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
S-1,2-bis(ethoxycarbonyl)ethyl O,O-dimethyl phosphorodithioate
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. It is also slightly toxic
via the dermal route, with reported dermal LD50 values of greater than
4000 mg/kg in rats.
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.
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.
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 slightly toxic in goldfish (10.7 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
on other organisms: The compound is highly toxic
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.
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.
in vegetation: Residues were found mainly associated
with areas of high lipid content in the plant. Increased moisture content
Technical malathion is a clear, amber liquid at room temperature.
- Chemical Name: diethyl (dimethoxy
- 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.
University and World Health Organisation