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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Common names include metomil and mesomile. Trade names include
Acinate, Agrinate, DuPont 1179, Flytek, Kipsin, Lannate, Lanox,
Memilene, Methavin, Methomex, Nudrin, NuBait, Pillarmate and SD
Methomyl is a highly toxic compound in EPA toxicity class I. It
is classified as Restricted Use Pesticide (RUP) by EPA because of
its high acute toxicity to humans. The Signal Words for products
containing methomyl depend upon the formulation of the product.
Restricted Use Pesticides may be purchased and used only by
certified applicators. Reentry periods for farm workers of 1 to 7
days are required, depending on the crop.
Methomyl was introduced in 1966 as a broad spectrum insecticide.
It is also used as an acaricide to control ticks and spiders. It
is used for foliar treatment of vegetable, fruit and field crops,
cotton, commercial ornamentals, and in and around poultry houses
and dairies. It is also used as a fly bait. Methomyl is effective
in two ways: (a) as a "contact insecticide," because it
kills target insects upon direct contact, and (b) as a
"systemic insecticide" because of its capability to
cause overall "systemic" poisoning in target insects,
after it is absorbed and transported throughout the pests that
feed on treated plants. It is capable of being absorbed by plants
without being "phytotoxic" or harmful, to the plant.
- Acute toxicity: Methomyl is highly toxic
via the oral route, with reported oral LD50 values of 17
to 24 mg/kg in rats , 10 mg/kg in mice, and 15 mg/kg
in guinea pigs . Symptoms of methomyl exposure are
similar to those caused by other carbamates and
cholinesterase inhibitors . These may include
weakness, blurred vision, headache, nausea, abdominal
cramps, chest discomfort, constriction of pupils,
sweating, muscle tremors, and decreased pulse. If there
is severe poisoning, symptoms of twitching, giddiness,
confusion, muscle incoordination, slurred speech, low
blood pressure, heart irregularities, and loss of
reflexes may also be experienced. Death can result from
discontinued breathing, paralysis of muscles of the
respiratory system, intense constriction of the openings
of the lung, or all three . It is moderately toxic via
inhalation with a reported 4-hour inhalation LC50 in male
rats of 0.3 mg/L . Inhalation of dust or aerosol may
cause irritation, lung and eye problems, with symptoms of
chest tightness, blurred vision, tearing, wheezing, and
headaches appearing upon exposure. Other systemic
symptoms of cholinesterase inhibition may appear within a
few minutes to several hours of exposure . It is
slightly toxic via the dermal route, with a reported
dermal LD50 of 5880 mg/kg in rabbits , and is
absorbed only slowly through the skin . However, if
sufficient amounts are absorbed through the skin,
symptoms similar to those induced by ingestion or
inhalation will develop . Within fifteen minutes to
four hours of exposure, the immediate area of contact may
show localized sweating and uncoordinated muscular
contractions . In rabbits, application of methomyl
resulted in mild eye irritation . Pain,
short-sightedness, blurring of distant vision, tearing,
and other eye disturbances may occur within a few minutes
of eye contact with methomyl .
- Chronic toxicity: Prolonged or repeated
exposure to methomyl may cause symptoms similar to the
pesticide's acute effects . Repeated exposure to small
amounts of methomyl may cause an unsuspected inhibition
of cholinesterase, resulting in flu-like symptoms, such
as weakness, lack of appetite, and muscle aches.
Cholinesterase-inhibition may persist for two to six
weeks. This condition is reversible if exposure is
discontinued. Since cholinesterase is increasingly
inhibited with each exposure, severe
cholinesterase-inhibition symptoms may be produced in a
person who has had previous methomyl exposure, while a
person without previous exposure may not experience any
symptoms at all . In a 24-month study with rats fed
doses of 2.5, 5 or 20 mg/kg/day, effects were only
observed at the highest dose tested, 20 mg/kg/day. At
this very high dose, red blood cell counts and hemoglobin
levels were significantly reduced in female rats . In
a 2-year feeding study with dogs, 5 mg/kg/day caused no
observed adverse effects . It is not likely that
chronic effects would be seen in humans unless exposures
were unexpectedly high, as with chronic misuse.
- Reproductive effects: Methomyl fed to
rats at dietary doses of 2.5 or 5 mg/kg for three
generations caused no adverse effect on reproduction, nor
was there any evidence of congenital abnormalities .
No fetotoxicity was observed in offspring of pregnant
rats given 33.9 mg/kg/day on day 6 to 21 of gestation
. Based on these data it appears unlikely that
methomyl will have reproductive effects.
- Teratogenic effects: No teratogenic
effects were found in the fetuses of female rabbits that
were fed approximately 15 to 30 mg/kg/day during the 8th
to 16th day of gestation . In rats, no embryonic or
teratogenic effects were observed at the highest dietary
dose administered, approximately 34 mg/kg/day . Thus,
methomyl does not appar to be teratogenic.
- Mutagenic effects: In a number of assays
(including Ames test, a reverse mutation assay, a
recessive lethal assay, three DNA damage studies, an
unscheduled DNA synthesis assay, and in vivo and in vitro
cytogenetic assays), methomyl was not mutagenic [8,39].
There is no evidence that methomyl is a mutagenic or
- Carcinogenic effects: There was no
evidence of carcinogenicity in either rats or dogs that
ingested high doses of methomyl in 2-year feeding studies
. Methomyl was not carcinogenic in 22- and 24-month
studies with rats fed doses of up to 20 mg/kg, nor in a
two-year study with mice fed dietary doses of up to 93.4
mg/kg/day . The evidence suggests that methomyl is not
- Organ toxicity: Lungs, skin, eyes,
gastrointestinal tract, kidneys, spleen, and
blood-forming organs have been affected in various
experiments, depending on route of entry, duration of
exposure, and dosage.
- Fate in humans and animals: Methomyl is
quickly absorbed through the skin, lungs, and
gastrointestinal tract and are broken down in the liver.
Breakdown products are readily excreted via respiration
and urine . Although they do not appear to accumulate
in any particular body tissue, they may alter many other
enzymes besides the cholinesterases .
- Effects on birds: Methomyl is highly
toxic to birds. The acute oral LD50 in bobwhite quail is
24.2 mg/kg . The oral LD50 of methomyl is 28 mg/kg in
hens. All deaths occurred within ten minutes of dosing.
The clinical signs of toxicity included tearing of the
eyes, salivation, occasional convulsions, and respiratory
disorders. In Japanese quail, the LD50 is 34 mg/kg .
The LD50 of a 90% pure formulation is 15.9 mg/kg in
eight-month-old mallards, and 15.4 mg/kg in three- to
four-month-old male pheasants . The LD50 for
starlings is 42 mg/kg and for redwinged blackbirds is 10
- Effects on aquatic organisms: Methomyl
is moderately to highly toxic to fish and highly toxic to
aquatic invertebrates. The 96-hour LC50 in rainbow trout
for a liquid formulation of methomyl is 3.4 mg/L and for
bluegill sunfish is 0.8 mg/L . The 48-hour LC50 for
Daphnia magna (a small, freshwater crustacean) is 0.0287
mg/L . A 28-day fish residue study indicated that
methomyl did not accumulate in fish tissue . Methomyl
is unlikely to bioconcentrate in aquatic systems .
- Effects on other organisms: Methomyl is
highly toxic to bees both by direct contact and through
ingestion . The LD50 for a 90% pure formulation of
methomyl is 11.0 to 22.0 mg/kg in mule deer .
Symptoms of acute poisoning in these animals included
drowsiness, drooling, diarrhea, and tremors .
- Breakdown in soil and groundwater:
Methomyl has low persistence in the soil environment,
with a reported half-life of approximately 14 days .
Because of its high solubility in water, and low affinity
for soil binding methomyl may have potential for
groundwater contamination . It is very mobile in
sandy loam and silty clay loam soils, but only slight
leaching was observed in a silt loam and in a sandy soil.
Methomyl is rapidly degraded by soil microbes .
Methomyl residues are not expected to be found in treated
soil after the growing season in which it is applied
- Breakdown in water: Aqueous solutions of
methomyl have been reported to decompose more rapidly on
aeration, in sunlight, or in alkaline media . The
estimated aqueous half-life for the insecticide is 6 days
in surface water and over 25 weeks in groundwater .
In one experiment, the hydrolysis half-lives of methomyl
in solutions at pHs of 6.0, 7.0 and 8.0 were 54, 38, and
20 weeks respectively. In pure water, the hydrolysis
half-life has been estimated to be 262 days .
- Breakdown in vegetation: Following soil
treatment, plants take up methomyl through their roots
and move it throughout the plant by a process called
"translocation." When methomyl is applied to
plants, its residues are short-lived . After it is
applied to leaves, it has a 3 to 5 day half-life .
Less than 3% methomyl remained in cabbage plants 1 week
after they were given foliar treatment with the
- Appearance: Methomyl is a white,
crystalline solid with a slight sulfurous odor.
- Chemical Name: S-methyl
N-(methylcarbamoyloxy) thioacetimidate 
- CAS Number: 16752-77-5
- Molecular Weight: 162.21
- Water Solubility: 57.9 g/l @ 25 C 
- Solubility in Other Solvents: v.s. in
methanol, acetone, ethanol, and isopropanol 
- Melting Point: 79 C 
- Vapor Pressure: 6.65 mPa @ 25 C
- Partition Coefficient: Not Available
- Adsorption Coefficient: 72 
- ADI: 0.03 mg/kg/day 
- MCL: Not Available
- RfD: 0.025 mg/kg/day 
- PEL: 2.5 mg/m3 (8-hour) 
- HA: 0.2 mg/L 
- TLV: Not Available
DuPont Agricultural Products
Walker's Mill, Barley Mill Plaza
P.O. Box 80038
Wilmington, DE 19880-0038
- Phone: 800-441-7515
- Emergency: 800-441-3637
References for the information in this PIP can be found in
Reference List Number 3
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide