A Florida State University research team has published a new study that estimates that exposure to lead has robbed Americans on average 2.6 IQ points per person.
The study is published in the Proceedings of the National Academy of Sciences.
"Most of what we think of as the lost generation and the greatest generation and baby boomers had a moderate amount of lead exposure," said Assistant Professor of Sociology Matt Hauer. "Generation X was exposed to very high amounts of lead, and now millennials and the generation following them have been exposed to very low amounts of lead. That follows the trajectory of leaded gasoline use."
Hauer and Associate Professor of Sociology Michael McFarland found that average lead-linked loss in cognitive ability was 2.6 points as of 2015. Though for those born between 1951 and 1980, this number was even greater.
IQ is a standard measure of intelligence derived from a series of standardized tests. The scores have been used for educational placement and assessment of intellectual disabilities. They have also been studied as a predictor of future job performance and income.
Researchers 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 vast amount of that lead exposure was through automotive exhaust, thanks to the use of leaded gasoline, which began in 1923 and ceased in 1996. The intervening seven decades is where lead's damage is most pronounced, said Hauer.
The researchers used publicly available 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."
Aaron Reuben, a doctoral student in clinical psychology at Duke University, was a coauthor on the study. Reuben said the body can defend itself against lead but only to an extent.
"Lead is able to reach the bloodstream once it's inhaled as dust, or ingested, or consumed in water," he said. "In the bloodstream, it's able to pass into the brain through the blood-brain barrier, which is quite good at keeping a lot of toxicants and pathogens out of the brain, but not all of them."
Lead is a known neurotoxicant. Its use in gasoline peaked between the late 1960s and the early 1980s. In addition to cognitive deficits, lead has been linked to changes in personality, premature brain aging, anemia, kidney damage, cardiovascular disease and harm to pregnant women and developing children.
Lead's use was not confined to gasoline, and it has not ceased in some countries, Hauer said.
"In developed countries, lead's historic use in paints, pipes and gasoline has left waterways, soil, airways and homes enriched with this neurotoxicant," he said. "That legacy continues to threaten the health and development of today's children. Less obvious but also important is the threat that lead holds for yesterday's children, many of whom are victims of what we term legacy lead exposures."
The reality is that the effects of lead will be felt for generations, Hauer said.
"Exposures appear to have lifespan consequences," he said. "The burden of this and that legacy of exposures is going to be with us for decades to come.
