Parathion, also called parathion-ethyl or diethyl parathion and locally known as "Folidol", is an

organophosphate In organic chemistry, organophosphates (also known as phosphate esters, or OPEs) are a class of organophosphorus compounds with the general structure , a central phosphate molecule with alkyl or aromatic substituents. They can be considered ...

insecticide and acaricide. It was originally developed by

IG Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for 'IG Dyestuffs'), was a German chemical and pharmaceutical conglomerate. Formed in 1925 from a merger of six chemical companies— BASF, Bayer, Hoechst, Agf ...

in the 1940s. It is highly toxic to non-target organisms, including humans, so its use has been banned or restricted in most countries. The basic structure is shared by parathion methyl.

History

Parathion was developed by Gerhard Schrader for the German trust

in the 1940s. After

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

and the collapse of IG Farben due to the war crime trials, the Western allies seized the

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

, 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 E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

" as used in the EU today. "E" stands for ''Entwicklungsnummer'' (German for "development number"). It is an irreversible acetylcholinesterase inhibitor. Safety concerns have later led to the development of parathion methyl, which is somewhat less toxic. In the EU, Parathion was banned after 2001. In

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

, the substance is no longer approved as a pesticide.

Handling properties

Pure parathion is a white crystalline solid. It is commonly distributed as a brown

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...

that smells of rotting eggs or

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chive, Welsh onion and Chinese onion. It is native to South Asia, Central Asia and northeas ...

. The insecticide is somewhat stable, although it darkens when exposed to sunlight.

Industrial synthesis

Parathion is synthesized from

diethyl dithiophosphoric acid Diethyl dithiophosphoric acid, sometimes mistakenly called diethyl dithiophosphate, is the organophosphorus compound with the formula (C2H5O)2PS2H. It is the processor for production of the organophosphate insecticide Terbufos. Although samples ...

(C₂H₅O)₂PS₂H by chlorination to generate diethylthiophosphoryl chloride ((C₂H₅O)₂P(S)Cl), and then the chloride is treated with sodium 4-nitrophenolate (the

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

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 Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor pe ...

rice Rice is the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

and

fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...

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 indirectly. After an insect (or a human) ingests parathion, an oxidase replaces the double bonded sulfur with oxygen to give

paraoxon Paraoxon is a parasympathomimetic which acts as an cholinesterase inhibitor. It is an organophosphate oxon, and the active metabolite of the insecticide parathion. It is also used as an ophthalmological drug against glaucoma. Paraoxon is one of ...

. :(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 electropositive. Parathion is a special case of

acetylcholinesterase inhibitor resistance Acetylcholinesterase inhibitors (AChEIs) also often called cholinesterase inhibitors, inhibit the enzyme acetylcholinesterase from breaking down the neurotransmitter acetylcholine into choline and acetate, thereby increasing both the level an ...

Degradation

Degradation of parathion leads to more water-soluble products.

Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysi ...

, which deactivates the molecule, occurs at the aryl ester bond resulting in diethyl thiophosphate and 4-nitrophenol. :(C₂H₅O)₂P(S)OC₆H₄NO₂ + H₂O → HOC₆H₄NO₂ + (C₂H₅O)₂P(S)OH Degradation proceeds differently under anaerobic conditions: the nitro group on parathion is reduced to the

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...

. :(C₂H₅O)₂P(S)OC₆H₄NO₂ + 6 H → (C₂H₅O)₂P(S)OC₆H₄NH₂ + 2 H₂O

Safety

Parathion is a

cholinesterase inhibitor Cholinesterase inhibitors (ChEIs), also known as anti-cholinesterase, are chemicals that prevent the breakdown of the neurotransmitter acetylcholine or butyrylcholine. This increases the amount of the acetylcholine or butyrylcholine in the syn ...

. It generally disrupts the

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes ...

by inhibiting acetylcholinesterase. It is absorbed via skin, mucous membranes, and orally. Absorbed parathion is rapidly metabolized to paraoxon, as described in Insecticidal activity. Paraoxon exposure can result in

headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

convulsions A convulsion is a medical condition where the body muscles contract and relax rapidly and repeatedly, resulting in uncontrolled shaking. Because epileptic seizures typically include convulsions, the term ''convulsion'' is sometimes used as a ...

, poor vision,

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenter ...

, abdominal pain, severe

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

unconsciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an awareness of self and environment or to respond to any human or environmental stimulus. Unconsciousness may occur as the r ...

, tremor, dyspnea, and finally

pulmonary edema Pulmonary edema, also known as pulmonary congestion, is excessive liquid accumulation in the tissue and air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia and respiratory failure. It is due ...

as well as respiratory arrest. Symptoms of poisoning are known to last for extended periods, sometimes months. The most common and very specific antidote is

atropine Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically given ...

, in doses of up to 100 mg daily. Because atropine may also be toxic, it is recommended that small frequently repeated doses be used in treatment. If human poisoning is detected early and the treatment is prompt (atropine and artificial respiration), fatalities are infrequent. Insufficient oxygen will lead to

cerebral hypoxia Cerebral hypoxia is a form of hypoxia (reduced supply of oxygen), specifically involving the brain; when the brain is completely deprived of oxygen, it is called ''cerebral anoxia''. There are four categories of cerebral hypoxia; they are, in ...

and permanent brain damage. Peripheral neuropathy including paralysis is noticed as late sequelae after recovery from acute intoxication. Parathion and related organophosphorus pesticides are used in hundreds of thousands of poisonings annually, especially suicides. It is known as ''Schwiegermuttergift'' (mother-in-law poison) in Germany. For this reason, most formulations contain a blue dye providing warning. Parathion was used as a

chemical warfare Chemical warfare (CW) involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from nuclear warfare, biological warfare and radiological warfare, which together make up CBRN, the military a ...

agent, most notably by an element of the British South Africa Police (BSAP) attached to the Selous Scouts during the

Rhodesian Bush War The Rhodesian Bush War, also called the Second as well as the Zimbabwe War of Liberation, was a civil conflict from July 1964 to December 1979 in the List of states with limited recognition, unrecognised country of Rhodesia (later Zimbabwe-Rh ...

. They used it to poison clothing that was then supplied to anti-government guerrillas. When the enemy soldiers put on the clothes, they were poisoned by absorption through the skin. Based on animal studies, parathion is considered by the U.S. Environmental Protection Agency to be a possible human

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...

. Studies show that parathion is toxic to fetuses, but does not cause birth defects. It is classified by the

United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on ...

(UNEP) as a persistent organic pollutant and by the

World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level o ...

(WHO) as Toxicity Class Ia (extremely hazardous). Parathion is toxic to bees,

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s, and other forms of wildlife.

Protection against poisoning

To provide the end user with a minimum standard of protection, suitable protective gloves, clothing, and a respirator with organic-vapour cartridges is normally worn. Industrial safety during the production process requires special ventilation and continuous measurement of air contamination in order not to exceed PEL levels, as well as careful attention to personal hygiene. Frequent analysis of workers' serum acetylcholinesterase activity is also helpful with regards to occupational safety, because the action of parathion is cumulative. Also, atropine has been used as a specific antidote.

References

External links

*
ATSDR - Methyl Parathion Expert Panel Report
U.S. Department of Health and Human Services (public domain)
CDC - NIOSH Pocket Guide to Chemical Hazards
U.S. Department of Health and Human Services (public domain) * Ethyl parathion: * Methyl parathion: {{Authority control Obsolete pesticides Organophosphate insecticides Acetylcholinesterase inhibitors Organothiophosphate esters Nitrobenzenes IARC Group 2B carcinogens Phenol esters Ethyl esters