Carbon isn't dangerous. Carbon can take a lot of heat and if it does oxidize it just makes CO2....plus soot is mostly carbon. That said, the only pure carbon you're likely to come across is graphite or diamond. If ur smoking out of a diamond bowl I'm comin to ur house!

Also remember, the only materials you really need to worry about are those that are exposed to significant heat. Like the bowl and stem. So a PVC bong is fine but not a pvc pipe.

Brass is okay.