Driveway sand.
Else we would be hearing about SuperFund sites all over the USA, from the 'contamination' caused by every mom and pop outfit that ever sandblasted a trailer frame clean.
Breathing the dust in over the long term can cause silicosis. About the same results as if you made a habit of standing out in the dust storms and breathed that over the same term. Try to avoid it. Not the samne as being toxic waste.
Cheers
Trev