Paraquat
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- For the British military operation to recapture South Georgia, see Operation Paraquat.
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| Paraquat | |
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| General | |
| Systematic name | 1,1'-dimethyl-4,4'-bipyridinium dichloride |
| Other names | paraquat dichloride; methyl viologen dichloride; Crisquat; Dexuron; Esgram; |
| 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: R24 R25 R36 R37 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 |
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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. As with many chemicals 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.
[edit] 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 three years ago. Sweden, supported by Denmark, Austria, and Finland, brought the The European Union commission to court. After years of further investigations, the verdict for Paraquat in EU will arrive in spring 2007.
[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 mammals and humans, and, as with the majority of chemicals, there are no specific antidotes. However, fullers 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.[1]
- 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.[2]
Paraquat-induced toxicity in rats has also been linked to Parkinson's-like pathological degenerative mechanisms. [3]
Long term exposures to paraquat would most likely cause lung and eye damage, 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.
[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, [4] 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". [5]
[edit] References
- ^ PAN UK, Paraquat, accessed 13 October 2006.
- ^ Center for Disease Control, Facts about Paraquat, accessed 13 October 2006.
- ^ Journal of Neuroscience, [1], accessed 24 October 2006.
- ^ 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.
- ^ 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
[edit] 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 world experts and the main manufacturer of Paraquat. Alternative sites may provide a different view but they may have less experience and ignore the views of millions of users who choose to use the product on their farms on a daily basis. Or other economical and political prefences than Syngenta
- Find more information here: http://www.epa.gov/pesticides/safety/healthcare/handbook/Chap12.pdf
- Links to external chemical sources
