Resonse
to
Comments
June
13,
2006
MEMORANDUM
SUBJECT:
Analysis
of
proposed
changes
to
sodium
chlorate's
application
rates
and
maximum
treated
area
on
potential
ecological
risks
presented
in
EFED's
reregistration
eligibility
decision
(
RED)
document.

FROM:
Brian
Anderson,
Biologist
Silvia
Termes,
Chemist
Environmental
Fate
and
Effects
Division
(
7507C)

THRU:
Dan
Rieder,
Branch
Chief
Environmental
Risk
Branch
3
Environmental
Fate
and
Effects
Division
(
7507C)

TO:
Molly
Clayton
Special
Review
and
Reregistration
Division
(
SRRD)
(
7505C)
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES,
AND
TOXIC
SUBSTANCES
Analysis
of
proposed
changes
to
sodium
chlorate
use
patterns
EFED
evaluated
changes
in
potential
exposures
and
risks
to
non­
target
aquatic
and
terrestrial
organisms
presented
in
the
EFED
chapter
of
the
reregistration
eligibility
decision
(
RED)
document
on
sodium
chlorate.
These
changes
in
risks
to
non­
target
organisms
are
the
result
of
a
proposal
to
change
the
maximum
labeled
application
rate
from
520
lbs
a.
i./
Acre
with
no
specified
maximum
treated
area
to
392
lbs
a.
i./
Acre
(
0.9
lbs
/
100
ft2)
with
a
maximum
applied
area
of
8000
ft2
(
approximately
1/
5
acre).
The
effect
of
these
changes
on
ecological
risks
presented
in
the
EFED
chapter
of
the
sodium
chlorate
RED
is
summarized
below.

Sodium
chlorate
is
used
in
both
agricultural
and
non­
agricultural
settings.
Changes
in
agricultural
use
patterns
were
not
proposed
at
this
time;
therefore,
agricultural
uses
are
not
considered
as
part
of
this
analysis.

Aquatic
Organisms.

EECs
presented
in
the
RED
for
non­
agricultural
uses
were
as
high
as
39
mg/
L
based
on
an
application
rate
of
620
lbs
a.
i./
Acre.
However,
the
sodium
chlorate
use
at
620
lbs
a.
i./
Acre
was
"
under
asphalt";
therefore,
EFED
presumed
that
aquatic
exposure
would
be
negligible
from
this
use.
The
next
highest
application
rate
was
520
lbs
a.
i./
Acre,
which
resulted
in
an
EEC
of
31
mg/
L
(
Table
3­
7
in
the
RED).

Based
on
a
reduction
in
the
highest
application
rate
for
non­
agricultural
uses
from
520
lbs
a.
i./
Acre
to
392
lbs
a.
i./
Acre
and
a
reduction
in
the
maximum
treated
area
from
100%
to
20%
of
an
acre
(
8000
ft2),
aquatic
EECs
would
be
expected
to
be
reduced
from
31
mg/
L
to
4.7
mg/
L
in
EFED's
standard
ecological
pond.

The
Agency's
LOC
was
not
exceeded
for
fish
or
invertebrates.
The
only
aquatic
LOC
that
was
exceeded
was
for
endangered
vascular
plants
(
RQ
=
12.6).
Therefore,
reduction
in
the
application
rate
and
treated
area
was
only
evaluated
for
vascular
plants.
Based
on
an
EEC
of
4.7
mg/
L
and
a
NOAEC
of
3.1
mg/
L
in
duckweed,
the
endangered
vascular
plant
RQ
would
be
reduced
from
12.6
to
1.5,
which
is
a
significant
improvement,
but
is
still
above
the
Agency's
LOC
of
1.0.
EFED
notes
that
several
required
studies
in
aquatic
plants
have
not
been
submitted;
therefore,
there
remains
additional
uncertainty
in
the
aquatic
plant
assessment
in
that
if
other
plants
are
more
sensitive,
the
RQs
would
be
greater.

Terrestrial
Organisms
Based
on
the
available
laboratory
studies,
sodium
chlorate
is
not
expected
to
be
acutely
toxic
to
mammals
or
birds;
however,
potential
acute
risk
to
terrestrial
organisms
was
identified
in
the
RED
based
on
the
high
application
rates
and
associated
high
EECs
on
potential
food
items
of
these
organisms.
In
addition,
sodium
chlorate
was
shown
to
induce
frank
reproductive
effects
in
bobwhite
quail
at
964
mg/
L;
the
no
adverse
effect
concentration
was
271
mg/
L
(
MRID
46729701).
Mammals
were
less
sensitive
than
birds
to
reproductive
effects.
A
free­
standing
NOAEC
of
500
mg/
L
(
meaning
that
no
reproductive
effects
were
observed
at
any
concentration
tested)
was
reported
in
a
2­
generation
reproduction
toxicity
study
in
rats
(
MRID
46524001).

The
highest
estimated
environmental
concentrations
presented
in
the
RED
were
substantially
higher
than
any
dose
or
concentration
tested
in
the
available
acute
or
chronic
toxicity
studies.
Reducing
the
maximum
application
rate
from
520
lbs
a.
i./
Acre
to
392
lbs
a.
i./
Acre
would
reduce
the
estimated
environmental
concentrations
of
chlorate
by
approximately
25%,
but
would
not
change
LOC
exceedances
presented
in
the
RED.
Reduction
of
the
maximum
treated
area
to
1/
5th
of
an
acre
would
be
expected
to
reduce
the
likelihood
that
a
terrestrial
organism
will
come
into
contact
and
consume
all
of
its
diet
from
that
area;
however,
localized
concentrations
(
and
resulting
risk
quotients)
within
the
treated
area
would
only
be
reduced
by
25%
of
the
values
presented
in
the
RED.
