What’s the fastest-acting, most lethal poison?

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Dear Cecil: With Russians dropping dead from polonium poisoning, I’ve begun to wonder about poisoning generally. What’s the fastest-acting, most lethal poison? What’s the most insidious, least detectable? JP, Syracuse, New York


Illustration by Slug Signorino

Cecil replies:

Toxicologists have a blunt way of rating a poison’s lethality. Discussed here before, it’s called the LD-50, or 50 percent lethal dose – the amount that on average kills half the target critters. As the term may suggest, a fair amount of guesswork is involved. Since most governments object to running toxicity tests on humans, researchers substitute lab animals, who don’t necessarily react like us. Individual susceptibility varies widely depending on metabolism, tolerance, etc; differing effectiveness among poison delivery methods is another wild card. A compound with a relatively high LD-50 might be carcinogenic and therefore deadlier in the long run, nicotine offering the salient example. So it’s hard to say definitively which poison is the fastest, most insidious, or tastiest. I’ll tell you about some of the deadlier toxins known, and you can make your own plans.

Poison is nature’s great equalizer. Snakes, spiders, Gila monsters, duck-billed platypuses – they’re all prepared to stick it to you before you stick it to them. According to my consultant Doug, the most potent venom of any land animal probably belongs to the inland taipan, a central Australian snake. For a 150-pound person, the LD-50 works out to two milligrams – about the weight of five dandelion seeds. The deadliest marine animal is a tougher call because estimates of venom toxicity vary greatly. Some nominate the hook-nosed sea snake or box jellyfish, but at least their venom is treatable. In contrast, if you’re bitten by the blue-ringed octopus or consume too much inexpertly prepared fugu (puffer fish), no antidote can save you.

These last two cases illustrate the importance of a poison’s delivery system. Both animals employ the same fatal substance, tetrodotoxin, but where the octopus purposely injects it as a venom, killing in minutes, the puffer fish is just poisonous to eat, with digestion metering the dose. If you’re one of the 30-plus victims each year, you’ll feel numbness and paralysis creep over you, fully aware but unable to do anything except die within four to six hours. The most poisonous animal substance is batrachotoxin, produced by the poison arrow frog of South America. As little as the weight of two grains of table salt will turn your lights out for good.

Not up for animal wrangling? Try plants and fungi. Ricin poisoning can be had from eating castor beans, the source of castor oil – the symptoms build slowly and gruesomely (basically your arteries plug up), culminating in death in a week or so. If injected or inhaled, a bit of ricin the size of a pin head could kill you. The most famous case of ricin poisoning was the 1978 assassination of Bulgarian dissident Georgi Markov, who was killed James Bond-style by a poke from an umbrella rigged to inject him with a tiny pellet of the toxin. Naturally there’s no antidote.

One of the deadliest known substances could be in your pantry now, namely the botulin toxin that causes botulism. Produced by the anaerobic bacterium Clostridium botulinum, this poison is primarily encountered via contaminated food, such as unpasteurized home-canned goods. Botulin is tasteless and odorless – you probably won’t know you’ve consumed the LD-50 of 0.4 billionth of a gram per kilogram of body weight till paralysis sets in.

Among the most insidious human-made poisons is dimethylmercury, which is readily absorbed through the skin even if you’re wearing latex gloves. In 1996 Dartmouth chemist Karen Wetterhahn spilled a drop or two on her gloved hand; symptoms appeared about four months later and in ten months she died. If nerve gas is more your thing, you won’t find many agents worse than sarin, soman, and VX. Sarin, which can kill in 60 seconds or less, became notorious when the Japanese cult Aum Shinrikyo used it to kill seven people in the city of Matsumoto in 1994 and 12 more on the Tokyo subway in 1995. VX, probably the deadliest of the three, may have been used by Iraq against Iran in 1988.

Finally we get to polonium, used to murder Russian ex-spy Alexander Litvinenko last November. Polonium is harder to come by than dimethylmercury but tough to beat for lethality. Due to intense emission of alpha particles from radioactive decay, it has an LD-50 of 10 to 50 billionths of a gram per kilogram of body weight, meaning one gram of vaporized polonium can kill nearly 1.5 million people. Least detectable poison? Some tout deuterium oxide, aka heavy water – though superficially indistinguishable from ordinary water, the extra neutron in each hydrogen nucleus interferes with cell processes, leading to death in weeks, plus the leftovers will chill fission in your atomic pile (the more common use). Downside: the stuff costs about $500 a quart at United Nuclear and you’ll need gallons, disqualifying it in my book as a cost-effective agent of death.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.