There are alternatives:

https://en.m.wikipedia.org/wiki/Antiknock_agent

MMT looks like it could be substituted, directly. Still nasty, but small usage, and removing lead & cadmium from our ecology should be high priority.

And, of course, replacing avgas engines with diesels would do it, as they can run on Jet-A or whatever.

This is all no-brainer territory.

The established aviation-engine manufacturers won't develop diesels,

& the upstarts keep going broke...

the LiquidPiston X-Engine is the brilliantest aviation engine I've ever considered, turning a Wankel rotary inside-out,

and the Astron Omega is .. insane ( I couldn't understand how the hell ANYBODY could even think of that ..

.. then I found out the inventor wasn't a piston-engines guy, he was a turbine-engines guy...

.. which explains it! )

I'd expect the IQ & life-potential of lives who grew-up near avgas-centric ( little ) airports to be damaged, consistently, by the lead.