In 1982 seven people died in the greater Chicago area after cyanide was substituted in acetaminophen capsules sold in stores. Once the association was made between the product (Extra Strength Tylenol) and random deaths by potassium cyanide, panic ensued. Over 100,000 stories regarding the case ran in US newspapers. While the perpetrator was never found (although there were suspicions of one individual), groundbreaking changes in the manufacturing industry set today’s standards for tamper-resistant packaging.
The threat of cyanide persists. In my novels, Dr. Lily Robinson uses cyanide as a fast way to eliminate her terrorist targets. Fast is the operative word. The time from initial exposure to symptoms can be seconds to minutes, making hydrogen cyanide (gas) and cyanogen chloride (gas or liquid) potential chemical terrorism agents. With high exposure, symptoms are rapid and usually catastrophic—syncope, seizure, coma, agonal respirations, and cardiovascular collapse.
In moderate exposure, the rapid onset of symptoms is life-threatening unless the antidote and supportive care are given emergently to the victims. The immediate recognition of signs and symptoms allows for possible treatment. Patients may experience giddiness, palpitations, dizziness, nausea, vomiting, headache, and hyperventilation. Although the scent of bitter almonds is associated with cyanide poisoning (particularly in vomitus or the contents from gastric lavage), the ability to detect the odor is genetically determined and absent in 20% to 40% of the population.
What’s interesting about this agent is the variety with which it is found in the environment. Cyanide can be a solid, liquid, or gas, and can be complexed with salts (most commonly sodium or potassium), with metals (such as gold, cobalt, mercury, or zinc), or with organic acids to produce nitriles such as acetonitrile. Cyanogenic glycosides are found naturally in many plant species. The Prunus species (peaches, plums, apricots) contain stones or pits, and apples have seeds that contain amygdalin, a cyanide precursor. Linamarin, another cyanogenic glycoside, is present in high concentrations in the cassava plant. Cyanide is also used in many industries, particularly metallurgy for mining and extracting gold, electroplating, pigment production, in agriculture, and in both clinical and research laboratories.
Cyanide acts as a respiratory poison and affects all the tissues of the body but primarily those with high oxygen utilization and low tolerance for hypoxic stress like the central nervous system and cardiac muscle. As little as 200 mg of sodium or potassium cyanide may be fatal when ingested, and hydrogen cyanide gas (HCN) is fatal at concentrations of 150–200 ppm. Both HCN and cyanide salts can also be absorbed through the skin. These characteristics make cyanide an ideal poison for assassins, terrorists, and mystery writers.
Cyanide can be measured in the blood, and concentrations vary depending on whether the patient is a smoker or nonsmoker. Whole blood concentrations >0.5–1 mg/L may be toxic (cigarette smokers may have concentrations up to 0.1 mg/L), while concentrations of >0.26 mg/L are considered lethal. Cyanide, with a whole blood half-life between 0.7–2 hours, is detoxified by the liver enzyme rhodanese (sulfurtransferase) to thiocyanate, which is excreted in the urine.
Hydroxocobalamin, vitamin B12a, is the antidote for cyanide poisoning. Hydroxocobalamin contains the cobalt ion, which has a higher affinity for cyanide than cytochrome oxidase and forms the nontoxic cyanocobalamin, which is excreted in the urine. This turns the urine a dark red!
Mystery authors like exotic poisons and toxins for their novels, and I do too. But sometimes, an old “salt” will do. As an author of suspense thrillers steeped with poison, cyanide works in a pinch. Oh, and like Dr. Lily Robinson, I’ve got that gene.
Adapted with permission from Lily Robinson and the Art of Secret Poisoning (nVision Publishing, 2011)