There's already benzol/benzene in your petrol. Its legally limited to 1% because of its toxicity. Its a carcinogen. And it pollutes groundwater when it leaks out of petrol station tanks.
Its what they used to put in petrol to get the octane up until they discovered how nasty bit was, so they replaced it with tetraethyl lead. Then they discovered how nasty it was, and that catalytic reactors were destroyed by it, so they went back to putting benzene in.
Its just an octane increaser.