Use
of
Pharmacokinetic
Data
to
Refine
Carbaryl
Risk
Estimates
from
Oral
and
Dermal
Exposure
Presented
To
The
FIFRA
Scientific
Advisory
Panel
By:
U.
S.
EPA
Office
Of
Pesticide
Programs
Health
Effects
Division
Presented
On:
December
2,
2004
Office
of
Prevention,
Pesticides
&
Toxic
Substances
U.
S.
Environmental
Protection
Agency
Washington,
D.
C.
20460
Table
of
Contents
Preface
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Page
1
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16
1.
Introduction
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2.
Use
of
Pharmacokinetic
Data
to
Refine
Carbaryl
Exposure
Estimates
from
Oral
and
Dermal
Exposure
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2.1
Summary
of
Carbaryl
Metabolism
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2.2.
Analysis
of
Bayer
Mixed­
dose
Pharmacokinetic
Studies
in
Rats
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2.3
Calculating
Plateau
Brain
Concentrations
After
Divided
Doses
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2.4.
Extrapolation
of
Results
From
Mixed­
dose
Study
to
Biomonitoring
Study
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Page
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3.
Summary
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Supporting
Tables
&
Figures
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Appendices
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Page
16
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16
List
of
Figures
Figure
1.
Chemical
structure
of
carbaryl
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Page
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16
Figure
2.
Extrapolated
Plateau
Brain
Concentration
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Page
8
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16
Figure
3.
Results
of
Agency
Exposure
Assessments
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Page
10
of
16
Figure
4.
Average
Total
Radioactive
Residue
(
ppm)
From
Mixed
Dose
Study
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Page
14
of
16
List
of
Tables
Table
1.
Average
Total
Radioactive
Residue
(
ppm)
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Page
11
of
16
Table
2.
Average
Total
Radioactive
Residue
(
ppm)
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Page
11
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16
Table
3.
Average
Total
Radioactive
Residue
(
ppm)
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Page
12
of
16
Table
4.
Half­
life
of
Total
Radioactive
Residue
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Page
13
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16
Table
5.
Average
Total
Radioactive
Residue
(
ppm)
From
Mixed
Dose
Study
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Page
14
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16
Table
6.
Total
Radioactive
Residue
(
TRR)
and
Metabolites
Identified
in
Brain
after
Mixed­
Dose
Study
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Page
15
of
16
Page
1
of
18
Preface
The
Food
Quality
Protection
Act
of
1996
requires
EPA
to
reassess
all
previously
approved
pesticide
tolerances
by
August,
2006.
EPA
issued
the
Interim
Reregistration
Eligibility
Decision
on
June
30,
2003.
That
assessment
is
available
at
http://
www.
epa.
gov/
oppsrrd1/
REDs/
carbaryl_
ired.
pdf.
On
October
27,
2004,
EPA
published
a
Federal
Register
Notice
(
OPP­
2003­
0376).
This
Federal
Register
Notice
indicated
that
Bayer
CropScience,
a
registrant
for
technical
carbaryl,
had
developed
pharmacokinetic
studies
in
rats
to
further
evaluate
the
risk
to
children
exposed
to
carbaryl
following
lawn
treatment
with
liquid
formulation.
On
December
2,
2004,
the
FIFRA
Scientific
Advisory
Panel
will
hold
a
one­
day
meeting
to
consider
the
pharmacokinetic
studies
and
extrapolation
approach
proposed
by
Bayer
CropScience.
This
approach
may
provide
a
more
refined
method
to
estimating
risk
by
the
use
of
internal
doses
to
calculate
peak
target
tissue
concentrations
associated
with
the
use
of
carbaryl,
instead
of
administered
dose,
as
typically
used
by
EPA.
The
purpose
of
the
current
document
is
to
briefly
summarize
background
information
regarding
the
metabolic
profile
for
carbaryl,
the
animal
pharmacokinetic
studies,
and
the
proposed
extrapolation
approach.
More
detailed
information
can
be
found
in
the
documents
developed
by
Bayer
CropScience
which
are
provided
to
the
panel
as
appendices.
Page
2
of
18
1.
Introduction
Carbaryl
is
an
N­
methylcarbamate
insecticide
with
many
agricultural
and
residential
uses,
which
include
uses
on
lawns,
gardens,
and
ornamental
plants.
The
primary
mode
of
toxic
action
for
carbaryl
is
inhibition
of
acetylcholinesterase
through
carbamylation
of
the
enzyme
active
site.
This
inhibition
leads
to
accumulation
of
acetylcholine
and
results
in
cholinergic
toxicity
due
to
continuous
stimulation
of
cholinergic
receptors.
The
binding
of
carbaryl
to
acetylcholinesterase
is
rapidly
reversible.
Figure
1.
Chemical
structure
of
carbaryl
The
exposure
of
key
concern
is
for
young
children
who
play
on
turf
treated
with
carbaryl
which
can
lead
to
oral
and
dermal
exposures
because
of
mouthing
behaviors
and
physical
contact
with
treated
turf.

The
endpoint
for
short­
term
incidental
oral
exposure
was
decreased
cholinesterase
activity
(
erythrocyte,
whole
blood,
plasma,
brain)
and
functional
observational
changes
in
a
developmental
neurotoxicity
study
in
rats;
the
no­
observedadverse
effect­
level
(
NOAEL)
was
1
mg/
kg/
day
and
the
lowest­
observed­
adverseeffect
level
was
10
mg/
kg/
day.
For
short­
term
dermal
exposure,
the
endpoint
was
decreased
cholinesterase
activity
(
erythrocyte
and
brain)
in
a
4­
week
dermal
toxicity
study
in
rats;
the
NOAEL
was
20
mg/
kg/
day
and
the
LOAEL
was
50
mg/
kg/
day.
The
NOAELs
from
these
two
studies
provide
the
'
low'
dose
in
the
carbaryl
pharmacokinetic
studies
summarized
below.

The
Agency
typically
assesses
human
risks
to
pesticides
by
comparing
the
noobserved
adverse­
effect­
level
(
NOAEL)
in
lab
animals
to
human
exposures
and
calculating
a
margin­
of­
exposure
(
MOE):
MOE
=
NOAEL/
Dose.

The
Bayer
approach
compares
internal
peak
or
plateau
doses
in
the
target
tissue,
brain,
rather
than
the
total
absorbed
dose.
Because
of
the
pharmacokinetic
and
pharmacodynamic
characteristics
of
carbaryl,
peak
tissue
concentrations
of
carbaryl
resulting
from
oral
exposure
do
not
overlap
the
peak
concentrations
from
dermal
exposure.
Also,
peak
or
plateau
tissue
concentrations
resulting
from
repeated
oral
exposure
that
reflect
childrens'
behavior
should
be
lower
than
peak
concentrations
from
a
single
bolus
administration
used
in
the
laboratory
studies.
Page
3
of
18
In
the
Bayer
proposal,
a
margin­
of­
exposure
would
be
calculated
by
comparing
peak
brain
concentrations
of
carbaryl
determined
after
dosing
rats
in
two
studies.
In
one
study,
rats
received
an
oral
dose
equivalent
to
the
oral
NOAEL.
In
the
other
study,
rats
received
concurrent
dermal
and
oral
exposure
at
doses
similar
to
those
expected
in
a
residential
setting.
In
the
mixed­
dose
study,
rats
received
two
oral
bolus
doses
rather
than
twenty
doses
per
hour
assumed
in
children
from
residential
exposure
and
the
Bayer
proposal
included
pharmacokinetic
calculations
extrapolating
brain
concentrations
expected
from
twenty
doses.

2.
Use
of
Pharmacokinetic
Data
to
Refine
Carbaryl
Exposure
Estimates
from
Oral
and
Dermal
Exposure
This
document
cites
2
recent
Bayer
metabolism
studies,
which
for
convenience,
shall
be
referred
to
as:


Bayer
metabolism
study:
Metabolism
of
[
14C]
Carbaryl
in
Rats.
Krolski,
et
al.
Bayer
CropScience.
May
7,
2004.
230
pages.
(
Appendix
2)


Bayer
mixed­
dose
study:
Metabolism
and
Pharmacokinetics
of
[
14C]
Carbaryl
in
Rats
Following
Mixed
Oral
and
Dermal
Exposure.
Krolski,
et
al.
Bayer
CropScience.
May
7,
2004.
53
pages.
(
Appendix
3)

2.1
Summary
of
Carbaryl
Metabolism
The
Bayer
proposal
to
calculate
a
margin­
of­
exposure
using
peak
target
tissue
concentrations
is
based
upon
these
pharmacokinetic
and
pharmacodynamic
characteristics:
1)
oral
absorption
of
carbaryl
is
rapid
and
complete;
2)
dermal
absorption
is
prolonged
in
comparison
to
oral
absorption;
3)
duration
of
binding
to
acetylcholinesterase
is
brief;
4)
plasma
half­
life
of
carbaryl
is
short;
and
5)
metabolites
are
generally
less
toxic
than
parent
carbaryl.
Because
of
these
characteristics,
peak
tissue
concentrations
of
carbaryl
resulting
from
oral
exposure
do
not
overlap
peak
concentrations
from
concurrent
dermal
exposure.
Also,
peak
or
plateau
tissue
concentrations
resulting
from
repeated
oral
exposure
should
be
lower
than
peak
concentrations
from
a
single
bolus
administration.

There
are
a
number
of
studies
characterizing
rat
and
human
metabolism
of
carbaryl.
Although
these
studies
were
conducted
for
different
time
periods
and
used
different
analytical
techniques,
they
showed
that
carbaryl
metabolism
is
similar
between
rats
and
humans.
Bayer's
analysis
focused
on
the
alpha
phase
of
kinetics,
which
is
the
first
phase
of
the
dose­
response
curve,
because
this
is
the
time
period
of
concern
for
children
on
treated
lawns.

Oral
absorption
of
carbaryl
is
rapid
and
essentially
complete.
The
near
complete
absorption
of
carbaryl
by
the
oral
route
is
shown
by
comparing
tissue
concentrations
after
oral
and
intravenous
(
i.
v.)
exposure
(
Bayer
metabolism
Page
4
of
18
study,
Appendix
2).
Tissue
concentrations
in
the
oral
group
of
1.08
mg/
kg
were
very
comparable
to
those
in
an
i.
v.
group
of
0.80
mg/
kg
at
the
same
time
periods
(
Tables
1
and
2).
The
near
complete
absorption
of
carbaryl
by
the
oral
route
is
also
shown
by
comparing
excretion
after
administration
by
oral
and
i.
v.
routes.
In
a
study
in
which
rats
received
a
single
dose
of
1
mg/
kg/
day
by
either
oral
or
intravenous
routes,
both
groups
had
88­
92%
excretion
of
administered
dose
in
urine
and
~
9%
in
feces
(
Struble).

Oral
absorption
of
carbaryl
occurs
rapidly.
Peak
radioactivity
in
brain,
plasma,
whole
blood,
and
red
blood
cells
was
reached
by
the
first
sampling
period
15
minutes
after
rats
received
an
oral
dose
of
1.08
mg/
kg
(
Table
2).

Dermal
absorption
is
both
a
slower
process
and
less
complete
than
oral
absorption.
For
dermal
exposure,
peak
radioactivity
in
the
same
tissues
was
not
reached
until
4
hours
after
a
dose
of
17.25
mg/
kg.
Peak
tissue
levels
after
a
dermal
dose
of
17.25
mg/
kg
were
approximately
an
order
of
magnitude
less
than
peak
tissue
levels
after
an
oral
dose
1.08
mg/
kg
(
Tables
2
and
3
in
Appendix).
The
dermal
absorption
values
from
a
guideline
study
were
5%
for
2
hr
exposure,
13%
for
10
hr
exposure,
and
25%
for
24
hr
exposure
(
Cheng).

The
duration
of
binding
of
carbaryl
to
cholinesterase
is
brief.
Although
the
half­
life
of
cholinesterase
inhibition
in
rats
was
reported
as
3.0
hours
in
the
Bayer
proposal,
more
recent
calculations
show
the
half­
life
is
1.7
hours
(
Brooks
and
Broxup).
The
half­
life
for
cholinesterase
inhibition
in
humans
is
2.6
hours
(
May).

The
elimination
half­
life
of
carbaryl
is
also
short.
The
plasma
half­
life
in
humans
after
oral
ingestion
of
1.0
mg/
kg
carbaryl
is
0.79
hours
(
May).
The
plasma
half­
life
in
rats
for
radioactivity
in
the
alpha
phase
in
the
2
recent
Bayer
metabolism
studies
varied
somewhat
depending
on
dose
and
route
of
exposure,
but
the
plasma
half­
life
after
oral
ingestion
of
1.0
mg/
kg
carbaryl
was
1.2
hours
(
Table
4
in
Appendix).
The
half­
life
tended
to
decrease
with
decreasing
dose.

Urine
is
the
major
route
of
excretion
in
rats
and
humans.
Chromatograms
of
urine
from
rat
and
human
studies
were
compared
by
one
author
(
Knaak,
1965
and
1968)
and
with
the
exception
of
one
metabolite,
had
the
same
peaks.
1­
Naphthol
is
a
major
urinary
metabolite
in
both
rats
and
humans,
accounting
for
approximately
40%
of
administered
dose
in
rats
and
humans
(
Totis
and
Knaak,
1968).

Principal
urinary
metabolites
identified
in
the
guideline
rat
studies
are
free
and
conjugated
naphthol
and
hydroxy
carbaryl
metabolites.
Carbaryl
metabolites
are
also
excreted
in
bile
and
undergo
extensive
enterohepatic
recirculation.
Bile
cannulated
rats
had
45%
excretion
in
bile,
42%
excretion
in
urine,
and
1%
in
feces
after
oral
administration
of
carbaryl
(
Marshall).
Page
5
of
18
A
biomonitoring
study
was
conducted
by
Bayer
to
quantify
exposure
after
application
of
carbaryl
to
residential
lawns
and
gardens.
Twenty­
four
hour
composite
urine
samples
were
collected
from
each
resident
beginning
2
days
prior
to
application
and
ending
3
days
after
application.
A
carbaryl
metabolite
(
1­
naphthol)
was
used
to
calculate
absorbed
dose
estimates
for
carbaryl.
Carbaryl
absorbed
dose
estimates
were
calculated
from
1­
naphthol
levels
using
factors
determined
in
an
analysis
of
rat
and
human
pharmacokinetic
data.
Many
individuals
potentially
experienced
multiple
exposures
as
they
re­
entered
lawns
where
carbaryl
had
been
applied.
The
excretion
profile
indicated
that
it
took
approximately
96
hours
for
elimination
and
that
approximately
50
percent
was
eliminated
in
the
first
24
hours,
which
made
calculation
of
absorbed
dose
estimates
difficult
because
of
the
potential
for
multiple
exposures
(
Carbaryl
Revised
HED
Risk
Assessment,
March
14,
2003).

The
following
metabolites
were
identified
in
tissues
in
the
recent
metabolism
studies
performed
by
Bayer.
Carbaryl
per
se
was
identified
in
brain,
fat,
liver;
1­
naphthol
was
identified
in
brain,
fat,
liver,
blood,
plasma,
RBC;
the
sulfate
conjugate
of
1­
naphthol
was
identified
in
plasma;
N­
hydroxymethyl
carbaryl
was
identified
in
brain.
Low
concentrations
of
carbaryl
per
se
were
found
briefly
in
plasma
after
i.
v.
exposure,
but
carbaryl
per
se
was
not
detected
in
plasma
following
oral
or
dermal
exposure.

The
Bayer
proposal
described
carbaryl
metabolism:

"
When
we
look
at
the
metabolic
profile
at
"
low"
dosages,
(
more
comparable
to
those
experienced
by
humans),
the
predominant
pathway
is
hydrolysis
of
the
carbamate
linkage,
although
there
is
a
small
and
insignificant
amount
of
oxidative
metabolism
on
the
ring
while
the
carbamate
linkage
is
intact.
When
we
look
at
the
metabolic
profile
at
"
low"
dosages,
(
more
comparable
to
those
experienced
by
humans),
the
primary
pathway
is
overwhelmingly
hydrolytic.
For
example,
at
both
the
LOAEL
and
NOAEL
in
the
rat
(
10
and
1
mg/
kg,
respectively),
the
primary
metabolite
seen
at
peak
plasma
concentration
of
total
radiocarbon
is
1­
naphthol.
The
other
carbaryl
metabolites
retaining
the
carbamate
linkage
(
3
and
4­
hydroxy
carbaryl)
represent
a
total
of
less
than
1
%
of
the
TRR
in
any
tissue
(
Krolski
et
al.,
2004a)
and
are
also
poorer
cholinesterase
inhibitors
than
carbaryl
(
Kuhr,
1971).
Additionally,
hydroxylated
metabolites
exist
almost
exclusively
as
their
secondary
metabolites
(
i.
e.,
glucuronide
and
sulfate
conjugates)
that
are
much
more
water
soluble
and
even
less
likely
to
interact
with
cholinesterase
because
of
this
water
solubility
and
increased
molecular
bulk."

See
Appendix
5,
Proposed
Metabolic
Pathway
in
Rats
(
Struble)
Page
6
of
18
Page
7
of
18
2.2.
Analysis
of
Bayer
Mixed­
dose
Pharmacokinetic
Studies
in
Rats
The
Bayer
pharmacokinetic
proposal
is
based
primarily
upon
a
pharmacokinetic
study
in
rats,
referred
to
as
the
Bayer
mixed­
dose
study
(
Metabolism
and
Pharmacokinetics
of
[
14C]
Carbaryl
in
Rats
Following
Mixed
Oral
and
Dermal
Exposure,
Krolski,
2004,
53
pages
­
Appendix
3).

Doses
in
the
Bayer
mixed­
dose
study
were
selected
to
mimic
exposure
estimated
for
children
playing
on
lawns
treated
with
carbaryl.
Children's
exposure
can
include
dermal
exposure
and
oral
exposure
from
mouthing
behaviors.
In
the
mixed­
dose
study,
rats
received
concurrent
dermal
and
oral
exposure:
rats
were
treated
dermally
for
2
hours
with
0.871
mg/
kg
and
received
two
oral
doses
of
0.0841
mg/
kg
at
a
1­
hour
interval.
Sacrifices
were
made
15
minutes,
30
minutes,
1
hour,
3
hours,
and
5­
hours
following
the
second
oral
dose.
Total
radioactive
residues
were
determined
for
whole
blood,
plasma,
red
blood
cells,
and
brain.
Metabolites
were
identified
in
plasma
or
brain
when
sufficient
residue
was
present.

Total
radioactive
residue
(
TRR)
in
all
tissues
had
peaked
at
the
first
sampling
period,
15
minutes
after
the
second
oral
dose
(
Table
5
and
Figure
5
in
Appendix).
TRR
in
brain
was
0.0206
ppm,
of
which
22%
was
carbaryl
per
se,
12%
was
1­
naphthol,
and
12%
was
1­
naphthol
sulfate
(
Table
6).
By
5
hours,
TRR
had
declined
to
0.0043
ppm,
of
which
15%
was
carbaryl
per
se,
6%
was
1­
naphthol,
and
19%
was
1­
naphthol
sulfate.
There
was
a
slight
increase
in
radioactivity
in
whole
blood
at
the
1
hour
sampling
period,
possibly
due
to
dermal
absorption.

2.3
Calculating
Plateau
Brain
Concentrations
After
Divided
Doses
Assumed
oral
exposure
for
a
toddler
is
20
exposures
per
hour
for
2
hours,
based
on
EPA's
SOPs
(
Agency's
SOPs
For
Residential
Exposure
Assessment).
However,
the
dosing
regimen
used
in
the
mixed­
dose
rat
study
was
2
oral
doses
given
1
hour
apart.
Because
of
carbaryl's
short
half­
life,
the
2
oral
bolus
doses
resulted
in
much
higher
peak
brain
concentrations
than
would
be
expected
to
occur
from
40
divided
doses.
Bayer
therefore
calculated
the
plateau
brain
concentrations
which
would
result
from
40
divided
doses
over
a
2
hour
period.

Each
individual
dose
would
be
0.00375
mg/
kg
(
0.15/
40).
The
brain
concentration
at
this
dose
was
extrapolated,
rather
than
determined
in
an
experiment.
Bayer's
explanation
for
this
regimen
was:

"
A
single
oral
dose
at
0.00375
mg/
kg
would
yield
brain
concentrations
several
fold
less
than
the
lowest
detection
limit.
Attempting
to
orally
dose
a
rat
20
times
per
hour
is
extremely
traumatic
to
the
animal
(
which
would
affect
the
results
and
not
be
allowed
by
the
American
Association
for
Accreditation
of
Laboratory
Animal
Care),
and
would
have
required
Page
8
of
18
several
people
to
dose
four
rats
at
this
frequency
resulting
in
additional
experimental
(
interperson)
uncertainty."
Page
9
of
18
Bayer
extrapolated
the
carbaryl
concentration
in
brain
from
a
dose
of
0.00375
mg/
kg
using
brain
concentrations
obtained
following
doses
of
0.084
mg/
kg,
1
mg/
kg,
and
10
mg/
kg
in
the
two
Bayer
studies.
The
extrapolated
plateau
brain
concentration
following
a
single
dose
of
0.00375
mg/
kg
was
0.000091
ppm
(
pages
15
and
16,
Bayer
proposal).

The
half­
life
of
carbaryl
in
brain
from
the
mixed­
dose
study
was
estimated
to
be
15
minutes
because
carbaryl
concentration
declined
from
0.0045
ppm
to
0.0023
ppm
between
the
15
minute
and
30
minute
sampling
periods
and
0.0023/
0.0045
=
51%
(
Table
6).
The
half­
life
of
total
radioactive
residues
(
TRR)
in
brain
from
the
mixed­
dose
study
was
estimated
to
be
19
minutes
because
TRR
declined
from
0.0206
ppm
to
0.0129
ppm
between
the
15
minute
and
30
minute
sampling
periods
(
Table
5).
Bayer
reported:
"
The
30
minute
concentration
is
62.7%
of
the
15
minute
concentration.
The
ratio
of
62.7%
to
50%
is
1.25,
which
adjusts
the
15
minute
period
to
19
minutes
or
0.33
hours"
(
email,
10/
12/
04).
Bayer
reported
that
there
was
not
a
significant
difference
between
15
minute
and
19
minute
values,
and
the
half­
life
of
19
minutes
was
used
to
estimate
the
plateau
value.

Bayer
next
estimated
the
plateau
brain
concentration
resulting
from
40
oral
exposures
of
0.00375
mg/
kg
to
be
0.0011
ppm
using
the
following
equation
and
explanation
excerpted
from
page
19
of
the
Bayer
proposal.
Calculations
are
shown
on
the
attached
spread
sheet
(
Appendix4)
(
MOE_
Derivation_
HtM_
EPAScenario_
10Jun04.
xls).

C
p
=
(
C
d_
event1
x
F)
+
(
C
d_
event2
thru
n)
x
F)

where
C
p
=
carbaryl
concentration
(
mg/
mL
or
ppm)
in
the
brain
at
plateau
or
peak;

C
d_
event1
thru
n
=
concentration
(
mg/
mL
or
ppm)
in
the
brain
(
0.000091
ppm)
at
each
incremental
time
step
(
min),
where
an
oral
dose
of
0.00375
mg/
kg
occurs
at
a
frequency
of
20
events
per
hour
or
once
every
3
minutes
(
0.00375
mg/
kg
=
0.15
mg/
kg/
day
/
40
events
per
day);

F
=
fraction
of
brain
level
eliminated
at
each
time
step
(
0.025
per
min
based
on
0.5
in
0.33
hrs
[
the
measured
carbaryl
half­
life
(
hrs)
in
brain
at
10
mg/
kg
following
oral
dosing
was
0.30
hours
and
the
estimated
carbaryl
half­
life
following
first
oral
dose
of
0.084
mg/
kg
and
concurrent
dermal
dose
of
0.871
mg/
kg
was
0.33
hours]).
Page
10
of
18
Carbaryl
Plateau
Brain
Level
(
ppm)
Following
Discrete
HtM
Oral
Doses
of
0.00375
mg/
kg
(
9.1E­
5
ppm
in
brain)
Every
3
Min
for
2
Hrs
(
Carbaryl
brain
half­
life
=
0.33
hrs)

0.00E+
00
1.00E­
04
2.00E­
04
3.00E­
04
4.00E­
04
5.00E­
04
6.00E­
04
7.00E­
04
8.00E­
04
9.00E­
04
1.00E­
03
1.10E­
03
1.20E­
03
1.30E­
03
0
10
20
30
40
50
60
70
80
90
100
110
120
Time
(
min)
Carbaryl
Brain
Level
(
ppm)
Figure
2
shows
that
the
extrapolated
plateau
brain
concentration
is
reached
after
approximately
90
minutes.
After
that
time,
repeated
exposures
do
not
result
in
appreciable
increases
in
brain
concentration
of
carbaryl.

Figure
2.
Extrapolated
Plateau
Brain
Concentration
Adapted
from
Figure
3,
page
19,
Bayer
proposal.
Page
11
of
18
2.4.
Extrapolation
of
Results
From
Mixed­
dose
Study
to
Biomonitoring
Study
A
second
component
of
Bayer's
proposal
is
to
extrapolate
peak
internal
doses
from
the
mixed­
dose
study
in
rats
to
absorbed
doses
in
the
biomonitoring
study.
In
the
biomonitoring
study
(
described
above
in
Summary
of
carbaryl
metabolism),
total
carbaryl
absorbed
dose
was
estimated
after
application
of
carbaryl
in
a
residential
setting.
This
absorbed
dose
in
the
biomonitoring
study
was
estimated
using
urine
concentrations
of
1­
naphthol
in
humans
which
were
converted
to
absorbed
carbaryl
equivalents.
The
1­
naphthol
to
carbaryl
conversion
factor
of
3.5
was
determined
from
an
analysis
of
human
and
rat
pharmacokinetic
data
(
Carbaryl
Revised
HED
Risk
Assessment,
March
14,
2003).
The
urine
samples
were
24
hour
composite
samples
collected
on
the
day
of
application
and
each
day
for
3
days
after
application.
Following
carbaryl
human
exposure,
carbaryl
is
rapidly
metabolized
and
1­
Naphthol
is
excreted
over
a
96­
hour
period.
EPA's
risk
assessment
estimated
exposure
using
two
different
approaches:


Assuming
total
carbaryl
dose
values
summed
over
a
96­
hour
period
equals
one
daily
dose

Assuming
total
carbaryl
dose
values
summed
for
a
24­
hour
period
equals
one
daily
dose
Bayer
compared
margins­
of­
exposure
(
MOEs)
calculated
in
the
manner
in
which
EPA
traditionally
assesses
exposure
to
the
method
in
Section
2.3,
above.
In
the
carbaryl
risk
assessment,
EPA
determined
an
MOE
of
4
by
dividing
the
NOAEL
for
incidental
oral
exposure
(
1
mg/
kg/
day
from
the
rat
developmental
neurotoxicity
study)
to
the
expected
toddler
exposure
(
0.25
mg/
kg/
day)
determined
from
EPA's
SOPs
For
Residential
Exposure
Assessment.

Bayer
reported
an
MOE
of
70
by
dividing
the
peak
brain
concentration
(
0.077
ppm)
in
rats
dosed
at
the
oral
NOAEL
by
extrapolated
plateau
brain
concentrations
(
0.0011
ppm)
for
repeated
oral
doses.

Because
estimated
plateau
brain
concentrations
may
more
closely
reflect
concentrations
at
the
target
tissue,
Bayer
proposed
extrapolating
results
from
the
rat
mixed­
dose
study
to
the
biomonitoring
study
using
an
adjustment
factor.
Because
70
divided
by
4
equals
17.5,
or
is
approximately
20,
Bayer
proposed
multiplying
results
in
the
biomonitoring
study
by
this
adjustment
factor.
Page
12
of
18
Carbaryl
Residential
Exposure
for
Children
3­
5
from
Households
using
Lawn
Treatments
(
Exposure
Duration:
days
0­
3)

0.0001
0.001
0.01
0.1
1
10
100
0
10
20
30
40
50
60
70
80
90
100
Percentile
of
Population
Exposure
(
mg/
kg/
day)
EPA
Estimate
from
biomonitoring
data
Exp=
0.42
mg/
kg/
day
Bayer
Estimate
from
biomonitoring
data
Exp=
0.09
mg/
kg/
day
EPA
SOP
Exp=
2
to
4
mg/
kg/
day
3.
Summary
Bayer
has
proposed,
that
because
of
carbaryl's
pharmacokinetic
and
pharmacodynamic
characteristics,
peak
or
plateau
concentrations
of
carbaryl
in
brain
are
a
more
accurate
indicator
of
risk
than
is
total
absorbed
dose.
These
characteristics
include
rapid
oral
absorption,
prolonged
dermal
absorption,
brief
inhibition
of
acetylcholinesterase,
and
short
half­
life
in
the
body.

The
Agency
has
completed
three
exposure
assessments
for
carbaryl.
One
assessment
is
a
deterministic
assessment
based
upon
the
Standard
Operating
Procedures
For
Residential
Exposure
Assessment.
The
other
two
exposure
assessments
included
a
probabilistic
model,
CARES
(
Cumulative
And
Aggregate
Risk
Evaluation
System),
which
calculated
distributions
of
exposures,
and
the
biological
monitoring
study
described
above
in
Section
3.1.
All
three
assessments
gave
similar
results
(
See
Figure
3).
The
Agency
has
based
its
current
regulatory
position
upon
the
results
of
the
deterministic
assessment
and
has
used
the
biological
monitoring
data
and
the
probabilistic
assessment
results
to
characterize
exposure
and
risks
associated
with
carbaryl
lawn
use.

The
three
exposure
assessments
described
above
all
gave
similar
results,
but
only
evaluated
total
exposure
and
did
not
consider
peak
exposure
in
the
target
tissue.
At
issue
in
this
SAP
meeting
is
whether
an
estimate
of
peak
exposure
in
target
tissue
is
appropriate
to
assess
carbaryl
exposure
and
if
these
results
can
modify
results
from
traditional
exposure
assessments.

Figure
3.
Results
of
Agency
Exposure
Assessments
Page
13
of
18
Supporting
Tables
&
Figures
Following
are
tables
and
figures
from
the
Bayer
metabolism
study
and
the
Bayer
mixeddose
study.

Table
1.
Average
Total
Radioactive
Residue
(
ppm).
Intravenous
dose
=
0.80
mg/
kg/
day
Time
(
hr)
Whole
Blood
Plasma
RBC
Brain
0.083
=
5min
1.2536
2.1310
1.0551
0.7360
0.167
=
10
min
1.1079
1.8310
0.9059
0.4137
0.333
=
20
min
0.9025
1.6940
0.6676
0.2299
0.5
0.7890
1.4345
0.4935
0.1431
1
0.5016
0.8508
0.2959
0.0562
2
0.3253
0.5798
0.1509
0.0251
4
0.1253
0.2080
0.0974
0.0130
8
0.064
0.1061
0.0488
0.0094
Table
2.
Average
Total
Radioactive
Residue
(
ppm).
Oral
dose
=
1.08
mg/
kg
Time
(
hr)
Whole
Blood
Plasma
RBC
Brain
0.25
=
15
min
0.9004
1.4414
0.4427
0.1253
0.5
=
30
min
0.7270
1.1922
0.3191
0.0613
1
0.5741
0.810
0.1828
0.0339
2
0.4079
0.5406
0.1016
0.0282
4
0.2875
0.4046
0.1146
0.0202
6
0.1517
0.1921
0.0659
0.0145
12
0.0471
0.0559
0.0220
0.0052
24
0.0180
0.0140
0.0073
0.0030
Page
14
of
18
Table
3.
Average
Total
Radioactive
Residue
(
ppm).
Dermal
dose
=
17.25
mg/
kg
Time
(
hr)
Whole
Blood
Plasma
RBC
Brain
0.25
=
15
min
0.0092
0.0090
0.0006
0.0051
0.5
=
30
min
0.0181
0.0287
0.0059
0.0068
1
0.0104
0.0119
0.0018
0.0020
2
0.0490
0.0968
0.0263
0.0089
4
0.0690
0.1467
0.0441
0.0111
6
0.0484
0.1020
0.0203
0.0052
12
0.0252
0.0441
0.0072
0.0046
24
0.0178
0.0239
0.0070
0.0034
Tables
1­
3
above,
were
adapted
from
Tables
6,
2,
and
4
respectively
of
Bayer
metabolism
study.
Page
15
of
18
Table
4.
Half­
life
of
Total
Radioactive
Residue
Tissue
(
Route)
10
mg/
kg
1
mg/
kg
0.084
mg/
kg
Plasma
(
Oral)
1.5
1.2
Plasma
(
IV)
1.8
(
0.40)
a
1.2
Plasma
(
Mixed)
b
0.50
RBC
(
Oral)
1.2
0.75
RBC
(
IV)
1.0
0.6
RBC
(
Mixed)
b
0.80
Brain
(
Oral)
0.8
(
0.30)
a
0.35
Brain
(
IV)
0.6
(
0.45)
a
0.25
Brain
(
Mixed)
b
0.33
aHalf­
life
of
actual
carbaryl
residues
in
the
alpha
phase
bIn
"
mixed­
dose
study",
samples
taken
following
the
second
oral
dose
from
a
study
where
rats
received
two
oral
doses
of
0.084
mg/
kg,
one
hour
apart
(
at
time
0
and
1
hr),
and
a
dermal
dose
of
0.871
mg/
kg
at
time
0,
which
remained
on
the
rats
skin
for
2
hours.

NOTE:
Bayer
reported
that:

"
It
was
not
possible
to
estimate
half­
life
for
carbaryl
itself
in
the
alpha
phase
following
oral
dosing
at
1
and
10
mg/
kg
because
it
dissipated
so
rapidly,
and
levels
beyond
the
peak
could
not
be
reliably
quantified
using
the
standard
flow
cell
radiometric
detector.
However,
at
0.084
mg/
kg
oral
dose
a
different
detection
method
was
employed
(
fraction
collector),
and
it
was
possible
to
estimate
half
life."

Adapted
from
Table
3,
page
12
of
Bayer
proposal.
Page
16
of
18
Table
5.
Average
Total
Radioactive
Residue
(
ppm)
From
Mixed
Dose
Studya.
Concurrent
oral
and
dermal
dosing.
Samples
taken
after
2nd
oral
dose
Time
(
hr)
Whole
Blood
Plasma
RBC
Brain
0.25
0.1633
0.2905
0.0664
0.0206
0.5
0.1075
0.2031
0.0570
0.0129
1
0.1237
0.1899
0.0382
0.0099
3
0.0511
0.0904
0.0161
0.0034
5
0.0359
0.0648
0.0127
0.0043
a
In
"
mixed­
dose
study",
samples
taken
following
the
second
oral
dose
from
a
study
where
rats
received
two
oral
doses
of
0.084
mg/
kg,
one
hour
apart
(
at
time
0
and
1
hr),
and
a
dermal
dose
of
0.871
mg/
kg
at
time
0,
which
remained
on
the
rats
skin
for
2
hours.

From
Table
1,
p
26
of
mixed­
dose
study
Figure
4.
Average
Total
Radioactive
Residue
(
ppm)
From
Mixed
Dose
Studya
aIn
"
mixed­
dose
study",
samples
taken
following
the
second
oral
dose
from
a
study
where
rats
received
two
oral
doses
of
0.084
mg/
kg,
one
hour
apart
(
at
time
0
and
1
hr),
and
a
dermal
dose
of
0.871
mg/
kg
at
time
0,
which
remained
on
the
rats
skin
for
2
hours.

From
Figure
7,
p
26
of
mixed­
dose
study
Page
17
of
18
Table
6.
Total
Radioactive
Residue
(
TRR)
and
Metabolites
Identified
in
Brain
after
Mixed­
Dose
Study
Time
TRR
(
ppm)
1­
Naphthol
Sulfate
1­
Naphthol
Carbaryl
%
TRR
TRR
(
ppm)
%
TRR
TRR
(
ppm)
%
TRR
TRR
(
ppm)

15
min
0.0206
12
0.0025
12
0.0025
22
0.0045
30
min
0.0129
18
0.0023
6
0.00077
18
0.0023
1
h
0.0099
23
0.0023
5
0.00050
15
0.0015
3
h
0.0034
28
0.00095
4
0.00014
13
0.00044
5
h
0.0043
19
0.00082
6
0.00026
15
0.00064
Adapted
from
Table
2,
p
17of
mixed­
dose
study
Page
18
of
18
Appendices
Appendix
1
E­
file
name:
Bayer
proposal.
pdf
Application
of
carbaryl
pharmacokinetic
data
in
the
estimation
of
potential
postapplication
health
risks
associated
with
broadcast
lawn
care
products.
Ross,
J;
Driver,
J;
Lunchik,
C.
Bayer
CropScience.
September
8,
2004.
40
pages.

Appendix
2
E­
file
name:
Bayer
metabolism
study.
pdf
Metabolism
of
[
14C]
Carbaryl
in
Rats.
Krolski,
et
al.
Bayer
CropScience.
May
7,
2004.
230
pages.

Appendix
3
E­
file
name:
Bayer
mixed­
dose
study.
pdf
Metabolism
and
Pharmacokinetics
of
[
14C]
Carbaryl
in
Rats
Following
Mixed
Oral
and
Dermal
Exposure.
Krolski,
et
al.
Bayer
CropScience.
May
7,
2004.
53
pages.

Appendix
4
E­
file
name:
MOE_
Derivation_
HtM_
EPAScenario_
10Jun04.
xls
Spreadsheet
for
calculation
of
plateau
brain
concentrations,
Bayer
CropScience.

Appendix
5
E­
file
name:
Proposed
Path
in
Rats.
pdf
Proposed
Path
in
Rats
