Did the nerve agent VX kill Kim Jong Nam?
February 24, 2017, 2:44 pm
As the History Channel video above indicates, nerve agents are potent acetylcholinesterase inhibitors that utilize the same mechanism as organophosphate insecticides such as parathion. Conceptually, the effect of VX exposure is simple: wherever in the body acetylcholine acts as a neurotransmitter, nerve agents cause unregulated, chaotic activity. There are generally 3 such sites:
- muscarinic sites: connections between nerves and secretory glands and smooth muscle
- nicotinic sites: neuromuscular junctions
- central sites: in the cerebrum and brainstem
The effects of nerve agents on these sites are predictable:
- muscarinic: massive respiratory secretions, bronchospasm, severe diaphoresis, vomiting, diarrhea, meiosis, and lacrimation
- nicotinic: voluntary muscle fasciculation and spasm, followed by fatigue and flaccidity
- central: seizures, central apnea
Victims exposed to nerve agents die of respiratory failure, due to a triple-whammy: airway obstruction and bronchospasm, dysfunction of voluntary muscles of respiration, and loss of central drive to breathe. With 3 separate types of effects, there are fittingly 3 antidotes:
- muscarinic effects: atropine
- nicotinic effects: pralidoxime (2-PAM)
- central effects: benzodiazepines such as diazepam
Despite the announcement that VX was identified, there are still some puzzling details that don’t seem to fit. Video of Mr. Kim after he was exposed to the agent does not seem to show muscle weakness, fasciculation, or copious secretions. Also, given that VX is often called one of the deadliest substances on the planet, the attackers did not seem to suffer serious effects. (It is not clear if they were wearing gloves, and a recent report suggests that one of the young women seen on the video vomited.) There has also been speculation that a binary weapon was involved, in which two harmless chemicals might have been combined to produce VX.
[Addendum: 2/24/17 14:32 CST]
According to emedicine.com, after dermal exposure of V-series agents onset of symptoms may be delayed for hours. I remember from the time I taught in the Department of Defense Domestic Preparedness Program that Dr. Fred Sidell, one of the nation’s experts on chemical weapons, stated that symptoms might not develop until 18 (!) hours after skin exposure to VX. This would be consistent with what we know about the attack on Mr. Kim. However, if the agent got in his eye, I would expect meiosis to produce markedly decreased vision.
Note also that VX is quite viscous, having high persistence and low volatility. Whereas the G-series nerve agents (tabun, soman, sarin) have approximately the consistency of water, VX is more like motor oil.