Health and safety


Toxicity

Methanol is extremely toxic. If ingested, as little as 10mg can cause permanent blindness and as little as 60mg can result in death. Because of its similarities to ethanol (the alcohol in beverages), it is often difficult, if not impossible to tell the difference between the two (such is the case with denatured alcohol). Methanol is toxic by two mechanisms. Firstly, methanol (whether it enters the body by ingestion, inhalation, or absorption through the skin) can be fatal due to its CNS depressant properties in the same manner as ethanol poisoning. Secondly, in a process of toxication, it is metabolised to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. The reaction to formate proceeds completely, with no detectable formaldehyde remaining.[2]. Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing the symptoms of hypoxia at cellular level, and also causing metabolic acidosis among a variety of other metabolic disturbances[3]. One of the common symptoms seen in methanol poisoning is permanent blindness by destruction of the optic nerve.[4] Fetal tissue will not tolerate methanol. If methanol has been ingested, a doctor should be contacted immediately. The usual fatal dose is 100–125 ml (4 fl oz). Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. This is treated using ethanol or fomepizole. It is in fact true that alcoholic beverages can act as an antidote for methanol poisoning if enough of the beverage is drunk. This is because they contain ethanol, which offsets the breakdown of the methanol, allowing it to leave the body unchanged. [5] Either of these drugs acts to slow down the action of alcohol dehydrogenase on methanol by means of competitive inhibition, so that it is excreted by the kidneys rather than being transformed into toxic metabolites.
The initial symptoms of methanol intoxication are those of central nervous system depression: headache, dizziness, nausea, lack of coordination, confusion, drowsiness, and with sufficiently large doses, unconsciousness and death. The initial symptoms of methanol exposure are usually less severe than the symptoms resulting from the ingestion of a similar quantity of ethanol.
Once the initial symptoms have passed, a second set of symptoms arises, 10 to as much as 30 hours after the initial exposure to methanol, including blurring or complete loss of vision and acidosis. These symptoms result from the accumulation of toxic levels of formate in the bloodstream, and may progress to death by respiratory failure. The ester derivatives of methanol do not share this toxicity.
Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of methanol. The result is known as methylated spirit or "meths" (UK use). (The latter should not be confused with meth, a common U.S. abbreviation for methamphetamine.)