Re. lead tetraethyl, unleaded gas has more benzene than leaded one as a side effect of the productive process, but the answer is more complicated. Benzene is on

Re. lead tetraethyl, unleaded gas has more benzene than leaded one as a side effect of the productive process, but the answer is more complicated. Benzene is only released in the environment when the engine is cold. The "replacement" for lead tetraethyl is a combination of better valves, higher octane rating when gasoline is produced, and electronic control of spark plugs. There's some feedback between these too, for example improved burning of fuel and the introduction of catalytic converter lets you increase the octane rating without suffering increased pollution from benzene.