Hydrogen Cyanide: Effects, Poisoning & Treatment
Hydrogen cyanide (HCN), also known as prussic acid, is a highly toxic chemical compound found in nature and industry that can cause life-threatening poisoning even in small amounts.
Things worth knowing about "Hydrogen Cyanide"
Hydrogen cyanide (HCN), also known as prussic acid, is a highly toxic chemical compound found in nature and industry that can cause life-threatening poisoning even in small amounts.
What is Hydrogen Cyanide?
Hydrogen cyanide (HCN), also referred to as prussic acid, is a colorless to pale yellow, highly volatile liquid with a characteristic bitter almond odor. It is one of the most potent known toxins and can be fatal even in very small quantities. Hydrogen cyanide occurs both naturally and as a byproduct of various industrial processes. The term cyanide refers broadly to compounds containing the cyanide ion (CN⁻).
Sources and Occurrence
Hydrogen cyanide is found in a variety of natural and industrial contexts:
- Natural sources: Certain foods such as bitter almonds, apricot kernels, cherry laurel leaves, cassava (manioc), and lima beans contain cyanogenic glycosides, which can release hydrogen cyanide during digestion or food processing.
- Industrial sources: HCN is used in the chemical industry for the production of plastics (e.g., acrylonitrile), pesticides, and electroplating processes.
- Combustion gases: When nitrogen-containing materials such as wool, silk, or certain synthetic polymers are burned, hydrogen cyanide is released as a combustion gas — a significant risk in house fires and industrial accidents.
- Tobacco smoke: Cigarette smoke contains trace amounts of hydrogen cyanide.
Mechanism of Action and Toxicology
Hydrogen cyanide acts as a cellular respiratory poison. The cyanide ion inhibits the enzyme cytochrome c oxidase, a key component of the mitochondrial electron transport chain. This blocks the ability of cells to use oxygen, even when oxygen levels in the blood are adequate — a condition known as histotoxic hypoxia or internal asphyxiation. The heart and brain are particularly vulnerable.
The estimated lethal oral dose in adults is approximately 1–3 mg of HCN per kilogram of body weight. Inhalation of concentrations as low as 100–300 ppm can be rapidly fatal.
Symptoms of Hydrogen Cyanide Poisoning
Symptoms depend on the dose and route of exposure and can develop very rapidly:
- Mild poisoning: Headache, dizziness, nausea, vomiting, rapid heartbeat, anxiety
- Moderate poisoning: Shortness of breath, confusion, altered consciousness, seizures, drop in blood pressure
- Severe poisoning: Loss of consciousness, cardiovascular collapse, cardiac arrest, death
A characteristic sign of cyanide poisoning is cherry-red discoloration of the skin and mucous membranes, caused by the unusually high oxygen content of venous blood due to impaired cellular oxygen utilization.
Diagnosis
Diagnosis of hydrogen cyanide poisoning is primarily clinical, based on symptoms and exposure history (e.g., fire incident, industrial accident, or ingestion of cyanogenic substances). Laboratory testing can measure blood cyanide concentrations, but this is rarely available in emergency settings. Supportive findings include elevated blood lactate levels (metabolic acidosis) and paradoxically high venous oxygen saturation.
Treatment and First Aid
Hydrogen cyanide poisoning is a medical emergency requiring immediate action:
- Rescuer safety: Rescuers must use appropriate respiratory protection before approaching a victim in a contaminated environment.
- Immediate measures: Remove the affected person from the hazardous area, call emergency services (911 or local emergency number), and ensure fresh air supply.
- Antidote therapy: The primary antidotes are hydroxocobalamin (binds cyanide to form non-toxic cyanocobalamin) and 4-DMAP (4-dimethylaminophenol) in combination with sodium thiosulfate, administered intravenously.
- Supportive care: 100% oxygen administration, cardiovascular stabilization, and cardiopulmonary resuscitation if required.
Hydrogen Cyanide in Food – Everyday Risks
The risk of hydrogen cyanide poisoning through food is low in everyday life but should not be overlooked. Bitter almonds, raw apricot kernels, and cassava contain cyanogenic glycosides. These can largely be broken down by sufficient heating, soaking, and rinsing. Special caution is advised for children, as even a small number of bitter almonds can cause dangerous poisoning. The European Food Safety Authority (EFSA) has established maximum limits for cyanogenic glycosides in food products.
References
- Baud, F. J. (2007). Cyanide: critical issues in diagnosis and treatment. Human and Experimental Toxicology, 26(3), 191–201. https://pubmed.ncbi.nlm.nih.gov/17615112
- European Food Safety Authority (EFSA): Evaluation of the safety of cyanogenic glycosides as food additives. EFSA Journal, 2019. https://www.efsa.europa.eu
- Casarett and Doull's Toxicology: The Basic Science of Poisons, 9th Edition. McGraw-Hill Education, 2019.
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