UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
August
31,
2005
MEMORANDUM
SUBJECT:
Thidiazuron:
HED
Response
to
Public
Comments­
Phase
4.
PC
Code:
120301,
Case
#:
4092,
DP
Barcode:
D320616.

FROM:
Toiya
Goodlow,
Chemist
and
Risk
Assessor
Reregistration
Branch
1
Health
Effects
Division
(
7509C)

THROUGH:
Whang
Phang,
Ph.
D.,
Branch
Senior
Scientist
Reregistration
Branch
1
Health
Effects
Division
(
7509C)

TO:
John
Pates
Jr.,
Chemical
Review
Manager
Special
Review
and
Reregistration
Division
(
7508C)

This
document
was
written
in
response
to
public
comments
submitted
for
the
Human
Health
Risk
Assessment
for
the
Thidiazuron
Reregistration
Eligibility
Decision
Document
(
RED).
All
comments
have
been
reviewed
by
RRB1/
HED
and
incorporated
into
the
Revised
Human
Health
Risk
Assessment
for
the
Thidiazuron
RED
(
D319302,
8/
31/
05,
T.
Goodlow)
as
deemed
appropriate
by
the
Agency.

Changes
include
the
following:

°
Based
on
the
additional
characterization
provided
by
the
registrant,
the
residue
chemistry
data
gaps
for
Guidelines
860.1850
and
860.1900,
Confined
and
Field
Accumulation
in
Rotational
Crops,
have
been
fulfilled.

°
As
decided
by
the
HED
Chemistry
SAC
(
Scientific
Advisory
Council)
on
August
24,
2005,
the
contribution
of
cotton
gin
byproducts
to
the
dietary
burden
for
ruminants
has
been
reduced
to
5%
of
the
diet
for
beef
cattle.
Dairy
cattle
were
not
considered
since
cotton
gin
byproducts
are
no
longer
used
as
a
feed
item
for
dairy
cattle.
Consequently,
the
submitted
ruminant
feeding
study
(
MRID
43781901)
is
now
upgradable.
In
order
for
this
study
to
be
acceptable
the
registrant
must
submit:
storage
stability
data,
raw
data
to
support
findings
in
the
study,
and
an
analytical
enforcement
method
that
simultaneously
quantifies
residues
of
thidiazuron
and
its
two
livestock
metabolites.
A
new
feeding
study
for
ruminants
is
no
longer
required.

The
20%
contribution
to
the
diet
as
listed
in
Table
1
was
not
used
for
thidiazuron
because
HED
is
in
the
process
of
revising
the
current
20%
value
for
cotton
gin
byproducts
to
reflect
diet
contributions
of
5%
for
finishing
beef.
However,
until
Table
1
revisions
are
completed,
reductions
to
the
diet
contribution
percentages
for
cotton
gin
byproducts
will
be
decided
on
a
case
by
case
basis.

°
The
poultry
feeding
study
requirement
(
Guideline
860.1480)
has
been
waived.
After
reevaluating
MRID
43940701,
HED
has
concluded
that
the
study
performed
at
the
5x
application
rate
demonstrates
sufficient
evidence
of
thidiazuron
residue
dissipation.

°
The
acute
inhalation
test
animal
was
changed
from
rabbit
to
rat
in
Table
4.1.1a.

°
The
repeated
dose
in
Table
4.1.1.1b
was
corrected
to
reflect
a
dose
of
73­
75%
(
U).

°
The
number
of
test
animals
was
corrected
for
the
chronic
dog
toxicity
study.

°
Appendix
3.0,
Section
3.1
was
revised
to
report
an
administered
radioactivity
of
0.2%.

The
following
comments
were
not
revised
in
the
risk
assessment:

°
Comment:
[
14C­
analine]
thidiazuron
was
fed
at
a
dose
exaggeration
of
(
13.3x)
to
a
lactating
cow
at
a
rate
of
20
ppm
for
seven
days.

Response:
MRID
42529002
entitled
M12
Thidiazuron:
The
Metabolism
of
14CThidiazuron
in
the
Cow,
reported
feeding
doses
of
both
10
ppm
and
20
ppm
in
the
lactating
cow
study.
Since
the
doses
are
interchanged
throughout
the
document,
the
Agency
cannot
state
the
dose
as
being
20
ppm
until
clarification
is
provided.
HED
is
requesting
that
the
registrant
verify
the
actual
dose
administered
in
the
study.

References
Goodlow,
Toiya.
DP
Barcode:
D319302.
August
31,
2005.
Thidiazuron:
Revised
HED
Chapter
of
the
Reregistration
Eligibility
Decision
Document
(
RED),
Phase
3­
Public
Comments.

Madden,
Barbara.
DP
Barcode:
D246944.
June
24,
1998.
Bromoxynil:
Revised
Human
Health
Risk
Assessment
for
Bromoxynil.

7509C:
RRB1:
TGoodlow:
CM#
2:
Rm
722H:
308­
0070:
8/
31/
05
WPhang:
8/
31/
05
