UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON
D.
C.,
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
PC
#
073301
Reregistration
Case
#
4049
DP
Barcode
D303568
February
23
,
2005
MEMORANDUM
Subject:
Sodium
Chlorate
(
CAS
Reg.
#
7775­
09­
9)
Amendment
to
the
Drinking
Water
Assessment
Requested
by
the
Health
and
Effects
Division
From:
Silvia
C.
Termes,
Chemist
(
ERB
III)
and
James
A.
Hetrick,
Senior
Scientist
(
ERB
I)
Environmental
Fate
and
Effects
Division
(
7507C)

and
Henry
P.
Nelson,
Senior
Scientist
Office
of
Science
Coordination
and
Policy
OPPTS
To:
Rossana
Louie
Reregistration
Division
and
Bonnie
Cropp­
Kohlli
Health
and
Effects
Division
Through:
Daniel
Rieder,
Branch
Chief
ERB
III
Environmental
Fate
and
Effects
Division
This
Memorandum
contains
the
additional
language
for
the
Drinking
Water
Assessment,
as
requested
by
the
Health
and
Effects
Division
in
the
meeting
dated
February
3rd,
2005.

A
Drinking
Water
Assessment
for
Sodium
Chlorate
was
submitted
on
01/
05/
2005
(
DP
Barcode
D303556).
­
2­

Sodium
Chlorate
Sodium
chlorate
is
used
as
a
desiccant/
defoliant
because
it
is
a
strong
oxidizer.
As
a
strong
oxidizing
agent,
chlorate
(
ClO
3
­,
oxidation
state
V)
gets
reduced
to
chlorine
species
in
lower
oxidation
states,
such
as
the
oxyanions
chlorite
(
ClO
2
­,
oxidation
state
III)
and
hypochlorite
(
ClO­,
oxidation
state
I),
chlorine
dioxide
(
oxidation
state
IV),
and
chloride
(
oxidation
state
­
I).
Thus,
at
least
some
and
possibly
substantial
reduction
of
the
applied
chlorate
is
likely
to
occur
in
the
field
prior
to
any
runoff
to
surface
water.
The
FIRST­
estimated
exposure
concentration
in
surface
water
represents
a
very
conservative
value
because
it
assumes
that
all
of
the
chlorinecontaining
chemical
species
entering
the
natural
water
body
is
in
the
form
of
chlorate
without
any
reduction.
Morever,
for
these
estimates
it
was
assumed
that
chlorate
was
persistent
in
soil
and
water­
sediments
under
aerobic
conditions,
persistent
in
abiotic
aquatic
media,
persistent
towards
direct
photolysis
in
water,
and
that
it
does
not
bind
to
soil.
That
is,
it
was
assumed
that
none
of
the
chlorate
was
reduced
in
the
field
prior
to
runoff
or
subsequently
reduced
in
the
water
body.

Under
environmental
(
terrestrial
field)
redox
conditions
and
based
on
chemical
equilibria
alone,
the
thermodynamically
favored,
end
reduction
product
of
chlorate
in
soil
and
in
water
is
the
chloride
anion.
Any
intermediate
chlorine
dioxide
that
may
form
under
environmental
conditions
will
undergo
photochemical
reactions
when
exposed
to
sunlight.
The
chlorine
oxyanions
chlorite
and
hypochlorite
(
other
possible
more
reduced
intermediates
in
the
ultimate
reduction
of
chlorate
to
chloride)
are
strong
oxidizers
in
themselves
and
thus,
they
are
also
reduced
and/
or
undergo
disproportionation
reactions.
Although
reduction
reactions
of
chlorate,
chlorite,
and
hypochlorite
are
said
to
occur
"
very
fast",
how
fast
they
occur
is
not
known
(
i.
e.,
the
actual
rate
constants
in
the
environment
are
not
known).
Therefore,
at
any
given
time
the
distribution
of
reduced
species
(
type
and
concentration)
cannot
be
estimated.
However,
it
is
unlikely
that
a
single
reduced
species
would
be
present.

The
additional
exposure
concentrations
estimates
for
chlorite
and
hypochlorite
are
also
conservative
because
they
are
based
on
the
assumptions
that
all
chlorate
had
been
reduced
completely
to
either
chlorite
or
hypochlorite,
and
furthermore
that
none
of
the
chlorite
or
hypochlorite
had
been
reduced.
