U.
S.
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
DC
20460
.
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
May
8,
2001
DPBarcode:
D273599
PC
Code
109001
MEMORANDUM
SUBJECT:
Tier
I
Estimated
Environmental
Concentrations
of
Oxadiazon
FROM:
José
Luis
Meléndez,
Chemist
Environmental
Risk
Branch
V
Environmental
Fate
and
Effects
Division
(
7507C)

THROUGH:
Mah
T.
Shamim,
Ph.
D.,
Chief
Environmental
Risk
Branch
V
Environmental
Fate
and
Effects
Division
(
7507C)

TO:
Margaret
Rice,
Acting
Branch
Chief
Veronique
LaCapra,
CRM
and
Tom
Myers,
Team
Leader
Special
Review
and
Reregistration
Division
(
7508C)

This
memo
presents
the
Tier
I
Estimated
Environmental
Concentrations
(
EECs)
for
oxadiazon,
calculated
using
FIRST
(
surface
water)
and
SCIGROW
(
ground
water)
for
use
in
the
human
health
risk
assessment.
For
surface
water,
the
acute
(
peak)
value
is
246
ppb
and
the
annual
average
value
is
100
ppb.
The
groundwater
screening
concentration
is
0.6
ppb.
These
values
generally
represent
upper­
bound
estimates
of
the
concentrations
that
might
be
found
in
surface
water
and
groundwater
due
to
the
use
of
oxadiazon
on
turf,
which
is
the
major
use
of
the
chemical.

Background
Information
on
FIRST:

FIRST
is
a
new
screening
model
designed
to
estimate
the
pesticide
concentrations
found
in
water
for
use
in
drinking
water
assessments.
It
provides
high­
end
values
on
the
concentrations
that
might
be
found
in
a
small
drinking
water
reservoir
due
to
the
use
of
pesticide.
Like
GENEEC,
the
model
previously
used
for
Tier
I
screening
level,
FIRST
is
a
single­
event
model
(
one
run­
off
event),
but
can
account
for
spray
drift
from
multiple
applications.
FIRST
takes
into
consideration
the
so
called
Index
Drinking
Water
Reservoir
by
representing
a
larger
field
and
pond
than
the
standard
GENEEC
scenario.
The
FIRST
scenario
includes
a
427
acres
field
immediately
adjacent
to
a
13
acres
reservoir,
9
feet
deep,
with
continuous
flow
(
two
turnovers
per
year).
The
pond
receives
a
spray
drift
event
from
each
application
plus
one
runoff
event.
The
runoff
event
moves
a
maximum
of
8%
of
the
applied
pesticide
into
the
pond.
This
amount
can
be
reduced
due
to
degradation
on
field
and
the
2
effect
of
binding
to
soil.
Spray
drift
is
equal
to
6.4%
of
the
applied
concentration
from
the
ground
spray
application
and
16%
for
aerial
applications.

FIRST
also
makes
adjustments
for
the
percent
crop
area.
While
FIRST
assumes
that
the
entire
watershed
would
not
be
treated,
the
use
of
a
PCA
is
still
a
screen
because
it
represents
the
highest
percentage
of
crop
cover
of
any
large
watershed
in
the
US,
and
it
assumes
that
the
entire
crop
is
being
treated.
Various
other
conservative
assumptions
of
FIRST
include
the
use
of
a
small
drinking
water
reservoir
surrounded
by
a
runoff­
prone
watershed,
the
use
of
the
maximum
use
rate,
no
buffer
zone,
and
a
single
large
rainfall
Background
Information
on
SCIGROW:

SCIGROW
provides
a
groundwater
screening
exposure
value
to
be
used
in
determining
the
potential
risk
to
human
health
from
drinking
water
contaminated
with
the
pesticide.
Since
the
SCIGROW
concentrations
are
likely
to
be
approached
in
only
a
very
small
percentage
of
drinking
water
sources,
i.
e.,
highly
vulnerable
aquifers,
it
is
not
appropriate
to
use
SCIGROW
for
national
or
regional
exposure
estimates.

SCIGROW
estimates
likely
groundwater
concentrations
if
the
pesticide
is
used
at
the
maximum
allowable
rate
in
areas
where
groundwater
is
exceptionally
vulnerable
to
contamination.
In
most
cases,
a
large
majority
of
the
use
area
will
have
groundwater
that
is
less
vulnerable
to
contamination
than
the
areas
used
to
derive
the
SCIGROW
estimate.

Modeling
Inputs
and
Results:

Tables
1
and
2
summarize
the
input
values
used
in
the
model
runs
for
FIRST
1.0
and
SCIGROW,
respectively.
The
lowest
non­
sand
K
D
was
used
in
FIRST
1.0.
The
median
K
OC
value
was
used
in
SCIGROW.
The
available
aerobic
soil
metabolism
half­
life
for
oxadiazon
was
extremely
high.
For
FIRST,
stability
was
assumed,
while
the
extrapolated
value
of
841
days
was
used
in
SCIGROW.
The
modeling
results
associated
with
maximum
allowable
rate
per
year
(
4
lb
ai/
A
applied
twice
at
6
months
interval)
are
presented
in
Table
3.
Attached
to
this
memo
are
copies
of
the
original
printouts
generated
from
FIRST
and
SCIGROW
runs.

cc:
Nancy
McCarroll
(
HED)
3
Table
1.
Environmental
Fate
and
Other
Input
Parameters
for
the
Estimation
of
Oxadiazon
using
FIRST
Parameter
Value
Source
Water
Solubility
(
25

C)
1
ppm
One­
Liner
Hydrolysis
Half­
Life
(
pH
7)
stable
MRID
41863603
Aerobic
Soil
Metabolism
Half­
Life
(
from
6
values)
essentially
stable
MRID
42772801
Aerobic
Aquatic
Metabolism
Half­
life
not
available
N/
A
Aqueous
Photolysis
Half­
Life
2.75
days
MRID
41897201
Soil/
Water
Partition
Coefficient
(
Lowest
non­
sand
K
d)
16.9
MRID
41898202
Pesticide
is
Wetted­
In
Yes
Labels
PCA
(
turf)
0.87
Default
Depth
of
Incorporation
(
Broadcast)
0.0
inch
Labels
Table
2.
Environmental
Fate
Input
Parameters
for
the
Estimation
of
Oxadiazon
using
SCIGROW.

Parameter
Value
Source
Organic
Carbon
Partition
Coefficient
(
median
K
OC)
2376
MRID
41898202
Aerobic
Soil
Metabolism
Half­
Life
(
median)
841
days
MRID
42772801
Table
3.
Modeling
Results
for
Use
of
Oxadiazon
on
(
Turf)
Golf
Courses
Parameter
Value
Source
Application
Method
Ground
Spray
Labels
Application
Rate
4.0
lb
a.
i./
A
Registrant
Applications
Permitted
per
Year
2
Registrant***

Application
Interval
(
days)
182
Registrant
FIRST
1.0
Peak
Untreated
Water
Concentration
246
ppb
N/
A
FIRST
1.0
Annual
Average
Untreated
Water
Concentration
100
ppb
N/
A
SCIGROW
Ground
Water
Concentration
0.6
ppb
N/
A
***
The
Registrant
supports
multiple
applications,
at
lower
application
rates.
4
RESULTS
OBTAINED
USING
FIRST
RUN
No.
1
FOR
OXADIAZON
ON
Turf
(
Golf
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Kd
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
4.000(
8.000)
2
182
16.9
1.0
GROUND(
6.4)
87.0
.0
FIELD
AND
RESERVOIR
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
RESERVOIR)
(
RES.­
EFF)
(
RESER.)
(
RESER.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.00
0
N/
A
2.75­
341.00
.00
341.00
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
MAY
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
246.388
100.013
RESULTS
OBTAINED
USING
SCIGROW
RUN
No.
1
FOR
OXADIAZON
INPUT
VALUES
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
APPL
(#/
AC)
APPL.
URATE
SOIL
SOIL
AEROBIC
RATE
NO.
(#/
AC/
YR)
KOC
METABOLISM
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
4.000
2
8.000
2376.0
841.0
GROUND­
WATER
SCREENING
CONCENTRATIONS
IN
PPB
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.592986
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
A=
836.000
B=
2381.000
C=
2.922
D=
3.377
RILP=
1.821
F=
­
1.130
G=
.074
URATE=
8.000
GWSC=
.592986
