I dont know exactly where it comes from but I wouldnt use any from that beach area. When I was stationed there, many of the storm drains from the roads dumped into the water there. You could see the piping where it dumps in right off the beach. That means trash, oil and who knows what else is mixing in with the sand.
If you can get on one of the boats to ship island or go east into Alabama or even as far as pensacola, that would be a better choice, IMHO