They use DE internally because it contains Zeolites, which are aluminum bonded, rocks, with microscopic holes capable of binding to radioactive, and toxic heavy metals, which you then excrete.
The blood brain barrier is the thinnest on a male, not a female. Men are the most at risk for DE poisoning to the brain, not even through contact, but inhalation.
For this reason, I switched to cellulose based media in my pool filter, never going back to DE period, food grade or otherwise, it's horrible to work with, and more hassle than it's worth.
Really that's half the reason I'm going aero is for the easy of use, people say it's so complicated... it isn't, it's very simple, it's just easier to mess up big, in a short time frame, but compared to any other system... no pretty simple.