Does it seem really low that they only extracted 72 particles? In their methods section they mention using 1kg of salt from each of the 17 brands.

Skimming FDA guidelines for defects in food, I see "action levels" like "average of 2 or more rodent hairs per 50g" for ground pepper, or "average of 1 or more whole insects per 50 grams" for cornmeal. 72 particles in 17 kg of salt sounds really shockingly clean given all the stuff in the oceans.