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 a ...

insecticide Insecticides are substances used to kill insects. They include ovicides and larvicides used against insect eggs and larvae, respectively. Insecticides are used in agriculture, medicine, industry and by consumers. Insecticides are claimed to b ...

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 and ...

. In the

USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

, it was known as carbophos, in

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

and

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

as maldison and in

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

as mercaptothion.

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 which is made from the starch of corn (called maize in many countries) and contains varying amounts of sugars: glucose, maltose and higher oligosaccharides, depending on the grade. Corn syrup is used in foods to softe ...

was used in the 1980s in Australia and California to combat the

Mediterranean fruit fly ''Ceratitis capitata'', commonly known as the Mediterranean fruit fly or medfly, is a yellow-and-brown fly native to sub-Saharan Africa. It has no near relatives in the Western Hemisphere and is considered to be one of the most destructive fr ...

. 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 to exempt their properties if they chose..

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 − form un ...

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 chemical 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. Part ...

at the synapse.

Production method

Malathion is produced by the addition of dimethyl dithiophosphoric acid to diethyl maleate or

diethyl fumarate In organic chemistry, an ethyl group (abbr. Et) is an alkyl substituent with the formula , derived from ethane (). ''Ethyl'' is used in the International Union of Pure and Applied Chemistry's nomenclature of organic chemistry for a saturated t ...

. The compound is chiral but is used as a

racemate In chemistry, a racemic mixture, or racemate (), is one that has equal amounts 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 racemates. ...

Medical use

Malathion in low doses (0.5% preparations) is used as a treatment for: *

Head lice The head louse (''Pediculus humanus capitis'') is an obligate ectoparasite of humans. Head lice are wingless insects that spend their entire lives on the human scalp and feeding exclusively on human blood. Humans are the only known hosts of thi ...

and

body lice The body louse (''Pediculus humanus humanus'', also known as ''Pediculus humanus corporis'') is a hematophagic ectoparasite louse that infests humans. It is one of three lice which infest humans, the other two being the head louse, and the cr ...

. 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 respon ...

for treatment of

pediculosis Pediculosis is an infestation of lice from the sub-order Anoplura, family Pediculidae. Accordingly, the infestation with head lice is named pediculosis capitis, while this with body lice, pediculosis corporis. Although ''pediculosis'' in humans ma ...

. 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 it is assumed to be caused by the lice having developed resistance against malathion. *

Scabies Scabies (; also sometimes known as the seven-year itch) is a contagious skin infestation by the mite ''Sarcoptes scabiei''. The most common symptoms are severe itchiness and a pimple-like rash. Occasionally, tiny burrows may appear on the skin ...

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

Safety

General

Malathion is of low toxicity. In arthropods it is metabolized into

malaoxon Malaoxon (Liromat, Malation oxon, Malthon oxon) is a chemical compound with the formula C10H19O7PS. More specifically, it is a phosphorothioate. It is a breakdown product of, and more toxic than, malathion. Air and water This chemical may ...

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 executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...

, no reliable information is available on adverse health effects of chronic exposure. In 1981, 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 Brien Thomas "B. T." Collins (October 17, 1940 – March 19, 1993) was an American politician from California and a member of the Republican party. Early years Born in New York City, Collins served as a Green Beret Captain during the Vietnam War ...

, director of the California Conservation Corps, publicly swallowed a mouthful of dilute malathion solution.

Carcinogenicity

Malathion is classified by the

IARC IARC may refer to: * International Aerial Robotics Competition * International Age Rating Coalition * International Agency for Research on Cancer * International Arctic Research Center * Israel Amateur Radio Club The Israel Amateur Radio Club (IA ...

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 hematological malignancy, blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include lymphadenopathy, enlarged lymph nodes, fever ...

. 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 Leopard frog is a generic name used to refer to various species in the true frog genus Lithobates. They all have similar coloration: brown or green with spots that form a leopard pattern. They are distinguished by their distribution and behavior ...

tadpoles.

Resistance

Because it is an acetylcholinesterase inhibitor, this resistance is a type of

AChEI resistance 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 and ...

. Malathion resistance is thought to always be due to either increased

carboxylesterase The enzyme carboxylesterase (or carboxylic-ester hydrolase, EC 3.1.1.1; systematic name carboxylic-ester hydrolase) catalyzes reactions of the following form: :a carboxylic ester + H2O \rightleftharpoons an alcohol + a carboxylate Most enzymes fr ...

concentrations or altered

acetylcholinesterase Acetylcholinesterase (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 Enzymes () are proteins that a ...

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://web.archive.org/web/20130509193404/http://www.atsdr.cdc.gov/tfacts154.html 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 Insecticides Organophosphate insecticides Phosphorodithioates