That is the question a student asked me after I had just finished a lecture on toxicology in which I had described the problem of cyanide poisoning by cassava, a tuber similar to the potato. With some varieties of cassava, a staple in some parts of Africa, there’s an issue. If not properly processed, it can harbour a lethal amount of cyanide. (This is not the case with the cassava grown in the Caribbean.) But soaking the peeled tuber in water for several days releases enzymes that degrade the cyanide-storage compound linamarin, causing the toxic cyanide to be dissipated into the air as hydrogen cyanide. Unfortunately, cases of acute cyanide poisoning have occurred when famine conditions forced a shortening of the soaking time. Since even proper processing doesn’t remove all the cyanide, chronic low-level exposure can lead to goitre or even “konzo,” a type of paralysis.
I’ve described the cyanide connection in lectures numerous times, but never before had I been asked a question about how I had acquired this knowledge. It did start me thinking. Indeed, I’ve never been to Africa, have never even seen a live cassava plant. I’ve never carried out any testing of cassava for cyanide. Truth be told, I wouldn’t even know how to go about it, although I think with a little digging I could figure it out. I do have a vague recollection of once eating fried cassava somewhere in the Caribbean, but that’s as close as I’ve come to experimenting with the tuber. So, in fact, how do I know about its chemistry? It all comes down to reading various accounts of cassava poisoning in toxicology and chemistry texts.
And how do the authors of these texts know what they are writing about? Chances are they haven’t had any closer cassava encounters than I have had. But they have read the peer-reviewed literature on the topic, have digested the facts and have managed to piece together the story. They would have read papers in a medical journal about how the symptoms of “konzo” were traced to cyanide poisoning and about how a link to cassava was discovered. Then in a chemical publication, they would have learned that the actual culprit, linamarin, was present in unprocessed cassava but not in the soaked version. Finally, a paper likely in a biochemistry journal would have revealed the action of enzymes on linamarin. Basically, then, what we call scientific knowledge is gained through a distillation of the relevant peer-reviewed literature. And that literature is the altar at which scientists worship. But as with religion, there is faith involved. Faith that the peer-reviewed literature can be trusted. That faith, however, cannot be blind. It should be tempered with a dose of skepticism. After all, that dreadful paper by Andrew Wakefield linking vaccination with autism, eventually withdrawn, was published in the Lancet, one of the world’s top journals. Reviewers of course cannot redo the experiments reported and have to trust that the results described were honestly obtained. If someone is going to commit fraud they can get away with it. At least until someone attempts to duplicate the work and finds they can’t. That’s when the excrement hits the fan.
