Methanol has a high toxicity in humans. If ingested, as little as 10 mL can cause permanent blindness by destruction of the optic nerve and 30 mL is potentially fatal,[8] although a fatal dose is typically 100–125 mL (4 fl oz). Toxic effects take hours to start and effective antidotes can often prevent permanent damage.[8] Because of its similarities to ethanol (the alcohol in beverages), it is difficult to differentiate 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.[9] The reaction to formate proceeds completely, with no detectable formaldehyde remaining.[10] Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing the symptoms of hypoxia at the cellular level, and also causing metabolic acidosis among a variety of other metabolic disturbances.[11] Fetal tissue will not tolerate methanol.
Methanol poisoning can be treated with the antidotes ethanol or fomepizole.[9][12][13] Both of these drugs act to reduce 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.[9] Further treatment may include giving sodium bicarbonate for metabolic acidosis and haemodialysis or haemodiafiltration can be used to remove methanol and formate from the blood.[9] Folinic acid or folic acid is also administered to enhance the metabolism of formate.[9]
The initial symptoms of methanol intoxication include central nervous system depression, headache, dizziness, nausea, lack of coordination, confusion, 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.[2] Once the initial symptoms have passed, a second set of symptoms arises, 10 to as many as 30 hours after the initial exposure to methanol, including blurring or complete loss of vision and acidosis.[9] 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 (such as aspartame) do not share this toxicity[citation needed]. Small amounts of methanol are produced by the metabolism of food and are generally harmless, being metabolized quickly and completely; it is the human body's inability to metabolize the compound in bulk (as it can with ethanol) which leads to its toxicity.
Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of methanol. The result is known as methylated spirit, "meths" (UK use) or "metho" (Australian slang). The latter should not be confused with meth, a common U.S. abbreviation for methamphetamine.
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Today's Featured Article - A Cautionary Tale - by Ian Minshull. In the early 1950s my father bought an Allis Chalmers B and I used it for all the row crop work with the mangolds and potatoes, rolling and the haymaking on our farm. The farm and the Allis were sold and I have spent a lifetime working on farms throughout the country. I promised myself that one day I would own an Allis. That time event
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