Clean dirt, obviously. Not dirt downstream from a chemical processing plant.
There's actually a word for it: geophagy. The practice of eating dirt to obtain nutrients. Often seen in rural societies among pregnant women. Those crazy country breeders.
Ellix Katz also sees eating local soil as a fast track integration into the wonderful microbial ecology of where you you live. "Be here now," he says. "Learn to love the flavour of the earth."
I love that.
Washing my (local Kipfler) potatoes a little less energetically.