A new study estimates that exposure to leaded gasoline blunted the IQ of half of the U.S. population.
The peer-reviewed report published in the journal Proceedings of the National Academy of Sciences on Monday (March 7) centered around individuals born before 1996, when the u.S. banned all gas containing lead, NBC News reports.
Participating researchers from Florida State University and Duke University discovered childhood lead exposure led to an estimated drop of 824 IQ million points, equaling an average of 2.6 points per person.
The study also showed older groups were more affected than others as they lived through eras in which leaded gas consumption skyrocketed.
Individuals born in the 1960s and 1970s were estimated to have lost up to six IQ points, while some others lost more than seven.
Exposure to leaded gasoline was most common as people inhaled auto exhaust, NBC News reports.
The research team used gas consumption, population estimates and other data as part of its study and concluded that as of 2015, more than 170 million Americans had blood lead levels significantly higher during their early childhood years, reaching levels exceeding five micrograms per deciliter, while 3.5 micrograms per deciliter is the reference value for blood lead levels to be considered high, although no amount is currently believed to be safe.
“This is important because we often think about lead as an issue for children, and of course it is,” said Michael McFarland, an associate professor of sociology at Florida State University and a faculty member of the university's Center for Demography and Population Health, who served as the principal study author. “But what we really wanted to know is what happens to those children who were exposed?”
McFarland confirmed that a 2-3 point IQ difference is nominal in many cases unless the person falls on the lower side of IQ distribution.
However, Sung Kyun Park, an associate professor of epidemiology and environmental health sciences at the University of Michigan School of Public Health, specified that a shifting average among a population basis could have significant consequences.
Lead was initially added to gasoline to help engines run more smoothly until it was replaced for safer alternatives as it has also been linked to heart and kidney disease, along with the recent findings in the study.