Murder mysteries often feature cyanide as a poison, but did you know you can be exposed to this toxin in everyday life too? Have you ever wondered how cyanide poisons and kills people, how much it takes before its toxic, and whether there is a cure? Here’s what you need to know.
Cyanide is the CN– ion (one carbon atom bonded to a nitrogen atom) and as a poison it is commonly administered as one of three compounds: hydrogen cyanide, a volatile, colourless liquid, and potassium and sodium cyanide, both white powders. Both potassium and sodium cyanide react with stomach acid to produce hydrogen cyanide, which can then go on to cause toxic effects.
Though cyanide has been used as a poison for centuries, it was first isolated in Sweden in 1782, by Swedish chemist Carl Scheele. Whilst different sources tell different stories, some claim that his exposure to cyanide was a contributing cause to Scheele’s death at the age of 43. He was also the first person to note the bitter almond smell of hydrogen cyanide – a smell which, it turns out, can only be detected by 40% of people for genetic reasons.
So, what happens when a person is poisoned with cyanide? Upon ingestion, cyanide binds to haemoglobin, the molecule in red blood cells responsible for carrying oxygen to the cells in our body. Haemoglobin then ferries it to the body’s tissues, where it can bind to an enzyme called cytochrome oxidase. This enzyme is a vital tool which cells require to make energy and with cyanide bound to it, they are unable to do so. It’s a bit like using treacle instead of petrol in your car; both fit in the tank but treacle will just clog the system.
The symptoms of cyanide exposure include headaches, nausea, vomiting, and elevated breathing and heart rates. With a high enough dose, these symptoms quickly progress to loss of consciousness, respiratory failure, and death.
How much cyanide is fatal depends on the route of exposure, the dose, and duration of exposure. Inhaled cyanide presents the greatest risk, followed by ingestion. Skin contact is not as much of a concern (unless it has been mixed with DMSO). A fatal dose for humans can be as low as 1.5 mg/kg body weight.
Cyanide is actually a relatively common toxin in the environment, and because of this the body can detoxify a small amount of cyanide. For example, you can eat the seeds of an apple, bite into a peach stone or smoke a cigarette without dying.
Perhaps the most well-known use of cyanide as a poison was in the Nazi concentration camps of World War II. There, the Nazis used Zyklon B, a cyanide-based pesticide to kill millions. Cyanide was also involved later in the war; though it’s commonly thought that Hitler committed suicide by shooting himself in the head, evidence has suggested that he in fact killed himself using a pill containing potassium cyanide, along with his wife of just 2 days, Eva Braun.
Cyanide poisoning is still a not-uncommon occurrence, though the exposure is often accidental. In particular, plastics such as nylon and polyurethanes release cyanide when burnt, so during fires cyanide poisoning can often occur. In the Grenfell Tower Fire of 2017 a number of the deaths were thought to be as a result of the inhalation of cyanide and other toxic gases produced by burning plastics.
As cyanide is such a fast-acting poison, it can be hard to administer any antidote in time. Thiosulfates are commonly administered in combination with nitrites, as they help convert the cyanide to thiocyanate, which can then be eliminated in urine. Vitamin B12a has also been used, which can bind the cyanide to form another harmless form of vitamin B12.
Cyanide poisoning can be detected in a number of ways; the most common is a simple, lab-based test. A tissue sample is added to 5% sodium hydroxide solution, which is in turn added to a solution containing 5% iron (II) sulfate and 1% iron (III) chloride. This is heated to 60˚C for 10 minutes, and then transferred to a solution of hydrochloric acid. The appearance of a blue colouration, caused by the formation of the iron-cyanide complex known as Prussian blue, indicates the presence of cyanide ions in the original sample.
Despite the ease of detection intentional cyanide poisonings still occur. This year the serial killer, Mohan Kumar – nicknamed “Cyanide Mohan” by the news media in India – was convicted of the murders of three young women and is suspected in another 17 deaths. Mohan, a 50-year-old former teacher, allegedly killed strictly for profit – he stripped the gold jewelry off the dead women and sold it. Let us not forget the Zimbabwe poachers who killed more than 300 elephants by poisoning their water hole with cyanide (not to mention the other animals that visited there) in order to sell their ivory tusks on the Asian market.
Makers of thriller movies and writers of murder mysteries tend to like cyanide for its dramatic tendencies – the quick gasping finish, the shocking immediacy of the way it kills. I had thought that an old, easily identified, messily visible poison like cyanide would fade away into our homicidal history. I say thought because if 2017 is anything to go by, that’s not particularly apparent. As the continuation of cyanide murder reminds us, we don’t easily set aside our past and we obviously – if unfortunately – hate to give up on a weapon with a history of working so well.