Document ID: EPA-HQ-ORD-2006-0187-0134
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-04-17T04:00Z

­

1
­
Review
of
Ethephon
by
M.
Lebowitz
Scientific
Issues:

According
to
the
WOE
document
(
3/
20/
06;
TXR
#
0053509),
"
ethephon
is
an
organophosphorus
compound
that,
upon
absorption
into
plants,
forms
ethylene
gas
which
is
an
important
component
of
the
plant
hormone
complex.
The
production
of
ethylene
by
plants
occurs
naturally
as
crops
mature
but
it
can
be
slow
during
periods
of
unfavorable
weather.
Ethylene
generated
from
ethephon
is
absorbed
by
the
plant
tissues
and
moderates
the
growth
process.
It
is
not
similar
in
structure
to
other
organophosphate
pesticides
[
but
no
info
was
provided
about
its
PBPK,
etc.].
Ethephon
registrants
have
submitted
many
toxicity
studies
to
support
the
continued
pesticidal
use
of
the
chemical,
and
among
these
studies
are
two
involving
direct
dosing
of
human
subjects
that
OPP
is
considering
using
to
establish
endpoints
to
assess
risk
from
exposure
to
ethephon.
The
WOE
document
compares
the
strengths
and
weaknesses
of
the
human
and
animal
toxicity
studies
and
discusses
how
the
human
studies
fit
in
with
the
animal
studies,
i.
e.,
are
the
human
data
consistent
with
animal
data
in
terms
of
types
of
effects
and
effect
levels
or
are
there
notable
differences
between
animals
and
humans."

According
to
the
WOE
document,
"
as
a
strong
acid,
ethephon
is
corrosive
to
the
skin
and
eyes
(
Category
I).
In
acute
and
subchronic
neurotoxicity
studies
in
rats,
there
were
signs
of
neurotoxicity
at
doses
of
500
mg/
kg
and
above
(
acute)
and
300
mg/
kg
(
subchronic).
In
dogs
there
were
no
clinical
signs
of
neurotoxicity
evident
at
75
mg/
kg/
day
although
plasma
and
RBC
cholinesterase
were
inhibited
in
animals
at
doses
as
low
as
7.5
mg/
kg/
day."

There
are
two
human
studies
under
consideration,
both
involving
direct
dosing
of
human
subjects
are
repeated
dose
oral
studies,
one
for
28
days
duration
(
MRID
00036510)
and
the
other
for
16
days
(
MRID
00066931).

In
a
non­
guideline
oral
toxicity
human
study
(
MRID
00036510),
ethephon
was
administered
by
capsule
in
a
powdered
formulation
(
10%
a.
i.
weight/
weight)
of
hydrated
silica
and
starch
to
human
adults
(
5/
sex)
at
an
average
dose
of
1.8
mg
a.
i./
kg/
day
or
placebo
0
mg/
kg/
day
(
3/
sex)
for
28
consecutive
days.
Administration
of
the
test
material
or
the
placebo
was
given
orally
by
capsule
divided
into
three
daily
doses.
Each
subject
received
2
capsules
postprandially
for
the
first
two
dosing
periods;
the
third
dose
was
given
at
the
end
of
the
work
day
in
order
to
simulate
as
closely
as
possible
ingestion
of
the
material
as
a
crop
residue.
The
capsules
were
dispensed
daily
(
5
days/
week)
by
an
assistant
who
observed
the
subjects
while
they
took
each
capsule
and
recorded
solicited
comments
related
to
the
ingestion
of
the
material
during
the
first
8
hours.
The
subjects
and
the
assistant
did
not
know
which
capsules
were
placebo
or
the
test
material.
Each
Friday,
the
subjects
received
a
supply
of
capsules
to
be
taken
during
the
two
day
weekend.
All
subjects
were
monitored
regularly
for
adverse
effects.
Hematology
measurements,
clinical
chemistry
and
urinalysis
were
conducted
initially
and
on
Days
7,
14,
21,
28
and
2
weeks
following
the
last
administration.
ChE
(
plasma
and
RBC)
­

2
­
determinations
were
conducted
using
the
 
pH/
hr
method
(
modified
Michel
method)
initially,
and
on
Days
1,
2,
7,
14,
28
and
2
weeks
after
the
last
administration.

The
ethephon
subjects,
though
exhibiting
normal
physical
appearance
and
behavior,
developed
symptoms
of
diarrhea,
increased
urination
and
bowel
movement.
Thus
3
females
and
one
male
experienced
a
sudden
`
onset
of
diarrhea'
or
an
urgency
of
bowel
movement
of
1­
4
days
duration
during
the
first
week
of
the
compound
administration;
the
one
male
experienced
also
loose
stools
for
2
weeks.
Another
male
complained
of
stomach
cramps
or
gas
for
the
duration
of
the
study.
One
subject
in
the
ethephon
group
was
asymptotic.
Five
subjects
experienced
increased
urgency
and
frequency
of
urination,
4
of
whom
experienced
this
symptom
throughout
the
study.
Two
subjects
experienced
decreased
appetite
while
a
third
one
(
experiencing
diarrhea)
experienced
increased
appetite
during
the
first
2
days
of
the
study.
It
was
stated
that
the
symptoms
were
"
consistent
with
exposure
to
a
cholinesterase
inhibitor".
The
WOE
document
states
"
the
clinical
signs
observed
in
the
study,
diarrhea
and
increased
frequency
of
urination,
are
consistent
with
a
cholinergic
mode
of
toxicity,
but
other
signs
associated
with
a
cholinesterase
inhibitor
such
as
pinpoint
pupils
(
miosis),
sweating,
runny
nose,
tearing,
salivation,
respiratory
distress
and
muscle
fasciculation
(
twitching),
were
not
seen
[
sic];
[
and]
the
test
subjects
reported
symptoms
as
they
considered
appropriate,
and
it
is
difficult
to
interpret
what
the
self­
reported
symptoms
mean
in
terms
of
a
biological
response.'
In
fact,
we
don't
know
if
symptoms
or
signs
associated
with
a
cholinesterase
inhibitor
were
seen;
they
may
not
have
been
monitored
or
specific
requests
for
their
reported
made
by
the
investigators.
However,
these
symptoms,
probably
related
to
irritant
effects,
are
important
results.

The
DER
and
the
WOE
documents
all
say
"
None
of
the
placebo
subjects
had
similar
complaints."
This
is
probably
not
correct
as
at
least
two
of
these
controls
were
symptomatic
as
well.
In
addition,
some
test
and
control
subjects
also
exhibited
some
atypical
lymphocytes
of
unknown
origin.

The
WOE
document
states
"
Unexpectedly,
plasma
and
RBC
ChE
activities
were
similar
or
slightly
higher
than
initial
values
in
the
test
subjects.
([
The]
details
of
the
ChE
determinations
were
not
provided.)"
However,
the
ChE
levels
were
not
related
to
the
diarrhea
occurring
in
the
subjects
upon
examination
of
the
time
of
symptom
occurrence
and
ChE
data
provided.
The
WOE
document
states
"
No
compound
effects
regarding
hematology,
clinical
chemistries
and
urinalysis
were
reported",
except
the
atypical
lymphocytes
of
some.

It
was
concluded
from
by
the
investigators
of
this
study
that
the
daily
dose
of
1.8
mg/
kg/
day
is
the
LOAEL
for
the
oral
ingestion
of
ethephon
in
human
subjects.
However,
that
is
quite
uncertain
since
lower
doses
were
not
given.

In
the
other
non­
guideline
oral
toxicity
human
study
(
MRID
00066931),
ethephon
was
administered
by
capsule
in
a
powdered
formulation
(
2.5%
a.
i.
weight/
weight)
of
hydrated
silica
and
starch
to
human
adults
(
10/
sex)
at
an
average
dose
of
0.5
mg
a.
i./
kg/
day
or
­

3
­
placebo
0
mg/
kg/
day
(
6
males
and
4
females)
for
16
consecutive
days
followed
by
a
29
day
recovery
period
(
phase
3).
The
dosing
phase
(
phase
II)
was
preceded
with
a
6
day
period
(
phase
I)
where
all
subjects
received
daily
placebos.
Administration
of
the
test
material
or
the
placebo
was
given
orally
by
capsule
divided
into
three
daily
doses.
Each
subject
received
2
capsules
postprandially
for
the
first
two
dosing
periods;
the
third
dose
was
given
at
the
end
of
the
work
day
in
order
to
simulate
as
closely
as
possible
ingestion
of
the
material
as
a
crop
residue.
The
capsules
were
dispensed
daily
(
5
days/
week)
by
an
assistant
who
observed
the
subjects
while
they
took
each
capsule
and
recorded
solicited
comments
related
to
the
ingestion
of
the
material
for
8
hours.
The
subjects
and
the
assistant
did
not
know
which
capsules
were
placebo
or
the
test
material
in
of
the
study
phases.
Each
Friday,
the
subjects
received
a
supply
of
capsules
to
be
taken
during
the
two
day
weekend.
All
subjects
were
monitored
regularly
for
adverse
effects.
Hematology
measurements
and
clinical
chemistry
were
conducted
on
blood
samples
collected
during
phases
I,
II
and
III
while
urinalysis
was
conducted
on
samples
collected
during
phase
II.
ChE
(
plasma
and
RBC)
determinations
were
conducted
using
the
 
pH/
hr
method
(
modified
Michel
method)
on
blood
collected
during
phases
I,
II,
and
III.

No
clinical
symptoms
were
reported,
but
it
is
not
known
if
this
was
an
omission
as
the
report
document
doesn't
state
that
there
were
no
symptoms
or
signs.
Hematological,
clinical
chemistry
values
and
urinalysis
parameters
were
comparable
to
the
placebo
controls.
The
updated
executive
summary
of
the
DER
for
the
16­
day
human
study
states:
"
Plasma
and
RBC
ChE
activities
were
significantly
inhibited
in
both
placebo
and
test
groups.
Therefore,
this
finding
makes
any
conclusions
regarding
the
effects
attributable
to
ethephon
administration
impossible.
This
is
in
contradiction
to
the
study
authors
overall
conclusion
that
a
daily
ethephon
oral
dosage
of
0.5
mg/
kg/
day
produces
significant
plasma
ChE
inhibition,
which
is
reversible
in
15
days."
The
investigators
say
"
Plasma
cholinesterase
was
significantly
inhibited
for
the
placebo
group
at
4,
8,
12,
and
16
days
during
the
dosage
period.
In
the
test
group,
plasma
cholinesterase
was
also
depressed
(
greater
than
the
placebo
group)
at
4,
8,
12,
and
16
days
during
the
dosage
period.
Recovery
does
occur
as
indicated
by
the
15
and
29
post
dosage
values.
RBC
cholinesterase
inhibition
was
similar
for
both
placebo
and
test
groups
(
slightly
depressed
in
both
groups)
on
days
4,
12,
and
16
of
the
dosage
period
and
day
15
of
the
recovery
period."
They
say
that
the
test
group
plasma
values
were
significantly
different
than
the
placebo
group
values.

It
appears
that
either
the
method
of
testing
cholinesterase
was
poor,
or,
less
likely,
something
else
was
depressing
plasma
cholinesterase
in
this
latter
study
while
increasing
it
in
the
former
study.
Possibly,
as
the
ethephon
risk
assessment
team
concluded,
measures
of
blood
cholinesterase,
either
plasma
or
RBC,
were
not
appropriate
for
endpoint
selection
for
ethephon.

According
to
the
WOE
document
"
The
OPP/
HED
RfD
Peer
Review
Committee
determined
on
February
10,
1994
that
the
reference
dose
(
RfD)
should
be
based
on
the
28­
day
study
in
human
subjects
(
MRID
00036510).
Clinical
signs
of
toxicity
were
observed
at
1.8
mg/
kg/
day
(
only
dose
tested)
and
included
diarrhea,
urgency
of
bowel
movements,
urinary
urgency
and
stomach
cramps.
­

4
­
A
Report
from
HED's
Hazard
Identification
and
Assessment
Review
Committee
(
HIARC)
dated
4/
1/
98
states
in
reference
to
the
28­
day
human
study:
"
This
human
study
is
considered
to
be
of
better
quality
and
the
findings
more
reliable
than
the
16­
day
human
study
previously
used
to
define
the
RfD."
Since
1994,
the
HIARC
has
repeatedly
(
8/
9/
94,
4/
1/
98,
7/
15/
02
and
11/
5/
02)
selected
the
28­
day
human
study
to
assess
all
relevant
exposure
scenarios,
and
at
the
last
HIARC
meeting,
a
weight
­
of
­
evidence
comment
regarding
endpoint
selection
was
included:
"
HIARC
had
considered
experimental
animal
studies
on
ethephon
and
concluded
this
human
study
was
most
appropriate
for
selection
of
the
endpoint
of
toxicity
for
risk
assessment.
The
clinical
signs
of
toxicity
in
this
human
study
occurred
at
dose
levels
that
were
much
lower
than
seen
in
experimental
animals."
"
Despite
the
limitations
of
the
study,
and
the
equivocal
nature
of
the
reported
findings,
the
HED
ethephon
risk
assessment
team
believes
that,
in
the
absence
of
data
ruling
out
the
observed
effects
as
inconsequential,
the
28­
day
human
study
is
the
most
appropriate
study
to
use
for
assessing
both
the
acute
and
chronic
dietary
risks
of
ethephon."

The
WOE
document
states:
"
A
number
of
conclusions
relevant
to
endpoint
selection
can
be
drawn
from
the
database
of
ethephon
oral
toxicity
studies
in
humans
and
animals:
(
1)
ethephon
is
neurotoxic
in
animal
studies
only
at
high
doses
(
300
mg/
kg
and
above),
(
2)
ethephon
inhibits
blood
cholinesterases,
in
particular
plasma
cholinesterase
in
animals
and
humans
at
relatively
low
doses,
(
3)
brain
acetylcholinesterase
is
insensitive
to
ethephon
in
adult
animals.
Accordingly,
The
team
then
debated
whether
to
use
effects
in
animals
(
LOAEL
approximately
80
mg/
kg/
day)
or
in
humans
(
LOAEL
of
1.8
mg/
kg/
day)
for
endpoint
selection,
and
opted
as
a
matter
of
prudence
to
base
endpoint
selection
on
effects
observed
in
humans."
I
concur
completely
with
the
last
statement.
[
This
is
much
lower
than
that
expected
from
the
animal
studies,
however,
the
second
study
informs
and
provides
the
level
of
uncertainty
to
allow
us
to
accept
this
LOAEL
and
use
it
as
a
POD.]
The
WOE
document
concludes
by
stating:
"
The
point
of
departure
for
the
dietary
assessments
use
of
a
LOAEL
was
applied
to
the
POD
to
obtain
a
reference
dose
of
0.06
mg/
kg/
day
for
assessment
of
both
acute
and
chronic
dietary
risks.
was
1.8
mg/
kg/
day
(
with
an
uncertainty
factor
of
10x
for
intraspecies
variability
and
a
3x
factor
for
use
of
a
LOAEL
 )"

Ethical
Issues:

John
Carley
did
an
excellent
job
of
reviewing
the
ethics
of
both
studies
(
memos
to
Ray
Kent
dated
Mar.
17,
2006,
provided
to
the
HSRB).
I
would
add
the
following:
The
value
of
the
research
to
society
is
based
on
the
value
of
the
product,
ethephon,
to
society,
and
must
be
assessed
separately.
The
research
studies,
though
flawed
and
with
their
many
limitations,
are
likely
to
have
sufficient
scientific
validity
such
that
the
ethics
of
the
studies
cannot
be
discounted
by
the
question
of
their
scientific
validity.
Further,
the
dosage
used
was
based
on
toxicological
­

5
­
findings
in
animals
sufficient
as
to
not
likely
cause
harm
to
the
subjects.
This
latter
consideration
probably
addresses
the
concerns
addressed
by
the
Helsinki
principles.
I
agree
that
a
risk­
benefit
analysis
should
have
been
conducted.
I
have
the
same
problems
with
the
apparent
lack
of
ethical
oversight,
proof
of
true
volunteerism,
informed
consent,
but
I
agree
that
"
there
is
no
clear
evidence
that
the
study
fell
short
of
the
requirements
of
FIFRA
section
12(
a)(
2)(
P)."

In
summary,
I
do
not
believe
that
there
is
clear
and
convincing
evidence
that
the
conduct
of
these
studies
was
fundamentally
unethical,
nor
was
it
conducted
with
any
intent
to
harm
participants.
However,
it
is
hoped
that
those
conducting
such
studies
will
follow
all
of
the
current
guidelines
and
principles
for
conducting
human
research.