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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 if swallowed. 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.
Additional recommended knowledge
The European Union allowed Paraquat in 2004. Sweden, supported by Denmark, Austria, and Finland, brought the European Union commission to court. On 11 July 2007 the court annulled the directive authorising Paraquat as an active plant protection substance.
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 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:
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 European Union, paraquat has been forbidden since July 10th 2007.
Pure paraquat ingested is highly toxic to mammals and humans potentially leading to acute respiratory distress syndrome (ARDS), and 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 800 μm) 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.
Even a single swig immediately spat out can cause death from fibrous tissue developing in the lungs leading to asphyxiation.
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 that could lead to death up to 30 days after ingestion. 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.
Long term exposures to paraquat would most likely cause lung and eye damage, but reproductive/fertility damage was not found by the EPA in their review. Some suspect a possible link to a greater incidence of Parkinson's disease.
Persons exposed to or contaminated by paraquat, with any suspected ingestion or absorption, should be treated by emergency medical services immediately. Prehospital care should follow these guidelines: 
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 United States 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". 
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Paraquat". A list of authors is available in Wikipedia.|