Nathan Kilah
Nathan Kilah is a Senior Lecturer in Chemistry at the University of Tasmania. He is passionate about sharing the importance of chemistry in our daily lives.
At the molecular level, poisons are chemicals typically with very specific functions. And whether naturally occurring or synthesised by humans, they play an important role in our lives, with many both danger and saviour. Nathan Kilah puts on the gloves to explain why the chemicals in toxins can harm or heal. As he reports, it all depends on the dose.
Make no mistake. Hundreds of people and animals were killed to bring you this story. Poisons are all around us, as are people with motives to use them for their hostile and cruel intentions.
At the molecular level, poisons are chemicals typically with very specific functions. In my professional life as a chemist I’ve handled many, including well-known substances like cyanide, carbon monoxide and mercury; war gases such as chlorine and arsenicals; and toxic alkaloids such as strychnine and nicotine. Many of these chemicals are reactive, which makes them useful tools in producing new molecules. Others have special properties that help in isolating other desirable molecules. Working with these chemicals takes preparation, good laboratory engineering, imaginative risk management (nerve!), and genuine humility and respect for the dangers in front of you.
Because when you entwine that chemistry above a certain dose with the chemistry of an unsuspecting victim, things start to go wrong very quickly.
Whether a poison is ingested, inhaled, absorbed or injected, the end result is often the same. Death. Untimely, undignified, often painful and frequently gory. But what makes a poison a poison? Where do poisons come from, and how are they useful (other than for poisoning)?
What is a poison?
On a biochemical level, a poison is a disrupter. The poison may disrupt the packaging of your cells, causing them to leak and lose function, or it may disrupt the information flow of your nervous system, leaving normally rapid-firing neurons perpetually on or off.
The common factor is that above a certain concentration, any chemical can be deadly. Even a molecule considered benign, such as water, can be a killer. In 2007 a radio game-show contestant died after consuming a large volume of water in an attempt to win a prize. The massive amount of water in her body disrupted the distribution of electrolytes in her blood, causing her cells to swell in response to the change of salt concentrations, and ultimately led to the loss of cellular function and death.
Flora and fauna
The majority of well-known poisons come from nature. Your average garden is a poisoner’s paradise, with lilies, hellebores, beans, mushrooms and more all capable of delivering death. Our ancestors worked out which plants and fungi could be eaten through the application of an early scientific method, and the safety net of a big enough tribe to survive mistakes.
Many plants have evolved poisonous defences to avoid being eaten. This is often in the leaves but is frequently concentrated in the fruits and seeds as a way to ensure subsequent generations.
The seeds of the strychnine tree (Strychnos nux-vomica) are particularly well known for their poisonous potential. Detailed descriptions of strychnine poisoning are truly horrific.
Ingested strychnine binds to the brain and nervous system, keeping neurotransmitted messages turned on while enhancing the sensory systems of the body. This heightened state makes the body very sensitive to stimulation, and the reaction to stimulation is muscle convulsions. These contort the entire body, so that only the tip of the head and the tip of the heels touch the ground as the torso and legs are tensed into an arch. Fists and jaw clamp shut, the mouth pulls into a grimace and the diaphragm locks tight for minutes at a time. If the poisoned individual lives through this suffocating period, they may restart the cycle, fully conscious, their exhausted body strained by further convulsions. Depending on the dose and the fortitude of the victim, the whole-body contractions may continue for a number of cycles before agonising death.
Despite strychnine’s well-deserved reputation, it remains part of Chinese and Ayurvedic traditional medical practices, albeit in very controlled doses, used to treat a range of conditions including diarrhoea, inflammation, paralysis, rheumatism and sexual function.
Rat poisons
You will no longer find arsenic, thallium or strychnine rat poisons at your local home and garden centre. It’s preferable to choose “first-generation” poisons like warfarin, coumatetralyl or salt, as these are safer for birds of prey, which often eat sick rats. Second-generation anticoagulant rodenticides such as brodifacoum, bromadiolone and difenacoum can also kill raptors. An even better option for home is a poison-free trap.
Poisons are also very effectively employed across the domains of animal life, with frogs, snakes, octopuses and many others capable of causing death. A small number of frogs of the genus Phyllobates produce batrachotoxins, which have been deployed in poison blow darts used in traditional hunting practices in Latin America, alongside the more common plant-based curare. These poisons function within the bloodstream, so prey killed by this method can be eaten without causing any ill effect.
More intentional poisoning involving members of the animal kingdom used extracts of blister beetles (family Meloidae). The active agent cantharidin, which the beetles use to protect their developing eggs, causes blisters and chemical burns. If taken internally, cantharidin can produce blisters that can cause bleeding, followed by vomiting and diarrhoea, and ultimately death.
The first test for cantharidin poisoning was grim. The content of the deceased’s stomach was concentrated, then placed on healthy, living skin with a bandage. If blisters formed underneath the bandage, then cantharidin was the poison. Another more obvious sign of cantharidin poisoning was priapism – a prolonged, rigid erection – that persisted after death.
This final display also highlights the blister beetle Lytta vesicatoria’s better-known name of “Spanish fly”, and its use in aphrodisiac potions made from cantharidin. Aphrodisiac preparations are said to have led to many poisonings throughout history. The most famous case involved the French nobleman Marquis de Sade, who is said to have poisoned two prostitutes with cantharidin-laced sweets in 1772.
Poisonings don’t always come packaged with a motive. Take, for example, the mass poisoning of French villagers by grains contaminated with the ergot fungus Claviceops purpurea.
This ergot fungus produces alkaloids that can cause hallucinations. The appearance of these hallucinations is so well-known that they have been called Saint Vitus’ dance when accompanied by twitching, burning sensations and feelings of suffocation, and Saint Anthony’s fire when the poisoned person appears to be demonically possessed or is behaving “like a witch”. Ergot poisoning has been implicated in witch trials – it’s posited that the erratic behaviour of a few poisoned individuals caused an irrational response in a larger group.
“Your average garden is a poisoner’s paradise, with lilies, hellebores, beans, mushrooms and more all very capable of delivering death.”
Ergot poisonings – also known as ergotoxicosis – can be widespread, as occurred in the French village of Pont-Saint-Esprit in 1951, when hundreds of people were poisoned by ergot through their local bakery. The effects on the body can be more severe. A related class of long-term ergot poisoning known as ergotism causes gangrene of the limbs as the toxin cuts off the blood supply. Plenty of fungal toxins may be present on mouldy food, so reconsider cutting visible mould off and eating the remainder – the threads of mycotoxin-producing mycelium may have travelled further than you realise.
Elemental poisons
There are other poisons from nature that require a bit more chemistry knowledge to obtain: those derived from minerals.
Arsenic has been known as a poison for centuries and kills by damaging cells and interfering with cellular respiration. Of note is the signature brew of the Italian professional poisoner, Guilia Tofana (died 1651). Her Acqua Tofana, thought to contain arsenic, lead and belladonna, was a tasteless liquid that could be added to a glass of wine or a meal.
It’s claimed that as many as 600 women used this potion to kill their husbands.
Indigenous fishing practices
Indigenous Australians used a highly effective method to catch fish. Crushed plant roots from legume species were added to waterways, where the active chemical rotenone stunned or killed the fish. This piscicide has also been used to rid waterways and lakes of invasive aquatic species. Rotenone is still widely available as a treatment for mites and lice in poultry.
A single dose wasn’t fatal, so as the killer nursed their ailing victim they continued dosing them with poison. This gradual progression towards death using Acqua Tofana highlights the challenge of separating poisoning from the symptoms of disease. Common signs of arsenic poisoning – such as vomiting, chills and fever – are consistent with many bacterial and viral infections, which were prevalent in the 17th century.
It was almost two centuries later, in the 1830s, that a reliable test for arsenic was developed by English chemist James Marsh. Motivated by having failed to prove the guilt of an arsenic poisoner (who later confessed to his crime), Marsh set out to construct a glass apparatus that could specifically establish the presence and quantity of arsenic.
His process – known as the Marsh test – was very successful and is considered to have deterred future deliberate poisonings with so-called “inheritance powders”. Marsh’s efforts represent one of the earliest techniques of modern chemical forensics.
Synthetic poisons
The arrival of modern chemical sciences made many of the old poisons less appealing for those with murderous intent, as restricted availability and ease of tracing meant the poisoner became much easier to identify.
But this hasn’t stopped the development of countless poisons. From the gases used in trenches during the Great War to chemical agents that enabled the Holocaust, humans seem to have an endless capacity for ingenious chemical horrors.
Spy vs spy I: Ricin in spy assassination
An umbrella seems an unusual weapon, but in 1978 the tip of one was used to deliver a lethal dose of ricin to Bulgarian dissident writer Georgi Markov. This protein, also known as a lectin, is produced by the castor bean plant. The same plant is used to produce castor oil, but the chemical properties of the ricin means it does not get extracted into the oil. The castor bean isn’t the only plant that produces lectins: four to five raw kidney beans contain enough for toxic effects.
Synthetic poisons are often chemical weapons developed by nation-states. The Chemical Weapons Convention currently has 193 member parties, and while some countries have been actively working to lower their stockpiles of chemical weapons, 15 states maintain declared chemical weapon production facilities. Certain countries have dipped into their military stockpiles for attacks, both foreign and domestic, as well as for more personalised targets.
In 2018 in Bristol, England, a synthetic poison of particular strength was deployed against former Russian/UK double agent Sergei Skripal. This “novichok” weapon (Russian for “newcomer”) was developed after the nerve gases sarin and VX. These weapons share common chemistry as they are all organophosphate nerve agents. The novichoks are intended to be deadlier, but easier to handle. Some are binary weapons and require two components to be mixed to become active. This works well for a two-person assassination squad, where neither poisoner is in possession of the entire weapon.
Poisons as medicine
A number of poisons from nature have long histories of use in traditional medicine. In these cases, keeping the poison’s dose quantity low can have a therapeutic rather than deadly effect. Atropine from the plant belladonna has been used as an antidote to organophosphate and nerve gas poisoning, and is also routinely used for dilating the pupils in eye exams. Hycoscine, also found in belladonna, is extracted from the Australian plant Duboisia myoporoides and chemically modified to make the drug hyoscine butylbromide, often used in the treatment of irritable bowel syndrome, among other ailments.
Popeye-fuel poisoning
Unintentional poisonings are surprisingly common. In late 2022, over 200 people in Australia became ill after eating contaminated spinach leaves grown at a horticultural farm in Victoria. The source of the contamination was the plant Datura stramonium, also known as the thornapple, which was inadvertently grown, picked, packaged, sold and then eaten by unsuspecting consumers. At least one person was hospitalised, but fortunately, there were no deaths.
The highly potent botulism toxin, produced by the bacterium Clostridium botulinum, causes paralysis and damage to the nervous system. Remarkably, this property has been used for a range of cosmetic procedures. Botox treatments have found application in treating migraines, overactive bladder and even in the treatment of rare gastrointestinal issues preventing patients from burping.
Medicines are also potent poisons when taken at the wrong dose. Even commonplace paracetamol can be deadly. This abundant medication causes severe liver damage when taken in excess, unfortunately resulting in around 50 deaths per year in Australia. The Therapeutic Goods Administration has moved to lower the pack sizes to avoid both intentional and unintentional overdose. The therapeutic range of pharmaceuticals vary widely, and one can easily enter dangerous levels if the instructions aren’t carefully followed. So make sure you follow the dose directed by your doctor or pharmacist.
Poisons appear formidable and enigmatic. Whether they are deployed as a cowardly weapon, as a biological defence, as a plot device for the whodunnit writer, or as a safe pharmacological dose, they demand our respect. Uncovering their nature is endlessly alluring – as the true antidote is often not a secret potion, but the chemistry that lies within.
Spy vs spy II: enhanced elemental poison
A highly specialised elemental poisoning occurred in 2006, when former Russian spy Alexander Litvinenko drank a cup of tea laced with polonium-210. This synthetic radioisotope emits massive amounts of energy in the form of alpha particles. The ingested polonium caused massive internal radiation damage, but did not penetrate outside of the body, which made detection difficult. The assassins were not particularly cautious with their highly potent polonium-210, and left a trail of radioactive material all across London, on credit cards, towels, restaurant tables, light switches, and down the sink of their hotel bathroom.
This article was published in Cosmos Print Magazine Issue 100 on September 14, 2023. You can purchase the magazine now for $17 or become a subscriber to receive four magazines a year for only $50 AUD (international prices will vary).