Probably from tetraethyl lead, which wasn’t banned in common fuels until the 70’s in the US.
That said, there are enough other sources of lead (e.g. old paint) that this isn’t guaranteed to be right.
That said, there are enough other sources of lead (e.g. old paint) that this isn’t guaranteed to be right.
Except in California, which had leaded fuel well into the 90's for rich people's collector cars. Another example of the do-as-I-say-not-as-I-do sorts of things that happen in California.
https://archive.epa.gov/epa/aboutepa/epa-takes-final-step-ph...