What is the chemical symbol for lead?

Pb, from plumbum - which also gives us plumber, because Roman water pipes were made of it, and plumb line, because a lead weight is what hangs on the end. The metal is soft, heavy, easily worked, melts at a low temperature and resists corrosion, which made it enormously useful and is exactly why it got everywhere.

It is also a potent neurotoxin with no safe level, and the twentieth century put it in petrol deliberately. Tetraethyl lead was added from the 1920s to stop engine knock, its inventor Thomas Midgley publicly poured it over his hands and inhaled it at a press conference to prove it was safe, and he then spent months recovering from lead poisoning. Workers at the plants died or were institutionalised. It took until the 1970s for regulation to begin and the 2020s for the last country to stop selling it.

The consequences are measurable in populations rather than individuals. Blood lead levels in children fell sharply everywhere the fuel changed, and a substantial literature links childhood lead exposure to lost IQ points and to behavioural effects, with some economists arguing it accounts for a share of the crime wave that rose and fell a couple of decades behind leaded petrol. Midgley also invented CFCs, which is a claim to have done more damage to the atmosphere than any other organism in history.