Chlorine
Dioxide
Environmental
Hazard
and
Risk
Assessment
Case
4023
Genevieve
Angle
Office
of
Pesticide
Programs
Antimicrobials
Division
U.
S.
Environmental
Protection
Agency
1200
Pennsylvania
Avenue,
NW
Washington,
DC
20460
April
6,
2006
Page
2
of
33
Chlorine
Dioxide
and
Sodium
Chlorite:
Environmental
Hazard
and
Risk
Assessment
Introduction
The
toxicity
endpoints
(
e.
g.
LC50,
NOEC)
included
in
this
section
are
based
on
the
results
of
sodium
chlorite
and
chlorine
dioxide
toxicity
studies
that
were
submitted
to
EPA
for
review.
Chlorine
dioxide
and
sodium
chlorite
are
used
as
antimicrobial
pesticides
at
numerous
use
sites.
Sodium
chlorite
is
used
as
a
precursor
in
the
generation
of
chlorine
dioxide.
The
antimicrobial
registered
uses
of
chlorine
dioxide/
sodium
chlorite
fall
into
several
major
categories
including
use
in
the
treatment
of
human
drinking
water
systems;
in
industrial
process
and
water
systems;
as
a
materials
preservative;
and
as
a
general
disinfectant
in
medical,
residential,
agricultural,
commercial
and
industrial
settings.
The
once­
through
cooling
tower
use
of
chlorine
dioxide/
sodium
chlorite
has
been
selected
for
risk
assessment
because
out
of
all
the
uses
of
these
chemicals,
it
is
the
one
expected
to
have
the
most
potential
for
environmental
exposure.
The
environmental
risk
assessment
will
be
conducted
using
sodium
chlorite
endpoints
because
under
environmental
conditions,
chlorine
dioxide
converts
mostly
into
chlorite
ions.
Currently,
a
quantitative
evaluation
of
the
likelihood
of
the
ecological
exposures
resulting
from
the
industrial
uses
of
chlorine
dioxide
and
sodium
chlorite
overlapping
spatially
and
temporally
with
the
exposures
resulting
from
the
agricultural
uses
of
chlorine
dioxide
and
sodium
chlorite
is
not
possible.
Therefore,
the
ecological
risks
are
not
aggregated
in
this
assessment.

Data
Gaps
Several
data
requirements,
necessary
to
support
the
once­
through
cooling
tower
use
of
chlorine
dioxide/
sodium
chlorite,
are
not
fulfilled:
72­
4/
850.1300
Fish
early
life­
stage
testing­
freshwater
TGAI1
72­
4b/
850.1400
Invertebrate
life­
cycle
testing
­
freshwater
TGAI
123­
1/
850.4225
Seedling
emergence
dose­
response
in
rice
TEP2
123­
1/
850.4250
Vegetative
vigor
dose­
response
in
rice
TEP
123­
2/
850.4400
Aquatic
vascular
plant
dose­
response
toxicity­
Lemna
sp.
TGAI
or
TEP
123­
2/
850.5400
Acute
algal
dose­
response
toxicity
­
4
species
TGAI
or
TEP
1TGAI
=
technical
grade
active
ingredient
2TEP
=
typical
end­
use
product
Page
3
of
33
Ecological
Hazard
Assessment:

I.
Toxicity
to
Terrestrial
Animals
A.
Birds,
Acute
and
Subacute
An
acute
oral
toxicity
study
using
the
technical
grade
of
the
active
ingredient
(
TGAI)
is
required
to
establish
the
toxicity
of
chlorine
dioxide/
sodium
chlorite
to
birds.
The
preferred
test
species
is
either
mallard
duck
(
a
waterfowl)
or
bobwhite
quail
(
an
upland
game
bird).
The
results
of
several
toxicity
studies
are
provided
in
the
following
table.

Table
1.
Acute
Oral
Toxicity
of
Chlorine
Dioxide
and
Sodium
Chlorite
to
Birds
Substance/%
Active
Ingredient
(
AI)
Organism
Endpoints/
Results
(
95%
conf.
interval)
mg/
kg
Reference
Study
Classification
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
382
(
300­
520)
NOAEL
=
175
Robaidek,
1985
ACC
#
259373
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
390
(
310­
490)
NOAEL
=
N.
R.
Robaidek
and
Johnson,
1985
ACC
#
257341
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
395
(
272­
573)
NOAEL
=
N.
R.
Fletcher,
1984
ACC
#
253378
acceptable
Sodium
Chlorite/
83%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
660
(
540­
810)
Fletcher,
1973
MRID
#
31610
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
467
(
372­
585)
Beavers,
1984
ACC
#
254177
acceptable
Sodium
Chlorite/
80%
Mallard
Duck
(
Anas
platyrhynchos)
LD50
>
31.25
Beavers,
1984
ACC
#
254176
supplemental
Sodium
Chlorite/
25%
Northern
bobwhite
(
Colinus
virginianus)
LD50
=
797(
420­
2594)
NOAEL=
125
MBA
Laboratories,
1984
ACC#
252854
acceptable
Note:
LD50=
Median
Lethal
Dose;
NOAEL=
No
Observed
Adverse
Effect
Level;
N.
R.=
Not
Reported
These
results
indicate
that
chlorine
dioxide/
sodium
chlorite
range
from
slightly
to
highly
toxic
to
birds
on
an
acute
oral
basis.
The
guideline
requirement
(
71­
1/
OPPTS
850.2100)
is
fulfilled.

Two
subacute
dietary
studies
using
the
technical
grade
of
the
active
ingredient
are
required
to
establish
the
toxicity
of
a
pesticide
to
birds.
The
preferred
test
species
are
mallard
duck
(
a
waterfowl)
and
bobwhite
quail
(
an
upland
gamebird).
Results
of
avian
subacute
dietary
tests
are
tabulated
below.
Page
4
of
33
Table
2.
Avian
Subacute
Dietary
Toxicity
of
Chlorine
Dioxide
and
Sodium
Chlorite
Substance/%
AI
Organism
LC50
(
ppm)
(
95
%
c.
i.)
NOAEC
(
ppm)
Reference
Study
Classification
Sodium
Chlorite/
80%
Mallard
Duck
(
Anas
platyrhynchos)
>
5000
5000
Johnson,
1984
MRID
#
94068008
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
>
5000
N.
R.
Fletcher,
1984
ACC
#
253378
acceptable
Sodium
Chlorite/
80%
Mallard
Duck
(
Anas
platyrhynchos)
>
5000
N.
R.
Fletcher,
1984
ACC
#
253378
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
>
5000
N.
R.
Johnson,
1984
MRID
#
94068005
acceptable
Sodium
Chlorite/
80%
Mallard
Duck
(
Anas
platyrhynchos)
>
5620
N.
R.
Beavers,
1984
ACC
#
254178
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
>
5620
N.
R.
Beavers,
1984
ACC
#
254179
acceptable
Sodium
Chlorite/
80%
Northern
bobwhite
(
Colinus
virginianus)
>
10,000
N.
R.
Fink,
1977
MRID
#
130649
acceptable
Sodium
Chlorite/
80%
Mallard
Duck
(
Anas
platyrhynchos)
>
10,000
N.
R.
Fink,
1977
MRID
#
130650
acceptable
Sodium
Chlorite/
25%
Mallard
Duck
(
Anas
platyrhynchos)
18686
(
8186­
109184)
N.
R.
MBA
Laboratories,
1983
ACC
#
252854
acceptable
Sodium
Chlorite/
25%
Northern
bobwhite
(
Colinus
virginianus)
2031(
1226­
3903)
417
MBA
Laboratories,
1984
ACC
#
252854
acceptable
Note:
LC50=
Median
Lethal
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration;
N.
R.=
Not
Reported
These
results
indicate
that
chlorine
dioxide/
sodium
chlorite
range
from
slighly
toxic
to
practically
non­
toxic
to
birds
on
a
subacute
dietary
basis.
The
guideline
requirement
(
71­
2/
OPPTS
850.2200)
is
fulfilled.

B.
Birds,
Chronic
Avian
reproduction
studies
using
the
technical
grade
of
the
active
ingredient
are
required
for
a
pesticide
when
any
of
the
following
conditions
are
met:
(
1)
birds
may
be
subject
to
repeated
or
continuous
exposure
to
the
pesticide,
especially
preceding
or
during
the
breeding
season,
(
2)
the
pesticide
is
stable
in
the
environment
to
the
extent
that
potentially
toxic
amounts
may
persist
in
animal
feed,
(
3)
the
pesticide
is
stored
or
accumulated
in
plant
or
animal
tissues,
and/
or
(
4)
information
derived
from
mammalian
reproduction
studies
indicates
reproduction
in
terrestrial
Page
5
of
33
vertebrates
may
be
adversely
affected
by
the
anticipated
use
of
the
product.
The
currently
registered
uses
of
chlorine
dioxide/
sodium
chlorite
do
not
require
avian
reproduction
testing.
II.
Toxicity
to
Freshwater
Aquatic
Animals
A.
Freshwater
Fish,
Acute
Two
fish
toxicity
studies
using
the
TGAI
are
required
to
establish
the
toxicity
of
a
pesticide
to
freshwater
fish.
The
preferred
test
species
are
rainbow
trout
(
a
cold
water
fish)
and
bluegill
sunfish
(
a
warm
water
fish).
The
results
of
studies
submitted
for
sodium
chlorite
are
provided
in
the
following
table.

Table
3.
Acute
Toxicity
of
Chlorine
Dioxide
and
Sodium
Chlorite
to
Freshwater
Fish
Substance/%
Active
Ingredient
(
AI)
Organism
Endpoints/
Results
(
ppm)
(
95%
conf.
interval)
Reference
Study
Classification
Sodium
Chlorite/
80%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
360
(
216­
600)
NOAEC
=
216
Barrows,
1984
MRID
#
94068007
acceptable
Sodium
Chlorite/
80%
Bluegill
(
Lepomis
macrochirus)
LC50
=
244
(
196­
304)
NOAEC
=
108
Larkin,
1984
ACC
#
254181
acceptable
Sodium
Chlorite/
80%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
360
(
216­
600)
NOAEC
=
216
Larkin,
1984
ACC
#
254180
acceptable
Sodium
Chlorite/
80.25%
Bluegill
(
Lepomis
macrochirus)
LC50
=
265
(
231­
309)
NOAEC
=
130
EG&
G
Bionomics,
1978
ACC
#
69809
supplemental
Sodium
Chlorite/
79%
Bluegill
(
Lepomis
macrochirus)
LC50
=
208
(
165­
262)
NOAEC
=
N.
R.
Sleight
III,
1971
MRID
#
131351
supplemental
Sodium
Chlorite/
79%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
50.6
(
38.8­
65.8)
NOAEC
=
N.
R.
Sleight
III,
1971
MRID
#
131351
supplemental
Sodium
Chlorite/
80%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
>
100
NOAEC
=
N.
R.
McMillen,
1985
ACC
#
253743
supplemental
Sodium
Chlorite/
80%
Bluegill
(
Lepomis
macrochirus)
LC50
>
100
NOAEC
=
N.
R.
McMillen,
1985
ACC
#
253743
supplemental
Sodium
Chlorite/
25%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
203
(
175­
236)
NOAEC
=
100
MBA
Laboratories,
1984
ACC
#
252854
acceptable
Page
6
of
33
Substance/%
Active
Ingredient
(
AI)
Organism
Endpoints/
Results
(
ppm)
(
95%
conf.
interval)
Reference
Study
Classification
Sodium
Chlorite/
25%
Bluegill
(
Lepomis
macrochirus)
LC50
=
222
(
207­
237)
NOAEC
=
186
MBA
Laboratories,
1983
ACC
#
252854
supplemental
Sodium
Chlorite/
81.5%
Bluegill
(
Lepomis
macrochirus)
LC50
=
310
(
270­
350)
NOAEC
=
220
Sousa,
1981
ACC
#
245697
acceptable
Sodium
Chlorite/
80.25%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
290
(
250­
340)
NOAEC
=
<
70
EG&
G
Bionomics,
1979
ACC
#
69810
acceptable
Sodium
Chlorite/
80%
Rainbow
trout
(
Oncorhynchus
mykiss)
LC50
=
340
(
220­
600)
NOAEC
=
130
Sousa
and
Surprenant,
1984
ACC
#
253379
acceptable
Sodium
Chlorite/
80%
Bluegill
(
Lepomis
macrochirus)
LC50
=
420
(
220­
600)
NOAEC
=
220
Sousa
and
Surprenant,
1984
MRID
#
94068006
acceptable
Note:
LC50=
Median
Lethal
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration;
N.
R.=
Not
Reported
These
results
indicate
that
chlorine
dioxide/
sodium
chlorite
range
from
slightly
toxic
to
practically
non­
toxic
to
freshwater
fish
on
an
acute
basis.
The
guideline
requirement
(
72­
1/
OPPTS
850.1075)
is
fulfilled.

B.
Freshwater
Fish,
Chronic
A
freshwater
fish
early
life­
stage
test
using
the
technical
grade
of
the
active
ingredient
is
required
for
a
pesticide
when
it
may
be
applied
directly
to
water
or
if
the
end­
use
product
is
expected
to
be
transported
to
water
from
the
intended
use
site,
and
any
of
the
following
conditions
are
met:
(
1)
the
pesticide
is
intended
for
use
such
that
its
presence
in
water
is
likely
to
be
continuous
or
recurrent
regardless
of
toxicity,
(
2)
any
aquatic
acute
LC50
or
EC503
is
less
than
1
mg/
l,
(
3)
the
EEC
(
estimated
environmental
concentration)
in
water
is
equal
to
or
greater
than
0.01
of
any
acute
LC50
or
EC50
value,
or
(
4)
the
actual
or
estimated
environmental
concentration
in
water
resulting
from
use
is
less
than
0.01
of
any
acute
LC50
or
EC50
value
and
any
one
of
the
following
conditions
exist:
studies
of
other
organisms
indicate
the
reproductive
physiology
of
fish
may
be
affected,
physicochemical
properties
indicate
cumulative
effects,
or
the
pesticide
is
persistent
in
water
(
e.
g.,
half­
life
greater
than
4
days).
The
preferred
test
species
is
rainbow
trout,
but
other
species
may
be
used.
Freshwater
fish
early
life­
stage
testing
is
required
for
chlorine
dioxide
and
sodium
chlorite
in
order
to
support
once­
through
cooling
tower
uses.
No
data
under
this
topic
have
been
submitted;
therefore
Guideline
72­
4/
OPPTS
850.1300
is
not
fulfilled.

3
EC50=
Median
Effective
Concentration
Page
7
of
33
C.
Freshwater
Invertebrates,
Acute
A
freshwater
aquatic
invertebrate
toxicity
test
using
the
TGAI
is
required
to
establish
the
toxicity
of
chlorine
dioxide
and
sodium
chlorite
to
freshwater
aquatic
invertebrates.
The
preferred
test
species
is
Daphnia
magna.
Results
of
this
test
are
tabulated
below.

Table
4.
Acute
Toxicity
of
Chlorine
Dioxide
and
Sodium
Chlorite
to
Freshwater
Invertebrates
Substance/%
Active
Ingredient
(
AI)
Organism
Endpoints/
Results
(
ppm)
(
95%
conf.
interval)
Reference
Study
Classification
Sodium
Chlorite/
80%
Daphnia
magna
EC50
=
0.027
(
0.021­
0.031)
NOAEC
=
0.003
Barrows,
1984
MRID
#
146162
acceptable
Sodium
Chlorite/
80%
Daphnia
magna
EC50
=
0.39
(
0.32­
0.54)
NOAEC
=
N.
R.
Hoberg
and
Surprenant,
1984
MRID
#
141149
acceptable
Sodium
Chlorite/
79%
Daphnia
magna
EC50
=
0.29
(
0.25­
0.33)
NOAEC
=
0.10
Vilkas,
1976
MRID
#
131350
acceptable
Sodium
Chlorite/
80%
Daphnia
magna
EC50
=
0.08
(
0.06­
0.10)
NOAEC
=
0.06
Larkin,
1984
ACC
#
254182
acceptable
Sodium
Chlorite/
80%
Daphnia
magna
EC50
=
0.146
(
0.12
­
0.18)
NOAEC
=
0.06
Nackord,
1984
MRID
#
94068009
acceptable
Sodium
Chlorite/
25%
Daphnia
magna
EC50
=
1.4
(
1.0­
1.9
)
NOAEC
=
0.4
MBA
Laboratories,
1984
ACC
#
252854
supplemental
Note:
EC50=
Median
Effective
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration;
N.
R.=
Not
Reported
These
studies
indicate
that
chlorine
dioxide
and
sodium
chlorite
range
from
very
highly
toxic
for
technical
grade
sodium
chlorite
a.
i.
to
moderately
toxic
for
the
formulated
product
to
aquatic
invertebrates
on
an
acute
basis.
The
guideline
requirement
(
72­
2/
OPPTS
850.1010)
is
fulfilled.

D.
Freshwater
Invertebrates,
Chronic
A
freshwater
aquatic
invertebrate
life­
cycle
test
using
the
technical
grade
of
the
active
ingredient
is
required
for
a
pesticide
if
the
end­
use
product
may
be
applied
directly
to
water
or
expected
to
be
transported
to
water
from
the
intended
use
site,
and
any
of
the
following
conditions
are
met:
(
1)
the
pesticide
is
intended
for
use
such
that
its
presence
in
water
is
likely
to
be
continuous
or
recurrent
regardless
of
toxicity,
(
2)
any
aquatic
acute
LC50
or
EC50
is
less
than
1
mg/
l,
(
3)
the
Page
8
of
33
EEC
in
water
is
equal
to
or
greater
than
0.01
of
any
acute
EC50
or
LC50
value,
or
(
4)
the
actual
or
estimated
environmental
concentration
in
water
resulting
from
use
is
less
than
0.01
of
any
aquatic
acute
EC50
or
LC50
value
and
any
of
the
following
conditions
exist:
studies
of
other
organisms
indicate
the
reproductive
physiology
of
invertebrates
may
be
affected,
physicochemical
properties
indicate
cumulative
effects,
or
the
pesticide
is
persistent
in
water
(
e.
g.,
half­
life
greater
than
4
days).
The
preferred
test
species
is
Daphnia
magna.
Freshwater
fish
early
life­
stage
testing
is
required
for
chlorine
dioxide/
sodium
chlorite
in
order
to
support
once­
through
cooling
tower
uses.
No
data
under
this
topic
have
been
submitted;
therefore
Guideline
72­
4b/
OPPTS
850.1400
is
not
fulfilled.

E.
Freshwater
Field
Studies
Freshwater
field
testing
is
required
for
pesticides
in
cases
where
there
are
risks
of
concern
from
labeled
use
patterns.
This
testing
was
not
required
for
chlorine
dioxide
and
sodium
chlorite
and
is
reserved
at
the
present
time.

III.
Toxicity
to
Estuarine
and
Marine
Animals
A.
Estuarine
and
Marine
Fish,
Acute
Acute
toxicity
testing
with
estuarine/
marine
fish
using
the
technical
grade
of
the
active
ingredient
is
required
for
a
chemical
when
the
end­
use
product
is
intended
for
direct
application
to
the
marine/
estuarine
environment
or
the
active
ingredient
is
expected
to
reach
this
environment
because
of
its
use
in
coastal
counties.
The
preferred
test
species
is
sheepshead
minnow.
Results
of
this
test
are
tabulated
below.

Table
5.
Acute
Toxicity
of
Chlorine
Dioxide/
Sodium
Chlorite
to
Estuarine/
Marine
Fish
Substance/%
Active
Ingredient
(
AI)
Organism
96
hr
LC50
mg/
L
(
ppm)
(
95%
conf.
interval)
NOAEC
mg/
L
(
ppm)
Reference
Study
Classification
Sodium
Chlorite/
79%
Sheepshead
minnow
(
Cyprinodon
variegatus)
75
(
62.6­
89.8)
13.9
Yurk
and
Overman,
1994
MRID
#
43259401
acceptable
Note:
LC50=
Median
Lethal
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration
The
results
indicate
that
chlorine
dioxide/
sodium
chlorite
are
slightly
toxic
to
estuarine/
marine
fish
on
an
acute
basis.
The
guideline
requirement
(
72­
3a/
OPPTS
850.1025)
is
fulfilled.

B.
Estuarine
and
Marine
Fish,
Chronic
Estuarine/
marine
fish
early
life­
stage
testing
is
not
required
for
the
currently
registered
uses
of
chlorine
dioxide
and
sodium
chlorite.
Since
freshwater
and
estuarine/
marine
fish
are
comparably
Page
9
of
33
sensitive
to
sodium
chlorite
on
an
acute
basis,
the
freshwater
early
life­
stage
endpoints
will
suffice
for
assessing
risk
to
estuarine/
marine
fish
species.
However,
as
noted
above,
the
data
requirement
for
freshwater
fish
early
life­
stage
testing
(
72­
4a/
850.1300)
has
not
been
fulfilled.

C.
Estuarine
and
Marine
Invertebrates,
Acute
Acute
toxicity
testing
with
estuarine/
marine
invertebrates
using
the
technical
grade
of
the
active
ingredient
is
required
for
a
pesticide
when
the
end­
use
product
is
intended
for
direct
application
to
the
marine/
estuarine
environment
or
the
active
ingredient
is
expected
to
reach
this
environment
because
of
its
use
in
coastal
counties.
The
preferred
test
species
are
the
mysid
shrimp
and
eastern
oyster.
Results
of
these
tests
are
tabulated
below.

Table
6:
Acute
Toxicity
of
Chlorine
Dioxide
and
Sodium
Chlorite
to
Estuarine/
Marine
Invertebrates
Substance/
%
Active
Ingredient
(
AI)
Organism
96­
hour
EC50
mg/
L
(
ppm)
(
95%
conf.
interval)
Reference
Study
Classification
Sodium
Chlorite/
79%
Eastern
oyster
(
Crassostrea
virginica)
21.4
(
14.3­
27.1)
NOAEC
=
14.3
Yurk
and
Overman,
1994
MRID
#
43259403
acceptable
Sodium
Chlorite/
79%
Mysid
(
Mysidopsis
bahia)
0.576
(
0.44­
0.75)
NOAEC=
N.
R.
Yurk
and
Overman,
1994
MRID
#
43259402
acceptable
Note:
EC50=
Median
Effective
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration
The
results
indicate
that
chlorine
dioxide/
sodium
chlorite
range
from
highly
toxic
to
slightly
toxic
to
estuarine/
marine
invertebrates
on
an
acute
basis.
The
guideline
requirements
(
72­
3b
and
72­
3c/
OPPTS
850.1035
and
850.1045)
are
fulfilled.

D.
Estuarine
and
Marine
Invertebrate,
Chronic
An
estuarine/
marine
invertebrate
life­
cycle
toxicity
test
is
required
for
a
pesticide
if
the
end­
use
product
may
be
applied
directly
to
estuarine
or
marine
waters,
or
is
expected
to
be
transported
to
these
waters
from
the
intended
use
site,
and
any
of
the
following
conditions
are
met:
(
1)
the
pesticide
is
intended
for
use
such
that
its
presence
in
water
is
likely
to
be
continuous
or
recurrent
regardless
of
toxicity,
(
2)
any
aquatic
acute
LC50
or
EC50
is
less
than
1
mg/
l,
(
3)
the
EEC
in
water
is
equal
to
or
greater
than
0.01
of
any
acute
EC50
or
LC50
value,
or
(
4)
the
actual
or
estimated
environmental
concentration
in
water
resulting
from
use
is
less
than
0.01
of
any
aquatic
acute
EC50
or
LC50
value
and
any
of
the
following
conditions
exist:
studies
of
other
organisms
indicate
the
reproductive
physiology
of
invertebrates
may
be
affected,
physicochemical
properties
indicate
cumulative
effects,
or
the
pesticide
is
persistent
in
water
(
e.
g.,
half­
life
greater
than
4
days).
Due
to
the
high
acute
toxicity
of
sodium
chlorite
to
estuarine/
marine
invertebrates,
lifecycle
testing
is
necessary;
however,
freshwater
invertebrates
tend
to
be
more
sensitive
than
estuarine/
marine
invertebrates
to
sodium
chlorite
on
an
acute
basis,
and,
therefore,
freshwater
life
Page
10
of
33
cycle
endpoints
will
suffice
for
assessing
risk
to
estuarine/
marine
invertebrate
species.
As
noted
above,
freshwater
invertebrate
life­
cycle
testing
(
72­
4b/
850.1400)
has
not
been
submitted.
E.
Estuarine
and
Marine
Field
Studies
No
estuarine
or
marine
field
study
testing
is
currently
required
for
chlorine
dioxide
and
sodium
chlorite.

IV.
Toxicity
to
Plants
A.
Terrestrial/
Semi­
aquatic
Currently,
terrestrial
plant
testing
is
not
required
for
pesticides
other
than
herbicides
except
on
a
case­
by­
case
basis
(
e.
g.,
labeling
bears
phytotoxicity
warnings,
incidents
of
plant
damage
have
been
reported,
or
literature
indicating
phytotoxicity
is
available).
The
once­
through
cooling
tower
use
of
chlorine
dioxide/
sodium
chlorite
requires
such
testing,
due
to
the
algaecidal
nature
of
the
chemical
and
the
likelihood
of
exposure
to
semi­
aquatic
plants
along
surface
waters
receiving
industrial
facility
outfall
from
the
cooling
system.
Results
of
these
tests
are
tabulated
below.

Table
7.
Toxicity
of
Chlorine
Dioxide/
Sodium
Chlorite
to
Terrestrial/
Semi­
aquatic
Plants
Substance/%
Active
Ingredient
(
AI)
Organism
EC25
(
ppm)
Reference
Study
Classification
Sodium
Chlorite/
80%
Monocots
&
Dicots
(
10
Species)
>
3.5
Backus
et
al.,
1990
MRID
#
41843101
acceptable
Sodium
Chlorite/
80%
Monocots
&
Dicots
(
9
Species)
>
3.5
Backus
et
al.,
1990
MRID
#
41843102
acceptable
Sodium
Chlorite/
80%
Buckwheat
(
Polygonum
convolvulus)
<
3.5
Backus
et
al.,
1990
MRID
#
41843102
acceptable
Note:
EC25=
Effective
Concentration
(
25th
Percentile)

The
results
indicate
that
chlorine
dioxide/
sodium
chlorite
are
moderately
toxic
to
terrestrial
plants.
The
guideline
requirement
(
122­
1/
OPPTS
850.4100
and
850.4150)
is
fulfilled.
However,
since
the
maximum
label
rate
for
many
of
the
chlorine
dioxide/
sodium
chlorite
once­
through
cooling
labels
was
not
used
in
these
tests,
it
is
necessary
to
conduct
Tier
II
testing
with
rice.
Guideline
123­
1/
OPPTS
850.4225
and
850.4250,
Seedling
Emergence
and
Vegetative
Vigor
testing
with
Rice
(
Oryza
sativa)
is
not
fulfilled.

B.
Aquatic
The
once­
through
cooling
tower
use
of
chlorine
dioxide/
sodium
chlorite
requires
that
5
aquatic
plant
tests
be
conducted
due
to
the
algaecidal
nature
of
the
chemical
and
the
likelihood
of
exposure
to
aquatic
plants
in
surface
waters
receiving
industrial
facility
outfall
from
the
cooling
system.
Guideline
123­
2/
OPPTS
850.4400
and
850.5400,
Vascular
Aquatic
Plant
and
Algal
Page
11
of
33
dose­
response
toxicity
testing
(
5
species),
is
not
fulfilled
because
only
one
study
(
1
species)
under
this
topic
has
been
submitted
and
5
are
required.
The
results
of
this
test
are
tabulated
below.
The
following
aquatic
plant
studies
are
still
required:
blue­
green
cyanobacteria
(
Anabaena
flos­
aquae),
freshwater
diatom
(
Navicula
pelliculosa),
marine
diatom
(
Skeletonema
costatum)
and
floating
macrophyte
(
Lemna
gibba).

Table
8.
Toxicity
of
Chlorine
Dioxide/
Sodium
Chlorite
to
Aquatic
Plants
Substance/%
Active
Ingredient
(
AI)
Organism
96
hr
EC50
(
ppm)
(
95%
conf.
interval)
Reference
Study
Classification
Sodium
Chlorite/
80%
Green
algae
(
Selenastrum
capricornutum)
1.32
(
1.18­
1.47)
NOAEC
=
<
0.62
Ward
and
Boeri,
1991
MRID
#
41880403
supplemental
Note:
EC50=
Median
Effective
Concentration;
NOAEC=
No
Observed
Adverse
Effect
Concentration
The
results
indicate
that
chlorine
dioxide/
sodium
chlorite
are
moderately
toxic
to
aquatic
plants.
Risk
Assessment
and
Characterization:

Risk
assessment
integrates
the
results
of
the
exposure
and
ecotoxicity
data
to
evaluate
the
likelihood
of
adverse
ecological
effects.
One
method
of
integrating
the
results
of
exposure
and
ecotoxicity
data
is
called
the
quotient
method.
For
this
method,
risk
quotients
(
RQs)
are
calculated
by
dividing
exposure
estimates
by
ecotoxicity
values,
both
acute
and
chronic:

RQ
=
EXPOSURE/
TOXICITY
RQs
are
then
compared
to
levels
of
concern
(
LOCs).
These
LOCs
are
criteria
used
by
OPP
to
indicate
potential
risk
to
nontarget
organisms
and
the
need
to
consider
regulatory
action.
The
criteria
indicate
that
a
pesticide
used
as
directed
has
the
potential
to
cause
adverse
effects
on
nontarget
organisms.
LOCs
currently
address
the
following
risk
presumption
categories:
(
1)
acute
high
­
the
potential
for
acute
risk
is
high,
regulatory
action
may
be
warranted
in
addition
to
restricted
use
classification;
(
2)
acute
restricted
use
­
the
potential
for
acute
risk
is
high,
but
this
may
be
mitigated
through
restricted
use
classification;
(
3)
acute
endangered
species
­
the
potential
for
acute
risk
to
endangered
species
is
high,
and
regulatory
action
may
be
warranted,
and
(
4)
chronic
risk
­
the
potential
for
chronic
risk
is
high,
and
regulatory
action
may
be
warranted.
Currently,
AD
does
not
perform
assessments
for
chronic
risk
to
plants,
acute
or
chronic
risks
to
nontarget
insects,
or
chronic
risk
from
granular/
bait
formulations
to
mammalian
or
avian
species.

The
ecotoxicity
test
values
(
i.
e.,
measurement
endpoints)
used
in
the
acute
and
chronic
risk
quotients
are
derived
from
the
results
of
required
studies.
Examples
of
ecotoxicity
values
derived
from
the
results
of
short­
term
laboratory
studies
that
assess
acute
effects
are:
(
1)
LC50
(
fish
and
birds)
(
2)
LD50
(
birds
and
mammals)
(
3)
EC50
(
aquatic
plants
and
aquatic
invertebrates)
and
(
4)
EC25
(
terrestrial
plants).
The
NOAEC
value
is
used
as
the
ecotoxicity
test
value
in
assessing
Page
12
of
33
chronic
effects.

Risk
presumptions,
along
with
the
corresponding
RQs
and
LOCs
are
tabulated
below.

Risk
Presumptions
for
Terrestrial
Animals
Risk
Presumption
RQ
LOC
Birds
and
Wild
Mammals
Acute
High
Risk
EEC1/
LC50
or
LD50/
sqft2
or
LD50/
day3
0.5
Acute
Restricted
Use
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOEC
1
1
abbreviation
for
Estimated
Environmental
Concentration
(
ppm)
on
avian/
mammalian
food
items
2
mg/
ft2
3
mg
of
toxicant
consumed/
day
LD50
*
wt.
of
bird
LD50
*
wt.
of
bird
Risk
Presumptions
for
Aquatic
Animals
Risk
Presumption
RQ
LOC
Acute
High
Risk
EEC1/
LC50
or
EC50
0.5
Acute
Restricted
Use
EEC/
LC50
or
EC50
0.1
Acute
Endangered
Species
EEC/
LC50
or
EC50
0.05
Chronic
Risk
EEC/
MATC2
or
NOEC
1
1
EEC
=
(
ppm
or
ppb)
in
water
2
MATC
=
maximum
allowable
toxicant
concentration
Page
13
of
33
Risk
Presumptions
for
Plants
Risk
Presumption
RQ
LOC
Terrestrial
and
Semi­
Aquatic
Plants
Acute
High
Risk
EEC/
EC25
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
Aquatic
Plants
Acute
High
Risk
EEC1/
EC50
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
1
EEC
=
(
ppb/
ppm)
in
water
1.
Environmental
Fate
Assessment
Summary
This
section
is
a
summary
of
the
Environmental
Fate
Risk
Assessment.

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
chloride/
acid.
Moreover,
chlorite
is
a
breakdown
product
of
chlorine
dioxide.

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).
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.
The
estimated
log
Kow
of
chlorine
dioxide
is
­
3.22
so
it
is
not
likely
to
bioaccumulate
in
aquatic
organisms.

Sodium
Chlorite
is
a
solid,
white
powder.
It
is
highly
water
soluble
and
immediately
dissociates
into
sodium
and
chlorite
ions.
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
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.
The
estimated
log
Kow
for
sodium
chlorite
is
­
7.17
and
it
is
not
likely
to
bioaccumulate
in
aquatic
organisms.
Page
14
of
33
Chlorate
and
chlorite
ions
show
a
tendency
to
undergo
biodegradation
under
anaerobic
conditions
only.
There
are
no
reports
indicating
these
ions
undergo
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.

2.
Environmental
Exposure
Assessment
The
Probabilistic
Distribution
Model
version
4
(
PDM4)
was
used
to
estimate
exposure
from
once­
through
cooling
tower
uses.
The
details
of
this
model
can
be
found
in
the
Chlorine
Dioxide
and
Sodium
Chlorite
Environmental
Modeling
Chapter.
The
model
was
used
to
provide
the
percentage
of
days
per
year
various
concentrations
are
exceeded
for
several
different
flow,
application,
and
dosing
scenarios.

Three
different
flow
regimes
were
considered:
high
flow
[
power
plants
with
average
stream
flow
rates
of
1000"
50
million
gallons
per
day
(
MGD)];
medium
flow
(
power
plants
with
average
stream
flow
rates
of
500"
50
MGD);
and
low
flow
(
power
plants
with
average
stream
flow
rates
of
100"
10
MGD).
These
plants
were
taken
from
the
NPDES
database
of
plant
codes;
12
plants
were
used
in
each
the
low
and
medium
flow
category,
and
6
plants
were
used
in
the
high
flow
category
(
see
Environmental
Modeling
Chapter,
page
5,
for
a
listing
of
these
plants).
The
7Q10
flow
rate
(
a
flow
rate
that
a
stream
is
expected
to
be
below
for
seven
consecutive
days
once
every
ten
years)
for
each
of
the
selected
plants
was
used
to
develop
a
mean
7Q10
flow
rate
for
each
category.
This
mean
7Q10
flow
rate
was
used
as
the
input
parameter
for
flow
in
the
PDM4
model.

Two
pesticide
application
scenarios,
continuous
feed
and
intermittent
feed,
were
used
in
the
modeling,
based
on
label
instructions.
For
continuous
feed
use,
the
label
rates
ranged
from
0.10
ppm
to
2.0
ppm
chlorine
dioxide/
sodium
chlorite
in
the
water.
For
intermittent
use,
the
label
rates
ranged
from
0.10
ppm
to
25
ppm
chlorine
dioxide/
sodium
chlorite
in
the
water.
A
single
label
contained
the
rate
of
800
ppm
chlorine
dioxide/
sodium
chlorite
and
did
not
specify
whether
this
was
for
continuous
or
intermittent
use.
It
is
believed
that
the
single
label
with
the
800
ppm
dose
rate
will
be
either
cancelled
or
amended
by
the
registrant
to
delete
this
dose.
The
concentrations
(
the
Aconcentrations
of
concern,@
or
COC)
used
in
the
model
were
endpoints
from
aquatic
organism
toxicity
studies
with
sodium
chlorite.

Exceedance
values
for
average
and
worst­
case
situations
were
modeled.
The
average
values
were
calculated
by
averaging
all
of
the
values
for
a
given
flow
category.
The
worst­
case
values
were
calculated
by
averaging
the
highest
(
peak)
values
for
a
given
flow
category.
Page
15
of
33
Additional
details
on
the
PDM4
model
and
the
specific
inputs,
assumptions,
and
output
can
be
found
in
the
Environmental
Modeling
Chapter.

Risk
to
Aquatic
Organisms
from
Once­
Through
Cooling
Use
of
Chlorine
Dioxide/
Sodium
Chlorite
Since
the
modeling
for
chlorine
dioxide/
sodium
chlorite
provides
results
as
percent
days
per
year
a
particular
concentration
is
exceeded,
Risk
Quotients
were
not
used
in
the
usual
way
to
provide
numeric
estimates
of
risk.
Instead,
the
endpoints
from
various
toxicity
studies
were
adjusted
to
determine
the
numeric
Level
of
Concern
(
LOC)
for
each
taxa
for
both
acute
and
chronic
effects.
The
adjustment
factor
is
the
same
as
the
one
used
with
the
RQ
method,
e.
g.
0.5
*
LC50
or
EC50
for
acute
effects,
and
0.05
*
LC50
or
EC50
for
acute
endangered
species
risks.
The
chronic
LOC
needs
no
adjustment.
The
modeling
results
provided
the
percentage
of
days
concentrations
were
exceeded
for
a
range
encompassing
the
numeric
LOCs.
When
a
specific
LOC
was
not
listed
in
the
modeling
output
tables,
the
percent
days
exceeded
for
the
LOC
was
interpolated
from
the
closest
numbers
above
and
below
the
specific
LOC.
The
percentage
of
days
was
then
multiplied
by
365
to
provide
the
number
of
days
per
year
the
LOC
is
exceeded.

Values
for
LOC
percent
days
exceeded
were
interpolated
where
necessary,
using
Tables
5
through
10
and
23
through
28
of
the
Environmental
Modeling
Chapter.
If
the
number
of
days
an
LOC
is
exceeded
is
greater
than
the
number
of
days
used
to
determine
the
endpoint
in
toxicity
testing,
risk
is
assumed.
This
assumes
that
the
number
of
days
exceeded
are
consecutive,
a
conservative
but
not
impossible
assumption.

In
the
following
tables,
Arisk@
indicates
that
the
LOC
was
exceeded
for
more
than
2
days
per
year
for
freshwater
invertebrates
and
for
more
than
4
days
per
year
for
all
other
organisms.
Where
there
is
risk,
the
number
of
days
the
LOC
was
exceeded
is
indicated
in
bold
type.
Page
16
of
33
Tables
9A­
L:
Number
of
Days
per
Year
Levels
of
Concern
are
Exceeded
by
the
Once­
Through
Cooling
Use
of
Chlorine
Dioxide/
Sodium
Chlorite
A.
Continuous
feed,
800
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
262.44
days]
{
363.54
days}
2.53
ppm
[
340.74
days]
{
365
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
365
days]
{
365
days}
0.001
ppm
[
365
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
246.74
days]
{
359.16
days}
3.75
ppm
[
325.86
days]
{
365
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
286.45
days]
{
365
days}
1.07
ppm
[
358.54
days]
{
365
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
365
days]
{
365
days}
0.029
ppm
[
365
days]
{
365
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
355.49
days]
{
365
days}
0.62
ppm
(
NOEC)
[
363.70
days]
{
365
days}

The
average
scenario
of
a
continuous
feed
of
800
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
fish,
endangered
and
nonendangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
a
continuous
feed
of
800
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
Page
17
of
33
plants.

B.
Continuous
feed,
800
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
170.82
days]
{
363.54
days}
2.53
ppm
[
296.74
days]
{
365
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
365
days]
{
365
days}
0.001
ppm
[
365
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
147.46
days]
{
359.16
days}
3.75
ppm
[
273.16
days]
{
365
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
216.34
days]
{
365
days}
1.07
ppm
[
324.96
days]
{
365
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
355.88
days]
{
365
days}
0.029
ppm
[
365
days]
{
365
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
320.12
days]
{
365
days}
0.62
ppm
(
NOEC)
[
335.35
days]
{
365
days}

The
average
scenario
of
a
continuous
feed
of
800
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
fish,
endangered
and
nonendangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
a
continuous
feed
of
800
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
18
of
33
C.
Intermittent
feed,
800
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
1.11
days]
{
3.46
days}
2.53
ppm
[
139.49
days]
{
223
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
356.19
days]
{
365
days}
0.001
ppm
[
365
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
0.35
days]
{
1.25
days}
3.75
ppm
[
89.53
days]
{
147.50
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
9.34
days]
{
21.77
days}
1.07
ppm
[
199.29
days]
{
313.35
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
259.52
days]
{
362.81
days}
0.029
ppm
[
338.65
days]
{
365
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
189.05
days]
{
297.88
days}
0.62
ppm
(
NOEC)
[
220.75
days]
{
341.31
days}

The
average
scenario
of
an
intermittent
feed
of
800
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
an
intermittent
feed
of
800
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
nonendangered
aquatic
plants.
Page
19
of
33
D.
Intermittent
feed,
800
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
1.73
days]
{
18.54
days}
2.53
ppm
[
73.88
days]
{
230.80
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
320.76
days]
{
365
days}
0.001
ppm
[
364.64
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
0.89
days]
{
10.11
days}
3.75
ppm
[
47.09
days]
{
168.96
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
6.54
days]
{
53.54
days}
1.07
ppm
[
105.97
days]
{
304.80
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
165.71
days]
{
359.16
days}
0.029
ppm
[
293.61
days]
{
365
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
100.48
days]
{
292.13
days}
0.62
ppm
(
NOEC)
[
120.43
days]
{
329.19
days}

The
average
scenario
of
an
intermittent
feed
of
800
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
an
intermittent
feed
of
800
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
nonendangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
20
of
33
E.
Intermittent
feed,
25
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
9.78x10­
7
days]
{
5.40x10­
6
days}
2.53
ppm
[
1.03
days]
{
3.05
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
249.07
days]
{
343.39
days}
0.001
ppm
[
329.96
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
1.24x10­
7
days]
{
7.01x10­
7
days}
3.75
ppm
[
0.53
days]
{
1.58
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
7.49x10­
5
days]
{
3.88x10­
4
days}
1.07
ppm
[
1.63
days]
{
4.80
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
12.15
days]
{
27.23
days}
0.029
ppm
[
204.15
days]
{
293.61
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
1.52
days]
{
4.50
days}
0.62
ppm
(
NOEC)
[
2.91
days]
{
7.65
days}

The
average
scenario
of
an
intermittent
feed
of
25
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates
and
endangered
and
non­
endangered
marine/
estuarine
invertebrates.
The
worst­
case
scenario
of
an
intermittent
feed
of
25
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
nonendangered
aquatic
plants.
Page
21
of
33
F.
Intermittent
feed,
25
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
4.42x10­
5
days]
{
5.29x10­
4
days}
2.53
ppm
[
1.34
days]
{
13.82
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
163.81
days]
{
341.49
days}
0.001
ppm
[
267.55
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
5.11x10­
6
days]
{
6.13x10­
5
days}
3.75
ppm
[
0.71
days]
{
7.33
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
2.55x10­
3
days]
{
0.03
days}
1.07
ppm
[
2.09
days]
{
21.58
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
8.03
days]
{
61.32
days}
0.029
ppm
[
125.34
days]
{
292.38
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
1.96
days]
{
20.25
days}
0.62
ppm
(
NOEC)
[
2.92
days]
{
27.80
days}

The
average
scenario
of
an
intermittent
feed
of
25
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates
and
endangered
and
non­
endangered
marine/
estuarine
invertebrates.
The
worst­
case
scenario
of
an
intermittent
feed
of
25
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
nonendangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
nonendangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
22
of
33
G.
Continuous
feed,
2.0
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
9.89x10­
3
days]
{
0.04
days}
2.53
ppm
[
47.99
days]
{
77.19
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
324.83
days]
{
364.86
days}
0.001
ppm
[
364.64
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
2.03x10­
3
days]
{
9.75x10­
3
days}
3.75
ppm
[
25.71
days]
{
42.54
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
0.23
days]
{
0.83
days}
1.07
ppm
[
74.64
days]
{
118.66
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
165.35
days]
{
275.21
days}
0.029
ppm
[
303.90
days]
{
364.52
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
70.08
days]
{
111.56
days}
0.62
ppm
(
NOEC)
[
91.07
days]
{
145.89
days}

The
average
scenario
of
a
continuous
feed
of
2.0
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
a
continuous
feed
of
2.0
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
nonendangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
23
of
33
H.
Continuous
feed,
2.0
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
0.10
days]
{
1.19
days}
2.53
ppm
[
22.60
days]
{
98.70
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
259.22
days]
{
364.57
days}
0.001
ppm
[
348.58
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
0.03
days]
{
0.41
days}
3.75
ppm
[
12.82
days]
{
62.60
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
0.68
days]
{
7.74
days}
1.07
ppm
[
34.31
days]
{
141.90
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
78.84
days]
{
264.26
days}
0.029
ppm
[
229.80
days]
{
363.55
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
32.30
days]
{
134.50
days}
0.62
ppm
(
NOEC)
[
42.03
days]
{
165.88
days}

The
average
scenario
of
a
continuous
feed
of
2.0
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
The
worst­
case
scenario
of
a
continuous
feed
of
2.0
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
freshwater
fish,
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
marine/
estuarine
fish,
endangered
and
nonendangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
24
of
33
I.
Continuous
feed,
0.10
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
negligible]
{
negligible}
2.53
ppm
[
0.06
days]
{
0.24
days}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
200.47
days]
{
310.07
days}
0.001
ppm
[
294.19
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
negligible]
{
negligible}
3.75
ppm
[
0.03
days]
{
0.12
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
6.55x10­
7
days]
{
3.96x10­
6
days}
1.07
ppm
[
0.09
days]
{
0.37
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
1.28
days]
{
3.94
days}
0.029
ppm
[
143.21
days]
{
225.21
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
0.09
days]
{
0.35
days}
0.62
ppm
(
NOEC)
[
0.23
days]
{
0.79
days}

The
average
scenario
of
a
continuous
feed
of
0.10
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates
and
endangered
marine/
estuarine
invertebrates.
The
worst­
case
scenario
of
a
continuous
feed
of
0.10
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates
and
endangered
marine/
estuarine
invertebrates.
Page
25
of
33
J.
Continuous
feed,
0.10
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
1.53x10­
7
days]
{
1.84x10­
6
days}
2.53
ppm
[
0.25
days]
[
2.92
days]

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
109.28
days]
{
304.56
days}
0.001
ppm
[
228.86
days]
{
365
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
1.10x10­
8
days]
{
1.20x10­
7
days}
3.75
ppm
[
0.13
days]
{
1.52
days}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
3.20x10­
5
days]
{
3.85x10­
4
days}
1.07
ppm
[
0.39
days]
{
4.60
days}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
1.88
days]
{
19.97
days}
0.029
ppm
[
77.42
days]
{
234.40
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
0.37
days]
{
4.31
days}
0.62
ppm
(
NOEC)
[
0.59
days]
{
6.67
days}

The
average
scenario
of
a
continuous
feed
of
0.10
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates
and
endangered
marine/
estuarine
invertebrates.
The
worst­
case
scenario
of
a
continuous
feed
of
0.10
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates,
endangered
and
non­
endangered
marine/
estuarine
invertebrates
and
endangered
and
non­
endangered
aquatic
plants.
Page
26
of
33
K.
Intermittent
feed,
0.10
ppm,
high
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
negligible]
{
negligible}
2.53
ppm
[
negligible]
{
negligible}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
0.09
days]
{
0.34
days}
0.001
ppm
[
16.06
days]
{
34.31
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
negligible]
{
negligible}
3.75
ppm
[
negligible]
{
negligible}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
negligible]
{
negligible}
1.07
ppm
[
negligible]
{
negligible}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
negligible]
{
1.83x10­
8
days}
0.029
ppm
[
0.05
days]
{
0.22
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
negligible]
{
negligible}
0.62
ppm
(
NOEC)
[
negligible]
{
negligible}

The
average
scenario
of
an
intermittent
feed
of
0.10
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
invertebrates.
The
worst­
case
scenario
of
an
intermittent
feed
of
0.10
ppm
in
a
high
flow
facility
results
in
acute
risk
to
endangered
freshwater
invertebrates.
Page
27
of
33
L.
Intermittent
feed,
0.10
ppm,
low
flow
scenario
Levels
of
Concern
(
LOC)

Taxa
Endpoint
value
from
study
(
ppm)
Acute
Nontarget
(
0.5*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}
Acute
Endangered
Species
(
0.05*
LC50)
[
average
#
of
days
exceeded]
{
worst
case
#
of
days
exceeded}

FW
fish
96hLC50
=
50.6
25.3
ppm
[
0
days]
{
0
days}
2.53
ppm
[
negligible]
{
negligible}

FW
invert.
48hEC50
=
0.027
0.0135
ppm
[
0.37
days]
{
4.26
days}
0.001
ppm
[
9.82
days]
{
70.08
days}

ME
fish
96hLC50
=
75
37.5
ppm
[
0
days]
{
0
days}
3.75
ppm
[
negligible]
{
negligible}

ME
mollusk
96hEC50
=
21.4
10.7
ppm
[
0
days]
{
0
days}
1.07
ppm
[
negligible]
{
negligible}

ME
invert.
96hLC50
=
0.576
0.288
ppm
[
8.40x10­
8
days]
{
1.01x10­
6
days}
0.029
ppm
[
0.24
days]
{
2.74
days}

Aquatic
plant
96hEC50
=
1.32
1.32
ppm
(
LC50)
[
negligible]
{
negligible}
0.62
ppm
(
NOEC)
[
negligible]
{
negligible}

The
average
scenario
of
an
intermittent
feed
of
0.10
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
freshwater
invertebrates.
The
worst­
case
scenario
of
an
intermittent
feed
of
0.10
ppm
in
a
low
flow
facility
results
in
acute
risk
to
endangered
and
non­
endangered
freshwater
invertebrates.

3.
Environmental
Risk
Assessment
a.
Terrestrial
Organisms
No
model
is
available
to
estimate
exposure
and
risk
to
birds
and
mammals
from
discharge
of
once­
through
cooling
system
effluents
into
surface
waters.
The
rapid
degradation
of
the
chemicals,
coupled
with
the
generally
low
toxicity
of
chlorine
dioxide
and
sodium
chlorite
to
birds
and
mammals,
make
risk
to
these
organisms
unlikely.
The
very
limited
data
available
to
assess
the
phytotoxicity
of
chlorine
dioxide/
sodium
chlorite
make
it
difficult
to
determine
the
risk
to
Page
28
of
33
terrestrial/
semi­
aquatic
plants.
b.
Aquatic
Organisms
Acute
risk
to
aquatic
organisms
is
anticipated
from
the
use
of
chlorine
dioxide/
sodium
chlorite
in
once­
through
cooling
towers
based
on
the
modeling
conducted.
At
the
highest
doses
there
is
risk
to
freshwater
and
marine/
estuarine
fish
and
invertebrates
and
aquatic
plants,
and
at
the
lowest
doses
there
is
risk
only
to
freshwater
invertebrates.
See
Table
9
A­
L
for
details.
Chronic
risk
to
aquatic
organisms
cannot
be
assessed
at
this
time
due
to
the
lack
of
chronic
toxicity
endpoints
for
fish
and
aquatic
invertebrates.
When
the
required
aquatic
chronic
toxicity
testing
described
above
is
submitted,
chronic
risk
to
these
organisms
will
be
assessed.

4.
Listed
Species
Section
7
of
the
Endangered
Species
Act,
16
U.
S.
C.
Section
1536(
a)(
2),
requires
all
federal
agencies
to
consult
with
the
National
Marine
Fisheries
Service
(
NMFS)
for
marine
and
anadromous
listed
species,
or
the
United
States
Fish
and
Wildlife
Services
(
FWS)
for
listed
wildlife
and
freshwater
organisms,
if
they
are
proposing
an
Aaction@
that
may
affect
listed
species
or
their
designated
habitat.
Each
federal
agency
is
required
under
the
Act
to
insure
that
any
action
they
authorize,
fund,
or
carry
out
is
not
likely
to
jeopardize
the
continued
existence
of
a
listed
species
or
result
in
the
destruction
or
adverse
modification
of
designated
critical
habitat.
To
jeopardize
the
continued
existence
of
a
listed
species
means
Ato
engage
in
an
action
that
reasonably
would
be
expected,
directly
or
indirectly,
to
reduce
appreciably
the
likelihood
of
both
the
survival
and
recovery
of
a
listed
species
in
the
wild
by
reducing
the
reproduction,
numbers,
or
distribution
of
the
species.@
50
C.
F.
R.
'
402.02.

To
facilitate
compliance
with
the
requirements
of
the
Endangered
Species
Act
subsection
(
a)(
2)
the
Environmental
Protection
Agency,
Office
of
Pesticide
Programs
has
established
procedures
to
evaluate
whether
a
proposed
registration
action
may
directly
or
indirectly
reduce
appreciably
the
likelihood
of
both
the
survival
and
recovery
of
a
listed
species
in
the
wild
by
reducing
the
reproduction,
numbers,
or
distribution
of
any
listed
species
(
U.
S.
EPA,
2004).
After
the
Agency=
s
screening­
level
risk
assessment
is
performed,
if
any
of
the
Agency=
s
Listed
Species
LOC
Criteria
are
exceeded
for
either
direct
or
indirect
effects,
a
determination
is
made
to
identify
if
any
listed
or
candidate
species
may
co­
occur
in
the
area
of
the
proposed
pesticide
use.
If
determined
that
listed
or
candidate
species
may
be
present
in
the
proposed
use
areas,
further
biological
assessment
is
undertaken.
The
extent
to
which
listed
species
may
be
at
risk
then
determines
the
need
for
the
development
of
a
more
comprehensive
consultation
package
as
required
by
the
Endangered
Species
Act.

Acute
risk
to
listed
birds
and
mammals
is
not
anticipated
from
the
use
of
chlorine
dioxide
and
sodium
chlorite
products
due
to
low
exposure
and
low
toxicity.
Further
discussion
is
needed
before
it
can
be
determined
if
there
are
risks
to
listed
aquatic
organisms
from
the
once
through
cooling
tower
use
of
chlorine
dioxide/
sodium
chlorite.
Page
29
of
33
Chronic
risks
to
listed
aquatic
organisms
cannot
be
assessed
at
this
time;
this
risk
will
be
assessed
when
required
chronic
toxicity
data
are
submitted
to
and
evaluated
by
the
Agency.
Page
30
of
33
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