1
U.
S.
ENVIRONMENTAL
PROTECTION
AGENCY
Washington,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
Date:
September
15,
2005
Chemical:
Thidiazuron
PC
Code:
120301
DP
Barcodes:

MEMORANDUM
SUBJECT:
Environmental
Fate
and
Effects
Division
Revised
Risk
Assessment
for
the
Reregistration
Eligibility
Decision
of
Thidiazuron
for
Use
on
Cotton
TO:
John
Pates,
Chemical
Review
Manager
Reregistration
Branch
I
Special
Review
and
Reregistration
Division
(
7508C)

FROM:
William
Evans,
Biologist
James
Hetrick,
Ph
D.,
Senior
Physical
Scientist
Edward
Odenkirchen,
Ph.
D.,
Senior
Biologist
Environmental
Risk
Branch
I
Environmental
Fate
and
Effects
Division
(
7507C)

APPROVED
BY:
Kevin
Costello,
Acting
Branch
Chief
Environmental
Risk
Branch
I
Environmental
Fate
and
Effects
Division
(
7507C)

This
memorandum
summarizes
the
attached
Environmental
Fate
and
Effects
Division's
(
EFED)
Thidiazuron
Environmental
Risk
Assessment
for
a
proposed
Reregistration
Eligibility
Decision
(
RED)
for
use
on
cotton.
All
environmental
fate
and
ecological
toxicity
Data
Evaluation
Records
(
DERs)
which
were
submitted
with
this
action
are
attached.

Use
of
Thidiazuron.
Thidiazuron
is
currently
registered
for
use
as
a
defoliant
(
herbicide)
to
aid
in
the
harvest
of
cotton.
The
maximum
single
application
rate
is
0.2
lb
ai/
A.
A
second
application
is
recommended
under
low
temperature
conditions
when
defoliation
does
not
reach
the
expected
level,
but
the
total
of
the
two
applications
must
not
exceed
0.3
lb
ai/
A.
The
intervals
between
applications
range
from
5­
7
days
in
some
of
the
labels,
while
the
other
labels
make
no
recommendations
in
this
regard.
The
Quantitative
Use
Assessment
prepared
by
BEAD
suggests
2
that
average
application
rates
may
range
from
0.05
­
0.07
lb
ai/
A.

Environmental
Fate
Summary
In
soil,
thidiazuron
is
persistent,
as
evidenced
by
laboratory
and
field
half­
lives
and
rotational
crop
intervals
on
the
order
of
one
year.
It
has
intermediate
soil
sorption
coefficients
(
sorption
coefficients
ranged
from
4.4
to
19
Freundlich
units).
Such
persistence
and
intermediate
mobility
would
allow
some
year
to
year
accumulation
over
time
and,
therefore,
more
opportunity
for
favorable
conditions
for
runoff
from
application
sites
to
occur.
For
example,
with
a
one
year
soil
half­
life
and
without
redistribution
or
dispersal
from
the
site
of
application,
theoretical
build­
up
in
soil
would
asymptotically
approach
twice
that
of
annually
applied
amounts.
Of
course,
given
time
and
variable
climatic
conditions,
redistribution
or
partitioning
of
thidiazuron
into
other
environmental
compartments
does
occur
(
via
runoff,
leaching,
plant
uptake,
etc.);
therefore,
maximum
build­
up
in
surface
soil
averages
less
than
the
theoretical
factor
of
two.

When
thidiazuron
reaches
surface
water,
photolysis
is
expected
to
be
the
major
route
of
transformation;
other
degradative
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
two
photoproducts.
One
of
the
photodegradates
is
a
structural
isomer
of
parent,
whereas
the
other
has
a
substantially
altered
chemical
structure.

Based
on
its
solubility
and
vapor
pressure
(
Henry's
law),
and
other
laboratory
evidence,
thidiazuron
is
non­
volatile.
Based
on
its
relatively
low
n­
octanol/
water
partitioning
coefficient,
thidiazuron
should
not
bioconcentrate.

No
foliar
dissipation
data
are
currently
available,
and
since
thidiazuron
is
used
to
defoliate
cotton
prior
to
harvest,
dislodgement
from
or
transformation
in/
on
leaves
may
be
an
important
fate
pathway.
The
effects
of
this
uncertainty
and
alternative
assumptions
are
considered
in
the
risk
assessment.

Ecological
Risk
Summary
This
assessment
is
based
on
mainly
on
toxicity
testing
with
typical
end
use
products
(
formulations)
containing
thidiazuron
as
the
only
active
ingredient.
In
addition
to
parent
thidiazuron,
we
have
also
factored
into
our
assessment
limited
data
for
three
of
its
transformation
products
(
degradates/
metabolites).

On
the
basis
of
testing
only
with
thidiazuron
and
its
degradates,
apparent
risks
may
be
underestimated
because:
1)
in
four
of
eleven
registered
products
thidiazuron
is
co­
formulated
with
either
of
two
other
registered
herbicides,
and
there
are
no
test
data
for
any
of
these
coformulated
products;
2)
there
are
no
data
for
mixtures
with
adjuvants
(
tank­
mix
data),
which
product
labels
state
improve
performance;
and
3)
there
are
no
test
data
with
mixtures
that
include
organophosphate
pesticides,
which
labels
state
may
increase
phytotoxicity.
3
Highlights
of
our
ecological
risk
concerns,
based
on
toxicity
testing
with
typical
end­
use
products
containing
thidiazuron
as
the
only
active
ingredient
and
the
modicum
of
data
on
three
transformation
products,
are
the
following:

<
Non­
target
Plants:
Non­
target
terrestrial
and
semi­
aquatic
dicots,
but
not
monocots,
are
at
potential
direct
and
indirect
ecological
risks.
Aquatic
plants
do
not
appear
to
be
at
risk.

<
Mammals:
Mammals
are
at
potential
chronic
risk,
but
not
acute.

<
Birds:
Potential
chronic
risk
to
birds
cannot
be
determined
because
of
the
absence
of
chronic
data.
Potential
acute
risks
to
birds
are
below
all
levels
of
concern.

A
principal
ecological
risk
concern
for
the
proposed
thidiazuron
use
on
cotton
is
the
potential
risks
to
non­
target
plants.
If
non­
target
plants
come
into
contact
with
thidiazuron,
these
plants
may
be
killed
or
damaged
enough
to
prevent
the
plant
from
reproducing
or
successfully
competing
with
other
plants
for
resources.
The
use
of
thidiazuron
could
apply
selective
pressure
to
dicots
along
field
edges,
resulting
in
changes
in
species
composition.

Even
though
thidiazuron
is
only
applied
at
cotton
harvest,
application
timing
is
a
consequential
factor
to
consider.
Reproduction
abnormalities
are
some
of
the
plant
injuries
that
can
occur
due
to
thidiazuron
exposure
during
particular
developmental
stages.
Although
the
plant
may
survive,
sterile
florets
or
non­
viable
seed
production
can
occur.
This
will
have
effects
on
the
non­
target
plant
populations
in
future
years.
Also,
plant
material
serves
as
a
primary
food
source
for
many
species
of
animals.
If
the
available
plant
material
(
including
seeds)
is
reduced
due
to
the
effects
of
thidiazuron,
this
may
have
negative
effects
throughout
the
food
chain.

The
risk
assessment
for
terrestrial
plants
was
based
on
risk
quotients
(
RQs)
calculated
from
toxicity
studies
using
a
typically
formulated
end­
use
product
(
TEP).
However,
it
appears
that
no
surfactants
or
other
adjuvants
were
added
to
the
product
during
the
studies,
and
all
labels
clearly
state
the
addition
of
adjuvants
has
been
shown
to
improve
the
performance.
Therefore,
the
risk
to
terrestrial
non­
target
plants
may
be
greater
than
thidiazuron
RQs
indicate.
Hence,
the
production
of
actual
tank­
mix
data
would
reduce
some
of
the
uncertainties
associated
with
risk
to
plants.

Additionally,
in
four
products
thidiazuron
is
co­
formulated
either
with
the
herbicide
diuron
or
the
herbicide
dimethipin
(
see
table
in
Use
section
of
this
document).
In
three
of
these
products,
diuron
comprises
33%
and
thidiazuron
67%
of
the
total
active
ingredients.
In
the
other
formulation,
dimethipin
comprises
80%
of
the
total
active
ingredients,
while
thidiazuron
comprises
only
20%.
Potential
effects
of
the
addition
of
these
other
two
chemicals
are
not
factored
into
the
risk
assessment.
Combining
(
adding)
known
effects
for
these
other
two
chemicals
with
those
for
thidiazuron,
or,
alternatively,
producing
specific
test
data
for
these
mixed
products
would
reduce
the
risk
uncertainties
associated
with
their
co­
application.

All
thidiazuron
labels
list
precautions
when
applying
the
products
adjacent
to
lettuce,
citrus,
or
4
cantaloupe.
The
labels
further
state
that
mixing
with
organophosphates
may
increase
non­
target
crop
phytotoxicity.
Special
restrictions
to
reduce
drift
to
lettuce
and
citrus
appear
on
all
the
labels.
In
addition,
an
incident
was
reported
to
have
caused
an
estimated
$
350,000
of
crop
loss
to
50
acres
of
lettuce
when
thidiazuron
allegedly
drifted
onto
150
acres.
Thidiazuron
products
can
not
be
applied
by
air
within
½
mile
of
lettuce
or
5
miles
downwind
of
the
point
of
application
when
citrus
is
in
flush
(
burst
of
new
growth,
as
in
springtime)
in
the
Rio
Grande
valley
of
Texas.
Ground
applications
are
restricted
to
100
feet
away
from
lettuce
and
½
mile
downwind
from
the
point
of
application
for
citrus.
Labels
do
not
specify
a
distance
for
cantaloupe.

Acute
risk
quotients
for
mammals
did
not
exceed
levels
of
concern
(
LOCs).
However,
chronic
risk
quotients
for
mammals
did
exceed
LOCs
for
mammals
feeding
on
short
grass
or
broadleaf
forage,
with
RQs
ranging
to
a
maximum
of
1.8.
To
further
investigate
the
chronic
risk
to
mammals,
in
addition
to
the
standard
default
foliar
dissipation
half­
life
of
35­
days,
EFED
evaluated
the
impact
of
a
hypothetical
half­
life
as
low
as
one
day
on
thidiazuron
residue
concentrations
on
reducing
risk.
We
also
evaluated
potential
effects
at
predicted
maximum
and
mean
residues
for
single
applications.
No
RQ
exceeds
the
chronic
level
of
concern
when
considering
mean
predicted
residues.

The
2­
generation
reproduction
study
with
rats
indicates
a
possible
concern
for
endocrine
disruption,
based
on
delayed
sexual
maturation
and
disruption
of
the
estrous
cycle.
When
appropriate
screening
and/
or
testing
protocols
have
been
developed,
thidiazuron
and
its
degradates
may
be
subject
to
additional
screening
and/
or
testing
to
better
characterize
effects
related
to
endocrine
disruption
in
mammals
or
other
organisms.

Acute
risk
quotients
for
birds
did
not
exceed
LOCs.
Chronic
risk
to
birds
cannot
be
evaluated
because
chronic
data
were
not
submitted.

Data
Gaps
Environmental
Fate:
Status
of
Environmental
Fate
Data.
Although
some
of
the
submitted
fate
studies
had
deficiencies,
taken
as
a
whole
and
within
the
constraints
stipulated
in
the
fate
assessment,
the
data
enable
the
Agency
to
adequately
assess
the
environmental
fate
of
thidiazuron.
Although
no
foliar
dissipation
studies
are
currently
available
to
the
Agency
(
these
are
not
generally
required),
having
such
data
would
make
any
fate
assessment
more
precise,
especially
in
the
case
of
a
defoliant
such
as
thidiazuron.
However,
as
discussed
in
the
fate
assessment,
if
dislodgement
from
or
transformation
in/
on
treated
plants
were
to
be
an
important
fate
pathway,
then
EFED's
inferences
from
existing
fate
studies
and
assumptions
for
exposure
modeling
for
parent
and
potential
degradates
should
reasonably
and
conservatively
cover
the
possibility.
If
the
registrant
wishes
to
demonstrate
that
definitive
data
on
foliar
dissipation
would
substantially
affect
any
of
our
inferences,
assumptions,
or
environmental
risk
conclusions,
then
the
registrant
should
submit
appropriate
data.
Otherwise,
except
for
spray­
drift
requirements,
the
Agency
needs
no
additional
environmental
fate
studies
at
this
time.
5
Ecological
Effects:
The
ecological
toxicity
data
base
is
fairly
complete,
however,
there
are
some
additional
key
studies
that
could
assist
in
reducing
the
uncertainties
in
this
risk
assessment.
The
details
are
summarized
below.

!
Non­
target
Terrestrial
Plant
­
Definitive
tier
II
EC25s
and
NOAECs
are
lacking
for
the
seedling
emergence
of
two
monocot
species
tested;
this
is
because
test
concentrations
were
not
low
enough
to
establish
these
endpoints.
However,
risk
quotients
from
the
tests
for
which
definitive
endpoints
were
established
were
below
levels
of
concern.
Furthermore,
concentrations
in
those
tests
for
which
endpoints
were
not
determined
were
sufficiently
low
to
establish
that,
when
compared
to
estimated
field
exposure
concentrations
that
correspond
to
the
currently­
labeled
application
rates,
risk
quotients
would
not
exceed
any
of
the
terrestrial
plant
LOCs.
Therefore,
since
projected
risk
quotients
for
monocots
are
below
levels
of
concern,
additional
tier
II
testing
with
a
typical
end­
use
product
that
contains
thidiazuron
as
the
only
active
ingredient
is
not
required
at
this
time
for
these
specific
crops
at
currently­
labeled
application
rates.

However,
there
are
other
considerations.
Even
though
all
labels
clearly
state
that
the
addition
of
adjuvants
has
been
shown
to
improve
performance,
it
appears
that
none
were
added
the
during
the
tests.
Therefore,
apparent
risk
to
terrestrial
non­
target
plants
may
be
greater
than
present
RQs
indicate.
The
production
of
actual
tank­
mix
data
would
reduce
this
uncertainty.

Additionally,
as
previously
mentioned,
three
thidiazuron
products
are
mixtures
of
thidiazuron
(
67%
of
total
active
ingredients)
and
diuron
(
33%
of
total
active
ingredients),
and
another
is
a
formulation
of
thidiazuron
(
20%
)
and
preponderantly
dimethipin
(
80%).
Potential
effects
of
the
mixtures
with
these
other
two
chemicals
are
not
factored
into
the
risk
assessment.
Combining
(
adding)
the
known
effects
for
these
other
two
chemicals
with
those
for
thidiazuron,
or,
alternatively,
producing
specific
test
data
for
these
mixed
products
would
reduce
the
uncertainties
associated
with
their
co­
application.

Concerning
the
potential
for
additional,
undetermined
risk,
the
current
labels
contain
warnings
and
specific
instructions
about
the
use
of
thidiazuron
in
the
vicinity
of
lettuce,
cantaloupe,
and
citrus.
The
language
from
one
of
the
labels
is
the
following:

"
Particular
care
should
be
taken
when
applying
Dropp
®
UltraTM
adjacent
to
lettuce,
citrus,
or
cantaloupe."

"
In
addition,
for
citrus
crops,
do
not
apply
Dropp
®
UltraTM
by
air
when
citrus
in
flush
is
within
five
(
5)
miles
downwind
of
the
point
of
application.
Do
not
apply
Dropp
®
UltraTM
by
ground
when
citrus
in
flush
is
within
one­
half
(
1/
2)
mile."

Labels
also
state
that
"
do
not
apply"
distances
from
lettuce
are
one­
half
(
1/
2)
mile
by
air
and
100
feet
by
ground.
6
!
Birds
­
Chronic
risks
to
birds
can
not
be
quantitatively
evaluated
at
this
time
because
chronic
data
were
not
submitted.
In
order
to
assess
this
potential
risk,
we
recommend
chronic
testing
with
an
upland
game­
bird
species
(
bobwhite
quail)
and
a
waterfowl
(
mallard
duck).

Recommended
Label
Language
If
thidiazuron
is
reregistered,
the
following
statements
should
be
included
in
the
"
ENVIRONMENTAL
HAZARDS"
labeling:

For
Manufacturing­
Use
Products
"
Do
not
discharge
effluent
containing
this
active
ingredient
into
lakes,
streams,
ponds,
estuaries,
oceans,
or
other
public
waters
unless
this
product
is
specifically
identified
and
addressed
in
an
NPDES
permit.
Do
not
discharge
effluent
containing
this
product
into
sewer
systems
without
previously
notifying
the
sewage
treatment
plant
authority.
For
guidance,
contact
your
State
Water
Board
or
Regional
Office
of
EPA."

For
End­
Use
Products
"
Do
not
apply
directly
to
water
or
to
areas
where
surface
water
is
present
or
to
intertidal
areas
below
the
mean
high
water
mark.
Do
not
contaminate
water
when
disposing
of
equipment
washwater
or
rinsate."

Surface
Water
Advisory
"
This
product
may
contaminate
water
through
drift
of
spray
in
wind.
This
product
has
a
high
potential
for
runoff
for
several
months
or
more
after
application.
Poorly
draining
soils
and
soils
with
shallow
water
tables
are
more
prone
to
produce
runoff
that
contains
this
product.
A
level,
well­
maintained
vegetative
buffer
strip
between
areas
to
which
this
product
is
applied
and
surface
water
features
such
as
ponds,
streams,
and
springs
will
reduce
the
potential
for
contamination
of
water
from
runoff.
Runoff
of
this
product
will
be
reduced
by
avoiding
applications
when
rainfall
is
forecasted
to
occur
within
48
hours.
Sound
erosion
control
practices
will
reduce
this
product's
contribution
to
surface
water
contamination."

Groundwater
Advisory
"
This
chemical
has
properties
and
characteristics
associated
with
chemicals
detected
in
ground
water.
Use
of
this
chemical
in
areas
where
soils
are
permeable,
particularly
where
the
water
table
is
shallow,
may
result
in
groundwater
contamination."
7
Spray
Drift
Management
Drift
is
transport
of
pesticides
through
air
away
from
the
target
site,
and
includes,
for
example,
spray
drift
and
volatilization.
Spray
drift,
the
movement
of
pesticide
droplets
off­
target
during
or
shortly
after
application,
has
been
well
studied,
and
is
not
dependent
on
the
properties
of
the
active
ingredient.
Short­
range
spray­
drift
and
resulting
exposures
to
non­
target
organisms
is
quantified
in
our
risk
assessments.
Currently,
when
specific
label
instructions
are
not
available,
we
account
for
spray
drift
in
both
drinking
water
and
ecological
exposure
assessments
by
the
use
of
default
assumptions
for
the
percentage
of
deposition
based
on
application
method.
We
have
established
default
spray
drift
percentages
for
pesticides
for
aerial
application,
ground
application,
and
orchard
airblast.

Default
values
for
drinking
water
exposure
scenarios
are
16%,
6.4%,
and
6.3%
of
the
application
rate
for
aerial,
ground
boom
and
airblast
applications,
respectively.
The
default
values
for
the
drinking
water
exposure
were
generated
using
AgDRIFT
version
1.03
which
uses
a
semimechanistic
model
(
AGDISP)
for
aerial
applications
and
is
based
an
empirical
data
set
(
Spray
Drift
Task
Force
data)
for
ground
boom
and
airblast
applications.
The
derivation
of
the
spray
drift
loading
values
is
described
in
Appendix
B
of
the
Guidance
for
Use
of
the
Index
Reservoir
in
Drinking
Water
Exposure
Assessments
and
is
based
on
the
following
application
and
wind
speed
assumptions:

For
ground
boom
applications
°
nozzle
height
no
more
than
4
feet
above
the
ground
or
crop
canopy
°
wind
speed
is
10
mph
or
less
at
the
application
site
and,
°
medium
or
coarser
spray
according
to
ASAE
572
definition
for
standard
nozzles.

For
aerial
applications
°
boom
width
less
than
75%
of
the
wingspan
or
90%
of
the
rotary
blade,
°
use
of
upwind
swath
displacement,
°
wind
speed
3
­
10
mph,
and
°
use
medium
or
coarser
spray
according
to
ASAE
572
definition
for
standard
nozzles.

For
orchard/
vineyard
airblast
applications
°
spray
is
not
directed
above
trees/
vines,
°
outward
pointing
nozzles
are
shut
off
at
row
ends
and
outer
rows,
and
°
wind
speed
is
3
­
10
mph
at
the
application
site
as
measured
by
an
anemometer
outside
of
the
orchard/
vineyard
on
the
upwind
side.

Default
values
for
ecological
exposure
scenarios
are
5%
for
aerial
applications
and
1%
for
ground
applications,
with
no
set
value
for
orchard
airblast.
For
the
ecological
assessment,
the
default
values
of
5%
for
aerial
applications
and
1%
for
ground
applications
were
established
based
on
open
literature
and
research
prior
to
establishment
of
the
Spray
Drift
Task
Force,
and
were
therefore
not
generated
using
AgDRIFT.
Testing
of
the
default
spray
drift
values
for
ecological
8
assessments
using
AgDRIFT
provides
context
for
the
default
assumptions.
Analysis
of
the
1%
ground
application
drift
percentage
using
AgDRIFT
(
with
the
same
assumptions
as
for
drinking
water
outlined
above)
indicates
that
the
default
value
likely
underestimates
drift
from
single
events
under
relatively
high
drift
conditions.
A
similar
underestimation
likely
occurs
for
the
5%
aerial
drift
value.

EECs
predicted
for
drinking
water
and
ecological
assessments
are
based
on
the
assumptions
of
drift
outlined
above
for
ground
and
aerial
applications.
Variance
from
these
assumptions
will
result
in
differences
in
predicted
concentrations.
For
the
ecological
assessment,
as
with
the
drinking
water
assessment,
variance
from
the
assumptions
behind
these
default
values
could
result
in
increased
risk.
In
general,
a
decrease
in
droplet
size
or
increase
in
wind
speed
at
the
time
of
application
will
result
in
higher
predicted
EECs
and
risk
to
non­
target
organisms.
Alternatively,
if
droplet
size
is
coarser
or
wind
speeds
are
lower,
exposures
due
to
drift
would
be
lower.

Transport
resulting
from
volatilization
is
highly
dependent
on
the
properties
of
the
active
ingredient
(
e.
g.,
Henry's
Law
constant)
as
well
as
a
number
of
environmental
parameters.
Based
on
its
physicochemical
properties,
thidiazuron
is
not
expected
to
volatilize.
1
Environmental
Fate
and
Effects
Division's
Risk
Assessment
for
the
Reregistration
Eligibility
Document
For
the
Use
of
Thidiazuron
on
Cotton
Page
2
of
129
Table
of
Contents
I.
Environmental
Risk
Conclusions
.
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Page
4
of
129
Environmental
Fate
Abstract
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Page
4
of
129
Terrestrial
Plant
Risks
of
Concern
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Page
4
of
129
Terrestrial
Vertebrate
Risks
of
Concern
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Page
5
of
129
II.
Introduction
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Page
6
of
129
Pesticide
Mode
of
Action
.
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Page
6
of
129
Uses
and
Use
Characterization
.
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Page
6
of
129
Risk
Assessment
Approach
.
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Page
8
of
129
Assessment
Endpoints
.
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Page
8
of
129
Measures
of
Effects
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Page
8
of
129
Measures
of
Exposure
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Page
10
of
129
Aquatic
Organisms
.
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Page
10
of
129
Active
Ingredient
and
Degradate
Aquatic
Organism
Exposure
Approach
.
.
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Page
10
of
129
Terrestrial
Plants
.
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Page
11
of
129
Terrestrial
Animals
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Page
12
of
129
Risk
Characterization
Approach
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Page
12
of
129
Problem
Formulation
Analysis
Plan
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Page
12
of
129
III.
Integrated
Environmental
Risk
Characterization
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Page
17
of
129
Risks
to
Aquatic
Organisms
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Page
17
of
129
Risk
to
Birds
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Page
17
of
129
Acute
Risks
­
Birds
.
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Page
17
of
129
Chronic
Risk
­
Birds
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Page
18
of
129
Risks
to
Mammals
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Page
18
of
129
Acute
Risks
­
Mammals
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Page
18
of
129
Chronic
Risk
­
Mammals
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Page
18
of
129
Risks
to
Non­
Target
Insects
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Page
20
of
129
Risks
to
Terrestrial
Plants
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Page
20
of
129
Endocrine
Disruption
Assessment
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Page
41
of
129
Endangered
Species
Assessment
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Page
42
of
129
IV.
Environmental
Fate
Assessment
.
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Page
43
of
129
Basis
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Page
43
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129
Fate
Assessment
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Page
44
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129
Abstract.
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Page
44
of
129
Physical/
Chemical
Properties
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Page
45
of
129
Transformation
Products
(
degradates/
metabolites)
.
.
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.
Page
49
of
129
V.
Drinking
Water
Assessment
Summary
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Page
52
of
129
VI.
Aquatic
Hazard,
Exposure,
and
Risk
Quotient
Calculation
.
.
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Page
53
of
129
Toxicity
to
Fish
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Page
53
of
129
Page
3
of
129
Toxicity
to
Aquatic
Invertebrates
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Page
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129
Toxicity
to
Aquatic
Plants
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Page
55
of
129
Aquatic
Exposure
.
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Page
55
of
129
Risk
Quotients
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Page
55
of
129
VII.
Terrestrial
Hazard,
Exposure,
and
Risk
Quotient
Calculation
.
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Page
56
of
129
Toxicity
to
Birds
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56
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129
Toxicity
to
Mammals
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56
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129
Toxicity
to
Non­
target
Insects
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57
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129
Toxicity
to
Earthworms
.
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58
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129
Toxicity
to
Non­
Target
Plants
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Page
59
of
129
Terrestrial
Plant
Exposure
and
Risk
Quotient
Calculations
.
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Page
60
of
129
Terrestrial
Exposure
for
Birds
and
Mammals
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62
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129
Terrestrial
Risk
Quotients
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63
of
129
APPENDIX
C:
Model
Input
Parameters
Derived
from
Environmental
Fate
Studies
for
Thidiazuron
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79
of
129
APPENDIX
LIST
APPENDIX
A:
Detailed
Drinking
Water
Assessment
Memo
.
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64
of
129
APPENDIX
B:
Chemical
Structural
Formulas,
Names
.
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Page
76
of
129
APPENDIX
D:
GENEEC
Input
&
Output
Files
for
Ecological
Assessment
.
.
.
.
Page
82
of
129
APPENDIX
E:
Ecological
Hazard
Data
.
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87
of
129
APPENDIX
F:
The
Risk
Quotient
Method
.
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105
of
129
APPENDIX
G:
Detailed
Risk
Quotients
.
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Page
108
of
129
APPENDIX
H:
Data
Requirements
for
Thidiazuron
.
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Page
124
of
129
Page
4
of
129
I.
Environmental
Risk
Conclusions
Environmental
Fate
Abstract
In
soil,
thidiazuron
is
persistent,
as
evidenced
by
laboratory
and
field
half­
lives
and
rotational
crop
intervals
on
the
order
of
one
year.
It
has
intermediate
soil
sorption
coefficients
(
sorption
coefficients
ranged
from
4.4
to
19
Freundlich
units).
Such
persistence
and
intermediate
mobility
would
allow
some
year­
to­
year
accumulation
over
time
and,
therefore,
more
opportunity
for
favorable
conditions
for
runoff
from
application
sites
to
occur.

When
thidiazuron
reaches
surface
water,
photolysis
is
expected
to
be
the
major
route
of
transformation;
other
degradative
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
two
photoproducts.
One
of
the
photodegradates
is
a
structural
isomer
of
parent,
whereas
the
other
has
a
substantially
altered
chemical
structure.
The
photolysis
process
requires
special
exposure
and
modeling
considerations.

Based
on
its
solubility
and
vapor
pressure
(
Henry's
law),
and
other
laboratory
evidence,
thidiazuron
is
non­
volatile.
Based
on
its
relatively
low
octanol/
water
partitioning
coefficient,
thidiazuron
should
not
bioconcentrate.

No
data
on
foliar
dissipation
are
currently
available
to
EFED.
Since
thidiazuron
is
used
to
defoliate
cotton
prior
to
harvest,
dislodgement
from
or
transformation
in/
on
leaves
may
be
an
important
fate
pathway.
The
effects
of
this
uncertainty
and
alternative
assumptions
on
the
risk
assessment
are
considered.

Terrestrial
Plant
Risks
of
Concern
Thidiazuron
poses
potential
risks
to
terrestrial
plants
based
on
the
results
of
a
screening­
level
assessment.
The
risk
quotients
exceed
the
levels
of
concern
for
non­
endangered
and
endangered
plants
adjacent
to
treated
sites
as
well
as
plants
inhabiting
semi 
aquatic
sites.
This
is
especially
true
for
dicots
for
both
single
and
multiple
applications.
The
RQs
resulting
from
single
applications
at
the
maximum
label
rates
range
from
0.39
to
9.09
for
non­
endangered
plants
and
up
to
as
high
as
52.63
for
endangered
plants.
The
RQs
for
multiple
applications
range
from
0.59
to
9.09
for
non­
endangered
species
and
up
to
52.63
for
endangered
species.

In
addition
to
the
RQ
calculations
from
the
maximum
label
rates,
EFED
completed
a
characterization
of
potential
risks
by
assessing
the
effect
of
RQ
calculations
using
EECs
predicted
from
modeling
with
average
application
rates
(
0.05
­
0.07
lb
ai/
A)
as
reported
in
the
BEAD
QUA
report.
When
the
average
application
rates
are
compared
to
the
maximum
allowable
application
rates,
RQs
are
reduced
by
at
least
one­
half,
but
levels
of
concern
are
still
exceeded,
except
for
the
single
ground
application
for
non­
endangered
species
scenario.

It
should
be
noted
that
RQs
for
this
risk
assessment
were
based
on
toxicity
studies
using
the
typical
end­
use
product
"
Thidiazuron
SC42"
(
presumably
DROPP
SC
(
Reg.
#:
264­
700)).
All
labels
clearly
state
the
addition
of
adjuvants
has
been
shown
to
improve
the
performance,
and
yet
Page
5
of
129
no
surfactants
or
adjuvants
were
added
to
the
product
during
the
studies.
Therefore,
the
risk
to
terrestrial
non­
target
plants
may
be
greater
than
RQs
indicate.
The
production
of
core
data
using
actual
tank­
mixes
may
assist
in
reducing
some
of
the
uncertainties
associated
with
risk.

Additionally,
as
previously
noted,
three
thidiazuron
products
are
mixtures
(
co­
formulations)
of
thidiazuron
(
67%
of
total
active
ingredients)
and
diuron
(
33%
of
total
active
ingredients),
and
still
another
is
a
combination
of
thidiazuron
(
20%
)
and
preponderantly
dimethipin
(
80%)
(
see
table
in
section
on
Use
and
Use
Characterization).
Adding
the
known
effects
of
these
other
two
chemicals
to
those
for
thidiazuron,
or,
alternatively,
having
test
data
specifically
for
these
products
would
reduce
the
risk
uncertainties
associated
with
their
co­
application.

Since
the
sole
use
of
thidiazuron
is
as
a
cotton
defoliant,
the
primary
concern
is
for
non­
target
plants
which
inhabit
areas
near
cotton
fields.
If
such
plants
are
sensitive
to
leaf
drop
and
other
symptoms
which
may
result
from
thidiazuron
exposure,
death,
severe
damage,
or
reproductive
impairment
could
occur.
This
damage
could
apply
selective
pressure
to
dicot
plants
along
field
edges
and
changes
in
species
composition
could
occur.

There
is
another
reason
to
believe
that
our
assessment
may
underestimate
risk
to
terrestrial
plants.
Thidiazuron
labels
state
that
mixing
with
organophosphates
may
increase
non­
target
crop
phytotoxicity.
Data
have
not
been
submitted
which
quantify
this
effect
on
thidiazuron
toxicity.

There
is
uncertainty
regarding
the
toxicity
of
thidiazuron
to
non­
target
plants
other
than
those
tested
in
the
laboratory.
However,
the
product
labels
for
thidiazuron
include
some
language
which
attempts
to
mitigate
potential
risk
for
some
of
those
crops.
All
labels
list
precautions
when
applying
the
products
adjacent
to
lettuce,
citrus,
or
cantaloupe.
Special
restrictions
to
reduce
spraydrift
potential
to
lettuce
and
citrus
appear
on
all
the
labels.

To
explore
the
apparent
risk
posed
by
spraydrift,
we
used
EFED's
current
AgDRIFT
computer
model
and
thidiazuron
phytotoxicity
data
to
estimate
plant
exposure
as
a
function
of
downwind
distances
from
application
areas.
Since
the
current
labels
lack
specific
information
on
droplet
size
or
boom
height,
we
also
looked
at
the
effects
of
varying
these.
We
then
compared
the
various
exposure
distributions
with
toxicity
level
percentiles
from
the
EC10
to
EC90
(
in
increments
of
ten).

As
can
be
seen
from
the
sequence
of
the
following
bar
graphs,
there
is
considerable
variation
with
droplet
size
or
boom
height
for
the
EC30
(
the
closest
toxicity
level
to
the
EC25).
The
no­
spray
zones
for
aerial
applications
for
the
EC30
effect
levels
range
from
slightly
over
60
feet
to
greater
than
1000
feet
for
lettuce,
the
most
sensitive
crop
tested
so
far.
Ground
application
no­
spray
zones
for
the
EC30
vary
from
about
3
to
200
feet.
Similar
trends
are
demonstrated
for
the
other
crops
for
which
slope
data
could
be
determined.
In
addition,
according
to
the
labels,
cantaloupe
and
citrus
many
be
more
sensitive
than
lettuce,
and
no
data
have
been
submitted
on
these
crops.
All
the
factors
influencing
the
downwind
drift
distance,
including
droplet
size,
wind
speed,
boom
height,
method
of
application,
and
targeted
toxicity
effect
should
be
considered
when
placing
restrictions
on
labels.

Terrestrial
Vertebrate
Risks
of
Concern
Page
6
of
129
Thidiazuron
may
pose
chronic
risk
to
mammals,
based
on
a
screening­
level
assessment.
Conclusions
are
derived
from
a
2­
generation
rat
study.
From
the
study,
the
reproductive
NOAEC
and
LOAEC
values
are
400
and
1200
mg/
kg­
diet,
respectively,
based
on
delayed
sexual
maturation
and
disruption
of
the
estrous
cycle.
To
estimate
risk,
we
used
two
screening­
level
methodologies,
and
found
that
they
give
different
results.
Risk
quotients
based
on
the
daily
dietary
dose
indicated
a
potential
chronic
risk
to
mammals.

II.
Introduction
Thidiazuron
is
undergoing
review
for
reregistration
under
Section
4
of
FIFRA
as
amended.
It
is
currently
registered
for
use
as
a
defoliant
to
aid
in
the
harvest
of
cotton.
Defoliation,
or
leaf
abscission,
is
a
natural
process
in
all
plants,
but
can
be
manipulated
in
cotton
plants
to
cause
them
to
drop
their
leaves
in
a
relatively
short
period
of
time
to
aid
in
the
efficiency
of
cotton
harvesting.

Pesticide
Mode
of
Action
Thidiazuron
is
a
phenylurea
herbicide
that
is
said
to
inhibit
regrowth
through
photosynthetic
electron
transport
inhibition
at
the
photosystem
II
receptor.
This
mode
of
action
increases
the
ethylene
concentration
in
the
leaves;
this
inhibits
the
transport
of
the
hormone
auxin,
and
results
in
leaf
drop.

While
the
defoliation
process
is
quite
complex,
it
can
be
simplified
as
being
governed
by
two
major
compounds
in
the
plant,
auxin
and
ethylene.
Auxin
is
a
growth­
promoting
hormone
that
stimulates
leaf
growth
and
development.
Ethylene
can
be
classified
as
a
ripening
agent
that
causes
leaf
drop.
Leaves
fall
from
the
plant
once
ethylene
moves
from
the
leaf
blade
to
the
base
of
the
petiole
and
stimulates
the
formation
of
an
abscission
(
separation)
layer.
The
amount
of
auxin
or
ethylene
present
in
the
leaves
of
the
cotton
plant
is
related
to
leaf
age.
Younger
leaves
have
a
higher
level
of
auxin,
whereas
older
leaves
have
lower
levels
of
auxin
and
higher
levels
of
ethylene.
This
is
why
older
leaves
are
more
conditioned
for
defoliation
than
younger
leaves.
Furthermore,
because
of
the
hormone
balance
of
younger
leaves,
low
rates
of
harvest
aids
often
have
no
effect,
and
higher
rates
may
actually
kill
the
leaf,
leading
to
desiccation
and
leaf
sticking.

Eventually,
all
the
leaves
on
a
cotton
plant
age
so
they
will
defoliate
naturally.
However,
cotton
producers
can
manipulate
these
hormone
levels
with
the
use
of
defoliants
so
all
the
leaves
abscise
(
separate
and
fall)
at
the
same
time.
When
these
defoliants
are
applied,
ethylene
levels
artificially
increase
so
the
abscission
process
begins.

Uses
and
Use
Characterization
Thidiazuron
is
used
exclusively
as
a
cotton
defoliant
to
aid
in
the
uniform
removal
of
both
mature
and
juvenile
leaves.
This
facilitates
machine
harvesting
and
helps
eliminate
sources
of
gin
trash
and
stains.
Because
of
its
purpose,
thidiazuron
is
applied
during
the
cotton
harvesting
period,
which
is
typically
in
late
August
and
early
September.
All
labels
indicate
that
citrus
trees
are
particularly
sensitive
to
thidiazuron.

All
current
products
containing
thidiazuron
and
their
corresponding
EPA
registration
numbers
are
Page
7
of
129
listed
in
the
following
table.
Product
label
statements
about
use
indicate
that
the
areas
potentially
at
direct
and/
or
indirect
risk
from
the
application
of
thidiazuron
in
the
manner
prescribed
by
the
labels
are
the
cotton
agronomic
environments.

EPA
Registration
Number
Product
Name
264­
622
Dropp
50WP
Cotton
Defoliant
264­
634
GINSTAR
EC
Cotton
Defoliant1
264­
661
Dropp
Ultra
Cotton
Defoliant2
264­
700
Dropp
SC
Cotton
Defoliant
264­
821
GINSTAR
®
4.5
SC
Cotton
Defoliant3
264­
822
Thidiazuron
Technical
Cotton
Defoliant
400­
505
Harvade
4198SC
Harvest
Growth
Regulant
for
Cotton4
51036­
401
Thidiazuron
50W
Cotton
Defoliant
51036­
402
Thidiazuron
Technical5
51036­
429
Thidiazuron­
Diuron
EC
Cotton
Defoliant1
51036­
430
Thidiazuron
4SC
Cotton
Defoliant
72167­
28
Nation's
AG
II
Thidiazuron
Technical5
72167­
30
Thidiazuron
50WSB
Cotton
Defoliant
1
12%
thidiazuron
and
6%
diuron
mixture
2
50%
thidiazuron
and
25%
diuron
mixture
3
30.3%
thidiazuron
and
15.1%
diuron
mixture
4
32.7%
dimethipin
and
8.4%
thidiazuron
mixture
5
For
cotton
defoliant
formulation
use
only
As
indicated
in
the
table
above,
thidiazuron
is
used
exclusively
as
a
cotton
defoliant
or
growth
regulant.
Three
of
the
thirteen
registered
thidiazuron
products
are
mixed
with
diuron
at
half
the
concentration
of
thidiazuron.
In
another
product
(
Harvade
4198SC),
dimethipin
is
present
at
approximately
four
times
the
concentration
of
thidiazuron.

In
the
case
of
the
mixed
products,
care
must
be
taken
when
calculating
the
use
rates
for
thidiazuron.
This
is
because
the
"
active
ingredient"
application
rates
given
on
the
labels
are
for
the
sums
both
active
ingredients.
Since
each
compound
is
different
in
physicochemical
properties
and
biological
activity,
it
is
more
meaningful,
useful,
and
transparent
to
separate
the
rates
for
each.
This
risk
assessment
was
conducted
for
that
fraction
of
the
application
rate
contributed
by
thidiazuron
only.
Page
8
of
129
The
maximum
single
application
rate
for
all
labels
on
which
thidiazuron
is
the
sole
active
ingredient
is
0.2
lb
ai/
A
(
EPA
Registration
Numbers
264­
622,
264­
700,
51036­
401,
51036­
430,
and
72167­
30).
A
second
application
is
recommended
under
low
temperature
conditions
when
defoliation
does
not
reach
the
expected
level,
but
the
total
of
the
two
applications
must
not
exceed
0.3
lb
ai/
A.
The
intervals
between
applications
range
from
5­
7
days
in
some
of
the
labels,
while
the
other
labels
make
no
recommendations
with
regard
to
intervals.

The
maximum
single
application
rate
when
thidiazuron
is
mixed
with
diuron
is
0.125
lb
of
thidiazuron
per
acre
and
0.0625
lb
of
diuron
per
acre
(
EPA
Registration
Numbers
264­
634,
264­
661,
and
51036­
429).
The
combined
rate
for
both
active
ingredients
is
0.1875
lb
ai/
A,
and
since
diuron
also
has
the
same
mode
of
action
as
thidiazuron,
the
combined
total
use
rate
is
approximately
the
same
as
in
the
products
which
contain
only
thidiazuron
as
the
sole
active
ingredient.
The
total
number
of
applications
is
not
specified
on
any
of
these
labels,
however,
the
maximum
combined
active
ingredient
dosage
is
not
to
exceed
0.1875
lb
ai/
A
per
season.

When
thidiazuron
is
mixed
with
dimethipin
the
maximum
single
application
rate
is
0.00625
lb
thidiazuron
and
0.1
lb
dimethipin/
A
(
EPA
Registration
Number
400­
505).
A
second
application
may
be
required
at
a
maximum
rate
per
acre
of
0.003
lb
thidiazuron
and
0.05
lb
dimethipin
5
­
7
days
after
the
initial
treatment.
The
maximum
yearly
application
should
not
exceed
0.01
lb
thidiazuron
and
0.16
lb
dimethipin/
A/
yr.

Risk
Assessment
Approach
For
terrestrial
risk,
we
consider
the
active
ingredient
thidiazuron
only.
For
aquatic
risk,
the
most
sensitive
toxicity
endpoint
measured
among
parent
thidiazuron,
aquatic
photodegradates
AE
F132147
and
AE
C421200
and
the
thidiazuron
metabolite
AE
F132145
is
used
to
calculate
risk
quotients.
Since
environmental
concentrations
of
thidiazuron
transformation
products
would
be
expected
to
be
less
than
potential
concentrations
of
thidiazuron,
use
of
the
transformation
product
toxicity
data
is
a
particularly
conservative
component
of
the
screening
assessment.
The
assessment
does
not
consider
any
additional
risk
posed
by
the
co­
formulations
of
thidiazuron
with
either
of
the
active
ingredients
diuron
or
dimethipin,
(
see
previous
section
for
specific
products
and
concentrations
of
each)
or
by
the
addition
of
adjuvants
(
surfactants).

Assessment
Endpoints
The
typical
assessment
endpoints
for
screening­
level
pesticide
ecological
risks
are
reduced
survival
and
reproductive
impairment
for
both
aquatic
and
terrestrial
animal
species.
These
effects
extend
to
a
consideration
of
direct
acute
and
direct
chronic
exposures.
The
assessment
endpoints
for
aquatic
plants
are
impairments
due
to
a
decrease
in
alga
cell
density
or
macrophyte
growth.
Terrestrial
plant
assessment
endpoints
are
impairments
due
to
shoot
weight,
shoot
length,
or
dry
weight.
There
are
currently
no
chronic
assessment
endpoints
for
reproductive
impairment
for
plants.
While
these
endpoints
are
measured
at
the
individual
level,
they
do
provide
insight
about
risks
at
higher
levels
of
biological
organization
(
e.
g.,
populations).

Measures
of
Effects
Page
9
of
129
The
screening
level
risk
assessment
process
relies
on
a
suite
of
toxicity
studies
performed
on
a
limited
number
of
organisms
in
the
following
broad
groupings:

°
Birds
(
mallard
duck
and
bobwhite
quail)
(
see
Toxicity
to
Birds
section)
°
Acute
data
are
complete
for
this
risk
assessment
°
Chronic
data
are
not
available.
°
Mammals
(
laboratory
rat)
(
see
Toxicity
to
Mammals
section)
°
Acute
data
are
complete
for
this
risk
assessment
°
Chronic
data
are
available
from
a
2­
generation
and
a
3­
generation
rat
study
°
Freshwater
fish
(
bluegill
sunfish,
rainbow
trout,
and
fathead
minnow)
(
see
Toxicity
to
Fish
section)
°
Acute
data
are
available
for
thidiazuron.
°
Acute
data
are
available
for
the
AE
F132145
metabolite
and
the
AE
F132147
and
AE
C421200
photodegradates,
and
these
data
are
incorporated
into
the
risk
assessment.
°
Chronic
freshwater
fish
data
are
available
for
thidiazuron
°
Freshwater
invertebrates
(
Daphnia
magna)
(
see
Toxicity
to
Aquatic
Invertebrates
section)
°
Acute
data
are
available
for
thidiazuron
°
Acute
data
are
available
for
the
AE
F132145
metabolite
and
the
AE
F132147
and
AE
C421200
photodegradates,
and
these
data
are
incorporated
into
risk
assessment
°
Chronic
data
are
available
for
thidiazuron
°
Estuarine/
marine
fish
(
sheepshead
minnow)
(
see
Toxicity
to
Fish
section)
°
Acute
data
are
available
for
thidiazuron.
°
No
chronic
data
are
available
°
Estuarine/
marine
invertebrates
(
Crassostrea
virginica
and
Mysidopsis
bahia)
(
see
Toxicity
to
Aquatic
Invertebrates
section)
°
Acute
data
are
available
for
thidiazuron
°
Chronic
data
are
not
available
°
Algae
and
aquatic
plants
(
see
Toxicity
to
Aquatic
Plants
section)
°
Data
are
available
for
green
algae,
blue­
green
algae,
marine
diatoms,
and
aquatic
vascular
macrophytes
for
thidiazuron.
°
Data
are
not
available
for
freshwater
diatoms.
°
Data
are
available
for
green
algae
for
the
AE
F132145
metabolite
and
the
AE
F132147
and
AE
C421200
photodegradates,
and
these
data
are
incorporated
into
risk
assessment.
°
Terrestrial
plants
(
corn,
soybean,
turnip,
oats,
wheat,
tomato,
onion,
cabbage,
lettuce,
cucumber)
(
see
Toxicity
to
Terrestrial
Plant
section)
°
Data
are
available
for
thidiazuron
°
Data
are
available
for
thidiazuron
SC42
formulated
product
Within
each
of
these
very
broad
taxonomic
groups,
an
acute
and
chronic
endpoint
is
selected
from
the
available
test
data,
as
the
data
sets
allow.
The
selection
is
made
from
the
most
sensitive
species
tested
within
that
organism
group.
Page
10
of
129
Additional
effects
data
were
available
for
other
taxa
and
for
aquatic
community
effects
measures.
These
have
been
incorporated
into
the
risk
characterization
as
other
lines
of
evidence.
These
data
include:

°
Acute
laboratory
toxicity
study
of
technical
and
formulated
product
with
oligochaete
worms
°
Toxicity
data
on
beneficial
insects
°
laboratory
tests
for
honeybee
contact
toxicity
°
laboratory
tests
for
predatory
mites
and
parasoid
wasps
In
addition,
a
search
of
EPA's
publically
accessible
Ecotoxicity
Database
(
http://
www.
epa.
gov/
ecotox)
for
relevant
toxicological
studies
revealed
no
additional
data
for
effects
on
mortality,
growth,
behavior,
reproduction,
population,
or
ecosystem
function
for
thidiazuron.
A
complete
discussion
of
all
toxicity
data
available
for
this
risk
assessment
and
the
resulting
measurement
endpoints
selected
for
each
taxonomic
group
are
included
in
Sections
VI
and
VII
of
this
document.

Measures
of
Exposure
Exposures
estimated
in
the
screening
level
risk
assessment
for
non­
target
organisms
are
not
specific
to
a
given
species.
Rather,
general
taxonomic
exposure
assumptions
are
made
that
provide
separate
exposure
measures
for
aquatic
and
terrestrial
plants
and
animals.
The
approaches
for
each
are
discussed
separately
below.

Aquatic
Organisms
In
addition
to
parent
thidiazuron,
effects
data
are
available
for
the
aqueous
photodegradates
AE
F132147
and
AE
C421200
and
the
metabolite
AE
F132145
in
fish,
aquatic
invertebrates,
and
aquatic
plants.
These
data
suggest
that
exposure
modeling
for
these
degradates
is
warranted.
The
following
sections
describe
the
general
analysis
approach
used
for
active
ingredient
and
the
three
transformation
products.

Active
Ingredient
and
Degradate
Aquatic
Organism
Exposure
Approach
This
risk
assessment
considers
thidiazuron
exposure
in
aquatic
organisms
(
animals
and
plants)
via
the
fraction
of
pesticide
dissolved
in
the
water
column.
Thidiazuron
is
assumed
to
be
introduced
to
surface
waters
via
runoff
and
spray
drift.
Currently,
no
monitoring
data
are
available
that
would
provide
information
on
thidiazuron
levels
in
surface
water
bodies
receiving
runoff
or
spray
drift
from
agricultural
fields
treated
with
the
pesticide.
Consequently,
aquatic
organism
exposure
is
estimated
through
the
use
of
runoff
and
spray
drift
models.
Aquatic
organism
exposures
are
based
on
a
set
of
standardized
receiving
surface
water
body
assumptions
(
water
body
size,
watershed
size,
proximity
to
field,
etc.)
that
result
in
reasonable
upper­
level
estimates
of
exposure.
For
this
risk
assessment
the
GENEEC
model
was
used
for
making
these
exposure
estimates.
GENEEC
is
the
most
conservative
exposure
model
available
in
OPP.
It
estimates
exposure
concentrations
in
aquatic
environments
representative
of
geographic
locations
where
cotton
is
grown
in
large
quantities.
If
exposure
concentrations
resulting
from
the
use
of
Page
11
of
129
GENEEC
yield
risk
quotients
below
all
aquatic
levels
of
concern,
it
is
concluded
that
direct
and
indirect
aquatic
risks
would
not
occur.
In
this
regard,
EFED
used
the
most
sensitive
toxicological
endpoint
available
from
data
on
thidiazuron
and
the
photoproducts
for
each
of
the
aquatic
organism
categories
(
i.
e.,
fish,
aquatic
invertebrates,
plants).

For
acute
aquatic
risk,
no
averaging
time
for
exposure
was
assumed
for
this
assessment.
The
use
of
the
instantaneous
peak
assumes
that
instantaneous
exposure
is
of
sufficient
duration
to
elicit
acute
effects
on
par
with
those
observed
over
more
protracted
exposure
periods
tested
in
the
laboratory,
typically
48
to
96
hours.
For
assessment
of
chronic
aquatic
invertebrate
risks
with
thidiazuron,
the
peak
water
concentration
was
again
used.
This
is
a
departure
from
the
normal
assessment
where
the
21­
day
average,
1­
in­
10
year
return
frequency
values
are
compared
to
the
measurement
endpoint
for
aquatic
invertebrate
chronic
risks.
The
decision
to
use
a
peak
concentration
exposure
measure
was
predicated
on
the
belief
that
the
LOCs
would
not
be
exceeded
even
if
the
higher
peak
concentrations
were
utilized.

As
discussed
in
the
Environmental
Fate
section
of
this
document
and
in
Appendix
D,
thidiazuron
undergoes
relatively
rapid
branching
photolysis
in
water
into
only
two
photoproducts.
Formation
of
these
products
is
in
constant
ratio
and
in
complementary
stoichiometric
yield
with
parent.
The
key
features
of
these
two
photoproducts
are
as
follows:

Photoproduct
I
(
AE
F132347,
see
chemical
structure
in
Appendix
B)
is
an
isomer
of
parent
differing
only
in
the
relative
positions
of
the
sulfur
atom
and
the
two
nitrogen
atoms
in
the
5­
membered
ring.
Like
parent,
photoproduct
I
is
moderately
ecotoxic
(
slightly
more
toxic
than
parent,
based
on
the
limited
data
discussed
in
the
main
text
of
this
document).
It
has
a
reviewercalculated
asymptotic
experimental
limit
of
production
of
77%
of
parent
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
This
product
was
stable
to
further
photolysis
under
the
experimental
study
conditions
and
durations
(
original
MRID
41188201,
related
follow­
up
MRIDs
41364910
and
43075202,
and
fate
overview
document
with
MRID
44436901).
Soil/
sediment
sorption
data
and
non­
photolytic
transformation
data
are
available
only
for
parent.
However,
based
on
its
isomeric
chemical
structure,
photoproduct
I,
except
for
photolysis,
would
be
expected
to
have
fate
properties
similar
to
parent.

Photoproduct
II
(
AE
C421200,
chemical
structure
in
Appendix
B)
is
a
substantially
degraded,
practically
non­
ecotoxic
product
(
based
on
the
limited
data
discussed
in
the
main
text
of
this
document),
and
has
a
complementary
asymptotic
limit
of
production
to
photoproduct
I
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
This
product
was
also
stable
to
further
photolysis
under
study
conditions.
Soil/
sediment
sorption
data
and
non­
photolytic
transformation
data
are
available
only
for
parent.
However,
because
of
its
degraded
nature
and
a
modicum
of
direct
evidence
indicating
that
photoproduct
II
is
practically
non­
toxic
for
ecological
risk
assessment
purposes,
EFED
assumed
that
photoproduct
II
does
not
contribute
to
ecological
risk,
and
ignored
its
potential
presence.

Aquatic
exposure
concentrations
are
derived
from
a
combination
of
GENEEC
model
runs
for
the
summation
of
thidiazuron
and
its
photoisomer
as
explicitly
derived
in
Appendix
D
Terrestrial
Plants
Page
12
of
129
The
focus
of
the
terrestrial
plant
exposure
assessment
is
on
terrestrial
plants
inhabiting
dry
and
semi­
aquatic
areas.
Potential
routes
of
exposure
to
pesticides
considered
are
runoff,
spray
drift
and
volatilization.
Since
thidiazuron
is
non­
volatile,
volatilization
is
not
a
concern.

Semi­
aquatic
areas
are
those
low­
lying
wet
areas
that
may
be
dry
at
certain
times
of
the
year.
EFED's
runoff
exposure
estimate
in
these
areas
is:
(
1)
based
on
a
pesticide's
water
solubility
and
the
amount
of
pesticide
present
in
the
top
one
inch
of
soil,
(
2)
characterized
as
"
sheet
runoff"
(
one
treated
acre
to
an
adjacent
acre)
for
dry
areas,
(
3)
characterized
as
"
channelized
runoff"
(
10
treated
acres
to
a
distant
low­
lying
acre)
for
semi­
aquatic
areas,
and
(
4)
based
on
percent
runoff
values
of
0.01,
0.02,
and
0.05
for
water
solubilities
of
<
10
ppm,
10­
100
ppm,
and
>
100
ppm,
respectively.

Spray
drift
exposure
from
ground
and
overhead
chemigation
applications
is
assumed
to
be
1%
of
the
application
rate.
Spray
drift
from
aerial,
airblast,
and
forced­
air
applications
is
assumed
to
be
5%
of
the
application
rate
with
an
application
efficiency
of
60%.
The
effects
of
multiple
applications
are
addressed
by
summing
the
application
rates
from
individual
applications.

Terrestrial
Animals
The
focus
of
the
terrestrial
wildlife
exposure
assessment
is
on
birds
and
mammals
with
the
exposure
route
emphasis
on
uptake
through
the
diet.
For
exposure
to
terrestrial
organisms,
such
as
birds
and
small
mammals,
OPP
looks
at
the
residues
of
pesticides
on
food
items,
and
assumes
that
organisms
are
exposed
to
a
single
pesticide
residue
in
a
given
exposure
scenario.
For
thidiazuron
spray
applications,
estimation
of
pesticide
concentrations
in
wildlife
food
items
focuses
on
quantifying
possible
dietary
ingestion
of
residues
on
vegetative
matter
and
insects.
The
residue
estimates
are
based
on
a
nomogram
that
relates
food
item
residues
to
a
pesticide's
application
rate.
Residues
may
be
compared
directly
with
dietary
toxicity
data
or
converted
to
an
oral
dose,
as
is
the
case
for
small
mammals.
The
screening­
level
risk
assessment
for
thidiazuron
uses
an
upper
bound
predicted
residue
as
the
measure
of
exposure.
For
mammals,
the
residue
concentration
is
converted
to
daily
oral
dose
based
on
fractions
of
body
weight
consumed
daily,
as
estimated
through
mammalian
allometric
relationships.

Risk
Characterization
Approach
For
this
assessment
of
thidiazuron
risks,
the
risk
quotient
(
RQ)
method
is
used
to
compare
exposure
and
measured
toxicity.
Estimated
environmental
concentrations
(
EECs)
are
divided
by
acute
and
chronic
toxicity
values.
The
RQs
are
compared
to
the
Agency's
levels
of
concern
(
LOCs).
These
LOCs
are
the
Agency's
interpretative
policy,
and
are
used
to
analyze
potential
risk
to
non­
target
organisms
and
the
need
to
consider
regulatory
action.
These
criteria
are
used
to
indicate
when
a
pesticide
used
as
directed
on
the
label
has
the
potential
to
cause
adverse
effects
on
non­
target
organisms.
Appendix
G
of
this
document
summarizes
the
LOCs
employed
in
this
risk
assessment.

Problem
Formulation
Analysis
Plan
Page
13
of
129
In
accordance
with
US
EPA's
"
Guidelines
for
Ecological
Risk
Assessment,"
April
1998,
and
"
Overview
of
the
Ecological
Risk
Assessment
Process
in
the
Office
of
Pesticide
Program,"
January
2004,
an
analysis
plan
and
rationale
were
developed
to
determine
if
current
label
uses
of
thidiazuron
indicate
a
likelihood
that
unreasonable
adverse
effects
to
nontarget
and
listed
animals
and
plants
could
potentially
impact
the
reregistration
eligibility
decision
under
the
Federal
Insecticide,
Fungicide,
and
Rodenticide
Act,
the
Food
Quality
Protection
Act,
and
the
Endangered
Species
Act.
Over
the
course
of
its
assessment,
OPP
has
attempted
to
refine
its
problem
formulation
by
integrating
registrant­
submitted
guideline
data
and
various
levels
of
exposure
refinements
and
information
on
usage
to
characterize
the
environmental
fate
and
ecological
effects
of
thidiazuron
and
its
degradates.

Thidiazuron
is
exclusively
used
as
a
cotton
defoliant
to
aid
in
the
machine
harvesting
of
cotton
by
removing
both
mature
and
juvenile
leaves.
EFED
made
several
assumptions
concerning
some
ambiguities
on
the
labels.
Three
of
the
product
labels
list
diuron
as
an
additional
active
ingredient,
and
another
label
lists
dimethipin,
but
none
of
these
labels
report
the
application
rates
of
each
active
ingredient
separately.
EFED
quantitatively
considered
the
risk
resulting
from
thidiazuron
only,
rather
than
the
combination
of
the
two
active
ingredients.
Thidiazuron
rates
were
calculated
from
total
product
application
rates
and
product
chemical
composition.
The
possible
additive
or
synergistic
effects
resulting
from
the
consideration
of
the
other
active
ingredients
were
not
evaluated.
Additional
information
provided
by
BEAD
and
other
sources
identified
more
typical
use
rates
and
frequencies
in
addition
to
the
maximum
rates
which
are
routinely
used
in
screening
level
assessments.
These
typical
rates
were
considered
in
the
terrestrial
plant
risk
characterization.

The
risk
assessment
considers
aquatic
and
terrestrial
risks
for
parent
thidiazuron.
In
addition,
it
considers
risks
posed
to
aquatic
organisms
from
AE
F132347
and
AE
C421200
(
photodegradates
formed
in
water)
and
the
metabolite
AE
F132345
by
using
aquatic
exposure
concentrations
derived
from
a
combination
of
GENEEC
model
runs
for
the
summation
of
thidiazuron
and
its
photoisomer
as
explicitly
derived
in
Appendix
D.

Risk
to
terrestrial
plants
from
the
formulated
product,
Thidiazuron
SC42
(
DROPP)
is
considered
in
the
risk
assessment.
Exposure
from
foliar
routes
of
exposure
are
primarily
explored
for
terrestrial
and
aquatic
plants
and
animals.
However,
this
risk
assessment
does
not
take
into
account
atmospheric
transport,
other
than
spray
drift,
in
estimation
of
environmental
concentrations.
Further,
it
does
not
account
for
ingestion
of
residues
by
animals
in
drinking
water
or
contaminated
grit,
ingestion
through
preening
activities,
or
uptake
through
inhalation
or
dermal
absorption
by
terrestrial
animals.
Exposure
to
terrestrial
animals
is
based
primarily
on
dietary
consumption
of
foliar
residues,
whereas
aquatic
exposures
assume
that
all
potential
routes
of
direct
exposure
are
accounted
for
and
are
based
on
standard
surface
water
modeling
used
in
EFED.

As
previously
discussed,
exposure
to
terrestrial
plants
inhabiting
dry
and
semi­
aquatic
areas
involves
runoff
assumptions
based
on
the
water
solubility
and
the
amount
of
pesticide
present
in
the
top
one
inch
of
soil.
This
runoff
exposure
is
characterized
as
"
sheet
runoff"
(
one
treated
acre
to
an
adjacent
acre)
for
dry
areas,
and
"
channelized
runoff"
(
10
treated
acres
to
a
distant
lowlying
acre)
for
semi­
aquatic
areas.
Terrestrial
plant
spray
drift
exposure
assumptions
are
based
on
Page
14
of
129
1%
of
the
application
rate
for
ground
applications
and
5%
for
aerial
applications
with
an
application
efficiency
of
60%.

Maximum
application
rates
on
vulnerable
soils
for
representative
crops
are
selected
for
modeling
environmental
concentrations
for
this
screening­
level
deterministic
(
risk
quotient
based)
risk
assessment.
This
assessment
is
not
intended
to
represent
a
site
or
time­
specific
analysis;
i.
e.,
assessments
are
intended
to
represent
a
national
level
exposure
based
on
vulnerable
soils
as
opposed
to
being
regionally
specific.
However,
if
exposures
exceed
LOCs,
the
assessment
will
be
refined
to
include
higher­
tiered
models
with
spatially
specific
use
scenarios.
Likewise,
the
most
sensitive
toxicity
endpoints
are
used
from
surrogate
test
species
to
estimate
treatment­
related
direct
effects
on
acute
mortality
and
chronic
reproductive,
growth,
and
survival
assessment
endpoints.
Toxicity
tests
are
intended
to
determine
pesticidal
effects
on
birds,
mammals,
fish,
terrestrial
and
aquatic
invertebrates
and
plants.
These
tests
include
short­
term
acute,
subacute
and
reproduction
studies
and
are
typically
arranged
in
a
hierarchical
or
tiered
system
that
progresses
from
basic
laboratory
tests
to
applied
field
studies.
These
studies
are
used
to
evaluate
the
potential
of
a
pesticide
to
cause
adverse
effects,
determine
whether
further
testing
is
required,
and
to
determine
the
need
for
precautionary
label
statements
to
minimize
the
potential
adverse
effects
to
nontarget
animal
and
plants
(
CFR
40
§
158.202,
2002).

The
conceptual
model
used
to
depict
the
ecological
risk
associated
with
thidiazuron
was
initially
generic
and
assumed
that
thidiazuron
was
capable
of
affecting
terrestrial
and
aquatic
animals
provided
environmental
concentrations
were
sufficiently
elevated
as
a
result
of
labeled
uses.
This
initial
conceptual
model
is
presented
below.
Page
15
of
129
Conceptual
Model
for
ThidiazuronRisk
Assessment
Thidiazuronapplied
to
agricultural
field
Runoff
Spray
drift
Water
body
Aquatic
plants
Aquatic
invertebrates
Aquatic
vertebrates
Riparian
Zone
Terrestrial
plants
Terrestrial
insects
Terrestrial
Mammals
Birds
Individual
fish
Reduced
survival
Reduced
growth
Reduced
reproduction
Food
chain
Decrease
in
abundance
Shift
in
prey
base
Habitat
integrity
Decreased
water
quality
Reduced
cover
Stream
destabilization
Stressor
Receptors
Attribute
Change
Groundwater
Atmospheric
deposition
Source
Page
16
of
129
Refined
Conceptual
Model
for
a
Screening
level
Assessment
of
Thdiazuronum
on
Cotton
Source:
Aerial
and
ground
Application
to
Cotton
Thidiazuron/
Degradates/
Products
Terrestrial
Plant
Exposure
from
Spray
Drift,
Runoff,
and
Sheet
Runoff
Receptor:
Plants
Adjacent
to
treated
sties
Receptor:
Plants
in
Semi­
Aquatic
Areas
Acute
Effects
to
Non­
endangered
and
Endangered
Plants
Acute
Effects
to
Non­
endangered
and
Endangered
Plants
Receptor:
Mammals
in
and
Adjacent
to
treated
sites
Direct
and
Indirect
Chronic
Effects
to
Non­
endangered
and
Endangered
Plants
However,
through
an
iterative
process
of
examining
fate
and
effects
data,
the
conceptual
model
has
been
refined
to
reflect
the
exposure
pathways
and
the
organisms
for
which
risk
is
most
likely.
Based
on
OPPs
screening
level
assessment,
the
refined
conceptual
model
for
depicting
the
risks
of
thidiazuron
primarily
focuses
on
risk
to
terrestrial
plants.
Additionally,
there
are
concerns
about
possible
chronic
effects
to
small
mammals,
depending
on
the
methodology
and
toxic
endpoints
used
to
calculate
the
risk
quotients.
Further,
since
there
are
no
chronic
data
currently
available
for
birds,
chronic
risk
to
birds
is
undetermined.
The
refined
conceptual
model
for
depicting
risks
to
nontarget
terrestrial
plants
is
presented
below.
Page
17
of
129
III.
Integrated
Environmental
Risk
Characterization
Risks
to
Aquatic
Organisms
The
results
of
the
risk
assessment
suggest
that
acute
and
chronic
risk
quotients
for
all
freshwater
and
marine
fish
and
invertebrates
are
below
all
levels
of
concern
established
by
the
Agency's
screening­
level
assessment.

The
acute
risk
quotients
ranged
from
<
0.0003
(
marine
fish)
to
0.002
(
freshwater
fish
and
estuarine
invertebrates).
Chronic
risk
quotients
ranged
from
0.002
(
freshwater
fish)
to
>
0.1
(
freshwater
invertebrates).
In
addition,
the
acute
risk
quotients
for
the
non­
endangered
and
endangered
species
are
well
below
all
established
levels
of
concern
for
aquatic
plants.
The
definitive
acute
risk
quotients
ranged
from
0.0005
to
0.013
and
the
endangered
species
risk
quotients
ranged
from
0.006
to
0.2.

Although
there
may
be
some
uncertainty
with
respect
to
chronic
risk
to
freshwater
and
marine
invertebrates
because
a
definitive
NOAEC
value
could
not
be
obtained,
it
is
possible
to
estimate
chronic
risk
based
on
a
21­
day
EC
10
value
which
was
obtained
in
the
chronic
freshwater
invertebrate
study.
The
21­
day
EC
10
value,
was
720
µ
g/
L
based
on
the
length
of
the
test
organisms.
Using
this
generated
EC
10
value,
the
definitive
21­
day
RQ
value
of
0.015
is
well
below
the
chronic
level
of
concern.
In
order
for
the
chronic
aquatic
invertebrate
LOC
to
be
exceeded,
the
test
would
have
to
be
repeated
to
test
levels
lower
than
11
µ
g/
L
(
nearly
10­
fold
the
current
test
level
of
100
µ
g/
L).
It
is
doubtful
that
definitive
NOAEC/
LOAECs
would
exceed
the
chronic
levels
of
concern.
Even
if
the
persistence
and
intermediate
mobility
were
taken
into
account
where
some
year­
to­
year
build­
up
in
soil
would
occur
(
asymptotic
limit
twice
that
of
annually
applied
amounts),
the
resulting
RQs
would
still
not
exceed
any
aquatic
LOCs.

Risk
to
Birds
Acute
Risks
­
Birds
Acute
risks
to
birds
for
this
use
are
below
all
levels
of
concern.

To
determine
potential
acute
risk
to
birds,
we
use
exposure
data
from
Hoeger
and
Kenaga
(
1972),
as
modified
by
Fletcher
et
al.
(
1994).
These
data
provide
maximum
and
mean
residue
concentrations
of
a
pesticide
on
various
terrestrial
food
items
on
the
basis
of
a
one
pound
per
acre
application
in
the
field.
Predicted
residue
concentrations
are
available
for
short
grass,
tall
grass,
broad­
leaved
plants/
small
insects,
and
seeds/
large
insects.

Toxicant
concentrations
on
food
items
following
multiple
applications
are
predicted
using
a
firstorder
residue
decline
method,
EFED's
"
ELLFATE"
model,
which
allows
determination
of
residue
dissipation
over
time
incorporating
degradation
half­
life.
Predicted
maximum
and
mean
EECs
resulting
from
multiple
applications
estimates
the
highest
one­
day
residue,
based
on
the
maximum
or
mean
initial
EEC
from
the
first
application,
the
total
number
of
applications,
interval
between
applications,
and
a
first­
order
degradation
rate,
consistent
with
EFED
policy.
The
input
parameters
for
the
cotton
scenario
were
based
on
a
maximum
single
application
of
0.2
lbs
a.
i./
A.
Page
18
of
129
For
multiple
applications,
a
follow­
up
application
of
0.1
lb
ai/
A
at
an
interval
between
5
and
7
days
is
allowed
on
all
labels,
and
for
this
scenario
EFED
used
the
ELLFATE
program
to
estimate
the
maximum
residue
concentrations
occurring
over
a
99­
day
period
based
on
a
35­
day
foliar
dissipation
half­
life
and
a
7­
day
interval
between
applications.
The
first
application
was
run
at
0.2
lb
ai/
A.
To
factor
in
the
second
application
of
0.1
lb
ai/
A
(
on
day
6),
the
maximum
residue
concentrations
from
it
were
added
to
those
remaining
from
the
first
application
(
on
day
0).

Acute
data
submitted
for
thidiazuron
indicate
that
the
dietary
LC50s
were
greater
than
5000
mg/
kg­
diet
for
bobwhite
quail
and
mallard
duck.
The
LD50s
were
greater
than
3160
mg/
kg­
bw
for
both
species.
Since
the
results
from
both
the
dietary
LC50
and
the
oral
gavage
LD50
classify
thidiazuron
as
practically
non­
toxic
to
birds
and
the
formulations
are
non­
granular,
the
dietary
LC50
for
bobwhite
quail
was
selected
for
risk
quotient
calculations.

The
resulting
acute
risk
quotients
(
Appendix
G)
at
all
sites
were
below
all
levels
of
concern
using
the
most
sensitive
LC50
of
>
5000
mg/
kg­
diet.
The
highest
RQ
observed
for
two
applications
of
0.2
lb
ai/
A
for
birds
foraging
in
short
grass
was
<
0.013.

Chronic
Risk
­
Birds
Chronic
risks
to
birds
cannot
be
quantitatively
evaluated
at
this
time
because
chronic
data
were
not
submitted.
However,
available
data
showing
that
chronic
levels
of
concern
for
mammals
are
exceeded
and
that
thidiazuron
is
persistent
in
the
field
suggest
that
there
is
also
potential
for
chronic
risk
to
birds
should
they
be
of
equal
of
greater
sensitivity
than
mammals.

Risks
to
Mammals
Acute
Risks
­
Mammals
Acute
risks
to
mammals
were
evaluated
using
the
rat
LD50
of
>
2000
mg/
kg­
bw.
There
were
no
acute
LOCs
exceeded
(
Appendix
G).
The
highest
risk
quotient
observed
for
the
15
g
mammal
foraging
on
short
grass
is
<
0.03,
well
below
the
endangered
species
LOC
of
0.1.

Chronic
Risk
­
Mammals
The
results
from
the
2­
generation
rat
study
was
used
to
assess
chronic
risk
to
mammals.
The
NOAEL
for
both
parental
and
offspring
toxicity
in
this
study
was
400
ppm
diet
(
35.4/
39.8
mg/
kg/
day
[
M/
F])
and
the
LOAEL
for
these
endpoints
was
1200
ppm
diet
(
108.5/
121.1
mg/
kg/
day
[
M/
F]).
Although
the
reproduction
performance
in
the
laboratory
was
not
adversely
affected
there
were
observed
delays
in
female
sexual
maturation
and
irregular
estrous
cycles
or
acyclicity
at
the
1200
ppm
dose,
F1
females).
Effects
on
the
timing
to
reach
sexual
maturity
and
disruptions
in
estrous
cycling
could
pose
adverse
reproduction
effects
in
wild
mammals
because
of
the
seasonality
of
reproduction
periods
in
the
wild
and
seasonal
influences
on
the
survival
of
offspring.
Therefore
the
NOAEL
for
wild
mammal
reproduction
risk
assessment
purposes
would
be
400
ppm
diet.
Page
19
of
129
A
3­
generation
rat
reproduction
study
was
also
performed.
This
study
was
classified
as
coresupplemental
in
1995
due
to
several
deficiencies
in
the
study
design.
Most
notable
of
these
was
that
there
was
no
measure
of
food
consumption
and
the
amount
of
food
consumed
was
estimated
by
using
default
food
consumption
values
developed
by
the
FDA
many
years
ago.
Since
this
study
is
the
only
chronic
study
currently
available,
EFED
will
use
this
data
for
this
assessment.

The
reproductive
NOAEC
and
LOAEC
values
based
on
reduction
of
litter
size
are
200
and
600
mg/
kg­
diet,
respectively.
By
standard
conversion
factors
the
NOAEL
and
LOAEL
are
10
and
30
mg/
kg­
bw/
da,
respectively.
The
mean
litter
size
data
from
the
study
is
summarized
in
the
following
table
and
indicate
that
significant
reductions
are
occurring
in
the
F3b
generation
at
the
highest
dose,
and
possibly
the
lowest
as
well.

The
quality
of
the
2­
generation
study,
devoid
of
the
inter­
litter
mating
problems
associated
with
the
3­
generation
study,
suggests
that
the
effects
measurement
endpoints
derived
from
this
study
be
used
in
preference
to
those
from
the
3­
generation
study.

Using
the
NOAEL
of
35.4
mg/
kg­
bw/
day
is
reasonable
because
the
percent
of
reproductive
impairment
that
is
significant
for
a
given
species
would
be
based
on
their
reproductive
strategy.
For
long­
lived
(
K­
selected
species),
episodic
reductions
in
reproduction
might
not
be
of
the
same
significance
as
short­
lived
(
r­
selected)
species.
Reproductive
impairment
for
a
short­
lived
species
could
be
enough
to
impact
any
number
of
species
with
low
generation
survival
rates
and
a
dependance
on
high
reproductive
output
for
population
continuance
(
r­
selected
species).

To
calculate
mammalian
risk
quotients,
we
preferentially
use
the
Nagy
small
mammal
assumptions
of
percent
body
weight
consumed
for
the
15,
35,
and
1000
g
mammals
and
divide
the
dietary
EEC
adjusted
for
food
consumption
by
the
NOAEL
(
expressed
as
mg/
kg­
bw/
day).
The
resulting
risk
quotients
are
presented
in
Tables
7
and
8
of
Appendix
G
and
indicate
that
LOCs
are
exceeded
for
mammals
(
herbivores/
insectivores)
foraging
in
short
grass
and
broadleaf
forage
and
small
insects.
The
risk
quotients
range
from
1.8
(
short
grass)
to
0.01
(
large
insects).
The
chronic
LOCs
are
not
exceeded
for
mammalian
granivores.

Another
method
of
calculating
risk
quotients
is
to
divide
the
dietary
EEC
for
each
of
the
forage
groups
by
the
NOAEC
(
expressed
as
mg/
kg­
diet).
Using
the
NOAEC
of
400
mg/
kg­
diet,
the
chronic
LOCs
are
not
exceeded
for
any
of
the
food
categories.
These
risk
quotients
are
presented
in
Table
9
of
Appendix
G.

There
are
uncertainties
associated
with
the
risk
quotient
exceedances.
As
mentioned
above,
there
was
no
measure
of
food
consumption
in
the
study
or
the
amount
of
pesticide
consumed.
Further,
there
are
no
measured
foliar
dissipation
half­
life
data
to
evaluate
residue
concentrations;
therefore,
the
EFED
standard
default
foliar
half­
life
of
35
days
was
used.

Chronic
risk
can
also
be
evaluated
for
single
applications
for
maximum
Fletcher
values
for
predicted
maximum
and
mean
residues.
Residues
calculated
for
mean
residues
did
not
exceed
the
LOC.
Page
20
of
129
Risks
to
Non­
Target
Insects
EFED
currently
does
not
estimate
risk
quotients
for
terrestrial
non­
target
insects.
Whenever
an
LD
50
is
<
11
µ
g/
bee,
an
appropriate
label
statement
is
required
to
protect
foraging
honeybees.
The
acute
contact
toxicity
study
to
honeybees
revealed
a
contact
LD
50
>
100
µ
g/
bee
for
the
technical
thidiazuron
and
a
contact
LD
50
>
98.1
µ
g/
bee
for
the
SC42
formulated
product.
This
classifies
thidiazuron
technical
and
the
formulated
product
as
practically
non­
toxic
to
honeybees.

The
two
other
non­
target
insect
OECD
studies,
which
investigated
the
lethal
and
sub­
lethal
effect
of
the
SC42
water
miscible
suspension
concentrate
500
g/
L
on
the
parasitoid
wasp
(
Aphidius
rhopalosiphi)
and
the
predatory
mite
(
Typhlodromus
pyri),
were
found
not
to
show
statistical
differences
from
the
controls
for
mortalities
or
reproduction
effects.
The
wasp
study
showed
the
percent
mortality
was
12.5%
in
the
highest
exposed
concentration
of
0.2
lb
ai/
A
compared
to
10%
in
the
controls.
The
percent
reduction
when
compared
to
the
control
was
27.3
and
38.1%
in
the
100
and
200
g
ai/
ha
treatment
groups,
respectively.
In
the
predatory
mite
study
the
mortalities
were
8%
in
the
treated
group
compared
to
13%
in
the
untreated
group,
and
the
mean
number
of
eggs
per
female
was
9.32
in
the
control
group
compared
to
8.99
in
the
200
g
ai/
ha
treatment.
Since
these
studies
showed
no
statistically
significant
effects
at
the
highest
maximum
single
rate
(
0.2
lb
ai/
A),
there
is
little
concern
for
non­
target
insects.

Risks
to
Terrestrial
Plants
RQs
for
terrestrial
plants
in
dry
and
semi­
aquatic
areas
are
calculated
for
multiple
and
single
spray
applications
for
endangered
and
non­
endangered
species.
As
mentioned
in
the
exposure
section,
the
runoff
scenarios
are
based
on
solubility,
and
since
the
solubility
of
thidiazuron
is
31
mg/
L
(
ppm),
the
percent
runoff
value
used
in
the
risk
quotient
calculations
was
0.02.
A
60%
application
efficiency
factor
is
also
included
in
the
runoff
calculations
for
aerial
applications.
The
detailed
procedures
for
terrestrial
exposure
and
plant
risk
quotient
calculations
are
discussed
in
the
terrestrial
exposure
section
of
this
assessment.
The
detailed
exposure
and
risk
quotient
calculations
are
tabulated
in
detail
in
Appendix
G,
and
a
summary
of
the
resulting
RQs
for
single
applications
is
presented
below.
Page
21
of
129
Terrestrial
Plant
Risk
Quotients
for
Single
Applications
Plant
Group
(
non­
Endangered
/
Endangered)
Type
of
Plant
Study
Type
of
Plant
(
monocot
/
dicot)
Most
Sensitive
EC25
(
Non­
Endangered)
or
NOAEC
/
EC05
(
Endangered)
Risk
Quotient
Range
(
Plants
Adjacent
to
Treated
Sites)
Risk
Quotient
Range
(
Plants
in
Semi­
Aquatic
Areas)

Nonendangered
Seedling
Emergence
Monocot
<
0.1783
>
0.03
­
>
0.07
>
0.17
­
>
0.22
Dicot
0.0152
0.39
­
0.79
1.97
­
2.63*

Vegetative
Vigor
Monocot
>
0.1783
<
0.01
­
<
0.06
<
0.01
­
<
0.06
Dicot
0.0011
1.82
­
9.09*
1.82
­
9.09*

Endangered
Seedling
Emergence
Monocot
0.1783
0.03
­
0.07
0.17
­
0.22
Dicot
0.0111
0.54
­
1.08*
2.7
­
3.6*

Vegetative
Vigor
Monocot
0.1783
0.01
­
0.06
0.01
­
0.06
Dicot
0.00019
10.53
­
52.63*
10.53
­
52.63*

*
Exceeds
terrestrial
plant
Levels
of
Concern
(
LOC)

Multiple
spray
applications
­
All
thidiazuron
labels
allow
two
applications.
The
sum
of
these
is
a
maximum
of
0.3
lb
ai/
A/
yr
(
0.2
lb
ai/
A
for
the
first
application
and
up
to
0.1
lb
ai/
A
for
the
second
application).
Only
one
label
specifies
that
intervals
between
applications
should
be
between
5­
7
days.

The
uncertainty
in
the
magnitude
of
exposure
to
multiple
applications
of
thidiazuron
is
great.
The
TERR­
PLANT
exposure
model
calculates
the
potential
exposure
for
terrestrial
plants
for
only
a
single
application
of
thidiazuron.
Since
thidiazuron
labels
allow
multiple
applications
to
each
crop,
the
magnitude
of
the
risk
to
plants
is
uncertain,
and
potentially
underestimated.
The
exposure
calculations
for
terrestrial
plants
assume
exposure
both
through
spray
drift
and
runoff
from
a
treated
field
after
a
heavy
rain
event.
The
likelihood
of
co­
occurrence
of
such
events
is
uncertain,
especially
for
multiple
applications,
and
as
a
result
the
estimated
exposure
values
may
be
conservative.
In
addition,
while
the
likelihood
of
exposure
to
non­
target
plants
through
drift
alone
is
significantly
greater,
the
same
plants
may
not
be
exposed
to
spray
drift
from
each
application,
because
wind
speed
and
direction
could
be
different
at
the
time
of
each
application.

Additional
information
on
the
effect
of
thidiazuron
on
terrestrial
plants
would
be
needed
to
evaluate
the
uncertainty
in
multiple
application
terrestrial
plant
RQs.
The
effects
of
multiple
applications
could
only
be
additive
if
the
affected
plants
could
not
recover
from
the
effects
of
successive
applications.
If
the
plants
could
recover
over
time,
the
effect
of
multiple
applications
could
be
greater
when
crops
are
treated
at
the
shortest
application
intervals.

Potential
risks
to
terrestrial
plants
are
possible
because
RQs
exceed
the
LOCs.
This
is
especially
true
for
dicots
for
single
applications
to
plants
inhabiting
dry
and
semi­
aquatic
areas.
The
RQs
Page
22
of
129
resulting
from
single
applications
to
dicots
range
from
0.39
to
9.09
for
non­
endangered
plants
and
up
to
53
for
endangered
plants.

Risk
to
monocot
species
appear
to
be
substantially
lower.
However,
definitive
EC25s
and
NOAECs
have
not
been
determined
because
tier
II
tests
were
not
conducted
for
some
of
the
more
sensitive
species
such
as
onion
and
oats.
These
EC25s
range
from
>
0.05
to
>
0.35
and
are
presented
in
more
detail
in
the
Appendix
C.

Definitive
tier
II
EC25s
and
NOAECs
are
lacking
for
the
seedling
emergence
of
two
monocot
species
tested
because
test
concentrations
were
not
low
enough
to
establish
these
endpoints.
However,
risk
quotients
from
the
tests
for
which
definitive
endpoints
were
established
were
below
levels
of
concern.
Furthermore,
compared
to
the
labeled
application
rates
for
field
use
and
corresponding
estimated
field
exposure
concentrations,
the
lowest
concentrations
for
the
tests
for
which
endpoints
were
not
determined
were
adequate
to
establish
that
risk
quotients
would
not
exceed
any
of
the
terrestrial
plant
LOCs
at
current
application
rates
for
thidiazuron.

Thidiazuron
inhibits
regrowth
by
uptake
through
the
roots
and
foliage.
When
thidiazuron
is
applied,
ethylene
levels
artificially
increase
so
the
defoliation
(
leaf
drop)
process
begins.
If
nontarget
plants
which
are
more
sensitive
than
cotton
come
into
contact
with
thidiazuron,
the
leaves
of
these
plants
may
be
killed
or
severely
damaged.
As
a
result,
the
plant
may
die,
or
the
damage
may
be
sufficient
to
prevent
the
plant
from
reproducing
or
successfully
competing
with
other
plants
for
resources.
The
use
of
thidiazuron
could
apply
selective
pressure
to
dicots
along
field
edges
resulting
in
changes
in
species
composition.

Even
though
thidiazuron
is
only
applied
at
cotton
harvest,
application
timing
is
a
consequential
factor
to
consider.
Reproduction
abnormalities
are
some
of
the
plant
injuries
that
can
occur
due
to
thidiazuron
exposure
during
particular
developmental
stages.
Late
season
annuals
complete
their
life­
cycle
in
one
year
beginning
with
seed
germination,
plant
growth,
and
reproduction.
Late
season
spraying
of
thidiazuron
could
cause
defoliation
during
the
plant
growth
phase
which
can
directly
affect
populations
and
may
reduce
their
capability
to
reproduce.
Biennials
are
plants
that
complete
their
life
cycles
in
two
years,
producing
foliage
the
first
year
and
flowers
the
following
year.
Defoliation
resulting
from
applications
of
thiadiazuron
in
the
late
season
may
inhibit
these
plants
from
reproducing
the
following
year.
Perennials
are
plants
that
grow
throughout
the
year
and
produce
flowers
and/
or
seeds
at
some
point
in
their
growing
season.
Late
blooming
perennials
may
be
impacted
by
spraying
of
thidiazuron
during
their
blooming
phase
and
thidiazuron
may
inhibit
the
plants'
ability
to
adequately
reproduce.
Although
the
plant
may
survive,
sterile
florets
or
non­
viable
seed
production
can
occur.
This
could
have
effects
on
nontarget
plant
populations'
ability
to
sustain
a
viable
population
in
future
years.

Plant
material
serves
as
a
primary
food
source
for
many
species
of
animals.
If
the
available
plant
material
(
including
seeds)
is
reduced
due
to
the
effects
of
thidiazuron,
this
may
have
negative
effects
throughout
the
food
chain.

The
exceedances
discussed
above
were
calculated
using
maximum
applications
rates
derived
from
the
thidiazuron
labels.
EFED
completed
a
characterization
of
potential
risks
by
assessing
the
effect
of
calculating
RQ
using
EECs
predicted
from
modeling
with
average
application
rates
(
0.05
Page
23
of
129
­
0.07
lb
ai/
A)
as
reported
in
the
BEAD
QUA
report.
In
the
table
below
the
average
application
rates
are
compared
to
the
maximum
allowable
application
rates.
Although
the
RQs
at
the
average
rates
are
reduced
by
at
least
one­
half,
only
the
risk
to
non­
endangered
species
caused
by
the
single
ground
application
would
be
eliminated
in
all
categories
expect
dicot
plants
(
vegetative
vigor).

The
RQ
values
for
both
maximum
and
average
application
rates
were
calculated
using
toxicity
data
for
the
most
sensitive
monocot
and
dicot
species.
Therefore,
although
RQs
for
dicots
in
the
table
below
exceed
the
acute
and
endangered
species
levels
of
concern,
not
all
plants
will
be
as
sensitive
as
lettuce,
the
most
sensitive
species
tested.
In
fact,
only
2
of
the
6
dicots
tested
exhibited
effects
in
the
seedling
emergence
test,
and
4
of
the
6
dicots
tested
exhibited
effects
in
the
vegetative
emergence
test.

However,
although
lettuce
was
the
most
sensitive
among
tested
plants,
it
is
uncertain
where
it
would
fall
on
a
sensitivity
distribution
among
plants
which
would
be
exposed
in
the
field.
Some
would
presumably
be
more
sensitive
than
lettuce,
and
some
less.
In
addition,
Bayer
has
indicated
that
"
thidiazuron
is
most
efficacious
when
the
target
plant
is
vegetatively
dormant
and
through
the
reproductive
cycle."
Seedling
emergence
and
vegetative
vigor
tests
are
acute
toxicity
tests
which
do
not
test
plants
when
they
are
vegetatively
dormant
nor
through
the
reproductive
cycle.
Therefore,
the
test
plants
in
the
laboratory
may
less
sensitive
than
non­
target
plants
in
the
field,
and
the
results
of
the
tests
may
underestimate
thidiazuron
toxicity.
Furthermore,
Bayer
indicated
that
"
defoliants
work
best
with
high
temperatures
and
high
humidity,
night
temperature
>
16C,
and
low
nitrogen
supplies."
Non­
target
plants
would
be
exposed
to
thidiazuron
under
the
same
climatic
conditions
which
make
it
an
effective
cotton
defoliant
when
it
is
applied.
Since
laboratory
tests
are
not
conducted
under
these
conditions,
test
plants
may
be
exposed
under
conditions
which
make
them
less
sensitive
to
thidiazuron
than
they
are
in
the
field.

The
risk
assessment
for
terrestrial
plants
was
based
on
RQs
calculated
from
toxicity
studies
using
a
TEP
(
typical
end­
use
product).
The
product
used
in
this
case
was
"
Thidiazuron
SC42",
presumably
DROPP
SC
(
EPA
Registration
Number
264­
700).
However,
it
appears
that
no
surfactants
or
adjuvants
were
added
to
the
product
during
the
study,
and
all
labels
clearly
state
the
addition
of
adjuvants
has
been
shown
to
improve
the
performance.
Therefore,
the
risk
to
terrestrial
non­
target
plants
may
be
greater
than
RQs
indicate.
The
production
of
actual
tank­
mix
data
would
reduce
some
of
the
uncertainties
associated
with
risk.
Page
24
of
129
Comparison
of
Maximum
and
Average
Application
Rate
Risk
Quotients
(
RQ)
Which
Exceed
the
Terrestrial
Plant
Levels
of
Concern
(
LOC)

Test
Plant
Group
Maximum
Application
Rate
RQ
Average
Application
Rate
RQ
Adjacent
Plants
Semi­
Aquatic
Areas
Adjacent
Plants
Semi­
Aquatic
Areas
Single
Ground
Application
­
Non­
Endangered
Species
(
max.
0.2
lb
ai/
A;
average
0.07
lb
ai/
A)

Seedling
emergence
Monocot
Dicot
2.63
Vegetative
vigor
Monocot
Dicot
1.82
1.82
Single
Aerial
Application
­
Non­
Endangered
Species
(
max.
0.2
lb
ai/
A;
average
0.07
lb
ai/
A)

Seedling
Emergence
Monocot
Dicot
1.97
Vegetative
Vigor
Monocot
Dicot
9.09
9.09
3.18
3.18
Single
Ground
Application
­
Endangered
Species
(
max.
0.2
lb
ai/
A;
average
0.07
lb
ai/
A)

Seedling
Emergence
Monocot
Dicot
3.6
1.32
Vegetative
Vigor
Monocot
Dicot
10.53
10.53
3.68
3.68
Single
Aerial
Application
­
Endangered
Species
(
max.
0.2
lb
ai/
A/
yr;
average
0.07
lb
ai/
A/
yr)

Seedling
Emergence
Monocot
Dicot
1.08
2.7
1.07
Vegetative
Vigor
Monocot
Dicot
52.63
52.63
18.42
18.42
1
The
following
equation
is
used
to
calculate
the
various
EC
x
levels:
[
EC
25
/
10­
0.67/
slope]
x
10­
a/
slope
=
EC
x
where
a
=
1.28,
0.84.
0.54,
0.25,
0,
­
0.25,
­
0.54,
­
0.84,
­
1.28
for
EC
10
,
EC
20
,
EC
30
,
EC
40
,
EC
50
,
EC
60
,
EC
70
,
EC
80
,
EC
90
,
respectively.
A
lognormal
toxicity
distribution
is
assumed.
This
assumption
of
normality
in
log
space
is
a
source
of
some
uncertainty
in
this
assessment.
For
example,
the
lettuce
vegetative
vigor
response
(%
inhibition
relative
to
control)
for
shoot
weight
was
12,
27,
12,
22,
and
40%
for
lowest
to
highest
doses
in
the
study.

Page
25
of
129
Additionally,
as
previously
stated,
four
thidiazuron
products
are
formulated
as
mixtures
with
other
herbicides
(
see
table
in
section
on
Use
and
Use
Characterization).
In
three
of
the
mixed
products,
thidiazuron
comprises
67%
of
total
active
ingredients
and
diuron
the
remaining
33%.
In
another
co­
formulated
product,
thidiazuron
comprises
only
20%
of
the
total
active
ingredients,
while
dimethipin
comprises
the
remaining
80%.
Plant
data
on
these
products
with
typical
adjuvants
would
reduce
the
undetermined
risk
associated
with
these
mixtures.
An
alternative
to
the
submission
of
such
data,
assuming
no
synergism
or
antagonism
among
compounds,
would
be
to
simply
add
the
known
effects
for
these
other
two
chemicals
to
those
for
thidiazuron.

Finally,
all
labels
list
precautions
when
applying
the
products
adjacent
to
lettuce,
citrus,
or
cantaloupe.
The
labels
further
state
that
mixing
with
organophosphates
may
increase
non­
target
crop
phytotoxicity.
Special
restrictions
to
reduce
drift
potential
to
lettuce
and
citrus
appear
on
all
the
labels.
Thidiazuron
products
cannot
be
applied
by
air
within
½
mile
of
lettuce
or
5
miles
downwind
of
the
point
of
application
when
citrus
is
in
flush
in
the
Rio
Grande
valley
of
Texas.
Ground
applications
are
restricted
to
100
ft
downwind
from
the
point
of
application
for
lettuce
or
½
mile
downwind
from
the
point
of
application
when
citrus
is
in
flush.
No
restrictions
are
prescribed
for
cantaloupe.

Phytotoxicity
and
Downwind
Distance
­
Spray
drift
from
aerial
and
ground
applications
may
also
impact
non­
target
plants
or
other
crops
grown
adjacent
to
cotton,
although
the
density
of
the
spray
droplets
is
expected
to
be
considerably
lower
in
these
areas.
Thidiazuron
labels
do
not
have
many
restrictions
on
how
and
under
what
conditions
the
product
may
be
applied.
For
example,
there
are
no
restrictions
on
droplet
size
or
boom
height.
Using
EFED's
current
AgDRIFT
computer
model
and
registrant
phytotoxicity
data,
it
is
possible
to
estimate
distances
downwind
from
application
areas
at
which
a
particular
toxic
effect
level
would
be
experienced
by
a
particular
tested
plant
species.
These
estimates
can
be
presented
for
combinations
of
aerial
and
ground
applications
for
varying
spray
droplet
size
in
the
form
of
three­
dimensional
bar
charts.
To
calculate
the
EC
10
­
90
values
in
increments
of
10,
the
EC
25
values
from
the
seedling
emergence
and
vegetative
vigor
studies
used
for
RQ
calculation
are
used
in
conjunction
with
the
toxicity
slopes
from
each
of
these
studies1.
Unfortunately
slopes
for
only
two
of
the
ten
crops
for
seedling
emergence
tests
and
four
of
the
ten
crops
tested
for
vegetative
vigor
are
currently
available.
These
EC
10
­
90
values
and
the
maximum
application
rate
for
cotton
were
entered
into
an
Excel
spreadsheet
with
Tier
1
Ag
DRIFT
(
version
2.01).
Calculated
downwind
deposition
levels
were
then
compared
to
the
EC
10
­
90
values
to
identify
the
downw
distance
at
which
the
EC
10
­
90
values
would
be
reached.

The
few
crops
for
which
downwind
distances
could
be
calculated
include
lettuce
and
turnip
for
the
seedling
emergence
tests,
and
lettuce,
cucumber,
tomato,
and
soybean
for
the
vegetative
vigor
tests.
Although
these
crops
were
the
most
sensitive
in
the
available
two
tests,
the
current
labels
Page
26
of
129
contain
warnings
and
specific
instructions
concerning
the
use
of
thidiazuron
on
lettuce,
cantaloupe,
and
citrus.
The
language
from
one
of
the
labels
is
the
following:

"
Particular
care
should
be
taken
when
applying
Dropp
®
UltraTM
adjacent
to
lettuce,
citrus,
or
cantaloupe."

"
In
addition,
for
citrus
crops,
do
not
apply
Dropp
®
UltraTM
by
air
when
citrus
in
flush
is
within
five
(
5)
miles
downwind
of
the
point
of
application.
Do
not
apply
Dropp
®
UltraTM
by
ground
when
citrus
in
flush
is
within
one­
half
(
1/
2)
mile."

The
bar
graphs
for
the
data
for
which
we
have
slopes
are
presented
on
the
following
pages
for
aerial
and
ground
application
under
varying
droplet
sizes.
Following
the
graphs
is
a
discussion
of
their
interpretation
and
EFED
policy
for
terrestrial
plants.
Page
27
of
129
10
20
30
40
50
60
70
80
90
t
urnip
let
t
uce
0
50
100
150
200
Percent
Effect
No­
Spray
Zone
(
f
t
)
Aerial:
Coarse
Spray
(
Seedling
emergence)
Page
28
of
129
10
20
30
40
50
60
70
80
90
t
urnip
let
tuce
0
50
100
150
200
250
300
Percent
Effect
No­
Spray
Zone
(
ft)
Aerial:
Medium
Spray
(
Seedling
emergence)
Page
29
of
129
10
20
30
40
50
60
70
80
90
0
200
400
600
800
1000
Pe
rce
nt
Effe
ct
Aerial:
Fine
Spray
(
Seedling
emergence)

turnip
lettuce
Page
30
of
129
10
20
30
40
50
60
70
80
90
soybean
tomato
cucumber
let
tuce
0
200
400
600
800
1000
Percent
Effect
No­
Spray
Zone
(
ft)
Aerial:
Coarse
Spray
(
Vegetative
vigor)
Page
31
of
129
10
20
30
40
50
60
70
80
90
soybean
t
omato
cucumber
let
t
uce
0
200
400
600
800
1000
Percent
Effect
No­
Spr
ay
Zone
(
ft)
Aerial:
Medium
Spray
(
Vegetative
vigor)
Page
32
of
129
10
20
30
40
50
60
70
80
90
soybean
cucumber
0
100
200
300
400
500
600
700
800
900
1000
Percent
Effect
No­
Spray
Zone
(
ft)
Aerial:
Fine
Spray
(
Vegetative
vigor)
soybean
tomato
cucumber
lettuce
Page
33
of
129
10
20
30
40
50
60
70
80
90
turnip
lettuce
0
1
2
3
4
5
6
7
8
9
10
Percent
Effect
No­
Spray
Zone
(
ft)
Ground:
Low
Boom,
Medium­
Coarse
Spray
(
Seedling
emergence)
Page
34
of
129
10
20
30
40
50
60
70
80
90
turnip
lettuce
0
2
4
6
8
10
12
14
Percent
Effect
No­
Spray
Zone
(
ft)
Ground:
HIgh
Boom,
Medium­
Coarse
Spray
(
Seedling
Emergence)
Page
35
of
129
10
20
30
40
50
60
70
80
90
turnip
lettuce
0
2
4
6
8
10
12
14
Percent
Effect
No­
Spray
Zone
(
ft)
Ground:
Low
Boom,
Medium
Spray
(
Seedling
emergence)
Page
36
of
129
10
20
30
40
50
60
70
80
90
t
urnip
let
t
uce
0
1
0
20
30
40
50
60
70
No­
Spr
ay
Zone
(
ft)
Ground:
HIgh
Boom,
Medium
Spray
(
Seedling
emergence)
Page
37
of
129
10
20
30
40
50
60
70
80
90
soybean
tomato
cucumber
let
tuce
0
50
100
150
200
250
300
350
400
Percent
Effect
No­
Spray
Zone
(
ft)
Ground:
Low
Boom,
Medium­
Coarse
Spray
(
Vegetative
vigor)
Page
38
of
129
10
20
30
40
50
60
70
80
90
soybean
tomato
cucumber
lettuce
0
100
200
300
400
500
600
Percent
Effect
No­
Spray
Zone
(
ft)
Ground:
HIgh
Boom,
Medium­
Coarse
Spray
(
Vegetative
vigor)
Page
39
of
129
10
20
30
40
50
60
70
80
90
soybean
cucumber
0
100
200
300
400
500
600
700
P
e
rcent
Effe
ct
No­
Spray
Zone
(
ft)
Ground:
Low
Boom,
Medium
Spray
(
Vegetative
vigor)
Page
40
of
129
10
20
30
40
50
60
70
80
90
soybean
t
omato
cucumber
let
t
uce
0
1
00
200
300
400
500
600
700
800
900
1
000
Pe
r
ce
n
t
Ef
fe
c
t
No­
Spray
Zone
(
ft)
Ground:
HIgh
Boom,
Medium
Spray
(
Vegetative
vigor)
Page
41
of
129
EFED
policy
with
regard
to
non­
endangered
terrestrial
plants
is
that
the
LOC
is
exceeded
when
the
environmental
exposure
concentration
is
greater
than
the
EC
25
.
In
the
case
of
thidiazuron,
aerial
application
is
the
most
common
mode
of
application,
and,
as
demonstrated
in
the
charts
above,
no­
spray
zones
for
the
EC
30
effect
levels
range
from
>
60
ft
for
course
sprays
to
over
1000
ft.
for
fine
sprays
for
the
most
sensitive
crop
tested
so
far
(
lettuce).
Ground
applications
indicate
that
no­
spray
zones
for
the
EC
30
effect
level
range
from
<
3
ft
for
low
boom,
medium­
course
spray
to
<
200
ft
for
high
boom
medium
sprays.
The
charts
also
show
similar
trends
for
the
other
crops.

The
endangered
species
terrestrial
plant
LOC
is
exceeded
when
the
environmental
concentration
is
greater
than
the
EC
05
.
Aerial
applications
of
thidiazuron
indicate
that
the
no­
spray
zone
the
EC
10
effect
level
ranges
from
>
95
ft.
for
course
sprays
to
>
1000
ft
for
fine
sprays
for
lettuce.
Ground
applications
ranges
from
>
95
ft
for
low
boom,
medium
course
sprays
to
<
1000
ft
for
high
boom,
medium
sprays.

The
results
of
this
analysis
indicate
that
downwind
distance
for
a
specific
EC
x
can
be
determined
for
four
of
the
crops
which
were
tested.
All
the
factors
influencing
the
downwind
drift
distance
including
droplet
size,
wind
speed,
boom
height,
method
of
application,
and
targeted
toxicity
effect
should
be
considered
when
placing
restrictions
on
labels.

Endocrine
Disruption
Assessment
The
2­
generation
reproduction
study
with
rats
indicates
the
potential
for
endocrine
disruption,
based
on
delayed
sexual
maturation
and
disruption
of
the
estrous
cycle.
The
reproductive
NOAEC
and
LOAEC
values
based
on
reduction
of
litter
size
are
400
and
1200
mg/
kg­
diet,
respectively.
The
measured
NOAEL
and
LOAEL
were
35.4
and
108.5
mg/
kg­
bw/
da,
respectively.
This
reproductive
effect
could
be
an
indicator
of
potential
endocrine
disruption
in
mammals
or
other
organisms.

EPA
is
required
under
the
Federal
Food,
Drug,
and
Cosmetic
Act
(
FFDCA),
as
amended
by
the
Food
Quality
Protection
Act
(
FQPA),
to
develop
a
screening
program
to
determine
whether
certain
substances
(
including
all
pesticide
active
and
other
ingredients)
"
may
have
an
effect
in
humans
that
is
similar
to
an
effect
produced
by
a
naturally
occurring
estrogen,
or
other
such
endocrine
effects
as
the
Administrator
may
designate."
Following
the
recommendations
of
its
Endocrine
Disruptor
Screening
and
Testing
Advisory
Committee
(
EDSTAC),
EPA
determined
that
there
was
scientific
bases
for
including,
as
part
of
the
program,
the
androgen
and
thyroid
hormone
systems,
in
addition
to
the
estrogen
hormone
system.
EPA
also
adopted
EDSTAC's
recommendation
that
the
Program
include
evaluations
of
potential
effects
in
wildlife.
For
pesticide
chemicals,
EPA
will
use
The
Federal
Insecticide,
Fungicide,
and
Rodenticide
Act
(
FIFRA)
and,
to
the
extent
that
effects
in
wildlife
may
help
determine
whether
a
substance
may
have
an
effect
in
humans,
FFDCA
authority
to
require
the
wildlife
evaluations.
As
the
science
develops
and
resources
allow,
screening
of
additional
hormone
systems
may
be
added
to
the
Endocrine
Disruptor
Screening
Program
(
EDSP).
When
the
appropriate
screening
and/
or
testing
protocols
being
considered
under
the
Agency's
EDSP
have
been
developed,
thidiazuron
and
its
degradates
may
be
subjected
to
additional
screening
and/
or
testing
to
better
characterize
effects
related
to
endocrine
disruption.
Page
42
of
129
Endangered
Species
Assessment
The
Agency's
level
of
concern
for
endangered
and
threatened
non­
target
terrestrial
plants
and
mammals
is
exceeded
for
the
use
of
thidiazuron
on
cotton.

Action
Area
For
listed
species
assessment
purposes,
the
action
area
is
considered
to
be
the
area
affected
directly
or
indirectly
by
the
Federal
action
and
not
merely
the
immediate
area
involved
in
the
action.
At
the
initial
screening­
level,
the
risk
assessment
considers
broadly
described
taxonomic
groups
and
so
conservatively
assumes
that
listed
species
within
those
broad
groups
are
collocated
with
the
pesticide
treatment
area.
This
means
that
terrestrial
plants
and
wildlife
are
assumed
to
be
located
on
or
adjacent
to
the
treated
site
and
aquatic
organisms
are
assumed
to
be
located
in
a
surface
water
body
adjacent
to
the
treated
site.
The
assessment
also
assumes
that
the
listed
species
are
located
within
an
assumed
area
which
has
the
relatively
highest
potential
exposure
to
the
pesticide,
and
that
exposures
are
likely
to
decrease
with
distance
from
the
treatment
area.
Section
II
of
this
risk
assessment
presents
the
pesticide
use
sites
that
are
used
to
establish
initial
collocation
of
species
with
treatment
areas.

If
the
assumptions
associated
with
the
screening­
level
action
area
result
in
RQs
that
are
below
the
listed
species
LOCs,
a
"
no
effect"
determination
conclusion
is
made
with
respect
to
listed
species
in
that
taxa,
and
no
further
refinement
of
the
action
area
is
necessary.
Furthermore,
RQs
below
the
listed
species
LOCs
for
a
given
taxonomic
group
indicate
no
concern
for
indirect
effects
upon
listed
species
that
depend
upon
the
taxonomic
group
covered
by
the
RQ
as
a
resource.
However,
in
situations
where
the
screening
assumptions
lead
to
RQs
in
excess
of
the
listed
species
LOCs
for
a
given
taxonomic
group,
a
potential
for
a
"
may
affect"
conclusion
exists
and
may
be
associated
with
direct
effects
on
listed
species
belonging
to
that
taxonomic
group
or
may
extend
to
indirect
effects
upon
listed
species
that
depend
upon
that
taxonomic
group
as
a
resource.
In
such
cases,
additional
information
on
the
biology
of
listed
species,
the
locations
of
these
species,
and
the
locations
of
use
sites
could
be
considered
to
determine
the
extent
to
which
screening
assumptions
regarding
an
action
area
apply
to
a
particular
listed
organism.
These
subsequent
refinement
steps
could
consider
how
this
information
would
impact
the
action
area
for
a
particular
listed
organism
and
may
potentially
include
areas
of
exposure
that
are
downwind
and
downstream
of
the
pesticide
use
site.

Species
Affected
The
preliminary
risk
assessment
for
listed
species
indicates
that
thidiazuron
exceeds
the
endangered
species
LOCs
for
the
following
combinations
of
analyzed
uses
and
species:

°
Use
of
thidiazuron
on
cotton
indicate
that
chronic
LOCs
are
exceeded
for
mammals
foraging
on
short
grass
and
broadleaf
forage
and
small
insects.

°
Use
of
thidiazuron
on
cotton
results
in
potential
risks
to
listed
species
of
plants.
Page
43
of
129
County­
level
location
data
for
listed
species
(
terrestrial
plants
and
mammals)
were
compared
with
county­
level
information
on
crop
production
to
identify
coarsely
overlaps
of
listed
species
with
the
proposed
labeled
uses
of
thidaizuron.
This
analysis
was
limited
to
those
counties
with
10
or
more
acres
of
land
in
production
for
the
labeled
crops.
The
results
are
presented
below:

Numbers
of
Listed
Plant
and
Mammal
Species
in
States
with
at
Least
10
Acres
of
Cotton
State
Number
of
Listed
Species
Plants
Mammals
Arkansas
2
­

California
49
9
Florida
5
4
Georgia
14
3
Kansas
1
­

Louisiana
­
2
Mississippi
­
1
Missouri
5
1
New
Mexico
5
5
North
Carolina
17
3
Oklahoma
­
1
South
Carolina
10
­

Tennessee
4
2
Texas
19
3
Virginia
2
1
IV.
Environmental
Fate
Assessment
Basis
This
assessment
is
based
on
an
integration
of:
1)
environmental
fate
study
data
from
previously
reviewed
studies,
in
some
cases
with
subsequent
amendments,
addenda,
or
other
written
explanatory
responses
or
updated
information;
2)
environmental
fate
study
data
from
the
current
review
of
new
fate
studies
submitted
to
support
the
re­
registration
of
thidiazuron;
3)
intrinsic
physical/
chemical
properties;
and
4)
information
from
product
labels.
As
with
all
EFED
fate
assessments,
it
does
not
take
into
consideration
any
alteration
of
the
environmental
fate
properties
of
thidiazuron
that
may
be
associated
with
the
addition
of
co­
formulated
pesticides
(
currently
Page
44
of
129
diuron
or
dimethipin);
so­
called
"
inert"
ingredients
(
formulants);
tank
mixtures
with
other
pesticides,
for
example,
organophosphates,
for
which
label
statements
indicate
increased
phytotoxicity;
or
tank
mixes
with
adjuvants,
such
as
surfactants
or
oils,
for
which
product
label
statements
indicate
"
improved
performance."

Status
of
Environmental
Fate
Data
Although
some
of
the
submitted
fate
studies
had
deficiencies,
taken
as
a
whole
and
within
the
constraints
stipulated
in
the
fate
assessment,
the
data
enable
the
Agency
to
adequately
assess
the
environmental
fate
of
thidiazuron.
Although
no
foliar
dissipation
studies
are
available
to
the
Agency
at
this
time
(
these
are
not
generally
required),
having
such
data
would
make
any
fate
assessment
more
precise,
especially
in
the
case
of
a
defoliant
such
as
thidiazuron.
However,
as
discussed
in
the
fate
assessment,
if
dislodgement
from
or
transformation
in/
on
treated
plants
were
to
be
an
important
fate
pathway,
then
EFED's
inferences
from
existing
fate
studies
and
assumptions
for
exposure
modeling
for
parent
and
potential
degradates
should
reasonably
and
conservatively
cover
the
possibility.
If
the
registrant
wishes
to
demonstrate
that
definitive
data
on
foliar
dissipation
would
substantially
affect
any
of
EFED's
inferences,
assumptions,
or
environmental
risk
conclusions,
the
registrant
should
submit
appropriate
data.
Otherwise,
except
for
spray­
drift
requirements,
the
Agency
needs
no
additional
environmental
fate
studies
at
this
time.

Required
field
spray­
drift
and
spray
droplet­
size
spectral
data
have
not
been
submitted.
However,
since
the
applicant
is
a
member
of
the
Spray
Drift
Task
Force
(
SDTF),
the
registrant
may
be
able
to
satisfy
the
spray­
related
requirements
with
data
the
SDTF
has
submitted
to
the
Agency.

Fate
Assessment
Abstract.
In
soil,
thidiazuron
is
persistent,
as
evidenced
by
laboratory
and
field
half­
lives
and
rotational
crop
intervals
on
the
order
of
one
year.
It
has
intermediate
soil
sorption
coefficients.
Such
persistence
and
intermediate
mobility
would
allow
some
year­
to­
year
accumulation
over
time
and,
therefore,
more
opportunity
for
favorable
conditions
for
runoff
from
application
sites
to
occur.
With
a
one­
year
half­
life,
build­
up
in
soil
could
asymptotically
approach
twice
that
of
annually
applied
amounts.

When
thidiazuron
reaches
surface
water
photolysis
is
expected
to
be
the
major
route
of
transformation;
other
degradative
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
two
photoproducts.
One
of
the
photodegradates
is
a
structural
isomer
of
parent,
whereas
the
other
has
a
substantially
altered
chemical
structure.
The
photolysis
process
requires
special
modeling
considerations.

Based
on
its
solubility,
vapor
pressure,
and
other
laboratory
evidence,
thidiazuron
is
non­
volatile.
Based
on
its
relatively
low
octanol/
water
partitioning
coefficient,
thidiazuron
should
not
bioconcentrate.

No
data
on
foliar
dissipation
are
available
to
EFED.
Since
thidiazuron
is
used
to
defoliate
cotton
prior
to
harvest,
dislodgement
from
or
transformation
in/
on
leaves
may
be
an
important
fate
pathway.
The
effect
of
this
uncertainty
and
alternative
assumptions
on
the
risk
assessment
are
considered.
Page
45
of
129
N
H
N
H
N
N
S
O
Physical/
Chemical
Properties
Thidiazuron's
chemical
structural
formula,
various
names
and
table
of
physical/
chemical
properties
are
as
follows:

Common
Name:
Thidiazuron
Other
Designations:
AE
B049537,
SN
49537,
NC
19211,
Hoe
080279
IUPAC
name:
1­
Phenyl­
3­(
1,2,3­
thiadiazol­
5­
yl)
urea
CAS
name:
N­
Phenyl­
N'­
1,2,3,­
thiadiazol­
5­
yl
urea
CAS
No.:
51707­
55­
2
(
330­
54­
1
also
found)
PC
Code
No.:
120301
Empirical
formula:
C
9
H
8
N
4
O
S
Molecular
Weight:
220.25
SMILES
string:
O=
C(
Nc1ccccc1)
Nc1cnns1
Page
46
of
129
Physical
and
Chemical
Properties
of
Thidiazuron
(
from
product
chemistry
review)

GLN
Requirement
MRID
Status
Result
or
Deficiency
830.6302
C
o
l
o
r
459340­
01
A
TGAI:
yellow
Brown;
PAI:
Brown
830.6303
Physical
state
"
"
"
A
TGAI:
amorphous
solid;
PAI:
crystalline
solid
830.6304
Odor
"
"
"
A
TGAI
&
PAI:
characteristics
Sulfur
like
odor
830.6313
Stability
to
normal
and
elevated
temperatures,
metals,
and
metal
ions
"
"
"
A
TGAI:
None
PAI:
None
830.6314
Oxidation/
reduction:
chemical
incompatibility
"
"
"
A
TGAI:
No
reaction
with­
H
2
O,
KMnO
4
,
Zn
or
CO
2
PAI:
No
reaction
with­
H
2
O,
KMnO
4
,
Zn
or
CO
2
830.6315
Flammability
NA
830.6316
Explodability
459340­
01
A
TGAI:
exotherm
onset
observed
at
116.30C
PAI:
NA
830.6317
Storage
stability
459340­
01
I
1
year
under
progress
830.6319
Miscibility
NA
830.6320
Corrosion
characteristics
459340­
01
I
1
year
under
progress
830.7000
pH
459340­
01
A
TGAI:
5.21
@
20
0C
PAI:
6.50
830.7050
UV/
Visible
absorption
459340­
01
A
8
max
=
238
nm;
,
=
985
M­
1
cm­
1
830.7100
Viscosity
NA
830.7200
Melting
point
459340­
01
A
PAI:
2230C
(
decomposition)

830.7220
Boiling
point
NA
830.7300
Relative
Density
459340­
01
A
TGAI:
0.324
gm/
cc
at
20
0C
830.7370
Dissociation
constants
in
water
413649­
01
(
cited)
A
PAI:
pKa
=
8.86
25
0C
830.7550
Partition
coefficient
(
n­
octanol/
water),
shake
flask
method
413649­
06
(
cited)
A
PAI:
K
o/
w
=
50.0
(
25
0C,
pH
=
7.3)

830.7840
Water
solubility:
column
elution
method;
shake
flask
method
413649­
06
417862­
02
(
cited)
A
PAI:
water
=
31.0
mg/
L
(
pH
=
7.0;
25
0C)
organic
solvents
(
g/
l):
acetone,
6.67;
CH
2
Cl
2
,0.003;
ethyl
acetate,
1.10;
hexane,
0.002;
MeOH,
4.20;
Toluene,
0.40
(
all
measured
at
20
0C)

830.7950
Vapor
pressure
942460­
01
(
cited)
A
PAI:
3.5
x
10­
9
mPa
@
20
0C
A
=
Acceptable;
N
=
Unacceptable
(
see
Deficiency);
N/
A
=
Not
Applicable.;
G
=
Data
gap;
I
=
In
progress
or
need
upgrade
As
the
table
shows,
thidiazuron
is
a
weak
organic
acid
with
a
pKa
of
approximately
8.9.
Therefore,
at
pHs
found
in
most
aquatic
and
terrestrial
environments,
it
exists
mainly
in
neutral
form
(>
99%
neutral
at
pH
7
or
below,
88%
at
pH
8,
and
42%
at
pH
9).
Thidiazuron
is
nonvolatile
as
indicated
by
its
reviewer­
calculated
Henry's
Law
constant
(
H
=
2.5
x
10­
16
atm
m3/
mol
and
dimensionless
K
H
=
1.0
x
10­
14
at
20
°
C)
and
by
collateral
data
showing
the
absence
of
thidiazuron
in
collection
traps
for
volatile
products
in
various
laboratory
degradation
and
2Half­
lives
are
based
on
first­
order
linear
regression
of
time
(
x­
axis)
versus
the
logarithm
of
the
relative
concentration
(
percent
of
radioactivity)
of
thidiazuron
(
y­
axis).
These
experimental
half­
lives
were
then
adjusted
by
the
reviewer
to
the
EFED
standard
temperature
of
25
°
C
and
to
the
standard
soil
moisture
content
of
75%
of
1/
3­
bar
water
potential
(
suction)
by
the
methods
described
in
the
next
footnote.

3MRID
46119601,
Allan,
J.
G.,
2003;
EFED
review
24
May
2004.
Experimental
half
lives
were
adjusted
by
the
reviewer
to
the
EFED
standard
temperature
of
25
°
C
by
use
of
the
Arrhenius
equation
and
to
the
standard
soil
moisture
content
of
75%
of
1/
3­
bar
water
potential
(
suction)
by
use
of
the
Walker
equation,
as
described
in
the
Data
Evaluation
Record
(
DER).
Actual
study
conditions
were
20
°
C
and
40%
maximum
water
holding
capacity
(
MWHC);
under
these
conditions
half­
lives
were
163,
355,
and
322
days,
respectively,
as
extrapolated
from
study
periods
lasting
160­
168
days.

4MRID
41950101,
Feyerabend,
M.,
1991;
EFED
review
28
Apr
1993.
Previous
reviewer
incorrectly
reported
the
half­
life
as
111
days
at
21
°
C
and
78%
of
1/
3­
bar.
The
111­
day
value
was
the
registrant­
reported
DT50,
not
the
half­
life.
Based
on
this
reviewer's
calculation
using
standard
semi­
logarithmic
transformed
data,
the
experimental
half­
life
is
182
days
(
95%
confidence
range
of
155­
221
days).
After
adjustment
to
25
°
C
and
75%
of
1/
3­
bar
soil
water
potential
by
the
method
described
by
the
reviewer
in
the
DER
for
MRID
46119601
(
see
previous
footnote),
the
standard
half­
life
becomes
140
(
119­
170)
days.
(
The
registrant's
calculated
half­
life
using
untransformed,
simple
first­
order
data
was
147
days
(
no
confidence
range
reported.)

Page
47
of
129
metabolism
studies.
Its
relatively
low
n­
octanol
to
water
partitioning
ratio
of
approximately
50
indicates
little
likelihood
of
bioconcentration.

Persistence­­
Degradation/
Metabolism
Half­
lives
In
standard
laboratory
studies,
thidiazuron
did
not
hydrolyze
(
MRID
42069203),
and
was
stable
against
anaerobic
metabolism
in
water
(
MRID
4266601)
and
soil
(
MRID
41945201).

Thidiazuron
was
relatively
long­
lived
in
aerobic
soil.
As
a
measure
of
its
persistence,
laboratory
aerobic
soil
metabolism
half­
lives2
in
four
soils
were
approximately
206
(
173­
254),
253
(
187­
393),
436
(
310­
737),
and
140
(
119­
170)
days
(
95%
confidence
intervals
in
parentheses
as
a
measure
of
precision).
The
first
three
listed
half­
lives
are
derived
from
MRID
461196013,
the
fourth
from
MRID
419501014.
The
average
of
these
four
values
is
259
days,
and
the
one­
tailed
upper
90%
confidence
bound
for
the
mean,
which
is
used
for
EFED
standard
environmental
modeling
purposes,
is
approximately
363
days
(
259­
day
average
plus
a
confidence
level
of
104
days).
Soil
metabolites
are
identified
in
a
Transformation
Products
(
degradates/
metabolites)
subsection
below.

Crop
rotational
intervals
also
provide
a
measure
of
thidiazuron's
persistence
in
soil.
Product
labels
list
rotational
crop
intervals
as
long
as
one
year.

Another
index
of
thidiazuron's
persistence
in
soil
is
dissipation
in
terrestrial
field
studies.
It
should
be
recognized,
however,
that
field
dissipation
is
punctuated
by
variable
climatic
events,
and
generally
involves
a
combination
of
physical
dispersal/
transport
(
leaching,
runoff,
volatilization)
and
chemical
and/
or
biochemical
transformation.
Furthermore,
transformation
does
not
necessarily
imply
detoxification,
since
byproducts
may
also
be
toxic.
Results
from
terrestrial
field
studies
are
as
follows:
Page
48
of
129
In
three
supplemental,
bare­
ground
field
studies
(
MRID
44454001),
each
conducted
for
18
months,
linear
first­
order
dissipation
half­
lives
were
237
days
(
California),
173
days
(
Florida),
and
161
days
(
North
Carolina).
Reviewer­
calculated
respective
times
required
for
90%
loss,
based
on
simple
first­
order
kinetics
were
approximately
800,
600,
and
500
days.
Corresponding
registrantcalculated
DT90
values,
based
on
a
two­
compartment
model,
were
1190,
655,
and
475
days.
Although
these
measures
of
field
persistence
are
conventionally
reported,
because
of
the
inherent
variability
and
randomness
in
dissipation
processes,
they
should
be
interpreted
only
in
a
crude,
qualitative
sense.
Three
transformation
products
were
sporadically
identified,
but
were
most
frequently
below
the
limit
of
quantitation;
therefore,
a
kinetic
pattern
could
not
be
established.
In
another
supplemental
study
in
Florida
(
MRID
41761105),
there
was
no
significant
dissipation
of
thidiazuron
during
a
nine­
month
study
period
in
which
only
small
amounts
of
two
transformation
products
were
detected.
Identified
soil
transformation
products
and
observations
concerning
mobility
are
discussed
separate
subsections
below.

Thus,
laboratory
aerobic
soil
metabolism
studies,
product
label
statements,
and
field
dissipation
studies
show
a
general
consistency
and
a
similar
degree
of
persistence
for
thidiazuron.
The
demonstrated
persistence
would
allow
some
year
to
year
accumulation.
With
the
hypothetical
assumption
that
there
is
no
significant
physical
movement
of
thidiazuron
from
a
site
of
application
for
several
years,
then,
with
the
upper
90%
confidence
bound
half­
life
of
approximately
one
year
and
with
uniform
annual
applications,
the
asymptotic
limit
of
build­
up
in
soil
would
result
in
soil
concentrations
that
would
approach
twice
that
of
the
yearly
application
amount.

Photolysis
of
thidiazuron
requires
special
consideration.
In
water
(
original
MRID
41188201,
related
follow­
up
MRIDs
41364910
,
43075202,
and
fate
overview
document
MRID
44436901),
it
undergoes
relatively
rapid
(
see
below),
pH
dependent,
branching
photolysis
into
two
photoproducts.
Formation
of
these
products
is
in
constant
ratio,
and
in
complementary
stoichiometric
yield
with
parent.
A
product
originally
identified
as
"
photoproduct
I"
and
subsequently
identified
as
AE
F132347
(
see
chemical
structure
in
Appendix
B)
is
an
isomer
of
parent
differing
only
in
the
relative
positions
of
the
sulfur
atom
and
the
two
nitrogen
atoms
in
the
5­
membered
ring.
Like
parent,
photoproduct
I
is
moderately
ecotoxic
(
slightly
more
ecotoxic
than
parent,
based
on
limited
data).
It
has
a
reviewer­
calculated
asymptotic
experimental
limit
of
production
of
approximately
77%
of
parent
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
This
product
was
stable
to
further
photolysis
under
the
experimental
study
conditions
and
durations.

Photoproduct
II
(
AE
C421200)
is
a
significantly
degraded,
practically
non­
ecotoxic
product,
and
has
a
complementary
reviewer­
calculated
asymptotic
limit
of
production
to
photoproduct
I
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
This
product
was
also
stable
to
further
photolysis
under
study
conditions.

Under
standard,
ideal
laboratory
exposure
conditions,
the
pH
dependent
photolysis
half­
lives
were
approximately
one
to
two
hours
(
adjusted
to
twelve
hours
of
sun
per
day).
[
Note:
When
these
half­
lives
are
put
directly
into
current
EFED
aquatic
modeling
scenarios,
because
of
water
depth,
clarity,
and
other
factors,
the
effective
or
practical
photolysis
half­
lives
become
equivalent
to
approximately
five
to
ten
days.]
For
the
purpose
of
aquatic
ecological
exposure
assessment,
we
protectively
assumed
the
pH
5
results
for
which
77%
of
parent
reaching
water
is
converted
to
the
stable
isomer
photoproduct
I
(
AE
F132347).
Under
these
conditions,
the
thidiazuron
photolytic
Page
49
of
129
half­
life
was
1.44
hours
(
0.0602
days).
Half­
lives
at
higher
pHs
were
somewhat
shorter
(
approximately
6%
shorter
at
pH
7
and
approximately
40%
shorter
at
pH
9.

To
further
simplify
exposure
estimates
for
aquatic
ecological
assessment,
rather
than
separately
apportioning
parent
and
photoproduct
I
exposures
and
toxicities,
we
chose
to
add
exposure
concentrations
of
parent
and
photoproduct
I
(
ignoring
the
practically
non­
toxic
ecotoxic
photoproduct
II),
and
use
the
toxicity
of
the
slightly
more
ecotoxic
photoproduct
I
for
parent
also.
Whether
we
use
this
simplified
procedure
or
add
the
separate
contributions
from
parent
and
photoproduct
I
makes
no
meaningful
difference
in
the
aquatic
ecological
risk
assessment
in
this
particular
case.
Appendix
D
describes
in
detail
the
special
quantitative
procedure
used
for
estimating
aquatic
exposure
concentrations.
For
surface
drinking
water
sources
for
humans,
we
provide
two
other
alternatives,
depending
on
potential
human
health
concerns
for
parent
and
photoproducts;
these
alternatives
are
discussed
in
the
Drinking
Water
Assessment
Appendix
A.
Because
of
thidiazuron's
demonstrated
persistence
in
soil,
modeled
concentrations
in
water
could
be
underestimated
by
as
much
as
a
factor
of
two.

A
unacceptable
laboratory
soil
photolysis
study
conducted
on
thin­
plated
soil
samples
had
numerous
flaws
and
inconsistencies
(
MRID
00156241
and
MRID
41364902,
the
latter
being
essentially
a
re­
submission
of
a
published
version
of
the
unpublished
former;
and
fate
overview
document
MRID
44436901,
which
summarized
study
issues
and
responses).
The
previously
cited
unacceptability
of
the
study
is
confirmed
by
the
current
reviewer
(
who
has
noticed
even
additional
study
irregularities).
Ostensibly,
the
study
authors
maintained
that
soil
photolysis
was
occurring
at
a
relatively
rapid
rate,
with
a
half­
life
on
the
order
of
one
hour
or
less,
and
that
the
only
significant
product
was
the
isomer
photoproduct
I
(
AE
F132347).
The
reviewer
notes
that
photoproduct
I
is
the
same
photoisomer
found
in
the
aqueous
photolysis
study
discussed
above.
In
view
of
the
study
unacceptability
and
the
inherent
marked
physical
differences
between
the
effectiveness
of
photolysis
on
soil
that
is
plated
thin
(
0.5
mm)
on
glass
an
that
applied
on
soil
in
the
field,
the
registrant
and
the
Agency
are
in
agreement
that
terrestrial
field
studies
would
serve
to
determine
the
relative
importance
of
soil
photodegradation.
In
all
field
studies
(
the
four
studies
discussed
above),
thidiazuron
was
sprayed
on
bare
soil
without
incorporation.
In
these
studies
thidiazuron
was
long­
lived,
and
there
was
only
minimal
evidence
of
photolysis.
Hence,
to
whatever
extent
photolysis
may
occur
in/
on
field
soil,
it
is
definitely
a
slow
process.

Transformation
Products
(
degradates/
metabolites)

Chemical
structures,
chemical
names,
and
other
forms
of
past
and
present
identifiers
are
in
Appendix
B.
Naming
conventions,
different
company
codes
for
the
same
compounds,
and
incorrectly
named
compounds
have
been
and
can
easily
be
tedious
sources
of
confusion
and
potential
error.
Major
photodegradates
in
water
and
soil
have
already
been
discussed.

In
the
two
submitted
laboratory
aerobic
metabolism
studies
identified
above,
no
major
(
defined
as
>
10%
of
applied
radioactivity)
organic
transformation
products
were
isolated
or
identified
in
any
of
a
total
of
four
soils
tested.
In
the
most
recent
study
(
MRID
46119601),
the
three
soils
tested
were
treated
with
thidiazuron
radiolabeled
with
14C
in
the
thiadiazol­
ring
position;
in
the
other
study
(
MRID
41950101),
the
one
soil
was
treated
with
thidiazuron
uniformly
radiolabeled
with
14C
in
the
phenyl
ring.
Such
labeling
insures
that
major
molecular
changes
can
be
monitored.
Page
50
of
129
In
the
three
soils
treated
with
the
thidiazol­
ring
label
(
MRID
46119601),
the
only
organic
transformation
product
identified
was
AE
F132345
(
thidiazolylurea
or
1,2,3­
thiaiazol­
5­
ylurea).
In
the
soil
in
which
metabolism
was
fastest,
AE
F132345
appeared
to
reach
an
approximately
flat
maximum
concentration
of
roughly
6­
9%
of
applied
radioactivity
during
the
period
from
approximately
88
days
to
study
end
at
168
days.
The
broad
plateau
is
evidence
that
AE
F132345
would
not
form
in
greater
yield,
and
that
it
may
be
a
persistent
metabolite.
Maximum
concentrations
of
AE
F132345
in
the
other
two
soils
were
roughly
1%
to
3%.
Extracted
substances
that
were
not
identified
in
any
soil
at
any
sampling
interval
comprised
no
more
than
roughly
1­
6%
of
applied
radioactivity.
Non­
extracted
14C
material
(
so­
called
"
bound"
residues)
in
these
soils
increased
variably
from
approximately
16­
32%
of
applied
at
study
end.
In
one
soil,
14CO
2
reached
a
broad
total
plateau
of
5­
12%
of
applied
radioactivity
during
later
study
periods.
In
the
two
other
soils,
14CO
2
totaled
around
1­
2%
and
6­
8%,
respectively,
during
later
study
periods.
For
all
three
soils,
volatile
organics
totaled
#
0.1%
of
applied
radioactivity.
The
data
evaluation
record
(
DER)
for
the
three­
soil
study
has
additional
details
for
individual
soils,
and
a
brief
comment
on
a
postulated
transformation
pathway.

In
the
one
soil
treated
with
the
uniformly
labeled
phenyl
ring
(
MRID
41950101),
three
very
minor
metabolites
were
identified,
and
at
least
one
these
may
have
been
an
initial
impurity.
All
concentrations
of
each
were
<
0.8%
of
applied
radioactivity.
The
three
minor
metabolites
were:
AE
F132347
(
0.8%),
the
compound
that
may
have
been
an
initial
impurity
and
which
is
the
same
compound
identified
above
as
photoproduct
I;
phenylurea
(
0.3%);
and
AE
F147706
(
0.8%).
(
Appendix
B
shows
chemical
structures
and
has
various
past
and
present
forms
of
identification.)
Of
extracted
substances,
approximately
3%
of
applied
radioactivity
was
not
identified.
By
the
end
of
the
361­
day
study,
unextracted
("
bound")
residues
increased
to
approximately
45%
of
applied,
and
14CO
2
accounted
for
approximately
21%.

In
the
supplemental
terrestrial
field
studies
cited
above
(
MRID
44454001
and
MRID
41761105),
three
transformation
products
were
detected,
but
rarely
above
the
limit
of
quantitation
of
0.01
parts
per
million
(
ppm).
The
three
compounds
were
AE
F132345,
AE
F132347
(
photoproduct
I),
and
phenylurea.
Since
they
were
almost
never
detected
above
the
limit
of
quantitation
of
0.01
ppm
for
any
sampling
interval,
no
kinetic
analysis
is
possible
for
them.
The
maximum
concentrations
for
the
sporadic
detections
of
these
products
ranged,
without
correlation,
from
roughly
<
4%
to
perhaps
as
high
as
19%
of
the
maximum
concentration
ever
detected
for
parent.

Thus,
based
on
laboratory
and
field
studies,
thidiazuron
undergoes
very
slow
transformation
in
soil
by
aerobic
metabolism,
with
an
indefinite
contribution
from
photolysis.
Laboratory
studies
further
suggest
that
the
identified
transformation
products
will
slowly
be
converted
in
soil
into
the
carbon
pool
of
bound
residues,
carbon
dioxide,
and
other
products
of
mineralization.

Mobility
in
Soil
Based
on
batch
equilibrium
sorption
coefficients
in
four
soils
(
MRID
41364909,
three
German
standard
soils
and
one
United
Kingdom
soil),
thidiazuron
has
intermediate
mobility,
as
indicated
by
Freundlich
adsorption
coefficients
of
approximately
4.4,
7.3,
16,
and
19
Freundlich
units.
Slopes
(
1/
n)
of
the
isotherms
ranged
from
approximately
0.7­
0.8.
Sorption
correlated
reasonably
well
Page
51
of
129
with
organic
carbon,
and
respective
Freundlich
coefficients
normalized
for
organic
carbon
(
Kfoc)
were
approximately
900,
800,
800,
and
500.
Soil
textural
identification
and
detailed
sorption
values
are
in
Appendix
C.

In
the
four
supplemental
terrestrial
field
studies
in
bare
soil
discussed
above,
no
significant
leaching
was
apparent
for
parent
or
transformation
products.
However,
because
of
imposed
experimental
limitations
that
were
common
to
each
study
(
for
example,
limits
of
quantitation
and
the
absence
of
a
water
balance
or
use
of
a
tracer)
potential
for
leaching
was
not
clearly
established.
However,
based
on
the
intermediate
range
of
its
sorption
coefficients
and
the
supplemental
field
evidence,
leaching
should
not
be
major
route
of
dissipation.
Model­
estimated
potential
exposure
to
thidiazuron
from
surface
and
ground
drinking
water
source
are
presented
in
the
separate
Drinking
Water
section
of
this
document.

The
one
major
metabolite
found
in
laboratory
aerobic
soil
studies,
1,2,3­
thiadiazol­
5ylurea
(
also
identified
as
thidiazolylurea,
AE
132345,
and
ZK
85290
),
had
somewhat
lower
sorption
coefficients
than
parent.
In
four
United
States
soils,
its
Freundlich
adsorption
coefficients
were
approximately
1.5,
8.3,
2.0,
and
1.7
Freundlich
units.
Values
for
1/
n
ranged
from
approximately
0.8­
1.
Sorption
also
correlated
reasonably
well
with
organic
carbon,
and
respective
Freundlich
coefficients
normalized
for
organic
carbon
(
Kfoc)
were
approximately
200,
280,
170,
and
340.
Soil
textural
identification
and
detailed
sorption
values
are
in
the
Data
Evaluation
Record
(
DER)
for
MRID
44436902.
As
was
the
case
for
parent
in
the
same
supplemental
field
studies,
no
significant
leaching
pattern
was
evident
for
this
metabolite,
which
was
detected
sporadically
and
without
correlation
at
<
0.05
ppm.
However,
as
previously
stated,
potential
for
leaching
was
not
clearly
established
in
the
field.

Assumptions/
Limitations/
Uncertainties
No
data
on
foliar
dissipation
are
available
to
EFED.
Since
thidiazuron
is
used
to
defoliate
cotton
prior
to
harvest,
dislodgement
from
or
transformation
in/
on
leaves
may
be
an
important
fate
pathway.
Although
photolysis
was
the
rapid,
major
route
of
transformation
in
water,
in
field
soil
parent
was
long­
lived
with
only
minimal
evidence
of
photolysis
or
leaching.
However,
in
laboratory
plates
of
thin
soil,
the
photoisomer
AE
F132347
(
photoproduct
I)
was
a
quickly­
formed
major
degradate.
Thus,
whether
photolysis
in
or
on
cotton
plants
is
a
major
fate
process
is
unclear,
and
can
be
decided
only
by
experiment.
However,
based
on
available
data,
if
photolysis
were
to
be
substantial
on
foliage,
it
is
a
reasonable
inference
that
the
same
major
structural
isomer
formed
in
water
and
soil
also
be
produced
on
foliage.
In
this
case,
EFED's
modeling
assumptions
for
parent
and
the
photoisomer
should
cover
the
possibility,
and,
within
standard
model
limitations,
our
estimated
water
exposure
concentrations
remain
essentially
the
same.

It
bears
repeating
that
thidiazuron
is
persistent
in
soil,
as
evidenced
by
laboratory
and
field
halflives
of
the
order
of
one
year,
and
that
it
has
intermediate
soil
sorption
coefficients.
Such
persistence
and
intermediate
mobility
allows
some
year­
to­
year
build­
up
in
soil
over
time
and,
therefore,
greater
opportunity
for
favorable
conditions
for
runoff
from
application
sites
to
occur.
With
the
hypothetical
assumption
that
there
is
no
significant
physical
movement
of
thidiazuron
from
a
site
of
application
for
several
years,
then,
with
a
one­
year
half­
life
and
uniform
annual
applications,
the
asymptotic
limit
of
build­
up
would
result
in
soil
concentrations
that
would
5EFED's
Pesticides
in
Ground
Water
Database
has
no
thidiazuron
data.
The
United
States
Geological
Survey
(
USGS),
as
part
of
a
large
water
monitoring
program,
does
not
analyze
for
thidiazuron.
The
EPA
STORET
water
quality
databases
have
no
useful
information.

Page
52
of
129
approach
twice
that
of
the
yearly
application
amount.
Runoff
concentrations
would
be
affected
similarly.

V.
Drinking
Water
Assessment
Summary
There
are
no
useful
water
monitoring
data
for
thidiazuron
in
EFED's
standard
monitoring
sources5.
The
exposure
estimates
in
this
assessment
come
from
the
two
EFED
Tier
1
screeninglevel
models:
1)
FIRST
(
Ver.
1.0;
Aug.
1,
2001)
for
surface
water
concentrations
resulting
from
runoff
and
spray
drift
into
an
Index
Reservoir
and
2)
SCI­
GROW
(
Ver.
2.3;
Nov.
4,
2003)
for
ground
water
concentrations
resulting
from
leaching.
These
models
and
their
descriptions
are
available
at
the
EPA
internet
site:

http://
www.
epa.
gov/
oppefed1/
models/
water.

As
described
in
the
Fate
Assessment,
when
thidiazuron
reaches
surface
water
photolysis
is
expected
to
be
the
major
route
of
transformation;
other
degradative
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
the
two
photoproducts
identified
as
AE
F132347
and
AE
C421200.
The
first
is
a
structural
isomer
of
parent,
while
the
latter
has
a
substantially
altered
chemical
structure.
The
photolysis
process,
chemical
identification,
and
special
modeling
and
computational
considerations
are
in
Appendix
A.
Ground
water
is
not
expected
to
be
impacted
by
these
degradates
because
all
field
studies
show
that
parent
is
long­
lived
in
soil
(
half­
lives
of
the
order
of
one
year)
with
only
minimal
evidence
of
photolysis.

Modeling
Results.
The
following
table
shows
the
FIRST­
derived
potential
surface
water
concentrations
for
the
three
respective
combinations
of
1)
parent
plus
both
aqueous
photodegradation
products
(
most
conservative),
2)
parent
plus
photodegradate
1,
and
3)
parent
only
(
least
conservative).
Degradate
modeling
is
based
on
mass
balance
using
simultaneous
decline
and
formation
over
time.
All
reported
concentration
combinations
are
in
terms
of
parent
mass
chemical
equivalents.
However,
concentrations
for
each
photodegradate
can
easily
be
separated.

The
tabulated
exposure
concentrations
are
for
a
single
aerial
application
at
a
maximum
rate
of
0.3
lb
a.
i./
acre.
However,
as
specifically
illustrated
in
Appendix
A,
whether
the
total
annual
maximum
is
applied
all
at
once
or
is
split
in
two
(
as
specified
on
product
labels),
differences
are
negligible
for
the
particular
case
of
thidiazuron
because
of
its
long
life
in
soil.
Again,
complete
model
input/
output
tables
with
detailed
explanations
of
the
computational
procedures
used
to
handle
the
photodegradates
are
in
Appendix
A.
Page
53
of
129
Surface
Water
Concentrations
(
derived
from
FIRST
model,
Ver.
1.0)

THREE
ALTERNATIVE
DEGREES
OF
PROTECTION
PEAK
DAY
(
ACUTE)
CONCENTRATION
(
ppb
or
:
g/
L)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
(
ppb
or
:
g/
L)

Parent
+
Both
Photoproducts
3.5
1.0
Parent
+
AE
F132347
(
photoproduct
1)
3.5
0.82
Parent
Only
3.4
0.068
The
next
table
shows
the
SCI­
GROW­
estimated
potential
groundwater
exposure
concentration.
Groundwater
is
not
expected
to
be
impacted
by
photodegradates
because
all
field
studies
show
that
parent
is
long­
lived
in
soil
(
half­
lives
on
the
order
of
one
year)
with
only
minimal
evidence
of
photolysis
or
leaching.
However,
as
previously
discussed,
dislodgeability,
photolysis
(
or
other
chemical
changes)
in
or
on
plant
surfaces
are
uncertain.
Therefore,
it
is
possible
that
photodegradates
identified
in
water
and
soil
or
other
compounds
may
form
in
or
on
cotton
plants,
reach
the
soil
surface
at
unknown
rates,
and
be
subject
to
unknown
degrees
of
leaching
or
runoff.
EFED's
assessment
cannot
specifically
account
for
this
absent
information.
However,
based
on
all
available
fate
evidence,
it
appears
that
photodegradation
would
be
the
most
likely
candidate
for
any
rapid
degradation
of
thidiazuron
that
may
occur
on
plants.
If
this
is
the
case,
then,
to
a
first
approximation,
the
physical
and
chemical
fate
properties
of
the
photodegradates
should
be
similar
to
parent,
and
any
resulting
loss
in
parent
would
be
offset
by
production
of
photodegradates.
Therefore,
combined
concentrations
of
all
these
compounds
should
approximate
those
given
in
the
table
for
parent
only.

Groundwater
Concentration
(
derived
from
SCI­
GROW
regression
model,
Ver.
2.3
)

Acute
and
Chronic
Concentration*:
0.066
ppb
(:
g/
L)

*
As
also
noted
in
Appendix
A,
the
SCI­
GROW­
estimated
groundwater
concentration
given
here
is
an
extrapolation
beyond
the
regression
model
limits
for
Koc.
SCI­
GROW
was
developed
using
Koc
values
ranging
from
approximately
32
to
180
mL/
g
of
organic
carbon,
whereas
the
median
Koc
value
for
thidiazuron
is
783
mL/
g.
Extrapolation
increases
uncertainty,
but
without
ability
to
estimate
confidence.

VI.
Aquatic
Hazard,
Exposure,
and
Risk
Quotient
Calculation
Appendix
F
summarizes
the
results
for
toxicity
studies
material
to
this
risk
assessment.
Discussions
of
the
effects
of
thidiazuron,
formulated
product,
and
degradates
on
aquatic
taxonomic
groups
are
presented
in
the
following
sections.

Toxicity
to
Fish
Page
54
of
129
An
acute
freshwater
fish
toxicity
classification
(
slightly
toxic,
moderately
toxic,
and
practically
non­
toxic)
for
thidiazuron
cannot
be
definitively
established
because
available
acute
toxicity
data
(
MRID
420692­
01
and
420692­
02)
do
not
establish
an
LC50
(
the
endpoint
critical
to
classification).
However,
the
available
data
for
parent
thidiazuron
indicate
that
no
mortality
nor
signs
of
intoxication
were
observed
at
the
highest
concentration
tested
19
and
32
mg/
L.

Additional
acute
freshwater
toxic
testing
was
performed
on
three
metabolites
of
thidiazuron.
The
LC50
for
the
photodegradate
AE
F132347
was
established
at
6,700
µ
g/
L
(
MRID
462035­
08),
indicating
that
this
degradate
is
more
toxic
than
the
parent
thidiazuron.
This
compound
is
classified
as
moderately
toxic
to
freshwater
fish.
The
metabolite
(
AE
F132345)
indicated
that
the
LC50
was
>
101,000
µ
g/
L
(
MRID
462035­
15)
and
suggest
that
this
compound
as
practically
nontoxic
to
freshwater
fish.
In
addition
the
metabolite
(
AE
C421200)
LC50
could
not
be
determined
definitively,
but
it
was
tested
up
to
103,000
µ
g/
L,
and
the
results
also
suggest
classification
of
this
metabolite
as
practically
non­
toxic
to
freshwater
fish.

The
acute
thidiazuron
LC50
for
marine
fish
was
not
determined
by
available
toxicity
data
(
MRID
418461­
01).
Lack
of
an
LC50,
precluded
a
toxicity
classification.
However,
the
data
do
suggest
that
the
NOAEC
for
thidiazuron
is
at
least
as
high
as
the
highest
dose
tested
(
36,000
µ
g/
L),
which
is
just
above
the
established
solubility
limit
of
the
compound
(
31,000
µ
g/
L).
No
sub­
lethal
effects
were
observed
in
this
study.
Because
of
the
lack
of
a
reported
LOAEC,
the
NOAEC
result
from
this
study
is
uncertain.
However,
it
is
unlikely
that
a
repeat
of
the
study
will
generate
an
acute
lethality
endpoint
consistent
with
screening
risk
assessment
methods
that
would
be
at
environmentally
relevant
concentrations.
There
are
no
data
for
either
the
formulated
product
or
the
degradates.

A
chronic
toxicity
study
was
submitted
for
freshwater
fish
early
life­
stage
(
fathead
minnow)
for
parent
thidiazuron.
The
NOAEC
of
the
parent
was
5,700
µ
g/
L
based
on
hatchability,
fry
survival,
and
total
survival
(
MRID
421320­
02).
A
chronic
full
life
cycle
test
was
not
submitted
for
freshwater
fish
or
marine/
estuarine
fish.

Toxicity
to
Aquatic
Invertebrates
Acute
freshwater
invertebrate
data
were
submitted
for
the
parent
thidiazuron
and
the
LC50
of
5,700
µ
g/
L
(
MRID
464053­
03)
classifies
the
parent
as
moderately
toxic
to
freshwater
invertebrates.
A
previous
study
conducted
in
1979
determined
the
LC50
to
be
10,000
µ
g/
L
(
MRID
099819).

Acute
freshwater
invertebrate
studies
on
the
major
transformation
products
were
also
submitted.
The
LC50
for
the
photodegradate
AC
F132347
was
>
12,000
µ
g/
L
(
MRID
462035­
09).
The
LC50s
for
the
AC
F132345
metabolite
(
MRID
462035­
16)
and
the
AE
C421200
photodegradate
(
MRID
462035­
12)
were
>
98,000
µ
g/
L.

Acute
marine
invertebrate
studies
show
that
the
mysid
shrimp
(
MRID
418416­
02)
and
the
eastern
oyster
embryo/
larvae
(
MRID
421320­
01)
LC50s
are
3,240
and
5,384
µ
g/
L,
respectively.
This
classifies
thidizuron
as
moderately
toxic
to
marine
acute
invertebrates.
No
studies
were
submitted
for
any
of
the
metabolites.
Page
55
of
129
A
chronic
daphnid
toxicity
study
was
also
available
for
thidiazuron.
The
LOAEC
was
determined
to
be
<
100
µ
g/
L
based
on
length
(
MRID
421320­
02/
436650­
01).
Even
though
a
definitive
NOAEC
could
not
be
obtained,
the
21­
day
EC10
was
found
to
be
720
µ
g/
L.
No
chronic
data
were
submitted
for
marine
invertebrates.

Toxicity
to
Aquatic
Plants
Aquatic
plant
testing
was
conducted
on
the
parent
thiadiazuron.
The
E50
was
determined
to
be
>
24,000
µ
g/
L
for
the
vascular
plant
(
Lemna
gibba)
based
on
frond
count
as
the
most
sensitive
parameter.
The
NOAEC
and
EC05
were
determined
to
be
8,600
and
570
µ
g/
L,
respectively
(
MRID
462035­
06).
Non­
vascular
plant
data
were
submitted
for
the
green
alga
(
Selenastrum
copricornatum),
blue­
green
algae
(
Anabaena
flos­
aquae),
and
the
marine
diatom
(
Skeletonema
costatum)
Skeletonema
costatum).
The
most
sensitive
of
these
non­
vascular
plants
was
the
marine
diatom
with
a
E50
of
850
µ
g/
L,
a
NOAEC
of
110
µ
g/
L,
and
EC05
of
56
µ
g/
L.
No
data
are
currently
available
for
the
freshwater
diatom
(
Navicula
pelliculosa).

Additional
non­
vascular
plant
data
(
green
alga)
was
submitted
for
the
photodegradate
AE
F132347,
the
metabolite
AC
F132345,
and
the
photodegradate
AE
C421200.
The
most
sensitive
of
these
metabolites
was
determined
to
be
the
AE
F132347
photodegradate,
with
EC50,
NOAEC,
and
EC05
values
of
980,
220,
and
310
µ
g/
L,
respectively.
All
these
studies
were
considered
as
Tier
1
studies
and
classified
as
supplemental
because
they
were
conducted
for
3
days
instead
of
5
days
as
required
by
the
USEPA.

Aquatic
Exposure
Aquatic
exposure
and
the
special
emphasis
on
photolysis
in
water
is
discussed
in
the
Environmental
Fate
Assessment
section
of
this
document
and
in
greater
detail
in
Appendix
D.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
the
two
photoproducts
identified
as
photoproduct
I
(
AE
F132347)
and
photoproduct
II
(
AE
C421200)
(
see
chemical
structures
in
Appendix
B).
The
first
is
a
structural
isomer
of
parent,
while
the
latter
has
a
substantially
altered
chemical
structure.

For
reasons
previously
stated,
including
the
toxicity
data
available
for
degradates,
the
exposure
concentrations
used
for
the
aquatic
risk
assessment
are
the
time
dependent
summations
of
the
concentrations
of
parent
thidiazuron
and
its
photoisomer
(
photoproduct
I).
Exposure
concentrations
were
derived
from
a
combination
of
GENEEC
model
runs,
as
given
explicitly
in
Appendix
D.
Resulting
concentrations
for
parent
plus
the
photoisomer
are
in
the
following
table:

Estimated
Environmental
Concentrations
(
ppb
or
:
g/
L)

Peak
4­
Day
Avg.
21­
Day
Avg.
60­
Day
Avg.
90­
Day
Avg.

11
11
9.7
8.6
8.2
Risk
Quotients
Page
56
of
129
The
methodology
for
calculating
RQs
is
presented
in
Appendix
G.
The
resulting
RQs
for
the
parent
toxicity
values
are
presented
in
detail
in
Appendix
G.

VII.
Terrestrial
Hazard,
Exposure,
and
Risk
Quotient
Calculation
Appendix
F
provides
tabular
summaries
of
the
toxicity
studies
material
to
the
risk
assessment
for
thidiazuron.
The
toxicities
of
thidiazuron,
formulated
products,
and
degradates
are
discussed
below
for
each
terrestrial
taxonomic
group
studied.

Toxicity
to
Birds
Acute
testing
through
oral
gavage
of
technical
thidiazuron
to
bobwhite
quail
indicates
that
the
LD
50
is
>
3160
mg/
kg­
body
weight
(
MRID
099819).
A
similar
study
was
not
submitted
for
the
mallard
duck.
However,
a
Japanese
quail
study
with
the
formulated
product
CP
503
WP
indicated
a
LD50
>
9989
mg/
kg­
bw
(
4995
mg
ai/
kg­
bw).
These
LD50
values
classify
thidiazuron
as
practically
non­
toxic
to
birds.

The
dietary
LC
50
for
both
species
is
>
5000
mg/
kg­
diet
for
the
technical
thidiazuron.
No
sublethal
effects
or
other
treatment
related
effects
were
observed
in
any
of
these
studies.
This
classifies
technical
thidiazuron
as
practically
non­
toxic
to
birds.
Chronic
testing
of
thidiazuron
was
not
submitted.
Details
of
the
results
are
tabulated
in
Appendix
F.

Toxicity
to
Mammals
Acute
testing
through
oral
gavage
of
technical
thidiazuron
(
AE
Bo49537
00
ID99
0003)
to
laboratory
rats
indicates
that
the
LD
50
is
>
2000
mg/
kg­
body
weight.
This
classifies
the
technical
thidiazuron
as
a
category
III
compound.

In
a
two­
generation
rat
reproduction
toxicity
study
(
MRID
46209601),
thidiazuron
(
99.5%
a.
i.)
was
administered
continuously
in
the
diet
to
Han
Wistar
(
HsdBrl
Han:
Wist)
rats
(
28
animals/
sex/
dose)
at
dose
levels
of
0,
100,
400,
or
1200
ppm
(
equivalent
to
0/
0,
8.8/
9.9,
35.4/
39.8,
and
108.5/
121.1
mg/
kg/
day
[
M/
F]).
The
first
(
P)
and
second
(
F1)
generation
parents
were
dosed
for
10
weeks
before
they
were
mated
to
produce
the
F1
and
F2
litters.
The
F1
pups
were
weaned
on
postnatal
day
(
PND)
21,
and
24
pups/
sex/
group
(
1
pup/
sex/
litter
as
nearly
as
possible)
were
randomly
selected
as
parents
of
the
F2
generation.

No
statistically
significant
(
P=
0.05)
effects
on
frank
reproduction
indices
were
evident
in
any
dose
group.
In
the
parental
animals,
no
treatment­
related
effects
were
observed
on
sperm
measures,
ovarian
follicles,
corpora
lutea,
pre­
coital
interval,
duration
of
gestation,
or
on
mating,
fertility,
gestation,
or
parturition
indices.
There
were
no
effects
of
treatment
on
the
post­
implantation
survival,
live
birth,
viability,
or
lactation
indices
or
on
the
sex
ratio
in
the
F1
and
F2
generations.
However,
at
1200
ppm,
body
weight
gains
were
decreased
in
the
P
males
(
statistics
not
performed)
during
pre­
mating
(
Weeks
0­
10)
by
10%,
and
overall
(
Weeks
0­
17)
by
10%
(
p#
0.05).
In
the
P
females
at
this
dose,
body
weight
gains
were
decreased
(
p#
0.01)
during
pre­
mating
by
16%.
Body
weight
gains
continued
to
be
decreased
(
p#
0.05)
by
10%
throughout
gestation
(
GD
0­
20).
At
1200
ppm,
body
weight
gains
were
decreased
(
97­
10%;
p#
0.05)
in
the
F1
pups
during
PND
1­
21
Page
57
of
129
and
during
PND
1­
28,
and
in
the
F2
pups
during
PND
1­
28
in
the
males,
and
during
PND
1­
21
and
PND
1­
28
in
the
females.
In
the
F1
females
at
this
dose,
an
increased
(
p#
0.01)
incidence
of
five
day
irregular
estrous
cycles
or
acyclicity
was
observed.
Vaginal
opening
in
F1
females
was
significantly
(
p#
0.01)
delayed
in
the
1200
ppm
dose
group
(
37.3
days
vs
34.3
days
for
controls)
but
the
reproductive
performance
of
thse
females
in
the
lab
was
unremarkable.
No
treatmentrelated
findings
in
any
generation
were
noted
at
100
or
400
ppm
(
P=
0.05).

The
NOAEL
for
both
parental
and
offspring
toxicity
in
this
study
was
400
ppm
diet
(
35.4/
39.8
mg/
kg/
day
[
M/
F])
and
the
LOAEL
for
these
endpoints
was
1200
ppm
diet
(
108.5/
121.1
mg/
kg/
day
[
M/
F]).
Although
the
reproduction
performance
in
the
laboratory
was
not
adversely
affected
there
were
observed
delays
in
female
sexual
maturation
and
irregular
estrous
cycles
or
acyclicity
at
the
1200
ppm
dose,
F1
females).
Effects
on
the
timing
to
reach
sexual
maturity
and
disruptions
in
estrous
cycling
could
pose
adverse
reproduction
effects
in
wild
mammals
because
of
the
seasonality
of
reproduction
periods
in
the
wild
and
seasonal
influences
on
the
survival
of
offspring.
Therefore
the
NOAEL
for
wild
mammal
reproduction
risk
assessment
purposes
would
be
400
ppm
diet.

A
three
generation
rat
study
with
thidiazuron
technical
was
also
available.
This
study
was
classified
as
Core/
Supplemental
because
several
deficiencies
were
noted
including
the
following:

°
Pup
body
weights
were
only
submitted
for
lactation
day
21.
The
guidelines
require
body
weight
data
on
days
0,
4
(
pre­
and
post­
cull),
7,
14,
and
21.

°
There
was
no
measure
of
food
consumption.
The
amount
of
pesticide
consumed
was
estimated
by
using
default
food
consumption
values
for
the
laboratory
rat
developed
by
FDA
years
ago.

°
A
dietary
analysis
was
conducted
but
was
not
provided
in
the
report.

°
Little
detail
was
provided
on
the
mating
design.
For
example,
EPA
guidelines
specify
that
sibling
from
the
same
litters
should
not
be
mated.
It
was
unclear
if
this
guideline
was
followed.

The
reproductive/
offspring
NOEL
was
200
ppm
(
10
mg
ai/
kg/
bw/
da)
based
on
a
decrease
in
litter
size.

The
quality
of
the
2­
generation
study,
devoid
of
the
inter­
litter
mating
problems
associated
with
the
3­
generation
study,
suggests
that
the
effects
measurement
endpoints
derived
from
this
study
be
used
in
preference
to
those
from
the
3­
generation
study.

Toxicity
to
Non­
target
Insects
Acute
contact
toxicity
studies
to
honeybees
revealed
contact
LD
50
s
of
>
100
µ
g
ai
/
bee
for
thidiazuron
technical
and
>
98.1
µ
g
ai
/
bee
for
the
SC42
water
miscible
suspension
concentrate
500
g/
L
(
MRID
462035­
01,
462035­
18).
These
results
classify
thidiazuron
as
practically
nontoxic
to
non­
target
insects.
In
addition,
a
72­
hour
acute
oral
toxicity
test
was
conducted
for
the
Page
58
of
129
SC42
water
miscible
suspension
concentrate
500
g/
L
in
accordance
with
OECD
guidelines
(
MRID
462035­
19).
This
study
resulted
in
an
oral
contact
LD
50
of
>
197.8
µ
g
ai/
bee.

Two
other
non­
target
insect
studies
investigated
the
lethal
and
sub­
lethal
effect
of
the
SC42
water
miscible
suspension
concentrate
500
g/
L
on
the
parasitoid
wasp
(
Aphidius
rhopalosiphi)
and
the
predatory
mite,
Typhlodromus
pyri,
when
exposed
on
a
glass
surface.
These
studies
were
performed
to
satisfy
the
OECD
guideline
requirements,
and
although
scientifically
sound,
do
not
fulfill
the
OPP
guideline
requirement.

The
parasitoid
wasp
study
(
MRID
46203520)
exposed
4
replicates
(
10
wasps/
replicate)
for
48
hours,
at
concentrations
of
100
and
200
g
ai/
ha
(
0.1
and
0.2
lb
ai/
A).
The
percent
mortality
was
5
and
12.5%,
respectively,
as
compared
to
10%
in
the
controls.
Therefore,
it
was
concluded
that
the
LC
50
was
>
200
g
a.
i./
ha
(
0.2
lb
ai/
A).
To
determine
reproductive
success
through
parasitation,
15
wasps
were
placed
on
aphid­
infested
oat
plants.
One
day
later
the
wasps
were
removed
and
the
plants
kept
for
12
additional
days.
The
parasitation
rate
was
determined
by
counting
the
number
of
mummies
for
each
individual
wasp.
The
percent
reductions
when
compared
to
the
control
were
27.3
and
38.1%
in
the
100
and
200
g
ai/
ha
treatment
groups,
respectively.

In
the
predatory
mite
study
(
MRID
46203521)
5
replicates
(
20
mites/
replicate)
were
exposed
to
200
g
ai/
ha
(
0.2
lb
ai/
A)
via
a
floating
glass
plate.
Dead
mites
and
escapees
(
mites
that
left
the
glass
plate
and
were
found
stuck
in
the
water
barrier)
were
counted
as
mortalities.
Mites
were
observed
over
a
14­
day
period;
the
mortalities
were
8%
in
the
treated
group
and
13%
in
the
untreated
group.
To
measure
reproductive
performance
the
number
of
eggs
per
female
was
determined
by
counting
the
numbers
of
females
and
eggs
from
day
7
to
day
14.
The
mean
number
of
eggs
per
female
was
9.32
in
the
control
group
and
8.99
in
the
200
g
ai/
ha
treated
group.

Toxicity
to
Earthworms
Acute
toxicity
studies
to
earthworms
(
Eisenia
foetida)
were
performed
in
accordance
with
OECD
guidelines
for
the
thidiazuron
SC
500
G/
L
(
42.6%
ai),
the
AE
F132347
photodegradate,
and
the
AE
F132345
metabolite
(
MRID
#
s
46203522,
46203507,
and
46203514).
All
studies
exposed
earthworms
at
nominal
test
concentrations
of
62.5,
125,
250,
500,
and
1000
mg/
kg
for
14
days.
Endpoints
observed
included
mortality
and
worm
body
weights.
A
definitive
LC
50
based
on
mortality
was
not
determined
for
any
of
the
tested
compounds,
however,
sub­
lethal
NOAECs
and
LOAECs
were
determined
based
on
worm
body
weight
loss.
The
results
are
presented
in
the
table
below.

Test
Substance
LC50
(
mg
ai/
kg)
NOAEC
(
mg
ai/
kg)
LOAEC
(
mg
ai/
kg)

SC
500
G/
L
>
426a
125
250
AE
F132347
photodegradate
>
1000
250
500
AE
F132345
metabolite
>
1000
62.5
125
Page
59
of
129
a
LC
50
>
1000
mg
product/
kg
Toxicity
to
Non­
Target
Plants
Terrestrial
plant
testing
(
seedling
emergence
and
vegetative
vigor)
is
required
for
herbicides
that
have
terrestrial
non­
residential
outdoor
use
patterns
and
that
may
move
off
the
application
site
through
volatilization
(
vapor
pressure
>
1.0
x
10­
5mm
Hg
at
25oC)
or
spraydrift
(
aerial
or
irrigation)
and/
or
that
may
have
endangered
or
threatened
plant
species
associated
with
the
application
site.

Currently,
terrestrial
plant
testing
is
not
required
for
pesticides
other
than
herbicides
except
on
a
case­
by­
case
basis
(
e.
g.,
labeling
bears
phytotoxicity
warnings,
or
incident
data/
literature
indicaate
phytotoxicity).
Since
thidiazuron
is
used
as
a
defoliant
on
cotton
to
inhibit
regrowth
and
removal
of
both
mature
and
juvenile
leaves
in
cotton,
non­
target
terrestrial
plant
data
are
required.

For
seedling
emergence
and
vegetative
vigor
testing
the
following
plant
species
and
groups
should
be
tested:
(
1)
six
species
of
at
least
four
dicotyledonous
families,
one
species
of
which
is
soybean
(
Glycine
max)
and
the
second
is
a
root
crop,
and
(
2)
four
species
of
at
least
two
monocotyledonous
families,
one
of
which
is
corn
(
Zea
mays).

Tier
I
tests
measure
the
response
of
plants,
relative
to
a
control,
at
a
test
level
that
is
equal
to
the
highest
use
rate
(
expressed
as
lbs
ai/
A).
If
effects
are
observed
in
this
test,
the
registrant
is
required
to
proceed
to
the
Tier
II
level.

Tier
I
terrestrial
plant
testing
for
the
seedling
emergence
test
conducted
in
1991
showed
that
the
response
of
the
tested
plants
was
less
than
25%
when
compared
to
the
controls.
However,
the
vegetative
vigor
test
conducted
in
1990
indicated
negative
growth
response
(>
25%)
in
one
of
the
four
monocots
(
onion)
and
five
of
the
six
species
of
dicots
tested.

Tier
II
tests
measure
the
response
of
plants,
relative
to
a
control,
and
five
or
more
test
concentrations.
Terrestrial
Tier
II
studies
are
required
for
all
low
dose
herbicides
(
those
with
the
maximum
use
rate
of
0.5
lbs
ai/
A
or
less)
and
any
pesticide
showing
a
negative
response
equal
to
or
greater
than
25%
in
Tier
I
tests.
The
registrant
may
opt
to
proceed
directly
to
Tier
II
testing.

Recent
data
submitted
(
2003)
combined
tier
I
and
II
testing
for
seedling
emergence
and
vegetative
vigor
(
MRID
#
s
459085­
01
and
459215­
01)
for
the
SC42
formulated
product.
The
seedling
emergence
tests
indicated
negative
growth
responses
to
plant
emergence
for
onion
and
oat
by
more
than
25%
at
the
maximum
single
application
label
rate
of
0.2
lb
ai/
A.
This
would
indicate
that
a
need
exists
for
tier
II
testing
for
these
two
monocot
species.
All
other
tested
species
showed
definitive
results
or
an
EC
25
above
the
maximum
single
application
rate.

All
of
the
dicot
plants
were
tested
at
the
tier
II
level
with
the
exception
of
turnip
and
cabbage
and
since
these
plants
are
not
among
the
most
sensitive
dicots
tested,
further
testing
will
not
be
required.
The
results
from
these
tests
are
detailed
in
Appendix
F
and
summarized
in
the
table
below.
Page
60
of
129
Terrestrial
Plant
Toxicity
Summary
for
Thidiazuron
SC
42
Study
Type
Most
sensitive
Crop
EC25
/
NOEC
or
EC05
(
lb
ai/
A)
Least
sensitive
Crop
/
Active
Ingredient
EC25
/
NOEC
or
EC05
(
lb
ai/
A)

Seedling
Emergence
Monocot
Onion
&
oat
<
0.1783
/
<
0.1783
Corn
&
wheat
>
0.1783
/
0.1783
Dicot
Turnip
0.0152
/
0.0031
Tomato
>
0.1783
/
>
0.1783
Vegetative
Vigor
Monocot
Onion,
corn,
&
oat
>
0.1783
/
0.1783
Wheat
>
0.1783
/
0.1783
Dicot
Lettuce
0.0011
/
0.00005
Turnip
&
cabbage
>
0.1783
/
<
0.1783
Terrestrial
Plant
Exposure
and
Risk
Quotient
Calculations
To
calculate
the
RQs
for
non­
endangered
plants
the
EC
25
value
of
the
most
sensitive
species
in
the
seedling
emergence
study
is
compared
to
runoff
and
drift
exposure
to
determine
the
RQ
(
EEC/
toxicity
value).
The
EC
25
value
of
the
most
sensitive
species
in
the
vegetative
vigor
study
is
compared
to
the
drift
exposure
to
determine
the
acute
RQ.
RQs
are
calculated
for
the
most
sensitive
monocot
and
dicot
species.

To
calculate
the
RQs
for
endangered
plants,
the
NOAEC
or
EC
05
value
of
the
most
sensitive
species
in
the
seedling
emergence
study
is
compared
to
runoff
and
drift
exposure
(
EEC/
toxicity
value).
The
NOAEC
or
EC
05
value
of
the
most
sensitive
species
in
the
vegetative
vigor
study
is
compared
to
the
drift
exposure
to
determine
the
acute
RQ.

Exposure
to
terrestrial
plants
inhabiting
dry
and
semi­
aquatic
areas
may
be
exposed
to
pesticides
from
runoff,
spray
drift
or
volatilization.
Volatilization
is
not
included
in
this
assessment.
Semiaquatic
areas
are
those
low­
lying
wet
areas
that
may
be
dry
at
certain
times
of
the
year.
EFED's
runoff
exposure
estimate
is:
(
1)
based
on
a
pesticide's
water
solubility
and
the
amount
of
pesticide
present
on
the
soil
surface
and
its
top
one
inch,
(
2)
characterized
as
"
sheet
runoff"
(
one
treated
acre
to
an
adjacent
acre)
for
dry
areas,
(
3)
characterized
as
"
channelized
runoff"
(
10
treated
acres
to
a
distant
low­
lying
acre)
for
semi­
aquatic
areas,
and
(
4)
based
on
percent
runoff
values
of
0.01,
0.02,
and
0.05
for
water
solubility
of
<
10
ppm,
10­
100
ppm,
and
>
100
ppm,
respectively.

Spray
drift
exposure
from
ground
and
overhead
chemigation
applications
is
assumed
to
be
1%
of
the
application
rate.
Spray
drift
from
aerial,
airblast,
and
forced­
air
applications
is
assumed
to
be
5%
of
the
application
rate
with
an
application
efficiency
of
60%.
The
effects
of
multiple
applications
are
addressed
by
summing
the
application
rates
from
individual
applications.

EECs
are
calculated
for
the
following
application
methods:
(
1)
unincorporated
ground
applications,
(
2)
incorporated
ground
application,
and
(
3)
aerial,
airblast,
forced­
air,
and
Page
61
of
129
chemigation
applications.
Formulas
for
calculating
EECs
for
dry
areas
adjacent
to
treatment
sites
and
EECs
for
semi­
aquatic
areas
follow.

EEC
Formulas:

Calculating
EECs
for
terrestrial
plants
inhabiting
dry
areas
adjacent
to
treatment
sites
Unincorporated
ground
application:

Runoff
=
maximum
application
rate
(
lbs
ai/
A)
x
runoff
value
x
number
of
applications
Drift
=
maximum
application
rate
x
0.01
Total
Loading
=
runoff
(
lbs
ai/
acre)
+
drift
(
lbs
ai/
A)

Incorporated
ground
application:

Runoff
=
[
maximum
application
rate
(
lbs
ai/
A)
÷
minimum
incorporation
depth
(
cm.)]
x
runoff
value
x
number
of
applications
Drift
=
maximum
application
rate
x
0.01
(
Note:
drift
is
not
calculated
if
the
product
is
incorporated
at
the
time
of
application.)
Total
Loading
=
runoff
(
lbs
ai/
A)
+
drift
(
lbs
ai/
A)

Aerial,
airblast,
forced­
air,
and
chemigation
applications:

Runoff
=
maximum
application
rate
(
lbs
ai/
A)
x
0.6
(
60%
application
efficiency
assumed)
x
runoff
value
x
number
of
applications
Drift
=
maximum
application
rate
(
lbs
ai/
A)
x
0.05
Total
Loading
=
runoff
(
lbs
ai/
A)
+
drift
(
lbs
ai/
A)

Calculating
EECs
for
terrestrial
plants
inhabiting
semi­
aquatic
low­
lying
areas
Unincorporated
ground
application:

Runoff
=
maximum
application
rate
(
lbs
ai/
A)
x
runoff
value
x
10
acres
x
number
of
applications
Drift
=
maximum
application
rate
x
0.01
Total
Loading
=
runoff
(
lbs
ai/
A)
+
drift
(
lbs
ai/
A)

Incorporated
ground
application:
Runoff
=
[
maximum
application
rate
(
lbs
ai/
A)/
minimum
incorporation
depth
(
cm)]
x
runoff
value
x
10
acres
x
number
of
applications
Drift
=
maximum
application
rate
x
0.01
(
Note:
drift
is
not
calculated
if
the
product
is
incorporated
at
the
time
of
application.)
Total
Loading
=
runoff
(
lbs
ai/
A)
+
drift
(
lbs
ai/
A)

Aerial,
airblast,
and
forced­
air
applications:
Page
62
of
129
Runoff
=
maximum
application
rate
(
lbs
ai/
acre)
x
0.6
(
60%
application
efficiency
assumed)
x
runoff
value
x
10
acres
x
number
of
applications
Drift
=
maximum
application
rate
(
lbs
ai/
A)
x
0.05
Total
Loading
=
runoff
(
lbs
ai/
A)
+
drift
(
lbs
ai/
A)

runoff
values
=
0.01,
0.02,
and
0.05
for
water
solubility
of
<
10
ppm,
10­
100
ppm,
and
>
100
ppm,
respectively
Incorporation
depth:
Use
the
minimum
incorporation
depth
prescribed
in
the
label.

Terrestrial
Exposure
for
Birds
and
Mammals
Terrestrial
exposure
estimations
differ
for
the
groups
of
terrestrial
organisms.
One
major
difference
in
the
way
in
which
exposure
scenarios
are
evaluated
for
terrestrial
species
is
the
methodology
used
for
non­
granular
and
granular
applications.
Since
the
sole
use
of
thidiazuron
is
limited
to
spray
applications
to
cotton,
exposure
scenarios
were
only
considered
for
non­
granular
applications.

Toxicant
concentrations
on
terrestrial
food
items
are
based
on
data
from
by
Hoerger
and
Kenaga
(
1972)
as
modified
by
Fletcher
et
al.
(
1994)
that
determined
residue
levels
on
various
terrestrial
items
immediately
following
toxicant
application
in
the
field.
These
values
are
summarized
in
the
table
below.

Estimated
Environmental
Concentrations
on
Avian
and
Mammalian
Food
Items
(
ppm)
Following
a
Single
Application
at
1
lb
ai/
A)

Food
Items
EEC
(
ppm)
Predicted
Maximum
Residue1
EEC
(
ppm)
Predicted
Mean
Residue1
Short
grass
240
85
Tall
grass
110
36
Broadleaf/
forage
plants
and
small
insects
135
45
Fruits,
pods,
seeds,
and
large
insects
15
7
1
Predicted
maximum
and
mean
residues
are
for
a
1
lb
ai/
a
application
rate
and
are
based
on
Hoerger
and
Kenaga
(
1972)
as
modified
by
Fletcher
et
al.
(
1994).

Toxicant
concentrations
on
food
items
following
multiple
applications
are
predicted
using
a
firstorder
residue
decline
method,
EFED's
"
FATE5"
model,
which
allows
determination
of
residue
dissipation
over
time
incorporating
a
degradation
half­
life.
Predicted
maximum
and
mean
EECs
resulting
from
multiple
applications
estimates
the
highest
one­
day
residue,
based
on
the
maximum
or
mean
initial
EEC
from
the
first
application,
the
total
number
of
applications,
interval
between
applications,
and
a
first­
order
degradation
rate,
consistent
with
EFED
policy.
Page
63
of
129
The
cotton
scenario
was
based
on
two
applications
spaced
7
days
apart.
The
first
application
was
at
the
maximum
single
application
rate
of
0.2
lbs
a.
i./
acre.
The
second
at
0.1
lbs
a.
i./
acre,
since
the
maximum
allowable
total
yearly
application
rate
is
0.3
lbs
ai/
A.
All
the
above
scenarios
used
the
default
35­
day
foliar
dissipation
half­
life
since
no
suitable
data
were
available.
For
comparative
purposes,
residues
were
also
calculated
based
on
a
1­
day
foliar
dissipation
half­
life
to
observe
the
effects
on
the
risk
quotients.
Results
are
discussed
in
the
risk
characterization
section.

Dietary
exposure
to
mammals
from
liquid
sprays
is
based
upon
EFED's
draft
1995
SOP
for
mammalian
risk
assessments
and
methods
used
by
Hoerger
and
Kenaga
(
1972)
as
modified
by
Fletcher
et
al.
(
1994).
The
concentration
of
thidiazuron
in
the
diet
that
is
expected
to
be
acutely
lethal
to
50%
of
the
test
population
(
LC
50
)
is
determined
by
dividing
the
LD
50
value
(
usually
a
rat
LD
50
)
by
the
amount
of
food,
as
percent
(
decimal
of)
body
weight
consumed.
A
risk
quotient
is
then
determined
by
dividing
the
EEC
by
the
derived
LC
50
value.
Acute
RQs
are
calculated
for
three
separate
weight
classes
of
mammals
(
15,
35,
and
1000
g),
each
presumed
to
consume
four
different
kinds
of
food
(
grass,
forage,
insects,
and
seeds).
Chronic
mammalian
RQs
are
calculated
using
the
most
sensitive
NOAEC
from
the
2­
generation
rat
study
and
the
residue
concentration
expected
on
food
items
from
Hoerger
and
Kenaga
(
1972)
as
modified
by
Fletcher
et
al.
(
1994).

Terrestrial
Risk
Quotients
The
methodology
for
calculating
RQs
is
presented
in
Appendix
F.
Resulting
RQs
for
the
parent
toxicity
values
are
presented
in
detail
in
Appendix
G.
Page
64
of
129
APPENDIX
A:
Detailed
Drinking
Water
Assessment
Memo
6EFED's
Pesticides
in
Ground
Water
Database
has
no
thidiazuron
data.
The
United
States
Geological
Survey
(
USGS),
as
part
of
a
large
water
monitoring
program,
does
not
analyze
for
thidiazuron.
The
EPA
STORET
water
quality
databases
have
no
useful
information.

7A
more
complete
environmental
fate
assessment
is
included
in
the
EFED
science
chapter
of
the
RED,
which
also
includes
sources
of
all
model
input
parameters.

Page
65
of
129
MEMORANDUM
24
August
2004
Subject:
Thidiazuron
(
PC
120301):
Drinking
Water
Assessment
(
D244574)

From:
Alex
Clem,
Environmental
Scientist,
EFED/
ERB
1
(
7507C)

Peer
Review:
James
Hetrick,
Senior
Physical
Scientist
EFED/
ERB
1
(
7507C)

Through:
Sid
Abel,
Chief,
EFED/
ERB
1
(
7507C)

To:
Felicia
Fort,
Team
Leader,
HED/
RRB
1
(
7509C)

This
memorandum
provides
you
with
the
potential
drinking
water
exposure
concentrations
for
thidiazuron
in
surface
water
and
ground
water
resulting
from
its
existing
use
as
a
cotton
defoliant/
harvest
aid.
Since
the
HED
MARC
has
not
yet
convened,
at
this
time
EFED
is
also
informing
you
of
two
major
transformation
products
formed
in
surface
water
(
not
ground
water)
that
may
be
of
potential
toxicological
interest
to
you.
We
also
describe
three
reasonable
exposure
alternatives
for
surface
water
involving
thidiazuron
and
the
two
byproducts.

There
are
no
useful
water
monitoring
data
for
thidiazuron
in
EFED's
standard
monitoring
sources6.
Our
exposure
estimates
come
from
the
two
EFED
Tier
1
screening­
level
models:
1)
FIRST
(
Ver.
1.0;
Aug.
1,
2001)
for
surface
water
concentrations
resulting
from
runoff
and
spray
drift
into
an
Index
Reservoir
and
2)
SCI­
GROW
(
Ver.
2.3;
Nov.
4,
2003)
for
ground
water
concentrations
resulting
from
leaching.
These
models
and
their
descriptions
are
available
at
the
EPA
internet
site:

http://
www.
epa.
gov/
oppefed1/
models/
water.

Before
proceeding
further,
we
now
provide
an
environmental
fate
capsule
for
thidiazuron7.
This
provides
basic
background
for
placing
the
drinking
water
assessment
in
perspective.
Included
within
are
key
assumptions,
limitations
or
uncertainties.

Environmental
Fate
Capsule:
In
soil,
thidiazuron
is
persistent,
as
evidenced
by
laboratory
and
field
half­
lives
of
the
order
of
one
year.
It
has
intermediate
soil
sorption
coefficients.
Such
persistence
and
intermediate
mobility
would
allow
some
year
to
year
accumulation
as
well
as
time
and,
therefore,
opportunity
for
favorable
conditions
for
runoff
from
application
sites
to
occur.
With
the
hypothetical
assumption
that
there
is
no
significant
physical
movement
of
thidiazuron
Page
66
of
129
from
a
site
of
application
for
several
years,
then,
with
a
one
year
half­
life
and
uniform
annual
applications,
the
asymptotic
limit
of
build­
up
would
result
in
soil
concentrations
that
would
approach
twice
that
of
the
yearly
application
amount.
Runoff
concentrations
would
be
affected
similarly.

When
thidiazuron
reaches
surface
water,
photolysis
is
expected
to
be
the
major
route
of
transformation;
other
degradative
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid,
and
occurs
by
branching
in
quantitative
yield
into
two
photoproducts.
One
of
the
photodegradates
is
a
structural
isomer
of
parent,
while
the
other
has
a
substantially
altered
chemical
structure.
These
degradates
are
identified
below
and
in
Appendix
1
by
chemical
names,
structural
formulas,
and
other
designations.
The
photolysis
process
and
special
modeling
considerations
are
discussed
briefly
below
and
in
detail
in
Appendix
2.
Ground
water
is
not
impacted
by
these
degradates
because
all
field
studies
show
that
parent
is
long­
lived
in
soil
(
halflives
of
the
order
of
one
year)
with
only
minimal
evidence
of
photolysis.

The
structural
isomer
is
AE
F132347
or
photoproduct
I
(
see
Appendix
1
for
chemical
identification).
It
has
a
maximum
experimental
limit
of
production
of
77%
of
parent
equivalents
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
Photoproduct
I
was
stable
to
further
photolysis
under
experimental
study
conditions.
The
second
photodegradate
is
AE
C421200
or
photoproduct
II
(
see
Appendix
1
for
chemical
identification).
Photoproduct
II
is
substantially
different
from
parent
thidiazuron,
and
has
a
complementary
asymptotic
limit
of
production
to
photoproduct
I
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
This
product
was
also
stable
to
further
photolysis
under
study
conditions.
Thus,
at
different
environmental
pHs,
parent
is
always
quantitatively
converted
in
complementary
proportions
into
the
two
photodegradates.

Assumptions/
Limitations/
Uncertainties:
Since
EFED
does
not
know
yet
whether
the
two
photodegradates
in
surface
water
will
be
of
toxicological
concern
to
HED,
we
assume
that
they
may
be,
and
present
three
alternative
exposure
combinations
that
cover
the
range
of
potential
surface
water
exposures
that
include
parent
and
the
two
aqueous
photoproducts.
One
alternative
is
the
most
conservative;
a
second,
least
conservative;
and
a
third
is
intermediate
in
nature.
These
are
discussed
below
and
in
more
detail
in
Appendix
2.
Among
the
three
exposure
assessments,
there
is
no
meaningful
difference
in
peak
(
acute)
surface
water
exposure
concentrations.
The
only
significant
change
for
any
of
the
three
is
in
the
annual
average
(
chronic)
concentrations.

We
have
no
data
on
foliar
dissipation.
Since
thidiazuron
is
used
to
defoliate
cotton
prior
to
harvest,
dislodgement
from
or
transformation
in
or
on
leaves
may
be
an
important
fate
pathway.
Although
photolysis
was
the
rapid,
major
route
of
transformation
in
water,
in
field
soil
parent
was
long­
lived
with
only
minimal
evidence
of
photolysis
or
leaching.
However,
in
laboratory
plates
of
thin
soil,
the
photoisomer
AE
F132347
(
photoproduct
I)
was
a
quickly
formed
major
degradate.
Thus,
whether
photolysis
in
or
on
cotton
plants
is
a
major
fate
process
is
unclear,
and
can
be
decided
only
by
experiment.
However,
based
on
available
data,
if
photolysis
were
to
be
substantial
on
foliage,
it
is
a
reasonable
inference
that
the
same
structural
isomer
would
form.
In
this
case,
our
surface
water
assumptions
and
three
options
still
cover
possibilities,
and,
within
standard
model
limitations,
our
estimated
surface
water
exposure
concentrations
remain
essentially
the
same.
Page
67
of
129
Modeling
Results.
Table
1
shows
the
FIRST­
derived
potential
surface
water
concentrations
for
the
three
respective
combinations
of
1)
parent
plus
both
aqueous
photodegradation
products
(
most
conservative),
2)
parent
plus
photodegradate
1,
and
3)
parent
only
(
least
conservative).
Degradate
modeling
is
based
on
mass
balance
using
simultaneous
decline
and
formation
over
time.
All
reported
concentration
combinations
are
in
terms
of
parent
mass
chemical
equivalents.
However,
if
desired,
concentrations
for
each
photodegradate
can
easily
be
separated.

Inspection
of
thidiazuron
product
labels
shows
that
no
more
than
two
annual
applications
of
thidiazuron
by
aerial
or
ground
spray
are
allowed;
their
summation
is
not
to
exceed
0.3
lb
of
the
active
ingredient
(
a.
i.)
per
acre.
The
maximum
single
application
rate
is
no
more
than
0.2
lb
a.
i./
acre,
with
split
applications
as
close
as
five
to
seven
days
apart.
The
exposure
concentrations
we
give
below
are
for
a
single
aerial
application
at
a
maximum
rate
of
0.3
lb
a.
i./
acre.
However,
as
specifically
discussed
and
illustrated
in
Appendix
2,
whether
the
total
annual
maximum
is
applied
all
at
once
or
is
split
in
two
(
as
specified
on
product
labels),
differences
are
negligible
for
the
particular
case
of
thidiazuron
because
of
its
long
life
in
soil.
Complete
model
input/
output
tables
with
detailed
explanations
of
the
computational
procedures
used
to
handle
the
photodegradates
are
in
Appendix
2.

Table
1.
Surface
Water
Concentrations
(
derived
from
FIRST
model,
Ver.
1.0)

THREE
ALTERNATIVE
DEGREES
OF
PROTECTION
PEAK
DAY
(
ACUTE)
CONCENTRATION
(
ppb
or
:
g/
L)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
(
ppb
or
:
g/
L)

Parent
+
Both
Photoproducts
3.5
1.0
Parent
+
AE
F132347
(
photoproduct
1)
3.5
0.82
Parent
Only
3.4
0.068
Table
2
shows
the
SCI­
GROW­
estimated
potential
groundwater
exposure
concentration.
Groundwater
is
not
expected
to
be
impacted
by
photodegradates
because
all
field
studies
show
that
parent
is
long­
lived
in
soil
(
half­
lives
of
the
order
of
one
year)
with
only
minimal
evidence
of
photolysis
or
leaching.
However,
as
previously
discussed,
dislodgeability,
photolysis
(
or
other
chemical
changes)
in
or
on
plant
surfaces
is
uncertain.
Therefore,
it
is
possible
that
photodegradates
identified
in
water
and
soil
or
other
compounds
may
form
in
or
on
cotton
plants,
reach
the
soil
surface
at
unknown
rates,
and
be
subject
to
unknown
degrees
of
leaching
or
runoff.
Our
assessment,
of
course,
cannot
specifically
account
for
this
absent
information.
However,
based
on
all
available
fate
evidence,
it
appears
that
photodegradation
would
be
the
most
likely
candidate
for
any
rapid
degradation
of
thidiazuron
that
may
occur
on
plants.
If
this
is
the
case,
then,
to
a
first
approximation,
the
physical
and
chemical
fate
properties
of
the
photodegradates
should
be
similar
to
parent,
and
any
resulting
loss
in
parent
would
be
offset
by
production
of
Page
68
of
129
photodegradates.
Therefore,
combined
concentrations
of
all
these
compounds
should
approximate
those
given
for
Table
2
for
parent
only.

Table
2.
Groundwater
Concentration
(
derived
from
SCI­
GROW
regression
model,
Ver.
2.3
)

Acute
and
Chronic
Concentration*:
0.066
ppb
(:
g/
L)

*
As
noted
in
Appendix
3,
the
SCI­
GROW­
estimated
groundwater
concentration
given
here
is
an
extrapolation
beyond
the
regression
model
limits
for
Koc.
SCI­
GROW
was
developed
using
Koc
values
ranging
from
approximately
32
to
180
mL/
g
of
organic
carbon,
whereas
the
median
Koc
value
for
thidiazuron
is
783
mL/
g.
Extrapolation
increases
uncertainty,
but
without
ability
to
estimate
confidence.
Page
69
of
129
N
H
N
H
N
N
S
O
NH
NH
C
O
N
S
N
NH
C
O
NH
C
N
APPENDIX
A­
1
Chemical
Structures,
Names,
and
Other
Designations
for
Thidiazuron
and
Two
Photoproducts
Thidiazuron
(
AE
B049537;
SN
49537;
NC
19211;
Hoe
080279;
DROPP)

IUPAC
name:
1­
phenyl­
3­(
1,2,3­
thiadiazol­
5­
yl)
urea.
CAS
name:
N­
phenyl­
N'­
1,2,3­
thiadiazol­
5­
ylurea.
CAS
No:
51707­
55­
2
(
330­
54­
1
also
found).
SMILES
string:
O=
C(
Nc1ccccc1)
Nc1cnns1
AE
F132347;
ZK
79173;
ZK
80178;
photoproduct
I;
photothidiazuron
(
peak
3
in
MRID
41188201)

IUPAC
name:
1­
phenyl­
3­(
1,2,5­
thiadiazol­
3yl)
urea
CAS
name:
N­
phenyl­
N
N
­
1,2,5­
thiadiazol­
3ylurea
CAS
No:
Not
reported.

AE
C421200;
photoproduct
II
(
peak
1
in
MRID
41188201)

1­
cyano­
3­
phenylurea
Page
70
of
129
APPENDIX
A­
2
INPUT/
OUTPUT
TABLES
FOR
FIRST
(
FQPA
INDEX
RESERVOIR
SCREENING
TOOL)
(
A
Tier
I
Simulation
Model
for
Drinking
Water
Exposure
Assessment)
(
Version
1.0;
August
1,
2001)

WITH
EXPLANATION
OF
THE
BASIS
FOR
APPLICATION
RATES
AND
FOR
HANDLING
THE
SPECIAL
CASE
OF
AQUEOUS
PHOTOLYSIS
Product
labels
specify
no
more
than
two
annual
applications
of
thidiazuron
by
aerial
or
ground
spray,
their
summation
not
to
exceed
0.3
lb
of
the
active
ingredient
(
a.
i.)
thidiazuron
per
acre.
The
maximum
single
application
rate
is
no
more
than
0.2
lb
a.
i./
acre,
with
split
applications
as
close
as
five
to
seven
days
apart.
However,
as
indicated
in
the
FIRST
input/
output
tables
below
for
model
runs
numbered
as
201
and
202,
which
are
for
a
hypothetical
single,
aerial
application
at
the
maximum
total
annual
rate
of
thidiazuron
of
0.3
lb/
acre,
whether
the
total
annual
maximum
is
applied
all
at
once
or
is
split
variously,
[
for
example,
(
0.1
+
0.2)
lb/
acre
or,
as
illustrated
in
runs
203
and
204
below,
(
0.15
+
0.15)
lb/
acre],
differences
are
negligible
for
our
purposes
for
the
particular
case
of
thidiazuron.

In
water,
photolysis
is
the
major
route
of
transformation
for
thidiazuron;
other
processes
are
essentially
negligible
by
comparison.
Aqueous
photolysis
is
rapid
(
see
below),
pH
dependent,
and
occurs
by
branching
into
two
photoproducts.
The
process
merits
special
modeling
consideration,
as
will
be
discussed.

Formation
of
the
two
photoproducts
is
in
constant
ratio
and
in
complementary
stoichiometric
yield
with
parent.
Photoproduct
I
(
AE
F132347,
see
chemical
structure
in
Appendix
1)
is
an
isomer
of
parent
differing
only
in
the
relative
positions
of
the
sulfur
atom
and
the
two
nitrogen
atoms
in
the
5­
membered
ring.
The
Health
Effects
Division
(
HED)
should
evaluate
the
relevance
of
this
compound
to
human
health.
Photoproduct
I
has
a
reviewer­
calculated
asymptotic
experimental
limit
of
production
of
77%
of
parent
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
This
product
was
stable
to
further
photolysis
under
experimental
study
conditions
and
durations
(
original
MRID
41188201,
related
follow­
up
MRIDs
41364910
and
43075202,
and
fate
overview
document
MRID
44436901).

Photoproduct
II
(
AE
C421200,
chemical
structure
in
Appendix
1)
is
a
substantially
degraded
product,
and
has
a
complementary
asymptotic
limit
of
production
to
photoproduct
I
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
This
product
was
also
stable
to
further
photolysis
under
study
conditions.
HED
should
consider
any
relevance
of
this
compound
to
human
health.

Of
the
three
compounds,
soil/
sediment
sorption
data
and
non­
photolytic
transformation
data
are
available
only
for
parent.
In
the
absence
of
these
data
for
the
photoproducts,
we
assume
they
share
the
same
properties
as
parent.
For
photoproduct
I,
because
of
its
particular
isomeric
chemical
structure,
we
have
a
relatively
high
degree
of
confidence
in
this
assumption.
For
photoproduct
II,
because
of
its
altered
structure,
we
have
a
lower
degree
of
confidence.
However,
photoproduct
II
is
formed
in
lower
yield
at
more
typical
pHs,
and
any
error
introduced
in
the
modeling
analysis
described
below
by
assuming
that
its
fate
properties
are
equivalent
to
those
of
parent
and
photoproduct
I
would
have
virtually
no
effect
on
peak
exposure
concentrations,
and
only
a
minor
effect
on
chronic
exposure
concentrations.
Page
71
of
129
For
the
purposes
of
this
assessment,
of
the
seven
possible
combinations
of
parent
plus
two
photoproducts,
two
cover
the
high
and
low
ends
of
potential
exposure.
A
third
combination,
is
intermediate
between
the
extremes,
and
could
be
considered
as
a
reasonable
alternative.
In
any
of
the
possible
cases,
the
only
significant
differences
in
exposure
occur
in
the
annual
average
(
chronic)
concentrations.
The
two
extreme
combinations
and
the
intermediate
alternative
are
the
following:

1)
The
high
end
of
exposure
(
most
conservative
for
risk
assessment)
corresponds
to
including
parent
plus
both
photoproducts
(
parent
+
photoproduct
I
+
photoproduct
II).
This
is
equivalent
to
saying
that,
in
effect,
parent
did
not
photolyze
or
that
photolysis
is
"
turned
off".
There
is
also
the
inherent
assumption
that
all
three
compounds
have
equivalent
toxicities.
Results
for
this
high­
end
exposure
analysis,
are
given
in
the
table
below
for
model
run
number
201.

2)
The
low
end
of
exposure
(
least
conservative
for
risk
assessment)
corresponds
to
including
only
parent
thidiazuron
concentrations
as
a
function
of
time.
Photolysis
is
"
turned
on,"
but
any
potential
exposure
risk
from
photoproducts
I
and
II
is
ignored.
Results
for
this
low­
end
exposure
analysis,
are
given
in
the
table
below
for
model
run
number
202.

3)
The
third
combination
is
parent
+
photoproduct
I.
This
is
an
intermediate
combination
between
the
extremes,
and,
based
on
chemical
structural
similarity,
could
be
considered
as
a
reasonable
exposure
alternative.

For
the
purposes
of
the
third
alternative,
we
assume
the
pH
5
results
for
which
parent
was
slightly
more
stable
and
for
which
77%
of
parent
reaching
water
is
converted
to
the
isomer
photoproduct
I
(
AE
F132347).
Under
these
conditions,
the
thidiazuron
photolytic
half­
life,
after
adjustment
of
continuous
experimental
radiation
intensity
to
12
hours
of
solar
intensity
at
40
deg.
North
latitude
at
end
of
March
or
beginning
of
September,
was
1.44
hours
or
0.0602
days.
These
are
reviewer­
calculated
values
from
MRID
41188201,
page
40,
Table
5a;
and
page
36,
Table
2,
and
are
in
close
agreement
with
those
of
the
study
author.
Alteration
of
latitude
or
date
of
application
have
but
minor
influence
on
results
for
our
purposes.
Half­
lives
at
higher
pHs
were
somewhat
shorter
(
approximately
6%
shorter
at
pH
7
and
approximately
40%
shorter
at
pH
9,
based
on
same
study
Table
2),
and
would
result
in
lower
chronic
exposures.

With
the
restrictions
on
chemical
kinetics
imposed
by
current
standard
Agency
simulation
models,
including
FIRST,
in
order
to
determine
the
exposure
contributions
from
parent
and
photoproduct
I,
it
is
necessary
to
do
some
external
calculations
using
the
output
from
two
simulations
or
"
runs."
As
described
and
derived
below,
one
model
run
is
with
aqueous
photolysis
"
turned
off,"
(
model
run
number
201),
the
other
with
photolysis
"
turned
on"
(
model
run
number
202).
This
is
an
accurate,
simple
accounting
procedure,
and
allows
the
full
time­
dependent
capabilities
of
the
FIRST
model
to
be
utilized.

The
following
reviewer­
derived
formulas
provide
the
combined
exposure
concentrations
for
parent
thidiazuron
and
the
isomer
photoproduct
I
for
the
described
photolysis
process:
Page
72
of
129
Ci(
t)
=
0.77[
Cp(
201)­
Cp(
202)],
where
Ci(
t)
=
concentration
of
photoisomer
as
a
function
of
time
0.77
=
the
branching
fraction
of
parent
that
is
photolyzed
to
photoisomer
Cp(
201)
=
concentrations
of
parent
given
in
Run
201
below,
which
are
concentrations
that
would
result
if
parent
were
stable
to
photolysis
(
photolysis
"
turned
off")
Cp(
202)
=
concentrations
of
parent
given
in
Run
202
below
with
observed
photolysis
"
turned
on."

Therefore,
the
summation
of
parent
and
photoisomer
concentrations
is
given
by:

Conc.
of
Parent
+
Conc.
of
Photoisomer
=
Cp(
202)
+
0.77[
Cp(
201)­
Cp(
202)]

Rounding
to
two
digits,
Table
1
shows
the
resulting
drinking
water
sums
of
parent
and
the
photoproduct
I
isomer
derived
from
the
FIRST
runs
201
and
202
below:

Table
1
PEAK
DAY
(
ACUTE)
CONCENTRATION
(
ppb
or
:
g/
L)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
(
ppb
or
:
g/
L)

3.5
0.82
Table
2.
RUN
No.
201
for
Thidiazuron
on
Cotton
(
Most
Conservative
with
Photolysis
"
Turned
Off")
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.300(
.300)
1
1
494.0
31.0
AERIAL(
16.0)
20.0
.0
FIELD
AND
RESERVOIR
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
RESERVOIR)
(
RES.­
EFF)
(
RESER.)
(
RESER.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
363.00
2
N/
A
.00­
.00
726.00
726.00
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
AUG
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
3.531
1.050
Page
73
of
129
Table
3.
RUN
No.
202
for
Thidiazuron
on
Cotton
(
Least
Conservative
with
Photolysis
"
Turned
On")
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.300(
.300)
1
1
494.0
31.0
AERIAL(
16.0)
20.0
.0
FIELD
AND
RESERVOIR
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
RESERVOIR)
(
RES.­
EFF)
(
RESER.)
(
RESER.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
363.00
2
N/
A
0.0602
7.46
726.00
7.39
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
AUG
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
3.442
.068
As
can
be
seen
from
the
three
tables
above,
the
only
significant
change
for
any
combination
is
in
the
annual
average
(
chronic)
concentrations.

Tables
4
and
5
below
for
runs
203
and
204
are
for
split
applications,
but
otherwise
correspond,
respectively,
to
the
above
runs
201
(
photolysis
"
turned
off")
and
202
(
photolysis
"
turned
on").
As
can
be
seen,
there
is
no
meaningful
difference
between
corresponding
runs
201
and
203
or
between
202
and
204.
Therefore,
the
effect
of
splitting
thidiazuron
applications
can
be
neglected.

Table
4.
RUN
No.
203
for
Thidiazuron
on
Cotton
with
Split
Applications
(
Most
Conservative
with
Photolysis
"
Turned
Off")
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.150(
.298)
2
7
494.0
31.0
AERIAL(
16.0)
20.0
.0
FIELD
AND
RESERVOIR
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
RESERVOIR)
(
RES.­
EFF)
(
RESER.)
(
RESER.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
363.00
2
N/
A
.00­
.00
726.00
726.00
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
AUG
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
3.508
1.043
Page
74
of
129
Table
5.
RUN
No.
204
for
Thidiazuron
on
Cotton
with
Split
Applications
(
Least
Conservative
with
Photolysis
"
Turned
On")
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.150(
.298)
2
7
494.0
31.0
AERIAL(
16.0)
20.0
.0
FIELD
AND
RESERVOIR
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
RESERVOIR)
(
RES.­
EFF)
(
RESER.)
(
RESER.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
363.00
2
N/
A
0.0602
7.46
726.00
7.39
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
AUG
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
3.355
.066
Page
75
of
129
APPENDIX
A­
3
INPUT/
OUTPUT
TABLE
FOR
SCI­
GROW
A
SCREENING
MODEL
FOR
EXPOSURE
TO
PESTICIDES
THROUGH
GROUNDWATER
(
Version
2.3;
Nov.
4,
2003)

Chemical:
Thidiazuron
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
Application
Number
of
Total
Use
Koc
Soil
Aerobic
rate
(
lb/
acre)
applications
(
lb/
acre/
yr)
(
ml/
g)
metabolism
(
days)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
0.300
1.0
0.300
7.83E+
021
230.0
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

Groundwater
Screening
Concentration
(:
g/
L
or
ppb)
=
6.60E­
021
1The
groundwater
value
estimated
from
the
SCI­
GROW
regression
model
is
an
extrapolation
beyond
tested
model
limits
for
Koc.
SCIGROW
was
developed
using
Koc
values
ranging
from
approximately
32
to
180
mL/
g
of
organic
carbon,
whereas
the
median
Koc
value
for
thidiazuron
is
783.
Using
extrapolated
values
increases
uncertainty
without
ability
to
estimate
confidence
beyond
subjective,
qualitative
statements.
Page
76
of
129
APPENDIX
B:
Chemical
Structural
Formulas,
Names,
and
Other
Designations
for
Thidiazuron
and
Transformation
Products
Page
77
of
129
H
N
C
O
HN
N
N
S
N
H
2
N
H
N
N
S
O
NH
C
O
NH
N
S
N
Thidiazuron
(
AE
B049537;
SN
49537;
NC
19211;
Hoe
080279;
DROPP)

IUPAC
name:
1­
phenyl­
3­(
1,2,3­
thiadiazol­
5­
yl)
urea.
CAS
name:
N­
phenyl­
N'­
1,2,3­
thiadiazol­
5­
ylurea.
CAS
No:
51707­
55­
2
(
330­
54­
1
also
found).
SMILES
string:
O=
C(
Nc1ccccc1)
Nc1cnns1
Thidiazolurea
(
AE
F132345;
ZK
85290)

IUPAC
name:
1,2,3­
thiadiazol­
5­
ylurea.
CAS
name:
Not
reported.
CAS
No:
Not
reported.

AE
F132347;
ZK
79173;
ZK
80178;
photoproduct
I;
photothidiazuron
(
peak
3
in
MRID
41188201)

IUPAC
name:
1­
phenyl­
3­(
1,2,5­
thiadiazol­
3yl)
urea
CAS
name:
N­
phenyl­
N
N
­
1,2,5­
thiadiazol­
3ylurea
CAS
No:
Not
reported.
Page
78
of
129
NH
C
O
NH
C
N
H
N
C
O
NH2
H
N
C
O
HN
N
N
S
HO
AE
C421200;
photoproduct
II
(
peak
1
in
MRID
41188201)

1­
cyano­
3­
phenylurea
ZK
44483;
BTS
13225
IUPAC
name:
phenylurea
CAS
name:
phenylurea
CAS
No:
not
reported
AE
F147706;
ZK
80062
IUPAC
name:
1­(
3­
hydroxyphenyl)­
3­(
1,2,3­
thiadiazol­
5­
yl)
urea
CAS
name:
N­(
3­
hydroxyphenyl)­
N'­
1,2,3­
thiadiazol­
5­
ylurea
CAS
No:
not
reported
Other
names:
1­
m­
hydroxyphenyl­
3­(
1,2,3­
thiadiazol­
5­
yl)­
urea
N­
m­
hydroxyphenyl­
N'­(
1,2,3­
thiadiazol­
5­
yl)
urea
Page
79
of
129
APPENDIX
C:
Model
Input
Parameters
Derived
from
Environmental
Fate
Studies
for
Thidiazuron
Page
80
of
129
Model
Input
Parameters
Derived
from
Environmental
Fate
Studies
for
Thidiazuron
Study
Model
Input
Value(
s)
Comments
Hydrolysis
(
161­
1)
Stable
(
at
pH
5,
7,
9)
MRID
42069203
Tschampel,
M.,
1991
EFED
review
28
Apr
1993
Photolysis
in
water
(
161­
2)
Assume
77%
of
parent
reaching
water
is
converted
to
the
stable
photoisomer
AE
F132347
(
photoproduct
I).
Parent
T1/
2
=
0.0602
days
(
1.44
hours)
at
pH
5
after
adjustment
of
continuous
experimental
radiation
intensity
to
12
hours
solar
intensity
at
40
deg.
North
latitude
at
end
of
March
or
beginning
of
September.
(
Somewhat
shorter
T1/
2
values
at
pH
7
(
approx.
6%
shorter)
and
pH
9
(
approx.
40%
shorter).

Degradates:
Branching
transformation
into
only
two
photoproducts
in
stoichiometric
yield.
Photoproduct
I
(
AE
F132347)
is
a
photoisomer
of
parent,
that,
like
parent,
is
moderately
ecotoxic
(
but
slightly
more
toxic
than
parent).
It
has
an
asymptotic
experimental
limit
of
production
of
77%
of
parent
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
Stable
to
further
photolysis
under
study
conditions.

Photoproduct
II
(
AE
C421200)
is
a
significantly
degraded,
practically
nonecotoxic
product,
and
has
an
asymptotic
limit
of
production
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
Stable
to
further
photolysis
under
study
conditions.
MRID
41188201;
MRID
41364910
(
a
supplement
to
MRID
41188201
responding
to
deficiencies
cited
in
DER;
addresses
characterization
of
previously
unidentified
photodegradates);
MRID
43075202
(
an
addendum
in
response
to
DER
for
MRID
41188201
that
addresses
light
sources
and
their
comparability);
MRID
44436901
(
Environmental
Fate
Overview
summarizing
DER
issues
and
responses).

Photolysis
on
soil
(
161­
3)
Not
a
model
input.
In
spite
of
numerous
study
flaws,
inconsistencies,
and
irregular
kinetics,
T1/
2
in
laboratory
soil
plates
is
apparently
relatively
short.
However,
the
major
identified
transformation
product,
AE
F132347
(
photoproduct
I)
is
the
same
photoisomer
found
in
aqueous
photolysis.
In
field
studies
on
bare
soil,
parent
was
long­
lived
with
only
minimal
evidence
of
photolysis.
Supplemental.
Essentially
the
same
study
authored
by
Klehr,
Iwan,
and
Riemann
was
submitted
with
MRID
00156241(
1981)
and
MRID
41364902
(
1983).
The
latter
MRID
is
a
essentially
a
published
version
of
the
former.
EFED
review
28
Apr
1993.
MRID
44436901
(
Environmental
Fate
Overview
summarizing
DER
issues
and
responses).
Page
81
of
129
Aerobic
Soil
Met.
(
162­
1).
All
half­
lives
adjusted
by
this
reviewer
to
25
°
C
and
75%
of
1/
3
bar
soil
suction.

MRID
41950101:
140
days­­
phenyl
label,
German
standard
sandy
loam
soil
2.3.

MRID
46119601:
206,
436,
and
253
days­­
thiadiazol
label
in
sandy
loam
(
UK),
loamy
sand
(
NC),
and
silt
loam
(
Il),
respectively.
Upper
90%
one­
tail
C.
I:
T1/
2
=
363
days
N=
4
(
140,
206,
436,
and
253
days)
Mean
T1/
2
=
259
days
Std.
Dev.
=
+
127
days
90%
C.
I.
=
+
104
days
(
Upper
90%
T1/
2
=
Mean
+
90%
C.
I.)
MRID
41950101,
Feyerabend,
M.,
1991;
EFED
review
28
Apr
1993.
Reviewer
incorrectly
reported
half­
life
as
111
days
at
21
°
C
and
78%
of
1/
3­
bar.
Value
should
be
182
days
(
based
on
semi­
log
transformed
data).
Halflife
becomes
140
days
after
adjustment
to
25
°
C
and
75%
of
1/
3­
bar
soil
water
potential.

MRID
46119601,
Allan,
J.
G.,
2003;
EFED
review
May
2004.
Half­
lives
at
20
°
C
and
40%
MWHC
were
163,
355,
and
322
days,
respectively,
extrapolated
from
study
periods
of
160­
168
days.

Anaerobic
Soil
(
162­
2)
Essentially
Stable
[
431­
day
extrapolated
regression
half­
life
from
anaerobic
period
lasting
90
days
(
from
day
30
to
day
120)
at
21C.
Large
95%
C.
I.
in
half­
life
of
230­
3400
days
(
0.6­
9.0
years);
r­
sq
=
0.39.]
MRID
41945201,
Feyerabend,
M.,
1991.
EFED
review
28
Apr
1993.

Anaerobic
Aquatic
Met.
(
162­
3)
Stable
MRID
4266601,
Leake
and
Allan,
1993;
EFED
review
May
2004.

Aerobic
Aquatic
Met.
(
162­
4)
No
data
submitted.
Default
=
2
x
aerobic
soil
T1/
2
T1/
2
=
2
x
364
days
=
728
days
No
data
submitted.

Sorption
(
163­
1)
Sand:
German
Std.
Soil
#
2.1
Loamy
sand:
German
Std.
Soil
#
2.2
Sandy
loam:
German
Std.
Soil
#
2.3
Sandy
clay
loam:
UK,
Schering
#
171
Respectively
(
Freundlich
units):
Kf/
ads
Kf/
oc/
ads
1/
n
r2
4.36
908
0.721
0.997
16.2
786
0.771
0.999
7.33
780
0.719
0.999
18.8
494
0.817
1.000
Koc
model
is
appropriate
(
r2
=
0.88)
N
=
4
values
Min
Kf,
Kfoc:
4.36,
494
Max
Kf,
Kfoc:
18.8,
908
Median
Kfd,
Kfoc:
11.8,
783
Average
Kfd,
Kfoc:
11.7+
6.9,
742+
176
MRID
41364909,
Bruhl,
R.,
1988.
EFED
review
28
Apr
2004.
Foreign
soils,
3
German
standard
soils
and
1
United
Kingdom
soil;
not
able
to
compare
these
4
soils
with
USDA
classification.
Page
82
of
129
APPENDIX
D:
GENEEC
Input
&
Output
Files
for
Ecological
Assessment
Page
83
of
129
INPUT/
OUTPUT
TABLES
FOR
GENEEC2
(
A
Tier
I
Simulation
Model
for
Aquatic
Ecological
Exposure
Assessment)
(
Version
2.0;
August
1,
2001)

WITH
EXPLANATION
OF
THE
BASIS
FOR
APPLICATION
RATES
AND
FOR
HANDLING
THE
SPECIAL
CASE
OF
AQUEOUS
PHOTOLYSIS
Product
labels
specify
no
more
than
two
annual
applications
of
thidiazuron
by
aerial
or
ground
spray,
their
summation
not
to
exceed
0.3
lb
of
the
active
ingredient
(
a.
i.)
thidiazuron
per
acre.
The
maximum
single
application
rate
is
no
more
than
0.2
lb
a.
i./
acre,
with
split
applications
as
close
as
five
to
seven
days
apart.
However,
as
indicated
in
the
GENEEC
input/
output
tables
below
for
model
runs
numbered
as
101
and
102,
which
are
for
a
hypothetical
single,
aerial
application
at
the
maximum
total
annual
rate
of
thidiazuron
of
0.3
lb/
acre,
whether
the
total
annual
maximum
is
applied
all
at
once
or
is
split
variously,
[
for
example,
(
0.1
+
0.2)
lb/
acre
or,
as
illustrated
in
runs
103
and
104
below,
(
0.15
+
0.15)
lb/
acre],
differences
are
negligible
for
our
purposes.

Photolysis
is
a
special
modeling
consideration
for
thidiazuron.
Thidiazuron
undergoes
relatively
rapid
branching
photolysis
in
water
into
only
two
photoproducts.
Formation
of
these
products
is
in
constant
ratio
and
in
complementary
stoichiometric
yield
with
parent.

Photoproduct
I
(
AE
F132347,
see
chemical
structure
in
Appendix
II)
is
an
isomer
of
parent
differing
only
in
the
relative
positions
of
the
sulfur
atom
and
the
two
nitrogen
atoms
in
the
5­
membered
ring.
Like
parent,
photoproduct
I
is
moderately
ecotoxic
(
slightly
more
toxic
than
parent,
based
on
the
limited
data
discussed
in
the
main
text
of
this
document).
It
has
a
reviewer­
calculated
asymptotic
experimental
limit
of
production
of
77%
of
parent
at
pH
5,
28%
at
pH
7,
and
17%
at
pH
9.
This
product
was
stable
to
further
photolysis
under
the
experimental
study
conditions
and
durations
(
original
MRID
41188201,
related
follow­
up
MRIDs
41364910
and
43075202,
and
fate
overview
document
with
MRID
44436901).
Soil/
sediment
sorption
data
and
non­
photolytic
transformation
data
are
available
only
for
parent.
However,
based
on
its
isomeric
chemical
structure,
photoproduct
I,
except
for
photolysis,
would
be
expected
to
have
fate
properties
similar
to
parent.

Photoproduct
II
(
AE
C421200,
chemical
structure
in
Appendix
II)
is
a
substantially
degraded,
practically
non­
ecotoxic
product
(
based
on
the
limited
data
discussed
in
the
main
text
of
this
document),
and
has
a
complementary
asymptotic
limit
of
production
to
photoproduct
I
of
23%
of
parent
at
pH
5,
72%
at
pH
7,
and
83%
at
pH
9.
This
product
was
also
stable
to
further
photolysis
under
study
conditions.
Soil/
sediment
sorption
data
and
non­
photolytic
transformation
data
are
available
only
for
parent.
However,
because
of
its
degraded
nature
and
a
modicum
of
direct
evidence
indicating
that
photoproduct
II
is
practically
non­
toxic
for
ecological
risk
assessment
purposes,
we
assume
that
photoproduct
II
does
not
contribute
to
ecological
risk,
and
ignore
its
potential
presence.

For
the
purposes
of
this
assessment,
we
shall
protectively
assume
the
pH
5
results
for
which
parent
was
slightly
more
stable
and
for
which
77%
of
parent
reaching
water
is
converted
to
the
stable
isomer
photoproduct
I
(
AE
F132347).
Under
these
conditions,
the
thidiazuron
photolytic
half­
life,
after
adjustment
of
continuous
experimental
radiation
intensity
to
12
hours
of
solar
intensity
at
40
deg.
North
latitude
at
end
of
March
or
beginning
of
September,
was
0.0602
days
or
1.44
hours.
These
are
reviewer­
calculated
values
from
Page
84
of
129
MRID
41188201,
page
40,
Table
5a;
and
page
36,
Table
2,
and
are
in
close
agreement
with
those
of
the
study
author.
Alteration
of
latitude
or
date
of
application
have
but
a
minor
influence
on
results
for
our
purposes.
Halflives
at
higher
pHs
were
somewhat
shorter
(
approximately
6%
shorter
at
pH
7
and
approximately
40%
shorter
at
pH
9,
based
on
same
study
Table
2).

To
further
simplify
exposure
estimates,
rather
than
separately
apportioning
parent
and
photoproduct
I
exposures
and
toxicities,
we
chose
to
add
exposure
concentrations
of
parent
and
photoproduct
I
(
ignoring
the
practically
nontoxic
photoproduct
II),
and
use
the
toxicity
of
the
slightly
more
toxic
photoproduct
I
for
parent
also.
Whether
we
use
this
simplified
procedure
or
add
the
separate
contributions
from
parent
and
photoproduct
I
makes
no
meaningful
difference
in
the
risk
assessment
in
this
particular
case.

With
the
restrictions
on
chemical
kinetics
imposed
by
current
standard
Agency
simulation
models,
including
GENEEC,
in
order
to
determine
the
exposure
contributions
from
parent
and
photoproduct
I,
it
is
necessary
to
do
some
external
calculations
using
the
output
from
two
simulations
or
"
runs."
One
model
run
is
with
aqueous
photolysis
"
turned
off,"
the
other
with
photolysis
"
turned
on."

The
following,
reviewer­
derived
formulas
account
for
the
photolysis
process
and
risk
assessment
approach
described
above:

Ci(
t)
=
0.77[
Cp(
101)­
Cp(
102)],
where
Ci(
t)
=
concentration
of
photoisomer
as
a
function
of
time
0.77
=
the
branching
fraction
of
parent
that
is
photolyzed
to
the
photoisomer
Cp(
101)
=
concentrations
of
parent
given
in
Run
101
below,
which
are
concentrations
that
would
result
if
parent
were
stable
to
photolysis
(
photolysis
"
turned
off")
Cp(
102)
=
concentrations
of
parent
given
in
Run
102
below
with
observed
photolysis
"
turned
on."

Therefore,
the
summation
of
parent
and
photoisomer
concentrations
is:

Conc.
of
Parent
+
Conc.
of
Photoisomer
=
Cp(
102)
+
0.77[
Cp(
101)­
Cp(
102)]

Rounding
to
two
digits,
the
resulting
aquatic
exposure
concentration
summations
derived
from
the
GENEEC
runs
and
used
for
the
aquatic
risk
assessment
are:

Concentrations
(
ppb
or
:
g/
L)

Peak
4­
Day
Avg.
21­
Day
Avg.
60­
Day
Avg.
90­
Day
Avg.

11
11
9.7
8.6
8.2
Applying
the
same
methodology
to
the
results
of
runs
103
and
104
for
split
applications
gives
the
analogous
equation:

Conc.
of
Parent
+
Conc.
of
Photoisomer
=
Cp(
104)
+
0.77[
Cp(
103)­
Cp(
104)]

As
is
apparent
from
the
tables,
corresponding
pairs
of
concentrations
are
virtually
the
same
as
for
the
single
application
at
the
maximum
annual
rate.
Page
85
of
129
In
all
cases,
peak
concentrations
are
virtually
the
same.
Minor
decreases
in
the
summation
of
parent
and
the
photoisomer
concentrations
over
time
reflect
primarily
the
77%
conversion
to
photoproduct
I.

RUN
No.
101
FOR
Thidiazuron
ON
Cotton
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.300(
.300)
1
1
494.0
31.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
364.00
2
N/
A
.00­
.00
728.00
728.00
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
10.87
10.84
10.65
10.23
9.93
RUN
No.
102
FOR
Thidiazuron
ON
Cotton
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.300(
.300)
1
1
494.0
31.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
364.00
2
N/
A
.0602­
7.46
728.00
7.39
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
10.57
9.84
6.59
3.29
2.27
Page
86
of
129
RUN
No.
103
FOR
Thidiazuron
ON
Cotton
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.150(
.298)
2
7
494.0
31.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
365.00
2
N/
A
.00­
.00
728.00
728.00
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
10.81
10.78
10.59
10.18
9.88
RUN
No.
104
FOR
Thidiazuron
run1
ON
Cotton
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Koc
(
PPM
)
(%
DRIFT)
(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
.150(
.298)
2
7
494.0
31.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
364.00
2
N/
A
.0602­
7.46
728.00
7.39
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
10.23
9.52
6.37
3.18
2.19
Page
87
of
129
APPENDIX
E:
Ecological
Hazard
Data
Page
88
of
129
Table
1:
Acute
Toxicity
of
Thidiazuron
to
Freshwater
Fish
Species
%
a.
i.
96­
hr
LC50,
µ
g/
L
(
confid.
int.)
NOAEC
(
µ
g/
L)
Study
Propertiesa
Toxicity
Classification
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Rainbow
trout
99.3
>
19,000
>
19,000
M,
S
slightly
toxic
42069202,
Schupner,
et.
al.
1991.
Coreb
Bluegill
sunfish
99.3
>
32,000
>
32,000
M,
S
slightly
toxic
42069201,
Schupner,
et.
al.
1991.
Coreb
EPA
PC
Code:
120301
­
Thidiazuron
Photodegradate
(
AE
F132347)

Rainbow
trout
97.4
w:
w
6700
(
5700
­
7900)
2300
M,
S
moderately
toxic
46203508,
Blankinshi
p,
A.
S..,
et.
al.,
2003.
core
EPA
PC
Code:
120301
­
Thidiazuron
metabolite
(
AE
F132345)

Rainbow
trout
97.4
w:
w
>
101,000
2300
M,
S
moderately
toxic
462035­
15,
Palmer,
S.
J.,
et.
al,
2003.
core
EPA
PC
Code:
120301
­
Thidiazuron
Photodegradate
(
AE
C421200)

Rainbow
trout
98.4
w:
w
>
103000
103,000
M,
S
Practically
nontoxic
462035­
11,
Palmer,
S.
J.,
et.
al.,
2003.
core
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.
b
The
compound
was
tested
to
the
limits
of
solubility.
No
mortalities
were
observed.
Page
89
of
129
Table
2:
Acute
Toxicity
of
Thidiazuron
to
Freshwater
Invertebrates
Species
%
a.
i.
48­
hr
EC50,
µ
g/
L
(
confid.
int.)
NOAEC
(
µ
g/
L)
Study
Propertiesa
Toxicity
Classification
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Daphnia
magna
99.5
w/
w
5,700
(
4700
­
9500)
1200
M,
S
moderately
toxic
462035­
03,
Blankinship,
A.
S..,
et.
al.,
2003.
core
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Daphnia
magna
98.4
10,000
(
9000
­
11,100)
5,600c
N,
S
moderately
toxic
00066167
(
Accession
#
099819),
Brown.
A.,
1979.
core
EPA
PC
Code:
120301
­
Thidiazuron
PhotometaB0lite
(
AE
F132347)

Daphnia
magna
97.4
w/
w
>
12,000
b
5100
M,
S
Slightly
toxic
462035­
09,
Blankinship,
A.
S..,
et.
al.,
2003.
core*

EPA
PC
Code:
120301
­
Thidiazuron
Urea
metaB0lite
(
AE
F132345)

Daphnia
magna
91
w/
w
>
98,000
c
12000
M,
S
Slightly
toxic
462035­
16,
Palmer,
S.
J.,
2003.
core
EPA
PC
Code:
120301
­
Thidiazuron
PhotometaB0lite
(
AE
C421200)

Daphnia
magna
98.4
>
99,000
c
24000
M,
S
Slightly
toxic
462035­
12,
Palmer,
S.
J.,
2003.
core
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.
b
A
definitive
LC50
could
not
be
determined
because
the
compound
was
tested
to
the
limit
of
solubility.
c
A
definitive
LC50
could
not
be
determined
due
to
the
lack
of
a
50%
mortality
at
the
highest
test
level.
Page
90
of
129
Table
3:
Acute
Toxicity
of
Thidiazuron
to
Estuarine
Fish
Species
%
a.
i.
96­
hr
LC50
µ
g/
L
(
confid.
int.)
NOAEC
(
µ
g/
L)
Study
Propertiesa
Toxicity
Classification
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Sheephead
minnow
99.3
>
36,000
<
36,000
M,
S
slightly
toxic
418461­
01,
Schupner,
J.
K.
et.
al.,
1991.
Coreb
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.
b
A
definitive
LC50
could
not
be
determined
because
the
compound
was
tested
to
the
limit
of
solubility.
Page
91
of
129
Table
4:
Acute
Toxicity
of
Thidiazuron
to
Estuarine/
Marine
Invertebrates
Species
%
a.
i.
96­
hr
LC50
µ
g/
L
(
confid.
int.)
NOAEC
(
µ
g/
L)
Study
Propertiesa
Toxicity
Classification
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Mysid
shrimp
99.3
3,240
(
2,890
­
3,770)
1400
M,
S
moderately
toxic
418461­
02,
Schupner,
J.
K.,
1991.
core
Eastern
oysterlarvae
embryo
99.3
5,384
(
4,768
­
6,157)
1060
M,
F­
T
moderately
toxic
421320­
01,
Ward,
S.
G.,
1991.
core
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.
Page
92
of
129
Table
5:
Chronic
(
Early­
life)
Toxicity
of
Thidiazuron
to
Fish
Species
%
a.
i.
NOAEC
(
µ
g/
L)
LOAEC
(
µ
g/
L)
Study
Propertiesa
Most
sensitive
parameter
MRID
,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Fathead
minnow
99.3
5700
>
5700
M,
F­
T
Hatchability,
fry
survial,
Total
survival
422703­
01,
Cohle,
P.,
1992.
Core
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.

Table
6:
Chronic
(
Life­
cycle)
Toxicity
of
Thidiazuron
to
Invertebrates
Species
%
ai
NOAEC
(
µ
g/
L)
LOAEC
(
µ
g/
L)
Study
Propertiesa
Most
sensitive
parameter
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Daphnid
99.3
<
100b
100
M,
S
Length
421320­
02c,
Blakemore,
G.
C,
et.
al.,
1991.
Core
a
M=
mean­
measured
chemical
concentrations,
N=
nominal
chemical
concentrations;
F­
T=
flow­
through;
S=
static.

b
21
day
survival
LC50
=
678
µ
g/
L
95%
c.
i.:
504
­
1010
µ
g/
L.
EC10
=
720
µ
g/
L
c
Up­
graded
to
Core
under
MRID
#
436650­
01.
Page
93
of
129
Table
7:
Acute
Toxicity
of
Thidiazuron
to
Aquatic
Plants
Species
%
a.
i.
EC50,
(
µ
g
ai/
L)
NOAEC
/
EC05
(
µ
g/
L)
a.
i.
Most
sensitive
parameter
Initial/
mean
measured
concentrations
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Vascular
Plant
Duckweed
(
Lemna
gibba)
99.5
>
24,000
8600
/
570
Frond
count
mean
462035­
06
Desjardins,
D.
et.
al.,
2003.
Core
Nonvascular
Plants
Green
algae
(
Selenastrum
capricornutum)
99.3
>
150
150
cell
growth
nominal
417611­
04
Hughes,
1990.
Core
Freshwater
diatom
(
Navicula
pelliculosa)

Blue­
green
algae
(
Anabaena
flosaquae
99.5
6000
2800
/
1800
Plant
biomass
mean
462035­
04,
Desjardins,
D.
et.
al.,
2003.
Supplemental
a
Marine
diatom
(
Skeletonema
costatum)
99.5
860
110/
56
Growth
rate
&
Plant
biomass
mean
462035­
05,
Desjardins,
D.
et.
al.,
2003.
Core
EPA
PC
Code:
120301
­
Thidiazuron
photometaboite
(
AE
F132347)

Vascular
Plant
Duck
weed
(
Lemna
gibba)

Nonvascular
Plants
Greeen
Algae
(
Scenedesmus
subspicatus)
97.4
980
220
/
310
Cell
density
mean
462035­
10,
Desjardins,
D.
et.
al.,
2003.
Supplemental
a
Freshwater
diatom
(
Navicula
pelliculosa)

Blue­
green
algae
(
Anabaena
flosaquae
Table
7:
Acute
Toxicity
of
Thidiazuron
to
Aquatic
Plants
Species
%
a.
i.
EC50,
(
µ
g
ai/
L)
NOAEC
/
EC05
(
µ
g/
L)
a.
i.
Most
sensitive
parameter
Initial/
mean
measured
concentrations
MRID,
Author,
Year
Status
Page
94
of
129
Marine
diatom
(
Skeletonema
costatum)

EPA
PC
Code:
120301
­
Thidiazuron
Urea
metabolite
(
AE
F132345)

Vascular
Plant
Duck
weed
(
Lemna
gibba)

Nonvascular
Plants
Greeen
Algae
(
Scenedesmus
subspicatus)
91
w/
w
ai
3400
1300
/
1200
Cell
density
mean
462035­
17,
Desjardins,
D.
et.
al.,
2003.
Supplemental
a
Freshwater
diatom
(
Navicula
pelliculosa)

Blue­
green
algae
(
Anabaena
flosaquae

Marine
diatom
(
Skeletonema
costatum)

EPA
PC
Code:
120301
­
Thidiazuron
Photodegradate
(
AE
C421200)

Vascular
Plants
Duck
weed
(
Lemna
gibba)

Nonvascular
plants
Green
Algae
(
Scenedesmus
subspicatus)
98.4
70000
49,000
/
53,000
Cell
density
mean
462035­
13,
Desjardins,
D.
et.
al.,
2003.
Supplemental
a
Freshwater
diatom
(
Navicula
pelliculosa)

Blue­
green
algae
(
Anabaena
flosaquae
Table
7:
Acute
Toxicity
of
Thidiazuron
to
Aquatic
Plants
Species
%
a.
i.
EC50,
(
µ
g
ai/
L)
NOAEC
/
EC05
(
µ
g/
L)
a.
i.
Most
sensitive
parameter
Initial/
mean
measured
concentrations
MRID,
Author,
Year
Status
Page
95
of
129
Marine
diatom
(
Skeletonema
costatum)

a
Since
the
study
duration
was
for
3
days
instead
of
5,
the
study
can
only
be
classified
as
a
Tier
1
study.

Table
8:
Acute
Toxicity
to
Thidiazuron
to
Birds
(
oral
administration)

Species
%
a.
i.
LD50,
mg/
kg­
bw
(
conf.
interval)
NOAEC,
mg/
kgbw
Effects
Toxicity
Classification
(
based
on
a.
i.)
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Bobwhite
quail
98.43
>
3160
3160
No
sub­
lethal
effects
or
other
treatment
related
effects
were
observed.
practically
nontoxic
00066168
(
Accession
#
099819),
Fletcher,
D.
1979.
core
EPA
PC
Code:
120301
­
Thidiazuron
formulated
product
(
CP
503
WP
50)

Japanese
Quail
50
>
9989a
9989a
No
sub­
lethal
effects
observed
practically
nontoxic
00038144,
(
Accession
#
095969),
Ross,
D.,
1976.
Supplemental
a
The
LD50
is
4995
mg
ai/
kg­
bw
when
adjusted
to
100%
ai.
Page
96
of
129
Table
9:
Acute
Toxicity
to
Thidiazuron
to
Birds
(
dietary
administration)

Species
%
a.
i.
LC50,
mg/
kgdiet
(
conf.
interval)
NOAEC,
mg/
kg­
diet
Effects
Toxicity
Classification
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Bobwhite
quail
98.4
>
5000
5000
No
sub­
lethal
effects
or
other
treatment
related
effects
were
observed.
practically
nontoxic
00816­
29,
Fletcher,
D.,
1981.
Core
Bobwhite
quail
99.5
>
5215
5215
No
sub­
lethal
effects
or
other
treatment
related
effects
were
observed.
practically
nontoxic
462035­
02,
Bowers,
L.
M.,
2003.
Core
Mallard
duck
98.43
>
5000
5000
No
sub­
lethal
effects
or
other
treatment
related
effects
were
observed.
practically
nontoxic
00066169
(
Accession
#
099819),
Fletcher,
D.
1979.
core
Bobwhite
quail
50
>
5000
5000
No
sub­
lethal
effects
or
other
treatment
related
effects
were
observed.
practically
nontoxic
0081629,
(
Accession
#
245834),
Fletcher,
D.,
1981
Core
Page
97
of
129
Table
10:
Mammalian
Acute
Oral
Toxicity
to
Thidiazuron
Species
%
a.
i.
LD50
(
mg
a.
i./
kg­
diet)
Toxicity
Classification
MRID
#,
Author,
Year
Statusa
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

laboratory
rat
(
Rattus
norvegicus)
98.7
>
2000
Category
III
46121501,
Coleman,
D.
G.,
2001
Acceptable
a
Status
(
acceptability)
based
on
HEDs
guidelines.
Page
98
of
129
Table
11:
Mammalian
Developmental
and
Chronic
Toxicity
to
Thidiazuron
Test
Type
%
a.
i.
NOAEC
(
mg
ai/
kgdiet
LOAEC
(
mg
ai/
kgdiet
Effects
MRID
#,
Author,
Year
Statusa
EPA
PC
Code:
120301
­
Thidiazuron
Technical
SN
49537
2­
generation
reproductive
(
rat)
400
ppm
(
35.4/
39.8
mg/
kg/
day
[
M/
F])
1200
ppm
(
108.5/
121.1
mg/
kg/
day
[
M/
F])
Delayed
sexual
maturity,
disrupted
estrous
cycling
46209601
3­
generation
reproductive
(
rats)
100
200
ppm
(
10
mg/
kg
bw/
da)
600
(
30
mg/
kg
bw/
da)
b
­
Decreased
F3
litter
size
at
200
ppm
429589­
01,
Rees,
S.
J.,
1992.
Core­
Supplementary
a
Status
(
acceptability)
based
on
HEDs
guidelines.
b
Based
on
decrease
epidermal
sperm
counts.

Table
12:
Acute
Contact
Toxicity
of
Thidiazuron
to
Non­
target
Insects
Species
%
a.
i.
Toxicity
endpoint
Toxicity
classification
MRID,
Author,
Year
Status
Contact
LD50
(
µ
g
ai/
bee)

EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Honey
bee
(
Apis
mellifera)
99.5
>
100
Practically
non­
toxic
462035­
01,
Kling,
A.,
2003.
Corea
EPA
PC
Code:
120301
­
Thidiazuron
AE
B049573
00
SC42
(
formulated
product)

Honey
bee
(
Apis
mellifera)
41.9
>
98.1
Practically
non­
toxic
462035­
18,
Waltersdorfer,
A.,
2002.
Coreb
a
Supplemental
for
Oral
LD50
of
>
105.25
µ
g/
bee.
b
Supplemental
for
Oral
LD50
of
>
197.8
µ
g/
bee.

Table
13:
Acute
Toxicity
of
Thidiazuron
to
Non­
target
Insects
Species
%
a.
i.
Toxicity
endpoint
Toxicity
classification
MRID,
Author,
Year
Status
LC50
(
lb
ai/
A)

EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Predatory
mite
(
Typlodromus
pyri)
41.9
>
0.1782
N/
A
462035­
21,
Waltersdorfer,
A.,
2002..
Supplemen
tala
EPA
PC
Code:
120301
­
Thidiazuron
AE
B049573
00
SC42
(
formulated
product)
Table
13:
Acute
Toxicity
of
Thidiazuron
to
Non­
target
Insects
Page
99
of
129
Parasoid
wasp
(
Aphidius
rhopalosiphi)
41.9
>
0.1782
N/
A
462035­
20,
Waltersdorfer,
A.,
2002.
Coreb
a
Non­
guideline
study.
Page
100
of
129
Table
14:
Acute
Toxicity
of
Thidiazuron
to
Earthworm
(
Eisenia
foetida)

Species
%
a.
i.
LC50
(
mg
ai/
kg)
(
Conf.
Interval)
NOAEC
(
mg
ai/
kg)
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron,
SC
500
G/
L
Earthworm
(
Eiseenia
foetide)
42.6
>
426a
53.3a
462035­
22Niestedt,
K.
M.,
2003.
Supplementalb
EPA
PC
Code:
120301
­
Thidiazuron
photometaboite
(
AE
F132347)

Earthworm
(
Eiseenia
foetide)
97.4
>
1000
250
462035­
07,
Sindermann,
et.
al.,
2003.
Supplementalb
EPA
PC
Code:
120301
­
Thidiazuron
photometaboite
(
AE
F1323457)

Earthworm
(
Eiseenia
foetide)
91
1000
62.5
462035­
14,
Sindermann,
et.
al.,
2003.
Supplementalb
a
LC
50
and
NOEC
>
1000
and
125
mg
product/
kg
b
Performed
under
OECD
guidelines.
Not
required
by
EPA.

Terrestrial
Plants
Terrestrial
plant
testing
(
seedling
emergence
and
vegetative
vigor)
is
required
for
herbicides
that
have
terrestrial
non­
residential
outdoor
use
patterns
and
that
may
move
off
the
application
site
through
volatilization
(
vapor
pressure
>
1.0
x
10­
5mm
Hg
at
25oC)
or
drift
(
aerial
or
irrigation)
and/
or
that
may
have
endangered
or
threatened
plant
species
associated
with
the
application
site.

Currently,
terrestrial
plant
testing
is
not
required
for
pesticides
other
than
herbicides
except
on
a
case­
by­
case
basis
(
e.
g.,
labeling
bears
phytotoxicity
warnings
incident
data
or
literature
that
demonstrate
phytotoxicity).

For
seedling
emergence
and
vegetative
vigor
testing
the
following
plant
species
and
groups
should
be
tested:
(
1)
six
species
of
at
least
four
dicotyledonous
families,
one
species
of
which
is
soybean
(
Glycine
max)
and
the
second
is
a
root
crop,
and
(
2)
four
species
of
at
least
two
monocotyledonous
families,
one
of
which
is
corn
(
Zea
mays).

Tier
1
tests
measure
the
response
of
plants,
relative
to
a
control,
at
a
test
level
that
is
equal
to
the
highest
use
rate
(
expressed
as
lbs
ai/
A).
If
effects
are
observed
in
this
test,
the
registrant
is
required
to
proceed
to
the
Tier
2
level.

Terrestrial
Tier
2
studies
are
required
for
all
low
dose
herbicides
(
those
with
the
maximum
use
rate
of
0.5
lbs
ai/
A
or
less)
and
any
pesticide
showing
a
negative
response
equal
to
or
greater
than
25%
in
Tier
1
tests.
The
registrant
may
opt
to
proceed
directly
to
Tier
2
testing.
Page
101
of
129
Tier
2
tests
measure
the
response
of
plants,
relative
to
a
control,
and
five
or
more
test
concentrations.
Results
of
Tier
1
and
2
toxicity
testing
on
the
technical/
TEP
material
are
tabulated
below.

Table
15
Toxicity
of
Thidiazuron
to
Terrestrial
Plants
(
Seedling
Emergence
­
Tier
1)

Species
%
a.
i.
Dose
(
Max.
Label
Rate)
(
lbs
ai/
acre)
%
Response
Endpoint
Affected
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Monocot
­
onion
99.3
0.2
<
25
none
418213­
01,
Downey,
S.,
1991.
core
corn
<
25
none
oat
<
25
none
wheat
<
25
none
Dicot
­
soybean
<
25
none
radish
(
root
crop)
<
25
none
lettuce
<
25
none
cucumber
<
25
none
tomato
<
25
none
carrot
<
25
none
Page
102
of
129
Table
16:
Toxicity
of
Thidiazuron
to
Terrestrial
Plants
(
Vegetative
Vigor
­
Tier
1)

Species
%
a.
i.
Dose
(
Max.
Label
Rate)
(
lbs
ai/
acre)
%
Response
Endpoint
Affected
MRID
Status
EPA
PC
Code:
120301
­
Thidiazuron
Technical
(
AE
B049537
00
ID99
0003)

Monocot
­
onion
99.3
0.2
>
25
weight
inhibition
418191­
01,
Downey,
S.,
1990.

core
corn
<
25
none
oat
<
25
none
wheat
<
25
none
Dicot
­
soybean
>
25
increased
suckering
radish
(
root
crop)
<
25
none
lettuce
>
25
necrosis,
weight
inhibition
cucumber
>
25
necrosis,
leaf
darkening,
deformity,
height
inhibition
tomato
>
25
deformity,
height
inhibition
carrot
<
25
none
Table
17:
Toxicity
of
Thidiazuron
SC500
g/
L
(
Thidiazuron
SC42)
to
Terrestrial
Plants
(
Seedling
Emergence
­
Tier
1
and
Tier
2)

Species
%
a.
i.
EC25,
(
lbs
ai/
acre)
NOAEC
/
EC05
(
lbs
ai/
acre)
Most
sensitive
parameter
MRID,
Author,
Year
Status
EPA
PC
Code:
120301
­
Thidiazuron
AE
B049573
00
SC42
(
formulated
product)

Monocot
42.6
Page
103
of
129
onion1
<
0.1783
<
0.1783/
<
0.1783
emergence
459085­
01,
Teixeira,
D.,
2003.
Supplemental
corn
>
0.1783
0.1783/
>
0.1783
emergence,
shoot
length,
dry
weight,
Core
oat1
<
0.1783
<
0.1783/
<
0.1783
emergence
Supplemental
wheat
>
0.1783
0.1783/
>
0.1783
emergence,
shoot
length,
dry
weight,
Core
Dicot
soybean
>
0.1783
0.1783/
0.1783
emergence,
shoot
length,
dry
weight,
Supplemental
turnip
(
root
crop)
2
0.0410
<
0.0223/
0.0031
shoot
length,
dry
weight
Core
lettuce2
0.0152
0.0111/
0.0039
emergence,
dry
weight
Core
cucumber
>
0.1783
0.1783/
<
0.1783
emergence,
shoot
length,
dry
weight
Supplemental
tomato
>
0.1783
0.1783/
>
0.1783
emergence,
shoot
length,
dry
weight
Supplemental
cabbage
>
0.1783
0.1783/
<
0.1783
emergence,
shoot
length,
dry
weight
Supplemental
1
Tier
2
tests
required
2Conducted
as
Tier
2
tests.
Page
104
of
129
Table
18:
Toxicity
of
Thidiazuron
SC500
g/
L
(
Thidiazuron
SC42)
to
Terrestrial
Plants
(
Vegetative
Vigor
­
Tier
1
and
Tier
2)

Species
%
a.
i.
EC25,
(
lbs
ai/
acre)
NOAEC
/
EC05
(
lbs
ai/
acre)
Most
sensitive
parameter
MRID
Status
EPA
PC
Code:
120301
­
Thidiazuron
AE
B049573
00
SC42
(
formulated
product)

Monocot
42.6
onion
>
0.1783
0.1783/
>
0.1783
shoot
length,
dry
weight
459215­
01,
Teixeira,
D.,
2003.
Core
corn
>
0.1783
0.1783/
>
0.1783
shoot
length,
dry
weight,
Core
oat
>
0.1783
0.1783/
>
0.1783
shoot
length,
dry
weight,
Core
wheat
>
0.1783
0.1783/
>
0.1783
shoot
length,
dry
weight,
Core
Dicot
soybean1
>
0.1783
0.0111/
0.0024
shoot
length,
dry
weight,
Core
turnip
(
root
crop)
>
0.1783
0.1783/
<
0.1783
shoot
length,
dry
weight
Core
lettuce1
0.0011
0.00019/
0.00005
dry
weight
Core
cucumber1
0.01783
0.0056/
0.0075
dry
weight
Core
tomato1
0.1426
0.0222/
0.0098
shoot
length
Core
cabbage1
>
0.1783
0.1783/
<
0.1783
shoot
length,
dry
weight
Core
1Conducted
as
Tier
2
tests.
Page
105
of
129
APPENDIX
F:
The
Risk
Quotient
Method
Page
106
of
129
The
Risk
Quotient
Method
is
the
means
used
by
EFED
to
integrate
the
results
of
exposure
and
ecotoxicity
data.
For
this
method,
RQs
(
RQs)
are
calculated
by
dividing
exposure
estimates
by
ecotoxicity
values
(
i.
e.,
RQ
=
EXPOSURE/
TOXICITY),
both
acute
and
chronic.
These
RQs
are
then
compared
to
OPP's
levels
of
concern
(
LOCs).
These
LOCs
are
criteria
used
by
OPP
to
indicate
potential
risk
to
non­
target
organisms
and
the
need
to
consider
regulatory
action.
EFED
has
defined
LOCs
for
acute
risk,
potential
restricted
use
classification,
and
for
endangered
species.

The
criteria
indicate
that
a
pesticide
used
as
directed
has
the
potential
to
cause
adverse
effects
on
nontarget
organisms.
LOCs
currently
address
the
following
risk
presumption
categories:
(
1)
acute
­
there
is
a
potential
for
acute
risk;
regulatory
action
may
be
warranted
in
addition
to
restricted
use
classification;
(
2)
acute
restricted
use
­
the
potential
for
acute
risk
is
high,
but
this
may
be
mitigated
through
restricted
use
classification
(
3)
acute
endangered
species
­
the
potential
for
acute
risk
to
endangered
species
is
high,
regulatory
action
may
be
warranted,
and
(
4)
chronic
risk
­
the
potential
for
chronic
risk
is
high,
regulatory
action
may
be
warranted.
Currently,
EFED
does
not
perform
assessments
for
chronic
risk
to
plants,
acute
or
chronic
risks
to
nontarget
insects,
or
chronic
risk
from
granular/
bait
formulations
to
mammalian
or
avian
species.

The
ecotoxicity
test
values
(
i.
e.,
measurement
endpoints)
used
in
the
acute
and
chronic
RQs
are
derived
from
required
studies.
Examples
of
ecotoxicity
values
derived
from
short­
term
laboratory
studies
that
assess
acute
effects
are:
(
1)
LC
50
(
fish
and
birds),
(
2)
LD
50
(
birds
and
mammals),
(
3)
EC
50
(
aquatic
plants
and
aquatic
invertebrates),
and
(
4)
EC
25
(
terrestrial
plants).
Examples
of
toxicity
test
effect
levels
derived
from
the
results
of
long­
term
laboratory
studies
that
assess
chronic
effects
are:
(
1)
LOAEL
(
birds,
fish,
and
aquatic
invertebrates),
and
(
2)
NOAEL
(
birds,
fish
and
aquatic
invertebrates).
The
NOAEL
is
generally
used
as
the
ecotoxicity
test
value
in
assessing
chronic
effects.

Risk
presumptions,
along
with
the
corresponding
RQs
and
LOCs
are
summarized
in
Table
G­
1.
Page
107
of
129
Table
1:
Risk
Presumptions
and
LOCs
Risk
Presumption
RQ
LOC
Birds1
Acute
Risk
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.5
Acute
Restricted
Use
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOAEC
1
Wild
Mammals1
Acute
Risk
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.5
Acute
Restricted
Use
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
(
or
LD50
<
50
mg/
kg)
0.2
Acute
Endangered
Species
EEC/
LC50
or
LD50/
sqft
or
LD50/
day
0.1
Chronic
Risk
EEC/
NOAEC
1
Aquatic
Animals2
Acute
Risk
EEC/
LC50
or
EC50
0.5
Acute
Restricted
Use
EEC/
LC50
or
EC50
0.1
Acute
Endangered
Species
EEC/
LC50
or
EC50
0.05
Chronic
Risk
EEC/
NOAEC
1
Terrestrial
and
Semi­
Aquatic
Plants
Acute
Risk
EEC/
EC25
1
Acute
Endangered
Species
EEC/
EC05
or
NOAEC
1
Aquatic
Plants2
Acute
Risk
EEC/
EC50
1
Acute
Endangered
Species
EEC/
EC05
or
NOAEC
1
1
LD50/
sqft
=
(
mg/
sqft)
/
(
LD50
*
wt.
of
animal)
LD50/
day
=
(
mg
of
toxicant
consumed/
day)
/
(
LD50
*
wt.
of
animal)

2
EEC
=
(
ppm
or
ppb)
in
water
Page
108
of
129
APPENDIX
G:
Detailed
Risk
Quotients
Page
109
of
129
Table
1:
Aquatic
Organism
Risk
Quotient
Calculations
for
Thidiazuron
(
or
Degradates)
on
Cotton
Scenario
Acute
Toxicity
Threshold,
LC50
or
EC50
(
µ
g
ai/
L)
Chronic
Toxicity
Threshold,
NOAEC
(
µ
g
ai/
L)
Peak
Water
Conc.
(
µ
g
ai/
L)
21­
day
Average
Water
Conc.
(
µ
g
ai/
L)
60­
day
Average
Water
Conc.
(
µ
g
ai/
L)
Acute
RQ
Chronic
Species
RQ
Pome
Fruit
(
0.32
lb
ai/
A/
App.;
3
app/
yr;
10
day
intervals;
ground
and
air
blast
equipment)

Freshwater
Fish
6700a
5700
11.00
9.70
8.60
0.002
0.002
Estuarine
fish
>
36,000
No
data
11.00
9.70
8.60
<
0.0003
­

Freshwater
Invert.
5,700
<
100
11.00
9.70
8.60
0.002
>
0.10
Estuarine
Invert.
(
shrimp)
3,240
No
data
11.00
9.70
8.60
0.003
­

Estuarine
Invert.
(
oyster)
5,384
No
data
11.00
9.70
8.60
0.002
­

aThidiazuron
photodegradate
AE
F132347
Page
110
of
129
Table
2:
Aquatic
Organism
Risk
Quotient
Calculations
for
Thidiazuron
on
Cotton
Scenario
Acute
Toxicity
Threshold,
LC50
or
EC50
(
µ
g
product/
L)
Endangered
Species
Toxicity
Threshold,
NOAEC
(
µ
g
product/
L)
Peak
Water
Conc.
(
µ
g
ai/
L)
Acute
RQ
Endangered
Species
RQ
Cotton
(
0.2
lb
ai/
A;
single
application
aerial
equipment
5%
drift)

Vascular
Plant
Aquatic
Vascular
Plant
(
Lemna
gibba)
>
24,000
8600
11
<
0.0005
0.001
Nonvascular
Plants
Green
algae
(
Selenastrum
capricornutum)
>
150
150
11
<
0.07
0.073
Blue­
green
algae
(
Anabaena
flos­
aquae)
6000
2800
11
0.002
0.004
Marine
diatom
(
Skeletonema
costatum)
860
110
11
0.013
0.10
Page
111
of
129
Table
3:
Avian
Acute
and
Chronic
Risk
Quotient
Calculations
for
Cotton­
Multiple
Applications
Food
Items
Acute
Toxicity
Threshold,
LC50
(
mg
ai
/
kg­
diet)
Chronic
Toxicity
Threshold,
NOEC
(
mg
ai/
kg­
diet)
Predicted
Maximum
Residue
Levels
(
EEC)(
mg
ai/
kgdiet
a
Acute
RQ
b
Chronic
RQ
c
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)

Short
grass
>
5000
No
data
62.62
<
0.013
­

Tall
grass
>
5000
No
data
30.54
<
0.006
­

Broadleaf
forage,
small
insects
>
5000
No
data
37.48
<
0.008
­

Fruit,
pods,
seeds,
large
insects
>
5000
No
data
4.16
<
0.001
­

a
ELLFATE
program.
(
Assumed
peak
residue
values
(
day
6)
from
first
application
at
0.2
lb
ai/
A
and
added
initial
residue
value
at
0.1
lb
ai/
A
for
second
application.)
a
*
indicates
an
exceedence
of
Endangered
Species
Level
of
Concern
(
LOC).
**
indicates
an
exceedence
of
Acute
Restricted
Use
LOC.
***
indicates
an
exceedence
of
Acute
Risk
LOC.
b
+
indicates
an
exceedence
of
Chronic
LOC.
Page
112
of
129
Table
4:
Avian
Acute
and
Chronic
Risk
Quotient
Calculations
for
Cotton
­
Single
Applications
Food
Items
Acute
Toxicity
Threshold,
LC50
(
mg
ai/
kgdiet
Chronic
Toxicity
Threshold,
NOEC
(
mg
ai/
kg­
diet)
Predicted
Maximum
Residue
Levels
(
EEC)(
mg
ai/
kg­
diet)
Acute
RQ
Chronic
RQ
(
Max.
Residue)
Chronic
RQ
(
Mean
Residue)

Cotton
(
0.2
lb
ai/
A/
App.)

Short
grass
>
5000
No
Data
48.0
<
0.010
­
­

Tall
grass
>
5000
No
Data
22
<
0.004
­
­

Broadleaf
forage,
small
insects
>
5000
No
Data
27
<
0.005
­
­

Fruit,
pods,
seeds,
large
insects
>
5000
No
Data
3.0
<
0.001
­
­
Page
113
of
129
Table
5:
Mammalian
(
Herbivore/
Insectivore)
Acute
Risk
Quotient
Calculations
for
Spray
Applications
Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Acute
Toxicity
Threshold,

LD50
(
mg/
kg­
bw)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
a
(
mg/
kg­
diet)
Acute
RQ
a
EEC
(
mg/
kgdiet
Acute
RQ
b
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)

15
95
Short
grass
>
2000
66.62
<
0.03
24
<
0.01
Broadleaf
forage,
small
insects
>
2000
37.48
<
0.02
12
<
0.01
Large
insects
>
2000
4.16
<
0.002
2
<
0.01
35
66
Short
grass
>
2000
66.62
<
0.02
24
<
0.01
Broadleaf
forage,
small
insects
>
2000
37.48
<
0.01
12
<
0.00
Large
insects
>
2000
4.16
<
0.001
2
<
0.01
1000
15
Short
grass
>
2000
66.62
<
0.00
24
<
0.01
Broadleaf
forage,
small
insects
>
2000
37.48
<
0.01
12
<
0.01
Table
5:
Mammalian
(
Herbivore/
Insectivore)
Acute
Risk
Quotient
Calculations
for
Spray
Applications
Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Acute
Toxicity
Threshold,

LD50
(
mg/
kg­
bw)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
a
(
mg/
kg­
diet)
Acute
RQ
a
EEC
(
mg/
kgdiet
Acute
RQ
b
Page
114
of
129
Large
insects
>
2000
4.16
<
0.010
2
<
0.01
Page
115
of
129
Table
6:
Mammalian
(
Granivore)
Acute
Risk
Quotient
Calculations
for
Spray
Applications
Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Acute
Toxicity
Threshold,

LD50
(
mg/
kg­
bw)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
a
(
mg/
kg­
diet)
Acute
RQ
b
EEC
(
mg/
kg­
diet)
Acute
RQ
b
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)

15
21
Seeds
>
2000
4.16
<
0.0004
1.94
<
0.0002
35
15
Seeds
>
2000
4.16
<
0.0003
1.94
<
0.0001
1000
3
Seeds
>
2000
4.16
<
0.0001
1.94
<
0.00003
a
ELLFATE
program.
(
Assumed
peak
residue
values
(
day
6)
from
first
application
at
0.2
lb
ai/
A
and
added
initial
residue
value
at
0.1
lb
ai/
A
for
second
application.)

b
RQ
=
EEC
LD
50
/
%
Body
wt.
consumed
Page
116
of
129
Table
7
:
Mammalian
(
Herbivore/
Insectivore)
Chronic
Risk
Quotient
Calculations
for
Spray
Applications
(
NOAEL
=
35.4
mg/
kg­
bw/
da)

Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Chronic
Toxicity
Threshold,

NOAEL
(
mg/

kgbw
da)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
a
(
mg/
kg­
diet)
Chronic
RQ
a
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)

15
95
Short
grass
35.4
67
1.8
*
23.73
0.64
Broadleaf
forage,

small
insects
35.4
37
1.0
*
12.33
0.33
Large
insects
35.4
4.2
0.1
1.96
0.05
35
66
Short
grass
35.4
67
1.2
*
23.73
0.44
Broadleaf
forage,

small
insects
35.4
37
0.7
12.33
0.23
Large
insects
35.4
4.2
0.08
1.96
0.04
1000
15
Short
grass
35.4
67
0.3
23.73
0.10
Table
7
:
Mammalian
(
Herbivore/
Insectivore)
Chronic
Risk
Quotient
Calculations
for
Spray
Applications
(
NOAEL
=
35.4
mg/
kg­
bw/
da)

Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Chronic
Toxicity
Threshold,

NOAEL
(
mg/

kgbw
da)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
a
(
mg/
kg­
diet)
Chronic
RQ
a
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
Page
117
of
129
Broadleaf
forage,

small
insects
35.4
37
0.2
12.33
0.05
Large
insects
35.4
4.2
0.02
1.96
0.01
Page
118
of
129
Table
8
:
Mammalian
(
Granivore)
Chronic
Risk
Quotient
Calculations
for
Spray
Applications
(
NOAEL
=
35.4
mg/
kg­
bw/
da)

Animal
Body
Weight
(
g)
%
Body
Weight
Consumed
Scenario
Chronic
Toxicity
Threshold,

NOAEL
(
mg/

kgbw
da)
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EECa
(
mg/
kg­
diet)
Chronic
RQ
a
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)

15
21
Seeds
35.4
4.16
0.02
1.94
0.01
35
15
Seeds
35.4
4.16
0.02
1.94
0.01
1000
3
Seeds
35.4
4.16
0.00
1.94
0.00
a
ELLFATE
program.
(
Assumed
peak
residue
values
(
day
6)
from
first
application
at
0.2
lb
ai/
A
and
added
initial
residue
value
at
0.1
lb
ai/
A
for
second
application.)

b
RQ
=
EEC
x
%
body
weight
consumed
NOEL
*
indicates
an
exceedence
of
Chronic
Level
of
Concern
(
LOC).

Table
9
:
Mammalian
Chronic
Risk
Quotient
Calculations
for
Spray
Applications
(
NOAEC
=
400
mg/
kg­
diet)

Scenario
Chronic
Toxicity
Threshold,

NOAEC
(
mg/

kgdiet
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
Cotton
(
0.2
lb
ai/
A
1st
App.;
0.1
lb
ai/
A
2ndapp;
7
day
intervals;
ground
and
air
blast
equipment)
Table
9
:
Mammalian
Chronic
Risk
Quotient
Calculations
for
Spray
Applications
(
NOAEC
=
400
mg/
kg­
diet)

Scenario
Chronic
Toxicity
Threshold,

NOAEC
(
mg/

kgdiet
Predicted
Maximum
Residue
Levels
Predicted
Mean
Residue
Levels
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
EEC
(
mg/
kg­
diet)
Chronic
RQ
a
Page
119
of
129
Short
grass
400
67
0.17
23.73
0.06
Tall
grass
400
31
0.08
10.15
0.03
Broadleaf
forage,
small
insects
400
37
0.09
12.33
0.03
Large
insects,
Seeds
400
4.2
0.01
1.96
0.00
a
ELLFATE
program.
(
Assumed
peak
residue
values
(
day
6)
from
first
application
at
0.2
lb
ai/
A
and
added
initial
residue
value
at
0.1
lb
ai/
A
for
second
application.)

b
RQ
=
EEC
x
%
body
weight
consumed
NOEL
*
indicates
an
exceedence
of
Chronic
Level
of
Concern
(
LOC).

a
RQ
=
EEC
NOEC
Exposure
and
Risk
to
Nontarget
Terrestrial
Plants
Page
120
of
129
Table
10:
Estimated
Environmental
Concentrations
(
lbs
ae/
A)
For
Dry
and
Semi­
Aquatic
Areas
for
a
Single
Application
of
Thidiauron.

Site/
Application
Method/
Rate
of
Application
in
lbs
ai/
A
Minimum
Incorporation
Depth
(
cm)
Runoff
Value
Sheet
Runoff
(
lbs
ai/
A)
Channelized
Runoff
(
lbs
ai/
A)
Drift1
(
lbs
ai/
A)
Total
Loading
to
Adjacent
Area
(
Sheet
Runoff
Drift)
Total
Loading
to
Semi­
aquatic
Area
(
Channel
Run­
off+
Drift)

Cotton
­
ground
Applications
(
0.2
lbs
ai/
ac/
app.)

0.2
0
0.02
0.004
0.040
0.002
0.006
0.04
Cotton
­
aerial
applications
(
0.2
lbs
ai/
ac/
app.)

0.2
0
0.02
0.002
0.020
0.010
0.012
0.030
1
Assumed
drift
at
1%
for
ground
applications
and
5%
for
aerial
applications.

Non­
endangered
Plant
Risk
Quotients
­
Single
Spray
Applications
of
Thidiazuron
The
EC
25
value
of
the
most
sensitive
species
in
the
seedling
emergence
study
is
compared
to
runoff
and
drift
exposure
to
determine
the
RQ
(
EEC/
toxicity
value).
The
EC
25
value
of
the
most
sensitive
species
in
the
vegetative
vigor
study
is
compared
to
the
drift
exposure
to
determine
the
acute
RQ.
RQs
are
calculated
for
the
most
sensitive
monocot
and
dicot
species
for
ground
and
aerial
applications.
Page
121
of
129
Table
11:
Acute
Non­
Endangered
Terrestrial
Plant
Risk
Quotient
Calculations
For
Single
Spray
Applications
of
Thidiazuron
Scenario
Toxicity
Threshold,
EC25
(
lb
ai/
ac)
Plants
Adjacent
to
Treated
Sites
Plants
in
Semi­
aquatic
Areas
Total
Drift
(
lb
ai/
ac)
Total
Loading(
Sheet
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Total
Drift
(
lb
ai/
ac)
Total
Loading
(
Channel
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Cotton
­
Ground
Applications
(
0.2
lbs
ai/
ac/
app.)

Seed
Emerg.
Monocot
<
0.1783
N/
A
0.006
>
0.03
N/
A
0.04
>
0.22
Dicot
0.0152
N/
A
0.006
0.39
N/
A
0.04
2.63
*

Veg
Vigor
Monocot
>
0.1783
0.002
N/
A
<
0.01
0.002
N/
A
<
0.01
Dicot
0.0011
0.002
N/
A
1.82
*
0.002
N/
A
1.82
*

Cotton
­
Aerial
Applications
(
0.2
lbs
ai/
ac/
app)

Seed
Emerg.
Monocot
<
0.1783
N/
A
0.012
>
0.07
N/
A
0.03
>
0.17
Dicot
0.0152
N/
A
0.012
0.79
N/
A
0.03
1.97
*

Veg
Vigor
Monocot
>
0.1783
0.01
N/
A
<
0.06
0.01
N/
A
<
0.06
Dicot
0.0011
0.01
N/
A
9.09
*
0.01
N/
A
9.09
*

*
indicates
an
exceedence
of
Acute
Risk
LOC.
Page
122
of
129
Endangered
Plant
Risk
Quotients
­
Single
Spray
Applications
of
Thidiazuron
The
endangered
plant
RQs
are
calculated
by
comparing
the
NOEC
or
EC
05
value
of
the
most
sensitive
species
in
the
seedling
emergence
study
to
runoff
and
drift
exposure
(
EEC/
toxicity
value).
The
NOEC
or
EC
05
value
of
the
most
sensitive
species
in
the
vegetative
vigor
study
is
compared
to
the
drift
exposure
to
determine
the
acute
RQ.
RQs
are
calculated
for
the
most
sensitive
monocot
and
dicot
species.

Table
12:
Acute
Endangered
Terrestrial
Plant
Risk
Quotient
Calculations
For
Single
Spray
Applications
of
thidiazuron
Scenario
Toxicity
Threshold,
NOEC
or
EC05
(
lb
ai/
ac)
Plants
Adjacent
to
Treated
Sites
Plants
in
Semi­
aquatic
Areas
Total
Drift
(
lb
ai/
ac)
Total
Loading(
Sheet
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Total
Drift
(
lb
ai/
ac)
Total
Loading
(
Channel
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Cotton
­
Ground
Applications
(
0.2
lbs
ai/
ac/
app)

Seed
Emerg.
Monocot
0.1783
N/
A
0.006
0.03
N/
A
0.04
0.22
Dicot
0.0111
N/
A
0.006
0.54
N/
A
0.04
3.60
(

Veg
Vigor
Monocot
0.1783
0.002
N/
A
0.01
0.002
N/
A
0.01
Dicot
0.00019
0.002
N/
A
10.53
(
0.002
N/
A
10.53
(

Cotton
­
Aerial
Applications
(
0.2
lbs
ai/
ac/
app)

Seed
Emerg.
Monocot
0.1783
N/
A
0.012
0.07
N/
A
0.03
0.17
Dicot
0.0111
N/
A
0.012
1.08
(
N/
A
0.03
2.70
(
Table
12:
Acute
Endangered
Terrestrial
Plant
Risk
Quotient
Calculations
For
Single
Spray
Applications
of
thidiazuron
Scenario
Toxicity
Threshold,
NOEC
or
EC05
(
lb
ai/
ac)
Plants
Adjacent
to
Treated
Sites
Plants
in
Semi­
aquatic
Areas
Total
Drift
(
lb
ai/
ac)
Total
Loading(
Sheet
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Total
Drift
(
lb
ai/
ac)
Total
Loading
(
Channel
runoff
+
Drift)

(
lb
ai/
ac)
RQa
Page
123
of
129
Veg
Vigor
Monocot
0.1783
0.01
N/
A
0.06
0.01
N/
A
0.06
Dicot
0.00019
0.01
N/
A
52.63
(
0.01
N/
A
52.63
(

a
Indicates
acute
risk
to
endangered
plants
Page
124
of
129
APPENDIX
H:
Data
Requirements
for
Thidiazuron
Page
125
of
129
Table
1:
Status
of
Environmental
Fate
Data
for
Thidiazuron
Guideline
No.
Study
MRID
Status
of
Required
Data
161­
1
Hydrolysis
420692­
03
Satisfied
28
Apr
1993
review
161­
2
Photodegradation
in
Water
411882­
01
413649­
10
(
a
supplement
to
411882­
01
addressing
deficiencies
in
characterization
of
previously
unidentified
degradates)
430752­
02
(
an
addendum
to
41188201
addressing
light
sources
and
their
comparability)
444369­
01
(
Environmental
Fate
Overview
summarizing
previous
DER
issues
and
responses)
Satisfied,
this
review.
(
Based
on
evidence
from
all
submissions,
and
as
interpreted
in
fate
assessment.)
No
further
data
needed
at
this
time.)

161­
3
Photodegradation
on
Soil
001562­
41
(
1981)
413649­
02
(
1983).
Virtually
the
same
study
authored
by
Klehr,
Iwan,
and
Riemann
was
submitted
with
00156241
and
41364902.
Essentially
a
published
version
of
the
former.
444369­
01
(
Environmental
Fate
Overview
summarizing
DER
issues
and
responses)
Supplemental
(
28
Apr
1993
review
and
present
review.)
However,
based
on
other
evidence,
no
further
data
needed
at
this
time.)

161­
4
Photodegradation
in
Air
N/
A
Table
1:
Status
of
Environmental
Fate
Data
for
Thidiazuron
Guideline
No.
Study
MRID
Status
of
Required
Data
Page
126
of
129
162­
1
Aerobic
Soil
Metabolism
All
half­
lives
adjusted
by
this
reviewer
to
25
°
C
and
75%
of
1/
3
bar
soil
suction.

419501­
01.
Previous
eviewer
incorrectly
reported
half­
life
as
111
days
at
21
°
C
and
78%
of
1/
3­
bar.
Value
should
be
182
days
(
based
on
semi­
log
transformed
data).
Half­
life
becomes
140
days
after
adjustment
to
25
°
C
and
75%
of
1/
3­
bar
soil
water
potential.
(
German
standard
sandy
loam
soil
2.3)

461196­
01.
Half­
lives
of
206,
436,
and
253
days­­
thiadiazol
label
in
sandy
loam
(
UK),
loamy
sand
(
NC),
and
silt
loam
(
Il),
respectively.
(
Half­
lives
at
20
°
C
and
40%
MWHC
were
163,
355,
and
322
days,
respectively,
extrapolated
from
study
periods
of
160­
168
days.)
Satisfied
28
Apr
1993
This
review.

162­
2
Anaerobic
Soil
Metabolism
419452­
01
Satisfied
28
Apr
1993
review
162­
3
Anaerobic
Aquatic
Metabolism
42666­
01
Satisfied
This
review.

162­
4
Aerobic
Aquatic
Metabolism
N/
A
163­
1
Leaching­
Adsorption/
Desorption
413649­
09
Satisfied
This
review
163­
2
Laboratory
Volatility
N/
A
163­
3
Field
Volatility
N/
A
164­
1
Terrestrial
Field
Dissipation
444540­
01
417611­
05
Supplemental
However,
no
further
data
needed
at
this
time.

164­
2
Aquatic
Field
Dissipation
N/
A
164­
3
Forestry
Dissipation
N/
A
165­
4
Accumulation
in
Fish
N/
A
Table
1:
Status
of
Environmental
Fate
Data
for
Thidiazuron
Guideline
No.
Study
MRID
Status
of
Required
Data
Page
127
of
129
165­
5
Accumulation­
aquatic
non­
target
N/
A
166­
1
Ground
Water­
small
prospective
N/
A
201­
1
Droplet
Size
Spectrum
SDTF
data
202­
1
Drift
Field
Evaluation
SDTF
data
Page
128
of
129
Table
2:
Ecological
Effects
Data
Requirements
for
Thidiazuron
Guideline
#
Data
Requirement
Formulation
MRID
#'
s
Study
Classification
71­
1
850.21
Avian
Oral
LD50
TGAI
099819
Core
71­
2
850.22
Avian
Dietary
LC50
TGAI
TGAI
TGAI
50%
TGAI
00816­
29
462035­
02
099819
245834
Core
71­
4
850.23
Avian
Reproduction1
TGAI
NA
NA
72­
1
850.1075
Freshwater
Fish
LC50
TGAI
Photodegradate
(
AE
F132347)
Metabolite
(
AE
F132345)
Photodegradate
(
AE
C421200)
42069202
42069201
462035­
15
462035­
11
Core
72­
2
850.101
Freshwater
Invertebrate
Acute
LC50
TGAI
Photodegradate
(
AE
F132347)
Metabolite
(
AE
F132345)
Photodegradate
(
AE
C421200)
462035­
03
099819
62035­
09
462035­
16
Core
72­
3(
a)
850.1075
Estuarine/
Marine
Fish
LC50
TGAI
418461­
01
Core
72­
3(
b)
850.1025
Estuarine/
Marine
Mollusk
EC50
TGAI
421320­
01,
Core
72­
3
©
850.1035
850.1045
Estuarine/
Marine
Shrimp
EC50
TGAI
418461­
01
Core
72­
4(
a)
850.14
Freshwater
Fish
Early
Life­
Stage
TGAI
422703­
01
Core
72­
4(
b)
850.1300
850.1350
Aquatic
Invertebrate
Life­
Cycle
TGAI
421320­
02
Core
72­
5
850.15
Freshwater
Fish
Full
Life­
Cycle
NA
Table
2:
Ecological
Effects
Data
Requirements
for
Thidiazuron
Guideline
#
Data
Requirement
Formulation
MRID
#'
s
Study
Classification
Page
129
of
129
122­
1(
a)
850.41
Seed
Germ./
Seedling
Emergence
TGAI
418213­
01
Core
122­
1(
b)
850.415
Vegetative
Vigor
TGAI
418191­
01
Core
122­
2
850.44
Aquatic
Plant
Growth
123­
1(
a)
850.4225
Seed
Germ./
Seedling
Emergence
(
Tier
2)
42.6
a.
i.
459085­
01,
Core/
supplemental
123­
1(
b)
850.425
Vegetative
Vigor
(
Tier
2)
42.6
a.
i.
459215­
01
Core/
supplemental
123­
2
850.44
Aquatic
Plant
Growth
(
Tier
2)
2
TGAI
462035­
04
462035­
05
462035­
06
462035­
10
462035­
13
462035­
17
417611­
04
Core/
Supplementa
l
141­
1
850.302
Honey
Bee
Acute
Contact
LD50
TGAI
41.9
462035­
01
462035­
18
Core
141­
2
850.303
Honey
Bee
Residue
on
Foliage
NA
1
This
test
may
be
recommend
if
chronic
mammalian
issues
can
not
be
resolved
