Exposure to lead in gasoline during childhood resulted in many millions of excess cases of psychiatric disorders over the last 75 years, a new study estimates.
Lead was banned from automobile fuel in 1996. The study, published Wednesday in the Journal of Child Psychology and Psychiatry, looked at its lasting impact in the U.S. by analyzing childhood blood lead levels from 1940 to 2015. According to the findings, the national population experienced an estimated 151 million excess mental health disorders attributable to exposure to lead from car exhaust during children’s early development.
The exposure made generations of Americans more depressed, anxious, inattentive or hyperactive, the study says.
The researchers — a group from Duke University, Florida State University and the Medical University of South Carolina — found that the exposure also lowered people’s capacity for impulse control and made them more inclined to be neurotic.
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Lead-associated mental health and personality differences were most pronounced for people born between 1966 and 1986, according to the study. Of that group, the greatest lead-linked mental illness burden was for Generation Xers born between 1966 and 1970, coinciding with peak use of leaded gasoline in the mid-1960s and mid-1970s.
People born during those years “can’t go back in time and change that,” said Aaron Reuben, a co-author of the study and a postdoctoral scholar in neuropsychology at Duke and the Medical University of South Carolina.
“Studies like ours today add more evidence that removing lead from our environment and not putting it there in the first place has more benefits than we previously understood,” Reuben said.
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The groups born around 1940 and 2015 had the lowest lead exposure and lead-associated mental illness, the study reported.
Though no longer in gasoline, lead is still present in other sources, such as some toys imported from other countries, water service lines that have not yet been updated, some soil and paint in old houses. (Lead paint was banned in 1978.)
There is no safe level of exposure to lead, according to the Centers for Disease Control and Prevention. Even small amounts are associated with developmental and learning difficulties, given that lead exposure is known to harm the brain and the nervous and reproductive systems. Children under 6 years old are most vulnerable to lead poisoning.
The study published Wednesday combined data on blood lead levels and estimates of historical lead exposure with findings from past studies, including a 2019 study of nearly 600 New Zealand residents that followed kids exposed to lead and measured their mental health over more than three decades.
Reuben, who was the lead author of that study, said the new research “doesn’t create new information about whether lead causes harm, nor do we say this is a study that proves causation — we’re really just taking existing evidence and applying it to the whole U.S. population.”
“We’re not at all concerned that we have in any way overestimated the harm,” he added.
Dr. Lisa Fortuna, chair of the American Psychiatric Association’s Council on Children, Adolescents and Their Families, praised the study.
“We don’t often get to see a lot of studies that look at environmental, or toxin-related, potential associated risks with the development of elevated rates of mental health problems in populations,” she said. “The research shed some light on the profound and lasting impact of environmental factors.”
The study’s findings should not be cause for panic, Fortuna said.
“It does not mean that people are, I would say, stuck with a mental illness. It doesn’t mean that they’re necessarily going to have a higher risk,” she said. “It’s really an issue of, ‘Here’s what’s happened at a population level.’”
The study comes a couple of years after Reuben and other researchers found that exposure to leaded gasoline lowered the IQ of about half the U.S. population. That study estimated that childhood exposure to lead from gasoline cost Americans about 824 million IQ points.
Lead was originally added to gasoline to improve engine performance. Use of leaded gas increased after World War II until it proved damaging to catalytic converters, which became required in the 1970s. Some of lead’s hazards were known long before it was banned from gasoline, but reducing exposure to it did not become a federal priority for many years.
Lead screenings are now recommended for all young children, with treatment such as chelation therapy available to remove the poison if levels are high.
Reuben said prevention is the best way to keep people safe.
“We’ve done a lot of good in the U.S. reducing lead exposures. Blood lead levels have gone way down, but they could go down further,” he said. “I hope that we can learn from the history about how much harm we caused in the U.S., and try to apply that moving forward.”
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