Nerve agent
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.
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. Atrophine for field use by military personnel is often loaded in an autoinjector, for ease of use in stressful conditions.
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).
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.
Nerve agents are covered by the Chemical Weapons Convention which took effect in 1997 and forbids their use for countries which have ratified it.Mechanism of action and antidotes
History
Different nerve agents
International law