Tony,

I understand your concern with anything containing pure silica crystals.
Silica is a component of sand and would be a significant part of all sand containing tracks (think Big Sandy, Belmont) the silica in polytrack is wax-coated, which I suspect would make it no more dangerous than running on the beach, if not safer. This is not the same as the the pure uncoated silica crystals that miners are exposed to. What we're talking about here is a coated coumpond that contains silica compound, like beach sand.
The fact that some jockeys are wearing masks could well be an irratioanal reaction to an unfounded rumor. The same logic would have them wearing masks every time they go to the beach.
I will continue to look for any evidence that any compenent or compound, as it exists in polytrack, that can cause any lung damage.

Bob