Page
1
of
4
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
July
5,
2006
MEMORANDUM
SUBJECT:
Piperonyl
Butoxide:
Risk­
Based
Application
Rate
for
Residential
Outdoor
Automatic
Mister
Systems
FROM:
Matthew
Crowley,
Environmental
Protection
Specialist
Reregistration
Branch
4
Health
Effects
Division
THRU:
Susan
Hummel,
Senior
Scientist
Reregistration
Branch
4
Health
Effects
Division
TO:
Cathryn
O'Connell,
Chemical
Review
Manager
Reregistration
Branch
2
Special
Review
and
Reregistration
Division
DP
Barcode(
s):
D325918
PC
Code:
067501
The
attached
document
addresses
a
request
from
the
Office
of
Pesticide
Program's
(
OPP)
Special
Review
and
Reregistration
Division
(
SRRD)
to
propose
a
risk­
based
application
rate
for
the
use
of
piperonyl
butoxide
(
PBO)
in
residential
outdoor
automatic
mister
systems.
Page
2
of
4
1.0
Background
and
Purpose
OPP's
Health
Effects
Division
(
HED)
previously
assessed
occupational
and
residential
exposures
and
risks
for
the
use
of
PBO
in
outdoor
residential
mister
systems
(
M.
Crowley,
D315334).
The
assessment
presented
risk
estimates
for
following
exposure
scenarios:

Occupational
 
Inhalation
exposure
during
mixing
and
loading
liquid
formulations
for
the
systems'
holding
tanks.

Residential
 
Inhalation
exposure
during
mixing
and
loading
liquid
formulations
for
the
systems'
holding
tanks;
 
Bystander
inhalation
exposure
during
outdoor
mister
applications;
 
Non­
dietary
incidental
oral
exposure
on
turf
following
outdoor
mister
applications.

Note:
Although
potential
for
dermal
exposure
exists,
a
toxicological
endpoint
was
not
identified;
therefore
a
quantitative
dermal
risk
assessment
was
not
performed.

Through
its
own
research
and
various
use
recommendations
from
product
labels,
registrants
and
their
representatives,
and
installation
companies,
HED
made
reasonable
assumptions
for
the
following
mister
system
parameters:

 
Number
and
size
of
holding
tanks
or
reservoirs;
 
Nozzle
coverage
(#
nozzles/
ft2),
height
(
off
the
ground),
spacing
(
perimeter
separation),
and
flow
rate
(
amount
product/
nozzle/
spray);
 
Number
of
automatic
dispersions
per
day;
 
Duration
of
each
spray;
 
Active
ingredient
concentration
and
product
dilution
rates.

HED
then
used
standard
assumptions
including
exposure
duration
(
i.
e.,
time
spent
outdoors),
outdoor
dilution
of
the
initial
air
concentration,
and
breathing
rates
to
estimate
exposure
and
risk.
Risks
of
concern
were
identified
for
short­/
intermediate­
term
bystander
inhalation
exposure
to
toddlers
following
2,
1­
minute
sprays.

The
purpose
of
this
document
is
to
present
an
application
rate,
in
terms
of
pounds
of
PBO
per
1,000
ft3
per
day,
where
these
inhalation
bystander
risks
are
not
of
concern.
From
this
risk­
based
application
rate
the
user
can
then
determine
the
system
parameters
listed
above
themselves
(
i.
e.,
number
of
30­
second
sprays
per
day
at
a
certain
dilution
to
reach
this
application
rate).
This
removes
from
the
outdoor
residential
mister
system
assessment
the
need
for
HED
to
assume
system
parameters.

2.0
Determination
of
Risk­
Based
Application
Rate
2.1
Exposure
Factors
and
Assumptions
Page
3
of
4
The
following
exposure
factors
and
assumptions
were
used
in
estimating
the
application
rate
at
which
short­/
intermediate­
term
toddler
inhalation
bystander
risks
from
the
use
of
PBO
in
outdoor
residential
mister
systems
are
not
of
concern.
It
is
assumed
that
the
risk
estimates
presented
for
the
other
previously
assessed
exposure
scenarios
(
i.
e.,
dermal
exposure
to
occupational
and
residential
handlers,
non­
dietary
incidental
oral
exposures,
short­/
intermediateterm
adult
bystander
inhalation,
etc.)
 
which
were
not
of
concern
 
will
remain
the
same
or
decrease.

 
Average
body
weight
for
a
toddler
is
15
kg;
 
The
lowest
observed
adverse
effects
level
(
LOAEL)
of
3.91
mg/
kg­
day
was
chosen
based
on
laryngeal
hyperplasia
and
metaplasia
from
a
subchronic
inhalation
toxicity
study
in
rats.
The
level
of
concern
(
LOC)
for
the
margin
of
exposure
(
MOE)
is
300.
 
Exposure
duration
is
expected
to
be
short­
term
(
1­
30
days),
and
intermediate­
term
(
1­
6
months)
 
long­
term
(>
6
months)
exposures
are
not
expected
for
this
use;
 
No
respiratory
protection
is
worn;
 
The
emission
is
to
be
treated
as
an
"
instant
release"
scenario.
All
active
ingredient
is
assumed
to
be
"
thrown
up"
in
the
air
immediately.
Further,
the
chemical
is
assumed
diluted
in
outdoor
air
at
a
ratio
of
1
to
100
(
i.
e.,
1%),
and
the
pesticide
is
assumed
to
remain
in
the
air
at
this
concentration
for
the
entire
duration
of
exposure;
 
Inhalation
rates
are
assumed
to
be
0.7
m3/
hour
(
toddler,
light
to
moderate
activities);
 
Exposure
period
is
assumed
to
be
3
hours
for
toddlers.

2.2
Risk­
Based
Application
Rate
Calculation
The
risk­
based
application
rate
(
lb
PBO/
1000
ft3­
day)
is
back­
calculated
from
the
toxicological
endpoint
of
concern
and
the
uncertainty
factors.

First,
estimate
the
potential
daily
dose
(
PDD):

LOAEL
(
mg/
kg­
day)
PDD
(
mg/
kg­
day)
=
LOC
for
MOE
Where:

NOAEL
=
Lowest
Observed
Adverse
Effect
Level
(
3.91
mg/
kg­
day)
LOC
for
MOE
=
300
3.91
PDD
(
mg/
kg­
day)
=
300
PDD
=
0.013
mg/
kg­
day
Next,
from
the
potential
daily
dose,
estimate
the
average
air
concentration
(
Ca),
diluted
by
outdoor
air,
to
which
the
toddler
can
be
exposed
for
the
3­
hour
exposure
period:

PDD
(
mg/
kg­
day)
*
BW
(
kg)
Ca
(
mg
PBO/
m3­
day)
=
BR
(
m3/
hr)
*
ED
(
hr)
Page
4
of
4
Where:

BR
=
Breathing
Rate
(
0.7
m3/
hr)
ED
=
Exposure
Duration
(
3
hrs)
BW
=
Body
Weight
(
15
kg)

0.013
mg/
kg­
day
*
15
kg
Ca
(
mg
PBO/
m3­
day)
=
0.7
m3/
hr
*
3
hr
Ca
=
0.093
mg
PBO/
m3­
day
Last,
from
the
diluted
air
concentration,
present
the
initial
air
concentration
(
Ci)
immediately
following
application
 
this
is
the
risk­
based
application
rate
(
conversion
to
lb
PBO/
ft3­
day
presented):

Ca
(
mg
PBO/
m3­
day)
Ci
(
lb
PBO/
ft3­
day)
=
CF1
(
ft3/
m3)
*
CF2
(
mg/
lb)
*
ODF
(%)

Where:

CF
1
=
Conversion
from
cubic
feet
to
cubic
meters
(
35
ft3/
m3)
CF
2
=
Conversion
from
milligrams
to
pounds
(
454,000
mg/
lb)
ODF
=
Outdoor
Dilution
Factor
(
1
%)

0.093
mg
PBO/
m3­
day
Ci
(
lb
PBO/
ft3­
day)
=
35
ft3/
m3
*
454,000
mg/
lb
*
1
%

Ci
=
0.00000058
lb
PBO/
ft3­
day
OR
Ci
=
0.00058
lb
PBO/
1000
ft3­
day
3.0
Characterization
of
Risk­
Based
Application
Rate
Assuming
chemical
dilution
at
a
ratio
of
1
to
100
(
i.
e.,
1%
of
the
product
released
is
available
during
the
exposure
period)
represents
a
reasonable
estimate
as
described
in
HED's
Standard
Operating
Procedures
for
Residential
Exposure
Assessments
(
i.
e.,
Residential
SOPs).
A
study
presenting
air
concentrations
at
different
intervals
following
mister
system
activations
would
greatly
refine
the
risk
assessment
and
provide
a
more
accurate
picture
of
exposure.
