Document ID: EPA-HQ-OPP-2005-0495-0010
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2005-12-21T05:00Z

­
A­
1­
APPENDIX
A
Environmental
Fate
Summaries
and
Structures
of
Imazapyr
Transformation
Products
The
non­
selective
herbicide
imazapyr
is
an
anionic,
organic
acid
that
is
non­
volatile
and
is
both
persistent
and
mobile
in
soil.
Commercial
formulations
contain
either
imazapyr
acid
or
the
imazapyr
isopropylamine
salt,
both
of
which
are
generally
dissolved
in
a
water
solution.
Imazapyr
is
mainly
in
anionic
form
at
typical
environmental
pHs,
and
the
behavior
of
the
acid
and
salt
forms
are
expected
to
be
similar.
Aqueous
photolysis
is
the
only
identified
route
of
degradation
for
imazapyr
in
the
environment.
Imazapyr
degraded
through
photolysis
in
water
with
half­
lives
ranging
between
2.5
and
5.3
days.
The
two
major
degradates
were:
2,3­
pyridinecarboxylic
acid
(
CL
9140,
22.7%)
and
7­
hydroxy­
furo[
3,4­
b]
pyridin­
5(
7H)­
one
(
CL
119060,
9.7%).
Laboratory
studies
show
imazapyr
is
essentially
stable
to
hydrolysis,
aerobic
and
anaerobic
soil
degradation
as
well
as
aerobic
and
anaerobic
aquatic
metabolism.
Field
study
observations
are
consistent
with
laboratory
studies
indicating
that
imazapyr
will
persist
in
soils
and
move
via
runoff
to
surface
water
and
leach
to
groundwater.
Imazapyr
does
not
bioconcentrate.
­
A­
2­

Table
A1.
Degradation
and
Metabolism
of
Imazapyr
Study
MRID
Study
Type
System
Imazapyr
half­
life
Maximum
transformation
products
(%
of
applied
radiation)

CL
288247
1
CL
252974
CL
119060
CL
9140
CL
252974
5
CO2
00132359
Hydrolysis
(
161­
1)
pH
5
at
25
°
C
Stable
ND2
ND
ND
ND
ND
ND
pH
7
at
25
°
C
Stable
ND
ND
ND
ND
ND
ND
pH
9
at
25
°
C
Stable
ND
6.9
ND
ND
ND
ND
00131617
Photolysis
in
water
(
161­
2)
pH
5
and
9
at
25
°
C
(
12
hour
exposure
cycle)
2.5
­
5.3
days
ND
ND
9.7
22.7
ND
NA3
40003713
Photolysis
in
soil
(
161­
3)
Loamy
sand
soil
Stable
(~
149
days)
ND
ND
ND
ND
ND
NA
41023201
Aerobic
Soil
Metabolism
(
162­
1)
Loamy
sand
soil
Stable
ND
ND
ND
ND
ND
7
45119701
Aerobic
Soil
Metabolism
(
162­
1)

(
Supplemental)
Loamy
sand
soil
(~
5.9
years)

>
296
days
ND
3
ND
ND
ND
6
00131619
Anaerobic
Soil
Metabolism
(
162­
2)
Loamy
sand
soil
Stable
(>
60
days)
ND
ND
ND
ND
ND
ND
40003712
Anaerobic
Aquatic
Metabolism
(
162­
3)
Total
system
>
120
days
ND
ND
ND
ND
ND
ND
41002301
45119702
Aerobic
Aquatic
Metabolism
(
162­
4)
Aerobic
Aquatic
Metabolism
(
162­
4)
­
Degradate
metabolism
Total
system
Total
system
(
CL
119060
metabolism)

(
CL
9140
metabolism)
>
120
days
4.9
days
3.6
days
ND
NA
NA
ND
NA
NA
ND
NA
NA
ND
20.4
NA
ND
ND
ND
1.1
44.9
53
42192101
Terrestrial
field
dissipation
(
164­
1)
Bare
ground
/
Silt
loam
soil
Hillsboro,
Oregon
143
days
NA
NA
NA
NA
NA
NA
42192102
Terrestrial
field
dissipation
(
164­
1)
Bare
ground
/
Sandy
loam
soil
Janesville,
North
Carolina
64
days
NA
NA
NA
NA
NA
NA
40003714
Forestry
Dissipation
(
164­
3)
Aerial
application,

residues
measured
12­
40
days
(
vegetation)

37­
44
days
(
litter)
NA
NA
NA
NA
NA
NA
­
A­
3­

1
See
chemical
structures
of
degradates
in
following
sections
of
Appendix
A.
2Not
detected.
3
Not
analyzed.
­
A­
4­
Table
A.
2.
Sorption
Coefficients
for
Imazapyr
in
11
Soils/
Sediments
MRID
Soil/
Sediment
Texture
Kd
(
mL/
g)
Koc
(
mL/
g
oc)

45119705
Sand
sediment
(
Florida)
0.11
31
45119705
Silt
loam
sediment
(
Missouri)
0.64
100
43423703
Loamy
sand
soil
0.04
15
43423703
Silt
loam
soil
0.86
82
43423703
Sandy
loam
soil
0.07
8.2
43423703
Loam
soil
0.23
17
43423703
Pond
sediment
3.4
150
00131620
Sandy
loam
soil
(
Princeton)
1.9
110
00131620
Loamy
sand
soil
(
Delaware)
0.52
100
00131620
Clay
loam
soil
(
North
Dakota)
0.84
18
00131620
Silt
loam
soil
(
Wisconsin)
2.4
53
Average
values
(
N
=
11)
0.998
61.9
Median
values
0.64
53
Lowest
non­
sand
value
0.23
17
Summary
of
Reviewed
Study
Reports
Hydrolysis
(
161­
1,
MRID
00132359,
Study
Status:
Acceptable).
Imazapyr
is
stable
to
hydrolysis
at
environmentally
relevant
pH
values
and
temperatures.
Imazapyr
was
stable
in
aqueous
buffer
solutions
(
pH
5
and
7)
and
distilled
water
(
pH
5.2)
for
up
to
30
days
at
25
±
1
°
C.
Imazapyr
degraded
slowly
in
an
aqueous
pH
9
buffer
solution.
The
only
identified
degradate
was
2­[(
1­
carbomyl­
1,2­
dimethylpropyl)
carbomyl]
nicotinic
acid
(
CL
252974).
Minor
degradates
were
not
identified.

Aqueous
Photolysis
(
161­
2,
MRID
00131617,
Study
Status:
Acceptable).
Imazapyr
is
susceptible
to
photolysis.
Imazapyr
degraded
with
a
half­
life
of
2.5­
5.3
days
in
distilled
water
or
buffer
solution
at
pH
5
or
9,
at
25
°
C,
irradiation
with
a
xenon
arc
lamp
(
12
hours/
day)
for
up
to
10
days.
Two
major
degradates
were
formed:
2,3­
pyridinecarboxylic
acid
(
CL
9140,
22.7%)
and
7­
hydroxy­
furo[
3,4­
b]
pyridin­
5(
7H)­
one
(
CL
119060,
9.7%).
Unidentified
degradates
comprised
­
A­
5­
up
to
7.1%
of
the
applied
radioactivity.
Imazapyr
was
stable
in
the
dark
during
the
10­
day
incubation
period.

Soil
Photolysis
(
161­
3,
MRID
40003712,
Study
Status:
Acceptable).
Imazapyr
degraded
slowly
on
irradiated
soil.
14C­
pyridine­
ring­
labeled
imazapyr
applied
at
a
rate
of
1.5
lb
ae/
acre,
degraded
with
an
extrapolated
half­
life
of
149
days
on
sandy
loam
soil
irradiated
a
4­
week
period.
No
degradate
was
>
10%
of
the
applied
radioactivity.
In
dark
controls,
imazapyr
was
95­
98%
of
the
applied
radioactivity
after
4
weeks.
Unidentified
residues
were
2.9­
4.9%
of
the
applied
radioactivity.

Aerobic
Soil
Metabolism
(
162­
1,
MRID
41023201,
Study
Status:
Acceptable).
Imazapyr
is
essentially
stable
to
degradation
in
soil
maintained
under
aerobic
conditions.
14C/
13Clabeled
imazapyr
was
added
to
Princeton
sandy
loam
soil
(
soil
moisture
75%
of
field
capacity)
at
a
concentration
of
1.5
ppm.
Samples
were
maintained
at
25
°
C
in
the
dark
for
up
to
365
days.
Volatiles
and/
or
CO
2
were
collected
in
traps.
At
365
days,
88%
of
the
applied
radioactivity
remained
as
parent
imazapyr
(
calculated
half­
life
of
5.9
years).
Unextractable
residues
averaged
4%
of
the
applied
radioactivity
during
the
study
and
accounted
for
5%
at
365
days.
Cumulative
14CO
2
accounted
for
up
to
7%
of
the
applied
radioactivity
after
365
days.
Material
balance
averaged
101%.

Aerobic
Soil
Metabolism
(
162­
1,
MRID
45119701,
Study
Status:
Supplemental).
The
aerobic
soil
metabolism
of
[
pyridine­
6­
14C]­
imazapyr
was
studied
for
121
days
in
Sassafras
sandy
loam
soil
(
pH
6.0,
organic
matter
2.0%;
soil
moisture
content
of
75%
of
1/
3
bar)
from
New
Jersey.
Samples
were
keep
in
the
dark
at
25
±
1
°
C.
[
14C]
Imazapyr
was
applied
at
the
nominal
rate
of
0.22
mg
ae./
kg
soil
(
equivalent
to
0.44
lb
ae/
acre
or
0.50
kg
ae/
ha
with
15­
cm
soil
incorporation).
Because
the
121­
day
study
period
was
short
compared
to
the
persistence
of
[
pyridine­
6­
14C]
imazapyr,
there
was
insufficient
time
for
the
full
pattern
of
formation
and
decline
of
products
to
develop.
At
study
end,
approximately
72%
of
the
amount
of
parent
recovered
at
the
beginning
of
the
study
remained.
A
structurally
similar
transformation
product,
2­[
4­
Isopropyl­
4­
methyl­
5­
oxo­
2­
imidazolin­
2­
yl]­
3­
hydroxy
pyridine,
was
present
at
approximately
7%
of
parent
radioactivity
recovered
at
the
beginning
of
the
study
and
increased
slowly
for
the
duration
of
the
study.
Volatilized
14CO
2
totaled
approximately
6%
of
initial
parent
radioactivity
at
121
days.

Two
additional
minor
transformation
products,
2­[(
1­
carbamoyl­
1,2­
dimethylpropyl)
carbamoyl]
nicotinic
acid
and
2­[
4­
isopropyl­
4­
methyl­
5­
oxo­
2­
imidazolin­
2­
yl]­
3­
carboxymethyl
pyridine,
were
each
detected
at
#
3%
of
the
applied,
but
may
have
been
artifacts
produced
during
sample
extraction
and
preparation.
Organic
volatiles
were
<
0.1%
of
applied
at
any
sampling
interval.
Material
balance
ranged
from
approximately
100%
to
97%.

The
extrapolated
first­
order
kinetics
regression
half­
life
for
parent
imazapyr
for
the
121­
day
period
is
296
days
(
r2
=
0.89,
95%
confidence
interval
of
247
to
370
days).
If
the
two
putative
artifact
compounds
are
assumed
to
be
parent
material
and
included
in
the
regression,
then
the
apparent
half­
life
increases
slightly
to
313
days
(
r2
=
0.90,
95%
confidence
interval
of
264
to
­
A­
6­
387
days).

Anaerobic
Soil
Metabolism
(
162­
2,
MRID
00131619,
Study
Status:
Acceptable).
Imazapyr
was
stable
in
sandy
loam
soil.
Sandy
loam
soil
(
1.8%
organic
matter,
pH
5.3­
6.5,
CEC
8.5
meq/
100
g)
was
treated
with
a
50:
50
mixture
of
14C
and
13C­
carboxy­
labeled
imazapyr
at
1
lb
ae/
acre.
Soil
moisture
was
adjusted
to
75%
of
0.33
bar.
Flasks
were
sealed
and
incubated
(
aerobically)
in
the
dark.
Radioactivity
in
the
water
extract
was
three­
fold
that
in
the
soil.

Anaerobic
Aquatic
Degradation
(
162­
3,
MRID
40003712,
Study
Status:
Acceptable).
Imazapyr
is
resistant
to
anaerobic
aquatic
degradation.
14C­
pyridine­
labeled
imazapyr,
applied
at
1.5
lb/
A,
was
incubated
in
an
anaerobic
sand
sediment:
water
system
in
the
dark
at
19­
22
°
C
for
up
to
4
months.
Imazapyr
comprised
96­
98%
of
the
recovered
radioactivity
at
all
sampling
intervals.

Aerobic
Aquatic
Metabolism
(
162­
4,
MRID
41002301,
Study
Status:
Acceptable).
Imazapyr
did
not
degrade
in
water
or
sediment
under
aquatic
conditions.
14C­
Imazapyr
was
added
to
a
series
of
water
and
soil
sediments
(
92%
sand)
collected
from
an
irrigation
pond
at
a
rate
of
1.5
lb/
A.
Sample
containers
were
maintained
under
positive
pressure
in
the
dark
at
25
°
C.
14CO
2
accounted
for
<
2%
of
the
applied
radioactivity
4
weeks
(
there
were
no
organic
volatiles).
Over
the
course
of
the
study,
>
96%
of
the
applied
radioactivity
remained
in
the
aqueous
phase
while
<
2%
was
bound
to
soil.
Analysis
by
thin­
layer
chromatography
determined
that
parent
imazapyr
accounted
for
>
97%
of
the
applied
radioactivity
after
4
weeks.

Aerobic
Aquatic
Metabolism
of
Two
Degradates
of
Imazapyr
(
162­
4,
MRID
45119702,
Study
Status:
Acceptable).
The
aerobic
degradation
of
the
imazapyr
degradation
products,
[
pyridine­
6­
14C]­
labeled
furo[
3,4­
b]
pyridine­
5­(
7H)­
one­
7­
hydroxy
(
CL
119060)
and
pyridine
2,3­
dicarboxylic
acid
(
CL
9140),
was
studied
in
each
of
two
pond
water:
sediment
systems.
A
pond
water:
sediment
system
(
water
pH
8.2;
sand
sediment
pH
7.7,
organic
matter
0.8%)
from
Florida,
and
a
pond
water:
sediment
system
(
water
pH
7.9;
silt
loam
sediment
pH
6.6,
organic
matter
1.1%)
from
Missouri
were
studied
for
14
days
in
darkness
at
25
±
1
°
C.
[
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
and
[
14C]
pyridine
2,3­
dicarboxylic
acid
were
applied
separately
at
the
nominal
rate
of
0.083
mg
ae/
L.
The
sediment:
water
ratio
used
was
175
g
wet
sediment:
200
mL
water.
For
both
test
compounds
and
systems,
aerobic
conditions
were
maintained
in
the
water
layers
of
the
sediment:
water
systems,
but
the
sediment
layers
remained
anaerobic
throughout
the
study.
Levels
of
parent
[
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxyand
[
14C]
pyridine
2,3­
dicarboxylic
acid
and
transformation
products
were
identified
only
in
the
water
layers.
To
compensate
for
the
failure
to
identify
and
quantify
residues
extracted
from
the
sediments
and
low
material
balances
during
later
sampling
intervals,
it
was
assumed
that
all
extracted
sediment
residues
were
unreacted
starting
materials.
These
extracted
sediment
residues
were
then
added
to
parent
materials
identified
and
quantified
in
the
water
phases
to
estimate
total
system
(
water
+
sediment
phases)
half­
lives.

In
the
water
layer,
the
major
nonvolatile
transformation
product
of
[
pyridine­
6­
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
was
Pyridine
2,3­
dicarboxylic
acid.
This
compound
was
­
A­
7­
detected
at
maximums
of
20%
of
applied
at
1
day
and
28%
at
3
days
in
the
sand
and
silt
loam
sediment
systems.
Nicotinic
acid
was
identified
as
a
nonvolatile
transformation
product,
and
detected
at
maximums
of
6%
at
2
days
and
10%
at
1
day
in
the
sand
and
silt
loam
sediment
systems,
respectively.
Unidentified
polar
products
increased
to
maximums
of
33­
41%
of
applied
at
7
days
in
both
systems.
For
both
test
systems,
nonextractable
[
14C]
residues
were
#
6%
at
any
sampling
interval.
14CO
2
was
a
major
volatile
transformation
product,
totaling
45%
for
sand
sediment:
water
systems.
The
first­
order
kinetics
regression
half­
life
for
[
pyridine­
6­
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
in
the
Florida
pond
system
(
water
+
sediment)
was
3.9
days
(
r2
=
0.95,
95%
confidence
interval
of
3.4
to
4.5
days).
The
Missouri
pond
system
first­
order
regression
half­
life
(
water
+
sediment)
for
[
pyridine­
6­
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
was
5.8
days
(
r2
=
0.80,
95%
confidence
interval
of
4.5
to
8.2
days).
The
average
halflife
for
the
Florida
and
Missouri
systems
for
[
pyridine­
6­
14C]
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
was
5
±
1
days
with
an
upper
90%
confidence
bound
on
the
mean
of
8
days.

No
major
nonvolatile
transformation
products
of
[
pyridine­
6­
14C]
pyridine
2,3­
dicarboxylic
acid
were
detected
in
the
water
layers.
Minor
nonvolatile
transformation
products
were
unidentified
polar
products.
For
both
sediments,
nonextractable
[
14C]
residues
were
#
3.9%
at
any
sampling
interval.
14CO
2
was
a
major
volatile
transformation
product,
totaling
53%
for
sand
sediment:
water
systems
and
23%
for
silt
loam
sediment:
water
systems
at
study
termination.
Organic
volatiles
were
<
0.1%
of
applied
at
any
sampling
interval.
The
first­
order
kinetics
regression
half­
life
for
of
[
pyridine­
6­
14C]
pyridine
2,3­
dicarboxylic
acid
for
the
Florida
pond
system
(
water
+
sediment)
was
3
days
(
r2
=
0.56,
95%
confidence
interval
of
1.9
to
5.9
days).
The
Missouri
pond
system
first­
order
regression
half­
life
(
water
+
sediment)
for
pyridine
2,3­
dicarboxylic
acid
was
4
days
(
r2
=
0.88,
95%
confidence
interval
of
3.5
to
5.5
days).
The
average
half­
life
for
the
Florida
and
Missouri
systems
for
pyridine
2,3­
dicarboxylic
acid
is
4
±
1.0
days
with
an
upper
90%
confidence
bound
on
the
mean
of
5.7
days.

Aerobic
Aquatic
Metabolism
of
Imazapyr
Photodegradation
Products
(
162­
4,
MRID
41891501,
Study
Status:
Supplemental).
This
study
addressed
the
aerobic
aquatic
metabolism
of
the
two
major
aqueous
photodegradation
products
of
imazapyr,
2,3­
pyridinedicarboxylic
acid
(
CL
9140)
and
7­
hydroxy­
furo[
3,4­
b]
pyridin­
5(
7H)­
one
(
CL
119060)
over
a
4­
week
period.
The
photoproducts
were
generated
by
irradiating
10
mg
of
imazapyr
in
50
mL
of
deionized
water
which
yielded
the
major
products
pyridine
2,3­
dicarboxylic
acid
and
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
(
22%
and
24%,
respectively).
The
photoproducts
were
added
to
pond
water
and
sediment
from
a
wetland
in
New
Jersey.
Evolved
CO
2
was
trapped
and
measured.
The
study
presented
evidence
that
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
is
rapidly
converted
to
pyridine
2,3­
dicarboxylic
acid
which,
in
turn,
is
metabolized
to
CO
2
.

Mobility
and
Persistence
Adsorption/
Desorption
(
163­
1,
MRID
45119705,
Study
Status:
Acceptable).
The
batch­
equilibrium
adsorption/
desorption
characteristics
of
14C­
6­
pyridine­
ring­
labeled­
imazapyr
and
the
metabolites
(
photoproducts)
pyridine
2,3­
dicarboxylic
acid
and
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
(
both
14C­
6­
labeled
in
the
pyridine
ring)
were
each
studied
separately
in
a
sand
­
A­
8­
sediment
from
Florida
[
pH­
7.7,
organic
carbon
­
0.47%]
and
a
silt
loam
sediment
from
Missouri
[
pH
­
6.6,
organic
carbon
­
0.64%].
The
equilibrating
solution
used
was
0.01
M
CaCl
2
,
at
a
soil/
solution
ratios
of
1:
2
(
w:
v).
The
desorption
phase
of
the
study
was
carried
out
at
20
±
1
°
C
for
27.5
hours
(
imazapyr),
24
hours
(
pyridine
2,3­
dicarboxylic
acid)
or
44
hours
(
furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­).
The
desorption
phase
was
conducted
once.
Supernatant
solutions
were
analyzed
using
LSC
and
HPLC.
Sediments
were
extracted
with
0.1
M
sodium
hydroxide
following
desorption,
analyzed
by
LSC.
Radioactivity
in
the
soil
residue
after
extraction
was
determined
by
combustion.

Imazapyr:
Freundlich
adsorption
parameters
and
average
simple
adsorption/
desorption
coefficients
are
given
in
Table
A­
1
below.
Average
simple
adsorption
coefficients
(
K
ads
)
for
the
experimental
concentration
range
were
0.144
and
0.639
mL/
g
for
the
sand
and
silt
loam
sediments,
respectively.
Corresponding
simple
adsorption
coefficients
adjusted
for
organic
carbon
(
K
oc
)
were
30.6
and
99.8
mL/
g
organic
carbon.

Pyridine
2,3­
dicarboxylic
acid:
Freundlich
adsorption
parameters
and
average
simple
adsorption/
desorption
coefficients
are
given
in
the
results
synopsis
and
in
Table
A­
2
below.
Average
simple
adsorption
coefficients
(
K
ads
)
were
1.02
and
38.74
mL/
g
for
the
sand
and
silt
loam
sediments,
respectively.
Corresponding
K
oc
values
were
217
and
6053
mL/
g
organic
carbon.

Furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­:
Freundlich
adsorption
parameters
and
average
simple
adsorption/
desorption
coefficients
are
given
in
the
results
synopsis
and
in
Table
A­
3
below.
Average
simple
adsorption
coefficients
(
K
ads
)
for
the
experimental
concentration
range
were
0.628
and
6.532
mL/
g
for
the
sand
and
silt
loam
sediments,
respectively.
Corresponding
K
oc
values
were
134
and
1020
mL/
g
organic
carbon.

Table
B­
1:
Adsorption
and
desorption
parameters
for
imazapyr
in
the
sediments.

Soil
Freundlich
Adsorption
Simple
Ads/
Des
Coefficient
Averages
Kf
ads
1/
N
R2
Kf
ads
oc
Kads
Kads
oc
Kdes
Kdes
oc
Sand
sediment
(
FL)
0.091
0.733
0.976
19.4
0.144
30.6
0.338
71.9
Silt
loam
sediment
(
MO)
0.523
0.887
0.999
81.7
0.639
99.8
1.02
159
Kf
ads
 
Freundlich
adsorption
coefficient;
1/
N
 
Slope
of
Freundlich
adsorption
isotherm.
Subscript
oc
indicates
sorption
per
unit
organic
carbon
([
K
x
100]/%
organic
carbon).
R2
­
Regression
coefficient
of
Freundlich
equation.
­
A­
9­
Table
B­
2:
Adsorption
and
desorption
parameters
for
Pyridine
2,3­
dicarboxylic
acid
in
the
sediments.

Soil
Freundlich
Adsorption
Simple
Ads/
Des
Coefficient
Averages
Kf
ads
1/
N
R2
Kf
ads
oc
Kads
Kads
oc
Kdes
Kdes
oc
Sand
sediment
(
FL)
0.699
0.811
0.998
149
1.02
217
1.60
340
Silt
loam
sediment
(
MO)
31.6
0.955
0.999
4940
38.7
6053
140
21,900
Kf
ads
 
Freundlich
adsorption
coefficient;
1/
N
 
Slope
of
Freundlich
adsorption
isotherm.
Subscript
oc
indicates
sorption
per
unit
organic
carbon
([
K
x
100]/%
organic
carbon).
R2
­
Regression
coefficient
of
Freundlich
equation.

Table
B­
3:
Adsorption
and
desorption
parameters
for
Furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxyin
the
sediments.

Soil
Freundlich
Adsorption
Simple
Ads/
Des
Coefficient
Averages
Kf
ads
1/
N
R2
Kf
ads
oc
Kads
Kads
oc
Kdes
Kdes
oc
Sand
sediment
(
FL)
0.551
0.939
0.998
117
0.628
134
1.89
402
Silt
loam
sediment
(
MO)
5.77
0.962
1.000
902
6.53
1020
16.9
2640
Kf
ads
­
Freundlich
adsorption
coefficient;
1/
N
­
Slope
of
Freundlich
adsorption
isotherm.
Subscript
oc
indicates
sorption
per
unit
organic
carbon
([
K
x
100]/%
organic
carbon).
R2
­
Regression
coefficient
of
Freundlich
equation.

Terrestrial
Field
Dissipation
(
164­
1,
MRID
42192101,
Study
Status:
Upgradable).
Arsenal
2AS,
the
isopropylamine
salt
of
imazapyr
(
22.6%
ae
in
aqueous
solution)
dissipated
with
a
calculated
half­
life
of
143
days.
However,
the
mode(
s)
of
dissipation
was
not
addressed.
The
test
material
was
applied
by
boom
sprayer
to
a
bareground
plot
of
silt
loam
soil
(
2.6%
organic
matter,
pH
5.1,
CEC
16.9
meq/
100
g)
located
in
Hillsboro,
Oregon.
Application
rate
was
1.53
lb
ae/
acre
(
0.75
lb
ae/
acre).
Sprinkler
irrigation
was
applied
at
0.5
to
3.0
inches,
1­
3
times/
month.
The
temperature
ranged
from
6
to
100
°
F,
total
precipitation
was
67
inches,
and
irrigation
total
was
29
inches.
Imazapyr
residues
were
found
primarily
in
the
0­
6­
inch
soil
layer.
In
the
6­
12­
inch
layer,
residues
were
#
6
ppb
at
1­
30
days,
14­
17
ppb
at
240
days,
and
6­
13
ppb
at
452
days.
In
the
deeper
soil
layers
residues
were
<
8
ppb
immediately
posttreatment,
and
not
detected
at
later
sampling
times.
A
half­
life
of
143
days
was
calculated.
Residues
in
a
control
plot
were
#
4
ppb.
Routes
of
dissipation
were
not
provided.

Terrestrial
Field
Dissipation
(
164­
1,
MRID
42192102,
Study
Status:
Upgradable).
Arsenal
2AS,
the
isopropylamine
salt
of
imazapyr
(
22.6%
ae
in
aqueous
solution)
dissipated
with
a
calculated
half­
life
of
64
days.
However,
the
mode(
s)
of
dissipation
was
not
addressed.
The
test
material
was
applied
by
backpack
sprayer
to
a
bareground
plot
of
sandy
loam
soil
(
2.3%
organic
matter,
pH
5.7,
CEC
6.75
meq/
100
g)
located
in
Janesville,
North
Carolina.
Application
rate
was
1.53
lb
ae/
acre
(
0.75
lb
ae/
acre).
Sprinkler
irrigation
was
applied
at
0.58
to
2.0
inches,
­
A­
10­
3­
5
times/
month.
The
temperature
ranged
from
18
to
98
°
F,
total
precipitation
was
67
inches
and
irrigation
totaled
22
inches.
Imazapyr
residues
were
found
primarily
in
the
0­
6­
inch
soil
layer,
averaging
300­
440
ppb
immediately
posttreatment
and
declining
to
7­
12
ppb
at
240­
360
days.
In
the
6­
12­
inch
layer,
residues
were
at
a
maximum
of
10­
21
ppb
at
14
days.
In
the
12­
18
inch
and
18­
24
inch
depths,
residues
reached
a
maximum
of
8­
14
ppb
and
7­
11
ppb,
respectively,
at
30
days.
In
the
deeper
soil
layers,
residues
were
#
6
ppb
at
all
sampling
times.
Residues
in
a
control
plot
were
#
3
ppb.
Routes
of
dissipation
were
not
provided.

Terrestrial
Field
Dissipation
(
164­
1,
MRID
45119706,
Study
Status:
Supplemental).
This
study
shows
that
imazapyr
is
prone
to
leach
and
is
relatively
long­
lived.
Cropped
corn
fields
in
Iowa
and
Nebraska
were
used
as
the
study
sites.
Apparent,
simple
first­
order
regression
halflives
at
all
sampled
depths
(
0­
36
inches)
were
94
days
in
Iowa
(
95%
confidence
limits
84­
107
days,
r2
=
0.88)
and
126
days
in
Nebraska
(
95%
confidence
limits
113­
143
days,
r2
=
0.88).
The
degree
to
which
the
apparent
loss/
dispersal
of
imazapyr
was
due
to
transformation,
plant
uptake,
volatilization,
leaching,
runoff,
etc.
was
not
determined.
There
was
no
analysis
for
transformation
products
(
degradates
or
metabolites),
no
measurement
of
plant
uptake,
and
there
was
no
water
or
simple
attempt
to
correlate
daily
rainfall/
irrigation
with
pesticide
disappearance
or
potential
for
movement
in
soil
during
the
course
of
study.
Therefore,
disappearance
half­
lives
represent
only
lower
limits
for
what
may
be
very
much
longer
effective
half­
lives,
and
cannot
be
assumed
to
be
attributable
to
degradation
or
detoxification
of
parent
(
or
any
possible
byproducts

For
the
present
study,
casual
inspection
of
the
soil
concentration
data
shows
quick
infiltration
of
imazapyr
into
moist
surface
soil,
and
close
correlation
between
rainfall/
irrigation
events
with
eventual
leaching
of
imazapyr
into
the
lower
soil
depths
(
down
to
30
or
36
inches).
Rainfall/
irrigation
was
said
to
be
typical
or
average
for
the
experimental
sites
in
Iowa
and
Nebraska.
These
penetrations
into
soil
are
evidence
of
high
mobility.
Furthermore,
the
leaching
occurred
in
soils
with
characteristics
that
are
not
usually
associated
with
high
potential
for
leaching.
The
soils
had
relatively
high
cation
exchange
capacities,
organic
matter,
and
moisture
retention
capacity.
Subsoil
clay
content
was
approximately
25­
30%.

Aquatic
Field
Dissipation
(
164­
2,
MRID
41891501,
Study
Status:
Supplemental).
Arsenal
2AS
rapidly
dissipated
from
shallow
ponds
in
Florida
and
Louisiana
during
summer
months.
Arsenal
2AS
applied
at
the
proposed
maximum
label
rate
of
1.5
lb
ae/
acre
dissipated
with
half­
lives
of
3
and
4
days
in
pond
water
and
sediment,
respectively.
In
a
similar
study
carried
out
in
Louisiana,
Arsenal
2AS
dissipated
with
half­
lives
of
2
and
4
days
in
pond
water
and
sediment,
respectively.
The
rapid
dissipation
of
imazapyr
observed
under
these
conditions
may
not
be
representative
of
conditions
at
other
proposed
use
sites.

Bioaccumulation
Forestry
Dissipation
(
164­
3,
MRID
40003714,
Study
Status:
Acceptable).
Imazapyr
applied
by
aerial
spray
to
a
forest
dissipated
primarily
by
runoff,
and
to
a
lesser
degree,
by
foliar
absorption.
Arsenal
was
applied
by
helicopter
at
2.24
kg/
ha
(
2
lb
ae/
acre)
with
Igepal
DM­
710
as
­
A­
11­
a
surfactant,
over
two
forested
watersheds
in
Fayette
and
Randolph
counties,
Alabama,
in
May
and
June,
1985.
Each
site
was
divided
into
two
water
sheds,
one
treated
and
one
control.

Description,
Fayette
county
site.
This
was
a
121­
ha
site
of
mixed
hardwoods.
Pines
in
the
plot
had
been
harvested
earlier.
The
application
took
place
over
4
days
due
to
weather
conditions
of
intermittent
fog
and
drizzle.
The
plot
was
drained
by
a
single
stream.
The
soil
was
sand
loam
(
1.92%
organic
matter,
CEC
3.7
meq/
100
g).

Description,
Randolph
county
site.
This
was
a
40­
ha
area
of
loblolly
pine
seedlings
and
mixed
hardwoods.
The
plot
was
drained
by
a
single
stream.
The
underlying
soil
was
loam
(
4.4%
organic
matter,
CEC
4.17
meq.
100
g).
Precipitation
was
measured
at
each
site,
and
stream
water
levels
were
monitored.
Samples
were
taken
of
water,
suspended
sediment,
vegetation
(
composited),
litter,
and
soil
(
up
to
20
inches
depth),
the
latter
by
area
of
ridge,
midslope
and
lower
slope.

Results,
Fayette
county.
Imazapyr
dissipated
from
vegetation
with
a
half­
life
of
12
days
(
highest
mean
residue,
about
100
ppb
at
3
days
posttreatment),
from
litter
with
a
half­
life
of
44
days,
from
0­
4­
inch
depth
of
bareground
soil
with
a
half­
life
of
24
days,
and
from
0­
4­
inch
depth
littercovered
soil
with
a
calculated
half­
life
of
19
days.
Residues
were
found
primarily
in
the
0­
12­
inch
soil
depth.
Residues
in
stream
grab
samples
were
highest
during
application
(
up
to
680
ppb)
and
following
storm
events.
Stream
residues
declined
to
trace
amounts
at
later
sampling
intervals.
Only
one
stream
sediment
sample
contained
a
detectable
residue,
52
ppb.

Results,
Randolph
county.
Imazapyr
dissipated
from
vegetation
with
a
half­
life
of
40
days
(
highest
mean
residue,
122
ppb
immediately
posttreatment),
from
litter
with
a
half­
life
of
37
days,
from
0­
4­
inch
depth
of
bareground
soil
with
a
half­
life
of
26
days,
and
from
0­
4­
inch
depth
littercovered
soil
with
a
calculated
half­
life
of
34
days.
Residues
were
found
primarily
in
the
0­
12­
inch
soil
depth.
Visual
observation
indicated
at
least
99%
kill
of
all
targeted
vegetation.

Bioconcentration
in
Aquatic
Non­
target
Organisms
(
165­
5,
MRID
45119707.
Study
Status:
Supplemental).
Parent
imazapyr
did
not
bioconcentrate
appreciably
in
the
fish
and
crayfish
species
tested
(
three
fish
and
one
crayfish
species
at
each
site,
total
of
seven
different
species).
There
were
no
tests
for
degradates
or
their
concentration
in
any
of
the
test
species.
It
should
be
noted
that
the
reported
limit
of
quantitation
for
parent
in
tissue
was
a
relatively
high
50
ppb.
In
several
instances,
for
unknown
or
unverified
reasons,
there
was
some
limited
mortality
of
some
test
species
and/
or
their
partial
disappearance,
such
that
for
some
sampling
intervals
there
were
insufficient
amounts
of
tissue
for
analysis.
However,
this
does
not
significantly
alter
the
general
conclusion
of
no
appreciable
bioconcentration
of
parent
above
a
concentration
of
50
ppb.

Bioconcentration
in
Aquatic
Non­
target
Organisms
(
165­
5,
MRID
45119709,
Study
Status:
Supplemental).
Under
test
conditions
(
28­
day
exposure
periods
at
mean
measured
concentrations
of
250
ppb
for
oysters
and
260
ppb
for
shrimp
followed
by
14­
day
depuration
periods),
overall
results
for
the
two
test
species,
oyster
and
shrimp,
are
essentially
the
same.
There
was
no
bioconcentration
of
pyridyl­
6­
14C­
imazapyr
[
bioconcentration
factor
(
BCF)
<
1)].
­
A­
12­
The
study
was
deficient
for
both
oyster
and
shrimp
because
of
relatively
high
levels
of
quantitation
(
LOQ;
72
ppb
for
oyster,
128
ppb
for
shrimp)
compared
to
exposure
concentrations.
Consequently,
because
of
the
relatively
low
and
variable
concentrations
of
residues
compared
to
the
LOQ,
uptake
and
depuration
rates
of
imazapyr
could
not
be
calculated
meaningfully,
and
no
metabolite
identification
work
was
conducted.
The
information
was
considered
supplemental,
but
no
additional
studies
are
required.
­
A­
13­
N
N
N
O
H
OH
O
N
N
N
OH
O
N
COOH
NH
O
NH
2
O
C
C
Structural
Formulas
for
Transformation
Products
of
Imazapyr
Imazapyr
(
CL
243997,
AC
243997)
IUPAC
name:
2­(
4­
Isopropyl­
4­
methyl­
5­
oxo­
2­
imidazolin­
2­
yl)
nicotinic
acid.
CAS
name:
2­[
4,5­
Dihydro­
4­
methyl­
4­(
1­
methylethyl)­
5­
oxo­
1H­
imidazol­
2­
yl]­
3­
pyridinecarboxylic
acid.
CAS
Number:
81334­
34­
1
CL
288247
CAS
name:
2­[
4­
Isopropyl­
4­
methyl­
5­
oxo­
2­
imidazolin­
2­
yl]­
3­
hydroxy
pyridine
CAS
Number:
NA
CL
252974
CAS
name:
2­[(
1­
Carbamoyl­
1,2­
dimethylpropyl)
carbamoyl]
nicotinic
acid
CAS
Number:
98323­
63­
8
­
A­
14­
O
N
O
OH
N
OH
O
O
OH
N
COOH
CL
119060
CAS
name:
Furo[
3,4­
b]
pyridin­
5(
7H)­
one,
7­
hydroxy­
CAS
Number:
90322­
54­
6
CL
9140
CAS
name:
Pyridine
2,3­
dicarboxylic
acid
CAS
Number:
89­
00­
9
Nicotinic
acid
CAS
name:
Pyridine
3­
carboxylic
acid
CAS
Number:
59­
67­
6
­
B­
1­
N
N
N
O
O
O
CH
3
CL
240000
CAS
name:
2­[
4­
Isopropyl­
4­
methyl­
5­
oxo­
2­
imidazolin­
2­
yl]­
3­
carboxymethyl
pyridine
CAS
Number:
NA