What molecule am I?
Malathion1 is an organophosphate insecticide that was by Jack T. Cassaday and co-workers at American Cyanamid (Stamford, CT). It and other dithiophosphate鈥搈aleate esters were claimed as compositions of matter in US Patent 2,578, 652 (1951). It acts as an acetylcholinesterase inhibitor to poison insects.
A liquid with a skunk- or garlic-like odor, malathion is still on the market today for commercial and domestic use despite findings that it and similar pesticides are probable carcinogens. It is considerably safer to use than the similar organophosphate parathion2, which has been banned or restricted worldwide.
In 2017, the US Environmental Protection Agency found that malathion would adversely affect almost all endangered species and their habitats. In 2021, based on EPA鈥檚 findings, the US Fish and Wildlife Service determined that the insecticide is likely to harm 78 species and 23 critical habitats. But during this period, EPA, Fish and Wildlife, and pesticide manufacturers collaborated to develop mitigation measures for malathion.
This past March, Fish and Wildlife concluded that, if the mitigation measures are put in place, . EPA expects to approve new malathion labels by late 2023. Environmental advocacy groups, however, strongly objected to Fish and Wildlife鈥檚 decision and would like stronger controls to be enacted. One advocate said that the agency ignored 鈥渢he best available science鈥� and chose 鈥渢o rely on unenforceable promises of good behavior by the pesticide makers rather than real on-the-ground conservation measures.鈥�
1. SciFinder: butanedioic acid, 2-[(dimethoxyphosphinothioyl)thio]-, 1,4-diethyl ester.
2. CAS Reg. No. 56-38-2.
Malathion acid hazard information
| Hazard class* | GHS code and hazard statement | |
|---|---|---|
| Acute toxicity, oral, category 4 | H302鈥擧armful if swallowed |  |
| Skin sensitization, category 1 | H317鈥擬ay cause an allergic skin reaction | |
| Carcinogenicity, category 1B | H350鈥擬ay cause cancer |  |
| Short-term (acute) aquatic hazard, category 1 | H400鈥擵ery toxic to aquatic life |  |
| Long-term (chronic) aquatic hazard, category 1 | H410鈥擵ery toxic to aquatic life with long-lasting effects | |
*Globally Harmonized System of Classification and Labeling of Chemicals.听
Malathion 听fast facts
| CAS Reg. No. | 121-75-5 |
| Empirical formula | C10H19O6PS2 |
| Molar mass | 330.36 g/mol听 |
| Appearance | Yellow to brown liquida |
| Melting point | 3 掳C听 |
| Boiling Point | 156鈥�157 掳C (0.7 Torr) |
| Water solubility | 143 mg/L |
a. Colorless when pure.
MOTW updates
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1. CAS Reg. No. 5119-48-2.
2. CAS Reg. No. 27570-38-3.
3. CAS Reg. No. 1972-08-3.
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