Lead may have been banned from gasoline in 1996, but millions of Americans are still dealing with the repercussions of decades of mass exposure to the heavy metal.
According to research published this week in the Journal of Child Psychology and Psychiatry, exposure to lead in the U.S. has contributed to an excess of 151 million mental disorder cases over the past 75 years. As of today, more than half of the U.S. population has been exposed to adverse lead levels, said the study.
“Lead’s potential contribution to psychiatry, medicine, and children’s health may be larger than previously assumed,” said the study authors.
A press release from Duke University explained that lead – a naturally occurring bluish-gray metal found in the Earth’s crust – was first added to gasoline in 1923. While the lead was added to keep car engines “healthy,” it would eventually have a negative impact on human health.
“Lead is neurotoxic and can erode brain cells and alter brain function after it enters the body,” Duke explained. “As such, there is no safe level of exposure at any point in life, health experts say. Young children are especially vulnerable to lead’s ability to impair brain development and alter brain health. Unfortunately, no matter what age, our brains are ill-equipped for keeping lead toxicity at bay.”
Per the Mayo Clinic, after lead builds up in the body over months and years it can severely affect mental and physical development and at high levels it can even be fatal. Lead has also been used in paint, batteries, solder, pipes, cosmetics and more over the years, said the clinic.
By the 1970s, the Clean Air Act and Environmental Protection Agency established standards for the amount of lead allowed in motor gasoline, according to the U.S. Energy Information Administration. Even though it was removed from gasoline used in most motor vehicles, the EIS noted that it is still allowed for aircraft, racing cars, farm equipment, and marine engines.
To study the impact of leaded gasoline on mental health in humans, Aaron Reuben, a postdoctoral scholar in neuropsychology at Duke University, along with colleagues at Florida State University, combined cross-sectional blood–lead level (BLL) data from National Health and Nutrition Examination Surveys (NHANES) with historic leaded-gasoline data to estimate US childhood BLLs from 1940 to 2015. With this data, they calculated population mental-health symptom elevations from known lead-psychopathology associations.
Their findings “suggest that Americans born before 1996 experienced significantly higher rates of mental health problems as a result of lead, and likely experienced changes to their personalities that would have made them less successful and resilient in life.” Generation X, identified as people born between 1966 and 1986 by the study authors, had the most pronounced differences.
“Humans are not adapted to be exposed to lead at the levels we have been exposed to over the past century,” said Reuben. “We have very few effective measures for dealing with lead once it is in the body, and many of us have been exposed to levels 1,000 to 10,000 times more than what is natural.”
Previously, numerous studies have linked lead exposure to neurodevelopmental and mental health problems such as conduct disorder, attention-deficit/hyperactivity disorder, and depression. This new research shows how widespread lead-linked mental illness symptoms have been. Michael McFarland, a professor in sociology at Florida State and one of the study authors, along with fellow sociology professor Mathew Hauer, said that their team has also found that lead stole 824 million IQ points from the U.S. population over the past century.
“We saw very significant shifts in mental health across generations of Americans,” Hauer said. “Meaning many more people experienced psychiatric problems than would have if we had never added lead to gasoline.”
“We estimate a shift in neuroticism and conscientiousness at the population level,” tied to lead exposure, McFarland added.
Going forward, Reuben said that researchers should continue to examine how lead exposure has played a role in our health and to protect new generations of children from exposure.