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4Jan 2013

Lead and Crime

Leaded gasoline/Photo: catchesthelight/flickr

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.

Comments

Its very difficult to think that crime is directly correlated to lead. I've read some amazing study on the causes and factors which directly impact crime rate in the book Freakonomics but how come there is so much noise on leaded gasoline. As far as the 90% figure is concerned, it definitely implies that rest of the 10% came out from minor causes! Still amazed.

It seems obvious enough that when a brain-affecting toxin is removed, IQ scores will improve. But what Cassandra finds more interesting is the idea that "58m crimes have been avoided". Is this true, and how can we possibly know? http://www.dui-lawyers-california.org

There must be a legal issue regarding this matter. Although I agree that the 90% number is too high, and I should have made that clearer in my piece, I do think my discussion of the neuroscience was pretty careful. There was no suggestion of a "violence switch," just a discussion of lead's effect at crowding out calcium and its effect on the development of both white matter and gray matter in the prefrontal cortex. Obviously, lead poisoning is not good for anybody's brain. But the story assumes there is a strong, systematic causal relationship between a reduction in IQ and violent crime. Nice article indeed. Thanks for posting!

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Agreed, Paul. There are lots of industrial compounds still in a stage of risk assessment. But lead isn't one of them. It's unambigously bad for us and the environment. And it's just crazy making (to me) that we don't pursue the obvious fixes. So a story like this, perfect or not, that calls attention to the problem is a story well worth reading.

I remember Herbert Needleman, whom Drum mentions, talking about this at a AAAS meeting years ago. I can't recall whether I wrote the story at the time, alas. Drum has done a service by bringing this to a larger group of readers. Maybe someone in as position to do something about lead exposure will take notice--and do something.

Thanks all for the thoughtful discussion. And, Kevin, really appreciate your response. As you can probably tell, I tried to make this a very careful discussion of your work because I don't want to undermine the message about the risks of lead.

The "violence switch" wording was mine, mostly to emphasize the lack of mechanism here. The effect of lead on cognition is well established and certainly one can make a case that that effect may contribute to violent or impulsive behavior. But until some smart scientist shows the biological process involved (hence my throw the switch analogy) then I argue for caution in correlation.

I do understand the focus on tetraethyl lead regarding more recent crime figures and I liked your discussion of leaded paint in a historical context. My point is mostly that there are alternate sources of lead exposure even recently and what we don't know is whether we see a culmulative effect of multiple exposures because, as we know, we do find bioaccumulation of heavy metals.

In other words, to repeat myself, it's a complicated picture. But I do think you raise important points and I heard very good things about your radio interview from some normally critical chemists. Oh and I'm going to put an update in the main text with your response to the 90 percent number.

BTW, I believe there's a book on industry efforts to suppress information about lead risks coming out this spring.

The link is not directly between IQ and violent crime. Low IQ does seem to be a factor in criminal propensity, but the lead-crime hypothesis is based on much more than this.

Deborah: Although I agree that the 90% number is too high, and I should have made that clearer in my piece, I do think my discussion of the neuroscience was pretty careful. There was no suggestion of a "violence switch," just a discussion of lead's effect at crowding out calcium and its effect on the development of both white matter and gray matter in the prefrontal cortex. This affects various behavioral attributes (impulse control, judgment, etc.) that are all plausibly associated with violent crime.

And the focus on leaded gasoline was deliberate. My piece was solely about the inexplicable rise and fall of crime in the postwar era. Although lead from other sources is just as dangerous as gasoline lead, none of it plausibly contributes in a major way to the rise of crime in the 60s and beyond, or to its decline beginning in the 90s.

Correlation is not Causation. A study of Mexico could make one conclude that the arrival of non-leaded gasoline started a trend to greater violent crime. Drug Lords and other independent factors need to be considered.

Hmm, I'm a little more skeptical of the strength of this story. I think this is a case of correlation being taken for causation. Obviously, lead poisoning is not good for anybody's brain. But the story assumes there is a strong, systematic causal relationship between a reduction in IQ and violent crime. Is there really such good evidence that this is the case? Yes, some violent criminals have low IQs. But is there high-quality evidence that a reduction in IQ actually leads to violent criminal behavior? IIRC, some (disputed) research indicates that sociopaths tend to have higher IQs than average, and the connection between violent crime and sociopathic traits seems clearcut.

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