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in 1996. EXTOXNET no longer updates this information, but it may be useful
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E X T O X N E T
A Pesticide Information Project of Cooperative Extension
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University of Idaho, and the University of California at Davis
and the Institute for Environmental Toxicology, Michigan State
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USDA/Extension Service/National Agricultural Pesticide Impact
EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Trade names include Cekuthoate, Chimigor 40, Cygon 400, Daphene,
De-Fend, Demos NF, Devigon, Dicap, Dimate 267, Dimet, Dimethoat
Tech 95%, Dimethopgen, Ferkethion, Fostion MM, Perfekthion,
Rogodan, Rogodial, Rogor, Roxion, Sevigor, Trimetion.
Dimethoate is moderately toxic compound in EPA toxicity class II.
Labels for products containing dimethoate must bear the Signal
Word WARNING. Dimethoate is a General Use Pesticide (GUP).
Dimethoate is an organophosphate insecticide used to kill mites
and insects systemically and on contact. It is used against a
wide range of insects, including aphids, thrips, planthoppers,
and whiteflies on ornamental plants, alfalfa, apples, corn,
cotton, grapefruit, grapes, lemons, melons, oranges, pears,
pecans, safflower, sorghum, soybeans, tangerines, tobacco,
tomatoes, watermelons, wheat, and other vegetables. It is also
used as a residual wall spray in farm buildings for house flies.
Dimethoate has been administered to livestock for control of
botflies. Dimethoate is available in aerosol spray, dust,
emulsifiable concentrate, and ULV concentrate formulations.
Unless otherwise specified, the data summarized in this profile
refer to the technical product.
is available in aerosol spray, dust, emulsifiable concentrate,
and ULV concentrate formulations.
- Acute toxicity: Dimethoate is moderately
toxic by ingestion, inhalation, and dermal absorption.
The reported acute oral LD50 values for the technical
product range from 180 to 330 mg/kg in the rat; although
an oral LD50 of as low as 28 to 30 mg/kg has been
reported, it is regarded by some as less reflective of
the toxicity of current products [2,13]. Reported oral
LD50 values in other species are 160 mg/kg in mice and
400 to 500 mg/kg in rabbits [2,13]. In guinea pigs, the
oral toxicity is reported as 550 to 600 mg/kg for the
pure and laboratory grade of the compound, but for the
technical grade is only 350 to 400 mg/kg . It is not
clear whether the increased toxicity results from
impurities present initially in the technical product or
whether these may be formed from degradation over time
. Reported dermal LD50 values for dimethoate are 100
to 600 mg/kg in rats, again with a much lower value for
an earlier product [2,13]. Dimethoate is reportedly not
irritating to the skin and eyes of lab animals [8,13].
Severe eye irritation has occurred in workers
manufacturing dimethoate, although this may be due to
impurities . Via the inhalation route, the reported
4-hour LC50 is greater than 2.0 mg/L, indicating slight
toxicity . Effects of acute exposure are those
typical of organophosphates. Symptoms of acute exposure
to organophosphate or cholinesterase-inhibiting compounds
may include the following: numbness, tingling sensations,
incoordination, headache, dizziness, tremor, nausea,
abdominal cramps, sweating, blurred vision, difficulty
breathing or respiratory depression, and slow heartbeat.
Very high doses may result in unconsciousness,
incontinence, and convulsions or fatality. Persons with
respiratory ailments, recent exposure to cholinesterase
inhibitors, impaired cholinesterase production, or liver
malfunction may be at increased risk from exposure to
dimethoate. High environmental temperatures or exposure
of dimethoate to visible or UV light may enhance its
- Chronic toxicity: There was no
cholinesterase inhibition in an adult human who ingested
18 mg (about 0.26 mg/kg/day) of dimethoate/day for 21
days. No toxic effects and no cholinesterase inhibition
were observed in individuals who ingested 2.5 mg/day
(about 0.04 mg/kg/day) for 4 weeks. In another study with
humans given oral doses of 5, 15, 30, 45 or 60 mg/day for
57 days, cholinesterase inhibition was observed only in
the 30 mg/day and higher dosage groups . Repeated or
prolonged exposure to organophosphates may result in the
same effects as acute exposure, including the delayed
symptoms. Other effects reported in workers repeatedly
exposed include impaired memory and concentration,
disorientation, severe depression, irritability,
confusion, headache, speech difficulties, delayed
reaction times, nightmares, sleepwalking, and drowsiness
or insomnia. An influenza-like condition with headache,
nausea, weakness, loss of appetite, and malaise has also
been reported .
- Reproductive effects: When mice were
given 9.5 to 10.5 mg/kg/day dimethoate in their drinking
water, there was decreased reproduction, pup survival,
and growth rates of surviving pups. Adults in this study
exhibited reduced weight gain, but their survival was not
affected. In a three-generation study with mice, 2.5
mg/kg/day did not decrease reproductive performance or
pup survival . Once in the bloodstream, dimethoate may
cross the placenta . Impaired reproductive function in
humans is not likely under normal conditions.
- Teratogenic effects: Dimethoate is
teratogenic in cats and rats [8,2]. A dosage of 12
mg/kg/day given to pregnant cats increased the incidence
of extra toes on kittens [2,8]. The same dosage given to
pregnant rats produced birth defects related to bone
formation, runting and malfunction of the bladder.
Dosages of 3 or 6 mg/kg/day were not teratogenic in cats
or rats . No effects were observed in cats and rats at
doses of 2.8 mg/kg/day. There were no teratogenic effects
seen in the offspring of mice given 9.5 to 10.5 mg/kg/day
dimethoate in their drinking water . It is not likely
that teratogenic effects will be seen in humans under
- Mutagenic effects: Mutagenic effects due
to dimethoate exposure were seen in mice. They were more
prominent in male mice given a single high dose of
dimethoate than in male mice given one twelfth of the
same dose daily for 30 days . Mutagenic effects are
unlikely in humans under normal circumstances.
- Carcinogenic effects: An increase in
malignant tumors was reported in rats given oral doses of
5, 15 or 30 mg/kg/day dimethoate for over a year. The
increases were not, however, dose dependent . That is,
higher doses did not necessarily result in higher tumor
rates. Thus the evidence of carcinogenicity, even with
high-dose, long-term exposure, is inconclusive. This
suggests carcinogenic effects in humans are unlikely.
- Organ toxicity: Target organs as
determined through animal tests include the testicles,
kidneys, liver, and spleen .
- Fate in humans and animals: Dimethoate
is rapidly metabolized by mammals. Rats excreted about 50
to 60% of administered doses in urine, expired air and
feces within 24 hours . Human volunteers excreted 76
to 100% of administered dimethoate within 24 hours .
The rate of metabolism and elimination varied in several
species tested. Amongst several mammalian species tested,
dimethoate appears to be less toxic to those animals with
higher liver-to-body weight ratios and to those with the
highest rate of dimethoate metabolism . Following
application of dimethoate to the backs of cows at 30
mg/kg, the concentration of dimethoate reached a maximum
level of 0.02 ppm in blood and milk in about 3 hours, and
decreased to 0.01 ppm within 9 hours .
- Effects on birds: Dimethoate is
moderately to very highly toxic to birds. In Japanese
quail, a 5-day dietary LC50 of 341 ppm is reported .
It may be very highly toxic to other birds; reported
acute oral LD50 values are 41.7 to 63.5 mg/kg in mallards
and 20.0 mg/kg in pheasants . Birds are not able to
metabolize dimethoate as rapidly as mammals do, which may
account for its relatively higher toxicity in these
- Effects on aquatic organisms: Dimethoate
is moderately toxic to fish, with reported LC50 values of
6.2 mg/L in rainbow trout, and 6.0 mg/L in bluegill
sunfish . It is more toxic to aquatic invertebrate
species such as stoneflies and scuds .
- Effects on other organisms: Dimethoate
is highly toxic to honeybees. The 24-hour topical LD50
for dimethoate in bees is 0.12 ug per bee .
- Breakdown in soil and groundwater:
Dimethoate is of low persistence in the soil environment.
Soil half-lives of 4 to 16 days, or as high as 122 days
have been reported, but a representative value may be on
the order of 20 days [12,19]. Because it is rapidly
broken down by soil microorganisms, it will be broken
down faster in moist soils. Dimethoate is highly soluble
in water, and it adsorbs only very weakly to soil
particles so it may be subject to considerable leaching
[12,19]. However, it is degraded by hydrolysis,
especially in alkaline soils, and evaporates from dry
soil surfaces. Losses due to evaporation of 23 to 40% of
applied dimethoate have been reported .
Biodegradation may be significant, with a 77% loss
reported in a nonsterile clay loam soil after 2 weeks
- Breakdown in water: In water, dimethoate
is not expected to adsorb to sediments or suspended
particles, nor to bioaccumulate in aquatic organisms
. It is subject to significant hydrolysis, especially
in alkaline waters. The half-life for dimethoate in raw
river water was 8 days, with disappearance possibly due
to microbial action or chemical degradation .
Photolysis and evaporation from open waters are not
expected to be significant .
- Breakdown in vegetation: Dimethoate is
not toxic to plants .
- Appearance: Dimethoate is a grey-white
crystalline solid at room temperature .
- Chemical Name: O,O-dimethyl
S-methylcarbamoylmethyl phosphorodithioate 
- CAS Number: 60-51-5
- Molecular Weight: 229.28
- Water Solubility: 25 g/L @ 21 C 
- Solubility in Other Solvents: s. in
methanol and cyclohexane; s.s in aliphatic hydrocarbons,
aromatic hydrocarbons, diethyl ether, carbon
tetrachloride, hexane, and xylene; v.s. in chloroform,
- Melting Point: 43-45 C (technical) 
- Vapor Pressure: 1.1 mPa @ 25 C 
- Partition Coefficient: 0.6990 
- Adsorption Coefficient: 20 
- ADI: 0.01 mg/kg/day 
- MCL: Not Available
- RfD: 0.0002 mg/kg/day 
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
Agricultural Products Group
P.O. Box 13528
Research Triangle Park, NC 27709-3528
- Phone: 800-669-2273
- Emergency: 800-832-4357
References for the information in this PIP can be found in
Reference List Number 5
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