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 recognize recently published papers of “outstanding scientific quality and originality.” The study is one of six published in 2022 to earn this recognition. 

“The level of competition to publish in PNAS is so high, so you’re honored 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 honor. 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 U.S. 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 standardized tests. Among other purposes, scores can be used for educational and job placement and the assessment of intellectual disabilities.  

The vast amount of the lead exposure the researchers examined came through 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 U.S. 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 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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