UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
DATE:
February
13,
2001
SUBJECT:
Oxadiazon.
(
List
B,
Case
No.
2485)
The
Outcome
of
the
HED
Metabolism
Assessment
Review
Committee
Meeting
Held
on
01/
30/
01.
DP
Barcode
272425.
Chemical
109001.

FROM:
Sheila
Piper,
Chemist
Chemistry
and
Exposure
Branch
Health
Effects
Division
(
7509C)

THROUGH:
Francis
B.
Suhre,
Branch
Senior
Scientist
Chemistry
and
Exposure
Branch
Health
Effects
Division
(
7509C)
and
Christine
Olinger,
Chair
of
HED
MARC
Reregistration
Branch
I
Health
Effects
Division
(
7509C)

TO:
Yan
W.
Donovan,
Chemist,
RAB1/
HED
(
7509C)
MARC
Executive
Secretary
Material
Reviewed
The
Metabolism
Assessment
Review
Committee
(
MARC)
met
on
January
30,
2001
to
consider
the
degradation
of
oxadiazon
(
2­
tert­
butyl­
4­(
2,4­
dichloro­
5­
isopropoxyphenyl)­

21,3,4­
oxadiazolin­
5­
one)
in
water.
Specifically,
MARC
was
asked
to
determine
which
degradates
should
be
included
in
the
risk
assessment.
EFED
supplied
information
that
was
presented
to
MARC
(
S.
Piper,
N.
McCarroll
and
J.
Melendez,
D271728,
1/
10/
01)
describing
degradates
found
or
having
the
potential
to
be
found
in
soil
and
water.

MARC
Conclusions
The
Committee
concluded
that
the
parent
compound,
oxadiazon
is
the
only
residue
to
be
included
in
a
drinking
water
risk
Page
­
2­
assessment.
Although,
MARC
expressed
concern
about
the
toxicity
of
other
metabolites
of
oxadiazon,
the
Committee
do
not
recommend
including
them
in
a
drinking
water
risk
assessment
because
they
are
not
likely
to
be
present
in
drinking
water.

Supporting
Reasons
The
Committee
considered
the
following
information
to
arrive
at
the
conclusion
shown
above:

­
The
major
degradate
observed
in
the
laboratory
studies
is
the
hydrolysate
1­
trimethylacetyl­
2­(
2,4­
dichloro­
5­
isopropoxyphenyl)
hydrazine
(
RP26123).
This
degradate
reached
a
maximum
of

45%
of
the
applied
on
day
31
at
pH
9
only.
RP26123
was
<
4%
in
all
the
other
laboratory
studies
at
all
samplings,
including
the
aerobic
soil
metabolism,
the
photolysis
on
soil,
and
a
supplemental
anaerobic
soil
metabolism
study.
The
available
data
indicates
that
metabolite
RP26123
should
be
a
minor
component
in
the
environment
under
most
conditions.
In
addition,
the
Committee
concluded
that
this
metabolite
is
not
likely
to
be
significantly
more
toxic
than
the
parent.

­
The
only
significant
route
of
degradation
for
the
chemical
oxadiazon
is
aqueous
photolysis.
Several
(
about
20)
minor
degradates
were
produced
in
the
laboratory
study;
only
one
was
slightly
above
the
10%
level
(
RP37084,
nomenclature
not
provided
by
the
registrant).
The
maximum
level
of
RP37084
was
only
11.5%
at
the
last
test
interval,
when
only
27.6%
of
the
applied
radioactivity
remained
undegraded.
Since
by
the
time
the
degradate
reached
11.5%
the
levels
of
oxadiazon
had
decreased
substantially
(
to
27.6%
of
the
applied),
it
appears
that
the
levels
of
the
degradate
would
not
increase
much
further.
Moreover
RP37084
was
not
an
important
metabolite
in
the
soil
photolysis
study
or
in
any
other
laboratory
study.
The
available
data
indicates
that
metabolite
RP37084
should
be
a
minor
component
in
the
environment
under
most
conditions.
In
addition,
the
Committee
concluded
that
this
metabolite
is
not
likely
to
be
significantly
more
toxic
than
the
parent.

Individuals
in
Attendance
1.
MARC
Members
Alberto
Protzel,
Christine
Olinger,
Rick
Loranger,
Leung
Cheng,
Page
­
3­
John
Doherty,
Abdallah
Khasawinah,
and
Sheila
Piper.

2.
Scientists
(
non­
MARC
members)

Nancy
McCarroll(
TOX1),
Mike
Ioannou(
TOX1),
Veronique
LaCapra(
SRRD),
and
Jose
Melendez(
EFED).

cc:
SF,
RF,
List
B
File,
S.
Piper,
N.
McCarroll
(
TOX1),
Jose
Melendez(
EFED)
RDI:
C.
Olinger:
2/
06/
01;
F.
B.
Suhre:
2/
09/
01
7509C:
CEB1:
CM­
2:
Room
810F:
308­
2717:
Oxadiazon
Page
­
4­
