Paraquat

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

1 History
2 Herbicide use
3 Health risks
4 Paraquat Pot
5 References
6 External links

Paraquat
Image:Paraquat.png
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 (pK_a)	?
Basicity (pK_b)	?
Structure
Molecular shape	?
Crystal structure	?
Dipole moment	? D
Hazards
MSDS	External MSDS
Main hazards	?
NFPA 704
Flash point	?°C
R/S statement	R: R24 R25 R36 R37 R38 S: ?
RTECS number	?
Supplementary data page
Structure and properties	n, ε_r, 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. It is dangerously poisonous to humans. Other members of this class include diquat, cyperquat, diethamquat, difenzoquat, and morfamquat. All of these are easily reduced to the radical ion, which generates superoxide radical that reacts with unsaturated membrane lipids.

[edit] History

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

[edit] 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.

[edit] Health risks

Pure paraquat ingested is highly toxic to animals and humans, and there are no specific antidotes. Death may be delayed 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.<ref>PAN UK, Paraquat, accessed 13 October 2006.</ref>

According to the Center for Disease Control, small to medium exposure 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 esophageal strictures.<ref>Center for Disease Control, Facts about Paraquat, accessed 13 October 2006.</ref>

Paraquat-induced toxicity in rats has also been linked to Parkinson's-like pathological degenerative mechanisms. <ref> Journal of Neuroscience, [1], accessed 24 October 2006.</ref>

[edit] 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, <ref>Pronczuk de Garbino J, Epidemiology of paraquat poisoning, in: Bismuth C, and Hall AH (eds), Paraquat Poisoning: Mechanisms, Prevention, Treatment, pp. 37-51, New York: Marcel Dekker, 1995.</ref> 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". <ref> Reigart, J. Routt and Roberts, James R. Recognition and Management of Pesticide Poisonings, 5th edition. Washington, DC: US Environmental Protection Agency, 1999. Book available online</ref>