just speculation but .....
i would expect that exposure to any lead from avgas is somewhat limited for each individual - unless one is really into the aroma of engine exhaust.
the pollutants that i have not heard much about concern auto brakes and tires:
Exact composition of each manufacturer’s pads is a closely guarded secret
although asbestos has been greatly reduced since the passing of drum brakes.
then there are tires:
natural and synthetic rubber, reinforcing chemicals, anti-degradants, adhesion promoters (which includes cobalt salts) and curatives (including sulfur)
these when multiplied by the millions of cars on the roads seems more to be concerned about breathing - the dust does go somewhere and not simply washed away by rain.
the ride to the airport has always been the most dangeruous part of jumping!
o yeah and one of my favorites - a DOE report from back in the early 90s on PVCs - seems when they are burned (like incinerators for garbage) at an insufficiently high temperature (non stoichiometric) there is a formation of dioxin - always a pleasant breathing experience.