In the recent New York City mayoral race, scary images of a return to a lawless city were flashed on the screen by one of the candidates who was against rolling back the “stop and frisk” policy. He felt a strong police force and stringent laws were responsible for the lower crime rates in the United States over the past several decades. Indeed, the violent crime rate went from 757.7 per 100,000 residents in 1992 to 386.3 per 100,000 in 2011. Obviously something was working right, but was it police policy or environmental policy? Yes, it appears there is a strong relationship between the Clean Air Act of 1970 and lower crime rates.

Rick Nevin, an economic consultant and advisor to the National Center for Healthy Housing, did a comprehensive study in 2007 that shows a strong relationship between childhood lead exposure and adult crime rates over the ensuing years. Although the half-life of lead in blood is usually 30 days, children usually have repeated and prolonged exposure, allowing for the lead to accumulate in teeth and bones. This high level translated to a doubling of delinquency rates. Nevin also explored emission data from 1941-1975 and correlated it to crime data from 1964-1998. His conclusions showed a very strong link with a consistent “lag-time” of 23 years, corresponding with infant lead exposure and the peak of violent crime.
Studies have long supported the belief that lead exposure affects IQ. Nevin cites studies indicating “that youths with IQ of 75–90 are seven times more likely to be incarcerated than those with IQ of 110–125” (Nevin, 2007). But it goes beyond IQ. Lead damages the frontal lobe. This is the area responsible for impulse control and reasoning. Lead also retards the growth of myelin, which “affects the speed of the signals that travel from neuron to neuron … [and] allows your brain to work in concert; you’re not as prone to impulse” (ibid). The effects of reduced or delayed myelination and reduced IQ and neurotransmission all affect logic and decision-making processes.

There are those that will ignore the data and continue to believe that tough policing is solely responsible for reduced crime across this country, as well as the eight other industrialized countries Nevin researched. But all the other countries he researched had the same arch of data points and similar lag-times. We know what lead does to brains. It is logical to assume that a deteriorated or delayed-growth brain would make impulsive choices. This isn’t to say that good, sound policing efforts should be scrapped. What it does say is just how environmental policy can affect us, even in ways that we may not see for years to come.

Nevin, Rick. “Understanding international crime trends: The legacy of preschool lead exposure”. Environmental Research. Volume 104, Issue 3, July 2007, Pages 315–336