Exposure to car exhaust from leaded gas is calculated to have lowered the IQ of about half of the U.S. population, according to a study published in the journal Proceedings of the National Academy of Sciences.
As many as 170 million people in the U.S. are believed to have been cognitively affected by car exhaust.
Researchers from Duke and Florida State University focused on people born before 1996, the year leaded gas was banned in the U.S.
They found some people were affected more than others.
People born in the 1960s and 1970s usually lost up to 6 IQ points.
Some lost more than 7 IQ points.
In some cases, a loss of IQ points in the single digits may not be significant.
But for people who already have a “below-average” cognitive ability, the loss in points could be enough to be classified as having an intellectual disability.
The study also found that Black children were exposed to lead more often than white children.
Lead was first added to gasoline in 1923, to help car engines run smooth and stay healthy.
Since the 1990s, lead has been replaced with other less harmful additives. Scientists and doctors have reiterated again and again that no amount of lead is safe for the human body.
In addition to affecting the brain, it has also been associated with heart and kidney disease.