1
Summary
of
the
2,4­
DB
Risk
Assessment
Uses
°
2,4­
DB
is
a
selective
herbicide
in
the
phenoxy
family
used
for
the
control
of
annual
and
perennial
broadleaf
weeds
in
alfalfa,
peanuts,
soybeans,
mint,
and
trefoil.

°
2,4­
DB
end­
use
products
are
formulated
either
as
soluble,
emulsifiable,
or
flowable
concentrates
and
either
ground
or
aerial
applications
may
be
made.

°
Total
annual
domestic
usage
of
herbicides
2,4­
DB
and
2,4­
DB­
DMAS
(
the
dimethylamine
salt)
is
approximately
375,000
pounds
active
ingredient.
In
terms
of
pounds
of
active
ingredient,
the
majority
of
use
is
on
peanuts
(
30%).
In
terms
of
acreage
treated,
the
only
crop
with
significant
acreage
treated
is
peanuts
(
35%).

Health
Effects
°
Liver
toxicity
in
chronic
and
subchronic
studies
included
increased
liver
weights,
changes
in
clinical
chemistries,
and
visable
changes.

°
Kidney
toxicity
in
dog
and
rat
studies
included
changes
in
kidney
weights,
changes
in
clinical
chemistries,
microscopic
changes,
and
changes
in
blood
parameters.

°
Marked
dermal
and
eye
irritation
was
observed
with
2,4­
DB­
DMA
(
the
acid)

°
Developmental
effects
in
rats
occurred
at
doses
two­
fold
higher
than
the
doses
which
caused
maternal
toxicity,
and
included
decreased
fetal
body
weight,
skeletal
variations
and
malformations,
early
resorptions,
and
eye
and
heart
deformations.

°
Offspring
toxicity
in
a
reproduction
study
included
mortality,
decreased
mean
litter
weight,
and
necropsy
findings.
Parental
toxicity
occurred
at
the
same
does
as
the
offspring
toxicity.

°
2,4­
DB
has
properties
that
could
indicate
Endocrine
Disrupting
Chemical
(
EDC)
properties.
These
include
decreased
body
weights
and
altered
liver
function
in
mice
exposed
to
this
herbicide.
When
the
appropriate
screening
and/
or
testing
protocols
being
considered
under
the
Agency's
Endocrine
Disrupting
Screening
Program
(
EDSP)
have
been
developed,
2,4­
DB
may
be
subjected
to
additional
screening
and/
or
testing
to
better
characterize
effects
related
to
endocrine
disruption.

°
2,4­
DB
is
not
considered
to
be
a
neurotoxicant.
2
°
2,4­
DB
is
not
considered
to
be
carcinogenic
Risks
Dietary
Risks
from
Food
°
Both
acute
dietary
risk
and
chronic
dietary
risk
results
are
below
the
Agency's
level
of
concern.

Drinking
Water
Assessment
°
2,4­
DB
is
mobile
in
mineral
soils.
Because
of
a
lack
of
monitoring
data
for
2,4­
DB,
estimated
environmental
concentrations
were
established
using
PRZM/
EXAMS
and
SCIGROW
modeling.

°
The
major
route
of
dissipation
for
2,4­
DB
was
transformation
to
2,4­
D
acid
and
2,4­
D
phenol.
Because
annual
use
of
2,4­
DB
is
less
than
1%
of
the
annual
use
of
2,4­
D,
the
drinking
water
assessment
is
addressed
in
the
2,4­
D
RED.

°
The
concentrations
of
2,4­
DB
estimated
in
water
were
less
than
the
Drinking
Water
Levels
of
Comparison.

Residential
Risks
°
There
are
no
residential
uses
for
2,4­
DB
and
2,4­
DB­
DMA.

Aggregate
Risk
°
There
are
no
residential
uses
for
2,4­
DB
and
2,4­
DB­
DMA;
therefore,
aggregate
risk
includes
only
the
food
and
drinking
water
risks
described
above.

°
There
are
no
concerns
for
aggregate
exposure
to
2,4­
DB
in
food
and
drinking
water.

Occupational
Risk
°
Chronic
occupational
exposures
are
not
expected
to
occur
because
2,4­
DB
is
applied
only
once
or
twice
during
the
growing
season
and
dissipates
rapidly.

°
Margins
of
Exposure
(
MOEs)
for
handler
exposures
were
calculated
for
short­
term
inhalation
exposures
and
intermediate­
term
combined
dermal
and
inhalation
exposures.
All
of
the
short­
term
MOEs
exceed
100
at
baseline.
All
of
the
intermediate­
term
3
mixer/
loader
combined
MOEs
exceed
100
if
a
single
layer
of
PPE
(
i.
e.
baseline
clothing
and
with
chemical
resistant
gloves)
is
worn.
The
intermediate­
term
MOEs
for
applicators
exceed
100
with
baseline
PPE.

°
2,4­
DB­
DMA
is
a
severe
eye
irritant
and
eye
protection
is
recommended.

°
Post­
application
exposures
can
occur
when
workers
enter
fields
recently
treated
with
2,4­
DB
and
2,4­
DB­
DMA.
Post­
application
inhalation
exposures
are
not
likely
to
occur
because
of
the
low
vapor
pressure
(
7.1e­
07
mm
Hg
at
23.6
°
)
.
All
MOEs
for
postapplication
risk
are
above
100
on
Day
0
which
indicates
that
the
risks
are
not
of
concern.

°
MOEs
for
post­
application
exposure
exceeded
100
on
day
0.

Ecological
Risks
Risk
to
Terrestrial
Organisms
°
Based
on
seedling
emergence,
acute
non­
endangered
and
endangered
Species
Risk
Presumption
Categories
exceed
the
Agency's
level
of
concern
for
terrestrial
plants
using
the
highest
application
rate
for
alfalfa,
soybeans,
and
peanuts.

°
Acute
Levels
of
Concern
(
LOCs)
for
small
birds
are
exceeded
based
on
avian
oral
gavage
studies.
The
Agency's
Restricted
Use
Level
of
Concern
is
exceeded
for
small
birds
feeding
on
tall
grass
and
broadleaf
plants/
insects.
However,
potential
risks
to
birds
based
on
dietary
feeding
studies
will
likely
be
low.

°
Mammalian
restricted
use,
endangered
species
LOCs,
and
chronic
LOCs
for
small
mammals
are
exceeded
when
the
highest
application
rates
are
applied
to
alfalfa.
In
addition,
endangered
species
LOC
exceedances
occur
for
uses
on
peanuts
and
soybeans.

°
The
potential
risk
to
pollinators
and
beneficial
insects
is
considered
low.

Risk
to
Aquatic
Organisms
°
The
Agency's
acute
LOCs
are
exceeded
for
endangered
freshwater
fish.

°
Acute
LOC
s
were
not
exceeded
for
aquatic
non­
vascular
plants.

°
Freshwater
invertebrates
are
not
likely
to
be
at
potential
risk
for
all
application
scenarios.

°
2,4­
DB
rapidly
degrades
to
2,4­
D
in
aquatic
environments,
and
is
characterized
as
slightly
toxic
to
freshwater
fish.
Potential
risks
from
2,4­
DB's
degradation
to
2,4­
D
in
the
environment
is
summarized
and
addressed
in
2,4­
D's
Registration
Eligibility
Decision
4
Science
Chapter.

°
No
data
were
available
to
assess
the
risks
to
estuarine/
marine
fish
and
invertebrates.

Risk
to
Endangered
Species
°
The
preliminary
risk
assessment
for
endangered
species
indicates
that
2,4­
DB
exceeds
the
endangered
species
LOCs
for
the
following
organisms
when
exposed
to
certain
application
scenarios:
freshwater
fish,
small
and
medium
sized
mammals,
small
and
medium­
sized
birds,
and
non­
target
terrestrial
plants.
