Lots of things are toxic, but tolerated in small amounts. Paracetamol for example - very useful at the correct dose but a single dose at 200 mg/kg of bodyweight is likely to kill the liver.
Ethylene glycol is moderately toxic with an oral LDLO** = 786 mg/kg for humans.
To put it in perspective, Paracetamol is more than 4 x as toxic with LDLo at 200 mg/kg of bodyweight.
There was huge EU scandal a few years ago with crappy wine sweetened with antifreeze killing people and causing much ill health. However that's a whole different ball game to tasting one wet finger tip. That said the effects are cumulative so a mechanic would be wise to use another option.
Ethylene glycol (Antifreeze) C2H6O2
Ethanol (booze) C2H6O
Methanol CH3OH
They use ethyl alcohol to treat methanol poisoning and for glycol overdose. Methanol is also used in some antifreeze mixtures. CH3OH tastes much like C2H6O but CH3OH is a cumulative brain poison. A small taste wont do any harm but cumulative absorption as liquid or vapours or through the skin is dangerous and insidious.
Methanol is a component of surgical alcohol where small amounts will be absorbed through the skin. So again keep it in perpective.
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Toxicity
Ethylene glycol is moderately toxic with an oral LDLo = 786 mg/kg for humans.[6] The major danger is due to its sweet taste. Because of that, children and animals are more inclined to consume large quantities of it than they are other poisons. Upon ingestion, ethylene glycol is oxidized to glycolic acid which is, in turn, oxidized to oxalic acid, which is toxic. It and its toxic byproducts first affect the central nervous system, then the heart, and finally the kidneys. Ingestion of sufficient amounts can be fatal if untreated.[7]
According to the annual report of the American Association of Poison Control Centers' National Poison Data System in 2007, there were about 1000 total cases resulting in 16 deaths. The 2008 American Association of Poison Control Centers' National Poison Data System annual report lists 7 deaths.(Toxicity, Ethylene Glycol)
** LDLo = "Lethal Dose Low" is the lowest published lethal dose.
Doing the sums -
A 75kg male would need to drink about about 60g of pure ethylene glycol to have a good chance of killing himself. Though he can be treated and may well survive.
Alternatively he could pop down to tescos and take all 32 x 500mg tablets they can legally sell. About 2 weeks later he'll most likely be dead from liver failure. There is no antidote.
By the way the sweetener aspartame metabolises to methanol.