Over at Sciencegeist they’ve throw down the gauntlet and asked bloggers to write about their favourite toxic chemical as part of a carnival of toxins that also play important roles in everyday life. It’s all part of the campaign by chemists and bloggers alike against ‘chemophobia’ – an irrational fear of the chemicals we find all around us in everyday life or even the very word ‘chemical’. Recently there seems to have been a spate of these articles in newspapers with chemical-free labels even popping up in labs where they ought to be choosing their words with a little more care!

Canaries provided a CO early warning system for miners

So I’m going to kick off Chemistry World’s contribution to the carnival with carbon monoxide: the silent killer. It’s now pretty much common knowledge that this diatomic molecule can kill, thanks to television images of people committing suicide by gassing themselves with car exhausts (this is much less likely today as catalytic converters mop up and transform much of the CO in exhaust fumes) and public health campaigns highlighting the dangers of the gas in the home. But John Scott Haldane, the father of noted geneticist J B S Haldane, was the first to realise that this colourless, odourless gas was responsible for the deaths of many miners. The CO that killed these miners was the result of incomplete combustion of carbon during coal dust explosions. J S Haldane, belonging to that intrepid class of chemists that is all but extinct now, used himself as a guinea pig to investigate the effects of CO. By exposed himself to potentially lethal doses of the chemical, he discovered the dangers it posed, which led to the introduction of canaries in mines as early warning signals of danger. Good for miners, bad for canaries! You can hear more about J S Haldane in Chemistry World’s podcast on carbon monoxide.

CO’s killing power comes from its affinity for the haemoglobin in red blood cells, binding to it preferentially over oxygen to form carboxyhaemoglobin. People exposed to CO are figuratively drowning in air – there’s plenty of oxygen all around them but their bodies just can’t absorb enough of it. And, in a grisly twist, carboxyhaemoglobin is bright red, giving victims of CO poisoning a hale and hearty rosy hue.

Unsurprisingly, this has led to boilers, and the deadly gas they can produce, becoming inextricably linked in people’s minds with danger – to be guarded against in the home and on holiday. In the US alone, it is estimated that 40,000 people seek medical attention for CO poisoning each year, so it’s clear it’s still a serious problem.

That’s the dark side of CO, but is there a lighter side? Oddly enough, it was discovered in the 1990s that this deadly gas has a memorable and vital physiological function. It acts as a neurotransmitter in certain parts of the brain involved in long-term memory and has functions in many other parts of the body that are only just being understood. CO joins hydrogen sulfide and nitric oxide as another small and toxic gaseous molecule, which is a vital poison that our bodies both produce and need to function properly. As a result, companies like Alfama are now developing drugs that release CO in minute amounts to treat diseases involving inflammation and a range of other conditions. This turnaround in the way CO is now viewed really gives wings to the old axiom ‘the dose makes the poison’.

Patrick Walter


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