“A new study calculates that exposure to car exhaust from leaded gas during childhood stole a collective 824 million IQ points from more than 170 million Americans alive today, about half the population of the United States.”
Lead went into gasoline in 1923 to keep engines healthy. The US did not ban it in car fuel until 1996. People born in the late 1960s, at peak use, lost up to six IQ points. Industry got 70 years of better engines, and half the country got the brain damage.