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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Malathion is also known as carbophos, maldison and mercaptothion.
Trade names for products containing malathion include Celthion,
Cythion, Dielathion, El 4049, Emmaton, Exathios, Fyfanon and
Hilthion, Karbofos and Maltox.
Malathion is a slightly toxic compound in EPA toxicity class III.
Labels for products containing it must carry the Signal Word
CAUTION. Malathion is a General Use Pesticide (GUP). It is
available in emulsifiable concentrate, wettable powder, dustable
powder, and ultra low volume liquid formulations.
Malathion is a nonsystemic, wide-spectrum organophosphate
insecticide. It was one of the earliest organophosphate
insecticides developed (introduced in 1950). Malathion is suited
for the control of sucking and chewing insects on fruits and
vegetables, and is also used to control mosquitoes, flies,
household insects, animal parasites (ectoparasites), and head and
body lice. Malathion may also be found in formulations with many
Formulation: It is
available in emulsifiable concentrate, wettable powder, dustable
powder, and ULV liquid formulations. Malathion may also be found
in formulations with many other pesticides.
- Acute toxicity: Malathion is slightly
toxic via the oral route, with reported oral LD50 values
of 1000 mg/kg to greater than 10,000 mg/kg in the rat,
and 400 mg/kg to greater than 4000 mg/kg in the mouse
[2,13]. It is also slightly toxic via the dermal route,
with reported dermal LD50 values of greater than 4000
mg/kg in rats [2,13]. Effects of malathion are similar to
those observed with other organophosphates, except that
larger doses are required to produce them [2,8]. It has
been reported that single doses of malathion may affect
immune system response . 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. The acute
effects of malathion depend on product purity and the
route of exposure . Other factors which may influence
the observed toxicity of malathion include the amount of
protein in the diet and gender. As protein intake
decreased, malathion was increasingly toxic to the rats
. Malathion has been shown to have different
toxicities in male and female rats and humans due to
metabolism, storage, and excretion differences between
the sexes, with females being much more susceptible than
males . Numerous malathion poisoning incidents have
occurred among pesticide workers and small children
through accidental exposure. In one reported case of
malathion poisoning, an infant exhibited severe signs of
cholinesterase inhibition after exposure to an aerosol
bomb containing 0.5% malathion .
- Chronic toxicity: Human volunteers fed
very low doses of malathion for 1 1/2 months showed no
significant effects on blood cholinesterase activity.
Rats fed dietary doses of 5 mg/kg/day to 25 mg/kg/day
over 2 years showed no symptoms apart from depressed
cholinesterase activity. When small amounts of the
compound were administered for 8 weeks, rats showed no
adverse effects on whole-blood cholinesterase activity
. Weanling male rats were twice as susceptible to
malathion as adults.
- Reproductive effects: Several studies
have documented developmental and reproductive effects
due to high doses of malathion in test animals . Rats
fed high doses of 240 mg/kg/day during pregnancy showed
an increased rate of newborn mortality. However,
malathion fed to rats at low dosages caused no
reproductive effects . It is not likely that malathion
will cause reproductive effects in humans under normal
- Teratogenic effects: Rats fed high doses
(240 mg/kg/day) showed no teratogenic effects. Malathion
and its metabolites can cross the placenta of the goat
and depress cholinesterase activity of the fetus .
Chickens fed diets at low doses for 2 years showed no
adverse effects on egg hatching . Current evidence
indicates that malathion is not teratogenic.
- Mutagenic effects: Malathion produced
detectable mutations in three different types of cultured
human cells, including white blood cells and lymph cells
[2,8]. It is not clear what the implications of these
results are for humans.
- Carcinogenic effects: Female rats on
dietary doses of approximately 500 mg/kg/day of malathion
for 2 years did not develop tumors . Adrenal tumors
developed in the males at low doses, but not at the high
doses , suggesting that malathion was not the cause.
Three of five studies that have investigated the
carcinogenicity of malathion have found that the compound
does not produce tumors in the test animals. The two
other studies have been determined to be unacceptible
studies and the results discounted [2,8,80]. Available
evidence suggests that malathion is not carcinogenic but
the data are not conclusive.
- Organ toxicity: The pesticide has been
shown in animal testing and from use experience to affect
the central nervous system, immune system, adrenal
glands, liver, and blood.
- Fate in humans and animals: Malathion is
rapidly and effectively absorbed by practically all
routes including the gastrointestinal tract, skin, mucous
membranes, and lungs. Malathion undergoes similar
detoxification mechanisms to other organophosphates, but
it can also be rendered nontoxic via another simple
mechanism, splitting of either of the carboxy ester
linkages. Animal studies indicate it is very rapidly
eliminated though urine, feces and expired air with a
reported half-life of approximately 8 hours in rats and
approximately 2 days in cows . Autopsy samples from
one individual who had ingested large amounts of
malathion showed a substantial portion in the stomach and
intestines, a small amount in fat tissue, and no
detectable levels in the liver. Malathion requires
conversion to malaoxon to become an active
anticholinesterase agent. Most of the occupational
evidence indicates a low chronic toxicity for malathion.
One important exception to this was traced to impurities
in the formulation of the pesticide .
- Effects on birds: Malathion is
moderately toxic to birds. The reported acute oral LD50
values are: in mallards, 1485 mg/kg; in pheasants, 167
mg/kg; in blackbirds and starlings, over 100 mg/kg; and
in chickens, 525 mg/kg [2,6]. The reported 5- to 8-day
dietary LC50 is over 3000 ppm in Japanese quail, mallard,
and northern bobwhite, and is 2639 ppm in ring-neck
pheasants . Furthermore, 90% of the dose to birds was
metabolized and excreted in 24 hours via urine .
- Effects on aquatic organisms: Malathion
has a wide range of toxicities in fish, extending from
very highly toxic in the walleye (96-hour LC50 of 0.06
mg/L) to highly toxic in brown trout (0.1 mg/L) and the
cutthroat trout (0.28 mg/L), moderately toxic in fathead
minnows (8.6 mg/L) and slightly toxic in goldfish (10.7
mg/L) [13,8,16]. Various aquatic invertebrates are
extremely sensitive, with EC50 values from 1 ug/L to 1
mg/L . Malathion is highly toxic to aquatic
invertebrates and to the aquatic stages of amphibians.
Because of its very short half-life, malathion is not
expected to bioconcentrate in aquatic organisms. However,
brown shrimp showed an average concentration of 869 and
959 times the ambient water concentration in two separate
- Effects on other organisms: The compound
is highly toxic to honeybees .
- Breakdown in soil and groundwater:
Malathion is of low persistence in soil with reported
field half-lives of 1 to 25 days . Degradation in
soil is rapid and related to the degree of soil binding
. Breakdown occurs by a combination of biological
degradation and nonbiological reaction with water .
If released to the atmosphere, malathion will break down
rapidly in sunlight, with a reported half-life in air of
about 1.5 days . It is moderately bound to soils, and
is soluble in water, so it may pose a risk of groundwater
or surface water contamination in situations which may be
less conducive to breakdown. The compound was detected in
12 of 3252 different groundwater sources in two different
states, and in small concentrations in several wells in
California, with a highest concentration of 6.17 ug/L
- Breakdown in water: In raw river water,
the half-life is less than 1 week, whereas malathion
remained stable in distilled water for 3 weeks .
Applied at 1 to 6 lb/acre in log ponds for mosquito
control, it was effective for 2.5 to 6 weeks . In
sterile seawater, the degradation increases with
increased salinity. The breakdown products in water are
mono- and dicarboxylic acids .
- Breakdown in vegetation: Residues were
found mainly associated with areas of high lipid content
in the plant. Increased moisture content increased
- Appearance: Technical malathion is a
clear, amber liquid at room temperature .
- Chemical Name: diethyl (dimethoxy
thiophosphorylthio) succinate 
- CAS Number: 121-75-5
- Molecular Weight: 330.36
- Water Solubility: 130 mg/L 
- Solubility in Other Solvents: v.s. in
most organic solvents 
- Melting Point: 2.85 C 
- Vapor Pressure: 5.3 mPa @ 30 C 
- Partition Coefficient: 2.7482 
- Adsorption Coefficient: 1800 
- ADI: 0.02 mg/kg/day 
- MCL: Not Available
- RfD: 0.02 mg/kg/day 
- PEL: 15 mg/m3 (8-hour) (dust) 
- HA: 0.2 mg/L (lifetime) 
- TLV: Not Available
Drexel Chemical Company
1700 Channel Avenue
Memphis, TN 38113
- Phone: 901-774-4370
- Emergency: Not Available
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