Formic Acid and Methanol Concentrations in Death Investigations

Abstract

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.

Toxic Alcohols: Aliphatic Saturated Alcohols

“…Antemortem methanol and formic acid concentrations in other six individuals, with hospital treatment such as bicarbonate, ethanol infusion, and hemodialysis, ranged from 680 to 4270 mg/l and 370 to 910 mg/l, respectively, whereas corresponding postmortem methanol and formic acid levels ranged from undetectable to 490 mg/l and undetectable to 480 mg/l, respectively. Hospital treatment of formic acid toxicity resulted in significantly reduced postmortem methanol and formic acid concentrations (Wallage and Watterson 2008). Very similar results were published by Hantson and Mahieu (2000) who measured formic acid concentrations in three fatalities due to methanol poisoning.…”

Elevated formic acid concentrations in putrefied post-mortem blood and urine samples

“…In another study, urinary FA concentrations in 20 healthy subjects ranged from 0.002 g/l to 0.03 g/l, the mean concentration being 0.013 g/l [6]. However, normal FA concentrations in post-mortem samples have remained unknown, since comprehensive studies on postmortem FA concentrations focus on methanol poisonings [4,11].…”

“…FA is commonly analyzed as its methyl derivative, methyl formate [4,11], or ethyl derivative, ethyl formate [10], using headspace gas-chromatography with flame ionization detection (HS GC-FID). Enzymatic methods have also been used to quantify FA in tissue samples [8,12].…”

Toxicology of Specific Substances

“…The analysis of formate in blood is done by gas chromatography after making a methyl or ethyl formate derivative. The analysis and concentration of formate in blood is useful in reaching a diagnosis and interpretation of methanol poisoning deaths, because complete metabolism of the alcohol has often occurred by the time of death, whereas formate concentrations remain elevated (Wallage and Watterson 2008).…”