Formic Acid and Methanol Concentrations in Death Investigations

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Methanol ingestion results in the formation of formic acid, a toxic metabolite that can cause metabolic acidosis. Methanol toxicity is therefore dependent on the amount of methanol ingested, the nature of treatment received, elapsed time since ingestion, and the accumulation of formic acid. Both methanol and formic acid concentrations are determined at this laboratory using headspace gas chromatography. An examination of 12 fatalities attributed to methanol poisoning is presented. Six individuals were found deceased, and their postmortem methanol and formic acid concentrations ranged from 84 to 543 mg/dL and 64 to 110 mg/dL, respectively. In the other six individuals, hospital treatment such as bicarbonate, ethanol infusion, and hemodialysis was administered. Antemortem methanol and formic acid concentrations ranged from 68 to 427 mg/dL and 37 to 91 mg/dL, respectively, whereas corresponding postmortem methanol and formic acid levels ranged from undetectable to 49 mg/dL and undetectable to 48 mg/dL, respectively. Hospital treatment of formic acid toxicity resulted in significantly reduced postmortem methanol and formic acid concentrations. Furthermore, the toxicological relevance of nine methanol-positive cases where postmortem methanol concentrations ranged from 3 to 142 mg/dL, with corresponding formic acid levels of less than 10 mg/dL, is discussed.