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Parathion, also called
parathion-ethyl or
diethyl parathion, is an
organophosphate compound. It is a potent
insecticide and
acaricide. It was originally developed by
IG Farben in the 1940s. It is highly toxic to non-target organisms, including humans. Its use is banned or restricted in many countries, and there are proposals to ban it from all use. Closely related is "methyl parathion" (see below).
Parathion-methyl
"Parathion-methyl" (CAS#298-00-0), also known as methyl parathion or dimethyl parathion, was also developed and is marketed for similar uses. It is a distinct compound with diminished toxicity. Some trade names of parathion-methyl include
Bladan M,
Metaphos,
ME605, and
E601.
History
Parathion was developed by Dr.
Gerhard Schrader for the
German trust
IG Farben in the 1940s. After the war and the collapse of IG Farben due to the war crime trials, the Western allies seized the
patent, and parathion was marketed worldwide by different companies and under different brand names. The most common German brand was
E605 (banned in Germany after 2002); this was not a food-additive "
E number" as used in the EU today. "E" stands for
Entwicklungsnummer (German for "development number").
Handling properties
When pure, parathion is a white crystalline solid, however it is commonly distributed as a brown
liquid that smells of rotting
eggs or
garlic. The insecticide is more or less stable, although it darkens when exposed to sunlight.
Industrial synthesis
Parathion is synthesized from
diethyl dithiophosphoric acid (C
2H
5O)
2PS
2H, which is obtained by treatment of
P2S5 with ethanol (
methanol is used to prepare methyl parathion). Diethyl dithiophosphoric acid is chlorinated to generate diethylthiophosphoryl chloride. The diethyl dithiophosphoric acid is then treated with
sodium 4-nitrophenolate (the
sodium salt of
4-nitrophenol).
: 2 (C2H5O)2P(S)SH + 3 Cl2 → 2 (C2H5O)2P(S)Cl + S2Cl2 + 2 HCl
: (C2H5O)2P(S)Cl + NaOC6H4NO2 → (C2H5O)2P(S)OC6H4NO2 + NaCl
Applications
As a pesticide, parathion is generally applied by spraying. It is often applied to
cotton,
rice and
fruit trees. The usual concentrations of ready-to-use solutions are 0.05 to 0.1%. The chemical is banned for use on many food crops.
Insecticidal activity
Parathion acts on the enzyme
acetylcholinesterase, but indirectly. After being ingested by insects (and unintentionally, by humans), the parathion becomes oxidized by
oxidases to give
paraoxon, replacing the double bonded sulfur with oxygen.
:(C2H5O)2P(S)OC6H4NO2 + 1/2 O2 → (C2H5O)2P(O)OC6H4NO2 + S
The phosphate ester is more reactive in organisms than the phosphorothiolate ester, as the phosphorus atoms become much more electronegative. Studies show that parathion is toxic to fetuses, but does not cause birth defects.
It is classified as a UNEP Persistent Organic Pollutant and WHO Toxicity Class, "Ia, Extremely Hazardous".
Parathion is very toxic to bees, fish, birds, and other forms of wildlife. In the US alone more than 650 agricultural workers have been poisoned since 1966, of which 100 died. In underdeveloped countries many more people have suffered fatal and nonfatal intoxications. The World Health Organization, PAN and numerous environmental organisations propose a general and global ban. Its use is banned or restricted in 23 countries and its import is illegal in a total of 50 countries.
See also
Pesticide toxicity to bees
References
External links
ATSDR - Methyl Parathion Expert Panel Report U.S. Department of Health and Human Services (public domain)
Ethyl parathion:
Methyl parathion:
Category:Insecticide brands
Category:Organophosphate insecticides
Category:Acetylcholinesterase inhibitors
Category:Phosphorothioates
Category:Nitrobenzenes
