Paraquat

For the British military operation to recapture South Georgia, see Operation Paraquat.

Paraquat
General
Systematic name	1,1'-dimethyl-4,4'-bipyridinium dichloride
Other names	paraquat dichloride; methyl viologen dichloride; Crisquat; Dexuron; Esgram; Gramuron; Ortho Paraquat CL; Para-col; Pillarxone; Tota-col; Toxer Total; PP148; Cyclone; Gramixel; Gramoxone; Pathclear; AH 501.
Molecular formula	C12H14Cl2N2
SMILES	[Cl-].[Cl-].C[n+]1ccc(cc1)c2cc[n+](C)cc2
Molar mass	257.16 g/mol
Appearance	off-white powder
CAS number	[1910-42-5]
Properties
Density and phase	1.25 g/cm³ solid
Solubility in water	high
Melting point	?°C (? K)
Boiling point	175 - 180 °C (dec)
Acidity (pKa)	?
Basicity (pKb)	?
Structure
Molecular shape	?
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	?
NFPA 704
Flash point	?°C
R/S statement	R: Template:R24 Template:R25 Template:R36 Template:R37 Template:R38 S: ?
RTECS number	?
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	?
Other cations	?
Related ?	?
Related compounds	pyridine, viologen
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Paraquat is the trade name for N,N'-Dimethyl-4,4'-bipyridinium dichloride, a viologen. Paraquat is used as a quaternary ammonium herbicide. As with many herbicides it is dangerously poisonous to humans if swallowed. Other members of this class include diquat (N,N'-Ethylene-2,2'-bipyridinium dibromide), cyperquat (1-Methyl-4-phenylpyridinium chloride), diethamquat (1,1′-Bis(diethylcarbamoylmethyl)-4,4′-bipyridinium dichloride), difenzoquat, and morfamquat. All of these are easily reduced to the radical ion, which generates superoxide radical that reacts with unsaturated membrane lipids.

History

Paraquat was first produced for commercial purposes in 1961 by ICI (now Syngenta) and is today among the most commonly used herbicides.

The European Union allowed Paraquat in 2004. Sweden, supported by Denmark, Austria, and Finland, brought the European Union commission to court. After years of further investigations, the verdict for Paraquat in EU will arrive in spring 2007.

Herbicide use

The compound is one of the most widely used herbicides in the world. It is quick-acting, non-selective, and kills green plant tissue on contact. It is redistributed within the plant but does not harm mature bark.

Being a herbicide, paraquat protects crops by controlling a wide range of annual and certain perennial weeds (unwanted plants) that reduce crop yield and quality by competing with the crop for water, nutrients, and light.

The key characteristics that distinguish the non-selective contact herbicide paraquat from other active ingredients used in plant protection products are:

• Paraquat is non-selective, which means it kills a wide range of annual grasses and broad-leaved weeds and the tops of established perennial weeds.
• Paraquat is very fast-acting.
• Paraquat is rain-fast within minutes of application.
• Paraquat becomes biologically inactive upon contact with soil.

In the United States, paraquat is available primarily as a liquid in various strengths. It is classified as "restricted use," which means that it can be used only by licensed applicators. As with many chemicals, caution must be exercised during use.

In the United Kingdom paraquat is available for garden use in small quantities usually mixed with diquat. It is also available in a wider range of formulations for agricultural use etc.

Health risks

Pure paraquat ingested is highly toxic to mammals and humans, and, as with the majority of poisons, there are no specific antidotes. However, fuller's earth or activated charcoal is an effective treatment, if taken in time. Death may be up to 30 days after ingestion. Diluted paraquat used for spraying is less so, thus the greatest risk of accidental poisoning is during mixing and loading paraquat for use.

In acute toxicity studies using laboratory animals, paraquat has been shown to be highly toxic by the inhalation route and has been placed in Toxicity Category I (the highest of four levels ) for acute inhalation effects. However, the EPA has determined that particles used in agricultural practices (400 to 800um) are well beyond the respirable range and therefore inhalation toxicity is not a toxicological endpoint of concern. Paraquat is toxic (Category II) by the oral route and moderately toxic (Category III) by the dermal route. Paraquat will cause moderate to severe eye irritation and minimal dermal irritation, and has been placed in Toxicity Categories II and IV (slightly toxic) for these effects.

According to the Center for Disease Control, ingesting paraquat causes symptoms such as liver, lung, heart, and kidney failure within several days to several weeks. Those who suffer large exposures are unlikely to survive. Chronic exposure can lead to lung damage, kidney failure, heart failure, and oesophageal strictures.

Paraquat-induced toxicity in rats has also been linked to Parkinson's-like pathological degenerative mechanisms. A study by the Buck Institute shows a connection between exposure to paraquat and iron in infancy and mid-life Parkinson's in laboratory mice.

• Remove patient from further contact with substance.
• Decontaminate with large volumes of water; remove patient's clothing.
• Avoid secondary contamination by contact either with substance or runoff from decontamination efforts.
• Establish and maintain a patent airway.
• The administration of supplemental oxygen is advised against; however, prudent patient care dictates that oxygen should not be withheld from persons exhibiting clinical signs and symptoms of hypoxia. Emergency medical services personnel should consult with their medical control physician for specific case-by-case guidance.
• Provide supportive treatment as indicated.
• Consider evacuation to an appropriate hospital by helicopter; if air evacuation is not available, expedite transport by ground ambulance.
• In the case of contamination of the eye, irrigate the affected eye with normal saline solution for at least 15 minutes.

Paraquat Pot

During the late 1960s, a controversial program sponsored by the US government sprayed paraquat on marijuana fields in South America. Since much of this marijuana was subsequently smoked by Americans, the US government's "Paraquat Pot" program stirred much debate. Perhaps in an attempt to deter people from using marijuana, representatives of the program warned that spraying rendered the crop unsafe to smoke. However, independent bodies have studied paraquat in this use. Jenny Pronczuk de Garbino, stated: "no lung or other injury in marijuana users has ever been attributed to Paraquat contamination".

On this topic, D.P. Morgan states in a US Environmental Protection Agency publication that: "Smoking Paraquat-contaminated marijuana does not result in lung damage as the herbicide is pyrolyzed to dipyridyl (which does not present a toxic hazard) during smoking".

Popular Culture References

In the movie The Big Lebowski, the dude calls the Big Lebowski ("the other Jeffrey Lebowski, the millionaire") a "human paraquat". This likely referens to the marijuana-destroying effects of paraquat (see above) than the poisonous effect of ingested paraquat on the human body.

External links

• France made EU allow P, Sweden takes EU commite to court
• The Official Website of the International "Stop Paraquat" Campaign
• The Paraquat Information Center, a site sponsored by the main manufacturer of Paraquat.
• Find more information here: http://www.epa.gov/pesticides/safety/healthcare/handbook/Chap12.pdf