UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
Chemical
name:
chlorsulfuron
Chemical
Number:
118601
DP
Barcode:
292626
July
26,
2004
MEMORANDUM
SUBJECT:
Review
of
DuPont's
phase
1
"
Error
Correction"
comments
on
the
spray
drift
analysis
for
chlorsulfuron
(
MRID
46128400).

TO:
Christina
Scheltema,
and
Susan
Jennings,
Special
Review
and
Reregistration
Division
(
7508C)

FROM:
Norman
Birchfield,
Senior
Biologist
Environmental
Risk
Branch
1
Kevin
Costello,
Risk
Assessment
Process
Leader
Environmental
Risk
Branch
4
THRU:
Elizabeth
Behl,
Chief
Environmental
Risk
Branch
4
Environmental
Fate
and
Effects
Division
(
7507C)

The
Environmental
Fate
and
Effects
Division
(
EFED)
described
spray
drift
risks
expected
from
chlorsulfuron
use
in
a
September
2,
2003
memo
to
the
Special
Review
and
Reregistration
Division.
DuPont
submitted
a
document
dated
November
18,
2003
during
the
phase
1
"
error
correction"
period
providing
itemized
comments
on
the
EFED
document.
None
of
the
DuPont
comments
represented
typographical
or
mathematical
errors
that
are
to
be
addressed
during
phase
1.
However,
some
of
the
DuPont
comments
suggested
that
changing
the
wording
in
certain
locations
would
improve
the
clarity
and
accuracy
of
the
assessment,
so
some
revisions
to
the
original
assessment
have
been
made.
A
revised
assessment
is
being
submitted
with
this
memo.
Although
the
spray
drift
assessment
has
been
modified,
none
of
the
overall
conclusions
of
the
assessment
have
changed.
Page
2
of
3
The
DuPont
comments
are
numbered
from
1
to
18.
A
response
to
each
comment
and
the
action
taken
to
addresss
the
comment
is
provide
below.

Reference
1,
2,
3,
5,
6,
7,
8,
9,
10,
12,
14,
15,
16,
18.
These
comments
did
not
identify
typographical
or
mathematical
errors
in
the
EFED
spray
drift
assessment.
No
changes
were
made
to
address
these
comments.

Reference
4:
On
page
2
of
the
RED
chapter,
under
"
Mode
of
Action,"
EFED
wrote
that:

"
Phytotoxicity
data
shows
that
chlorsulfuron
affects
both
seedling
emergence
and
the
vegetative
vigor
at
low
levels."

In
response,
DuPont
commented
that
"
Chlorsulfuron
is
not
a
seedling
germination
or
emergence
inhibitor.
Seeds
germinate
and
emerge
on
seed
reserves.
The
effect
produced
by
chlorsulfuron
is
relevant
to
early
seeding
growth
and
is
observed
following
soil
uptake
by
young
plants."

For
the
sake
of
clarity,
EFED
has
revised
the
sentence
to
read:

"
Phytotoxicity
data
show
that
chlorsulfuron
affects
plants
in
both
seedling
emergence
and
the
vegetative
vigor
tests
at
low
levels."

Reference
11:
DuPont
identified
an
incorrect
definition
of
the
EC
25
effect
level.
The
description
has
been
modified
to
better
describe
the
EC
25
and
EC
05
toxicity
levels.
The
original
wording,
found
on
page
6
under
"
Toxicity,"
read:

"
The
EC
25
effect
level
measures
an
effect
occurring
to
25%
of
the
population.
The
effect
may
be
reductions
in
measured
dry
weight
or
length."

These
sentences
have
been
replaced
with:

"
The
EC
x
effect
level
represents
an
X%
effect
to
a
group
of
plants.
The
dose
required
to
cause
a
25%
reduction
in
the
average
shoot
height
of
a
group
of
plants
is
an
example
of
an
EC
25
toxicity
level.
Reduction
in
the
dry
weight
of
the
plant
can
also
be
used
in
calculating
the
EC
x."

Reference
13:
DuPont
took
issue
with
the
following
statement
on
pages
6
and
7
of
the
EFED
RED
chapter:

"
Moreover,
homogenous
crop
test
plant
seed
lots
lack
the
variation
that
occurs
in
natural
populations,
so
the
range
of
effects
seen
from
tests
is
likely
to
be
smaller
than
would
be
expected
from
wild
populations."

DuPont
commented
that
"
The
variability
in
a
population/
species
can
work
both
ways.
Within
a
Page
3
of
3
population
some
plants
are
much
less
sensitive
to
herbicide
exposures
and,
therefore,
the
natural
population
as
a
whole
is
more
robust
and
less
susceptible
to
serious
disturbance
from
a
minor
event
such
as
spray
drift."

The
original
sentence
was
not
written
to
suggest
that
plants
in
the
field
could
only
be
more
sensitive
than
plants
tested
in
the
laboratory.
Although
DuPont's
comment
is
one
of
scientific
interpretation,
and
not
an
error
correction,
EFED
modified
the
wording
referenced
by
DuPont
to
better
convey
the
intended
message:

"
Moreover,
homogenous
crop
test
plant
seed
lots
lack
the
variation
that
occurs
in
natural
populations,
so
the
test
plants
are
likely
to
have
less
variation
in
response
than
would
be
expected
from
wild
populations."

EFED
will
respond
to
comments
from
the
registrants
and
others
on
the
potential
sensitivity
of
non­
target
plants
to
chlorsulfuron
after
the
close
of
the
upcoming
public
comment
period.

Reference17:
DuPont
reports
the
availablity
of
additional
information
characterizing
the
effects
of
chlorsulfuron
on
non­
target
plants.
DuPont
does
not
provide
the
citations,
but
offers
to
provide
them
to
the
Agency
on
request.
DuPont
should
provide
relevant
data
it
believes
could
be
useful
for
a
more
complete
risk
assessment.
