U.
S.
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
DC
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
PC
Code:
109001
DP
Code:
D290003
MEMORANDUM
DATE:
June
11,
2003
SUBJECT:
Comments
to
60­
Day
Response
by
Registrant
to
the
EFED
Reregistration
Elegibility
Decision
Chapter
of
Oxadiazon
TO:
Mark
J.
Seaton,
Ph.
D.,
Chemical
Review
Manager
Margaret
Rice,
Branch
Chief
Reregistration
Branch
II
Special
Review
and
Reregistration
Division
(
7508C)

FROM:
Faruque
A.
Khan,
Ph.
D.,
Environmental
Scientist
Miachel
Rexrode,
Ph.
D.,
Fishery
Biologist
José
Luis
Meléndez,
Chemist
Environmental
Fate
and
Effects
Division
THROUGH:
Mah
T.
Shamim,
Ph.
D.,
Chief
Environmental
Risk
Branch
V
Environmental
Fate
and
Effects
Division
The
registrant
of
oxadiazon,
Bayer
Environmental
Science,
submitted
a
60­
Day
Response
to
the
Environmental
Fate
and
Ecological
Effects
(
EFED)
Risk
Assessment
for
the
Reregistration
Elegibility
Decision
of
Oxadiazon.
The
registrant
presented
the
following
comments:

Comment:
The
registrant's
new
name
is
Bayer
Environmental
Science.
Response:
All
references
to
"
Aventis"
or
"
Aventis
Environmental
Science"
will
be
changed
to
"
Bayer"
or
"
Bayer
Environmental
Science."

Comment:
The
Tier
II
Aquatic
Plant
Testing
(
123­
2)
has
been
met
by
submission
of
MRID#
41610108
and
41610105.
Response:
EFED
agrees,
the
requirement
does
not
apply.
The
EFED
Risk
Assessment
for
the
Reregistration
Eligibility
Decision
of
Oxadiazon
will
be
revised
accordingly.

Comment:
EFED
required
Acute
and
Chronic
Sediment
Toxicity
Testing
for
oxadiazon
(
similar
comments
appear
in
the
cover
memo,
and
in
Appendix
G).
The
registrant
believes
that
the
requirement
may
not
be
applicable
for
this
chemical.
Response:
Oxadiazon
is
a
persistent,
lipophilic
compound
that
has
a
strong
capacity
to
bind
to
particulate
and
organic
carbon
in
the
water
column.
This
combination
of
chemical/
physical
attributes
and
the
relatively
2
high
toxicity
profile
to
fish
and
invertebrates
suggest
concern
for
accumulation
in
the
sediments.
Since
sediments
can
act
as
a
repository
for
lipophilic
compounds,
there
can
be
direct
impact
to
aquatic
organisms
through
respiration,
ingestion,
dermal
contact,
and/
or
indirect
impact
through
alterations
of
the
food
chain.
According
to
monitoring
that
has
been
conducted
on
aquatic
ecosystems
in
suburban
watersheds,
one
of
the
chemicals
most
frequently
detected
in
water
(
low
ppt)
and
sediment
(
low
ppb)
was
oxadiazon
(
Armbrust
et.
al.,
2003).
Both
liquid
and
granular
formulations
labels
of
oxadiazon
specify
that
the
chemical's
effectiveness
is
improved
if
it
is
wetted
in
after
application.
Furthermore,
both
labels
recommend
mowing
the
grass
prior
to
application.
Although
the
turf
could
present
a
barrier
towards
erosion,
it
also
appears
that
oxadiazon
can
quickly
runoff
during
the
period
after
the
application,
but
thereafter,
the
chemical
could
reach
soil
surfaces
or
be
intercepted
by
the
foliage.
The
exact
mechanism
of
runoff
for
oxadiazon
from
a
turf
site
to
an
adjacent
body
of
water
can
show
variation
with
time.
While
oxadiazon
is
expected
to
bind
to
soil
particles,
the
turf
scenarios
offer
vegetation
interception.
EFED
believes
that
the
sediment
testing
outlined
in
the
RED
is
consistent
with
Division
policy
and
is
still
a
requirement.

Comment:
EFED
required
a
phototoxicity
study
on
fathead
minnow
because
oxadiazon
is
a
LDPH,
which
could
be
the
cause
of
enhanced
toxicity
in
the
presence
of
solar
radiation.
The
registrant
objects
to
this
requirement.
Similar
comments
appear
in
the
cover
memo,
and
Chapter
3
of
the
document.
Response:
Enhanced
toxicity
of
oxadiazon
to
aquatic
organisms
after
light
exposure
is
an
uncertainty.
The
inhibition
of
protoporphyrinogen
oxidase,
the
rapid
accumulation
of
protoporphyrin
IX
with
the
resulting
generation
of
singlet
oxygen
(
free
radicals)
and
eventual
cell
membrane
destruction
suggest
that
exposure
to
this
compound
may
increase
toxicity
to
aquatic
organisms.
This
issue
was
evaluated
by
EFED's
Aquatic
Biology
Tech
Team
(
ABTT)
with
recommendations
that
phototoxicity
studies
be
conducted
on
"
herbicides
with
this
mode
of
action
to
determine
if
animals
exposed
to
LDPHs
and
intense
light
(
similar
to
sunlight)
show
increased
toxicity
relative
to
controls
exposed
to
LDPHs
and
low
intensity
light.
The
results
of
these
studies
will
help
to
determine
if
animals
that
are
exposed
to
sunlight
in
LDPH
use
areas
are
at
higher
risk
than
guideline
toxicity
studies
suggest".

The
ABTT
has
requested
that
a
LDPH
phototoxicity
protocol
be
submitted
for
review
by
the
registrants
for
evaluation
by
EFED
prior
to
study
initiation
since
fish
and
other
aquatic
organisms
are
expected
to
be
exposed
to
LDPHs
through
run­
off.
Aquatic
organisms
inhabiting
small,
shallow
water
bodies,
exposed
to
high
levels
of
solar
radiation
would
be
expected
to
be
at
greatest
risk
for
potential
phototoxic
effects.
Therefore,
the
ABTT
is
requesting
a
small
fish
species
be
used
in
a
phototoxicity
assay
to
assess
the
potential
of
light
enhanced
LDPH
toxicity.

The
ABTT
requests
that
the
study
adequately
address
the
following
issues
and
suggests
the
paper,
"
Photoenhanced
Toxicity
of
a
Carbamate
Insecticide
to
Early
Life
Stage
Anuran
Amphibians",
and
other
studies
in
the
peer­
reviewed
scientific
literature
serve
as
sources
of
additional
guidance:

Species
The
fathead
minnow
may
be
an
appropriate
test
species
because
of
existing
toxicity
protocols
which
may
be
adapted
for
this
study.

Exposure
Duration
A
subchronic
exposure
duration
would
be
adequate
for
proof
of
principle.
A
single
exposure
may
not
allow
adequate
time
for
porphyrin
accumulation,
however,
a
life­
cycle
is
not
necessary
to
identify
a
phototoxic
effect.
3
Dosing
A
range
finding
study
should
be
conducted
under
defined
low
light
conditions
to
identify
an
LC50
value
and
lower
dose
levels
expected
to
be
similar
to
controls.
Doses
used
in
the
phototoxicity
study
should
not
be
expected
to
result
in
significant
mortality
in
low
light
controls.
Dissolved
concentrations
of
the
test
chemical
should
be
confirmed
by
an
appropriate
analytical
method.

Endpoints
Behavioral
observations
should
be
made
in
addition
to
measurements
of
mortality,
growth,
weight,
morphology,
and
appearance.
Ideally,
measurements
of
protoporphyrin
and
heme
concentrations
in
the
blood
and
protox
activity
in
the
liver
of
each
test
organisms
should
be
made.

Light
sources
Artificial
light
may
be
preferred
to
natural
light
that
will
vary
in
different
regions
and
seasons
as
well
as
with
weather.
If
artificial
light
is
used,
the
light
should
resemble
full,
natural
sunlight
as
closely
as
possible,
particularly
around
400
nm.
The
most
important
wavelength
for
porphyrin
induced
phototoxicity
in
~
400
nm.
No
matter
what
the
light
source,
the
duration
and
intensity
of
UV
and
visible
light
should
be
reported
at
all
wavelengths
(
200­
800
nm).
At
this
point
EFED
does
not
have
a
specific
recommendation
for
an
artificial
light
source.

Dark,
Light,
and
Positive
Controls
As
this
study
is
intended
to
identify
potential
effects
of
light
on
LDPH
toxicity,
an
appropriate
study
protocol
should
include
a
dark,
or
low
light,
control
group.
Another
group
not
exposed
to
chemicals
but
exposed
to
full
light
should
be
included
(
a
full
light
control).
In
addition
to
the
dark
and
light
controls,
a
positive
control
group
using
protoporphyrin
IX
may
be
useful.

Exposure
Chambers
and
Light
Filters
Light
intensity
should
be
measured
inside
test
chambers
if
glass
or
any
other
material
is
placed
between
the
light
source
and
the
test
animals.
Any
filters
should
be
cured
under
the
study
light
for
72­
hours
prior
to
study
initiation
to
ensure
consistent
transmittance.

References:

1
Matringe,
M.,
J.­
M.
Camadro,
P.
Labbe,
and
R.
Scalla.
1989.
Protoporphyrinogen
oxidase
as
a
molecular
target
for
diphenyl
ether
herbicides.
Biochem.
J.
260:
231­
235.

2
Birchfield,
N.
B.,
and
J.
E.
Casida.
1997.
Protoporphyrinogen
oxidase
of
mouse
and
maize:
Target
site
selectivity
and
thiol
effects
on
peroxidizing
herbicide
action.
Pesticide
Biochemistry
and
Physiology
57,
36­
43.

3
Halling,
B.
P.,
D.
A.
Yuhas,
V.
F.
Fingar,
and
J.
W.
Winkleman.
1994.
"
Protoporphyrinogen
oxidase
inhibitors
for
tumor
therapy"
in
Porphyric
Pesticides:
Chemistry,
Toxicology,
and
Pharmaceutical
Applications,
(
S.
O.
Duke
and
C.
A.
Rebeiz,
Eds.)
pp.
280­
290,
American
Chemical
Society
Symposium
Series
559,
Am.
Chem.
Soc.,
Washington,
D.
C.,
1994.

4
Birchfield,
N.
B.
Protoporphyrinogen
Oxidase
as
a
Herbicide
Target:
Characterization
of
the
[
3
H]
Desmethylflumipropyn
Binding
Site.
Dissertation.
University
of
California,
Berkeley.
1996.

5
American
Society
for
Testing
and
Materials.
1994.
Standard
guide
for
conducting
the
frog
embryo
4
teratogenesis
assay­
Xenopus.
E
1439­
91.
In
Annual
Book
of
ASTM
Standards,
Vol
11.5,
pp.
825­
835.
Philadelphia,
PA.

Comment:
Environmental
Risk
Conclusions.
d.
Likelihood
of
Water
Contamination:
"
The
turf
itself
offers
a
vegetative
interception
layer
(
including
thatch),
that
prevents
rapid
deposition
of
the
oxadiazon
on
the
surface
of
the
soil."
Chapter
2:
Introduction.
b.
Use
Characterization:
"
Since
efficacy
(
pre
emergent
control
is
based
on
oxadiazon
reaching
and
remaining
in
the
soil,
product
labels
may
specify
to
mow,
if
necessary,
before
application,
and
to
irrigate,
if
rain
is
not
expected
shortly."
Chapter
4:
Environmental
Fate
and
Transport
Assessment.
Section:
Fate
and
Transport
Processes
­
Summary:
"
Thus,
oxadiazon
can
be
transported
as
sorbed
species
to
erodible
soil
particles
via
surface
runoff
to
nearby
surface
water
bodies."
The
registrant
points
out
that
"
soil
particles
are
not
usually
eroded
from
established
turf
and
so
this
route
of
transport
to
surface
water
bodies
is
unlikely."
Response:
Taken
individually,
each
statement
makes
sense
in
context.
However,
EFED
recognizes
that
all
the
sentences
do
not
appear
to
be
consistent,
and
will
amend
them
in
the
EFED
Chapter
to
clarify
their
meaning
and
context.

Comment:
The
registrant
indicates
that
the
percentage
of
use
of
oxadiazon
on
golf
courses
is
77%
instead
of
65%.
The
former
value
agrees
with
the
HED
report.
Response:
EFED
agrees
and
will
make
the
necessary
changes
in
the
RED.

Comment:
Usage
information
was
obtained
from
BEADS
Qualitative
Use
Assessment,
"
Appendix
K,"
which
is
not
present
in
the
document.
Response:
EFED
submits
that
the
correct
identification
of
the
appendix
is
Appendix
H.

Comment:
RP­
17623
and
G
315
are
product
codes,
and
not
trade
names.
Response:
This
will
be
corrected
in
the
EFED
document.

Comment:
The
rat
NOAEC
is
200
ppm.
It
is
stated
in
several
places
that
it
is
100
ppm
(
Table
2,
Table
C­
5,
Appendix
F).
Response:
EFED
will
make
this
correction
and
the
RQ's
will
be
recalculated
to
reflect
this
change.

Comment:
The
avian
reproduction
study
using
mallard
resulted
in
a
NOAEC>
1000
ppm
(
highest
dose
tested).
Since
the
study
did
not
define
a
NOAEC,
the
study
was
classified
as
supplemental.
The
registrant
requests
reconsideration
of
the
study
classification.
Response:
EFED
agrees
(
the
highest
terrestrial
EEC
is
960
ppm)
and
will
make
the
appropriate
changes
in
the
RED.

Comment:
Individual
growth
data
for
the
rainbow
trout
had
not
been
provided
by
the
registrant.
These
data
were
provided
with
this
submission.
Response:
The
data
has
been
evaluated
and
the
rainbow
trout
early
life
stage
study
(
MRID41811601)
has
been
upgraded
to
core.
5
Comment:
In
Appendix
C:
Ecological
Toxicity
Data.
Section:
Aquatic
Plants,
a
sentence
reads:
"
Tier
I
of
Tier
II
Aquatic
Plant
growth
testing
using
the
TEP
is
required
for
fungicides."
Response:
Inadvertently
the
word
fungicides
was
used
instead
of
herbicides.
This
will
be
corrected
in
the
final
report.

Comment:
In
Appendix
C.
Table
C.
13,
a
study
report
was
not
referenced.
Response:
The
cited
study
will
be
referenced:
Anabaena
flos­
aquae
study
(
MRID#'
s
41610108
and
42659001).

Comment:
Chapter
5:
Drinking
Water
Assessment:
EFED
used
the
tiered
approach
in
estimating
drinking
water
concentrations.
The
reported
concentrations
in
the
EFED
report
are
the
most
conservative
(
Tier
I).
At
a
later
time,
HED
requested
additional
refinements
and
EFED
issued
a
revised
drinking
water
memorandum.
The
revised
Estimated
Drinking
Water
Concentrations
(
EDWCs)
using
standard
Percent
of
Crop
Area
(
PCA)
for
golf
courses
produced
the
worst
case
drinking
water
exposure
assessment
for
oxidiazon.
The
registrant
sponsored
and
submitted
a
GIS
study
related
to
PCA
calculation
for
golf
courses
conducted
in
Florida,
where
most
of
the
oxadiazon
is
used.

Response:
Concurrently
with
the
60­
Day
Response,
the
registrant
submitted
the
following
document:
Andrish,
S.
D.,
et.
al.
2003.
"
Estimated
Drinking
Water
Concentrations
of
Oxadiazon
Residues
in
the
Index
Reservoir
Associated
with
Use
on
Golf
Course
Turf,"
an
unpublished
report
performed
by
Waterborne
Environmental,
Inc.,
Leesburg,
VA,
and
sponsored
by
Bayer
CropScience,
Research
Triangle
Park,
NC,
Report
No.
WEI
746.29,
B004306.
(
MRID#
45920102).
EFED
will
not
be
able
to
complete
the
review
of
the
submitted
study
within
the
60­
day
response
period.
EFED
intend
to
complete
the
review
process
in
near
future.
In
the
meantime,
EFED
will
continue
to
use
EFED's
guidance
document
in
estimating
drinking
water
concentrations
for
pesticides
using
recommended
adjusting
factors
for
the
golf
courses
scenario.
