacoum Rat unknown unknown 6.5 >80 Backmann and Sullivan
1983 f

Brodifacoum Rat 0.1 1 NA 113.5 (t 1/2 ) Fischer et al. 2003 (48190801)

Brodifacoum Possum 0.1 1 20

- 30 >252 Eason et al. 1996

Brodifacoum Rabbit unknown unknown 2.5 NA Brechenridge et al.
1985 f

Brodifacoum Sheep 0.2 or 2.0 1 NA >128 Laas et al. 1985 e

Brodifacoum Dog unknown unknown 6 NA Woody et al. 1992 f

Brodifacoum Dog unknown unknown 0.9

- 4.7 NA Robben et al. 1998 f

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

c the elimination half

- life of 350 days is for a single oral dose of 0.02 or 0.15 mg a.i./kg; elimination was not biphasic

d the elimination half

- life of 128 days is the terminal phase for a single oral dose of 0.35 mg a.i./kg; elimination was biphasic

e Ci ted in US EPA (2004) Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative Approach

f cited in Eason et al. 2001

Hawkins et al. (1991) administered brodifacoum to rats in a single oral dose of 0.2 mg a.i./kg. Elimination was biphasic, with half

- lives of 63 days for brodifacoum in the initial 28 days and 282 in the terminal phase. These differences are not statistical ly significant, but mean liver concentrations of brodifacoum were significantly higher throughout the study.

Bratt and Hudson (1979) found that radiolab e led brodifacoum was rapidly and almost completely absorbed when administered to rats in a single oral dose (0.25 mg a.i./kg). After 10 days, 11 to 14% of the dose had been eliminated in urine and feces, but 74.6% of the dose was still retained in body tissues. Almost half the dose administered was detected in the carcass and skin, with lesser amounts in t he liver (22.8%), pancreas (2.3%), kidney (0.8%), spleen (0.2%), and heart (0.1%). The estimated half

- life of brodifacoum in rat tissue was 150

- 200 days.

Fisher et al. (2003) administered single oral doses of 0.1 mg a.i./kg brodifacoum to 20 rats. Rats

w ere monitored for 5 days after dosing for symptoms of anticoagulant poisoning. Groups of sixPage 52 of 183 or seven rats were euthanized at weeks 1, 18, and 24. The livers were removed post

- mortem for analysis of brodifacoum residue by HPLC. Brodifacoum elimination half

- life in rat liver tissue was estimated to be 113.5 days.

Batten and Bratt (1990) orally dosed male rats with a single dose of radiolabeled brodifacoum at 0.02, 0.15, or 0.35 mg a.i./kg. The highest concentration of radioactivity in the liver was found 1 day after dosing, but 21 to 34% of the dose was still detected after 13 weeks and >11% after 104
weeks. The elimination half

- life for the 2 lowest doses was 350 days. For rats dosed at 0.35 mg a.i./kg, a near

- lethal dose (LD50 = 0.39 to 0.56 mg a.i./kg), elimination from the liver was biphasic and consisted of a rapid phase (days 1 to 4) in which the half

- life was approximately 4 days and a slower phase (days 28 to 84) in which the half

- life was 128 days. Two rats dosed at that level died during the study. Signs of brodifacoum toxicosis were observed in some survivors. Some dosed rats also had gained less body

- weight and displayed signs of internal hemorrhage when dissected.

Based on those findings, the authors concluded that the existence of biphasic kin etics in the liver for brodifacoum has two important consequences. First, half

- lives determined based on the initial, or fast, phase of elimination may underestimate the potential persistence of the chemical. The second consequence of biphasic liver kineti cs is that the chemical concentration in the liver at the beginning of the terminal, or slow phase, is independent of the initial dose.

Parmar et al. (1987) also reported biphasic elimination of radio

- labeled brodifacoum from rat liver. The initial phase occurred from days 2 to 8 after dosing, followed by a prolonged terminal phase when the elimination half

- lives were 130 and 170 days. However, the results were presented only in an abstract with too few details provided to adequately evaluate the results

r eported.

Belleville (1991) orally dosed rats with 0.06 mg a.i./kg brodifacoum on 4 occasions at weekly intervals. After 6 months, 21% of the total brodifacoum dose was retained in hepatic tissue ( Table 3

- 7 ). The hepatic half

- life calculated for the 158 d ays after the final dose (days 22

- 180) was 136 days for brodifacoum.Page 53 of 183 Table 3

- 7. Hepatic Concentrations in Rats Dosed with Brodifacoum at 0.06 mg a.i./kg on Days 0, 7, 14, and 21 (adapted from Belleville 1991, MRID# 42065009)

Time after initial dose Brodifacoum (mg a.i./kg)
22 days 2.01 ± 0.15

49 days 1.50 ± 0.48

77 days 0.98 ± 0.32

4 months 0.85 ± 0.15

6 months 0.87 ± 0.16

Studies in species other than rats also indicate that brodifacoum can be retained in animal tissue for a prolonged period of time. Eason et al. (1996) detected brodifacoum residue 9 months after administration of a sublethal dose of 0.1 mg a.i./kg in possu ms. Laas et al. (1885) examined retention of brodifacoum in sheep tissues and its excretion via feces after a single, sublethal oral dose of either 0.2 or 2.0 mg a.i./kg in 14 sheep. Sheep were sacrificed at several intervals over a 128 day period after do sing and liver, carcass, and fat tissues analyzed for residue. Brodifacoum was detected in the liver after 128 days, at concentrations of 0.64 and 1.07 mg a.i./kg dry weight (equivalent to 0.22 and 0.36 mg a.i./kg wet weight), respectively, for the 2 doses . Residue was also detected for up to 8 days in fat and up to 15 days in the carcass. Breckenridge et al. (1985) reported a plasma elimination half

- life of about 2.5 days for rabbits dosed with brodifacoum, and Woody et al. (1992) observed an elimination h alf

- life for brodifacoum in serum of 6 ± 4 days in four dogs.

Vandenbroucke et al. (2008) orally dosed groups of mice with 6.44 μg/mouse, which is approximately one

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

- life of brodifacoum in liver as 307.4 days and
the half

- life in plasma as 91.7 days.

3.2.2 Elimination of Difethialone

Data available for difethialone suggest that this rodenticide is not as persistent as brodifacoum ( Table 3

- 8 ). Available elimination half

- lives in blood and liver tissues of mammals range 2.2

- 38.9 days and 28.5

- 108 days, respectively.Page 54 of 183 Table 3

- 8. Retention of Difethialone 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)

Difethialone Mouse 20.77 μg/mouse 1 38.9 28.5 (t 1/2 ) Vandenbroucke et al.
2008

Difethialone Rat 0.5 1 2.3 108 (t 1/2 ) Belleville 1986 (42065010)
Lechevin and Poche
1988

Difethialone Rat 0.06 4 (at weekly intervals) NA 74 (t 1/2 ) Belleville 1991 (42065009)

Difethialone Dog unknown unknown 2.2

- 3.2 NA Robben et al 1998 c

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

c cited in Eason et al. 2001

Vandenbroucke et al. (2008) orally dosed mice with approxi mately one

- half the LD 50 of
difethialone , 20.77 μg/mouse. Difethialone was then assayed in liver tissue and blood plasma from euthanized mice at various times up to 21 days after dose administration. The study authors
estimated the elimination half

- life in liver as 28.5 days and the half

- life in plasma as 38.9 days. Studies submitted to EPA (Belleville 1986 and 1991, MRID#s 42065010 and 42065009 respectively) indicate that the half

- life of difethialone may be several times greater than Vendenbroucke et al ( 2008). Belleville (1991) orally dosed rats with 0.06 mg a.i./kg difethialone on 4 occasions at weekly intervals. After 6 months, 7% of the total difethialone dose was retained in hepatic tissue. The hepatic half

- life calculated for the 158 days after the f inal dose (days 22

- 180) was 74 days for difethialone.

3.2.3 Elimination of Warfarin The available information for warfarin indicates it is generally less persistent in the blood and body tissues than brodifacoum ( Table 3

- 9) . Available elimination half

- lives in blood and liver tissues of mammals range from 0.2 to 14.9 days and 26.2 to 66.8 days, respectively.

Table 3

- 9. Retention of Warfarin 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)

Warfarin Mouse 5985 μg/mouse 1 14.9 66.8 (t 1/2 ) Vandenbroucke et al.
2008

Warfarin Rat unknown unknown 0.7 (male)

1.2 (female) NA Pyrola 1968 dPage 55 of 183 Warfarin Rat 1.0 1 NA 26.2 (t 1/2 ) Fisher et al. 2003 (48190801)

Warfarin Rabbit unknown unknown 0.2 NA Breckenridge et al
1985 d

Warfarin Possum unknown unknown 0.5 NA Eason et al. 1999 c

Warfarin Pig unknown unknown NA 30

- 40 O’Brien et al 1987 d

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

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

d cited in Eason et al. 2001

In contrast to the other anticoagulants, warfarin is extensively metabolized and the major route of excretion is in the urine. Meehan (1984) states that approximately half the warfarin consumed by a rat remains in the body after 6 hours, suggesting that up to 50% may be eliminated in this time period. EPA (1982) noted that only 7.6% of the warfarin consumed in bait by 11 rats remained
in the carcass after a 5

- day feeding period. Ford (1993; cited in Poché and Mach 2001) reported a
half

- life of 42 h ours in the gastro

- intestinal tract, which supports the conclusion that a portion of the consumed warfarin dose is rapidly eliminated from the body. However, there is evidence that warfarin residues that are not excreted though urine and fecal matter may a ccumulate in various body tissues, especially in the liver. Though warfarin concentrates in the liver, measurable amounts have also been found in the adrenal glands, lungs, bone marrow, kidneys, and lymph nodes (Machlin 1984).

Vandenbroucke et al. (2008) orally dosed groups of mice with 5.985 mg warfarin/mouse, which is approximately one

- half of the LD 50 dose. Warfarin 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 warfarin in liver tissue to be 66.8 days and
the half

- life in blood plasma to be 14.9 days.

Fisher et al. (2003) administered a single dose of 1.0 mg a.i./kg to 20 rats. Rats were monitored for 5 days after dosing for symptoms of anticoagulant poisoning. Groups of six or seven rats
were euthanized at weeks 1, 18, and 24. The livers were removed post

- mortem for analysis of warfarin residue by HPLC. Warfarin elimination half

- life in rat liver tissue was estimated to be 26.2 days.

The discrepancies between the half

- lives estimated in Vandenbroucke et al. (20 08) and Fisher et al. (2003) may be partially a result of the different test organisms as there is some indication that elimination times for warfarin may vary among species. For example, O’Brien et al. (1987; cited in Eason et al. 2001) found comparativel y rapid clearance of warfarin in pigs, with concentrations declining to very low levels after approximately 30 days. In addition, Wantabe etPage 56 of 183 al. 2010 examined the differences in metabolism of warfarin in birds in order to study differences in species sensi tivities to this rodenticide. Liver samples from domestic chickens ( Gallus gallus ), ostriches ( Struthio camelus ), mallard ducks ( Anas platyrhunchos ), snowy owls ( Bubo
scandiacus ) and a great horned owl ( B. virginianus ) were used to measure the metabolism o f warfarin to its hydroxylated degradates. Results of the study indicated that owls had the lowest metabolism of warfarin. Therefore, relative to the other species tested, owls may have a limited ability to detoxify warfarin. This could potentially lead to increased warfarin sensitivity in owls, relative to OPP's typical test species ( e.g. , mallard ducks).

Half

- life values for blood plasma also vary greatly among species. Breckenridge et al. (1985) intravenously dosed male New Zealand white rabbits with 20 μmol/kg warfarin. Blood samples were taken at regular intervals and analyzed for warfarin concentration. The study authors reported a plasma elimination half

- life for warfarin of 5.6 hours in rabbits.

3.2.4 Elimination of Chlorophacinone Available data on the retention times for chlorophacinone are provided in Table 3

- 10 . Data on elimination from blood are available from 2 studies (half

- life ranges from 0.4 to 11.7 days). One
available liver elimination half

- life is available (35.4 days).

Table 3

- 10. Retention of Chlorophacinone 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)

Chlorophacinone Mouse 336 μg/mouse 1 11.7 35.4 (t 1/2 ) Vandenbroucke et
al. 2008

Chlorophacinone Rat 4

- 5 1 0.4 NA Belleville 1981 (00155540)

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

Belleville (1981) orally administered radio

- labeled chlorophacinone to rats with either a single dose of 1 to 1.26 mg a.i./rat (~4 to 6 mg a.i./kg) or 3 daily doses of 1.43 a.i/rat (~6 to 7 mg a.i./kg). The compound was rapidly absorbed and metabolized; 90% was excreted wit hin 48 hours and 100% with 4 days. Elimination was almost totally via the feces; < 1% was via urine
and CO 2 . The half life in blood was 9.8 hours, with the maximum concentration attained after 4
to 8 hours. The maximum blood concentration in rats that rece ived 3 doses was 1.8 to 3.7 times higher than that from rats receiving a single dose, indicating that chlorophacinone can accumulate in the body. Concentrations in body tissues after 4 hours and 48 hours were highest in the liver, but chlorophacinone was a lso present in kidneys, lungs, heart, muscle, fat, and other parts of the carcass ( Table 3

- 11 ).Page 57 of 183 Table 3

- 11. Chlorophacinone Residue in Rats 4 and 48 hours After Oral Dose of 1.26 mg a.i. per Rat (adapted from Belleville 1981, MRID# 00155540)

Organ Residue (μg a.i./g)

48 h after

dosing 48 h after dosing

Liver 31.1 2.9

Kidney 6.6 1.2

Lung 4.5 0.4

Heart 3.1 0.2

Muscle (thigh) 2.0 0.1

Fat 1.2 0.7

Carcass 5.2 0.3

3.2.5 Elimination of Diphacinone Available data on the retention times for diphacinone are provided in Table 3

- 12 . Yu et al. (1982) studied the metabolism and disposition of diphacinone in rats and mice. Rats given a single oral dose of radiolabeled diphacinone at either 0.18 or 0.4 mg a. i./kg, about 70% of the dose was eliminated in feces and 10% in urine within 8 days, whereas about 20% of the dose was retained in body tissues. Mice given a single dose of 0.6 mg a.i./kg eliminated most diphacinone within 4 days, and only 7% was retained in body tissues. In both rats and mice, most radioactivity (59 to 69%) was detected in the liver and the kidneys (9 to 12%). Radioactivity was also detected in the brain, heart, spleen, lungs, blood, muscle, fat, and gonads. Several major
metabolites were identified, and parent diphacinone in excreta and liver accounted for only about 20% of the dose. In another study, cattle that received a single injection of 1 mg a.i./kg had almost constant residue concentrations in liver and kidney at 30, 60, and 90 day s after dosing (Bullard et al. 1979).

Table 3

- 12. Retention of Diphacinone 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)

Diphacinone Pig 12.5 3 or 5 NA 5.43 (t 1/2 ) Fisher 2006

Diphacinone Rat 1.5 1 NA 3 (t 1/2 ) Fisher et al. 2003 (48190801) Diphacinone Cattle 1.0 1 NA > 90 Bullard et al. 1976

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

Diaz and Whitacre (1976) orally dosed rats with diphacinone (0.32 mg a.i./kg/day) for 1 or 2 days. Rats dosed for 2 days were sacrificed 72 hours after the second dose and those dosed for 1Page 58 of 183 day were sacrificed after 48 hours. In rats dosed for 2 days, about 45% of the total dose administered was excreted (86% in feces, 14% in urine) and 25% was retained in body tissues 72
hours after the last dose. The remaining 30% of the dose was not recovered. The body tissues retaining the most diphacinone at 96 hours were the hide and tail, liver, intestine, blood, and the carcass ( Table 3

- 13 ). In rats dosed for 1 day and sacrificed after 48 hours, about 5% of the dose was excreted and 61% retained; the remainder was not recovered.

Table 3

- 13. Percentage of Diphacinone Retained by Rats Dosed for 1 or 2 Days with 0.32 mg a.i./kg (adapted from Diaz and Whitacre 1976)

Organ % of dose retained per group a

48 h after 1

dose 72 h after 2

doses

Intestine 22.1 4.1

Liver 19.4 5.4

Hide and tail 10.9 6.5

Carcass 3.9 3.8

Blood 1.8 4.0

Muscle 0.8 0.4

Kidney 0.7 0.3

Testis not reported 0.8

Lung 0.5 0.2

Fat 0.2 0.4

Heart 0.1 0.2

Spleen 0.1 0.1

Brain < 0.1 < 0.1

a because only 66

- 70% of the total dose was recovered, percentages in tissues are likely to be higher than the
values tabulated

3.2.6 Elimination of Bromethalin
Available data on the non

- anticoagulant rodenticide bromethalin indicate that it is rapidly eliminated from the blood ( Table 3

- 14 ). While there are no data on the elimination half

- life of bromethalin in liver, a metabolism study was conducted in Fischer 344 rats following oral
administration of 14 C

- bromethalin at 1 mg/kg to assess the half

- life of bromethalin in blood plasma (MRID# 0004724). Blood samples were taken from the orbital sinus at 0.25, 0.5, 1, 2, 4, and 24 hours, and at 2, 3, 4, 6, 8, 11, 14, 17, and 21 days after dosing. Based on radiolabeled material, the plasma half

- life was 134 ho urs (5.6 days).Page 59 of 183 Table 3

- 14. Retention of Bromethalin in Blood and Liver

Rodenticide Species Dose (mg a.i./kg) No. doses Blood t 1/2 a (days) Liver
retention a,b
(days) Reference (MRID)

Bromethalin Rat 1 1 5.6 NA MRID 0004724

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

3.2.7 Discussion of Elimination Half

- life Data Toxicokinetic data presented in this section indicate that, of the anticoagulants, brodifacoum is more persistent in animal tissue than all other chemicals evaluated. For example, brodifacoum was detected in rat livers up to 200 days post exposure to a single oral dose of 0.2 mg a.i./kg (Hawkins et al. 1991), and up to 11.7% was detected in livers of rats after 104 weeks following a single dose of 0.15 mg a.i./kg (Batte n and Bratt 1990). Other studies discussed in section 3.2 provide further evidence of the long

- term retention of brodifacoum in body tissues, and half

- lives range up to 307.4 days in liver tissue and 91.7 days in plasma (Vandenbroucke et al. 2008). The

s tudy by Vandenbroucke et al. (2008) suggests that difethialone may be much less persistent in the body than brodifacoum, with a liver half

- life of 28.5 days and a plasma half

- life of 38.9 days. However, a half

- life for difethialone of up to approximately 100 days has been also been reported (Belleville 19 86 ).

Persistence data available for warfarin show variation among the species tested; however, most of the information on tissue retention indicates that it is generally less persistent in the body than
b rodifacoum. A liver half

- life of up to 66.8 days has been calculated for warfarin in rats (Vandenbroucke et al. 2008), though other estimates are less than this value. Most data indicate that the plasma half

- lives are <1 day. Available data also show th at chlorophacinone and diphacinone may be less persistent than brodifacoum, difethialone and warfarin. Liver half

- life for chlorophacinone is 35.4 days (Vandenbroucke et al. 2008). Half

- lives for diphacinone have been estimated to be shorter in some spec ies (ranging from 3

– 5.43 days), but liver retention times in cattle were determined to be >90 days (Fisher 2006, Fisher et al. 2003, Bullard et al. 1976).

Available data on the non

- anticoagulant rodenticide bromethalin indicate that it is rapidly
elimin ated by the body. While there are no data on the elimination half

- life of bromethalin in liver, a metabolism study was conducted in rats indicated a plasma half

- life of 5.6 days.

Brodifacoum may persist in animal tissues for several months after exposure compared to days to several weeks for the other rodenticides evaluated. These data suggest that brodifacoum is longer lived in animal tissues relative to the other rodenticides evaluated. This could potentially result in greater opportunity for secondary e xposure to occur. Figures 3

- 5 and 3

- 6 allow for visualPage 60 of 183 comparison of the liver and blood plasma half

- lives for the assessed rodenticides, respectively.
Due to the lack of whole

- body elimination data, liver half

- lives selected from the range of
available da ta were used as a conservative representation of whole body elimination in animals consuming bait. If liver half

- lives were not available, as in the case of bromethalin, the blood plasma half

- life was used. Calculations that estimated accumulation of roden ticides in target
animals and non

- target wildlife used the most conservative half

- life value available, except in the case of difethialone, where variation associated with differing study designs was reduced by utilizing the half

- life value from Vandenbrou cke et al. (2008).

Figure 3

- 5. Liver half

- life values for all evaluated chemicals. Half

- life values represented as a range were plotted using the reported value. Circles represent values used to calculate dose accumulation in animals for primary and secondary exposure. No liver half

- life data were reported for bromethalin. A plasma ha lf

- life of 5.6 days has been reported for bromethalin. 1 10 100 1000 Brodifacoum

Difethialone

Warfarin

Chlorophacinone

Diphacinone

Bromethalin

T 1/2 (half

- life days)Page 61 of 183 Figure 3

- 6. Blood plasma half

- life values for all evaluated chemicals. Half

- life values represented as a range were plotted using the reported value. Circles represent values used to calculate dose accumulation of bromethalin for primary and secondary exposure.



### 3.3 Estimated Accumulation of Dose over Time

As indicated previou sly, the rodenticides considered in this white paper typically cause mortality several days after exposure, which may allow target animals to feed for several days upon rodenticide bait before dying. This can lead to doses that far exceed the lethal dose. A compound that accumulates in body tissues may pose greater risk to primary and secondary consumers, especially if repeated sublethal exposure results in the accumulation of a lethal dose or if additional exposures occur before the lethal dose has taken i ts effect ( i.e., leading to a dose that is beyond what is sufficient to cause mortality). Considerable differences exist in accumulation of the anticoagulants considered in this assessment, which may have important consequences for both primary and seconda ry risk. The purpose of this section is to quantify the extent to which an accumulated dose may exceed the median lethal dose of target animals.

To do this, EFED simulated rodenticide doses (D t , Equation 1 ) in target animals ( i.e. , house mouse and Norway rat) over time. This analysis assumed that 100% of the daily diet of the target animals is represented by the rodenticide bait and that they eliminate the rodenticide according to
half

- lives presented in Table 3

- 15. In Equation , th e variable “C” represents the concentration of the pesticide in the bait. Elimination rate constants (k) are calculated according to Equation 2

. Food intake (FI) was calculated according to the allometric equation for rodents provided by
USEPA 1993. In thi s approach, it was assumed that bait consumed by the target animals was dry. 0.1 1 10 100 1000 Brodifacoum

Difethialone

Warfarin

Chlorophacinone

Diphacinone

Bromethalin

T 1/2 (half

- life days)Page 62 of 18 3 In order to allow for comparisons of half

- lives among chemicals, liver half

- lives for brodifacoum, difethialone, warfarin, and chlorophacinone from the same study by
Vandenbrouc ke et al. (2011) were selected. Although this approach reduces variability due to differences attributed to laboratories, it is not necessarily the most conservative approach that could be undertaken. For instance, the liver half

- life value for difethialon e that was reported by Vandenbroucke (28 days) is lower than provided in other studies (74 days from Belleville, 1991). Though a liver half

- life value is available for diphacinone, it is based on pig data, which differs from the organisms used in the other studies. There is some indication from the available half

life studies that species react to anticoagulant rodenticides differently. Therefore, this pig value may overestimate or underestimate the liver half

- life of rats for this chemical. For bromethalin

, there is no available data on the liver half

- life for bromethalin, so a blood plasma value is used instead. It is uncertain how a blood plasma half

- live would differ from the liver half

- life for this
chemical.

This analysis assumes that the liver half

- life adequately represents the elimination from the entire body during this time. As discussed in section 3.2.2 , rapid elimination of unbound or unabsorbed rodenticide is initially eliminated in feces. However, 100% absorption was assumed, which is expec ted to account for long term accumulation not represented by the use of the first

order elimination constant.

Target animals were assumed to be a house mouse (assumed weight of 23 g) or a Norway rat (assumed weight of 485 g), since products relevant to the NOIC are intended for use on these pests. These body weights are from Whitaker (1996), and they are consistent with theoretical analyses of this type in previous risk assessments ( e.g. , see EPA 2011).

Equation 1. 

### C FI e D D k

t t 

### * * ) 1 ( 

### + **= −** 

**−**

Equation 2

. 

## ( **)**

2 / 1 

### 2 ln t k **=**

Equation 3. FI = 0.621 * Wt 0.564Page 63 of 183 Table 3

- 15. Elimination half

- lives for rodenticides. Values based on elimination rates from
liver.

Rodenticide Elimination half

- life (days)

Brodifacoum 307.4

Difethialone 28.5

Warfarin 66.8 Chlorophacinone 35.4 Diphacinone 5.5

Bromethalin 5.6* *Value is based on elimination from blood plasma.

Toxicity studies discussed in section 3.1 provide information on the time to death for mammals after dosing with or feeding on the rodenticides considered in this white paper. This information is important for putting this dose accumulation analysis in co ntext for the various rodenticides. A rodenticide that is fast acting and causes death to occur after only a few days will greatly reduce the opportunity for dose accumulation. Bromethalin caused death within a day of presentation of feed for and mammals; all test animals were dead within 1

- 5 days of dosing or beginning to feed. However, a recent study by Pitt et al. (2011) found that time to death for house mice, Polynesian rats ( Rattus exulans ), and black rats ( Rattus rattus ) offered bromethalin may be m ore rapid than suggested in registrant submitted data for the Norway rat, which may reduce the potential for bromethalin to accumulate in prey organisms. Data from this study also suggest that house mice
and Polynesian rats exposed to bromethalin bait may stop feeding on the bait after reaching a lethal dose, further reducing the potential for accumulation. Warfarin also caused death to occur within a day of dosing and within three days of presentation of feed for mammals. All mortality
for mammals occurre d within 9

- 13 days in the studies available. In toxicity studies with the remaining rodenticides (brodifacoum, difethialone, chlorophacinone, and diphacinone), death
first occurred within 3

- 4 days of the dose, and death was last observed within 9

- 13 days. No clear trend related to dosing or feeding was apparent. Observed time to death for each of the
rodenticides assessed is summarized in Table 3

- 16 below. In summary, onset of death was most rapid for bromethalin and warfarin, though observed times where death occurred was more prolonged for mammals dosed with or fed warfarin. Time to death was approximately the same for brodifacoum, difethialone, chlorophacinone, and diphacinone.Page 64 of 183 Table 3

- 16. Observed times where mortalities were observed in acute ora l toxicity studies with rats exposed to rodenticides.

Rodenticide Time after initial dose where mortality was observed (days)

Brodifacoum 4

- 9

Difethialone 4

- 12

Warfarin 1

- 13 Chlorophacinone 4

- 13 Diphacinone 3

- 9

Bromethalin 1

- 5

Tables 3

- 17 and 3

- 18 show the accumulation of rodenticide residues in the house mouse and Norway rat, respectively. Rodenticide residues in the house mouse and Norway rat with a diet of
rodenticide bait are above the LD 50 (adjusted) within one day of feeding for the majo rity of the
rodenticides considered here.

Table 3

- 17. Estimated Body Burden Over Time for House Mouse (mg/kg

- bw)*

Day Brodifacoum Difethialone Warfarin (0.025%) Warfarin (0.054%) Chlorophacinone Diphacinone Bromethalin

1 7.9 4.0 39.6 85.5 7.9 7.9 15.8

2 15.8 7. 8 78.7 170.0 15.7 14.9 29.8

3 23.7 11.6 117.5 253.7 23.3 21.0 42.2

4 31.5 15.3 155.8 336.6 30.7 26.5 53.1

5 39.4 18. 9 193.8 418.6 38.1 31.2 62.7

6 47.2 22.4 231.4 499.7 45.2 35.5 71.3

7 55.0 25. 8 268.5 580.0 52.3 39.2 78.8

8 62.8 29.1 305.3 659.5 59.2 42.4 85.4

9 70.6 32.4 341.7 738.2 65.9 45.3 91.3

10 78.3 35 .6 377.8 816.0 72.6 47.9 96.5

11 86.1 38.7 413.4 893.0 79.1 50.1 101.1

12 93.8 41.7 448.7 969.3 85.5 52.1 105.2

13 101.5 4 4.6 483.7 1044.7 91.7 53.8 108.7

14 109.2 47.5 518.2 1119.4 97.8 55.4 111.9

* Highlighted cells indicate range of days where mortalities were observed in acute oral toxicity studies with rats.Page 65 of 183 Table 3

- 18. Estimated Body Burden Over Time for Norway Rat (mg/kg

- bw)*

Day Brodifacoum Difethialone Warfarin (0.025%) Warfarin (0.054%) Chlorophacinone Diphacinone Bromethalin

1 2.1 1.0 10.5 22.6 2.1 2.1 4.2

2 4.2 2.1 20.8 45.0 4.1 3.9 7.9

3 6.3 3.1 31.1 67.2 6.2 5.6 11.2

4 8.3 4.0 41.2 89.1 8.1 7.0 14.1

5 10.4 5.0 51.3 110.8 10.1 8.3 16.6

6 12.5 5.9 61.2 132.3 12.0 9.4 18.9

7 14.6 6.8 71.1 153.5 13.8 10.4 20.9

8 16.6 7.7 80.8 174.6 15.7 11.2 22.6

9 18.7 8.6 90.5 195.4 17.5 12.0 24.2

10 20.7 9.4 100.0 216.0 19.2 12.7 25.5

11 22.8 10.2 109.4 236.4 20.9 13.3 26.8

12 24.8 11.0 118.8 256.6 22.6 13.8 27.8

13 26.9 11 .8 128.0 276.5 24.3 14.3 28.8

14 28.9 12.6 137.2 296.3 25.9 14.7 29.6

* Highlighted cells indicate range of days where mortalities were observed in acute oral toxicity studies with rats.

Tables 3

- 19 and 3

- 20 provide daily ratios of the body burden to the adjusted LD 50 for the house mouse and the Norway rat consuming the rodenticides considered in this white paper. Highlighted cells indicate the range of days were mortalities were observed in acute oral toxici ty studies with rats. For warfarin, estimated doses in target animals are 4x to 204x the LD 50 at days when mortality was observed in the acute oral toxicity study with the rat assuming that bait is continuously being consumed over the duration of the simulation. For brodifacoum, difethialone and bromethalin, estimated doses in target animals ranged from 2x to 82x the LD 50 . For chlorophacinone and diphacinone, estimated doses ranged from 3x to 13x the LD 50 . This analysis indicates that target a nimals continually consuming rodenticide bait may contain doses that are
orders of magnitude above the levels that are sufficient to cause mortality. This is of particular concern for secondary consumers that may prey upon target mammals because they could potentially receive elevated doses of rodenticides.Page 66 of 183 Table 3

- 19. Ratio of estimated body burden to LD 50 for House Mouse*

Day Brodifacoum Difethialone Warfarin (0.025%) Warfarin (0.054%) Chlorophacinone Diphacinone Bromethalin

1 9 4 8 17 1 2 4

2 18 8 15 33 2 4 7

3 27 12 23 50 2 6 10

4 37 15 30 66 3 8 13

5 46 19 38 82 4 9 16

6 55 22 45 97 4 11 18

7 64 26 52 113 5 12 19

8 73 29 60 129 6 13 21

9 82 33 67 144 6 13 23

10 91 36 7 4 159 7 14 24

11 100 39 81 174 8 15 25

12 109 42 88 189 8 16 26

13 118 45 94 204 9 16 27

14 127 48 101 218 9 16 28

* Highlighted cells indicate range of days where mortalities were observed in acute oral toxicity studies with rats.

Table 3

- 20. Ratio of estimated body burden to LD 50 for Norway rat*

Day Brodifacoum Difethialone Warfarin (0.025%) Warfarin (0.054%) Chlorophacinone Diphacinone Bromethalin

1 5 2 4 9 0.4 1 2

2 10 4 9 19 0.9 3 4

3 16 7 13 28 1 4 6

4 21 9 17 37 2 4 7

5 26 11 21 46 2 5 9

6 31 13 26 55 2 6 10

7 36 15 30 64 3 7 11

8 41 17 34 73 3 7 12

9 46 18 38 82 4 8 13

10 52 20 42 90 4 8 14

11 57 22 46 99 4 8 14

12 62 24 50 107 5 9 15

13 67 25 54 116 5 9 15

14 72 27 57 124 5 9 16 *Highlighted cells indicate range of days where mortalities were observed in acute oral toxicity studies with rats.Page 67 of 183 Available residue data for the anticoagulant rodenticides indicate that, regardless of the rodenticide used, they accumulate in animal tissues when continuously exposed to rodenticide
bait. While warfarin has the potential to accumulate 4

- 17X the LD 50 for rats within one day of feeding on bait, onset of death was also shown to occur within one day in the gavage study, which may limit the ability of prey organisms to accumulate a dose lethal to avian and mammalian predators/scavengers. The remaining rodenti cides caused death within 2

- 3 days after dosing in the acute oral studies. Of these, chlorophacinone is expected to accumulate the least, followed by diphacinone, bromethalin, difethialone, and brodifacoum. Difethialone is expected to accumulate at least 9

- 42X the LD 50 for mammals, while brodifacoum is expected to
accumulate at least 21

- 82X the LD 50 for mammals before death.

T he information available from the accumulation of dose in primary consumers calculated in this section indicate that, of the anti coagulants, brodifacoum and difethialone accumulate in body tissues to a greater extent than warfarin, chlorophacinone, and diphacinone. For bromethalin, dose accumulation calculations using a blood half

- life of 5.6 days indicate that this chemical has

po tential to accumulate in body tissues 4

- 16X the LD 50 ; however, death is expected to occur within five days of exposure, reducing the availability of contaminated animals for secondary

consumers. In addition, a recent study by Pitt et al. (2011) found that time to death for house mice, Polynesian rats ( Rattus exulans ) and black rats ( Rattus rattus ) offered bromethalin may be more rapid than suggested in registrant submitted data for the Norway rat, which may reduce the potential for bromethalin to accumulate in some prey organisms. Data from this study also suggest that house mice and Polynesian rats exposed to bromethalin bait may stop feeding on the bait after reaching a lethal dose, further reducing the potential for accumulation.



### 3.4 Measured Rodenticide Res idues

As discussed in the estimated accumulation of dose section above, the potential to accumulate rodenticides within body tissues may contribute substantially to the risks of these compounds. Measured residue values from various field and laboratory studies p rovide useful information on the potential for each of these rodenticides to accumulate in body tissues under field conditions. In addition, these data allow a means to test the assumptions employed in the theoretical analysis by comparing estimated and em pirical concentrations of the rodenticides in mammals.

Most of the available measured data on concentration of anticoagulants in rodents is from studies that involved a single, sublethal oral dose. One uncertainty in using these data is that they may
und er represent the uptake of an anticoagulant by a rodent because rats and mice entering a baiting station will not die for several days or more after ingesting a lethal dose and may continue consuming bait. For example, a wild Norway rat feeding only on bro difacoum bait may ingest a dose that is equivalent to 80x the LD 50 (ICI Americas, Inc. 1978b). In a study where treated and untreated baits were available to rats, they still ingested doses of brodifacoum thatPage 68 of 183 were 40x the LD 50 (ICI Americas, Inc. 1978b). In a situation of repeat exposure for several days or more, anticoagulants may circulate in the blood at higher levels and for a longer time than suggested by studies in which a single, sublethal dose was administered (Belleville 1981).

Data are availab le for a variety of small and medium sized mammalian granivores and omnivores exposed to brodifacoum, difethialone, and warfarin. No data were identified for bromethalin or other exposed taxonomic groups ( e.g., birds, reptiles, and invertebrates). For all studies, it was assumed by the Agency the concentrations were reported by the study authors as wet weights of
the mammals. Information on whole

- body residues in target species exposed to the rodenticides considered in this assessment is provided in Table 3

- 21

.

In studies with brodifacoum, mean concentrations ranged from 0.35 to 8.63 mg a.i./kg

- bw, while individual brodifacoum concentrations ranged from 0.1 to 25.97 mg a.i./kg

- bw. Two residue
studies indicate that the amount of whole

- body residue in the t arget species may be related to the amount of active ingredient in the bait. Kaukeinen (1982) provides mean tissue residue levels in voles exposed to brodifacoum bait in the laboratory. Separate groups of males and females were exposed for 4 days to 50 mg a.i./kg bait or 10 mg a.i./kg bait. Residues were 5.21 mg a.i./kg and 2.17 mg a.i./kg for males and females, respectively, exposed to 50 mg a.i./kg bait but only 0.53 mg a.i./kg and 0.40 mg a.i./kg for males and females exposed to 10 mg a.i./kg bait. In fi eld trials for vole control in orchards, Merson et al. (1984) collected voles 1 to 7 days after bait application. Two collections of voles exposed to 50 mg a.i./kg bait had mean whole

- body residues of 2.07 mg a.i./kg and 4.07 mg a.i./kg, whereas those expo sed to 10 mg a.i./kg bait had a mean residue level of 0.35 mg a.i./kg. For those studies that used bait currently registered bait concentrations, measured residue values are similar to the estimated body burden in rats after feeding on brodifacoum bait for 1 to 14 days (2.1 to 28.9 mg a.i/kg

- bw; Table 3

- 18 ).

When considering two studies available for difethialone, mean concentrations ranged from 2.0 to 3.1 mg a.i./kg

- bw, while individual difethialone concentrations ranged from 0.77 to 2.67 mg a.i./kg

- bw. S avorie (2005) assessed the accumulation of formulated difethialone pellets in male albino rat carcasses using two different feeding studies. In the first scenario, animals were offered bait for 3 days and then euthanized. In the second scenario, animals we re offered bait until poisoning death occurred (usually between 4 and 7 days). Rats that were euthanized on day 3 had a mean residue of difethialone in the body of 2.8 mg a.i./kg

- carcass. Rats that were fed continuously with the same diet had a mean time of death of 5.2 days (range of 4

- 7 days) and the mean difethialone residue was 3.1 mg a.i./kg

- carcass. These residue values are similar to the estimated body burden in rats after feeding on difethialone bait for 3 to 5 days (3.1 to 5.0 mg a.i./kg

- bw).

Mean warfarin concentration from six studies ranged from 0.038 to 104 mg a.i./kg

- bw, individual concentrations were not reported. The highest mean residue values in this range comePage 69 of 183 from a study by Aulerich et al. (1987) where rabbits were fed low concentra tion warfarin bait (52 or 67 mg a.i./kg bait) for 35 days, resulting in residue values of 82 and 104 mg a.i./kg

- bw, respectively. This may indicate that mammals consuming small amounts of warfarin bait over an extended period of time may survive poisoning. This study may suggest that mammals have the potential to accumulate many times the lethal dose of warfarin. If these low bait concentrations were used to estimate accumulation of dose as above, the calculated doses in Norway rats after 35 days are simila r to the measured values in rabbits (64.3 and 82.8 mg a.i./kg

- bw for the 52 and 67 mg a.i./kg

- bait, respectively); however, the weight of the rabbits used in this study were roughly an order of magnitude larger than the Norway rat. Since registered warfari n baits contain 0.025% a.i. (250 mg a.i/kg

- bait) or 0.054% a.i. (540 mg a.i./kg

- bait), the low dose values found in the majority of the residue studies may not reflect true field conditions.

Mean chlorophacinone concentrations ranged from 0.122 to 1.58 m g a.i./kg

- bw, with individual concentrations ranging from the limit of detection to 4.1 mg a.i./kg

- bw. Most of these studies assessed the efficacy of field application of chlorophacinone bait at the registered concentrations of either 0.005% a.i. (50 mg a. i./kg

- bait) or 0.01% (100 mg a.i./kg

- bait) to treat ground squirrel or vole populations in California. Since the majority of these studies are field based, the number of days that prey organisms were exposed to the bait is unknown; however, estimated resid ue values for the Norway rat, which approximates the weight of the ground squirrels tested, are similar to measured residues (2.1 mg a.i./kg

- bw for 1 day accumulation and 4.1 mg a.i./kg

- bw for 2 day accumulation).

Mean diphacinone concentration ranged fr om 0.9 to 1.4 mg a.i./kg

- bw. Individual concentrations ranged from 0.48 to 3.4 mg a.i./kg

- bw. Similar to chlorophacinone, most of these studies assessed the efficacy of field application of chlorophacinone bait at the registered concentrations
of either 0. 005% a.i. (50 mg a.i./kg

- bait) or 0.01% (100 mg a.i./kg

- bait) to treat ground squirrel populations in California. Since the majority of these studies are field based, the number of days that prey organisms were exposed to the bait is unknown; however, esti mated residue values for the Norway rat, which approximates the weight of the ground squirrels tested, are similar to measured residues (2.1 mg a.i./kg

- bw for 1 day accumulation and 3.9 mg a.i./kg

- bw for 2 day accumulation).

Comparisons of measured and ca lculated residues in rodents showed general agreement for the rodenticides considered in the assessment, with the exception of warfarin. This indicates that the conservative assumptions used in the accumulation of dose analyses did not impact overall risk
characterization.Page 70 of 183 Table 3

- 21. Residue Levels of Anticoagulant Rodenticides in Primary Consumers

Rodenticide Mg a.i./kg bait Target species Site Sample size Days exposed Mean whole

- carcass residue in mg a.i /kg

- carcass (range) Reference

Brodifacoum 50 Rat Field 50 Unknown Most < 7 Some up to 11

- 13 Kaukeinen 1993 a

Brodifacoum 50 Rat Field 6 Unknown 2.7 (0.1

- 6.6) ICI America 1979c

Brodifacoum 50 Rat Field 5 male
4 female 3 juvenile Unknown 7.08 (3.92

- 9.17) 5.61 (1.39

- 12.19)
8.63 (1.77

- 25.97) Howald 1997

Brodifacoum 50 Vole Field 74 1

- 7 4.07 ± 0.20 (SE) Merson et al. 1984

Brodifacoum 50 Vole Field 62 1

- 7 2.07 ± 0.17 (SE) Merson et al. 1984

Brodifacoum 50 Vole Lab 15 male
15 female 4

4 5.21 ± 2.06 (sd) 2.17 ± 1.17 (sd) Kaukeinen 1982

Brodifacoum 25 b Deer mouse Field 10 4

- 9 2.71 (0.68

- 4.25) Howald et al. 2001

Brodifacoum 20 b Mouse Lab nr 3 2.21 Anonymous 1981 a

Brodifacoum 20 b Mouse Lab 10 1 0.44 Newton et al. 1990

Brodifacoum 10 b Vole Lab 15 male
15 female 4

4 0.53 ± 0.24 (sd) 0.40 ± 0.20 (sd) Kaukeinen 1982

Brodifacoum 10 b Vole Field 43 1

- 7 0.35 ± 0.03 (SE) Merson et al. 1984

Difethialone 25 Rat Lab 20 3 2.0 ± 0.51 (sd) (0.77

- 2.67) Goldade et al. 2001

Difethialone 23.94 Rat Lab 10
10 3

4

- 7 2.8 (2.1

- 3.3) 3.1 (1.9

- 4.3) Savarie 2005
MRID# 46656501

Warfarin 200 c Mouse Lab 17 3 2.95 ± 0.26 (SE) Townsend et al. 1984

Warfarin 67 c Rabbit Lab nr 35 104 Aulerich et al. 1987 (E39689)

Warfarin 50 c Mouse Lab 62 3 1.63 ± 0.1 (SE) Townsend et al. 1981 (J004518/E54919)

Warfarin 50 c Mouse Lab 18 3 1.58 ± 0.1 (SE) Townsend et al. 1984Page 71 of 183 Warfarin 52 c Rabbit Lab nr 35 82 Aulerich et al. 1987 (E39689)

Warfarin 10 c Mouse Lab 15 3 0.42 ± 0.04 (SE) Townsend et al. 1984
Chlorophacin

one 100 Ground squirrel Field 10 unknown 1.27 ± 0.56 (sd) (0.237

– 2.24) Baroch 1996
MRID# 43922201 Chlorophacin

one 50 Ground squirrel Field 10 unknown 0.52 ± 0.31(sd) (0.244

– 1.29) Chlorophacin

one 50 Ground squirrel Field 10 unknown 0.57 ± 0.27 (sd) (0.123

– 0.896) Baroch 1996
MRID# 43922202

Chlorophacin

one 100 Ground squirrel Field 38 unknown 6 carcasses: <LOD=0.025
32 carcasses: 0.159 ± 0.141(sd)

(0.025

– 0.546) Ramey et al. 2007
Primus et al. 2001 (E 0165)

Chlorophacin

one 50 Ground squirrel Field 16 1

- 15 0.122 (<LOD, 0.265) Primus et al. 2001 (E 0165) Matschke, 1999 Chlorophacin

one 50 Microtus sp. vole Field 3 1

- 15 1.58 (0.26

- 4.1)

Chlorophacin

one 50 and 100 Valley pocket gopher Field 8 1

- 13 0.357 (<LOD, 1.21) Primus et al. 2001 (E 0165 )
Stewart et al 2000 Chlorophacin

one 50 Ground squirrel Field 21 2

- 15 0.28 (0.02

– 0.71) Salmon et al 2002
MRID# 45855101
Goodall et al. 2002

MRID# 46117303 Chlorophacin

one 100 Ground squirrel Field 16 2

- 15 1.41 (0.30

– 2.72) Chlorophacin

one 50 Ground squirrel Field 16 2

- 15 0.26 (<LOD, 1.01) Chlorophacin

one 100 Ground squirrel Field 20 2

- 15 0.51 (<LOD

– 1.31)

Chlorophacin

one 50 Black t ai led

pr ai rie dogs (8)

and one

cottont ai l rabbit Field 9 2

- 15 0.58 (0.01, 1.25) MRIDs 47333602,
47333603 and

48294401Page 72 of 183 Chlorophacin

one NA Black

- t ai led

pr ai rie dog Field 8 unknown 1.48 (0.85, 2.24)
Chlorophacin

one 50 Laboratory rat Field 5 5 0.47 (0.21

- 0.93) Baroch 1997

MRID# 44631402 Chlorophacin

one 50 Laboratory rat Lab 4 5 0.45 (0.18

- 0.81) Ahmed et al. 1996

MRID# 44631401

Diphacinone 50 Ground squirrel Field 10 unknown 1.4 (0.6

- 3.4) Baroch 1994a
MRID# 43534601

Diphacinone 50 Ground squirrel Field 7 unknown 0.9 (0.48

- 1.89) Baroch 1994b
MRID# 43534602

Diphacinone 100 Ground squirrel Field 10 unknown 1.4 (0.6

- 2.6) Baroch 1994a
MRID# 43534601

Diphacinone 50 and 100 d Ground squirrel Field 76 unknown 0.98 Goodall et al. 2002
MRID# 46117303 nr = not reported
NA = not available

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

b baits registered in the U.S. are 0.005% a.i.

c baits registered in the U.S. are 0.025% a.i.

d the study did not allow for distinguishing among squirrels exposed to 50 mg a.i./kg and 100 mg a.i./kg b ai tsPage 73 of 183 

## 4 Primary Exposure and Risk

For the purpose of this assessment, primary exposure is defined as exposure to primary consumers ( i.e., those species likely to directly eat bait). Primary risk is influenced by factors including toxicity

, toxicokinetics (chemical accumulation and elimination in the body), concentration of active ingredient in the bait, and availability of bait for consumption. For each of the evaluated chemicals, risk is assessed in several ways:

**•** single day dose

- based exposure to bait based on allometric equations that allow fo r differentiation among taxa, feeding rates, and body size is compared to acute oral LD 50 toxicity values;

**•** six day dose

- based exposure to bait based on metabolism rate in the body and allometric equations that allow for differentiation among taxa, feeding guild, and body size is compared to acute oral LD 50 toxicity values; and

**•** Dietary exposure (concentration of chemical active ingredient in bait) is compared to acute dietary LC 50 values. Further lines of evidence include an analysis of the number of days of bait consumption required
to reach the median lethal dose of rodenticide and the grams of bait individuals would need to

c onsume in order to accumulate the median lethal dose.



### 4.1 Risks based on the Acute Oral LD 50

4.1.1 Calculation of Dose

- base d Ingestion Rates for Birds and Mammals

For the dose

- based exposure method, exposure is calculated as mg a.i./kg

- bwt, where kg

- bwt is the kilograms of the individual consuming bait for three standard weight classes of birds and mammals. Exposure (food dry weight consumption) estimates were derived using allometric equations based on body weight (USEPA 1993). For these primary consumers of rodenticide bait, the default weight classes of birds are small (20 g), medium (100 g), and large (1000 g), and
the def ault weight classes for mammals are small (15 g), medium (35 g), and large (1000 g). These are the standard bird and mammal body weights used in EFED risk assessments ( T

- REX
documentation , version 1.4.1, December 2008) . Allometric equations were used for t he generic bird and mammal. In addition, allometric equati ons for passeriform birds and rodent mammals
were also used as these would best approximate those individuals with high potential for consuming bait and they would give the most conservative exposur e estimates.

Animal exposure was determined based on daily food intake rates (dry weight), assuming 100%
of their diet consisted of bait

, and the bait contained no water. With the exception of onePage 74 of 183 warfarin label (EPA Reg. No. 3282

- 3), all baits are waxy

- type blocks, pellets, bait bits, paste, or
meal ; water content in these bait types was assumed to be very low. For EPA Reg. No. 3282

- 3

, the product is in powder form and is to be mixed into the users own bait matrix. Water content
for end mixture to w hich animals are exposed will vary, but for consistency in this analysis it was assumed that the water content was insignificant. Also, i t was assumed that the form of the
bait (block, pellets, bits, etc .) would not influence rate of intake or total intake. Formulas for calculation of dose estimates are provided in Box 4

- 1 , and the resulting oral consumption (dose) estimates based on one day of feeding exclusively on bait are listed in Table 4

- 1 . Intake rates
base d on the generic bird and mammal allometric equations can be found in Appendix B . All
three evaluated size classes of Passeriformes will consume more food, and, thus, consume more
rodenticide th a n the equivalent weight class of the generic bird based on th e allometric equations. Based on the allometric equations, small rodents (15 g) have higher food intake rates than small generic mammals, medium sized rodents (35 g) have food intake rates similar to
medium

- sized generic mammals, and large rodents (1000 g) have lower food intake rates than large generic mammals.

Risk estimations based on passerines and generic birds are similar; therefore; only the numeric quantities associated with passerines will be presented in the text. All intake rates and RQ
calcula tions for both passerines and generic birds are presented in Appendix B . Similarities and differences in risk conclusions will be discussed in the main text. A similar approach is used for the rodents and generic mammal risk estimation.

Box 4

- 1. Formulas for Calculation of Rodenticide Intake (mg a.i./kg

- bwt) based on Consumption of Bait.

Passeriform bird food intake (g, dry weight ): FI (g dry

- wt/day) = 0.398 * Wt(g) 0.850

Generic bird food intake (g, dry weight): FI (g dry

- wt/day) = 0.648 * Wt(g) 0.651

Rodent mammal food intake (g, dry weight ): FI (g dry

- wt/day) = 0.621 * Wt(g) 0.564

Generic mammal food intake (g, dry weight ): FI (g dry

- wt/day) = 0.235 * Wt(g) 0.822

Active ingredient intake (mg a.i./kg

- bwt/day) = FI (g dry

- wt/day) * C mg a.i./kg

- bait / (Wt(g)/1000)

Where: Wt(g) = weight (in grams) of the bird or mammal consumer C(mg a.i./kg

- bait) = concentration of rodenticide in baitPage 75 of 183 Table 4

- 1 Estimated rodenticide daily intake rates for passeriforms and rodents (mg a.i./kg

- bwt)

Passeriforms Rodents 20 g 100 g 1000 g 15 g 35 g 1000 g

Brodifacoum 13 10 7.1 10 6.6 1.5

Difethialone 6.4 5.0 3.5 4.8 3.3 0.8 Warfarin (0.025%) 63 50 35 48 33 7.6 Warfarin (0.054%) 137 108 76 103 71 17 Chlorophacinone 13 10 7.1 10 6.6 1.5 Diphacinone 13 10 7.1 10 6.6 1.5

Bromethalin 25 20 14 19 13 3.1

4.1.2 Calculation of Weight

- Adjusted LD 50 s for Birds and Mammals

Weight

- adjusted LD 50 values for birds and mammals were used to calculate risk quotients

. S caling factors derived from Mineau et al . (1996) for birds are used in this assessment, just as is
done in T

- REX v.1.4.1. A chemical

- specific scaling factor was available for brodifacoum (0.76)
from Mineau et al . (1996)

, and for all other chemicals, the default scaling factor (1.15) was used to adjust the avian LD 50 s. Using additional data, Mineau et al . (2001) provided an alternative scaling factor for brodifaco um (0.88) and a chemical

- specific scaling factor for chlorophacinone (

- 0.53). Mammalian weight

- adjusted LD 50 values were calculated using the “body weight 3⁄4 ”

a djustment (USEPA 1995, 2011). Formulas for calculating the adjusted LD 50 s for birds and
mammals a re presented in Box 4

- 2

. Avian LD 50 s adjusted using the scaling factors presented in Mineau et al. (1996) and mammalian LD 50 s adjusted using the standard scaling factor are provided in Table 4

- 3 . All adjusted LD 50 s (including those calculated using scali ng factors presented in Mineau et al . (2001)) are provided in Appendix B

.Page 76 of 183 Box 4

- 2. Formulas for Calculation of Weight

- adjusted Avian and Mammalian LD 50 s.

Adjusted avian LD 50 : Adj LD LD AW

TW x

. ( )

50 50 1

**= **  ** **  ** **  ** −**  where:

Adj. LD 50 = adjusted LD 50 (mg/kg

- bw)

LD 50 = endpoint reported from bird study (mg/kg

- bw)

TW = body weight of tested animal *

AW = body weight of assessed animal (20g, 100g, and 1000g)

x = scaling factor for birds**

Adjusted mammalian LD 50 : **( )**  25

. 0

50 50 . ** **  ** **  ** ** 

**=** AW TW LD LD Adj where:

Adj. LD 50 = adjusted LD 50 (mg/kg

- bw)

LD 50 = endpoint reported from mammal study (mg/kg

- bw)

TW = body weight of tested animal ***

AW = body weight of assessed animal (15g, 35g, 1000g)

*Average body weight of birds on day 0 of study, if not available, the default values of 1580g (mallard) or 178g (bobwhite) are used. ** Scaling factors: EFED default 1.15 (Mineau et al., 1996)

, Brodifacoum 0.76 (Mineau et al., 1996)

, B rodifacoum 0.88 (Mineau et al., 2001) , Chlorophacinone

- 0 .53 (Mineau et al., 2001)

** * Average body weight of rats on day 0 of study, if not available, the default value of 350 g is used.

Table 4

- 2. LD 50 values (mg a.i./kg

- bwt): unadjusted and adjusted based on asses sed animal weight

Birds 1 Mammals 2
Unadjusted 20 g 100 g 1000 g Unadjusted 15 g 35 g 1000 g

Brodifacoum 0.25 0.65 0.44 0.25 0.48 0.96 0.78 0.34

Difethialone 0.30 0.21 0.27 0.38 0.56 1.11 0.90 0.39

Warfarin 525 273 347 490 3.0 5.7 4.6 2.0 Chlorophac

inone 258 182 232 328 6.26 11.6 9.4 4.1

Diphacinone 1630 1163 1480 2091 1.9 4.8 3.9 1.7

Bromethalin 4.6 3.27 4.16 5.88 2.2 3.7 3.0 1.3

1 LD 50 values were adjusted using scaling factors presented in Mineau et al . (1996).

2 LD 50 values were adjusted using the default mammalian scaling factor.

4.1.3 Avian risks based on acute oral LD 50 toxicity

RQs are calculated by dividing the daily rodenticide a.i. intake ( Table 4

- 1 ) from each weight class by the weight

- adjusted LD 50 ( Table 4

- 2 ). Details of these calculations are presented inPage 77 of 183 Appendix B . RQs for three weight classes of passerines are provided in Table 4

- 3

. For brodifacoum and difethialone, all RQs exceeded the ac ute risk LOC (RQs range from 9 to 30).
For warfarin bait containing 0.025% a.i, the acute risk LOC was not exceeded for any weight class. For warfarin bait containing 0.054 % a.i, the acute risk LOC was exceeded for small passerines (RQ = 0.50). For chlorophacinone and diphacinone, no RQs exceeded the acute risk LOC (RQs r ange from <0.01 to 0.07). All bromethalin RQs exceeded the ac ute risk LOC (RQs range from 2.4 to 7.8).

As indicated previously, mortality due to rodenticide consumption may not occur until several days after initial exposure

. A useful characterization for comparing risks among the chemicals considered in this white paper is to calculate how long it would take an individual to consume
the quantity of bait needed to reach the LD 50 based on the estimated daily food intake ( Box 4

- 1
and Table 4

- 1 ) and chemical

- specific elimination rates ( Section 3. 3.2 )

. Exposure was determined based on daily food intake rates (dry weight) for passerines , assuming 100% of their
diet consisted of dry bait. It was assumed that the form of the bait would not influence inta ke. Based on the assumed weights , the percent of a.i. in the bait, and daily food intake, the concentration within the animal at the end of a day’s feeding was determined. As discussed in
Section 3.2

, a f irst

- order exponential decay model was used to esti mate daily elimination of the evaluated chemicals from the body. For all anticoagulants, daily residual body burdens were estimated using liver half

- lives. For bromethalin, daily residual body burden was estimated using blood plasma half

- life, as no liver half

- life data were available. The day (or 24

- hr interval) during which the LD 50 (mg a.i./kg

- bwt) was reached is provided for
each chemical in Table 4

- 3

.

For brodifacoum, difethialone, and bromethalin, less than one day of feeding on bait would
enable t he individual passerine to consume sufficient material to reach the LD 50 . For warfarin, days to reach the LD 50 depended on body weight and bait concentration. The range was from 1

- 2 days for small passerines consuming 0.054% warfarin bait to 14

- 16 days for large passerines consuming 0.025% warfarin bait. As chlorophacinone is less toxic than many of the other evaluated chemicals, more consumption days were needed to reach the LD 50 (from 16

- 17 days for small passerines to 117

- 118 days for large passerines). For diphacinone, the LD 50 was not reached when body burden was calculated after 365 days of bait consumption, as diphacinone is less toxic and has faster elimination rates than the other evaluated chemicals. Furthermore, after approximately one month, ther e was little change in the total body burden (mg diphacinone/kg

bwt) as the asymptote for body burden was reached ( Table 4

- 3 ).

A second characterization useful for comparing risks among rodenticides considered in this white paper is mass of bait required to be consumed for an individual to reach the LD 50 as a body burden concentration ( Table 4

- 3 ). For chemicals estimated to require less than one day of bait

cons umption to reach the LD 50 , bait consumption was estimated as:Page 78 of 183 Weight

- adjusted LD 50 (mg a.i /kg

- bwt) * weight of assessed bird (g) / a.i. concentration (mg a.i./kg

- bait)

.

For chemicals estimated to require more than one day of bait consumption to reach th e LD 50 , bait consumption was estimated based on the upper bound of the estimated days of consumption:

Days of consumption * 0.398 * weight of assessed bird (g) 0.85

.

For brodifacoum, difethialone, and bromethalin, a small amount of bait relative to body weight of the individual would be required to reach the LD 50 . Across all labels, the maximum grams of bait per placement that can be used are 454 g bait/placement for brodifacoum and difethialone and 170 g bait/placement for bromethalin ( Table 2

- 4 ). Therefore, it is possible for passerines to consume sufficient bait at one placement to reach the median lethal dose for these chemicals.

For small and medium sized passerines consuming warfarin bait, sufficient bait would be available at one placement (s ome labels allow for a maximum of 454 g warfarin bait/placement) for an individual to consume the median lethal dose. The largest passerines would require multiple days of bait from multiple stations to reach the median lethal dose.

For passerines consumi ng chlorophacinone or diphacinone bait, consumption would need to occur at multiple placements for multiple days for the median lethal dose to be reached. Maximum placement size for chlorophacinone is 20 g bait/placement, and maximum placement size for dip hacinone is 199 g bait/placement.

Table 4

- 3 RQs for Passeriforms Based on Consumption of Bait and Days to Consume an

LD 50 - dose

RQ 1 Days to consume sufficient bait to

reach the LD 50 Bait (g) to consume to

reach the LD 50 20 g 100 g 1000 g 20 g 100 g 1000 g 20 g 100 g 1000 g

Brodifacoum 19.61* 22.67* 27.89* <1 <1 <1 0.3 0.9 5.1

Difethialone 29.80* 18.39* 9.22* <1 <1 <1 0.2 1.1 15 Warfarin (0.025%) 0.23 0.14 0.07 4

- 5 7

- 8 14

- 15 25 160 2100 Warfarin (0.054%) 0.50* 0.31 0.16 1

- 2 3

- 4 6

- 7 10 80 990 Chlorophacinone 0.07 0.04 0.02 16

- 17 30

- 31 117

- 118 86 620 17000 Diphacinone 0.01 0.01 <0.01 >365 >365 >365 >1800 >7300 >52000

Bromethalin 7.76* 4.76* 2.40* <1 <1 <1 0.7 4.2 59

1 * RQ exceeds Acute Risk LOC.

Finally, body burden and associated RQs were calculated with the assumption that bait was consumed exclusively for six days. Estimated daily food intake ( Box 4

- 1 and Table 4

- 1 ) and
chemical

- specific elimination rates ( Section 3. 3.2 ) were used to determine 6

- day accumulation concentrations (mg a.i./kg

- bwt) ( Table 4

- 4 ). RQs are calculated by dividing the cumulative
rodenticide a.i. from each weight class by the weight

- adjusted LD 50 ( Table 4

- 2 ). Details of thesePage 79 of 183 calculations are presented in Appendix B . RQs for three weight classes of passerines a re provided in Table 4

- 4

.

For brodifacoum and difethialone, all RQs exceeded the ac ute risk LOC (RQs range from 20 to
76 ). For warfarin baits containing 0.025% a.i, the acute risk LOC was exceeded for small and medium sized passerines (RQ = 1.36 and 0.84 , respectively). For warfarin baits containing
0.054 % a.i, the acute risk LOC was exceeded for all size classes of passerines (RQs range from 0.91 to 2.94). For chlorophacinone and diphacinone, no RQs exceeded the acute risk LOC (RQs range from 0.01 to 0.4 0). RQs assuming six days of feeding on bait were not calculated for bromethalin as exposed animals are not expected to continue feeding on bait for six days after initial exposure.

After adjusting exposure to six days of exclusive feeding and accounting for metabolism through
the use of estimated half

- lives, LOC exceedance conclusions are the same for all evaluated anticoagulants except warfarin. Assuming a one

- day or a six

- day exposure period, acute risk
LOCs were exceeded for brodifacoum and difethialo ne, and acute risk LOCs were not exceeded for chlorophacinone and diphacinone. When accumulation of warfarin over a 6

- day exposure interval is calculated, RQs for all bait concentrations and bird sizes except for large passerines consuming 0.025% a.i. bait exceeded the acute risk LOC. This indicates a change in the risk picture for warfarin when bait exposure and consumption is extended over time.

Table 4

- 4 Accumulation of rodenticide (mg a.i./kg

- bwt) after 6 days of consumption and associated RQs for pas seriforms
Six day accumulation (mg a.i./kg

- bwt) RQ 1

20 g 100 g 1000 g 20 g 100 g 1000 g

Brodifacoum 76 60 42 117* 135* 166*

Difethialone 36 28 20 168* 104* 52* Warfarin (0.025%) 371 292 206 1.36* 0.84* 0.42 Warfarin (0.054%) 802 630 446 2.94* 1.81* 0.91* Chlorophacinone 73 57 40 0.40 0.25 0.12 Diphacinone 56 44 31 0.05 0.03 0.01

Bromethalin 112 88 62 NA 2 NA NA

1 * RQ exceeds Acute Risk LOC.

2 NA

- not applicable. Animals consuming bromethalin are not expected to continue feeding on bromethalin bait for six days.

The one

- day

- exposure RQs, days of bait consumption to reach the LD 50 , and six

- day

- exposure RQs for generic birds are listed in Appen dix B . In addition to the RQs and bait consumption rates for the generic birds; alternative RQ and bait consumption analyses were conducted using the unadjusted LD 50 s and the brodifacoum and chlorophacinone LD 50 s adjusted following
Mineau et al . (2001) for both passerine and generic birds ( Appendix B ). Although the resultingPage 80 of 183 RQs values were different, these alternative analyses yielded the same LOC exceed a nces as for the passeriform birds consuming bait using the adjusted LD 50 s following Mineau et al

. (1996) with a few exceptions. For the 0.054% warfarin bait, the one

- day

- exposure RQ for small passerines using the adjusted LD 50 exceeded the LOC (RQ=0.50); however, the RQ for small generic birds using the adjusted LD 50 and the RQs for both small passerin es and small generic birds using the unadjusted LD 50 did not exceed the LOC (RQs = 0.26, 0.16, and 0.15, respectively).

With the exception of chlorophacinone and diphacinone, the following conclusions can be made for birds in a generic class and for alternative LD 50 adjustments. When days of bait consumption
to reach the LD 50 were compared between passerine and generic birds of the same weight class or between adjusted and unadjusted LD 50 s of the same weight class, most differences were less
than thre e days. When grams of bait consumed to reach the LD 50 were compared between passerine and generic birds of the same weight class or between adjusted and unadjusted LD 50 s of the same weight class, most differences were small relative to the total amount of bait that
needed to be consumed.

Chlorophacinone is less acutely toxic to birds and the concentration of the a.i. in the bait is low; therefore, more time is needed for individual birds to consume a median lethal dose. In addition,
the elimination half

- l ife is relatively short (35 days), thus further increasing the time to reach the median lethal dose. The chlorophacinone

- specific scaling factor (Mineau et al . 2001) was based on data from six avian species with a median LD 50 of 25.45, indicating the speci es used for development of the scaling factor were more sensitive to chlorophacinone than the bobwhite quail data available to the USEPA (LD 50 = 258 mg a.i./kg

- bwt, MRID 41513101 )

. In addition,
the data used in Mineau et al . (2001) indicated that chloropha cinone sensitivity increased as bird weight increased, which is counter to the sensitivity trend across all chemicals as presented by
Mineau et al . (2001).

As with chlorophacinone, diphacinone is also less acutely toxic to birds and the concentration of
the a.i. in the bait is low. The elimination half

- life was very short (5.5 days). Based on estimated feeding rates, even if birds were to exclusively feed on diphacinone bait for a year, the median
lethal dose would still not be attained.

4.1.4 Mammalian risks based on acute oral LD 50 toxicity

RQs were calculated by dividing the rodenticide a.i. intake ( Table 4

- 1 ) from each weight class by the weight

- adjusted LD 50 ( Table 4

- 2 ). Details of these calculations are presented in Appendix B . RQs for three weight classes of rodents are provided in Table 4

- 5 . For all evaluated chemicals except chlorophacinone, the acute risk LOC was exceeded (exceeding RQs ranged from 0.70 to 18.05) for all three weight classes. For chlorophacinone, RQs for small andPage 81 of 183 medium rodents (0.82 and 0.70, respectively) exceeded the acute risk LOC; however, the RQ for large rodents (0.38) did not exceed the acute risk LOC.

As indicated previously, mortality due to rodenticide consumption may not occur until several days after initial exposure

. A characterization useful for comparing risks among the chemicals is
to calculate how long (days ) it would take an individual to consume the quantity of bait needed
to reach the LD 50 based on the estimated daily food intake ( Box 4

- 1 and Table 4

- 1 ) and
chemical

- specific elimination rates ( Section 4. 3.2 )

. Exposure was determined based on daily food intake rates (dry weight) for rodents , assuming 100% of their diet consisted of bait and the
bait contained no water. It was assumed that the form of the bait would not influence intake. Based on the assumed weights , the percent of a.i. in the bait, and daily food intake, the
concentration within the animal at the end of a day’s feeding was determined. As discussed in
Section 3.2 .2

, a f irst

- order exponential decay model was used to estimate daily elimination of the evaluated chemicals from the body. For all anticoagulants, daily residual body burdens were
estimated using liver half

- lives. For bromethalin, daily residual body burden was estimated using blood plasma half

- life, as no liver half

- life data were available. The day (or interval) during
which the LD 50 (mg a.i./kg

- bwt) was reached is provided for each chemica l in Table 4

- 5

.

For all evaluated chemicals except for chlorophacinone, less than one day of feeding on bait
would enable the individual to consume sufficient material to reach the LD 50 . For chlorophacinone, days to reach the LD 50 ranged from one to thre e days depending on body weight. Comparing consumption time across chemicals and within weight class for the rodents provides an indication of the relative risk based on differing acute toxicities and concentration of
a.i. in the bait. For all evaluated ro denticides, there was little difference in days to reach the LD 50 via bait consumption.

A second characterization useful for comparing risks among rodenticides considered in this white paper is mass of bait required to be consumed for an individual to rea ch the LD 50 as a body burden concentration ( Table 4

- 5 ). For chemicals estimated to require less than one day of bait consumption to reach the LD 50 , bait consumption was estimated as:

Weight

- adjusted LD 50 (mg a.i /kg

- bwt) * assessed mammal weight (g) / a.i. concentration (mg a.i./kg

- bait)

.

For chemicals estimated to require more than one day of bait consumption to reach the LD 50 , bait consumption was estimated based on the upper bound of the estimated days of consumption:

Days of consumption * 0.621 * weight of assessed mammal (g) 0.564

.

For all chemicals except chlorophacinone, maximum placement sizes ( Table 2

- 4 ) are sufficient to enable rodents to consume sufficient bait to reach the median lethal dose from one placement. For chlorophacinone, small and medium sized rodents could consume sufficient bait to reach thePage 82 of 183 median lethal dose from one placement, while large rodents would require feedings from multiple placements.

Table 4

- 5 RQs for Rodents Based on Consumption of Bait and Days to Cons ume an LD 50 - dose

RQ 1 Days to consume sufficient bait

to reach the LD 50 Bait (g) to consume to

reach the LD 50 15 g 35 g 1000 g 15 g 35 g 1000 g 15 g 35 g 1000 g

Brodifacoum 9.93 * 8.48 * 4.55 * <1 <1 <1 0.3 0.5 6.7

Difethialone 4.30 * 3.67 * 1.97 * <1 <1 <1 0.7 1.3 16
Warfarin (0.025%) 8.36 * 7.14* 3.83* <1 <1 <1 0.3 0.7 8.0
Warfarin (0.054%) 18.05 * 15.42* 8.27* <1 <1 <1 0.2 0.3 3.7 Chlorophacinone 0.82 * 0.70* 0.38 1

- 2 1

- 2 2

- 3 6 9 61 Diphacinone 2.63* 2.24* 1.20* <1 <1 <1 1.1 2.1 25

Bromethalin 5.12* 4.38* 2.35* <1 <1 <1 0.6 1.1 13

1 * RQ exceeds Acute Risk LOC.

Finally, body burden and associated RQs were calculated with the assumption that bait was consumed exclusively for six days. Estimated daily food intake ( Box 4

- 1 and Table 4

- 1 ) and
chemical

- specific elimination rates ( Section 4. 3.2 ) were used to determine 6

- day accumulation concentrations (mg a.i./kg

- bwt) ( Table 4

- 4 ). RQs are calculated by dividing the cumulative
rodenticide a.i. from each weight class by the weight

- adjusted LD 50 ( Ta ble 4

- 2 ). Details of these calculations are presented in Appendix B . RQs for three weight classes of rodents are provided
in Table 4

- 6

.

For brodifacoum and difethialone, all RQs exceeded the ac ute risk LOC (RQs range from 20 to
76 ). For warfarin baits co ntaining 0.025% a.i, the acute risk LOC was exceeded for small and medium sized passerines (RQ = 1.36 and 0.84, respectively). For warfarin baits containing
0.054 % a.i, the acute risk LOC was exceeded for all size classes of passerines (RQs range from
0.91 to 2.94). For chlorophacinone and diphacinone, no RQs exceeded the acute risk LOC (RQs range from 0.01 to 0.40). RQs assuming six days of feeding on bait were not calculated for bromethalin as exposed animals are not expected to continue feeding on bait f or six days after initial exposure.

When a six day feeding exposure is assumed, all RQs (range from 2.1 to 106) exceed the acute risk LOC for all evaluated anticoagulants. These conclusions are the same the conclusions when a single day exposure was assu med ( Table 4

- 5 ) with the exception that under a single day exposure, the acute risk LOC for large rodents consuming chlorophacinone was not exceeded.Page 83 of 183 Table 4

- 6 Accumulation of Rodenticide (mg a.i./kg

- bwt) after 6 days of Consumption and Associated RQs fo r Rodents
Six day accumulation (mg a.i./kg

- bwt) RQ 1

15 g 35 g 1000 g 15 g 35 g 1000 g

Brodifacoum 57 39 9 59* 51* 27*

Difethialone 27 19 4 24* 21* 11* Warfarin (0.025%) 279 193 45 49* 42* 22* Warfarin (0.054%) 602 416 96 106* 90* 48* Chlorophacinone 54 38 9 4.7* 4.0* 2.1 * Diphacinone 42 29 7 11.6* 9.9* 5.3*

Bromethalin 84 58 14 NA 2 NA NA

1 * RQ exceeds Acute Risk LOC.

2 NA

- not applicable. Animals consuming bromethalin are not expected to continue feeding on bromethalin bait for six days.

The one

- day

- exposure RQs, days of bait consumption to reach the LD 50 , and six

- day

- exposure RQs for generic mammals are listed in Appendix B . In addition to the RQs and bait consumption rates for the generic mammals; alternative RQ and bait consumption analyses were conducted using the unadjusted LD 50 s. These alternative analyses yielded the same LOC
exceedances as for the rodents co nsuming bait using the adjusted LD 50 s. In addition, estimated days to consume the LD 50 and grams of bait required to consume the LD 50 were also similar.



### 4.2 Risks based on the acute dietary LC 50

A second risk estimation method for primary consumption of bai t depends on the concentration of a.i. in the bait and the dietary LC 50

. The LC 50 (mg a.i./kg

- diet) is obtained from 5

- day exposure dietary toxicity studies. RQs are calculated as a ratio of a.i. concentration in the bait
and the LC 50

.

4.2.1 Avian risks based on the acute dietary LC 50

Concentration of a.i. in the baits, avian LC 50 s, and RQs are provided in Table 4

- 7 . Based on 5

- day dietary exposure, the acute risk LOC was exceeded for brodifacoum, difethialone, warfarin
baits with 0.054% a.i. , and chlorophacinone. Acute risk LOCs were not exceeded for warfarin baits with 0.025% a.i., diphacinone, and bromethalin.

With the exception of chlorophacinone and bromethalin, these results generally concur with the
conclusions from the bird acute ora l RQ results. For some anticoagulants, multiple exposures to the active ingredient for several days appear to be more effective and require less total chemical ingestion in order to attain mortality (Ashton et al. 1987). The Ashton et al (1987) studyPage 84 of 183 concl udes that in order to reach the median lethal dose for chlorophacinone, the total dose of ingested chlorophacinone over a 5

- day period can be smaller if it is administered in several small daily amounts rather than in one single large amount.

It is not e xpected that individuals feeding on bromethalin bait will continue to feed on it over multiple days. When bromethalin was introduced into the dietary matrix in the dietary toxicity test, birds tended to reduce food consumption over the course of the study; thereby, reducing their exposure to bromethalin. As such, the chemical appears to have less risk potential as the LOC when considering the dietary toxicity study was not exceeded

.

Table 4

- 7. Avian RQs based on dietary toxicity LC 50 s

Chemical Bait c oncentration (mg a.i./kg

- bait) LC 50 (mg a.i./kg

- diet) RQ 1

Brodifacoum 50 1.33 38*

Difethialone 25 0.56 45* Warfarin (0.025%) 250 625 0.4 0 Warfarin (0.054%) 540 625 0.86* Chlorophacinone 50 56 0.89*

Diphacinone 50 906 0.06

Bromethalin 100 210 0.48

1 * RQ exceeds Acute Risk LOC.

4.2.2 Mammalian risks based on dietary toxicity

Concentration of a.i. in the baits, LC 50 s, and RQs are provided in Table 4

- 8 . Mammalian LC 50 data was not available for difethialone. Based on 5

- day dietary exposure, the acute risk LOC was exceeded for brodifacoum, warfarin baits with 0.025% a.i. and 0.054% a.i., chlorophacinone, and diphacinone. Toxicity data for RQ calculation based on acute d ietary tests were not available for difethialone and bromethalin. These results generally concur with the conclusions from the mammal acute oral RQ results.

Table 4

- 8. Mammalian RQs based on dietary toxicity LC 50 s

Chemical Concentration in bait (mg a.i./kg

- bait) LC 50 (mg a.i./kg

- diet) RQ 1

Brodifacoum 50 0.53 94*

Difethialone 25 N D N D Warfarin (0.025%) 250 4.41 57* Warfarin (0.054%) 540 4.41 123* Chlorophacinone 50 1.14 44 *

Diphacinone 50 2.31 22*Page 85 of 183 Table 4

- 8. Mammalian RQs based on dietary toxicity LC 50 s

Chemical Concentration in bait (mg a.i./kg

- bait) LC 50 (mg a.i./kg

- diet) RQ 1

Bromethalin 100 ND ND

1 * RQ exceeds Acute Risk LOC.

ND

– no quantitative mammalian dietary toxicity data, RQ could not be calculated



### 4.3 Uncertainties

A description of assumptions, uncertainties, strengths, and limitations of the basic ecological risk assessment as conducted by EFED is described in Chapter 6 of the Agency’s Overview Document (USEPA 2004) and include those related to the effects assessmen t. Uncertainties relating to toxicity estimates were discussed in Section 3.1.5 , and uncertainties relating to
accumulation and elimination of the evaluated rodenticides were discussed in Sections 3.2 and
3.3

.

An additional uncertainty is the use of s caling factors to adjust the LD 50 s to account for weight differences between the tested animals and the assessed animals. For birds, weight

- adjusted

LD 50 s were calculated based on equations presented in Mineau et al . (1996) and Mineau et al

. (2001). RQs, d ays to consume sufficient bait to reach the median lethal dose, and grams bait required for consumption to reach the median lethal dose were calculated based on the unadjusted LD 50 s, as well as LD 50 s based on the non

- chemical specific adjustment in Mineau et
al . (1996), chemical specific adjustment for brodifacoum in Mineau et al . (1996), and the chemical specific adjustments for brodifacoum and chlorophacinone in Mineau et al . (2001). For mammals, the unadjusted LD 50 s and LD 50 s based on the “body weight 3⁄4 ” a djustment (USEPA 1995, 2011) were used to calculate RQs, days to consume sufficient bait to reach the median lethal dose, and grams bait required for consumption to reach the median lethal dose. Although there were differences in the calculated RQs, days to consume sufficient bait to reach the median lethal dose, and grams bait required for consumption to reach the median lethal dose, none of these differences were large enough to alter the risk conclusions.



### 4.4 Summary of Rodenticide Risks to Bait

- consuming Birds and Mammals

The assessment of primary exposure risks for wildlife involved a series of assessment methodologies that encompassed toxicity

, toxicokinetics , concentration of active ingredient in the bait, and availability of bait for consumption

.Page 86 of 183 B ased on the analysis of number of days to consume sufficient bait to reach the LD 50 and the quantity (grams) of bait to consume to reach the LD 50 , the following general conclusions can be
made:

**•** smaller primary consumers are at a greater risk than larger primary consumers;

**•** brodifacoum, difethialone, and bromethalin pose greater primary risk to birds than warfarin, c hlorophacinone, and diphacinone;

**•** risks to non

- target mammals are similar across all evaluated rodenticides,

**•** non

- target mammals are generally more at risk from consumption of bait than birds; and

**•** Longer exposure to bait increases the likelihood that a non

- target mammal or bird will
consume sufficient bait to reach the LD 50

.

As with all rodenticides, brodifacoum and difethialone represent a le thal primary risk to non

target small mammals that may eat either loose treated bait or utilize a bait station. In addition, the quantitative assessment also demonstrates that bait containing these two rodenticides constitutes a primary exposure risk conc ern for larger mammals as well as all avian size classes. This conclusion is consistent across all primary exposure risk analyses performed (single oral dose, six

- day accumulated dose, and dietary concentration). EPA’s analysis indicates birds and

mamma ls could attain a median lethal dose (LD 50 ) of either brodifacoum or difethialone upon feeding for less than day on treated bait. The brevity of feeding required to reach a potentially lethal exposure represents an increased opportunity (relative to all o ther rodenticides assessed)
for non

- target birds and mammals to chance upon loose treated bait and be lethally exposed.

Warfarin also demonstrates a primary exposure risk concern to small mammals. The assessment of warfarin indicates a risk to large mamma ls for all assessment methods employed as well. EPA’s analysis indicates that feeding on treated bait for less than a day is sufficient to attain a
median lethal dose in all evaluated size classes of mammals, suggesting a similar opportunity,
relative to brodifacoum and difethialone, for non

- target mammals to chance upon treated bait and consume a lethal dose. In contrast, warfarin’s primary exposure risk for birds is limited to small passeriforms and other medium sized birds. These results are dependent on the assessment method EPA considered. While a single day dose risk assessment suggests only a risk to small passeriforms from the highest concentration formulation, accounting for the potential for multiple day accumulation on a dose basis expands the concerns to include passeriforms and other small and medium sized birds at all formulation concentrations assessed. The dietary assessment does not consider body weight as a determinant factor. However, this assessment method still predicts a risk concern at the highest formulation concentration. EPA’s analysis
indicates that attainment of a lethal warfa rin dose can occur after 1 to 7 days of feeding (0.0 54% warfarin bait) or after 4 to 15 days of feeding (0.025% warfarin bait), depending on body weight

o f the passerine in question . This finding suggests that, for birds there is less of an opportunity for chance lethal encounters with warfarin when compared with brodifacoum and difethialone, since it would require multiple days of feeding on warfarin trea ted bait.Page 87 of 183 For bromethalin, as can be expected for a relatively fast acting compound (target mortality 1 to 7 days, Pitt et al . 2011, and registrant submitted studies), acute risk concern levels are exceeded for all mammalian size classes feeding on treate d bait based on a single day of exposure. Primary risk to birds from bromethalin exceeds risk concern levels in all assessment methodologies with the exception of the dietary exposure methodology, which returns a risk quotient that closely approaches but d oes not exceed the acute risk LOC. EPA’s analysis indicates that less than a single day’s feeding of bromethalin bait is sufficient to attain a median lethal dose in birds and mammals, suggesting that like brodifacoum and difethialone, adverse effects to non

- target wildlife are likely from primary exposure events with treated bait.

Two anticoagulant alternatives, chlorophacinone and diphacinone, also present primary exposure risk concerns for nearly all rodent and mammal sizes assessed using all primary exposure assessment methods (large rodents consuming chlorophacinone bait for one day are not expected to experience risk concerns). EPA’s analysis indicates that <1 day (diphacinone) and <1 to 3 days (chlorophacinone) of feeding on bait are sufficient t o attain a median lethal dose in mammals. This is not materially different from the other rodenticides with respect to the opportunity for non

- target mammals to chance upon and feed lethally on treated bait. In contrast to mammals, avian risk is below co ncern levels for these two compounds. This may be a limitation in the analysis of primary exposure models terminating at six days ( i.e., longer exposure periods might provide sufficient exposure to bait for adverse accumulation to occur); however, the ana lysis indicates that, unlike brodifacoum and difethialone, a very consistent and protracted feeding period for either diphacinone or chlorophacinone is required to attain a lethal dose in birds ( i.e., daily feedings for the former versus weeks to months fo r the latter ).



## 5 Secondary Exposure and Risk

Secondary exposure is defined for the purpose of this assessment as exposure to secondary consumers (i.e., predators and scavengers). Secondary risk is influenced by factors, including: toxicity to primary and secondary consumers, elimination rates of each of the rodenticides in both primary and secondary consumers, and time to death.

As noted above, a compound that is rapidly metabolized or excreted from a primary consumer may result in a lesser secondary exposure compared to compounds that accumulate wi th repeated sublethal exposures, even if repeated exposure occurs weeks or months after initial exposure (Eason and Murphy 2000). When considering rodenticides with similar toxicity, the rodenticides that are more rapidly cleared from the body are less likely to pose secondary risk compared to those that accumulate over time. This is because the rapidly cleared rodenticide is less likely toPage 88 of 183 accumula te to a level that would cause mortality to secondary consumers. Rodenticides that are slower to cause death are expected to prolong the availability of contaminated prey items and increase the dose that a secondary consumer may receive from eating target animals that have
consumed a dose of rodenticide that is beyond the lethal dose ( Section 3.3.2 ). The toxicity of the rodenticide to the secondary consumer would also affect the risk of mortality that would result from exposure. In summary, rodenticides that are eliminated more slowly and have greater potential to accumulate within body tissues, take longer to kill the primary consumer, and have greater toxicity to secondary consumers are expected to present greater secondary risk.

Risk quotients for secondary consumers were calculated in three ways, including two theoretical methods and one empirical:

1) Dose

- based exposure of secondary consumers to contaminated prey was calculated by the following 3 steps: (a) Estimate rodenticide concentration in primary consumers; (b) convert concentrations in primary consumers to doses in secondary consumers using food intake allometric equations; and (c) compare the estimated doses in secondary consumers to weight adjusted LD50 toxicity values.

2) Dietary exp osure that compared estimated active ingredient concentrations in primary consumers to LC50 values, and

3) Empirical residue data from carcass analyses were also used to characterize potential exposure to secondary consumers.

Further lines of evidence that are considered in this assessment include an analysis of the number of target species secondary consumer birds and mammals would need to consume in order to accumulate a lethal dose of rodenticide and available data on secondary toxicity from secondar y feeding studies. These analyses can be used to directly compare the risks of the rodenticides
considered in this assessment.



### 5.1 Rodenticide Ingestion through Consumption of Contaminated
Carcasses

- Theoretical Analysis

Secondary risk was quantitatively ex amined using a theoretical approach to calculate exposure. Similar to the analysis of primary risks, exposure in primary and secondary consumers is estimated using allometric equations of daily food intake as presented in the Wildlife Exposure

Factors Han dbook (EPA 1993).Page 89 of 183 Rodenticide intake based on consumption of bait by the primary consumers (prey) was
calculated as described in Section 3.3.1 . For this theoretical analysis, rodenticide accumulation in prey (house mouse and Norway rat) was calculated f or a one day period, a three day period and a six day period (assuming consumption of 100% bait as diet over this time period) in order
to bracket the available feeding durations from residue studies submitted to the agency and occurring in open literature

. For bromethalin , a recent study by Pitt et al. (2011) found that time to death for house mice, Polynesian rats ( Rattus exulans ), and black rats ( Rattus rattus ) offered bromethalin may be more rapid than suggested in registrant submitted data for the Norw ay rat, which may reduce the potential for bromethalin to accumulate in prey organisms. Data from this study also suggest that house mice and Polynesian rats exposed to bromethalin bait may stop feeding on the bait after reaching a lethal dose, further red ucing the potential for accumulation. Based on this information, rodenticide accumulation in prey was calculated for a one day period and a three day period only for this chemical. See Tables 3

- 21 and 3

- 22 for rodenticide body
burden over time for the hous e mouse and Norway rat for the rodenticides considered here.

The calculated body burden in the prey was then used to estimate rodenticide exposure in the secondary consumer using the general food intake allometric equations described in Section 3.1
above . Secondary consumers were assumed to be mammals weighing 50g, 1000g, or 3000g, or birds weighing 100g, 1000g, or 5000g. For example, American kestrels range from 100

- 150g,
red

- tailed hawks range from 900

- 1000g and bald eagles range from 4000

- 5000g (Dunni ng 1984). These weights were assumed based on the range of secondary consumers identified in rodenticide incidents in the Environmental Incident Information System (EIIS) and in the secondary feeding studies discussed in Section 5.3 below. The rodenticide dose expected to be consumed by secondary consumer birds feeding daily on house mice and Norway rats are shown

in Tables 5

- 1 and 5

- 2 , respectively. The daily rodenticide intake for secondary consumer mammals feeding on house mice and Norway rats are shown in Tables 5

- 3 and 5

- 4 , respectively.

Table 5

- 1. Calculated Rodenticide Daily Intake for Secondary Consumer Birds Based on Consumption of House Mouse (mg a.i./kg

- bwt/day)

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class 100 g 1000 g 5000 g 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum 3.21 1.44 0.82 9.61 4.30 2.45 19.16 8.58 4.89

Difethialone 1.61 0.72 0.41 4.70 2.11 1.20 9.08 4.06 2.32 Warfarin (0.025%) 16.1 7.19 4.10 47.7 21.4 12.2 93.9 42.0 24.0 Warfarin (0.054%) 34.7 15.5 8.86 103 46.1 26.3 203 90.8 57.8 Chlorophacinone 3.21 1.44 0.82 9.45 4.23 2.41 18.4 8.22 4.69 Diphacinone 3.21 1.44 0.82 8.54 3.82 2.18 14.4 6.44 3.67

Bromethalin a 6.42 2.88 1.64 17.1 7.66 4.37

-- -- --

a Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.Page 90 of 183 Table 5

- 2. Calculated Rodenticide Daily Intake for Secondary Consumer Birds Based on Consumption of Norway Rat (mg a.i/kg

- bwt/day)*

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight
Class 100 g 1000 g 5000 g 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum 0.85 0.38 0.22 2.54 1.14 0.65 5.07 2.27 1.29

Difethialone 0.43 0.19 0.11 1.24 0.56 0.32 2.40 1.08 0.61 Warfarin (0.025%) 4.25 1.90 1.09 12.6 5.65 3.22 24.9 11.1 6.35 Warfarin (0.054%) 9.18 4.11 2.34 27.3 12.2 6.96 53.7 24.0 13.7 Chlorophacinone 0.85 0.38 0.22 2.50 1.12 0.64 4.86 2.18 1.24 Diphacinone 0.85 0.38 0.22 2.26 1.01 0.58 3.81 1.71 0.97

Bromethalin a 1.70 0.76 0.43 4.53 2.03 1.16

-- -- -- *Currently registered chlorophacinone and diphacinone products for home

- owner use are not labeled for use on rats.

a Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

Table 5

- 3. Calculated Rodenticide Daily Intake for Secondary Consumer Mammals Based on Consumption of House Mouse (mg a.i./kg

- bwt/day)

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 3 Day Accumula tion in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class 50 g 1000 g 3000 g 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum 2.90 1.70 1.40 8.67 5.09 4.18 17.28 10.14 8.34

Difethialone 1.45 0.85 0.70 4.24 2.49 2.05 8.18 4.80 3.95 Warfarin (0.025%) 14.5 8.50 6.99 43.0 25.2 20.8 84.7 49.7 40.9 Warfarin (0.054%) 31.2 18.4 15.1 92.9 54.5 44.8 183 107 88.3 Chlorophacinone 2.90 1.70 1.40 8.52 5.00 4.11 16.6 9.71 7.99 Diphacinone 2.90 1.70 1.40 7.70 4.52 3.72 13.0 7.61 6.26

Bromethalin a 5.79 3.40 2.79 15.4 9.05 7.45

-- -- --

a Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

Table 5

- 4. Calculated Rodenticide Daily Intake for Secondary Consumer Mammals Based on Consumption of Norway Rat (mg a.i/kg

- bwt/day)

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight
Class 50 g 1000 g 3000 g 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum 0.77 0.45 0.37 2.29 1.35 1.11 4.57 2.68 2.21

Difethialone 0.38 0.22 0.18 1.12 0.66 0.54 2.17 1.27 1.05 Warfarin (0.025%) 3.83 2.25 1.85 11.4 6.68 5.49 22.4 13.2 10.8 Warfarin (0.054%) 8.28 4.86 3.99 24.6 14.4 11.9 48.4 28.4 23.4 Chlorophacinone 0.77 0.45 0.37 2.26 1.32 1.09 4.38 2.57 2.11Page 91 of 183 Diphacinone 0.77 0.45 0.37 2.04 1.20 0.98 3.43 2.02 1.66

Bromethalin a 1.53 0.90 0.74 4.08 2.40 1.97

-- -- -- *Currently registered chlorophacinone and diphacinone products for home

- owner use are not labeled for use on rats.

a Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day
accumulation scenari o only.

5.1.1 Risk Calculation and Characterization

Weight

- adjusted LD 50 values for birds and mammals were used to calculate risk quotients. In keeping with EFED policy regarding scaling factors, weight

- adjusted LD 50 values were calculated using the standard adjustment for mammals discussed above, and scaling factors derived from Mineau et al. (1996) for birds. A chemical

- specific scaling factor (slope = 0.7589) was only available for brodifacoum from Mineau et al. ( 1996), so this scaling factor was used to adjust the avian LD 50 for that rodenticide. Avian LD 50 s for the other rodenticides were adjusted using the default scaling factor of 1.15. Mineau et al. (2001) contains additional data, with a
recalculated avian scaling factor for brodifacoum (slope =

- 0.12) and an additional scaling factor for chlorophacinone (slope =

- 1.53). Avian LD 50 s for these rodenticides using the chemical specific scaling factors were included for consideration as part of Appendix C . Weight

- adjusted
LD50 values for birds and mammals were calculated as described in Section 3.1 . Risk quotients were also calculated using unadjusted LD 50 values for secondary mammals and birds. Results of these alternate calculations did not change the overall risk conclusions ( Appendix C ). Therefore, RQs were calculated by dividing the exposure estimates of rodenticide intake from
Tables 5

- 1 to 5

- 4 for birds and mammals consuming house mice and Norway rats for each weight class by the most sensitive LD 50 adjusted to the weights of the secondary animals as presented in Section 3

.

5.1.1.1 Acute Dose

- based RQs for Secondary Birds

RQs for secondary birds consuming contaminated house mice are provided in Table 5

- 5

. Based on this theoretical analysis, RQs calculat ed for secondary birds consuming house mice exposed to brodifacoum and difethialone exceed acute LOCs. No LOCs are exceeded for RQs calculated for warfarin, diphacinone, and chlorophacinone, except for small secondary birds consuming prey exposed to the h igher concentration of warfarin (0.054%) bait for six days. Bromethalin shows varying results, where RQs exceeded acute LOC for small secondary birds consuming small prey exposed to bromethalin bait for one day, and all weight classes assessed for small

pr ey exposed to bromethalin bait for three days. Given that prey exposed to bromethalin may stop feeding on the bait after consuming a lethal dose, the one day accumulation scenario is more likely than the three day accumulation scenario for this chemical.Page 92 of 183 Table 5

- 5. Secondary Bird Acute RQs Based on Consumption of Contaminated House Mouse

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight
Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class 100 g 1000 g 5000 g 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum 6.60* 5.15* 4.33* 19.77* 15.42* 12.96 39.40* 30.74* 25.84*

Difethialone 5.48* 1.85* 0.83* 17.09* 5.42* 2.43* 32.98* 10.45* 4.68* Warfarin (0.025%) 0.05 0.01 0.01 0.14 0.04 0.02 0.27 0.09 0.04 Warfarin (0.054%) 0.10 0.03 0.01 0.30 0.09 0.04 0.58* 0.19 0.08 Chlorophacinone a 0.01 <0.01 <0.01 0.04 0.01 0.01 0.08 0.02 0.01 Diphacinone a <0.01 <0.01 <0.01 0.01 < 0.01 < 0.01 0.01 < 0.01 < 0.01

Bromethalin b 1.52* 0.48 0.22 4.06* 1.29* 0.58*

-- -- -- Bolded (*) RQs exceed acute risk LOC (0.5).

a Current registered baits in the U.S. are for use on House Mouse only.

b Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

RQs for secondary birds consuming contaminated Norway rats are provided in Table 5

- 6

. For secondary birds consuming Norway rats exposed to brodifacoum, RQs exceed acute LOC for all scenarios. RQs for difethialone exceed for all scenarios, except medium and large birds consuming rats exposed to difethialone bait for one day. For bromethalin, RQs only exceeded acute LOC for small predators/scavengers consuming prey animals exposed to bromethalin bait for three days. Again, available data suggest that secondary exposure to bromethalin is limited due to reduced feeding consumption that has been reported to occur after consumption of a lethal dose by primary consumers (Pitt et al., 2011). None of the RQs exceed the LOC for warfarin, chlorophacinone or diphacinone.Page 93 of 183 Table 5

- 6. Secondary Bird Acute RQs Based on Consumption of Contaminated Norway Rat

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight
Class 3 Day Accumulation in Prey by Secondary Consumer Weight
Class 6 Day Accumulation in Prey by Secondary Consumer Weight
Class 100 g 1000 g 5000 g 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum 1.75* 1.36* 1.15* 5.25* 4.08* 3.43* 10.43* 8.14* 6.84*

Difethialone 1.54* 0.49 0.22 4.52* 1.43* 0.64* 8.73* 2.77* 1.24* Warfarin (0.025%) 0.01 <0.01 <0.01 0.04 0.01 0.01 0.07 0.02 0.01 Warfarin (0.054%) 0.03 0.01 <0.01 0.08 0.02 0.01 0.15 0.05 0.02 Chlorophacinone a <0.01 <0.01 <0.01 0.01 <0.01 <0.01 0.02 0.01 <0.01 Diphacinone a <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

Bromethalin b 0.40 0.13 0.06 1.07* 0.34 0.15

-- -- -- Bolded (*) RQs exceed acute risk LOC (0.5).

a Current registered baits in the U.S. are for use on House Mouse only.

b Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

5.1.1.2 Acute Dose

- based RQs for Secondary Mammal

RQs for secondary mammals consuming contaminated house mice are provided in Table 5

- 7

. For mammals consuming house mice exposed to rodenticide bait for three days, RQs for all rodenticides exceed the, except for mammals in all weight classes assessed cons uming house mice exposed to chlorophacinone bait for one day. RQs for secondary mammals consuming contaminated Norway rats are provided in Table 5

- 8 . RQs for brodifacoum, difethialone, and warfarin exceed the acute LOC in all scenarios, except for small ma mmals consuming rats exposed to difethialone bait for one day. This may be a result of the relatively small concentration of difethialone in bait (25 mg a.i./kg

- bait) compared to the other chemicals (50 to 540 mg a.i./kg

- bait). Chlorophacinone shows varyin g results, where RQs only exceeded the acute LOC for medium and large predators/scavengers consuming Norway rats exposed to chlorophacinone bait for 6 days. RQs for diphacinone exceed acute LOC for mammals consuming rats exposed to diphacinone bait for thr ee or six days, but not for rats exposed to diphacinone bait for o ne day. Bromethalin RQs exceed a cute LOC in all assessed scenarios except for small mammals consuming rats exposed to bromethalin bait for one day.

Table 5

- 7. Secondary Mammal Acute RQs Based on Consumption of Contaminated House Mouse

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class 50 g 1000 g 3000 g 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum 3.71* 4.60* 4.98* 11.10* 13.78* 14.91* 22.13* 27.46* 29.72*Page 94 of 183 Difethialone 1.62* 2.01* 2.17* 4.74* 5.88* 6.37* 9.15* 11.35* 12.28* Warfarin (0.025%) 2.97* 3.68* 3.99* 8.81* 10.93 11.83* 17.35* 21.53* 23.30* Warfarin (0.054%) 6.41* 7.95* 8.61* 19.03* 23.61* 25.56* 37.48* 46.51* 50.33* Chlorophacinone a 0.28 0.35 0.38 0.84* 1.04* 1.12* 1.63* 2.02* 2.18* Diphacinone a 0.94* 1.16* 1.26* 2.49* 3.09* 3.35* 4.20* 5.21* 5.64*

Bromethalin b 1.62* 2.01* 2.17* 4.31* 5.35* 5.79*

-- -- -- Bolded (*) RQs exceed acute risk LOC (0.5).

a Current registered baits in the U.S. are for use on House Mouse only.

b Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

Table 5

- 8. Secondary Mammal Acute RQs Based on Consumption of Contaminated Norway Rat

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight
Class 3 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class 50 g 1000 g 3000 g 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum 0.98* 1.22* 1.32* 2.94* 3.65* 3.95* 5.86* 7.27* 7.87*

Difethialone 0.43 0.53* 0.58* 1.25* 1.56* 1.68* 2.42* 3.00* 3.25* Warfarin (0.025%) 0.79* 0.97* 1.05* 2.33* 2.89* 3.13* 4.59* 5.70* 6.17 Warfarin (0.054%) 1.70* 2.11* 2.28* 5.04* 6.25* 6.76* 9.92* 12.31* 13.32* Chlorophacinone a 0.08 0.09 0.10 0.22 0.27 0.30 0.43 0.53* 0.58* Diphacinone a 0.25 0.31 0.33 0.66* 0.82* 0.89* 1.11* 1.38* 1.49*

Bromethalin b 0.43 0.53* 0.58* 1.14* 1.42* 1.53*

-- -- -- Bolded (*) RQs exceed acute risk LOC (0.5).

a Current registered baits in the U.S. are for use on House Mouse only.

b Given bromethalin’s rapid mode of action, RQs for this chemical were calculated based on a one day and three day accumulation scenario only.

5.1.1.3 Acute Dietary

- based RQs for Secondary Birds and Mammals

RQs were also calculated based on subacute dietary LC 50 values and expected concentration of the rodenticides in prey items. Daily rodenticide intake values (mg a.i./kg

- bw/day) for primary consumers based on their consumption of bait, as shown above in Section 3.3.1, were used as an
estimate of the a.i. conce ntration in prey items after one day of feeding. This value can be considered as the dietary concentration (mg a.i./kg diet) for secondary consumers. RQs were calculated by dividing this value by the LC 50 s for birds and mammals, as listed above in Sectio n 3 . RQs for secondary birds and mammals are presented in Tables 5

- 9 for birds and mammals. Based on a subacute dietary exposure of secondary birds exposed to the house mouse or Norway rat, RQs exceed the acute LOC for brodifacoum and difethialone, while RQs for warfarin, chlorophacinone, diphacinone, and bromethalin do not exceed the acute LOC. For secondaryPage 95 of 183 mammals exposed to the house mouse or Norway rat, RQs exceed the acute LOC for all assessed rodenticides. Dietary data is not available for difethial one and bromethalin so these chemicals could not be included in this analysis.

Table 5

- 9. Subacute Dietary RQs for Birds and Mammals Consuming Target

Mammals Containing Rodenticides

Chemical Birds Mammals Consuming

House Mouse Consuming Norway Rat Consuming

House Mouse Consuming Norway Rat

Brodifacoum 17.8* 4.71* 44.7* 11.2*

Difethialone 20.7* 5.48* ND ND Warfarin (0.025%) 0.19 0.05 26.6* 7.05* Warfarin (0.054%) 0.41 0.11 57.5* 15.2* Chlorophacinone 0.32 0.09 20.42* 5.41* Diphacinone 0.02 < 0.01 10.1* 2.68*

Bromethalin 0.20 0.05 ND ND

ND = no data Bolded (*) RQs exceed acute risk LOC (0.5).

5.1.1.4 Number of Target Mammals Sufficient to Reach LD 50 of Secondary Consumers

In a final analysis, the number of individuals of the target species (i.e., house mouse and Norway rat) necessary for consumption of an LD 50 dose in secondary birds and mammals was calculated. Two scenarios were developed to represent the low and high end of potential risk. In the first scenario, secondary birds and mammals consu med house mice and Norway rats exposed to rodenticide bait for one day. This scenario represents the low end of exposure and can be applied to all assessed rodenticides. In the second scenario, secondary birds and mammals consumed house mice and Norway ra ts exposed to rodenticide bait for six days. Since six days of accumulation is not likely for prey organisms feeding on bromethalin, the analysis for this chemical was based on a three day accumulation scenario. For this analysis the dose of the
rodenticid e in the secondary consumer was calculated after having consumed the prey exposed to bait for one, three or six days. This value was then compared to the weight

- adjusted LD 50 value for the secondary animals.

Table 5

- 10 shows the number of house mice a se condary bird would need to consume in order to reach a median lethal dose for each assessed rodenticide. Depending on body weight and exposure scenario, secondary mammals could receive the LD 50 dose of brodifacoum from consuming less than 1 up to 5 mice, w hile difethialone would require less than 1 up to 27 mice. Secondary birds exposed to bromethalin through contaminated prey would need to consumePage 96 of 183 anywhere from less than 1 up to 104 mice, depending on body weight and accumulation scenario, in order to reac h the LD 50 . The range of warfarin contaminated mice needed to reach
the LD 50 dose in secondary birds is quite large, ranging from 3 to over 3400 depending on weight class assessed, warfarin concentration considered, and accumulation scenario. For chloropha cinone and diphacinone, secondary birds would need to consumer 23 to 12,000 and 183 to 74,000 mice, respectively, in order to reach their respective LD 50 values.

Table 5

- 10. Number of House Mice Consumed to Reach a LD 50 in Secondary Birds

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class** 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum < 1 2 5 < 1 < 1 < 1

Difethialone < 1 4 27 < 1 < 1 5 Warfarin (0.025%) 38 539 3429 7 92 586 Warfarin (0.054%) 18 249 1587 3 43 271 Chlorophacinone 130 1836 11690 23 321 2045 Diphacinone 821 11602 73852 183 2590 16483

Bromethalin 1 16 104 < 1 6 39 **For bromethalin, numbers are based on 3 day accumulation in prey.

Table 5

- 11 shows the number of Norway rats a secondary bird would need to consume in order
to reach the LD 50 value for each rodenticide. Rats were exposed to the various rodenticide baits for one, three or six days as described above. For brodifacoum, a se condary bird could receive a median lethal dose from consuming less than 1 rat, while difethialone would require 1 to 5 rats. Secondary birds exposed to bromethalin through contaminated prey would need to consume anywhere from less than 1 to 17 rats, depen ding on body weight and accumulation scenario, in
order to reach the LD 50 . The range of warfarin contaminated rats needed to reach the LD 50 in secondary birds is quite large, ranging from less than 1 to over 600 depending on weight class assessed, warfarin concentration considered, and accumulation scenario. For chlorophacinone, secondary birds would need to consume 4 to 2094 rats in order to reach the LD 50 . The range of diphacinone contaminated rats needed to reach the LD 50 in secondary birds is quite lar ge, ranging from 33 to over 13,000.Page 97 of 183 Table 5

- 11. Number of Norway Rats Consumed to Reach a LD 50 in Secondary Birds

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class** 100 g 1000 g 5000 g 100 g 1000 g 5000 g

Brodifacoum < 1 < 1 < 1 < 1 < 1 < 1

Difethialone < 1 < 1 5 < 1 < 1 < 1 Warfarin (0.025%) 7 97 614 1 17 105 Warfarin (0.054%) 3 45 284 < 1 8 49 Chlorophacinone 23 329 2094 4 58 366 Diphacinone 147 2079 13232 33 464 2953

Bromethalin < 1 3 17 < 1 1 7 **For bromethalin, numbers are based on 3 day accumulation in prey.

Table 5

- 12 shows the number of house mice a secondary mammal would need to consume in
order to reach the LD 50 . Mice were exposed to the various rodenticide baits for one, three or six days as described above. Depending on body weight and exposure scenario, secondary mammals
could receive an LD 50 dose of brodifacoum and warfarin from consuming less than 1 to 5 mice, while difethialone would requir e up to eleven mice. Predators/scavengers exposed to bromethalin through contaminated prey would need to consume anywhere from 1 to 11 mice, depending on body weight and accumulation scenario, in order to reach the LD 50 dose. For diphacinone, the range of contaminated mice needed to reach the LD 50 in secondary mammals is anywhere from less than 1 to 13, while chlorophacinone would require up to 60 mice depending on weight class
assessed and accumulation scenario.

Table 5

- 12. Number House Mice Consumed to Reach a LD 50 in Secondary Mammals

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class** 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum < 1 2 5 < 1 < 1 < 1

Difethialone < 1 5 11 < 1 < 1 2 Warfarin (0.025%) < 1 3 6 < 1 < 1 < 1 Warfarin (0.054%) < 1 1 3 < 1 < 1 < 1 Chlorophacinone 3 27 60 < 1 5 11 Diphacinone < 1 8 18 < 1 2 4

Bromethalin < 1 5 11 < 1 2 4 **For bromethalin, numbers are based on 3 day accumulation in prey.

Table 5

- 13 shows the number of Norway rats a secondary mammal would need to consume in
order to reach the LD 50 . Rats were exposed to the various rodenticide baits for one, three or six days as described above. Based on this analysis, secondary m ammals would be exposed to anPage 98 of 183 LD 50 dose of brodifacoum, difethialone, warfarin, and bromethalin after consuming less than 1 Norway rat, expect for large mammals exposed to 1 day of accumulation, which would require up to 2 rats. For diphacinone, the range contaminated rats needed to reach the LD50 in secondary
mammals is anywhere from less than 1 to 3, while chlorophacinone would require up to 11 rats depending on weight class assessed and accumulation scenario.

Table 5

- 13. Number Norway Rats Consumed to Reach a LD 50 in Secondary Mammals

Chemical 1 Day Accumulation in Prey by Secondary Consumer Weight Class 6 Day Accumulation in Prey by Secondary Consumer Weight Class** 50 g 1000 g 3000 g 50 g 1000 g 3000 g

Brodifacoum < 1 < 1 < 1 < 1 < 1 < 1

Difethialone < 1 < 1 2 < 1 < 1 < 1 Warfarin (0.025%) < 1 < 1 1 < 1 < 1 < 1 Warfarin (0.054%) < 1 < 1 < 1 < 1 < 1 < 1 Chlorophacinone < 1 5 11 < 1 < 1 2 Diphacinone < 1 1 3 < 1 < 1 < 1

Bromethalin < 1 < 1 2 < 1 < 1 < 1 **For bromethalin, numbers are based on 3 day accumulation in prey.



### 5.2 Rodenticide Ingestion through Consumption of Contaminated
Carcasses

- Residue Analysis

The determination of rodenticide intake for individuals consuming rodenticide poisoned animals
or carcasses can be calculated in a manner similar to the approach for individuals consuming bait directly ( Section 4.1 ) when empirical residue data are available. Rodenticide whole

- carcass residue data is available from open

- literature studies for all chemicals considered in this white paper ( See Section 3.2).

In field and laboratory studies, rodenticide whole

- carcass residue was determined in mammals after exposure to bait. Data are available for a variety of small and medium sized mammalian granivores and omnivores exposed to brodif acoum, difethialone, and warfarin. No data were identified for bromethalin or other exposed taxonomic groups ( e.g., birds, reptiles, and invertebrates). For all studies, it was assumed the concentrations were reported using wet weights of the mammals.

5.2.1 Me asured Residues of Rodenticides in Contaminated Carcasses

The maximum mean residue values in rats for brodifacoum and difethialone, 6.98 mg a.i./kg

- bw (calculated as the weighted average of means reported in Howald, 1997) and 3.1 mg a.i./kg

- bwPage 99 of 183 (Savarie, 2 005) respectively , are used for this assessment as they represents conservative measured values based on the available data (see Section 3.2 for more information on available residue data). These residue values are greater than the calculated residue for rats exposed to brodifacoum or difethialone bait for one day (2.1 mg a.i./kg

- bw and 1.0 mg a.i/kg

- bw, respectively). In fact, these values are almost the same as the calculated residue for rats exposed to brodifacoum or difethialone for three days (6.3 mg a.i/kg

- bw and 3.1 mg a.i./kg

- bw).

For warfarin, the mean residue value in mice of 2.95 mg a.i./kg

- carcass is used because the bait

concentra tion used in the study (Townsend et al., 1984) approximates the concentration found in registered warfarin baits for commensal uses. This value is an order of magnitude less than the calculated residue for mice exposed to the high or low concentration warf arin bait for one day (85.5 mg high concentration a.i./kg

- bw and 39.6 mg low concentration a.i./kg

- bw). This difference may be a function of the variable elimination half

- life for this chemical based on species discussed previously.

The maximum reported mean value for chlorophacinone, 1.58 mg a.i./kg

- bw (Primus et al. 2001), is for the California vole. This value is used for this assessment as it represents the conservative measured value based on the available data. Although this value is less than the calculated residue for mice exposed to chlorophacinone bait for one day (7.9 mg a.i./kg

- bw), it is within a factor of 6 of the calculated value. This difference may be a function of the relatively rapid elimination half

- life for this chemical, uncertainty in exposures that occurred in the field study relative to assumptions in the theoretical calculations, or species differences (field study for vole versus theoretical calculations mice).

The maximum reported mean residue value for diphacinone, 1.4 mg a. i./k g

- bw (Primus et al. 2001), is for the California ground squirrel. This value, which is similar to the calculated residue for rats exposed to diphacinone bait for one day (2.1 mg a.i./kg

- bw) is used for this assessment because it represents the conserva tive measured value based on available data. The slight differences in residue values may be a function of the relatively rapid elimination half

- life for this chemical, uncertainly in exposures that occurred in the field study relative to assumptions in
th e theoretical calculations, or species differences (field study for ground squirrel versus theoretical calculations for rats.)

Table 5

- 14. Measured Mean Whole

- Carcass Residue and Estimated Body Burden After 1 Day Rodenticide Accumulation in Primary Consum ers

Chemical Empirical Residue Levels Theoretical Residue Levels

Mg a.i./kg
bait Species Mean whole

carcass residue (mg a.i./kg

- bw) Mg a.i./kg
bait Species Estimated Body Burden (mg a.i./kg

- bw)

Brodifacoum 50 Rat 6.98 b 50 Norway Rat 2.1Page 100 of 183 Difethialone 25 Rat 3.1 25 Norway Rat 1.0

Warfarin 200 a Mouse 2.95 250 House

Mouse 36.9

Chlorophacinone 50 Vole 1.58 50 House

Mouse 7.9

Diphacinone 50 Ground Squirrel 1.4 50 Norway Rat 2.1

a baits registered in the U.S. are 0.025% a.i.

b Value calculated as the weighted average of the means reported in Howald 1997

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

- bw, where kg

- bw is the kilograms of the consuming individual for three weight classes of birds and mammals. This analysis used the same weight classes for secondary birds and mammals, calculated food intake, and weight

- adjusted LD 50 values as the theoretical analysis described in Section 5.1 above. However, the calculation for daily rodenticide intake used the residue values selected for this analysis (concentration in whole prey animal) instead of the concentration of bait.

5.2.2 Risk Calculation and Characterization for Consumption of Contaminated Carcasses

The acute LOC was exceeded for secondary birds for brodifacoum and difethialone; however, RQs for secondary birds exposed to warfarin did not exceed the acute LOC. RQs for secondary birds exposed to chlorophacinone or diphacinone on an acute basis did not exceeded the acute LOC ( Table 5

- 15 ). If the max imum individual residue value for each rodenticide was used to calculate risk quotients instead of the mean value, LOC exceedances for secondary birds would not change.

Carnivore/scavenger mammalian RQs for brodifacoum and difethialone exceeded the acute LOC. For warfarin, chlorophacinone, and diphacinone, RQs did not exceed the acute LOC ( Table 5

- 15 ). Although the use of the maximum individual residue value would increase RQs, LOC exceedances for secondary mammals would not change with the exception of sm all mammals exposed to chlorophacinone and diphacinone.Page 101 of 183 Table 5

- 15. Secondary Acute RQs based on a Single

- dose of Rodenticide through Consumption of Contaminated Carcasses

Predator Birds Mammals

Predator Weight Class 100 g 1000 g 5000 g 50 g 1000 g 3000 g

Brodifacoum 6.42* 5.01* 4.21* 3.59* 4.46* 4.83*

Difethialone 4.64* 1.47* 0.66* 1.41* 1.75* 1.89*

Warfarin < 0.01 < 0.01 < 0.01 0.26 0.32 0.34 Chlorophacinone < 0.01 < 0.01 < 0.01 0.07 0.08 0.08 Diphacinone < 0.01 < 0.01 < 0.01 0.19 0.23 0.25
Bolded (*) RQs exceed acute risk LOC (0.5).

For toxic response elicited from the dietary exposure route extended over several days, exposure is measured as mg a.i./kg

- diet. Toxicity is measured by the LC 50 obtained from the dietary studies (5 days on treated diet) for birds and mammals. Avian RQs based on dietary studies are provided in Table 5

- 16 .Carnivore/scavenger bird RQs for brodifacoum and difethialone exceeded Acute Risk LOCs. Warfarin RQs for carnivo re/scavenger birds did not exceed any LOCs. RQs for birds exposed to chlorophacinone and diphacinone in their diet do not exceed
Acute Risk LOCs.

Mammalian RQs based on dietary studies are provided in Table 5

- 16 . RQs for brodifacoum and
warfarin exceed t he acute risk LOC. There are no available mammalian dietary data for difethialone or bromethalin. For the alternative rodenticides with conforming labels, mammalian RQs for chlorophacinone and diphacinone exceeded the acute LOC.

Table 5

- 16. Secondary Die tary RQs based on a 5

- day Exposure of Rodenticide through Consumption of Contaminated Carcasses

Birds Mammals

Brodifacoum 5.25* 13.17*

Difethialone 5.54* ND
Warfarin < 0.01 0.67* Chlorophacinone 0.02 1.39* Diphacinone < 0.01 ND
ND = no data Bolded (*) RQs exceed acute risk LOC (0.5).Page 102 of 183 

### 5.3 Secondary Exposure Studies

Toxicity studies are available for several species of birds and mammals that represent potential secondary consumers of rodenticides. In these studies, small mammals were fed diets containing one of the rodenticides, and these animals died or were sacrificed. These contaminated carcasses were fed to the birds and mammals ( i.e. , secondary consumers) being evaluated in the studies. Though these types of secondary exposure studies provi de information on the potential effects from rodenticide 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 th e sensitivity of the exposed animals to the rodenticide.

Birds

In the studies cited, raptors or avian scavengers were exposed to rodenticide in whole or ground carcasses, which were usually those of rats or mice, or in fortified meat. Most prey animals were fed treated bait, although some were dosed orally. Most studies involved only 1 rodenticide but often more than 1 raptor or scavenger species was tested. Mortality was included as a measurement endpoint in all studies. Some studies also reported signs of toxicosis ( e.g., bleeding, prolonged blood

- coagulation time, abnormal behavior, or regurgitation) in surviving test animals. Although exposure scenarios, test species, and the number of test animals varied among the studies, collectively these studies provide useful information to characterize secondary hazards from short

- term exposure. The studies are summarized and tabulated below.

Brodifacoum was tested in 12 studies involving 8 species of birds. Of 149 individuals exposed to
brodifacoum

- poisoned prey (at various doses), 63 (42%) individuals died ( Table 5

- 17 ). Mortality occurred in 11 of 20 barn owls ( Tyto alba ), 6 of 6 red

- tailed hawks ( Buteo jamaicensis )
and red

- shouldered hawks ( Buteo lineatus ), 13 of 65 American kestrels ( Falco sparverius ), 1 o f 4 Eurasian harriers ( Circus pygargus ), and 32 of 50 laughing gulls ( Larus atricilla ). No deaths occurred in 4 golden eagles ( Aquila chrysactos ) tested by Marsh and Howard (1978), but 3 bled externally. Some studies did not report whether signs of toxicos is were observed in surviving birds. In those studies that examined survivors for signs of toxicosis, such as external bleeding, internal hemorrhaging, and/or prolonged blood

- coagulation time, about one

- third of the survivors visually examined or necropsie d exhibited symptoms of toxicity.

There are no secondary studies involving exposures of birds to difethialone or bromethalin.

The four studies available for warfarin indicate that this chemical causes low mortality rates in secondary birds exposed to m ammals that consumed 50 or 500 mg a.i. kg

- bait. In the warfarin studies, 2 (5%) of 23 individuals birds died ( Table 5

- 18 ); no adverse signs were reported in the
survivors.Page 103 of 183 No mortality occurred in 8 chlorophacinone studies that, in total, included 112 in dividual birds from 9 species ( Table 5

- 19 ). Birds tested included 28 carrion crows ( Corvus corone ), 20 Eurasian buzzards, 20 American kestrels, 20 black

- billed magpies, 10 red

- tailed hawks, 6 white storks ( Ciconia ciconia ), 4 tawny owls ( Strix aluco ), 2 barn owls, and 2 great horned owls. Some survivors showed signs of intoxications, mostly prolonged blood

- coagulation time.

About 9% mortality was recorded in 3 diphacinone studies that involved 34 individual birds from 5 species ( Table 5

- 20 ). Test species were barn owls, great horned owls, saw

- whet owls ( Aegolius acadicus ), golden eagles, and American crows ( Corvus brachyrhynchos ). Thirteen (42%) of the survivors displayed some signs of toxicity.Page 104 of 183 Table 5

- 17. Observed Effects of Brodifacoum on Birds Consuming Contaminated Carcasses

Secondary species Prey offered to birds No. prey offered daily per bird No. days
birds exposed No. birds exposed No. birds

dead No. survivors with signs of brodifacoum toxicity a Reference (MRID)

Barn owl Rats fed choice of 0.002%
bait b and untreated food for 5 days 1

- 2 1
3

6
10 1

2

1

2 0

2

1

2 0
No survivors
No survivors
No survivors Mendenhall and Pank
1980 (MRID 46750931

40077202 00094694)

Barn owl Mice fed 0.002% bait b for 1 day 3

2

2 1
3

6 6
2 c

2 c 4
0

0 nr

nr 2 (eb/ct) Newton et al. 1990 and Wyllie 1995 e

Barn owl Mice fed 0.005% bait for

1

- 2 days Enough to provide
50

- 220 μg a.i. per day 15 4 1 3 (eb/ih) Gray et al. 1994 e

Barn owl Rats fed 0.005% bait 4 total 5

- 7 4 1 0 Lee 1994 e

Red

- tailed

hawk Rats fed 0.005% bait for 3 days limited d 4 4 4 No survivors

Marsh and Howard
1978 (MRID # 00080243) Red

shouldered
hawk Mice fed 0.005% bait for 3 days limited d 4 2 2 No survivors

Golden eagle Rats fed 0.005% bait for 3 days limited d 4 4 0 3 (eb)

American

kestrel Voles fed 0.005% bait for 3 days 1

1 2

6 10
10 0

4 (ct) Savarie and LaVoie
1979 (MRID 80244)

American

kestrel Ground
vole tissue 0.3 mg a.i./kg 0.8 mg a.i./kg 1.6 mg a.i./kg 3.2 mg a.i./kg 6.0 mg a.i./kg ad libitum 5
5
5
5
5 8
8
8
8
8 0

1
0
0

4 nr

nr

nr

nr

nr LaVoie 1990 e

Eurasian
buzzard Mice fed 0.005% bait 5 6 5 4 1 (bl) Lutz 1987 ePage 105 of 183 Australasian
harrier Rabbit dosed at 6.5 mg a.i./kg 1 1 4 1 nr Godfrey 1985 e

Laughing gull Ground, spiked rat
tissues at 0.72 mg a.i./kg 1.62 mg a.i./kg 3.41 mg a.i./kg 7.26 mg a.i./kg 14.0 mg a.i./kg ad libitum 5
5
5
5
5 5
5
5
5
5 3
5
5
5
5 0
No survivors
No survivors
No survivors
No survivors ICI Americas, Inc
1979a (MRID 80236)

Laughing gull Ground, spiked rat
tissues at 0.13 mg a.i./kg 0.34 mg a.i./kg
0.84 mg a.i./kg 2.10 mg a.i./kg 5.26 mg a.i./kg ad libitum 5
5
5
5
5 5
5
5
5
5 0

1
0

4

4 0
0 1 (eb)

0

0 ICI Americas, Inc
1979b (MRID 80236)

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

b registered baits are 0.005% a.i.

c the 2 owls that survived the initial 1

- day exposure were subsequently re

- exposed for 3 days and again for 6 days; the owls were allowed to recover for 75 to 79 days between exposure periods

d the amount of food offered to the raptors was “limited” to prevent overindulgence on any given day

e Cited in US EPA (2004) Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative ApproachPage 106 of 183 Table 5

- 18. Observed Effects of Warfarin on Birds Consuming Contaminated Carcasses

Secondary species Prey offered to birds No. prey offered daily per bird No. days birds exposed No. birds exposed No. birds

dead No. survivors with signs of

warfarin toxicity a Reference (MRID)

Tawny owl Mice fed bait for 3 days 1 every other day 90
28 4

2 c 0
0 0
0 Townsend et al.
1981

Black

- billed

magpie Rats fed 0.05% bait c

for 4

- 7 days Ad libitum 5 14 0 0 Mach 1997

Barn owl Rats fed 0.005% bait c 4 total 5

- 7 4 2 nr Lee 1994 b

Eurasian
buzzard Rat/mouse Ad libitum 18 1 0 nr Telle 1955 b

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

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

c ra t and mouse registered baits in the U.S. are 0.025% a.i. and 0.054% a.i

Table 5

- 19. Observed Effects of Chlorophacinone on Birds Consuming Contaminated Carcasses

Secondary species Prey offered to birds No. prey offered daily per bird No. days birds exposed No. birds exposed No. birds

dead No. survivors with signs of chlorophacinone toxicity a Reference (MRID)

Barn owl Rats fed choice of
0.005% bait or
untreated bait for 5 days 1

- 2 10 2 0 0 Mendenhall and
Pank 1980

MRID #
46750931

Black

- billed

magpie Rats fed 0.005% bait for 5 days Ad libitum 5 20 0 0 Baroch 1997

MRID#
44631402

American

kestrel Voles fed 0.01% bait
until dead 1 1 every 3 days 21

61 10

10 0

0 10 (eb/ih) 10 (eb/hi) Radvanyi et al.
1988
E39765Page 107 of 183 Red

- tailed

hawk Voles fed 10 g
0.0005% bait daily for up to 9 days 2 6 5 0 0 Askham 1988

E73126
Askham and
Poch é 1992 Great horned
owl Voles fed 10 g 0.005% bait daily for up to 9 days 2 6 1 0 0

Tawny owl Mice fed 0.0075%
bait b Ad libitum 10 4 0 (ct)

Riedel et al.
1991 c Eurasian
buzzard Mice fed 0.0075%
bait b Ad libitum 7
10
5

- 5

- 5 d

40 4

6
3
3 0
0

0
0 (ct) (ct) (ct) (ct)

Carrion crow Mice fed 0.0075%
bait b Ad libitum 10 4 0 (ct)

Eurasian
buzzard Mice fed 0.0075%
bait b 4 7 4 0 0 Anonymous
1978 c

Carrion crow Mice fed 0.0075%
bait b 3

- 4 3
5 12

12 0

0 0

0 Sterner 1978 c

White stork Mice fed 0.0075%
bait b Ad libitum (treated/untreated) 3

14 3
3 0
0 1 or 2 (ct) 1 or 2 (ct)

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

b baits registered in the U.S. are either 0.005% or 0.01% a.i.

c Cited in US EPA (2004) Potential Risks of Nine Rodentici des to Birds and Nontarget Mammals: a Comparative Approach and Joermann 1998

d the 3 5

- day treatment periods are separated by 3 days when the birds were fed untreated micePage 108 of 183 Table 5

- 20. Observed Effects of Diphacinone on Birds Consuming Contaminated Car casses

Secondary species Prey offered to birds No. prey offered daily per bird No. days birds exposed No. birds exposed No. birds

dead No. survivors with signs of diphacinone

toxicity a Reference (MRID)

Great horned
owl Mice fed choice of
0.01% bait or
untreated food for 10 days 2 5 3 2 1 (ct) Mendenhall and
Pank 1980

MRID #
46750931

Saw

- whet owl Mice fed choice of
0.01% bait or
untreated food for 10 days 2 5 1 1 No survivors Mendenhall and
Pank 1980

MRID #
46750931

Barn owl Mice fed choice of
0.01% bait or
untreated food for 10 days Ad libitum 10 2 0 0 Mendenhall and
Pank 1980

MRID #
46750931

American

crow Rats red 0.005% bait
until death 1

1

- 2 b 1

6 10

11 0
0 0 5 (eb/ct) Massey et al.
1997

Golden eagle Meat laced at 2.7 mg a.i./kg a.i. 454 g 5
10 4
3 0
0 4 (eb/ct) 3 (eb/ct) c Savarie et al.
1979

MRID#
00079312

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

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

c general weakness of all eagles was observed after 5 daysPage 109 of 183 Mammals

For the rodenticides considered in this assessment, 12 studies were found in which mammalian predators or scavengers were exposed to a rodenticide in whole or ground carcasses, usually rats or mice, or in spiked meat.

Mortality of 8 (42%) of 19 individua ls (foxes, mustelids, domestic dogs) occurred in 4 brodifacoum studies. Test subjects included 5 red foxes ( Vulpes vulpes ) and gray foxes ( Urocyon cinereoargenteus ), 4 mongooses ( Herpestes auropunctatus ), 4 weasels ( Mustela sp.) and 6 domestic dogs. Signs of toxicity were reported for most survivors ( Table 5

- 21 ).

There are no secondary studies on the toxicity of difethialone to mammals.

In 7 studies involving warfarin, only 9 (9%) of 100 individuals died after eating warfarin

- treated rodents ( Table 5

- 22 ) . Dead animals included 3 mink, 3 least weasels ( Mustela nivalis ), and 3 dogs.

Laboratory studies with chlorophacinone and diphacinone indicate that these chemicals present a hazard to mammal predators and scavengers. In 8 chlorophacinone studies, 32 (58 %) of 55 individuals died, including 7 of 8 mongooses, 3 of 7 coyotes, 1 of 4 red foxes, 18 of 35 ferrets, and 3 of 4 weasels ( Table 5

- 23 ). In 3 diphacinone studies, 19 (58%) of 33 test animals died after feeding on rodents fed diphacinone, liver tissue fr om owls fed diphacinone, or fortified meat. Species affected included mink ( Mustela vison ), mongooses, ermine, deer mice, rats, and dogs ( Table 5

- 24 ).

In one study with bromethalin, 4 dogs survived with no observed adverse effects after feeding for
14 da ys on rats that were poisoned for 1 day ( Table 5

- 25 ).Page 110 of 183 Table 5

- 21. Observed Effects of Brodifacoum on Mammals Consuming Contaminated Carcasses

Secondary species Prey offered to

mammals No. prey offered daily per

mammal No. days

mammals exposed No.

mammals exposed No.

mammals
dead No. survivors with signs of
brodifacoum

toxicity a Reference (MRID)

Red fox and

Gray fox Rats dosed at 15 mg a.i./kg c 400 g 1
3

4 2

1

2 0

1

1 2 (eb/ih)
No survivors

1 (eh/ih) ICI Americas,
Inc 1978a

Mongoose Rats fed 0.002% bait c for 5 days 1 1
3

6
10 1

1

1

1 0

1
0

0 nr No survivors

nr

nr Pank and Hirata
1976

Weasel Mice fed 0.002% bait c Ad libitum 16

- 25 4 4 No survivors Anonymous
1981 b
Dog (domestic) Rats dosed at 15 mg a.i./kg c 650 g 1

- 4 6 1 4 (eb/ih) ICI America, Inc
1978a

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

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

c rat and mouse registered baits in the U.S. are 0.005% a.i.

Table 5

- 22. Observed Effects of Warfarin on Mammals Consuming Contaminated Carcasses

Secondary species Prey offered to

mammals No. prey offered daily per

mammal No. days
mammals exposed No.
mammals exposed No.
mammals
dead No. survivors with signs of

warfarin toxicity a Reference (MRID)

Mink Nutria fed 0.025% bait
for at least 7 days Ad libitum 8

- 15 3 3 No survivors Evans and Ward
1967 b

Mink Rabbits fed 25 or 67 mg a.i./kg bait c for 5
weeks Ad libitum 28 50 0 0 Aulerich et al
1987Page 111 of 1 83 Least weasel Mice fed 0.001% bait, 0.005% bait,
Or 0.02% bait for 3 days c Ad libitum 90
29

- 90

12

- 57 2

2

2 0

1

2 2 (ct) 1 (ct)
No survivors Townsend et al.
1984

European

ferret Prairie dogs fed 0.05%
bait c for 15 days 1 7 10 0 0 Carlet and Mach
1997

MRID#
44995003

European

ferret Prairie dogs fed 0.05%
bait c for 15 days Ad libitum 5 10 0 0 Mach 1998

MRID#
44820001

Raccoon Rats fed 0.025% bait for 5 days 1
3 5
5 8
10 d 0
0 0
0 EPA 1982

Dog (domestic) Nutria fed 0.025% bait for at least 7 days Ad libitum 8

- 16 3 1 2 (eb/ct) Evans and Ward
1967 b

Dog (domestic) Mice fed 0.025% bait, 0.05% bait,
Mice dosed with 2.5 mg a.i., 10 mg a.i., 40 mg a.i. 4

- 10
10

1

1

1 56
56
56
25

17 4

1

1

1

1 0
0
0

1

1 0
0
0
No survivors
No survivors Prier and Derse
1962 b

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

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

c ra t and mouse registered baits in the U.S. are 0.025% a.i.

d the 10 test animals included the 8 individuals from the first trial plus 2 additional untested individuals

Table 5

- 23. Observed Effects of Chlorophacinone on Mammals Consuming Contaminated Carcasses

Secondary species Prey offered to

mammals No. prey offered daily per

mammal No. days
mammals exposed No.
mammals exposed No.
mammals

dead No. survivors with signs of chlorophacinone toxicity a Reference (MRID)Page 112 of 183 Mongoose Rats fed 0.005% bait
for 5 days 1 1
3
5

6

7
9
10 1

1

2

1

1

1

1 0

1

2

1

1

1

1 nr no survivors
no survivors
no survivors
no survivors
no survivors
no survivors Pank and Hirata
1976
MRID# 2467

Coyote Ground squirrels fed 15 g of 0.01% bait for 6 days 1 5 7 3 0 Marsh and
Howard 1986

MRID#
42760902

European

ferret Rats fed 0.005% bait for 5 days Ad libitum 5 20 11 nr Ahmed et al.
1996

MRID#
44631401

European

ferret Prairie dogs fed 25 g of 0.0025% bait daily for 6 days c 4 (1 every other day) 8 6 5 nr Fisher and Timm
1987

European

ferret Voles/mice fed
0.0075% bait c 5 total 4 2 1 d (ct) Bachhuber and
Beck 1988 f Red fox Mice fed 0.0075%
bait c 20 total 4 1 1 e no survivors

European

ferret Muskrats fed 0.0075%
bait c Ad libitum 4
8 2

1 0

1 1 (bl)
no survivors Jobsen 1798 f

European

ferret Voles fed 0.0075%
bait c Ad libitum 3 4 0 (ct) Anonymous
1983 f

Weasel Mice fed 0.005% bait At libitum 90 4 3 0 Anonymous
1981 fPage 113 of 183 a eb = external bleeding; ih = internal hematoma; bl = bleeding (unspecified); ct = increased blood coagulation time; nr = not reported

b ground squirrels were fed no

- choice for 3 days followed by 3 days in which they had a choice of bait or untreated labor atory chow

c baits registered in the U.S. are either 0.005% or 0.01% a.i.

d individual recovered from moribund state after administration of antidote, but assumed ‘dead’ without antidote treatment

e individual was sacrificed but considered ‘dead’ based on coagulation index

f Cited in US EPA (2004) Potential Risks of Nine Rodenticides to Birds and Nontarget Mammals: a Comparative Approach and Joerma nn 1998

Table 5

- 24. Observed Effects of Diphacinone on Mammals Consuming Contaminated Carcasses

Secondary species Prey offered to

mammals No. prey offered daily per

mammal No. days

mammals exposed No.

mammals exposed No.

mammals
dead No. survivors with signs of diphacinone

toxicity a Reference (MRID)

Mink Nutria fed 0.01% carrot bait for up to 10 days Ad libitum 5

- 18 3 3 no survivors Evans and ward
1967 b

Mongoose Rats fed 0.005% bait for 5 days 1 1
3
5

6

7
8
10 1

1

2

1

1

1

1 0

1

2

1

1

1

1 nr no survivors
no survivors
no survivors

no survivors
no survivors
no survivors Pank and Hirata
1976
MRID# 2467 Ermine Deer mice fed 0.01% bait for 10 days 2 5 2 1 nr

Striped skunk Deer mice fed 0.01% bait for 10 days 2 5 5 0 nr

Deer mouse Liver from diphacinone poisoned
owls 1 g daily 7 4 1 3 (ct)

Rat Meat containing 0.5 mg a.i./kg Ad libitum 6 8 4 nr Savarie et al.
1979Page 114 of 183 Dog (domestic) Nutria fed 0.01% carrot bait for up to 10 days Ad libitum 6

- 10 3 3 no survivors Evans and Ward
1967 b

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

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

Table 5

- 25. Observed Effects of Bromethalin on Mammals Consuming Contaminated Carcasses

Secondary species Prey offered to

mammals No. prey offered daily per

mammal No. days

mammals exposed No.

mammals exposed No.

mammals
dead No. survivors with signs of
bromethalin

toxicity a Reference (MRID)

Dog (domestic) Ground meat from rats
fed 0.005% a.i. bait for 1 day 600 g 14 4 0 0 Van Lier 1981Page 115 of 183 

### 5.4 Uncertainties

In addition to the uncertainties discussed in the primary risk characterization section ( Section 4 of this document), the following uncertainties apply to the analysis of secondary risk:

Accumulation of dose: Calculations used to estimate accumulation of rodenticides in target animals are dependent on available toxicity data and the eliminat ion potential for each chemical. Though this analysis assessed accumulation in both the house mouse and Norway rat, the LD50 values used are from laboratory rat studies. These species may have different sensitivities to the various rodenticides. However, E FED does not anticipate the sensitivity ranges for these species are greatly different given that the rodenticides are formulated to kill both mice and rats and available information suggests that target animals accumulate internal doses of rodenticides
be yond the median lethal dose. This analysis also made the conservative assumptions that prey animals consumed 100% of their diet as bait for the duration of the accumulation period (1 to 6 days) and that100% of residues in the prey is available to the consu mer. To determine how conservative calculated body burdens in target animals are and to provide a lower end secondary exposure estimate, a n empirical analysis on whole body residues in prey was conducted. Risks were similar when considering both the estima ted and empirical residues , indicating that the conservative assumptions in the estimated residue levels did not impact overall risk
characterization.

In addition, elimination half

- lives used to assess the accumulation of rodenticides in target
animals are based on liver half

- lives, where available, which is a conservative surrogate value for what is likely a multi compartment process. However, the conservative nature of these liver half

life values are potentially counterbalanced by EFED’s use of first order elimination equations, which likely underestimate elimination half

- lives that are generally biphasic in nature. In addition, LD 50 values used to calculate RQs are based on external doses and as such do not account for absorption either. In order to a llow for comparisons of half

- lives among chemicals,
liver half

- lives for brodifacoum, difethialone, warfarin, and chlorophacinone from the same study by Vandenbroucke et al. (2011) were selected. Although this approach reduces variability
due to difference s attributed to laboratories, it is not necessarily the most conservative approach that could be undertaken. For instance, the liver half

- life value for difethialone that was reported by Vandenbroucke (28 days) is lower than provided in other studies (74 d ays from Belleville, 1991). This difference does not impact the ultimate risk characterization for difethialone, but it may mean that the potential for risk has been underestimated for this chemical, especially in the number of target animals that is required to reach an LD 50 dose in secondary consumers. Though
a liver half

- life value is available for diphacinone, it is based on pig data, which differs from the organisms used in the other studies. There is some indication from the available half

- life studies that species react to anticoagulant rodenticides differently. Therefore, this pig value mayPage 116 of 183 overestimate or underestimate the liver half

- life of rats for this chemical. For brome thalin, there
is no available data on the liver half

- life for bromethalin, so a blood plasma value is used instead. It is uncertain how a blood plasma half

- live would differ from the liver half

- life for this
chemical.

Secondary toxicity data: For this assessment, EFED used standard bird and mammal test species to estimate weight

- adjusted LD 50 values for secondary animals. This approach was employed because acceptable secondary toxicity studies were not available for all of the assessed
rodenticides and use of the standard test species, which were common among all of the rodenticides, allowed for comparisons of results among chemicals. However, this method may
not be conservative. As discussed in the toxicity section above, for diphacinone, an LD 50 of 96. 8

mg a.i /kg

- bwt is available for one raptor species (American kestrel, Falco sparverius ) (Rattner et
al . 2011). This study suggests that American kestrels may be more sensitive than the standard test species ( i.e., based on the available studies, 17 to 21 times more sensitive than bobwhite quail and 33 times more sensitive than mallard ducks). None of the other evaluated rodenticides
have data for which an LD 50 for raptors, or, more generally, predatory birds is available. If the sensitivity of the American kestrel to diphacinone is representative of other species of raptors, this information suggests that raptors may be more sensitive to diphacinone than either bobwhite quail or mallard duck. The potential for increased sensitivity of raptors to warfarin wa s observed by Watanabe et al (2010), who demonstrated that hydroxylation rates of warfarin in the great horned owl ( Bubo virginianus ) and snowy owl ( Bubo scandiacus ) were much less than that observed in mallards, chickens ( Gallus gallus ), and laboratory ra ts. This study suggests that raptors may metabolize and detoxify warfarin at slower rates compared to mallard ducks. Taken together, these data may indicate that raptors, which represent secondary consumers of rodenticides, are more sensitive to rodenticid es when compared to the standard test species used to derive the RQs calculated in this assessment.

Secondary exposure data: Though secondary exposure studies provide information on the potential effects from rodenticide exposure that may occur under fiel d conditions, it is often not possible to quantify the level of exposure or the sensitivity of the exposed animals because rodenticide residues are not quantitatively sampled in either the prey organisms or secondary consumers. Most studies exposed prey an imals ( i.e. , rats, mice, or voles) to the rodenticide for a variable number of days before providing the moribund animals to the predators. Even in those instances where predators were fed ground meat spiked with specific doses of rodenticide, the study de signs vary too widely and the sample sizes are far too small to draw any quantitative conclusions. In addition, secondary exposure studies are not available for all of the assessed
rodenticides.

Residue data: Available residue studies used in empirical ri sk characterization vary widely in the study organisms used, sample design, and analytical methods. Many of the studies are fieldPage 117 of 183 studies which makes it difficult to quantify the level of exposure. In addition, residue data was
not available for all of the assessed rodenticides.



### 5.5 Discussion of Risks of Rodenticides to Secondary Birds and Mammals

The assessment of secondary exposure risks for wildlife involved a series of assessment methodologies that encompassed both theoretical accumulation of rodenticides in a prey base as well as empirical measurements of rodenticide residues in prey. Based on the analysis of number of prey organisms necessary to reach an LD50 dose in secondary birds and mammals, the following general conclusions can be made: 1) brodifacoum, difethialone, and bromethalin pose greater secondary risk than warfarin, chlorophacinone , and diphacinone, 2) mammals are more at risk from consumption of contaminated prey than birds, 3) smaller secondary consumers are at a greater risk than larger secondary consumers, and 4) prey that have accumulated more rodenticide through longer exposur e periods pose greater secondary risks to secondary birds and
mammals.

For brodifacoum and difethialone, a combination of toxicity and biological persistence results in a trigger for secondary exposure risk concerns for all mammals and birds regardless o f the assessment method (theoretical and empirical). The delayed time to mortality for brodifacoum coupled with its slow clearance time results in small mammal target accumulation of this rodenticide to levels that are two orders of magnitude above the let hal toxicity endpoints ( i.e.

, LD 50 values) suggesting an enhanced opportunity for secondary exposure. Furthering the concern for secondary exposure, an analysis of the number of target individuals necessary for consumption to achieve a lethal dose in the s econdary consumers reveals that brodifacoum residue in a single prey item is sufficient to trigger lethal risk concerns for birds and mammals. These conclusions are supported by available data from secondary toxicity studies where 63% of secondary birds an d 42% of secondary mammals fed brodifacoum contaminated prey organisms died. For difethialone, an analysis of the number of target individuals necessary for consumption of a lethal dose in the secondary consumers reveals that, on average, birds would need to consume <1 to 27 mice or <1 to 5 rats, depending on weight class and accumulation scenario assessed, to reach a lethal dose. For mammals, <1 to 2 rat would be sufficient to reach a lethal dose, while up to 11 mice would be necessary to reach the media n lethal dose. The difference in risk can be attributed primarily to the faster clearance times in mammalian prey. However, as noted in the assessment, there is an uncertainty associated with the clearance rate for difethialone, and adoption of a biologica l half

- life more in

- line with brodifacoum would yield results similar to that chemical. In addition, secondary toxicity studies may provide further information on the secondary exposure risk concerns for difethialone; however, none are currently available.Page 118 of 183 For warfarin, there are no LOC exceedances for avian wildlife except for secondary consumer birds in the smallest weight class assessed consuming mice exposed to the highest concentration of warfarin for six days. An analysis of the number of target ind ividuals necessary to reach an

LD 50 dose in secondary birds supports this conclusion since birds would need to consume 3 to 1,587 mice or <1 to 284 rats exposed to the high concentration warfarin (0.054%) bait, depending on weight class and accumulation sc enario assessed. Birds exposed to the low concentration warfarin (0.025%) bait would have to consume 7 to 3,429 mice or 1 to 614 rats to reach the median lethal dose. Based on this calculation it is not likely that secondary birds of the weight classes ass essed would be able to consume enough mice or rats necessary to accumulate a lethal dose. However, this analysis suggests that small birds consuming small and large prey exposed to warfarin bait for six consecutive days may be at risk. I n this case, birds would only need to consume up to approximately 6 mice or 1 rat, depending on concentration of warfarin bait, to reach a lethal dose. This analysis is somewhat conservative because it assumes that prey animals are consuming 100% of their diet as bait for 6 consecutive days. Secondary toxicity studies had no mortalities and few signs of warfarin toxicity were observed. C onclusions for mammalian secondary risk are somewhat mixed and depend on the concentration of bait and the analysis method. However, seconda ry toxicity studies conducted with secondary mammals indicate that there is the potential for lethal exposure to occur. These conclusions are further supported by an analysis of the number of target species necessary for consumption of a lethal
dose in the secondary consumers, which reveals that residue levels in less than one prey item is sufficient to trigger lethal risk concerns for mammals, except for larger mammals consuming
mice.

There are no LOC exceedances identified for avian wildlife exposed to chlorophacinone based on risk calculations. An analysis of the number of target species necessary to reach an LD 50 dose in secondary birds supports this conclusion since birds would need to consume 23 to > 11,000 mice or 4 to 2,094 rats to reach the median lethal dose. Based on this calculation it is not likely that secondary birds of the weight classes assessed would be able to consume enough mice or rats necessary to accumulate a lethal dose. Available secondary toxicity data, where no
mortalities and few signs of chlorophacinone toxicity were observed, support this conclusion. For mammals, there were LOC exceedances for all mammals on a dietary basis considering both theoretical and empirical estimates of exposure. On an acute basis, empirical data would suggest
that there are no LOC exceedances for mammals exposed to chlorophacinone residues in prey. However, theoretical exposure calculations yield concerns for all mammals eating mice exposed to a single dose and an accumulation dose. These conclusions a re supported by available data from secondary toxicity studies where 58% of secondary mammals fed chlorophacinone contaminated prey organisms died and signs of chlorophacinone toxicity were observed in survivors. These conclusions are further supported by an analysis of the number of target individuals necessary for consumption of a lethal dose in the secondary consumers reveals that,
mammals would need to consume <1 to 60 mice or < to 11 rats to reach a lethal dose. It isPage 119 of 183 important to note that mammals in the smallest weight class assessed would be at greater risk than larger mammals. Mammals in this weight class would need to consume <1 to 3 mice, depending on the accumulation scenario, or < 1 rat.

For diphacinone, there were no LOC exceedances as a resu lt of secondary exposure for avian wildlife considering both theoretical and empirical estimates of exposure. An analysis of the number of target individuals necessary to reach an LD 50 dose in secondary birds supports this
conclusion since birds would need to consume 183 to >17000 mice or 33 to >13,000 rats to reach the median lethal dose. Based on this calculation it is not likely that secondary birds of the weight classes assessed would be able to consume enough mice necessary to accumulate this
dose. How ever, secondary toxicity studies conducted with selected raptors indicate that there may be differences in sensitivity for these birds as compared to the species that effects endpoints used the risk assessment, potentially leading to underestimation of ris ks of diphacinone to secondary birds. A study by Rattner et al. (2011) found that American Kestrels ( Falco sparverius ) may be nearly 20 times more sensitive to diphacinone than the species (bobwhite quail and mallard duck) providing endpoints for this asse ssment. For further understanding of the implications of this observation on the findings of the risk assessment as a whole, the reader is directed to the cumulative evaluation of all lines of evidence elsewhere in the document ( Section

7 ). For mammals, ri sk concerns were identified for all mammals on a dietary basis considering both theoretical and empirical estimates of exposure. On an acute basis, empirical data would suggest that there were no LOC exceedances for mammals exposed to diphacinone residues in prey. However, RQs based on theoretical exposure calculations exceeded LOCs for all mammals eating mice exposed to a single dose and an accumulation dose. These conclusions are further supported by an analysis of the number of target species necessary f or consumption of an LD 50 dose in the secondary consumers reveals that mammals would need to consume <1 to 18 mice or <1 to 3 rats to reach this dose. It is important to note that mammals in the smallest weight class assessed would be at greater risk than larger mammals. Mammals in this weight class would need to consume less than one mouse or rat exposed to diphacinone bait for one to six days.

For the non

- anticoagulant rodenticide, bromethalin, there are LOC exceedances for birds based on the single or al dose and the six

- day accumulation for all weight classes assessed except for the medium and large weight classes consuming rats. An analysis of the number of target individuals necessary for consumption of a lethal dose in the secondary consumers reveal s that
birds would need to consume <1 to 104 mice and <1 to 17 rats to reach an LD 50 dose. The small and medium weight classes assessed would be at greater risk than larger birds. Birds in the smallest weight class would only need to consume 1 mouse or rat exposed to bromethalin bait, while birds in the medium weight class would need to consume up to 3 rats exposed to bromethalin bait. There are no secondary feeding studies available to support or refute this risk conclusion for birds. For mammals, RQs base d on theoretical exposure calculations exceeded LOCs for all mammals on a single oral dose, six

- day accumulation, and dietary basis. However,Page 120 of 183 in the absence of bromethalin residue data this could not be assessed empirically. Secondary toxicity studies indi cate that there is limited toxicity to mammals exposed to bromethalin residues in prey organisms. An analysis of the number of target species necessary for consumption of a lethal dose in the secondary consumers reveals that residue in <1 to 11 mice
and <1 to 2 rats is sufficient to trigger lethal risk concerns for mammals. H owever, a recent study by Pitt et al. (2011) found that time to death for house mice, Polynesian rats ( Rattus
exulans ), and black rats ( Rattus rattus ) offered bromethalin may be more rapid than suggested in registrant submitted data for the Norway rat, which may reduce the potential for bromethalin to accumulate in prey organisms. Data from this study also suggest that house mice and Polynesian

rats ex posed to bromethalin bait may stop feeding on the bait after reaching a lethal dose, further reducing the potential for accumulation. In addition, an analysis of the grams of bait necessary to

consume an LD 50 dose in primary consumers previously discussed (see Section 4 ) suggests that large mammals would only need to consume 13 grams of bait to reach this dose, which is significantly less than would be required to reach an LD 50 dose in a secondary consumer. Risk assessment based on dietary concentration and dietary toxicity supports this contention for birds. However, the absence of bromethalin residue data limits the confidence in the assumption of low prey accumulation.



## 6 Wildlife Incidents

6.1 Mortality Incidents

6.1.1 Introduction

This section reviews reported incidents of wildlife mortality that have been linked to rodenticide exposure. As the ecological risks from exposure to rodenticides are only to terrestrial vertebrates (as opposed to aquatic organisms, plants, or invertebrat es), the incident review was carried out only for incidents of adverse effects to wild terrestrial vertebrates (hereafter referred to as ‘wildlife’). The incidents generally involved mortality

, but occasionally included incapacitated
animals which recover ed after treatment by a veterinarian . Incidents to pets and domesticated animals were not included in this analysis, but are reviewed in the HED document

“ Rodenticides: Tier 2 Pet Incident Report in Support of NOIC” (October, 2011)

. In this report,
the A gency evaluates wildlife mortality incidents for the four rodenticides involved in the NOIC (brodifacoum, difethialone, warfarin, and bromethalin) as well as chlorophacinone and diphacinone, which are rodenticides with current conforming labels that may se rve as alternatives for residential commensal rodent control. In addition, the Agency compiles and
evaluates incid ents of documented rodenticide exposure s in wildlife which were not necessarily associated with any observed adverse effects. These exposure incidents were generally reports of anticoagulant rodenticides being measured in the liver tissues of wild animals which were determined to die from causes unrelated to rodenticide poisoning.Page 121 of 183 Reported incidents for each of the active ingredients are summarized as counts of reported
incidents and compiled based on three variables: exposure type (primary or secondary), certainty level, and location (rural/field versus urban/suburban). The certainty levels indicate the
likelihood that a particular rodenticide ingredient caused the effects observed in the animal. These levels were assigned to the incidents by the EPA when the incident records were entered
into the Ecological Incident Information System ( EIIS ) . For this analysis, incidents were furt her categorized by exposure type and location using the methods described in the next section. The purpose of the exposure type categorization was to evaluate how many of the incidents were likely related to primary exposure, i.e. animals directly consumi ng the rodenticide bait, versus secondary exposure, i.e. animals consuming other animals that ingested the bait and had detectable levels of rodenticide residues in their bodies. The purpose of the location categorization was to evaluate the occurrence of incidents in urban/suburban areas, which are thought to be predominantly related to residential and commercial uses, versus incidents that occurred in rural/field areas which may be related to agricultural uses of rodenticides. The analyses performed in this section focus on incidents that have been reported in the United
States. Incidents from other countries are dealt with separately in Section 6.1.2

Interpretation of incident data is difficult and may be confounded by a number of factors (see
Section 6 .1.2.1 for a discussion of limitations and uncertainties). The report of an incident can demonstrate that a complete exposure pathway result ing in an effect (i.e.

, mortality) has
occurred

. The lack of incidents or the presence of fewer incidents in and of itself for various chemicals does not necessarily suggest that fewer incidents are occurring or that one chemical is safer than another. However, incident data can corroborate results from the deterministic risk assessment presented in this assessment

. In addition, the incident data were used in this

assessment to describe general land use patterns where effects have occurred and to describe whether mortality has been reported for different exposure types (e.g., primary exposure vs. secondary exposure s) as described in more detail in subsequent sections.

The number of incidents that have been reported are thought to represent a very small fraction of
actual incidents that have occurred. Also, a number of factors may influence reporting frequency
th at can differ across the chemicals including location of the labeled uses (agricultural vs. commensal rodent control), timing of high

- end use relative to efforts to document incidents (for example, warfarin use has been low relative to its peak for a numbe r of years), and chemical properties such as persistence in a carcass . For these reason s , it is difficult to make meaningful comparisons across the different rodenticides with respect to the number of incidents for each

one

. Nonetheless, some comparisons of primary and secondary risks can be made when incorporating all lines of evidence used to describe potential risks in this document, including the presence of incidents. Overall conclusions related to all lines of evidence, including risk
characteriza tion and incident reports, are presented in Section 7 of this assessment.Page 122 of 183 6.1.2 Methods

Databases

Incidents were primarily obtained from the Ecological Incident Information System (EIIS), a database of incidents of adverse effects to nontarget wild animals and plants attributed to pesticide exposure which is maintained by the Environmental Fate and Effects Division (EFED) of the Office of Pesticide Programs (OPP). 1 A summary of each of the incidents for the
rodenticides considered in this assessment is pro vided in Appendix D

.

E cological incident reports entered into EIIS are generally from two main sources: pesticide registrants and state government offices. The majority of the reported incidents used for this analysis were provided by the states (predominantly New York and California); registrant
submitted incidents make up a smaller number of reported incidents.

Incidents recorded in EIIS were cross

- referenced with those found in the Incident Data System (IDS). The IDS database, unlike EIIS, is maintained by the Information Technology and Resources Management Division (ITRMD) of OPP. IDS tracks incident reports submitted by registrants in compliance to the Federal Insecticide Fungicide and Rodenticide Act (FIFRA) section 6(a)(2) regulations (which requires registrants to report incidents of adverse effects) as well as incident reports that are obtained from other sources, such as offices of state governments. In most cases, incidents within the EIIS corresponded with an incident report

reco rded in IDS

The Contaminant Exposure and Effects

– Terrestrial Vertebrate (CEE

- TV) 2 Database maintained by the U.S. Geological Survey was also queried for rodenticide

- related wildlife incident s. O nly
one incident was identified that was linked to the in gredients evaluated here and was not already
recorded in EIIS.

The Avian Incident Monitoring System 3 (AIMS), an on

- line database of pesticide

- related avian incidents that is maintained by the American Bird Conservancy, was also consulted, but no unique rodenticide incidents were identified in this database that were not in EIIS.

The ITRMD maintained Aggregate Incidents Database was not consulted primarily due to the fact that EIIS and IDS provide more robust reports. The Aggregate Incidents Database provides only counts for mammalian and fish incidents (grouped), terrestrial plan ts, and other non

- target

1 EFED is a division part of OPP. OPP is one of the offices that is part of the Office of Chemical Safety and Pollution Prevention (OCSPP).

2 http://www.pwrc.usgs.gov/contaminants

- online/pages/CEETV/CEETVintro.htm

3 http://www.abcbirds.org/abcprograms/policy/toxins/aims/aimsPage 123 of 183 wildlife. Other than providing the relative counts, these reports are not accompanied by any certainty , legality, location information, pathology report, or residue analysis. Therefore, this database was not queried for wildlife morality incident reports.

An incident report within EIIS will have information about the legality of use ( e.g ., registered use or a misuse), certainty (how certain a particular pesticide caused the incident), and use
location associated with that inciden t (see below). The legality index refers to the determination of the incident investigation as to whether the rodenticide used linked to the incident was in compliance with the label. In all but 25 of the incidents evaluated for this report, the legality was “undetermined ,” typically because information was not available to linking the incident to a specific product and use. A few incidents were excluded from the analysis because they were associated with intentional misuse of rodenticides, primarily be cause products labeled for commensal rodent controls were intentionally used to control pest species not on the label, such as squirrels.

An important consideration when examining the incident data is that one reported wildlife mortality incident does not necessarily correspond with a single dead animal. Several of the rodenticide incidents involved multiple animals of the same species and sometimes multiple animals of different species. Since brodifacoum had the majority of incidents associated with it, this separate analysis is of the totals of the individual organisms affected was performed along with the number of incidents only for this chemical.

A certainty index was assigned for each active ingredient linked to each incident. The certainty
index indicates the likelihood that a particular ingredient was the cause of the adverse effects observed in the incident. Certainty index values range from “unlikely” to “highly probable” “Unrelated” is also a certainty category used in EIIS but incidents wit h this certainty value were excluded from the analysis. 27 incidents in which rodenticide residues were detected in tissue but were assigned a certainty of “unlikely” are discussed in Section 6.1.2 because they provide information on rodenticide exposure in wildlife. In many cases, the certainty index value was determined by the wildlife pathologist who performed the necropsy and compiled the chemical residue analysis results (where applicable). I n incidents where the certainty determination was not provided in the submitted report, staff of EFED assigned the certainty index based on tissue residue data and other diagnostic and circumstantial evidence provided in the incident report. However, whe never the submitted report included a certainty conclusion made by the wildlife pathologist who investigated the incident, this conclusion was never altered.

Characterizing Incidents as Primary and Secondary Exposure

An attempt was also made to character ize the exposure type of each incident as either “primary” or “secondary.” Primary exposure refers to incidents where the animal was exposed to thePage 124 of 183 rodenticide through direct consumption of bait, whereas secondary exposure refers to incidents
where animal s prey or scavenge on other animals which consumed rodenticide bait. This designation was based primarily on the diet of the species affected. For example, raptors such as owls, hawks, and eagles were assigned an exposure code of “S” due to their carnivo rous feeding habits and the likelihood that they preyed or scavenged upon a rodenticide

- exposed animal. In contrast, strict herbivores such as squirrels and deer were assigned “P” because they likely fed on the bait directly. For omnivorous species such as crows, raccoons, and opossums, for which the exposure could have been either primary or secondary, the findings of the necropsy analysis and reported the gastrointestinal (GI) were consulted when available. When the GI contents to contain granules or m aterial resembling bait, probable primary exposure was assigned. When the necropsy analysis noted bone fragments or tissues of another organism in the GI tract, probable secondary exposure was assigned. Finally, when the incident involved an omnivorous

s pecies and the necropsy report provided no useful information on the contents of the GI tract,
unknown exposure was assigned.

Characteriz ing the Location of Incidents

One question that was investigated through analysis of incident data is whether use o f rodenticide baits by homeowners and businesses to control commensal rodents in urban and suburban areas pose a hazard to nontarget wildlife. This question was investigated by considering the locations of the reported incidents relative to u rban

, suburba n , and rural areas. When possible, the locations of incidents were categorized as being “urban/suburban” or “rural” based on the location where the affected animals were found. This categorization was often based on information provided in the incident r eport on the land use type of the site of the
incident and is recorded in the Habitat field of EIIS. In some instances, this field was entered as “not reported” (N/R) due to lack of information. In other case s , the location category was often
determined from information given in the wildlife pathologist report on the location where the carcass was picked up. In some reports, the actual address of the site of the incident was provided. In those instances, the address was located using mapping software to ascertain its proximity to developed areas. A few incidents , including ones that occurred from use in zoos or from use in island rat eradication programs, were not considered representative of either typical urban or rural areas and thus were pooled with the “not reported” incidents. This spatial type of analysis was only performed for brodifacoum as the incident reports were numerous and detailed enough to conduct that type of analysis.

6.1.3 Primary Exposure Incidents

6.1.3.1 Brodifacoum

Counts of reported wildlife mortality incidents occurring in the United States, w hich are
attributed to exposure to brodifacoum

, are provided below ( Tab l e 6

- 1 )

. Counts are shownPage 125 of 183 accumulated by three factors, (1) whether the exposure was believed to be primary or secondary ( or unknown), (2) whether the incident occurred in a rural or urban/suburban location (or unknown), and (3) the certainty level assigned indicating the likelihood that the given active ingredient was the cause of the incident. Because some incidents involv e the death of multiple animals, Table 6

- 2 provides a summary of the number of mortalities observed in incidents
attributed to brodifacoum. A summary of each of these incidents included in these counts are provided in Appendix D

.

Table 6

- 1

. Summary of W ildlife Incidents Linked to Brodifacoum Exposure.

Exposure Location Possible Probable Highly Probable Total
Primary Rural 1 0 3 4

Urban /Suburban 1 8 25 34

Unknown 0 5 1 6

Total 2 13 29 44
Secondary Rural 5 9 36 50

Urban /Suburban 7 29 61 97

Unknown 5 12 22 39

Total 17 50 119 186

Unknown R ural 4 2 2 8

Urban /Suburban 1 5 13 19

Unknown 3 1 1 5

Island (rat eradication) 0 0 2 2

Other (Zoo) 0 2 1 3

Total 8 10 19 37

Grand Total 27 73 167 267Page 126 of 183 Table 6

- 2 . Summary of Number of Mortalities (Total Number of Individuals Affected) in Wildlife Incidents Linked to Brodifacoum Exposure

Exposure Location Possible Probable Highly Probable Total
Primary Rural 0 0 10 10

Urban /Suburban 0 10 40 50

Unknown 1 12 1 14

Total 1 22 51 74
Secondary Rural 4 14 49 67

Urban /Suburban 6 24 55 85

Unknown 4 12 32 48
Other (Golf Course, Military base) 0 1 1 2

Total 14 51 137 2 02

Unknown Rural 4 29 6 39

Urban /Suburban 1 5 10 16

Unknown 4 1 3 8

Other (Zoo) 0 28 5 33

Total 9 63 24 9 6

Grand Total 24 136 212 372

Many wildlife mortality incidents have been attributed to primary poisoning by brodifacoum, and the majority of the primary incidents have been linked to rodenticide poisoning with high certainty. Of the 35 incidents which were attributed to primary poisoning, all but one has a certainty index rating of “probable” or “highly probable.” Most of these incidents have involved deer, squirrels, chipmunks, and passerine birds , all of which are believed to have been poisoned by directly consuming brodifacoum bait. Of the 35 primary

- exposure incidents , 25 (71%) were identified as occurring in urban or suburban/residential areas. This indicates that use of
brodifacoum as a rodenticide represents a complete exposure pathway for non

- target wildlife via primary exposure that can result in mortality for birds and mammals.

Stone et al. (1999) report ed on six primary poisoning incidents of white

- tailed deer which occurred on Fire Island, a barrier island on the south shore of Long Island, NY. Four of the
incidents were associated with brodifacoum and two were associated with diphacinone . The incidents were believed to have resulted from outdoor residential use of rodenticides by
homeowners on the island. They concluded that the risk of deer ingesting rodenticide bait is high in suburban residential areas like Fire Island

, where favorable habitat and restriction of hunting creates high deer density, and thus the population food limited. A similar situation occurred in the winter of 2008 on Big Pine Key in southern Florida, where the death of three keyPage 127 of 183 deer ( Odocoileus virginianus clavium ) was linked to exposure to anticoagulant bait placed by homeowners in the area (EIIS Incident I020713

- 00 2). Surveys of wildlife mortality following the use of brodifacoum by the US Fish and Wildlife Service for rat eradication on islands also has documented mortality of birds of species which would likely have been exposed by primary exposure ( e.g . emperor goose, gray

- crowned rosey finch, and rock ptarmigan), although the majority of mortality was to species which could have been exposed by secondary exposure (Ornithological Council, 2010).

An additional 37 incidents could not be identified as being caused by primary or secondary poisoning. Most of these incidents were of omnivorous species which potentially could have consumed either the bait directly or a living or dead animal which had fe d on the bait. The most common species in this group are the American crow ( Corvus brachyrhynchos ) , the red fox ( Vulpes vulpes ) , the gray fox ( Urocyon cinereoargenteus ) , and the raccoon ( Procyon lotor )

. These incidents were also associated with residentia l and commercial uses of bait, with 19 of the
37 incidents ( 51 %) occurring in areas identified as urban or suburban, whereas only 8 out of (2 2 %) occurred in areas identified as rural. The location could not be characterized in the remaining 10 incidents.

Spat i al an alysis was performed on wildlife incidents which occurred in the state of New York ( Figure 6

- 1 ). Symbols are used to distinguish incidents associated with primary exposure (triangles) and secondary exposure (stars). Only incident reports whi ch had exact location information where the carcasses were found were included in this analysis. Locations of incidents were overlaid on a graphical representation of human population density by county. Figure 1shows that reported primary incidents (as w ell as secondary incidents) have been reported in areas of high population density. The majority of primary incidents were clustered in the highly populated urban and or suburban/residential areas of New York City, Albany, Buffalo, Syracuse, and Utica. T he association of reported primary wildlife mortality incidents with urban could in part be the result of more people being present in urban areas to observe and report dead carcasses, thereby making the reporting rates higher in those areas compared to ru ral areas. Thus, it is not known if there is a difference in the frequency of occurrence of primary incidents
between urban and rural areas ; however, the incident data do show that primary incidents involving brodifacoum occur in urban/suburban areas

.Page 128 of 183 Figure 6

- 1 . Spatial analysis of wildlife mortality incidents attributed to primary and secondary exposure to brodifacoum in New York State

.

6.1.3.2 Difethialone

Counts of reported wildlife mortality incidents occurring in the United St ates, which are
attributed to exposure to difethialone are provided below ( Tab l e 6

- 3 ). Counts are shown accumulated by three factors, (1) whether the exposure was believed to be primary or secondary (or unknown), (2) whether the incident occurred in a rural or urban/suburban location (or unknown), and (3) the certainty level assigned indicating the likelihood that the given active ingredient was the cause of the incident. There was one reported incident attributed to primary exposure and 4 re p orted inc idents attributed to secondary exposure. All reported incident for difethialone (primary and secondary exposures) occurred in urban/suburban areas. A summary
of each of these incidents included in these counts are provided in Appendix D

.Page 129 of 183 Table 6

- 3

. Summary of Wildlife Incidents Linked to Difethialone Exposure

Exposure Location Possible Probable Highly Probable Total
Primary Rural 0 0 0 0

Urban/Suburban 1 0 0 1

Unknown 0 0 0 0

Total 1 0 0 1
Secondary Rural 0 0 0 0

Urban/Suburban 0 4 0 4

Unknown 0 0 0 0

Total 0 4 0 4

Grand Total 1 4 0 5

6.1.3.3 Warfarin

Counts of wildlife mortality incidents reported to the Agency which are attributed to primary and secondary poisoning warfarin are shown in Table 6

- 4

. T hree incidents have been identified as being caused by primary exposure to warfarin. This indicates that use of warfarin as a rodenticide represents a complete exposure pathway for non

- target wildlife via primary exposure that can result in mortality for birds and mammals. Two of the incid ents were assigned a certainty level of “probable” and the other one was assigned a level of “possible.” Species affected include squirrels and northern bobwhite quail

. T wo incidents occurred in 1981 and one
occurred in 1971. The lack of recent reported incidents involving warfarin may be attributed to
decreased use ; however, primary incidents were reported during the years when warfarin use was widespread

. The number of incidents are too few to draw any conclusions concerning the frequency of incidents with use in rural versus urban/suburban areas. A summary of each of these incidents included in these counts are provided in Appendix D

.

Table 6

- 4 . Summary of Wildlife Mortality Incidents Linked to Warfarin Exposure

Exposure Location Possible Probable Highly
Probable Total
Primary Rural 1 0 0 1

Urban /Suburban 0 0 0 0

Unknown 0 2 0 2

Total 1 2 0 3 Secondary Rural 0 1 0 1

Urban /Suburban 0 1 0 1

Unknown 0 1 2 3

Total 0 3 2 5

Grand Total 1 5 2 8Page 130 of 183 6.1.3.4 Bromethalin

One primary incident has been reported for bromethalin ( Table 6

- 5 ) . That incident involved the death of a chipmunk following consumption of a rodenticide bait product which contained
bromethalin. This indicates that use of bromethalin as a rodenticide repre sents a complete exposure pathway for non

- target wildlife via primary exposure that can result in mortality for
mammals.

The low number of primary incidents for bromethalin could be explained, at least in part, by the failure of investigations of wildli fe incidents to identify this ingredient as the cause of primary poisoning incidents. This may be attributed to two factors. First, b romethalin has a different
chemical structure compared to anticoagulant rodenticides and requires a different analytical

m ethod for detection and quantification . B romethalin is not normally included in the analytical screen for rodenticides conducted on tissue from wildlife carcasses, which normally include only a screen of anticoagulant rodenticides ( P ersonal communication

, Joseph Okoniewski, New York Department of Environmental Conservation and Stella McMillin, California Department of Fish & Game). Second , bromethalin poisoning does not result in clinical signs that are obvious in gross necropsy examinations, and thus the re may not be cues that would trigger the investigator to seek analysis to detect bromethalin. A summary of each of these incidents included in these counts are provided in Appendix D

.

Table 6

- 5

. Summary of Wildlife Mortality Incidents Linked to Brome thalin Exposure

Exposure Possible Probable Highly Probable Total

Primary 0 1 0 1

Total 0 1 0 1

6.1.3.5 Chlorophacinone

Chlorophacinone is linked to 11 total incidents, six of which can be attributed to primary poisoning ( Table 6

- 6 )

. The primary exposure incidents involved quail, turkeys, and squirrels. Primary incidents have occurred in both rural and urban/suburban locations. This indicates that
use of chlorophacinone as a rodenticide represents a complete exposure pathway for no n

- target wildlife via primary exposure that can result in mortality for birds and mammals

. A summary of each of these incidents included in these counts are provided in Appendix D

.

Table 6

- 6 . Summary of Wildlife Mortality Incidents Linked to Chlorophacinone Exposure

Exposure Location Possible Probable Highly Probable Total
Primary Rural 1 1 1 3

Urban/Suburban 1 1 1 3

Total 2 2 2 6Page 131 of 183 Table 6

- 6 . Summary of Wildlife Mortality Incidents Linked to Chlorophacinone Exposure

Exposure Location Possible Probable Highly Probable Total Secondary Rural 0 0 1 1

Urban/Suburban 0 1 0 1

Unknown 0 1 1 2

Total 0 2 2 4

Unknown Rural 0 0 1 1

Grand Total 2 4 5 11

6.1.3.6 Diphacinone

Diphacinone is linked to 19 total incidents, 10 of which are for primary consumers ( Table 6

- 7 ). The primary exposure incidents involved deer, squirrels, pigeons and kangaroo rats Primary
incidents have occurred in both rural and urban/suburban locations. This indicates that use of
di phacinone use as a rodenticide represents a complete exposure pathway for non

- target wildlife via primary exposure that can resul t in mortality to birds and mammals

. A summary of each of
these incidents included in these counts are provided in Appendix D

.

Table 6

- 7 . Summary of Wildlife Mortality Incidents Linked to Diphacinone Exposure

Exposure Location Possible Probable Highly Probable Total
Primary Rural 0 1 0 1

Urban/Suburban 1 1 3 5

Unknown 1 2 1 4

Total 2 4 4 10
Secondary Rural 0 0 2 2

Urban/Suburban 0 2 0 2

Unknown 1 2 2 5

Total 1 4 4 9

Grand Total 3 8 8 19

6.1.4 Secondary Exposure Incidents

6.1.4.1 Brodifacoum

Analysis of incident reports attributed to brodifacoum exposure show 186 incidents assoc iated with secondary exposure. The majority of these incidents (16 4 out of 186

, 88 %) had high certainty for being caused by brodifacoum, with a certainty index value of “probable” or “highly probable.” This is because most of the incidents were identified by the presence of brodifacoumPage 132 of 183 residues in the liver of the poisoned species, oft en along with supporting evidence of anticoagulation poisoning from the necropsy examination. Indecent reports pertained to mortalities of a wide variety of raptor species , including hawks , eagles, and owls

. A variety of predatory and scavenger mammals w ere also reported in association with brodifacoum poisoning , including foxes, coyotes, bobcats, and mountain lions. Brodifacoum has no labeled
field uses (other than island eradication programs) and is only currently labeled for use to control
commensal r odents; therefore, t hese incidents show that use of brodifacoum for control of commensal rodents can result in secondary poisoning of raptors and mammalian predators which commonly feed on rodents.

Incidents of wildlife mortality from secondary exposure to brodifacoum have been reported throughout the United States. The largest numbers of reported incidents have be en from New
York and California , which is thought to be due to the presence of a more comprehensive or systematic programs for investigating and reporting pesticide

- related wildlife incidents in those

states compared to other states. States other than New York and California that have reported secondary exposure incidents for rodenticides included in this NOIC include Florida, Georgia, Virgini a, Massachusetts, Wisconsin, and Kansas. Additionally, incidents of widespread wildlife mortality attributed to secondary exposure to rodenticides have been documented in numerous other countries, including Canada (Alber et al., 2009), France (Berny et al ., 1997), Britain (Shore et al, 1999), and New Zealand (Eason et al., 2001, Dowding et al., 2006).

As with primary incidents, the location of reported secondary poisoning incidents was associated with use in urban and suburban areas. Ninety

- three out of 18 3 reported incidents (51%) are associated with secondary exposure to brodifacoum (excluding the one with an unlikely certainty) were located in areas known to be urban or suburban areas, whereas 5 0 out of 18 3 (2 7 %) were located in rural areas

. All 5 of the incidents of secondary poisoning by difethialone

a lso occurred in an urban area. The map of reported secondary incidents in New York State
shows that many secondary incidents have been reported in urban areas, with clusters of secondary incidents (a s well as primary incidents) occurring near the urban centers of New York City, Albany, Buffalo, Syracuse, and Utica ( Figure 6

- 1 ).

A spatial analysis of brodifacoum incidents reported in California (all of which were attributed to secondary exposure) in dicated that numerous incidents have been reported in or near the metropolitan areas of Los Angeles, San Francisco, and Sacramento ( Figure 6

- 2 ). Most of the reported secondary poisoning incidents were located in counties with dense human population,
and t he majority occurred near major metropolitan areas such as Los Angeles, Santa Barbara, San Francisco, and Sacramento. Other incidents with exact location information are scattered throughout the state but generally occur in areas that have moderate to hig h population densities as indicated by the legend on the California map.Page 133 of 183 In a study conducted by McMillin et al (2008), the California Department of Fish and Game’s Pesticide Investigations Unit (in conjunction with the Endangered Species Recovery Program ’s Urban Kit Fox Project), San Joaquin Kit Foxes were monitored from the Bakersfield, CA population. This study corresponds with the EIIS incident number I016100

- 001. Necropsies and
live r tissue samples were collected from kit fox carcasses. A non

- urban population of kit foxes
from Lokern Natural Area (a 40,000 acre habitat 30 miles west of Bakersfield) was used as a control. Between 1999 and 2007, tissue samples from various animals were analyzed for residues of anticoagulant rodentic i des. The fox car casses were part of an ongoing monitoring effort dating back to 1977 from which 10

- 20 carcasses are collected from both the Bakersfield and Lokern area per year. The compounds identified included brodifacoum and chlorophacino ne. Out of the 30 San Joaquin Kit Foxes analyzed from the Bakersfield population , 2 7 contained at least one antico a gulan t and the most commonly detected from that
set was brodifacoum (26 out of 30 or 87%)

. Chlorophacinone residues were detected in one fox (3%). All con t rol foxes f rom the Lokern population had no antico a gulant residues detected.
The authors report that results from this study confirm that San Joaquin Kit Foxes are exposed to anticoagulants in urban environments.Page 134 of 183 Figure 6

- 2 . Distribution of wildlife mortality incidents attributed to brodifacoum and difethialone reported in California.

In conclusion, available incident data show that brodifacoum has been associated with a number of incidents of secondary poisoning of wildl ife throughout the United States . Since the only registered uses of brodifacoum are for commensal rodent use , this suggests that for the uses considered for this NOIC, brodifacoum represents a complete exposure pathway for secondary
mammals and birds . Inc idents have been reported in urban and suburban areas. The occurrence of secondary poisoning incidents in urban and suburban areas is not surprising because products for commensal rodent control are heavily used urban and residential areas, and rodent pre dators such as hawks, owls, foxes, and coyotes are often abundant in urban parks and residential areas.

6.1.4.2 Difethialone

A series of mortalities was reported in Golden Gate Park in San Francisco in 2007 following widespread use of difethialone in bait station s which were used at the park for rodent controlPage 135 of 183 (incidents I018414

- 001 through I018414

- 005). The four secondary exposure incidents included
three red tailed hawks ( Buteo jamiacensis) and one red fox ( Vulpes vulpes).

6.1.4.3 Warfarin

Counts of wildlife mortality incidents reported to the Agency that are attributed to secondary poisoning by warfarin are shown in Table 6

- 4

. Five of the 8 reported incidents were attributed to secondary exposure to warfarin. These incidents were all link ed to warfarin with high certainty, with two incidents assigned a certainty level of “highly probable” and the other three with the certainty level of “probable.” Species affected were all raptors, including two bald eagle s ( Haliaeetus leucocephalus ), a p eregrine falcon ( Falco mexicanus ), a great horned owl ( bubo virginianus ), and a Cooper’s hawk ( Accipiter cooperii ). These incidents occurred when use of warfarin was more widespread than it is today. One incident occurred in the mid 1980’s,
three occurre d in the 1990’s, and one occurred in the year 2000.

6.1.4.4 Bromethalin

N o incident of wildlife mortality has been reported that has provided convincing evidence of secondary exposure to bromethalin. One incident was reported involving the death and incapacita tion of several raptors that were being held in captivity on Amicalola Falls State Park, Georgia, as part of an educational program (I014717

- 001). Rodenticides that were reportedly in use in the park were products that contained bromadiolone and bromethal in. However, evidence in this case strongly suggests that the raptors died from exposure to anticoagulant rodenticides rather than from bromethalin. Both gross pathological and microscopic examinations observed moderate to severe hemorrhaging in the carc asses of the dead birds. In addition, the incapacitated birds were treated with vitamin K (an antidote to anticoagulant poisoning) and recovered. Finally, while no use of a product containing brodifacoum was reported, analysis of a liver samples from the raptors found brodifacoum at 77 mg/kg

- bw in an owl and at 7 mg/kg

- bw
in a hawk.

As previously mentioned , bromethalin is not normally included in the analytical screen for rodenticides conducted on tissue from wildlife carcasses, which normally include only a screen of anticoagulant rodenticides. Furthermore, bromethalin poisoning does not result in clinica l signs that are obvious in gross necropsy examinations, and thus there may not be cues that would trigger the investigator to seek analysis to detect bromethalin. Therefore, the lack of reported secondary incidents for bromethalin does not necessarily in dicate that poisoning of nontarget wildlife by secondary exposure to bromethalin is not occurring.

6.1.4.5 Chlorophacinone

Counts of wildlife mortality incidents for chlorophacinone are provided in Table 6

- 6

. Chlorophacinone has four incidents associated with s econdary poisoning. One of the incidentsPage 136 of 183 was in an urban/suburban location, one was in a rural location, and two other s were in
uncharacterized location s. Incidents involved mortality of both avian and mammalian predators. The avian predator was the red

- tailed hawk ( Buteo jamiacensis ) and the mammalian predator was the bobcat ( Lynx rufus )

.

After the above analysis was completed, the Agency received two additional incidents of secondary poisoning of wildlife linked to chlorophacinone. One was the poisoning of a bald eagle in Nebraska in 2007, and one was a poisoning of an American badger ( Taxidea taxus) in California in 2009. A certainty level of “highly probable” was assigned to each incident for chlorophacinone being the cause of death. Both in cidents occurred in rural locations.

It should be noted chlorophacinone is widely used in agricultural sites for control of rodent pe s ts other than commensal rodents. As most if not all of the chlorophacinone incidents may be
associate d with these uses , they do not necessarily provide evidence of secondary risk concern for use in bait products for commensal rodent control.

6.1.4.6 Diphacinone

Diphacinone has nine incidents associated with secondary exposure. Two incidents were located in rural locations, th ree were located in urban/suburban locations, and the other five incidents
were in locations that could not be characterized. Incidents involved mortality of both avian and mammalian predators. Avian predators include the turkey vulture ( Cathartes aura ) , the red

tailed hawk ( Buteo jamiacensis ), the barred owl ( Strix varia ), and the Snowy Owl ( Bubo
scandiacus ). Mammalian predators include the San Joaquin Kit Fox ( Vulpes macrotis mutica ), raccoon ( Procyon sp.), coyote ( Canis latrens ), and mountain lion ( P uma concolor ).

It should be noted diphacinone is widely used in agricultural sites for control of rodent pests other than commensal rodents. As most if not all of the chlorophacinone incidents may be associated with these uses, they do not necessarily provide evidence of secondary risk concern for use in bait products for commensal rodent control ; however, these incidents do suggest that there is risk of secondary poisoning in both birds and mammals from diphacinone use.



### 6.2 Open Literature Evaluations

Some researchers who have studied wildlife mortality incidents caused by anticoagulant rodenticides have reported a large proportion of incidents occurring in highly populated areas when compared to rural or agricultural areas. Stone et al. (2003) found t hat 39% of positive cases of rodenticide mortality of raptors in the state of New York between 1998 and 2001 occurred in the New York City/Long Island region . This is consistent with the current analysis involving brodifacoum incidents reported in New Yor k State ( Figure 6

- 1 ). The authors of thisPage 137 of 183 paper stated that “urban and suburban origins were more common than rural origins,” although
noted that the difference could be at least in part due to greater probability of discovery and reporting of incidents in heavily populated areas.

Murray (2010) reports on cases of anticoagulant poisoning of wildlife investigated by a wildlife
clinic in central Massac husetts between 2006 and 2010. Of the nine raptors they positively identified as being killed by brodifacoum intoxication, six were found in urban areas, two from suburban towns, and one from a farm.

A study of anticoagulant rodenticide exposure in owl s from Western Canada from 1998 through 2003 found that the majority of owls (42%) with positive detections of rodenticides came from the Upper Fraser Valley, and area characterized with relatively high population as well as intensive agriculture. The hig hest brodifacoum liver residue was observed in a barred owl ( Strix

varia ) from an urban area in West Vancouver, and the highest bromadiolone liver residue was observed in a barred owl from Surrey, and suburb of Vancouver.

Lima and Salmon (2010) studied the distribution of detections of anticoagulant rodenticides in raptor carcasses collected in San Diego County and the largely agricultural counties of Fresno, Kern, and Madera. A spatial analysis of the location of raptor incidents found an association o f carcasses with positive detections of rodenticides with locations in urban areas with higher population density, a pattern similar to the one observed with wildlife mortality incidents in this current paper ( Figure 6

- 2 ).

As noted by Stone et al. (2003), the tendency for more reported incidents to be located in urban/suburban areas may in part be the result of greater rate of reporting of wildlife mortality incidents in areas with higher human population. In urban/suburban areas, more people are
present to observe and report wildlife carcasses, and thus more mortality incidents are likely to be reported to authorities for investigation. S ince no data exists on carcass reporting rates in urban and suburban areas, it is not possible to make conclusions on the relative frequency of secondary poisoning incidents between urban/suburban areas and rural areas. The authors reported that it is clear that a sizable number of secondary poisoning incidents do occur in urban/suburban areas, indicating that use of re sidential and commercial uses of rodenticides for
commensal rodent control can result in secondary poisoning for wildlife predators and scavengers in these areas.

An available radiotelemetry study with bobcats ( Lynx rufus ) in southern California (Riley et al., 2007) provides evidence that secondary exposure to rodenticides is associated with their use of urban areas. When the livers of dead radiocollared bobcats were analyzed, the total concentration of anticoagulant rode nticides was significantly related to the percentage of thePage 138 of 183 animal’s home range that was made up of developed areas and to the percentage of radiolocations which occurred in developed areas.

In another study in California, Lima and Salmon (2010) found that many more raptor carcasses
contained brodifacoum and difethialone , which are generally used for commensal rodent control around structures, whereas relatively few contained chlorophacinone, diphacinone, and warfarin

, which are registered for agricultural uses in California. The authors’ findings support the conclusion that residential and commercial uses of rodenticides in urban and suburban areas pose

a concern for secondary poisoning of wi ldlife

.

The most likely cause of secondary poisoning of wildlife is from predatory and scavenger animals consuming rats and mice that have been contaminated by consumption of bait containing anticoagulant rodenticides ; however, this is not always the case . Poisoning of two mountain lions ( Felis concolor ) in Sim i Hills area near Los Angeles was suspected of being caused by tertiary poisoning when the lions consumed a coyote which had in turn consumed rodents poisoned by brodifacoum and bromadiolone (Riley et al., 2007). In investigating the mortality of New Zealand dotterels ( Charadrius obscures ) following an application of brodifacoum for in a rat eradication program in New Zealand, Dowding et al. (2006) found that sandhoppers ( Talorchestia spp.), a terre strial crustacean commonly found on beaches, accumulated brodifacoum and served as a potential route of secondary exposure to the dotterels and other birds which feed on them. Also, some of the mortality of captive birds at the Philadelphia Zoo
which foll owed use of a rodenticide bait stations containing brodifacoum was suspected of being caused by the birds consuming insects which had consumed bait from the stations (EIIS incidents
I011274

- 001 and I011274

- 001).

After analyzing mortality incidents to wild life (Stone et al. 1999), and more recent specifically to raptors (Stone et al., 2003), wildlife managers of the New York Department of Environmental Conservation concluded that “brodifacoum appears to have the greatest potential for nontarget mortality of all anticoagulants currently in use” (Stone et al., 2003). While they did not do a comparative analysis, Thomas et al. (2010) conducted a probabilistic analysis which related
observed liver residues of brodifacoum, difethialone to mortality in predatory birds. They
concluded that the use of brodifacoum and difethialone to control rodents in Canada pose a risk to raptors, with an estimate that 11% of the sampled great horned owl population was at risk of mortality from exposure to these rodenticides

.

6.2.1 Summ ary and Analysis of Numbers of Incidents

In this section

, wildlife incidents reported in the United States were summarized, and the relative amount of incidents in various types of environments (e.g., urban, suburban, and rural) and types of exposures (i. e., primary and secondary) were documented for the rodenticides included in this

assessment. Only recent (2003 to 2008) incidents were included in this analysis to attempt toPage 139 of 183 capture recent use patterns. The purpose of this assessment was to document the types of exposures and incident locations associated with recent incidents

. In addition, the number of incidents reported may be a function of many factors, one of which is the chemical ’s use.

As previously discussed, w arfarin, chlorophacinone, and diphacinone are used in agricultural settings to control several other mammal pests (e.g., voles, gophers, prairie dogs, and rabbits), and thus the incident counts and usage data included in this analysis for those rodenticide s include those non

- commensal rodent uses. T wo wildlife incidents have been reported for the
neurotoxic rodenticide bromethalin. One of these incidents was not included because it had a certainty index of “unlikely,” and the other one was not included be cause it occurred prior to 2002. Therefore, for this analysis, the incident count for bromethalin is zero.

The counts of incidents associated with rodenticide active ingredients are shown in Figure 2

. The number of incidents a ttributed to brodifacoum (133) greatly exceeded the number for all
other rodenticides . The large number of secondary poisoning incidents accounts for a large proportion (74%) of the reported brodifacoum incidents.

Difethialone had 6 reported incidents du ring this time. It was similar to brodifacoum in having more secondary exposure incidents (5) than primary exposure incidents (1). Diphacinone had five reported incidents and chlorophacinone had four

. Both primary and secondary incidents were reported f or these indandione rodenticides during these years . Only one wildlife incident was attributed to warfarin during this time, and that one was a primary poisoning incident.

Figure 6

- 3 . Number of reported wildlife incidents during the years 2000

- 2011, excluding
incidents associated with misuse and those with a certainty value less of unrelated and unlikely

. 0 20 40 60 80 100 120 140

Unknown

Primary

SecondaryPage 140 of 183 Figure 6

- 3 compares the proportion of all reported wildlife mortality incidents that were attributed to primary and secondary exposures. For brodifacoum, the majority of incidents (71%) were attributed to secondary poisoning, whereas only 14% of the incidents were attributed
to p rimary exposure. Difethialone had a similar pattern with 80% of incidents being attributed to secondary poisoning an d 20% being attributed to primary poisoning. In contrast, secondary exposure incidents comprised smaller proportions of total incidents for chlorophacinone and diphacinone. The percentage of incidents attributed to secondary poisoning were 33 % for
chloro phacinone and 50% for diphacinone. Percentages are not displayed for warfarin because only one wildlife incident was reported during this time, which was attributed to primary poisoning. When incidents from earlier years are included, 62.5% (5 out of 8) were attributed to secondary exposure and 37.5% (3 out of 8) were attributed to primary exposure. Again, a number of factors may influence the relative number of primary and secondary incidents including species affected, and location and behavior of affe cted animals.



### 6.3 Exposure Incidents

Over the last two decades, widespread accumulation of residues of anticoagulant rodenticides, in the liver tissue of various predatory and scavenging wildlife species has been documented. This
section reviews reported incidents of anticoagulant rodenticides being detected and measured in tissue of wildlife without necessarily evidence of adverse effects. Anticoagulant rodenticide residues have been found to be prevalent in populations of avian and mammal species which feed on rodents, being reported in every recent publication involving monitoring of rodenticide
residues in wildlife which was reviewed for this effort

. Although some of these studies rely on the carcasses of dead animals others studies also analyzed inca pacitated animals or were part of
surveillance efforts for West Nile Virus. The studies show that when wildlife pathologists (whether it was a pointed effort or secondary to other purposes in the study) looked for
rodenticide residues in wildlife, they us ually found them. Table 6

- 8 summarizes the percent of
detections of rodenticides in liver tissues as reported in published wildlife monitoring studies. These studies generally investigated the presence of rodenticides in carcasses of wild animals
that di ed from causes unrelated to rodenticide poisoning (e.g. killed in automobile accidents or caught in traps) or that were found dead from unknown causes. The percentages given represent the prevalence of rodenticides observed in the sampled population of ca rcasses. The prevalence of detections ranging from 18% in tawny owls ( Stix aluco ) in Britain to 100% in great horned
owls in central Massachusetts and mountain lions in southern California. Species in which widespread accumulation of anticoagulant rodenticides in liver tissue has been observed include owls, hawks, vultures, mustelids, bobcats, and mountain lions. While this information does not provide an indication of risk, it does provide evidence that a complete route of exposure exists for predatory and scavenging birds and mammals for rodenticides and that exposure is relatively widespread

.Page 141 of 183 Table 6

- 8 . Prevalence of Anticoagulant Rodent icides in Liver Samples of Wildlife

Location, Years, and Description of Collection (Reference) Land
Use Species
Examined Percentage with Positive D et ection s 1,2

All 3 Brodif a Difeth Warf Chloroph Diphac

Central Massachusetts,
2006

- 2010.
Dead or incapacitated birds brought to wildlife clinic. (Murray 2011)

Mix ed Red

- tailed
hawks ( Buteo jamaicensis ) 89% (71/80) 89% (71/80) 1.3% (1/80) ND 0% (0/80) 0% (0/80)

Barred owls ( Strix varia ) 75% (30/40) 73% (29/40) 2.5% (1/40) ND 0% (0/40) 0% (0/40)

Eastern
screech owl ( Megascops

asio ) 87% (20/23) 87% (20/23) 0% (0/23) ND 0% (0/23) 0% (0/23)

Great horned
owl ( Bubo virginianus ) 100% (18/18) 100% (18/18) 0% (0/18) ND 0% (0/18) 0% (0/18)

San Diego County, California.
Dead birds delivered to Publi c Health
Services for West Nile Virus
surveillance. (Lima and Salmon 2010) Urban Various
raptors 92% (49/53) 83% (44/53) 9.4% (5/53) 0%
0/53 0%
0/53 0%
0/53

Central Valley, California. Dead birds collected by public and delivered to the CA Dept. of Fish &
Game (Lima and Salmon 2010) Agr. Various
raptors 79% (34/43) 12% (5/43) 0% (0/43) 0% (0/43) 4.7% (2/43) 0% (0/43)Page 142 of 183 New York State, 1998

- 2001 Dead birds submitted by the public to the NY Depart. of Environ. Conserv., augmented by dead birds collected as part of a West Nile Virus surveillance

program (Stone et al., 2003) Mix ed Various raptors and
vultures 49% (128/265) 41% (108/265) ND 0.75% (2/265) 0.38% (1/265) 1.1% (3/265)

British Columbia and Yukon Territory, Canada, 1988

- 2003. Dead birds collected by individuals
and wildlife rehabilitation centers. (Albert et al, 2009) Mixed Barn owl ( Tyto alba ) 62% (48/78) 45% (17/78) 13% (10/78) 1% (1/78) 0% (0/78) 4% (3/78)

Barred owls ( Strix varia ) 92% (23/25) 68% (17/25) 4% (1/25) 4% (1/25) 16% (4/25) 4% (1/25)

Great horned
owl ( Bubo virginianus ) 70% (43/61) 46% (28/61) 5% (3/61) 5% (3/61) 5% (3/60) 7% (/61)

Southern California near Los Angeles,
1997

- 2003
Radiotracked animals found dead in
suburban area north and west of Los Angeles, (Riley et al. 2007) Urban Bobcat ( Lynx rufus ) 90% (35/39) 79% (31/39) 26% (10/39) 0% (0/39) 0% (0/39) 31% (12/39)

Mountain lion ( Puma
concolor ) 100% (4/4) 100% (4/4) 25% (1/4) 0% (0/4) 0% (0/4) 0% (0/4)

Britain , 1990

- 1993 Dead birds submitted by the public to
the Predatory Bird Monitoring Scheme (Walker et al. 2008) Mixed Tawny owl ( Stix aluco ) 18% (16/88) 8.0% (7/88) ND ND ND ND

Britain , 2003

- 2005
Dead b irds submitted by the public to
the Predatory Bird Monitoring Scheme (Walker et al. 2008) Mixed Tawny owl ( Stix aluco ) 20.2% (17/84) 1.2% (1/84) ND ND ND NDPage 143 of 183 Britain , 1993

- 2000
Dead b irds submitted by the public to
the Predatory Bird Monitoring Scheme (Shore et al. 2005) Mixed Barn owl ( Tyto alba ) 40% (21/53) 3.8% (2/53) ND ND ND ND

Britain , 2007

- 2008
Dead b irds submitted by the public to
the Predatory Bird Monitoring Scheme (Walker et al. 20 10 ) Mixed Barn owl ( Tyto alba ) 81% (79/98) 29% (28/97)? ND 0% (0/98) 4.1% (4/98) 0% (0/98)

Kestrel ( Falco
tinnunculuc ) 68% (15/22) 27% (6/22) ND 0% (0/22) 0% (0/22) 0% (0/22)

Red Kite ( Milvus
milvus ) 91% (29/32) 53% (17/32) ND 3.1% (1/32) 3.1% (1/32) 3.1% (1/32)

Britain
1992

- 1994 Animals accidentally killed on roads and in traps

. (Shore et al. 1996) Unkn. Polecat ( Mustela putorius ) Liver:
29% (7/24)
Stomach

wall:
40% (2/5) Liver:
4.2% (1/24)
Stomach

wall:
0% (0/5) ND ND ND ND

Britain
1992

- 1997 Animals killed accidentally on roads and in traps. Includes 24 liver samples reported in Shore et al 1996. (Shore et al. 1999) Unkn. Polecat ( Mustela putorius ) 26% (13/50) 2.0% (1/50) ND ND ND ND

Britain
1996

- 1997 Animals trapped or shot by gamekeepers. (McDonald et al. 1998) Rural Stout ( Mustela

erminea ) 22.5%
9/40 2.5% (1/40) ND 0% (0/40) ND ND

Weasel ( Mustela
nivalis ) 30%
3/10 0% (0/3) ND 0% (0/10) ND NDPage 144 of 183 Mapara Wildlife Management Reserve, New Zealand, 1993

- 1995. Mustelids were trapped and birds were shot following rat eradication program using brodifacoum. (Murphy et al. 1998) Rural Stout ( Mustela

erminea ) 78%
31/40 78%
31/40 ND ND ND ND

Weasel ( Mustela
nivalis ) 71.4% (10/14) 71.4% (10/14) ND ND ND ND

Ferrets ( Mustela furo ) 56% (9/16) 56% (9/16) ND ND ND ND

1 Includes unquantifiable (trace) detections. ND=not determined (i.e., compound was not included in the rodenticide analytical screen).

2 Brodif=Brodifacoum, Difeth=Difethialone, Warf=Warfarin, Chloroph=Chlorophacinone, Diphac=Diphacinone

3 Detection of one or more of all of the anticoagulant rodenticides analyzed in the study.Page 145 of 183 Brodifacoum residues are prevalent in the tissue of owls, hawks, eagles and vultures. Numerous monitoring studies have found brodifacoum present in over half of individuals of one or more species studied (Murray 2011; Lima and Salmon, 2010; Albert et al., 2009 ). Murray (2011) found that the prevalence of brodifacoum in great horned owls ( Bubo virginianus ), red

- tailed hawks ( Buteo jamaicensis ), and eastern screech owls ( Megascops asio ) in Massachusetts to be 100%, 89%, and 87%, respectively. Alberts et al., (2009) re port a prevalence of brodifacoum of
68 % in barred owls in western Canada. Lima and Salmon (2010) report a prevalence of
brodifacoum of 83 % in various raptors monitored in San Diego County, CA. Brodifacoum has
also been found to be prevalence in wildlife monitored in Europe, with Walker et al (2010) finding brodifacoum in 53 % of red kites and 29 % of barn owls ( Tyto alba ) in Britain. Brodifacoum was by far the most frequently detected rodenticide in studies monitoring raptors
and vultures in the United Sta tes, including in Massachusetts (Murray 2011), San Diego County, CA (Lima and Salmon, 2010), and New York State (Stone et al., 2003). In 2000, the California Dept. Fish and Game detected brodifacoum in four golden eagles ( Aquila chrysaetos ), that were
fou nd dead in Ventura County, CA (CEE

- TV database, records 232266, 232273, 232274, 232218). Difethialone was also detected in raptors in Central Massachusetts (Murray 2011) and in San Diego County, CA, although with fai rly low prevalence (1.3

- 9.4%).

Difeth ialone, w arfarin, chlorophacinone, and diphacinone have been detected in raptors monitored in New York State (Stone et al., 2003), Western Canada (Albert et al., 2009), and Britain (Walker et al., 2010); however, the prevalence was generally considerably lower than for
brodifacoum

. Difethialone has been found to be moderately prevalent in some studies , with
percent detect ions of 9.4% of raptors in San Diego County (Lima and Salmon, 2010) and 5

- 13% of raptors in Western Canada ( Albert et al, 2009)

. In gen eral, warfarin, chlorophacinone, and diphacinone were detected in no more than 7% of individuals. The single exception was barred owls in Western Canada, in which chlorophacinone was detected in 16% of individuals (Albert et al, 2009).

The Predator Mon itoring Scheme (PBMS) in Britain provides information on the prevalence of rodenticides in the liver tissue of raptors in Britain over the last two decades. PBMS (http://pbms.ceh.ac.uk) is a long

- term national monitoring program run by the Centre for
Ecol ogy and Hydrology that measures concentrations of contaminants in predatory birds in Britain. This program analyzes contaminants in carcasses of dead birds that were submitted by the public. Results of analysis for brodifacoum and difenacoum for birds su bmitted during the periods of 1990

- 1993 and 2003

- 2205 were published by Walker et al. (2008), and results for birds submitted during 2007 and 2008 were published by Walker et al. (2010). Table 6

- 9 provides a summary of results compiled from both papers fo r brodifacoum , and difenacoum

. The most recent results from 2007

- 2008 show that these two compounds are present in the tissue of a high percentage of barn owls, kestre ls ( Falco tinnunculuc ) , and red, and a somewhat lower
percentage s of tawny owls

. Unlike the United States, the frequency of detection was generallyPage 146 of 183 higher for difethialone than for brodifacoum. The prevalence of brodifacoum appear s to have increased from the early 1990’s to the early 2000’s, and then increased even more in the period
of 200 7

- 2008. Better analytical methodology could be partially responsible for this observed
increa se.

Table 6

- 9 . Percent of Positive Detections of Difenacoum and Brodifacoum in Four Raptor Species Analyzed by the Predator Monitoring Scheme in Britain. Species Years Percentage (Ratio) with Positive Detection

Difena coum Brodif acoum
Barn Owl 1990

- 1993 13.9% (33/237) 1.3% (3/237)

2003

- 2005 20.1% (39/194) 3.1% (6/194)

2007

- 2008 62.2% (61/98) 28.6% (28/98)

Kestrel 1990

- 1993

-- -- 2003

- 2005 50.7% (37/73) 11.0% (8/73)

2007

- 2008 54.5% (12/22) 27.3% (6/22)

Red Kites 1990

- 1993

-- -- 2003

- 2005

-- -- 2007

- 2008 87.5% (28/32) 53.1% (17/32) Tawny Owl 1990

- 1993 5.7% (5/88) 8.0% (7/88)

2003

- 2005 6.0% (5/84) 1.2% (1/84)

Brodifacoum and difethialone also have been found to be widespread in the liver tissues of predatory mammals. During a long

- term radiotelemetry study conducted in a mountainous suburban area north and west of Los Angeles, CA, from 1997 through 2003, b rodi facoum was found in 79% of 39 bobcats analyzed and 100% of four mountain lions . Difethialone was
somewhat prevalent, being found in 26% of bobcats and 25% of mountain lions. Diphacinone was found in 31% of the bobcats examined, but only 4 (10%) had measu rable levels above the minimum detectable limit of 0.25 ppm. Warfarin was found in 1 of the 39 bobcats, and chlorophacinone was found in none. No diphacinone, chlorophacinone, or warfarin w as found in any of the four mountain lions analyzed (Riley et al. , 2007)

.

Monitoring conducted in New Zealand has also found brodifacoum to be widespread in
mammals in the weasel family (Mustilidae). Murphy et al. (1998) studied the prevalence of brodifacoum in mustelids in a wildlife management reserve in New Zealand after this area was baited with this rodenticide in an attempt to eradicate rats between 1993 and 1995. They foundPage 147 of 183 brodifacoum present in the liver tissue of 78% of stouts (n=30), 71% of weasels (n=14), and 56% of ferrets (n=16).

The Ecological Incident Information System (EIIS) also contains some information on tissue
residues of rodenticides in cases where the cause of death was determined to be unrelated to rodenticide poisoning. Concentrations for the 27 rodenticide incidents in EIIS with a certaint y index assignment of “unrelated” are shown in Table 6

- 10 . These data all came from wildlife in the state of California that was analyzed for rodenticides by the California Department of Fish & Game. Results of many of the cases of exposure incidents in California wildlife are also recorded in the Contaminant Exposure and Effects

- Terrestrial Vertebrates (CEE

- TV) database managed by the US Geological Survey ( http://www.pw rc.usgs.gov/contaminants

online/pages/CEETV/CEETVintro.htm ). Brodifacoum was identified in all of these cases. Brodifacoum liver concentrations ranged from 0.004 ppm to 0.66 ppm, with a mean of 0.17 ppm. Brodifacoum concentrations ranged from 0.07 ppm to 1.1 ppm, with a mean of 0.39 ppm. Diphacinone was detected in two cases, two coyotes which had liver concentrations of 0.081 and 0.13 ppm. Chlorophacinone was detected in one case, a coyote which had a liver concentration of 0.43 ppm.

Table 6

- 10 . Liver Tissue Concentrations of Rodenticides from Records of the EIIS Database for Cases in which t he Cause of Death was Unrelated to Rodenticide Poisoning

Incident ID Year Species Rodenticide Concentration (ppm)

R000

- 02

- 051 2000 Bobcat ( Lynx rufus ) Brodifacoum 0.024

R000

- 02

- 007 1998 C oyote ( Canis latrans ) Brodifacoum 0.50 Diphacinone 0.081 Chlorophacinone 0.43
R000

- 02

- 008 1998 C oyote ( Canis latrans ) Brodifacoum 0.50

R000

- 02

- 009 1998 C oyote ( Canis latrans ) Brodifacoum 0.66
Bromadiolone 0.22
R000

- 02

- 004 1995 Great horned owl ( Bubo virginianus ) Brodifacoum 0.015

R000

- 02

- 01 2 1998 C oyote ( Canis latrans ) Brodifacoum 0.04

R000

- 02

- 013 1998 C oyote ( Canis latrans ) Brodifacoum 0.08

R000

- 02

- 018 1999 C oyote ( Canis latrans ) Brodifacoum 0.33

R000

- 02

- 020 1999 C oyote ( Canis latrans ) Brodifacoum 0.03

R000

- 02

- 021 1999 C oyote Brodifacoum 0.03Page 148 of 183 Table 6

- 10 . Liver Tissue Concentrations of Rodenticides from Records of the EIIS Database for Cases in which t he Cause of Death was Unrelated to Rodenticide Poisoning

Incident ID Year Species Rodenticide Concentration (ppm) ( Canis latrans )
R000

- 02

- 022 1999 C oyote ( Canis latrans ) Brodifacoum 0.28

R000

- 02

- 023 1999 C oyote ( Canis latrans ) Brodifacoum 0.06

R000

- 02

- 015 1999 C oyote ( Canis latrans ) Brodifacoum 0.36

R000

- 02

- 016 1999 C oyote ( Canis latrans ) Bromadiolone 0.07
Brodifacoum 0.3
R000

- 02

- 017 1999 C oyote ( Canis latrans ) Bromadiolone 0.09
Brodifacoum 0.23
R000

- 02

- 038 1999 Golden eagle ( Aquila chrysaetos ) Brodifacoum 0.02

R000

- 02

- 042 2000 Golden eagle ( Aquila chrysaetos ) Brodifacoum 0.026

R000

- 02

- 043 2000 Golden eagle ( Aquila chrysaetos ) Brodifacoum 0.004

R000

- 02

- 044 2000 Golden eagle ( Aquila chrysaetos ) Brodifacoum 0.01

R000

- 02

- 031 1999 Kit fox ( Vulpes velox ) Bromadiolone 0.72
Brodifacoum 0.47
R000

- 02

- 039 1999 Kit fox ( Vulpes velox ) Brodifacoum 0.22

R000

- 02

- 050 2000 Kit fox ( Vulpes velox ) Brodifacoum 0.18

R000

- 02

- 010 1998 Raccoon ( Procyon lotor ) Brodifacoum 0.082
Bromadiolone 1.1 Diphacinone 0.13
R000

- 02

- 011 1998 Raccoon ( Procyon lotor ) Bromadiolone 0.41
Brodifacoum 0.011
R000

- 02

- 027 1999 Red

- shouldered hawk ( Buteo Laneatus ) Brodifacoum 0.015

R000

- 02

- 028 1999 Red

- tailed hawk ( Buteo jamaicensis ) Brodifacoum 0.01

R000

- 02

- 029 1999 Red

- shouldered hawk ( Buteo Laneatus ) Brodifacoum 0.01
Bromadiolone 0.28Page 149 of 183 6.3.1 Uncertainties and Limitations

Many steps must successfully occur for a rodenticide

- related wildlife kill to be reported to the EPA. First, the animal killed must be observed. Since rodenticide incidents usually involve only one or a few animals per incident, they li kely often go unnoticed. Carcasses of poisoned wildlife are often difficult to observe because the animals actively seek cover before dying, or may happen to die in an area where they are obscured by vegetation (Vyas, 1999). Furthermore,
studies have sho wn that the majority of bird carcasses are removed by scavengers within one day (Balcomb, 1986; Wobeser and Wobeser, 1992), thus there often may be only a short window of opportunity for wildlife carcasses to be observed. Wildlife kills also must be repor ted to the appropriate wildlife agency or organization which is capable of diagnosing the cause. That agency or organization must have a program in place for investigating wildlife kills through conducting necropsy examinations and conducting residue analy sis of tissue samples, and must have adequate funding available to pay for the analysis. The residue analysis must include an analysis for the rodenticide active ingredient that caused the poisoning and the methodology must be adequate to detect the ingre dient at the levels present in the tissue. Finally, the agency or organization must document the incident into a report and that report must be made available to the EPA. If any of these steps fail to take place, the incident will not be known to the EPA

. Furthermore, the nature of rodenticide incidents is that only one or a few dead animals are typically discovered per incident. Even if several non

- target animals are poisoned by a rodenticide, the carcasses of the killed animals would likely be widely scattered. Mortality incidents involving one or a few animals are less likely to be observed, reported, and investigated than ones involving large numbers of animals. For these reasons, the Agency believes that the
rodenticide

- related wildlife incidents reported here represent only a fraction of the incidents which are occurring.

Wildlife mortality incidents attributed to rodenticide exposure differ from those that are related to most other pesticides. Because of the delayed toxicity of rodenticides

, th e discovery of animals killed by rodenticide poisoning is typically removed, both spatially and temporally, from the exact site of rodenticide use. Therefore, when a dead animal that has been poisoned by a rodenticide is discovered, there is often no susp icion at that time that an animal died as the result exposure to rodenticides. Typically, incidents are only linked to rodenticide exposure only when
the y are reported to some authority, usually a state fish and wildlife office, and that office
conducts a n investigation to diagnose the cause of the incident . Investigations of wildlife mortality incidents usually begin with a necropsy examination. Observation of hemorrhaging and bleeding during the necropsy may cause suspicion that the mortality was cause d by an anticoagulant rodenticide, which may trigger a toxicological analysis for rodenticides. Animals poisoned by bromethalin, which is not an anticoagulant , usually do not have any diagnostic symptoms that are obvious in the necropsy exam. The investi gating agency may then take tissue samples from the animal, normally from the liver, and have laboratory analyses performed toPage 150 of 183 screen for the presence of various anticoagulant rodenticides, as well as other pesticides. Only when the residue analysis finds one or more rodenticide s in the tissue of the dead animal does the incident become diagnosed as a suspected or confirmed rodenticide incident. Because this analysis only identifies the presence of the active ingredient, the causal agent of a rodenticide incident is generally identified only on an active ingredient basis, not a product.

Because of the reliance on detection of residues in the tissue of the carcasses, wildlife mortality incidents may go undetected if the rodenticide ingredient that caused the death is not included in the screen of rodenticides performed on the tissue sample, or if the analytical method is not sensitive enough to detect the rodenticide at the levels present. Incidents caused by bromethalin in particular may be underreported because the rodenticide screens conducted in investigations of wildlife mortality incidents often only include anticoagulant compound, but not bromethalin, and thus the number of bromethalin incidents may be underreported. Furthermore, since bromethalin poisoning does not produce toxicity symptoms that are easily observed in gross morphology examinations, the necropsy examination generally do not provide cues that would cause the investigator to suspect bromethalin poisoning and include it in the toxicolo gical analysis. Therefore, a lack of reported bromethalin incident s may not necessarily reflect a lack effects in
the field

.

Only states which have personnel and resources devoted to investigating and reporting on wildlife mortality incidents report such incidents to the EPA. Only two states, New York and California, have had programs that have systematically reported wildlife mortality incidents, and thus are responsible for the majority of the Agency’s known rodenticide incidents. Most of the
inciden ts have been reported from only two states, New York and California, which have had
effective and well

- funded incident investigation and reporting programs. Reporting of wildlife incidents in many states have been inconsistent because of sporadic funding o f wildlife programs. Many states have never reported any rodenticide

- related wildlife mortality incidents
to the EPA.

Changes in the level of effort that states devote to monitoring and reporting wildlife incidents change overtime due to a changes of resources. During the late 1990’s, many dead birds were collected and analyzed by some state and local health departments as part of surveillance for West Nile virus, resulting in a temporary increase in incident reporting during those years. Reporting of rodenticide

- related incidents decreased after these West Nile virus surveillance programs were discontinued. In recent y ears, reductions of state budgets has impacted funding for state programs that are responsible for investigating wildlife mortality incidents, further reducing the incident reporting rates.

Reporting of rodenticide

- related wildlife incidents by pesticid e registrants has also decreased. Changes made in 1998 to the FIFRA 6(a)(2) relaxed reporting requirements and resulted inPage 151 of 183 reduced numbers of incident reports submitted by registrants. Registrants are now only required to submit individual reports on “ma jor” wildlife incidents, whereas “minor” wildlife incidents may be reported only as aggregated counts without information on the individual events. Since no information is generally provided on individual minor incidents, these incidents cannot be
entered in the EIIS database and are not included in analyses based on EIIS data. The majority
of rodenticide

- related incidents fall into the “minor” category of the 6(a)(2) rule because they involve mortality of only one or a few individual animals.

The Nat ional Wildlife Health Center (NWHC) of the US Geological Survey investigates and reports on wildlife mortality incidents. However, the NWHC generally only becomes involved with investigations of only larger

- scale mortality events, such as those caused by wildlife disease outbreaks. They normally are not involved with mortality events involving only one or a few animals, especially when the cause is easily diagnosed, as is true for most rodenticide

- related incidents. For this reason, wildlife mortality in cidents caused by rodenticides are generally lacking from the USGS/NWHC Quarterly Mortality Reports.

The Agency recognizes that there are limitations with available information on rodenticide

related wildlife incidents and use of rodenticides, that ther e are limi ted information linking
incidents and rodenticide use. Reporting of rodenticide

- related incidents to the EPA has been limited and inconsistent. Incidents from those states may not be completely representative of adverse effects occurring in ot her states. Also, the frequency of reported rodenticide

- related wildlife incidents are influenced by factors other than those directly related to the frequency of
effects in the field . For example, more incidents may be reported in areas with high human populations in part because more people are there to observe and report the carcasses of the poisoned animals. This difference in reporting rates likely affected the analysis of the prevalence
of incidents in rural/field versus urban/suburban locations as the reporting rate is likely greater in
urban/suburban areas . The rate of occurrence of incidents related to a particular rodenticide ingredient is possibly related to the amount of use of that ingredient.

Since several rodenticides accumulate in a nimal tissue over time, more than one rodenticide active ingredient is sometimes found in tissue of animal carcasses, and thus the same incident may be associated with exposure to more than one active ingredient. This is of particular interest
for the ant icoagulant rodenticides, which have the same mode of action. Sometimes, the level of detection of one rodenticide ingredient predominated and indicated that it is likely the primary cause of death, but in other cases the primary cause is unclear. In such cases, the uncertainty is reflected in the certainty value assigned to each ingredient. In the summary counts of incidents for various ingredients shown in Tables 6

- 1 through 6

- 7 , incidents are counted for each active ingredient and thus incidents linked to multiple active ingredients were included in the counts for
more than one active ingredient.Page 152 of 183 Some of the rodenticides considered in this document have uses to control pests other than
commensal rodents. Chlorophacinone , diphacinone, and warfarin have numerous products registered for use to control agricultural mammalian pests such as prairie dogs, voles, gophers
and rabbits. Bro methalin is registered for use to control moles as well as rats and mice. Unfortunately

, the intended target species of the use of rodenticides associated with wildlife mortality incidents is usually unknown. I ncidents considered in this analysis thus may include
ones for uses other than commensal rodent control. Therefore, i nferences made concerning the relative frequency an d proportions of incidents for these rodenticides may be influenced by these other uses and may not be completely representative of the commensal rodent use s . For example, since chlorophacinone and diphacinone have many uses for controlling agricultural

p ests, they may be used more in rural areas where reporting rates of incidents are lower. In addition, chlorophacinone and diphacinone have register ed uses that allow broadcast application of bait over large areas, which may not be representative of uses f or commensal rodent control in and around buildings. Rodenticide bait containing chlorophacinone and diphacinone for use to control commensal rodents have only been registered in the United States in the past three years.
Since most reported incidents fo r these ingredients took place during years before these new products were registered, they likely are largely associated with use s to control agricultural pests
other than commensal rodents

.

Finally, uncertainty is introduced by changes in use patterns over time, particularly relative to incident collection or survey efforts. The most dramatic shifts in usage occurred mostly in the
late 1980’s , when there was a large shift in the rodenticide market from warfarin to second

generat ion anticoagulant rodenticides.

6.3.2 Incident Conclusions

Despite the uncertainties described above , incident data provide compelling evidence that use of rodenticides for commensal rodent control can cause mortality of nontarget wildlife as the result of pr imary and secondary exposure. Investigation of many wildlife mortality incidents diagnosed rodenticide exposure as the cause of death with high certainty. This confirms that a complete exposure route exists for non

- target species of nontarget wildlife to be exposed to
rodenticides at lethal doses.

From this evaluation of wildlife mortality and exposure incident associated with rodenticide active ingredients, the following conclusions are evident :

**•** Incident data support the conclusion that all rodenticid e ingredients pose a risk of primary poisoning of nontarget mammals , both in urban and rural areas. Some of these mortality incidents result from large mammals such as deer consuming rodenticide bait.Page 153 of 183 **•** Incidents of mortalities to birds that represent pri mary consumers of rodenticides have been reported for brodifacoum, warfarin, chlorophacinone and diphacinone.

**•** Uses of brodifacoum, difethialone, warfarin, chlorophacinone and diphacinone as rodenticides represent complete exposure pathways for non

- target w ildlife via secondary exposure that can result in mortality for birds and mammals. This conclusion is supported by reported incidents in species of mammals and birds that represent predators and scavengers of target pests of rodenticides.

**•** Although f ew inc idents have been reported for bromethalin, this may be because this ingredient is not often included in analysis of tissue residues in investigations of wildlife mortality incidents.

**•** Considerable numbers of incidents of primary and secondary poisoning occu r in urban and suburban areas, suggesting that residential and commercial uses of rodenticides for
commensal rodent control can result in primary and secondary poisoning of nontarget
wildlife.

**•** Studies in the United States and elsewhere have reported frequent detections of residues
of brodifacoum in numerous species of avian and mammalian predators and scavengers

. D ifethialone has also been detected in several studies . Accumulated residues of other rodenticides considered in this document ( i.e., warf arin, chlorophacinone, and diphacinone) have been reported less frequently in survey data in the open literature

.



## 7 Synthesis of C onclusion s

All of the anticoagulants identified in the NOIC present risk to terrestrial wildlife in one form or another. However, there are differences in the risk picture relative to taxonomic group, body size and dietary parameters. This assessment was not conduc ted with the primary purpose of comparing risks across the rodenticides. However, over the course of the conduct of the assessment a few comparative conclusions are evident. Potential primary and secondary risks
were identified for all rodenticides asses sed, but brodifacoum stands out for risks to terrestrial wildlife, particularly for secondary exposure potential based on the lines of evidence considered
in this assessment. The results of this analysis confirm those from previous analyses and are

summar ized in Table s 7

- 1 through 7

- 4

.Page 15 4 of 183 Table 2

- 1. Avian RQ analysis: primary exposure of passerine birds to bait and secondary exposure of carnivore/scavenger birds to residues in consumed rodents.

Body weights (g) Brodif

acoum Difeth

ialone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Single day dose RQ 20 19.61* 29.80* 0.23 0.50* 0.07 0.01 7.76*

100 22.67* 18.39* 0.14 0.31 0.04 0.01 4.76*

1000 27.89* 9.22* 0.07 0.16 0.02 <0.01 2.40*

Six day dose RQ 20 117* 168* 1.36* 2.94* 0.40 0.05 34*

100 135* 104* 0.84* 1.81* 0.25 0.03 21*

1000 166* 52* 0.42 0.91* 0.12 0.01 11*

Dietary RQ NA 38* 45* 0.40 0.86* 0.89* 0.06 0.48Theoreticalsecondary exposure House mouse consumption: 1 day accumulation in prey RQ 100 6.60* 5.84* 0.05 0.10 0.01 <0.01 1.52*

1000 5.15* 1.85* 0.01 0.03 <0.01 <0.01 0.48

5000 4.33* 0.83* 0.01 0.01 <0.01 <0.01 0.22

Norway rat consumption: 1 day accumulation in prey RQ 100 1.75* 1.54* 0.01 0.03 <0.01 <0.01 0.40

1000 1.36* 0.49 <0.01 0.01 <0.01 <0.01 0.13

5000 1.15* 0.22 <0.01 <0.01 <0.01 <0.01 0.06

House mouse consumption: 3 day accumulation in prey RQ 100 19.77* 17.09* 0.14 0.30 0.04 0.01 4.06*

1000 15.42* 5.42* 0.04 0.09 0.01 <0.01 1.29*

5000 12.96* 2.43* 0.02 0.04 0.01 <0.01 0.58*

Norway rat consumption: 3 day accumulation in prey RQ 100 5.25* 4.52* 0.04 0.08 0.01 <0.01 1.07*

1000 4.08* 1.43* 0.01 0.02 <0.01 <0.01 0.34

5000 3.43* 0.64* 0.01 0.01 <0.01 <0.01 0.15

House mouse consumption: 6 day accumulation in prey RQ 100 39.40* 32.98* 0.27 0.58* 0.08 0.01 NA

1000 30.74* 10.45* 0.09 0.19 0.02 <0.01 NA

5000 25.84* 4.68* 0.04 0.08 0.01 <0.01 NA

Norway rat consumption: 6 100 10.43* 8.73* 0.07 0.15 0.02 <0.01 NAPage 155 of 183 day accumulation in prey RQ 1000 8.14* 2.77* 0.02 0.05 0.01 <0.01 NA

5000 6.84* 1.24* 0.01 0.02 <0.01 <0.01 NA House mouse consumption: dietary RQ NA 17.81* 2069* 0.19 0.41 0.32 0.02 0.20

Norway rat consumption: dietary RQ NA 4.71* 5.48* 0.05 0.11 0.09 < 0.01 0.05EmpiricalSecondaryExposure Single day dose RQ 100 4.42* 4.64* <0.01 <0.01 <0.01 ND

1000 5.01* 1.47* <0.01 <0.01 <0.01 ND

5000 4.21* 0.66* <0.01 <0.01 <0.01 ND

Dietary RQ NA 5.25* 5.54* <0.01 0.02 <0.01 ND

NA = not applicable; ND = no data ; * = RQ exceeds the LOC of 0.5Page 156 of 183 Table 2

- 2. Avian Risk Characterization: Additional lines of evidence

Body weights (g) Brodif

acoum Difeth

ialone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Days to consume sufficient bait to reach the LD 50 20 <1 <1 4

- 5 1

- 2 16

- 17 >365 <1

100 <1 <1 7

- 8 3

- 4 30

- 31 >365 <1

1000 <1 <1 14

- 15 6

- 7 117

- 118 >365 <1

Grams bait consumed to reach
the LD 50 20 0.3 0.2 25 10 86 >1800 0.7

100 0.9 1.1 160 80 620 > 7300 4.2

1000 5 15 2100 990 17000 >52000 59Secondary exposure Number of house mice consumed to reach the LD50: 1 day accum. in prey 100 <1 <1 38 18 130 821 1

1000 2 4 539 249 1836 11602 16

5000 5 27 3429 1587 11690 73852 104

Number of Norway rats to consume to reach the LD50: 1 day accum. in prey 100 <1 <1 7 3 23 147 <1

1000 <1 <1 97 45 329 2079 3

5000 <1 5 614 284 2094 13232 17
Secondary feeding study summary counts (#mortalities/ #tested) NA 63/149 ND 2/23 0/112 3/34 NDIncident datasummarycounts primary exposure NA 3 0 1 3 1 0

secondary exposure NA 164 3 5 3 5 0

unknown exposure NA 21 0 0 1 0 0

NA = not applicable; ND = no data ; * = RQ exceeds the LOC of 0.5Page 157 of 183 Table 2

- 3. Mammalian RQ analysis: primary exposure of rodents to bait and secondary exposure of carnivore/scavenger mammals to residues in consumed rodents.

Body weights (g) Brodif

acoum Difeth

ialone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimaryexposure Single day dose RQ 15 9.93* 4.30* 8.36 * 18.05* 0.82 * 1.97 * 5.1*

35 8.48* 3.67* 7.14 * 15.42 * 0.70 * 1.68 * 4.4*

1000 4.55* 1.97* 3.83 * 8.27 * 0.38 0.90 * 2.4*

Six day dose RQ 15 59* 24* 49* 106* 4.7 * 11.6 * 23*

35 51* 21* 42* 90* 4.0 * 9.9 * 19*

1000 27* 11* 22 * 48* 2.1 * 5.3 * 10*

Dietary RQ NA 94* ND 57 * 123* 44* 22 * NDTheoretical secondary exposure House mouse consumption: 1 day accumulation in prey RQ 50 3.71* 1.62* 2.97* 6.41* 0.28 0.94* 1.62*

1000 4.60* 2.01* 3.68* 7.95* 0.35 1.16* 2.01*

3000 4.98* 2.17* 3.99* 8.61* 0.38 1.26* 2.17*

Norway rat consumption: 1 day accumulation in prey RQ 50 0.98* 0.43 0.79* 1.70* 0.08 0.25 0.43

1000 1.22* 0.53* 0.97* 2.11* 0.09 0.31 0.53*

3000 1.32* 0.58* 1.05* 2.28* 0.10 0.33 0.58*

House mouse consumption: 3 day accumulation in prey RQ 50 11.10* 4.74* 8.81* 19.03* 0.84* 2.49* 4.31*

1000 13.78* 5.88* 10.93* 23.61* 1.04* 3.09* 3.53*

3000 14.91* 6.37* 11.83* 25.56* 1.12* 3.35* 5.79*

Norway rat consumption: 3 day accumulation in prey RQ 50 2.94* 1.25* 2.33* 5.04* 0.22 0.66* 1.14*

1000 3.65* 1.56* 2.89* 6.25* 0.27 0.82* 1.42*

3000 3.95* 1.68* 3.13* 6.76* 0.30 0.89* 1.53*

House mouse consumption: 6 day accumulation in prey RQ 50 22.13* 9.15* 17.35* 37.48* 1.63* 4.20* NA

1000 27.46* 11.35* 21.53* 46.51* 2.02* 5.21* NA

3000 29.72* 12.28* 23.30* 50.33* 2.18* 5.64* NA

Norway rat consumption: 6 day accumulation in prey RQ 50 5.86* 2.42* 4.59* 9.92* 0.43 1.11* NA

1000 7.27* 3.00* 5.70* 12.31* 0.53* 1.38* NA

3000 7.87* 3.25* 6.17* 13.32* 0.58* 1.49* NAPage 158 of 183 House mouse consumption: dietary RQ NA 44.69* ND 26.64* 57.54* 20.42* 10.11* ND

Norway rat consumption: dietary RQ NA 11.23* ND 7.05* 15.23* 5.41* 2.68* NDEmpiricalsecondaryexposure Single Day RQ 50 3.59* 1.41* 0.26 0.07 0.19 ND

1000 4.46* 1.75* 0.32 0.08 0.23 ND

3000 4.83* 1.89* 0.34 0.08 0.25 ND

Dietary RQ NA 13.17* NA 0.67* 1.39* 0.61* ND

NA = not applicable; ND = no data ; * = RQ exceeds the LOC of 0.5Page 159 of 183 Table 2

- 4. Mammalian Risk Characterization: Additional lines of evidence from the mammal risk assessment.

Body weights (g) Brodif

acoum Difeth

ialone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Days to consume sufficient bait to reach the LD 50 15 <1 <1 <1 <1 1

- 2 <1 <1

35 <1 <1 <1 <1 1

- 2 <1 <1

1000 <1 <1 <1 <1 1

- 2 <1 <1

Grams bait consumed to reach
the LD 50 15 0.3 0.7 0.3 0.2 6 1.1 0.6

35 0.5 1.3 0.7 0.3 9 2.1 1.1

1000 6.7 16 8.0 3.7 61 25 13Secondary exposure Number of house mice consumed to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 3 <1 <1

1000 2 5 3 1 27 8 5

3000 5 11 6 3 60 18 11

Number of Norway rats to consume to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 <1 <1 <1

1000 <1 <1 < 1 <1 5 1 <1

3000 <1 2 1 <1 11 3 2
Secondary feeding study summary counts (#mortalities/ #tested) NA 8/19 ND 9/100 32/55 19/33 0/4Incident datasummarycounts primary exposure NA 41 1 2 3 9 1

secondary exposure NA 22 1 0 1 4 0

unknown exposure NA 16 0 0 0 0 0

NA = not applicable; ND = no data ; * = RQ exceeds the LOC of 0.5Page 160 of 183 Table 7

- 4. Additional lines of evidence from the mammal risk assessment.

Body weights (g) Brodif

acoum Difeth

ialone Warfarin (0.025%) Warfarin (0.054%) Chloro

phacinone Dipha

cinone Brometh

alinPrimary exposure Days to consume sufficient bait to reach the LD 50 15 <1 <1 <1 <1 1

- 2 <1 <1

35 <1 <1 <1 <1 1

- 2 <1 <1

1000 <1 <1 <1 <1 1

- 2 <1 <1

Grams bait consumed to reach
the LD 50 15 0.3 0.7 0.3 0.2 6 1.1 0.6

35 0.5 1.3 0.7 0.3 9 2.1 1.1

1000 6.7 16 8.0 3.7 61 25 13Secondary exposure Number of house mice consumed to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 3 <1 <1

1000 2 5 3 1 27 8 5

3000 5 11 6 3 60 18 11

Number of Norway rats to
consume to reach the LD50: 1 day accum. in prey 50 <1 <1 <1 <1 <1 <1 <1

1000 <1 <1 <1 <1 5 1 <1

3000 <1 2 1 <1 11 3 2
Secondary feeding study summary counts (#mortalities/ #tested) NA 8/19 ND 9/100 32/55 19/33 0/4Incident datasummarycounts primary exposure NA 41 1 2 3 9 1

secondary exposure NA 22 1 0 1 4 0

unknown exposure NA 16 0 0 0 0 0

NA = not applicable; ND = no data ; * = RQ exceeds the LOC of 0.5Page 161 of 183 

### 7.1 Primary Exposure Risk Conclusions

7.1.1 Quantitative Risk Assessment Results across the Rodenticides As with all rodenticides, brodifacoum and difethialone represent a lethal primary risk to non

target small mammals that may eat either loose treated bait or utilize a bait station. In addition, the quantitative assessment also demonstr ates that bait containing these two rodenticides constitutes a primary exposure risk concern for larger mammals as well as all avian size classes. This conclusion is consistent across all primary exposure risk analyses performed (single oral dose, six

- day accumulated dose, and dietary concentration). EPA’s analysis indicates birds and
mammals could attain a median lethal dose (LD 50 ) of either brodifacoum or difethialone upon feeding for less than day on treated bait. The brevity of feeding required to r each a potentially lethal exposure represents an increased opportunity (relative to all other rodenticides assessed)
for non

- target birds and mammals to chance upon loose treated bait and be lethally exposed.

Warfarin also demonstrates a primary exposure risk concern to small mammals. The assessment of warfarin indicates a risk to large mammals for all assessment methods employed as well. EPA’s analysis indicates that feeding on treated bait for less than a day is sufficient to attain a
median lethal dose in all evaluated size classes of mammals, suggesting a similar opportunity, relative to brodifacoum and difethialone, for non

- target mammals to chance upon treated bait and consume a lethal dose. In contrast, warfarin’s primary exposure risk for birds is limited to small passeriforms and other medium sized birds. These results are dependent on the assessment method EPA considered. While a single day dose risk assessment suggests only a risk to small passeriforms from the highest concentration formulatio n, accounting for the potential for multiple day accumulation on a dose basis expands the concerns to include passeriforms and other small and medium sized birds at all formulation concentrations assessed. The dietary assessment does not consider body weig ht as a determinant factor. However, this assessment method still predicts a risk concern at the highest formulation concentration. EPA’s analysis
indicates that attainment of a lethal warfa rin dose can occur after 1 to 7 days of feeding (0.0 54%
warfarin bait) or after 4 to 15 days of feeding (0.025% warfarin bait), depending on body weight of the passerine in question . This finding suggests that, for birds there is less of an opportunity for chance lethal encounters with warfarin when compared with brodi facoum and difethialone, since it would require multiple days of feeding on warfarin treated bait.

For bromethalin, as can be expected for a relatively fast acting compound (target mortality 1 to 7 days, Pitt et al . 2011, and registrant submitted studies) , acute risk concern levels are exceeded for all mammalian size classes feeding on treated bait based on a single day of exposure. Primary risk to birds from bromethalin exceeds risk concern levels in all assessment methodologies with the exception of the dietary exposure methodology, which returns a risk quotient that closely approaches but does not exceed the acute risk LOC. EPA’s analysis indicates that less than a single day’s feeding of bromethalin bait is sufficient to attain a median lethal dose in birds andPage 162 of 183 mammals, suggesting that like brodifacoum and difethialone, adverse effects to non

- target wildlife are likely from primar y exposure events with treated bait.

Two anticoagulant alternatives, chlorophacinone and diphacinone, also present primary exposure risk concerns for nearly all rodent and mammal sizes assessed using all primary exposure assessment methods (large rodent s consuming chlorophacinone bait for one day are not expected to experience risk concerns). EPA’s analysis indicates that <1 day (diphacinone) and <1 to 3 days ( chlorophacinone ) of feeding on bait are sufficient to attain a median lethal dose in
mammals. This is not materially different from the other rodenticides with respect to the opportunity for non

- target mammals to chance upon and feed lethally on treated bait. In contrast to mammals, avian risk is below concern levels for these two compounds. Thi s may be a limitation in the analysis of primary exposure models terminating at six days ( i.e., longer exposure periods might provide sufficient exposure to bait for adverse accumulation to occur); however, the analysis indicates that, unlike brodifacoum a nd difethialone, a very consistent and protracted feeding period for either diphacinone or chlorophacinone is required to attain a lethal dose in birds ( i.e., daily feedings for the former versus weeks to months for the latter ).

7.1.2 Incident Analysis Findings as they Relate to Primary Exposure Risks

The quantitative risk assessment results cannot provide direct evidence relating risks to wildlife
for various land uses ; however, the incident data can be used to characterize the spatial locations
of m ortalities that have been attributed to specific rodenticides . The incident data show a sizable number of primary incidents occurring in urban/suburban areas. One can conclude that residential and commercial use of rodenticides in these areas pose comple te exposure pathways to a variety of wildlife and that primary exposure lethal incidents involving non

- target wildlife

can occur

.

Incident data support the quantitative risk assessment’s contention that primary exposure to
brodifacoum poses lethal risk to a variety of sizes of mammals and birds. Available incidents
represent ing primary brodifacoum exposure include mortalities of non

- target mammalian
wildlife for species ranging in size from chipmunks to white

- tailed deer

. These incidents ar e consistent with results of the deterministic assessment. For birds, incidents concluded to represent likely primary exposure involved sizes ranging from robins through geese . A gain , these
incidents are consistent with the risk model predictions. Incide nt data indicate that likely lethal events from primary exposure to brodifacoum for non

- target wildlife can occur in rural, suburban
and urban environments.

The incident data set for difethialone is much more limi ted than brodifacoum

. Analysis of the

tox icity and retention time of difethialone indicates that it is toxicologically similar to brodifacoum, suggesting that the lack of observed incidents for this ingredient is likely due to thePage 163 of 183 low use or to other factors not related to risk. Nevertheless, th ere is a lethal incident involving a species likely directly exposed to difethialone treated bait: the Key deer, in a suburban
environment and this incident is consistent with the primary risk assessment . There are no incidents involving difethialone and b ird species expected to involve primary exposure to treated
bait materials ; however, the lack of primary avian incidents involving this chemical neither supports or refutes the primary risk assessment findings.

Warfarin incidents with non

- target wildlif e generally parallel the findings of the quantitative risk assessment for primary exposure to this chemical , i.e., risk was identified in the assessment for primary birds and mammals and there are incidents involving these taxa . Little can be said regardi ng the land use characteristics in areas where incidents were reported. This may be more a factor of the age of the incidents reports and the relative low recent use of warfarin than any real differences in the pattern of occurrence of wildlife exposures.

The incident data set for primary animals exposed to bromethalin is limited to a reported mortality of a chipmunk and this incident involved a commensal rodent control product. This limited information is consistent with a quantitative risk assessment th at indicates a risk to small mammals exposed to treated bait, yet provides little support risk assessment predictions for larger mammal. There are no incidents involving bromethalin and bird species expected to involve primary exposure to treated bait mate rials. There may be an extenuating issue that explains the absence of reported incidents for this chemical. As discussed in the incident sections, bromethalin is not a commonly assayed compound when investigating wildlife mortality incidents.

Chlor ophac inone incidents of high certainty involving mammals of likely primary exposure to bait are scarce but include reports or mortalities in squirrels (Central Park, New York) which would be in agreement with the primary exposure risk assessment predictions for small mammals. Larger mammal incidents attributable to primary exposure to this chemical are not reported. An incident report with a likely primarily exposed bird (California quail in an orchard) suggests a possible lack of appropriate conservatism in th e chlor ophacinone primary risk assessment. The report of this incident identified crop content in the mortal individual as containing physical residue of parafinized rodenticide pellets.

The diphacinone incident data set for mammals is similar to that for chlorophacinone , in that the only incident involves a squirrel in a n urban setting (Central Park, New York). Again , as for chlorophacinone , there is a diphacinone incident involving a likely primarily exposed bird, i.e., a turkey, again suggesting a possible lack of quantitative risk assessment conservatism. This incident involved birds feeding in the vicinity of a prairie dog town, not a commensal rodent control operation.Page 164 of 183 7.1.3 Implications for Mitigation

For primary exposure lethalities to non

- targe t wildlife to occur, the organisms must encounter the treated bait formulation and ingest it.

The RMD mitigations for all rodenticides required the placement of commensal rodent control chemicals in bait boxes and in forms not readily removable from the box. It is qualitatively anticipated that bait boxes represent a reduction in the geographic extent of bait dispersal across the landscape relative to other application methods that may involve scattering of bait. Exposed bait ( e.g ., sc attered pellets, u ncovered place packs, and exposed bait blocks) may offer an increased opportunity for casual encounter with rodenticides when compared with a more focally placed bait box, and indeed, for such chemicals as brodifacoum, difethialone, bromethalin and
warfar in, only a few feeding episodes are sufficient to cause mortality. Moving to bait boxes is likely to result in a reduction of encounters of wildlife with rodenticide s

.

In addition to the issue of geographical distribution of rodenticide, the requirement for bait boxes

m a y further limit access of non

- target animals to the bait itself. Because b ait boxes are optimized for the commensal rodent body size (mice and rats), larger mammals ( e.g., deer) are physically limited by the box portal size , which prevent s them from reaching the bait within. Bird behavior and feeding patterns suggest that they would be unlikely to enter bait boxes to feed even if the bird was small enough to enter. In addition

, the requirement for bait to be not readily
removable from the boxes indicates that even boxes disturbed by larger organisms will present a reduced opportunity for contact with the enclosed bait.

The RMD also required that commensal rodent control bait box placement occur within and not
more than 50 feet from the exterior of structures. This likely represents a reduced opportunity for wildlife to encounter rodenticides. By geographically limiting the areas that may be treated
with the chemicals the wildlife

, co

- occurrence will be likely limited to individual anim als and species that are more tolerant of human activities and only in areas immediate to human
structures and sites of habitation.

The RMD also required that second generation rodenticides (including brodifacoum and difethialone) be applied in a domestic setting by a licensed applicator. There are opportunities with this requirement to further reduce the potential for wildlife to encounter these rodenticides. Effective rodent control methods employed by licensed applicators probably incorporate an integ rated pest management approach. In addition to the rodenticide ap plication, licensed applicators will likely take additional steps to limit the shelter, water

, and food resources surrounding infested domestic areas. This integrated approach may have the a ncillary effect of reducing the attractiveness of such residential areas to wildlife, thereby potentially reducing
encounters of non

- target wildlife with rodenticides.Page 165 of 183 

### 7.2 Secondary Exposure Risk Conclusions

7.2.1 Quantitative Risk Assessment Results Across the Rodenticides

Rodenticide intake based on consumption of bait by the primary consumers (prey) was
calculated for the house mouse and Norway rat. For this analysis

, rodenticide accumulation in

prey over a one or six day period was calculated in order to bracket the available data from residue studies submitted to the agency and occurring in open literature. Accumulation was determined based on daily food intake rates for the prey, assuming 100% of their diet consisted
of dry bait

. It was assumed that the form of the bait would not influence intake. Based on the assumed weight of the primary consumers, the percent active ingredient in the bait, and daily food intake, the concentration within the prey animal at the end of a day’s feeding was
determined. Ac cumulation of rodenticide within the prey animal over time was calculated using
an elimination rate constant based on t he liver half

- lives for each chemical to approximate
elimination.

Exposure to secondary consumers was determined in a similar manner. Secondary consumers were assumed to be mammals weighing 50g, 1000g, or 3000g, or birds weighing 100g, 1000g, or 5000g. These weights were assumed based on the range of secondary consumers identified in
rodenticide incidents in the Environmental Incident I nformation System (EIIS) database . The general equation for food intake was used to calculate the daily rodenticide intake for predator/scavenger birds and mammals consuming house mice and Norway rats exposed to rodenticide bait for three or six days.

RQ s were also calculated based on subacute dietary LC 50 values and expected concentration of the rodenticides in prey items. Daily rodenticide intake values (mg a.i./kg

- bw/day) for primary consumers based on their consumption of bait were used as an estimat e of the a.i. concentration in prey items after one day of feeding. This value can be considered as the dietary concentration (mg a.i./kg diet) for secondary consumers. RQs were calculated by dividing this value by the

LC 50 values for birds and mammals

.

A combination of toxicity and biological persistence with brodifacoum and difethialone results in a trigger for secondary exposure risk concerns for all assessed mammals and birds

, regardless of the method used to estimate exposure (theoretical and empiri cal). The delayed time to mortality for brodifacoum, coupled with its slow clearance time, results in accumulation of this rodenticide
in target mammal s to levels that are two orders of magnitude above the median lethal dose . This suggests an enhanced oppo rtunity for secondary exposure in that the rodenticide body burden reaches levels far above that which is necessary to kill the target organism . S ubsequent ingestion of these targets (live or moribund) by wildlife represents dietary doses may occur in exce ss of concentrations in the rodenticide bait itself. These factors combine to yield risk quotients forPage 166 of 183 brodifacoum and difethialone that indicate that there are concerns for lethality in all assessed
size s of mammalian and avian scavengers/predators consum ing rats and mice.

The warfarin quantitative analysis for secondary risks to mammalian wildlife is similar to brodifacoum and difethialone. However, the avian scavenger/predator results depart from the
observations for the other two rodenticides . Only the smallest scavenger/predator birds, consuming the smallest target pest and only the pests consuming bait over protracted periods of
time is sufficient to raise risk concerns.

The bromethalin secondary risk assessment results are similar to br o difacoum and difethialone with respect to mammals. As with warfarin, the b ird risk assessment results for bromethalin depart somewhat from brodifacoum and difethialone

. For birds that consume target animals exposed to bromethalin, n o rat consumption triggered ri sk concerns yet mouse consumption triggered concerns in all size avian scavenger/predators regardless of exposure duration.

Mammalian secondary risk concerns for diphacinone and chlorophacinone are triggered for consumption of target pests (mice only as these compounds are not labeled for rats). Both of
thes e compounds d o not present secondary risk concerns for birds. Available toxicity data for diphacinone suggest that raptors are more sensitive than the test species used to derive the RQs
for seconda ry avian species

. Although incorporation of the raptor data would not materially
affect conclusions of the deterministic risk assessment, it may at least in part explain the presence of secondary poisoning incidents for diphacinone in the absence of LOC exceedances (See Section 7.2.4).

7.2.2 Secondary Feeding Studies

Concerns for secondary risks with brodifacoum are supported by available data from secondary toxicity studies showing mortality in 63 % of predator/scavenger birds and 42% of predator/scavenger mammals fed brodifacoum contaminated target organisms

. Seconda ry feeding studies include data on mammalian species including foxes, mongoose. Weasels , and dogs and avian species including hawks, kestrels, owls, and gulls. No secondary feeding data are
available for difethialone.

In the case of warfarin, secondary feeding studies involving mammal predators/scavengers show mixed results and for some species

, the differences extended to a dose

- dependent response. No mortalities were observed in raccoons and European ferrets (no dose dependency and bait
concentration s equal to or higher levels found in US registered products). Other studies showed lethalities in mink, least weasels and dogs, though the results often involved few test organisms. These findings with warfarin do little to support or refute globally the results of the quantitative analysis and may reflect a wide range in sensitivity of predator and scavenger mammals toPage 167 of 183 warfarin. Another possible explanation for high variability, given the span of dates when the studies were conducted, is that r esponses may also reflect differences in active ingredient potency as discussed in the primary toxicity section’s description of available acute toxicity results. Avian secondary feeding studies involved testing of four species. In three of the four species test ed there was no observed mortality. I nterestingly

, the results from feeding tests, when considering the weights of the birds, do not completely parallel the results of the quantitative secondary risk assessment. Fo r example no mortality was observed in t he feeding
studies with black

- billed magpies (~170 g bodyweight) while the risk assessment suggests a concern for a 100 gram bird. Conversely, mortality results were mixed for larger birds of similar weights (death in barn owls but not in tawny owls both ~400

- 500 g body weight). These discrepancies may indicat e that allometric relationships for predicting effects of warfarin toxicity
do not completely explain the factors contributing to species sensitivity variability.

Bromethalin secondary feeding data are limited to a single case. In that study

, domestic dogs (n = 4) were fed intoxicated rats . No mortalities were observed. For this chemical, t he number of species tested is limited and so there is insufficient evidence from these data alone to make
defi nitive conclusions regarding the accuracy of the secondary quantitative risk assessment results. No bird feeding studies were available for bromethalin.

Chlorophacinone secondary toxicity results include studies with five mammal species. Mortality

response s were variable and ranged from approximately 50 percent to 100 percent of individuals tested. In one single species, the European ferret, different studies yielded h ighly variable results, ranging from zero to 100 percent mortality of tested individuals . It should be noted again that all these studies involve a low number of test individuals and differences in perceived sensitivity may be as much a product of low num ber of individuals as from real differences in toxic response across species. Avian feeding studies with chlorophacinone span 10 species with a wide range of bodyweights (170 to 4400 g). In no cases were mortalities observed

, which is
consistent with th e secondary risk assessment.

Diphacinone secondary feeding data span studies from seven mammal species. The effects range from 0 to 100 percent mortality in tested individuals. Of particular note is the study involving actual secondary feeding with rats . This is of note because (1) the secondary exposure risk assessment used a rat acute toxicity endpoint as a surrogate for predators and scavengers and (2) the assumed prey item concentrations in the risk assessment were 10 to 20 times higher than
tested in the feeding study. The feeding study with rats yielded a 50 percent mortality response under conditions of similar toxicity and lower exposure than modeled conditions showing risk. Looking back on the quantitative risk results, substituting the modele d diphacinone dietary concentrations with the actual concentrations used in the feeding study would still trigger secondary acute risk concerns. These results are considered supportive of the secondary risk assessment with mammals. Avian feeding studies with diphacinone span 5 species of varying bodyweights. In three specie s there were no mortalities, which is expected based on thePage 168 of 183 secondary risk assessment results. In the case s of two owl species, mortalities were observed

, which is contrary to the ris k assessment results. However, as discussed earlier, this may be explained by the toxicity data used to derive RQs for secondary birds in that these data were less
conservative than available data for a raptorial species exposed to this chemical.

7.2.3 Analysi s of the Opportunity for Secondary Exposure Lethality

As evaluated in the secondary risk assessment, residues reach levels in target organisms that, when consumed by predators and scavengers

, can result in risk of mortality . When considering
those risks among the assessed rodenticides

, it is important to consider the likelihood of predators and scavengers encountering enough intoxicated target prey to reach potential lethal doses. Furthering the evaluation of secondary exposure of rodenticides are the r esults of analyses of the number of individual target organisms necessary for dietary consumption to achieve a lethal dose in predator s and scavengers. The fewer the number of intoxicated target organisms necessary to reach a lethal dose, the less efficie ntly and intently a predator or scavenger must locate and consume these organisms to reach lethal body burdens. The analysis considered different bodyweights of predator/scavengers consuming either rats or mice which
have ingested bait for a single day o r up to six days. Again, compounds that can present a lethal dose to predators and scavengers after consumption of target organisms with only a single day of exposure are likely to represent greater opportunities for lethal secondary exposure events than those which require multiple days of target organism exposure in target organisms

With br o difacoum, and rats as a diet, every size predator/scavenger mammal need only consume a fraction of single target organism to reach lethal endpoint exposures. Compar ing these results to other NOIC rodenticides does not reveal a marked difference among the chemicals (diphacinone and chlorophacinone are not labeled for rat control). Obviously, owing to the smaller size of targeted mice, consumption of these organisms i ntoxicated with brodifacoum must be slightly more intensive for the predator/scavengers to reach lethal endpoint exposure (<1 to 5 organisms). These results are similar to the results for the other NOIC rodenticides. However, the brodifacoum results are substantially lower than diphacinon e and chlorophacinone

, suggesting an increased opportunity for chance encounter with brodifacoum intoxicated target organisms to trigger a lethal incident with predator/scavenger wildlife.

Similar analyses were conducted to determine the target organism numbers necessary to trigger lethal incidents in scavenger/predator birds. Brodifacoum results indicate that consumption of only a fract ion of an intoxicated rat, regardless of rat exposure duration, is needed to reach lethal endpoint exposures in all bird sizes modeled. The results for difethialone are similar to those of brodifacoum; however, for warfarin and bromethalin, the results indicate that a secondary bird
would need to consume many more target mammals to reach the median lethal dose . For brodifacoum, mouse consumption would have to be higher than for rats , though not substantiallyPage 169 of 183 so (<1 to 5 organisms consumed) and again res ults are comparable to difethialone and slightly
lower than bromethalin . However, similar analyses conducted with warfarin, chlorophacinon e , and diphacinone reveal that consumption of intoxicated target organisms must reach drastically larger and more int ent levels to reach lethal exposure endpoints. This suggests that brodifacoum has a substantially greater opportunity to result in mortality following exposure of a predator/scavenger bird to intoxicated target organisms.

7.2.4 Incident Analysis Findings as they Relate to Secondary Exposure Risks

As in the case of primary exposure risk assessment, the quantitative secondary exposure risk assessment cannot, by itself, provide evidence that land use is or is not a factor in where secondary exposure wildlife mo rtalities may occur. Again incident data are important in this regard and demonstrate for some chemicals that such incidents of wildlife mortality involving predators and scavengers do occur in urban and suburban land use areas.

Incident data support the quantitative risk assessment’s conclusion that secondary exposure to
brodifacoum poses lethal risk to a variety of sizes of mammals and birds. The presence of a large number of secondary mortality incidents together with the results of the deterministic risk assessment increase confidence in the conclusion that brodifacoum exposure poses a secondary
risk concern to birds and mammals. From available incidents concluded to represent likely secondary exposure to brodifacoum, non

- target mammalian wildlife include lethalities in species ranging foxes to mountain lions , consistent with the modeled size classes determined in this

assessment to be at risk. For birds, incidents involving likely secondary exposure s included a variety of raptors

, which was again consistent with the risk predictions for larger birds. There are incidents involving corvid species that are closer to the lowest bodyweight assessed, but it is not completely known if all these are primary or secondary exposure results. Incident data indicate that likely lethal events from secondary exposure to brodifacoum for non

- target wildlife

can occur in rural, suburban and urban environments.

The incident data set for difethialone is much more limi ted than brodifacoum

. Nevertheless,
there are lethal incident s involving predatory birds and mammals

. These results are consistent with the secondary risk assessment findings. All the available incidents are associated with
suburban and urban areas

.

Warfarin incidents with non

- target secondary mammals are not available. The lack of secondary mammal incidents cannot be considered to be supportive or contrary to the finding of the secondary risk assessment. Secondary incidents with warfarin include a variety of raptorial species and these result s are not inconsistent with the conclusions of the secondary risk

assessment that did not identify risks for larger secondary birds . However the incidents are in partial agreement with the mixed available secondary feeding toxicity studies. On balance, t hePage 170 of 183 quantitative risk assessment may be lacking appropriate levels of conservatism with respect to raptorial birds and there exists a real concern for secondary exposure raptor mortality with
warfarin

. Incident data indicate that likely lethal events from secondary exposure to warfarin for

non

- target wildlife can occur in rural, suburban and urban environments.

The incident data set for secondary animals exposed to bromethalin is limited to birds . This
limited information is can neither support nor refute the mammalian secondary risk assessment
but is consistent with the quantitative risk assessment for secondary exposure in birds.

Chlorophacinone incidents of high certainty involving mammals and birds of likely secondary exposure include reports of mortalities in wild felines (bobcats) and raptors (red

- tailed hawk). The mammal incident is consistent with the secondary risk assessment findings ; however, t he bird incident is inconsistent with the secondary risk assessment. It may be possible that
chl orophacinone mirrors diphacinone in terms of the sensitivity of raptors being possibly greater than the test species employed in the risk assessment (i.e.

, a 20 fold increase in sensitivity). If the chlorophacinone secondary risk assessment was adjusted f or this possible increased sensitivity in raptors the secondary risk conclusions would then be consistent with reported incidents for dietary subacute portions of the analysis but not for the single oral dose analysis.
On balance

, secondary lethalities to birds may occur but the strength of this prediction for this
chemical is limited.

Dip hacinone incidents of high certainty involving mammals and birds of likely secondary exposure but include reports of mortalities in wild canids, mustilids and felids (fo x, coyote, raccoon, and mountain lion) and raptors (snowy and barred owls, red

- tailed hawk). The mammal incidents are consistent with the secondary risk assessment findings. The bird incidents are inconsistent with the modeling portions of secondary risk assessment but consistent with available feeding studies, especially for owls. If the diphacinone secondary risk assessment was adjusted for the possible increased sensitivity in raptors the secondary risk conclusions would still yield risk quotients be low concern levels. On balance

, secondary lethalities to birds may occur but the strength of this prediction for this chemical is limited, though the uncertainty in concluding the possibility of a lethal risk is less than for chlorophacinone

.

7.2.5 Implicatio ns for Mitigation

For secondary exposure lethalities in non

- target wildlife to occu r, the organisms must encounter prey organisms exposed to the treated bait formulation and ingest them

. The RMD mitigations for all rodenticides required the placement of commensal rodent control chemicals in bait boxes and in forms not readily removable from the box. It is qualitatively anticipated that bait boxes represent a reduction in the geographic extent of bait dispersal across the landscape relative to other appl ication methods that may involve scattering of bait. APage 171 of 183 scattered bait may offer an increased opportunity for casual encounter of prey species with
rodenticides and therefore

, for wide ranging p redators and scavengers

, an increased opportunity to have significant proportions of the diet composed of intoxicated prey. For bait boxes, the placement of rodenticides is more geographically focused and can be expected to involve much less of the prey base for the wide ranging predators and scavengers. Moving to bait boxes is likely to result in a reduction of encounters of predatory and scavenger wildlife with rodenticide. Bait boxes are optimized for the commensal rod ent body size (mice and rats). L arger mammals are physi cally limited by the box portal size preventing them from reaching the bait within. For predators that may utilize a variety of body size prey items, narrowly focusing the sizes of rodenticide exposed prey could reduce the proportion of exposed prey in the total diet and so reduce the overall availability of a rodenticide to the predator.

The RMD also required that commensal rodent control bait box placement occur within and not more than 50 feet from the exterior of structures. This likely represents a reduced opportunity
for prey wildlife to encounter rodenticides. By geographically limiting the areas that may be
treated with the chemicals the prey wildlife co

- occurrence will be likely limited to individual animals and species that are more tolerant o f human activities and only in areas immediate to
human structures and sites of habitation. A gain this reduces the variety of prey items likely to encounter bait, as compared to widespread applications of rodenticides and so reduces the variety
and possibl y the proportion of the diet exposed organisms contribute to predators and

scavengers.

The RMD required that second generation rodenticides (including brodifacoum and difethialone) be applied in a domestic setting by a certified applicator. There are opp ortunities with this requirement to further reduce the potential for wildlife to encounter these rodenticides. Effective rodent control methods employed by certified applicators likely take an integrated approach. In addition to the rodenticide ap plicatio n applicators will likely take additional steps to limit the shelter, water and food resources surrounding infested domestic areas. This integrated approach may have the ancillary effect of reducing the attractiveness of such residential areas to wildlife

, thereby potentially reducing encounters of non

- target wildlife with rodenticides.



## 8 References

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