Page
1
of
23
Exposure
Assessment
Approaches
For
Chemicals
Used
As
Soil
Fumigants
Consideration
Of
The
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
PERFUM)
­
A
Case
Study
With
Iodomethane
Presented
To
The
FIFRA
Science
Advisory
Panel
By:

U.
S.
EPA
Office
Of
Pesticide
Programs
Health
Effects
Division
Presented
On:

August
24/
25,
2004
Page
2
of
23
1
INTRODUCTION
On
August
24­
25,
August
26­
27,
and
September
9­
10,
2004,
the
FIFRA
Scientific
Advisory
Panel
(
SAP)
will
hold
three
separate
meetings
to
consider
and
review
three
fumigant
bystander
exposure
models.
At
the
August
24­
25
meeting
the
SAP
will
review
the
Probabilistic
Exposure
and
Risk
model
for
FUMigants
(
PERFUM)
using
iodomethane
as
a
case
study.
On
August
26­
27,
the
SAP
will
review
the
Fumigant
Exposure
Modeling
System
(
FEMS)
using
metam
sodium
as
a
case
study.
On
September
9­
10,
the
SAP
will
review
the
SOil
Fumigant
Exposure
Assessment
system
(
SOFEA(
copyright))
using
telone
as
a
case
study.
In
preparing
for
these
meeting,
preparation
of
this
document,
and
development
of
questions
for
the
Panel,
the
Agency
has
worked
closely
with
scientists
from
the
California
Department
of
Pesticide
Regulation
who
have
significant
experience
with
inhalation
exposure
modeling.

The
purpose
of
this
document
is
to
provide
general
background
information
for
the
FIFRA
Science
Advisory
Panel
(
SAP)
meeting
pertaining
to
the
evaluation
of
the
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
or
PERFUM).
PERFUM
represents
a
potential
evolution
of
the
Agency's
current
methodology
for
calculating
exposures
to
bystanders
who
can
be
exposed
by
being
in
close
proximity
to
fields
treated
with
soil
fumigants
prior
to
planting
crops
such
as
strawberries
or
tomatoes.
PERFUM
was
developed
by
the
registrants
(
i.
e.,
manufacturers
or
licensees)
of
the
soil
fumigant
iodomethane.
At
the
upcoming
SAP
meeting,
a
detailed
PERFUM
case
study
will
be
presented
based
specifically
on
iodomethane
data
for
illustrative
purposes
by
its
developers.
More
specific
background
materials
pertaining
to
the
theories
and
code
included
in
PERFUM
than
there
are
in
this
document,
are
available
in
the
following
which
has
been
provided
by
its
developers
for
consideration
(
available
at:
http://
www.
epa.
gov/
oscpmont/
sap/
2004/#
top).

A
Probabilistic
Exposure
And
Risk
Model
For
Fumigant
Bystander
Exposures
Using
Iodomethane
As
A
Case
Study,
Reiss
and
Griffin,
July,
2004
The
Agency
has
a
broad
range
of
goals
for
this
meeting
in
that
it
wishes
to
evaluate
the
methodologies
inherent
in
PERFUM
from
a
general
perspective
to
(
1)
determine
their
scientific
validity
and
(
2)
determine
if
there
is
any
general
applicability
for
evaluating
risks
associated
with
many
or
all
soil
fumigants.
There
are
three
key
criteria
that
the
Agency
considers
when
considering
the
integration
of
a
model
into
its
risk
assessment
process
and
these
include:
(
1)
public
availability;
(
2)
peer
review
for
scientific
validity;
and
(
3)
adherence
to
Agency
guidelines
for
model
development.
In
order
to
have
PERFUM
considered
by
the
Agency
and
by
the
SAP
the
developers
of
PERFUM
have
agreed
to
make
it
available
for
public
use.

The
Agency
is
currently
involved
in
the
development
of
a
comparative
risk
assessment
for
6
pesticides
that
are
used
for
soil
fumigation
purposes.
Some
of
these
chemicals
also
have
other
allowed
uses
but,
for
clarity,
the
discussion
within
this
document
focuses
only
on
soil
fumigation
since
it
is
of
key
concern
and
it
accounts
for
the
majority
of
the
annual
usage
for
each
chemical.
The
chemicals
which
are
included
in
this
assessment
are:
chloropicrin,
dazomet,
iodomethane
(
i.
e.,
methyl
iodide),
methyl
bromide,
metam­
sodium
(
or
other
salts),
and
telone
(
or
1,3­
dichloropropene).
Each
of
these
chemicals
(
or
their
breakdown
products,
metam­
sodium
and
dazomet
both
emit
MITC
or
methyl
isothiocyanate
which
is
the
volatile
component)
are
extremely
Page
3
of
23
volatile
especially
when
compared
to
most
common
pesticides.
Most
common
pesticides
are
considered
semi­
volatile
organic
chemicals
(
or
SVOCs)
while
soil
fumigants
would
be
considered
volatile
organic
chemicals
(
or
VOCs).
The
volatility
of
each
material
is
the
key
characteristic
associated
with
their
use
and
achieving
a
satisfactory
measure
of
efficacy.
This
volatility,
however,
can
lead
to
a
potential
for
human
exposures
because
it
leads
to
transport
away
from
targeted
application
areas
to
non­
target
receptors
such
as
nearby
human
populations.

The
Agency's
goal
for
this
risk
assessment
is
to
quantify
emissions
from
treated
fields
and
use
them
as
a
determinant
of
human
risks.
Emissions
from
treated
fields
can
be
categorized
in
two
ways
including:

(
1)
Known
Source:
include
those
directly
associated
with
a
single
application
(
or
series
of
associated
applications)
adjacent
to
a
receptor
where
the
source
and
emissions
specific
to
the
application(
s)
can
be
quantified.
An
example
would
be
treating
a
field
that
borders
a
residential
subdivision
then
defining
the
amount
of
off­
target
residue
movement
associated
with
that
specific
application.
The
concept
of
a
buffer
zone
as
a
risk
management
tool
is
commonly
associated
with
these
situations.

(
2)
Multiple
Source
(
Ambient
Air):
includes
those
associated
with
multiple
applications
or
general
use
within
a
region
where
many
non­
quantifiable
applications
can
possibly
contribute
to
overall
exposure
levels.
In
general,
ambient
exposures
within
a
region
cannot
be
easily
attributed
to
specific
application
events.
An
example
of
this
type
of
emission
might
be
those
air
concentrations
measured
at
a
school
location
when
the
school
is
located
within
a
growing
region
where
fumigants
are
extensively
used.
The
concept
of
a
localized
use
cap
as
a
risk
management
tool
is
commonly
associated
with
these
types
of
exposures.

A
discussion
and
quantification
of
each
type
of
emission
will
ultimately
be
included
in
the
Agency
risk
assessment
for
soil
fumigants,
however,
the
focus
of
this
document
and
the
upcoming
SAP
meeting
is
the
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
or
PERFUM)
which
is
intended
to
quantify
emissions
from
single,
known
applications
(
e.
g.,
treating
a
field
with
a
subdivision
immediately
adjacent
to
its
perimeter).

In
order
to
quantify
emissions
from
single
application
events,
the
Agency
currently
uses
an
approach
that
first
considered
the
monitoring
data
available
for
each
of
the
six
soil
fumigants
along
with
a
deterministic
modeling
approach.
It
was
clear
that
given
the
breadth
of
the
uses
associated
with
soil
fumigants
(
e.
g.,
varied
atmospheric
conditions,
application
methods,
and
emission
reduction
technologies
such
as
tarping
or
watering
in)
that
use
of
monitoring
data
alone
for
risk
assessment
purposes
was
limited
by
the
relatively
small
number
of
samples
which
can
reasonably
be
generated
for
different
times
after
treatment,
distances
from
the
application
site,
and
use
patterns.
This
conclusion
led
to
the
development
of
the
Agency's
current
modeling
approach
and
the
possible
evolution
of
that
approach
represented
by
PERFUM.
The
model­
based
approach
considers
temporal
and
spatial
factors,
extrapolating
from
available
monitoring
data,
thus
providing
an
estimate
of
the
range
of
exposures
which
are
possible
at
different
times
and
locations
when
input
parameters
are
varied.
Use
of
a
model
and
monitoring
data
are,
however,
intertwined
in
a
general
sense
because
monitoring
data
are
used
as
the
basis
for
estimating
emission
factors
used
in
the
model.
Page
4
of
23
The
Agency
is
currently
using
a
deterministic
modeling
approach
for
defining
air
concentration
gradients
downwind
of
applications
for
each
chemical.
In
this
approach,
the
Agency
has
based
its
analysis
on
a
standardized
set
of
meteorological
conditions
intended
to
represent
a
stable
atmosphere
and
unidirectional
wind
patterns
that
is
intended
to
provide
highend
estimates
of
exposure.
To
this
end,
the
Agency
has
developed
a
methodology
based
on
the
Office
of
Air
model
ISC3
(
Industrial
Source
Complex
Model)
that
is
routinely
used
for
regulatory
purposes.
ISC3
is
a
steady­
state
Gaussian
plume
model
which
can
be
used
to
assess
pollutant
concentrations
from
a
wide
variety
of
sources.
ISC3
is
a
publically
available
system
and
can
be
downloaded
from
the
Agency
(
http://
www.
epa.
gov/
scram001/
tt22.
htm#
isc).

Stakeholders
have
commented
to
the
Agency
a
belief
that
these
standardized
meteorological
conditions
are
not
representative
of
actual
atmospheric
conditions
where
soil
fumigants
are
used
and
therefore
solely
provide
screening
level
results
which
are
inadequate
for
risk
mitigation
decision
making
purposes.
To
this
end,
the
iodomethane
registrant
has
submitted
to
the
Agency
the
PERFUM
model
for
consideration.
PERFUM
integrates
actual
meteorological
data
into
ISC3
which
then
provides
for
the
calculation
of
multi­
directional
air
concentration
gradients
based
on
these
data.
As
with
the
Agency's
approach,
these
resulting
concentration
gradients
would
ultimately
be
used
as
a
determinant
of
human
health
risks.
Additionally,
it
should
also
be
noted
that
the
PERFUM
model
uses
a
probability
based
approach
for
integrating
emission
data
which
are
unique
to
this
system.

This
document
describes
the
Agency's
current
approach
for
model
use
in
Section
2:
Summary
Of
Current
Modeling
Approach.
Section
3:
Overview
of
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
PERFUM)
provides
a
brief
summary
of
the
approaches
that
have
been
incorporated
into
the
system.
Section
4:
Charge
To
Panel
details
the
specific
questions
pertaining
to
the
use
of
PERFUM
which
the
Agency
would
like
the
SAP
panel
to
address
in
its
deliberations.
Page
5
of
23
2
SUMMARY
OF
CURRENT
MODELING
APPROACH
The
goals
of
the
Agency
in
its
fumigant
assessment
are
to
develop
health
protective
measures
of
risk
for
populations
in
close
proximity
to
fields
that
have
been
treated
with
soil
fumigants
as
well
as
to
explain
and
reduce,
whenever
possible,
the
uncertainties
associated
with
these
analyses.
In
order
to
achieve
these
goals,
the
Agency
first
considered
monitoring
data
specific
to
each
chemical
but
due
to
the
limitations
of
those
data
and
the
flexibility
that
modeling
represents
have
focused
on
model
results
as
the
key
predictor
of
risks.

The
Agency's
current
exposure
assessment
approach
is
based
on
a
deterministic
use
of
the
Agency's
Industrial
Source
Complex
Model
(
ISC)
which
is
routinely
used
by
the
Office
of
Air
for
regulatory
decision
making
purposes.
It
is
available
from
the
following
website
at
the
Technology
Transfer
Network
Support
Center
for
Regulatory
Air
Models
(
or
SCRAM)
(
http://
www.
epa.
gov/
scram001/
tt22.
htm#
isc).
ISC
is
a
steady­
state
Gaussian
plume
model
which
can
be
used
to
assess
pollutant
concentrations
from
a
wide
variety
of
sources
associated
with
an
industrial
complex
or
from
other
types
of
sources
such
as
an
agricultural
field
in
this
case.
This
model
can
account
for
the
following:
settling
and
dry
deposition
of
particles;
downwash;
point,
area,
line,
and
volume
sources;
plume
rise
as
a
function
of
downwind
distance;
separation
of
point
sources;
and
limited
terrain
adjustment.
ISC
can
operate
in
both
long­
term
and
short­
term
modes
but
has
been
used
in
the
short­
term
mode
for
the
purposes
of
this
assessment.

The
Agency's
current
approach
is
summarized
herein.
Section
2.1
Input
Variables
And
Settings
Used
For
ISC
Calculations
describes
the
current
modeling
approaches
used
by
the
Agency
including
a
description
of
the
specific
inputs
and
ISC
settings
used
for
the
calculations.
Section
2.2
Outputs
Based
on
Current
Modeling
Approach
provides
examples
of
the
outputs
from
ISC
that
might
be
presented
for
consideration
by
risk
managers.
To
ensure
a
level
of
consistency
in
the
evaluation
of
the
PERFUM
model,
the
examples
presented
below
to
describe
the
current
Agency
methodology
are
also
based
on
a
case
study
using
iodomethane.

2.1
Input
Variables
And
Settings
Used
For
ISC
Calculations
In
order
to
define
concentration
gradients
associated
with
the
use
of
soil
fumigants,
which
are
ultimately
determinants
of
exposure,
the
Agency
utilized
ISC
by
equating
treated
agricultural
fields
to
an
area
source
coupled
with
inputs
that
reflected
a
range
of
potential
atmospheric
conditions
and
application
equipment/
techniques
used
for
the
different
fumigant
chemicals.
In
order
to
do
this,
the
Agency
considered
various
combinations
of
four
categories
of
input
variables
including:

°
Field
Size;
°
Atmospheric
Conditions;
°
Application
Equipment
and
Control
Technologies;
and
°
Field
Emissions
Associated
With
Application
Equipment
and
Control
Technology.

[
Note:
As
a
convention,
the
Agency
has
used
similar
input
variables
for
all
of
the
6
soil
fumigant
chemicals
wherever
possible.
This
allows
for
an
easier
determination
of
the
relative
risks
amongst
the
6
soil
fumigants.
Some
input
factors
such
as
emission
data,
however,
are
by
nature
chemicalspecific
and
have
been
treated
as
such
in
analyses
completed
by
the
Agency.
This
is
the
rationale
Page
6
of
23
behind
providing
a
separate
section
which
details
how
the
emission
data
were
analyzed
for
iodomethane.]

Field
Size:
The
Agency
generically
is
using
a
range
of
field
sizes
for
single
application
events
from
1
acre
up
through
40
acres.
Specifically,
the
Agency
based
its
calculations
on
field
sizes
of
1,
5,
10,
20,
and
40
acres.
It
is
believed
that
most
distinct
soil
fumigation
application
events
will
be
within
this
range
of
areas
treated.
It
is
also
acknowledged
larger
fields
could
be
treated
on
a
single
day.
Results
could
easily
be
scaled
to
those
larger
acreages
if
needed.
These
field
sizes
are
also
essentially
consistent
with
analyses
completed
by
the
California
Department
of
Pesticide
Regulation
which
allows
for
easy
comparison
with
their
results.
Field
geometry
can
also
impact
the
results
of
ISC
modeling.
For
ease,
the
Agency
has
by
convention
completed
all
of
its
analyses
based
on
the
use
of
square
fields.

Atmospheric
Conditions:
ISC
calculates
downwind
air
concentrations
using
hourly
meteorological
conditions,
that
include
wind
speed
and
atmospheric
stability
(
for
a
more
detailed
discussion
of
stability
see
http://
www.
epa.
gov/
scram001/
userg/
relat/
pcramtd.
pdf).
The
higher
the
letter
associated
with
a
stability
class
the
more
stable
the
atmosphere
becomes.
The
lower
the
wind
speed
and
the
more
stable
the
environment,
the
higher
the
air
concentrations
are
going
to
be
close
to
a
treated
area
(
or
source).
Conversely,
if
wind
speed
increases
or
the
atmosphere
is
less
stable,
then
air
concentrations
are
lowered
in
proximity
to
the
treated
area
thereby
lowering
the
potential
for
exposure.
Atmospheric
stability
is
essentially
a
measure
of
how
turbulent
the
atmosphere
is
at
any
given
time.
Stability
is
affected
by
solar
radiation,
wind
speed,
cloud
cover,
and
temperature
among
other
factors.
Instability
in
the
atmosphere
increases
the
movement
of
airborne
residues
because
they
are
more
readily
pushed
up
into
the
atmosphere
and
moved
away
from
the
source
thereby
lowering
concentrations
in
close
proximity
to
the
source
(
e.
g.,
treated
field).

In
order
to
simplify
modeling
the
transport
of
soil
fumigant
vapors
from
a
treated
field,
a
single
wind
direction,
wind
speed,
and
stability
category
are
used
for
a
given
duration
of
concern
(
i.
e.,
24
hours).
The
Agency
has
decided
to
present
a
series
of
results
based
on
a
range
of
possible,
and
plausible,
meteorological
conditions
to
allow
for
a
better
characterization
of
risks
compared
to
just
completing
the
analyses
based
on
a
single
set
of
meteorological
conditions.
The
different
conditions
considered
by
the
Agency
are
presented
in
Table
1.

For
comparative
purposes,
the
California
Department
of
Pesticide
Regulation,
in
its
determination
of
buffer
zones
for
methyl
bromide,
based
its
decisions
upon
a
windspeed
of
1.4
m/
s
and
a
class
C
atmospheric
stability
value
for
a
24­
hour
period.
During
the
daytime
hours,
Page
7
of
23
these
conditions
represent
a
stable
atmosphere
which
is
relatively
calm
but
this
stability
is
not
considered
overly
calm
for
nighttime
conditions.
We
believe
these
values
provide
higher­
end
air
concentrations.
[
Note:
This
is
supported
by
an
analysis
methyl
bromide
buffer
zones
by
DPR
available
at:
www.
cdpr.
ca.
gov/
docs/
dprdocs/
methbrom/
mebrmenu.
htm.]

Table
1:
Meteorological
Combinations
Used
in
ISC
Calculations
Wind
Speed
(
mph)
Wind
Speed
(
meters/
second)
Stability
Category#

2.25^
1.0^
F^

2.25
1.0
D
3.1*
1.4*
C*

4
1.8
C
5
2.2
C
6
2.7
C
7
3.1
C
8
3.6
C
9
4.0
C
10
4.5
C
10
4.5
B
#
=
The
lower
the
assigned
"
letter"
the
less
stable
the
atmosphere.
Categories
A
to
D
are
generally
seen
in
daylight
conditions.
Nighttime
conditions
are
generally
even
more
stable
than
even
the
most
stable
daylight
conditions.
^
=
Conditions
only
used
for
1
hour
exposure
duration.
*
=
Conditions
used
in
DPR
assessment
and
risk
management
decisions
for
methyl
bromide.

Application
Equipment
and
Control
Technologies:
Application
equipment
and
control
technologies
are
varied
and
depend
on
many
factors
including
the
environmental
fate
characteristics
of
the
chemical,
terrain
where
the
chemical
is
being
used,
economic
considerations,
and
other
agricultural
practices.
Application
equipment
can
take
many
forms
but
applications
typically
involve
the
use
of
some
sort
of
probe
that
is
used
to
inject
material
beneath
the
surface
of
the
soil,
a
broadcast
application
of
a
liquid
solution
or
solid
material
across
the
surface
of
a
treated
area,
or
the
delivery
of
chemicals
through
some
sort
of
plumbed
system
throughout
the
treated
area
(
e.
g.,
some
chemicals
are
delivered
via
irrigation
water).
Page
8
of
23
Along
with
the
various
application
methods
there
are
a
number
of
control
technologies
that
are
intended
to
minimize
the
emissions
from
treated
fields.
These
can
take
many
forms
but
essentially
involve
one
of
three
basic
techniques
that
include:
(
1)
change
in
injection
depth
and
probe
design;
(
2)
use
of
tarping
or
bedding
techniques;
and
(
3)
watering­
in.

Ultimately,
the
goal
of
the
Agency
is
to
codify
different
combinations
of
application
methods
and
control
technologies
in
order
to
have
these
serve
as
a
systematic
basis
for
risk
assessments.
The
ability
to
do
this,
however,
varies
depending
upon
the
data
available
for
each
chemical.
In
some
cases,
such
as
methyl
bromide,
there
is
a
preponderance
of
data
that
allows
for
characterization
based
on
a
large
number
of
possibilities
as
described
by
the
California
Department
of
Pesticide
Regulations
in
its
permit
conditions
which
are
presented
on
their
website
(
http://
www.
cdpr.
ca.
gov/
docs/
legbills/
mebrbuffer.
pdf).

The
situation
with
iodomethane
differs
somewhat
in
that
it
has
not
been
registered
yet
with
any
regulatory
agency
so
no
permit
conditions
or
official
labeling
exists
at
this
point.
To
complete
its
analysis,
the
Agency
used
proposed
label
language
and
the
monitoring
data
that
are
available.
The
available
data
have
been
reviewed
and
three
basic
categories
of
application
methods
have
been
identified
to
date
(
Table
2).

Table
2:
Summary
Of
Application
Methods
For
Iodomethane
Application
Method
Emission
Reduction
Technology
Combination
#

Shallow
shank,
broadcast
flat
fume
Tarped
1
Shallow
shank,
raised
bed
Tarped
2
Drip
irrigation,
raised
bed
Tarped
3
Field
Emissions
Associated
With
Application
Equipment
and
Control
Technology:
Emissions
from
treated
fields
are
generally
characterized
as
the
amount
of
residues
that
are
offgassing
from
a
unit
area
per
unit
time.
Emissions
quantified
in
this
manner
are
referred
to
as
flux
(

g/
m2­
s).
Flux
rates
are
specific
to
the
conditions
of
the
field
experiment
for
which
they
were
generated
but
can
be
used
in
a
generic
sense
by
normalizing
the
data
to
the
maximum
application
rate
which
was
175
pounds
per
acre.
Flux
rates
were
calculated
using
the
backcalculation
method
with
ISC.
The
ISC
back­
calculation
method
estimates
flux
rates
by
extrapolating
from
the
available
field
air
monitoring
data,
assuming
a
Gaussian
plume
distribution,
to
estimate
the
flux
rate.
The
normalized
flux
rates
which
were
determined
for
iodomethane
are
summarized
below
in
Table
3.
Page
9
of
23
Table
3:
Summary
Of
Normalized
Flux
Rates
For
Iodomethane
Application
Method
Emission
Reduction
Technology
24
Hour
Flux
Rates
(

g/
m2
­
s)
Combination
#

Shallow
shank,
broadcast
flat
fume
Tarped
107
(
Manteca
Site
Data)
1
Shallow
shank,
raised
bed
Tarped
85
2
Drip
irrigation,
raised
bed
Tarped
66
3
Note:
These
values
are
subject
to
change
as
the
Agency
was
finalizing
these
calculations
during
the
time
this
document
was
prepared.
Detailed
information
concerning
these
flux
calculations
will
be
presented
by
the
Agency
at
the
SAP
meeting
during
introductory
remarks.

Other
Settings/
Parameters:
Along
with
the
input
variables
described
above
that
have
been
considered
by
the
Agency
in
this
assessment
there
are
other
parameters
(
or
settings)
that
must
be
defined
in
order
to
complete
an
ISC
analysis.
These
parameters
include
(
see
Figure
1):

°
Rural
conditions
are
used;

°
Mixing
height
692
m
for
rural
settings
(
based
on
DPR
analysis);

°
Receptor
height
at
ground
level
(
similar
to
DPR
analysis);

°
Source
(
i.
e.,
the
treated
field)
is
treated
as
an
area
source;

°
Source
(
i.
e.,
the
treated
field)
is
square
oriented
in
north/
south
direction;

°
Grid
origin
is
SW
corner
of
field;

°
Receptors
are
centerline
of
field
to
the
south,
buffers
are
from
edge
of
field;

°
Release
height
is
0
meters;

°
Flux
rates
determined
from
monitoring
data
using
ISC­
based
back
calculation
method
as
no
direct
measurements
of
flux
were
available
for
this
analysis
(
i.
e.,
sometimes
referred
to
as
indirect
flux
calculation
method);

°
Deposition
is
not
accounted
for
and
is
expected
to
be
minimal
due
to
volatility
of
chemical;
and
°
Standard
regulatory
default
options
as
defined
in
ISC
User's
Guide
Volume
1
have
been
used.
Page
10
of
23
2.2
Outputs
Based
on
Current
Modeling
Approach
Examples
of
the
kinds
of
outputs
which
can
be
generated
by
ISC
based
on
inputs
similar
to
those
described
above
are
presented
in
this
section.
For
the
purposes
of
this
example,
the
outputs
represent
24
hour
average
concentrations
at
selected
downwind
receptor
points.
The
receptor
points
are
illustrated
in
Figure
1
along
with
the
unidirectional
nature
of
the
meteorological
conditions
(
i.
e.,
wind
direction)
upon
which
the
assessment
is
based.
Page
11
of
23
The
results
based
on
the
Agency's
methodology
were
calculated
using
a
test
case
similar
to
one
of
those
included
as
a
case
study
in
the
PERFUM
background
document.
The
test
case
which
was
evaluated
considered
the
exposures
of
individuals
surrounding
a
field
that
had
been
treated
via
a
tarped
shallow
shank,
broadcast
flat
fume
application.
For
comparative
purposes,
the
Agency
has
summarized
the
results
based
on
its
deterministic
approach
for
this
scenario
below.
These
results
include
air
concentrations
(

g/
m3)
at
selected
receptor
points
downwind
for
a
variety
of
meteorological
conditions
(
Table
4).
The
conditions
considered
in
this
analysis
range
from
a
stable
atmosphere
conducive
to
higher
concentrations
in
close
proximity
to
treated
areas
to
conditions
that
are
much
less
stable
which
lead
to
lower
concentrations
in
proximity
to
treated
areas.

Table
4:
ISC
Calculated
Air
Concentrations
At
Selected
Distances
Downwind
(

g/
m3)
For
Pre­
Plant
Agricultural
Field
Fumigations
ER
Fld
Size
(
A)
DW
Dist.
(
M)
Air
Concentrations
At
Differing
Meteorological
Conditions
1
m/
s
2.3
mph
1.4
m/
s
3.1
mph
1.8
m/
s
4
mph
2.2
m/
s
5
mph
2.7
m/
s
6
mph
3.1
m/
s
7
mph
3.6
m/
s
8
mph
4.0
m/
s
9
mph
4.5
m/
s
10
mph
4.5
m/
s
10
mph
Stab
D
Stab
C
Stab
C
Stab
C
Stab
C
Stab
C
Stab
C
Stab
C
Stab
C
Stab
B
0.47
1
25
2116
976
759
621
506
441
380
342
304
214
100
935
395
307
251
205
178
153
138
123
73
500
170
48
37
30
25
22
19
17
15
6
1000
59
15
11
9.4
7.6
6.6
5.7
5.1
4.6
1.7
2500
15
2.9
2.3
1.8
1.5
1.3
1.1
1.0
0.9
0.3
5000
5.3
0.8
0.6
0.5
0.4
0.4
0.3
0.3
0.3
0.1
40
25
5278
2342
1822
1491
1215
1058
911
820
729
507
100
3314
1418
1103
902
735
640
551
496
441
300
500
1456
564
438
359
292
255
219
197
175
99
1000
942
309
240
196
160
139
120
108
96
43
2500
434
93
72
59
48
42
36
32
29
9.7
5000
186
30
23
19
16
14
12
11
9.4
3.4
Note:
ER
=
emission
rate
which
defines
flux
in
terms
of
the
percentage
of
the
amount
applied.
The
emission
rate
of
47
percent
or
0.47
for
this
application
method
was
calculated
by
dividing
the
flux
rate
of
107

g/
meter
squared
­
second
by
the
application
rate
of
175
pounds/
acre/
day
after
conversion
to
similar
units
and
adjustment
of
the
flux
rate
to
a
24
hour
value.
The
flux
data
upon
which
this
analysis
is
based
is
from
the
Manteca
flat
fume
study.
There
was
another
flat
fume
application
study
available
that
was
conducted
in
Watsonville
California.
However,
for
illustrative
purpose,
the
Agency
has
provided
concentration
estimates
based
on
the
Manteca
information.
Page
12
of
23
The
air
concentrations
presented
in
Table
4
would
then
be
used
to
calculate
a
risk
estimate
for
each
condition.
The
Agency
uses
Margins
of
Exposure
to
represent
non­
cancer
risks
which
are
calculated
using
the
following
formula:

MOE
=
HEC
(

g/
m3)
Air
Concentration
(

g/
m3)

Where:

MOE
=
Margin
of
exposure,
value
used
to
represent
risk
or
how
close
a
chemical
exposure
is
to
being
a
concern
(
unitless);
Air
Concentration
=
The
concentration
in
air
to
which
an
individual
could
be
exposed
(

g/
m3);
and
HEC
=
Human
equivalent
concentration
is
the
air
concentration
of
a
toxicant
at
a
level
at
which
an
effect
might
occur
(
e.
g.,
NOAEL
or
LOAEL)
after
it
has
been
adjusted
to
pharmacokinetic
differences
between
the
test
animal
species
and
humans.

In
the
PERFUM
case
study
a
"
threshold"
HEC
value
was
used
for
the
purposes
of
calculating
simulated
risk
estimates
120

g/
m3.
This
does
not
represent
the
actual
HEC
or
"
threshold"
being
considered
by
the
Agency
at
this
point
and
is
only
used
for
illustrative
purposes.
The
Agency
wishes
to
focus
discussion
at
the
SAP
meeting
on
the
methodologies
contained
in
PERFUM
that
could
potentially
lead
to
an
evolution
in
the
manner
in
which
the
Agency
calculates
exposure
concentrations
such
as
in
Table
4
and
not
on
other
risk
assessment
related
issues
specific
to
the
iodomethane
case
study
example.
As
such,
the
Agency
has
not
included
any
risk
estimates
in
this
document
for
the
case
study.
Page
13
of
23
3
OVERVIEW
OF
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
PERFUM)

The
Probabilistic
Exposure
And
Risk
Model
For
Fumigants
(
PERFUM)
is
a
modeling
tool
that
could
potentially
represent
an
evolution
in
the
manner
in
which
the
Agency
calculates
exposures
from
soil
fumigants.
It
is
the
methodologies
included
in
PERFUM
that
the
Agency
wishes
the
SAP
panel
to
consider
in
its
deliberations.
This
section
contains
a
very
brief
overview
of
the
PERFUM
system
and
how
the
outputs
might
differ
from
those
generated
using
the
current
Agency
approach
for
calculating
exposures.
Definitive
discussions
of
PERFUM
can
be
found
in
the
following
(
http://
www.
epa.
gov/
oscpmont/
sap/
2004/#
top).

A
Probabilistic
Exposure
And
Risk
Model
For
Fumigant
Bystander
Exposures
Using
Iodomethane
As
A
Case
Study,
Reiss
and
Griffin,
July,
2004
The
purpose
of
this
discussion
is
to
provide
readers
with
a
way
to
easily
contrast
the
Agency
approach
and
the
approaches
included
in
PERFUM.
Much
of
the
discussion
in
this
section
and
the
graphics
included
herein
are
excerpted
directly
from
the
above
document.
It
should
also
be
noted
that
the
PERFUM
developers
used
data
specific
to
the
soil
fumigant,
iodomethane,
as
the
basis
for
the
case­
study
included
in
this
document
(
i.
e.,
exposures
were
evaluated
for
each
of
the
different
categories
of
application
methods
described
above
in
Table
2).
The
Agency
believes
that
the
methods
applied
in
this
analysis
have
generic
applicability
to
all
fumigants
and
wishes
that
PERFUM
be
considered
in
this
manner
yet
keeping
in
mind
that
some
of
the
inputs
used
for
this
analysis
have
to
be
specific
to
iodomethane
in
order
to
complete
the
case
study
analysis.

The
PERFUM
model
was
developed
with
three
critical
design
considerations
in
mind
including:
(
1)
integration
of
actual
meteorological
data
into
an
analysis;
(
2)
the
variability
associated
with
emissions
from
treated
fields;
and
(
3)
the
need
to
evaluate
uncertainty
associated
with
the
input
parameters
throughout
a
modeling
analysis.
PERFUM
is
based
on
an
EPA
model
(
ISCST).
The
PERFUM
approach
utilizes
historical
meteorological
datasets
and
provides
characterization
of
the
potential
downwind
concentrations.
Specifically,
for
an
emission
profile,
PERFUM
calculates
the
downwind
concentrations
in
all
directions
around
the
field
for
every
day
for
a
5­
year
period
for
every
source
of
meteorological
data
considered.
From
these
concentration
calculations,
PERFUM
establishes
distances
from
the
field,
in
all
directions,
where
the
concentration
declines
to
a
user
defined
threshold.
The
PERFUM
"
modeling
toolbox"
also
contains
an
additional
program
that
can
calculate
margins
of
exposure
(
MOEs)
for
a
defined
concentration
isopleth
around
a
treated
field.
Page
14
of
23
Specifically,
in
the
case
study
developed
based
on
iodomethane,
the
following
options/
inputs
were
considered:

°
Flux
data
from
6
distinct
field
monitoring
studies
that
evaluated
emissions
from
flat
fume,
raised
bed,
and
drip
irrigation
applications;
°
Emissions
on
the
day
of
application
and
the
days
immediately
following
were
considered;
°
Direct
and
indirect
flux
estimates
for
the
Manteca
study
were
compared;
°
Meteorological
data
from
4
sources
including
National
Weather
Service,
Automated
Surface
Observing
System,
California
Irrigation
Management
Information
System,
and
Florida
Automated
Weather
Network
were
considered;
°
The
impact
of
mixing
height
and
the
replacement
of
missing
meteorological
data
were
evaluated;
and
°
An
uncertainty
analysis
was
completed
that
evaluated
emission
inputs,
meteorology
and
other
general
modeling
issues
such
as
the
treatment
of
"
calm
wind"
periods;
terrain
impacts;
seasonal
variation
in
applications,
and
exposures
from
multiple
fields.

The
following
graphically
describe
a
number
of
issues
that
were
considered
in
the
development
of
PERFUM,
analysis
of
the
data,
interpretation
of
the
results
compared
to
the
current
Agency
practice.
Figure
2
provides
a
description
of
the
receptor
grid
which
is
used
in
the
PERFUM
analysis.
Table
5
provides
numerical
estimates
for
the
number
of
receptors
considered
in
a
PERFUM
analysis.

Table
5.
Receptor
Points
for
Various
Field
Sizes
Grid
Type
Field
Size
(
acres)
Number
of
Spokes
Number
of
Rings
Number
of
Receptors
(
Spokes*
Distances)

Fine
1
96
28
2,688
5
132
28
3,696
10
152
28
4,256
20
188
28
5,264
40
232
28
6,496
Coarse
1
24
28
672
5
33
28
924
10
38
28
1,064
20
47
28
1,316
40
58
28
1,624
Page
15
of
23
Figure
2.
Receptor
Grid
For
A
5
Acre
Field
(
5
acre
field
in
center;
blue
line
is
an
example
of
a
spoke)
Page
16
of
23
Figure
3
provides
a
comparison
of
emission
rates
from
two
fields
treated
via
flat
fume
application.
This
figure
also
illustrates
variability
in
emissions
and
a
general
decline
in
air
concentrations
over
time.
It
should
also
be
noted
that
Manteca
data
were
selected
as
the
basis
for
the
analysis
conducted
by
the
Agency.

Figure
3.
Estimated
Flux
Rate
Versus
Mean
Time
Since
Application
For
Flat
Fume
Applications
Page
17
of
23
Figures
4
and
5
provide
a
summary
of
the
meteorological
data
used
for
the
PERFUM
analysis.
Figure
4
illustrates
the
locations
of
the
meteorological
stations
that
were
considered
as
sources
of
data
in
Southern
California
which
is
anticipated
to
be
an
area
of
substantial
iodomethane
use.
Figure
5
presents
windrose
data
for
the
Bakersfield
ASOS
station
which
illustrates
how
wind
directions
and
speed
changed
over
the
selected
period
at
that
station.

Figure
4.
Locations
of
Meteorological
Stations
in
California
Page
18
of
23
Figure
5.
Wind
Rose
Plot
For
Bakersfield
Page
19
of
23
Figure
6
provides
a
comparison
of
the
distributions
of
daily
average
windspeeds
for
selected
meteorological
stations
in
both
California
and
Florida.
Note
that
the
results
of
this
analysis
can
be
used
to
assist
in
the
characterization
of
the
deterministic
inputs
used
by
the
Agency
and
summarized
in
Table
4
Figure
6.
Distribution
Of
Daily
Average
Wind
Speeds
at
the
Meteorological
Stations
Page
20
of
23
Figure
7
provides
an
example
of
the
isopleths
that
can
be
produced
using
PERFUM.
The
example
provided
below
is
for
a
5
acre
field.
It
also
illustrates
how
the
results
can
be
used
for
regulatory
purposes
and
for
examination
of
exposures
which
may
exceed
any
specified
threshold
concentration.

Figure
7.
Example
Concentration
Estimates
For
A
5
Acre
Field
(
Red
line
shows
contour
at
reference
concentration;
black
line
shows
the
buffer
zone).
Page
21
of
23
4
CHARGE
TO
PANEL
This
section
presents
the
charge
questions
the
Agency
wishes
the
panel
to
consider
in
its
deliberations
pertaining
to
PERFUM.
The
nature
of
these
questions
are
varied
and
range
from
issues
pertaining
to
the
documentation,
design,
and
operation
of
PERFUM
to
the
manner
in
which
results
are
presented.
For
simplicity,
the
Agency
has
grouped
the
questions
by
subject
matter
that
reflect
critical
elements
pertaining
to
the
use
of
PERFUM
and
results
generated
by
PERFUM.
The
key
subject
matter
areas
include:
(
1)
documentation;
(
2)
system
design/
inputs;
and
(
3)
how
results
are
presented.

Critical
Element
1:
Documentation
Question
1:
The
background
information
presented
to
the
SAP
panel
by
the
PERFUM
developers
provides
both
user
guidance
and
a
technical
overview
of
the
system.
Please
comment
on
the
detail
and
clarity
of
this
document.
Are
the
descriptions
of
the
specific
model
components
scientifically
sound?
Do
the
algorithms
in
the
annotated
code
perform
the
functions
as
defined
in
this
document?
Please
discuss
any
difficulties
encountered
with
respect
to
loading
the
software
and
evaluating
the
system
including
the
presented
case
study?

Critical
Element
2:
System
Design/
Inputs
Question
2:
In
Section
2.3:
Development
of
the
PERFUM
Modeling
System
of
the
background
document,
a
series
of
detailed
individual
processes
and
components
included
in
PERFUM
are
presented.
The
key
processes
include
(
1)
incorporation
of
ISCST3
into
PERFUM,
(
2)
probabilistic
treatment
of
flux
rates;
and
(
3)
development
of
a
receptor
grid.
Please
comment
on
these
proposed
processes,
the
nature
of
the
components
included
in
PERFUM
and
the
data
needed
to
generate
an
analysis
using
PERFUM?
Are
there
any
other
potential
critical
sources
of
data
or
methodologies
that
should
be
considered?

Question
3:
The
determination
of
appropriate
flux/
emission
rates
is
critical
to
the
proper
use
of
the
PERFUM
model
as
these
values
define
the
source
of
fumigants
in
the
air
that
can
lead
to
exposures.
Upon
its
review
of
how
flux
rates
can
be
calculated,
the
Agency
has
identified
a
number
of
questions
it
would
like
the
panel
to
consider.
In
PERFUM,
flux
rates
were
treated
as
a
probabilistic
variable
with
an
uncertainty
developed
from
the
statistical
bounds
of
the
flux
calculation.
For
each
measurement
period
a
standard
error
is
generated
that
reflects
the
measurement
uncertainty
of
the
flux
rate.
PERFUM
then
perturbs
the
concentration
estimates
within
each
period
by
the
standard
error
using
Monte
Carlo
methods
to
simulate
the
uncertainty
in
the
flux
estimates.
What,
if
any,
refinements
are
needed
for
this
process
including
the
manner
in
which
flux
values
were
calculated
for
each
monitoring
period
to
generate
the
standard
error
estimates?
How
appropriate
is
it
to
use
a
flux/
emission
factor
from
a
single
monitoring
study
(
or
Page
22
of
23
small
number
of
studies)
and
apply
it
to
different
situations
such
as
for
the
same
crop
in
a
different
region
of
the
country?
Please
comment
on
PERFUM's
capability
to
adequately
consider
multiple,
linked
application
events
as
well
as
single
source
scenarios?
Does
PERFUM
appropriately
address
situations
where
data
are
missing?
In
the
back­
calculation
approach
used
for
estimating
emission
rates,
the
regression
of
measured
versus
modeled
values
can
be
forced
through
the
origin
or
not.
Which
approach
does
the
panel
prefer
and
what
are
the
implications
of
each
approach?

Question
4:
The
integration
of
actual
time­
base
meteorological
data
into
ISCST3
is
one
of
the
key
components
that
separates
the
PERFUM
methodology
from
that
being
employed
by
the
Agency
in
its
current
assessment.
There
are
several
potential
sources
of
these
data
including
the
National
Weather
Service,
Federal
Aviation
Administration,
California
Irrigation
Management
Information
System
(
CIMIS),
and
the
Florida
Automated
Weather
Network
(
FAWN).
The
Agency
is
also
aware
that
there
are
several
approaches
that
can
be
used
to
process
meteorological
data
and
acknowledges
that
PERFUM
used
PCRAMMET
which
is
a
standard
Agency
tool
for
this
purpose
as
well
as
other
techniques
in
some
cases
(
e.
g.,
for
the
FAWN
&
CIMIS
data).
Various
datasets
from
both
California
and
Florida
were
used
as
the
basis
for
the
PERFUM
case
study.
Please
comment
on
the
methods
used
to
select
monitoring
station
locations?
What
criteria
should
be
used
to
identify
meteorological
regions
for
analysis
and
how
should
specific
monitoring
data
be
selected
from
within
each
region.?
Please
comment
on
the
manner
that
data
from
the
selected
various
stations
were
processed?
Data
quality
and
uncertainty
associated
with
these
data
vary
with
the
source.
Does
the
panel
agree
with
the
approaches
used
to
characterize
these
factors?
Anemometer
sampling
height
has
been
identified
as
a
concern
by
the
Agency
in
preparation
for
this
meeting.
What
are
the
potential
impacts
of
using
data
collected
with
different
anemometer
heights
in
an
analysis
of
this
nature?
Does
PERFUM
treat
stability
class
inputs
appropriately?
Does
PERFUM
appropriately
calculate
bounding
air
concentration
estimates
by
concurrently
using
upper­
bound
meteorological
and
emission/
flux
inputs?

Question
5:
The
Agency
model,
ISCST3
is
the
basis
for
the
PERFUM
approach.
This
model
has
been
peer
reviewed
and
is
commonly
used
for
regulatory
purposes
by
the
Agency.
PERFUM
also
uses
other
Agency
systems
such
as
PCRAMMET.
Please
recommend
any
parameters
that
should
be
altered
to
optimize
the
manner
that
they
are
used
in
PERFUM?
Does
the
panel
agree
with
the
manner
in
which
the
receptor
grid
was
developed,
and
if
not,
please
provide
suggestions
for
improving
this
approach?
ISCST3,
as
integrated
into
PERFUM,
was
run
assuming
rural,
flat
terrain
which
would
be
typical
of
treated
farm
fields
but
might
not
be
typical
of
surrounding
residential
areas.
Does
the
panel
concur
with
this
approach?
What
are
the
implications
of
such
an
approach?
What
improvements
can
be
made
to
this
approach?
ISCST3,
as
integrated
into
PERFUM,
was
run
in
regulatory
mode
which
includes
the
use
of
the
"
calms"
processing
routine.
Does
the
panel
concur
with
this
approach?
If
not,
please
suggest
a
suitable
alternative?

Critical
Element
3:
Results
Question
6:
Soil
fumigants
can
be
used
in
different
regions
of
country
under
different
conditions
and
they
can
be
applied
with
a
variety
of
equipment.
Please
comment
on
whether
the
methodologies
in
PERFUM
can
be
applied
generically
in
order
to
assess
a
wide
variety
of
fumigant
uses?
What
considerations
with
regard
to
data
needs
and
model
inputs
should
be
Page
23
of
23
considered
for
such
an
effort?

Question
7:
Please
comment
on
whether
PERFUM
adequately
identifies
and
quantifies
airborne
concentrations
of
soil
fumigants
that
have
migrated
from
treated
fields
to
sensitive
receptors?
The
Agency
is
particularly
concerned
about
air
concentrations
in
the
upper
ends
of
the
distribution.
Are
these
results
presented
in
a
clear
and
concise
manner
that
would
allow
for
appropriate
characterization
of
exposures
that
could
occur
at
such
levels?
The
PERFUM
model
calculates
the
concentration
distributions
both
in
all
directions
and
for
only
the
maximum
concentration
direction.
Can
the
panel
comment
on
how
accurately
the
model
approximates
both
of
these
distributions?

Question
8:
A
sensitivity/
uncertainty
analysis
has
been
conducted
and
is
described
in
the
PERFUM
background
document.
What
types,
if
any,
of
additional
contribution/
sensitivity
analyses
are
recommended
by
the
panel
to
be
the
most
useful
in
making
scientifically
sound,
regulatory
decisions?
What
should
be
routinely
reported
as
part
of
a
PERFUM
assessment
with
respect
to
inputs
and
outputs?
Are
there
certain
tables
and
graphs
that
should
be
reported?
What
types
of
further
evaluation
steps
does
the
panel
recommend
for
PERFUM?
