OVERVIEW
OF
HEXAZINONE
RISK
ASSESSMENT
Introduction
This
document
summarizes
EPA's
human
health
findings
and
conclusions
for
the
herbicide
hexazinone,
as
presented
fully
in
the
documents:
HED
Chapter
for
the
Hexazinone
Tolerance
Reassessment
Eligibility
Decision,
dated
June
5,
2002,
and
Tier
I
Estimated
Environmental
Concentrations
of
Hexazinone,
dated
April
16,
2002
and
addenda.
The
purpose
of
this
overview
is
to
assist
the
reader
in
better
understanding
the
conclusions
reached
in
the
tolerance
reassessment
decision
by
identifying
the
key
features
and
findings
of
the
risk
assessment.
This
overview
was
developed
in
response
to
comments
and
requests
from
the
public,
which
indicated
that
the
risk
assessments
were
difficult
to
understand,
that
they
were
too
lengthy,
and
that
it
was
not
easy
to
compare
the
assessments
for
different
chemicals
due
to
the
use
of
different
formats.

The
Federal
Food,
Drug,
and
Cosmetic
Act
(FFDCA),
as
amended
by
the
Food
Quality
Protection
Act
(FQPA)
of
1996,
requires
EPA
to
review
all
the
tolerances
for
registered
chemicals
in
effect
on
or
before
the
date
of
the
enactment
of
FQPA.
In
reviewing
these
tolerances,
the
Agency
must
consider,
among
other
things,
aggregate
risks
from
non­
occupational
sources
of
pesticide
exposure,
whether
there
is
increased
susceptibility
to
infants
and
children,
and
the
cumulative
effects
of
pesticides
with
a
common
mechanism
of
toxicity.
The
tolerances
are
considered
reassessed
once
the
safety
finding
has
been
made
or
a
revocation
occurs.
A
Reregistration
Eligibility
Decision
(RED)
for
hexazinone
was
completed
in
September
1994,
prior
to
FQPA
enactment;
therefore,
it
needed
to
be
updated
to
consider
the
provisions
of
the
Act.

FQPA
stipulates
that
when
determining
the
safety
of
a
pesticide
chemical,
EPA
shall
base
its
assessment
of
the
risk
posed
by
the
chemical
on,
among
other
things,
available
information
concerning
the
cumulative
effects
to
human
health
that
may
result
from
dietary,
residential,
or
other
nonoccupational
exposure
to
other
substances
that
have
a
common
mechanism
of
toxicity.
The
reason
for
consideration
of
other
substances
is
due
to
the
possibility
that
low­
level
exposures
to
multiple
chemical
substances
that
cause
a
common
toxic
effect
by
a
common
mechanism
could
lead
to
the
same
adverse
health
effect
as
would
a
higher
level
of
exposure
to
any
of
the
substances
individually.
A
person
exposed
to
a
pesticide
at
a
level
that
is
considered
safe
may
in
fact
experience
harm
if
that
person
is
also
exposed
to
other
substances
that
cause
a
common
toxic
effect
by
a
mechanism
common
with
that
of
the
subject
pesticide,
even
if
the
individual
exposure
levels
to
the
other
substances
are
also
considered
safe.

EPA
did
not
perform
a
cumulative
risk
assessment
as
part
of
the
Tolerance
Reassessment
Decision
(TRED)
for
hexazinone
because
the
Agency
has
not
yet
initiated
a
comprehensive
review
to
determine
if
there
are
any
other
chemical
substances
that
have
a
mechanism
of
toxicity
common
with
that
of
hexazinone.
For
purposes
of
this
risk
assessment,
EPA
has
assumed
that
hexazinone
does
not
have
a
common
mechanism
of
toxicity
with
other
substances.
2
In
the
future,
the
registrant
may
be
asked
to
submit,
upon
EPA's
request
and
according
to
a
schedule
determined
by
the
Agency,
such
information
as
the
Agency
directs
to
be
submitted
in
order
to
evaluate
issues
related
to
whether
hexazinone
shares
a
common
mechanism
of
toxicity
with
any
other
substance
and,
if
so,
whether
any
tolerances
for
hexazinone
need
to
be
modified
or
revoked.
The
Agency
has
developed
a
framework
for
conducting
cumulative
risk
assessments
on
substances
that
have
a
common
mechanism
of
toxicity.
This
guidance
was
issued
on
January
16,
2002
(67
FR
2210­
2214)
and
is
available
from
the
OPP
Website
at:
http://
www.
epa.
gov/
pesticides/
trac/
science/
cumulative_
guidance.
pdf.

The
risk
assessment,
and
documents
pertaining
to
the
Agency's
report
on
FQPA
tolerance
reassessment
progress
and
risk
management
decision
for
hexazinone
are
available
on
the
Internet
at
http://
www.
epa.
gov/
pesticides/
reregistration/
status.
htm
and
in
the
public
docket
for
viewing.
The
Agency's
report
on
FQPA
tolerance
reassessment
progress
and
risk
management
decision
for
hexazinone
will
be
announced
in
the
Federal
Register.

Use
Profile
Herbicide:
Hexazinone
is
a
herbicide
registered
for
use
on
alfalfa,
blueberries,
pasture
and
range
grasses,
pineapple,
and
sugarcane.
It
is
also
registered
for
use
on
ornamental
plants,
forest
trees,
and
non­
crop
areas.
Hexazinone
works
through
the
inhibition
of
photosynthesis
and
is
used
to
control
a
variety
of
woody
plants
and
weed
species
including
geratum,
alder,
and
alexander
grass.
There
are
no
registered
residential
uses
of
hexazinone
products.

Formulations:
Hexazinone
is
formulated
as
a
dry
flowable
(DF),
emulsifiable
concentrate
(EC),
soluble
concentrate
(SC),
and
as
a
granular
(G).
The
range
of
percentage
of
active
ingredient
in
the
product
formulations
is
10­
90%.

Rates,
Methods
and
Timing
of
Application:
The
application
rates
range
from
0.5­
5.0
lbs.
active
ingredient
per
acre.
For
agricultural
uses,
the
number
of
applications
per
year
(or
season)
are
typically
limited
to
one.
For
forestry
uses,
the
number
of
applications
are
typically
1­
2
applications
over
a
20
to
40
year
period
in
the
East
and
1­
2
applications
over
a
60
to
80
year
period
in
the
West.
Hexazinone
formulations
may
be
applied
pre­
or
post­
emergence
by
layby,
broadcast,
directed
spray,
or
basal
soil
treatments
using
ground
or
aerial
equipment.
Hexazinone
is
mainly
an
early
season
use,
pre­
harvest
intervals
(PHIs)
range
from
180­
234
days
for
most
uses,
but
PHIs
are
30
and
45
days
for
alfalfa
and
blueberry,
respectively.

Use
Summary:
Approximately
975,000
pounds
of
hexazinone
active
ingredient
are
used
in
the
U.
S.
annually.

Major
Use
Sites
For
Hexazinone:
Alfalfa
represents
approximately
35%
of
the
total
hexazinone
usage
and
forestry
approximately
60%
of
the
usage.
None
of
the
crops
that
comprise
the
remaining
5%
of
use
represents
more
than
1%
of
the
total
usage.
3
Registrant:
Dupont
Human
Health
Risk
Assessment
Acute
Dietary
(Food)
Risk
(For
a
complete
discussion,
see
section
4.2.2
of
the
Human
Health
Risk
Assessment)

Because
no
effects
attributed
to
a
single
exposure
were
identified
for
the
general
population,
the
acute
dietary
exposure
and
risk
assessment
includes
females
13­
50
only.
Acute
dietary
risk
from
food
is
calculated
considering
what
is
eaten
in
one
day
(in
this
instance,
the
full
range
of
consumption
values
as
well
as
the
range
of
residue
values
in
food).
A
risk
estimate
that
is
less
than
100%
of
the
acute
Population
Adjusted
Dose
(aPAD)
(the
dose
at
which
an
individual
could
be
exposed
on
any
given
day
and
no
adverse
health
effects
would
be
expected)
does
not
exceed
the
Agency's
level
of
concern.
The
aPAD
is
the
reference
dose
(RfD)
adjusted
for
the
FQPA
Safety
Factor.
Table
1
presents
the
results
of
the
acute
dietary
(food)
exposure
and
risk
analysis
for
females
(13­
50
years
of
age).

Table
1.
Acute
Dietary
(Food)
Exposure
and
Risk
Population
Subgroup
Exposure
(mg/
kg/
day)
%
aPAD
Females
(13­
50
years)
0.003611
<1.0
°
The
acute
dietary
risk
estimate
does
not
exceed
the
aPAD.
The
acute
dietary
risk
estimate
for
females
13­
50
years
old
is
<1.0%
of
the
aPAD.

°
Because
the
toxic
endpoint
for
acute
dietary
exposure
concerns
in
utero
exposure,
the
risk
assessment
is
done
for
females
of
childbearing
age
(13­
50)
only.
For
the
female
(13­
50
years)
population
subgroup,
the
acute
No
Observed
Adverse
Effect
Level
(NOAEL)
of
400
mg/
kg/
day
was
established,
based
on
decreased
fetal
weight,
malformed
kidneys,
&
skeletal
abnormalities
in
a
rat
developmental
toxicity
study.
The
LOAEL
was
900
mg/
kg/
day.

°
An
uncertainty
factor
(UF)
of
100
was
applied
to
the
doses
selected
for
the
risk
assessment
to
account
for
interspecies
extrapolation
(10x)
and
intraspecies
variability
(10x).

°
For
acute
dietary
exposure,
the
FQPA
safety
factor
was
reduced
to
1X
since
the
toxicology
database
for
hexazinone
contains
acceptable
developmental
and
reproduction
studies
in
the
rat
and
rabbit,
and
there
is
no
quantitative
or
qualitative
evidence
of
increased
susceptibility
in
the
fetuses
or
offspring
in
these
studies.
The
risk
assessment
will
not
underestimate
the
exposure
and
risks
posed
by
hexazinone.
4
°
The
acute
RfD
for
females
13­
50:
400
mg/
kg/
day
(NOAEL)
÷
100
(UF)
=
4.0
mg/
kg/
day.
The
acute
PAD
for
females
13­
50:
4.0
mg/
kg/
day
÷
1
(FQPA)
=
4.0
mg/
kg/
day.

°
The
acute
dietary
exposure
analysis
is
based
on
the
Dietary
Exposure
Evaluation
Model
(DEEM
™
).
The
DEEM
™
analysis
evaluated
individual
food
consumption
as
reported
by
respondents
in
the
USDA
1989­
92
Continuing
Surveys
for
Food
Intake
by
Individuals
(CSFII).
The
data
are
based
on
the
reported
consumption
of
more
than
10,000
individuals
over
three
days.
For
the
acute
exposure
assessment,
individual
one­
day
food
consumption
data
are
used
on
an
individual­
by­
individual
basis.

°
The
acute
dietary
exposure
assessment
for
hexazinone
is
a
tier
I
analysis.
This
is
the
most
conservative
type
of
analysis
done
by
the
Agency
and
it
assumes
that
residues
on
foods
as
consumed
are
equal
to
the
tolerance
levels
and
that
100%
of
each
crop
is
treated.

°
The
dietary
exposure
assessment
included
residue
estimates
of
hexazinone
(parent)
and
metabolites
B,
C,
C­
1,
C­
2,
and
F
for
ruminant
commodities
and
metabolites
A,
B,
C,
D,
and
E
for
plant
commodities.
The
metabolites
and
parent
hexazinone
are
assumed
to
have
equal
toxicity
based
upon
similarity
in
chemical
structure.

°
Because
existing
data
were
inadequate
to
calculate
residue
estimates
for
pasture
and
rangeland
grass
and
grass
hay,
EPA
constructed
the
maximum
theoretical
dietary
burden
(MTDB)
of
hexazinone
to
livestock
using
protective
assumptions
for
the
contributions
of
other
hexazinonetreated
feed
items.
Thus,
tolerances
for
meats
and
milk
can
be
reassessed.
Additional
field
trial
data
for
grass
forage
and
grass
hay,
as
well
as
rotational
crop
studies
for
corn
and
wheat
are
required.
Because
of
the
relatively
low
volume
of
use
on
pasture
and
rangeland,
data
from
these
confirmatory
studies
are
not
expected
to
significantly
change
current
dietary
risk
estimates.

Chronic
Dietary
(Food)
Risk
(For
a
complete
discussion,
see
section
4.2.3
of
the
Human
Health
Risk
Assessment)

Chronic
dietary
risk
from
food
is
calculated
by
using
the
average
consumption
values
for
food
and
average
residue
values
for
those
foods
over
a
70­
year
lifetime.
A
risk
estimate
that
is
less
than
100%
of
the
chronic
PAD
(cPAD)
(the
daily
dose
at
which
an
individual
could
be
exposed
over
the
course
of
a
lifetime
and
no
adverse
health
effects
would
be
expected)
does
not
exceed
the
Agency's
level
of
concern.
Table
2
presents
the
results
of
the
chronic
dietary
(food)
exposure
and
risk
analysis.

Table
2.
Chronic
Dietary
(Food)
Exposure
and
Risk
Population
Subgroup
Exposure
(mg/
kg/
day)
%
cPAD
General
U.
S.
0.002167
4.3
Population
Subgroup
Exposure
(mg/
kg/
day)
%
cPAD
5
All
infants
(<
1
year)
0.003752
7.5
Children
(1­
6
years)
0.0077449
15.5
Children
(7­
12
years)
0.003964
7.9
Females
(13­
50
years)
0.001308
2.6
°
The
chronic
dietary
risk
estimate
for
all
population
subgroups
does
not
exceed
the
cPAD,
all
population
subgroups
are
<16%
of
the
cPAD.

°
For
all
populations,
the
chronic
NOAEL
of
5.00
mg/
kg/
day
was
established,
based
on
severe
body
weight
decrement,
decreased
food
consumption,
and
clinical
chemistry
changes
such
as
anemia,
decreases
in
RBC
counts,
hemoglobin,
and
hematocrit
in
a
one
year
chronic
dog
study
at
the
LOAEL
of
38
mg/
kg/
day.

°
An
uncertainty
factor
(UF)
of
100
was
applied
to
the
doses
selected
for
the
risk
assessment
to
account
for
interspecies
extrapolation
(10x)
and
intraspecies
variability
(10x).

°
For
chronic
dietary
exposure,
the
FQPA
safety
factor
was
reduced
to
1X
for
the
same
reasons
noted
above
for
acute
dietary
exposure.

°
The
chronic
RfD:
5.0
mg/
kg/
day
(NOAEL)
÷
100
(UF)
=
0.05
mg/
kg/
day.
The
chronic
PAD:
0.05
mg/
kg/
day
÷
1
(FQPA)
=
0.05
mg/
kg/
day.

°
The
chronic
dietary
exposure
analysis
is
based
on
the
Dietary
Exposure
Evaluation
Model
(DEEM
™
).
For
chronic
dietary
(food)
assessments,
a
three­
day
average
of
consumption
for
each
population
subgroup
is
combined
with
average
residues
in
commodities
to
determine
average
exposures
in
mg/
kg/
day.

°
The
chronic
dietary
(food)
exposure
assessment
for
hexazinone
was
a
tier
I
analysis.
This
is
the
most
conservative
type
of
analysis
the
Agency
performs
and
it
assumes
that
residues
on
foods
as
consumed
are
equal
to
the
tolerance
levels
and
that
100%
of
each
crop
is
treated.

Drinking
Water
Dietary
Risk
(For
a
complete
discussion,
see
section
4.3
of
the
Human
Health
Risk
Assessment)

Drinking
water
exposure
to
pesticides
can
occur
through
surface
and/
or
ground
water
contamination.
EPA
considers
acute
(one
day)
and
chronic
(lifetime)
drinking
water
risks
and
uses
6
either
modeling
or
actual
monitoring
data,
if
available,
to
estimate
those
risks.
Modeling
is
carried
out
in
tiers
of
increasing
refinement,
but
is
designed
to
provide
a
conservative
estimate
of
potential
exposure.
To
determine
the
maximum
allowable
contribution
from
water
allowed
in
the
diet,
EPA
first
looks
at
how
much
of
the
overall
allowable
risk
is
contributed
by
food
and
then
determines
a
Drinking
Water
Level
of
Comparison"
(DWLOC)
to
ascertain
whether
modeled
or
monitored
Estimated
Environmental
Concentrations
(EECs)
exceed
this
level.

The
hexazinone
drinking
water
exposure
assessment
is
based
upon
review
of
environmental
fate
studies
which
suggest
that
the
parent
and
degradates
are
likely
to
be
persistent
and
mobile
in
the
environment.
Leaching
and
runoff
are
expected
to
be
the
primary
dissipation
routes.
Estimated
Environmental
Concentrations
(EECs)
in
surface
waters
were
estimated
using
Tier
I
modeling
(FIRST).
The
EECs
in
groundwater
were
estimated
using
an
available
small­
scale
prospective
groundwater
monitoring
study
from
California.
In
addition,
there
are
monitoring
data
available
from
the
state
of
Maine
that
were
used
for
comparison
purposes
only.

°
The
use
of
hexazinone
on
alfalfa
was
modeled
for
the
purpose
of
assessing
surface
drinking
water
exposure
to
the
chemical
and
its
degradates.
Alfalfa
is
the
food/
feed
item
with
the
greatest
percent
of
crop
treated
with
hexazinone.

°
Estimated
Environmental
Concentrations
(EECs)
for
surface
water
were
estimated
using
FIRST
(Tier
I)
modeling.
This
model
is
a
screening
tool
designed
to
provide
high­
end
estimates
of
the
concentrations
that
might
be
found
in
a
small
drinking
water
reservoir
due
to
the
use
of
the
pesticides.

°
EECs
for
ground
water
are
based
on
monitoring
data
from
the
small­
scale
prospective
groundwater
monitoring
study
in
California.
The
results
of
this
study
were
compared
and
confirmed
with
monitoring
done
in
the
State
of
Maine.

°
The
parent­
hexazinone,
G3170,
and
all
degradates
with
conjoined
cyclohexyl
and
triazine
rings
(specifically,
A,
A­
1,
B,
C,
D,
1
(JS472),
and
2
(JT677))
are
residues
of
concern
for
risk
assessment
in
water.
The
Agency
assumes
they
have
similar
toxicity
as
the
parent.
Drinking
water
DWLOCs
and
EECs
are
compared
in
Table
3.
7
Table
3.
Acute
and
Chronic
Drinking
Water
DWLOC
and
EEC
Comparisons
Population
Subgroup
Acute
Scenario
Chronic
Scenario
Acute
DWLOC
Ground
Water
EEC
Surface
Water
EEC
Chronic
DWLOC
Ground
Water
EEC
Surface
Water
EEC
U.
S.
General
420
42
47
Females
(13­
50
years)
120,000
42
130
420
42
47
All
infants
420
42
47
Children
(1­
6
years)
420
42
47
°
For
acute
drinking
water
risk,
potential
(peak)
EECs
of
hexazinone
in
either
ground
water
(42
ppb)
or
surface
water
(130
ppb)
are
below
the
acute
DWLOC
for
females
(13­
50
years)
(120,000
ppb).

°
For
chronic
drinking
water
risk,
the
potential
(average)
EECs
of
hexazinone
in
either
ground
water
(42
ppb)
or
surface
water
(47
ppb)
are
below
the
chronic
DWLOC
for
all
population
subgroups
(420
ppb).

Blueberry
Use
In
Maine
A
significant
portion
of
the
wild
blueberry
crop
in
the
state
of
Maine
is
treated
with
hexazinone.
It
may
be
applied
pre­
or
post­
emergence
at
use
rates
of
0.5
to
2
lb
ai/
acre.
Wild
blueberries
produce
a
berry
crop
every
other
season,
with
hexazinone
being
typically
applied
in
the
non­
bearing
year.
A
Special
Local
Need
(SLN)
label
for
Maine,
allows
use
45
days
before
harvest.
Hexazinone
is
the
primary
factor
in
increasing
the
wild
blueberry
crop
three­
fold
over
the
past
15
years.
Hexazinone
has
a
half
life
of
90
days,
is
highly
soluble,
and
prone
to
leaching.
Because
most
of
the
wild
blueberry
fields
are
on
highly
leachable
sandy
loam
soils,
there
is
concern
that
ground
and
surface
water
may
be
impacted
by
hexazinone
use.
Water
monitoring
has
been
conducted
since
1985
and
hexazinone
is
detected
in
both
ground
and
surface
water.
Long
term
test
well
data
from
1989­
1995
found
concentrations
of
hexazinone
in
the
25­
29
ppb.
In
response,
the
Maine
Board
of
Pesticides
Control
implemented
a
Best
Management
System
in
1996
to
reduce
surface
and
groundwater
impact.
The
measures
implemented
by
the
State,
include
classifying
hexazinone
as
a
Restricted
Use
Pesticide.
Users
must
become
certified
applicators
by
attending
training
on
proper
application
techniques.
In
addition,
on­
going
field
training
is
provided
for
workers
using
hexazinone.
Application
is
not
allowed
within
50
feet
of
a
water
source
or
well,
airblast
application
is
prohibited,
low
use
rates
are
suggested
except
when
weed
pressure
is
high,
and
alternative
weed
control
measures
are
recommended,
such
as
cutting/
mowing,
burning,
and
hand
pulling
of
weeds.
Recent
monitoring
from
1998­
2001
found
8
concentrations
from
0.08
­3.8
ppb
in
both
ground
and
surface
water
which
are
significant
reductions
from
the
levels
found
in
the
previous
monitoring.
The
Best
Management
System
implemented
by
the
State
appears
to
be
lowering
the
levels
of
hexazinone
in
ground
and
surface
water.
The
Agency
supports
these
efforts
and
anticipates
their
continued
modification
and
improvement
may
further
reduce
the
levels
of
hexazinone
in
ground
and
surface
water
from
hexazinone
application
to
blueberries.
Nonetheless,
the
levels
of
hexazinone
found
in
ground
and
surface
water
in
Maine
are
well
below
the
acute
DWLOC
(12,000
ppb)
and
the
chronic
DWLOC
(430
ppb)
and
thus,
below
the
Agency's
level
of
concern.

Forestry
Use
and
Tribal
Communities
About
60%
of
hexazinone
usage
is
on
forestry
sites
for
woody
plant
and
weed
control.
Shortly
following
a
logging
operation,
hexazinone
may
be
applied
to
control
brush
in
preparation
for
the
replanting
of
tree
seedlings.
Depending
on
weed
intensity,
hexazinone
may
be
applied
a
second
time
the
next
season
after
the
seedlings
have
been
planted.
The
goal
is
to
suppress
the
competing
vegetation
and
allow
the
seedlings
the
opportunity
to
establish
their
root
system
and
help
them
increase
their
growth
size
above
the
competing
vegetation.
In
Eastern
forests,
because
of
the
species
of
trees
grown,
hexazinone
may
typically
be
applied
1­
2
times
during
a
20
to
40
year
period.
In
Western
forests,
hexazinone
may
typically
be
applied
1­
2
times
during
a
60
to
80
year
period.
In
some
forested
areas
where
hexazinone
is
applied,
Native
Americans
gather
plant
materials
that
are
used
in
their
diets,
in
the
making
of
traditional
basketry,
for
medicinal
purposes,
and
in
ceremonial
activities.

USEPA,
(Region
IX)
is
working
with
the
California
Department
of
Pesticide
Regulation
(DPR),
the
U.
S.
Forest
Service
(USFS)
and
Native
American
tribes
in
California
to
determine
the
potential
exposure
to
forestry
herbicides,
including
hexazinone,
glyphosate,
and
triclopyr,
that
may
be
occurring
to
Native
Americans
through
their
use
of
forest
plant
materials.
In
response
to
the
health
concerns
raised
by
the
Native
American
communities,
DPR
and
Region
IX
launched
a
risk
assessment
effort
in
1997.
This
effort
includes
five
steps:
DPR
measured
plant
residue
and
surface
water
levels
following
herbicide
application;
DPR
agreed
to
assess
the
total
exposures
and
risks
involved
using,
where
appropriate,
the
monitoring
data
collected;
informing
tribal
physicians
of
state
regulations
requiring
pesticide
illness
reporting;
participation
in
mediated
meetings
with
Native
American
communities
to
determine
the
key
issues
surrounding
herbicide
use;
and
a
video
production
about
inadvertent
exposure
to
herbicides.
In
addition,
the
USFS
is
working
with
local
Indian
tribes,
and
has
established
"no
spray"
zones
where
plant
materials
may
be
gathered
free
of
pesticide
residues.
They
are
also
working
to
reduce
pesticide
usage,
prevent
runoff,
and
minimize
exposure
by
posting
application
sites
and
providing
bulletins
alerting
the
public
where
applications
have,
or
will
occur.

EPA
is
aware
of
this
ongoing
work
and
will
continue
to
coordinate
with
the
registrant­
Dupont,
Region
IX,
California
DPR,
U.
S.
Forest
Service,
and
other
entities,
as
appropriate,
to
ensure
that
potential
exposures
and
risks
are
better
characterized.
In
addition,
the
Agency
is
working
to
develop
risk
analysis
software
that
will
assess
risk
from
chemicals
in
food,
air,
water,
and
other
sources
for
9
Native
American
and
Alaska
native
sub­
populations
whose
subsistence
ways
of
life
may
result
in
exposures
to
toxic
chemicals
that
are
significantly
different
from
those
of
other
population
sub­
groups.

Residential
Risk
Hexazinone
is
not
registered
for
home
use
nor
is
it
used
in
and
around
schools,
or
parks.
Based
on
present
use
patterns
and
labeled
uses,
there
should
be
no
residential
exposure
to
hexazinone.
Thus,
there
is
no
residential
exposure
to
assess
or
aggregate
with
the
dietary
and
drinking
water
exposure.

Aggregate
Risk
(For
a
complete
discussion,
see
section
5.0
of
the
Human
Health
Risk
Assessment)

Aggregate
risk
examines
the
combined
risk
from
exposure
through
food,
drinking
water,
and
residential
uses.
Using
the
DWLOC
approach,
all
risks
from
these
exposures
must
be
less
than
100%
of
the
aPAD
or
cPAD.
For
hexazinone,
the
aggregate
risks
are
limited
to
food
and
water
exposure,
because
there
are
no
residential
uses.

°
Combining
both
the
acute
dietary
(food)
risk
estimates
with
the
surface
and
ground
water
EECs
(drinking
water)
for
hexazinone,
the
acute
aggregate
(food
+
drinking
water)
risk
is
less
than
100%
of
the
aPAD;
and
therefore,
is
not
of
concern
to
the
Agency.

°
Combining
both
the
chronic
dietary
(food)
risk
estimate
with
the
surface
and
ground
water
EECs
(drinking
water)
for
hexazinone,
the
chronic
aggregate
(food
+
drinking
water)
risk
is
less
than
100%
of
the
cPAD,
and
therefore,
is
not
of
concern
to
the
Agency.

Occupational
and
Ecological
Risk
(For
a
complete
discussion,
see
section
4.2
of
the
Human
Health
Risk
Assessment)

Because
hexazinone
is
under
review
for
tolerance
reassessment
only,
no
occupational
or
ecological
risk
assessment
would
normally
be
conducted.
Occupational
and
ecological
risk
management
decisions
were
made
as
part
of
the
1994
Hexazinone
RED.
The
Agency
reevaluated
labeled
uses
and
determined
the
personal
protective
equipment
and
restricted
entry
intervals
included
in
the
RED
are
health
protective.
In
addition,
ecological
tests
indicate
hexazinone
is
non­
toxic
to
birds,
bees,
and
fish.
10
Tolerance
Reassessment
Summary
(For
a
complete
discussion,
see
Hexazinone
Residue
Chemistry
Chapter
for
the
Tolerance
Reassessment
Eligibility
Decision
(TRED),
dated
5/
20/
2002.)

The
Agency
has
reassessed
all
25
tolerances
for
hexazinone
and
can
make
an
FQPA
safety
determination.
Anticipated
residues
for
commodities
included
in
the
dietary
risk
assessment
are
equal
to
the
tolerance
levels
and
it
was
assumed
that
100%
of
each
crop
was
treated.
Acute
and
chronic
dietary
risks
from
exposure
to
hexazinone
do
not
exceed
the
Agency's
level
of
concern.
Tolerances
for
residues
of
hexazinone
in/
on
plant,
livestock,
and
processed
commodities
are
currently
expressed
in
terms
of
the
combined
residues
of
hexazinone
and
its
metabolites
(calculated
as
hexazinone).
Field
trial
data
for
pasture
and
rangeland
grass
hay
will
be
required
as
well
as
rotational
crop
studies
for
corn
and
wheat,
and
are
considered
confirmatory.
Final
tolerances
are
being
proposed
as
part
of
this
Tolerance
Reassessment
Decision
(TRED).
Additional
tolerances
may
be
revised
once
the
field
trial
data
and
rotational
crop
studies
have
been
submitted
to
and
reviewed
by
the
Agency.

Table
4.
Tolerance
Reassessment
Summary
for
Hexazinone.

Commodity
Current
Tolerance
(ppm)
a
Tolerance
Reassessment
(ppm)
Comment/
Correct
Commodity
Definition
Tolerances
presently
listed
under
40
CFR
§180.396(
a):

Alfalfa
green
forage
2.0
2.0
Alfalfa,
forage
Alfalfa
hay
8.0
4.0
Tolerance
should
be
reduced
based
on
re­
calculation
of
expected
residues.
Alfalfa,
hay
Blueberries
0.2
0.6
Tolerance
should
be
increased
based
on
the
combined
LOQ
(0.55
ppm)
of
the
enforcement
method.
Blueberry
Cattle,
fat
0.1
Revoke
b
Cattle,
mbyp
0.1
0.1
Cattle,
meat
0.1
0.1
Goat,
fat
0.1
Revoke
b
Goat,
mbyp
0.1
0.1
Goats,
meat
0.1
0.1
Grasses,
pasture
10
TBD
c
Grass,
forage
Commodity
Current
Tolerance
(ppm)
a
Tolerance
Reassessment
(ppm)
Comment/
Correct
Commodity
Definition
11
Grasses,
rangeland
10
TBD
c
Grass,
hay
Hog,
fat
0.1
Revoke
b
Hog,
mbyp
0.1
Revoke
b
Hog,
meat
0.1
Revoke
b
Horses,
fat
0.1
Revoke
b
Horses,
mbyp
0.1
0.1
Horses,
meat
0.1
0.1
Milk
0.5
0.2
Tolerance
should
be
reduced
based
on
re­
calculation
of
expected
residues.

Pineapple
0.5
0.6
Tolerance
should
be
increased
based
on
the
combined
LOQ
(0.55
ppm)
of
the
enforcement
method.

Sheep,
fat
0.1
Revoke
b
Sheep,
mbyp
0.1
0.1
Sheep,
meat
0.1
0.1
Tolerances
needed
under
40
CFR
§180.396(
a):

Alfalfa,
seed
2.0
Tolerances
presently
listed
under
40
CFR
§180.396(
c):

Sugarcane
0.2
0.6
Tolerance
should
be
increased
based
on
the
combined
LOQ
(0.55
ppm)
of
the
enforcement
method.

Sugarcane
molasses
5.0
4.0
Tolerance
should
be
reduced
based
on
re­
calculation
of
expected
residues.

Sugarcane
molasses
d
5.0
4.0
Tolerance
should
be
reduced
based
on
re­
calculation
of
expected
residues.
a
Expressed
in
terms
of
the
combined
residues
of
hexazinone
and
its
metabolites
(calculated
as
hexazinone).
b
Tolerances
for
fat
are
not
required
(Category
3,
40
CFR
§180.6).
c
TBD:
These
tolerances
require
additional
field
trial
data
and
may
be
revised
once
the
data
have
been
submitted
to
and
reviewed
by
the
Agency.
d
For
reassessment
counting
purposes,
the
Agency
will
count
the
sugarcane
molasses
tolerances
as
two
reassessments
to
reflect
the
tolerances
which
existed
both
in
40
CFR
Part
185
(185.3575)
and
Part
186
(186.3575)
at
the
start
of
FQPA.
12
CODEX
HARMONIZATION
No
maximum
residue
limits
(MRLs)
for
hexazinone
and
its
metabolites
have
been
established
or
proposed
by
Codex
for
any
agricultural
commodity.
Therefore,
no
compatibility
questions
exist
with
respect
to
U.
S.
tolerances.

Summary
of
Pending
Data
The
Agency
is
requesting
a
28­
day
inhalation
study
on
a
formulation
with
hexazinone
because
of
the
concern
for
potential
inhalation
exposure.
Additional
field
trial
data
for
grass
hay
and
rotational
crop
studies
for
corn
and
wheat
are
required.
