Safety
Formic acid has low toxicity (hence its use as a food additive), with an LD50 of 1.8 g/kg (oral, mice). The concentrated acid is, however, corrosive to the skin.
Formic acid is readily metabolized and eliminated by the body. Nonetheless, it has specific toxic effects; the formic acid and formaldehyde produced as metabolites of methanol are responsible for the optic nerve damage, causing blindness seen in methanol poisoning. Some chronic effects of formic acid exposure have been documented. Some experiments on bacterial species have demonstrated it to be a mutagen. Chronic exposure to humans may cause kidney damage. Another effect of chronic exposure is development of a skin allergy that manifests upon re-exposure to the chemical.
Concentrated formic acid slowly decomposes to carbon monoxide and water, leading to pressure buildup in the container it is kept in. For this reason, 98% formic acid is shipped in plastic bottles with self-venting caps.
The hazards of solutions of formic acid depend on the concentration. The following table lists the EU classification of formic acid solutions:
| Concentration (weight percent) | Classification | R-Phrases |
|---|---|---|
| 2%–10% | Irritant (Xi) | R36/38 |
| 10%–90% | Corrosive (C) | R34 |
| >90% | Corrosive (C) | R35 |
An assay for formic acid in body fluids, designed for determination of formate after methanol poisoning, is based on the reaction of formate with bacterial formate dehydrogenase.
Formic acid in 85% concentration is not flammable, and diluted formic acid is on the US Food and Drug Administration list of food additives. The principal danger from formic acid is from skin or eye contact with the concentrated liquid or vapors. The US OSHA Permissible Exposure Level (PEL) of formic acid vapor in the work environment is 5 parts per million parts of air (ppm).
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