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5706
J.
Agric.
Food
Chem.
2001,
49,
5706-5709
Novel
Field
Sampling
Procedure
for
the
Determination
of
Methiocarb
Residues
in
Surface
Waters
from
Rice
Fields
Thomas
M.
Primus,*·;
Dennis
J.
Kohler,"
:Mike Avery,=
Pat
Bolich,
IM.
0.
vVay,"
and
John
J.
Johnston
7
Analytical Chemistry Project, APHIS/:'fational Wildlife Research Center, U.S. Department of Agriculture,
4101 LaPorte Avenue, Ft. Collins, Colorado 80521; Bird Research Program, APHIS/National Wildlife
Research Center, U.S. Department
of
Agriculture, 2820
East
University Avenue,
Gainesville, Florida 32641; Louisiana State University Agricultural Center,
P.O.
Box
1429,
Crowley, Louisiana 70527; and Texas Agricultural Experiment Station,
Route
7,
Box 999, Beaumont, Texas 77713
Methiocarb
was
extracted
from
surface
water
samples
collected
at
experimental
rice field
sites
in
Louisiana
and
Texas.
The
sampling
system
consisted
of a
single-stage
90-=
Empore
extraction
disk
unit
equipped with a
battery-powered
vacuum
pump.
After
extraction,
the
C-18
extraction
disks
were
stored
in
an
inert
atmosphere
at
-10
°C
and
shipped
overnight
to
the
laboratory.
The
disks
were
extracted
with
methanol
and
the
extracts
analyzed
by
reversed-phase
high-performance
liquid
chromatography
with
a
methanol/water
mobile phase.
Methiocarb
was
detected
by
ultraviolet
absorption
at
223
nm
and
quantified
with
the
use
of
calibration
standards.
Recoveries
from
control
surface
water
samples
fortified
at
5.0, 10, 50,
and
100
ng/mL
methiocarb
averaged
92 ± 7%. A
method
limit
of
detection for
methiocarb
in
rice field surface
water
was
estimated
to be 0.23 ng/mL
at
223
nm.
Keywords:
Methiocarb; mesurol; high-performance liquid chromatography;
solid
phase extraction
disks;
water
rnTRODUCTION
Bird
damage
to
seeded rice is a
persistent
problem
in
the
southern
United
States
that
costs
producers
millions
of dollars
annually
(1,
2).
Currently,
there
is
no commercially available effective
bird
repellent
reg-
istered
for rice seed. Wildlife biologists
have
been
searching
for
an
effective repellent
to
minimize
the
damage
to rice for decades. Rice
farmers
have
always
had
problems
with
bird
depredation
during
planting
season.
Birds
feed
on
the
seed
after
surface
water
is
removed
during
the
seed
soaking
stage
of
germination.
For
a few days
after
water
is removed from
the
fields,
germinating
rice
seed
is
an
attractive
source
of
food to
various
bird
species.
After
sprouts
reach
a couple of
inches
in
height,
the
depredation
subsides
as
the
seed
endosperm
is no longer available to
the
birds
as a source
of food.
Damage
due
to
bird
depredation
is
severe
enough
in
some cases
that
nearly
100% of
the
rice seed
is
consumed
and
replanting
is
the
only option.
Methiocarb [3,5-dimethyl-4-(methylthio)phenol methyl-
carbamate]
has
been
known
as
an
effective
bird
repel-
lent
for quite some time
and
is
considered to be insoluble
in
water.
Methiocarb causes gastrointestinal
malaise
for
many
avian
species
when
ingested.
Methiocarb
is
an
N-methylcarbamate
currently
registered
as a mollisci-
cide.
Methiocarb
has
been shown to
be
an
effective
bird
repellent
(3)
when
applied to rice
seed
in
cage
and
pen
trials
(4).
A
seed
tre<itment
with
methiocarb
and
a
t
U.S. Department
of
Agriculture, Ft. Collins,
Co.
l
U.S. Department
of
Agriculture, Gainesville, FL.
I
Louisiana State University Agricultural Center.
•
Tex~
Agricultural Experiment Station.
Table
1.
Ninety-Six
Hour
LC
50
Acute
Oral
Toxicity
Data
species
mean
(m!PL)
range
(m!PL)
Pteronarcys
(stoneflies)
0.005
0.004-0.006
rainbow
trout
0.80
0.63-0.89
·
..
bluegill
0.21
0.12-0.36
commercially
available
adhesive
were
applied
to
rice
seed to
produce
a 0.075% methiocarb-fortified rice seed,
which
was
distributed
in
flooded fields
aerially
for
efficacy
trials.
The
fields
remained
flooded for
three
to
six days for
seed
soaking
and
were
then
drained
to allow
germination
to proceed.
The
water
is
typically
drained
back
into
rivers
or
nearby
estuaries.
Although
methio-
carb
has
a
human
health
risk
as
it
is
a
cholinesterase
inhibitor
and
therefore
can affect
the
nervous
system,
the
risk
as a
seed
treatment
to
humans
would
be
extremely
minimal.
A more
pressing
concern
would
be
the
toxicity
to
aquatic
organisms.
As
shown
in
Table
1
the
acute
oral
toxicity for cold-water
fish
(rainbow
trout)
and
warm-water
fish
(bluegill) is
high.
The
acute
oral
toxicity for
aquatic
invertebrates
is considered to be very
high
(5).
Therefore,
during
the
experimental
phase
of
field efficacy
trials
a
simple
method
to
monitor
the
methiocarb
residues
in
rice
field
surface
waters
was
needed to
supply
data
for
potential
registration
inquiries
and
to
ascertain
the
effectiveness of
the
adhesive
used
to
limit
the
loss of
methiocarb
bound
to
the
rice seed.
Field
trials
in
small
test
plots
were
set
up
for
residue
analysis
in
Louisiana
and
Texas.
Several
methods
for
the
determination
ofmethiocarb
in
water
are
available.
However,
water
samples
of
500
mL
in
volume
are
expensive to
ship
and
therefore
a
simple
field
extraction
method
was
pursued
that
local
operations
personnel
could use
to
collect
samples.
10.102W010540v
CCC:
$20.00
©
2001
American
Chemical
Society
Published
on
Web
11/17/2001
