­
G­
1­
APPENDIX
G.
The
Risk
Quotient
Method
and
Levels
of
Concern
The
risks
to
terrestrial
and
aquatic
organisms
are
determined
based
on
a
method
by
which
risk
quotients
(
RQs)
are
compared
with
levels
of
concern
(
LOCs).
This
method
provides
an
indication
of
a
chemical's
potential
to
cause
an
effect
in
the
field
from
effects
observed
in
laboratory
studies,
when
used
as
directed.
Risk
quotients
are
expressed
as
the
ratio
of
the
estimated
environmental
concentration
(
EEC)
to
the
species­
specific
toxicity
reference
value
(
TRV):

RQ
EEC
TRV
=

Units
for
EEC
and
TRV
should
be
the
same
(
e.
g.,
:
g/
L
or
ppb).
The
RQ
is
compared
to
the
LOC
as
part
of
a
risk
characterization.
Acute
and
chronic
LOCs
for
terrestrial
and
aquatic
organisms
are
given
in
recent
Agency
guidance
(
EPA,
2004)
and
summarized
in
Table
F­
1
below.

Table
E1.
Level
of
concern
(
LOC)
by
risk
presumption
category
(
U.
S.
EPA
2004).
Risk
Presumption
RQ
LOC
Mammals
and
Birds
Acute
Risk
a
EECb/
LC50
or
LD50/
sqftc
or
LD50/
day
d
0.5
Acute
Restricted
Use
e
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
f
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOEC
1
Aquatic
Animals
Acute
Risk
EECg/
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/
NOEC
1
Terrestrial
and
Semi­
aquatic
Plants
Acute
Risk
EEC/
EC25
1
Acute
Endangered
Species
EEC/
EC05
or
NOEC
1
Aquatic
Plants
Acute
Risk
EECh/
EC50
1
Acute
Endangered
Species
EECg/
EC05
or
NOEC
1
aPotential
for
acute
toxicity
for
receptor
species
if
RQ
>
LOC
(
EPA,
2004).
bEstimated
environmental
concentration
(
ppm)
on
avian/
mammalian
food
items
cmg/
ft2
dmg
of
toxicant
consumed
per
day
ePotential
for
acute
toxicity
for
receptor
species,
even
considering
restricted
use
classification,
if
RQ
>
LOC
(
EPA,
2004).
fPotential
for
acute
toxicity
for
endangered
species
of
receptor
species
if
RQ
>
LOC
(
EPA,
2004).
gEEC
=
ppb
or
ppm
in
water
hEEC
=
lbs
a.
i./
A
For
acute
exposure
to
terrestrial
and
aquatic
plants,
an
LOC
of
1
is
used.
Currently
the
Agency
does
not
perform
assessments
for
chronic
risk
to
plants
or
acute/
chronic
risks
to
non­
target
insects.

For
the
Tier
1
aquatic
assessment
of
Imazapyr
acute
exposure
is
represented
by
the
maximum
24­
­
G­
2­
hour
EEC
value
EEC
value
calculated
using
GENEEC
2.
EECs
used
to
assess
acute
and
chronic
risk
to
avian
and
mammalian
species
to
Imazapyr
were
calculated
using
the
Tier
1
model
T­
REX.

The
Agency
has
developed
an
Endangered
Species
Protection
Program
to
identify
pesticides
whose
use
may
cause
adverse
impacts
on
endangered
and
threatened
species,
and
to
implement
mitigation
measures
that
will
eliminate
the
adverse
impacts.
At
present,
the
program
is
being
implemented
on
an
interim
basis
as
described
in
a
Federal
Register
notice
(
54
FR
27984­
28008,
July
3,
1989),
and
is
providing
information
to
pesticide
users
to
help
them
protect
these
species
on
a
voluntary
basis.
As
currently
planned,
the
final
program
will
call
for
label
modifications
referring
to
required
limitations
on
pesticide
uses,
typically
as
depicted
in
county­
specific
bulletins
or
by
other
site­
specific
mechanisms
as
specified
by
state
partners.
A
final
program,
which
may
be
altered
from
the
interim
program,
will
be
described
in
a
future
Federal
Register
notice.
The
Agency
is
not
imposing
label
modifications
at
this
time.
Rather,
any
requirements
for
product
use
modifications
will
occur
in
the
future
under
the
Endangered
Species
Protection
Program.

Limitations
in
the
use
of
Imazapyr
may
be
required
to
protect
endangered
and
threatened
species,
but
these
limitations
have
not
been
defined
and
may
be
formulation
specific.
The
Agency
will
notify
the
registrants
if
any
label
modifications
are
necessary.
Such
modifications
would
most
likely
consist
of
the
generic
label
statement
referring
pesticide
users
to
use
limitations
contained
in
county
Bulletins.

Literature
Cited
EPA
(
U.
S.
Environmental
Protection
Agency).
2004.
Overview
of
the
Ecological
Risk
Assessment
Process
in
the
Office
of
Pesticide
Programs,
U.
S.
Environmental
Protection
Agency:
Endangered
and
Threatened
Species
Effects
Determinations.
Office
of
Prevention,
Pesticide,
and
Toxic
Substances.
January
23.
