HEXAZINONE
TOLERANCE
REASSESSMENT
ELIGIBILITY
DECISION
REPORT
OF
THE
HAZARD
IDENTIFICATION
ASSESSMENT
(HIARC)
REVIEW
OF
4/
25/
02
DuPONT
COMMENTS
2
HAZARD
IDENTIFICATION
1.1
Acute
Dietary
Reference
Dose
Females
13­
50
pp.
3­
5
For
setting
the
acute
reference
dose
(ARfD)
for
females
of
childbearing
age,
the
Agency
has
selected
a
rat
developmental
study
with
NOAELs
of
100
and
400
mg/
kg
for
maternal
and
fetal
effects,
respectively.
The
Agency
assigned
an
additional
10x
database
uncertainty
factor
(UFdb)
because
a
rabbit
developmental
study
was
unacceptable
due
to
uncertainties
in
the
LOEL.
A
UFdb
factor
of
10x
rather
than
3x
was
used
because,
based
on
extrapolation
to
the
rabbit
pilot
NOEL
of
50
mg/
kg
in
the
previous
study,
it
was
concluded
the
difference
between
rabbits
and
rats
may
be
greater
than
3x.
The
resulting
ARfD
was
0.4
mg/
kg
(400
mg/
kg
/
1000).

Immediately
after
the
HIARC
report
issued,
the
Registrant
submitted
a
new
rabbit
developmental
study
(DuPont­
7405,
MRID
45677801)
to
the
Agency.
The
new
rabbit
developmental
study
was
conducted
using
current
guidelines
and
confirmed
the
results
of
the
previous
rabbit
developmental
study.
The
maternal
and
fetal
rabbit
NOEL
was
50
mg/
kg/
day.
The
maternal
and
fetal
LOEL
was
125
mg/
kg/
day
based
on
weight
effects,
which
were
only
slight
in
the
fetus.
A
higher
dose,
175
mg/
kg/
day
produced
severe
maternal
toxicity.

Once
the
new
rabbit
study
is
reviewed,
if
it
is
selected
as
the
basis
of
the
ARfD,
the
registrant
believes
the
extra
10x
UFdb
should
be
removed.
If
selected,
this
would
result
in
an
ARfD
of
0.5
mg/
kg
(50
mg/
kg
/
100).
This
is
essential
the
same
(slight
improvement)
as
the
current
ARfD,
and
thus
there
will
be
essentially
no
change
in
the
acute
dietary
risk
assessment.

2.3
Chronic
Reference
Dose
Last
line
page
6
–
typographical
error.
"The
LOAEL
is…
based
on…[
findings
listed]
and
clinical
observations
of
thinnest
in
one
male."
Should
read
"thin
appearance
in
one
male."

1.4
Occupational/
Residential
Exposure
It
is
not
clear
to
the
Registrant
why
the
occupational
and
residential
exposure
Sections
2.4.1
through
2.6
were
included
in
a
food
Tolerance
Reassessment.
There
are
no
residential
uses
of
hexazinone,
that
could
contribute
to
the
aggregate
exposure.
It
is
the
Registrant's
understanding
that
occupational
exposure
assessment
is
beyond
the
scope
of
Tolerance
Reassessment.
Occupational
exposure
was
addressed
under
the
1994
Reregistration
Eligibility
Document.
It
was
noted
that
a
number
of
the
major
uses
of
hexazinone
were
outside
the
scope
of
the
Worker
Protection
Standard
(WPS).
While
agricultural
uses
and
use
on
sod
farms
was
within
WPS;
use
on
pastures,
rangeland,
plants
grown
for
other
than
commercial
purposes,
ornamental
plants
in
parks
and
golf
course,
and
no­
agricultural
uses
such
as
vegetation
along
rights­
of­
way
were
outside
of
the
scope
of
WPS.
No
worker
exposure
assessment
was
conducted.

Therefore
the
Registrant
considers
the
selection
of
Occupational/
Residential
endpoints
(e.
g.,
dermal
and
inhalation
exposure
scenarios)
to
not
be
relevant
to
Tolerance
Reassessment.
Nonetheless,
we
offer
the
following
comments
to
the
endpoint
selection,
should
these
endpoints
be
considered
relevant
in
the
future.

2.4.2
Dermal
Absorption
The
review
states
that
"No
dermal
absorption
study
is
available."
It
would
be
clearer
to
say
that
"No
dermal
penetration
study
is
available.
For
an
estimate
of
dermal
penetration,
the
NOAEL
from
the
21­
day
rabbit
dermal
toxicity
study…."
Also,
for
clarification,
add
the
MRID
of
the
rabbit
21­
day
study
(MRID
41309005).

The
Agency
extrapolated
a
dermal
absorption
factor
by
comparing
the
NOAEL
in
a
21­
day
dermal
study
in
rabbits
to
the
LOAEL
from
a
rabbit
developmental
range­
finding
study.
A
25%
dermal
absorption
factor
was
derived.

Rabbit
Pilot
Developmental
LOAEL
(oral)
=
250
mg/
kg
=
25%
Rabbit
21­
Day
Dermal
NOAEL
1000
mg/
kg
However,
the
new
rabbit
developmental
study
(DuPont­
7405,
MRID
45677801)
indicates
there
is
a
greater
difference
between
oral
and
dermal
toxicity
than
indicated
by
the
above
calculation.
Further,
since
no
LOAEL
was
actually
established
on
the
Rabbit
21­
Day
Dermal
study,
use
of
a
dermal
NOAEL
in
comparison
to
an
oral
LOAEL,
overestimates
the
potential
dermal
penetration.
Based
on
the
new
rabbit
developmental
study,
dermal
absorption
is
no
greater
than
12.5%

Rabbit
Developmental
LOAEL
(oral)
=
125
mg/
kg
=<
12.5%
Rabbit
21­
Day
Dermal
NOAEL
>
1000
mg/
kg
2.4.3
Short­
Term
(1
Day
–
1
Month)
Dermal
Exposure
and
2.4.4
Intermediate
Term
(1­
6
Months)
and
Long­
Term
(>
6
Months)
Dermal
Exposures
Under
2.4.3,
the
Agency
states
the
Dose
and
Endpoint
for
Risk
Assessment
for
short­
term
dermal
Exposure
is
Not
Applicable
and
that
No
Hazard
and
No
Quantification
are
required
(based
on
no
effects
in
the
21­
day
dermal
study
in
rabbits).
However,
in
the
next
section
(2.4.4)
the
Agency
proceeds
to
select
longer­
term
dermal
endpoints
based
on
the
chronic
dog
study
NOEL
(5
mg/
kg/
day)
and
a
25%
dermal
absorption
factor
(i.
e.
equivalent
to
20
mg/
kg/
day).
For
intermediate­
term
scenarios,
we
believe
selection
of
a
subchronic
endpoint
would
be
more
appropriate
than
selection
of
the
chronic
dog
study
with
a
25%
absorption
factor.
It
is
also
consistent
wit
the
Agency
guidance
document,
Toxicology
Endpoint
Selection
Process
(February,
1997).
Based
on
the
labeled
uses
for
hexazinone,
we
do
not
believe
a
long­
term
dermal
exposure
scenario
is
relevant.
It
is
difficult
to
identify
a
scenario
where
there
would
be
daily,
lifetime
uninterupted
dermal
exposure
to
hexazinone.

·
The
registrant
believes
that
the
route
specific
rabbit
dermal
study
is
the
most
appropriate
study
to
estimate
subchronic
human
dermal
exposure.
The
Agency
has
concluded
that
the
repeated
dose
rabbit
study
(MRID
41309005)
meets
guidelines
and
is
acceptable.
It
measured
the
proper
endpoints
to
identify
hexazinone
toxicity
(including
body
weights,
clinical
chemistry,
liver
histology).
Considering
lifespan
differences,
it
is
of
appropriate
duration
for
short
term
and
intermediate
endpoint
selection.

·
However,
if
the
Agency
deems
that
the
duration
of
the
subchronic
rabbit
dermal
study
is
insufficient,
acceptable
subchronic
oral
studies
of
longer
duration
(90
days)
are
available.
The
NOAELs
from
the
rat
and
dog
90­
day
studies
were
84
and
29
mg/
kg,
respectively.
Again
the
dog
is
the
most
sensitive
species,
but
the
subchronic
NOAEL
is
more
appropriate.

·
As
noted
in
the
discussion
above,
the
25%
absorption
factor
derived
by
comparing
a
LOAEL
on
a
rabbit
pilot
developmental
study
to
the
NOAEL
on
the
rabbit
subchronic
dermal
study
overestimated
the
Dermal
Absorption
Factor
which,
in
reality,
is
likely
to
be
less
than
12.5%.
Using
the
dog
subchronic
NOAEL
(29
mg/
kg/
day)
and
applying
a
more
appropriate
dermal
absorption
factor
<12.5%
would
result
in
an
estimated
dermal
endpoint
of
>
232
mg/
kg/
day.
This
is
much
more
comparable
to
the
actual
dermal
NOAEL
determined
from
the
21­
day
rabbit
study.

Also
typographical
error
in
2.4.4
"thinnest
in
one
males"
should
read
"thin
appearance
in
one
male"

2.4.6
Intermediate
(1­
6
Months)
and
Long­
Term
(>
6
Months)
Inhalation
Exposure
Typographical
error
"thinnest
in
one
males"
should
read
"thin
appearance
in
one
male"

4
MUTAGENICITY
For
clarification,
we
recommend
inserting
the
following
wording
into
the
last
sentence
of
the
mutagenicity
overview
(additions
are
in
bold).
"Because
unambiguous
positive
results
were
achieved,
it
was
concluded
that
the
study
provided
adequate
evidence
that
INA­
3674­
112
(hexazinone
technical)
is
clastogenic
in
vitro
in
an
acceptable
study.
However,
negative
results
were
obtained
in
two
studies
which
assessed
chromosome
damage
in
vivo."

General
Comment:
for
consistency
with
the
rest
of
the
document,
INA­
3674­
112
should
be
changed
to
hexazinone
or
hexazinone
technical.

Guideline
870.5300:
Gene
Mutation
Assay
in
Mammalian
Cells
Conclusion
should
be
bolded
as
with
others
studies.
"There
was,
however,
no
indication
that
INA­
3674­
112
induced
mutagenic
effect
in
either
the
presence
or
the
absence
of
S9
activation."

Guideline
870.5395:
Mouse
Bone
Marrow
Micronucleus
Assay
Change
the
last
sentence
from
"It
satisfy
the
requirements…."
to
"It
satisfies
the
requirements…."

Guideline
870.5375:
Structural
Chromosome
Aberration
Assay;
In
vitro
Cytogenetic
Assay
Mid
paragraph
"In
the
presence
of
S­
9
mix,
no
statistically
significant
increases
in
chromosome
aberrations
were
seen
in
Trial
1;
however,
very
low
positive
control
values
indicated
a
problem
with
the
S9­
mix."
Delete
the
latter
part
of
the
sentence;
it
is
incorrect.
Positive
control
values
in
both
trials
produced
strong
positive
results
(Trial
1
28­
32%
abnormal
cells,
Trial
2
36­
40%
abnormal
cells).

Guideline
870.5385:
Structural
Chromosome
Aberration
Assay;
In
vivo
Cytogenetic
Assay
Fourth
sentence
of
second
paragraph,
"Few
or
no
analyzable
cell
were
available…"
should
be
"Few
or
no
analyzable
cells
were
available…"

After,
"Unacceptable….
The
study
does
not
satisfy
the
requirement
for
FIFRA
Test
Guidelines."
add,
"However,
this
Guideline
is
fulfilled
by
an
acceptable
mouse
micronucleus
study."

5
FQPA
CONSIDERATIONS
4.3
Developmental
Toxicity
5.3.2.
Developmental
Toxicity
in
the
Rabbit
Last
paragraph
should
be
upgraded
to
indicate
a
Rabbit
Developmental
Toxicity
(45677801)
has
just
been
submitted
but
not
yet
been
reviewed.

5.7
Determination
of
the
Need
for
Developmental
Neurotoxicity
Study
4.6.1
Evidence
that
suggest
requiring
a
Developmental
Neurotoxicity
Study
Atrazine
should
not
be
considered
as
evidence
suggesting
requirement
of
a
developmental
neurotoxicity.
Although
atrazine
and
hexazinone
contain
a
triazine
ring,
there
are
significant
structural
differences
that
contribute
substantial
differences
in
the
biological
response
to
these
molecules
by
laboratory
animals.
EPA
reached
a
similar
conclusion
in
the
Toxicology
Disciplinary
Chapter
for
the
Tolerance
Reassessment
and
Evaluation
Decision
Document,
Section
1.0
–
Hazard
Characterization
(May
16,
2002).
The
critical
structural
differences
include
substitutions
of
a
cyclohexyl
and
a
methyl
group
on
the
ring
nitrogens
and
the
presence
of
two
ring
oxo
groups
in
hexazinone.
As
a
result,
hexazinone
is
less
aromatic
in
character
than
the
chloro­
s­
triazines.
Collectively,
these
structural
differences
are
considered
to
contribute
differences
in
toxicological
properties.
Hexazinone
has
been
classified
as
a
triazine­
dione
by
EPA,
which
further
indicates
this
Agency
acknowledges
its
differences
from
the
chloro­
striazine
herbicide
class.

Hexazinone
has
been
extensively
tested
for
safety
to
mammals.
A
key
difference
between
hexazinone
and
atrazine
and
other
members
of
the
chloro­
s­
triazine
class
is
that
chronic
exposures
to
the
latter
produce
a
characteristic
mammary
tumor
response
in
Sprague­
Dawley
rats.
The
mode
of
action
for
this
chloro­
s­
triazine
induced
tumor
response
has
been
associated
with
altered
endocrine
activity
unique
to
this
rat
strain.
In
contrast
hexazinone
does
not
induce
rat
mammary
tumors,
which
indicates
the
absence
of
the
endocrine
modulation
responsible
for
this
effect.
Additional
evidence
supporting
the
absence
of
endocrine
effects
with
hexazinone
includes
the
absence
of
endocrine
organ
effects
and
effects
on
reproduction
and
development.
The
differences
in
chemical
structures
are
considered
to
be
critical
to
the
observed
differences
in
toxicological
response
between
hexazinone
and
the
chloro­
s­
triazines.

7.
Data
Gaps
"HIARC
has
requested
a
28­
day
inhalation
study
because
of
the
concern
for
inhalation
exposure
based
on
the
use
pattern"

·
It
is
unclear
as
to
which
use
pattern
is
being
considered.
There
are
no
residential
uses
of
hexazinone.
Most
of
the
use
patterns
are
outside
the
scope
of
WPS.
Since
no
use
patterns
of
concern
are
identified,
it
is
impossible
to
determine
duration
of
exposure.
·
On
the
same
page
that
it
requests
a
28­
day
inhalation
study,
the
Agency
notes
that
it
already
has
an
unreviewed
21­
day
inhalation
study
(MRID
#
00063972,
HLR
447­
76).
In
that
study,
groups
of
ten
male
rats
were
exposed
6
hours/
day,
5
day/
week
for
3
weeks
to
0
(control)
or
2.5
mg/
L
of
90%
wettable
powder
formulation
of
hexazinone.
Using
the
guidance
in
(Whalan
EPA,
1997)
this
represents
an
exposure
of
greater
than
600
mg/
kg/
day
(2.25
mg
hexazinone
a.
i./
L
x
11.38
L/
hr
respiration
x
6
hr/
day
exposure/
0.25
kg
body
weight
).
Histopathology
examination
indicated
that
lung
changes
were
similar
between
control
and
hexazinone
exposed
rats.
Intermittent
weight
losses
were
noted
throughout
the
test
period
but
all
rats
showed
a
normal
rate
of
weight
gain
during
the
recovery
period
.
The
Registrant
acknowledges
that
this
is
an
old
study
which
was
conducted
prior
to
issuance
of
current
guidelines.
However,
it
clearly
indicates
that
repeated
exposure
to
hexazinone
dust
poses
negligible
inhalation
risk.
It
also
suggests
that
no
further
inhalation
testing
is
required
since
no
lung
toxicity
was
identified
and
since
the
exposure
producing
minimal
to
moderate
toxicity
was
two
orders
of
magnitude
higher
than
the
chronic
NOAEL
that
has
just
been
selected
by
the
Agency
to
set
an
inhalation
endpoint.
Therefore
the
oral
endpoint
selected
is
overly
protective.
In
the
interest
of
conservation
of
animals
we
strongly
urge
that
available
information
be
considered
before
the
Agency
request
another
study
and
the
repeated
dose
inhalation
be
removed
as
a
data
gap.

For
the
rabbit
developmental
toxicity
data
gap
we
recommend
changing
the
statement
"is
expected
to
be
submitted"
to
"was
not
submitted
in
enough
time
for
review
prior
to
issuance
of
this
document"
