The latest novichok case raises the question of whether the British couple Dawn Sturgess and Charlie Rowley were exposed to the same source of the nerve agent that poisoned the Russian former spy Sergei Skripal and his daughter Yulia in March.

There has been no official comment on this question, but it is scientifically plausible that the agent might persist for long enough, particularly if it was contained in some way.

Novichok is not a single chemical, but a family of nerve agent compounds that the Soviet Union developed in the 1970s and 80s from chemicals normally used for insecticides and other non-military purposes. Like sarin and mustard gas, their exact chemical structures and properties are considered classified in the UK, the US and other countries.

“How long they take to degrade is certainly not data that is publicly available, but from discussions with people at [the defence laboratory] Porton Down, I understand they are slow to degrade,” said Alastair Hay, an environmental toxicologist at the University of Leeds who investigated the use of chemical weapons against Iraqi Kurds in Halabja in 1988. “This is one of the reasons the Skripals were unconscious for so long – it doesn’t break down readily in the body.”

Novichok chemicals left in the environment would degrade in two main ways: through hydrolysis – being broken down by water – and evaporation. Traditional nerve agents such as sarin are relatively susceptible to these processes. The fact that sarin evaporates quickly means people are rapidly exposed through breathing it in during a chemical attack.

Novichok agents are understood to evaporate far more slowly. “They’ve been deliberately designed by chemists to be more robust and hang around for longer,” said Andrea Sella, a professor of inorganic chemistry at University College London.



The flip-side is that they pose a lower risk to people in the vicinity of a contaminated area. Hay said: “Direct contact is the most likely route of exposure.”

The authorities are now engaged in an urgent and expanded cleanup operation. They will also be hunting for forensic evidence that might be relevant for both cases. Access to a bulk sample would give scientists far more information than what they have been able to ascertain so far from blood samples from the Skripals and trace samples from their front door.

“There’s the feeling that there’s a little crock of forensic gold out there,” Sella said. “That would give them a real chemical fingerprint which would give you far more information.”

• This article was amended on 10 July 2018 because an earlier version referred to mustard gas as an organophosphate compound. This has been corrected.

