Toxicity and Eliminatio

Primary Exposure and RPrimary Exposure and R

Characterization

Primary Exposure and R

Characterization

Presentation to the SAP

November 29, 2011

Christine Hartless, Ph.D. Christine Hartless, Ph.D.

Environmental Fate and Effects Division
Outline

• Analysis approach flowchart• Avian and mammalian acute toxicity endpoints• Single-day primary exposure and risk estimation• Multiple-day primary exposure and risk estimation day primary exposure and risk estimation• Quantity of bait consumed to reach LD50 body burden• Primary exposure conclusions
Primary consumer

• Animals that eat plants, seeds, 

fruits, etc.

• Primary exposure occurs when 

these animals have an opportunity to consume rodenticide bait. to consume rodenticide bait.
Dose-based methodology flo

Toxicity endpoints Concentration Half-life in Scaled t

oxi

cit

y

of a.i. in bait

1 d d ti id

consume

r

Sca ed o c y led t

oxi

cit

y

endpoints based on body weights

1

-

day ro

denti

cide 

intake via allometric food intake equations

Daily body-bsingle day in

Sca ed o c yendpoints based on body weights

Body burde

1-day exposure RQs 6 days bait g bait consumed and days to reach LD6-day exposure RQsg bait consumed and days to reach LD50
Toxicity endpoint selec

• Acute oral (single dose) for birds and mammals• Acute dietary (5-day exposure) for birds and mamm• Most anticoagulant studies were conducted over a

time period (30 days observation after exposure)

• Values for RQ calculations based on most sensitiv

commonly tested species*:

• Bi dr

ds 

– mall d d k b b hit il llar

d

duc

k or 

b

o

b

white quail

• Mammals – laboratory rat* other available data evaluated in characterization other available data evaluated in characterization
Selected avian and mammali

toxicity values for RQ calculat

Chemical

Birds Mammals

LD50 LC50 LD50 LC5

Brodifacoum 0.25 1.33 0.48 0.5

Difethialone Difethialone 0 30 . 0 56 . 0 56 . No d

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 No d

LD50 = m

g a.i./k

g-bw

50 g g

LC50 = mg a.i./kg-diet
Avian acute dose LD50s (mg a.i./k

BrodifDifethWarfaChloroDiphaBrome

0.1 1 10 100 1000 10000

Endpoint for RQ calculations

LD50 (m
Avian acute dietary LC50s (mg a.i./

BrodifDifethWarfaChloroDiphaBrome

0.1 1 10 100 1000 10000

Endpoint for RQ calculations

LC50 (m
Mammalian acute dose LD50s (mg a

BrodifDifethWarfaChloroDiphaBrome

0.1 1 10 100 1000 10000

Endpoint for RQ calculations

LD50 (m
Mammalian acute dietary LC50s (mg 

BrodifDifethWarfaChloroDiphaBrome

0.1 1 10 100 1000 10000

Endpoint for RQ calculations

LC50 (m
Body Weight Scaling of Avian 

• Scaled to 20, 100, and 1000 g• Mineau et al.,1996 (default and chemic• Mineau et al., 2001 (chemical specific)

• Also evaluated unadjusted LD50

Photo credits: USFWS
Body Weight Scaling of Mammali

• Scaled to15, 35, and 1000 g• Standard USEPA approach (USEP

Standard USEPA approach (USEP

• Also evaluated unadjusted LD50

Photo credits: USFWS
Unadjusted and adjusted avian 

Chemical Unadjusted Adjusted for body w

20 g 100 g 

Brodifacoum 0.25 0.65 0.44 

Difethialone 0.30 0.21 0.27 

Warfarin 525 273 347 

Chlorophacinone 258 182 232 

Diphacinone 1630 1163 1480 

Bromethalin 4.6 3.27 4.16 

LD50 = m

g a.i./k

g-bw

50 g g
Unadjusted and adjusted mamma

Chemical Unadjusted Adjusted for body w

15 g 35 g 

Brodifacoum 0.48 0.96 0.78 

Difethialone 0.56 1.11 0.90 

Warfarin 3.0 5.7 4.6 

Chlorophacinone 6 26 . 11 6. 9 4. 

Diphacinone 1.9 4.8 3.9 

Bromethalin 2.2 3.7 3.0 

LD50 = m

g a.i./k

g-bw

50 g g
Toxicity value uncertaintie

• Missing endpoints: mammalian dietary LC50 endpoints for difethialone and bromethalin• Toxicity endpoints based on administered dose, not bioav

dose

• Li it d d t / t i it d t il bl Li

mit

e

d pre

d

a

tor/scavenger 

toxicity 

d

a

ta avail

abl

e

• Large range in LD50 values within chemical, some spannin

orders of magnitude orders of magnitude

• Scaling factors provide adjustment for test animal body we

may introduce additional variation among chemicals

• LD/LC50 estimates: some studies have low confidence in e

value as slope was very shallow
One-day exposure to ba

Toxicity endpoints Concentration Half-life in Scaled t

oxi

cit

y

of a.i. in bait

1 d d ti id

consume

r

Sca ed o c yendpoints based on body weights

1

-

day ro

denti

cide 

intake via allometric food intake equations

Daily body-bsingle day in

Body burde

1-day exposure RQs 6 days bait g bait consumed and days to reach LD6-day exposure RQsg bait consumed and days to reach LD50
Daily rodenticide intake bas

Bait concentration

Chemical % a.i. mg 

Brodifacoum 0 005 . 

Difethialone 0.0025 

Warfarin 

0.025 

0.054 

Chlorophacinone 0.005 

Diphacinone 0.005 

Bromethalin 0.010 

Allometric equations (USEPA 1993)

• Estimation of daily feeding rates of a i for 3 weight c

Estimation of daily feeding rates of

a.i. for

3 weight c

•generic birds and passerines•generic mammals and rodents

D il d b di t kD

aily 

dosebase

d in

t

a

ke: 

dividing daily a.i. intake by body weight to obtain mg a.i./kg-b
RQs based on one day dose-

(LD50) exposure in birds

Brodi

RQ = 0.5

DifethWarfaWarfaChloroDiphaBrom

0.001 0.01 0.1 1 10 100 RQ

20 g100 g1000 g

Passerine, adjusted LD50Generic, adjusted LD50 Generic, unadjusted 

Passerine, unadjust
RQs based on one day dose-

(LD50) exposure in mamm

Brodi

RQ = 0.5

DifethWarfaWarfaChlorDiphaBrom

0.1 1 10 100 RQ

Rodent, adjusted LD50Generic, adjusted LD50 Generic, unadjusted 

Rodent, unadjusted 

15 g35 g1000 g
Summary: one-day dose-based 

Dose-Based RQs Dietary- Bait availabili

Chemical Based RQs Bait availabili

consumption r

1 Day 6 Day

Birds

Brodifacoum

Difethialone

Warfarin (0.025%)Warfarin (0.054%)

Chl h i Chlorop

hacinone

Diphacinone

Bromethalin

Mammals

Brodifacoum

Difethialone

Warfarin (0.025%)

Warfarin (0 054%) Warfarin (0.054%)

Chlorophacinone

Diphacinone

Bromethalin

All evidencesuggests risk

Predominant evidenceof risk

Equivocal evidenceof risk

All evidencesuggests low ri
There is a potential for 

accumulation from day day...

...does it matt...does it matt
Six-day exposure to ba

Toxicity endpoints Concentration Half-life in Scaled t

oxi

cit

y

of a.i. in bait

1 d d ti id

consume

r

Sca ed o c yendpoints based on body weights

1

-

day ro

denti

cide 

intake via allometric food intake equations

Daily body-bsingle day in

Body burde

1-day exposure RQs 6 days bait g bait consumed and days to reach LD6-day exposure RQsg bait consumed and days to reach LD50
Chemical accumulatio

• Estimation of accumulated chemical loads 

a.i./kg-bw) based on:

• Daily feeding rates• Accumulation and elimination rates of chemicals

• Whole-body elimination rates (half-lives) n

available

• Data available for liver and blood plasma h

Data available for liver and blood plasma h

lives for most chemicals

• Accumulation in body based on liver half-l

• Most values from one study to allow for method consistenc• Bromethalin: blood plasma half-life, no liver data available

• Used in primary and secondary exposure analysis
Half-lives for calculation 

dose accumulation

Rodenticide Test Species Compartment

Elim

half-l

B dif ro acoum

Mouse Live

r 3

Difethialone Mouse Liver 2

Warfarin Mouse Liver 

Chlorophacinone Mouse Liver 

Diphacinone Pig Liver 

Bromethalin Rat Blood 
Liver and blood plasma ha

B dif ro a

Difethia

WarfarChloroDiphacBrome

0.1 1 10 100 1000

Liver half-life (days) used in accumulation calculations

hal

-

Liver half life (days) used in accumulation accumulation calculations calculations

Blood plasma half-life (days)used in accumulation calculations
Accumulation equation

dt

= (FI

* C / (wt/1000)) + d(t 

dt (FI

C

/ (wt/1000))

+

d(t

-

where:

dt = dose (mg a.i./kg-bw) at day 

t

FI f d i t k ( d t) b d ll t i FI = 

foo

d in

t

a

ke 

(g, 

dry wt)

base

d on allome

t

ric 

C = concentration of a.i. in bait (mg a.i./kg-diet) 

wt = weight (grams) of the bird or mammal conswt

= weight (grams) of the bird or mammal cons

k = ln(2)/t1/2t1/2 = h

alf-lif

e (days)

of 

c

h

emical in liv

er (blood for 

1/2

a e (days) o c e ca e (b ood o 
Accumulation in 100 g gene

10000 6-day 

accumulation

1000

Warfarin, 0.054%Warfarin, 0.025%

100

ChlorophacinoBrodifacoumDifethialone

aBromethalin.i./kg-bw

10

Diphacinone

mg a

1

0 5 10 15 20 25 30 35 

Days
RQs based on six day dose-

(LD50) exposure in birds

Brodi

RQ = 0.5

DifethWarfaWarfaChloroDiphaBrom

0.001 0.01 0.1 1 10 100 RQ

20 g100 g1000 g

1-day exposure, adjusted LD506-day exposure, adjusted LD50

**not expected to eat b
RQs based on six day dose-

(LD50) exposure in mamm

Brodi

RQ = 0.5

DifethWarfaWarfaChlorDiphaBrom

0.1 1 10 100 RQ

1-day exposure, adjusted LD506-day exposure, adjusted LD50

**not expected to eat b

15 g35 g1000 g
Summary: one- and six-day dose-ba

Dose-Based RQs Dietary- Bait availabili

Chemical Based RQs Bait availabili

consumption r

1 Day 6 Day

Birds

Brodifacoum

Difethialone

Warfarin (0.025%)Warfarin (0.054%)

Chl h i Chlorop

hacinone

Diphacinone

Bromethalin Not assessed

Mammals

Brodifacoum

Difethialone

Warfarin (0.025%)

Warfarin (0 054%) Warfarin (0.054%)

Chlorophacinone

Diphacinone

Bromethalin Not assessed

All evidencesuggests risk

Predominant evidenceof risk

Equivocal evidenceof risk

All evidencesuggests low ri
What if chemical was 

incorporated in the dietary matrix...

...does that m

a difference
Exposure and toxicity values 

dietary-based assessment

Toxicit

y end

point Concentrat

of a i in b

Calculate RQs

LC (mg a i /kg

y p of

a.i. in b

Chemical Bait concentration (mg a.i./kg-bait) LC50 (mg

a.i./kg

Birds Mam

Brodifacoum 50 1.33 0

Difethialone 25 0.56 no 

Warfarin 

250 

625 5

540

Chlorophacinone 50 72 7

Diphacinone 50 906 4

Bromethalin 100 210 no 
RQs based on dietary (LC50) to

Chemical Birds Mammals

Brodifacoum 38* 94*

Difethialone 45* no data

Warfarin (0 025%) Warfarin (0.025%) 0 40 . 57

*

Warfarin (0.054%) 0.86* 123*

Chlorophacinone 0.89* 44*

Diphacinone 0.06 22*

Bromethalin 0.48 no data

* = exceed acute risk LOC (0.5)

( )
Summary: all RQ analyses

Dose-Based RQs Dietary- Bait availabili

Chemical Based RQs Bait availabili

consumption r

1 Day 6 Day

Birds

Brodifacoum

Difethialone

Warfarin (0.025%)Warfarin (0.054%)

Chl h i Chlorop

hacinone

Diphacinone

Bromethalin Not assessed

Mammals

Brodifacoum

Difethialone No data

Warfarin (0.025%)

Warfarin (0 054%) Warfarin (0.054%)

Chlorophacinone

Diphacinone

Bromethalin Not assessed No data

All evidencesuggests risk

Predominant evidenceof risk

Equivocal evidenceof risk

All evidencesuggests low ri
RQs say concerns exist 

rodenticides...

...but will non but will non

-targ

targ

really be exposed 

enough bai

experience toxicexperience toxic
Bait consumption opportun

Toxicity endpoints Concentration Half-life in Scaled t

oxi

cit

y

of a.i. in bait

1 d d ti id

consume

r

Sca ed o c yendpoints based on body weights

1

-

day ro

denti

cide 

intake via allometric food intake equations

Daily body-bsingle day in

Body burde

1-day exposure RQs 6 days bait g bait consumed and days to reach LD6-day exposure RQsg bait consumed and days to reach LD50
How much bait does a 100 g bir

to consume? (part 1

)

1000

(p )

W

100

B

a.i./kg-bw

10

mg 

1) Is body 

? 2) YES

– calculate

1

0 1 2

3

4

5

6

7

8

9 10 

burden 

≥ LD50

? 2) YES

– calculate

grams bait needed treach LD50.

0 1 2

3

4

5

6

7

8

9 10 

Days
How much bait does a 100 g bir

to consume? (part 2)

1000 3) NO. Is body burden

≥ LD

?

(p )

W

1) Is body 

burden 

≥ LD50

?

burden

≥ LD50

?

100

B

a.i./kg-bw

2) NO. Is bod

y

3) YES. For day 6, bo

burden is > LD50

10

mg a) y burden 

≥ LD50

?

4) Grams bait consu

1

0 1 2

3

4

5

6

7

8

9 10 

4) Grams bait consu

bait intake for 1 day x 

0 1 2

3

4

5

6

7

8

9 10 

Days
Birds: grams bait to reach b

burden equivalent to LD

Brodi

1 day feed 1 day feed

DifethWarfa

5 days 42 days

WarfaChloro

19 days

3 days

5 days

17days

>365 da

y

s

DiphaBrom

19 days

>365 days

y

>365 days

0.1 1 10 100 1000 10000 100000

grams ba

20 g generic birds1000 g generic birds

grams ba
Mammals: grams bait to re

body burden equivalent to 

Brodi

1 day feed 1 day feed

DifethWarfaWarfaChlor

2 days 2 days

DiphaBrom

2 days

2 days

0.1 1 10 100

grams ba

15 g generic mammals1000 g generic mammals

grams ba
Primary Exposure: Summary of Co

Dose-Based RQs Dietary- Bait availabili

Chemical Based RQs Bait availabili

consumption r

1 Day 6 Day

Birds

Brodifacoum

Difethialone

Warfarin (0.025%)Warfarin (0.054%)

Chl h i Chlorop

hacinone

Diphacinone

Bromethalin Not assessed

Mammals

Brodifacoum

Difethialone No data

Warfarin (0.025%)Warfarin (0 054%) Warfarin (0.054%)

Chlorophacinone

Diphacinone

Bromethalin Not assessed No data

All evidencesuggests risk

Predominant evidenceof risk

Equivocal evidenceof risk

All evidencesuggests low ri