Just a little blurb I found on DE:
Make sure the DE you use meets World Health Organization (WHO) safety standards. WHO cautions that DE with a crystalline silica content over three percent (3%) is dangerous for ingestion by humans or animals. Safe Solutions, Inc. DE has less than 1% free silica. Swimming pool DE ranges from 60% to 70% free silica.
I googled 'food grade DE' and got lots of hits.