Children exposed to leaded gasoline likely caused a spike in mental health illness and personality changes that affected entire generations of people in the United States, a new study has found.
Experts say the research, published in the Journal of Child Psychology and Psychiatry Wednesday, also raises serious questions about the impact of lead exposure on Canadians, who for decades used similar leaded fuel blends in their vehicles.
“I was exposed. We all were,” said Anne-Marie Nicol, an environmental health scientist at Simon Fraser University and the B.C. Centre for Disease Control.
“There’s no reason to believe the health effects would be any different in Canada than the U.S.”
'Lead-poisoned the entire population'
The U.S. researchers used national health survey data to estimate childhood blood-lead levels from 1940 to 2015. They then compared it to a number of mental health symptoms that have been linked to lead exposure.
By 2015, the researchers estimated there were 151 million excess mental disorders attributable to lead exposure, with the highest impacts found among people born between 1966 and 1986.
Mathew Hauer, a study co-author and an associate professor at Florida State University’s Center for Demography and Population Health, said the rise and fall of lead exposure in gasoline tracked with the rising prevalence of mental illness to the point where millions of people had their personalities altered.
“It goes far beyond a couple of adverse health effects,” Hauer said. “The amount of lead exposure in the U.S. is gargantuan.”
“We essentially lead-poisoned the entire population.”
Over 75 years, Hauer said lead exposure doubled the risk of schizophrenia for 89 million Americans, while quadrupling the risk of attention deficit disorder (ADHD) among another 170 million U.S. adults. The research also found a spike in anxiety, depression and neuroticism and a decrease in conscientiousness over the same period.
The authors note that lead exposures would have also occurred from lead pipes, contaminated food and soil, and airborne dust from lead-emitting industries and waste incineration, among other sources. However, all of the mental health disorders tracked in the study rose and fell with the prevalence of lead in gasoline.
The estimates presented in the study, they say, should be considered “likely floors for lead-attributable psychiatric disease rather than ceilings.”
Nicol, who wasn't involved in the research, said there is clear evidence lead can cause a variety of mental health disorders. But she also warned the study leaned on correlational evidence at the population scale. She said more work needs to be done to say with certainty that lead is causing the illnesses.
“These kind of correlational studies are kind of clues,” Nicol said. “Certainly, we can use it to craft policy and it’s something we certainly need to follow up to understand that X causes Y.”
Leaded gas exposure much worse than Flint, Mich., water crisis
About 10 years ago, a tainted municipal water source in Flint, Mich., poisoned locals with blood-lead concentrations of about five micrograms per 100 millilitres of blood. The ongoing crisis has garnered international media attention and led to hundreds of millions of dollars in legal settlements. But it's nowhere close to the lead levels found in many people's blood half a century ago.
“The amount of lead in children that were exposed to lead in the 1960s and '70s is somewhere between two to six times that level,” said Hauer.
In Canada, long-term health surveys show that in 1978-1979, about 27 per cent of the population aged six to 79 had lead concentrations double that in Flint and well within the range of what was considered harmful in the U.S. study.
Since the 1970s, leaded gasoline was slowly phased out in both Canada and the U.S. By 1990, Canada banned lead in gasoline, while the U.S. followed suit in 1996. Recent Canadian surveys show blood-lead levels have declined more than 70 per cent over the past four decades, with similar results across all ages in the U.S.
The latest research linking leaded gas with mental health outcomes builds off a paper published in 2022 in which Hauer and his colleagues linked leaded gasoline exposure to an average loss of 2.6 IQ points per person as of 2015. The researchers found higher losses were likely among those born between 1951 and 1980.
More than half the current U.S. population has been exposed to harmful lead levels through gasoline, and Hauer warned those impacts don't stop with its ban. By 2100, about five per cent of the population will still be living with lead poisoning they faced during childhood, he said.
“Early life exposure is very significant for the rest of your life,” said the researcher. “We find really there is no safe level of lead exposure.”
Critic says regulatory system still 'broken'
Tim Takaro, a doctor and researcher in occupational and environmental health at SFU, said the mix of chemical exposures Canadians have faced, including lead, has been essentially the same as the U.S. population.
Takaro, who was also not involved in the research, said there’s no reason to think a study in Canada wouldn’t reveal equivalent drops in mental health and IQ as seen in the U.S.
“It’s phenomenal numbers,” he said. “If the IQ of a population goes down, that has a profound effect on learning, interaction between people, and you could say progress.”
For Takaro, the bigger concern is the lack of regulatory oversight that allowed companies to expose millions of people to lead, and the long list of neurotoxic chemicals that continue to appear in consumer products today.
He pointed to heavy metals like mercury, cadmium and even the continued use of lead. But also phthalates used to make plastic bendable, pesticides to protect crops, and per- and polyfluoroalkyl substances (PFAS) — the latter a group of 4,700 “forever chemicals” used in everything from cosmetics and food packaging to carpets, diapers and clothing.
Unlike in Europe, where the regulatory burden is on companies to show consumer products are safe, in Canada, many consumer products are not adequately tested, according to Takaro.
“Our problem is that we live in this chemical soup and we enable these industries driven by profit to put out more petrochemical-based products without adequately testing them before,” he said.
“We have a regulatory system that is broken.”
