I forget exactly when I first came across the idea that environmental lead, leftover from decades of leaded gasoline, was a factor in mental acuity, violent tendencies, and potentially crime. It must have been at least 20-25 years ago. Since then, the story has only gotten more interesting. For many reasons, our shift away from massive amounts of environmental lead — in gasoline, paints, and other applications — has been a significant public health victory, benefiting children and adults alike.
Recently, Mother Jones published a long article putting together the pieces of the environmental lead story which strongly suggest a link between environmental lead and crime rates. It’s a fascinating read, revealing one of the main tendencies public health professionals must have to cope with — human vanity and ego.
The story begins in the 1930s, when leaded gasoline was introduced as a way of dealing with engine knock. Violent crime per 100,000 people began to rise about 20 years later, in a manner that was soon described as an epidemic:
But what kind? Karl Smith, a professor of public economics and government at the University of North Carolina-Chapel Hill, has a good rule of thumb for categorizing epidemics: If it spreads along lines of communication, he says, the cause is information. Think Bieber Fever. If it travels along major transportation routes, the cause is microbial. Think influenza. If it spreads out like a fan, the cause is an insect. Think malaria. But if it’s everywhere, all at once—as both the rise of crime in the ’60s and ’70s and the fall of crime in the ’90s seemed to be—the cause is a molecule.
This kind of thinking about epidemics is indicative of how well the article traverses the complexities of the hypothesis and the resulting evidence. For instance, the insight about the 20-odd-year latency linking lead exposure and trends in violent crime came decades down the road, so to speak, but the biology of lead ingestion made sense — an infant’s exposure to lead lowers IQ, increases problems with hyperactivity, increases the odds of developing learning disabilities, and leads to behavioral problems. Once researchers adjusted for this 20-year exposure-to-result window, the correlations locked into place, and were observable in every setting they measured.
There was also the vaunted dose-response curve — where lead levels were lower relative to the national average, crime rates were lower; where they were higher, crime rates were higher. This is why we’ve gotten the mental model of “cities are hotbeds of crime” into our heads. It turns out that as environmental lead levels have dropped, the crime rates between urban and rural areas have drawn even — cities have returned to their pre-lead crime levels.
This is where human hubris enters the picture. Instead of looking for an environmental explanation, law enforcement and criminology experts have pitched all sorts of other ideas and theories out there, all flattering to law enforcement — more cops, “broken windows” theory, tougher sentences — to explain the drops in crime we’ve seen since the 1990s (i.e., 20 years after we stopped putting lead in gasoline).
The lead hypothesis has had an uphill battle because of this, despite thousands of acres in cities that still have abundant residual environmental lead. Deposits accumulated through decades of car exhaust and paint flakes are everywhere, and are stirred up every summer with dry weather, foot traffic, construction, and children at play. Remediation of these areas could generate billions in savings — less crime, smarter kids, fewer health effects — but getting the investment in place is unlikely, partly because policymakers and police want to take the credit for the drop in crime.
What does this have to do with scientific publishing? Of course, the research was published in journals. But the story is always bigger than the research. Research occurs as fragments that someone else has to tie together. As I’ve written before, we need to continue to cultivate the ambassadors of science — those people who can tell a story based on disparate scientific insights, and generate valid, evidence-based education and behavioral or policy changes.
Scientific papers are one things. Scientific progress requires a lot more.