Malathion is an

organophosphate In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...

insecticide Insecticides are pesticides used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. The major use of insecticides is in agriculture, but they are also used in home and garden settings, i ...

which acts as an

acetylcholinesterase inhibitor Acetylcholinesterase inhibitors (AChEIs) also often called cholinesterase inhibitors, inhibit the enzyme acetylcholinesterase from breaking down the neurotransmitter acetylcholine into choline and acetate, thereby increasing both the level an ...

. In the

USSR The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

, it was known as carbophos, in

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

as maldison and in

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

as mercaptothion. The compound's name is presumably related to

malic acid Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ( ...

(2-hydroxybutanedioic acid) owning to the 2-substituted diethyl malate substructure.

Pesticide use

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. A malathion mixture with

corn syrup Corn syrup is a food syrup that is made from the starch of corn/maize and contains varying amounts of sugars: glucose, maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to soften Mouthfeel, texture, add vol ...

was used in the 1980s in Australia and California to combat the Mediterranean fruit fly. In Canada and the US starting in the early 2000s, malathion was sprayed in many cities to combat

west Nile virus West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...

. Malathion was used over the last couple of decades on a regular basis during summer months to kill mosquitoes, but homeowners were allowed an exemption for their properties if they chose. In the United Kingdom, malathion was withdrawn from sale in 2002.

Mechanism of action

Malathion is an

, a diverse family of chemicals. Upon uptake into the target organism, it binds irreversibly to the

serine Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − ...

residue in the active catalytic site of the cholinesterase enzyme. The resultant phosphoester group is strongly bound to the cholinesterase, and irreversibly deactivates the enzyme which leads to rapid build-up of

acetylcholine Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...

at the synapse.

Production method

Malathion is produced by the addition of dimethyl dithiophosphoric acid to diethyl maleate or diethyl fumarate. The compound is chiral but is used as a

racemate In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as r ...

Medical use

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 The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respo ...

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 noted when malathion was applied to lice found on schoolchildren in the Bristol area in the UK, and is caused by the tested population of lice having developed resistance against malathion. *

Scabies Scabies (; also sometimes known as the seven-year itch) is a contagious human skin infestation by the tiny (0.2–0.45 mm) mite ''Sarcoptes scabiei'', variety ''hominis''. The word is from . The most common symptoms are severe itchiness a ...

Preparations include Derbac-M, Prioderm, Quellada-M and Ovide.

Safety

General

Malathion is of low toxicity. In arthropods it is metabolized into malaoxon which is 61x more toxic, being a more potent inhibitor of acetylcholinesterase. According to the

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

, no reliable information is available on adverse health effects of chronic exposure. In 1989, Malathion was sprayed over a area to control an outbreak of Mediterranean fruit flies in California. In order to demonstrate the chemical's safety, B. T. Collins, director of the California Conservation Corps, publicly swallowed a mouthful of dilute malathion solution.

Carcinogenicity

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. Exposure to organophosphates is associated with

non-Hodgkin's lymphoma Non-Hodgkin lymphoma (NHL), also known as non-Hodgkin's lymphoma, is a group of blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include enlarged lymph nodes, fever, night sweats, weight loss, and tire ...

. Malathion used as a fumigant was not associated with increased cancer risk. Between 1993 and 1997, as part of the Agricultural Health Study, no clear association between malathion exposure and cancer was reported.

Amphibians

Malathion is toxic to leopard frog tadpoles.

Risks

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, and malaoxon is 1,000 times more potent than malathion in terms of its acetylcholinesterase inhibition. Indoor spillage of malathion can thus be more poisonous than expected, as malathion breaks down in a confined space into the more toxic malaoxon. It is cleared from the body quickly, in three to five days.

Resistance

Because it is an acetylcholinesterase inhibitor, this resistance is a type of AChEI resistance. Malathion resistance is thought to always be due to either increased carboxylesterase concentrations or altered

acetylcholinesterase Acetylcholinesterase (HUGO Gene Nomenclature Committee, HGNC symbol ACHE; EC 3.1.1.7; systematic name acetylcholine acetylhydrolase), also known as AChE, AChase or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme th ...

s. COE because it metabolizes malathion but into ''non''-malaoxon products, altered AChEs because we mean specifically those altered to be less sensitive to malathion and malaoxon.

References

External links

Malathion Technical Fact Sheet - National Pesticide Information Center

Malathion General Fact Sheet - National Pesticide Information Center

* ttps://www.atsdr.cdc.gov/toxfaqs/tfacts154.pdf ATSDR ToxFAQs
CDC - NIOSH Pocket Guide to Chemical Hazards

Re-evaluation of Malathion
by the Pest Management Regulatory Agency of Canada * {{Authority control Acetylcholinesterase inhibitors Antiparasitic agents Endocrine disruptors Organophosphate insecticides Phosphorodithioates Ethyl esters IARC Group 2A carcinogens