In its various forms, lead has been used in many everyday products for millennia. The Romans even added it to wine as a sweetener. Its most widespread use, however, was its addition to petrol. And it is this use that has been associated with increased mental health disorders, according to a new study published in the Journal of Child Psychology and Psychiatry.
Americans, especially those born between 1966 and 1986 (largely so-called generation X), have probably suffered from an additional 151 million mental health disorders that would not have occurred without the use of leaded petrol.
The study finds increases in anxiety and depression, attention deficit hyperactivity disorder (ADHD), and neuroticism, as well as decreases in conscientiousness.
Although the toxicity of lead for humans has been known for almost as long as it has been used, the full extent of its effects and the exposure levels at which they manifest is still being uncovered.
Tetraethyl lead started to be added to petrol in 1921 when three engineers at General Motors discovered that it greatly improved engine performance and reduced "knocking" -- uneven burning of the fuel that can damage engine parts.
Concerns about the safety of leaded petrol arose immediately when one of the engineers who made the discovery, as well as several workers producing the additive, fell sick, and some died of mysterious illnesses. Still, the US surgeon general dismissed these concerns, citing a lack of evidence of the effects at the low exposure levels linked with driving.
The discussion on the effects of lead exposure at the time was dominated by industry-sponsored studies, as recounted in a 2009 book, Lead Wars: The Politics of Science and the Fate of America's Children. Simultaneously, leaded paint was also marketed as the best paint for its washability and brightness.
In the 1970s, the invention of the catalytic converter, which does not work with leaded petrol, and an accumulating body of evidence on the negative consequences of lead exposure for human health, saw the beginning of the phase out of leaded petrol. (Regulation was also introduced in the US to ban leaded paint for residential purposes in 1978).
Even though its use had already decreased, the UK banned leaded petrol in 1999, and Algeria was the last country to officially ban it in 2021.
The resulting gradual reduction of lead in the environment has offered a useful setting for researchers to widen our understanding of the widespread consequences of lead exposure among children and adults. For example, a study in Sweden compared children born in areas closer to motorways, who would have been more exposed to lead emissions from cars, to those born farther away.
By studying how the differences in these two groups changed over time as leaded petrol was phased out, they found that lead exposure lowers educational outcomes, increases the risk of criminal activity, and can lower lifetime earnings.
These effects on crime, educational attainment and engagement in "risky behavior" have been found in the US, too.
Lead mimics calcium in the body, disrupting most systems that need calcium to function. It is linked to losses of cognitive function as well as kidney and cardiovascular diseases, high blood pressure and even fertility issues. For example, exploiting the fact that leaded petrol was still allowed in Nascar races, a study from the US finds higher death rates from cardiovascular disease in older adults who live near Nascar circuits precisely when the races are on.
First estimate of effects on US society
The new study in the Journal of Child Psychology and Psychiatry builds on known associations of lead exposure to mental health from two studies in Chicago and New Zealand. Given the relationship between lead exposure and these outcomes, measured childhood lead exposure, and lead emissions each year, the researchers calculated the fraction of the changes in the mental health of Americans born in different years that can be attributed to lead.
This approach is not perfect, as other things were changing over time. Still, the study offers a first estimate of the effects of leaded petrol on American society.
Since lead was not just used in petrol, its harmful legacy is probably even larger. And other applications of lead are growing. For example, it is used in the batteries that power electric vehicles.
Importantly, such a study would not be feasible in the UK, as no representative national data on lead exposure has been collected. Yet lead particles from leaded petrol are still found on the streets of London today. So it is likely that lead has caused, and perhaps continues to cause, significant physical and mental health disorders in the UK.