Q: A lot of raws are coming out of China which is known for its low-quality control. How can someone determine if the raws are safe to brew/use, and not contaminated with some sort of heavy metal?
OR will the filtering process sufficiently remove any unsafe contaminants to the point where heavy metals are not worth considering?
A: Well, I have a small sample size of about 10 clients who have had AAS raw powders tested for heavy metals. Most of them went for the big four toxic heavy metals (As, Pb, Cd, Hg), some went over that (Sn, Al...). Not a single AAS raw sample was anywhere near dangerous, or even notable levels.
I'd worry much more about stuff such as impurities from degradation (mostly cause PIP), impurities from chinese giving up on recrystallization a little bit too soon, mixed up compounds, residual solvents etc...