Parathion, also called parathion-ethyl or diethyl parathion, is an organophosphate insecticide and acaricide. It was originally developed by IG Farben in the 1940s. It is highly toxic to non-target organisms, including humans, so its use has been banned o + some more technical info; chemically it is O,O-diethyl O-(4-nitrophenyl) phosphorothioate, a lipophilic, low-water-solubility liquid that was applied as foliar sprays, soil treatments and seed dressings. Parathion requires metabolic activation in target organisms via oxidative desulfuration to the corresponding oxon, which is a potent acetylcholinesterase inhibitor; this bioactivation explains both its insecticidal potency and its high mammalian toxicity. Environmental behavior is governed by adsorption to organic matter, susceptibility to hydrolysis to p-nitrophenol under alkaline conditions, and photodegradation; volatility is low but residues can persist in soils and biota depending on conditions. Handling, storage and disposal pose significant human health and ecological risks because of acute cholinergic toxicity, and most regulatory frameworks now prohibit or strictly limit its manufacture, sale and use.
Technical parathion formulations typically consist predominantly of the active O,O-diethyl O-(4-nitrophenyl) phosphorothioate with the remainder made up of synthesis byproducts, degradation products and solvent residues; typical active ingredient content in historical technical material is roughly 85 to 95 percent, with total impurities in the single digits by weight under good manufacturing and storage. Important related compounds and impurities include the oxidized oxon analog paraoxon, which is substantially more potent as an acetylcholinesterase inhibitor and can be present at trace to low percentage levels depending on oxidation during manufacture or storage; p-nitrophenol and its salts from hydrolysis, which can appear at low ppm to low percent levels under poor storage or hydrolytic conditions; residual phosphorothioate and phosphoric acid derivatives such as diethyl thiophosphate or diethyl phosphate; unreacted precursors and minor isomeric or polymeric byproducts formed during synthesis. Analytical control normally targets paraoxon at the lowest practicable limit because of its high acute toxicity, with additional specification limits or monitoring for p-nitrophenol, solvent residues and total volatile impurities determined by accepted methods such as GC-MS, LC-MS or HPLC.
Parathion was used as a broad-spectrum insecticide and acaricide against chewing and sucking pests in crops such as cotton, citrus and cereals, and for certain vector control applications; its high mammalian toxicity led to phased restrictions and withdrawals in most jurisdictions.
Use of parathion is now banned or severely restricted in most countries; limited manufacture or research use may occur under strict regulatory controls in a few places, but routine agricultural use has been largely discontinued globally.
Another common name is parathion-ethyl; it is also referred to as diethyl parathion or O,O-diethyl O-(4-nitrophenyl) phosphorothioate.
Parathion itself is metabolically activated to paraoxon by oxidative desulfuration, and paraoxon binds covalently to the active site serine of acetylcholinesterase, inhibiting the enzyme and causing accumulation of acetylcholine at synapses, resulting in overstimulation of muscarinic and nicotinic receptors and the characteristic cholinergic signs and symptoms.
