UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PESTICIDES
AND
TOXIC
SUBSTANCES
MEMORANDUM
SUBJECT:
TRED
for
Tebuthiuron
(Chemical
#
105501,
DP
Barcode
D279066)

FROM:
Mark
Corbin,
Environmental
Scientist
Environmental
Risk
Branch
1
Environmental
Fate
and
Effects
Division
(7507C)

THRU:
Dana
Spatz,
Acting
Branch
Chief
Environmental
Risk
Branch
1
Environmental
Fate
and
Effects
Division
(7507C)

TO:
Daniel
Helfgot
Special
Review
Branch
Special
Review
and
Reregistration
Division
(7508C)

Wilhelmena
Livingston
Special
Review
Branch
Special
Review
and
Reregistration
Division
(7508C)

EFED
has
completed
a
drinking­
water
assessment
for
the
reassessment
of
tolerances
for
the
herbicide
Tebuthiuron.
This
assessment
considers
Tebuthiuron,
and
to
the
extent
possible,
the
degradate
"Compound
104,"
which
the
Health
Effects
Division
has
determined
is
of
toxicological
concern.
Compound
104
was
the
only
degradate
of
Tebuthiuron
of
toxicological
concern
that
was
detected
in
the
environmental
fate
studies
reviewed.
Tier
II
(PRZM
version
3.12/
EXAMS
version
2.97.5)
surface
water
modeling
for
Tebuthiuron
use
on
rangeland/
pasture
at
4
pounds
active
ingredient
per
acre
(lbs
ai/
A)
using
the
index
reservoir
predicts
the
1
in
10
year
annual
maximum
(acute)
concentration
of
15.1
:
g/
L.
The
1
in
10
year
annual
average
concentration
(non­
cancer
chronic)
of
Tebuthiuron
is
predicted
to
be
1.5
:
g/
L
.
The
36
year
annual
average
concentration
(cancer
chronic)
of
Tebuthiuron
is
predicted
to
be
0.6
:
g/
L.
SCIGROW
(version
2.1)
modeling
estimates
the
acute
and
chronic
concentration
of
Tebuthiuron
residues
in
shallow
groundwater
is
181
:
g/
L.
Monitoring
data
was
evaluated
from
the
USGS
NAWQA
program
and
from
preliminary
data
from
the
USGS
Reservoir
Pilot
Monitoring
Project.
Both
surface
and
ground
water
data
from
the
NAWQA
program
were
evaluated
for
annual
maximum
(peak)
and
time
weighted
mean
concentrations.
Only
surface
water
data
was
available
from
the
USGS
Reservoir
Pilot
Monitoring
study
which
was
also
evaluated
for
annual
N
N
S
N
CH
3
CH
3
C
H
3
C
H
3
O
N
H
CH
3
maximum
and
time
weighted
mean
concentrations.
EFED
proposes
using
the
estimated
environmental
concentrations
(EECs)
from
modeling
as
upper
bound
estimates
of
exposure.
Acute
(annual
maximum)
concentrations
and
chronic
(time
weighted
mean)
concentrations
from
monitoring
data
are
summarized
below.
In
general
these
concentrations
are
less
than
the
estimates
from
modeling.
EFED
proposes
using
the
model
results
as
acute
and
chronic
EECs
for
the
risk
assessment
because
Tebuthiuron
is
persistent
and
data
from
edge
of
field
runoff
studies
conducted
in
the
1980's
indicate
concentrations
higher
than
those
found
in
the
NAWQA
and
USGS
Reservoir
studies
can
occur.

Drinking
water
environmental
concentrations
for
Compound
104
cannot
be
estimated
due
to
a
lack
of
fate
and
monitoring
data
.
Compound
104
was
detected
at
a
maximum
concentration
of
0.004
mg/
L
in
ground
water
in
a
Small
Scale
Retrospective
study
(MRID
42390901)
submitted
in
1992.
However
the
concentrations
were
detected
four
years
after
application
of
Tebuthiuron
and
may
not
be
representative
of
the
maximum
concentrations
present
beneath
the
site
after
application.
Compound
104
was
detected
at
6.9%
of
applied
parent
at
the
end
of
the
aerobic
soil
metabolism
study
but
was
noted
to
still
be
increasing
at
the
end
of
the
study.
It
is
suspected
that
the
percent
applied
of
Compound
104
would
have
increased
if
the
experiment
had
run
longer.
Compound
104
appears
to
have
similar
mobility
to
Tebuthiuron
and
has
a
long
half
life.
Therefore,
EFED
is
unable
to
estimate
how
much
degradate
might
have
been
produced
if
the
study
had
run
longer.

Introduction
Tebuthiuron
is
a
non­
selective
herbicide
used
primarily
on
pastureland,
rights­
of­
way,
and
other
non­
agricultural
sites.
Tebuthiuron
is
used
predominantly
in
Texas,
Oklahoma,
and
New
Mexico
based
on
information
provided
by
the
registrant
and
BEAD.
Information
on
publically
supplied
drinking
water
available
from
the
USGS
(Selley,
et
al,
1998;
"Estimated
Use
of
Water
in
the
United
States
in
1995".
USGS
Circular
1200)
was
reviewed.
Both
surface
and
ground
water
sources
are
used
for
publically
supplied
water
in
Texas,
Oklahoma
and
New
Mexico.
Ground
water
provides
approximately
89%
of
New
Mexico's
public
water,
while
surface
water
provides
66%
and
83%
of
public
water
to
Texas
and
Oklahoma
respectively.
Reviewing
population
served
information
indicates
that
88%
of
New
Mexico's
population
relies
on
ground
water
while
58%
of
Texas
and
74%
of
Oklahoma's
population
rely
on
surface
water.

Chemical
Name:
N­[
5­(
1,1­
dimethylethyl)­
1,3,4­
thiadiazol­
2­
yl]­
N,
N'­
dimethylurea
Compound
104:
N­[
5­(
1,1­
dimethylethyl)­
1,3,4­
thiadiazol­
2­
yl]­
N­
methylurea
Chemical
Structure:
Environmental
Fate
As
reported
in
the
1994
RED
Tebuthiuron
is
persistent
and
mobile,
and
that
the
"principal
route
of
dissipation
appears
to
be
transport
to
ground
and
surface
water."
This
assessment
was
based
on
a
suite
of
required
environmental
fate
studies
that
lacked
only
a
field
dissipation
study.
This
study
has
since
been
submitted
and
reviewed
and
found
to
be
marginally
acceptable
with
field
dissipation
half
lives
of
385
days
(Florida),
770
days
(California),
and
575
days
(Nebraska).

The
quickest
observed
route
of
Tebuthiuron
degradation
in
laboratory
studies
was
soil
photolysis
(half­
life
39.7
days.)
Tebuthiuron
is
stable
in
laboratory
studies
to
hydrolysis,
aqueous
photolysis,
and
aerobic
aquatic
metabolism.
Tebuthiuron
was
also
stable
during
a
9­
month
aerobic
soil
metabolism
study,
with
a
calculated
half­
life
of
35.4
months.

Soil
partition
coefficients
(Kd)
from
adsorption/
desorption
studies
were
0.11,
0.62,
0.82
and
1.82,
indicating
that
Tebuthiuron
is
very
mobile
over
a
range
of
soil
types.
The
corresponding
Koc
values
relating
to
these
studies
ranged
from
31
to
151,
with
a
median
of
76
l/
kg.
The
soil
adsorption
of
Tebuthiuron
appears
to
be
related
to
the
amount
of
organic
carbon
in
the
soil.

Degradate
104
(Compound
104
was
the
only
degradate
of
Tebuthiuron
of
toxicological
concern
that
was
detected
in
the
environmental
fate
studies
reviewed)
was
at
6.9%
and
rising
by
the
end
of
the
study.
That
is
the
highest
concentration
of
any
degradate
in
any
lab
study.
Based
on
data
reviewed
at
the
time
of
the
RED,
the
degradate
appears
to
have
similar
mobility
to
parent
Tebuthiuron.

For
full
details
of
the
environmental
fate
assessment
for
Tebuthiuron,
see
the
1994
Reregistration
Eligibility
Document,
which
can
be
found
on
the
internet
at
http://
www.
epa.
gov/
pesticides/
reregistration/
status.
htm.

SURFACE
WATER
MONITORING
DATA
ASSESSMENT
National
NAWQA
Data
The
United
States
Geological
Survey
(USGS)
is
collecting
surface
and
ground
water
data
from
selected
watersheds
in
order
to
catalog
the
quality
of
water
resources
in
the
United
States.
The
National
Water
Quality
Assessment
(NAWQA)
program
began
in
1991
and
consists
of
chemical,
biological
and
physical
water
quality
data
from
59
study
units
across
the
United
States.
EFED
evaluated
the
occurrence
of
Tebuthiuron
in
surface
water
from
the
national
data
set.
Tebuthiuron
was
detected
in
surface
water
from
locations
in
30
states.
Compared
with
current
usage
which
is
predominantly
located
in
Texas,
Oklahoma,
and
New
Mexico,
the
occurrence
in
so
many
locations
is
reflective
of
past
usage
due
to
the
persistence
of
Tebuthiuron.
Tebuthiuron
was
detected
above
the
limit
of
detection
in
1155
samples
from
a
total
national
dataset
of
6625
samples
(17.4%).
This
rate
of
detection
is
greater
than
for
most
pesticides
included
as
analytes,
in
spite
of
its
limited
use.
EFED
analyzed
the
occurrence
of
Tebuthiuron
in
surface
water
from
each
sampling
location
within
each
state
on
an
annual
basis.
Each
year
of
data
from
an
individual
sample
location
was
evaluated
and
the
annual
maximum
concentration
and
time
weighted
mean
were
calculated.
For
the
purposes
of
this
assessment
only
the
upper
bound
time
weighted
mean
concentration
from
the
NAWQA
data
is
presented.
The
upper
bound
annual
time
weighted
mean
concentrations
were
estimated
by
setting
detections
at
or
below
the
detection
limit
at
the
value
of
the
detection
limit.

Analysis
of
the
national
NAWQA
surface
water
data
set
for
Tebuthiuron
is
presented
below.
The
annual
maximum
concentrations
ranged
from
2.83
to
0.003
(estimated
below
limit
of
quantitation)
:
g/
L
and
the
upper
bound
time
weighted
means
ranged
from
0.26
to
0.00
:
g/
L.
No
degradate
data
was
available
in
this
dataset
for
analysis.
The
annual
maximum
concentrations
and
time
weighted
mean
concentrations
were
ranked
and
percentiles
generated
for
the
dataset.
The
results
of
the
analysis
are
summarized
in
Table
1.

Table
1
Summary
of
Percentiles
for
Surface
Water
Annual
Maximum
and
Time
Weighted
Mean
Tebuthiuron
Concentrations
from
the
National
NAWQA
Data.

Percentile
National
NAWQA
Annual
Maximum
(
:
g/
L)
National
NAWQA
Time
Weighted
Mean
(
:
g/
L)

Maximum
2.
83
0.
26
99.9%
1.99
0.24
99%
0.21
0.06
95%
0.09
0.03
90%
0.06
0.02
50%
0.01
0.01
The
analysis
above
includes
the
entire
national
NAWQA
data
which
consists
of
surface
water
results
from
all
59
NAWQA
study
units.
In
order
to
assess
the
impact
of
high
Tebuthiuron
usage
on
the
analysis,
EFED
completed
an
additional
analysis
focusing
on
only
data
from
those
study
units
located
in
areas
of
high
Tebuthiuron
usage.
This
focused
assessment
is
intended
to
indicate
if
exposure
to
Tebuthiuron
in
surface
water
in
those
areas
where
the
herbicide
is
used
predominantly
(i.
e.
Texas,
Oklahoma,
and
New
Mexico)
is
greater
in
these
areas
than
on
a
national
basis.
The
study
units
for
the
focused
analysis
were
selected
by
overlaying
Tebuthiuron
usage
data
taken
from
registrant
supplied
information
with
the
NAWQA
study
units.

As
with
the
national
NAWQA,
the
focused
NAWQA
data
annual
maximum
concentrations
ranged
from
2.83
to
0.01
:
g/
L
and
the
upper
bound
time
weighted
means
ranged
from
0.26
to
0.01
:
g/
L.
No
degradate
data
was
available
in
this
dataset
for
analysis.
The
annual
maximum
concentrations
and
time
weighted
mean
concentrations
were
ranked
and
percentiles
generated
for
the
dataset.
The
results
of
the
analysis
are
summarized
in
Table
2.
Analysis
of
surface
water
data
from
those
locations
where
Tebuthiuron
usage
is
higher
indicates
that
while
the
range
of
concentrations
is
the
same
for
both
annual
maximum
and
time
weighted
mean,
the
concentrations
at
the
higher
percentiles
(>
90%)
are
higher
for
the
focused
data.
Table
2
Summary
of
Percentiles
for
Surface
Water
Annual
Maximum
and
Time
Weighted
Mean
Tebuthiuron
Concentrations
from
the
Focused
NAWQA
Data.

Percentile
Focused
NAWQA
Annual
Maximum
(
:
g/
L)
Focused
NAWQA
Time
Weighted
Mean
(
:
g/
L)

Maximum
2.
83
0.
26
99.9%
2.77
0.26
99%
2.27
0.25
95%
0.69
0.19
90%
0.33
0.05
50%
0.01
0.01
USGS
Reservoir
and
Finished
Water
­
Pilot
Monitoring
Study,
1999­
2000
The
USGS
recently
issued
preliminary
data
from
a
cooperative
study
between
the
USGS
and
USEPA
for
"Pesticides
in
Water­
supply
Reservoirs
and
Finished
Drinking
Water
­
A
Pilot
Monitoring
Program".
The
study
consists
of
the
analysis
of
samples
from
12
drinking
water
reservoirs
across
the
United
States
(including
Texas
and
Oklahoma).
EFED
has
reviewed
the
preliminary
data
for
the
occurrence
of
Tebuthiuron.
Tebuthiuron
was
analyzed
in
all
samples
using
the
same
analytical
methodology
as
the
USGS
NAWQA
program
(Schedule
2001).
Degradates
of
Tebuthiuron
were
not
analyzed
in
this
study.
Source
water
samples
were
collected
from
drinking
water
intakes
within
each
reservoir
and
treated
water
samples
were
collected
post­
treatment.
Treated
and
intake
samples
were
typically
collected
on
the
same
date
within
several
hours
of
each
other.
In
addition,
samples
were
collected
and
analyzed
from
the
reservoir
outfall
(untreated)
from
selected
locations.
Several
outfall
locations
coincide
with
source
water
intakes
and
therefore
the
intake
and
outfall
samples
are
the
same.

Tebuthiuron
was
detected
in
232
out
of
627
analysis
for
a
detection
frequency
of
37%.
The
highest
peak
concentration
of
Tebuthiuron
was
0.032
:
g/
L
detected
in
the
treated
water
of
the
Oklahoma
Reservoir.
The
maximum
concentrations
and
time
weighted
mean
concentrations
were
calculated
for
each
subset
of
the
data
(intake,
treated,
and
outfall)
for
each
location.
The
results
are
presented
in
Table
3
and
4.
In
addition,
the
maximum
concentrations
and
time
weighted
mean
concentrations
were
ranked
and
percentiles
generated
for
the
data
set.
The
results
of
ranking
are
presented
in
Tables
5
and
6.
Table
3
Summary
of
Time
Weighted
Mean
Tebuthiuron
Concentrations
from
the
USGS
Reservoir
Data
from
1999­
2000.

State
Intake
Sample
Time
Weighted
Mean
(
:
g/
L)
Treated
Sample
Time
Weighted
Mean
(
:
g/
L)
Reservoir
Outfall
Time
Weighted
Mean
(
:
g/
L)

SD
0.011
0.010
0.009
NY
0.010
0.011
OH
0.011
0.010
0.011
CA
0.009
0.010
TX
0.008
0.008
LA
0.010
0.010
0.010
NC
0.010
0.010
OK
0.018
0.020
0.011
MO
0.009
0.011
0.008
PA
0.008
0.008
SC
0.008
0.008
0.008
IN
0.011
0.011
0.006
Table
4
Summary
of
Maximum
Tebuthiuron
Concentrations
from
the
USGS
Reservoir
Data
from
1999­
2000.

State
Intake
Sample
Maximum
(
:
g/
L)
Treated
Sample
Maximum
(
:
g/
L)
Reservoir
Outfall
Maximum
(
:
g/
L)

SD
0.016
0.016
0.010
NY
0.016
0.016
OH
0.015
0.010
0.012
CA
0.012
0.018
TX
0.010
0.010
LA
0.016
0.016
0.010
NC
0.011
0.010
OK
0.030
0.032
0.024
MO
0.010
0.016
0.010
PA
0.020
0.010
SC
0.010
0.016
0.010
IN
0.016
0.016
0.020
Table
5
Summary
of
Percentiles
for
Surface
Water
Annual
Time
Weighted
Mean
Tebuthiuron
Concentrations
from
the
USGS
Reservoir
Data
from
1999­
2000.

Percentile
Time
Weighted
Mean
Concentration
from
Intake
Samples
(
:
g/
L)
Time
Weighted
Mean
Concentration
from
Treated
Samples
Time
Weighted
Mean
Concentration
from
Outfall
Samples
(
:
g/
L)

Maximum
0.
018
0.020
0.011
99.9%
0.018
0.020
0.011
99%
0.017
0.019
0.011
95%
0.014
0.015
0.011
90%
0.011
0.011
0.011
50%
0.010
0.010
0.009
Table
6
Summary
of
Percentiles
for
Surface
Water
Maximum
Tebuthiuron
Concentrations
from
the
USGS
Reservoir
Data
from
1999­
2000.

Percentile
Maximum
Concentration
from
Intake
Samples
(
:
g/
L)
Maximum
Concentration
from
Treated
Samples
(
:
g/
L)
Maximum
Concentration
from
Outfall
Samples
(
:
g/
L)

Maximum
0.
030
0.032
0.024
99.9%
0.030
0.032
0.024
99%
0.029
0.030
0.024
95%
0.025
0.024
0.023
90%
0.020
0.018
0.022
50%
0.016
0.016
0.010
The
data
above
indicate
that
Tebuthiuron
is
found
at
a
high
frequency
of
detection
(greater
than
17%
in
NAWQA
data
and
greater
than
37%
in
the
USGS
Reservoir
data).
The
maximum
concentration
detected
in
these
two
studies
is
2.83
ppb
from
the
NAWQA
study.
Time
weighting
of
these
data
indicate
that
long
term
exposure
is
generally
less
than
1
ppb.
The
high
frequency
of
detection
is
likely
a
function
of
the
persistence
of
Tebuthiuron
in
the
environment.
The
low
concentrations
detected
(compared
with
edge
of
field
studies
discussed
below)
may
be
a
function
of
the
use
of
Tebuthiuron
which
is
focused
on
rangeland/
pasture
which
is
typically
in
arid
and
semi­
arid
environments
and
is
not
likely
applied
in
proximity
to
surface
water
bodies
assessed
by
NAWQA
and
USGS
Reservoir
studies.
Additional
Monitoring
Data
Four
supplemental
watershed/
runoff
studies
were
conducted
in
Idaho,
Oklahoma,
Texas,
and
Arizona
between
1980
and
1984.
The
four
studies
represent
typical
application
scenarios
for
the
time
with
variable
rates
of
application
between
1
and
3
lbs
a.
i./
acre.
The
maximum
label
rate
is
4
lbs
a.
i./
acre
suggesting
that
these
studies
do
not
represent
a
worse
case
scenario.
Tebuthiuron
was
applied
to
varying
percentages
of
four
small
watersheds
ranging
between
13
acres
(Oklahoma)
to
303
acres
(Arizona).
Surface
water
and
"hydrosoil"
samples
were
collected
up
to
9
months
after
application
at
the
Idaho
site
(24
samples),
7
months
after
application
at
the
Oklahoma
site
(7
samples),
7
months
after
application
at
the
Texas
site
(6
samples),
and
3
months
after
application
at
the
Arizona
site
(53
samples).

Analytical
results
from
the
four
watershed/
runoff
studies
reported
concentrations
of
Tebuthiuron
in
surface
water
ranging
from
less
than
1
:
g/
L
(measured
at
the
conclusion
of
the
Texas
study)
up
to
180
:
g/
L
(measured
5/
5/
81
in
the
Oklahoma
study)
and
hydrosoil
residues
from
<
50
:
g/
L
up
to
140
:
g/
L.
EFED
revisited
the
analytical
data
from
the
four
runoff
studies
in
Idaho,
Oklahoma,
Texas,
and
Arizona.
Analysis
of
the
data
from
1980
through
1981
indicate
that
the
maximum
concentration
detected
for
each
site
respectively
is
180
:
g/
L
for
Oklahoma,
14
:
g/
L
for
Idaho,
70
:
g/
L
for
Texas,
and
54
:
g/
L
for
Arizona.
Time
weighted
mean
concentrations
were
calculated
for
each
dataset
with
the
results
showing
98
:
g/
L
in
Oklahoma,
7
:
g/
L
in
Idaho,
37
:
g/
L
in
Texas,
and
24
:
g/
L
in
Arizona.
These
concentrations
are
higher
than
those
observed
in
other
surface
water
monitoring
studies
(NAWQA
and
USGS
Reservoir
Pilot
Monitoring)
and
those
concentrations
predicted
using
PRZM/
EXAMS.
The
samples
analyzed
were
collected
from
catchment/
weir
ponds
within
a
watershed
unlike
the
other
surface
water
monitoring
data
which
is
generally
collected
from
flowing
streams
and
drinking
water
reservoirs.
The
concentrations
from
these
runoff
studies
are
better
compared
to
the
edge
of
field
effect
predicted
by
PRZM/
EXAMS.
The
comparison
with
PRZM/
EXAMS
suggests
that
the
modeling
may
under
predict
the
concentrations
that
would
be
expected
in
a
waterbody
adjacent
to
a
treatment
area.

GROUND
WATER
MONITORING
DATA
ASSESSMENT
A
small
scale
retrospective
ground
water
monitoring
study
was
completed
on
a
rangeland
site
at
a
ranch
near
Sarita,
Texas.
The
study
was
conducted
in
a
portion
of
a
540
acre
area
treated
with
Tebuthiuron
in
March
1986
by
aerial
broadcast
in
70
foot
wide
strips.
Tebuthiuron
was
applied
at
rates
between
1.5
and
1.75
lbs
a.
i./
acre
for
rangeland
brush
control.
Higher
application
up
to
2
lbs
a.
i./
acre
were
applied
in
bands
to
thick
stands
of
live
oak
and
along
fence
lines.
In
some
areas
at
the
site
overlap
of
rangeland
and
fence
line
treatments
resulted
in
total
application
of
up
to
4
lbs
a.
i./
acre.

A
total
of
16
soil
borings,
14
test
pits,
and
5
ground
water
monitoring
wells
were
performed
to
complete
site
characterization.
The
site
characterization
gives
a
high
level
of
confidence
that
this
study
was
performed
with
a
reasonable
"high
exposure"
scenario.
The
site
is
comprised
of
eolian
sands
over
fluvial
deposits.
Monitoring
wells
were
installed
to
avoid
discontinuous,
restrictive
clay
layers
that
are
found
beneath
some
portions
of
the
site.
Using
the
site
characterization
data,
a
study
protocol
was
developed
and
field
work
began
in
May
1990
and
included
the
installation
of
an
additional
5
ground
water
monitoring
wells.
A
program
of
ground
water
analysis
was
begun
in
which
seven
of
the
ten
ground
water
monitoring
wells
were
sampled
every
other
month
beginning
in
June
1990
and
ending
June
1991.

Analysis
of
soil
samples
indicated
that
Tebuthiuron
was
still
present
in
soil
at
depths
greater
than
three
feet
below
ground
surface
and
appeared
to
be
in
contact
with
shallow
ground
water
beneath
portions
of
the
study
site.
No
degradate
was
detected
in
soil
samples
above
the
limit
of
detection
of
0.01
mg/
L.
The
data
suggest
that
Tebuthiuron
is
persistent
and
mobile
in
soil
at
the
study
site.

Analysis
of
ground
water
samples
collected
beneath
the
study
site
indicate
that
Tebuthiuron
was
present
above
the
limit
of
detection
(0.001
mg/
L)
in
six
of
the
seven
wells
at
the
site
and
was
detected
above
the
limit
of
quantitation
(0.003
mg/
L)
in
three
of
the
seven
wells
with
a
maximum
concentration
of
0.023
mg/
L
four
years
after
application.
Compound
104
was
detected
above
the
limit
of
detection
in
three
wells
and
was
detected
at
concentrations
above
the
limit
of
quantitation
in
one
well
with
a
maximum
concentration
of
0.004
mg/
L
four
years
after
application.
This
data
indicate
that
Tebuthiuron
and
its
primary
degradate
are
persistent
and
mobile
in
ground
water
up
to
four
years
after
application.

NAWQA
Data
EFED
evaluated
the
occurrence
of
Tebuthiuron
in
ground
water
from
the
national
data
set.
Tebuthiuron
was
detected
in
228
ground
water
samples
out
of
a
total
of
5303
samples
(4.3%).
It
is
difficult
to
compare
analytical
results
from
ground
water
monitoring
wells
within
a
given
geographic
area.
A
significant
amount
of
ancillary
data
is
necessary
in
order
to
compare
wells
across
an
area.
Examples
of
the
data
that
is
needed
is
aquifer
type,
well
construction,
and
sampling
methodology.
Even
with
ancillary
data
it
is
difficult
to
compare
analytical
results
within
a
region
due
to
variations
in
geology,
geochemistry
of
ground
water,
and
groundwater
usage
patterns
and
history.
Because
this
information
is
not
readily
available
for
this
data
set,
EFED
has
conducted
a
general
analysis
of
the
data.
The
maximum
concentration
detected
across
all
samples
is
17.3
:
g/
L
with
a
detection
limit
of
0.010
:
g/
L,
while
the
average
concentration
among
all
reported
Tebuthiuron
data
is
0.016
:
g/
L.
Depth
to
ground
water
across
the
entire
NAWQA
data
ranged
from
near
surface
to
greater
than
600
feet
below
ground
surface
with
an
average
depth
of
33
feet
below
ground
surface.
Depth
to
ground
water
in
the
focused
NAWQA
study
units
from
Texas,
Oklahoma,
and
New
Mexico
ranged
from
2
to
177
feet
below
ground
surface
with
an
average
depth
of
17
feet
below
ground
surface.
The
depth
to
ground
water
data
suggest
that
the
peak
and
average
concentrations
are
representative
of
the
shallowest
aquifers.

SURFACE,
GROUND
AND
DRINKING
WATER
ASSESSMENT
Because
Tebuthiuron
is
not
included
among
regulated
or
unregulated
chemicals
required
as
analytes
in
testing
of
public
drinking
water
supplies,
drinking­
water
monitoring
results
are
not
available.
Therefore,
drinking
water
exposure
assessments
are
supplemented
with
modeling
predictions.
Surface
water
concentrations
of
Tebuthiuron
were
modeled
using
the
PRZM/
EXAMS
(Tier
II)
programs
for
pasture/
rangeland
using
EFEDs
standard
scenario
for
alfalfa
in
Texas.
The
alfalfa
scenario
was
chosen
because
its
hydrologic
and
agronomic
practices
closely
match
those
of
pasture/
rangeland.
Groundwater
concentrations
were
modeled
using
the
SCI­
GROW
program.
Input
parameters
used
Tier
II
(PRZM
version
3.12/
EXAMS
version
2.97.5)
modeling
were
selecting
using
Agency
guidance
("
Guidance
for
Chemistry
and
Management
Practice
Input
Parameters
for
Use
in
Modeling
the
Environmental
Fate
and
Transport
of
Pesticides"
dated
August
6,
2000)
and
EFED
calculated
degradation
rate
constants
from
review
of
registrant
submitted
environmental
fate
studies.
The
assessment
strategy
was
designed
to
assess
concentrations
of
the
parent
compound
alone.

Tier
II
(PRZM­
EXAMS)
surface
water
modeling
for
Tebuthiuron
(parent
only)
using
the
index
reservoir
with
the
percent
cropped
area
(PCA=
0.87
for
default
PCA)
estimates
the
concentration
of
Tebuthiuron
is
not
likely
to
exceed
the
concentrations
in
Table
7.

Table
7.
PRZM­
EXAMS
Predicted
Parent
Tebuthiuron
Concentrations
in
the
Index
Reservoir
Simulation
Scenarios
Concentration
(
:
g/
L)

1
in
10
year
Mean
of
Annual
Means
Crop
and
Location
Scenario
Peak
96
Hour
21
Day
60
Day
90
Day
Annual
Mean
Pasture,
Milam
Co.,
TX
Index
Reservoir
17.4
16.6
13.2
8.1
6.0
1.7
0.7
Index
Reservoir
w/
PCA
(0.87)
15.1
14.4
11.5
7.0
5.2
1.5
0.6
SCI­
GROW
predicts
a
concentration
of
Tebuthiuron
in
shallow
ground
water
of
181
µg/
L.
Appendix
A
provides
a
detailed
discussion
of
the
modeling
efforts
for
PRZM/
EXAMS
and
SCIGROW
APPENDIX
A
MODELING
DISCUSSION
DRINKING
WATER
ASSESSMENT
Uncertainties,
Assumptions
and
Limitations
Input
parameters
used
in
Tier
II
(PRZM/
EXAMS)
modeling
were
selecting
using
Agency
guidance
("
Guidance
for
Chemistry
and
Management
Practice
Input
Parameters
for
Use
in
Modeling
the
Environmental
Fate
and
Transport
of"
dated
August
6,
2000)
and
EFED
calculated
degradation
rate
constants
from
review
of
registrant
submitted
environmental
fate
studies.

Tebuthiuron
is
used
primarily
on
pasture
and
rangeland
in
Texas,
Oklahoma,
and
New
Mexico,
therefore,
only
one
scenario
was
simulated
to
estimate
runoff
concentrations.
EFED
selected
a
scenario
in
Texas
for
alfalfa
representing
an
EFED
standard
scenario
developed
for
use
in
modeling
the
respective
crops.
Alfalfa
was
selected
as
the
scenario
most
closely
representing
pasture/
rangeland
(the
alfalfa
scenario
was
developed
based
on
a
pasture
setting).
These
scenarios
were
developed
to
approximately
represent
the
90
th
percentile
site
for
runoff
vulnerability
in
a
high
usage
state.
Application
timing
was
taken
from
registrant
provided
information
and
recent
labels.

The
standard
scenario
for
alfalfa
is
based
on
usage
patterns
in
Milam
County,
Texas.
The
soil
is
a
Lufkin
sandy
loam
in
Major
Land
Use
Area
(MLRA)
87.
The
Lufkin
sandy
loam
is
characterized
as
a
Hydrologic
Group
D
soil.

The
index
reservoir
represents
potential
drinking
water
exposure
from
a
specific
area
with
specific
cropping
patterns,
weather,
soils,
and
other
factors
(use
of
an
index
reservoir
for
areas
with
different
climates,
crops,
pesticides
used,
sources
of
water,
and
hydrogeology
creates
uncertainties).
If
a
community
derives
its
drinking
water
from
a
large
river,
then
the
estimated
exposure
would
likely
be
higher
than
the
actual
exposure.
Conversely,
a
community
that
derives
its
drinking
water
from
smaller
bodies
of
water
with
minimal
outflow
would
likely
get
higher
drinking
water
exposure
than
estimated
using
the
index
reservoir.
Areas
with
a
less
humid
climate
that
use
a
similar
reservoir
and
cropping
patterns
would
likely
get
less
pesticides
in
their
drinking
water
than
predicted
levels.
A
single
steady
flow
has
been
used
to
represent
the
flow
through
the
reservoir.
Discharge
from
the
reservoir
also
removes
chemical
from
it
so
this
assumption
will
underestimate
removal
from
the
reservoir
during
wet
periods
and
overestimates
removal
during
dry
periods.
This
assumption
can
both
underestimate
or
overestimate
the
concentration
in
the
pond
depending
upon
the
annual
precipitation
pattern
at
the
site.
The
index
reservoir
scenario
uses
the
characteristic
of
a
single
soil
to
represent
the
soil
in
the
basin.
In
fact,
soils
can
vary
substantially
across
even
small
areas,
and
thus,
this
variation
is
not
reflected
in
these
simulations.
The
index
reservoir
scenario
does
not
consider
tile
drainage.
Areas
that
are
prone
to
substantial
runoff
are
often
tile
drained.
This
may
underestimate
exposure,
particularly
on
a
chronic
basis.
EXAMS
is
unable
to
easily
model
spring
and
fall
turnover
which
results
in
complete
mixing
of
the
chemical
through
the
water
column
at
these
times.
Because
of
this
inability,
Shipman
City
Lake
has
been
simulated
without
stratification.
There
is
data
to
suggest
that
Shipman
City
Lake
does
indeed
stratify
in
the
deepest
parts
of
the
lake
at
least
in
some
years.
This
may
result
in
both
over
and
underestimation
of
the
concentration
in
drinking
water
depending
upon
the
time
of
the
year
and
the
depth
the
drinking
water
intake
is
drawing
from.
PRZM/
EXAMS
is
a
field­
scale
model
which
treats
watersheds
as
large
fields.
It
assumes
that
the
entire
area
of
the
watershed
is
planted
with
the
crop
of
interest
(i.
e.,
100%
crop
coverage).
This
assumption
may
not
hold
for
areas
larger
than
a
few
hectares,
such
as
watersheds
containing
drinking
water
reservoirs.
Therefore,
pesticide
concentrations
(peak
and/
or
long­
term
average)
were
estimated
with
PRZM/
EXAMS
(the
index
reservoir
modification
changes
the
surface
water
body
parameters
used
in
EXAMS)
and
the
model
results
from
PRZM/
EXAMS
were
adjusted
by
a
factor
that
represents
the
maximum
percent
crop
area
found
for
the
crop
or
crops
being
evaluated.
Percent
crop
areas
(PCAs)
were
derived
on
a
watershed
basis
with
GIS
tools
using
1992
Census
of
Agriculture
data
and
8­
digit
Hydrologic
Unit
Code
(HUC)
coverage
for
the
coterminous
United
States.
The
maximum
PCA
derived
from
this
project
was
selected
to
represent
the
modeled
crop
or
crops.
The
PCA
assumes
the
distribution
of
the
crops
within
a
county
is
uniform
and
homogeneous
throughout
the
county
area.
Distance
between
the
treated
fields
and
the
water
body
is
not
addressed.

The
PCA
is
a
watershed­
based
modification.
Implicit
in
its
application
is
the
assumption
that
currently­
used
field­
scale
models
reflect
basin­
scale
processes
consistently
for
all
pesticides
and
uses.
In
other
words,
we
assume
that
the
large
field
simulated
by
the
coupled
PRZM
and
EXAMS
models
is
a
reasonable
approximation
of
pesticide
fate
and
transport
within
a
watershed
that
contains
a
drinking
water
reservoir.
If
the
models
fail
to
capture
pertinent
basin­
scale
fate
and
transport
processes
consistently
for
all
pesticides
and
all
uses,
the
application
of
a
factor
that
reduces
the
estimated
concentrations
predicted
by
modeling
could,
in
some
instances,
result
in
inadvertently
passing
a
chemical
through
the
screen
that
may
actually
pose
a
risk.
Some
preliminary
assessments
made
in
the
development
of
the
PCA
suggest
that
PRZM/
EXAMS
may
not
be
realistically
capturing
basin­
scale
processes
for
all
pesticides
or
for
all
uses.
A
preliminary
survey
of
water
assessments
which
compared
screening
model
estimates
to
readily
available
monitoring
data
suggest
uneven
model
results.
In
some
instances,
the
screening
model
estimates
are
more
than
an
order
of
magnitude
greater
than
the
highest
concentrations
reported
in
available
monitoring
data;
in
other
instances,
the
model
estimates
are
less
than
monitoring
concentrations.
Because
of
these
concerns,
the
SAP
recommended
using
the
PCA
only
for
"major"
crops
in
the
South.
For
other
crops,
development
of
PCAs
will
depend
on
the
availability
of
relevant
monitoring
data
that
could
be
used
to
evaluate
the
result
of
the
PCA
adjustment.
Table
A­
1.
Input
Parameters
for
Tebuthiuron
for
PRZM
(Version
3.12)
for
Index
Reservoir
and
PCA.

Variable
Description
Variable
(Units)
Input
Value
Source
of
Info/
Reference
Application
date(
s)
(day/
mo/
yr)
APD,
APM,
IAPYR
(day/
mo/
yr)
1
times
per
year
Product
label
or
location­
specific
Incorporation
depth
DEPI
(cm)
0
Product
label
Application
rate
TAPP
(kg
a.
i.
ha
­1
)
4.48
Aerial
granular
Product
label
Application
efficiency
APPEFF
(decimal)
1.00
Spray
Drift
Task
Force
Data
Spray
drift
fraction:
For
aquatic
ecological
exposure
assessment,
use
0.05
for
aerial
spray;
0.01
for
ground
spray.
For
drinking
water
assessment,
use
0.16
for
aerial
0.064
for
ground
spray.
DRFT
(decimal)
0.00
Spray
Drift
Task
Force
Data
Foliar
extraction
FEXTRA
(frac./
cm
rain)
0.5
(default)
Default
or
field
data
Decay
rate
on
foliage
PLDKRT
(day
­1
)
0.0
(default)
Default
or
field
data
Volatilization
rate
from
foliage
PLVKRT
(day
­1
)
0.0
(default)
Default
or
field
data
Plant
uptake
factor
UPTKF
(frac.
of
evap)
0.0
(default)
Default
or
field
data
Dissolved
phase
pesticide
decay
rate
in
surface
horizon
(aerobic
soil
metabolism)
DWRATE
(surface)
(day
­1
)
T1/
2
=>
1060
days
Rate
constant
=
0.00065/
day
MRID
41328001
Adsorbed
phase
pesticide
decay
rate
in
surface
horizon
(aerobic
soil
metabolism)
DSRATE
(surface)
(day
­1
)
T1/
2
=>
1060
days
Rate
constant
=
0.00065/
day
MRID
41328001
Dissolved
phase
pesticide
decay
rate
in
subsequent
subsurface
horizons
(aerobic
or
anaerobic
soil
metabolism)
DWRATE
(subsurface
horizons)
(day
­1
)
T1/
2
=>
1060
days
Rate
constant
=
0.00065/
day
MRID
41328001
Adsorbed
phase
pesticide
decay
rate
in
subsequent
subsurface
horizons
(aerobic
or
anaerobic
soil
metabolism)
DSRATE
(subsurface
horizons)
(day
­1
)
T1/
2
=>
1060
days
Rate
constant
=
0.00065/
day
MRID
41328001
Pesticide
partition
or
distribution
coefficients
for
each
horizon
(Leaching/
Adsorption/
Desorption)
Kd
0.84
Average
Kd
MRID
40768401
Table
A­
2.
Input
Parameters
for
Tebuthiuron.
chm
Files
Used
in
EXAMS
(Version
2.97.
5)
for
Index
Reservoir
and
PCA.

Variable
Description
Variable
(Units)
Input
Value
Source
of
Info/
Reference
Henry's
law
constant
HENRY
(atm­
m
3
mole
­1
)
2.4
x
10
­10
Atm
m
3
/mol
From
registrant
or
product
chemistry
Bacterial
biolysis
in
water
column
(aerobic
aquatic
metabolism)
KBACW
(cfu/
mL)
­1
hour
­1
30
days
Rate
constant
=0.00096/
hr
MRID
41372501
Bacterial
biolysis
in
benthic
sediment
(anaerobic
aquatic
or
aerobic
aquatic
metabolism)
KBACS
1
(cfu/
mL)
­1
hour
­1
365
days
MRID
41913101
Direct
photolysis
(aqueous
photolysis)
KDP
(hour
­1
)
T1/
2
=30
days
Rate
constant
=0.00096/
hr
MRID
41365101
Base
hydrolysis
KBH
(mole
­1
hour
­1
)
30
days
(stable)
Rate
constant
=0.00096/
hr
1994
RED
Neutral
hydrolysis
KNH
(mole
­1
hour
­1
)
30
days
(stable)
Rate
constant
=0.00096/
hr
1994
RED
Acid
hydrolysis
KAH
(mole
­1
hour
­1
)
30
days
(stable)
Rate
constant
=0.00096/
hr
1994
RED
Partition
coefficient
for
sediments
(Leaching/
Adsorption/
Desorption)
need
Kd
from
soil
closest
to
crop
scenario
KPS
(mL
g
­1
or
L
kg
­1
)
Kd
=
0.84
Average
Kd
MRID
40768401
Molecular
weight
MWT
(g
mole
­1
)
228.3
From
registrant
or
product
chemistry
Aqueous
solubility
(Multiply
water
solubility
by
10)
SOL
(mg
L
­1
)
=
0.800
2,500
ppm
@
20°
C
From
registrant
or
product
chemistry
Vapor
pressure
VAPR
(torr)
2
x
10
­6
Torr
From
registrant
or
product
chemistry
Sediment
bacteria
temperature
coefficient
QTBAS
2
Standard
value
Water
bacteria
temperature
coefficient
QTBAW
2
Standard
value
Table
A­
3.
PRZM­
EXAMS
Predicted
Tebuthiuron
Concentrations
in
the
Index
Reservoir
Simulation
Scenarios
Concentration
(
:
g/
L)

1
in
10
year
Mean
of
Annual
Means
Crop
and
Location
Scenario
Peak
96
Hour
21
Day
60
Day
90
Day
Annual
Mean
Pasture,
Milam
Co.,
TX
Index
Reservoir
17.4
16.6
13.2
8.
1
6.0
1.
7
0.7
Index
Reservoir
w/
PCA
(0.87)
15.1
14.4
11.5
7.
0
5.2
1.
5
0.6
TX
Alfalf
­
08/
06/
2001
"
Texas
Claypan
Area,
Milam
County,
Texas;
MLRA
J­
87"
***
Record
3:
0.71
0.36
0
25
1
1
***
Record
6
­­
ERFLAG
4
***
Record
7:
0.43
0.109
1
172.8
4
1
600
***
Record
8
1
***
Record
9
1
0.25
100
100
1
90
88
89
0
76
***
Record
9a­
d
1
26
0101
1601
0102
1602
0103
1503
1603
0104
1604
0105
1605
0106
1506
1606
0107
1607
.003
.003
.003
.004
.004
.004
.003
.001
.000
.001
.001
.000
.001
.001
.000
.000
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
0108
1608
0109
1609
0110
1610
0111
1611
0112
1612
.001
.000
.000
.001
.001
.002
.002
.002
.003
.003
.110
.110
.110
.110
.110
.110
.110
.110
.110
.110
***
Record
10
­­
NCPDS,
the
number
of
cropping
periods
36
***
Record
11
300847
201047
010848
1
300848
201048
010849
1
300849
201049
010850
1
300850
201050
010851
1
300851
201051
010852
1
300852
201052
010853
1
300853
201053
010854
1
300854
201054
010855
1
300855
201055
010856
1
300856
201056
010857
1
300857
201057
010858
1
300858
201058
010859
1
300859
201059
010860
1
300860
201060
010861
1
300861
201061
010862
1
300862
201062
010863
1
300863
201063
010864
1
300864
201064
010865
1
300865
201065
010866
1
300866
201066
010867
1
300867
201067
010868
1
300868
201068
010869
1
300869
201069
010870
1
300870
201070
010871
1
300871
201071
010872
1
300872
201072
010873
1
300873
201073
010874
1
300874
201074
010875
1
300875
201075
010876
1
300876
201076
010877
1
300877
201077
010878
1
300878
201078
010879
1
300879
201079
010880
1
300880
201080
010881
1
300881
201081
010882
1
300882
201082
010883
1
***
Record
12
­­
PTITLE
Tebuthiuron
­
1
applications
@
4.48
kg/
ha
***
Record
13
36
1
0
0
***
Record
15
­­
PSTNAM
Tebuthiuron
***
Record
16
050648
0
8
2
4.48
1
0
050649
0
8
2
4.48
1
0
050650
0
8
2
4.48
1
0
050651
0
8
2
4.48
1
0
050652
0
8
2
4.48
1
0
050653
0
8
2
4.48
1
0
050654
0
8
2
4.48
1
0
050655
0
8
2
4.48
1
0
050656
0
8
2
4.48
1
0
050657
0
8
2
4.48
1
0
050658
0
8
2
4.48
1
0
050659
0
8
2
4.48
1
0
050660
0
8
2
4.48
1
0
050661
0
8
2
4.48
1
0
050662
0
8
2
4.48
1
0
050663
0
8
2
4.48
1
0
050664
0
8
2
4.48
1
0
050665
0
8
2
4.48
1
0
050666
0
8
2
4.48
1
0
050667
0
8
2
4.48
1
0
050668
0
8
2
4.48
1
0
050669
0
8
2
4.48
1
0
050670
0
8
2
4.48
1
0
050671
0
8
2
4.48
1
0
050672
0
8
2
4.48
1
0
050673
0
8
2
4.48
1
0
050674
0
8
2
4.48
1
0
050675
0
8
2
4.48
1
0
050676
0
8
2
4.48
1
0
050677
0
8
2
4.48
1
0
050678
0
8
2
4.48
1
0
050679
0
8
2
4.48
1
0
050680
0
8
2
4.48
1
0
050681
0
8
2
4.48
1
0
050682
0
8
2
4.48
1
0
050683
0
8
2
4.48
1
0
***
Record
17
0
1
0
***
Record
19
­­
STITLE
Lufkin
Sandy
Loam;
HYDG:
D
***
Record
20
100
0
0
0
0
0
0
0
0
0
***
Record
26
0
0
0
***
Record
33
3
1
10
1.55
0.215
0
0
0
0.0006540.000654
0
0.1
0.215
0.105
1.16
0.84
2
8
1.55
0.215
0
0
0
0.0006540.000654
0
1
0.215
0.105
1.16
0.84
3
82
1.6
0.32
0
0
0
0.0006540.000654
0
2
0.32
0.2
0.29
0.84
***
Record
40
0
YEAR
10
YEAR
10
YEAR
10
1
1
1
­­­­

7
YEAR
PRCP
TCUM
0
0
RUNF
TCUM
0
0
INFL
TCUM
1
1
ESLS
TCUM
0
0
1.0E3
RFLX
TCUM
0
0
1.0E5
EFLX
TCUM
0
0
1.0E5
RZFX
TCUM
0
0
1.0E5
SET
MODE
=
3
CHEM
NAME
IS
Tebuthiuron
Read
ENV
c:\
mark\
przmexam\
exam\
irtxalf.
exv
SET
MWT(*)
=
228.3
SET
SOL(*,*)
=
2500.0
SET
PRBEN
=
0.05
SET
VAPR(
1)=
0.20E­
05
SET
KBACW(*,*,
1)=
0.00096
SET
KBACS(*,*,
1)=
0.0
SET
QTBAS(*,*,
1)=
2.0
SET
QTBAW(*,*,
1)=
2.0
SET
KDP(*,
1)=
0.00096
SET
KBH(*,*,
1)=
0.000
SET
KNH(*,*,
1)=
0.000
SET
KAH(*,*,
1)=
0.000
SET
KPS(*,
1)=
0.84
SET
YEAR1
=
1948
READ
PRZM
P2E­
C1.
D48
RUN
READ
PRZM
P2E­
C1.
D49
CONTINUE
READ
PRZM
P2E­
C1.
D50
CONTINUE
READ
PRZM
P2E­
C1.
D51
CONTINUE
READ
PRZM
P2E­
C1.
D52
CONTINUE
READ
PRZM
P2E­
C1.
D53
CONTINUE
READ
PRZM
P2E­
C1.
D54
CONTINUE
READ
PRZM
P2E­
C1.
D55
CONTINUE
READ
PRZM
P2E­
C1.
D56
CONTINUE
READ
PRZM
P2E­
C1.
D57
CONTINUE
READ
PRZM
P2E­
C1.
D58
CONTINUE
READ
PRZM
P2E­
C1.
D59
CONTINUE
READ
PRZM
P2E­
C1.
D60
CONTINUE
READ
PRZM
P2E­
C1.
D61
CONTINUE
READ
PRZM
P2E­
C1.
D62
CONTINUE
READ
PRZM
P2E­
C1.
D63
CONTINUE
READ
PRZM
P2E­
C1.
D64
CONTINUE
READ
PRZM
P2E­
C1.
D65
CONTINUE
READ
PRZM
P2E­
C1.
D66
CONTINUE
READ
PRZM
P2E­
C1.
D67
CONTINUE
READ
PRZM
P2E­
C1.
D68
CONTINUE
READ
PRZM
P2E­
C1.
D69
CONTINUE
READ
PRZM
P2E­
C1.
D70
CONTINUE
READ
PRZM
P2E­
C1.
D71
CONTINUE
READ
PRZM
P2E­
C1.
D72
CONTINUE
READ
PRZM
P2E­
C1.
D73
CONTINUE
READ
PRZM
P2E­
C1.
D74
CONTINUE
READ
PRZM
P2E­
C1.
D75
CONTINUE
READ
PRZM
P2E­
C1.
D76
CONTINUE
READ
PRZM
P2E­
C1.
D77
CONTINUE
READ
PRZM
P2E­
C1.
D78
CONTINUE
READ
PRZM
P2E­
C1.
D79
CONTINUE
READ
PRZM
P2E­
C1.
D80
CONTINUE
READ
PRZM
P2E­
C1.
D81
CONTINUE
READ
PRZM
P2E­
C1.
D82
CONTINUE
READ
PRZM
P2E­
C1.
D83
CONTINUE
Tebuthiuron
on
Pasture
in
Texas
WATER
COLUMN
DISSOLVED
CONCENTRATION
(PPB)

YEAR
PEAK
96
HOUR
21
DAY
60
DAY
90
DAY
YEARLY
­­­­
­­­­
­­­­­­­
­­­­­­
­­­­­­
­­­­­­
­­­­­

1948
4.558
4.303
3.627
2.252
1.678
0.491
1949
1.216
1.148
0.928
0.598
0.445
0.137
1950
10.440
9.861
7.831
4.873
3.605
0.958
1951
21.420
20.230
16.060
9.896
7.466
2.015
1952
9.117
8.612
6.840
4.257
3.149
0.871
1953
1.768
1.667
1.292
0.788
0.586
0.179
1954
0.148
0.139
0.109
0.072
0.056
0.023
1955
9.022
8.536
6.810
4.244
3.140
0.854
1956
0.178
0.168
0.133
0.082
0.065
0.034
1957
9.876
9.328
7.405
4.575
3.386
0.872
1958
4.589
4.334
3.435
2.109
1.567
0.455
1959
4.282
4.044
3.158
1.989
1.485
0.430
1960
17.050
16.270
12.910
7.886
5.853
1.724
1961
5.934
5.671
4.674
2.912
2.156
0.707
1962
16.330
15.490
12.420
7.693
5.694
1.553
1963
0.679
0.642
0.511
0.314
0.233
0.095
1964
9.273
8.762
7.099
4.369
3.235
0.870
1965
1.998
1.887
1.499
0.933
0.697
0.201
1966
3.022
2.854
2.266
1.400
1.041
0.291
1967
3.743
3.509
2.710
1.747
1.370
0.391
1968
0.294
0.282
0.225
0.138
0.103
0.049
1969
9.944
9.392
7.351
4.667
3.694
1.060
1970
0.232
0.227
0.206
0.167
0.143
0.055
1971
8.399
7.933
6.245
3.891
2.909
0.808
1972
5.950
5.620
4.455
2.741
2.031
0.587
1973
3.450
3.304
2.655
1.641
1.215
0.354
1974
1.165
1.108
0.878
0.558
0.431
0.139
1975
4.268
4.034
3.206
1.986
1.470
0.438
1976
5.716
5.398
4.275
2.646
1.968
0.585
1977
0.300
0.283
0.222
0.136
0.109
0.057
1978
18.300
17.290
13.730
8.536
6.323
1.642
1979
2.098
1.967
1.660
1.234
1.057
0.346
1980
0.203
0.191
0.150
0.099
0.078
0.034
1981
33.920
32.280
25.780
15.920
11.780
3.384
1982
5.063
4.782
4.043
2.524
1.871
0.570
1983
2.171
2.050
1.633
1.031
0.765
0.224
SORTED
FOR
PLOTTING
­­­­­­
­­­
­­­­­­­


PROB
PEAK
96
HOUR
21
DAY
60
DAY
90
DAY
YEARLY
­­­­
­­­­
­­­­­­­
­­­­­­
­­­­­­
­­­­­­
­­­­­­
0.027
33.920
32.280
25.780
15.920
11.780
3.384
0.054
21.420
20.230
16.060
9.896
7.466
2.015
0.081
18.300
17.290
13.730
8.536
6.323
1.724
0.108
17.050
16.270
12.910
7.886
5.853
1.642
0.135
16.330
15.490
12.420
7.693
5.694
1.553
0.162
10.440
9.861
7.831
4.873
3.694
1.060
0.189
9.944
9.392
7.405
4.667
3.605
0.958
0.216
9.876
9.328
7.351
4.575
3.386
0.872
0.243
9.273
8.762
7.099
4.369
3.235
0.871
0.270
9.117
8.612
6.840
4.257
3.149
0.870
0.297
9.022
8.536
6.810
4.244
3.140
0.854
0.324
8.399
7.933
6.245
3.891
2.909
0.808
0.351
5.950
5.671
4.674
2.912
2.156
0.707
0.378
5.934
5.620
4.455
2.741
2.031
0.587
0.405
5.716
5.398
4.275
2.646
1.968
0.585
0.432
5.063
4.782
4.043
2.524
1.871
0.570
0.459
4.589
4.334
3.627
2.252
1.678
0.491
0.486
4.558
4.303
3.435
2.109
1.567
0.455
0.514
4.282
4.044
3.206
1.989
1.485
0.438
0.541
4.268
4.034
3.158
1.986
1.470
0.430
0.568
3.743
3.509
2.710
1.747
1.370
0.391
0.595
3.450
3.304
2.655
1.641
1.215
0.354
0.622
3.022
2.854
2.266
1.400
1.057
0.346
0.649
2.171
2.050
1.660
1.234
1.041
0.291
0.676
2.098
1.967
1.633
1.031
0.765
0.224
0.703
1.998
1.887
1.499
0.933
0.697
0.201
0.730
1.768
1.667
1.292
0.788
0.586
0.179
0.757
1.216
1.148
0.928
0.598
0.445
0.139
0.784
1.165
1.108
0.878
0.558
0.431
0.137
0.811
0.679
0.642
0.511
0.314
0.233
0.095
0.838
0.300
0.283
0.225
0.167
0.143
0.057
0.865
0.294
0.282
0.222
0.138
0.109
0.055
0.892
0.232
0.227
0.206
0.136
0.103
0.049
0.919
0.203
0.191
0.150
0.099
0.078
0.034
0.946
0.178
0.168
0.133
0.082
0.065
0.034
0.973
0.148
0.139
0.109
0.072
0.056
0.023
1/
10
17.425
16.576
13.156
8.081
5.994
1.667
MEAN
OF
ANNUAL
VALUES
=
0.652
STANDARD
DEVIATION
OF
ANNUAL
VALUES
=
0.696
UPPER
90%
CONFIDENCE
LIMIT
ON
MEAN
=
0.824
RUN
No.
2
FOR
Tebuthiuron
INPUT
VALUES
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

APPL
(#/
AC)
APPL.
URATE
SOIL
SOIL
AEROBIC
RATE
NO.
(#/
AC/
YR)
KOC
METABOLISM
(DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

4.000
1
4.000
72.0
1060.0
GROUND­
WATER
SCREENING
CONCENTRATIONS
IN
PPB
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

181.451200
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

A=
1055.000
B=
77.000
C=
3.023
D=
1.886
RILP=
6.390
F=
1.657
G=
45.363
URATE=
4.000
GWSC=
181.451200
