Haven't heard that about the grass clippings thanks for the warning, they sift thru it almost like they were out on the lawn, lots left that dries up for them to scratch thru. I rake the run and put fresh in every week, well, until the grass practically stopped growing here recently. Today they got a heap of mowed over leaves and very little grass. I'll need to check about the grass and impacted crops.
DE should be food grade, but it does come with a warning about using it without a mask (which I don't do) as it could cause respiratory problems. I usually spread it in the early morning when there is no wind. However, when I would scoop the old coop roost area, I would notice fine particles in the air, either PDZ or DE, I don't know. I tried not to breath that fine dust. The PDZ does have some dust, but this morning when I scooped out the new roosting area they went in to for the first time last night, I noticed very little dust. I used an organic spray in the coop instead of the DE just because of the possibility of problems. I will still use DE in their dusting areas and around the coop, as it only gets cleaned weekly.