Why is ordinary soap and water adequate to decontaminate possible nerve agents?

In the news it was announced that anyone who might have been exposed in the recent Salisbury nerve agent incident should wash any potentially contaminated clothing as normal using regular detergent and water; other personal items can be cleaned with wipes.

The agent in question (identified only as Novichok, a family of chemicals) has been described as the most potent ever made.

How is it that ordinary cleaning can suffice as a method of decontamination? Is it a very unstable molecule? Does water (or detergent, or detergent solution, or alcohol solution) act strongly to decompose such chemicals? If unstable in water, how can it remain stable in the body to act? Could any viable agent remain in the wash waste water (going down the drain) after washing and pose a hazard downstream?

Edited:

The focus of my question is entirely about the apparent paradox of a chemical able to remain stable in an everyday environment, yet readily destroyed/decomposed by everyday means. In the specific case, a chemical which happens to be lethal in trace quantity that can persist, yet simple washing apparently destroys all trace, removing any potential for harm.

• Not sure why the close votes. A perfectly reasonable chemistry question. – matt_black Mar 13 '18 at 14:32
• @ToddMinehardt Then the fact that a wide range, if not most, "modern" nerve agents are based on a common fluorophosphonate core which is the target for the hydrolysis to less harmful substances should alleviate the worry. Every question relates to this single chemical feature. – matt_black Mar 13 '18 at 15:55

1 Answer

Nerve agents are usually susceptible to hydrolysis leading to non-toxic degradation products

Most modern nerve agents are based on fluorophosphonate cores. That is they contain a $\ce{PFO(OR)(X)}$ core where R is some organic radical (-iPr in sarin) and X can be a range of radicals (Me- in sarin, OR or N=R in novichok agents).

Most are not very stable in storage as they are subject to degradation from hydrolysis so have to made not long before use or have to be made ultra pure to avoid any contaminants catalysing their degradation by acid or base hydrolysis. As a result any were deployed as binary agents (where two tables components are mixed inside the weapon to create the active ingredient).

The key to their reactivity is the P-F bond which is easily hydrolysed to give much less harmful products. This hydrolysis is not fast enough to degrade the compounds inside the body before they kill you but is fast enough that they don't hang about for long periods in the environment after use (it is worth bearing in mind that they are extremely powerful inhibitors of acetylcholinesterase, without which your nervous system can't function: it doesn't take a big dose or a long time for them to work). It is also something that can be accelerated by washing. It seems likely, for example, that mildly contaminated clothing can be decontaminated by a standard domestic clothes washing cycle as this would dramatically accelerate any hydrolysis reactions.

It is also worth noting that, if the contamination were large enough, you would notice it very rapidly. So any residual contamination in people not already ill would be of a very low level and easily rendered insignificant by washing.-

• Side question: does hydrolysis follow the half-life pattern? In other words, even if the majority of such an agent were quickly destroyed, could some quantity of the original agent survive "decontamination" (i.e. remain un-hydrolyzed, even in water)? Is the washing approach viable only because of the assumption of "mild" contamination and that half-life is short enough that assumed residual quantities are brought down to no more than a molecule here and a molecule there? – Anthony X Mar 17 '18 at 17:20