As far as the silica in the mix, that blew in on the day, September 8, 2001, the terrorists filled the envelopes in a public park in Boca Raton, FL.
If they filled the envelopes in a public park, then down wind, or in the soil, there would be left over spores. Someone would eventually get an infection.
Are there any infections???
More likely the envelopes were filled overseas, or in an apartment or beach house along the ocean side of Florida, maybe along the beach, that was subsequently burned. I've tried to get fire records of all the places that were torched about that time....mid Aug to Sept. 2001. So far have not.