Stardate 20020221.1143

(Captain's log): Benjamin Rush and Bob Standaert both write to inform me that I identified the wrong mechanism of lethality for cyanide. Carbon monoxide kills the way I described, but cyanide and sulfide have a different mechanism. Standaert says:

You indicate that cyanide kills by binding to hemoglobin (the oxygen carrying iron protein in blood), such that the blood cannot carry oxygen; that is incorrect. Carbon monoxide kills that way, but cyanide does not, nor does sulfide. Cyanide has a number of effects, and it does bind hemoglobin, but the primary lethal target is cytochrome c oxidase, an iron protein involved in the transfer of electrons (extracted from food) to molecular oxygen; this protein is also the main lethal target of sulfide. It is located in the mitochondria of respiring cells, not in red blood cells. People who get cyanide poisoning have plenty of oxygen in their blood, they just can't use the oxygen to burn fuel. Here is a good summary of the effects.

http://www.nbc-med.org/SiteContent/HomePage/WhatsNew/MedAspects/Ch-10electrv699.pdf

Poisoning a water supply with cyanide would be difficult. Dumping potassium cyanide into a reservoir would not work because it would be essentially impossible to get the concentration high enough that consuming some reasonable volume of the tainted of water (e.g., a liter or less) would deliver a lethal dose. Also, unless the water were terribly hard (alkalinwe), the cyanide would be in equilibrium with significant amounts of hydrogen cyanide, which would slowly outgas at low concentration into the breeze.

The only fatal scenario I can imagine would be if the terrorists tapped into a local plumbing system (one building, or one drinking fountain, for example) where they could spike the water heavily enough to deliver fatal doses. This would be tragic for the affected individuals and might cause a panic, but it would hardly inflict the sort of mass casualties these people seek.

The unfortunate problem is that these people have demonstrated an ability to climb the learning curve.

In fact, it really does depend on how big an incident terrorists are trying to create. If they're looking for casualties at the level of NYC, then they'd need a ton or so of cyanide to get any important effect. Even if they actually had had potassium cyanide, 4 kilos into a water supply would have been a waste of time (unless, as Bob says, it was concentrated); most of us are routinely exposed to low concentrations in our everyday lives in food and smoke (as his referenced document makes clear) and we have metabolic mechanisms to deal with it. The only reasonable use of it as a terror weapon would have been to try to create an event similar to the Tokyo subway gassing, and even for that cyanide is not a very good choice because if you're not killed by it then it probably doesn't leave any harmful effects at all. (Chlorine would have been better; it causes permanent lung damage, and it's even easier to make than cyanide gas.)

Now if you really want to talk about something nasty, there's arsine (arsenic trihydride). It's used in the semiconductor industry, and the lethal dose is unbelievably small. Where a dangerous concentration of cyanide is 150 ppm, a dangerous concentration of arsine is .05 ppm. I read that arsine causes red blood cells to burst which leads to circulatory collapse. It is awful. They also use phosphine (phosphorus trihydride) which is also damned nasty, and that's why if you hear the fire alarm in a semiconductor fab, you run to the exit. Fortunately, both phosphine and arsine are extremely carefully controlled and are not at all easy to make.