Lead added to fuel is in the form of an organic compound, so I'd expect the opposite effect. Obviously there's more distribution post combustion, but from a bio-availability standpoint spraying tetraethyl lead around in equivalent quantities would be a much more severe problem.

Naively (without looking at data for concentrations in various environments), I could buy that people regularly handling / being around leaded aviation fuel are worse off than those breathing the (dilute) exhaust products.