Cyanide poisoning in mining — DTM&H MCQ

Correct answer: E — Hydrogen cyanide from ore processing

The correct answer is E, hydrogen cyanide from ore processing. Artisanal and small scale gold mining uses cyanide leaching to extract gold from crushed ore, and in a poorly ventilated tunnel volatilised hydrogen cyanide gas can accumulate rapidly. Hydrogen cyanide blocks cytochrome c oxidase, halting oxidative phosphorylation, which produces the acute triad of dyspnoea, cough and cyanosis seen here as tissue hypoxia develops despite adequate arterial oxygen content. The rapid onset, group exposure pattern, and setting (confined mine tunnel with ore processing) are the discriminating features that point to cyanide rather than the chronic occupational lung diseases also listed. Management follows National Poisons Information Service guidance: removal from exposure, high flow oxygen, and hydroxocobalamin for moderate to severe poisoning. Why the other options are wrong: B, Carbon monoxide poisoning: CO causes hypoxia with a classically cherry red skin appearance rather than cyanosis, and is more associated with combustion (fires, engines) than cyanide leaching of ore. C, Mercury vapour inhalation: mercury is used in amalgamation gold extraction but produces a subacute pneumonitis and chronic neurotoxicity (tremor, erethism, gingivitis) rather than the acute cyanotic respiratory distress described. D, Silicosis: this is a chronic fibrotic lung disease from years of crystalline silica dust exposure, not an acute presentation after a single fume exposure incident. E, Asbestosis: also a chronic, insidious fibrotic disease developing over decades, incompatible with acute onset after one tunnel exposure. Key point: acute cyanotic respiratory distress after fume exposure in gold mining points to hydrogen cyanide toxicity from cyanide ore leaching, treated with oxygen and hydroxocobalamin, whereas mercury, silica and asbestos exposures produce chronic, not acute, disease.

Reference: Royal College of Emergency Medicine and National Poisons Information Service, Antidote Guideline for the Stocking of Antidotes by Emergency Departments in the UK, 2021 update, section on Cyanide (sodium thiosulfate and hydroxocobalamin), rcem.ac.uk