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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. Nerve agents can be absorbed through the skin, requiring that those likely to be subjected to such
agents wear a full body suit in addition to a gas mask.
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 unpleasant results described above.
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 person affected with nerve agents, that person will be incapacitated for several days. Atropine for field use by military
personnel is often loaded in an autoinjector, for ease of use in stressful
conditions.
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 so far not been used on a large scale in warfare. Iraq briefly used chemical weapons, including nerve
agents, during the Iran-Iraq war of 1981-1988; the Kurdish village of
Halabja was exposed to nerve agents, and controversy still rages as to whether this
was a deliberate or accidental act. Nerve agents were not eventually used by Iraq in the Gulf War, despite widespread fears to the contary. However, 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 (see Sarin gas attack on the Tokyo
subway).
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, this latter being invented in the 1950s at Porton Down in England.
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 considered innocuous for humans and their food animals; but there is considerable
concern about the effects of long-term exposure to these chemicals by farm workers and animals alike.
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
- 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.
- Short History of the Development of Nerve Gases, http://www.mitretek.org/home.nsf/homelandsecurity/HistoryNerveGases
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