Rhododendron Poison – Truth behind the science of Sherlock Holmes

// December 27th, 2009 // How Things Work, Poisons, Science in the Movies

I saw Sherlock Holmes last night with SexyMan, the cinema was packed and we sat in the second row from the front. I watched the movie like a fan watches a tennis match, but surprisingly it was still good!

It might have helped that any great expectations had been dashed by a friend on facebook, but nonetheless I thought it was an enjoyable, action-packed, fast-paced fast-talking very sexy flick.

But then I’m not a film critic. I am, however, a science geek. This post has been carefully written to avoid spoilers, but if you want to play it safe go and see the movie and come back in 3 hours. K?

At one point in the movie they talk about rhododendron poison, but don’t explain at all what it is.

Rhododendrons (and azaleas, the dwarf (midget) version) are a moderately toxic group of plants. If you’re out strolling the mountains near the eastern side of the Black Sea in Turkey, or generally in the USA or UK, then don’t eat this plant:

Rhododendron ponticum.

Not all members of the genus are poisonous, but play it on the safe side and don’t eat random plants.

It’s not HUGELY poisonous, about 100 grams need to be ingested by a 25 kg child to seriously poison them, but it is a problem for livestock – particularly sheep, goats and cows – who munch on the flowers and get seriously sick.

Of course, if you boiled it down and concentrated the liquid… well that’s a different story. The toxin is water soluble, so it can be extracted from the leaves and flowers.

The toxin is called grayanotoxin. It binds to specific sodium ion channels in cell membranes (which I’ve talked about before) and prevents inactivation, causing persistent activation of muscle and nerve cells. This causes a range of symptoms based on where the activated cells are located, such as muscle weakness, vomiting, sweating, salivation, seizures, and either dangerously slow or dangerously fast heartbeat, depending on the dose. In the end, it can cause death.

Don’t think you’re safe just because you don’t make a habit of eating plants – the toxin is also found in the nectar of flowers, and bees that feast on them can make “mad honey.” It took out an army in 401 BC lead by Xenophon of Athens against Persia – hundreds of soldiers vomiting and unable to walk for a day. No-one died, unlike in 67 BC, where the army of Mithradates IV killed Pompey the Great’s soldiers while they were incapacitated. It’s biological warfare, victory has never tasted sweeter.

Mad honey is still a problem today – not so much the stuff in a grocery store (which is diluted and problem tested and stuff) but organic honey direct from the beehive can be risky. Plus some men use it as an aphrodisiac. Idiots.

That’s the rhododendron poison, making a comeback after 2400 years on a big screen near you! What did you think of the movie? There were lots of sciencey deductions made that weren’t very well explained, so if you have any questions, post a comment and I’ll do me best!