The Tragedy of Leaded Gas

In December 1973, the EPA issued new regulations governing the use of lead in gasoline. These rules, authorized as part of the Clean Air Act and signed into law by President Nixon, were subject to years of political and legal wrangling. Automobile manufacturers insisted the regulations would damage car engines; oil companies warned about a spike in gasoline prices; politicians worried about the negative economic impact. In 1975, a consortium of lead producers led by the Ethyl Corporation and DuPont sued the EPA in an attempt to stop the regulations from taking effect. They argued that “lead is naturally present in the environment” and that the health impact of atmospheric lead remained unclear.

The EPA won the lawsuit. In a March 1976 opinion, the U.S. Court of Appeals of the District of Columbia established the so-called precautionary principle, noting that the potential for harm – even if it has not been proven as fact – still leaves society with an obligation to act. “Man’s ability to alter his environment,” wrote the judges, “has developed far more rapidly than his ability to foresee with certainty the effects of his alterations.” And so the phaseout of leaded gasoline took hold: by 1990, the amount of lead in gasoline had been reduced by 99 percent.*

This federal regulation is one of the most important achievements of the American government in the post WWII era. That it’s a largely unanticipated achievement only makes it more remarkable. According to the latest data, the removal of lead from gasoline is not simply a story of clean air and blue skies. Rather, it has become a tale of sweeping social impact, a case-study in how the removal of a single environmental toxin can influence everything from IQ scores to teenage pregnancy to rates of violent crime.

For the last several years, Jessica Wolpaw Reyes, an economist at Amherst College, has been studying the surprising impact of this environmental success. Her studies take advantage of a natural experiment: for a variety of “mostly random” reasons, including the distribution network of petroleum pipelines, the number of pumps available at gas stations and the local assortment of cars, the phaseout of leaded gasoline didn’t happen at a uniform rate across the country. Rather, different states showed large variation in their consumption of leaded gasoline well into the 1980s. If lead poisoning was largely responsible for the spike in criminal behavior – rates of violent crime in America quadrupled between 1960 and 1991 - then the removal of lead should predict the pace of its subsequent decline. (In many American cities, crime has returned to pre-1965 levels.) In other words, the first states to transition fully to unleaded gasoline should also be the first to experience the benefits.

That’s exactly what Reyes found. In a 2007 study, Reyes concluded that “the phase-out of lead from gasoline was responsible for approximately a 56 percent decline in violent crime” in the 1990s. What’s more, Reyes predicted that the Clean Air Act would continue to generate massive societal benefits in the future, “up to a 70 percent drop in violent crime by the year 2020.” And so a law designed to get rid of smog ended up getting rid of crime. It’s not the prison-industrial complex that keeps us safe. It’s the EPA.

As Reyes herself noted, these correlations raise far more questions than they answer. She concluded her 2007 paper, for instance, by noting that if the causal relationship between lead and crime were real, and not a statistical accident, then the rate of lead removal should also be linked to other behavioral problems, including substance abuse, teenage pregnancy, and childhood aggression. Violent crime, after all, does not exist in a vacuum.

In an important new working paper, Reyes has expanded on her previous research, showing that exposure to lead in early childhood has far-reaching negative effects. By employing data on more than eleven thousand children from the National Longitudinal Survey of Youth (NLSY), she has revealed the relationship between levels of lead in the blood and impulsive behavior in a number of domains. Consider the steep decline in teenage pregnancy in the 1990s, which has proved difficult to explain. According to Reyes, changes in lead levels caused by the Clean Air Act have played a very significant role:

“To be specific, we can consider the change in probability associated with a change in blood lead from 15 µg/dl to 5 µg/dl, a change that approximates the population-wide reduction that resulted from the phaseout of lead from gasoline. This calculation yields a predicted 12 percentage point decrease in the likelihood of pregnancy by age 17, and a 24 percentage point decrease in the likelihood of pregnancy by age 19 (from a 40% chance to a 16% chance). This is undoubtedly large: the lead decrease reduces the likelihood of teen pregnancy by more than half.

Similar patterns held for aggressive behavior and criminal behavior among teenagers. In both cases, the rise and fall of these social problems appears to be closely correlated with the rise and fall of leaded gasoline. In short, says Reyes, exposure to lead “triggers an unfolding series of adverse behavioral outcomes.” It makes it harder to children to resist their most risky impulses, whether having unprotected sex or getting into a violent fight. (Other research shows that lead is closely linked to lower IQ scores: the typical increase in lead levels caused by leaded gasoline decreases IQ scores, on average, by roughly six points.) Placed in this context, the correlation with crime rates is no longer so surprising. Rather, it’s the natural outgrowth of a poisoned generation of children, unable to fully control themselves.

There’s one last interesting conclusion in Reyes’ new study. Because the NLSY survey contained information about parental income and education, she was able to see how leaded gasoline impacted kids across the socioeconomic spectrum. While most environmental toxins disproportionately harm poor families – they can’t afford to live in less polluted places – leaded gasoline was, in the words of Dr. Herbert Needleman, an “equal opportunity pollutant…not limited to poor African-American children.” In fact, as Reyes points out, atmospheric lead was one of the few adverse environmental influences that wealthier families could not escape, as “it was in the very air children breathed.” As a result, Reyes’ analysis shows that the children of higher-income parents were, on average, more harmed by leaded gasoline, showing a steeper drop-off across a range of negative behavioral outcomes. “In a way, the advantaged children had more to lose,” Reyes writes. “Consequently, gasoline lead may have been an equalizer of sorts.”

There are, of course, inherent limitations to these sorts of econometric studies. There might be hidden confounds, or systematic differences between generations of children that are unaccounted for by the statistical model. As Jim Manzi has pointed out, the variation in the state-by-state adoption rates of unleaded gasoline might not be quite as random as it seems, but instead be linked to subtle “differences in political economy that in turn will affect changes in crime rates.” Society is more complicated than our statistics.

But it’s important to note that the link between lead and societal problems is not merely a statistical story. Rather, it is rooted in decades of neurological evidence, which tell the same causal tale at a cellular level. Lead has long been recognized as a neurotoxin, interfering with the release of transmitters in the brain. (The chemical seems to have a particular affinity for the NMDA receptor, a pathway essential for learning and memory.) Other studies have shown that high levels of lead to apoptosis, a fancy word for the mass suicide of brain cells. And then there’s the Cincinnati Lead Study, which has been tracking 376 children born between 1979 and 1984 in the poorer parts of the city. While the study has shown a strong link between lead exposure and violent crime – for every 5 ug/dl increase in blood levels at the age of six, the risk of arrest for a violent crime as a young adult increases by nearly 50 percent – it has also investigated the impact of this exposure to lead on the brain. In a 2008 paper published in PLOS Medicine, a team of researchers led by Kim Cecil used MRI scans to measure the brain volume of enrolled subjects who are now between the ages of 19 and 24. The scientists found a clear link between lead levels in early childhood and the loss of brain volume in adulthood. Most telling was where the loss occurred, as the scientists found the greatest damage in the prefrontal cortex, a region closely associated with impulse control, emotional regulation and goal planning. (The correlations were strongest among male subjects, which might explain why men with lead exposure are more prone to antisocial behavior.)

At the end of her new working paper, Reyes makes an argument for “strengthening the threads” between disparate disciplines, closing the explanatory gap between policy-makers, public health professionals, environmentalists and social scientists. As she notes, it’s becoming increasingly clear that the boundaries of these fields overlap, and that any complete explanation of a complex social phenomena (say, the fall in crime rates) must also concern itself with leaded gasoline, the prefrontal cortex and economic inequality. “The foregoing results suggest that lead – and other environmental toxicants that impair behavior – may be missing links in social scientists’ explanations of social behavior,” Reyes writes. “Social problems may be, to some degree, rooted in environmental problems.”

*Despite the legal decision, the lead industry continued to fight the implementation of the EPA regulations. As Gerald Markowitz and David Rosner argue in Lead Wars, the main impetus for the removal of lead from gasoline was not the new rules themselves but rather the introduction of catalytic converters, which were installed to combat sulfur emissions. Because lead damaged the platinum catalyst in the converter, General Motors and other car manufacturers were eventually forced to call for the end of leaded gasoline. 

Via: Marginal Revolution

Reyes, Jessica Wolpaw. "Lead exposure and behavior: Effects on antisocial and risky behavior among children and adolescents." NBER Working Paper, August 2014

Reyes, Jessica Wolpaw. "Environmental policy as social policy? The impact of childhood lead exposure on crime." The BE Journal of Economic Analysis & Policy 7.1 (2007).

Markowitz, Gerald, and David Rosner. Lead Wars: The Politics of Science and the Fate of America's Children. Univ of California Press, 2013. p. 77-80