It is a glycoprotein that interferes with protein synthesis in the cell, causing cell death. Ricin is obtained from the beans of the castor oil plant (Ricinus communis), which is cultivated to extract the oil – the ricin remains in the solid fibre. Nevertheless, here is a representative selection, in ascending order, of five truly deadly poisons, all at least a hundred times more toxic than cyanide, arsenic or strychnine. And yet when in 1996 an American professor got just a drop or two of the compound dimethyl mercury on her rubber gloves, it penetrated the gloves and her skin, sending her into a fatal coma some months later. If we swallowed liquid mercury metal (as distinct from inhaling the vapour), it would very likely pass straight through us harmlessly. The chemical state of a substance is important, as is how we ingest it. The LD50 of tetrodoxotin, by comparison, is around 300 micrograms per kg if orally ingested, and as little as 10 micrograms per kg if injected.Īssessing toxicity is not easy. On this scale, for example, sodium cyanide comes out at around 6 milligrams per kg. The LD50 (Lethal Dose, 50%) – the amount needed to kill 50% of the test population – is how toxicity is most often assessed, and is usually quoted per kilogram of body weight. It also crops up in the blue-ringed octopus and was more recently discovered in tiny frogs in Brazil. Incidentally, this was the poison favoured by evil assassin Rosa Klebb in James Bond film From Russia With Love. The fish is a delicacy in Japan, but can be lethal if prepared incorrectly. More poisonous than these, but still not near the top of the tree, is tetrodotoxin, the pufferfish toxin that poisons around 50 Japanese people every year. But these are not the most toxic substances known. When asked to name a poison, people may well think of cyanide, arsenic or strychnine.
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