    
1
  
17
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
Chemical:
MCPB,
MCPB
Sodium
PC
Code:
019202,
019201
DP
Barcodes:
D314042,
D314043,
D314045,
D319762
MEMORANDUM
DATE:
22
February
2006
SUBJECT:
Comment
Phase
III
for
Reregistration
of
MCPB
and
MCPB
Sodium
FROM:
Marie
Janson,
Environmental
Scientist
Ed
Odenkirken,
Senior
Scientist
Amer
Al­
Mudallal,
Chemist
Nadar
Elkassabany,
Acting
Branch
Chief
Environmental
Risk
Branch
1
Environmental
Fate
and
Effects
Division
(
7507C)

TO:
Susan
Lewis,
Branch
Chief
Demson
Fuller,
CRM
James
Parker,
CRM
Registration
Branch
1
SRRD
Division
(
7505C)

Attached
please
find
the
Environmental
Fate
and
Effects
Division's
(
EFED)
revised
comments
environmental
risk
assessment
for
the
proposed
registration
of
MCPB
as
an
herbicide
on
peas.
Supported
formulations
of
MCPB
are
Thistrol
®
Herbicide
(
71368­
5)
and
Sodium
MCPB
Solution
(
71368­
7).

The
registrant's
comments
on
the
draft
risk
assessment
which
dealt
with
substantive
questions
on
science
or
interpretation
are
addressed
in
this
Phase
III,
the
response
to
public
comment.
    
2
  
17
Environmental
Fate
and
Ecological
risk
assessment
Potential
risks
to
non­
target
organisms
MCPB
Task
Force
comment
#
1
Chronic
Risk
to
Freshwater
Fish
Although
no
chronic
freshwater
fish
toxicity
data
were
submitted
for
MCPB,
longer­
term
exposure
will
be
effectively
to
the
metabolite
MCPA.
This
is
because
ß­
oxidation
potential
is
universal
in
animals
(
as
mentioned
in
the
introduction).
It
should
be
noted
that
in
the
MCPA
RED
it
was
determined
that
chronic
risks
to
freshwater
fish
and
invertebrates
were
low
and
OPP
inferred
that
chronic
risk
to
estuarine/
marine
fish
and
invertebrates
would
also
be
low
under
the
assumption
that
the
acute:
chronic
ratio
of
toxicity
endpoints
remains
constant
across
freshwater
and
estuarine/
marine
organisms.
In
view
of
the
relatively
minor
use
of
MCPB
and
as
MCPA
is
the
proximate
metabolite
in
most
species,
the
MCPB
Task
Force
contends
that
no
significant
errors
would
be
introduced
by
extrapolation
from
the
MCPA
data
for
these
risk
assessments.

MCPB
Task
Force
comment
#
2
Chronic
Risk
to
Freshwater
Invertebrates
Similar
considerations
to
those
stated
above
for
fish
are
appropriate.

EFED
response
comments
#
1
and
#
2
The
risk
assessment
for
aquatic
organisms
estimated
exposure
concentrations
on
the
basis
of
residual
MCPB
plus
the
degradate
MCPA.
If
both
are
assumed
to
be
of
equal
toxic
potency,
no
bias
has
been
introduced
to
the
risk
assessment
by
this
assumption.
However,
A
comparison
of
MCPB
toxicity
data
with
the
available
toxicity
for
MCPA
published
in
the
EPA
RED
chapter
for
that
compound,
indicates
that
some
differences
in
toxic
potency
may
exist
for
the
two
compounds.
Using
common
aquatic
species
tested
for
each
compound
(
acid
equivalent)
the
following
comparisons
can
be
made:

Species
Test
Type
MCPB
Result
MCPA
Result
Rainbow
trout
96­
h
LC50
3.9
mg
ae/
L
96
mg
ae/
L
Daphnid
48­
h
LC50
50
mg
ae/
L
82
mg
ae/
L
The
aquatic
organism
comparisons
would
suggest
that
MCPA
(
acid
equivalent)
is
less
toxic
that
the
MCPB.
Therefore,
assuming
equal
potency
between
the
two
compounds,
and
adding
the
exposures
together
would
likely
overestimate
risk
for
aquatic
organisms.
This
finding,
however,
does
not
alter
the
conclusions
of
the
aquatic
risk
assessment,
which
suggests
no
concern
for
acute
effects
in
freshwater
aquatic
organisms.
Chronic
data
for
risks
to
freshwater
fish,
freshwater
invertebrates,
estuarine
marine
fish
and
acute
estuarine
marine
fish
for
MCPB
were
calculated
via
acute
to
chronic
ratios
from
MCPA
data
due
to
lack
of
submitted
data
for
MCPB.
    
3
  
17
There
were
no
LOC
exceedences
for
chronic
risks
to
freshwater
fish,
freshwater
invertebrates,
estuarine
marine
fish
and
acute
estuarine
marine
fish
for
MCPB
based
on
values
calculated
from
MCPA
on
a
acute
to
chronic
ratio
for
both
Oregon
and
California
scenarios.

However,
there
is
low
confidence
in
these
numbers
due
to
interspecies
differences
and
toxicity
differences
between
MCPB
and
MCPA
for
freshwater
fish
and
invertebrates.
Higher
uncertainty
exists
with
estuarine
marine
acute
and
chronic
fish.
Estuarine
marine
invertebrates
were
calculated
with
acute
to
chronic
ratio
but
with
little
confidence.
LOCs
were
exceeded
for
acute
estuarine
marine
invertebrates
(
RQs
0.07
­
0.01)
for
acute
restricted
use
and
acute
endangered
species.

Therefore,
acute
estuarine
marine
fish
and
acute
estuarine
marine
invertebrates
for
MCPB
are
requested
because
no
estuarine
marine
studies
were
submitted
for
MCPB,
low
confidence
in
estuarine
marine
and
invertebrate
calculations
from
acute
to
chronic
ratios
and
the
apparent
differences
in
endpoints
for
MCPA
and
MCPB.
These
endpoint
differences
are
as
follows:
MCPA
is
less
toxic
to
acute
freshwater
fish
(
96
mg
ae/
L)
than
MCPB
(
3.9
mg
ae/
L)
However,
MCPB
is
more
toxic
to
acute
freshwater
invertebrates
(
50
mg
ae/
L)
than
MCPA
(
82
mg
ae/
L).
Therefore,
chronic
studies
for
freshwater
fish
and
invertebrates
will
be
requested
due
to
endpoint
differences
and
low
confidence
in
acute
to
chronic
ratios
as
mentioned
above.
The
chronic
studies
for
estuarine
marine
fish
and
estuarine
invertebrates
are
reserved
based
on
the
outcome
of
acute
estuarine
marine
fish
and
invertebrate
submitted
studies.

The
following
table
of
endpoints
was
used
to
calculate
chronic
freshwater
fish
and
invertebrate
RQ's
with
acute
to
chronic
ratios
for
freshwater
fish
and
invertebrates.

Summary
of
endpoints
(
LC50
or
EC50,
mg
ae/
L)
for
MCPA
acute
and
chronic
aquatic
toxicity
studies
ORGANISM
GROUP
MCPA
(
acute)
MCPB
(
acute)
MCPA
(
chronic)
MCPB
(
chronic)

freshwater
fish
(
rainbow
trout)
96
(
MCPA
DMAS)
3.9
No
data
No
data
freshwater
fish
(
fathead
minnow)
only
chronic
freshwater
fish
study
for
MCPA
No
data
No
data
12
No
data
freshwater
inverts
(
Daphnid)
only
one
study
chronic
freshwater
invertebrate
study
for
MCPA
82
(
MCPA
DMAS)
50
11
No
data
estuarine/
marine
fish
Atlantic
Silverside
179
(
MCPA
Acid)
No
data
No
data
No
data
estuarine/
marine
inverts
eastern
oyster
4.9
(
MCPA
sodium
salt)
No
data
No
data
No
data
    
4
  
17
Summary
of
endpoints
(
LC50
or
EC50,
mg
ae/
L)
determined
by
acute
and
chronic
ratios
ORGANISM
GROUP
MCPB
(
acute)
MCPB
(
chronic)

freshwater
fish
3.9
.5
a
Acute
to
chronic
ratio
freshwater
inverts
50
6.7b
Acute
to
chronic
ratio
estuarine/
marine
fish
7.3c
Acute
to
chronic
.9d
Acute
to
chronic
estuarine/
marine
invert
2.9e
Freshwater
/
estuarine
marine
ratio
.4f
aMCPB
Freshwater
fish
(
chronic)
.5=
[
12(
chronic
freshwater
fish
MCPA
)
/
96(
acute
freshwater
fish
MCPA)]
x3.9(
acute
freshwater
fish
MCPB)
b
MCPB
Freshwater
invertebrate
(
chronic)
6.7=[
11(
chronic
freshwater
invertebrate
MCPA
)
/
96(
acute
freshwater
invertebrate
MCPA)]
x
50(
acute
freshwater
invertebrate
MCPB)
cMCPB
Estuarine
marine
fish
(
acute)
7.3=[
96(
acute
freshwater
fish
MCPA
)
/
179(
acute
estuarine
marine
fish
MCPA)]
x
3.9(
acute
freshwater
fish
MCPB)
dMCPB
Estuarine
marine
fish
(
chronic)
.9=(.
5
chronic
freshwater
fish
MCPB
)
/
3.9(
acute
freshwater
fish
MCPB)]
x
7.3(
acute
estuarine
marine
fish
MCPB)
eMCPB
Estuarine
marine
invertebrates
(
acute)
2.9=[
50(
acute
freshwater
invertebrate
MCPB
)
/
82(
acute
freshwater
invertebrates
MCPA)]
x
4.9(
acute
estuarine
marine
invertebrates
MCPA)
FMCPB
Estuarine
marine
invertebrates
(
chronic)
.4
=[
50(
acute
freshwater
invertebrate
MCPB
)
/
82(
acute
freshwater
invertebrates
MCPA)]
x
4.9(
acute
estuarine
marine
invertebrates
MCPA)
x[
11(
chronic
freshwater
invertebrate
MCPA
)
/
82(
acute
freshwater
invertebrates
MCPA)]

Summarized
Chronic
Aquatic
Organism
Risk
Quotients
for
MCPB
Acid
a,
b
    
5
  
17
Application/
Scenario
Freshwater
Fishc,
d
Freshwater
Invertebrates
e,
f
Estuarine
Fishc,
d
Estuarine
Invertebrates
e,
f
Peas
(
ground
spray
application)
Oregon
0.06
<.
01
0.03
0.07
Peas
(
aerial
spray
application)
Oregon
0.06
<.
01
0.04
0.08
Peas
(
ground
spray
application)
California
0.07
<.
01
0.04
0.10
Peas
(
aerial
spray
application)
California
0.07
<.
01
0.04
0.10
a
Detailed
calculations
of
PRZM
3.12/
EXAMS
2.98
modeling
for
peas
grown
in
Oregon
and
California
are
provided
in
Appendix
B.
bChronic
toxicity
thresholds
(
LC50
or
EC50)
calculated
by
acute
to
chronic
ratio
with
values
from
MCPA
were
.5
and
6.7
mg
ae/
L
for
freshwater
fish
and
freshwater
invertebrates,
respectively.
Chronic
toxicity
thresholds
(
LC50
or
EC50)
calculated
by
acute
to
chronic
ratio
with
values
from
MCPA
were
.9
and
.4
mg
ae/
L
for
estuarine
marine
fish
and
estuarine
marine
invertebrates,
respectively.
Chronic
Fish
C
EECs
for
Oregon
bean
Scenario
were
28.1
and
31.5
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively.
DEECs
for
California
lettuce
Scenario
were
36.4
and
38.9
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively
Chronic
Invertebrates
eEECs
for
Oregon
bean
Scenario
were
29.0
and
32.5
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively.
FEECs
for
California
lettuce
Scenario
were
39.0
and
41.7
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively.

Summarized
Acute
Aquatic
Organism
Risk
Quotients
for
MCPB
Acid
a,
b
Application/
Scenario
Freshwater
Fisha,
b
Freshwater
Invertebrates
a,
b
Estuarine
Fisha,
b
Estuarine
Invertebrates
a,
b
Peas
(
ground
spray
application)
Oregon
<
0.01
<
0.01
<
0.01
0.07
Peas
(
aerial
spray
application)
Oregon
<
0.01
<
0.01
<
0.01
0.08
Peas
(
ground
spray
application)
California
0.01
<
0.01
<
0.01
0.10
Peas
(
aerial
spray
application)
California
0.01
<
0.01
<
0.01
0.10
For
an
estuarine
marine
and
freshwater
ratio
MCPB
and
MCPA:
Acute
toxicity
thresholds
(
LC50
or
EC50)
calculated
with
acute
estuarine
marine
fish
and
estuarine
invertebrate
values
from
MCPA
179
and
4.9
respectively;
Values
from
MCPB
were
3.9
and
50
mg
ae/
L
for
acute
freshwater
fish
and
freshwater
invertebrates,
respectively.

Acute
Fish
and
Invertebrates
    
6
  
17
a
EECs
for
Oregon
bean
Scenario
were
29.5
and
33.1
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively.
BEECs
for
California
lettuce
Scenario
were
40.4
and
43.2
µ
g/
L
for
ground
spray
and
aerial
spray,
respectively.

MCPB
Task
Force
comment
#
3
Chronic
Risk
to
Birds
An
avian
reproduction
study
was
submitted
for
the
proximate
metabolite
MCPA.
The
MCPB
Task
Force
contend
that
this
is
applicable
to
MCPB
as
this
metabolite
will
dominate
exposures
of
a
repeat
nature.

EFED
response
comments
#
3:

Terrestrial
wildlife
exposures
were
conducted
solely
on
the
exposure
for
MCPB.
MCPA
was
not
included
in
the
exposure
assessment.
A
comparison
of
MCPB
toxicity
data
with
the
available
toxicity
for
MCPA
published
in
the
EPA
RED
chapter
for
that
compound,
indicates
that
some
differences
in
toxic
potency
may
exist
for
the
two
compounds.
Using
common
avian
species
tested
for
each
compound
(
acid
equivalent)
the
following
comparisons
can
be
made:

Species
Test
Type
MCPB
Result
MCPA
Result
Bobwhite
LD50
257
221­
377
The
comparison
for
bobwhite
quail
would
suggest
that
the
acute
potency
of
MCPB
lies
within
the
range
of
toxicity
for
acid
equivalent
MCPA.
EFED
considered
MCPA
as
a
substitute
for
MCPB
for
chronic
risk
to
birds,
because
the
LD50
for
bobwhite
quail
suggests
that
the
acute
potency
of
MCPB
lies
within
the
range
of
toxicity
for
acid
equivalent
MCPA.
Also,
rapid
dissociation
of
MCPB
to
MCPA
is
expected
to
occur
in
the
bird
gut
due
to
the
chemical
properties
of
MCPB.
Therefore,
the
terrestrial
model
TREX
was
used
to
determine
the
chronic
risk
to
birds.
MCPA
NOAEC
of
1000
mg/
kg­
diet
(
MRID
#
435052­
01)
.
Chronic
RQs
ranged
from
0.02
to
0.36.
which
is
below
LOC
of
1.
No
further
studies
are
required
for
chronic
risk
to
birds
for
MCPB
at
this
time.

Uncertainties
and
data
gaps
MCPB
Task
Force
comment
#
4
Terrestrial
field
dissipation
Evidence
presented
in
this
document
indicates
that
MCPB
has
a
half­
life
of
between
4
and
11
days
in
soil,
dependent
on
conditions.
Data
indicate
that
by
day
120
there
is
no
parent
or
metabolite
material
detectable
in
the
soil.
The
pea
crop
is
sprayed
with
MCPB
before
flowering,
which
means
that
spray
application
takes
place
at
least
two
months
(
and
probably
longer)
before
harvest.
The
subsequent
crops
will
not
normally
be
planted
until
at
least
3
to
4
months
after
spray
application
and
no
residue
of
MCPB
will
be
expected
to
remain
to
affect
succeeding
crops.
Further,
the
major
metabolites
of
MCPB
in
soil
are
carbon
dioxide
and
MCPA,
although
the
latter
is
not
seen
to
accumulate
after
the
first
few
days
following
application.
Thus,
it
is
the
contention
of
the
Task
Force
that
sufficient
data
exist
to
render
this
study
unnecessary,
and
a
waiver
will
be
applied
for
on
this
basis.
    
7
  
17
EFED
Response
comment
#
4:
The
purpose
of
field
dissipation
studies
for
pesticides
with
terrestrial
uses
is
to
determine
the
extent
of
pesticide
residue
dissipation
under
actual
use
condition.
A
guideline
field
dissipation
study
will
generate
data
required
for
the
evaluation
of
mobility,
degradation,
and
dissipation
of
residues.
Terrestrial
field
dissipation
studies
are
required
because
pesticide
dissipation
may
proceed
at
a
different
rate
under
field
conditions
and
therefore
result
in
the
formation
of
levels
of
degradates
differing
from
those
observed
in
laboratory
studies.
EFED
recommends
that
the
registrant
submit
a
guideline
terrestrial
field
dissipation
study.

MCPB
Task
Force
comment
#
5
Multigeneration
study
­
It
has
already
been
mentioned
that
the
mammalian
reproduction
study
for
MCPA
will
serve
as
a
surrogate
for
MCPB
and
has
been
accepted
as
such
in
EPA's
HED
evaluation.

EFED
response
comments
#
5
The
rabbit
study
is
the
most
sensitive
endpoint
for
MCPB
and
will
remain
in
the
risk
assessment
for
assessing
chronic
LOCs
for
mammals.

Stressor
Source
and
Distribution
MCPB
Task
Force
comment
#
6
Paragraph
2
It
is
stated
that
no
data
are
available
for
MCPB
biodegradation
in
water.
A
water/
sediment
study
is
available
for
MCPB
(
Van
Dijk
2003),
and
was
summarised
in
detail
in
a
previous
submission.
In
this
study
two
sediments
collected
in
Holland
were
used
to
determine
degradation
rate
in
accordance
with
OECD
Guideline
308.
The
sediments
differed
mainly
in
their
organic
carbon
content,
but
degradation
of
MCPB
was
similar
for
both,
with
a
DT50
of
9.3
to
10
days
in
the
aqueous
phase
and
16
to
18
days
in
the
entire
system.
There
was
no
evidence
for
selective
accumulation
of
MCPB
in
the
sediment
phase,
and
as
with
other
systems,
degradation
was
via
MCPA.
After
an
initial
small
build­
up
of
MCPA,
this
metabolite
was
removed
from
the
system
more
rapidly
than
it
was
created,
so
that
it
only
transiently
exceeded
10%
of
added
radioactivity,
and
in
only
one
of
the
systems.
These
findings
are
consistent
with
the
known
degradation
rate
of
MCPA
in
water/
sediment
studies.

EFED
response
comment
#
6
EFED
is
unaware
of
any
guideline
water/
sediment
study
for
MCPB
submitted
to
the
Agency.
Since
no
aerobic
aquatic
metabolism
studies
have
been
submitted
to
the
Agency,
EFED
used
twice
the
aerobic
soil
metabolism
half­
life
as
a
substitute
for
the
aerobic
aquatic
metabolism
half­
life
input
parameter
in
the
PRZM/
EXAMS
modeling
in
accordance
with
EFED's
PRZM/
EXAMS
modeling
input
parameter
guidance
(
Guidance
for
Selecting
Input
Parameters
in
Modeling
the
Environmental
Fate
and
Transport
of
Pesticides,
Version
II,
February
28,
2002).
A
guideline
aerobic
aquatic
metabolism
study
should
provide
data
on
the
effects
of
pesticide
exposure
to
aerobic
conditions
in
water
or
sediment
during
the
period
of
dispersal
of
the
pesticide
throughout
the
aquatic
environment
and
to
compare
rates
of
formation
of
metabolites
with
those
observed
under
conditions
of
anaerobic
aquatic
metabolism.
The
Registrant
need
to
submit
a
    
8
  
17
guideline
aerobic
aquatic
metabolism
study
to
satisfy
the
data
requirement.

MCPB
Task
Force
comment
#
7
Paragraph
3
The
solubility
of
MCPB
in
water
is
strongly
dependant
on
pH
(
see
earlier
comment,
Bass
1999,
MRID
45735301)
such
that
at
pH
7,
concentration
will
be
about
4400
mg/
l
rather
than
the
quoted
200,000.
This
will
likely
have
a
minimal
effect
on
any
risk
assessment.

EFED
response
comment
#
7
The
solubility
value
of
200,000
mg/
l
(
2kg/
l
)
for
MCPB
sodium
salt
in
water
was
provided
in
the
study
MRID
42714301
(
MCPB
Sodium
Salt:
Determination
of
Physical
Chemical
Properties,
P
Sydney,
1993)
that
was
submitted
to
the
Agency.
The
same
solubility
value
of
200,000
mg/
l
for
MCPB
sodium
salt
in
water
is
also
quoted
in
the
WSSA
(
Weed
Science
Society
of
America)
Herbicide
Handbook.
Ahrens
W.
H.,
Ed.,
1994
Champaign,
IL.
p.
352,
the
material
data
sheet
for
the
formulated
product
"
Tropotox
(
R)
Plus",
and
in
the
OSU
extension
pesticide
properties
database.
The
above
mentioned
study
(
MRID
45735301)
does
not
provide
a
solubility
value
for
MCPB
sodium
salt
in
water.

However,
it
should
be
noted
that,
using
the
solubility
value
of
4400
mg/
l
instead
of
the
value
of
200,000
mg/
l
in
the
PRZM/
EXAMS
modeling
will
have
no
effect
on
the
estimated
concentrations
of
MCP
in
water.

MCPB
Task
Force
comment
#
8
Page
11,
paragraph
2
Aerobic
degradation
is
established
in
a
number
of
publications
to
have
a
DT50
in
the
region
of
6
days.
This
has
been
mentioned
in
a
previous
submission.
It
is
inappropriate
to
use
the
value
of
26
days.
It
is
not
clear
from
whence
this
value
is
derived.
The
study
quoted
(
John
et
al
1994a,
MRID
43247601)
shows
a
rapid
decline
in
MCPB
with
a
small
(
about
1%)
residue
remaining
after
65
days.
This
residue
shows
no
decline
between
days
65
and
120.
The
major
metabolites
are
MCPA
and
HMCPA
either
free
or
conjugated.
The
question
is
how
this
profile
should
be
converted
to
an
assessment
factor.
Both
the
original
study
director
and
the
contract
reviewer
chose
to
apply
a
dual
approach
with
an
overall
rate
and
an
initial
rate.
The
initial
rate
has
been
accepted
for
use
in
the
EU;
the
difference
is
one
of
calculation
 
see
table
below.
Half
lives
calculated/
used
for
MCPB
based
on
John
et
al
(
1994a)
    
9
  
17
The
study
director's
calculation
assumed
first­
order
kinetics
and
achieved
an
initial
value
of
6.8
days
with
a
secondary
value
of
31
days.
EPA's
reviewer
used
a
least
squares
fit
to
give
values
which
are
higher
but
which
show
a
lower
correlation
coefficient.
As
there
was
no
evidence
of
further
decomposition
after
the
65­
day
point,
this
is
arguably
inappropriate.
It
must
be
presumed
that
under
the
experimental
conditions,
the
residue
at
65
days
is
firmly
bound
and
will
not
degrade,
so
that
further
prolongation
will
artificially
increase
the
"
half­
life"
value.
Presumably,
the
value
of
26
days
adopted
for
calculations
is
derived
as
a
"
composite"
half­
life
based
on
MCPB,
MCPA
and
HMCPA
conjugate,
although
it
is
stated
elsewhere
that
the
latter
two
values
make
very
little
difference.
This
value
is
at
variance
with
other
published
information
which
is
generally
closer
to
the
6
days
calculated
by
the
study
director.
It
should
be
further
noted
that
in
the
study
by
Goodyear
(
1993,
MRID
43015501),
which
was
reviewed
and
which
was
conducted
according
to
Guideline
No.
162­
2,
anaerobic
conditions
were
established
after
a
calculated
halflife
of
MCPB
had
been
exceeded.
This
was
4
days.
A
subsequent
anaerobic
half­
life
of
approx.
11
days
has
been
calculated
from
these
data.
This
relationship
is
in
accord
with
that
predicted
by
structure/
function
from
other
phenoxy
herbicides
i.
e.
the
anaerobic
degradation
rate
is
significantly
less
than
the
aerobic
rate.
It
should
also
be
noted
that
in
column
leaching
studies
(
John
et
al
1994b,
MRID
43466401)
conducted
according
to
Guideline
N163­
1,
four
soil
types
and
aquatic
sediment
were
used.
Preliminary
investigations
established
the
half­
life
of
MCPB
in
these
soils,
and
these
values
ranged
from
4.75
to
7.13
days
(
see
table
below).
    
10
  
17
In
these
circumstances
the
use
of
a
single
experimental
value
for
risk
assessment
is
questionable.
Specifically,
both
the
adopted
value
and
the
tripling
of
this
value
are
inappropriate.
The
best
estimate
of
aerobic
half­
life
in
soil
is
approximately
6
days.
Application
of
this
figure
is
likely
to
have
significant
influence
on
the
risks
calculated.
Comments
on
photolysis
in
the
subsequent
paragraph
are
noted.
The
Task
Force
agrees
with
the
later
statement
to
the
effect
that
following
considerations
of
water
depth,
etc.,
photolysis
is
not
an
important
route
of
degradation
for
MCPB
in
the
environment.

EFED
Response
comment
#
8:
    
11
  
17
The
aerobic
soil
metabolism
half­
life
of
26
days
was
calculated
using
linear
regression
of
the
natural
logarithm
of
the
mean
value
of
the
percent
of
applied
total
residue
over
the
whole
duration
of
the
study
(
0­
120
days).
All
reported
data
points
were
used
with
the
exception
of
day
3
because
of
the
loss
of
some
extract
and
overheating
problems
during
the
sample
analysis.
For
the
PRZM/
EXAMS
modeling
purposes,
the
aerobic
soil
metabolism
half­
life
of
26
days
was
multiplied
by
three
(
26
x
3
=
78
days)
to
represent
the
90th
upper
percentile
of
the
mean,
in
accordance
with
EFED's
PRZM/
EXAMS
modeling
input
parameter
guidance
(
Guidance
for
Selecting
Input
Parameters
in
Modeling
the
Environmental
Fate
and
Transport
of
Pesticides,
Version
II,
February
28,
2002),
since
there
was
only
one
soil
used
in
the
aerobic
soil
metabolism
study
(
MRID
43247601).
Multiplying
the
half
life
by
a
factor
of
3
is
used
to
account
for
variability
in
half­
lives
in
the
field
which
represent
approximately
90th
percentile
of
the
mean.
It
should
be
noted
that
the
use
of
a
half­
life
of
78
days
in
the
modeling
did
not
trigger
any
exceedance
for
any
of
the
aquatic
species
considered
in
the
risk
assessment.

MCPB
Task
Force
comment
#
9
Page
20,
paragraph
1
Preliminary
identification
of
Data
Gaps
and
Methods.
Task
Force
comments
on
aerobic
and
anaerobic
aquatic
biodegradation
have
already
been
made
in
the
context
of
the
summary.
It
is
unlikely
that
soil
photolysis
would
be
an
important
route
of
degradation
as
MCPB
is
unlikely
to
remain
on
the
soil
surface
for
significant
periods.

EFED
response
comment
#
9:
Although
the
photodegradation
on
soil
study
(
MRID
43829901)
was
determined
to
be
unacceptable
and
does
not
satisfy
the
data
requirement,
It
appears
that
MCPB
is
stable
to
photodegradation
on
soil
and
hence,
no
new
study
is
required
at
this
time.

MCPB
Task
Force
comment
#
10
Page
20,
Paragraph
2
Refer
to
MCPA
data
for
chronic
toxicity
studies
for
fish
and
invertebrates,
as
previously
discussed.
EFED
response
comment
#
10:
Refer
to
EFED
response
to
comment
1
and
2.

MCPB
Task
Force
comment
#
11
Page
28
 
Residues
Studies
Residues
studies
conducted
on
peas
in
Northern
Europe
are
available.
These
used
application
rates
of
1.6
kg/
ha
and
were
thus
>
90%
of
the
rate
used
in
the
USA.
Immediately
following
application
whole
plants
showed
concentrations
ranging
from
35­
62
ppm
and
these
residues
declined
rapidly
thereafter
so
that
by
28
days
residues
in
all
crops
were
below
0.21
ppm.
All
values
were
based
on
fresh
weight.
In
the
absence
of
specific
US
data
it
may
be
more
appropriate
to
use
these
values
than
those
from
a
model
system.
Thus,
conservatively
an
initial
concentration
of
approximately
70
ppm
is
arguably
more
applicable
than
the
Kenaga
default
value.
Similarly,
application
of
first­
order
kinetics
to
this
value
and
the
28­
day
residue,
indicates
a
half­
life
just
less
than
3.5
days.
This
refinement
is
a
more
realistic
value
than
the
35
days
currently
incorporated
into
the
risk
assessment.
These
considerations
are
likely
to
have
a
significant
impact
on
the
outcome
of
EPA's
assessment.
    
12
  
17
EFED
response
to
comment
#
11:
These
residue
studies
have
not
yet
been
submitted
to
the
Agency,
and
when
they
are
submitted
in
the
future,
then
they
will
be
reviewed
at
that
time.

MCPB
Task
Force
comment
#
12
Page
32,
Table
3G
The
studies
tabulated
were
all
conducted
at
Springborn
Laboratories,
USA
in
1992.
Studies
performed
in
this
laboratory
during
the
period
with
various
phenoxy
acids
have
given
results
which
are
atypical
of
similar
studies
performed
elsewhere.
This
has
been
reviewed
in
detail
for
Selenastrum
capricornutum
and
MCPA
(
MRID
45554404).
An
independent
consultant's
report
of
the
various
studies
conducted
with
this
active
ingredient
and
test
organism
has
been
submitted
to
EPA
in
connection
with
the
MCPA
RED.
A
document
containing
additional
investigations
with
the
related
compound
MCPP­
p,
where
concurrent
investigations
were
compared
with
those
in
other
laboratories,
is
in
preparation
and
will
be
submitted
to
EPA
shortly.
A
critique
of
the
studies
with
MCPB
is
attached
to
this
overview
and
demonstrates
why,
in
the
opinion
of
the
MCPB
Task
Force,
the
majority
of
these
studies
conducted
at
Springborn
Laboratories
are
considered
unacceptable.
Replacement
studies
have
been
performed
as
follows:

Duckweed
(
Lemna
gibba)
Billing
and
Albuquerque
2003
This
study
performed
at
HLS
in
the
UK
to
OPPTS
850.4400
and
the
OECD
draft
Guideline
for
Lemna
species,
reports
a
EbC50
of
37
mg/
l
(
expressed
as
acid)
with
a
NOAEC
at
2.8
mg/
l.
Selenastrum
capricornutum
Albuquerque
and
Utting
2003
This
study
reports
an
EbC50
at
41
mg/
l
(
expressed
as
acid)
and
a
NOEC
0.87
mg/
l
Navicula
pelliculosa
Albuquerque
and
Firth
2003
This
study
reports
an
EbC50
of
1.5
mg/
l
with
a
NOEC
0.56
mg/
l
The
reports
for
these
studies
have
been
submitted
to
EPA.
The
MCPB
Task
Force
considers
that
the
toxicity
values
derived
from
these
recent
guideline
and
GLP­
compliant
studies
are
more
appropriate
for
use
in
risk
assessment
than
those
from
the
earlier
Springborn
studies.
The
study
with
the
blue­
green
alga
Anabaena
flos­
aquae
was
not
repeated
as
the
initial
result
was
not
ratelimiting
in
determining
toxicity.
Similarly,
there
is
currently
no
additional
study
with
the
marine
diatom
Skeletonema
costatum.
EFED
response
to
comment
#
12:

When
these
studies
are
submitted
then
they
will
be
reviewed
according
to
SOP.
According
to
our
Overview
of
the
Ecological
Risk
Assessment
Process
Office
of
Pesticides
Document
,
all
submitted
studies
will
be
included
in
the
risk
assessment
after
they
are
individually
reviewed.

MCPB
Task
Force
comment
#
13
Terrestrial
effects,
characterisation
 
birds,
chronic
Because
MCPB
is
metabolised
to
MCPA
by
the
process
of
ß­
oxidation,
which
is
ubiquitous
in
animal
and
avian
species,
the
MCPB
Task
Force
considers
that
the
avian
reproduction
study
for
MCPA
can
serve
as
an
acceptable
surrogate
for
a
study
with
MCPB.

EFED
response
to
comment
#
13:
Refer
to
comment
#
3
    
13
  
17
MCPB
Task
Force
comment
#
14
Mammals,
sub­
chronic
and
developmental/
reproductive
Effects
noted
in
the
dog
study
are
established
as
having
limited
relevance.
As
stated
in
EPA's
HED
chapter
the
dog
has
an
impaired
ability
to
excrete
various
organic
acids,
including
MCPB
and
MCPA,
and
is
thus
not
typical
of
other
species.
Timchalk
("
Comparative
inter­
species
pharmacokinetics
of
phenoxyacetic
acid
herbicides
and
related
organic
acids.
Evidence
that
the
dog
is
not
a
relevant
species
for
evaluation
of
human
health
risk";
Toxicology
200,
pages
1­
19,
2004,
MRID
46328601)
has
extensively
reviewed
this
for
related
compounds
2,4­
D
and
MCPA
and
shown
that
of
the
species
tested,
the
dog
is
an
outlier.
It
is
possible
that
other
carnivorous
species
would
show
a
similar
reaction,
although
this
has
not
been
tested
experimentally;
but,
for
the
majority
of
wild
mammals,
results
from
the
dog
are
not
relevant.

Kinetic
studies
have
shown
that
there
is
saturation
of
renal
excretion
of
MCPA
in
the
rat
at
doses
around
80­
100
mg/
kg/
day.
It
is
therefore
likely
that
in
the
rat
90
day
study
decreased
food
consumption
and
bodyweight
gains
seen
at
the
high
dose
level
reflect
a
direct
effect
of
compound,
rather
than
simple
palatability.
On
this
basis
this
high
dose
should
be
considered
an
effect
level.
This
means
that
for
the
rat
90
day
study
the
NOAEL
should
be
set
at
500
ppm
in
diets
(
approx
35
mg/
kg/
day).
MRID#
40041701
In
determining
developmental
effects,
it
should
be
noted
that
no
developmental
changes
were
seen
in
the
rabbit
study
at
the
dose
of
20
mg
a.
i/
kg/
day.
Although
it
is
accepted
that
maternal
effects
were
seen
in
rabbits
at
this
level,
the
value
of
20
mg/
kg/
day
is
logically
the
NOEL
for
developmental
toxicity.

In
the
rat
reproduction
study,
pup
effects
were
confined
to
the
high
dose;
which
corresponds
to
450
ppm
in
the
diet.
As
growth
reduction
was
confined
to
pups
in
the
lactation
and
perilactational
period,
it
is
important
to
note
that
the
effective
dose
rate
during
this
period
is
considerably
in
excess
of
the
mean
for
the
study
as
a
whole
(
see
above).
The
NOEC
from
the
one­
generation
study
(
Milburn
2004,
MRID
46411201)
is
a
more
appropriate
value
to
use
for
determining
the
LOAEL
and
NOAEL
for
these
parameters.

EFED
response
comment
#
14:
The
dog
study
will
remain
in
the
risk
characterization
for
risk
characterization
purposes
because
wild
canine
mammals
may
be
exposed
to
MCPB
Other
comments
are
to
be
answered
by
HED
MCPB
Task
Force
comment
#
15
Page
37
 
Terrestrial
Field
Studies
It
is
stated
here
that
the
requirement
for
terrestrial
field
studies
was
waived.
The
MCPB
Task
Force
accepts
that
this
is
a
logical
position
and
recommends
that
Table
I.
c.
be
corrected
accordingly.

EFED
response
comment
#
15:
Table
Ic
is
terrestrial
field
dissipation
(
164­
2)
which
is
a
different
study
than
terrestrial
field
studies
(
124­
1).
Terrestrial
field
studies
(
124­
1)
was
waived.
Therefore,
no
changes
will
be
made
to
Table
Ic.
    
14
  
17
IV
Risk
Characterization
MCPB
Task
Force
comment
#
16
Non­
target
aquatic
animals
and
plants
The
statement
that
"
MCPA
has
been
shown
to
be
less
toxic
to
aquatic
organisms
than
the
parent
MCPB"
is
not
correct
when
the
newer
studies
submitted
are
taken
into
account.
This
means
that
the
inclusion
of
MCPA
metabolites
remains
an
appropriate
approach.

EFED
response
comment
#
16:
When
the
newer
studies
are
submitted
for
MCPB
and
MCPA
these
will
then
be
reviewed.
Therefore,
statement
"
MCPA
has
been
shown
to
be
less
toxic
to
aquatic
organisms
than
the
parent
MCPB"
will
remain
in
the
assessment.

MCPB
Task
Force
comment
#
17
Non­
target
terrestrial
animals
and
plants,
Table
4c
summary
of
end
points
The
mammalian
LD50
from
MRID
116340
should
be
"
1570"
rather
than
the
"
832"
quoted
in
this
table.
An
additional
study
is
submitted
(
Wainwright
2002)
which
shows
that
the
LD50
both
acute
and
oral
for
the
honey
bee
is
considerable
in
excess
of
the
value
quoted
in
this
table.
As
no
risk
to
bees
is
established
in
the
risk
assessment
this
will
have
no
practical
impact
on
the
outcome.

EFED
response
comment
#
17:
The
mammalian
LD50
from
MRID
116340
table
4c
is
correct
with
the
value
of
832
ae/
kg
bw
which
was
the
endpoint
used
for
RQ
evaluation.
This
value
is
discussed
throughout
the
chapter.

MCPB
Task
Force
comment
#
18
Birds
Page
46,
paragraph
4
The
comments
regarding
uncertainty
in
EC05
values
are
noted.
Inherently
these
values
will
have
high
uncertainty,
because
the
studies
from
which
they
are
derived
use
relatively
small
groups
of
plants
(
as
recommended
in
the
relevant
guideline).
Thus,
in
a
group
of
20
seedlings
an
EC05
represents
a
single
affected
plant.
It
is
unlikely
that
repeat
studies
in
the
range
EC05
to
EC25
would
produce
significant
clarification
of
the
"
true"
value.
It
can
be
argued
that
the
use
of
EC05
values
represents
extrapolation
beyond
what
is
justified
by
the
data
requirement.

EFED
response
comment
#
18:
Comment
noted.
However,
no
changes
will
be
incorporated
into
the
risk
assessment.

MCPB
Task
Force
comment
#
19
    
15
  
17
Risk
Description
Birds
Paragraph
2
It
is
agreed
that
there
is
a
significant
difference
in
acute
lethality
when
MCPB
is
administered
as
a
gavage
dose
compared
to
that
when
mixed
with
the
diet.
Consideration
of
the
properties
of
MCPB
(
shared
with
other
phenoxy
herbicides)
indicates
that
at
least
for
small
birds
the
use
of
the
dietary
study
LC50
value
is
more
representative
of
potential
effects
in
the
field
than
that
of
the
gavage
LC50.
In
the
gavage
case,
birds
are
deprived
of
food
for
18
hours
before
dosing.
Thus,
the
entire
dose
is
deposited
in
an
empty
crop
where
it
is
available
for
absorption
immediately.
By
contrast,
mixture
with
the
diet
ensures
that
the
dose
is
received
in
a
more
realistic
manner.
For
highly
water­
soluble
compounds
such
as
MCPB,
absorption
will
be
rapid
and
followed
by
equally
rapid
excretion.
When
dosing
is
spread
over
a
period
of
time,
as
with
admixtures
in
feed,
this
process
is
allowed
to
reach
equilibrium
and
produces
a
more
realistic
prediction
of
effect.
It
can
be
argued
that
larger
birds
may
consume
food
as
available
in
a
non­
uniform
manner
and
thus,
effectively,
receive
the
dose
over
a
shorter
period.
Even
in
these
instances,
admixture
with
the
feed
will
attenuate
absorption
and
thus
the
feed
contamination
route
is
more
realistic.
For
the
small
bird
species
(
which
are
considered
most
at
risk)
the
daily
food
intake,
in
terms
of
wet
weight,
often
exceeds
the
bird's
body
weight
and
it
is
self­
evident
that
this
cannot
be
consumed
in
a
single
meal.
Thus,
in
all
these
circumstances
assessments
based
on
the
dietary
route
are
more
realistic.
It
should
also
be
recognized
that
the
"
sub­
lethal
effects
observed
in
both
studies"
were
in
the
dietary
studies
confined
to
reduced
food
consumption;
no
clinical
signs
were
seen
in
either
the
bobwhite
quail
or
the
mallard
duck
at
any
of
the
dietary
concentrations
examined.
Although
this
is
undoubtedly
an
adverse
effect
over
a
longer
period,
in
terms
of
an
acute
risk
assessment
it
would
serve
to
limit
exposure,
and
is
a
further
indication
that
the
dietary
route
is
more
representative
of
field
conditions.
The
evaluators
may
be
interested
to
know
that
a
similar
debate
has
been
held
in
the
EU.
A
recent
report
from
the
Scientific
Committee,
based
on
questions
relating
to
the
active
ingredient
pirimicarb
methyl,
is
attached.
In
Europe,
these
decisions
from
the
Scientific
Committee
are
considered
generic
and
have
been
accepted
for
the
phenoxy
herbicides.

EFED
response
comment
#
19:
For
the
purpose
of
this
screening
level
assessment,
the
more
conservative
RQs
(
in
this
case,
dose­
based)
are
used
to
estimate
risk.
At
the
screening
level,
there
appears
to
be
a
considerable
difference
between
the
dose­
based
and
dietary­
based
RQs.
This
is
likely
partly
due
to
the
inherent
uncertainties
surrounding
the
two
acute/
subacute
toxicity
tests.
Each
of
these
studies
has
limitations
for
estimating
the
risk
to
wild
species
exposed
to
pesticides
in
the
environment.
Both
studies
have
a
fixed
exposure
period
and
do
not
allow
for
the
differences
in
response
of
individuals
to
different
durations
of
exposure.
With
the
acute
oral
study,
the
chemical
is
administered
in
a
single
dose.
This
does
not
mimic
wild
bird
exposure
through
multiple
feedings.
Also,
it
does
not
account
for
the
effect
of
different
environmental
matrices
on
absorption
rate
into
the
gastrointestinal
tract
of
the
animal.
With
the
acute
dietary
study,
the
endpoint
is
reported
as
the
concentration
mixed
with
food
that
produces
a
response
rather
than
as
the
dose
ingested.
Although
food
consumption
sometimes
allows
for
estimation
of
a
dose,
calculations
of
the
mg/
kg/
day
are
confounded
by
undocumented
spillage
of
feed
and
how
consumption
is
measured
over
the
duration
of
the
test.
Usually,
if
measured
at
all,
food
consumption
is
estimated
once
at
the
end
of
the
five­
day
exposure
period.
Group
housing
of
birds
    
16
  
17
undergoing
testing
only
allows
for
a
measure
of
the
average
consumption
per
day
for
a
group
and
consumption
estimates
can
be
further
confounded
if
birds
die
within
a
treatment
group.
In
addition,
the
dietary
study
utilizes
young
birds.
The
exponential
growth
of
young
birds
complicates
the
estimate
of
the
dose;
controls
often
nearly
double
in
size
over
the
duration
of
the
test.
Since
weights
are
only
taken
at
the
initiation
of
the
exposure
period
and
at
the
end,
the
dose
per
body
weight
(
mg/
kg)
is
difficult
to
estimate
with
any
precision.
The
interpretation
of
this
test
can
be
further
confounded
by
dietary
consumption.
Estimation
of
the
acute
LC50
value
is
not
only
a
function
of
the
intrinsic
toxicity
of
the
pesticide,
but
also
the
willingness
of
the
birds
to
consume
treated
food.

In
addition
to
the
uncertainties
surrounding
the
two
toxicity
studies
utilized
for
estimating
acute
risk
to
birds,
other
factors,
not
normally
taken
into
account
in
a
screening
level
risk
assessment
may
narrow
the
differences
between
the
dose­
based
and
dietary­
based
acute
RQs
for
birds.
The
factors
include
differences
in
gross
energy
and
assimilative
efficiency
of
laboratory
feed
versus
food
items
in
the
field,
basic
maintenance
metabolic
rates
between
wild
birds
and
captive
birds,
seasonal
free
living
dietary
requirements
for
wild
birds
(
including
gorging
behavior)
and
specific
food
avoidance
behavior.
These
uncertainties
may
either
overestimate
or
underestimate
the
risk
in
a
screening
level
assessment.

Since
liver
abnormalities
in
birds
were
observed
in
both
acute
dose­
based
and
acute
dietary
based
MCPB
studies
and
mortalities
occurred
at
all
concentration
levels
in
the
acute
dose­
based
bobwhite
quail
study
comments;
conclusions
in
the
risk
assessment
concerning
acute
risk
to
birds
will
remain
the
same
in
this
assessment.

MCPB
Task
Force
comment
#
20
Mammals
The
special
considerations
relating
to
the
dog
and
also
the
NOEC
for
developmental
toxicity
have
already
been
mentioned
previously.
These
differences,
if
accepted
by
EPA,
will
likely
impact
on
the
risk
assessment.
The
low
maternal
NOEL
in
the
rabbit
developmental
toxicity
study
is
derived
from
the
study
with
gavage
dosing.
The
limitations
of
this
procedure
were
discussed
above
with
respect
to
birds,
although
similar
considerations
apply
to
mammals.
It
is
therefore
unlikely
that
any
affect
on
foraging
behaviour
will
be
seen
in
practice.

EFED
response
comment
#
20:
As
previously
stated
the
dog
study
will
be
used
in
risk
characterization
and
the
rabbit
value
is
the
same
because
it
is
the
most
sensitive
endpoint.
Please
refer
to
comment
#
14
and
comment#
19
for
further
explanation.

MCPB
Task
Force
comment
#
21
Terrestrial
Plants
in
Dry
Land
and
Semi­
aquatic
areas
First
paragraph,
page
51
The
MCPB
Task
Force
will
consider
a
label
amendment
to
require
medium
or
coarser
droplet
size
for
all
applications.

EFED
response
comment
#
21:
Comment
noted.
When
a
label
amendment
is
negotiated
with
risk
managers,
EFED
will
be
able
to
incorporate
this
information
in
the
risk
assessment.
    
17
  
17
MCPB
Task
Force
comment
#
22
Review
of
Incident
Data
The
MCPB
Task
Force
accepts
that
the
lack
of
mortality
incidents
in
the
EIIS
database
is
not
definitive
evidence
of
a
lack
of
hazard
to
aquatic
and/
or
terrestrial
organisms.
However,
it
is
also
consistent
with
the
low
risk
predicted
from
the
toxicity
studies.

EFED
response
comment
#
22:
The
EIIS
database
is
dependent
on
reported
incident
information
and
can
not
be
compared
to
low
risk
predicted
from
toxicity
studies
due
to
reporting
inconsistencies.
