For what it's worth, only the piston engined aircraft burn high octane fuel with lead in it.
It's getting to where they are few and far between any more so IMO they aren't adding enough lead to the air to cause a problem.
Modern jet engines burn jet fuel which has no lead in it at all.
As for the toxicity of lead, it is very small. Because lead is heavy it rapidly settles to the ground and seldom gets into the air we breath.
The only way to get enough lead into a human body (without being shot) to cause any problem of any kind is to eat it.
The idea of people eating it was popularized back when a study of intelligence was conducted in the Chicago area. The kids in the ghetto areas did rather poorly on the intelligence tests.
Because lead can hamper the development of the brain in children, the theory that the kids were eating the peeling paint from the buildings walls came about.
A massive program to ban all lead based paints was started resulting in almost no lead in any paint today. (This greatly raised the price of titanium which in the form of titanium-oxide now provides the white base for most of the paint sold.)
The anti hunters/firearms people have jumped onto the bandwagon and are now blaming the deaths of dozens of Condors on lead fragments the birds supposedly ate when they were eating the gut piles from hunted animals. (Anyone who hunts knows there is almost no lead in these gut piles because jacketed hunting bullets retain almost 100 percent of the lead core and in over 90 percent of the shots the bullet ends up buried in the dirt or a tree on the far side of the animal).
With this theory in hand, the anti-hunters have managed to make the use of any bullet containing lead even in the smallest amount illegal in parts of California. There is a lot of talk about making this ban nation wide in the US.
OK. OK! I'll get off the soapbox so we can get back to talking about Royal Enfields.