I'm more worried about any leaching effects it could have.
"Abrasive blasting media from coal slag will typically contain nickel and vanadium and a variety of other metals depending on the source of the coal used to make the slag"
A friend of mine who i had a talk about it with said people have used for it forever without any issues, but i say how would they know if any problems they might of had was pinpointed to the blasting grit, and think it was something else, or just unexplained. It's like the great carbon debate, where everyone takes it as safe, but as the years go by it's become more suspect, and more studied to actually cause health issues in fish, one being HITH.
This stuff is suspect to me. Just a advisory to make a mental note on it :-)
I'm not into the image, but into the hobby...