Could exposure to lead in the environment be the cause of excessive violence in the 20th century? In New Orleans, lead levels [in the soil] can vary dramatically from one neighborhood to the next—and the poorest neighborhoods tend to be the worst hit. At the neighborhood level, these match up well with crime rate maps. Maps by Karen Minot in “America’s Real Criminal Element: Lead” from: http://www.motherjones.com/environment/2013/01/lead-crime-link-gasoline
Crime rates have gone down in most urban areas over the past 20 years or so. Politicians and police chiefs (especially in Rudy Giuliani’s New York) attribute this to better policing, stronger enforcement, fighting major crime through cracking down on minor crimes via “broken windows” policies, and higher rates of arrest and incarceration. Some social scientists have attributed the falling crime rates to the changing demographics – fewer young men in their 20’s after the Baby Boom generation. Others claim there is a connection between the economy and criminal activity – when one improves, the other goes down, and vice versa. Or was it the crack epidemic in the 1970’s that led to the increase in crime, and when that had run its course, crime rates plunged? Or was it Roe v. Wade, legalizing abortion in the 1970’s, and preventing the birth of unwanted children that would have grown up to be criminals in the 1990’s (??!!). None of these theories is borne out by facts, however.
So what could be the cause, then, of this precipitous drop in crime? Mark Kleiman, in his book “When Brute Force Fails: How to Have Less Crime and Less Punishment,” says “Given the decrease in lead exposure among children since the 1980s and the estimated effects of lead on crime, reduced lead exposure could easily explain a very large proportion — certainly more than half — of the crime decrease of the 1994-2004 period. A careful statistical study relating local changes in lead exposure to local crime rates estimates the fraction of the crime decline due to lead reduction as greater than 90%.”
On the individual level, high childhood blood lead levels are consistently associated with higher adult arrest rates for violent crime. On the aggregate, geographic levels, research going back to at least 2007 has shown that there is a spatial linkage between areas with high lead levels and high crime rates. And the statistics were looked at for many cities in the U.S., large and small, as well as nine other countries, and they all seem to follow the trend: when the lead was taken out of gasoline, crime decreased about 20 years later. New York City, for instance, had strong childhood lead-poisoning policies put in place in the 1970’s, just in time for the drop in crime when the children born in that period were no longer being impacted by lead in the environment. “Childhood lead exposure can lead to psychological deficits that are strongly associated with aggressive and criminal behavior. In the late 1970s in the United States, lead was removed from gasoline under the Clean Air Act. Using the sharp state-specific reductions in lead exposure resulting from this removal, this article finds that the reduction in childhood lead exposure in the late 1970s and early 1980s is responsible for significant declines in violent crime in the 1990s, and may cause further declines into the future. The elasticity of violent crime with respect to lead is estimated to be approximately 0.8.” from: “Environmental Policy as Social Policy? The Impact of Childhood Lead Exposure on Crime,” by Jessica Wolpaw Reyes, National Bureau of Economic Research, NBER Working Paper No. 13097, 2007 http://www.nber.org/papers/w13097.pdf?new_window=1
The Washington Post notes that “The United States has had two spikes of lead poisoning: one at the turn of the 20th century, linked to lead in household paint, and one after World War II, when the use of leaded gasoline increased sharply. Both times, the violent crime rate went up and down in concert, with the violent crime peaks coming two decades after the lead poisoning peaks. Other evidence has accumulated in recent years that lead is a neurotoxin that causes impulsivity and aggression, but these studies have also drawn little attention. In 2001, sociologist Paul B. Stretesky and criminologist Michael Lynch showed that U.S. counties with high lead levels had four times the murder rate of counties with low lead levels, after controlling for multiple environmental and socioeconomic factors,” From The Washington Post, 2007, “Research Links Lead Exposure, Criminal Activity: Data May Undermine Giuliani's Claims” http://www.washingtonpost.com/wp-dyn/content/article/2007/07/07/AR2007070701073_pf.html
“A scatter-plot of the relationship between air Pb and the latent 22 year aggravated assault rate in New Orleans showing the best fit linear solution (r2 = 0.853, p < 0.001).” from “The urban rise and fall of air lead (Pb) and the latent surge and retreat of societal violence” in Environment International, 2012, by Mielke and Zahran at http://www.sciencedirect.com/science/article/pii/S0160412012000566
I apologize that this figure is so small and hard to read, but you can see the trend line clearly, and the correlation is unmistakable, even without being able to read the axes! Taking into account lead emissions and aggravated assault, the model developed in this study explains 90% of the variation in the six US cities examined. “Prevention of children's lead exposure from lead dust now will realize numerous societal benefits two decades into the future, including lower rates of aggravated assault,” (Mielke and Zahran, 2012).
Of course, even though lead has been banished from gasoline in the US, we are not out of the woods yet: “As it turns out, tetraethyl lead is like a zombie that refuses to die. Our cars may be lead-free today, but they spent more than 50 years spewing lead from their tailpipes, and all that lead had to go somewhere. And it did: It settled permanently into the soil that we walk on, grow our food in, and let our kids play around….. Lead in soil doesn't stay in the soil. Every summer, like clockwork, as the weather dries up, all that lead gets kicked back into the atmosphere in a process called resuspension. The zombie lead is back to haunt us,” (Kevin Drum, Mother Jones)
The Mother Jones article is really worth reading in its entirety (2 pages) at http://www.motherjones.com/environment/2013/01/lead-crime-link-gasolineand see the blog post "The Grime Behind the Crime," by Monbiot for more info on this interesting theory. http://www.monbiot.com/2013/01/07/the-grime-behind-the-crime/
Thanks, Shaky Sherpa, for sending me the Mother Jones link, and Julia Radcliffe, over in Glasgow, for sending me the Monbiot link.
UPDATE, 2/20/2013 “Lead Exposure on the Rise Despite Decline in Poisoning Cases: Leaded gasoline and lead paint are gone, but other sources are keeping the danger high"
I just saw this in the Scientific American. It seems as though we all still have lead levels in our blood that are too high, even if people are not being poisoned by lead as much anymore. Even though lead is not put in automobile fuel anymore, and lead paint is not as much of an issue, after having been phased out in the 1970's, there is still danger of lead exposure.
And although some of the people who commented on the article scoffed at the potential contribution of ammunition to lead exposure, I remember back in the '90s when I worked at the DEP, the big brouhaha that ensued over the clean-up of the NYPD firing range in Pelham Bay Park and the extreme lead contamination that was present. All that soil had to be removed and put somewhere. This problem is more prevalent and wide-spread than you might think. (think Vieques, PR, and many other current and former military installations, etc.)
“Lead Exposure on the Rise Despite Decline in Poisoning Cases: Leaded gasoline and lead paint are gone, but other sources are keeping the danger high” in the Scientific American, Feb. 17, 2013 http://www.scientificamerican.com/article.cfm?id=lead-exposure-on-the-rise Excerpt:
“Lead is still prevalent in our environment for many reasons. Because lead does not degrade, heavy emissions from the past accumulate in soil. Winds, especially during drought—like that afflicting the Midwest for the past year or so—kick it up as dust, and runoff from heavy rains and flooding can re-suspend the particles in the atmosphere. Trees take up soil particles, too, but when forests burn in wildfires, as has been occurring more frequently worldwide with global warming in recent years, that lead is released back into the air. Fires also release lead from old houses and buildings coated with lead paint that was applied prior to the U.S. ban. Lead smelting and refining is still an enormous industry worldwide, sending more of the metal into the environment. Aviation gas used in planes still contains lead.
Lead is still present in drinking water in many communities, where it can leach from lead pipes in homes, apartment buildings and municipal water system, or from brass fittings or solder used in plumbing. Another 25,000 to 30,000 tons of lead enters the U.S. environment each year from hunting and shooting-range ammunition, fishing-line weights, discarded batteries and electronic waste, said Mark Pokras at Tufts University. Coal-burning power plants in developed nations also generate some lead in emissions and more so in ash, and the steep rise in coal power in China has boosted levels worldwide because regulations are more lax.”