Half of Americans alive today were exposed to “clinically concerning” lead levels during their childhood — and their IQ scores shrank as a result, a new study found.
Specifically, an estimated 824 million IQ points of more than 170 million Americans, who were adults as of 2015, were lost from childhood exposure to car exhaust from leaded gas, according to a Duke University news release. Leaded gas was banned from fueling new U.S. vehicles in 1996 after it was added to gasoline starting in 1923.
On average, nearly three IQ points were stolen from each American cognitively impacted from leaded gas exposure before 1996, according to researchers from Duke and Florida State University.
Those born before the 1996 ban “may now be at greater risk for lead-related health problems, such as faster aging of the brain,” the release said of the study published March 7 in Proceedings of the National Academy of Sciences.
Leaded gasoline use peaked during the late 1960s until the early 1980s and exposure from car exhaust resulted in it making its way into the bloodstream of many Americans, according to the findings. Lead can “reach the bloodstream once it’s inhaled as dust, or ingested, or consumed in water.”
During this time, the average blood lead level for Americans “was routinely three to five times higher” than what’s currently considered of “clinical concern” — 3.5 micrograms of lead per deciliter of blood, according to study authors.
Additionally, 90% of Americans born between 1950 to 1981 had blood lead levels over 5 micrograms of lead per deciliter of blood, the research noted.
“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,” Assistant Professor of Sociology Matt Hauer, one of the researchers, said in a news release from Florida State University.
“That follows the trajectory of leaded gasoline use.”
Lead is a neurotoxin that harms the health of both humans and animals. It’s a natural element that comes from the Earth’s crust, according to the U.S. Environmental Protection Agency.
“Society frequently operates under the presumption that environmental exposures are safe until proven otherwise,” Michael McFarland, another researcher, told McClatchy News. “Leaded gasoline wasn’t needed as an antiknock agent (there were alternatives available), it was profitable.” Antiknock agents are gasoline additives.
“An abundance of incontrovertible evidence occurring across decades was required to ban it,” McFarland added. “By documenting the widespread consequences of lead exposure, our study underscores the folly in such thinking and the need to alter it to avoid future environmental calamities.”
More on the study
“In developed countries, lead’s historic use in paints, pipes, and gasoline has left numerous waters, soils, airways, and homes enriched with this neurotoxicant—threatening the health and development of today’s children,” researchers wrote in the study.
The research examined childhood lead exposure from gasoline in Americans alive in 2015 by analyzing a few different public data sources.
This included data on childhood blood lead levels from the National Center for Health Statistics from 1976 to 2016, leaded-gas use from the U.S. Geological Survey and population statistics from the Human Mortality Database.
In 2015, out of 318 million Americans, just 131 million had estimated blood levels below 5 micrograms of lead per deciliter of blood — the threshold for clinical concern at the time — when they were kids. This means most Americans had blood lead levels higher than the 2015 threshold as children.
Blood lead levels were “relatively low” for those born in the 1940s before they “increased dramatically” for adults who are now middle-aged, the study reported. This was followed by a dramatic decrease in younger people, such as Americans born between 2001 and 2015.
As a result, the study says, “a total of 824,097,690 million IQ points were lost because of childhood lead exposure among the US population by 2015” — an average of 2.6 IQ points per person. However, this varied between age groups.
For example, the research found 20.8 million Americans born between 1966 to 1970 lost an average of 5.9 IQ points from childhood lead exposure.
“The vast majority of leaded gasoline–exposed cohorts (i.e., those born in the mid-1960s to 1980s) experienced meaningful cognitive loss,” they wrote.
Over 7% of those born in 1966 to 1970 and 1971 to 1975 lost an average 7.4 IQ points, which has potential to result in “diagnosable intellectual disability,” according to the study.
“By 2030, early childhood lead exposure will have reduced population IQ by 709,054,633 points.”
Some study limitations included how the data came from “several distinct collection efforts” and how some blood lead levels were “predicted rather than observed for the years 1940 to 1975,” authors acknowledged. Additionally, there was a lack of data for those who immigrated to the U.S. after age 4.
“This study represents an important step toward discerning the full and manifold consequences that lead exposure has placed on the U.S. population,” authors concluded.
Aaron Reuben, another researcher who authored the study, told McClatchy News that “we cannot assume that what happened in the past will stay in the past.”
“We need to better understand what a history of childhood lead exposure means for the course a person’s life will take, including their risk for disease in adulthood and in late life.”
More on lead exposure
Researchers pointed out how Michigan’s lead Flint water crisis, which began in 2014, “returned the issue of legacy lead contamination to the public’s attention.” There, the city’s water became contaminated with lead.
Alongside contaminated drinking water, harmful lead exposure can also come from dust produced by peeling paint in homes built before 1978, “when lead-based paints were banned,” according to the Centers for Disease Control and Prevention. Other sources include soil, toys, jewelry, aviation gas emitted from airplanes and more.
The CDC advises parents to have their children’s blood tested for lead exposure, especially since there’s “often no apparent symptoms when a child is exposed to lead.” It can cause slowed growth, learning and behavioral issues, hearing and speech issues and more, according to the agency, which warns this “can cause long-term harm.”
Even America’s national symbol, the bald eagle, has been extensively harmed by lead exposure, among other creatures.
A recent study found 46% of bald eagles and 47% of golden eagles in the country are poisoned by lead, NBC News reported.
“All scavengers and humans are at risk of lead toxicity when consuming meat shot with lead ammo (bullets or pellets) especially the avian scavengers such as eagles, hawks and vultures,” Robyn Graboski, who works at a Pennsylvania wildlife center that’s seen bald eagles suffer from lead poisoning, previously told McClatchy News.
Lead poisoning can cause a slow death that can last weeks for birds if it goes untreated and affects their ability to fly.
In terms of early childhood lead exposure, it “will remain a hallmark of the U.S. population for the foreseeable future,” study authors wrote.
“Our findings indicate that we must put more resources towards eliminating existing lead hazards in our environment, including lead service lines, exfoliating lead paint in old homes, and lead in aviation fuel for piston aircraft, so today’s children can avoid the fate of their parents — and that those of us with a history of childhood lead exposure are not re-exposed throughout our lives,” Reuben told McClatchy News.
“If you think you had high lead exposures as a child, because you grew up along a busy road or near a lead-emitting facility, it does not mean that you are fated to suffer from problems going forward,” Reuben added.
“But it can’t hurt to let your doctor know, in case it might raise your risk of health conditions that have been linked to lead exposure, such as cardiovascular disease.”
