Ummm, I'm not sure that that would cause that huge of a problem, certainly not something that comes out in 15 years and kills you in 6 months. That just sounds silly. Most likely, the sand (which can only burn/melt/liquify under INTENSE temps, like, lightening) would just cause you to cough if you actually inhaled it. Most of it probably wouldn't even get that far, as it would get stuck on your mucous (that's the point of it). At the very worst, it could make tiny cuts in your trachea or lungs. But that would likely only cause infection in people with compromised immune systems. Broken glass would likely be very noticable, so it would be neglible in this "problem."

Quick fix? Inspect your weed before you smoke it! If you're really worried, get a magnifiying glass or whatever...