Friday, January 4, 2013

Is lead the cause of all of our troubles?

Pretty picture, bad molecule.
Kevin Drum is a political blogger for the progressive magazine Mother Jones; he's written a very interesting article about the drop in violent crime in the United States that we've seen over the last 30 years. Mr. Drum examines every alternate hypothesis (poverty, demographics, the Levitt/Dubner Roe v. Wade hypothesis, the end of the crack wars, etc.) and discards them in favor of his hypothesis: that the removal of tetraethyllead from gasoline is responsible for the drop in violent crime. Mr. Drum goes further and argues for a broad policy of lead abatement in older, poorer neighborhoods as a means of both improving public health and long-term economic output (I'm not kidding.)

I'll be very interested to see how far this article and its hypothesis will travel. It could just be the obsession of one Internet-famous blogger, or it could be the starting gun for a variety of interesting policy shifts. But I want to lay down a couple of markers:

Is there a difference between inorganic and organic lead? Mr. Drum does a little bit of sleight of hand (for this nitpicky chemist, anyway) and seems to equate alkylated lead in gasoline (tetraethyllead) with inorganic lead in house paint (lead carbonate, etc). It's probably because the public health folks tend to measure just for lead concentrations in the blood without reference to the source. (Also, how are different lead compounds metabolized?) (See update below.) 

The connection between low [lead] and neurotoxicity and the public health consequences: To quote Drum:
For starters, it turns out that childhood lead exposure at nearly any level can seriously and permanently reduce IQ. Blood lead levels are measured in micrograms per deciliter, and levels once believed safe—65 μg/dL, then 25, then 15, then 10—are now known to cause serious damage. The EPA now says flatly that there is "no demonstrated safe concentration of lead in blood," and it turns out that even levels under 10 μg/dL can reduce IQ by as much as seven points. An estimated 2.5 percent of children nationwide have lead levels above 5 μg/dL.
The most influential study that I am aware of (Lanphear et al., 2005) argues that the largest drops in IQ are seen with the lowest concentrations of lead. I'd love to know if this has been confirmed -- it seems like a really big deal. In case you think it doesn't really matter, one of the broader trends that we're seeing is young families with children moving back into urban cores and occupying older homes. While there's common defenses (lead abatement is supposed to be done with certified contractors, the classic "all the lead paint's been painted over a zillion times" line), I suspect that the actual effective treatments are more costly than the public health folks (and Mr. Drum) would like to admit.

A new front in the chemophobia wars: I found this quote in Mr. Drum's article from an economics professor rather chilling:
[Professor Smith] 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. (emphasis mine)
I am familiar with Professor Smith and generally like his thoughts. I might even believe that this is a true-ish statement. That said, I find that last thought to be potentially disastrous for chemistry in the hands of an already chemophobic media and public.

UPDATE: A commenter challenges my question about the accuracy of treating organic and inorganic lead the same. A quick search of Google indicates that the commenter is correct, as you can see below, and that tetraethyllead is combusted into inorganic lead compounds.

So it's probably purely inorganic lead that folks are exposed to on a routine basis (the text notes that most actual tetraethyllead acute/chronic exposure is occupational.)

UPDATE 2: I suppose that I should actually say whether or not I agree with Kevin Drum. I agree with him that exposure to lead is bad, and I've read enough of the medical literature to conclude that (as I have noted in the past) I will do whatever it takes to avoid exposing my family to environmental lead (e.g. wiping down the old house I used to live in, monitoring blood lead levels in my children, selecting housing based on potential lead exposure, etc.) I see the avoidance costs as relatively low, and the benefits to my kids (a potential couple of IQ points, mebbe) as worth it.

Whether or not we should embark on nationwide urban lead abatement (and whether or not it will pay off) is a different story, and I am somewhat less convinced. That said, I could imagine worse places to spend the relatively small amount of money ($20 billion) that Mr. Drum is proposing. 

8 comments:

  1. leaded gas use was widespread in Europe, and the exposure average there was probably just as bad or worse than in US due to higher population density. I don't believe the crime statistics from Europe would support the hypothesis that a lead-exposed child will turn into a crazy violent slum-dweller adult

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  2. I am going to say it is much more likely to be economic rather than chemical causes, I'm sure there are hundreds of books discussing that. Sounds like an interesting read though.

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  3. Milkshake, you should read the whole article--it does discuss the correlations in countries other than the US. Chemjobber, regarding the organic vs inorganic distinction, I agree that the article doesn't address it (and Drum is not a chemist), but I would assume a good deal of the lead that came out of the car exhaust was inorganic in any event, since it already engaged in combustion chemistry in the engine. A lot of good chemists comment on this site, and someone might know enough combustion and environmental chemistry to have an insightful answer into what sort of lead was in exhaust (and subsequently in soil) vs paint. But I don't think it's fair to express skepticism about the article on that point, since the ambiguity is not self-evidently incorrect. First time commenting here, by the way--in general I think your site is great.

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    1. the graphs presented are an impressive example of a biased data presentation. Please note the changing offset time intervals in various graphs (like between the measured average schoolchildren led blood level and the resulting murder rate when the kids grow up). In one graph it is 12 years. In another 15 years . In another 22 years. And so on. The correlation is nearly perfect because it introduced by hand.

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    2. Thank you for your kind words, and thank you especially for your counter-skepticism. To be clear, I am sure that both are bad, I am just not sure that they're equivalent. I'm going to clarify above.

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  4. Not a chemist, but does this article go any way toward answering your question? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1567786/ Comparative observations on inorganic and organic lead neurotoxicity

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  5. Hoping you can comment on the "all the lead paint's been painted over a zillion times" line. My understanding is that lead in paint is stable and isn't hazardous unless you touch it - so it starts flaking/chipping, if somehow it hasn't been painted over a zillion times, or you start sanding. Do you know of any evidence as to whether that is/isn't the case?

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  6. Isn't this a classical case of "correlation does not mean causation"?

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