Its interesting that a mention was made of 100LL having more lead than four star, mainly because I read an article about the dangers of unleaded. Apparently the lead in four star and supposedly 100LL is ejected from the exhaust and falls to the ground and stays there. So unless you are standing with your nose to the exhaust pipe it is virtually harmless. Whilst flying this lead gets dispersed in the atmos.(and I should think light aircraft pollution compared to cars is not worth worrying about)
However the replacement chemicals used in unleaded to provide the lubrication are VERY carcigenic and do not fall directly to the ground. The fuel itself should not be sniffed (one of the things most people do during preflight)or allowed to touch the skin and you should avoid the fumes from the exhaust at all costs. Cars have cats to reduce this danger (but are no good until warmed up) but aeroplanes do not.
So leaded does not appear to be the great evil that the press made it out to be......