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Parathion (C10H14NO5PS) is an organophospate insecticide primarily used on fruit, cotton, wheat, vegetables, and nut crops. (#EPA) It has been attributed to numerous mass human poisonings due to its high toxicity. (#Timbrell, 2004)

Lead author

Just the facts

Physical Information

Name: Parathion

Use: insecticide


Recommended daily intake:

Absorption: inhalation, oral, dermal

Sensitive individuals: humans and animals

Toxicity/symptoms: Acute: nausea, vomiting, abdominal cramps, diarrhea, excessive salivation, headache, weakness, difficult breathing, blurring or dimness of vision, convulsions, central nervous system depression, paralysis, coma, and respiratory failure
Chronic: depressed red blood cell cholinesterase activity, nausea, and headaches

Regulatory facts: OSHA PEL (permissible exposure limit) = 0.1 mg/m³ (skin) (averaged over an 8-hour workshift)
NIOSH IDLH (immediately dangerous to life or health) = 10 mg/m³

General facts:



Chemical Structure

Structure retrieved from University of Wisconsin  

Chemical Description

  • Molecular weight: 291.27 g/mol
  • Pure parathion is a pale yellow liquid, while the technical grades are brown.
  • Parathion is practically insoluble in water, slightly soluble in petroleum oils, and miscible with many organic solvents.
  • Parathion has a garlic-like odor, with an odor threshold of 0.47 milligrams per cubic meter (mg/m3).
  • The vapor pressure: 3.78 × 10^-5^ mm Hg at 20 °C
  • Log octanol/water partition coefficient (log Kow): 3.83
  • Boiling point (760 mm Hg): 707ºF (375ºC)
  • Freezing point: 43ºF (6.1ºC)


Pharmacology and Metabolism

Organophosphates such as parathion cause an exaggerated pharmacological effect rather than a direct toxic action and the toxicity may be either cumulative, following chronic exposure, or acute after a single exposure. Organophosphates bind to the enzyme acetylcholinesterase (AChe) because of similarities with the natural substrate for the enzyme, a neurotransmitter present in the nervous system called Acetylcholine (ACh). Because organophosphorous compounds inhibit AChe, ACh accumulates leading to excessive stimulation of the nerve. This leads to death of insects. (See Cholinesterase Inhibitor.

The same process occurs in humans and other mammals. However, Organophosphates have been developed in such a way that some Organophosphates are relatively non-toxic in mammals at low exposure levels. At higher levels humans will suffer the same consequences as insects. (#Timbrell, 2002)

Discovery and Development

Main Article: Chemical Weapons
Parathion was developed by the German trust IG Farben in the 1940s. Dr. Gerhard Schrader synthesized the insecticide while he was looking for chemicals that would increase agricultural yields needed to feed the Army during World War II. After the war the Western allies seized the chemical plants and scientists and parathion was thereafter marketed worldwide by different companies and under different brand names (#Tucker, 2006).

Health Effects

Parathion is extremely toxic from acute (short-term) inhalation, oral, and dermal exposures. Acute exposure of humans to parathion mainly affects the central nervous system. Symptoms of Acute Exposure:

* blood
* respiratory system
* eyes
* nausea
* vomiting
* abdominal cramps
* diarrhea
* excessive salivation
* headache

* weakness
* difficult breathing
* blurring or dimness of vision
* convulsions
* central nervous system depression
* paralysis
* coma
* respiratory failure


Chronic (long-term) inhalation and oral exposure of humans and animals to parathion have been observed to result in depressed cholinesterase inhibition, nausea, and headache (#EPA).


OSHA PEL (permissible exposure limit) = 0.1 mg/m³ (skin) (averaged over an 8-hour workshift)

NIOSH IDLH (immediately dangerous to life or health) = 10 mg/m³



EPA. Technology Transfer Network. Air Toxics Website on Parathion. Accessed July 8, 2007

ATSDR. Medical Management Guidelines for Parathion. Accessed July 8, 2007

Tucker, Johnathon B. War of Nerves: Chemical Warfare from World War I to Al-Qaeda. Pantheon Books, 2006.

Timbrell, John. Introduction to Toxicology. 3rd Edition. p. 114-115 . CRC Press, 2002

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