VX is an extremely toxic synthetic chemical compound in the organophosphorus class, specifically, a thiophosphonate. In the class of nerve agents, it was developed for military use in chemical warfare after translation of earlier discoveries of organophosphate toxicity in pesticide research. In its pure form, VX is an oily, relatively non-volatile, liquid that is amber-like in color. Because of its low volatility, VX persists in environments where it is dispersed.
VX, short for "venomous agent X", is one of the best known of the V nerve agents and was first discovered at Porton Down in England during the early 1950s based on research first done by Dr. Gerhard Schrader, a chemist working for IG Farben in Germany during the 1930s. Now one of a broader V-series of agents, they are classified as nerve agents and have been used as a chemical weapon in various recorded deadly attacks. VX fatalities occur with exposure to tens of milligram quantities via inhalation or absorption through skin; VX is thus more potent than sarin, another nerve agent with a similar mechanism of action. On such exposure, these agents severely disrupt the body's signaling between the nervous and muscular systems, leading to a prolonged neuromuscular blockade, flaccid paralysis of all the muscles in the body including the diaphragm, and death by asphyxiation.
The danger of VX, in particular, lies in direct exposure to the chemical agent persisting where it was dispersed, and not through its evaporating and being distributed as a vapor (i.e. it is not a "vapor hazard"). VX is considered an area denial weapon due to these physical and biochemical characteristics. As a chemical weapon, it is categorized as a weapon of mass destruction and is banned by the Chemical Weapons Convention of 1993, where production and stockpiling of VX exceeding 100 grams (3.53 oz) per year is outlawed. The only exception is for "research, medical or pharmaceutical purposes outside a single small-scale facility in aggregate quantities not exceeding 10 kg (22 lb) per year per facility".