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Nerve agent

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Nerve agents (also known as nerve gases, though these chemicals are liquid at room temperature) are a class of phosphorus-containing organic chemicals (organophosphates[?]) that inhibit the acetylcholinesterase[?] enzyme in animals and which are used as insecticides and chemical weapons. Poisoning by a nerve agent leads to contraction of pupils, profuse salivation, convulsions, involuntary urination and defecation, and eventual death by asphyxiation as control is lost over respiratory muscles. When sprayed as an aerosol, nerve agents can be absorbed through the skin and eyes and therefore protection against these agents requires a full body suit rather than only a gas mask.

Table of contents

Mechanism of action and antidotes

Muscle contraction is stimulated by the release of acetylcholine molecules at the motor nerve endings; within a fraction of a second, the acetylcholine is normally destroyed by acetylcholinesterase to end the muscle contraction until the next nerve impulse. When nerve agents block the action of the acetylcholinesterase enzyme, acetylcholine is not removed, with the result that muscle contractions do not stop, with the above mentioned extremely unpleasant or fatal effects.

Atropine and related "anticholinergic" drugs act as antidotes to nerve agent poisoning, because they block acetylcholine receptors, but they are poisonous in their own right. While they will save the life of a soldier they will also render him unfit for combat for about a week.

History

This class of compounds was first discovered in the late 1930s in Germany during research on improved insecticides. The Nazi government soon classified all work on these compounds and continued development through World War II; three of the most widely known agents, sarin, soman, and tabun were developed at that time for use as chemical warfare agents, but were not used in combat. At that time, the Germans believed that the Allies also knew of these compounds, assuming that because these compounds were not discussed in the Allies' scientific journals, information about them was being suppressed. In actuality, the Allies first learned about these agents when shells filled with them were captured towards the end of the war.[1]

Nerve agents have not been used on large scales in wars, though there have been persistent reports of entire Kurdish villages in Iraq being killed by the use of nerve agents during the 1980s. Although in the event, nerve agents were not actually used by Iraq in the Gulf War, the widespread use of anticholinergic drugs as a prophylaxis against nerve gas attack has been proposed as a possible cause of Gulf war syndrome

One of the most widely publicised uses of nerve agents was the 1995 terrorist attack in which operatives of the group Aum Shinrikyo released sarin into the Tokyo subway system.

Different nerve agents

The three agents discovered by the Germans together with cyclosarin are known as the G-series nerve agents. The only other known agents are the so-called V-series (VE, VG, VM, VX) of which VX (O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate) is the most well known.

A number of insecticides, such as dichlorvos[?], malathion[?] and parathion[?] are nerve agents. The metabolism of insects is sufficiently different from mammals that these compounds are relatively innocuous to humans and their food animals; but there is considerable concern about the safety of these chemicals where farm workers are exposed to concentrated solutions of these chemicals when used as insecticidal sheep dips etc.

International law

Nerve agents are covered by the Chemical Weapons Convention which took effect in 1997 and forbids their use for countries which have ratified it.

References

  1. We All Fall Down: The Prospects of Biological and Chemical Warfare, Robin Clarke, Allen Lane the Penguin Press , 1968 , quotes Brigadier General Rothschilds's book Tomorrow's Weapons to the effect that the Allies knew nothing about these agents until they captured German munitions near the end of the war.
  2. Short History of the Development of Nerve Gases, http://www.mitretek.org/home.nsf/homelandsecurity/HistoryNerveGases



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