Paraquat

Paraquat is the trade name for N,N'-Dimethyl-4,4'-bipyridinium dichloride or viologen, 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.

Characteristics

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 grass 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.

When used in accordance with manufacturers’ recommendations, paraquat can deliver safe, effective weed control, generating social and economic benefits, while protecting the land for future generations.

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

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.

Health Risks

Paraquat is dangerously poisonous, and many people have died of paraquat poisoning. See http://www.pan-uk.org/pestnews/actives/paraquat.htm

Paraquat like many chemicals can be harmful if the guidelines for safe use are not followed.

According to the Center for Disease Control, paraquat exposure can lead to several health risks, such as liver, lung, heart, and kidney failure in a matter of weeks after exposure to a medium dose of paraquat. However, when following the safety guidelines paraquat proves to be a very useful tool for weed control.

Paraquat Pot

During the late 1970s, 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.

Reassurance for those who “accidentally inhaled”

In the late 1960s the US government, perhaps in an attempt to deter people from using marijuana, warned that much of the crop had been sprayed with paraquat and, therefore, was unsafe to smoke.

However, independent bodies have studied paraquat in this use. Jenny PronCzuk de Garbino, (Ref: 1) 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: 2).

External links

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. http://www.pan-uk.org/pestnews/actives/paraquat.htm offers
CDC Basic Facts about Paraquat http://www.bt.cdc.gov/agent/paraquat/basics/facts.asp
Find more information here: http://www.epa.gov/pesticides/safety/healthcare/handbook/Chap12.pdf
A more extensive list of paraquat health information and risks can be found here: http://www.bt.cdc.gov/agent/paraquat/basics/facts.asp

References