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Researchers Find Childhood Exposure to Lead Reduced Americans’ IQ by 2.6 Points on Average

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The editorial board of the Proceedings of the National Academy of Sciences (PNAS) journal is honouring a pair of Florida State University researchers for their 2022 study which found that childhood exposure to lead has robbed Americans an average of 2.6 IQ points per person.  

Associate professor of sociology Michael McFarland and assistant professor of sociology Matt Hauer are the lead authors of a study which was published in PNAS in 2022. 

Along with co-author Aaron Rueben, a post-doctoral scholar at Duke University, McFarland and Hauer earned the Cozarelli Prize, which PNAS established in 2005 to recognise recently published papers of “outstanding scientific quality and originality.” The study is 1 of 6 published in 2022 to earn this recognition. 

Their study found that the average loss in cognitive ability due to lead exposure was 2.6 IQ points per person, with those born between 1951 and 1980 experiencing the greatest loss. Lead exposure was estimated using serial, cross-sectional blood-lead level (BLL) data from a nationally representative sample of US children aged 1 to 5 from 1976 to 1980 to 2015 to 2016.

“The level of competition to publish in PNAS is so high, so you’re honoured to have just done that,” McFarland said. “To then compete with the work of people in the academy from all over the world, all social science disciplines is an honour. We’re grateful people saw value in the work we’re doing.”  

The researchers used data from the National Center for Health Statistics and the US Geological Survey. A standard deviation for IQ points is about 15 points, Hauer said, before noting that makes 2.6 points per person, “pretty significant”.  

IQ is a standard intelligence measure derived from a series of standardised tests. Among other purposes, scores can be used for educational and job placement and the assessment of intellectual disabilities.  

The vast amount of lead exposure the researchers examined came through the automotive exhaust, due to the use of leaded gasoline, which began in 1923 and ceased in 1996. Lead’s damage is most pronounced, Hauer said, in the intervening seven decades.  

McFarland and Hauer found that estimated lead-linked deficits were greatest for people born between 1966 and 1970, a population of about 20.8 million people, which experienced an average deficit of 5.9 IQ points per person.  

The study was picked up by numerous national and international media outlets, including NBC News and Discover Magazine. Hauer thinks it was the far-reaching implications of the study that fed interest.  

“Half the US population was exposed to high levels of lead when they were children,” he said. “That is a substantial segment of the US population.” 

Harkening to the decades-long fight by citizens and special interest groups to remove lead from gasoline, McFarland said he hopes the study fuels the discussion about dangerous substances and the environment. 

“People were up against an industry that didn’t want to change because they were making money – similar to what we saw with cigarettes – an industry that is fighting science and public health officials,” he said. “I think that one of the things our study shows is the damage of the assumption or policy of safe until proven otherwise.”  

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