Malathion is an organophosphate insecticide which acts as an
acetylcholinesterase inhibitor. In the USSR, it was known as
New Zealand and
Australia as maldison and in South
Africa as mercaptothion.
2 Mechanism of action, production method
3 Medical use
4.2 Attention-deficit/hyperactivity disorder
5 See also
7 External links
Malathion is a pesticide that is widely used in agriculture,
residential landscaping, public recreation areas, and in public health
pest control programs such as mosquito eradication. In the US, it
is the most commonly used organophosphate insecticide.
Malathion mixture with corn syrup was used in the 1980s in Australia
and California to combat the Mediterranean fruit fly. In Canada and
the US, malathion was[when?] sprayed in many cities to combat west
Malathion was used over the last couple of decades[when?]
on a regular basis during summer months to kill mosquitoes, but
homeowners were allowed to exempt their properties if they
chose. Today,
Winnipeg is the only major city in
Canada with an ongoing malathion adult-mosquito-control
Mechanism of action, production method
Malathion is an acetylcholinesterase inhibitor, a diverse family of
chemicals that includes sarin and carbaryl. Upon uptake into the
target organism, it binds irreversibly to several, random serine
residues on the cholinesterase enzyme, with a peroxide as the leaving
group. The resultant phosphoester group is strongly bound to the
cholinesterase, and irreversibly deactivates the enzyme which leads to
rapid build-up of acetylcholine at the synapse.
It is produced by the addition of dimethyl dithiophosphoric acid to
diethyl maleate. The compound is chiral but is used as a racemate.
Malathion in low doses (0.5% preparations) is used as a treatment for:
Head lice and body lice.
Malathion is approved by the US Food and Drug
Administration for treatment of pediculosis. It is claimed to
effectively kill both the eggs and the adult lice, but in fact has
been shown in UK studies to be only 36% effective on head lice, and
less so on their eggs. This low efficiency was found when
malathion was applied to lice found on schoolchildren in the Bristol
area in the UK and it is assumed[by whom?] to be caused by the lice
having developed resistance against malathion.
Preparations include Derbac-M, Prioderm, Quellada-M and Ovide.
Malathion is of low toxicity; however, absorption or ingestion into
the human body readily results in its metabolism to malaoxon, which is
substantially more toxic. In studies of the effects of long-term
exposure to oral ingestion of malaoxon in rats, malaoxon has been
shown to be 61 times more toxic than malathion. It is cleared from
the body quickly, in three to five days. According to the United
States Environmental Protection Agency there is currently no reliable
information on adverse health effects of chronic exposure to
malathion. Acute exposure to extremely high levels of malathion
will cause body-wide symptoms whose intensity will be dependent on the
severity of exposure. Symptoms include skin and eye irritation,
cramps, nausea, diarrhea, excessive sweating, seizures and even death.
Most symptoms tend to resolve within several weeks.
in untreated water is converted to malaoxon during the chlorination
phase of water treatment, so malathion should not be used in waters
that may be used as a source for drinking water, or any upstream
In jurisdictions which spray malathion for pest control, it is often
recommended to keep windows closed and air conditioners turned off
while spraying is taking place, in an attempt to minimize entry of
malathion into the closed environment of residential homes.
In 1981, B. T. Collins, director of the California Conservation
Corps, publicly swallowed a mouthful of dilute malathion solution and
survived. This was an attempt to demonstrate malathion's safety
following an outbreak of Mediterranean fruit flies in California.
Malathion was sprayed over a 1,400 sq mi (3,600 km2)
area to control the flies.
In 1976, numerous malaria workers in
Pakistan were poisoned by
isomalathion, a contaminant that may be present in some preparations
of malathion. It is capable of inhibiting carboxyesterase enzymes
in those exposed to it. It was discovered that poor work practices had
resulted in excessive direct skin contact with isomalathion contained
in the malathion solutions. Implementation of good work practices, and
the cessation of use of malathion contaminated with isomalathion led
to the cessation of poisoning cases.
Malathion is flammable. Patients using this agent should not be
exposed to heat sources when it is applied, such as blow dryers,
cigarettes or cooking flames.
A May 2010 study found that in a representative sample of US children,
those with higher levels of organophosphate pesticide metabolites in
their urine were more likely to have attention-deficit/hyperactivity
disorder, but no causal relationship was established. Each 10-fold
increase in urinary concentration of organophosphate metabolites was
associated with a 55% to 72% increase in the odds of ADHD. The study
was the first investigation on children's neurodevelopment to be
conducted in a group with no particular pesticide exposure.
Malathion is classified by the IARC as probable carcinogen (group 2A).
Malathion is classified by US EPA as having "suggestive evidence of
carcinogenicity". This classification was based on the occurrence
of liver tumors at excessive doses in mice and female rats and the
presence of rare oral and nasal tumors in rats that occurred following
exposure to very large doses. Researchers conducted a study involving
participants from six Canadian provinces and found that exposure to
organophosphates as a group and malathion alone was associated with
Malathion used as a fumigant was not
associated with increased cancer risk. Between 1993 and 1997, as part
of the Agricultural Health Study, researchers surveyed 19,717
pesticide applicators about their past pesticide exposures and health
histories and no clear association between malathion exposure and
cancer was reported.
Although current EPA regulations do not require amphibian testing, a
2008 study done by the University of Pittsburgh found that "cocktails
of contaminants", which are frequently found in nature, were lethal to
leopard frog tadpoles. They found that a combination of five widely
used insecticides (carbaryl, chlorpyrifos, diazinon, endosulfan, and
malathion) in concentrations far below the limits set by the EPA
killed 99% of leopard frog tadpoles.
1989 California medfly attack
Pesticide toxicity to bees
^ Tomlin, C.D.S. (ed.). The
Pesticide Manual - World Compendium, 11th
ed., British Crop Protection Council, Surrey, England 1997, p. 755
^ Hansch, C., Leo, A., D. Hoekman. Exploring QSAR - Hydrophobic,
Electronic, and Steric Constants. Washington, DC: American Chemical
Society., 1995., p. 80
^ a b c d "NIOSH Pocket Guide to Chemical Hazards #0375". National
Institute for Occupational Safety and Health (NIOSH).
^ a b c "Malathion". Immediately Dangerous to Life and Health
Concentrations (IDLH). National Institute for Occupational Safety and
^ "alanwood.net". Retrieved 2007-09-16.
Malathion for mosquito control, US EPA
^ Bonner MR, Coble J, Blair A, et al. (2007). "
Malathion Exposure and
the Incidence of Cancer in the Agricultural Health Study". American
Journal of Epidemiology. 166 (9): 1023–1034. doi:10.1093/aje/kwm182.
^ Edwards JW, Lee SG, Heath LM, Pisaniello DL (2007). "Worker exposure
and a risk assessment of malathion and fenthion used in the control of
Mediterranean fruit fly
Mediterranean fruit fly in South Australia". Environ. Res. 103 (1):
38–45. doi:10.1016/j.envres.2006.06.001. PMID 16914134.
^ Winnipeg.ca-UD: Public Works: Insect Control Branch
^ Colovic, MB; Krstic, Danijela Z.; Lazarevic-Pasti, Tamara D.;
Bondzic, Aleksandra M.; Vasic, Vesna M. (2013). "Acetylcholinesterase
Inhibitors: Pharmacology and Toxicology". Current Neuropharmacology.
11 (3): 315–335. doi:10.2174/1570159X11311030006. PMC
3648782 Freely accessible. PMID 24179466.
^ National Guideline Clearinghouse Guidelines for the diagnosis and
treatment of pediculosis capitis (head lice) in children and adults
^ Amy J. McMichael; Maria K. Hordinsky (2008). Hair and Scalp
Diseases: Medical, Surgical, and Cosmetic Treatments. Informa Health
Care. pp. 289–. ISBN 978-1-57444-822-1. Retrieved 27 April
^ Downs AM, Stafford KA, Harvey I, Coles GC (1999). "Evidence for
double resistance to permethrin and malathion in head lice". Br. J.
Dermatol. 141 (3): 508–11. doi:10.1046/j.1365-2133.1999.03046.x.
^ Julia A. McMillan; Ralph D. Feigin; Catherine DeAngelis; M. Douglas
Jones (1 April 2006). Oski's pediatrics: principles & practice.
Lippincott Williams & Wilkins. pp. 1–.
ISBN 978-0-7817-3894-1. Retrieved 27 April 2010.
^ British National Formulary 54th Ed. Sept 2007.
ISBN 978-0-85369-736-7. ISSN 0260-535X
^ "AHFS Drug Information". American Society of Health-System
Pharmacists. 13 January 2011. Retrieved 17 January 2011.
^ a b Edwards D (2006). "Reregistration Eligibility Decision for
Malathion" (PDF). US Environmental Protection Agency - Prevention,
Pesticides and Toxic Substances EPA 738-R-06-030 journal: 9.
^ Maugh II, Thomas H. (16 May 2010). "Study links pesticide to ADHD in
children". Los Angeles Times.
^ "US Department of Health and Human Services: Agency for Toxic
Substances and Disease Registry - Medical Management Guidelines for
Malathion". Retrieved 2008-04-02.
^ "California Death Index, 1940-1997 [Database Online]". Provo, Utah:
The Generations Network. 2000. Retrieved 2009-12-14.
^ Bonfante, Jordan (1990-01-08). "Medfly Madness". TIME. Retrieved May
^ Baker EL, Warren M, Zack M, et al. (1978). "Epidemic malathion
Pakistan malaria workers". Lancet. 1 (8054): 31–4.
doi:10.1016/S0140-6736(78)90375-6. PMID 74508.
^ a b Bouchard, M. F.; Bellinger, D. C.; Wright, R. O.; Weisskopf, M.
G. (2010). "Attention-Deficit/Hyperactivity Disorder and Urinary
Organophosphate Pesticides". Pediatrics. 125 (6):
e1270–7. doi:10.1542/peds.2009-3058. PMC 3706632 .
Organophosphate Pesticides Linked to ADHD". Medscape Today. May 17,
2010. Retrieved Dec 11, 2012.
^ Reregistration Eligibility Decision for
Malathion (Revised), US EPA,
Malathion Technical Fact Sheet
^ "Low Concentrations Of Pesticides Can Become Toxic Mixture For
Amphibians". Science Daily. November 18, 2008. Retrieved December 11,
Malathion Technical Fact Sheet - National
Pesticide Information Center
Malathion General Fact Sheet - National
Pesticide Information Center
Pesticide Information Profile - Extension Toxicology Network
CDC - NIOSH Pocket Guide to Chemical Hazards
Malathion by the
Pest Management Regulatory Agency of
Malathion in the
Pesticide Properties DataBase (PPDB)
Ectoparasiticides / arthropod (P03A)
‡Withdrawn from market
§Never to phase III
Pest control: Insecticides
Chromated copper arsenate
Lead hydrogen arsenate
Insect growth regulators
Pyrethrin (I, II; chrysanthemic acid)
Acetylcholine metabolism and transport modulators
Inhibitors: Reversible: Carbamates: Aldicarb
Thiofanox; Stigmines: Distigmine
Terestigmine; Others: Acotiamide
Irreversible: Organophosphates: Acephate
Dimethyl 4-(methylthio)phenyl phosphate
VX; Others: Demecarium
Fasciculins (green mamba toxins) (1, 2, 3, 4)
Onchidal (Onchidella binneyi)
Reactivators: Asoxime chloride
Many of the other AChE inhibitors listed above
Botulinum toxin (A, C, E)
Botulinum toxin (B, D, F, G)
Others: Bungarotoxins (β-bungarotoxin, γ-bungarotoxin)
LPHN agonists: α-Latrotoxin
Atracotoxin (e.g., robustoxin, versutoxin)
See also: Receptor/signaling modulators • Muscarinic acetylcholine
receptor modulators • Nicotinic acetylcholine receptor modulators
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