OFFICE
OF
PREVENTION,
PESTICIDES,
AND
TOXIC
SUBSTANCES
This
HIARC
report
was
revised
in
response
to
the
Error
Review
memo
submitted
by
the
Industry
Task
Force
II
on
2,4­
D
Research
Data
(
See
MRID
No.
46147201).
This
report
supercedes
the
previous
HIARC
report,
TXR
No.
0051866.
UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
TXR
NO.
0052303
DATE:
January
15,
2004
MEMORANDUM
SUBJECT:
2,4­
D
­
Second
Report
of
the
Hazard
Identification
Assessment
Review
Committee.

FROM:
Linda
L.
Taylor,
Ph.
D.
Reregistration
Branch
I
Health
Effects
Division
(
7509C)

THROUGH:
Jess
Rowland,
Co­
Chair
and
Karen
Whitby,
Co­
Chair
Hazard
Identification
Assessment
Review
Committee
Health
Effects
Division
(
7509C)

TO:
William
Hazel,
Risk
Assessor
Reregistration
Branch
I
Health
Effects
Division
(
7509C)

Mark
Seaton,
CRM
Reregistration
Branch
2
Special
Review
and
Reregistration
Division
(
7508C)

PC
Code:
030001
On
April
8,
2003,
the
Health
Effects
Division
(
HED)
Hazard
Identification
Assessment
Review
Committee
(
HIARC)
reviewed
the
recommendations
of
the
toxicology
reviewer
for
2,4­
dichlorophenoxyacetic
acid
[
2,4­
D]
with
regard
to
the
acute
and
chronic
Reference
Doses
(
RfDs)
and
the
toxicological
endpoint
selection
for
use
as
appropriate
in
occupational/
residential
exposure
risk
assessments.
The
potential
for
increased
susceptibility
of
infants
and
children
from
exposure
to
2,4­
D
was
also
evaluated
as
required
by
the
Food
Quality
Protection
Act
(
FQPA)
of
1996.
The
conclusions
drawn
at
this
meeting
are
presented
in
this
report.
2
Committee
Members
in
Attendance
Members
present
were:
Jess
Rowland,
Elizabeth
Doyle,
Brenda
Tarplee,
William
Burnam,
Ayaad
Assaad,
Pamela
Hurley,
John
Liccione,
Susan
Makris,
Elizabeth
Mendez,
P.
V.
Shah,
William
Dykstra
Member(
s)
in
absentia:
Paula
Deschamp,
Jonathan
Chen,
Donna
Davis
Data
evaluation
prepared
by:
Linda
Taylor
Also
in
attendance
were:
Whang
Phang,
Michael
Metzger,
William
Hazel,
Tim
Dole,
Mark
Seaton,
Mark
Corbin,
Santhini
Ramasamy
Data
Evaluation
/
Report
Presentation
Linda
L.
Taylor
Toxicologist
3
INTRODUCTION
On
April
8,
2003,
the
Health
Effects
Division
(
HED)
Hazard
Identification
Assessment
Review
Committee
(
HIARC)
reviewed
the
recommendations
of
the
toxicology
reviewer
for
2,4­
D
with
regard
to
the
acute
and
chronic
Reference
Doses
(
RfDs)
and
the
toxicological
endpoint
selection
for
use
as
appropriate
in
occupational/
residential
exposure
risk
assessments.
The
potential
for
increased
susceptibility
of
infants
and
children
from
exposure
to
2,4­
D
was
also
evaluated
as
required
by
the
Food
Quality
Protection
Act
(
FQPA)
of
1996.

I.
FQPA
HAZARD
CONSIDERATIONS
1.
Adequacy
of
the
Toxicity
Data
Base
The
HIARC
concluded
that
the
toxicology
database
for
2,4­
D
is
complete.
The
core
toxicology
studies
are
available
for
FQPA
considerations
for
the
acid
form
of
2,4­
D
and
include
both
the
rat
and
rabbit
developmental
toxicity
studies
and
the
rat
two­
generation
reproduction
study.

Additionally,
both
rat
and
rabbit
developmental
toxicity
studies
are
available
for
the
four
amine
salts
[
diethanolamine
(
DEA),
dimethylamine
(
DMA),
isopropylamine
(
IPA),
and
triisopropanol­
amine
(
TIPA)]
and
two
esters
[
butoxyethyl
(
BEE)
and
2­
ethylhexyl
(
EHE)]
of
2,4­
D.

2.
Evidence
of
Neurotoxicity
The
HIARC
concluded
that
there
is
a
concern
for
neurotoxicity
resulting
from
exposure
to
2,4­
D.
Acute
Neurotoxicity
EXECUTIVE
SUMMARY:
In
an
acute
neurotoxicity
study
[
MRID
43115201],
Fischer
344
rats
(
10/
sex/
dose)
were
orally
gavaged
once
with
2,4­
D
at
doses
of
0
(
corn
oil),
15,
75,
or
250
mg/
kg
(
actual:
0,
13,
67
or
227
mg/
kg).
Neurobehavioral
evaluations,
consisting
of
Functional
Observational
Battery
(
FOB)
and
motor
activity,
were
conducted
at
Day
­
1
(
prestudy),
Day
1
(
approximately
5­
6
hrs
postdosing,
peak
time
of
effect)
and
Days
8
and
15.
At
terminal
sacrifice
(
Day
15),
animals
were
euthanized
and
neuropathological
examination
performed
on
control
and
treated
animals
(
5/
sex/
dose).

There
were
no
treatment­
related
mortalities,
and
no
significant
differences
were
noted
in
the
mean
body
weights
or
mean
body­
weight
gains.
Treatment­
related,
clinical
signs
[
uncoordinated
movement/
behavior]
were
observed
in
the
high­
dose
rats
only
[
Day
2,
2/
10
males
and
5/
10
females;
Day
3,
2/
10
males,
1/
10
females;
Day
4,
0/
10
males,
1/
10
females].
4
Clinical
signs
and
neurobehavioral
evaluation
revealed
treatment­
related
changes.
During
the
Day
1
FOB
evaluations,
increased
incidences
of
incoordination
(
6/
10,
males;
4/
10,
females)
and
slight
gait
abnormalities,
described
as
forepaw
flexing
or
knuckling,
were
observed
in
high­
dose
animals
(
8/
10,
males;
8/
10
females).
Slight
gait
abnormalities,
observed
in
a
single
mid­
dose
female,
were
judged
to
be
treatment­
related,
although
no
other
signs
of
toxicity
were
evident
at
this
dose
level.
Minimal
gait
abnormalities,
not
judged
to
be
treatment­
related,
were
observed
in
one
low­
dose
female
and
one
each
midand
high­
dose
male.
On
the
Day
2
and
Day
3
clinical
examinations,
incoordination
was
noted
in
high­
dose
animals.
The
incidence
of
incoordination
decreased
to
control
levels
by
Day
4
in
males
and
Day
5
in
females.
In
high­
dose
animals,
total
motor
activity
was
significantly
lower
at
Day
1
only.
No
treatment­
related
gross
or
neuropathological
findings
were
present
at
any
dose
level.

The
NOAEL
for
neurotoxicity
is
67
mg/
kg,
based
on
an
increased
incidence
of
incoordination
and
slight
gait
abnormalities
[
described
as
forepaw
flexing
or
knuckling
at
the
LOAEL
of
227
mg/
kg.
The
NOAEL
for
systemic
toxicity
was
227
mg/
kg
[
the
highest
dose
tested]
in
males
and
females.

This
acute
neurotoxicity
is
classified
Acceptable/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.6200]
for
an
acute
neurotoxicity
study
in
the
rat.

Subchronic
Neurotoxicity
EXECUTIVE
SUMMARY:
In
this
chronic
toxicity/
carcinogenicity
study
with
a
chronic
neurotoxicity
screening
battery
substudy
[
MRID
43293901],
50
Fischer
344
rats/
sex/
group
[
main
study];
15/
sex/
group
[
substudy]
were
administered
2,4­
dichlorophenoxyacetic
acid
[
96.4%]
via
the
diet
for
up
to
24
months
at
concentrations
of
0
[
basal
diet],
5
mg/
kg/
day,
75
mg/
kg/
day,
and
150
mg/
kg/
day
[
achieved
doses
were
4.6,
71.2,
and
141.1
mg/
kg/
day
[
males]
and
4.6,
68.0,
and
138.9
mg/
kg/
day
[
females],
respectively.
Additionally,
10
rats/
sex/
group
were
sacrificed
at
12
months
[
interim
sacrifice].
NOTE:
This
DER
presents
the
results
of
the
interim
[
one­
year]
sacrifice
and
neurotoxicity
substudy.

There
were
no
treatment­
related
deaths
or
clinical
signs
of
toxicity.
Decreased
body
weight
was
observed
throughout
the
first
year
of
the
study
at
the
high­
dose
level
in
both
sexes
[
males
91%/
females
88%
of
control
at
the
interim
sacrifice]
and
at
the
mid­
dose
level
in
females
[
94%
of
control
at
the
interim
sacrifice].
At
90
days,
the
decrease
in
body
weight
was
very
slight
in
the
high­
dose
males
[
96%
of
control]
and
somewhat
greater
in
the
mid­
[
95%
of
control]
and
high­
dose
[
90%
of
control]
females.
Body­
weight
gains
were
decreased
throughout
the
first
year
at
the
mid­
and
high­
dose
levels
in
both
sexes,
although
statistical
significance
was
not
always
attained
in
males
at
the
mid­
dose
level
[
2­
week
interval
(
males:
mid­
dose
90%/
high­
dose
84%;
females:
mid­
dose
81%/
high­
dose
63%
of
control);
3­
month
interval
(
males:
mid­
dose
98%/
high­
dose
88%;
females:
mid­
5
dose
87%/
high­
dose
75%
of
control);
and
1­
year
interval
(
males:
mid­
dose
95%/
high­
dose
82%;
females:
mid­
dose
89%/
high­
dose
73%
of
control).
Consistent
with
the
decreased
body­
weight
gains
was
a
slight
decrease
in
food
consumption,
which
was
observed
in
both
sexes
at
the
high­
dose
level.

Ophthalmology
findings
were
comparable
among
the
groups
at
the
interim
sacrifice.
Decreased
RBC
[
mid­
and
high­
dose
females
(
6
&
12
months)
and
high­
dose
males
(
12
months)],
HCT
[
mid­
and
high­
dose
females
and
high­
dose
males
(
6
&
12
months)],
HGB
[
high­
dose
females
(
6
months)],
WBC
9high­
dose
females
(
6
months)],
and
platelet
counts
[
mid­
and
high­
dose
females
and
high­
dose
males
(
6
&
12
months)
were
observed.
A
dose­
related
increase
in
aspartate
aminotransferase,
alanine
aminotransferase,
and
alkaline
phosphatase
was
observed
in
the
mid­
and
high­
dose
males
at
6
months
but
not
at
12
months.
The
mid­
and
high­
dose
females
displayed
a
dose­
related
increase
in
alkaline
phosphatase
values
at
both
the
6
and
12­
month
intervals.
Cholesterol
levels
were
decreased
in
the
mid­
(
males
at
12
months
only)
and
high­
dose
rats
of
both
sexes
at
both
time
intervals.
T4
values
were
decreased
at
both
time
points
in
both
sexes
at
the
mid­
and
high­
dose
levels,
although
the
mid­
dose
males
at
6
months
did
not
attain
statistical
significance.
The
only
urinalysis
finding
was
a
decrease
in
specific
gravity
,
which
was
observed
in
both
sexes
and
time
points
at
the
mid­
and
high­
dose
levels.

Thyroid
weights
[
absolute
and
relative]
were
statistically­
significantly
increased
in
the
mid­
dose
females
[

20%
greater
than
control]
and
in
both
sexes
at
the
high­
dose
level
[

20%
greater
than
control]
at
the
12­
month
interim
sacrifice.
Decreased
testes
weights
[
absolute
and
relative
to
brain]
were
observed
at
the
high­
dose
level
at
12
months
[

15%
lower
than
control].
Kidney
weights
[
absolute
and
relative]
were
increased
at
the
12­
months
sacrifice
in
males
at
the
mid­
[
7%­
12%
greater
than
control]
and
high­
dose
[
8%­
16%
greater
than
control]
levels
[
dose­
related].

Gross
pathology
findings
included
decreased
fat
in
high­
dose
females
[
4/
10]
and
multifocal
pale
foci
in
the
lungs
[
1/
10
mid­
dose,
10/
10
high­
dose
females].
Microscopically,
there
were
increased
incidences
of
lesions
in
the
bone
marrow
[
decreased
hematopoiesis
in
highdose
females],
eyes
[
bilateral
retina
degeneration
in
1
male
and
10
females
at
high
dose],
kidney
[
proximal
tubule
degeneration
in
mid­
and
high­
dose
males
and
females],
liver
[
altered
tinctorial
properties
in
mid­
dose
females
and
both
sexes
at
high
dose],
lungs
[
multifocal
,
subacute
to
chronic
inflammation
(
mid­
dose
females,
both
sexes
at
high
dose),
alveolar
histiocytosis
in
females
at
high
dose],
adipose
tissue
[
atrophy
in
mid­
and
high­
dose
females],
testes
[
atrophy
at
high
dose],
and
thyroid
[
decreased
secretory
material,
epithelial
cells­
high­
dose
females].

The
NOAEL
is
5
mg/
kg/
day.
The
LOAEL
of
75
mg/
kg/
day
is
based
on
decreased
body
weight
(
females)/
body­
weight
gain
(
both
sexes),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
platelets
(
females)],
clinical
chemistry
parameters
[
increased
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
6
(
both
sexes),
decreased
cholesterol
(
both
sexes),
and
decreased
T4
(
both
sexes)],
and
urinalysis
[
decreased
specific
gravity
(
both
sexes)],
increased
kidney
weights
(
males),
increased
incidence
of
degeneration
of
the
descending
proximal
tubules
(
both
sexes),
hepatocellular
hypertrophy
with
altered
tinctorial
properties
(
females),
lung
inflammation
(
females),
adipose
tissue
atrophy
(
females).
At
the
high­
dose
level,
there
also
were
microscopic
lesions
in
the
eyes
(
both
sexes),
liver
(
males),
testes
(
males),
thyroid
(
females),
and
lungs
(
males).

NEUROTOXICITY
PHASE
OF
STUDY
No
treatment­
related,
hand­
held,
FOB
observations
were
noted
at
any
of
the
evaluation
periods.
Relative
forelimb
grip
strength
was
significantly
increased
in
both
sexes
at
the
high­
dose
level,
but
there
was
no
treatment­
related
change
in
absolute
grip
strength.
There
was
no
treatment­
related
effect
on
motor
activity.
In
agreement
with
the
chronic
toxicity
portion
of
the
study,
an
increased
incidence
of
bilateral
retinal
degeneration
was
observed
in
the
high­
dose
females.

The
NOAEL
for
neurotoxicity
is
75
mg/
kg/
day,
based
on
increased
relative
forelimb
grip
strength
and
increased
incidence
of
bilateral
retinal
degeneration
at
the
LOAEL
of
150
mg/
kg/
day.

This
chronic
toxicity/
neurotoxicity
study
in
the
rat
is
classified
Acceptable/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.
6200;
§
82­
7]
for
a
subchronic
neurotoxicity
study
in
the
rat.

Evidence
from
Other
Guideline
Studies
Clinical
signs
indicative
of
neurotoxicity
[
ataxia,
decreased
motor
activity,
myotonia,
prostration,
lateral
recumbency,
and
impairment
or
loss
of
the
righting
reflex]
were
observed
in
pregnant
rabbits
after
oral
administration
[
days
6­
18
of
gestation]
of
2,4­
D
and
its
amine
salts
and
esters.
Similar
clinical
signs
[
ataxia,
decreased
motor
activity,
stiffness
of
limbs]
were
observed
in
the
rat
developmental
toxicity
studies
in
dams
dosed
with
the
two
esters
[
2­
EHE
and
BEE]
and
two
of
the
amines
[
DMA
and
TIPA],
mainly
at
the
high­
dose
level.
In
a
2,4­
D
subchronic
oral
(
capsules)
toxicity
study
in
dogs,
tremors
were
observed
in
dogs
that
died
during
the
study
following
4,
9,
and
13
weeks
of
dosing.
Other
clinical
signs
in
the
dogs
included
thin,
languid
appearance
and
anorexia.
7
Table
2.
Clinical
Signs
Indicative
of
Neurotoxicity
Chemical
subchronic
rat
rat
developmental
toxicity
rabbit
developmental
toxicity
2,4­
D
hunched
posture,
depressed
activity
none
ataxia,
decreased
motor
activity,
loss
of
righting
reflex,
cold
extremities
BEE
unilateral/
bilateral
cataracts,
resulting
in
decreased
in
visual
placing
reflex
ataxia,
emaciation,
negative
activity
decreased
activity,
prostration,
transient
lateral
recumbency,
cold
to
the
touch
DEA
hunched
posture
none
decreased
motor
activity,
wobbly
gait
DMA
cataracts
decreased
motor
activity,
ataxia
decreased
motor
activity,
myotonia,
ataxia,
impaired/
loss
of
righting
reflex
EHE
thin
appearance,
hunched
posture,
languid
behavior,
ataxia,
anorexia,
squinted
eyes,
retinal
degeneration,
bilateral
cataracts
ataxia,
decreased
motor
activity,
bradypnea
decreased
motor
activity,
ataxia,
impaired/
loss
of
righting
reflex
IPA
bilateral
retinal
degeneration
excessive
salivation
myotonia,
lateral
recumbency,
cold
extremities
TIPA
unilateral/
bilateral
opaque
eyes/
cataracts
stiffness
of
limbs,
excessive
salivation
myotonia,
lateral
recumbency
Other
Data
From
the
Literature
In
a
published
article
[
Neurotoxicology
and
Teratology,
18
(
6):
691­
696
(
1996).
Central
Nervous
System
Myelin
Deficit
in
Rats
Exposed
to
2,4­
Dichlorophenoxyacetic
Acid
Throughout
Lactation],
2,4­
D
exposure
through
mother's
milk
[
100
mg/
kg/
day
administered
to
dam
i.
p.;
DMSO;
Wistar
rats]
during
the
period
of
rapid
myelination
[
postnatal
days
15
to
25]
resulted
in
a
myelin
deficit
in
the
pup's
brain.
The
brains
of
male
and
female
rats
showed
a
significant
decrease
in
myelin
markers,
such
as
monohexosylceramide,
as
well
as
phospholipids
and
free
fatty
acids
and
an
increase
of
cholesteryl
esters.
Histological
studies
revealed
myelin
deficit
in
some
brain
regions.

In
a
published
article
[
Neurotoxicology
and
Teratology,
21
(
4):
451­
465
(
1999).
Behavioral
Alterations
Induced
in
Rats
by
a
Pre­
and
Postnatal
Exposure
to
2,4­
Dichlorophenoxyacetic
Acid],
2,4­
D
neonatal
exposure
[
dams
dosed
orally
(
70
mg/
kg/
day)
from
gestation
day16
to
postnatal
day
23;
after
weaning
on
PND
23,
pups
were
either
maintained
on
untreated
diet
or
administered
2,4­
D
diets
(
70
mg/
kg/
day)
until
PND
90]
induced
delay
of
the
ontogeny
of
righting
reflex
and
negative
geotaxis
accompanied
by
motor
abnormalities,
stereotypic
behaviors
[
excessive
grooming
and
vertical
head
movements],
and
hyperactivity
in
the
open
field.

In
a
published
article
[
Mol.
Chem.
Neuropathol.
30,
175­
185
(
1997).
2,4­
8
Dichlorophenoxyacetic
Acid
Through
Lactation
Induces
Astrogliosis
in
Rat
Brain],
dams
were
injected
i.
p.
with
70
mg/
kg
2,4­
D
from
PND
9
to
PND
25,
and
astroglial
immunoreactivity
in
the
mesencephalon,
cerebellum,
and
hippocampus
was
compared
in
the
25
day­
old
pups.
Neurotoxicity
was
observed
in
reactive
gliosis
in
all
hippocampal
layers
and
in
cerebellar
and
raphe
regions.

In
an
abstract
of
a
study
in
ICR
mice,
it
states
that
the
2,4­
D
group
displayed
increased
serum
cholinesterase
[
ChE]
activity
and
decreased
brain
ChE
activity
following
oral
exposure
for
up
to
14
days;
J.
Appl.
Tox,
10
(
4),
257­
266
(
1990)].

In
a
published
article
[
Neurobehavioral
Toxicology
and
Teratology
(
1983),
5,
331­
335.
Neurobehavioral
Assessment
of
2,4­
Dichlorophenoxyacetic
Acid
(
2,4­
D)
in
Rats],
male
Fischer
344
rats
[
90
days
of
age]
displayed
a
significant
increase
in
fore­
and
hindlimb
grip
strength
following
exposure
to
2,4­
D
[
via
gavage
twice
weekly
for
5
weeks
(
20,
40,
80
mg/
kg)
and
5
days/
week
for
4
weeks
(
10,
20,
40
mg/
kg/
day)].

In
a
published
article
[
Evangelista
de
Duffard,
A.
M.
,
N.
De
Aldrete,
M.,
and
Duffard,
R.
(
1990).
Changes
in
brain
serotonin
and
5­
hydroxyindoleacetic
acid
levels
induced
by
2,4­
dichlorophenoxyacetic
acid
butyl
ester.
Toxicol.
64,
265­
270],
adult
offspring
of
Wistar
dams
fed
69
mg/
kg/
day
2,4­
D
butyl
ester
during
lactation
had
increased
brain
concentrations
of
serotonin
and
5­
hydroxyindoleacetic
acid,
but
in
utero
exposure
without
exposure
via
lactation
had
no
effect
on
the
postnatal
status
of
these
neurotransmitters.

In
an
abstract
[
J.
Appl.
Toxicol.
(
1986),
6(
4):
291­
295.
The
effect
of
topically
applied
nbutylester
of
2,4­
dichlorophenoxyacetic
acid
on
the
immune
response
in
mice],
evidence
of
clinical
toxicity,
myotonia
and
depression,
and
histopathological
alterations
in
the
CNS
[
perivascular
edema
and
ganglial
cell
necrosis]
were
reported
following
acute
dermal
application
[
up
to
500
mg/
kg]
to
CD­
1
mice.
Subacute
2,4­
D
ester
exposure
[
up
to
300
mg/
kg/
day
for
3
weeks]
produced
minimal
clinical
or
pathological
alterations.
Although
no
effect
was
observed
on
antibody
production,
2,4­
D
did
enhance
the
B­
and
T­
lymphocyte
proliferative
responses.
It
was
stated
that
the
immunosuppressive
effects
of
acute
2,4­
D
ester
exposure
were
unlikely
a
direct
immunological
alteration
but
rather
a
secondary
manifestation
of
the
clinical
syndrome.

The
acute
oral
toxicity
of
2,4­
D,
the
DEA,
DMA,
IPA,
and
TIPA
salts,
and
the
BEE
and
EHE
esters
in
rats
is
similar,
with
consistent
clinical
signs
of
toxicity
being
ataxia,
myotonia,
and
decreased
limb
tone.
Following
acute
inhalation
exposure,
the
clinical
signs
of
toxicity
included
decreased
activity
and
closed
eyes
[
information
from
JMPR,
1996].
Clinical
signs
of
central
nervous
system
depression
and/
or
abnormalities
in
electroencephalograms
were
reported
in
acute
studies
on
beagle
dogs.
9
3.
Developmental
Toxicity
Study
Conclusions
Developmental
Toxicity
in
Rats
[
2,4­
D]:
EXECUTIVE
SUMMARY:
In
a
developmental
toxicity
study
[
Accession
No.
00251031],
pregnant
Fischer
344
rats
[
35/
group]
were
administered
2,4­
dichlorophenoxyacetic
acid
[
97.5%]
via
gavage
at
dose
levels
of
0
[
corn
oil],
8
mg/
kg/
day,
25
mg/
kg/
day,
and
75
mg/
kg/
day
from
gestation
day
[
GD]
6
through
gestation
day
15.

There
were
no
treatment­
related
deaths.
Two
[
one
control
and
one
low­
dose]
dams
delivered
prematurely
on
gestation
day
19,
and
in
both
instances
the
offspring
produced
were
of
similar
size
and
development
as
those
from
full­
term
delivery.
Clinical
signs
were
comparable
among
the
groups.
Body
weights
were
comparable
among
the
groups
throughout
the
study,
but
dams
at
the
high­
dose
level
displayed
a
decrease
in
body­
weight
gain
during
the
dosing
period
[
79%
of
control
for
GD
6­
15;
57%
of
control
for
GD
6­
10],
although
statistical
significance
was
not
attained.
The
corrected
body­
weight
gain
was
comparable
among
the
groups.
Food
consumption
data
were
not
reported.

There
was
a
slight
decrease
in
pregnancy
rate
with
increasing
dose
[
85%,
85%,
80%
and
77%].
The
numbers
of
corpora
lutea,
implantations,
and
live
fetuses
were
comparable
among
the
groups,
and
there
were
no
dead
fetuses.
The
number
of
resorptions,
as
well
as
pre­
and
post­
implantation
losses,
were
not
adversely
affected
by
treatment.
The
number
of
the
dams
with
100%
resorptions
was
2,
0,
1,
and
1
[
control,
low­,
mid­,
and
high­
dose
groups,
respectively].
One
control,
2
low­,
4
mid­,
and
2
high­
dose
dams
had
late
resorptions.
Fetal
body
weight
and
crown­
rump
length
were
comparable
among
the
groups,
as
was
the
sex
ratio.

There
were
no
statistically­
significant
or
treatment­
related
differences
in
the
incidence
of
fetal
external
or
visceral
malformations
and
no
statistically­
significant
differences
in
the
incidence
of
skeletal
malformations.
The
increased
incidence
of
skeletal
malformations
at
the
high­
dose
level
was
considered
treatment­
related
and
included
the
presence
of
7th
cervical
ribs
[
4
fetuses
in
3
litters
vs
none
in
the
control]
and
the
presence
of
14th
rudimentary
ribs
[
4
fetuses
in
3
litters
vs
none
in
the
control].
Skeletal
variations
were
increased
at
the
high­
dose
level
and
included
malaligned
sternebrae
[
15
fetuses
in
10
litters
vs
7
fetuses
in
7
litters
of
the
control];
reduced
ossification
of
the
vertebral
arches
[
6
fetuses
in
5
litters
vs2
fetuses
in
1
litter
of
the
control];
and
unossified
sternebrae
#
5
or
#
6
[
73
fetuses
in
22
litters
(
3.32
fetuses/
litter)
vs
62
fetuses
in
24
litters
(
2.58
fetuses/
litter)].
Although
none
of
the
increases
attained
statistical
significance,
they
were
attributed
to
treatment
since
some
of
the
findings
[
maligned
sternebrae,
14th
rudimentary
ribs,
and
reduced
ossification
of
vertebral
arches]
were
also
observed
in
the
F1b
pups
of
dams
fed
2,4­
D
at
80
mg/
kg/
day
[
actual
dose

75
mg/
kg/
day]
in
the
2­
generation
reproduction
study
in
the
same
strain
of
rat.
Additionally,
skeletal
variations
of
the
ribs
[
2nd
wavy
ribs,
lumbar
ribs]
and
missing
sternebrae
were
observed
in
another
developmental
toxicity
study
using
a
different
strain
of
rat
[
Sprague­
Dawley]
at
a
comparable
dose
of
87.5
mg/
kg/
day
10
[
2,4­
D].

The
maternal
toxicity
NOAEL
is
25
mg/
kg/
day,
and
the
maternal
toxicity
LOAEL
is
75
mg/
kg/
day,
based
on
decreased
body­
weight
gain.

The
NOAEL
for
developmental
toxicity
is
25
mg/
kg/
day,
and
the
developmental
toxicity
LOAEL
is
75
mg/
kg/
day,
based
on
increased
incidence
of
skeletal
malformations
and
variations.

This
developmental
toxicity
study
is
classified
Acceptable/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.3700;
§
83­
3(
a)]
for
a
developmental
toxicity
study
in
the
rodent.

Developmental
Toxicity
in
Rats
[
2,4­
D
amine
salts
and
esters]:
The
rat
developmental
toxicity
studies
on
the
amine
salts
and
esters
show
comparable
results
[
fetal
effects
very
similar].
Differences
noted
may
be
due
to
dose
selection
and
experimental
variation.
The
acid
was
selected
as
the
representative
form
for
risk
assessment.
The
lower
NOAEL
in
the
study
with
EHE
is
not
a
concern
since
the
effect
is
minimal.
The
results
[
NOAEL/
LOAELs]
of
the
rat
developmental
toxicity
studies
on
the
esters
and
amine
salts
of
2,4­
D
are
summarized
in
the
table
below
for
comparison.
It
should
be
noted
that
Sprague­
Dawley
rats
were
used
in
these
studies,
while
the
study
performed
on
2,4­
D
was
with
Fischer
344
rats.

Table
3.
Developmental
Toxicity
of
2,4­
D
and
its
Esters
and
Salts
in
Rats
Guideline
STUDY
RESULTS
870.3700
[
§
83­
3a]
Developmental
Toxicity
­
Fischer
344
rats
[
0,
8,
25,
and
75
mg/
kg/
day]

MRID
000251031
[
1983]

WIL
Research
Laboratories,
Inc.
Classification:
Acceptable/
Guideline
2,4­
D
(
97.5%
a.
i
.)
Maternal
NOAEL:
25
mg/
kg/
day
Maternal
LOAEL:
75
mg/
kg/
day,
based
on
decreased
body­
weight
gains.
Survival
was
not
affected
by
treatment.

Developmental
NOAEL:
25
mg/
kg/
day
Developmental
LOAEL:
75
mg/
kg/
day,
based
on
an
increased
incidence
of
skeletal
malformations
[
presence
of
7th
cervical
ribs
and
14th
rudimentary
ribs]
and
skeletal
variations
[
malaligned
sternabrae,
reduced
ossification
of
vertebral
arches,
and
unossified
sternebrae
#
5
or
#
6].
Table
3.
Developmental
Toxicity
of
2,4­
D
and
its
Esters
and
Salts
in
Rats
Guideline
STUDY
RESULTS
11
870.3700
[
§
83­
3a]
Developmental
toxicity
­
CD
®
[
Sprague­
Dawley
derived]
rats
[
0,
25,
75,
185
mg/
kg/
day]
{
17,
51,
and
125
mg/
kg/
day}
(
JMPR
17,
50,
120
mg/
kg/
day)

MRID
41527101
[
1990]

Bio/
dynamics,
Inc.
Classification:
Acceptable/
Guideline
BEE
ester
of
2,4­
D
(
95.6%;
acid
equivalent
65.1­
65.8%)
Maternal
NOAEL:
75
{
51}
mg/
kg/
day
Maternal
LOAEL:
185
{
125}
mg/
kg/
day,
based
on
decreased
body­
weight
gain
on
days
6­
16,
decreased
food
consumption,
RBC,
increased
reticulocytes.
One
non­
pregnant
dam
displayed
ataxia
and
negative
activity.
There
were
no
deaths.

Developmental
NOAEL:
75
{
51}
mg/
kg/
day
Developmental
LOAEL:
185
{
125}
mg/
kg/
day,
based
on
an
increased
incidence
of
skeletal
variations
[
incompletely
ossified
supraoccipital,
squamosal(
s),
maxilla,
and
4th
sternebrae,
and
14
rib
pairs,
short
ribs,
rudimentary
first
lumbar
rib(
s),
and
unilateral
14th
rib(
s)]

870.3700
[
§
83­
3a]
Developmental
toxicity
­
Sprague­
Dawley
Crl:
CD
BR
VAF/
Plus
rats
[
0,
15,
75,
and
150
mg/
kg/
day]
{
10.2,
50.8,
and
101.6
mg/
kg/
day}
(
JMPR
11,
55,
110
mg/
kg/
day)

MRID
41920906
[
1990]

Springborn
Laboratories,
Inc.
Classification:
Acceptable/
Guideline
DEA
salt
of
2,4­
D
(
73.09%;
acid
equivalent
49.5%)
Maternal
NOAEL:
15
{
10.2}
mg/
kg/
day
Maternal
LOAEL:
75
{
50.6}
mg/
kg/
day,
based
on
decreased
body­
weight
gain.
There
were
no
deaths.
At
HDT,
reduced
food
consumption
during
dosing.

Developmental
NOAEL:
15
{
10.2}
mg/
kg/
day
Developmental
LOAEL:
75
{
50.8}
mg/
kg/
day,
based
on
an
increased
incidence
of
skeletal
malformations/
variations
[
reduced
ossification
of
skull,
14th
rudimentary
rib(
s),
7th
cervical
rib(
s),
bent
rib(
s)].
There
was
one
dead
fetus
and
reduced
pup
body
weight
(
92%
C)
at
HDT.

870.3700
[
§
83­
3a]
Developmental
Toxicity
­
Crl:
CD
®
BR
VAF/
Plus
®
rats
[
15,
60.2,
and
120.4
mg/
kg/
day]
{
12.5,
50,
and
100
mg/
kg/
day}

MRID
41735201
[
1990]

Argus
Research
Laboratories,
Inc.
Classification:
Acceptable/
Guideline
DMA
salt
of
2,4­
D
(
66.18%;
acid
equivalent
55.5%)
Maternal
NOAEL:
15
{
12.5}
mg/
kg/
day
Maternal
LOAEL:
60.2
{
50}
mg/
kg/
day,
based
on
decreased
body­
weight
gain
and
food
consumption.
There
were
no
deaths.
At
HDT,
clinical
signs
[
ataxia,
decreased
motor
activity,
bradypnea]

Developmental
NOAEL:
60.2
{
50}
mg/
kg/
day
Developmental
LOAEL:
120.4
{
100}
mg/
kg/
day,
based
on
decreased
fetal
body
weight,
increased
incidence
of
wavy
ribs
and/
or
incompletely­
ossified
ribs
and
delays
in
ossification
of
the
ribs,
sternum,
and
hyoid.

870.3700
[
§
83­
3a]
Developmental
Toxicity
­
Sprague­
Dawley
Crl:
CD
BR
VAF/
Plus
rats
[
15.1,
45.2,
and
135.7
mg/
kg/
day]
{
10,
30,
and
90
mg/
kg/
day}

MRID
42304601
[
1992]

Argus
Research
Laboratories,
Inc.
Classification:
Acceptable/
Guideline
EHE
ester
of
2,4­
D
(
95.4%;
acid
equivalent
63.25%)
Maternal
NOAEL:
15.1
{
10}
mg/
kg/
day
Maternal
LOAEL:
45.2
{
30}
mg/
kg/
day,
based
on
decreased
body­
weight
gain
[
GD
6­
9]
and
an
increased
incidence
of
clinical
signs
[
perivaginal
staining].
There
were
no
deaths.
At
HDT,
additional
clinical
signs
[
ataxia,
decreased
motor
activity,
bradypnea]
and
lower
food
intake
during
dosing
period;
one
abortion
Developmental
NOAEL:
15.1
{
10}
mg/
kg/
day
Developmental
LOAEL:
45.2
{
30}
mg/
kg/
day,
based
on
an
increased
incidence
of
delayed
sternebrae
ossification.
At
HDT,
increased
incidence
of
skeletal
malformations
[
wavy
ribs,
bent
scapulae,
fused
sternebrae].
Table
3.
Developmental
Toxicity
of
2,4­
D
and
its
Esters
and
Salts
in
Rats
Guideline
STUDY
RESULTS
12
870.3700
[
§
83­
3a]
Developmental
Toxicity
­
CD
®
[
Sprague­
Dawley­
derived]
rats
[
0,
22,
65,
and
190
mg/
kg/
day]
{
17,
51,
and
150
mg/
kg/
day}
(
JMPR
9,
25,
74
mg/
kg/
day)

MRID
41527103
[
1990]

Bio/
dynamics,
Inc.
Classification:
Acceptable/
Guideline
IPA
salt
of
2,4­
D
(
50.2%;
acid
equivalent
39.6%)
Maternal
NOAEL:
65
{
51}
mg/
kg/
day
Maternal
LOAEL:
190
{
150}
mg/
kg/
day,
based
on
one
death
[
following
one
dose;
GD
7],
decreased
body­
weight
gain
[
GD
6­
9]
and
food
consumption
[
GD
6­
11].

Developmental
NOAEL:
65
{
51}
mg/
kg/
day
Developmental
LOAEL:
190
{
150}
mg/
kg/
day,
based
on
a
slight
increase
in
the
incidence
of
skeletal
malformations
[
hole
in
cranium,
presence
of
cervical
ribs,
absence
of
sacral
&
caudal
vertebrae],
skeletal
variations,
and
external
malformations
[
hindlimb
flexure,
constriction
at
base
of
tail,
filamentous
tail,
protrusion
of
brain
tissue
through
opening
in
brain].

870.3700
[
§
83­
3a]
Developmental
Toxicity
­
CD
®
[
Sprague­
Dawley
­
derived]
rats
[
0,
32.5,
100,
and
325
mg/
kg/
day]
{
17,
51,
and
175
mg/
kg/
day}
(
JMPR
12,
37,
120
mg/
kg/
day)

MRID
41527102
[
1990]

Bio/
dynamics,
Inc.

Classification:
Acceptable/
Guideline
TIPA
salt
of
2,4­
D
(
72.2%;
acid
equivalent
38.7%)
Maternal
NOAEL:
not
determined
Maternal
LOAEL:
32.5
{
17}
mg/
kg/
day,
based
on
decreased
body­
weight
gain
on
days
6­
9.
At
HDT
[
325
{
175}
mg/
kg/
day],
there
were
2
deaths
[
GD
9,
11]
and
2
moribund
sacrifices
[
GD
9,
12];
stiffness
of
limbs
(
days
6,
8,
&
20);
negative
BWG
[
GD
6­
9],
decreased
BWG
throughout
study,
reduced
food
intake
during
dosing
period.

Developmental
NOAEL:
32.5
{
17}
mg/
kg/
day
Developmental
LOAEL:
100
{
51}
mg/
kg/
day,
based
on
a
significant
increase
in
the
incidence
of
skeletal
malformations
and
fetal
incidence
of
total
skeletal
variations.
At
HDT,
decreased
number
of
males/
litter,
reduced
pup
body
weight;
external
[
filamentous
tail,
absent
eye
bulge,
small
eye
bulge]
&
visceral
[
anophthalmia,
microphthalmia,
folded
retina,
aortic
arch
malformation,
distended
lateral
cerebral
ventricle,
cardiac
interventricular
septal
defect]
malformations.

Developmental
Toxicity
in
Rabbits
[
2,4­
D]:
EXECUTIVE
SUMMARY:
In
a
developmental
toxicity
study
[
MRID
41747601],
artificially­
inseminated
female
New
Zealand
White
rabbits
[
20/
group]
were
administered
2,4­
Dichlorophenoxyacetic
acid
[
96.1%]
at
dose
levels
of
0
[
aqueous
0.5%
methylcellulose],
10
mg/
kg/
day,
30
mg/
kg/
day,
and
90
mg/
kg/
day
from
gestation
day
6
through
gestation
day
18.
NOTE:
All
dose
concentrations
were
corrected
for
the
96.1%
purity
of
the
test
material.

There
were
no
treatment­
related
deaths.
Two
high­
dose
does
aborted
[
days
21
and
24].
Treatment­
related
clinical
signs
of
toxicity
were
observed
in
the
two
does
that
aborted
[
days
21
and
24,
after
13
doses
each]
and
included
ataxia
in
both
[
days
16­
19
and
after
day
13],
and
decreased
motor
activity,
loss
of
righting
reflex,
extremities
that
were
cold
to
the
touch,
and
dried
feces
in
doe
that
aborted
on
day
21.
Body
weights
were
comparable
among
the
groups
throughout
the
study,
but
body­
weight
gains
were
decreased
at
the
high­
dose
level
[
73%
of
control]
during
the
dosing
period
[
days
6­
19;
statistical
significance
was
not
attained].
During
days
7­
8,
the
low­
and
mid­
dose
groups
showed
no
body­
weight
gain,
and
the
high­
dose
group
displayed
a
negative
body­
weight
gain
[­
0.01
grams]
compared
to
the
control
[+
0.01
gram].
During
days
15­
19,
the
high­
dose
group
13
displayed
no
body­
weight
gain,
and
corrected
body­
weight
gain
was
decreased
at
the
highdose
level
[
77%
of
control;
statistical
significance
was
not
attained]
also.
Food
consumption
was
comparable
among
the
groups.

Pregnancy
rates
were
comparable
among
the
groups.
Comparable
numbers
of
corpora
lutea,
implantations,
and
live
fetuses
were
observed
among
the
groups,
and
there
were
no
dead
fetuses.
One
control
doe
had
100%
resorptions.
The
number
of
resorption
and
preand
post­
implantation
losses
were
comparable
among
the
groups
also.
Gravid
uterine
weights
were
comparable
among
the
groups.

Mean
fetal
body
weight
was
comparable
among
the
groups.
At
the
high­
dose
level,
there
was
a
significant
increase
in
the
percent
of
live
male
fetuses
[
71.2%]
compared
to
the
control
[
52.8%]
and
other
dose
groups
[
low:
54.4%;
mid:
59.4%].
At
the
high­
dose
level,
the
fetal
incidence
[
3
fetuses
of
one
litter;
p<
0.01]
of
hindlimbs
turned
inward
was
increased
compared
to
the
control
(
0)
and
other
treatment
groups
(
0),
and
the
same
fetuses
displayed
domed
head
[
hydrocephaly].
This
finding
is
not
considered
treatmentrelated
There
were
no
apparent
differences
in
the
incidence
of
external,
visceral,
or
skeletal
variations,
anomalies,
retardations,
or
malformations
among
the
groups.

The
maternal
toxicity
NOAEL
is
30
mg/
kg/
day,
based
on
abortions,
decreased
bodyweight
gain,
and
clinical
signs
of
toxicity
[
decreased
motor
activity,
ataxia,
loss
of
righting
reflex,
extremities
cold
to
the
touch]
at
the
maternal
toxicity
LOAEL
of
90
mg/
kg/
day.

The
developmental
toxicity
NOAEL
is
30
mg/
kg/
day,
based
on
abortions
at
the
developmental
toxicity
LOAEL
of
90
mg/
kg/
day.

This
developmental
toxicity
study
is
classified
Acceptable/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.3700;
§
83­
3(
b)]
for
a
developmental
toxicity
study
in
the
rabbit.

Developmental
Toxicity
in
Rabbits
[
2,4­
D
amine
salts
and
esters]:
In
the
developmental
toxicity
studies
on
the
amine
salts
and
esters
of
2,4­
D,
comparable
results
were
noted
to
those
following
2,4­
D
exposure.
Although
BEE
showed
more
severe
maternal
effects
than
the
other
compounds,
this
would
not
impact
FQPA
assessment.
The
results
[
NOAEL/
LOAELs]
of
the
rabbit
developmental
toxicity
studies
on
the
esters
and
amine
salts
are
summarized
in
the
table
below
for
comparison.
14
Table
4.
Developmental
Toxicity
of
2,4­
D
and
its
Esters
and
Salts
in
Rabbits
Guideline
STUDY
RESULTS
870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
0,
10,
30,
and
90
mg/
kg/
day]

MRID
41747601
[
1990]

Classification:
Acceptable/
Guideline
2,4­
D
(
96.1%
a.
i
.)
Maternal
NOAEL:
30
mg/
kg/
day
Maternal
LOAEL:
90
mg/
kg/
day,
based
on
clinical
signs
[
ataxia,
decreased
motor
activity,
loss
of
righting
reflex,
cold
extremities],
abortion
(
2),
decreased
body­
weight
gains.
Survival
was
not
affected
by
treatment.

Developmental
NOAEL:
30
mg/
kg/
day
Developmental
LOAEL:
90
mg/
kg/
day,
based
on
abortions.

870.3700
[
§
83­
3b]
Developmental
Study
­
rabbits
[
0,
15,
45,
110
mg/
kg/
day]
{
10,
30,
75
mg/
kg/
day}

MRID
41527101
[
1990]

Classification:
Acceptable/
Guideline
BEE
ester
of
2,4­
D
(
95.6%;
acid
equivalent
65.8)
Maternal
NOAEL:
15
{
10}
mg/
kg/
day
Maternal
LOAEL:
45
{
30}
mg/
kg/
day,
based
on
mortality/
morbidity,
clinical
signs
[
decreased
activity,
prostation,
myotonia,
transient
lateral
recumbency,
cold
to
touch,
perineal
soiling/
blood,
red
urine],
and
decreased
body­
weight
gain.
Deaths:
mid
dose
[
sacrificed
day
21,
another
died
day
24].
At
HDT
[
4
sacrificed
(
days
14,
15,
18,
21),
4
died
(
days
11,12,13,19].

Developmental
NOAEL:
110
mg/
kg/
day
[
HDT].

870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
0,
15,
30,
and
60
mg/
kg/
day]
{
10.2,
20.3,
40.6
mg/
kg/
day}

MRID
42055501
[
1991]

Classification:
Acceptable/
Guideline
DEA
salt
of
2,4­
D
(
73.09%;
acid
equivalent
49.5%)
Maternal
NOAEL:
15
mg/
kg/
day
Maternal
LOAEL:
30
mg/
kg/
day,
based
on
decreased
bodyweight
gain
and
food
consumption.
At
HDT,
one
doe
died,
slight
increase
in
resorptions/
post
implantation
loss].

Developmental
NOAEL:
30
mg/
kg/
day
Developmental
LOAEL:
60
mg/
kg/
day,
based
on
the
number
of
litters
with
fetuses
with
7th
cervical
rib(
s).

870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
12,
36.1,
108.4
mg/
kg/
day]
{
10,
30,
and
90
mg/
kg/
day}

MRID
42224001
[
1991]

Classification:
Acceptable/
Guideline
DMA
salt
of
2,4­
D
(
66.18%;
acid
equivalent
55.5%)
Maternal
NOAEL:
30
mg/
kg/
day
Maternal
LOAEL:
90
mg/
kg/
day,
based
on
mortality/
morbidity,
clinical
signs
of
toxicity
[
decreased
motor
activity,
ataxia,
impaired/
loss
of
righting
reflex,
myotonia],
and
decreased
bodyweight
gain
and
food
consumption.
At
HDT,
2
found
dead
[
day
10],
2
found
dead
day
18,
one
sacrificed
day
17.
Clinical
signs
occurred
by
day
7.

Developmental
NOAEL:
90
mg/
kg/
day
[
HDT].
Table
4.
Developmental
Toxicity
of
2,4­
D
and
its
Esters
and
Salts
in
Rabbits
Guideline
STUDY
RESULTS
15
870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
15.1,
45.2,
and
113
mg/
kg/
day]
{
10,
30,
and
75
mg/
kg/
day}

MRID
42304603
[
1992]

Classification:
Acceptable/
Guideline
EHE
ester
of
2,4­
D
(
95.4%;
acid
equivalent
63.25%)
Maternal
NOAEL:
30
mg/
kg/
day
Maternal
LOAEL:
75
mg/
kg/
day,
based
on
mortality/
morbidity,
clinical
signs
of
toxicity
[
decreased
motor
activity,
ataxia,
impaired/
loss
of
righting
reflex,
bradypnea],
and
decreased
bodyweight
gain
in
does
that
died.
At
HDT,
2
does
were
sacrificed
moribund
[
days
15,
16],
one
doe
aborted
[
day
23].
Since
no
deaths
were
observed
at
50
mg/
kg/
day
in
the
rangefinding
study,
the
one
mid­
dose
death
at
day
21
was
not
considered
treatment­
related
Developmental
NOAEL:
75
mg/
kg/
day
[
HDT].

870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
13,
38,
and
95
mg/
kg/
day]
{
10,
30,
75
mg/
kg/
day}

MRID
42158704
[
1991]

Classification:
Acceptable/
Guideline
IPA
salt
of
2,4­
D
(
50.1%;
acid
equivalent
39.6%)
Maternal
NOAEL:
could
not
be
determined.
Maternal
LOAEL:
13
{
10}
mg/
kg/
day,
based
on
decreased
bodyweight
gain
throughout
the
dosing
period
[
75%
of
control].
At
mid­
and
high­
dose
levels
[
38
{
30}
and
95
{
75}
mg/
kg/
day],
there
were
2
mid­
dose
[
days
16,
24]
and
3
high­
dose
[
days
12,
20,
21]
deaths
and
4
high­
dose
does
were
sacrificed
moribund
[
days
12,
13,
14,
20]
and
clinical
signs
[
lateral
recumbency,
cold
extremities,
myotonia,
perineal
staining,
blood
in
urine].

Developmental
NOAEL:
95
{
75}
mg/
kg/
day
[
HDT].

870.3700
[
§
83­
3b]
Developmental
Toxicity
­
rabbits
[
19,
56,
and
140
mg/
kg/
day]
{
10,
30,
75
mg/
kg/
day}

MRID
42158705
[
1991]

Classification:
Acceptable/
Guideline
TIPA
salt
of
2,4­
D
(
73.1%;
acid
equivalent
39.2%)
Maternal
NOAEL:
19
{
10}
mg/
kg/
day
Maternal
LOAEL:
56
{
30}
mg/
kg/
day,
based
on
mortality/
morbidity,
clinical
signs
of
toxicity
[
lateral
recumbency,
myotonia,
perineal
staining,
blood
in
urine],
and
decreased
bodyweight
gain.
Deaths:
one
mid­
dose
doe
[
day
18];
3
high­
dose
does
were
sacrificed
moribund
[
days12,
14,
15].
At
HDT,
stiffness
of
limbs
was
displayed
[
3
does
on
GD
6,
all
others
by
GD
8]

Developmental
NOAEL:
140
{
75}
mg/
kg/
day
[
HDT]

4.
Reproductive
Toxicity
Study
Conclusions
Reproductive
Toxicity
Study:
EXECUTIVE
SUMMARY:
In
a
2­
generation
reproduction
study
[
MRID
(
Accession
No.
259442­
259446,
265489)],
30
male/
30
female
F0
Fischer
344
rats/
sex/
group
were
administered
2,4­
D
[
97.5%
a.
i.]
via
the
diet
for
105
days
prior
to
mating
and
through
gestation
and
lactation
of
two
litters
and
for
30
days
after
weaning
the
last
litter
at
target
dose
levels
of
0,
5,
20,
and
80
mg/
kg/
day.
Rats
were
mated,
one
male
with
one
female.
The
resulting
F1a
litters
were
weaned
at
day
28
post
partum.
After
a
2­
week
rest
period,
the
F0
parental
rats
were
re­
bred
using
different
male/
female
combinations
to
produce
the
F1b
litters,
from
which
30
males/
30
females/
group
were
selected
to
become
the
F1
parents.
The
F1
generation
[
30
rats/
sex/
group]
was
administered
the
test
material
at
target
dose
levels
of
0,
5,
and
20
16
mg/
kg/
day
[
high­
dose
level
dropped
due
to
excess
toxicity;
there
were
an
insufficient
number
of
F1b
pups]
in
utero
and
continuously
via
the
milk
or
feed
for
125
days
postnatally
and
prior
to
mating
and
through
gestation
and
lactation
of
two
litters
[
F2a
and
F2b]
and
for
30
days
after
weaning
the
last
litter.

There
were
no
apparent
treatment­
related
deaths,
and
clinical
signs
were
comparable
among
the
groups
throughout
the
study.
During
the
pre­
mating
dosing
period,
body
weights
of
the
F0
parental
animals
were
slightly
lower
[
males
95%­
97%
(
by
week
6)/
females
95%­
96%
(
by
week
13)
of
control]
at
the
high­
dose
level
for
both
sexes.
Bodyweight
gains
of
the
F0
high­
dose
males
were
decreased
initially
[
weeks
2­
3
(
86%
of
control]
and
overall
[
weeks
0­
13
and
weeks
0­
40
(
93%
of
control],
as
were
those
of
the
high­
dose
females
[
weeks
0­
1
(
79%
of
control);
weeks
0­
13
(
92%
of
control)
and
weeks
0­
40
(
94%
of
control)]
compared
to
the
controls.

The
high­
dose
F0
dams
displayed
a
significantly
lower
body
weight
throughout
[
F1A
litter]
gestation
(
94%­
95%
of
control)
and
by
gestation
day
20
during
F1b
pregnancy
[
90%
of
control].
The
high­
dose
F0
dams
displayed
significantly
reduced
body­
weight
gains
compared
to
the
controls
during
both
gestation
periods,
with
the
greater
deficit
being
observed
during
the
second
gestation
period
[
F1a
litters:
days
0­
7
(
67%*
of
control);
days
13­
20
(
95%
of
control;
days
0­
20
(
87%
of
control);
F1b
litters:
days
0­
7
(
70%*
of
control);
days
13­
20
(
59%**
of
control);
days
0­
20
(
67%**
of
control)].
The
high­
dose
F0
dams
displayed
decreased
body
weight
on
day
7
of
lactation
[
both
litters;
92%­
93%
of
control],
but
body
weights
were
significantly
increased
compared
to
the
controls
at
day
28
of
lactation
[
F1a
(
108%/
F1b
111%
of
control].
Body­
weight
gains
were
significantly
reduced
during
lactation
days
1­
7
for
both
litters
[
F1a
(
40%
of
control);
F1b
(
6%
of
control)].
Overall,
however,
the
high­
dose
dams
displayed
positive
body­
weight
gain
during
lactation
days
1­
28
compared
to
negative
body­
weight
gains
in
the
control
and
other
dose
groups.

Food
consumption
[
g/
rat/
day]
during
the
pre­
mating
period
was
slightly
lower
[
94%­
95%
of
control]
in
the
high­
dose
females
during
a
few
weeks,
but
on
a
g/
kg/
day
basis,
both
sexes
at
the
high­
dose
level
displayed
a
slight
increase
[
104%
of
control]
in
food
consumption
compared
to
the
controls.
During
the
first
week
of
the
two­
week
rest
period
following
the
weaning
of
the
first
litter,
the
F0
dams
displayed
a
significant
decrease
in
food
consumption
[
83%­
84%
of
control].
Food
consumption
was
decreased
at
the
highdose
level
during
both
gestation
periods
[
F1a
during
first
2
weeks
(
91%­
93%
of
control);
F1b
during
third
week
(
82%
of
control)].
A
significant
decrease
in
food
consumption
was
observed
throughout
lactation
[
both
litters]
at
the
high­
dose
level
[
F1a
litter
(
58%
of
control
for
days
1­
28);
F1b
litter
(
71%­
83%
of
control)].
At
necropsy,
no
treatmentrelated
adverse
effects
were
observed
at
any
dose
level,
although
the
F0
females
displayed
increased
kidney
weights
at
all
dose
levels
but
there
was
no
dose
response.

There
were
no
apparent,
treatment­
related,
adverse
effects
on
body
weights
or
body­
17
weight
gains
of
the
F1
parental
animals
during
the
pre­
mating
dosing
period
at
the
two
remaining
dose
levels,
although
the
mid­
dose
[
20
mg/
kg/
day;
the
highest
dose
in
the
F1
generation]
males
displayed
an
initial
decrease
in
body­
weight
gain
[
weeks
35­
36
(
91%**
of
control)
and
weeks
36­
37
(
89%**
of
control)].
At
20
mg/
kg/
day,
there
were
no
significant
differences
in
body
weights
in
the
F1
dams
during
gestation
[
F2a
litters
95%­
99%;
F2b
litters
95%­
96%
of
control]
or
body­
weight
gains
F2a
litters
85%
(
days
7­
13);
F2b
litters
83%
(
days
0­
7);
86%
(
days
13­
20);
90%
(
days
0­
20)
of
control],
and
comparable
body
weights/
gains
were
observed
during
lactation
[
both
litters].
Food
consumption
was
comparable
among
the
groups
[
both
sexes]
throughout
the
study.
At
necropsy,
no
treatment­
related
adverse
effects
were
observed
at
either
dose
level,
although
the
F1
males
and
females
displayed
slightly
increased
kidney
weights
at
the
20
mg/
kg/
day
dose
level,
and
the
females
at
this
dose
level
displayed
a
slight
increase
in
liver
weight.

F0
Generation.
No
apparent
adverse
effect
was
observed
on
fertility.
Pre­
coital
intervals
were
comparable
among
the
groups.
The
duration
of
gestation
was
significantly
increased
in
the
high­
dose
[
80
mg/
kg/
day]
F0
females
producing
the
F1b
pups
[
22.5
days
vs
21.9
days].
The
gestation
survival
index
was
comparable
among
the
groups
for
the
F1a
pups
but
significantly
decreased
for
the
F1b
litters
[
31.7%
vs
97.8%].
There
was
a
significant
decrease
in
the
number
of
F1a
female
fetuses
at
the
high­
dose
level
[
39%
vs54%].
The
number
of
F1b
pups
born
dead/
dying
by
day
1
[
110]
was
significantly
increased
at
the
high­
dose
level
compared
to
the
control
[
5].
F1a
litter
size
was
slightly
lower
at
the
highdose
level
compared
to
the
control
[
9.0
vs
10.1],
but
F1b
litter
size
was
significantly
lower
than
the
control
[
5.1**
vs
9.5].
F1a
pup
viability
was
comparable
throughout
weaning,
but
F1b
pup
viability
was
significantly
lower
throughout
the
weaning
period.
There
was
a
significant
decrease
in
F1b
pup
survival
to
lactation
day
4
at
the
high­
dose
level
[
86.3%]
compared
to
the
control
[
100%]
and
other
dose
levels
[
98%
and
99.6%],
as
well
as
survival
to
lactation
day
28
[
71.4%
vs
100%
(
control)
and
other
dose
groups
99.4%
and
100%].
Decreased
pup
body
weight
[
F1a
males
89%/
females
90%
of
control
(
day
1),
75%/
81%
of
control
(
day
28);
F1b
males
78%/
females
85%
of
control
(
day
1),
73%/
76%
of
control
(
day
28)]
and
body­
weight
gains
[
F1a
males
68%/
females
70%
of
control
(
days
1­
4),
75%/
80%
of
control
(
days
4­
28);
F1b
males
26%/
females
43%
of
control
(
days
1­
4),
76%/
78%
of
control
(
days
4­
28)]
were
observed
at
the
high­
dose
level,
with
the
F1b
litters
displaying
the
greater
effect.
At
the
mid­
dose
level,
there
was
a
slight
decrease
in
body
weight
[
F1a
males93%/
females
94%
of
control
(
day
28);
F1b
males
84%/
females
87%
of
control
(
day
28)]
and
body­
weight
gains
[
F1a
males
92%/
females
93%
of
control
(
days
4­
28);
F1b
males
83%/
females
85%
of
control
(
days
4­
28)],
with
the
deficits
being
greater
in
the
F1b
litters.

Skeletal
anomalies
and
reduced
ossification
were
observed
in
the
high­
dose
F1b
pups
[
80
mg/
kg/
day]
that
were
dead
at
birth
[
only
dose
level
examined].

F1
Generation.
No
apparent
adverse
effect
was
observed
on
fertility
at
either
dose
level.
18
Pre­
coital
intervals
and
gestation
lengths
were
comparable
among
the
groups.
The
gestation
survival
index
and
the
viability
index
were
comparable
among
the
groups
for
both
the
F2a
and
F2b
litters.
Litter
size,
body
weights,
and
the
sex
ratio
were
comparable
among
the
groups
in
both
the
F2a
and
F2b
litters.

Degenerative
changes
in
the
tubules
of
the
cortical
region
[
high­
dose
F0
males]
and
outer
medullary
regions
[
mid­
and
high­
dose
F0
males,
mid­
dose
F1
males
(
highest
dose
tested
in
this
generation)]
of
the
kidneys
were
found
in
a
subsequent
histopathological
examination.
The
original
reviewer
noted
that
these
effects
on
the
kidney
were
not
found
originally
but
during
a
subsequent
re­
examination
of
the
tissues,
casting
doubt
on
the
quality
of
the
histopathological
examination
of
the
reproductive
organs.
However,
the
RfD/
QA
Peer
Review
Committee
determined
that,
based
on
the
lack
of
effects
on
reproductive
organs
in
the
chronic
and
subchronic
studies
at
similar
or
higher
dose
levels,
reevaluation
of
these
tissues
[
testes
and
ovaries]
is
not
necessary
[
HED
Document
No.
011908,
dated
5/
9/
96].

The
NOAEL
for
parental
toxicity
is
5
mg/
kg/
day
(
target
dose;
actual
dose
range
3.8­
13.5
mg/
kg/
day)
and
the
parental
LOAEL
is
20
mg/
kg/
day
(
target
dose;
actual
dose
range
14­
48
mg/
kg/
day),
based
on
decreased
female
body
weight/
body­
weight
gain
(
F1)
and
male
renal
tubule
alteration
(
F0
and
F1).

The
NOAEL
for
reproductive
toxicity
is
20
mg/
kg/
day
(
target
dose;
actual
dose
range
18­
35
mg/
kg/
day),
and
the
LOAEL
for
reproductive
toxicity
is
80
mg/
kg/
day
(
target
dose;
actual
dose
range
69­
114
mg/
kg/
day),
based
on
an
increase
in
gestation
length.

The
NOAEL
for
offspring
toxicity
is
5
mg/
kg/
day
(
target
dose;
actual
dose
range
7.2­
13.5
mg/
kg/
day),
and
the
LOAEL
for
offspring
toxicity
is
20
mg/
kg/
day
(
target
dose;
actual
dose
range
26­
48
mg/
kg/
day),
based
on
decreased
pup
body
weight
[
F1b].
At
80
mg/
kg/
day
(
target
dose;
actual
dose
range
76.1­
133
mg/
kg/
day),
there
was
an
increase
in
pup
deaths.

This
reproduction
study
is
classified
Acceptable/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.3800;
§
83­
4]
for
a
2­
generation
reproduction
study
in
the
rat.

5.
Additional
Information
from
Literature
Sources
In
a
published
article
[
Neurotoxicology
and
Teratology,
18
(
6):
691­
696
(
1996).
Central
Nervous
System
Myelin
Deficit
in
Rats
Exposed
to
2,4­
Dichlorophenoxyacetic
Acid
Throughout
Lactation],
2,4­
D
exposure
through
mother's
milk
[
100
mg/
kg/
day
administered
to
dam
i.
p.;
DMSO;
Wistar
rats]
during
the
period
of
rapid
myelination
[
postnatal
days
15
to
25]
resulted
in
a
myelin
deficit
in
the
pup's
brain.
The
brains
of
male
and
female
rats
showed
a
significant
decrease
in
myelin
markers,
such
as
19
monohexosylceramide,
as
well
as
phospholipids
and
free
fatty
acids
and
an
increase
of
cholesteryl
esters.
Histological
studies
revealed
myelin
deficit
in
some
brain
regions.

In
a
published
article
[
Neurotoxicology
and
Teratology,
21
(
4):
451­
465
(
1999).
Behavioral
Alterations
Induced
in
Rats
by
a
Pre­
and
Postnatal
Exposure
to
2,4­
Dichlorophenoxyacetic
Acid],
2,4­
D
neonatal
exposure
[
dams
dosed
orally
(
70
mg/
kg/
day)
from
gestation
day16
to
postnatal
day
23;
after
weaning
on
PND
23,
pups
were
either
maintained
on
untreated
diet
or
administered
2,4­
D
diets
(
70
mg/
kg/
day)
until
PND
90]
induced
delay
of
the
ontogeny
of
righting
reflex
and
negative
geotaxis
accompanied
by
motor
abnormalities,
stereotypic
behaviors
[
excessive
grooming
and
vertical
head
movements],
and
hyperactivity
in
the
open
field.

In
a
published
article
[
Mol.
Chem.
Neuropathol.
30,
175­
185
(
1997).
2,4­
Dichlorophenoxyacetic
Acid
Through
Lactation
Induces
Astrogliosis
in
Rat
Brain],
dams
were
injected
i.
p.
with
70
mg/
kg
2,4­
D
from
PND
9
to
PND
25,
and
astroglial
immunoreactivity
in
the
mesencephalon,
cerebellum,
and
hippocampus
was
compared
in
the
25
day­
old
pups.
Neurotoxicity
was
observed
in
reactive
gliosis
in
all
hippocampal
layers
and
in
cerebellar
and
raphe
regions.

In
a
published
article
on
applicators
whose
exposures
were
mostly
limited
to
chlorophenoxy
herbicides,
urinary
levels
of
2,4­
D
obtained
at
the
time
of
maximum
2,4­
D
use
were
compared
to,
among
other
parameters,
reproductive
hormone
levels.
It
was
concluded
that
herbicide
applicators
with
high
urinary
levels
of
2,4­
D
[
back
pack
and
boom
spray
application]
exhibited
elevated
LH
levels.
[
Biomarker
correlations
of
urinary
2,4­
D
levels
in
foresters:
genomic
instability
and
endocrine
disruption.
Environmental
Health
Perspectives
(
2001).
109
(
5):
495­
500]

In
a
published
article
on
agricultural
exposure
to
commercial
formulations
of
chlorophenoxy
herbicides,
a
significant
reduction
was
found
1
to
12
days
after
exposure
in
the
following
variables:
(
1)
circulating
helper
(
CD4)
and
suppressor
T
cells
(
CD8),
cytotoxic
T
lymphocytes
(
CTL),
natural
killer
cells
(
NK),
and
CD8
cells
expressing
the
surface
antigens
HLA­
DR
(
CD8­
DR),
and
lymphoproliferative
response
to
mitogen
stimulations.
All
immunological
values
found
50­
70
days
after
exposure
were
comparable
with
concentrations
before
exposure,
but
mitogenic
proliferative
responses
of
lymphocytes
were
still
significantly
decreased.
The
authors
concluded
that
the
findings
suggest
that
agricultural
exposure
to
commercial
2,4­
D
and
MCPA
formulations
may
exert
short­
term
immunosuppressive
effects.
[
Faustini,
A.,
Settimi,
L.,
Pacifici,
R.,
et
al.
(
1996).
Immunological
changes
among
farmers
exposed
to
phenoxy
herbicides:
preliminary
observations.
Occupational
and
Environmental
Medicine
53,
583­
585.]

In
a
published
study
in
CD­
1
mice,
pregnant
mice
were
administered
a
"
commercial
2,4­
D
formulation"
on
gestation
days
6­
16
in
drinking
water
at
concentrations
ranging
from
0
to
1.0%
of
the
formulated
product
[
equivalent
to

0­
650
mg/
kg/
day
"
expressed
as
the
amine
20
derivative".
The
effect
of
2,4­
D
on
immune
function
was
evaluated
in
the
offspring
7
weeks
after
birth.
It
was
reported
that
the
dams
tolerated
repeated
exposure
in
the
drinking
water
"
without
difficulty"
[
no
effects
were
reported].
The
offspring
exhibited
decreased
body
weight
with
minor
reductions
in
kidney
weights
at
0.1
and
1.0%.
A
generalized
suppression
of
lymphocyte
stimulation
by
concanavalin
A
[
Con
A]
was
observed
at
the
high
dose.
Cytometric
studies
of
the
lymphocyte
subpopulations
demonstrated
an
increased
relative
count
of
B
cells
and
reduced
T
cytotoxic
or
suppressor
cells
at
1.0%.
The
humoral
immune
response,
antibody
production
against
sheep
red
blood
cells,
and
peritoneal
macrophage
phagocytic
function
were
not
altered
by
2,4­
D.
It
was
concluded
by
the
authors
that
since
the
immune
alterations
in
the
offspring
were
observed
many
weeks
after
exposure,
it
appears
as
though
2,4­
D
exposure
during
gestation
causes
permanent
changes
in
cell
types
associated
with
immune
function.
It
is
stated
also
that
since
"
2,4­
D
is
not
considered
a
persistent
chemical,
it
is
unlikely
that
2,4­
D
residues
are
contributing
significantly
to
the
observed
immune
alterations."
[
Toxicology
2001
Aug
13:
165
(
1):
39­
49]
However,
in
another
published
article
[
Crit
Rev
Toxicol
2002
Jul;
32
(
4):
233­
57],
it
is
stated
that
there
is
no
evidence
that
2,4­
D
in
any
of
its
forms
activates
or
transforms
the
immune
system
in
animals
at
any
dose.
NOTE:
2,4­
D
degrades
in
the
environment
to
form
the
metabolite
2,4­
dichlorophenol,
and
the
RfD
for
this
metabolite
[
0.003
mg/
kg/
day]
is
based
on
impaired
immunological
function
[
1997].

The
National
Toxicology
Program
is
conducting
a
multi­
species
study
into
the
mechanisms
of
peroxisomal
proliferation,
and
2,4­
D
was
selected
as
a
model
noncarcinogenic,
weak
peroxisomal
proliferator
[
Drug
Metabolism
and
Disposition
(
1997).
The
American
Society
for
Pharmacology
and
Experimental
Therapeutics,
Vol.
25,
No.
9.
Article:
Sex­
Dependent
Differences
in
the
Disposition
of
2,4­
Dichlorophenoxyacetic
Acid
in
Sprague­
Dawley
Rats,
B6C3F1
Mice,
and
Syrian
Hamsters.
R.
J.
Griffin,
V.
B.
Godfrey,
Y­
C
Kim,
and
L.
T.
Burka]

In
a
published
article
[
Arbuckle,
T.
E.,
Schrader,
S.
M.,
Cole,
D.,
et
al.
(
1999).
2,4­
Dichlorophenoxyacetic
acid
residues
in
semen
of
Ontario
farmers.
Reproductive
Toxicology
13:
421­
429],
measurable
levels
of
2,4­
D
were
found
in
semen
and
were
of
the
same
order
of
magnitude
as
those
measured
in
the
24­
hour
urine
samples
following
a
brief
period
of
exposure.

In
an
abstract
[
J.
Appl.
Toxicol.
(
1986),
6(
4):
291­
295.
The
effect
of
topically
applied
nbutylester
of
2,4­
dichlorophenoxyacetic
acid
on
the
immune
response
in
mice],
evidence
of
clinical
toxicity,
myotonia
and
depression,
and
histopathological
alterations
in
the
CNS
[
perivascular
edema
and
ganglial
cell
necrosis]
were
reported
following
acute
dermal
application
[
up
to
500
mg/
kg]
to
CD­
1
mice.
Subacute
2,4­
D
ester
exposure
[
up
to
300
mg/
kg/
day
for
3
weeks]
produced
minimal
clinical
or
pathological
alterations.
Although
no
effect
was
observed
on
antibody
production,
2,4­
D
did
enhance
the
B­
and
T­
lymphocyte
proliferative
responses.
It
was
stated
that
the
immunosuppressive
effects
of
acute
2,4­
D
ester
exposure
were
unlikely
a
direct
immunological
alteration
but
rather
a
secondary
21
manifestation
of
the
clinical
syndrome.

Adult
offspring
of
Wistar
dams
fed
69
mg/
kg/
day
2,4­
D
butyl
ester
during
lactation
had
increased
brain
concentrations
of
serotonin
and
5­
hydroxyindoleacetic
acid,
but
in
utero
exposure
without
exposure
via
lactation
had
no
effect
on
the
postnatal
status
of
these
neurotransmitters.
Evangelista
de
Duffard,
A.
M.
,
N.
De
Aldrete,
M.,
and
Duffard,
R.
(
1990)].
Changes
in
brain
serotonin
and
5­
hydroxyindoleacetic
acid
levels
induced
by
2,4­
dichlorophenoxyacetic
acid
butyl
ester.
Toxicol.
64,
265­
270].

In
a
published
article
[
Toxicol.
Appl.
Pharmacol.
22,
14­
28
(
1972).
Pre­
and
Postnatal
Studies
on
2,4,5­
Trichlorophenoxyacetic
Acid,
2,4­
Dichlorophenoxyacetic
Acid
and
Their
Derivatives
in
Rats],
increased
fetal
mortality,
decreased
fetal
body
weight,
and
skeletal
malformations
were
observed
in
the
offspring
of
dams
administered
2,4­
D
at
dose
levels
of
100
and
150
mg/
kg/
day
from
gestation
day
6
through
15
[
not
at
50
mg/
kg/
day].

6.
Pre­
and/
or
Postnatal
Toxicity
The
HIARC
concluded
that
there
is
concern
for
pre­
and/
or
postnatal
toxicity
resulting
from
exposure
to
2,4­
D.

A.
Determination
of
Susceptibility:
There
is
qualitative
evidence
of
susceptibility
in
the
rat
developmental
toxicity
study
with
the
acid
and
DEA
where
fetal
effects
[
skeletal
malformations
and
variations]
were
observed
at
a
dose
level
that
produced
less
severe
maternal
toxicity
[
decreased
body­
weight
gain
and
food
consumption].
In
the
previous
assessment
by
the
HIARC,
these
effects
were
not
considered
to
be
severe
in
nature
[
HIARC;
TXR
No.
0050426];
however,
based
on
a
reassessment
of
the
effects
observed,
it
was
determined
that
the
presence
of
7th
cervical
ribs
and
14th
rudimentary
rib
are
considered
malformations.
and
therefore,
are
evidence
of
qualitative
susceptibility.
Additionally,
abortions
were
observed
in
the
rabbit
developmental
toxicity
study
on
2,4­
D,
which
is
evidence
of
qualitative
susceptibility.

There
is
no
evidence
of
increased
[
quantitative
or
qualitative]
susceptibility
in
the
2­
generation
reproductive
study
in
rats
on
2,4­
D.
There
is
no
evidence
of
increased
susceptibility
[
quantitative
or
qualitative]
in
the
prenatal
developmental
toxicity
study
in
rats
[
except
DEA]
and
rabbits
on
the
amine
salts
or
esters
of
2,4­
D.

B.
Degree
of
Concern
Analysis
and
Residual
Uncertainties
Since
there
is
qualitative
evidence
of
susceptibility
of
the
young
following
exposure
to
2,4­
D
and
DEA
in
the
rat
developmental
toxicity
study,
HIARC
performed
a
Degree
of
Concern
Analysis
to
1)
determine
the
level
of
concern
for
the
effects
observed
when
considered
in
the
context
of
all
available
toxicity
data;
22
and
2)
identify
any
residual
uncertainties
after
establishing
toxicity
endpoints
and
traditional
uncertainty
factors
to
be
used
in
the
risk
assessment
of
this
chemical.
If
residual
uncertainties
are
identified,
HIARC
examines
whether
these
residual
uncertainties
can
be
addressed
by
a
special
FQPA
safety
factor
and,
if
so,
the
size
of
the
factor
needed.
The
results
of
the
HIARC
Degree
of
Concern
analysis
for
2,4­
D
and
DEA
follow.

There
is
low
concern
for
the
qualitative
susceptibility
seen
in
the
rat
developmental
toxicity
study
with
the
acid
and
DEA
since
the
dose­
response
in
each
case
was
well
characterized;
there
were
clear
NOAELs/
LOAELs
for
maternal
and
developmental
toxicities;
and
the
developmental
effects
were
seen
in
the
presence
of
maternal
toxicity.
There
are
no
residual
uncertainties
for
pre
and/
or
postnatal
toxicities,
since
the
doses
selected
for
overall
risk
assessments
will
address
the
concerns
seen
in
the
prenatal
developmental
toxicity
studies
on
2,4­
D
and
DEA
and
in
the
rabbit
developmental
toxicity
study
on
2,4­
D.

It
is
noted
that
2,4­
D
affects
thyroid
hormone
homeostasis
following
oral
exposure,
and
there
is
a
concern
for
endocrine
disruption.
Effects
on
the
gonads
in
rats
[
decreased
testes
and
ovarian
weights,
atrophy
of
the
ovary,
uterus
and
testis,
degeneration
of
the
seminiferous
epithelium,
decreased
spermatozoa
in
epididymis,
testicular
degeneration,
increase
in
gestation
length]
and
dogs
[
increased
testes
weight,
juvenile
testes
and
prostate,
and
hypospermatogenesis]
are
seen
following
exposure
to
2,4­
D
and/
or
its
amine
salts
and
esters.
Although
there
are
data
on
thyroid
hormone
levels
in
the
adult
animal,
there
are
no
data
with
respect
to
thyroid
hormones
in
the
young;
therefore,
there
is
no
information
on
whether
the
young
are
more
sensitive
with
respect
to
this
endpoint.
There
is
no
developmental
neurotoxicity
[
DNT]
study
available
on
2,4­
D,
and
the
HIARC
determined
previously
that
a
DNT
study
is
required
[
HED
Document
No.
014234].
There
have
been
no
studies
on
2,4­
D
that
specifically
assess
its
endocrine
disruption
potential,
and
there
no
data
on
other
hormonal
imbalances.
Thyroid
effects
[
increased
thyroid
weight,
increased
T3/
decreased
T4,
and
follicular
cell
hypertrophy]
have
been
observed
in
the
rat
following
subchronic
exposure
to
2,4­
D
and
its
amine
salts
and
esters
and
following
chronic
exposure
to
2,4­
D
[
decreased
T4,
increased
thyroid
weight,
thyroid
masses,
and
follicular
cell
hyperplasia
(
males;
interim
sacrifice
only)/
hypertrophy
(
females;
interim
sacrifice
only)].
Additionally,
there
is
some
concern
for
immunotoxicity
following
exposure
to
2,4­
D.
There
are
clear
NOAELs
for
each
of
the
above­
mentioned
effects,
which
occur
only
at
high­
dose
levels;
above
the
doses
selected
for
overall
risk
assessment.
Therefore,
there
are
no
residual
uncertainties
with
regard
to
these
effects.
However,
the
HIARC
concluded
that
a
2­
generation
reproduction
study
using
the
current
protocol
is
required
to
address
both
the
concern
for
thyroid
effects
[
comparative
assessment
between
the
young
and
adult
animals]
and
immunotoxicity,
as
well
as
a
more
thorough
assessment
of
the
gonads
and
23
reproductive/
development
endpoints.
The
Task
Force
should
consult
the
Agency
on
the
protocol
for
this
study.

C.
Special
FQPA
Safety
Factor(
s):
Based
on
the
above­
described
data,
no
special
FQPA
Safety
Factor
is
needed
[
1X],
since
there
are
no
residual
uncertainties
for
pre­
and/
or
postnatal
toxicity.

The
Special
FQPA
Safety
Factor
recommended
by
the
HIARC
assumes
that
the
exposure
databases
(
dietary
food,
drinking
water,
and
residential)
are
complete
and
that
the
risk
assessment
for
each
potential
exposure
scenario
includes
all
metabolites
and/
or
degradates
of
concern
and
does
not
underestimate
the
potential
risk
for
infants
and
children.

7.
Recommendation
for
a
Developmental
Neurotoxicity
Study
The
HIARC
concluded
that
there
is
a
concern
for
developmental
neurotoxicity
resulting
from
exposure
to
2,4­
D.
HIARC
previously
determined
that
a
DNT
study
with
2,4­
D
is
required
[
HED
Document
No.
014234].

A.
Evidence
that
Support
Requiring
a
Developmental
Neurotoxicity
Study:


There
is
evidence
of
neurotoxicity

clinical
signs
(
ataxia,
decreased
motor
activity,
myotonia,
prostration,
lateral
recumbency,
and
impaired/
loss
of
the
righting
reflex,
cold
to
the
touch)
in
pregnant
rabbits
following
dosing
during
gestation
days
6­
15
in
studies
on
2,4­
D
itself
and
its
amine
salts
and
esters;


tremors
in
dogs
that
died
on
test
following
repeat
exposure
to
2,4­
D;


incoordination
and
slight
gait
abnormalities
(
forepaw
flexing
or
knuckling)
were
observed
following
acute
dosing
in
the
acute
neurotoxicity
study
on
2,4­
D.


increased
fore­/
hindlimb
grip
strength
in
the
high­
dose
females
were
observed
in
the
chronic
neurotoxicity
study
on
2,4­
D.


ataxia,
decreased
motor
activity,
and
stiffness
of
limbs
were
observed
in
the
rat
developmental
toxicity
studies
in
dams
dosed
with
2­
EHE,
DMA,
and
BEE.


There
is
evidence
of
neuropathology
[
an
increased
incidence
of
bilateral
retinal
degeneration
in
the
high­
dose
females
in
the
chronic
neurotoxicity
study
on
2,4­
D
24
and
retinal
degeneration/
cataracts
in
subchronic
oral
toxicity
studies
on
2,4­
D
esters
and
amine
salts]


There
is
evidence
of
developmental
toxicity

in
the
rat
[
skeletal
malformations
(
presence
of
7th
cervical
ribs
and
14th
rudimentary
ribs)
and
skeletal
variations
(
retarded
skeletal
ossification
and
malaligned
sternebrae)
at
a
dose
level
that
produced
maternal
decreased
body­
weight
gain
and
food
consumption
following
2,4­
D
exposure.


in
the
2­
generation
reproduction
study
in
rats,
similar
findings
[
14th
rudimentary
ribs,
reduced
ossification
of
vertebral
arches,
and
malaligned
sternebrae]
were
observed
in
the
F1b
pups.


malformations
[
folded
retina,
anophthalmia,
microphthalmia,
distended
lateral
cerebral
ventricle,
hole
in
cranium,
among
others]
were
demonstrated
in
the
rat
developmental
toxicity
studies
following
exposure
to
IPA
and
TIPA.


delay
of
the
ontogeny
of
righting
reflex
and
negative
geotaxis
accompanied
by
motor
abnormalities,
stereotypic
behaviors
[
excessive
grooming
and
vertical
head
movements],
and
hyperactivity
in
the
open
field
was
observed
following
neonatal
exposure
to
2,4­
D.


adult
offspring
of
Wistar
dams
fed
2,4­
D
butyl
ester
during
lactation
had
increased
brain
concentrations
of
serotonin
and
5­
hydroxyindoleacetic
acid,
but
in
utero
exposure
without
exposure
via
lactation
had
no
effect
on
the
postnatal
status
of
these
neurotransmitters.


2,4­
D
exposure
through
mother's
milk
[
Wistar
rats]
during
the
period
of
rapid
myelination
[
postnatal
days
15
to
25]
resulted
in
a
myelin
deficit
in
the
pup's
brain.

B.
Evidence
that
Support
Not
Requiring
a
Developmental
Neurotoxicity
Study:

Neurotoxicity
was
demonstrated
at
relatively
high
dose
levels
in
adult
animals.
There
is
no
evidence
of
qualitative
or
quantitative
susceptibility
in
the
rabbit
developmental
toxicity
study
on
2,4­
D
or
in
the
rat
2­
generation
reproduction
study
on
2,4­
D.
Additionally,
there
is
no
evidence
of
qualitative
or
quantitative
susceptibility
in
either
the
rat
or
rabbit
developmental
toxicity
study
on
any
of
the
amine
salts
or
esters
of
2,4­
D.

On
April
8,
2003,
based
on
the
weight
of
evidence
presented,
the
HIARC
25
reaffirmed
the
previous
conclusion
[
HED
Document
No.
014234]
that
a
developmental
neurotoxicity
[
DNT]
study
in
rats
is
required
for
2,4­
D.
In
addition,
the
HIARC
determined
that
a
repeat
2­
generation
reproduction
study
[
using
the
new
protocol]
is
required
to
address
concerns
for
endocrine
disruption
[
thyroid
and
immunotoxicity
measures].
The
registrant
should
consult
the
Agency
for
the
protocol.

In
determining
the
size/
magnitude
of
the
Database
Uncertainty
Factor
(
UF
DB),
the
HIARC
conducted
a
dose
analysis
as
described
below:

°
It
is
assumed
that
the
DNT
study
will
be
conducted
at
dose
levels
similar
to
those
used
in
the
2­
generation
rat
reproduction
study
(
0,
5,
20
or
80
mg/
kg/
day)
where
the
offspring
NOAEL
was
5
mg/
kg/
day
and
the
LOAEL
was
20
mg/
kg/
day.
In
the
DNT,
the
method
of
administration
will
be
dietary,
similar
to
that
of
the
reproduction
study.

°
It
is
likely
that
the
results
of
the
DNT
study
will
impact
the
currently
selected
endpoints
for
overall
risk
assessments
because
the
lowest
dose
tested
in
the
DNT
(
5
mg/
kg/
day)
may
become
an
effect
level
(
i.
e,
LOAEL).
If
so,
then
a
10X
may
be
applied
which
may
result
in
an
extrapolated
NOAEL
of
0.5
mg/
kg/
day.

°
The
potential
dose
for
risk
assessments
from
the
DNT
(
0.5
mg/
kg/
day)
will
be
lower
than
the
doses
currently
used
for
the
overall
risk
assessments:
Acute
Dietary
(
25
mg/
kg/
day
for
Females
13­
50
years
old
and
67
mg/
kg/
day
for
the
General
Population),
Chronic
Dietary
(
5
mg/
kg/
day)
and
Non
Dietary:
(
range
5
­
25
mg/
kg/
day).

Given
these
circumstances,
HIARC
does
not
have
sufficient
reliable
data
justifying
selection
of
an
additional
safety
factor
for
the
protection
of
infants
and
children
lower
than
the
default
value
of
10X
UF
DB
.
26
II.
HAZARD
IDENTIFICATION
1.
Acute
Reference
Dose
(
aRfD)
­
FEMALES
13­
50
YEARS
OLD
Study
Selected:
Developmental
Toxicity
Study­
Rats
Guideline
#:
OPPTS
870.3700;
§
83­
3(
a)

MRID
No.:
Accession
No.
00251031
Executive
Summary:
In
a
developmental
toxicity
study
[
Accession
No.
00251031],
pregnant
Fischer
344
rats
[
35/
group]
were
administered
2,4­
dichlorophenoxyacetic
acid
[
2,4D;
97.5%]
via
gavage
at
dose
levels
of
0
[
corn
oil],
8
mg/
kg/
day,
25
mg/
kg/
day,
and
75
mg/
kg/
day
from
gestation
day
[
GD]
6
through
gestation
day
15.

There
were
no
treatment­
related
deaths.
Two
[
one
control
and
one
low­
dose]
dams
delivered
prematurely
on
gestation
day
19,
and
in
both
instances
the
offspring
produced
were
of
similar
size
and
development
as
those
from
full­
term
delivery.
Clinical
signs
were
comparable
among
the
groups.
Body
weights
were
comparable
among
the
groups
throughout
the
study,
but
dams
at
the
high­
dose
level
displayed
a
decrease
in
body­
weight
gain
during
the
dosing
period
[
79%
of
control
for
GD
6­
15;
57%
of
control
for
GD
6­
10],
although
statistical
significance
was
not
attained.
The
corrected
body­
weight
gain
was
comparable
among
the
groups.
Food
consumption
data
were
not
reported.

The
was
a
slight
decrease
in
pregnancy
rate
with
increasing
dose
[
85%,
85%,
80%
and
77%].
The
numbers
of
corpora
lutea,
implantations,
and
live
fetuses
were
comparable
among
the
groups,
and
there
were
no
dead
fetuses.
The
number
of
resorptions,
as
well
as
pre­
and
post­
implantation
losses,
were
not
adversely
affected
by
treatment.
The
number
of
the
dams
with
100%
resorptions
was
2,
0,
1,
and
1
[
control,
low­,
mid­,
and
high­
dose
groups,
respectively].
One
control,
2
low­,
4
mid­,
and
2
high­
dose
dams
had
late
resorptions.
Fetal
body
weight
and
crown­
rump
length
were
comparable
among
the
groups,
as
was
the
sex
ratio.

There
were
no
statistically­
significant
or
treatment­
related
differences
in
the
incidence
of
fetal
external,
visceral,
or
skeletal
malformations.
There
was
an
increased
incidence
of
skeletal
variations
at
the
high­
dose
level
that
included
the
presence
of
7th
cervical
ribs
[
4
fetuses
in
3
litters
vs
none
in
the
control],
presence
of
14th
rudimentary
ribs
[
4
fetuses
in
3
litters
vs
none
in
the
control];
malaligned
sternebrae
[
15
fetuses
in
10
litters
vs
7
fetuses
in
7
litters
of
the
control];
reduced
ossification
of
the
vertebral
arches
[
6
fetuses
in
5
litters
vs2
fetuses
in
1
litter
of
the
control];
and
unossified
sternebrae
#
5
or
#
6
[
73
fetuses
in
22
litters
(
3.32
fetuses/
litter)
vs
62
fetuses
in
24
litters
(
2.58
fetuses/
litter)].
Although
none
of
the
increases
attained
statistical
significance,
they
were
attributed
to
treatment
since
some
of
the
variations
[
maligned
sternebrae,
14th
rudimentary
ribs,
and
reduced
ossification
of
vertebral
arches]
were
also
observed
in
the
F1b
pups
of
dams
fed
2,4­
D
at
80
mg/
kg/
day
27
[
actual
dose

75
mg/
kg/
day]
in
the
2­
generation
reproduction
study
in
the
same
strain
of
rat.
Additionally,
skeletal
variations
of
the
ribs
[
2nd
wavy
ribs,
lumbar
ribs]
and
missing
sternebrae
were
observed
in
another
developmental
toxicity
study
using
a
different
strain
of
rat
[
Sprague­
Dawley]
at
a
comparable
dose
of
87.5
mg/
kg/
day
[
2,4­
D].

The
maternal
toxicity
NOAEL
is
25
mg/
kg/
day,
and
the
maternal
toxicity
LOAEL
is
75
mg/
kg/
day,
based
on
decreased
body­
weight
gain.

The
NOAEL
for
developmental
toxicity
is
25
mg/
kg/
day,
and
the
developmental
toxicity
LOAEL
is
75
mg/
kg/
day,
based
on
increased
incidence
of
skeletal
malformations
[
7th
cervical
ribs
and
14th
rudimentary
ribs]
and
skeletal
variations
[
malaligned
sternebrae,
reduced
ossification
of
the
vertebral
arches,
and
unossified
sternebrae
#
5
or
#
6].

Dose
and
Endpoint
for
Establishing
aRfD:
Developmental
NOAEL
=
25
mg/
kg/
day,
based
on
increased
incidence
of
skeletal
malformations
and
variations
at
the
LOAEL
of
75
mg/
kg/
day.

Uncertainty
Factor
(
UF):
1000X
[
10
for
intraspecies
variation;
10
for
interspecies
variation;
and
10X
database
(
UF
DB)
uncertainty
factor.

Comments
about
Study/
Endpoint/
Uncertainty
Factor:
The
endpoint
is
presumed
to
occur
after
a
single­
dose
exposure.
These
effects
are
considered
treatment­
related,
based
on
the
weight­
of­
evidence
from
the
reproduction
and
developmental
toxicity
studies
in
rats.

2.
Acute
Reference
Dose
(
aRfD)
­
GENERAL
POPULATION
Study
Selected:
Acute
Neurotoxicity
Study
­
Rats
Guideline
#:
OPPTS
870.6200;
§
81­
8
MRID
No.:
43225201
EXECUTIVE
SUMMARY:
In
an
acute
neurotoxicity
study
[
MRID
43115201],
Fischer
344
rats
(
10/
sex/
dose)
were
orally
gavaged
once
with
2,4­
D
at
doses
of
0
(
corn
oil),
15,
75,
or
250
mg/
kg
(
actual:
0,
13,
67
or
227
mg/
kg).
Neurobehavioral
evaluations,
consisting
of
Functional
Observational
Battery
(
FOB)
and
motor
activity,
were
conducted
at
Day
­
1
(
prestudy),
Day
1
(
approximately
5­
6
hrs
postdosing,
peak
time
of
effect)
and
Days
8
and
15.
At
terminal
sacrifice
(
Day
15),
animals
were
euthanized
and
neuropathological
examination
performed
on
control
and
treated
animals
(
5/
sex/
dose).
Acute
RfD
(
Females
13­
50
years
old
)
=
25
mg/
kg
(
NOAEL)
=
0.025
mg/
kg
1000
(
UF)
28
There
were
no
treatment­
related
mortalities,
and
no
significant
differences
were
noted
in
the
mean
body
weights
or
mean
body­
weight
gains.
Treatment­
related,
clinical
signs
[
uncoordinated
movement/
behavior]
were
observed
in
the
high­
dose
rats
only
[
Day
2,
2/
10
males
and
5/
10
females;
Day
3,
2/
10
males,
1/
10
females;
Day
4,
0/
10
males,
1/
10
females].

Clinical
signs
and
neurobehavioral
evaluation
revealed
treatment­
related
changes.
During
the
Day
1
FOB
evaluations,
increased
incidences
of
incoordination
(
6/
10,
males;
4/
10,
females)
and
slight
gait
abnormalities,
described
as
forepaw
flexing
or
knuckling,
were
observed
in
high­
dose
animals
(
8/
10,
males;
8/
10
females).
Slight
gait
abnormalities,
observed
in
a
single
mid­
dose
female,
were
not
judged
to
be
treatment­
related
since
no
other
signs
of
toxicity
were
evident.
Minimal
gait
abnormalities,
not
judged
to
be
treatment­
related,
were
observed
in
one
low­
dose
female
and
one
each
mid­
and
high­
dose
male.
On
the
Day
2
and
3
clinical
examinations,
incoordination
was
noted
in
high­
dose
animals.
The
incidence
of
incoordination
decreased
to
control
levels
by
Day
4
in
males
and
Day
5
in
females.
In
high­
dose
animals,
total
motor
activity
was
significantly
lower
at
Day
1
only.
No
treatment­
related
gross
or
neuropathological
findings
were
present
at
any
dose
level.

The
NOAEL
for
neurotoxicity
is
67
mg/
kg,
based
on
an
increased
incidence
of
incoordination
and
slight
gait
abnormalities
[
described
as
forepaw
flexing
or
knuckling]
at
the
LOAEL
of
227
mg/
kg.
The
NOAEL
for
systemic
toxicity
was
227
mg/
kg
[
the
highest
dose
tested]
in
males
and
females.

Dose
and
Endpoint
for
Establishing
RfD:
NOAEL
=
67
mg/
kg,
based
on
an
increased
incidence
of
incoordination
and
slight
gait
abnormalities
[
described
as
forepaw
flexing
or
knuckling]
at
the
LOAEL
of
227
mg/
kg.

Uncertainty
Factor
(
UF):
1000X
[
10
for
intraspecies
variation;
10
for
interspecies
variation;
and
10X
database
(
UF
DB)
uncertainty
factor.

Comments
about
Study/
Endpoint/
Uncertainty
Factor:
The
study
is
appropriate
for
a
single
dose
exposure
with
the
effects
of
concern
via
the
oral
route
and
length
of
exposure
for
an
acute
dietary
exposure.
There
is
evidence
of
neuropathology
[
retinal
degeneration]
in
female
rats
at
the
one­
year
[
repeat
exposure]
assessment
in
the
chronic
neurotoxicity
study
in
rats,
which
triggers
the
need
for
a
developmental
neurotoxicity
study
in
rats.

Acute
RfD
(
General
Population)
=
67
mg/
kg
(
NOAEL)
=
0.067
mg/
kg
1000
(
UF)
29
3.
Chronic
Reference
Dose
(
cRfD)

Study
Selected:
Chronic
Oral
Toxicity
Study
­
Rat
Guideline
#:
OPPTS
870.4100;
§
83­
1
MRID
No.:
43612001
EXECUTIVE
SUMMARY:
In
a
combined
chronic
toxicity/
carcinogenicity
study
[
MRID
43612001],
50
Fischer
344
rats/
sex/
group
were
administered
2,4­
dichlorophenoxyacetic
acid
[
96.4%]
via
the
diet
for
up
to
24
months
at
concentrations
of
0,
5
mg/
kg/
day,
75
mg/
kg/
day,
and
150
mg/
kg/
day.
The
achieved
doses
were
4.77,
73.15,
and
144.98
mg/
kg/
day
[
males]
and
4.89,
73.11,
and
143.52
mg/
kg/
day
[
females],
respectively.
Additionally,
10
rats/
sex/
group
were
sacrificed
at
12
months
[
interim
sacrifice].
NOTE:
The
interim
sacrifice
data
were
reported
in
MRID
43293901,
HED
Document
No.
011614,
along
with
the
chronic
neurotoxicity
screening
battery
substudy.

There
were
no
treatment­
related
deaths
or
clinical
signs
of
toxicity.
Decreased
body
weight
was
observed
throughout
the
study
at
the
high­
dose
level
in
both
sexes
[
males
92%­
96%/
females
74%­
90%
of
control]
and
at
the
mid­
dose
level
in
females
[
86%­
90%
of
control].
At
week
13,
decreased
body
weight
was
very
slight
in
the
high­
dose
males
[
96%
of
control]
and
somewhat
greater
in
the
high­
dose
females
[
90%
of
control].
At
study
termination,
both
sexes
displayed
decreased
body
weight
at
the
high­
dose
level
[
males
92%/
females
74%
of
control]
with
the
females
displaying
a
greater
effect
than
males.
The
mid­
dose
females
also
displayed
a
decrease
in
body
weight
at
study
termination
[
86%
of
control].
Body­
weight
gains
were
decreased
throughout
the
study
in
females
[
3­
month
interval
(
86%
and
74%
of
control);
6­
month
interval
(
88%
and
71%
of
control),
and
overall
(
77%
and
52%
of
control)]
at
the
mid­
and
high­
dose
levels,
respectively.
Similarly,
high­
dose
males
displayed
decreased
body­
weight
gains
throughout
the
study
[
83%­
87%
of
control].
Consistent
with
the
decreased
body­
weight
gains
was
a
decrease
in
food
consumption,
which
was
observed
at
the
mid­
dose
level
in
females
[­
3.9%]
and
in
both
sexes
at
the
high­
dose
level
[
males
(­
4.7%)/
females
(­
11.6%)].

Ophthalmology
findings
at
study
termination
consisted
of
increased
incidences
of
constricted
blood
vessels,
fundus
and
hyper­
reflective,
fundus
in
the
high­
dose
males
and
an
increased
incidence
of
lens
opacity
in
the
high­
dose
females
compared
to
the
control
and
lower
dose
groups.
Decreased
RBC,
HCT,
and
HGB
values
were
observed
at
various
time
points
in
the
mid­
and
high­
dose
females,
and
platelet
counts
were
decreased
at
various
time
points
in
both
sexes
at
the
mid­
and
high­
dose
levels.
Elevations
in
creatinine
were
observed
in
both
sexes
at
the
mid­
and
high­
dose
levels
throughout
the
study,
except
at
termination
when
comparable
levels
were
observed
among
the
male
groups.
Increased
aspartate
aminotransferase
[
mid­
and
high­
dose
males],
alanine
aminotransferase
[
mid­
and
high­
dose
males],
and
alkaline
phosphatase
[
mid­
and
high­
dose,
both
sexes],
and
decreased
glucose
levels
[
mid­
dose
females,
high­
dose
both
sexes],
cholesterol
[
mid­
and
high­
dose,
both
sexes],
and
triglycerides
[
mid­
dose
females
and
high­
dose
both
sexes]
30
were
observed
throughout
the
study,
although
a
dose
response
was
not
always
apparent.
There
was
a
dose­
related
decrease
in
T4
values
throughout
the
study
in
both
sexes
at
the
mid­
and
high­
dose
levels,
and
the
females
displayed
the
greater
effect
except
at
study
termination.

Thyroid
weights
were
increased
in
the
mid­
dose
females
and
in
both
sexes
at
the
high­
dose
level
at
the
12­
month
interim
sacrifice.
At
study
termination,
thyroid
weights
were
increased
in
both
sexes
at
the
mid­
and
high­
dose
levels,
although
the
mid­
dose
males
did
not
attain
statistical
significance
and
the
increase
at
the
mid­
dose
level
[
both
sexes]
was
greater
than
at
the
high­
dose
level.
Decreased
testes
weights
were
observed
at
the
highdose
level
at
both
the
interim
and
terminal
sacrifices
and
at
the
mid­
dose
level
at
study
termination,
although
statistical
significance
was
not
attained
at
the
mid
dose.
Decreased
ovarian
weights
were
observed
at
the
high­
dose
level
at
both
sacrifice
times
and
in
the
mid­
dose
females
at
study
termination.
The
decreases
in
testes
and
ovarian
weights
are
consistent
findings
in
other
studies
on
2,4­
D
and
its
salts/
esters.
Kidney
weights
were
increased
only
at
the
interim
sacrifice
in
males
at
the
mid­
and
high­
dose
levels
[
doserelated

Gross
pathology
findings
included
decreased
fat
in
high­
dose
females
at
both
sacrifice
times,
multifocal
pale
foci
in
the
lungs
[
interim:
1
mid­
dose,
10
high­
dose
females;
terminal:
4
high­
dose
males,
one
control,
4
mid­,
40
high­
dose
females],
and
lens
opacity
in
high­
dose
females
at
termination.
Microscopically,
there
were
increased
incidences
of
lesions
in
the
bone
marrow
[
decreased
hematopoiesis
in
high­
dose
females
at
the
interim
sacrifice],
eyes
[
retina
degeneration
in
1
male
and
9
females
at
high
dose],
kidney
[
proximal
tubule
degeneration
in
mid­
and
high­
dose
males
and
females],
liver
[
altered
tinctorial
properties
in
mid­
dose
females
and
both
sexes
at
high
dose],
lungs
[
multifocal
alveolar
histiocytosis
in
mid­
dose
females
and
both
sexes
at
high
dose],
adipose
tissue
[
atrophy
in
mid­
dose
female,
both
sexes
at
high
dose],
testes
[
atrophy
at
high
dose],
and
thyroid
[
hyperplasia­
high­
dose
males;
hypertrophy
and
epithelial
cells­
high­
dose
females]
at
the
interim
sacrifice.
At
study
termination,
there
were
increased
incidences
of
cataracts
and
retina
degeneration
of
the
eyes
in
both
sexes
at
the
high­
dose
level,
and
the
severity
of
the
retina
degeneration
was
increased
also.
In
the
liver,
there
was
an
increased
incidence
of
increased
size
of
the
hepatocytes
with
altered
tinctorial
properties
in
both
sexes
at
the
high­
dose
level.
In
the
lungs,
both
the
incidence
and
severity
of
inflammation
were
increased
at
the
high­
dose
level
in
both
sexes,
and
the
incidence
of
atrophy
of
the
adipose
tissue
was
increased
at
the
high­
dose
level
in
both
sexes
at
termination.
Tumor
incidence
was
not
affected
by
treatment.

The
NOAEL
is
5
mg/
kg/
day.
The
LOAEL
of
75
mg/
kg/
day
is
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC
(
females),
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
31
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
decreased
testes
and
ovarian
weights,
and
microscopic
lesions
in
the
lungs
(
females).
At
the
high­
dose
level,
there
were
microscopic
lesions
in
the
eyes,
liver,
adipose
tissue,
and
lungs.
There
was
no
treatment­
related
increase
in
the
incidence
of
any
tumor.

Dose
and
Endpoint
for
Establishing
cRfD:
NOAEL
=
5
mg/
kg/
day,
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
at
the
LOAEL
of
75
mg/
kg/
day.
The
NOAEL
for
maternal
and
offspring
toxicity
in
the
2­
generation
reproduction
study
is
also
5
mg/
kg/
day,
based
on
decreased
maternal
body
weight/
gain
[
F1]
and
male
renal
tubule
alteration
[
F0
and
F1]
at
the
LOAEL
of
20
mg/
kg/
day.

Uncertainty
Factor(
s):
1000X
[
10
for
intraspecies
variation;
10
for
interspecies
variation;
and
10X
database
(
UF
DB)
uncertainty
factor.

Comments
about
Study/
Endpoint/
Uncertainty
Factor:
Previously,
the
2,4­
D
RfD
was
based
on
the
chronic
dog
study.
HIARC
chose
instead
to
use
the
rat
as
the
more
relevant
species
for
risk
assessment,
based
upon
a
number
of
arguments
put
forward
by
the
registrant
[
refer
to
ATTACHMENT
A].
Arguments
were
provided
to
support
the
hypothesis
that
use
of
the
dog
data
as
the
basis
for
regulation
exaggerates
the
apparent
severity
of
effects
anticipated
because
of
the
limited
renal
capacity
of
dogs
to
excrete
organic
acids.
Points
of
consideration
included:
(
1)
the
data
show
the
dog
to
have
a
decreased
clearance,
relative
to
that
predicted
from
the
allometric
relationship,
whereas
humans,
rats,
mice,
and
other
species
all
fit
the
relationship.
This
observation
is
true
for
2,4­
D,
as
well
as
triclopyr,
MCPA,
and
other
organic
acids.
The
decreased
capacity
of
the
dog
to
eliminate
organic
acids
results
in
higher
blood
levels
in
the
dog
relative
to
those
found
in
the
rat
and
consequently,
effects
are
seen
at
lower
dose
levels
in
the
dog
than
in
the
rat.
(
2)
Although
absorption
and
distribution
of
2,4­
D
and
other
organic
acids
is
similar
across
all
species
evaluated,
the
half­
life
of
elimination
for
dogs
is
significantly
longer
than
for
all
other
species
considered.
Dogs
exhibited
half­
lives
of
31
to
106
hours
for
doses
of
1
to
5
mg/
kg.
In
other
species
[
mice,
rats,
pigs,
cats,
and
humans],
half­
lives
ranged
from
0.75
to
11.6
hours
for
similar
doses.
(
3)
Although
the
primary
means
of
elimination
of
2,4­
D
and
other
acids
is
via
the
kidney,
the
difference
in
the
elimination
pattern
among
dogs
and
other
mammalian
species
persuaded
HIARC
that
the
rat
was
a
better
predictor
than
the
dog
of
the
potential
toxicity
of
2,4­
D
to
man.
32
4.
Incidental
Oral
Exposure:
Short­
Term
(
1­
30
days)

Study
Selected:
Developmental
Toxicity
Study
­
Rats
Guideline
#
OPPTS
870.3700
§
83­
3(
a)

MRID
No.:
Accession
No.
00251031.

EXECUTIVE
SUMMARY:
See
under
Acute
RfD
[
females
13­
50]

Dose
and
Endpoint
for
Risk
Assessment:
Maternal
NOAEL
=
25
mg/
kg/
day,
based
on
decreased
maternal
body­
weight
gain
at
the
LOAEL
of
75
mg/
kg/
day.

Comments
about
Study/
Endpoint:
This
endpoint
(
systemic
toxicity)
is
appropriate
for
the
population
(
infants
and
children)
and
duration
(
short­
term)
of
concern.

5.
Incidental
Oral
Exposure:
Intermediate­
Term
(
1
­
6
Months)

Study
Selected:
Subchronic
Oral
Toxicity
­
Rat
Guideline
#:
OPPTS
870.3100;
§
82­
1
MRID
No.:
41991501
EXECUTIVE
SUMMARY:
In
a
subchronic
oral
toxicity
study
[
MRID
41991501],
10
Fischer
344
rats/
sex/
group
were
administered
2,4­
dichlorophenoxyacetic
acid
[
96.1%
a.
i.]
via
the
diet
for
13
weeks
at
concentrations
of
0,
1
mg/
kg/
day,
15
mg/
kg/
day,
100
mg/
kg/
day,
and
300
mg/
kg/
day.

There
were
no
treatment­
related
deaths.
Clinical
signs
of
toxicity
occurred
mainly
in
the
high­
dose
females
and
included
hunched
posture
[
1
high­
dose
female
during
weeks
13­
14],
depressed
activity
[
all
high­
dose
females
during
first
week],
and
few/
no
feces
[
4
highdose
males
and
all
high­
dose
females
during
week
1;
5
high­
dose
females
during
week
12;
1
high­
dose
female
during
week
13].

There
was
a
dose­
related
increase
in
the
incidence
of
pale/
opaque
eyes
in
both
sexes
[
1/
10
controls,
2/
10
at
1,
15,
and
100
mg/
kg/
day
and
4/
10
at
300
mg/
kg/
day
in
males;
1/
10
controls,
2/
10
at
1
mg/
kg/
day,
1/
10
at
15
mg/
kg/
day,
4/
10
at
100
mg/
kg/
day,
and
8/
10
at
300
mg/
kg/
day
in
females].

Decreased
body
weights
were
observed
throughout
the
study
at
the
high­
dose
level
[
both
Chronic
RfD
=
5
mg/
kg/
day
(
NOAEL)
=
0.005
mg/
kg/
day
1000
(
UF)
33
sexes],
with
the
magnitude
of
the
deficit
increasing
with
time
[
males
85%/
77%
and
females
79%/
72%
of
control
at
weeks
6/
13,
respectively],
and
decreased
body­
weight
gains
[
weeks
0­
6:
males
72%/
females
50%
of
control;
overall:
males
63%/
females
43%
of
control]
were
observed
in
both
sexes
at
the
highest
dose
level
throughout
the
study.
At
the
next
highest
dose
level,
decreased
body
weight
[
93%
of
control
at
13
weeks;
both
sexes]
and
body­
weight
gain
[
overall
males
91%/
females
89%
of
control]
were
observed.
A
corresponding
decrease
in
food
consumption
was
observed
in
both
sexes
at
the
two
highest
dose
levels.

Complete
cataract
formation
was
observed
in
7
high­
dose
[
300
mg/
kg/
day]
females
and
in
one
female
at
the
next
highest
[
100
mg/
kg/
day]
dose,
and
posterior
subcapsular
cataract
was
observed
in
5
high­
dose
females.
Treatment­
related
alterations
in
hematology
[
statistically
significant
decreases
in
RBC,
HGB,
HCT,
platelet
count,
absolute
and
corrected
leukocyte
counts,
and
lymphocyte
counts]
were
observed
at
the
6­
and/
or
13­
week
intervals
at
the
high­
dose
level
[
both
sexes],
and
decreased
platelet
counts
were
observed
in
both
sexes
at
the
next
highest
dose
level
at
week
13.
Alterations
in
clinical
chemistry
[
decreased
thyroxine
and
triiodothyronine
levels]
were
observed
at
100
and
300
mg/
kg/
day
at
both
intervals
in
one
or
both
sexes.

Changes
in
absolute
and/
or
relative
organ
weights
[
adrenals,
brain,
thymus,
heart,
kidneys,
testes
with
epididymides
(
males),
ovaries
(
females),
pituitary,
liver
(
increased),
thyroids/
parathyroids
(
increased)]
were
observed
primarily
at
the
high­
dose
level
[
both
sexes],
and
many
of
these
changes
may
be
attributable
to
decreased
body
weight.
Gross
findings,
mainly
in
the
high­
dose
group,
included
small
testes
and
epididymis
and
opaque
eyes
[
females].
Treatment­
related
histopathological
changes
were
observed
primarily
in
the
high­
dose
group
and
included
centrilobular
hepatocellular
hypertrophy
[
liver],
bilateral
retinal
degeneration
and
cataract
formation
[
females],
atrophy
of
the
testes
[
males],
hypertrophy
of
the
zona
glomerulose
[
adrenal
cortex,
both
sexes]
and
follicular
cells
[
thyroid,
females],
atrophy
of
the
thymus
[
both
sexes]
and
spleen
[
both
sexes],
congestion
and
edema
of
the
bone
marrow
[
both
sexes],
brush
border
loss
in
proximal
tubular
cells
[
kidney,
both
sexes].
Many
of
the
lesions
correlated
well
with
the
alterations
observed
in
hematology
and
clinical
chemistry
parameters
and/
or
organ­
weight
data
of
the
high­
dose
groups.

The
NOAEL
is
15
mg/
kg/
day,
based
on
decreased
body
weight/
body­
weight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T3
(
females)
and
T4
(
both
sexes)]
parameters,
and
cataract
formation
in
females
at
the
LOAEL
of
100
mg/
kg/
day.

Dose
and
Endpoint
for
Risk
Assessment:
NOAEL
=
15
mg/
kg/
day,
based
on
decreased
body
weight/
body­
weight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T
3
(
females)
and
T
4
(
both
sexes)]
parameters,
and
cataract
formation
in
females
at
the
LOAEL
of
100
mg/
kg/
day.
34
Comments
about
Study/
Endpoint:
The
dose/
endpoint
are
derived
from
a
study
of
appropriate
duration
and
are
relevant
for
the
population
of
concern
(
infants
and
children).

6.
Dermal
Absorption
Dermal
Absorption
Factor:
5.8%

EXECUTIVE
SUMMARY:
14C­
labeled
2,4­
D
acid
was
applied
to
the
skin
of
the
ventral
forearm
of
6
male
volunteers
in
a
0.25%
acetone
solution
at
a
rate
of
4

g/
cm2.
The
acetone
solution
was
pipetted
onto
the
area
marked
by
a
ring
and
evaporated
by
gentle
blowing
during
application;
the
solvent
was
on
the
skin
for
only
a
few
seconds.
The
skin
sites
were
left
unprotected,
and
the
subjects
were
ask
not
to
wash
the
area
for
24
hours.
Urine
was
collected
for
5
days
for
measurement
of
excreted
radioactivity.
To
correct
for
incomplete
urinary
recovery,
prior
to
the
dermal
study,
the
volunteers
received
intravenous
injection
of
a
tracer
dose
of
the
radiolabeled
test
material
in
the
weight
range
of
the
cutaneous
exposure.
Urine
was
also
collected
for
5
days
for
measurement
of
radioactivity.

Excretion
of
radioactivity
in
the
urine
following
dermal
application
was
5.8%
±
2.4%
and
after
i.
v.
administration
was
100%
±
2.5%.

Reference:
Feldman.
R.
J.
And
Maibach,
H.
I.
(
1974).
Percutaneous
Penetration
of
Some
Pesticides
and
Herbicides
in
Man.
Toxicol.
Appl.
Pharmacol.
28:
126­
132.

7.
Dermal
Exposure:
Short­
Term
(
1­
30
days)
Exposure
Study
Selected:
Developmental
Toxicity
Study
­
Rats
Guideline
#:
OPPTS
870.3700
§
83­
3(
a)

MRID
No.:
Accession
No.
00251031
EXECUTIVE
SUMMARY:
see
under
Acute
RfD
[
females
13­
50]

Dose
and
Endpoint
for
Risk
Assessment:
Developmental/
Maternal
NOAEL
=
25
mg/
kg/
day,
based
on
increased
incidence
of
skeletal
malformations
and
skeletal
variations
and
decreased
maternal
body­
weight
gain
at
the
LOAEL
of
75
mg/
kg/
day.

Comments
about
Study/
Endpoint:
An
acceptable
21­
day
dermal
toxicity
study
is
available
on
2,4­
D,
in
which
no
systemic
or
dermal
toxicity
was
observed
following
exposure
up
to
the
limit
dose
[
1000mg/
kg/
day].
However,
there
was
no
assessment
of
some
effects
of
concern
[
e.
g.,
immunotoxicity
(
thymus
effects);
T3/
T4
measurements]
in
this
dermal
study,
although
the
thyroids
were
weighed
at
study
termination
and
no
effects
were
observed.
Since
dermal
absorption
is
rather
low
[
5.8%],
lack
of
an
effect
on
the
thyroid
35
might
be
expected;
i.
e.,
the
limit
dose
equates
to
58
mg/
kg/
day,
and
thyroid
effects
following
oral
exposure
are
observed
at
oral
dose
levels
of
100
mg/
kg/
day
and
above.
Because
of
the
concerns
for
developmental
effects,
which
are
not
evaluated
in
the
dermal
study,
the
HIARC
selected
the
rat
developmental
toxicity
study.
Since
an
oral
NOAEL
was
selected,
a
dermal
absorption
factor
of
5.8%
should
be
used
in
route­
to­
route
extrapolation.

8.
Dermal
Exposure:
Intermediate­
Term
(
1
­
6
Months)

Study
Selected:
Subchronic
Oral
Toxicity
Study
­
Rat
Guideline
#:
OPPTS
870.3100;
§
82­
1
MRID
No.:
41991501
EXECUTIVE
SUMMARY:
See
Intermediate­
Term
Incidental
Oral
Exposure
Dose
and
Endpoint
for
Risk
Assessment:
NOAEL
=
15
mg/
kg/
day,
based
on
decreased
body
weight/
body­
weight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T
3
(
females)
and
T
4
(
both
sexes)]
parameters,
and
cataract
formation
in
females
at
the
LOAEL
of
100
mg/
kg/
day.

Comments
about
Study/
Endpoint:
The
21­
day
dermal
toxicity
study
was
not
selected
since
there
was
no
assessment
of
thyroid
hormones.
The
selected
dose
would
also
address
the
developmental
toxicity
concerns.

9.
Dermal
Exposure
Long­
Term
(>
6
Months)

Study
Selected:
Chronic
Oral
Toxicity
Study­
Rat
Guideline
#:
OPPTS
870.4100;
§
83­
1
MRID
No.:
43612001
EXECUTIVE
SUMMARY:
see
Chronic
RfD.

Dose
and
Endpoint
for
Risk
Assessment:
NOAEL
=
5
mg/
kg/
day,
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
at
the
LOAEL
of
75
mg/
kg/
day.
The
NOAEL
for
maternal
and
offspring
toxicity
in
the
2­
generation
reproduction
study
is
also
5
mg/
kg/
day,
based
on
decreased
maternal
body
weight/
gain
[
F1]
and
male
renal
tubule
alteration
[
F0
and
F1]
at
the
LOAEL
of
20
mg/
kg/
day.
36
Comments
about
Study/
Endpoint:
This
dose/
endpoint/
study
were
used
to
establish
the
Chronic
RfD.

10.
Inhalation
Exposure:
Short
­
Term
(
1­
30
days)

Study
Selected:
developmental
toxicity
study
­
ratsGuideline
#:
OPPTS
870.3700
§
83­
3(
a)

MRID
No.:
Accession
No.
00251031
EXECUTIVE
SUMMARY:
See
Acute
RfD
[
Females
13­
50
years
old]/
Short­
Term
Incidental
Oral
Dose
and
Endpoint
for
Risk
Assessment:
Developmental/
Maternal
NOAEL
=
25
mg/
kg/
day,
based
on
increased
incidence
of
skeletal
malformations
and
skeletal
variations
and
decreased
maternal
body­
weight
gain
at
the
LOAEL
of
75
mg/
kg/
day.

Comments
about
Study/
Endpoint:
An
oral
study
was
selected
because
of
the
developmental
toxicity
concerns,
and
there
is
no
repeated
dose
inhalation
study
available
on
2,4­
D.
Since
an
oral
dose
was
selected,
absorption
via
inhalation
is
assumed
to
be
equivalent
to
oral
absorption.

11.
Inhalation
Exposure:
Intermediate­
Term
(
1­
6Months)

Study
Selected:
Subchronic
Oral
Toxicity
Study­
rat
Guideline
#:
OPPTS
870.3100;
§
82­
1
MRID
No.:
41991501
EXECUTIVE
SUMMARY:
See
Intermediate­
Term
Incidental
Oral
Exposure
Dose
and
Endpoint
for
Risk
Assessment:
NOAEL
=
15
mg/
kg/
day,
based
on
decreased
body
weight/
body­
weight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T
3
(
females)
and
T
4
(
both
sexes)]
parameters,
and
cataract
formation
in
females
at
the
LOAEL
of
100
mg/
kg/
day.

Comments
about
Study/
Endpoint:
See
under
Short­
Term
Inhalation.

12.
Inhalation
Exposure:
Long­
Term
(>
6
Months)

Study
Selected:
Chronic
Oral
Toxicity
Study
­
Rat
OPPTS
870.4100;
§
83­
1
MRID
No.:
43612001
EXECUTIVE
SUMMARY:
see
Chronic
RfD
37
Dose/
Endpoint
for
Risk
Assessment:
NOAEL
=
5
mg/
kg/
day,
based
on
decreased
bodyweight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
at
the
LOAEL
of
75
mg/
kg/
day.
The
NOAEL
for
maternal
and
offspring
toxicity
in
the
2­
generation
reproduction
study
is
also
5
mg/
kg/
day,
based
on
decreased
maternal
body
weight/
gain
[
F1]
and
male
renal
tubule
alteration
[
F0
and
F1]
at
the
LOAEL
of
20
mg/
kg/
day.

Comments
about
Study/
Endpoint:
See
Short­
Tern
Inhalation.
This
dose/
endpoint/
study
were
used
to
establish
the
Chronic
RfD.

13.
Margins
of
Exposure
Summary
of
target
Margins
of
Exposure
(
MOEs)
for
risk
assessment.

Route
Duration
Short­
Term
(
1­
30
Days)
Intermediate­
Term
(
1
­
6
Months)
Long­
Term
(>
6
Months)

Occupational
(
Worker)
Exposure
Dermal
100
100
100
Inhalation
100
100
100
Residential
(
Non­
Dietary)
Exposure
Oral
1000
1000
N/
A
Dermal
1000
1000
1000
Inhalation
1000
1000
1000
For
Occupational
Exposure:
Short­
term,
intermediate­
term,
and
long­
term
dermal
and
inhalation
exposure
risk
assessments,
A
MOE
of
100
is
required.
This
is
based
on
the
conventional
uncertainty
factor
of
100X
(
10X
for
intraspecies
extrapolation
and
10X
for
interspecies
variation).

For
Residential
Incidental
Oral
Exposure:
Short­
term
and
intermediate­
term
risk
assessments,
a
MOE
of
1000
is
required.
This
is
based
on
the
conventional
uncertainty
factor
of
100X
(
10X
for
intraspecies
extrapolation
and
10X
for
interspecies
variation)
and
10X
for
an
incomplete
database
[
lack
of
a
developmental
neurotoxicity
study
in
rats,
a
2­
38
generation
reproduction
study
in
rats
with
thyroid
and
immunotoxicity
assessments.

For
Residential
Dermal
and
Inhalation
Exposure:
Short­
term,
intermediate­
term,
and
long­
term
risk
assessments,
a
MOE
of
1000
is
required.
This
is
based
on
the
conventional
uncertainty
factor
of
100X
(
10X
for
intraspecies
extrapolation
and
10X
for
interspecies
variation)
and
10X
for
an
incomplete
database
[
lack
of
a
developmental
neurotoxicity
study
in
rats,
a
2­
generation
reproduction
study
in
rats
with
thyroid
and
immunotoxicity
assessments].

14.
Recommendation
for
Aggregate
Exposure
Risk
Assessments
As
per
FQPA,
1996,
when
there
are
potential
residential
exposures
to
the
pesticide,
aggregate
risk
assessment
must
consider
exposures
from
three
major
sources:
oral,
dermal
and
inhalation
exposures.
The
toxicity
endpoints
selected
for
these
routes
of
exposure
may
be
aggregated
as
follows:

a)
A
common
toxicological
endpoint
[
increased
incidence
of
skeletal
malformations
and
skeletal
variations
and
decreased
maternal
body­
weight
gain]
was
selected
for
assessment
of
short­
term
oral,
dermal
[
oral
equivalents],
and
inhalation
[
oral
equivalents]
exposures;
therefore,
these
routes
can
be
aggregated
for
these
exposure
scenarios.

b)
A
common
toxicological
endpoint
[
decreased
body
weight/
body­
weight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T
3
(
females)
and
T
4
(
both
sexes)]
parameters,
and
cataract
formation
in
females]
was
selected
for
assessment
of
intermediate­
term
oral,
dermal
[
oral
equivalents],
and
inhalation
[
oral
equivalents]
exposures;
therefore,
these
routes
can
be
aggregated
for
these
exposure
scenarios.

c)
A
common
toxicological
endpoint
[
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females)],
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
]
was
selected
for
assessment
of
long­
term
oral,
dermal
[
oral
equivalents],
and
inhalation
[
oral
equivalents]
exposures;
therefore,
these
routes
can
be
aggregated
for
these
exposure
scenarios.

III.
CLASSIFICATION
OF
CARCINOGENIC
POTENTIAL
39
1.
Combined
Chronic
Toxicity/
Carcinogenicity
Study
in
Rats
MRID
No.
43049001
EXECUTIVE
SUMMARY:
see
under
Chronic
RfD.

Discussion
of
Tumor
Data
A
variety
of
benign
and
malignant
tumors
commonly
seen
at
different
sites
in
aging
Fischer
344
rats
were
seen
both
in
the
treated
and
control
animals,
but
none
showed
statistical
significance
in
individual
tumor
types
in
any
treated
group
when
compared
to
controls.
There
was
no
treatment­
related
increase
in
the
incidence
of
any
tumor.

This
study
was
performed
to
address
whether
the
finding
of
an
increased
incidence
of
astrocytomas
of
the
brain
found
in
the
1986
rat
study
[
Accession
Nos.
263112­
263114]
was
attributable
to
2,4­
D.
In
the
1986
study,
there
was
a
significant
trend
for
astrocytomas
in
male
rats
but
no
pair­
wise
significance.
The
incidence
in
both
the
treated
and
control
males
exceeded
the
historical
control
incidence
for
this
tumor.
Additionally,
the
CPRC
concluded
that
the
doses
used
in
the
1986
rat
study
were
not
adequate
[
1,
5,
15,
45
mg/
kg/
day]
to
assess
the
carcinogenic
potential
of
2,4­
D.
The
1995
repeat
chronic
toxicity/
carcinogenicity
study
in
rats
was
performed
at
higher
dose
levels
[
5,
75,
150
mg/
kg/
day].

Adequacy
of
the
Dose
Levels
Tested:
The
dose
levels
were
considered
adequate.
The
highest
dose
tested
did
not
alter
survival
or
cause
any
clinical
signs.
Decreased
body
weight
was
observed
throughout
the
study
at
the
high­
dose
level
in
both
sexes
[
males
92%­
96%/
females
74%­
90%
of
control]
and
at
the
mid­
dose
level
in
females
[
86%­
90%
of
control;
at
week
13,
high­
dose
males
[
96%
of
control]
and
high­
dose
females
[
90%
of
control];
at
study
termination,
both
sexes
at
the
high­
dose
level
[
males
92%/
females
74%
of
control];
mid­
dose
females
[
86%
of
control].
Body­
weight
gains
were
decreased
throughout
the
study
in
females
[
3­
month
interval
(
86%
and
74%
of
control);
6­
month
interval
(
88%
and
71%
of
control),
and
overall
(
77%
and
52%
of
control)]
at
the
midand
high­
dose
levels,
respectively.
Similarly,
high­
dose
males
displayed
decreased
bodyweight
gains
throughout
the
study
[
83%­
87%
of
control].
Consistent
with
the
decreased
body­
weight
gains
was
a
decrease
in
food
consumption.
Additionally,
there
were
treatment­
related
alterations
in
clinical
chemistry
parameters
[
increases
in
ALT,
AST,
AP,
and
decreases
in
cholesterol].
Decreases
in
T
4
concentration,
increases
in
absolute/
relative
thyroid
weights,
and
histopathological
lesions
in
the
eyes
[
cataracts
and
retina
degeneration],
liver,
lungs,
adipose
tissue.

2.
Carcinogenicity
Study
in
Mice
MRID
No.
43879801/
43597201
40
EXECUTIVE
SUMMARY:
In
a
carcinogenicity
study
[
MRID
43879801
and
43597201],
50
B
6
C
3
F
1
CRL
BR
mice/
sex/
group
were
administered
2,4­
dichlorophenoxyacetic
acid
[
96.4%]
via
the
diet
for
104
weeks
at
concentrations
of
0,
5
mg/
kg/
day
[
both
sexes],
62
[
males]/
150
[
females]
mg/
kg/
day,
and
120
[
males]/
300
[
females]
mg/
kg/
day.
Additionally,
10
mice/
sex/
group
were
sacrificed
at
52
weeks
[
interim
sacrifice].

There
were
no
treatment­
related
deaths
or
clinical
signs
of
toxicity
in
either
sex.
Body
weight,
body­
weight
gain,
and
food
consumption
were
comparable
among
the
male
groups
throughout
the
study.
Females
at
the
high­
dose
level
displayed
a
slightly
lower
body
weight
at
the
3­
and
6­
month
intervals
[
96%
of
control].
Body­
weight
gains
were
decreased
significantly
at
all
dose
levels
in
the
females
at
the
3­
month
interval
[
93%,
94%,
and
86%
of
control
at
the
low­,
mid­,
and
high­
dose,
respectively],
and
the
high­
dose
females
continued
to
display
a
reduced
body­
weight
gain
at
the
6­
month
[
91%
of
control]
and
12­
month
[
91%
of
control]
intervals.
There
were
no
consistent
changes
in
food
consumption
in
the
female
groups.

Ophthalmology
and
hematology
parameters
[
RBC,
HGB,
HCT,
platelets]
were
comparable
among
the
groups
[
both
sexes];
no
thyroid
parameters
were
monitored.

There
was
a
dose­
related
increase
in
kidney
weights
in
both
sexes.
In
males,
increased
kidney
weights
[
absolute
and
relative]
were
observed
at
the
mid­
and
high­
dose
levels
at
the
terminal
sacrifice
only.
In
females,
increased
kidney
weights
were
observed
at
the
midand
high­
dose
levels
at
both
the
interim
and
terminal
sacrifices.

Gross
pathology
findings
were
comparable
among
the
groups
[
both
sexes].
Microscopically,
there
was
an
increased
incidence
of
lesions
in
the
kidneys
of
both
sexes
at
the
mid­
and
high­
dose
levels.
In
males
at
the
interim/
terminal
sacrifices,
renal
lesions
were
characterized
as
degeneration
with
regeneration
of
the
descending
limb
of
the
proximal
tubule
in
the
mid­
[
20%/
50%]
and
high­
dose
[
100%/
96%]
males
vs
none
in
the
low
dose
or
control
males;
decreased
vacuolization
of
the
renal
proximal
tubule
in
mid­
[
80%/
78%]
and
high­
dose
[
100%/
96%]
males
vs
0%
in
the
low­
dose
and
control
males.
Additionally
at
the
terminal
sacrifice,
there
was
an
increased
incidence
of
mineralization
of
the
tubule(
s)
in
the
mid­
[
58%]
and
high­
[
72%]
dose
males
compared
to
the
low
and
control
groups
[
38%
and
32%,
respectively].
In
females,
the
renal
lesions
were
characterized
by
hypercellularity
in
the
descending
part
of
the
proximal
tubule
at
both
the
interim
and
terminal
sacrifices
at
the
mid­
[
80%/
64%]
and
high­
dose
[
100%/
50%]
levels
vs
0%
in
the
low­
and
control
females.
There
was
no
treatment­
related
increase
in
any
tumor
type
in
either
sex.

The
NOAEL
is
5
mg/
kg/
day.
The
LOAEL
of
62
mg/
kg/
day
[
males]/
150
mg/
kg/
day
[
females]
is
based
on
an
increased
absolute
and/
or
relative
kidney
weights
and
an
increased
incidence
of
renal
microscopic
lesions.
There
was
no
treatment­
related
increase
in
the
incidence
of
any
tumor
type.
41
This
carcinogenicity
study
is
classified
ACCEPTABLE/
Guideline,
and
it
satisfies
the
guideline
requirement
[
OPPTS
870.
4200;
§
83­
2]
for
a
carcinogenicity
study
in
the
mouse.

Discussion
of
Tumor
Data:
A
variety
of
benign
and
malignant
tumors
commonly
seen
in
this
strain/
age
of
mice
were
seen
at
different
sites
in
both
treated
and
control
mice
of
both
sexes,
but
none
showed
statistical
significance
in
individual
tumor
types
in
any
treated
group.
There
was
no
treatment­
related
increase
in
the
incidence
of
any
tumor
type.

Adequacy
of
the
Dose
Levels
Tested
In
males,
the
high
dose
[
125
mg/
kg/
day]
did
not
cause
any
adverse
effect
on
survival,
body
weight
decrements,
clinical
signs,
or
alterations
in
hematology
but
did
increase
the
absolute
and
relative
kidney
weights
and
induce
histopathological
lesions
in
the
kidneys.
In
the
original
design
of
this
study
when
male
mice
were
fed
higher
doses
[
150
and
300
mg/
kg/
day],
the
study
had
to
be
aborted
after
419
days
due
to
significant
decrements
in
body­
weight
gain
[
7%
to
11%
at
150
mg/
kg/
day
and
20%
to
27%
at
300
mg/
kg/
day].
The
CPRC
concluded
that
"
it
is
apparent
that
for
males,
while
a
dose
of
300
mg/
kg/
day
was
definitely
excessive,
150
mg/
kg/
day
was
also
approaching,
and
possibly
exceeding
an
adequate
dose."
Therefore,
based
on
the
bodyweight
data
of
the
"
aborted"
study
and
the
renal
effects
[
dose­
related
increases
in
absolute/
relative
kidney
weights
and
renal
lesions]
seen
at
125
mg/
kg/
day
in
the
present
study,
it
was
determined
that
the
high
dose
tested
was
adequate
to
assess
the
carcinogenicity
of
2,4­
D
in
B6C3F1
mice.

3.
Classification
of
Carcinogenic
Potential:
In
accordance
with
the
Draft
Carcinogen
Risk
Assessment
Guidelines
[
1996],
the
HED
Carcinogenicity
Peer
Review
Committee
[
CPRC]
classified
2,4­
D
acid
as
a
Group
D
chemical
[
Not
Classifiable
as
to
Human
Carcinogenicity]
[
TXR
#
0050017].

IV.
MUTAGENICITY
The
HIARC
concluded
that
there
is
not
a
concern
for
mutagenicity
resulting
from
exposure
to
2,4­
D
or
its
amine
salts
and
esters.

Ames
tests,
with
and
without
metabolic
activation,
were
negative
consistently.
Negative
results
were
also
observed
in
a
mouse
bone
marrow
micronucleus
assay
and
in
UDS
assays
in
rat
hepatocytes.
Conflicting
results
were
obtained
in
Drosophila;
positive
effects
were
observed
in
larvae,
and
negative
results
were
observed
in
adults
after
feeding
or
injection.
Conflicting
results
were
also
seen
in
in
vitro
mammalian
cell
cytogenetics
assays:
2,4­
dichlorophenoxyacetic
acid
was
negative
for
structural
chromosomal
damage
up
to
an
insoluble
level
but
positive
in
the
presence
of
metabolic
activation
at
high
doses.
The
positive
evidence,
however,
tends
to
be
weak
and
generally
not
supported
by
the
data
from
in
vivo
cytogenetic
assays.
Overall,
the
pattern
of
responses
observed
both
in
in
vivo
and
in
vitro
tests
indicates
that
2,4­
dichlorophenoxyacetic
acid
was
not
mutagenic,
although
some
cytogenetic
effects
were
observed.
42
V.
HAZARD
CHARACTERIZATION
The
herbicide
2,4­
dichlorophenoxyacetic
acid
[
2,4­
D;
CAS
No.
94­
75­
7]
is
a
white
powder.
The
empirical
formula
is
C
8
H
6
Cl
2
O
3
and
the
molecular
weight
is
221.04.
Other
parameters
include:
melting
point
[
140.5

C],
boiling
point
[
130

C
at
1
mm
Hg
(
isopropyl
ester);
water
solubility
900
mg/
L
at
25

C
(
acid);
vapor
pressure
0.02
mPa
at
25

C
(
acid);
partition
coefficient
2.81.
2,4­
D
is
used
on
grass­
like
crops
and
under
tree
canopies
to
kill
broadleaf
weeds.
In
plant
crops,
2,4­
D
is
regulated
as
parent
only.
In
animal
commodities,
both
parent
and
the
2,4­
dichlorophenol
metabolite
require
regulation.
This
latter
metabolite
was
included
in
the
drinking
water
exposure
assessment
as
a
result
of
the
recent
section
18
dietary
exposure
and
risk
analysis.
The
herbicide
is
a
plant
auxin;
therefore,
residues
are
partially
systemic.
When
applied
to
plants,
2,4­
D
is
absorbed
through
the
roots
and
leaves
within
4­
6
hours
and
distributed
in
the
plant
via
the
phloem
[
WHO,
1984].
Once
absorbed,
2,4­
D
selectively
eliminates
broadleaf
plants
[
due
to
their
larger
leaf
area
and
hence,
greater
absorption]
by
mimicking
the
effect
of
auxins
[
i.
e.,
plant
growth­
regulating
hormones]
and
stimulating
growth,
rejuvenating
old
cells,
and
overstimulating
young
cells,
leading
to
an
abnormal
growth
pattern
and
death
in
some
plants
[
Mullison,
M.
T.
(
1987).
Environmental
Fate
of
Phenoxy
Herbicides.
Fate
of
Pesticides
in
the
Environment.
Publication
3320,
pages
121­
131,
California
Agricultural
Experiment
Station].

2,4­
D
and
its
amine
salts
and
esters
are
not
acutely
toxic
via
the
oral,
dermal,
and
inhalation
routes
of
exposure
[
Toxicity
Category
III],
with
the
exception
of
DEA,
which
shows
moderate
[
Toxicity
Category
II]
toxicity
via
the
oral
and
dermal
routes.
2,4­
D
and
its
amine
salts
and
esters
are
not
skin
irritants
[
Toxicity
Categories
III
and
IV]
and
none
is
a
skin
sensitizer.
The
acid
and
amine
forms
of
2,4­
D
show
severe
eye
irritation
[
Toxicity
Category
I]
and
the
ester
forms
show
irritation
clearing
in
7
days
or
less
[
Toxicity
Category
III].

The
metabolism
and
excretion
of
2,4­
D
have
been
investigated
in
a
number
of
species
including
humans.
In
general,
2,4­
D
undergoes
limited
metabolism
primarily
involving
minor
conjugation
of
the
parent
acid
that
is
then
excreted
in
the
urine.
No
detectable
metabolites
of
2,4­
D
have
been
reported
in
the
rat;
i.
e.,
only
the
parent
acid
is
found
in
rat
urine.
In
addition
to
2,4­
D
itself,
2,4­
D
conjugates
have
been
found
in
the
urine
of
dogs,
humans,
mice,
and
hamsters
following
oral
exposure.
The
mechanisms
responsible
for
the
renal
clearance
of
2,4­
D
have
been
investigated
in
several
species
also.
This
phenoxy
herbicide
is
actively
secreted
by
the
proximal
tubules
in
a
manner
similar
to
PAH,
and
this
mechanism
of
renal
clearance
for
2,4­
D
is
consistent
with
results
seen
with
other
phenoxy
acids.
It
has
been
suggested
that
the
observed
dose­
dependent
non­
linear
pharmacokinetics
of
2,4­
D
are
primarily
due
to
the
saturation
of
this
renal
secretory
transport
system.

Following
subchronic
oral
exposure
at
dose
levels
of
2,4­
D
at
or
above
the
threshold
of
saturation
for
renal
clearance,
the
primary
target
organs
are
the
eye
[
retinal
degeneration,
cataract
formation],
thyroid
[
increased
thyroid
weight,
increased
T3/
decreased
T4,
and
follicular
cell
hypertrophy],
kidney
[
brush
border
loss
in
proximal
tubule],
adrenals
[
hypertrophy],
and
ovaries/
testes
[
atrophy].
These
changes
are
also
observed
following
exposure
to
the
amine
salts
43
and
esters
of
2,4­
D.

Developmental
toxicity,
characterized
mainly
as
an
increased
incidence
of
skeletal
variations
in
the
rat,
was
observed
following
exposure
to
2,4­
D
and
its
amine
salts
and
esters.
Malformations
were
observed
only
at
dose
levels
that
were
at
or
above
the
threshold
of
saturation
of
renal
clearance.
Developmental
toxicity
was
not
observed
in
the
rabbit.
at
any
dose
level,
with
the
exception
of
an
increased
number
of
litters
with
fetuses
with
7th
cervical
ribs
following
exposure
to
DEA.

Reproductive
toxicity,
characterized
as
an
increase
in
gestation
length,
was
observed
following
exposure
to
2,4­
D
at
a
dose
level
above
the
threshold
of
saturation
of
renal
clearance.

Neurotoxicity
was
demonstrated
following
exposure
to
2,4­
D
at
relatively
high
dose
levels.
Clinical
signs
of
neurotoxicity
[
ataxia,
decreased
motor
activity,
myotonia,
prostration,
lateral
recumbency,
and
impaired/
loss
of
the
righting
reflex,
cold
to
the
touch]
were
observed
in
pregnant
rabbits
following
exposure
to
2,4­
D
and
its
amine
salts
and
esters.
Neuropathology
[
retinal
degeneration]
was
observed
following
2,4­
D
exposure
in
several
studies
in
female
rats.
Incoordination
and
slight
gait
abnormalities
(
forepaw
flexing
or
knuckling)
were
observed
following
acute
dosing
and
increased
forelimb
grip
strength
was
observed
following
chronic
exposure
to
2,4­
D
at
dose
levels
that
exceeded
the
threshold
of
saturation
of
renal
clearance.

2,4­
D
is
classified
as
a
Group
D
chemical
[
not
classifiable
as
to
human
carcinogenicity].
Based
on
the
overall
pattern
of
responses
observed
in
both
in
vitro
and
in
vivo
genotoxicity
tests,
2,4­
D
was
not
mutagenic,
although
some
cytogenic
effects
were
observed.

VI.
DATA
GAPS/
REQUIREMENTS
(
1)
developmental
neurotoxicity
study
in
the
rat;
(
2)
2­
generation
reproduction
study
with
special
emphasis
on
the
thyroid
and
immunotoxic
effects;
(
3)
subchronic
inhalation
study.
44
VII.
ACUTE
TOXICITY
Acute
Toxicity
of
2,4­
dichlorophenoxyacetic
acid
Guideline
No.
Study
Type
MRIDs
#
Results
Toxicity
Category
81­
1
Acute
Oral
00101605
LD
50
=
699
mg/
kg
III
81­
2
Acute
Dermal
00101596
LD
50
>
2000
mg/
kg
III
81­
3
Acute
Inhalation
00161660
LC
50
>
1.79
mg/
L
III
81­
4
Primary
Eye
Irritation
41125302
severe
eye
irritant
I
81­
5
Primary
Skin
Irritation
42232701
non­
irritating
IV
81­
6
Dermal
Sensitization
00161659
not
a
dermal
sensitizer
­

81­
8
Acute
Neurotoxicity
43115201
NOAEL
=
67
mg/
kg/
day
45
Table
2a.
Acute
Toxicity
Data
on
the
Amine
Salts
and
Esters
of
2,4­
Dichlorophenoxyacetic
Acid
Guideline
No.
Study
Type
%
MRID
#(
S)
Results
Toxicity
Category
870.1100
Acute
Oral
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
66.2
50.2
72.2
95.6
94.4
41920901
41642801
00252291
41413501
40629801
41209001
rat
LD50
=
910
mg/
kg
rat
LD50
=
433
mg/
kg
rat
LD50
=
2322/
1646
mg/
kg
rat
LD50
=
1220/
1074
mg/
kg
rat
LD50
=
866
mg/
kg
rat
LD50
=
896
mg/
kg
III
II
III
III
III
III
870.1200
Acute
Dermal
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
66.2
50.2
72.2
95.6
94.4
41920911
47016539
00252291
41413502
40629802
41209002
rabbits
LD50
>
2000
mg/
kg
rat
LD50
=
1122
mg/
kg

/
909
mg/
kg

rabbits
LD50
>
2000
mg/
kg
rabbits
LD50
>
2000
mg/
kg
rabbits
LD50
>
2000
mg/
kg
rabbits
LD50
>
2000
mg/
kg
III
II
III
III
III
III
870.1300
Acute
Inhalation
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
66.2
50.2
72.2
95.6
94.4
41986601
47016540
40085501
41957601
40629803
42605202
rat
LC50
>
3.5
mg/
L
rat
LC50
>
3.5
mg/
L
rat
LC50
=
3.8
mg/
L
rat
LC50
=
0.78
mg/
L
rat
LC50
=
4.6
mg/
L
rat
LC50
>
5.4
mg/
L
III
III
III
III
III
III
870.2400
Primary
Eye
Irritation
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
66.2
50.2
72.2
95.6
94.4
41920902
41642803
41920902
41413504
41125302
41413504
severe
eye
irritant
severe
eye
irritant
severe
eye
irritant
severe
eye
irritant
irritation
clearing
in
7
days
or
less
irritation
clearing
in
7
days
or
less
I
I
I
I
III
III
870.2500
Primary
Skin
Irritation
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
66.2
50.2
72.2
95.6
94.4
41920903
41642804
41920903
41413505
40629805
41413505
slight
skin
irritant
not
a
skin
irritant
slight
skin
irritant
moderate
skin
irritant
very
mild
irritant
not
a
skin
irritant
IV
IV
IV
III
IV
IV
870.2600
Dermal
Sensitization
DEA
salt
DMA
salt
IPA
salt
TIPA
salt
BEE
ester
EHE
ester
73.09
96.9
50.2
72.2
95.6
94.4
41920904
41642805
00401069
41413506
40629806
41233701
not
a
dermal
sensitizer
not
a
dermal
sensitizer
not
a
dermal
sensitizer
not
a
dermal
sensitizer
not
a
dermal
sensitizer
not
a
dermal
sensitizer
46
VIII.
SUMMARY
OF
TOXICOLOGY
ENDPOINT
SELECTION
Summary
of
Toxicological
Dose
and
Endpoints
for
Exposure
Scenario
Dose
Used
in
Risk
Assessment,
UF
Special
FQPA
SF
and
Level
of
Concern
for
Risk
Assessment
Study
and
Toxicological
Effects
Acute
Dietary
(
Females
13­
50
years
of
age)
NOAEL
=
25
mg/
kg/
day
UF
=
1000
Acute
RfD
=
0.025
mg/
kg/
day
FQPA
SF
=
1X
aPAD
=
acute
RfD(
0.025)
FQPA
SF
=
0.025
mg/
kg/
day
rat
developmental
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
skeletal
malformations
and
skeletal
variations
Acute
Dietary
(
General
population
including
infants
and
children)
NOAEL
=
67
mg/
kg/
day
UF
=
1000
Acute
RfD
=
0.067
mg/
kg/
day
FQPA
SF
=
1X
aPAD
=
acute
RfD
(
0.067)
FQPA
SF
=
0.067
mg/
kg/
day
acute
neurotoxicity
study
in
rats
LOAEL
=
227
mg/
kg/
day
based
on
gait
abnormalities
Chronic
Dietary
(
All
populations)
NOAEL=
5
mg/
kg/
day
UF
=
1000
Chronic
RfD
=
0.005
mg/
kg/
day
FQPA
SF
=
1X
cPAD
=
chronic
RfD
(
0.005)
FQPA
SF
=
0.005
mg/
kg/
day
rat
chronic
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
.

Short­
Term
Incidental
Oral
(
1­
30
days)
NOAEL=
25
mg/
kg/
day
Residential
LOC
for
MOE
=
1000
Occupational
=
NA
rat
developmental
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
maternal
body­
weight
gain
and
skeletal
malformations
and
skeletal
variations
Exposure
Scenario
Dose
Used
in
Risk
Assessment,
UF
Special
FQPA
SF
and
Level
of
Concern
for
Risk
Assessment
Study
and
Toxicological
Effects
47
Intermediate­
Term
Incidental
Oral
(
1­
6
months)
NOAEL
=
15
mg/
kg/
day
Residential
LOC
for
MOE
=
1000
Occupational
=
NA
subchronic
oral
toxicity
­
rat
LOAEL
=
100
mg/
kg/
day
based
on
decreased
body
weight/
bodyweight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T3
(
females)
and
T4
(
both
sexes)]
parameters,
and
cataract
formation.

Short­
Term
Dermal
(
1
to
30
days)
Oral
study
NOAEL=
25
mg/
kg/
day
(
dermal
absorption
rate
=
5.8%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
rat
developmental
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
maternal
body­
weight
gain
and
skeletal
malformations
and
skeletal
variations
Intermediate­
Term
Dermal
(
1
to
6
months)
Oral
study
NOAEL
=
15
mg/
kg/
day
(
dermal
absorption
rate
=
5.8%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
subchronic
oral
toxicity
­
rat
LOAEL
=
100
mg/
kg/
day
based
on
decreased
body
weight/
bodyweight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T3
(
females)
and
T4
(
both
sexes)]
parameters,
and
cataract
formation.

Long­
Term
Dermal
(>
6
months)
Oral
study
NOAEL=
5
mg/
kg/
day
(
dermal
absorption
rate
=
5.8%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
rat
chronic
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
.

Short­
Term
Inhalation
(
1
to
30
days)
Oral
study
NOAEL=
25
mg/
kg/
day
(
inhalation
absorption
rate
=
100%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
rat
developmental
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
maternal
body­
weight
gain
and
skeletal
malformations
and
skeletal
variations
Exposure
Scenario
Dose
Used
in
Risk
Assessment,
UF
Special
FQPA
SF
and
Level
of
Concern
for
Risk
Assessment
Study
and
Toxicological
Effects
48
Intermediate­
Term
Inhalation
(
1
to
6
months)
Oral
study
NOAEL
=
15
mg/
kg/
day
(
inhalation
absorption
rate
=
100%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
subchronic
oral
toxicity
­
rat
LOAEL
=
100
mg/
kg/
day
based
on
decreased
body
weight/
bodyweight
gain,
alterations
in
some
hematology
[
decreased
platelets
(
both
sexes)]
and
clinical
chemistry
[
decreased
T3
(
females)
and
T4
(
both
sexes)]
parameters,
and
cataract
formation.

Long­
Term
Inhalation
(>
6
months)
Oral
study
NOAEL=
5
mg/
kg/
day
(
inhalation
absorption
rate
=
100%)
Residential
LOC
for
MOE
=
1000
Occupational
LOC
for
MOE
=
100
rat
chronic
toxicity
study
LOAEL
=
75
mg/
kg/
day
based
on
decreased
body­
weight
gain
(
females)
and
food
consumption
(
females),
alterations
in
hematology
[
decreased
RBC,
HCT,
and
HGB
(
females),
platelets
(
both
sexes)]
and
clinical
chemistry
parameters
[
increased
creatinine
(
both
sexes),
alanine
and
aspartate
aminotransferases
(
males),
alkaline
phosphatase
(
both
sexes),
decreased
T4
(
both
sexes),
glucose
(
females),
cholesterol
(
both
sexes),
and
triglycerides
(
females)],
increased
thyroid
weights
(
both
sexes
at
study
termination),
and
decreased
testes
and
ovarian
weights
.

Cancer
(
oral,
dermal,
inhalation)
Classification:
Group
D
[
not
classifiable
as
to
human
carcinogenicity]

UF
=
uncertainty
factor,
FQPA
SF
=
Special
FQPA
safety
factor,
NOAEL
=
no
observed
adverse
effect
level,
LOAEL
=
lowest
observed
adverse
effect
level,
PAD
=
population
adjusted
dose
(
a
=
acute,
c
=
chronic),
RfD
=
reference
dose,
MOE
=
margin
of
exposure,
LOC
=
level
of
concern,
NA
=
Not
Applicable
NOTE:
The
Special
FQPA
Safety
Factor
recommended
by
the
HIARC
assumes
that
the
exposure
databases
(
dietary
food,
drinking
water,
and
residential)
are
complete
and
that
the
risk
assessment
for
each
potential
exposure
scenario
includes
all
metabolites
and/
or
degradates
of
concern
and
does
not
underestimate
the
potential
risk
for
infants
and
children.
ATTACHMENT
A
49
I.
Introduction
The
Registrant's
2,4­
D
Task
Force
[
MRID
45861201]
assessed
the
relevance
of
dog
data
for
evaluation
of
human
health
risk
from
exposure
to
2,4­
D
and
related
organic
acids.
The
Registrant's
2,4­
D
Task
Force
contends
that
the
"
unique"
sensitivity
of
the
dog
to
2,4­
D
[
and
other
phenoxy
acids]
is
due
primarily
to
the
dog's
low
capacity,
relative
to
other
species,
to
excrete
organic
acids
and
thus
is
not
a
suitable
surrogate
for
humans.
This
decreased
capacity
of
the
dog
is
associated
with
organic
acids
that
share
common
pharmacokinetic
properties;
e.
g.,
(
1)
extensive
but
reversible
plasma
protein
binding;
(
2)
weak
acids
that
are
highly
ionized
at
physiological
pH;
(
3)
limited
metabolism
of
the
parent
acid;
and
(
4)
urinary
excretion
primarily
involving
a
saturable
active
secretion.
Thus,
it
was
recommended
that,
based
on
pharmacokinetic
arguments,
the
2,4­
D
rodent
database
would
be
significantly
more
relevant
for
extrapolation
of
risk
to
humans
than
that
of
the
dog.

II.
Background
on
Renal
Excretion
and
Allosteric
Scaling
Renal
Excretion.

The
excretion
of
organic
acids
in
the
urine
is
the
net
result
of
filtration,
secretion,
and
reabsorption.
Renal
clearance
mechanisms
for
organic
acids
are
ubiquitous
in
mammalian
species,
although
qualitative
differences
between
species
may
account
for
observed
discrepancies
in
clearance
capacity.
For
organic
acids,
like
2,4­
D,
that
are
eliminated
primarily
unmetabolized
in
the
urine,
at
low
dose
levels,
the
rate
of
urinary
excretion
is
directly
proportional
to
the
plasma
drug
concentration.
The
proportionality
constant
being
compound
and
species
dependent.
The
volume
of
plasma
that
is
cleared
of
a
compound
into
the
urine
over
time
is
called
renal
clearance
[
mL/
hr].
A
reduction
in
the
renal
clearance
of
an
organic
acid
will
result
in
slower
elimination
from
the
body,
leading
to
higher
concentrations
of
the
compound
in
blood.

Allosteric
Scaling.

It
is
well
established
in
biology
that,
in
many
cases,
if
the
log
of
a
biological
parameter
(
e.
g.
water
intake,
basal
O
2
consumption,
creatinine
clearance
etc)
is
plotted
against
the
log
of
body
weight
for
several
species,
a
straight
line
is
obtained.
This
relationship
between
a
biological
parameter
(
Y)
and
body
weight
(
W)
is
said
to
be
an
allometric
relationship,
expressed
by
the
power
equation
Y
=
aWb
.
A
plot
log
Y
vs.
log
W
for
several
species
results
in
a
straight
line
and
is
called
an
allometric
plot;
the
values
of
w
and
a
in
the
power
equation
are
dependant
on
the
parameter
being
studied.
If
data
for
a
biological
parameter
are
listed
for
several
species,
an
allometric
plot
of
the
data
would
allow
one
to
predict
the
value
of
the
parameter
for
an
unlisted
species,
if
its
bodyweight
is
known.
Significant
deviations
from
the
predicted
value
may
then
be
attributed
to
particular
physiological
idioisyncrasies
of
the
unlisted
species.

The
allometric
approach
has
been
used
(
Timchalk,
1998)
to
compare
the
pharmacokinetic
ATTACHMENT
A
50
parameters
of
2,4­
D
and
other
organic
acid
in
the
dog
and
other
species.
Allometric
plots
of
pharmacokinetic
parameters
for
2,4­
D
and
other
acids
were
obtained
and
evaluated.
It
was
concluded
that
with
respect
to
2,4­
D,
2,
4,
5­
T,
and
other
organic
acids
and
excretion
by
the
dog,
the
data
show
the
dog
to
have
a
decreased
renal
clearance
and
longer
T1/
2
relative
to
that
predicted
from
the
allometric
relationship,
whereas
humans,
rats,
mice,
and
other
species
all
fit
the
relationship
[
this
is
illustrated
below
using
data
on
2,4­
D
and
triclopyr].

III.
Allometric
Plots
with
Triclopyr
and
2,4­
D
From
studies
on
triclopyr
[
also
an
organic
acid],
there
is
good
evidence
for
a
high­
affinity,
lowcapacity
active­
secretory
process
that
was
saturated
by
low
plasma
triclopyr
concentrations.
As
plasma
triclopyr
concentrations
increased,
tubular
reabsorption
begins
to
exceed
secretion,
resulting
in
decreased
renal
clearance.
In
comparisons
among
several
species,
the
volume
of
distribution,
normalized
for
body
weight,
was
constant
across
all
species.
While
clearance
and
half­
life
could
be
allometrically
scaled
to
body
weight
for
the
rat,
monkey,
and
human,
the
dog
had
a
much
slower
clearance
and
longer
half­
life
for
triclopyr
elimination
than
predicted
allometrically.
The
data
demonstrate
that
the
pharmacokinetics
of
triclopyr
in
the
dog
are
markedly
different
than
the
rat,
monkey,
and
human.

To
illustrate,
a
comparison
of
triclopyr
volume
of
distribution
[
Vd],
clearance
[
Cl],
and
half­
life
vs
body
weight
[
W]
for
rat,
monkey,
dog,
human,
and
mouse
is
shown
below.
The
volume
of
distribution
for
triclopyr
was
well
described
for
all
species
by
the
equation
V
d
=
0.08
W1.09
[
Figure
7A].
The
relationship
between
clearance
[
mL/
hr]
and
body
weight
for
the
rat,
monkey,
and
human
was
well
described
by
the
equation
Cl
=
86
W0.78
[
Figure
7B].
The
clearance
of
triclopyr
in
the
dog
was
clearly
lower
than
in
rat,
monkey,
and
human
and
was
not
adequately
described
by
scaling
to
other
species.
Similarly,
analysis
of
elimination
half­
life
vs
body
weight
indicated
that
the
dog
was
an
outlier
[
Figure
7C].
The
relationship
between
half­
life
and
body
weight
for
the
other
species
was
described
by
the
equation
t
1/
2
=
4.68
W0.06.
ATTACHMENT
A
51
Figure
.
Triclopyr
allometric
relationship
between
body
weight
and
(
A)
volume
of
distribution
Vd
(
all
species);
(
B)
renal
clearance
Clr
(
excluding
dog);
and
(
C)
elimination
half­
life
t1/
2
(
excluding
dog).
This
figure
was
adapted
from
Timchalk
and
Nolan
(
1997).

Similarly,
a
comparison
of
2,4­
D
volume
of
distribution
[
V
d],
clearance
[
Cl],
and
half­
life
vs
body
weight
[
W]
for
rat,
dog,
human,
pig,
calf,
and
mouse
is
shown
below.

The
volume
of
distribution
for
2,4­
D
was
well
described
for
all
species
by
the
equation
Vd
=
0.12W1.11
[
Figure
2A].
In
all
species,
the
Vd
was
relatively
small
and
equivalent
to
the
volume
of
blood
and
extracellular
water.
The
relationship
between
renal
clearance
(
mL
hr­
1)
and
body
water
for
mice,
rats,
pigs,
calves,
and
humans
was
well
described
by
the
equation
Clr
=
37
W0.86]
[
Figure
2B].
The
clearance
of
2,4­
D
in
the
dog
was
clearly
lower
than
in
all
other
species
and
was
not
adequately
described
by
scaling.
Likewise,
analysis
of
elimination
half­
life
vs
body
weight
indicated
that
the
dog
was
an
outlier.
If
the
dog
was
excluded,
the
relationship
for
the
other
species
was
described
by
the
equation
t
1/
2
=
2.14
W0.27
[
Figure
2C].
ATTACHMENT
A
52
Figure
2.
2,4­
D
allometric
relationship
between
body
weight
and
(
A)
volume
of
distribution
Vd
(
all
species);
(
B)
renal
clearance
Clr
(
excluding
dog);
and
(
C)
elimination
half­
life
t1/
2
(
excluding
dog).
Note:
for
rat
and
dog
there
were
3
data
sets.
Rat:
3
sets
at
5
mg/
kg;
Dog:
2
sets
at
5
and
1
at
1
mg/
kg.

IV.
Conclusion.

The
decreased
relative
capacity
of
the
dog
to
eliminate
organic
acids
results
in
higher
blood
levels
in
the
dog
relative
to
those
found
in
the
rat
and
consequently,
effects
are
seen
at
lower
dose
levels
in
the
dog
than
in
the
rat.
Although
the
precise
mechanism
for
this
difference
is
not
known,
an
evaluation
of
the
data
on
the
organic
acid
triclopyr
suggests
increased
reabsorption
by
the
dog.
For
2,4­
D,
the
most
likely
mechanism
[
according
to
the
registrant]
is
a
low
capacity
to
actively
secrete
2,4­
D
from
the
kidney,
although
reabsorption
of
2,4­
D
cannot
be
excluded
as
a
potential
mechanism.
While
there
is
definitely
substantial
evidence
that
the
dog
has
a
lower
clearance
capacity
for
organic
acids
than
what
is
predicted
using
allometric
scaling,
although
the
mechanism
to
explain
the
difference
is
not
clear,
it
is
not
considered
an
unique,
species­
specific,
mechanism
and
therefore,
the
data
on
the
dog
cannot
be
ruled
out.
However,
the
difference
in
the
elimination
pattern
among
dogs
and
other
mammalian
species
persuaded
HIARC
that
the
rat
was
a
better
predictor
than
the
dog
of
the
potential
toxicity
of
2,4­
D
to
man.
ATTACHMENT
A
53
Additional
information
considered:

(
1)
Both
the
dog
and
human
excrete
2,4­
D
conjugate
in
addition
to
2,4­
D
acid,
whereas
the
rat
excretes
only
2,4­
D
acid.

(
2)
Variation
in
excretion
of
2,4­
D
observed
among
human
subjects
[
males]
may
be
due
to
decreased
capacity
to
excrete
organic
acids
and/
or
differences
in
reabsorption
from
the
tubular
filtrate.

(
3)
Data
indicate
that
there
is
a
sex­
dependent
difference
in
the
deposition
of
2,4­
D
in
Sprague­
Dawley
rats
[
male
rats
demonstrate
a
greater
ability
to
clear
2,4­
D
relative
to
females]
and
the
human
pharmacokinetic
data
available
on
2,4­
D
are
for
males
only.

(
4)
In
the
recently­
submitted
study,
rats
and
dogs
of
both
sexes
were
administered
either
5
or
50
mg/
kg
[
orally]
in
side­
by­
side
comparison
of
the
pharmacokinetics,
metabolism,
and
excretion
of
2,4­
D.
The
pharmacokinetics
of
2,4­
D
in
dogs
were
essentially
proportional
in
relation
to
dose
level,
which
may
indicate
that
the
clearance
mechanism
is
saturated
at
both
dose
levels.
In
the
rat,
the
pharmacokinetics
were
not
proportional.
There
was
a
disproportional
increase
in
the
area
under
the
curve
[
AUC]
in
the
rat
with
respect
to
the
increase
in
dose
level
[
a
10­
fold
increase
in
dose
resulted
in
up
to
a
59­
fold
increase
in
AUC
and

19­
fold
increase
in
the
C
max
in
plasma],
suggesting
that
the
clearance
mechanism
was
saturated
at
the
high­
dose
level
[
50
mg/
kg]
in
the
rat.

(
5)
In
the
rat,
effects
are
observed
at
dose
levels
greater
than
50
mg/
kg,
or
when
the
clearance
mechanism
has
been
saturated,
which
also
occurs
in
the
dog
but
at
a
lower
dose
level
[
5
mg/
kg].

(
6)
The
Task
Force's
opinion
that
the
RfD
decision
on
triclopyr
is
a
precedent
for
not
utilizing
the
dog
data
in
risk
assessment
is
in
error.

In
a
letter
dated
2/
4/
03,
the
Industry
Task
Force
II
on
2,4­
D
Research
Data
concludes
that
the
use
of
the
rat
in
preference
to
the
dog
"
is
not
without
precedent
within
the
Agency
for
other
renallyexcreted
organic
acid
herbicides."
Reference
is
made
to
the
October
21,
1996
RfD
Committee
memo
on
triclopyr
and
their
reconsideration
of
the
Reference
Dose
[
HED
Document
No.
012093].
The
Committee
concluded
that
"
the
biological/
toxicological
significance
of
the
kidney
effects
in
the
one­
year
dog
study
is
questionable
and
they
appear
to
be
the
result
of
physiological
adaptation
and
may
not
be
of
toxicological
significance."
[
emphasis
added].
It
was
also
concluded
by
the
Committee
that
the
dog
is
not
the
appropriate
animal
model
for
kidney
toxicity
testing
of
triclopyr,
although
no
specific
explanation
was
offered
for
this
latter
conclusion.
It
appears
that
since
the
effects
observed
in
the
dog
were
considered
adaptative
[
not
toxic],
the
study/
dog
was
not
considered
appropriate.

The
effects
observed
in
the
triclopyr
dog
study
were
increases
in
serum
creatinine
and
blood
urea
nitrogen.
It
appears
that
physiological
adaptation
was
the
reason
for
concluding
the
dog
to
be
ATTACHMENT
A
54
inappropriate
for
use
in
setting
the
RfD,
not
an
unique
sensitivity
or
lower
capacity
to
excrete
organic
acids,
which
is
the
argument
presented
by
the
Task
Force
for
2,4­
D.
