It still sounds like [something of a risk](http://en.wikipedia.org/wiki/Diatomaceous_earth#Safety_considerations): &gt;Inhalation of crystalline silica is harmful to the lungs, causing silicosis. Amorphous silica is considered to be low toxicity, but prolonged inhalation cause changes to the lungs.[24] Diatomaceous earth is mostly amorphous silica, but contains some crystalline silica, especially in the saltwater forms.[25] In a study of workers, those exposed to natural DE for over 5 years had no significant lung changes, while 40% of those exposed to the calcined form had developed pneumoconiosis.