In an attention- getting story this week (more than 17,000 Facebook likes as of this morning), Mother Jones political blogger Kevin Drum poses a fascinating question – is long-time contamination from 20th century leaded gasoline one of the major causes of violent crime? Cleverly titled, "America's Real Criminal Element: Lead", the story delves into research that consistently maps out a connection between lead exposure and crime rates.
He begins by looking at the notable late 20th-early 21st century drop in violent crime in this country (barring, of course, mass murder which has ticked up), pointing out that the coast to coast reduction cannot logically be attributed to a patchwork of local police initiatives. What's needed, Drum says, is a coast to coast explanation, something in the national environment. Perhaps, for instance, a chemical exposure.
But what chemical compound? "What molecule could be responsible for a steep and sudden decline in violent crime?" Drum asks. "Well, here's one possibility: Pb(CH2CH3)4". In other words, tetraethyl lead, the anti-knock compound introduced by the American auto industry in the 1920s, slowly phased out in the 1970s, and officially banned by the U.S. government in the 1980s. The story goes on to detail research that demonstrates a strong correlation between the rise and fall of leaded gasoline and the rise and fall of violent crime rates. Drum also points out that lead is a notable neurotoxin, known to damage the developing brain so that an association between behavior issues and exposure has additional credibility.
Drum isn't the first journalist to find this a noteworthy story. The Washington Post covered the same research in 2007 and, further, used a similar opening anecdote (Rudy Giuliani's war on New York City crime). USA Today also drew these connections five years ago. I almost hesitate to mention this, but the now-disgraced neuroscience writer, Jonah Lehrer, wrote the research up on his old Wired science blog last year. Drum himself has written about the issue before as well, such as a post last summer titled, "Less lead, less crime."
But in this latest story, he goes much farther in embracing lead as the primary cause of violent crime, so much farther that that it's worth asking whether leaded gasoline, as he asserts, does explain as much as 90 percent of the rise and fall of violent crime. Does it trump drugs, poverty, urban gang warfare, education, and other such issues to the point that they account for a bare ten percent of the crime statistics? That's a harder case to make, partly because as Drum himself notes correlation is not causation: the fact, for instance, that falling crime follows a pattern of falling lead exposure doesn't rule out many other influences.
And the neuroscience itself is more complicated than he suggests. As he notes, lead toxicity can interfere with myelination, the sheathing of nerve cells that helps enable efficient information processing. But so can malnutrition and other environmental influences. And while this effect is definitely associated with a reduction of cognitive function (a connection dating back to the use of lead pipes and drinking vessels in ancient Rome) there's no straightforward mechanism here, no clear biological pathway by which the metallic element lead somehow turns on a violence switch in the human brain.
I wondered also about the focus on leaded gasoline when there are other troubling routes of exposure. USA Today, for example, did a terrific series this year on contamination from shuttered factories, many still tucked into urban neighborhoods. And leaded paint contamination continues to be a serious problem in old buildings; the most common lead compound in that case is not tetraethyl lead but lead carbonate (PbCO3). Drum, in fact, addresses the lead paint question in a follow up post today, linking heavy use of such paint in the early 20th century to homicide rates.
In other words, it's not that tetraethyl lead is some special form of the poison – the point is that lead exposure in any form is dangerous. And that's the real message here. The connection with crime remains somewhat complicated but there's nothing complicated about the fact that lead, in all its forms, remains one of the most troubling of all industrial exposures. And whether Drum gets it perfect here or not, he does get the main point right. We need to keep reminding ourselves – and our government – that we all benefit by, as they say, getting the lead out.
— Deborah Blum
UPDATE: Following this post, Kevin Drum posted a clarification on that 90 percent number that I complained about above. It's very nicely done and you can read it here.