The widespread use of leaded gasoline in the United States throughout much of the 20th century has left a profound legacy of mental health challenges, according to a groundbreaking study published in the Journal of Child Psychology and Psychiatry. The research estimates that lead exposure during childhood has contributed to 151 million psychiatric cases across the country over the past 75 years, altering the mental health landscape for generations of Americans.
Researchers Aaron Reuben from Duke University, along with Michael McFarland and Mathew Hauer from Florida State University, traced the impact of lead exposure to the years when leaded gasoline emissions were at their peak. Using historical data on blood-lead levels, fuel consumption, and demographic statistics, the study examined how exposure affected mental health outcomes and personality traits on a national scale.
"Humans are not adapted to be exposed to lead at the levels we have been exposed to over the past century," said Reuben, emphasizing the lasting effects of this toxic metal. Lead exposure is neurotoxic, eroding brain cells and disrupting brain function. Health experts agree that no level of lead exposure is safe, particularly for young children whose developing brains are especially vulnerable.
The study found that lead exposure was linked to significant increases in psychiatric conditions, including depression, anxiety, and attention-deficit disorders. The researchers calculated what they termed "mental illness points," quantifying the psychological toll of leaded gasoline emissions. "We saw very significant shifts in mental health across generations of Americans," said Hauer. These changes not only increased diagnosable mental health conditions but also caused milder psychological distress, affecting quality of life for millions.
Leaded gasoline consumption surged in the 1960s and peaked in the 1970s before being banned in the U.S. in 1996. As a result, individuals born during that time-particularly Generation X, spanning 1965 to 1980-were among those most affected. Reuben noted that nearly every American born during this period faced dangerously high levels of lead exposure from car exhaust.
The implications of lead exposure extend beyond mental health. Earlier research by the same team estimated that lead exposure robbed Americans of 824 million IQ points over the past century. McFarland said the study highlights broader shifts in personality traits at the population level, including increased neuroticism and reduced conscientiousness. These traits could have cascading effects on societal resilience and productivity.
Efforts to address the lead legacy continue. In October, the Environmental Protection Agency (EPA) issued regulations requiring cities to identify and replace lead plumbing over the next decade, allocating $2.6 billion for the effort. Earlier this year, the agency also lowered the acceptable levels of lead in soil, estimating that one in four U.S. households may require remediation.
"This study is a wake-up call about how widespread exposures to toxic chemicals contribute to the epidemic of mental health problems in children and adults," said Bruce Lanphear, a population health scientist at Simon Fraser University, who was not involved in the research.
Despite decades of bans, lead is still used in products such as paint, bullets, and airplane fuel. Reuben urged society to move away from lead entirely, stating, "The more we learn about lead the more we understand that the costs of using it-to children, families, and society-are always greater than the benefits."
As of 2015, over 170 million Americans-more than half the U.S. population-had clinically concerning levels of lead in their blood as children. The study's authors hope their findings will underscore the importance of eliminating remaining sources of lead exposure and protecting future generations from its far-reaching consequences.
