U.
S.
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
DC
20460
.
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
MEMORANDUM
SUBJECT:
Tier
I
Estimated
Environmental
Concentrations
of
Dimethipin,
for
use
in
Human
Health
Risk
Assessment
(
PC
Code
118901;
DP
Barcode
D293574)

FROM:
Larry
Liu,
Ph.
D.,
Environmental
Scientist
ERB
V,
Environmental
Fate
and
Effects
Division
(
7507C)

THROUGH:
Mah
T.
Shamim,
Ph.
D.,
Chief
Environmental
Risk
Branch
V
Environmental
Fate
and
Effects
Division
TO:
Susan
Stanton
HED
This
memo
presents
the
Tier
I
Estimated
Environmental
Concentrations
(
EECs)
for
dimethipin,
estimated
using
FIRST
for
surface
water
and
SCIGROW
for
groundwater
in
the
human
health
risk
assessment.

For
dimethipin,
the
surface
water
acute
(
peak)
value
is
11.9
ppb
and
the
chronic
(
average
56­
day)
value
is
7.3
ppb
based
on
the
application
on
cotton.
The
groundwater
screening
concentration
is
423.2
ppb
for
dimethipin.
Details
of
the
application
scenarios
that
were
evaluated
are
presented
in
Table
3.

Should
the
results
of
this
assessment
indicate
a
need
for
further
refinement,
please,
contact
us
as
soon
as
possible
so
that
we
may
schedule
a
Tier
II
assessment.

Dimethipin
Fate
Properties
Environmental
Fate
Dimithipin
(
2,3­
dihydro­
5,6­
dimethyl­
1,4­
dithi­
ine
1,1,4,4­
tetraoxide;
Harvade)
is
used
primarily
(
95%)
as
a
cotton
defoliant,
with
minor
uses
(
5%)
as
post­
directed
weed
control
in
cotton
in
tank
2
mixes
with
other
herbicides.
The
maximum
seasonal
rate
is
0.56
lb
a.
i./
A.
The
majority
of
applications
are
made
at
0.31
lb
a.
i./
A,
with
a
small
number
of
applications
at
0.23
or
0.38
lb
a.
i./
A.
It
is
applied
both
by
ground
rig
and
by
air.

Listed
below
are
the
fate
properties
for
dimethipin:

Water
solubility
=
4,600
ppm
(
25
C)
Vapor
pressure
=
<
3.87x10­
7
mm
Hg
(
24
C)
Kow
=
0.75
(
25
C)

Study
Type
Half­
Life/
Kd/
Koc
Hydrolysis
pH
5
stable
pH
7
stable
pH
9
stable
Aqueous
photolysis
pH
5
59
days
pH
7
224
days
pH
9
198
days
Soil
Photolysis
86.6
days
Aerobic
Soil
408
days
Anaerobic
Aquatic
277
days
Adsorption
Kd
Koc
clay
0.09
3.27
sand
<
0.01
<
1
sandy
loam
<
0.01
<
1
loam
<
0.01
<
1
Field
Dissipation
Georgia
­
136
day
(
bare
ground);
117
days
(
cropped)

Mississippi
­
25
day
Environmental
Persistence
Dimethipin
degrades
slowly
under
laboratory
and
field
conditions,
with
the
apparent
primary
route
of
dissipation
in
the
field
being
leaching
coupled
with
photodegradation
at
the
soil
surface
and
3
metabolic
degradation
throughout
the
soil
column.

In
buffered
aqueous
solutions,
Dimithipin
was
stable
to
hydrolysis
with
half­
lives
>
2
years
at
pHs
3­
9
and
photodegraded
slowly
to
very
slowly
with
half­
lives
ranging
from
60
days
(
pH
5)
to
224
days
(
pH
7)
at
pH
5­
9.
In
sandy
loam
soil,
dimethipin
photodegraded
with
a
half­
life
of
75
days.
In
metabolism
studies,
dimethipin
degraded
under
aerobic
conditions
with
a
half­
life
of
408
days
and
under
anaerobic
aquatic
conditions
with
a
half­
life
of
277
days.

Octanol/
water
partitioning
(
Kow)
data
provided
by
the
registrant
indicates
a
low
potential
for
dimethipin
to
accumulate
in
fish
(
Kow
for
dimethipin
=
0.7).

Expected
Mobility
Dimethipin
has
very
high
mobility
in
soils
ranging
from
sand
to
clay,
with
Freundlich
adsorption
coefficients
of

0.09.
In
field
studies
using
bare
ground
and
cropped
plots,
dimethipin
leached
to
a
depth
of
75­
90
cm.

Volatilization
is
not
expected
to
be
a
significant
since
the
reported
vapor
pressure
is
<
3.87
x
10­
7
mm
Hg
at
24

C.

Degradate
Profile
No
major
transformation
products
were
identified
in
any
study.
2,3­
Dihydro­
5­
hydroxymethyl­
6­
methyl­
1,4­
dithiin­
1,1,4,4­
tetraoxide
(
H­
5)
was
a
minor
transformation
product
at
<
2%
of
the
applied
in
the
photodegradation
in
water
study
only.
The
saturated
carboxylic
acid
of
dimethipin
was
identified
in
the
anaerobic
aquatic
study
but
was
not
quantified.

Summary
of
Environmental
Fate
Studies
for
Dimethipin
Degradate
Maximum
Degradate
Concentration
(%
of
applied)
in
Study:

Hydrolysis
(
161­
1)
Aqueous
Photo.
(
161­
2)
Soil
Photo.
(
161­
3)
Aerobic
Soil
(
162­
1)
Anaerobic
Aquatic
(
162­
3)
Field
Diss.
(
164­
1)

2,3­
Dihydro­
5­
hydroxymethyl­
6­
methyl­
1,4­
dithiin­
1,1,4,4­
tetraoxide
(
aka
H­
5)
Not
detected
2%
@
pH
5
0.8%
@
pH
9
Not
detected
Not
detected
Not
detected
Not
analyzed
Saturated
carboxylic
acid
of
Dimethipin
Not
analyzed
Not
detected
Not
detected
Detected,
but
not
quantified
Not
detected
Not
analyzed
4
Background
Information
on
FIRST:

FIRST
is
a
new
screening
model
designed
to
estimate
the
pesticide
concentrations
found
in
water
for
use
in
drinking
water
assessments.
It
provides
high­
end
values
on
the
concentrations
that
might
be
found
in
a
small
drinking
water
reservoir
due
to
the
use
of
pesticide.
Like
GENEEC,
the
model
previously
used
for
Tier
I
screening
level,
FIRST
is
a
single­
event
model
(
one
run­
off
event),
but
can
account
for
spray
drift
from
multiple
applications.
FIRST
uses
a
Drinking
Water
Reservoir
instead
of
a
pond
as
the
standard
scenario.
The
FIRST
scenario
includes
a
427
acres
field
immediately
adjacent
to
a
13
acres
reservoir,
9
feet
deep,
with
continuous
flow
(
two
turnovers
per
year).
The
pond
receives
a
spray
drift
event
from
each
application
plus
one
runoff
event.
The
runoff
event
moves
a
maximum
of
8%
of
the
applied
pesticide
into
the
pond.
This
amount
can
be
reduced
due
to
degradation
on
field
and
the
effect
of
binding
to
soil.
Spray
drift
is
equal
to
6.4%
of
the
applied
concentration
from
the
ground
spray
application
and
16%
for
aerial
applications.

FIRST
also
makes
adjustments
for
the
percent
crop
area.
While
FIRST
assumes
that
the
entire
watershed
would
not
be
treated,
the
use
of
a
PCA
is
still
a
screen
because
it
represents
the
highest
percentage
of
crop
cover
of
any
large
watershed
in
the
US,
and
it
assumes
that
the
entire
crop
is
being
treated.
Various
other
conservative
assumptions
of
FIRST
include
the
use
of
a
small
drinking
water
reservoir
surrounded
by
a
runoff­
prone
watershed,
the
use
of
the
maximum
use
rate,
no
buffer
zone,
and
a
single
large
rainfall.

Background
Information
on
SCI­
GROW:

SCI­
GROW
provides
a
groundwater
screening
exposure
value
to
be
used
in
determining
the
potential
risk
to
human
health
from
drinking
water
contaminated
with
the
pesticide.
Since
the
SCI­
GROW
concentrations
are
likely
to
be
approached
in
only
a
very
small
percentage
of
drinking
water
sources,
i.
e.,
highly
vulnerable
aquifers,
it
is
not
appropriate
to
use
SCI­
GROW
for
national
or
regional
exposure
estimates.
SCI­
GROW
estimates
likely
groundwater
concentrations
if
the
pesticide
is
used
at
the
maximum
allowable
rate
in
areas
where
groundwater
is
exceptionally
vulnerable
to
contamination.
In
most
cases,
a
large
majority
of
the
use
area
will
have
groundwater
that
is
less
vulnerable
to
contamination
than
the
areas
used
to
derive
the
SCIGROW
estimate.

Modeling
Inputs
and
Results:

Table
1
and
Table
2
summarize
the
input
values
used
in
the
model
runs
for
FIRST
and
SCIGROW
respectively.
Fate
parameters
were
obtained
from
studies
submitted
by
the
registrant
and
modified,
if
necessary,
according
to
the
Guidance
for
Selecting
Input
Parameters
in
Modeling
the
Environmental
Fate
and
Transport
of
Pesticides,
Version
ll
(
February
28,
2002).
The
modeling
results
associated
with
maximum
allowable
rate
per
year
for
representative
crops
are
presented
in
Table
3.
Attached
to
this
memo
are
copies
of
the
original
printouts
generated
from
FIRST
and
SCI­
GROW
runs.
5
Table
1.
Environmental
Fate
Input
Parameters
for
FIRST.

Parameter
Dimethipin
Value
Water
Solubility
(
25
C)
4,600
mg/
L
Hydrolysis
Half­
Life
(
pH
7)
Stable
Aerobic
Soil
Metabolism
Half­
Life
(
mean
value
plus
t
90,
n­
1
x
 
)
/
n1/
2)
408
days
1,224
days
(
3x)

Aerobic
Aquatic
Metabolism
Half­
Life
n/
a
Aqueous
Photolysis
Half­
Life
(
at
pH
7)
224
Soil
Water
Partition
Coefficient
(
Koc)
1
Pesticide
is
Wetted­
In
No
PCA
0.20
Depth
of
Incorporation
(
Aerial)
0.0
Table
2.
Environmental
Fate
Input
Parameters
for
SCI­
GROW.

Parameter
Dimethipin
Value
Organic
Carbon
Partition
Coefficient
(
K
OC)
1
Aerobic
Soil
Metabolism
Half­
Life
408
days
Table
3.
Application
Information
and
Modeling
Results
for
Use
of
Dimethipin
on
Cotton.

Parameter
Dimethipin
value
Application
Method
Aerial
spray
Maximum
Application
Rate
per
Season
(
the
seasonal
maximum
rate
was
used
in
the
modeling)
0.562
lbs
a.
i/
acre
Application
Frequency
once/
year
Incorporation
Depth
0
inch
Application
Interval
(
days)
N/
A
FIRST
Peak
Untreated
Water
Concentration
11.9
ppb
FIRST
Annual
Average
Untreated
Water
Concentration
7.3
ppb
SCI­
GROW
Ground
Water
Concentration
423.2
ppb
6
FIRST
run
for
the
use
of
dimethipin
on
cotton
RUN
No.
100
FOR
dimethipin
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
%
CROPPED
INCORP
ONE(
MULT)
INTERVAL
Kd
(
PPM
)
(%
DRIFT)
AREA
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
0.562(
0.562)
1
1
1.0
4600.0
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.)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

1224.00
2
N/
A
224.00­
27776.00
816.00
792.71
UNTREATED
WATER
CONC
(
MICROGRAMS/
LITER
(
PPB))
Ver
1.0
AUG
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
DAY
(
ACUTE)
ANNUAL
AVERAGE
(
CHRONIC)
CONCENTRATION
CONCENTRATION
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
11.897
7.304
SCI­
GROW
run
for
the
use
of
dimethipin
on
cotton
RUN
No.
111
FOR
dimethipin
INPUT
VALUES
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
APPL
(#/
AC)
APPL.
URATE
SOIL
SOIL
AEROBIC
RATE
NO.
(#/
AC/
YR)
KOC
METABOLISM
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
0.562
1
0.562
1.
408.0
GROUND­
WATER
SCREENING
CONCENTRATIONS
IN
PPB
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
423.152
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
