What is the ruling on eating dust, and does this ruling apply to salt and dust dissolved in water?

Scholars have differed on the issue of eating soil (turāb). Some have prohibited it, some have deemed it disliked (makrūh), and some have permitted it if it causes no harm. If harm is proven by experience or by the report of doctors, then it becomes prohibited. Al-Nawawi reported that Sheikh Ibrahim al-Marwazi said, "It is appropriate that we rule it prohibited if harm becomes apparent in it." The author of Al-Muhadhdhab definitively ruled it prohibited. Whereas Al-Subki said, "Eating clay is not prohibited, because no sound hadith has been reported concerning it, unless it harms due to its abundance, in which case it becomes prohibited."

As for salt, whether it is mineral or marine, it has benefit in improving food and is needed. Consuming a small amount of it does no harm. However, if a person consumes an amount that causes harm, it becomes prohibited, due to the Prophet's (peace be upon him) saying: "There is no harm [to oneself] and no inflicting of harm [on others]."