Tens of millions of Americans born before 1996 suffered psychiatric disorders as a direct result of being exposed to toxic lead.
A major review estimated that leaded car exhausted fumes breathes in before that date are linked to 151million cases of depression, anxiety and ADHD.
Older studies have also suggested that Americans exposed to these fumes have lost 824million cumulative IQ points since 1940.
US authorities banned adding lead to gasoline in 1996 – but for five decades prior, Americans had been breathing in fumes full of the heavy metal.
Using national data on lead levels in children’s blood and population statistics, researchers from Duke University estimated the amount of lead all Americans alive in 2015 had been exposed to. They then determined the affect that lead exposure would have on mental health.
Lead is known to cause harm to the nervous system, and in turn affect psychology. When breathed in, lead-filled smog enters the blood stream through the lungs, where the particles get absorbed by the body, causing inflammation that may lead neurons to decay.
This can delay development, cause behavioral problems and damage the nervous system, all of which can be linked to or cause psychiatric problems.
Aaron Reuben, the study co-author and a neuropsychology researcher from Duke University said: ‘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’.
In December 2022, reality TV star Christina Hall announced on her Instagram story that she had lead and mercury poisoning. She said she suspected that her work renovating old houses, which sometimes contain lead pipes, fixtures and solder, may have made her sick. She has not spoken about exhaust fumes
From 1923 to 1996, lead was used in gasoline to help keep engines working smoothly. Lead use peaked in 1960-1970, and was outlawed shortly before the start of the 21st century.
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Mathew Hauer, the study co-author and sociologist at Florida State University said: ‘Many more people experienced psychiatric problems than would have if we had never added lead to gasoline.’
In 1923, people started adding lead to gasoline to help it run more smoothly through engines. It was also added to paint, solder and used to manufacture pipes that delivered drinking water.
Since the 1980s, health authorities have moved to phase the heavy metal out of the products that Americans rely on.
When leaded gas is vaporized, it releases the lead into the air, where it can be inhaled by humans or settle into the soil.
Though there has been particular focus on the effects of lead in drinking water, the authors of the new paper, published in the Journal of Child Psychology and Psychiatry, said that the product that had the widest reaching effects by far was car exhausts.
The researchers used data from the national data on blood levels in children, leaded-gas use over time and general population statistics to estimate the average levels of lead in peoples blood from 1940 to 2015.
This number gave them an idea of how much lead they were exposed to over a lifetime.
They then used that number to calculate the impact that lead had on mental health, intelligence and personality.
Generally, the higher the levels of lead exposure, the greater toll their mental health took.
Using these estimations, they calculates that there were 151million additional mental illnesses created by lead exposure since 1940.
From 1976-1980, for example, they estimated over 19million Americans had levels of lead in their blood above the CDC recommended threshold of 3.5 micrograms of lead per .1 liter of blood. That represented roughly 99 percent of the population at the time.
Their estimations show a steady decrease in the amount of people with high levels of blood-lead levels – hitting an all time low from 2011-2015 of 1.4 percent of the population, representing around 280,000 people.
They predicted that lead contamination in the blood was most common in people born between 1965-1980, because leaded gasoline usage peaked between the 1960’s and 1970’s.
Children are more vulnerable to lead exposure because their brains area still developing. Damage done to the nervous system during crucial developmental years may never repair, but according to the researchers, at any age, lead toxicity can harm the brain.
The study authors said: ‘Childhood lead exposure has likely made a significant, underappreciated contribution to psychiatric disease in the US over the past century’.
The above map from pressure group the Natural Resources Defense Council (NRDC) shows populations served by drinking water with the highest levels of lead found in their water at home, usually due to old pipes. Florida had the highest concentration of lead piping, a separate study showed
However, they note, it isn’t that every person who was exposed to high levels of lead immediately developed mental health problems.
Instead, long term exposure to the heavy metal likely created low-level, frequent damage to the nervous system.
This sustained damage could then open a person up to developing psychological conditions – making normal, troubling events of life harder to deal with, for example.
Dr Reuben compared this to a person who has a mild physical sickness, like a low-grade fever. He said: ‘You wouldn’t go to the hospital or seek treatment, but you would struggle just a bit more than if you didn’t have the fever.’
This isn’t the first study linking lead to mental effects.
A 2022 study from the same research group from Duke and FSU found that leaded car exhaust exposure might have ‘stolen’ a collective 824million IQ points from 170million Americans since 1940.
In a 2019 study, researchers from the US, UK and New Zealand which followed 579 children from NZ over 30 years determined that high childhood blood lead levels lead to long term changes in personality and mental health.
The kids with high lead levels grew into adults who were less conscientious, agreeable and more likely to have depression, ADHD or anxiety.
Other studies have linked lead to a host of other health problems. This includes hearing problems, infertility, high blood pressure and kidney dysfunction.
The combined weight of evidence on the harms of lead has led to mass government intervention. Most recently, the EPA announced that it would free up billions in funding to help replace lead plumbing in small water systems.
They mandated that the pipes be replaced by the end of the decade.
