Why cars use unleaded fuel.

Lead is extremely toxic. Studies show that exposure to high concentrations of lead, mostly in young children, can result in damage to the central nervous system, and may be associated with high blood pressure in adults. Airborne lead concentrations throughout the country have decreased 89 percent since 1984, directly due to the phaseout of leaded gasoline, as well as to the majority of cars equipped with pollution control devices that require using unleaded fuel.

Unleaded gasoline is allowed to contain no more than 5/100ths of a gram of lead per gallon.