Double agent Sergei Skripal was poisoned with a little-known nerve agent from a group of chemical compounds known as Novichok. The Soviets once developed these weapons to circumvent the Chemical Weapons Convention.
"Novichok" means the "new guy" in Russian – even if it isn't actually that "new" today.
The family of compounds, which were developed in the 1970s and 80s, comprise numerous nerve agents. All contain an organophosphorous core.
Novichok-5 and Novichok-7 are supposed to be the most dangerous – up to eight times more poisonous than VX – one of the most deadly chemical weapons in the world. But in total, there are more than a hundred structural variants in the Novichok family.
Production under civilian cover
Some of the less dangerous compounds were made public during the Soviet era – published in public journals as organophosphate insecticides. This was an apparent attempt to disguise a military research program as a civilian one.
Even more, the new chemical weapon itself was an attempt to mislead the international community.
"The reason Novichok compounds were actually manufactured was to work around the Chemical Weapons Convention,"Dr. Michelle Carlin told DW. Carlin is a toxicologist at the Northumbria University in Newcastle, Great Britain.
The trick the Soviet chemists used was as follows: They produced two compounds in the form of an ultrafine powder. Each of the two components was either not toxic or was of limited toxicity and was therefore not banned at the time.
"If they made them as two separate components that were non-toxic, then it wasn't illegal – only when it was mixed," Carlin says.
Today, things have changed. The compounds themselves are banned in the Chemical Weapons Convention.
Still, not too much is known about the chemistry of Novichok.
A nerve signal overload
While it remains unclear which, exactly, of the many Novichok variants was used to poison Skripal and his daughter, the medical effects of the poison are well understood.
"They react very similarly to other nerve agents" Carlin says.
In essence, the nerve agent triggers a protein chain reaction, resulting in an uncontrolled bombardment of body tissue and organs with nerve signals by a neurotransmitter called acetylcholine.
"The signals continue and overload the tissues and the organs. Essentially, we end up with excess salivation, problems with breathing, because we can't control the muscles. It can lead to paralysis, convulsions and ultimately death if the dose is high enough or the exposure long enough."
Since Novichok agents are much more potent than other known chemical weapons substances, they go to work quicker – or, a smaller dose can do the same damage.
Doctors treat Novichok poisoning by administering two kinds of medicines: Pralidoxime accelerates the production of an enzyme called cholesterase – which is what the Novichok nerve agent blocks. Freeing up cholesterase production is essential to stop the uncontrolled bombardment of organs and muscles with the acetylcholine nerve signals.
Secondly, doctors administer atropine, which is an antidote not only applicable to Novichok agents. "It's also used for cases of overdose with other organophosphate compounds, like insecticides and pesticides," toxicologist Carlin explains.
When Novichok agents get into the environment, they pose a danger only for a limited time period. "When the nerve agents interact with the moisture in the atmosphere, they actually degrade." Also, one can wash the compounds off with water.
Assassins who use such substances, however, are taking a big risk.
"If the nerve agent consists of two non-toxic agents, it's obviously easier to handle," Carlin says. "But at the point where the components are mixed, it could become a problem."