OVERVIEW
OF
OXADIAZON
RISK
ASSESSMENTS
Introduction
This
document
summarizes
EPA's
human
health
and
ecological
risk
findings
and
conclusions
for
the
selective,
pre­
emergent
and
early
post­
emergent
herbicide,
oxadiazon,
as
presented
fully
in
the
documents,
"
Human
Health
Risk
Assessment
for
Oxadiazon,"
dated
March
5,
2002,
and
"
EFED
Risk
Assessment
for
the
Reregistration
Eligibility
Decision
of
Oxadiazon,"
dated
March
5,
2002.

The
purpose
of
this
summary
is
to
assist
the
reader
by
identifying
the
key
features
and
findings
of
these
risk
assessments
and
to
better
understand
the
conclusions
reached
in
the
assessments.
References
to
relevant
sections
in
the
complete
documents
are
provided
to
allow
the
reader
to
find
the
place
in
these
assessments
where
a
more
detailed
explanation
is
provided.
This
summary
was
developed
in
response
to
comments
and
requests
from
the
public
which
indicated
that
the
risk
assessments
were
difficult
to
understand,
that
they
were
too
lengthy
and
that
it
was
not
easy
to
compare
the
assessments
for
different
chemicals
due
to
the
use
of
different
formats.

Tolerances
The
Federal
Food,
Drug,
and
Cosmetic
Act
(
FFDCA),
as
amended
by
the
Food
Quality
Protection
Act
(
FQPA)
of
1996,
requires
EPA
(
the
Agency)
to
review
the
allowable
food
residue
concentrations
("
tolerances")
for
registered
chemicals
in
effect
on
or
before
the
date
of
the
enactment
of
FQPA.
In
reviewing
these
tolerances,
the
Agency
must
consider,
among
other
things,
aggregate
risks
from
non­
occupational
sources
of
pesticide
exposure,
whether
there
is
increased
susceptibility
to
infants
and
children,
and
the
cumulative
effects
of
pesticides
with
a
common
mechanism
of
toxicity.
The
tolerances
are
considered
reassessed
once
the
safety
finding
has
been
made
or
a
revocation
occurs.

There
are
no
food
or
feed,
or
anticipated
food
or
feed
uses
for
oxadiazon.
The
Registrant
is
not
supporting
any
tolerances
for
oxadiazon
in
the
United
States.
Likewise,
there
are
no
Canadian
or
Mexican
tolerances
for
oxadiazon.
Revocation
of
tolerances
for
residues
of
oxadiazon
on
food
and
feed
has
been
proposed
(
Federal
Register:
August
1,
2001,
Vol.
66,
Number
148)
and
tolerances
will
be
revoked
in
FY2003.
Consequently,
dietary
exposure
from
food
is
not
a
concern
for
this
product.

Cumulative
Risk
Assessment
EPA
did
not
perform
a
cumulative
risk
assessment
as
part
of
the
Reregistration
Eligibility
Decision
(
RED)
for
oxadiazon
because
the
Agency
has
not
yet
initiated
a
comprehensive
review
to
determine
if
there
are
any
other
chemical
substances
that
have
a
mechanism
of
toxicity
common
with
that
of
oxadiazon.
For
purposes
of
this
risk
assessment,
EPA
has
assumed
that
oxadiazon
2
does
not
have
a
common
mechanism
of
toxicity
with
other
substances.
In
the
future,
the
registrant
may
be
asked
to
submit,
upon
EPA's
request
and
according
to
a
schedule
determined
by
the
Agency,
such
information
as
the
Agency
directs
to
be
submitted
in
order
to
evaluate
issues
related
to
whether
oxadiazon
shares
a
common
mechanism
of
toxicity
with
any
other
substance.
The
Agency
has
developed
a
framework
for
conducting
cumulative
risk
assessments
on
substances
that
have
a
common
mechanism
of
toxicity.
This
guidance
was
issued
on
January
16,
2002
(
67
FR
2210­
2214)
and
is
available
from
the
Office
of
Pesticide
Programs
(
OPP)
Website
at:
http://
www.
epa.
gov/
pesticides/
trac/
science/
cumulative_
guidance.
pdf.

Availability
of
Documents
The
risk
assessments
and
associated
documents
for
oxadiazon
are
available
on
the
Internet
at
http://
www.
epa.
gov/
pesticides/
reregistration/
status.
htm
and
in
the
public
docket,
located
in
Room
119,
Crystal
Mall
#
2,
1921
Jefferson
Davis
Highway,
Arlington,
VA,
for
viewing.
Public
comments
will
be
invited
and
welcomed
for
60
days.
The
Agency's
report
on
the
risk
management
decision
for
oxadiazon
will
also
be
announced
in
the
Federal
Register
once
public
comments
are
considered,
and
any
revisions
to
the
risk
assessments
have
been
completed.

Use
Profile
$
Herbicide:
Oxadiazon
is
a
pre­
emergent
or
early
post­
emergent
oxadiazole
herbicide
used
to
control
grassy
weeds
(
e.
g.
goosegrass
and
crabgrass)
and
broadleaf
weeds
in
turf
and
ornamentals.
Oxadiazon
works
by
interfering
with
the
pathway
for
chlorophyll
production,
and
results
in
a
breakdown
of
plant
tissue
on
exposure
to
light.
Oxadiazon
is
labeled
for
professional
use
only.
The
label
indicates
that
the
purchase,
storage
and
application
of
this
pesticide
are
limited
to
commercial
nursery,
turf
and
landscape
personnel.
The
product
is
not
available
to
homeowners.

$
Uses:
Oxadiazon
is
registered
for
commercial
use
on
turf
grown
on
golf
courses
(~
77%
of
total
use)
and
in
apartment/
condominium
complexes,
parks,
athletic
fields,
playgrounds,
and
cemeteries
(~
12%
of
total
use).
In
addition,
oxadiazon
is
used
on
sod
farms
and
on
conifer
nurseries
and
landscapes
(
i.
e.
industrial
sites,
ornamental,
roadside
plantings,
woody,
ornamental
shrubs,
vines
and
trees,
and
herbaceous
ornamentals).
Oxadiazon
use
sites
are
classified
as
non­
food
sites
(
i.
e.
primarily
golf
course
fairways
and
roughs),
residential
outdoor
use,
roadsides
and
nurseries.

$
Annual
Poundage:
Approximately
249,000
pounds
are
used
on
52,000
acres
annually.
Oxadiazon
is
used
primarily
in
southern
states
(~
71%)
and
predominantly
on
golf
courses
(~
77%).

$
Formulations:
Granular
(
predominant
formulation,
~
90%
of
total
use),
wettable
powder,
3
soluble
concentrate,
and
emulsifiable
concentrate.

$
Method
of
Application:
Granular
formulas
are
applied
using
manual
spreaders
(
i.
e.
belly
grinder,
push
type
spreader)
or
tractor­
drawn
spreaders.
Methods
of
application
associated
with
the
other
formulations
and
use­
patterns
of
oxadiazon
include:
chemigation,
groundboom,
rights­
of­
way
sprayer,
handgun
sprayer,
backpack
sprayer,
low
pressure
handwand,
high
pressure
handwand,
and
lawn
handgun.

$
Use
Rates:
The
frequency
of
application
ranges
from
1
to
3
applications
per
season.
Oxadiazon
can
be
applied
at
a
minimum
application
rate
of
2.0
pounds
active
ingredient
per
acre
(
ai/
A)
up
to
a
maximum
application
rate
of
4.0
pounds
ai/
A
to
turf
and
ornamentals.
The
registrant
is
supporting
a
maximum
yearly
rate
of
8
pounds
ai/
A.

$
Registrant:
Bayer
Environmental
Science
(
formerly
Aventis
Environmental
Science
USA),
a
business
group
of
Bayer
Crop
Science,
Inc.

Human
Health
Risk
Assessment
In
acute
studies,
oxadiazon
is
only
slightly
toxic.
Oxadiazon
is
classified
as
"
likely
to
be
carcinogenic
to
humans"
based
on
studies
that
showed
an
increase
in
the
incidence
of
liver
tumors
in
two
species
(
mice
and
rats)
following
exposure
to
oxadiazon.
In
both
subchronic
and
chronic
studies,
the
primary
target
organ
is
the
liver.

Dietary
(
Food)
Risk:

There
are
no,
nor
are
there
anticipated
to
be,
food
or
feed
uses
for
oxadiazon.
The
registrant
is
not
supporting
any
tolerances
for
oxadiazon
in
the
United
States.
Likewise,
there
are
no
Canadian
or
Mexican
tolerances
for
oxadiazon.
A
request
for
revocation
of
tolerances
for
residues
of
oxadiazon
on
food
and
feed
has
been
granted,
and
tolerances
will
be
revoked
in
FY2003.
Consequently,
dietary
exposure
from
food
is
not
a
concern
for
this
product.

Drinking
Water
Dietary
Risk:

(
For
a
complete
discussion,
see
section
4.2.2
and
5.0
of
the
Human
Health
Risk
Assessment)

Drinking
water
sources
include
groundwater
and
surface
water.
The
transfer
and
accumulation
of
chemicals
in
drinking
water
can
result
in
acute
and/
or
chronic
exposures
in
humans.
The
Agency
uses
a
drinking
water
level
of
concern
(
DWLOC)
as
a
benchmark
in
making
a
determination
of
the
risk
associated
with
exposure
from
pesticides
in
drinking
water.
The
DWLOCs
represent
the
maximum
contribution
to
the
human
diet
(
in
ppb
or
µ
g/
L)
that
may
be
attributed
to
residues
of
a
pesticide
in
drinking
water.
Risks
from
drinking
water
are
assessed
by
comparing
the
DWLOCs
to
the
estimated
drinking
water
concentrations
(
EDWCs)
of
a
chemical
4
in
surface
water
and
groundwater.
The
Metabolism
Assessment
Review
Committee
(
MARC)
concluded
that
the
only
residue
of
concern
with
respect
to
oxadiazon
is
the
parent
compound,
because
major
degradates
would
be
minor
components
in
the
environment.
Moreover,
those
degradates
are
not
likely
to
be
significantly
more
toxic
than
the
parent.
Leaching
of
oxadiazon
from
surface
soil
to
groundwater
is
expected
to
be
low
or
negligible,
unless
the
soil
is
very
porous
or
has
cracks
that
enhance
flow.
Since
this
stable
compound
can
be
adsorbed
to
particulate
and
organic
matter,
oxadiazon
residues
can
persist
in
soil
and
sediments.
In
the
absence
of
measured
environmental
concentrations
of
oxadiazon
from
monitoring
studies,
and
based
on
environmental
fate
characteristics,
potential
oxadiazon
concentrations
in
unfinished
drinking
water
were
estimated
using
Tier
II
PRZM/
EXAMS
(
surface
water)
and
Tier
I
SCIGROW
(
ground
water)
models.
The
PRZM/
EXAMS
model
as
used
here
includes
a
standard
citrus
grove
scenario
that
has
been
modified
in
an
attempt
to
account
for
the
use
of
oxadiazon
on
turf.
The
modified
scenario
includes
a
two­
inch
layer
of
thatch,
and
is
referred
to
as
the
Florida
Turf
Scenario.
The
linked
PRZM/
EXAMS
model
is
typically
used
by
EPA
in
estimating
pesticide
concentrations
in
surface
waters.
The
PRZM
model
estimates
the
amount
of
pesticide
that
reaches
a
body
of
surface
water
as
a
result
of
runoff.
The
EXAMS
model
estimates
pesticide
concentrations
by
taking
into
account
different
mechanisms
for
dissipation,
weather
patterns,
and
periodic
application
of
pesticide,
for
several
years.
The
SCIGROW
model
is
typically
used
for
Tier
1
screening
purposes
for
pesticides
applied
to
soils.
The
SCIGROW
model
estimates
likely
groundwater
concentration
if
the
pesticide
is
used
at
the
maximum
allowable
rate
in
areas
where
groundwater
is
exceptionally
vulnerable
to
contamination.

$
Using
the
PRZM/
EXAMS
model,
the
contribution
of
surface
water
to
the
EDWC
for
oxadiazon
was
estimated
to
be
181
ppb
(
µ
g/
L)
for
an
acute
exposure,
and
65
ppb
(
µ
g/
L)
for
a
chronic
(
non­
cancer)
exposure.

$
Using
the
SCIGROW
model,
the
contribution
of
groundwater
to
the
EDWC
for
oxadiazon
was
estimated
to
be
0.59
ppb
(
µ
g/
L).

$
These
values
generally
depict
worst­
case
scenarios,
and
represent
the
upper­
bound
estimates
of
the
concentration
of
oxadiazon
that
might
be
found
in
surface
and
ground
water
due
to
the
application
of
oxadiazon
to
turf.
5
Acute
Drinking
Water
Risk
$
Acute
DWLOCs
were
calculated
for
oxadiazon
based
on
results
of
a
developmental
toxicity
study
in
which
pregnant
rats
were
administered
oxadiazon
via
gavage
on
Gestation
Days
six
through
15.

$
The
No
Observable
Adverse
Effect
Level
(
NOAEL)
was
12
mg/
kg/
day,
with
the
toxicity
endpoint
being
a
reduction
in
maternal
body
weight
gain
at
the
Lowest
Observable
Adverse
Effect
Level
(
LOAEL)
of
40
mg/
kg/
day.
For
risk
assessment
purposes,
an
uncertainty
factor
of
100
was
applied
(
based
on
a
10x
for
interspecies
extrapolation
and
a
10x
for
intraspecies
variation),
resulting
in
a
theoretical
acute
Population
Adjusted
Dose
(
aPAD)
of
0.12
mg/
kg/
day.

$
Based
on
a
comparison
of
DWLOCs
to
the
corresponding
PRZM/
EXAMS
and
SCIGROW
values
(
Table
1),
the
Agency
concludes
that
acute
exposure
to
residues
of
oxadiazon
in
surface
and
ground
drinking
water
is
not
a
concern.

Table
1.
Summary
of
Acute
DWLOC
Calculations
for
Oxadiazon
Population
Subgroup1
Acute
Scenario
Theoretical
aPAD
mg/
kg/
day
Acute
Food
Exp
mg/
kg/
day
Max
Acute
Water
Exp
mg/
kg/
day2
PRZM/
EXAMS
Surface
Water
EDWC
(

g/
L)
SCIGROW
Ground
Water
EDWC
(

g/
L)
Acute
DWLOC
(

g/
L)
3
U.
S.
Population
0.12
0.00
0.12
181
0.59
4200
Females
13­
50
years
old
0.12
0.00
0.12
181
0.59
3600
Infants
<
1
year
old
0.12
0.00
0.12
181
0.59
1200
Children
1­
6
years
old
0.12
0.00
0.12
181
0.59
1200
1
Default
body
weights
and
consumption
values
for
calculation
of
the
DWLOCs
were:
2L/
70
kg
(
adult
male),
2L/
60
kg
(
adult
female)
and
1L/
10
kg
(
child),
respectively.
2
Maximum
acute
water
exposure
(
mg/
kg/
day)
=
[(
acute
PAD
(
mg/
kg/
day)
­
acute
food
exposure
(
mg/
kg/
day)]
3
Acute
DWLOC(

g/
L)
=
[
maximum
chronic
water
exposure
(
mg/
kg/
day)
x
body
weight
(
kg)]
[
water
consumption
(
L)
x
10­
3
mg/

g]

Chronic
Drinking
Water
Risk
$
Chronic
DWLOCs
were
calculated
based
on
a
chronic
toxicity/
carcinogenicity
study,
in
which
rats
were
administered
oxadiazon
in
their
feed
for
104
weeks.
°
The
NOAEL
was
0.36
mg/
kg/
day,
with
the
endpoint
being
adverse
liver
effects
in
male
rats
at
a
LOAEL
of
3.5
mg/
kg/
day.
For
risk
assessment
purposes,
an
uncertainty
factor
of
100
was
applied
(
10x
for
intraspecies
variation
and
10x
for
interspecies
extrapolation).
Therefore,
the
theoretical
chronic
Population
Adjusted
Dose
(
cPAD)
was
taken
to
be
6
0.0036
mg/
kg/
day.
°
Using
the
PRZM/
EXAMS
model
estimates,
the
EDWCs
for
surface
water
(
65

g/
L)
were
higher
than
the
DWLOCs
calculated
for
infants
and
children
(
36

g/
L)
(
Table
2)
and
thus,
potentially
of
concern.

Table
2.
Summary
of
Chronic
DWLOC
Calculations
for
Oxadiazon
Population
Subgroup1
Chronic
Scenario
Theoretical
cPAD
mg/
kg/
day
Chronic
Food
Exp
mg/
kg/
day
Max
Chronic
Water
Exp
mg/
kg/
day2
PRZM/
EXAMS
Surface
Water
EDWC
(

g/
L)
SCIGROW
Ground
Water
EDWC
(

g/
L)
Chronic
DWLOC
(

g/
L)

U.
S.
Population
0.0036
0.00
0.0036
65
0.59
126
Females
13­
50
years
old
0.0036
0.00
0.0036
65
0.59
108
Infants
<
1year
old
0.0036
0.00
0.0036
65
0.59
36
Children
1­
6
years
old
0.0036
0.00
0.0036
65
0.59
36
1
Default
body
weights
and
consumption
values
for
calculation
of
the
DWLOCs
were:
2L/
70
kg
(
adult
male),
2L/
60
kg
(
adult
female)
and
1L/
10
kg
(
child),
respectively.
2
Maximum
Chronic
Water
Exposure
(
mg/
kg/
day)
=
[
Chronic
PAD
(
mg/
kg/
day)
­
Chronic
Dietary
Exposure
(
mg/
kg/
day)]
3
Chronic
DWLOC(

g/
L)
=
[
maximum
chronic
water
exposure
(
mg/
kg/
day)
x
body
weight
(
kg)]
[
water
consumption
(
L)
x
10­
3
mg/

g]

Cancer
Drinking
Water
Risk
In
accordance
with
the
EPA
Draft
Guidelines
for
Carcinogen
Risk
Assessment
(
July,
1999),
the
Cancer
Assessment
Review
Committee
(
CARC)
classified
oxadiazon
into
the
category
"
Likely
to
be
Carcinogenic
to
Humans"
based
on
the
following
weight­
of­
the­
evidence
considerations:

°
Treatment­
related
benign
and
malignant
liver
tumors
were
observed
in
two
species.
There
was
clear
evidence
that
oxadiazon
induced
a
statistically
significant
increase
in
liver
tumors
in
male
Wistar
rats
and
male
and
female
ICR­
JCL
mice.
The
findings
of
liver
tumors
are
consistent
with
the
results
of
earlier
studies
in
male
F­
344
rats
and
male
and
female
CD
mice.
The
positive
results
from
an
in
vitro
cell
transformation
assay
are
in
concordance
with
the
results
of
in
vivo
rodent
bioassays.
°
Oxadiazon
was
not
mutagenic.
However,
it
causes
cell
transformation
in
vitro;
these
results
are
in
concordance
with
the
carcinogenicity
seen
in
in
vivo
rodent
studies.

The
Committee
recommended
a
low
dose
linear
extrapolation
approach
for
the
quantification
of
human
cancer
risk
based
on
the
most
potent
liver
tumors
in
rats
and
mice.
The
Q
1*
is
7.11
x
10­
2.
Data
submitted
by
registrants
was
inadequate
to
demonstrate
the
mode
of
action
for
oxadiazon­
induced
liver
tumors
in
rodents.

$
For
the
cancer
exposure
calculations,
the
Agency
used
multi­
year
mean
water
7
concentration
values.
The
DWLOC
cancer
is
the
concentration
in
drinking
water
as
a
part
of
the
aggregate
chronic
exposure
that
results
in
a
negligible
cancer
risk
(
1.0
x
10­
6).

$
Using
the
PRZM/
EXAMS
and
SCIGROW
model
estimates,
EDWCs
for
both
surface
(
56

g/
L)
and
ground
water
(
0.59

g/
L)
were
higher
than
the
cancer
DWLOC
(
0.49

g/
L)
(
Table
3)
and
thus,
potentially
of
concern.

Table
3.
Summary
of
Cancer
DWLOC
Calculations
for
Oxadiazon
Population
Q*
Negligible
Risk
Level1
Target
Max
Exposure2
mg/
kg/
day
Chronic
Food
Exposure
mg/
kg/
day
Max
Water
Exposure3
mg/
kg/
day
PRZM/
EXAMS
Surface
Water
EDWC
(

g/
L)
SCIGROW
Ground
Water
EDWC
(

g/
L)
Cancer
DWLOC4
(

g/
L)

U.
S.
Pop
7.11e­
02
0.000001
0.000014
0.000000
0.00001400
56
0.59
0.490000
1
DWLOC
CANCER
was
calculated
for
U.
S.
population
only.
Default
body
weights
and
consumption
values
for
calculation
of
the
DWLOCs
were:
2L/
70
kg
2
Target
Maximum
Exposure
(
mg/
kg/
day)
=
[
negligible
risk/
Q*]
3
Maximum
Water
Exposure
(
mg/
kg/
day)
=
[
Target
Maximum
Exposure
­
(
Chronic
Food
Exposure
+
Residential
Exposure
(
Lifetime
Average
Daily
Dose))]
4
Cancer
DWLOC(

g/
L)
=
[
maximum
water
exposure
(
mg/
kg/
day)
x
body
weight
(
kg)]
[
water
consumption
(
L)
x
10­
3
mg/

g]
2
As
noted
above,
the
Tier
II
PRZM/
EXAMS
model
for
estimating
surface
water
exposure
incorporates
a
standard
citrus
scenario
that
has
been
modified
to
include
a
two­
inch
layer
of
thatch.
The
linked
PRZM/
EXAMS
model
is
typically
used
by
EPA
in
estimating
pesticide
concentrations
in
surface
waters.
The
SCIGROW
model
for
estimating
groundwater
exposures
is
typically
used
for
Tier
1
screening
purposes
for
pesticides
applied
to
soils.
The
SCIGROW
model
estimates
likely
groundwater
concentration
if
the
pesticide
is
used
at
the
maximum
allowable
rate
in
areas
where
groundwater
is
exceptionally
vulnerable
to
contamination.
The
Agency
feels
that
taken
together,
these
models
provides
a
conservative,
high­
end
estimate
of
exposure
from
drinking
water.

Residential
Exposure
and
Hazard:
(
For
a
complete
discussion,
see
section
4.3.3
of
the
Human
Health
Risk
Assessment)

$
The
short­
term
and
intermediate­
term
margins
of
exposure
(
MOEs)
for
dermal
exposures
were
calculated
based
on
a
NOAEL
of
12
mg/
kg/
day
from
a
developmental
toxicity
study
in
which
pregnant
rats
were
administered
oxadiazon
via
gavage
on
Gestation
Days
six
through
15.
The
toxicity
endpoints
were
a
reduction
in
maternal
body
weight
gain,
increased
fetal
resorptions,
postimplantation
loss,
and
increased
incidence
of
incomplete
ossification
at
40
mg/
kg/
day.
Based
on
results
of
a
dermal
penetration
study,
the
dermal
absorption
rate
of
9%
was
used.

$
The
unit
risk
value
for
cancer
(
Q
1
*
=
7.11
x
10­
2
mg/
kg/
day­
1
)
was
calculated
from
studies
in
which
male
mouse
liver
adenomas
and/
or
carcinoma
tumor
rates
were
determined.

$
The
target
MOE
of
100
for
residential
exposure
scenarios
was
selected
based
on
the
8
uncertainty
factors
of
10x
for
intraspecies
variation
and
10x
for
interspecies
extrapolation.

$
Oxadiazon
is
registered
for
commercial
use
on
lawns
and
turf
grown
in
apartment/
condominium
complexes,
parks,
and
playgrounds;
therefore,
the
potential
for
post­
application
residential
exposure
exists
during
activities
such
as
mowing
the
lawn,
doing
yard
work,
and
playing
golf.

$
Negligible
inhalation
exposure
is
anticipated
in
those
exposure
scenarios,
due
to
the
low
chemical
vapor
pressure
of
oxadiazon
and
the
dilution
of
the
vapor
outdoors.
Dermal
absorption
is
the
route
of
exposure
that
is
a
concern.

$
Residential
postapplication
dermal
exposure
assessments
assumed
residents
wear
the
following
attire:
short
sleeved
shirt,
short
pants,
shoes
and
socks,
and
no
gloves
or
respirator.

$
The
duration
of
exposures
range
from
two
to
four
hours
per
day,
and
the
frequency
of
exposures
was
three
per
year
for
35
years.

$
Data
used
to
develop
residential
exposure
estimates
were
conservative
in
that
the
highest
mean
postapplication
turf
transferable
residue
value
from
the
Jazzercize
study
(
MRID
No.
43517801)
along
with
the
data
from
the
wettable
powder
formulation,
instead
of
the
more
commonly
used
granular
formulation,
were
used.

$
Other
assumptions
and
all
equations
used
for
the
assessment
of
each
exposure
scenario
can
be
found
in
the
Revised
Occupational
and
Residential
Exposure
Assessment
and
Recommendations
for
the
Reregistration
Eligibility
Decision
document
for
Oxadiazon,
dated
July
15,
2001.

Residential
Risk,
Postapplication
(
noncancer):

Utilizing
wettable
powder
application
study
data,
all
of
the
non­
cancer
risk
scenarios
developed
for
adults
and
toddlers
had
short­
term
and
intermediate­
term
dermal
MOEs
greater
than
100,
and
thus
are
not
of
concern.

Residential
Risk,
Postapplication
(
cancer):

The
Agency's
level
of
concern
for
non­
occupational
cancer
risk
is
1.0
x
10­
6.
The
cancer
risks
for
adult
residential,
dermal,
postapplication
exposures
to
oxadiazon
were
between
6.22
x
10­
6
to
7.51
x
10­
8,
indicating
that
for
some
exposure
scenarios
the
cancer
risk
slightly
exceeds
the
EPA's
level
of
concern.
9
Aggregate
Risk:

Because
there
are
no
remaining
food
tolerances
for
oxadiazon,
the
EPA
has
not
assessed
this
pesticide
with
respect
to
the
FQPA.
Additionally,
EPA
did
not
perform
an
aggregate
risk
assessment
as
part
of
this
reregistration
review
for
oxadiazon,
for
the
reasons
outlined
below.
The
DWLOC
values
for
oxadiazon
that
were
calculated
as
part
of
the
human
health
risk
assessment
are
based
on
conservative
default
values
since
no
monitoring
data
were
available
on
oxadiazon.
As
noted
previously,
data
used
to
develop
residential
exposure
estimates
were
also
conservative.
The
highest
mean
postapplication
turf
transferable
residue
values,
along
with
the
data
from
the
wettable
powder
formulation
(
instead
of
the
granular
formulation)
were
used
to
derive
those
estimates.
Thus,
combining
a
conservative
estimate
of
oxadiazon
in
drinking
water
with
a
conservative
residential
exposure
estimate
would
only
result
in
an
even
more
conservative
expression
of
aggregate
risk.

Worker
Exposure
and
Hazard:
(
For
a
complete
discussion,
see
Section
4.3
of
the
Human
Health
Risk
Assessment).

EPA
has
determined
that
there
are
potential
exposures
to
occupational
mixers,
loaders,
applicators,
or
other
occupational
handlers
during
standard
use­
patterns
associated
with
oxadiazon.

$
Fourteen
major
exposure
scenarios
were
identified
for
occupational
exposure
of
handlers.

$
These
scenarios
include
mixing,
loading
and
applying
through
the
use
of
ground
spray,
granular
and
lawn
application
methods.

$
The
exposure
scenarios
are
of
short­
term
(
1­
7
days)
and
intermediate­
term
(
1
week
to
several
weeks);
use
patterns
do
not
indicate
any
long­
term
use.

$
The
short­
term
and
intermediate­
term
MOEs
were
calculated
based
on
a
NOAEL
of
12
mg/
kg/
day
from
a
developmental
toxicity
study
in
which
pregnant
rats
were
administered
oxadiazon
via
gavage
on
Gestation
Days
six
through
15.
The
toxicity
endpoints
were
a
reduction
in
maternal
body
weight
gain,
increased
fetal
resorptions,
postimplantation
loss,
and
increased
incidence
of
incomplete
ossification
at
40
mg/
kg/
day.

$
The
EPA's
Cancer
Assessment
Review
Committee
has
classified
oxadiazon
as
"
Likely
to
be
Carcinogenic
to
Humans".
The
cancer
unit
risk
value
(
Q
1
*
=
7.11
x
10­
2
mg/
kg/
day­
1)
was
calculated
from
studies
in
which
male
mouse
liver
adenomas
and/
or
carcinoma
tumor
rates
were
determined.

$
For
risk
assessment
purposes,
inhalation
and
dermal
exposure
estimates
were
made
using
the
following
criteria:
a
career
duration
of
35
years;
a
lifetime
of
70
years;
exposure
frequencies
of
three
(
representing
the
maximum
number
of
applications
per
season)
and
thirty
(
representing
applications
to
multiple
sites
per
season).

$
The
target
MOE
of
100
for
occupational
exposure
scenarios
was
selected
based
on
the
uncertainty
factors
of
10x
for
intraspecies
variation
and
10x
for
interspecies
extrapolation.

$
Since
the
effects
from
dermal
and
inhalation
exposure
are
based
on
the
same
oral
study
(
i.
e.
rat
development
study),
the
doses
for
these
routes
and
durations
were
aggregated.
10
$
The
percent
absorbed
following
dermal
exposure
was
taken
to
be
9%.

Worker
Risk
(
noncancer):

$
Calculation
of
non­
cancer
occupational
risk
based
on
combined
dermal
and
inhalation
exposure
indicates
that
only
one
scenario
(
i.
e.
low­
pressure
handwand­
wettable
powder
formulations)
had
an
MOE
of
46
with
the
highest
feasible
level
of
mitigation.

$
All
other
potential
exposure
scenarios
provide
at
least
one
application
rate
with
total
MOEs

100
at
baseline,
or
with
PPE
or
engineering
controls.

$
Dermal
exposure,
rather
than
inhalation
exposure,
appears
to
be
the
main
contributor
to
the
total
MOE
for
the
low­
pressure
handwand­
wettable
powder
formulation
scenario
as
well
as
the
majority
of
occupational
exposures.

Worker
Risk
(
cancer):

The
Agency's
level
of
concern
for
cancer
risk
begins
at

1.0
x
10­
4.
The
Agency
attempts
to
put
additional
safeguards
in
place
to
decrease
the
risk
(
i.
e.
mitigate)
to

1.0
x
10­
6,
when
possible.

$
With
respect
to
oxadiazon,
the
Agency
developed
a
number
of
scenarios
for
potential
occupational
exposure,
ranging
from
mixing
and
loading
wettable­
powder
formulations
to
applying
granular
formulations.

$
Based
on
those
scenarios,
the
Agency
estimates
that
the
risk
of
developing
cancer
from
occupational
dermal
and
inhalation
exposures
to
oxadiazon
ranges
from
1.65
x
10­
2
to
4.66
x
10­
7
during
"
baseline"
conditions
(
i.
e.
long
pants,
long­
sleeves,
no
gloves).

$
Cancer
risk
ranges
from
1.05
x
10­
3
to
1.38
x
10­
7
when
personal
protective
equipment
(
PPE;
i.
e.
long
pants,
long­
sleeved
shirt,
with
chemical­
resistant
gloves)
was
used.

$
The
Agency
estimates
that
cancer
risk
decreases
to
a
range
of
4.92
x
10­
5
to
1.10
x
10­
8
with
engineering
controls.
Engineering
controls
included
the
use
of
PPE
along
with
water
soluble
packaging
for
wettable
powder
formulations.

$
Overall
these
data
suggest
that
when
PPE
and
engineering
controls
are
used,
none
of
the
evaluated
scenarios
have
cancer
risks
that
exceed
1.0
x
10­
4
(
the
Agency's
level
of
concern).

Worker
Risk,
Postapplication
(
noncancer):

°
For
short­
and
intermediate­
term
non­
cancer
risks,
mowing
(
e.
g.
golf
courses,
roadsides,
and
sod
farms)
and
harvesting
(
e.
g.
sod
farms)
activities
were
considered
for
postapplication
occupational
exposure.

$
All
occupational
postapplication
activities
had
MOEs
of
300­
10000.
11
Worker
Risk,
Postapplication
(
cancer):

Cancer
risks
for
occupational
postapplication
scenarios,
including
the
current
minimum12
hour
period
in
which
reentry
is
prohibited,
were
estimated
to
range
from
9.92
x
10­
6
to
3.01
x
10­
7
.

Ecological
Risk
Characterization
To
estimate
potential
ecological
risk,
the
Agency
integrates
the
results
of
exposure
and
ecotoxicity
studies
using
the
quotient
method.
Risk
quotients
(
RQs)
are
calculated
by
dividing
exposure
estimates
by
ecotoxicity
values,
both
acute
and
chronic,
for
various
wildlife
species.
RQs
are
then
compared
to
the
levels
of
concern
(
LOCs).
Generally,
the
higher
the
RQ,
the
greater
the
potential
risk.
The
potential
risks
identified
below
can
be
further
characterized
by
considering
when,
where
and
how
a
specific
pesticide
is
used.

Environmental
Fate
and
Transport
°
Environmental
fate
studies
indicate
that
oxadiazon
persists
in
the
environment
bound
to
organic
matter.
°
In
clear,
shallow
bodies
of
water,
oxadiazon
not
bound
to
organic
matter
may
be
degraded
by
sunlight.
Alternatively,
oxadiazon
is
defined
as
a
light­
dependent
peroxidizing
herbicide
(
LDPH),
which
suggests
that
toxicity
is
greater
in
the
presence
of
light.
°
Studies
indicate
that
after
application
to
soil,
oxadiazon
remains
near
the
surface,
and
can
be
transported
via
runoff
to
nearby
surface
water
bodies.

$
Leaching
from
surface
soils
to
groundwater
is
expected
to
be
low
or
negligible,
unless
the
soil
is
very
porous.

$
Since
this
stable
compound
can
bind
to
particulate
and
organic
matter,
oxadiazon
residues
can
accumulate
in
sediments
at
the
bottom
of
bodies
of
water.

$
Oxadiazon
may
accumulate
in
aquatic
organisms
such
as
fish;
however,
as
observed
in
studies
using
bluegill
sunfish,
the
tendency
toward
bio­
accumulation
can
be
offset
by
a
rapid
rate
of
removal.
12
Nontarget
Aquatic
Organism
Risk
Acute
Assessments
$
In
studies
using
freshwater
fish
(
Rainbow
trout/
Bluegill)
and
estuarine
fish
(
Sheepshead
minnows),
oxadiazon
was
moderately
toxic
on
an
acute
basis
(
LC
50
=
0.88
ppm
and
1.5
ppm,
respectively).

$
In
studies
with
estuarine/
marine
invertebrates
(
Mysid),
oxadiazon
demonstrated
a
high
acute
toxicity
(
EC
50
=
0.27
ppb),
but
the
chemical
appears
to
be
moderately
toxic
on
an
acute
basis
to
freshwater
invertebrates
(
Daphnids
LC
50
=
2.18
ppm).

$
Limited
data
show
that
oxadiazon
is
toxic
to
non­
vascular
aquatic
plants
(
marine
diatoms
EC
50
=
5.2
ppb)
and
vascular
aquatic
plants
(
duckweed
EC
50
=
41
ppb).

$
The
EPA's
risk
assessments
suggest
that
acute
exposures
pose
low
risk
to
fish
(
RQ
=
0.1­
0.2)
and
invertebrates
(
RQ=
0.3
­
0.5),
there
is
some
uncertainty
about
the
role
of
sunlight
on
oxadiazon
toxicity
in
clear,
shallow
bodies
of
water.

$
For
aquatic
plants,
RQs
for
acute
exposure
are
relatively
high,
ranging
from
1.1
to
4.2
for
duckweed,
and
8.5
to
33
for
diatoms,
depending
on
application
rates
and
formulation.

Chronic
Assessments
$
To
assess
the
risk
to
freshwater
fish
from
chronic
exposure
to
oxadiazon,
a
No
Observeable
Adverse
Effect
Concentration
(
NOAEC)
of
0.88
ppb
and
a
Lowest
Observeable
Adverse
Effect
Concentration
(
LOAEC)
of
1.7
ppb
were
used,
based
on
effects
on
egg
hatches
in
studies
using
Rainbow
trout.

$
To
assess
the
risk
to
freshwater
invertebrates
from
chronic
exposure
to
oxadiazon,
a
NOAEC
of
30.0
ppb
and
a
LOAEC
of
35.0
ppb
were
used,
based
on
the
incidence
of
reproductive
effects
in
studies
using
Daphnids.

$
Chronic
exposure
to
oxadiazon
may
result
in
chronic
risk
to
freshwater
and
estuarine/
marine
fish.
RQs
range
from
94
to
139
(
freshwater)
and
55
to
81
(
estuarine/
marine),
depending
on
application
rate
and
formulation.

$
Chronic
exposure
to
oxadiazon
may
result
in
chronic
risk
to
freshwater
and
estuarine/
marine
invertebrates.
RQs
range
from
2.9
to
4.5
(
freshwater)
and
23
to
37
(
estuarine/
marine),
depending
on
application
rate
and
formulation.

Oxadiazon
residues
can
accumulate
in
sediments
and
may
increase
the
risk
from
chronic
exposure
of
benthic
and
epibenthic
organisms
(
aquatic
organisms
that
live
in
or
on
the
sediment)
to
the
pesticide.
In
order
to
better
understand
this
potential
risk,
EPA
is
requiring
appropriate
sediment
toxicity
testing
(
acute
and
chronic)
on
this
compound.
Also,
enhanced
toxicity
through
exposure
to
high
levels
of
solar
radiation
may
increase
toxic
risk
to
aquatic
organisms
that
inhabit
small,
shallow
water
bodies.
Therefore,
EPA
is
requiring
a
study
on
the
phototoxicity
of
oxadiazon
in
fathead
minnows.
13
Nontarget
Terrestrial
Organism
Risk
Mammals
To
estimate
the
potential
adverse
effect
of
a
chemical
on
wild
mammals,
the
concentration
of
the
chemical
in
the
diet
that
is
expected
to
be
acutely
toxic
to
50%
of
the
test
animals
is
determined
by
dividing
the
LD
50
value
by
the
per
cent
body
weight
consumed.
An
RQ
is
then
determined
by
dividing
the
estimated
environmental
concentration
by
the
acute
toxicity
value.
RQ
values
are
calculated
for
four
different
kinds
of
food
(
i.
e.
short
grass,
tall
grass,
forage/
insects,
and
seeds).
The
per
cent
body
weight
consumed
by
herbivores
and
insectivores
corresponding
to
three
weight
categories
(
15,
35,
and
1000
g)
is
assumed
to
be
95%,
66%,
and
15%,
respectively.

$
In
studies
with
rats,
oxadiazon
was
practically
non­
toxic
on
an
acute
basis
(
LD
50
>
5,000
mg/
kg).
Reproductive
effects
were
noted
at
>
200
ppm
that
resulted
in
inactive
mammary
tissue
and
fetal/
neonatal
death.

$
According
to
the
EPA's
risk
assessment,
at
proposed
use
rates
(
2.0
­
4.0
lbs
ai/
A),
oxadiazon
should
not
pose
an
acute
risk
to
mammals
(
RQ
<
0.2).

$
At
application
rates
of
2.0
­
4.0
lbs
ai/
A
(
2
applications/
6
months)
and
two
split
applications
(
1.0
lbs
ai/
A
applied
4
times/
6
months
and
1.3
lbs
ai/
A
applied
3
times/
6
months),
model
estimates
indicate
that
oxadiazon
may
pose
a
chronic
risk
to
mammals
that
eat
plants
and
insects.
RQs
range
from
1.5
to
9.9.

Birds
$
In
studies
with
avian
species
(
Northern
Bobwhite
quail
and
mallard
duck),
oxadiazon
appears
to
be
practically
non­
toxic
on
a
subacute
basis
(
LC
50
>
5,000
ppm
for
both
species)
and
an
acute
basis
(
LD
50>
2,150
mg/
kg
and
LD
50
=
1,040
mg/
kg,
respectively).

$
In
chronic
studies,
no
reproductive
effects
were
observed
at
500
ppm.
At
greater
than
1,000
ppm,
mortality
was
observed
in
adult
females
(
Bobwhite
quail).

$
Chronic
exposure
to
oxadiazon
may
result
in
low
toxic
risk
to
birds
that
feed
on
plants
and
grass
(
e.
g.
ducks,
geese;
RQs
=
1.0
­
2.0).
The
split
application
scenario
appears
to
lower
the
risk
(
RQ
<
1).

$
Birds
may
be
exposed
to
granular
pesticides
through
ingestion
when
foraging
for
food
or
grit.
Model
estimates
suggested
no
acute
risk
to
birds
from
exposure
to
granular
oxadiazon
(
RQ
<
1.5
­
2.0).

Insects
$
Oxadiazon
was
practically
non­
toxic
to
honey
bees
in
acute
exposure
studies
(
LD
50
>
25
µ
g/
bee).
14
Endangered
Species
Risk
The
endangered
species
LOCs
for
liquid
and
granular
formulations
of
oxadiazon
are
exceeded
for
chronic
risk
to
birds
and
mammals,
and
acute
and
chronic
risk
to
freshwater
and
estuarine
fish,
invertebrates,
and
aquatic
vascular
plants.
Although
the
data
are
outstanding,
it
is
likely
that
endangered
terrestrial
plants
are
at
risk
since
oxadiazon
is
an
herbicide.
Per
the
Endangered
Species
Act,
the
Agency
is
currently
engaged
in
a
Proactive
Conservation
Review
with
the
Fish
and
Wildlife
Service
and
the
National
Marine
Fisheries
Service.
Subsequent
to
the
completion
of
this
process,
the
Agency
will
reassess
the
potential
risk
of
oxadiazon
to
federally
listed
threatened
and
endangered
species.

Summary
of
Pending
Data
The
following
data
requirements
have
been
initially
identified
by
the
Agency:

Toxicology
Data
$
28­
Day
Inhalation
Study
Product
and
Residue
Chemistry
Data
$
Current
Confidential
Statement
of
Formula
containing
nominal
concentration
and
upper
limits
for
all
components,
and
the
lower
limits
for
the
active
ingredient.

Occupational
Exposure
Data
$
Concurrent
Transfer
Coefficient
measurements
along
with
Transferable
Turf
Residue
studies.

Ecological
Effects
$
Early­
Life
Stage
Estuarine
Fish
°
Life
Cycle
Estuarine
Invertebrate
°
Seedling
Emergence
and
Vegetative
Vigor­
using
a
liquid
TEP
to
represent
both
granular
and
liquid
formulations
(
note
in
the
case
that
liquid
formulations
are
not
supported
for
reregistration,
only
seedling
emergence
testing
would
be
required;
vegetative
vigor
testing
is
not
required
for
granular
formulations)
°
Aquatic
plant
testing
(
TierII)
is
required
because
oxadiazon
has
outdoor
nonresidential
terrestrial
uses
that
may
move
off­
site
by
runoff
and/
or
aerial
spray
drift.
The
following
species
should
be
tested
at
Tier
II:
Kirchneria
subcapitata
(
Selenastrum
capricornutum),
Skeletonema
costatum,
and
Anabaena
flos­
aquae.
°
Acute
and
Chronic
Sediment
Toxicity
Testing
­
Oxadiazon
shows
a
high
K
OC,
combined
with
a
high
persistence
exhibited
in
the
aerobic
soil
metabolism,
and
the
anaerobic
aquatic
metabolism
(>
10
days).
These
fate
properties
indicate
that
there
may
be
risk
to
benthic­
15
dwelling
aquatic
invertebrates,
however
the
potential
for
risk
cannot
be
assessed
until
data
have
been
submitted.
The
Chronic
Sediment
Toxicity
Testing
data
requirement
is
triggered,
with
Chironomus
tentans
and
the
Acute
Chronic
Sediment
Toxicity
Testing
data
requirement
is
triggered,
with
both
Hyalella
azteca,
and
Chironomus
tentans.
°
Phototoxicity
studies
on
fathead
minnow.
A
subchronic
exposure
duration
would
be
adequate
for
proof
of
concept.
Behavioral
observations
should
be
conducted
in
addition
to
mortality,
growth,
and
morphology.
All
studies
should
be
conducted
under
defined
light
conditions.
