UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON
D.
C.,
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
PC
Code:
118601
DP
Barcode:
D313382
Date:
February
15,
2005
MEMORANDUM
SUBJECT:
Response
to
Comments
on
the
Environmental
Fate
and
Ecological
Risk
Assessment
of
Chlorsulfuron
TO:
Susan
Jennings,
Chemical
Review
Manager
Special
Review
and
Reregistration
Division
FROM:
Brian
D.
Kiernan,
Biologist
Environmental
Risk
Branch
IV
Environmental
Fate
and
Effects
Division
(
7507c)

Kevin
Costello,
Risk
Assessment
Process
Leader
Environmental
Risk
Branch
IV
Environmental
Fate
and
Effects
Division
(
7507c)

APPROVED
BY:
Elizabeth
Behl,
Branch
Chief
Environmental
Risk
Branch
IV
Environmental
Fate
and
Effects
Division
The
Environmental
Fate
and
Effects
Division
has
completed
its
response
to
public
comment
on
the
re­
registration
eligibility
decision
risk
assessment
for
chlorsulfuron.

Comments
regarding
Environmental
Fate
Page
11:
DuPont
provided
risk
assessments
for
several
products
which
compete
with
chlorsulfuron
in
the
cereal
and
fallow
herbicide
market.
DuPont
concluded
that
the
theoretical
soil
concentrations
the
estimated
show
that
products
containing
chlorsulfuron
deliver
less
overall
chemical
load
to
the
environment
than
older
generation
products.

Response:
The
purpose
of
the
risk
assessment
performed
by
OPP
for
the
chlorsulfuron
RED
is
not
to
compare
the
environmental
fate
properties
of
chlorsulfuron
to
its
alternatives,
but
to
assess
potential
risks
from
the
use
of
chlorsulfuron.
A
comparative
risk
assessment
was
not
provided.
­
2­

Pages
18,
24:
DuPont
asserts
that
data
published
between
1983
and
1999should
be
used
in
addition
to
DuPont
studies
and
others
summarized
in
the
USDA
ARS
Pesticide
Properties
Database
should
be
used
in
the
risk
assessment.

Response:
The
environmental
fate
parameters
used
as
input
in
the
surface
and
ground
water
models
were
derived
from
data
submitted
to
the
Agency
by
DuPont.
These
data
were
generated
under
the
rules
of
Good
Laboratory
Practices,
as
required.
The
dataset
provided
by
DuPont
in
its
comments
is
useful
for
further
characterization
of
the
degradation
of
chlorsulfuron
in
aerobic
soils,
but
cannot
be
used
as
provided
as
a
substitute
for
the
data
submitted
under
GLP.

A
majority
of
these
studies
should
not
directly
be
used
in
this
chlorsulfuron
risk
assessment
for
several
reasons,
including
that
soils
were
used
in
the
study
which
are
not
representative
of
soil
conditions
where
chlorsulfuron
might
be
used
in
the
United
States.
One
such
study
used
tropical
soils
from
Brazil
(
DuPont
reference
13);
another
study
used
high
organic
matter
volcanic
soils
from
New
Zealand
(
DuPont
reference
8).
Other
studies,
which
were
either
performed
by
DuPont
(
DuPont
references
2,
9,
15
and
18)
or
were
funded
by
grants
from
DuPont
(
DuPont
references
7),
had
not
previously
been
submitted,
presumably
because
they
had
not
been
conducted
under
GLP.
One
literature
study
was
published
in
Italian,
and
could
not
be
evaluated.

Raw
data
from
these
studies
were
not
submitted,
limiting
our
ability
to
evaluate
the
halflives
DuPont
derived
from
these
studies.
Further,
in
its
review
of
a
1991
submission
by
DuPont
(
Priester,
1991),
a
"
summary
abstracted
from
summaries
of
Du
Pont
Agricultural
Products
Reports,"
EFED
wrote
that
"
the
author
(
of
Brown,
1983)
concluded
that
these
study
parameters
should
be
limited
to
initial
degradation
rates
and
should
not
be
extrapolated
to
predict
chlorsulfuron
field
behavior
as
the
degradation
becomes
distinctly
non­
first
order
at
very
long
times."
Therefore,
the
validity
of
the
assumption
that
the
DT
50
is
an
appropriate
substitute
for
the
aerobic
soil
metabolism
half­
life
is
uncertain,
and
the
estimate
of
the
DT
90
with
the
assumption
of
actual
first­
order
kinetics
is
even
more
uncertain.

Finally,
the
weight
of
evidence
from
these
studies
does
suggest
that
the
degradation
of
chlorsulfuron
in
soils
is
dependant
on
pH
and
temperature.
These
trends
are
noted
in
the
EFED
review
of
a
1991
submission
by
DuPont,
and
in
the
chlorsulfuron
RED.
The
1991
EFED
review
states
that
"(
t)
he
additional
studies
provided
information
indicating
that
chlorsulfuron
degradation
in
the
soil
is
dependent
on
temperature
(
degradation
was
more
rapid
at
higher
temperatures
than
at
lower
temperatures),
pH
(
chlorsulfuron
degradation
was
always
more
rapid
in
soils
with
a
lower
pH
and
clay
content)
and
moisture
content
(
an
increase
in
moisture
levels
resulted
in
lower
14CO
2
yields)."

Such
information
could
be
useful
for
region­
specific
refinement
of
the
risk
to
non­
target
­
3­

plants
exposed
to
chlorsulfuron
via
runoff.
However,
these
data
do
not
affect
calculations
of
risk
to
plants
exposed
via
drift
of
chlorsulfuron.

Comments
regarding
ecological
effects:

1)
Page
33.
DuPont
comment
that
the
low
use
rates
relative
to
other
herbicide
classes
results
in
proportionally
lower
off­
target
exposure.

Response:
While
the
use
rates
of
chlorsulfuron
and
other
sulfonylureas
are
lower
than
many
classes
of
herbicides,
it
does
not
necessarily
follow
that
potentially
adverse
effects
to
non­
target
species
are
less.
The
toxicity
of
chlorsulfuron
and
other
sulfonylureas
to
plants
is
greater
than
that
of
most
other
herbicide
classes,
allowing
them
to
be
efficacious
at
lower
application
rates.
While
uncertainties
exist,
there
is
enough
evidence
that
tiny
amounts
of
chlorsulfuron
affect
plant
function
to
warrant
cautionary
statements.

2)
Page
34.
DuPont
indicates
that
rates
of
application
for
cereals
range
from
0.0078
to
0.023
lbs
ai/
A.

Response:
While
this
is
correct,
the
maximum
rate
for
other
uses
is
higher.
Chlorsulfuron
can
be
applied
to
pasture/
rangeland
at
a
rate
of
up
to
0.0625
lbs
ai/
A,
and
this
rate
was
also
used
in
the
risk
assessment.
Based
on
current
registered
uses,
rates
as
high
as
0.5
lbs
ai/
A/
yr
are
permitted.

3)
Page
35.
DuPont
asserts
that
newer
plant
studies
submitted
should
supersede
previously
submitted
studies,
because
a
NOEC
was
established.
They
note
that
previously
submitted
studies
required
an
extrapolated
EC
05,
which
greatly
over
estimates
potential
risks.
Additionally,
DuPont
(
Page
40)
suggests
recalculation
of
RQs
based
on
recently
submitted
studies.

Response:
The
endpoints
from
the
new
terrestrial
studies
were
used
and
recalculated
RQs
were
incorporated
into
the
risk
assessment.
The
aquatic
plant
studies,
while
adding
valuable
data
to
the
risk
characterization,
did
not
supercede
previous
studies
because
they
were
not
performed
in
a
manner
more
consistent
with
Agency
guidelines
than
previous
studies.

4)
Pages
39
and
40.
DuPont
comments
on
the
conservative
nature
of
EFED's
four
terrestrial
plant
exposure
scenarios
and
suggests
a
number
of
variables
be
incorporated
into
the
models
(
such
as
wind
direction
at
application
and
structure
of
border
vegetation).

Response:
The
screening­
level
risk
assessment
for
chlorsulfuron
is
conservative,
and
used
standard
scenarios
and
methods.
Since
the
screening­
level
assessment
indicated
that
chlorsulfuron
poses
risk
to
non­
target
plants,
a
refined
spray
drift
assessment
has
been
performed
and
incorporated
into
the
assessment.
­
4­

This
refined
spray
drift
assessment
considered
both
application
to
turf
at
a
rate
of
0.0625
lbs
ai/
A,
and
aerial
and
ground
application
to
wheat
at
a
mid­
range
application
rate
of
0.012
lbs
ai/
A.
The
dose­
response
data
for
all
of
the
test
species
from
the
guideline
plant
studies
were
used
in
this
assessment,
not
just
that
for
the
most
sensitive
species.
Bar
graphs
show
the
level
of
effect
(
based
on
vegetative
vigor
study
data)
that
was
calculated
with
the
AgDrift
model
for
each
species
at
distances
of
up
to
1000
feet
from
the
treated
field.
The
droplet­
size
spectrum
simulated
was
based
on
a
survey
of
likely
spray
set­
ups
among
applicators
in
Washington
and
Oregon
conducted
by
the
Spray
Drift
Task
Force.
An
analysis
of
typical
wind
speeds
in
wheat­
growing
areas
of
the
United
States
is
also
presented.

The
results
of
the
refined
spray
drift
assessment
provide
further
insight
into
the
potential
for
plant
risk
from
exposure
to
chlorsulfuron.
The
scenarios
show
that
even
with
less
than
conservative
assumptions,
there
are
likely
to
be
effects
to
many
plant
species
from
chlorsulfuron
spray
drift
exposure
alone.
The
multiple
scenarios
modeled
show
potential
reductions
in
risk
that
might
be
expected
from
changes
in
application
method
or
spray
release
height.
This
refined
assessment
does
not
consider
the
additional
risk
that
would
be
posed
by
runoff
in
addition
to
the
spray
drift.

The
assessment
does
not
explicitly
consider
the
structure
of
border
vegetation
or
other
variables.
The
Spray
Drift
Task
Force
identifies
spray
quality
(
droplet
size),
release
height,
and
wind
speed
as
the
most
important
factors
affecting
drift
from
aerial
and
ground
applications
and
these
factors
are
considered.

5)
Pages
44­
46
DuPont
comments
that
the
chlorsulfuron
research
included
in
the
risk
assessment
are
only
"
a
subset
of
the
relevant
literature"
available
on
the
subject.
Additionally,
DuPont
questions
the
relevance
of
the
studies
to
actual
"
drift
exposure
and
field
growth
conditions."

Response:
While
it
is
true
that
the
literature
highlighted
is
a
subset
of
available
literature,
it
was
included
in
this
risk
assessment
due
to
the
sensitivity
to
chlorsulfuron
of
the
species
studied.
The
inclusion
of
these
studies
is
intended
to
illustrate
the
uncertainties
surrounding
sub­
lethal
effects
of
chlorsulfuron.
There
are
questions
regarding
the
applicability
of
these
studies
to
actual
field
conditions,
but
they
present
sound
data
regarding
the
potential
of
chlorsulfuron
to
affect
non­
target
plant
reproduction
at
rates
as
low
as
1.6
x
10­
10
lbs
ai/
A,
while
exhibiting
no
sustained
visible
damage
(
Fletcher
et
al.,
1996).
This
rate
is
far
lower
than
the
9.8
x
10­
6
lbs
ai/
A
(
0.011
g
ai/
ha)
DuPont
asserts
as
the
most
sensitive
endpoint
found
in
the
literature
(
p
46).

To
better
illustrate
the
range
of
sensitivity
to
chlorsulfuron
exhibited
by
plants,
a
review
of
endpoints
available
from
the
Agency's
ECOTOX
database
has
been
incorporated
into
the
risk
assessment.
Because
of
the
uncertainties
involved,
these
endpoints
are
considered
­
5­

only
qualitatively
in
the
risk
assessment;
however,
they
may
be
representative
of
potential
effects
in
the
environment.

6)
DuPont
states
that
"
regulatory
studies
on
foliar
effects
are
protective
of
reproductive
effects."
Additionally,
DuPont
suggests
that
reproductive
effects
do
not
occur
in
the
absence
of
foliar
effects.
The
comments
present
a
series
of
studies
that
"
demonstrate
that
exposure
levels
of
chlorsulfuron
applied
at
sensitive
reproductive
stages
of
plants
can
reduce
yields,
however
only
at
or
above
rates"
that
produce
foliar
effects.
Table
16
of
the
comments
(
page
45)
then
compares
the
lowest
rate
which
caused
reproductive
effects
in
each
study
to
the
EC
25
for
peas
and
soybeans,
and
to
the
most
sensitive
EC
25
from
lab
studies
(
rape)
for
the
other
studies.
Since
the
EC
25
is
lower
for
each
comparison,
except
for
soybeans,
DuPont
claims
that
the
regulatory
EC
25
endpoint
is
"
protective"
for
reproductive
effects.

Response:
The
product
labels,
which
warn
of
reduced
seed
production
on
target
plants
if
applied
improperly,
suggest
reproductive
effects
in
the
absence
of
foliar
damage.
Studies
such
as
Fletcher
et
al.
(
1996)
support
this
possibility,
and
in
the
absence
of
definitive
evidence
to
the
contrary,
it
is
discussed
in
the
risk
assessment.

The
discussion
presented
by
DuPont
does
not
refute
potential
reproductive
effects
from
exposure
to
chlorsulfuron
(
or
other
sulfonylurea
herbicides).
First,
the
vegetative
vigor
study
is
not
intended
to
directly
measure
reproductive
effects,
and
is
not
conducted
for
a
period
long
enough
to
measure
them.
Neither
is
it
designed
to
include
application
at
the
most
reproductively
sensitive
growth
stage
for
each
plant
tested.
It
is
uncertain
how
the
application
rate
which
resulted
in
reduced
shoot
weight
for
25%
of
the
tested
plants
would
compare
to
the
rate
that
would
result
in
eventual
reductions
in
yield.

Therefore,
the
EC
25
for
rape
is
not
directly
comparable
to
the
application
rate
which
caused
yield
reductions
in
cherries,
sunflower,
smartweed,
foxtail,
alfalfa
or
bindweed.
It
is
not
clear
if
the
most
sensitive
EC
25
shown
for
other
sulfonylureas
corresponds
to
plants
tested
in
reproduction/
yield
studies.
As
DuPont
points
out
in
other
comments,
the
EC
25
for
rape
is
the
most
sensitive
among
those
tested
in
the
lab.
However,
EFED's
revised
spray
drift
shows
that
there
is
a
range
of
sensitivities
among
tested
species.

The
range
of
plants
used
in
testing
is
limited
to
annuals
despite
the
fact
that
woody
plants
and
other
perennials
are
commonly
found
in
agricultural
areas.
Cherries
were
the
most
sensitive
to
yield
reduction
among
the
plants
tested
in
the
cited
studies.
The
degree
to
which
other
woody
plants
are
sensitive
to
yield
reduction
effects
from
chlorsulfuron
exposure
is
uncertain;
further
data
on
reproductive
response
of
plant
species
exposed
to
chlorsulfuron
would
help
to
better
assess
the
possible
risk.

7)
Page
48
DuPont
suggests
that
use
of
the
EC
25
for
dry
shoot
weight
is
transient
and
is
not
likely
to
result
in
season­
long
injury."
Additionally,
DuPont
comments
on
the
suitability
of
­
6­

current
regulatory
test
species.

Response:
It
is
possible
that
the
contention
that
the
effect
of
chlorsulfuron
on
shoot
dry
weight
is
transient,
but
current
guideline
studies
do
not
address
this
possibility
and
thus
cannot
be
directly
determined
to
be
true.
However,
because
the
actual
distribution
of
plant
responses
cannot
be
assessed,
conservative
assumptions
are
used
in
the
risk
assessment.
EFED
agrees
that
the
saturation
of
foliage
with
varying
concentrations
at
a
constant
volume
is
probably
not
representative
of
actual
drift
conditions.
However,
the
refined
spray
drift
assessment
indicates
that
based
on
the
laboratory
dose­
response
relationships
in
the
submitted
plant
studies,
the
estimated
amount
of
chlorsulfuron
exposure
through
drift
would
exceed
the
rate
which
equates
to
EC
70
effects
in
greater
than
50%
of
plants
hundreds
of
feet
from
the
treated
field.
This
finding
of
potential
risk
does
not
take
runoff
exposure
into
account.

EFED
agrees
that
there
are
uncertainties
connected
with
translating
laboratory
data
to
potential
effects
in
the
field.
The
study
cited
by
DuPont
for
comparison
of
laboratory
and
field
data
for
pyridyloxy
compounds
indicated
less
sensitivity
in
the
field,
although
the
conditions
under
which
the
studies
were
conducted
were
not
described.
EFED
has
detailed
uncertainties
in
its
risk
assessment.

8)
The
Weed
Science
Society
of
America
wrote
that
their
"
primary
concern
is
the
apparent
discrepancy
between
the
calculated
RQ's
and
the
performance
record
for
chlorsulfuron
that
has
been
established
through
twenty
years
of
use
on
as
much
as
five
million
acres
per
year.
If
the
non­
target
impacts
under
field
conditions
were
comparable
to
the
calculated
RQs,
we
would
expect
a
much
more
robust
body
of
scientific
(
and
anecdotal)
evidence
documenting
severe
non­
target
impacts.
We
are
not
certain
of
the
reasons
for
the
discrepancies
between
the
apparent
and
assessed
risks,
but
we
are
certain
careful
analysis
and
refinement
are
warranted."
They
go
on
to
state
"
in
today's
competitive
economy
significant
impacts
on
crop
yield
and
quality
are
seldom
ignored
so
it
is
unlikely
that
widespread
non­
target
impacts
have
been
systematically
overlooked."

Response:
Chlorsulfuron
effects,
at
least
until
recently,
have
been
almost
impossible
to
confirm
in
the
field,
even
for
experts.
The
potentially
more
subtle
effects
on
plant
populations
in
a
given
ecosystem
are
less
likely
to
be
reported.
Given
the
potential
for
effects
at
distances
greater
than
1000
feet
from
the
application
area,
cause
and
effect
relationships
may
not
be
suspected.
Therefore,
the
lack
of
numerous
reported
incidents
should
not
be
interpreted
as
lack
of
adverse
effects
to
the
environment.
Data
on
the
impact
of
chlorsulfuron
on
plant
yield
would
address
the
appreciable
uncertainty
in
estimates
of
chronic
risk
to
plants.

9)
The
WSSA
states
that
they
"
are
also
concerned
that
several
statements
in
the
risk
assessment
indicate
that
non­
target
impacts
of
chlorsulfuron
are
difficult
to
recognize
in
the
field
and
that
they
cannot
be
verified
because
they
occur
below
the
conventional
level
of
­
7­

detection
for
chlorsulfuron."
The
WSSA
suggests
that
this
was
true
only
when
the
chemical
first
came
out,
but
that
methods
are
now
adequately
sensitive.

Response:
Several
researchers
have
experimentally
determined
adverse
effects
of
chlorsulfuron
at
nominal
rates
as
low
as
7.1
x
10­
6
lbs
ai/
A.
EFED
is
not
aware
of
advances
in
technology
allowing
detection
of
chlorsulfuron
at
this
concentration.

10)
The
WSSA
recommends
"
that
timing
of
applications,
frequency
of
applications,
method
of
application
and
percent
area
treated
also
be
considered,
especially
when
assessing
range
and
pasture
uses."

Response:
The
risk
assessment
for
pasture
and
rangeland
uses
is
based
on
instructions
on
the
chlorsulfuron
product
label.
Because
this
use
is
recently
registered,
actual
use
data
are
not
available.
