When lead additives were first discovered to improve gasoline octane quality, they were also found to cause many problems with vehicles. Notable among these was a very significant build up of deposits in the combustion chamber and on spark plugs, which caused durability problems.

To relieve these problems, lead scavengers were added to gasoline at the same time as the lead to encourage greater volatility in the lead combustion by-products so they would be exhausted from the vehicle. These scavengers continue to be used today with leaded gasoline.

Ultimately, a significant portion of these additives is emitted from vehicles. This is important because, unfortunately, the National Cancer Institute has found these lead scavengers, most notably ethylene dibromide, to be carcinogenic in animals and have been identified as potential human carcinogens. Therefore, their removal along with the removal of lead may result in significant benefits to health.