I'm not much of an environmentalist by modern standards, I guess. I think what the government and the environmental wackos have done to HALON is criminal. But the lead issue stops even me in my tracks, for it is definitely a poison, and known to be harmful. HOW harmful (in avgas), I don't know, but I think it's probably wise to be rid of it in all fuels. Oh, and by the way, if we don't get rid of it, the environmentalists will "help" us do so. I don't want that.
Whether wise or not, like it or not, lead will eventually disappear from avgas, and not just for environmental reasons. It is an expensive solution, and it is becoming ever more difficult to use it. The lead itself is now produced only in Britain and Russia, and only a small handful of refineries produce leaded fuel. The move is on to consolidate that production so that fewer and fewer refineries touch it.
Any tank, truck or pipeline that transports leaded fuel is automatically contaminated with lead, and cannot be used for anything else without a very expensive cleaning process.
There are obvious costs here, and some that are not so obvious. For example, if only one company makes 100LL, then transport costs to distant locations soar. 100LL needs dedicated transport, storage and pipelines, all of which push the price much higher for ALL fuels, not just the leaded fuels.