In Germany and Austria, there was a tax on salt for cooking until recently (1993 and 1995, respectively). To avoid that people buy the cheap road salt and use it for cooking, such a bitter component was actually added, usually magnesium chloride (sometimes also capsaicin).
Many German sources still say you shouldn’t eat road salt for that reason, so maybe this is still done (though it is of course possible, that those sources are just outdated).
If you don’t want to communicate with non-Signal users and are always within range of a public or known Wifi network where ever you are in Afghanistan, then I guess this is fine.