The addition of lead to gasoline in the United States was responsible for 151 million cases of psychiatric disorders such as depression, anxiety, and hyperactivity among Americans, a new study concludes. The cost of doing the same thing to what the rest of the world calls petrol is yet to be calculated, but presumably scales with cars using the product.
In 1922 the idea of adding lead to fuel to improve fuel efficiency and protect car engines from knocking apparently seemed brilliant – spewing out a metal even the ancient Romans knew was toxic, what could go wrong? Quite a lot, as it turned out. However, chemical engineer Thomas Midgley, Jr., who was also responsible for ozone-depleting chlorofluorocarbons, was undeterred, and enlisted the power of two of the world’s mightiest industries behind him.
The United States eventually banned leaded petrol in 1996, and other nations slowly followed suit, but we are still discovering the cost. In 2015 more than 170 million people – over half the population – had been exposed to dangerous levels of lead in the blood while their brains were still developing.
A mountain of research shows that exposure to lead during childhood damages the developing brain, with consequences both for the mental health of the individual affected, and those around them. Establishing how large that effect has been, given the need to separate it from many other factors that can cause the same problems, is trickier, but Dr Aaron Reuben of Duke University has tried.
Most research on the epidemiological effects of leaded petrol has focused on its influence on crime. That remains a very contentious topic, since plenty of people have other pet theories. Nevertheless, it’s unambiguous that US crime rates peaked just at the time when the people most exposed to airborne lead reached the prime crime-committing ages, and declined thereafter. Numerous other countries have the same pattern, shifted slightly to reflect the fact lead exposure usually started and finished later in those places.
There has also been a lot of work on reduced IQ and loss of income, but Reuben and Professors Michael McFarland and Matt Hauer of Florida State University have looked at a neglected aspect; the mental health of those exposed. In some ways this is an even more difficult question to assess using public data, because our reporting of mental health has changed so much over the years. People who would now get treatment for anxiety or depression were once told to pull themselves together, and their condition might never be recorded.
To address this, the team used evidence of the link between different levels of lead exposure and mental illness observed in two small closely-studied populations to calculate the consequences in what they call “General Psychopathology points”. They then scaled this up by known levels of exposure in the American population. “This is the exact approach we have taken in the past to estimate lead’s harms for population cognitive ability and IQ,” McFarland said in a statement. That work concluded that the US population lost a cumulative 824 million IQ points to leaded gasoline.
Bad as that sounds, the mental health effects are arguably worse. “We saw very significant shifts in mental health across generations of Americans,” Hauer said. “Meaning many more people experienced psychiatric problems than would have if we had never added lead to gasoline.”
The effects the trio are measuring are not just an increase in sadness or susceptibility to stress within normal levels, but diagnosable depression, anxiety, and conditions like schizophrenia. The authors calculate there were an extra 151 million of those. Even allowing for many people suffering more than one additional disorder, that means tens of millions of people affected to a diagnosable degree.
Yet that doesn’t mean everyone else got off unscathed. The team estimate the US experienced 602 million additional Psychopathology factor points. “For most people, the impact of lead would have been like a low-grade fever,” Reuben 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.”
Indeed, McFarland argues, the entire culture of the nation has shifted in the direction of greater neuroticism and reduced conscientiousness. Then again, given the higher risk of physical ill-health like heart disease and kidney failure, being neurotic might be rational.
The good news is that American children today are generally exposed to much lower lead levels, although there are exceptions where water comes through leaded pipes or contaminated soil gets recirculated. On the other hand, with those most exposed now in their 50s and reaching the peaks of their careers, while potentially suffering additional declines, even those not badly exposed themselves are living in a society shaped by those who were. Meanwhile, hundreds of millions of children in other countries are still exposed.
The study is published in the Journal of Child Psychology and Psychiatry.
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