Here's a link to the MSDS for sand:
http://www.jtbaker.com/msds/englishhtml/s0722.htm
All you need to do is read the first few lines in section 3. Sounds -way- more dangerous than the bass trap materials we are discussing.
Again, if -you- aren't comfortable taking the risk then don't.
Don't forgot the sunblock and OSHA approved respirator next time you head to the beach...
Best Regards,
Mike.