Malathion

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Malathion
Skeletal formula of malathion Malathion.png
Skeletal formula of malathion
3D representation of malathion Malathion-3D-sticks.png
3D representation of malathion
Space filling model of malathion, showing van der Waals radii for each atom Malathion-3D-vdW.png
Space filling model of malathion, showing van der Waals radii for each atom
Names
IUPAC name
Diethyl 2-[(dimethoxyphosphorothioyl)sulfanyl]butanedioate
Other names
  • 2-(Dimethoxyphosphinothioylthio) butanedioic acid diethyl ester
  • S-(1,2-Dicarbethoxyethyl) O,O-dimethyldithiophosphate
  • Carbofos
  • Maldison
  • Mercaptothion
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.004.089 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
UNII
  • InChI=1S/C10H19O6PS2/c1-5-15-9(11)7-8(10(12)16-6-2)19-17(18,13-3)14-4/h8H,5-7H2,1-4H3 Yes check.svgY
    Key: JXSJBGJIGXNWCI-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C10H19O6PS2/c1-5-15-9(11)7-8(10(12)16-6-2)19-17(18,13-3)14-4/h8H,5-7H2,1-4H3
    Key: JXSJBGJIGXNWCI-UHFFFAOYAK
  • O=C(OCC)C(SP(=S)(OC)OC)CC(=O)OCC
Properties
C10H19O6PS2
Molar mass 330.35 g·mol−1
AppearanceClear colorless liquid
Odor mercaptan-like, skunk-like, or garlic
Density 1.23 g/cm3
Melting point 2.9 °C (37.2 °F; 276.0 K)
Boiling point 156 to 157 °C (313 to 315 °F; 429 to 430 K) at 0.7 mmHg (93 Pa)
145 mg/L (20 °C (68 °F; 293 K)) [1]
Solubility in diethyl ether very soluble
Solubility in ethanol soluble
Solubility in acetone soluble
log P 2.36 (octanol/water) [2]
Pharmacology
P03AX03 ( WHO ) QP53AF12 ( WHO )
Hazards
GHS labelling: [3]
GHS-pictogram-exclam.svg GHS-pictogram-pollu.svg
Warning
H302, H317, H410
P261, P264, P270, P272, P273, P280, P301+P312+P330, P302+P352, P333+P313, P363, P391, P501
Flash point 163 °C; 325 °F; 436 K (greater than)
Lethal dose or concentration (LD, LC):
  • 5400 mg/kg (oral, rat, male)
  • 5700 mg/kg (oral, rat, female)
  • >2000 mg/kg (dermal, rat) [4]
  • 644 mg/kg (oral, rat)
  • 8790 mg/kg (dermal, rabbit) [3]
>5.2 mg/L (inhalation, rat)
NIOSH (US health exposure limits): [5]
PEL (Permissible)
15 mg/m3 (TWA, skin)
REL (Recommended)
10 mg/m3 (TWA, skin)
IDLH (Immediate danger)
250 mg/m3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion.

Contents

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. [6] In the US, it is the most commonly used organophosphate insecticide. [7]

A malathion mixture with corn syrup was used in the 1980s in Australia to combat the Mediterranean fruit fly. [8] In Canada and the US starting in the early 2000s, malathion was sprayed in many cities to combat west Nile virus. [9]

In the United Kingdom, malathion was withdrawn from sale in 2002. [10]

Mechanism of action

Malathion is an acetylcholinesterase inhibitor, a diverse family of chemicals. Upon uptake into the target organism, it binds irreversibly to the serine 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 at the synapse. [11]

Production method

Malathion is produced by the addition of dimethyl dithiophosphoric acid to diethyl maleate or diethyl fumarate in the presence of catalytic amounts of triethylamine and hydroquinone at elevated temperature:

(CH3O)2PS2H + C8H12O4 → C10H19O6PS2

This process produces the S enantiomer. [12]

Medical use

Malathion in low doses (0.5% preparations) is used as a treatment for head lice and body lice infection (pediculosis) in the US, where it is approved by the US Food and Drug Administration. [13] [14] In some areas in the UK, head lice had developed a resistance to malathion as of 1999, and it was ineffective against 64% of cases. This is believed to be caused by development in the lice of an enzyme-mediated malathion specific esterase, able to destroy malathion bound to the acetylcholine receptor. [15]

It is also used for the treatment of scabies. [16] [ page needed ]

Preparations include Derbac-M, Prioderm, Quellada-M and Ovide. [17] [18]

Risks

General

Malathion is of low toxicity. It metabolizes to the more toxic malaoxon in many species.

In arthropods it is metabolized into malaoxon which is 61x more toxic, being a more potent inhibitor of acetylcholinesterase. [4] 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. [19] [20]

Absorption or ingestion into the human body also readily results in its metabolism to malaoxon, which is substantially more toxic. [19] It is cleared from the body quickly, in three to five days.[ medical citation needed ] According to the United States Environmental Protection Agency, no reliable information is available on adverse health effects of chronic exposure. [21]

In 1981, Malathion was sprayed over a 1,400 sq mi (3,600 km2) 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. [22]

Carcinogenicity

Malathion is classified by the IARC as probable carcinogen (group 2A). Malathion is classified by US EPA as having "suggestive evidence of carcinogenicity". [4] 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. 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. [23]

Toxicity to Amphibians

Malathion is toxic to leopard frog tadpoles. [24]

Regulation

Different organizations and governments have set different drinking water quality standards for malathion.

The World Health Organization has determined that while malathion can last in water for months and years, it usually does not last in water for longer than one to two weeks; and since the amount of malathion found in drinking water is usually lower than a level that would lead to concerns about health that there is no need to set a drinking water guideline for the level of malathion allowed in water. [25]

In contrast, the Canadian government has set a maximum acceptable concentration of 0.29 mg/L of malathion in drinking water, and requires that drinking water should be monitored for the chemical when there is a reason to suspect it is in the water and might need to be removed. [26]

Australia has a much lower maximum level of 0.07 mg/L of malathion in drinking water. [27]

The European Union has set their level still lower at 0.10 μg/L for any one pesticide in drinking water, including malathion. [28]

The United States does not have an official maximum contaminant level for malathion, but proposes a lifetime health advisory of 0.5 mg/L. [29]

See also

References

  1. ↑ Tomlin, C.D.S., ed. (1997). The pesticide manual: a world compendium (11th ed.). Farnham, Surrey, UK: British Crop Protection Council. p. 755. ISBN   9781901396119.
  2. ↑ Hansch, C.; Leo, A.; Hoekman, D. (1995). Exploring QSAR. Washington, DC: American Chemical Society. p. 80. ISBN   0-8412-2993-7.
  3. 1 2 Sigma-Aldrich Co., Malathion.
  4. 1 2 3 Keigwin Jr RP (May 2009). Reregistration Eligibility Decision for Malathion (Revised) (PDF). US Environmental Protection Agency - Prevention, Pesticides and Toxic Substances (Report). p. 9. EPA 738-R-06-030 Journal.
  5. ↑ "NIOSH Pocket Guide to Chemical Hazards".
  6. ↑ Malathion for mosquito control, US EPA
  7. ↑ 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 . PMID   17720683.
  8. ↑ 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 in South Australia". Environ. Res. 103 (1): 38–45. Bibcode:2007ER....103...38E. doi:10.1016/j.envres.2006.06.001. PMID   16914134.
  9. ↑ Shapiro, H.; Micucci, S. (2003-05-27). "Pesticide use for West Nile virus". Canadian Medical Association Journal . 168 (11): 1427–1430. PMC   155959 . PMID   12771072. An extensive re-evaluation of malathion was completed by the US Environmental Protection Agency in 2000. The PMRA has also re-evaluated malathion and approved its use as a mosquito adulticide.
  10. ↑ "Withdrawn chemicals / RHS Gardening".
  11. ↑ Colovic, Mirjana B.; 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 . PMID   24179466.
  12. ↑ USpatent 2578652A,Cassaday, Jack T.,"Addition product of diester of dithiophosphoric acid and maleic acid and its esters, and method of preparation",published 1951-12-18,issued 1951-12-18, assigned to American Cyanamid Co.and Wyeth Holdings LLC
  13. ↑ "Guidelines for the diagnosis and treatment of pediculosis capitis (head lice) in children and adults 2008". National Guideline Clearinghouse. Archived from the original on 2013-02-26. Retrieved 2013-01-22.
  14. ↑ McMichael, Amy J.; Hordinsky, Maria K. (2008). Hair and Scalp Diseases: Medical, Surgical, and Cosmetic Treatments. Informa Health Care. pp. 289–. ISBN   978-1-57444-822-1 . Retrieved 27 April 2010.
  15. ↑ 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. PMID   10583056. S2CID   25087526.
  16. ↑ Julia A. McMillan; Ralph D. Feigin; Catherine DeAngelis; M. Douglas Jones (1 April 2006). Oski's pediatrics: principles & practice. Lippincott Williams & Wilkins. ISBN   978-0-7817-3894-1 . Retrieved 27 April 2010.
  17. ↑ Mehta, Dinesh K. (13 September 2007). British National Formulary (BNF). British National Formulary (54th Revised ed.). Pharmaceutical Press. ISBN   978-0-85369-736-7. ISSN   0260-535X.
  18. ↑ "AHFS Drug Information". American Society of Health-System Pharmacists. 13 January 2011. Retrieved 17 January 2011.
  19. 1 2 Edwards D (July 2006). "Reregistration Eligibility Decision for Malathion" (PDF). US Environmental Protection Agency - Prevention, Pesticides and Toxic Substances EPA 738-R-06-030 Journal: 9. Archived from the original (PDF) on 2008-05-21.
  20. ↑ Rodriguez, O. P.; Muth, G. W.; Berkman, C. E.; Kim, K.; Thompson, C. M. (February 1997). "Inhibition of various cholinesterases with the enantiomers of malaoxon". Bulletin of Environmental Contamination and Toxicology. 58 (2): 171–176. Bibcode:1997BuECT..58..171R. doi:10.1007/s001289900316. ISSN   0007-4861. PMID   8975790. S2CID   29903092.
  21. ↑ "US Department of Health and Human Services: Agency for Toxic Substances and Disease Registry - Medical Management Guidelines for Malathion". Archived from the original on October 21, 2002. Retrieved 2008-04-02.
  22. ↑ Bonfante, Jordan (1990-01-08). "Medfly Madness". Time. Archived from the original on July 24, 2008. Retrieved May 21, 2009.
  23. ↑ "Active Ingredient Fact Sheets". npic.orst.edu.
  24. ↑ "Low Concentrations Of Pesticides Can Become Toxic Mixture For Amphibians". Science Daily. November 18, 2008. Retrieved December 11, 2012.
  25. ↑ World Health Organization, ed. (2022). Guidelines for drinking-water quality (Fourth edition incorporating the first and second addenda ed.). Geneva: World Health Organization. ISBN   978-92-4-004506-4.
  26. ↑ Health Canada (2023-01-20). "Guidelines for Canadian drinking water quality – Malathion: Management strategies, international considerations" . Retrieved September 29, 2025.
  27. ↑ "Maldison (Malathion)". Australian Drinking Water Guidelines 6 2011, v3.9. 2011. Retrieved September 29, 2025.
  28. ↑ "Water for Human Consumption Directive - Quality Criteria". European Chemicals Agency (ECHA). October 2015. Retrieved Sep 29, 2025.
  29. ↑ US EPA (March 2018). "2018 Edition of the Drinking Water Standards and Health Advisories Tables" (PDF). EPA 822-F-18-001. Retrieved Sep 29, 2025.
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