There are 2 different kinds of powdered DE
The DE produced for pool filters is DE calcined at high heat with transforms it into crystalline Silicon Dioxide, basically finely powdered sand. It is not safe to ingest or breathe in the dust. Breathing it in can cause the lung disease Silicosis.
Powdered DE used for insect control is Food Grade DE, it is natural amorphous silicon dioxide (Diatomite) , which has a very low content of any crystaline SiO2. It is safe to use around the garden (you still want to avoid breathing in the fine dust though or getting it into your eyes) It will also slowly break down in the soil and provide plant-available Silicon. For applying to plant surfaces for insect control it is best to mix it with water and spray it on.
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