Stardate 20020220.1408

(On Screen): Cyanide is an example of a blood poison. Like sulfide (which is ten times as poisonous per weight) cyanide kills by binding to the iron in our blood. It binds stronger than oxygen does so that oxygen can't displace it, which means that the ability of the blood to carry oxygen is destroyed. The person dies in a manner similar to suffocation, even though they still have access to air and can still breath, because their blood no longer oxygenates in the lungs. Depending on the dose, death takes four or five minutes.

Cyanide can be absorbed from the digestive tract if it is a dissolved ion, or can be breathed as hydrogen cyanide gas (technically, hydrocyanic acid). The gas hits fluid in the lungs, and dissolves and ionizes, and the cyanide ion then diffuses through the lung tissue and into the blood where it binds to the iron.

Potassium Ferrocyanide is a salt which consists of a potassium cation and a ferrocyanide anion. Ferrocyanide is an iron atom with a lot of cyanide ions already attached. It is not poisonous; it's one of the chemicals that is usually included in kid's toy chemistry sets, in fact, because it is not dangerous and because you can do some cool things with it. Ferric ferrocyanide is an extremely deep blue, but ferric amonium sulfate and potassium ferrocyanide are nearly colorless. So making solutions of each and mixing them is neat to see: two clear fluids turn dark blue.

The cyanide ions are already bound to iron in the ferrocyanide anion, so it doesn't threaten the iron in our blood and won't kill us that way. With a huge amount of work you can liberate a bit of cyanide gas from it, but not enough to be worth the effort as a weapon.

Enough of anything will kill you, of course, but it takes a hell of a lot of this stuff to cause a problem. The fatal ingested dose for rats is 6.4 grams per kilogram of body weight (to cause a 50% death rate, known as LD50). For a man weighing 75 kilograms, he would have to consume about a pound of the stuff. That makes it about half as poisonous as table salt (for which the rat LD50 is 3 grams per kilo of body weight).

Early reports were that a group of four Morroccans were arrested in Rome with "ten pounds of cyanide". If true, that would have been damned scary; that's a hell of a lot of cyanide, and if it had been injected somehow into the water supply it could have made a lot of people sick or even killed them. The LD50 dose for sodium cyanide is 6.4 milligrams per kilo. Ten pounds is about 4500 LD50 doses for 75 kg humans.

If it had been mixed with some sort of decent acid (say, from a few car batteries) then it would have produced huge volumes of cyanide gas which is about twice as poisonous as the salt, and could have killed dozens of people. So the first reports were indeed a matter for concern.

But it now turns out that what they really had was Potassium Ferrocyanide.

It's not completely clear what these four expected to do with it. I think the most likely explanation is that they thought they were buying a lethal chemical when they saw "cyanide" on the label. In actual fact, real cyanide is closely controlled. Here in the US you have to sign forms and show ID and you better have a good explanation of what you want it for, or they won't sell it to you. (It is used industrially, and a common use for it is electroplating. It is very useful for dissolving gold, for instance. But it's also easy to screw up with it bigtime and kill yourself or someone else, which is why they're careful with it.)

What we're seeing is that a lot of these third world terrorists are not really very well educated. They've been making stupid mistakes. There was evidence, for instance, that al Qaeda was attempting to buy supplies of uranium on the black market and that what they were being sold was useless U-238 instead of fissionable U-235. By the same token, the guys in Rome may have thought they were carrying poison; in fact about all it would have done is to make the water taste funny and maybe make it turn blue if there was any natural iron dissolved in it.

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