Over 170 million U.S.-born adults in 2015 were exposed to harmful Levels of lead as children, a new study estimates. Researchers used blood-lead Levels, census, and leaded gasoline consumption data to examine how widespread early childhood lead exposure was in the country between 1940 and 2015.In a paper published in the Proceedings of the National Academy of Sciences on Monday, they estimated that half the U.S. adult population in 2015 had been exposed to lead Levels surpassing five micrograms per deciliter — the Centers for Disease Control and Prevention threshold for harmful lead exposure at the time.
The scientists from Florida State University and Duke University also found that 90% of children born in the U.S. between 1950 and 1981 had blood-lead Levels higher than the CDC threshold. The researchers found a significant impact on cognitive development: on average, early childhood exposure to lead resulted in a 2.6-point drop in IQ.
Study lead author Michael McFarland, an associate professor of sociology at Florida State University, said the findings were “infuriating” because it was long known that lead exposure was harmful, based on anecdotal evidence of lead’s health impacts throughout history. Though the U.S. has implemented tougher regulations to protect Americans from lead poisoning in recent decades, the public health impacts of exposure could last for several decades; experts told the Associated Press.
Schwaba said the study’s use of an average to represent the cognitive impacts of lead exposure could result in an overestimation of effects on some people and underestimation on others. Previous research on the relationship between lead exposure and IQ found a similar impact over a shorter study period.
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