A new study estimates that exposure to leaded gasoline lowered the IQ of about half the population of the United States.
Researchers from Florida State University and Duke University studied the the effects of lead exposure from gas on people born before 1996, the year the U.S. banned leaded gasoline. The results from the study showed that lead exposure cost America an estimated 824 million points, or an average of 2.6 points per person.
The researchers used this data as well as population estimates to determine that as of 2015, more than 170 million Americans had had extremely high blood lead levels in their early childhood years. Lead, a neurotoxin, is not safe under any capacity. Currently, 3.5 micrograms per deciliter is the reference for high blood lead levels; researchers determined roughly half the U.S. population had blood lead levels above five micrograms per deciliter as children.
“This is important because we often think about lead as an issue for children, and of course it is,” said Michael McFarland, an FSU associate professor of sociology and principal study author, told NBC News. “But what we really wanted to know is what happens to those children who were exposed? If you’re more toward cognitive impairment, a couple points can mean a lot.”
Certain ages were more affected than others, likely due to longer and higher exposure. People born in the 1960s and ’70s, for example, lost an estimated six points on average.
Additionally, there were racial disparities in lead exposure. The study found that Black children have been exposed to lead at a higher rate than white children, with most Black adults under age 45 experiencing “considerably higher” levels of blood lead levels in early life than their White counterparts. Researchers believe this is likely due to environmental contamination and infrastructure issues that affect drinking water in low-income and minority areas, such as the ongoing water crisis in Flint, Michigan.
McFarland clarified that a two to three point IQ difference doesn’t have major complications on an individual for the most part, but on a large-scale population, the shift can have large consequences. The entire bell curve of IQ shifts, with more of the population at what was once the extreme low end of IQ scores. Also, prolonged lead exposure can be fatal. Lead exposure is more likely to effect children, but it can also put adults at risk for chronic diseases such as dementia and heart disease.