Science Questions

Why are some parts of rhubarb poisonous?

Sun, 2nd Nov 2008

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Question

Paul Anderson asked:

When I was a lad I was told that rhubarb stems could be eaten but the leaves are poisonous. Whyís that?

Answer

Helen - They contain something called oxalic acid. The reason itís in the leaves is because itís there to put predators (herbivores who come along and munch them) off. Itís not good for them and itís not very good for us as well. You would have to eat an awful lot of it to actually kill yourself. The lethal dose: LD50 which is enough to kill off 50% of the rats that are given the dose of 375mg per kg of rat. That would equate in humans to around 5kg of leaves which anyone would believe is rather a lot. Yes. Itía problem. It acts through your kidneys. Itís a compound that actually interacts with metal ions and can form crystals and trigger kidney stones. That can be a problem. Symptoms include weakness, burning of the throat and mouth, difficulty breathing and if youíre really unlucky Ė a coma. Stear away from those rhubarb leaves I think is the answer.

Chris - What I want to know is who discovered that you could eat the bit in the middle but not the bit at each end.

Helen - So many questions on food. Thereís the weirdest foods in the world that youíd never imagine. Someone, I think, tries anything.

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