You opened the drive's case? If there is powder in the drive and on the platters, it is probably something wearing and leaving residue behind. I doubt it will be harmful to you unless you ingest it. But the read/write heads are probably shot now.
What are the side effects from this powder? It’s not like abestos? Becuase when I hit the hard drive with a hammer, it started smelling for a few secondsLikely ground down from a head failure.
Do not go around sniffing this stuff.