Chlorine
Dioxide
Environmental
Fate
and
Transport
Assessment
Case
4023
A.
Najm
Shamim,
Ph.
D.
Office
of
Pesticide
Programs
Antimicrobials
Division
U.
S.
Environmental
Protection
Agency
1200
Pennsylvania
Avenue,
NW
Washington,
DC
20460
February
23,
2006
Page
2
of
3
EXECUTIVE
SUMMARY
Chlorine
dioxide
is
inherently
unstable
under
ambient
conditions.
Chlorine
dioxide,
chlorite
and
chlorate
have
a
tendency
to
act
as
reactants
to
each
other
as
well
as
products
for
each
other,
given
the
right
conditions
(
temperature,
pH).
There
are
no
measured
or
estimated
environmental
parameters
to
estimate
the
environmental
concerns.
Chlorine
dioxide
converts
into
ions
like
chlorite,
chlorate
or
chloride
and
is
likely
to
migrate
into
ground
water.
Chlorine
dioxide
is
used
a
s
a
disinfectant
in
many
waste
water
treatment
plants
and
there
is
concern
from
its
residual
presence
as
chlorite/
chlorate
in
high
concentrations
in
some
areas.

Chlorine
dioxide
and
sodium
chlorite
are
being
assessed
together,
as
these
inorganics
are
a
unique
set
of
chemicals:
Chlorine
dioxide
is
produced
by
a
reaction
of
sodium
chlorite
(
and
sometime
sodium
chlorate)
and
hypochlorite/
acid.
Moreover,
chlorite
is
a
breakdown
product
of
chlorine
dioxide.

Major
antimicrobial
uses
of
chlorine
dioxide
and/
or
sodium
chlorite
are
as
water
disinfectants
and
pulp/
paper
industry
disinfectants.
Therefore,
a
major
route
of
contamination
for
chlorine
dioxide
or
chlorite
ions
is
through
drinking
water
and
as
disinfectant
use
in
paper/
pulp
industry.

Chlorine
dioxide
is
a
greenish
yellow
gas
at
room
temperature.
It
is
a
free
radical
(
has
an
unpaired
electron),
and
hence,
it
is
an
unstable
molecule.
In
the
presence
of
sunlight,
its
half
life
is
about
thirty
minutes.
A
closed
container
with
>
10%
(
v/
v)
chlorine
dioxide
is
potentially
explosive.
Chlorine
dioxide,
when
used
(
as
a
disinfectant),
is
generated
on
site.
It
is
highly
water
soluble
(~
3
g/
L).

Sodium
Chlorite
is
a
solid,
white
powder.
It
is
highly
water
soluble
and
immediately
dissociates
into
sodium
and
chlorite
ions.

Abiotic
degradation:

Chlorine
dioxide:
It
has
a
short
half
life,
and
in
the
presence
of
sunlight,
whether
it
is
in
water
or
as
a
gaseous
molecule,
its
breakdown
products
are:
chloride
and
chlorate
ions,
between
pH
4
and
7.
Ultimately,
oxygen
is
formed.
At
pH
lower
than
4,
its
breakdown
products
are
chlorite
and
chlorate.
Chlorite
is
the
dominant
breakdown
product.

Sodium
chlorite:
It
dissolves
in
water,
and
its
breakdown
products
are:
chloride
and
chlorate
ions,
under
similar
conditions
as
chlorine
dioxide.
It
is
common
to
see
chemical
degradation
if
sodium
chlorite
is
in
water
and
also
in
the
presence
of
suspended
soil
particles
containing
ions,
like
Fe(
II),
Mn(
II),
I­,
S­
2,
through
redox
reactions.

The
end
products
are
chloride
and
oxygen.
The
same
end
products
are
obtained
when
sodium
chlorite
is
heated.
Page
3
of
3
Biotic
Degradation:

Chlorate
and
chlorite
ions
show
a
tendency
to
undergo
biodegradation
under
anaerobic
conditions
only.
There
are
no
reports
indicating
these
ions
under
go
biodegradation
under
aerobic
conditions.
Biodegradation
for
chlorate
and
chlorite
have
been
observed
in
anoxic
ground
water,
sediments
and
some
soils.
The
end
products
are
again
the
same:
chloride
and
oxygen.

No
adsorption/
desorption
constants
(
Kds)
have
been
measured
or
reported
in
published
literature
for
either
chlorite
or
chlorate.
Since
these
are
ions,
they
are
likely
to
be
mobile
and
travel
from
surface
to
ground
water
easily.

The
estimated
log
Kow
of
chlorine
dioxide
is
­
3.22
and
for
sodium
chlorite
is
­
7.17
and
both
are
not
likely
to
bioaccumulate
in
aquatic
organisms.

BIBLIOGRAPHY
EPA,
2005.
Estimation
Program
Interface
(
EPI)
Suite.
US
Environmental
Protection
Agency.
http://
www.
epa.
gov/
oppt/
exposure/
docs/
episuite.
htm.
Accessed
2005.

World
Health
Organization
(
WHO),
2002.
Chlorine
Dioxide:
Concise
International
Chemical
Assessment
Document
37.
Geneva,
Switzerland.
