UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
DATE:
February
25,
2002
SUBJECT:
Tebuthiuron.
(List
A,
Case
No.
0054)
The
Outcome
of
the
HED
Metabolism
Assessment
Review
Committee
Meeting
Held
on
01/
22/
02.
Chemical
1105501.
TXR#
0050409
FROM:
Sheila
Piper,
Chemist,
CEB/
HED
(7509C)
Mark
Corbin,
EPS,
Environmental
Risk
Branch
1
(7507C)

THROUGH:
Francis
B.
Suhre,
Branch
Senior
Scientist
Chemistry
and
Exposure
Branch
Health
Effects
Division
(7509C)

TO:
Yan
W.
Donovan,
Chemist,
RAB1/
HED
(7509C)
Executive
Secretary,
MARC
Material
Reviewed
The
Metabolism
Assessment
Review
Committee
(MARC)
met
on
January
22,
2002
to
consider
the
degradation
of
tebuthiuron
[N­[
5­(
1,1­
dimethylethyl)­
1,3,4­
thiadiazol­
2­
yl]­
N,
N'dimethylurea
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
(M.
Corbin,
1/
16/
02)
describing
degradates
found
or
having
the
potential
to
be
found
in
soil
and
water.

MARC
Conclusions
The
Committee
concluded
that
the
parent
compound
and
degradate
104
should
be
included
in
the
drinking
water
risk
assessment.
Although,
MARC
expressed
concern
about
the
toxicity
of
other
metabolites
of
tebuthiuron,
the
Committee
did
not
recommend
including
them
in
a
drinking
water
risk
assessment
because
they
are
not
likely
to
be
present
in
drinking
water.

Supporting
Reasons
Page
­2­
N
N
S
N
CH
3
CH
3
C
H
3
C
H
3
O
N
H
CH
3
N
N
S
N
CH
3
CH
3
C
H
3
C
H
3
O
NH
2
The
Committee
considered
the
following
information
to
arrive
at
the
conclusion
shown
above:

­
Available
data
indicate
that
the
parent
and
degradate
104
are
persistent
and
mobile
in
the
environment.
Tebuthiuron
is
frequently
detected
in
ground
and
surface
water
monitoring
studies.
The
degradate
104
was
detected
in
a
retrospective
ground
water
monitoring
study
and
was
a
major
degradate
in
a
terrestrial
field
dissipation
study
accounting
for
up
to
23%
of
the
mass
applied.
The
degradate
104
was
also
found
in
aerobic
soil
metabolism
and
soil
photolysis
studies
comprising
close
to
7%
of
the
mass
applied.
In
addition,
due
to
the
structural
similarity
of
degradate
104
to
tebuthiuron
(104
lacks
an
N­
methyl
group)
and
lack
of
toxicity
information
on
degradate
104,
MARC
assumes
that
it
has
similar
toxicity
to
the
parent.

The
chemical
structures
of
tebuthiuron
and
degradate
104
Tebuthiuron:
[N­[
5­(
1,1­
dimethylethyl)­
1,3,4­
thiadiazol­
2­
yl]­
N,
N'­
dimethylurea]
104:
N­[
5­(
1,1­
dimethylethyl)­
1,3,4­
thiadiazol­
2­
yl
N­
methylurea
Individuals
in
Attendance
1.
MARC
Members
Abdallah
Khasawinah,
Norman
Birchfield,
Christine
Olinger,
Rick
Loranger,
Leung
Cheng,
John
Doherty,
Bill
Wassell,
Yan
Donovan,
David
Nixon,
and
Sheila
Piper.

2.
Scientists
(non­
MARC
members)

Ken
Dockter(
RRB2),
Robert
Fricke(
RRB2),
Paula
Deschamp(
RRB2),
and
Mark
Corbin(
EFED).

cc:
SF,
RF,
List
B
File,
S.
Piper,
P.
Deschamp
(RRB2),
Mark
Corbin
(EFED)
RDI:
C.
Olinger:
2/
22/
02;
F.
B.
Suhre:
2/
25/
02
7509C:
CEB1:
CM­
2:
Room
810F:
308­
2717:
Tebuthiuron
