VX, IUPAC name O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate, is an extremely toxic
substance that has no known uses except in chemical warfare as a nerve agent. It is a
tasteless and odorless liquid. As a chemical weapon, it is classified as a weapon of mass
destruction by the United Nations in UN Resolution 687. The production and stockpiling of VX
was outlawed by the Chemical Weapons Convention of 1993.
The VX nerve agent is the best-known of the V-series of nerve agents and is considered
an area denial weapon due to its physical properties.
Discovery Ranajit Ghosh, a chemist at the Plant Protection
Laboratories of the British firm Imperial Chemical Industries, was investigating a class
of organophosphate compounds. Like Gerhard Schrader, an earlier investigator of organophosphates,
Ghosh found that they were quite effective pesticides. In 1954, ICI put one of them on
the market under the trade name Amiton. It was subsequently withdrawn, as it was too
toxic for safe use. The toxicity did not go unnoticed, and samples of it had been sent
to the British Armed Forces research facility at Porton Down for evaluation. After the evaluation
was complete, several members of this class of compounds became a new group of nerve agents,
the V agents. The best-known of these is probably VX, assigned the UK Rainbow Code Purple Possum,
with the Russian V-Agent coming a close second. This class of compounds is also sometimes
known as Tammelin's esters, after Lars-Erik Tammelin of the Swedish Defence Research Agency.
Tammelin was also conducting research on this class of compounds in 1952, but did not widely
publicize his work. Chemical characteristics
With its high viscosity and low volatility, VX has the texture and feel of motor oil.
This makes it especially dangerous, as it has a high persistence in the environment.
It is odorless and tasteless, and can be distributed as a liquid, both pure and as a mixture with
a polymer in the form of thickened agent, or as an aerosol.
VX is an acetylcholinesterase inhibitor, i.e. it works by blocking the function of the enzyme
acetylcholinesterase. Normally, an electric nerve pulse would cause the release of acetylcholine
over a synapse that would stimulate muscle contraction. The acetylcholine is then broken
down to non-reactive substances by the acetylcholinesterase enzyme. If more muscle tension is needed the
nerve must release more acetylcholine. VX blocks the action of acetylcholinesterase,
thus resulting in initial violent contractions, followed by sustained supercontraction restricted
to the subjunctional endplate sarcoplasm and prolonged depolarizing neuromuscular blockade,
the latter resulting in flaccid paralysis of all the muscles in the body. Sustained
paralysis of the diaphragm muscle causes death by asphyxiation.
Synthesis VX is produced via the "transester process".
This entails a series of steps whereby phosphorus trichloride is methylated to produce methyl
phosphonous dichloride. The resulting material is reacted with ethanol to form a diester.
This is then transesterified with N,N-diisopropylaminoethanol to produce the mixed phosphonite. Finally,
this immediate precursor is reacted with sulfur to form VX.
VX can also be delivered in binary chemical weapons which mix in-flight to form the agent
prior to release. Binary VX is referred to as VX2, and is created by mixing O-(2-diisopropylaminoethyl)
O′-ethyl methylphosphonite with elemental sulfur as is done in the Bigeye aerial chemical
bomb. It may also be produced by mixing with sulfur compounds, as with the liquid dimethyl
polysulfide mixture in the canceled XM-768 8-inch binary projectile program.
Solvolysis Like other organophosphorus nerve agents,
VX may be destroyed by reaction with strong nucleophiles. The reaction of VX with concentrated
aqueous sodium hydroxide results in competing cleavage of the P-O and P-S esters, with P-S
cleavage dominating. This is somewhat problematic, as the product of P-O bond cleavage remains
toxic. In contrast, reaction with the hydroperoxide anion leads to exclusive cleavage of the P-S
bond. Biological effects
VX is the most toxic nerve agent ever synthesized for which activity has been independently
confirmed. The median lethal dose for humans is estimated to be about 10 milligrams through
skin contact and the LCt50 for inhalation is estimated to be 30–50 mg·min/m³.
Early symptoms of percutaneous exposure may be local muscular twitching or sweating at
the area of exposure followed by nausea or vomiting. Some of the early symptoms of a
VX vapor exposure to nerve agent may be rhinorrhea and/or tightness in the chest with shortness
of breath. Miosis may be an early sign of agent exposure but is not usually used as
the only indicator of exposure. Treatment
Primary consideration should be given to removal of the liquid agent from the skin before removal
of the individual to an uncontaminated area or atmosphere. After removal from the contaminated
area, the casualty will be decontaminated by washing the contaminated areas with household
bleach and flushing with clean water. After decontamination, the contaminated clothing
is removed and skin contamination washed away. If possible, decontamination is completed
before the casualty is taken for further medical treatment.
An individual who has received a known nerve-agent exposure or who exhibits definite signs or
symptoms of nerve-agent exposure should immediately have the nerve agent antidote drugs atropine
and pralidoxime, and a sedative/antiepileptic such as diazepam injected. In several nations
the nerve agent antidotes are issued for military personnel in the form of an autoinjector such
as the United States military Mark I NAAK. Atropine works by binding and blocking a subset
of acetylcholine receptors, so that the buildup of acetylcholine produced by loss of the acetylcholinesterase
function can no longer affect their target. VX block the enzymatic activity of acetylcholinesterase
by binding to the active site of the enzyme. The phosphate group on VX is then transferred
from VX to AChE, inactivating the enzyme and producing an inactive metabolite of VX. The
injection of pralidoxime removes the phosphate group from AChE, reactivating it, thereby
reversing the effects of VX. If pralidoxime is not given soon enough, the inactivated
enzyme will "age", resulting in a much stronger AChEW-phosphate that pralidoxime cannot reverse.
Diagnostic tests Controlled studies in humans have shown that
minimally toxic doses cause 70–75% depression of erythrocyte cholinesterase within several
hours of exposure. The serum level of ethyl methylphosphonic acid, a VX hydrolysis product,
was measured to confirm exposure in one poisoning victim.
History For an in-depth discussion, see main article
on nerve agent history The chemists Ranajit Ghosh and J.F. Newman
discovered the V-series nerve agents at ICI in 1952, patenting diethyl S-2-diethylaminoethyl
phosphono- thioate in November 1952. Further commercial research on similar compounds ceased
in 1955 when its lethality to humans was discovered. The US went into production of large amounts
of VX in 1961 at Newport Chemical Depot. There was evidence of a combination of chemical
agents having been used by Iraq against the Kurds at Halabja in 1988 under Saddam Hussein.
Hussein later testified to UNSCOM that Iraq had researched VX, but had failed to weaponize
the agent due to production failure. After U.S. and allied forces had invaded Iraq, no
VX agent or production facilities were found. However, UNSCOM laboratories detected traces
of VX on warhead remnants. In December 1994 and January 1995, Masami
Tsuchiya of Aum Shinrikyo synthesized 100 to 200 grams of VX which was used to attack
three persons. Two persons were injured and one 28-year-old man died, who is believed
to be the only fully documented victim of VX ever in the world. The VX victim, whom
Shoko Asahara had suspected as a spy, was attacked at 7:00 am on December 12, 1994 on
the street in Osaka by Tomomitsu Niimi and another AUM member, who sprinkled the nerve
agent on his neck. He chased them for about 100 yards before collapsing, dying 10 days
later without ever coming out of a deep coma. Doctors in the hospital suspected at the time
he had been poisoned with an organophosphate pesticide. But the cause of death was pinned
down only after cult members arrested for the subway attack confessed to the killing.
Ethyl methylphosphonate, methylphosphonic acid and diisopropyl-2-(methylthio) ethylamine
were later found in the body of the victim. Unlike the cases for sarin, VX was not used
for mass murder. Some countries known to possess VX are the
United States, Russia, and Syria. A Sudanese pharmaceutical facility, the Al-Shifa pharmaceutical
factory, was bombed by the U.S. in 1998 acting on information that it produced VX and that
the origin of the agent was associated with both Iraq and Al Qaeda. The US had obtained
soil samples identified as containing O-ethyl hydrogen methylphosphonothioate, a chemical
used in the production of VX which may also have commercial applications. Chemical weapons
experts later suggested that the widely used Fonophos organophosphate insecticide could
have been mistaken for EMPTA. US VX stockpile elimination
In the late 1960s, the US canceled its chemical weapons programs and began the destruction
of its stockpiles of agents by a variety of methods. Early disposal included the US Army's
CHASE program, in which old ships were filled with chemical weapons stockpiles and then
scuttled. CHASE 8 was conducted on June 15, 1967, in which the S.S. Cpl. Eric G. Gibson
was filled with 7,380 VX rockets and scuttled in 7,200 feet of water, off the coast of Atlantic
City, New Jersey. In fiscal year 2008, the US Department of
Defense released a study finding that the U.S. had dumped at least 124 tons of VX into
the Atlantic Ocean off the coasts of New York/New Jersey and Florida, between 1919 and 1970.
This material consisted of nearly 22,000 M55 rockets, 19 bulk containers holding 1,400
pounds each, and one M23 chemical landmine. Incineration was used for VX stockpile destruction
starting in 1990 with Johnston Atoll Chemical Agent Disposal System in the North Pacific
with other incineration plants following at Deseret Chemical Depot, Pine Bluff Arsenal,
Umatilla Chemical Depot and Anniston Army Depot with the last of the VX inventory destroyed
on December 24, 2008. The Newport Chemical Depot began VX stockpile
elimination using chemical neutralization in 2005. VX was hydrolyzed to much less toxic
byproducts by using concentrated caustic solution, and the resulting waste was then shipped off-site
for further processing. Technical and political issues regarding this secondary byproduct
resulted in delays, but the depot completed their VX stockpile destruction in August,
2008. The remaining VX stockpile in the US will
be treated by the Blue Grass Chemical Agent-Destruction Pilot Plant, part of the Program Executive
Office, Assembled Chemical Weapons Alternatives program. The program was established as an
alternative to the incineration process successfully used by the Army Chemical Materials Agency,
which completed its stockpile destruction activities in March 2012. The Blue Grass Pilot
Plant has been plagued by repeated cost over-runs and schedule slippages since its inception.
Worldwide VX stockpile elimination Worldwide, VX disposal has continued since
1997 under the mandate of the Chemical Weapons Convention.
In Russia, the US is providing support for these destruction activities with the Nunn-Lugar
Global Cooperation Initiative. The Initiative has been able to convert a former chemical
weapons depot at Shchuchye, Kurgan Oblast, into a facility to destroy those chemical
weapons. The new facility, which opened in May 2009, has been working on eliminating
the nearly 5,950 tons of nerve agents held at the former storage complex. However, this
facility only holds about 14% of Russian chemical weapons that are stored throughout seven sites.
Another such destruction plant for Russia, built for €140 million and paid for by Germany
opened in 2009. In popular culture
One of the best-known references to VX in popular culture is its use in the 1996 film
The Rock, which centers on a threatened VX attack on San Francisco from the island of
Alcatraz. The film uses a certain artistic license, notably with VX being ascribed corrosive
powers it does not possess, permitting an early scene in which a VX victim is shown
with his face melting, rather than dying through asphyxiation. It also shows the hero applying
an intracardiac injection of atropine as a defense against VX contamination, rather than
the more usual intramuscular injection of a combination of atropine and pralidoxime.
In the BBC One spy drama Spooks, an episode named "I Spy Apocalypse" features an EERE
turned real life emergency. A dirty bomb was reported to have exploded in Parliament Square
and later the Morningside area of Edinburgh. The bomb was confirmed to have dispersed VX
in quantities that exceeded the lethal dose across much of the south east of England.
It is later found that the emergency is a well constructed and believable exercise designed
to test the MI5 officers to their limits. Another reference to VX is found in the 2012
art-house dark comedy film It's a Disaster. The film centers around four couples that
gather for a regular couples brunch and later learn about a multi-city VX attack on the
United States that may threaten their lives. See also
Dugway sheep incident References
External links Oxford website on Nerve Agents
Questions and Answers for VX CDC Facts About VX
U.S. Army's Chemical Materials Agency CBW Info
National Academies: Health effects of VX DA PAM 385-61 US Army Toxic Chemical Agent
Safety Standards Decommissioning Surplus VX - Article from
NYTimes.com