EdB, since you like to read.....

About TEL in 100LL avgas from Shell #mce_temp_url#

Note the part about turbos on plane. Probably more popular than 20 yrs ago. No way to get the octane for the boost needed.

I don't think the article mentions catalytic convertors that are on cars that are not on ICE planes. TEL would junk them out.

I'm sure you realize that 100LL (aka avgas) is a drop in the bucket re. volume refined compared to worldwide auto fuel. Maybe the big fish should get the first attention.

I suspect a bigger concern for just about every thing that starts out or continues with combustion is carbon monoxide. Is it more harmful than lead? I think you could seal up your garage and sit in a tub filled with old fishing sinkers & live to a ripe old age. But, start your lawnmower or generator in that garage & your remaining life will be measured in minutes. 

Cancer is a maybe, CO is no-argument. But I'm not sure lead was ever suspected as cancer agent?