UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON
D.
C.,
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
MEMORANDUM
May
18,
2006
SUBJECT:
Qualitative
Assessment
of
Dichlorvos
(
DDVP)
in
Drinking
Water
and
Volatilization
from
Use
of
Trichlorfon
Turf
DP
Barcode:
327193
PC
Codes:
057901
(
Trichlorfon)
084001
(
Dichlorvos)

TO:
Dayton
Eckerson,
Chemical
Review
Manager
Special
Review
Branch
Special
Review
and
Reregistration
Division
Sue
Hummel,
Chemist
Reregistration
Branch
4
Health
Effects
Division
FROM:
R.
David
Jones,
Ph.
D.,
Senior
Agronomist
Environmental
Risk
Branch
4
THROUGH:
Dana
Spatz,
Risk
Assessment
Process
Leader
Environmental
Risk
Branch
2
Elizabeth
Behl,
Chief
Environmental
Risk
Branch
4
Environmental
Fate
and
Effects
Division
The
purpose
of
this
document
is
to
assess
the
nature
of
exposure
to
dichlorvos
(
PC
Code
084001),
also
known
as
dichlorvos,
formed
from
the
application
of
trichlorfon
(
PC
Code
057901).
The
reregistration
of
trichlorfon
was
completed
in
January
1997
(
OPP,
1997)
and
tolerance
reassessment
was
completed
in
September
2001
(
OPPTS,
2001).
In
those
documents,
only
trichlorfon
parent
was
considered
in
the
risk
assessment,
and
it
was
decided
that
assessment
and
management
of
risk
of
dichlorvos
resulting
from
trichlorfon
application
would
be
handled
in
the
reregistration
process
for
dichlorvos.

This
memorandum
describes
qualitatively
the
nature
of
dichlorvos
formation
from
trichlorfon
and
the
implications
for
evaluating
the
resultant
dichlorvos
exposure
through
drinking
water
and
inhalation.
The
fate
and
transport
properties
of
both
chemicals
are
briefly
reviewed,
as
well
as
the
use
patterns
for
trichlorfon.
This
is
followed
by
a
discussion
of
drinking
water.
There
are
a
number
of
assumptions
in
estimates
of
dichlorvos
formation
from
trichlorfon
that
add
uncertainty
to
the
estimated
drinking
water
concentrations
reported
in
the
existing
trichlorfon
assessment:

 
Conversion
of
trichlorfon
to
dichlorvos:
Data
reviewed
indicates
that
trichlorfon
mostly
degrades
to
dichlorvos,
which
subsequently
degrades
to
other
compounds
and
that
the
rate
of
formation
and
degradation
are
pH
dependant.
Where
trichlorfon
is
used
and
pH
is
neutral
or
low,
the
assumption
used
in
modeling
that
100%
of
trichlorfon
is
converted
to
dichlorvos
is
a
conservative
one.
This
is
particularly
the
case
east
of
the
Mississippi
River.
In
these
areas,
the
maximum
fraction
of
dichlorvos
formed
from
trichlorfon
will
be
less
than
the
approximately
25%
seen
in
the
pH
7
hydrolysis
study.
In
areas
with
higher
pH
the
conversion
efficiency
could
run
as
high
as
the
52%
seen
in
the
pH
9
hydrolysis
study.
Higher
pHs
are
found
in
arid
and
semi­
arid
areas
in
the
western
United
States
where
pedogenic
lime
accumulates,
and
soils
formed
from
carbonatic
parent
materials,
e.
g.
limestone.
The
practical
lower
pH
limit
for
turf
is
6,
as
lime
is
generally
applied
to
maintain
turf
at
this
pH.
On
the
upper
end,
pH s
higher
than
8.5
are
seldom
seen
in
the
environment
where
plant
stands
can
be
maintained.
Most
commonly,
soil
pH
for
turf
is
between
6
and
7.
Based
on
this
information,
the
modeled
estimates
of
DDVP
derived
from
trichlorforn
use
on
turf
would
be
estimated
to
decrease
from
the
concentrations
estimated
in
the
risk
assessment.
The
peak
1­
in­
10­
year
Drinking
Water
Estimated
Concentration
would
be
in
the
range
of
122
µ
g
L
­
1
in
areas
where
the
pH
is
9
or
greater.
If
the
trichlorfon
turf
use
area
were
limited
to
east
of
Mississippi
where
pH
is
7
or
less
(
i.
e.
other
than
karst
areas
and
where
soils
with
higher
pH
occur),
the
peak
1­
in­
10­
year
Drinking
Water
Estimated
Concentration
would
be
in
the
range
of
59
µ
g
L
­
1
.

 
Use
of
adjustment
factors
and
model
scenario:
Drinking
water
estimates
from
turf
uses
were
adjusted
in
previous
modeling
by
the
default
PCA
for
agricultural
crops
(
0.87);
this
factor
is
not
generally
used
for
turf.
Golf
course
adjustment
factors
are
currently
available
to
take
into
account
percentages
of
areas
treated
in
golf
courses.
However,
golf
course
adjustment
factors
do
not
apply
to
other
turf
uses
(
e.
g.
urban
uses,
sod
farms)
and
trichlorfon
use
is
dominated
by
use
on
residential
lawns.
Loading
to
surface
water
from
application
in
Florida
does
provide
estimated
drinking
water
concentrations
that
are
greater
than
those
that
would
occur
in
most
of
the
country;
these
values
do
not
reflect
exposure
in
other
parts
of
the
country
where
less
intense
rainfall
occurs.

 
Label
requirement
to
 
wet
in 
trichlorfon
after
application:
Provided
irrigation
is
not
applied
in
amounts
that
cause
runoff
to
occur,
this
practice
will
significantly
reduce
off­
site
movement
due
to
runoff
from
storm
events.
However,
without
significant
additional
analysis,
the
amount
of
reduction
cannot
be
quantified.

 
Maximum
label
rate
for
trichlorfon:
Modeling
of
dichlorvos
concentrations
from
trichlorfon
application
were
based
on
molecular
weight
and
the
labeled
maximum
application
rate
of
trichlorfon
on
turf.
The
maximum
application
rate
of
trichlorfon
(
8.2
lb.
a.
i./
A)
is
significantly
higher
than
that
of
dichlorvos
(
0.2
lb.
a.
i./
A),
with
more
frequent
and
more
closely
spaced
applications
allowed.

 
Effects
of
volatilization:
The
amount
of
dichlorvos
available
for
volatilization
will
be
somewhat
mitigated
by
the
irrigation
( 
wetting
in )
required
on
the
trichlorfon
labels,
but
the
extent
of
the
reduction
cannot
be
quantified
without
significant
further
analysis.
The
maximum
amount
of
dichlorvos
available
for
volatilization
from
trichlorfon
application
varies
with
pH,
and
is
of
most
concern
in
places
with
soil
pH
above
7.

Fate
and
Transport
Properties
of
Trichlorfon
The
fate
and
transport
properties
of
trichlorfon
are
discussed
in
the
RED
for
trichlorfon
(
OPP,
1997).
Trichlorfon
degradation
appears
to
be
strongly
influenced
by
pH.
In
a
hydrolysis
study
conducted
at
at
25
°
C,
the
trichlorfon
degradation
half­
life
was
104
days
at
pH
5;
34
hours
at
pH
7;
and
31
minutes
at
pH
9.
The
maximum
measured
dichlorvos
formed
from
trichlorfon
also
varied
with
pH,
with
a
maximum
percentage
converted
of
2.1%
at
pH
5;
25%
at
pH
7;
and
52%
at
pH
9.
The
formation
of
dichlorvos
from
trichlorfon
is
not
a
 
hydrolysis
reaction 
per
se,
but
a
dehydrochlorination.
This
reaction
occurs
abiotically
in
aqueous
solution
and
the
reaction
products
are
found
in
the
 
hydrolysis 
study.
The
other
degradates
found
in
the
hydrolysis
study
are
des­
methyldichlorvos,
and
dichloroacetaldehyde,
resulting
from
hydrolysis
of
dichlorvos
directly
(
Edwards,
2000),
thus,
they
are
secondary
degradates
formed
from
dichlorvos.
The
maximum
amount
of
dichlorvos
measured
in
the
hydrolysis
study
is
controlled
by
the
relative
formation
and
degradation
rates
of
dichlorvos
rather
than
a
competitive
degradation
pathway
for
trichlorfon.
However,
because
the
original
data
for
the
hydrolysis
study
is
not
available,
this
supposition
cannot
be
confirmed
at
present.
Aqueous
photolysis
is
very
slow,
with
an
estimated
half­
life
greater
than
2000
days
(
after
correction
for
degradation
in
the
dark
control).
Soil
photolysis
is
also
slow,
with
a
corrected
half­
life
of
54
days
or
more,
although
this
result
is
highly
uncertain.
Given
the
background
variability
in
the
soil
photolysis
study
it
is
not
certain
that
soil
photolysis
is
even
occurring,
as
all
identified
degradates
were
found
in
other
degradation
studies.

There
are
three
metabolism
studies
for
trichlorfon:
an
aerobic
soil
metabolism
study;
an
anaerobic
soil
metabolism
study;
and
a
pond­
water
study.
These
studies
provide
information
on
aerobic
degradation
in
the
water
column,
independent
of
the
bed
sediment.
Trichlorfon
degraded
with
a
6.4
day
half­
life
in
the
aerobic
soil
metabolism
study;
no
DDVP
was
detected
in
the
study.
However,
the
experiment
was
designed
so
that
any
dichlorvos
that
formed
and
volatilized
would
be
converted
to
CO
2
for
measurement.
The
other
degradates
found
were
2,
2,
2­
trichloroacetic
acid,
2,
2­
dichloracetic
acid
and
(
1­
hydroxy­
2,2­
dichlorovinyl)
phosphate
(
HDCP).
The
results
of
this
study
would
be
consistent
with
the
hydrolysis
results
if
the
study
was
conducted
at
low
pH,
but
the
pH
of
this
study
was
apparently
not
reported.
Trichlorfon
degraded
with
a
1.8
day
half­
life
under
anaerobic
conditions
in
soil.
There
are
indications
in
the
Data
Evaluation
Record
that
this
study
was
carried
out
at
pHs
between
7
and
9,
but
the
specific
pH
is
not
reported.
Degradates
were
glyoxilic
acid,
dichloroacetic
acid,
dichlorvos,
HDCP
and
2,2­
dichloroethanol.
However,
DDVP
was
never
present
at
more
than
1%
of
the
applied
trichlorfon
concentration.
The
pond
water
study
was
conducted
at
two
pH s
 
5
and
8.5.
At
pH
5,
no
degradation
was
observed
over
the
24
duration
of
the
study.
At
pH
8.5,
there
was
rapid
loss
of
trichlorfon
with
no
detectable
amounts
after
8
h.
Dichlorvos
was
formed,
and
the
concentration
peaked
at
56%
at
8
h
after
study
initiation.
It
is
not
clear
whether
additional
degradates
were
monitored
or
identified.

Trichlorfon
is
highly
mobile
in
soil,
with
estimated
K
d
 
s
ranging
from
0.4
to
0.6
L
kg
­
1
.
Trichlorfon
does
not
appear
to
be
volatile.
A
soil
volatility
study
found
less
than
1%
of
the
applied
trichlorfon
in
organic
traps.
However,
the
study
was
conducted
at
pH
4.3,
so
little
dichlorvos
would
be
expected
to
be
formed.

Submitted
field
dissipation
studies
were
not
acceptable
because
of
analyte
recovery
problems.
A
lysimeter
study
was
submitted
for
consideration
as
a
field
dissipation
study,
but
was
found
to
be
unacceptable
for
that
purpose.
The
pH
in
the
lysimeter
study
was
5.5,
which
is
lower
than
soil
pHs
normally
found
in
soils
where
turf
is
grown
(
turf
is
usually
limed
to
pH s
between
6
and
7).
Furthermore,
a
pH
of
5.5
would
not
be
conducive
to
the
formation
of
large
amounts
of
dichlorvos
from
trichlorfon,
based
on
laboratory
degradation
studies.

Fate
and
Transport
Properties
of
Dichlorvos
The
fate
and
transport
properties
of
dichlorvos
are
described
more
completely
in
the
EFED
RED
chapter
for
dichlorvos
(
Edwards,
2000).
Dichlorvos
appears
to
dissipate
through
volatilization,
abiotic
degradation,
and
perhaps
also
by
aerobic
metabolic
pathways.
Dichlorvos
is
prone
to
volatilization,
with
a
vapor
pressure
of
1.2
x
10
­
2
torr.
Degradation
half­
life
by
hydrolysis
at
pH
5
is
11
days
and
decreases
to
124
hours
and
21.1
hours
at
pH
7
and
9
respectively.
Degradates
formed
by
hydrolysis
are
DCA,
DAA,
desmethyl
dichlorvos,
and
glyoxilic
acid.
There
was
no
discernable
aqueous
photolysis,
and
the
soil
photolysis
half­
life
was
estimated
at
10.6
days.
As
with
trichlorfon,
the
uncertainties
around
the
dichlorvos
soil
photolysis
half­
life
are
very
high.
The
half­
life
of
dichlorvos
in
an
aerobic
soil
metabolism
study
was
10
hours,
with
DAA,
DCA
and
2,
2­
dichloroethanol
detected
as
degradates.
In
an
anaerobic
soil
metabolism
study
conducted
at
a
pH
of
6.8,
dichlorvos
degraded
with
a
half­
life
of
6.3
days.
Degradates
in
this
study
were
dichloroacetic
acid,
dichloroacetaldehyde
and
dichloroethanol.
Dichlorvos
is
mobile
through
soil
with
a
K
oc
of
36.9
L
kg­
OC
­
1
but
is
not
likely
to
be
persistent
enough
to
occur
in
groundwater.
With
two
exceptions,
2,
2,
2­
trichloroacetic
acid
and
methyl
(
2,
2,
2­
trichloro
hydroxyethyl)
phosphonate,
all
degradates
found
in
the
trichlorfon
degradation
studies
were
found
in
the
dichlorvos
studies.
Both
of
the
trichloro
degradates
were
found
only
in
small
amounts,
less
than
2%
of
the
applied
trichlorfon.
This
strongly
suggests
that
trichlorfon
mostly
degrades
to
dichlorvos,
which
subsequently
degrades
to
other
compounds.
The
increasing
maximum
dichlorvos
fractions
found
in
the
trichlorfon
hydrolysis
study
would
be
consistent
with
the
changing
ratios
of
the
degradation
rates
with
pH.
At
pH
5,
trichlorfon
is
forming
dichlorvos
at
a
rate
1/
10
as
fast
of
that
rate
at
which
dichlorvos
is
degrading,
so
little
dichlorvos
is
found
from
trichlorfon
at
this
pH.
In
contrast,
at
pH
9,
dichlorvos
is
being
formed
from
trichlorfon
about
10
times
faster
than
it
is
degrading,
so
dichlorvos
accumulates
before
it
can
be
degraded.

Trichlorfon
Use
Based
on
usage
data
from
1994
to
1999,
about
1
million
pounds
of
trichlorfon
are
used
per
year.
Most
of
this
is
used
by
lawn
care
operators
(
74%),
though
a
significant
fraction
is
used
on
golf
courses
(
18%).
The
remainder
of
the
use
is
in
minor
uses
such
as
landscaping,
institutional
turf,
greenhouses,
nurseries,
and
livestock.
For
comparison,
the
estimated
use
of
dichlorvos
on
turf
and
turf­
type
sites
is
less
than
6000
lb/
year.

The
trichlorfon
label
allows
a
maximum
single
application
rate
on
turf
of
8.2
lb
a.
i./
acre,
with
a
maximum
of
3
applications
per
year
at
a
7
day
interval
(
ground
spray).
In
contrast,
the
dichlorvos
label
allows
a
maximum
of
4
applications
per
year
at
0.2
lb
a.
i./
acre
with
a
30
day
interval.

Drinking
water
characterization
A
quantitative
drinking
water
exposure
assessment
at
Tier
2
was
conducted
by
Ibrahim
Abel­
Saheb
(
2003)
for
dichlorvos.
This
assessment
included
dichlorvos
from
the
degradation
of
naled
and
trichlorfon.
The
EECs
for
the
dichlorvos
derived
from
the
turf
use
of
trichlorfon
are
235
µ
g
L
­
1
for
the
peak
1­
in
ten
year
DWEC;
6.24
µ
g
L
­
1
for
the
1­
in­
ten­
year
annual
mean;
and
3.25
µ
g
L
­
1
for
the
overall
mean.
These
values
reflect
the
use
of
the
default
PCA
of
0.87,
a
conversion
to
a
dichlorvos
based
on
molecular
weight,
and
the
assumption
of
100%
conversion
of
trichlorfon
to
dichlorvos.
The
simulation
was
conducted
using
the
Florida
turf
scenario.

The
PCA
of
0.87
reflects
the
maximum
fraction
of
agricultural
land
found
in
any
HUC­
8
basin
in
the
United
States.
Given
that
the
default
PCA
reflects
agricultural
land,
it
is
not
particularly
apt
for
turf
use,
which
is
dominantly
an
urban,
mostly
non­
agricultural
use.
Standard
practice
is
to
use
a
PCA
of
1.0
for
the
turf
use
because
of
this
fact,
which
is
likely
an
overestimate
for
turf
uses.
In
cases
where
the
only
turf
use
is
on
golf
courses,
there
are
factors
that
can
be
applied
when
the
use
is
restricted
to
tees
and
greens,
or
tees,
greens,
and
fairways
(
OPP,
2005).
However,
these
factors
are
not
applicable
to
urban
or
other
turf
uses
of
trichlorfon,
which
is
dominated
by
residential
applications.
While
estimates
of
the
fraction
of
turf
in
drinking
watersheds
are
not
available,
it
is
known
that
the
amount
of
urban
land
in
some
drinking
water
watersheds
can
be
significant
and
that
pesticides,
particularly
insecticides
that
frequently
used
on
lawns
are
found
with
high
frequency
in
surface
water
downstream
from
urban
areas.

Loading
to
surface
water
from
application
in
Florida,
as
simulated
using
the
Florida
turf
scenario
does
provide
DWECs
that
are
greater
than
those
that
would
occur
in
most
of
the
country
and
are
thus
used
for
screening­
level
assessment.
However,
these
values
do
not
necessarily
reflect
exposure
in
other
parts
of
the
country
where
less
intense
rainfall
occurs.

As
noted
above,
the
conversion
efficiency
of
trichlorfon
to
dichlorvos
is
pH
dependent,
ranging
from
2%
at
pH
5,
to
52%
at
pH
9.
The
practical
lower
pH
limit
for
turf
is
6,
as
lime
is
generally
applied
to
maintain
turf
at
this
pH.
On
the
upper
end,
pH s
higher
than
8.5
are
seldom
seen
in
the
environment
where
plant
stands
can
be
maintained.
Commonly,
soil
pH
is
between
6
and
7.
Higher
pHs
are
found
in
arid
and
semi­
arid
areas
in
the
western
United
States
where
pedogenic
lime
accumulates,
and
soils
formed
from
carbonatic
parent
materials,
e.
g.
limestone.
Based
on
this
information,
the
modeled
estimates
of
DDVP
derived
from
trichlorforn
use
on
turf
would
be
estimated
to
decrease
from
the
concentrations
estimated
in
the
risk
assessment.
The
peak
1­
in­
10­
year
Drinking
Water
Estimated
Concentration
from
the
drinking
water
assessment
would
be
in
the
range
of
122
µ
g
L
­
1
in
areas
where
the
pH
is
9
or
greater
(
based
on
52%
formed).
If
the
trichlorfon
turf
use
area
were
limited
to
east
of
Mississippi
where
pH
is
7
or
less
(
i.
e.
other
than
karst
areas
and
where
soils
with
higher
pH
occur),
the
peak
1­
in­
10­
year
Drinking
Water
Estimated
Concentration
would
be
in
the
range
of
59
µ
g
L
­
1
(
25%
formed).

It
is
a
label
requirement
that
trichlorfon
be
 
wetted
in 
after
application.
This
likely
is
necessary
so
that
it
is
carried
into
the
soil
to
the
target
organisms,
and
also
to
decrease
loss
from
volatilization.
Provided
irrigation
is
not
applied
in
amounts
that
cause
runoff
to
occur,
this
practice
will
significantly
reduce
off­
site
movement
due
runoff
from
storm
events.
However,
with
significant
additional
analysis,
the
amount
of
reduction
cannot
be
quantified.

Volatilization
As
noted
above,
it
appears
that
regardless
of
pH,
trichlorfon
mostly
forms
dichlorvos
in
the
degradation
process.
However,
the
relative
rate
of
formation
and
degradation
of
dichlorvos
at
different
pH s
controls
the
maximum
amount
of
dichlorvos
that
accumulates
from
a
particular
application
of
trichlorfon.
As
noted
above,
most
soils
nationally
are
below
pH
7.
This
is
particularly
the
case
east
of
the
Mississippi
River.
In
these
areas,
the
maximum
fraction
of
dichlorvos
formed
trichlorfon
will
be
less
than
the
approximately
25%
as
measured
in
the
pH
7
hydrolysis
study.
In
areas
with
higher
pH,
which
will
usually
be
arid
or
semiarid,
or
in
soils
with
a
carbonatic
parent
material
(
these
are
often
karst
areas),
the
conversion
efficiency
could
run
as
high
as
the
52%
seen
at
pH
9.
The
amount
of
dichlorvos
available
for
volatilization
will
be
somewhat
mitigated
by
the
irrigation
required
on
the
trichlorfon
labels,
but
the
extent
of
the
reduction
cannot
be
quantified
without
significant
further
analysis.

References
D288834.
Abdel­
Saheb,
Ibrahim.
2003.
Revised
Drinking
Water
Assessment
for
DDVP
(
PC
Code
084001),
from
Naled
(
PC
Code34401),
and
from
Trichlorfon
(
PC
Code
057901).
Internal
EPA
Memorandum
to
Eric
Olsen
and
Susan
Hummel,
dated
March
16,
2003.

Edwards,
Joanne,
2000,
Phase
1
Comments
for
Dichlorvos.
Internal
EPA
Memorandum
to
Pam
Noyes,
http://
www.
epa.
gov/
oppsrrd1/
op/
ddvp/
efedrisk.
pdf
Office
of
Pesticide
Programs.
2005.
Golf
Course
Adjustment
Factors
for
Modifying
Estimated
Drinking
Water
Concentrations
and
Estimated
Environmental
Concentrations
Generated
by
Tier
I
(
FIRST)
and
Tier
II
(
PRZM/
EXAMS)
Models.
http://
www.
epa.
gov/
oppefed1/
models/
water/
golf_
course_
adjustment_
factors.
htm
Office
of
Pesticide
Program.
1997.
Reregistration
Eligibility
Decision:
Trichlorfon.
EPA
738­
R­
96­
017.
http://
www.
epa.
gov/
oppsrrd1/
REDs/
0104.
pdf
Office
of
Prevention,
Pesticides,
and
Toxic
Substances.
2001.
Report
on
FQPA
Tolerance
Reassessment
Progress
and
Interim
Risk
Management
Decision
(
TRED):
Trichlorfon.
EPA
738­
R­
01­
009.
http://
www.
epa.
gov/
oppsrrd1/
REDs/
trichlorfon_
tred.
pdf
cc
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