Heavy Lead
I did a course at University of East Anglia, which studied Environmental Control and Public Health. This was many years ago when we still had 4 star petrol. Our tutor said that the lead from car exhausts would quickly fall onto the ground and be washed down the drains at the next rainfall. He said that unless you dropped your sandwiches on the tarmac, you would not ingest these lead particles.
Just for perspective, 100LL contains 2 grams of TetraEthyl Lead (TEL.) per gallon of fuel. When this is burnt it produces Water, Carbon Monoxide and some Lead.
I still miss the 5 star, having had some motorcycles that needed it. Also this 5% / 10% Ethanol fuel has wrecked 4 of my Fibreglass motorcycle fuel tanks, which now need to be replaced with Alloy or Steel Tanks.