UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON
D.
C.,
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
DP
Barcodes:
303547
and
316943
June
9,
2005
MEMORANDUM
SUBJECT:
Response
to
Comments
on
Sodium
Chlorate
Submitted
by
EKA
(
May
13th,
2005)
and
the
Sodium
Chlorate
Reregistration
Task
Force
(
May
2nd,
2005).

FROM:
Brian
Anderson,
Biologist
Silvia
Termes,
Chemist
THRU:
Daniel
Rieder,
Branch
Chief
Stephanie
Syslo,
RAPL
Environmental
Risk
Branch
3
TO:
Jacqueline
Guerry,
Chemical
Review
Manager
Special
Review
and
Re­
registration
Division
(
SRRD)

Response
to
Comments
Submitted
by
Michael
S.
Wenk
on
behalf
of
EKA
on
May
13th,
2005.

Comment
1.
We
see
in
the
market
place
two
distinct
applications.
a.
As
a
defoliant/
desiccant
on
a
variety
of
crops,
and
b.
As
weed
control
in
non­
agricultural
areas
Our
own
sales
of
sodium
chlorate
outside
the
traditional
market
of
pulp
bleaching
are
only
for
the
defoliant
application.
We
have
not
sold
any
sodium
chlorate
for
several
years
to
the
weed
control
application.
Our
assessment
is
that
sodium
chlorate
has
been
replaced
by
other
products.
We,
therefore,
intend
not
to
maintain
registration
for
sodium
chlorate
for
this
application.

In
the
defoliant/
desiccant
market,
it
seems
that
the
common
practice
is
a
one
time
application
of
sodium
chlorate
without
a
repeat
treatment
within
30
days
as
assumed
in
your
assessment.
However,
we
found
anecdotal
reference
to
a
repeat
application
within
a
few
days
after
the
initial
dose.
We
are
investigating
whether
this
is
still
practical.
Based
­
2­

on
our
current
practical
knowledge,
we
have
not
seen
application
rates
of
more
than
12
pounds
sodium
chlorate
per
acre.

U.
S.
EPA
Response.
All
cancelled
labels
will
be
removed
from
EFED's
assessment
upon
receipt
of
proper
written
notification
from
the
registrant.
Also,
if
all
labels
are
clarified
to
preclude
repeat
applications
in
agricultural
practice,
then
the
assessment
will
be
changed
accordingly.
The
assessment
may
also
be
amended
if
data
become
available
suggesting
that
repeated
chlorate
applications
occur
at
intervals
less
than
30
days
between
applications.

Comment
2.
Based
on
work
performed
in
Europe
and
published
in
"
GB
Rikken,
AMG
and
CG
van
Ginkel
(
1996):
Transformation
of
(
per),
Chlorate
into
Chloride
by
a
Newly
Isolated
Bacterium;
Reduction
and
Dismutation,
Applied
Microbiology
and
Biotechnology,
45,
page
420­
426",
sodium
chlorate
is
reduced
to
sodium
chloride
very
effectively
in
the
environment.
Sodium
chlorite
will
be
intermittently
formed,
but
does
not
accumulate
as
the
further
breakdown
of
chlorite
is
much
faster
than
the
limiting
step
of
the
chlorate
reduction.
Therefore,
we
would
not
consider
that
sodium
chlorite
is
a
viable
product
of
the
environmental
reduction
of
sodium
chlorate.

U.
S.
EPA
Response:
A
copy
of
the
cited
paper
has
been
requested
and
will
be
evaluated
and
included,
if
appropriate,
in
the
assessment.
However,
note
that
in
the
assessment
chlorite
was
considered
as
a
reduction
product
of
chlorate
that
can
further
be
reduced
to
other
species
in
lower
oxidation
states.
What
was
done
in
the
assessment
was
to
consider
a
thermodynamics
equilibrium
approach
to
estimate
which
was
the
"
end,
predominant
product"
of
reduction
of
chlorate.
This
took
into
account
all
of
the
reduced
species
that
may
form
from
chlorate.
We
concluded
that
the
end
product
of
chlorate
and
other
oxyanions/
oxides
of
chlorine
at
lower
oxidation
states
is
chloride.
Thermodynamics
can
only
tell
us
what
reactions
may
occur,
but
not
that
they
will
occur
and
at
what
rate
(
i.
e.,
the
kinetics
of
reaction).
Although
we
have
not
seen
this
study
yet,
the
observed
behavior
(
i.
e.,
chloride
as
the
end
reduction
product)
is
consistent
with
our
conclusions
using
a
thermodynamics
approach.

It
is
very
likely
that
the
rates
of
formation/
decline
(
i.
e.,
kinetics)
of
intermediate
reduced
species
is
very
dependent
on
the
redox
conditions
of
a
site
where
chlorate
was
used.
Because
the
variability
in
physical
and
chemical
properties
of
use
sites,
it
was
decided
that
a
general,
thermodynamics
approach
was
appropriate
for
sodium
chlorate.

Comments
from
Eliot
Harrison
on
behalf
of
the
Sodium
Chlorate
Reregistration
task
force
on
May
2,
2005
Comment
1.
The
assertion
that
chlorite
is
a
reduction
product,
in
the
environment,
of
chlorate
is
incorrect.
Under
similar
reaction
conditions,
in
terms
of
pH
and
redox
potential,
­
3­

chlorite
is
always
more
reactive
than
chlorate.
The
only
products
formed
as
a
result
of
chlorate
decomposition
are
chloride
and
oxygen.
In
order
for
chlorate
to
be
converted
to
chlorite,
two
reactions
would
have
to
occur
sequentially.
First,
chlorate
would
have
to
be
reduced
in
a
strongly
acidic
medium
to
chlorine
dioxide.
Then,
chlorine
dioxide
would
have
to
be
absorbed
in
an
alkaline
medium
and
subsequently
reduced
in
a
one­
electron
reaction
to
chlorite.
While
these
two
sequential
reactions
constitute
the
basis
for
the
manufacture
of
sodium
chlorite
they
cannot
be
replicated
in
the
environment.
The
soil
study
conducted
by
Erco
with
sodium
chlorite
(
Soil
Decomposition
of
Sodium
Chlorate,
MRID#
46335504)
clearly
showed
that
chlorite
can
be
converted
to
chlorate
in
the
environment
but
that
chlorate
does
not
form
chlorite.
In
the
study,
chlorite
decayed
to
chloride
relatively
rapidly
in
soil
and
approximately
12­
15%
of
chlorite
was
converted
to
chlorate.
No
chlorite
was
reformed
from
chlorate
after
a
significant
(
128
days)
aging
period.
If
the
Agency
needs
additional
information
in
order
to
validate
this
study,
please
let
us
know
as
soon
as
possible.

U.
S.
EPA
Response.
The
Agency
disagrees
with
the
Task
Force
response
that
chlorite
cannot
form
from
chlorate.
The
Agency
considered
all
of
the
potential
reduction
products
of
chlorate
(
including
chlorite)
to
estimate
which
would
be
the
end­
reduction
product
of
chlorate
and
of
all
of
the
possible
species
at
a
lower
oxidation
state.
We
use
a
thermodynamics
equilibrium
approach
to
estimate
that
the
end­
product
of
chlorate
and
the
other
species
at
lower
oxidation
states
is
chloride.
We
used
available
thermodynamics
data
for
the
chlorine
system.
However,
thermodynamics
only
indicates
species
that
can
form,
but
not
that
the
reaction
will
occur
and
at
what
rate
(
i.
e.,
the
kinetics
of
reaction).
Therefore,
from
a
thermodynamics
approach
it
is
valid
to
consider
chlorite
as
a
potential
intermediate
in
the
reduction
of
chlorate
to
the
end­
product
chloride.

Although
the
study
(
MRID
46335504)
was
reviewed,
it
was
very
succinct
in
the
description
of
experimental
procedures,
lack
of
good
soil
characterization
and
raw
data.
We
request
that
additional
information
be
submitted
to
consider
this
study
as
supplemental
information.
But
note,
the
observed
formation
of
chlorate
from
chlorite
applies
only
to
that
particular
system
(
not
characterized
in
terms
of
redox
conditions
of
the
soil
media
and
conditions)
and
it
does
not
represent
all
sites
where
chlorate
may
be
used.
Also
note,
that
we
covered
and
considered
disproportionation
reactions
(
i.
e.,
one
reaction
product
in
a
higher
oxidation
state
of
chlorine
and
in
a
lower
oxidation
state
of
chlorine).
Disproportionation
reactions
are
very
common
for
chemical
species
of
an
element
that
can
exist
in
multiple
oxidation
states.

The
bottom
line
for
chlorate
is
that
the
end
product
of
chlorate
reduction
is
chloride
and
that
intermediate
lower
oxidation
state
species
can
form,
but
they
can
also
be
reduced
to
chloride.
How
fast?
It
depends
on
the
redox
characteristics
of
the
media,
including
pH,
as
all
of
these
reactions
are
redox
potential
and
pH­
dependent.
Therefore,
many
of
these
reduced
species
could
either
have
very
high
rates
of
formation/
decline
and
be
considered
­
4­

"
transient
species"
or
the
reaction
rates
of
formation
are
so
slow
that
they
may
not
form
in
appreciable
concentrations
Comment
2.
A
2­
generation
reproduction
study
in
the
rat
(
MRID
46542401)
was
recently
submitted
to
the
Agency.
In
the
study,
the
test
animals
were
dosed
with
chlorate
at
levels
ranging
from
10­
500
mg/
kg/
day,
through
mating
and
gestation
and
until
the
end
of
lactation
in
both
the
FO
and
F1
generations.
No
reproductive
effects
were
observed
at
any
of
the
treatment
levels.
Accordingly,
the
study
demonstrates
that
chlorate
is
not
a
reproductive
toxin.

U.
S.
EPA
Response:
These
data
will
be
included
in
the
risk
assessment
after
they
have
been
reviewed
by
the
Agency
if
the
study
is
considered
acceptable.

Comment
3.
Chronic
aquatic
studies
were
not
conducted
with
chlorate
since
all
the
acute
aquatic
studies
showed
that
chlorate
is
practically
non­
toxic
to
aquatic
organisms.
In
addition,
the
ratio
of
the
EECs
to
the
toxic
concentration
that
the
Agency
calculated
for
the
agricultural
uses
of
chlorate
is
<
0.01,
which
is
below
the
level
of
concern.
The
task
force
believes
that
the
ratio
is
actually
significantly
lower
since
the
EEC's
derived
by
the
Agency
assumed
no
degradation
of
chlorate
in
soil
and
no
foliar
interception.
Both
of
these
assumptions
are
highly
unrealistic
for
cotton,
which
is
greater
than
90%
of
chlorate
agricultural
use.
Chlorate
application
in
cotton
occurs
at
a
time
when
the
cotton
bolls
are
mature
so
that
chlorate
is
typically
applied
to
a
canopy
of
cotton.
Consequently,
almost
all
of
the
applied
chlorate
will
directly
contact
plant
material.

U.
S.
EPA
Response:
An
early
life­
stage
study
in
fish
and
reproduction
toxicity
studies
in
aquatic
invertebrates
are
recommended
if
a
pesticide
is
expected
to
be
transported
to
water
from
the
intended
use
site,
AND
exposure
is
likely
to
be
either
continuous
or
recurrent
regardless
of
toxicity.
Also,
chronic
testing
is
still
required
if
the
half­
life
in
water
is
>
4
days
regardless
of
the
proximity
of
the
EEC
to
the
LC50
or
EC50
in
aquatic
organisms.
Chlorate's
half­
life
in
water
is
>
4
days.

Comment
4.
Although
the
Agency
recognized
that
the
non­
agricultural
uses
of
sodium
chlorate
are
probably
spot
treatments,
the
application
rates
(
page
15
of
the
risk
assessment)
and
the
derived
EEC's
assumed
broad
use.
The
Task
Force
believes
that
sodium
chlorate
has
minimal
non­
agricultural
use
(
as
a
herbicide)
and,
usage
is
confined
to
spot
treatment.
On
page
15
of
the
risk
assessment,
the
Agency
identified
twelve
(
12)
products
that
are
registered
for
non­
agricultural
use.
Of
these
products,
six
(
see
below)
are
not
currently
registered
in
any
states,
and,
therefore,
are
not
commercially
available.
­
5­

Ferti­
Lome
Special
Vegetation
Killer,
Reg.
No.
7401­
173
Perkerson's
Triate
Weed
Killer,
Reg.
No.
690­
48
Tri­
Kil
Nonselective
Weed
and
Grass
Killer,
Reg.
No.
9754­
1
AllPro
Baracide
SPS
Pelleted
herbicide,
Reg.
No.
769­
978
Prometon
5PS,
Reg.
No.
53883­
97
Perkerson's
Tri­
Clor
Weed
Killer,
Reg.
No.
690­
44
Four(
4)
of
the
products
(
Barespot
MonoborChlorate,
BarespotWeed
and
Grass,
Barespot
BD
and
Barespot
Ureabor)
are
packaged
in
50
lb.
containers
and
another
product
­
Grass,
Weed
and
Vegetation
Killer
(
Reg.
No.
5887­
46)
­
is
packaged
in
a
one­
quart
container.
These
package
sizes
are
clearly
indicative
of
a
product
used
for
spot
treatment
since
they
treat
substantially
less
than
one
acre.
No
information
was
available
for
the
remaining
product
(
Riverdale
Killsall
Liquid,
Reg.
No.
228­
133)
but
the
use­
instructions
for
this
product
are
clearly
oriented
toward
spot
treatment.
The
Task
Force
will
encourage
all
end­
use
registrants
to
submit
revised
labels
to
the
Agency
that
will
specify
the
non­
agricultural
uses
of
chlorate
are
limited
to
spot
treatment.
Assuming
this
is
done,
the
EEC's
and
risk
characterization
for
the
non­
agricultural
uses
will
need
to
be
revised.

U.
S.
EPA
Response:
The
assessment
included
all
active
labels
that
were
current
at
the
time
the
assessment
was
prepared.
EFED
will
alter
its
assessment
accordingly
upon
notification
of
label
cancellations
and
submission
of
revised
labels
and
refined
use
patterns.

Comment
5.
It
is
our
understanding
that
the
main
flame
retardants
used
with
chlorate
are
water
and
urea,
neither
which
is
expected
to
have
any
effect
on
chlorate
persistence.

U.
S.
EPA
Response:
Although
urea
is
a
common
flame
retardant,
other
flame
retardants
are
also
used,
and
water
should
not
be
used
as
the
sole
flame
retardant
formulated
with
chlorate.
In
addition,
chlorate
is
formulated
with
other
active
ingredients,
and
the
possible
effects
of
these
active
ingredients
on
the
fate
and
toxicity
of
chlorate
is
not
known.

Comment
6.
Sodium
chlorate
has
a
very
weak
antimicrobial
activity
so
it
is
unlikely
to
be
used
as
a
preservative
in
other
pesticide
products.
In
addition,
if
used
in
this
way,
sodium
chlorate
would
have
to
be
registered
as
a
preservative.

U.
S.
EPA
Response:
EFED
did
not
suggest
in
its
assessment
that
chlorate
is
used
as
a
preservative,
but
is
used
both
as
an
inert
and
active
ingredient
in
pesticide
formulations.
Association
of
specific
inert
ingredients
with
active
ingredients
is
confidential
information;
therefore,
the
Agency
cannot
specify
which
active
ingredient(
s)
chlorate
is
formulated
with
as
an
inert
substance.
However,
based
on
agreement
with
the
Special
Review
and
Reregistration
Division
(
SRRD),
EFED's
assessment
did
not
consider
potential
chlorate
exposure
resulting
from
these
uses.
The
assessment
did
include
uses
where
sodium
chlorate
is
formulated
with
other
active
ingredients.
It
is
uncertain
if
these
other
active
ingredients
could
affect
the
fate
or
toxicity
of
sodium
chlorate.
­
6­

Comment
7.
The
task
force
is
unaware
of
any
use
of
chlorate
as
a
soil
sterilant.
As
noted
above,
chlorate
has
very
weak
antimicrobial
activity.

U.
S.
EPA
Response:
Product
labels,
material
safety
data
sheets
(
MSDS)
on
sodium
chlorate,
and
State
Agencies
are
just
a
few
of
many
sources
reporting
that
sodium
chlorate
is
a
soil
sterilant.
One
example
of
each
is
below:
°
The
label
for
weed
killer
&
prepaving
preparation,
(
EPA
Registration
Number
7701­
34)
indicates
that
chlorate
is
applied
as
a
non­
selective
weed
killer,
soil
sterilant,
and
in
pre­
paving
preparation.
Although
this
label
was
cancelled
in
2004
and
was,
therefore,
not
included
in
our
assessment,
similar
statements
are
included
on
other
sodium
chlorate
end­
use
products.
°
The
MSDS
on
sodium
chlorate
prepared
by
Kerr­
McGee
(
2003)
indicates
that
sodium
chlorate
is
a
"
semi­
permanent
soil
sterilant."
°
The
state
of
California
reports
that
chlorate's
soil
sterilant
properties
last
3
to
6
months
(
http://
www.
oehha.
ca.
gov/
water/
pals/
chlorate.
html).
