1
Terrestrial
Investigation
Model
x
2.0
Inhalation
Exposure
2
Development
Goals
°
Tool
reliant
on
existing
fate
data
sets
°
Consider
adapting
existing
Agency
approaches
°
Relate
exposure
to
available
toxicity
information
3
Inhalation
Conceptual
Model
Directly
applied
spray
Volatilization
of
residues
on
plant
canopy
Volatilization
of
residues
in
soil
Suspension
of
residues
associated
with
soil
particulate

+
/­

X

proposed
model
addresses
+/­
optional
approaches
can
address
X
not
addressed
4
Assumes
a
complete
dispersion
of
spray
mass
within
the
column
of
air
for
the
duration
of
the
exposure
window
Inhalation
of
Directly
Applied
Spray
DID
mg
kg
A
RHF
V
BW
rate
respired
inhalation
(
/
)
(
)(
/
(
)(
)

(
)(
)

=
1
1000
where:
DID
=
Droplet
Inhalation
Dose
mg/
kg
A
rate
=
application
rate
from
label
converted
to
mg/
m2
RH
=
height
of
spray
release
(
m),
user
defined
(
defaults
1
m
ground
spray,
3
m
aerial
application)

F
respired
=
volumetric
droplet
spectrum
segregated
by
upper
size
limit
of
respired
particles
for
birds
(
7
um)

V
inhalation
=
inhalation
volume
(
L)

1000
=
units
conversion
m3
to
L
BW
=
bird
weight
(
kg)
5
Inhalation
of
Vapor
Phase
Pesticide
VID
mg/
kg
=
(
Cair)(
Vinhalation
)

body
weight
where:
VID
=
Vapor
Inhalation
Dose
Cair
=
concentration
of
the
pesticide
in
air
at
time
t
(
mg/
L)

Vinhalation
=
inhalation
volume
(
L)

body
weight
=
bird
weight
(
kg)
6
Inhalation
Volume
where:
Vinhalation
=
Inhalation
volume
(
L)

Rrate
=
respiration
rate
(
l/
min),

ED
=
Exposure
duration
(
min)

(
)(
)

V
R
ED
inhalation
rate
=
7
Inhalation
Rate
R
BW
rate
=
×
(
).

284
3
1000
0
77
where:
Rrate
=
Respiration
rate
(
L/
min)

BW
=
bird
weight
(
kg)
8
Concentration
In
Air
°
Approaches
by
OPP
and
other
programs
within
the
Agency
°
Available
data
set
on
physical
chemical
properties
9
Concentration
In
Air
(
cont.)

USEPA's
Office
of
Solid
Waste
Hazardous
Waste
Identification
Rule
(
HWIR)
Farm
Foodchain
Model
(
USEPA,
1999)

PV
Cv
Bv
Vg
ave
ag
air
=
(
)(
)(
)

1000
 
where:
PV
=
plant
concentration
due
to
vapor
(
mg/
kg
DW)

CvAve
=
the
vapor
phase
concentration
of
chemical
in
air
(
µ
g/
m3)

Bv
=
the
air­
to­
plant
biotransfer
factor
([
ug/
g
DW]/[
ug/
g
air])

Vgag
=
an
empirical
correction
factor
(
unitless)

1000
=
a
units
conversion
factor
(
g/
m3)

 air
=
the
density
of
air
(
constant
at
1.19
g/
L)
10
The
Air­
to­
Plant
Biotransfer
Factor
°
Important
component
of
the
HWIR
model
°
Each
compartment
is
in
mass
terms
°
Plant
component
is
dry
weight
11
The
Air­
to­
Plant
Biotransfer
Factor
(
)

Bv
B
MAF
Bv
air
vol
leaf
leaf
ecf
=






 







 
 
9
100
100
where,
Bv
=
the
air­
to­
plant
biotransfer
factor
([
µ
g/
g
DW]/[
ug/
g
air])

 air
=
the
density
of
air
(
constant
at
1.19
g/
L)

Bvol
=
the
biotransfer
factor
((
µ
g/
L
freshweight
leaf)/
µ
g/
L
air)

MAFleaf
=
the
moisture
content
in
leaf
(%)

 leaf
=
the
density
of
the
leaf
(
g/
L
fw)

Bvecf
=
the
empirical
correction
factor
for
Bv
(
unitless)
12
The
Air­
to­
Plant
Biotransfer
Factor
Key
to
Bv
is
Bvol,
or
the
volumetric
biotransfer
for
fresh
plant
material
log
Bvol
=
1.065
log
Kow
­
log(
H/
RT)
­
1.654
where:
Bvol
=
the
biotransfer
factor
((
ug/
L
fresh
weight
leaf)/
ug/
L
air)

Kow
=
octanol/
water
partition
coefficient
H
=
Henry's
Law
constant
(
atm/
m3/
mol)

R
=
the
universal
gas
constant
(
8.205E­
05
atm/
m3/
mol­
K)

T
=
air
temperature
(
constant
at
298.1
K)
13
Could
HWIR
Approach
be
Adopted
for
Avian
Inhalation?

°
HWIR
equilibrium
model
is
for
continuous
sources
of
atmospheric
contaminant
°
No
limitation
to
contaminant
mass
applied
°
Pesticide
application
deals
with
finite
masses
of
applied
chemical
°
Equilibrium
models
for
pesticides
should
conserve
pesticide
mass
applied
14
Other
OPP
Approaches
to
Two
Compartment
models
°
Interim
rice
model
for
sediment:
water
pesticide
concentration
estimation
°
Equilibrium­
based
°
Mass
of
applied
pesticide
is
conserved
°
Relies
of
existing
chemical
property/
fate
data
set
15
Two
Compartment
Model
Sediment/
Water
W
M
V
m
K
con
T
T
sed
d
=
+
109
where:
MT
=
the
total
mass
of
pesticide
in
kg
applied
to
1
ha
VT
=
volume
of
water
msed,
=
the
mass
of
sediment
109
=
units
convert
for
mass
from
kg
to
µ
g.

Kd
=
the
sediment:
water
partition
coefficient
16
Two
Compartment
Model
Plant/
Air
(
)

C
C
m
V
m
B
air
plant
plant
air
plant
vol
plant
=
+














1000
 
where:
Cair
=
concentration
in
air
mg/
L
Cplant
=
the
pesticide
residue
in
plants
(
mg/
kg
fresh
weight)

from
model
predictions
for
diet
mplant
=
the
mass
of
plant
per
hectare
(
kg/
ha)

Vair
=
the
volume
of
air
1
ha
to
crop
canopy
height
(
m3)

1000
=
units
conversion
m3
to
L
Bvol
=
the
volume­
based
biotransfer
factor
((
ug/
L
freshweight
leaf)/
ug/
L
air)
as
calculated
by
the
HWIR
model

plant
=
the
density
of
the
crop
tissue
assumed
as
fresh
leaf
kg/
L
17
Limitations
to
Equilibrium
Model
°
Does
not
account
for
application
to
soil
surface
°
Bare
ground
applications
°
Unintercepted
pesticide
°
Equilibrium
assumption
does
not
readily
work
with
air
exchange
°
Does
not
address
relationship
between
height
in
canopy
and
residue
°
Basing
plant
associated
mass
on
Fletcher
et
al.
residues
18
"
Fletcher
Residues"
for
Air
Concentration
Estimation
°
Foliage
residues
are
assumed
to
be
only
a
function
of
application
rate
°
Does
not
consider
the
growth
stage
of
the
plant
°
Canopy
cover
or
percent
cover
°
Biomass
°
Relating
residues
back
to
mass
applied
to
plants
may
over
or
underestimate
application
rate
°
Need
to
explore
alternative
residue
estimate
methods
eg.
Residue
mg/
kg
=
application
rate
X
percent
cover
biomass
19
Scenarios
for
Inhalation
Exposure
°
Droplet
Exposure
 
First
time
step
following
application
°
Vapor
Phase
Exposure
 
Every
time
step
bird
is
on
field
 
In­
field
residents
°
Active
feeding
periods
on
field
°
Inactive
periods
when
on
field
 
Note:
current
model
does
not
adjust
respiration
for
inactivity
 
Edge
residents
°
Active
feeding
periods
on
field
20
Relating
Inhalation
Exposure
to
Available
Toxicity
Data
°
No
Agency
requirement
for
acute
inhalation
toxicity
testing
in
birds
°
TIM
2.1
relies
on
avian
single
oral
dose
toxicity
°
Model
goal
is
to
evaluate
cumulative
exposure
from
multiple
routes
°
Need
a
method
to
relate
inhaled
dose
exposure
to
available
toxicity
endpoints
21
SAP
2000
°
Presented
conceptual
approach
of
using
inhalation
to
oral
relationships
for
other
taxa
to
birds:

°
SAP
cautioned
that
such
approaches
must
consider
differences
in
respiratory
physiology
LD50
inhlation
mammal
=
LD50
inhalation
bird
LD50
oral
mammal
LD50
oral
bird
LD50
inhlation
mammal
=
LD50
inhalation
bird
*
X
LD50
oral
mammal
LD50
oral
bird
22
Respiratory
Physiology
°
Agency
does
not
have
an
avian
respiratory
toxicokinetic
model
°
Agency
evaluated
basic
mammalian
and
avian
respiratory
system
differences
that
may
affect
toxicant
availability
23
Factors
Affecting
Uptake
by
Diffusion
°
Agency
focus
on
surface
area
and
exchange
tissue
thickness
°
Other
factors
remain
to
be
evaluated
­
Cross
current
vs.
alveolar
systems
and
concentration
gradient
Fick's
law
of
diffusion
 
Q
=
­
D*
A*( 
u/
 
x)*
 
t
 
Q
­
mass
uptake,

D
­
chemical
specific
diffusion
constant,

A
­
surface
area
of
the
diffusion
site,

 
u
­
concentration
gradient,

 
x
­
tissue
thickness,

 
t
­
duration
of
diffusion
24
Respiratory
Surface
Area
°
Respiratory
surface
area
is
1.16
times
greater
in
birds
than
mammals
°
Relationship
is
stable
for
body
weights
of
1
to
2000
g
Surface
area
birds
=
60.6*
BW0.883
Surface
area
mammals=
52.1*
BW0.883
Maina
et
al.
(
1989)
25
Exchange
Tissue
Thickness
°
Relationship
between
birds
and
mammals
is
not
constant
across
all
weights
°
Avian
exchange
tissue
thickness
is
from
half
to
one
third
mammal
thickness
for
bodyweights
1
to
2000g
Mean
harmonic
thickness
birds=
116.51*
BW0.044
Mean
harmonic
thickness
mammals
=
237.66*
BW0.090
Maina
et
al.
(
1989)
26
Relating
Area
and
Thickness
to
Relative
Diffusion
Rate
°
From
Fick's
law
diffusion
rate
is
directly
proportional
to:
Q
=
surface
area
/
thickness
°
Comparing
Q
for
birds
and
mammals
yields
relative
differences
in
diffusion
rate
°
Qavian/
Qmammal
ranges
from
2.4
to
3.4
for
bodyweights
of
1
to
2000g
°
For
a
given
inhaled
mass,
birds
will
absorb
more
than
mammals
by
at
least
a
factor
equivalent
to
Qavian/
Qmammal
27
Developing
a
Route
Relative
Potency
Factor
Fre
=
Oral
LD50(
mammal)
mg/
kg(
Qa/
Qm)

Inhalation
LD50
(
mammal)
mg/
kg
where,
Fre
=
the
avian
route
equivalency
factor
Qa/
Qm
=
the
ratio
of
avian
to
mammalian
pulmonary
membrane
diffusion
rates
28
Applying
Fre
to
Inhalation
Exposure
Estimates
°
Uses
existing
toxicity
data
for
mammals
°
Comparison
with
avian
oral
toxicity
allows
for
consideration
of
biochemical
differences
in
sensitivity
°
Considers
some
basic
physiological
differences
between
bird
and
mammal
respiratory
systems
equivalent
oral
dose
mg/
kg
=
(
model
inhalation
dose
mg/
kg)(
Fre)
29
Limitations
to
Fre
Approach
°
Assumes
that
toxic
modes
of
action
are
similar
for
oral
and
respiratory
route
in
birds
and
mammals
°
Cross­
current
vs
alveolar
structure
not
addressed
°
Does
not
consider
potential
enzymatic
differences
in
avian
and
mammalian
lung
°
Assumes
dose
response
relationship
is
similar
for
oral
and
inhalation
routes
30
Mortality
0
0.2
0.4
0.6
0.8
1
Exposure
Scenario
Mortlity
Rate
(

n=

10000)
Food
and
Dew
Food,
Dew,
Vapor
Inhalation
Food,
Dew,
Spray
Inhalation
Food,
Dew,
Vapor,
Spray
Inhalation
Impact
of
Inhalation
Exposure
on
Risk
Assessment
Chem
X
Scenario
°
Field
Resident
Insectivore
°
0.5
lb
ai/
acre,
aerial
application
at
8am
°
Henry's
constant
2.02
E­
07
Average
Total
Dose
at
Death
1
1.2
1.4
1.6
1.8
2
Exposure
Scenario
m
g/

kg
oral
dos
e
equivale
nt
Food
and
Dew
Food,
Dew,
Vapor
Inhalation
Food,
Dew,
Spray
Inhalation
Food,
Dew,
Vapor,
Spray
Inhalation
31
Mortality
0
0.2
0.4
0.6
0.8
1
Exposure
Scenario
Mortlity
Rate
(

n=

10000)
Food
and
Dew
Food,
Dew
,
Vapor,
Spray
Inhalation
Henry's
2.02
E­
07
Food,
dew
,
Vapor,
Spray
Inhalation:
Henry's
2.02
E­
05
Average
Total
Dose
at
Death
1
1.5
2
2.5
3
3.5
4
Exposure
Scenario
m
g/

k
g
oral
dos
e
e
quivale
nt
Food
and
Dew
Food,
Dew,
Vapor,
Spray
Inhalation:
henry's
2.02
E­
07
Food,
Dew,
Vapor,
Spray
inhlation:
Henry's
2.02
E­
05
The
Impact
of
Alternative
Henry's
Constants
on
Risk
Assessment
32
Next
Steps
°
Examination
and
comparison
of
air
concentration
models
with
available
air
measurement
data
°
Sensitivity
analysis
(
parameter
influences
on
exposure
estimates
and
risk
estimates)

°
Modifications
for
other
factors
influencing
respiratory
toxicity
°
Longer
term
investigation
of
PBTK
models
