|Serine (left) and Sarin (right)|
I don't spend much time listening to the news but when they started talking about chemical weapons in Syria recently, I did ask myself whether Sarin might be involved. To be honest, the rhetoric did sound a lot like the mythical Weapons of Mass Destruction that committed the US and UK to an unwinnable war in Iraq. But everyone now seems to agree that Sarin was used in anger in the Ghouta suburbs of Damascus six weeks ago on 21 Aug 2013. Ghouta being held by, or disputed with, anti-government forces, somebody decided to lob in some missiles loaded with Sarin. One piece of unexploded ordnance was found to contain 60kg of the stuff. This is nothing like the quantity of material that caused the holocaust at Los Alfaques. Sarin also has a higher molecular weight (140 daltons), than propylene (42 daltons) at Los Alfaques. So 60kg (Sarin's density as a liquid is close to water's) has a little over 400 moles of the nerve gas which, when vaporised will fill about 9cu.m. The difference is that you could wade through a vat of propylene if you had to, so long as you weren't smoking a casual cigar, whereas a tiny quantity of Sarin on the skin will certainly cause irrepairable neuro-muscular damage and probably a quick and painful death.
How tiny? The conventional way to measure the toxicity of fumes is the LCt50, which is the product of [the concentration] x [the time of exposure] that will kill (L for Lethal) 50% of those exposed. Typically it is given in milligram-minutes per cubic metre (mg-min/m^3). This metric works because of an observation by Nobel Prize winner Fritz Haber that exposure to 100g for one minute is effectively the same as exposure to 10g for 10 minutes. The relationship is known as Haber's Rule. Haber should know, because although he got his Nobel in 1918 for inventing a process to make Ammonia cheaply, he'd spent the previous several years developing chlorine and other more potent products as chemical weapons in WWI. So he was never a candidate for the Peace Prize. The fact that the British developed and used their own chemical arsenal and temporarily blinded a young Gefreiter A. Hitler in 1918 is one reason why Schrader, Ambros et al. were never authorized to use any of their Sarin on the Allies. Im Gegenteil, the Wehrmacht held the advancing Russians off from the IG Farben factory at
Wuppertal-Elberfeld long enough to dump 10,000 tons of the stuff in the River Oder. As poisons go Sarin is quite unstable and in an aqueous environment is quickly rendered harmless.
Sarin's LCt50 is given as 70mg-min/m^3 or 100mg-min/m^3 or 55mg-min/m^3. Call it 60mg-min for ease of calculating that 60kg exploding from one of those deadly missiles could fill a million cubic meters with enough gas to half-kill someone or kill half of everyone. Sarin is heavier than air but volatile, and the cloud would have to be 2m thick to reach the lungs of adults - the amount needed to kill by through-the-skin exposure is much higher than 60mg. If optimally dispersed that one missile could handily kill half the people in an area 1km x 500m. As it was, fatalities in Ghouta are reported as between 280 and 1800. Which is bracketted by the effects of 22tons of propylene at Los Alfaques (dead=220) and 300,000 tons of carbon dioxide at Lake Nyos (dead=1700). A map of the Ghouta atrocity appears to show that optimum dispersal was being aimed at because the eight strikes are evenly dispersed with about 2.5km between them. For comparison, Agatha Christie's bitter-almonds hydrogen cyanide has a LCt50 of 2000+ mg-min/m^3, or about 30x less toxic than Sarin, and similar to the toxicity of chlorine and mustard gas. Botox, which I've written about before, is 2000x more lethal that Sarin and acts by preventing the production of the neurotransmitter acetylcholine as Sarin prevents its breakdown.
I'll leave you with a final irony. Chemical-weaponeer Fritz Haber was born a Hasidic Jew in Breslau, then in Prussia now in Poland. Workers in his research institute developed a cyanide-based insecticide called Zyklon-A (Methyl cyanoformate). Production of Zyklon-A was stopped when Zyklon-B (active ingredient Hydrocyanic (Prussic) acid HCN) came on stream. Zyklon-B was, of course, used to kill some millions of Haber's co-religionists in the World War that he never lived to see or contribute his chemical expertise to. He'd done enough in the previous war.
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