In my previous post (Does less lead mean less crime?), I wrote about research showing how the rise and decline in environmental lead levels could account for the bulk of crime trends in the US since the 1940s. (In fact, lead exposure is correlated to crime as far back as the 1870s.)
At the end of my post, I asked about the seemingly growing gap between lead exposure levels and crime rates since the early 2000s. Rick Nevin, a Senior Economist with ICF International and one of the researchers at the forefront of investigating the lead/crime connection, reached out to HIP to address that question and write a guest blog providing more information about his research, how lead exposure is driving the aging of the U.S. prison population, and the implications that may have for the criminal justice system.
At HIP, we are passionate about understanding the complex ways that social, political and economic factors interact with the environment to impact health outcomes, and the relationship between lead exposure and crime is a perfect example of this dynamic. We thank Rick for contributing his time to help us learn more about this phenomenon and sharing his professional and personal perspective on the topic.
I want to thank HIP for this opportunity to present more evidence linking lead exposure and crime trends. The ongoing strength of this relationship has important implications for debates over the death penalty, criminal justice racial disparities, and mass incarceration.
I knew very little about the effects of lead poisoning, or crime data, when I began work in 1994 on an Economic Analysis of lead paint hazard regulations. My initial bias was to doubt that the costs of that regulation were justified by benefits. I was mistaken: costs were far lower than benefits associated with how lead exposure affects IQ, education, and lifetime earnings. My client also mentioned that we didn’t even count crime prevention benefits, suggested by recent research. I was aware of studies showing a strong relationship between lead exposure and leaded gasoline use in the past, and I wondered if there might be a relationship between crime trends and earlier gas lead trends. What I found was a stunning visual fit with a 23-year lag, consistent with early childhood lead exposure affecting the peak age of violent offending.
In 2000, Environmental Research published my first peer-reviewed study on lead exposure and USA violent crime trends. The same journal published my 2007 study on lead exposure and international crime trends, and my 2009 study on lead exposure and education trends. My 2009 study reported related shifts in incarceration rates by age and race, and showed that the lead research literature demonstrates all of the accepted indicators of causation: lead exposure is not just correlated with subsequent trends in intellectual disability, education achievement, and crime rates – lead poisoning caused those societal trends.
I have acknowledged that the strength and consistency of societal impacts from preschool lead exposure sounds like a bad science fiction plot. As an economist, starting out with a healthy skepticism about the costs of lead poisoning prevention, I am also an unlikely advocate for this improbable plotline, but the evidence is overwhelming.
Historic Trends: Dangerous Dust, Delinquency, and Crime
The most pervasive cause of lead poisoning is lead in dust, contaminated by lead in paint and air lead fallout. Lead in dust is ingested via normal hand-to-mouth activity as children learn to crawl. The bloodstream carries lead to the brain where it causes neurodevelopmental damage. Behavioral impacts are most evident after affected children reach adolescence, during another period of rapid brain growth.
Variations in biological vulnerability and lead exposure severity result in different outcomes for individual children, but higher risks of delinquent behavior among youths with preschool lead exposure have been documented by Denno, Needleman, Dietrich, and Wright. My study in 2000 found that homicide rates from 1900-1998 were also largely explained by the use of lead in paint and gasoline from 1879-1977.
The use of lead paint fell over the 1920s and 1930s but we didn’t ban lead paint until 1978. From the 1940s through the 1980s, average blood lead tracked trends in air lead fallout from leaded gasoline, as lead paint exposure changed slowly with changes in the housing stock. Many children in the 1960s had additive exposure to city air lead and lead paint in old homes, sending “large numbers of comatose and convulsing children” to inner city hospitals. Lead in dust from lead paint in older homes is the main cause of USA preschool lead exposure today.
My 2000 study also found that 90% of violent crime rate variation from the early-1960s to 1998 was explained by earlier lead exposure trends. The time-lag relationship between lead exposure and violent crime has now been confirmed in state and city crime studies. My 2007 study found that lead exposure also explained most of the violent and property crime rate variation across decades in the USA, Britain, Canada, France, Australia, Finland, Italy, West Germany, and New Zealand. The best-fit lag was 18 years for property crime and 23 years for violent crime, consistent with peak ages of offending. In seminal reporting on this issue, Kevin Drum calls this “an astonishing body of evidence. We now have studies at the international level, the national level, the state level, the city level, and even the individual level.”
Ongoing Trends: Shifts in Arrests and Incarceration by Age
The crime decline in recent years has been slower than the earlier decline in blood lead because steep arrest rate declines for youths have been partially offset by rising arrest rates for older adults. From 1991-2013, arrest rates for children under 10 fell by 83% for violent crime and 94% for property crime, and juvenile (under 18) arrest rates fell by 63% for violent crime and 71% for property crime, as arrest rates for adults ages 50 and older increased. In absolute terms, the violent crime arrest rate for juveniles was twice the rate for ages 35-49 in 1991, but the juvenile rate was lower in 2013. The property crime arrest rate for children under 10 was about the same as the rate for ages 35-49 in 1991, but the 2013 rate for children under 10 was just 7% of the 2013 rate for ages 35-49. This shift in arrest rates shows ongoing massive declines for youths born across decades of declining lead exposure, smaller arrest rate declines for adults born in the early years of the lead exposure decline, and increasing arrest rates for older adults born when lead exposure was increasing.
The shift in arrest rates has caused a corresponding shift in prison incarceration. From 2001 to 2013, incarceration rates fell by 59% for males ages 18-19 and 30% for males in their 20s, but increased 33% for men ages 40-44 and surged 86% for men ages 45-54. Proponents of “tough-on-crime” sentencing credit prison incapacitation for much of the USA crime decline – “when a criminal is locked up, he’s not ransacking your house” – but the largest arrest rate declines have occurred among younger age groups with large contemporaneous incarceration rate declines.
From 2000 to 2013, there was also a 69% decline in the number of juveniles in adult prisons, and a 46% decline in juveniles placed on probation. Juveniles in local jails also fell 40% from 2000-2014, and the number of youths in residential placement fell 50% from 1999-2013 (juvenile offenders account for 90% of youths in residential placement). The largest percentage declines were recorded by the youngest juveniles, including an 82% decline in the number of children under age 13 in residential placement. Mendel reports that lead exposure can explain juvenile justice trends that cannot be explained by reform efforts or other crime theories.
Ongoing declines in juvenile arrests reflect blood lead declines over the 1990s (the birth years of juveniles in 2007-2013). The percent of children ages 1-5 with blood lead above 5 mcg/dl fell from 31.4% in 1988-1991 to 2.6% in 2007-2010, due to new homes without lead paint, demolition and renovation of old housing, and implementation of the Residential Lead Hazard Reduction Act of 1992 (including regulations that were the subject of my 1990s analysis).
Future Trends: A Road Less Traveled
Two decades after I first saw the correlation between gasoline lead and crime, the research on this issue is still ignored in many news stories related to lead poisoning. Jim Haner, who wrote extensively about lead poisoning for the Baltimore Sun, was the only reporter who wrote about my study in 2000, just a few years after Freddie Gray was poisoned by lead paint in Baltimore, steering his life toward academic and crime problems shared by many lead poisoning victims. In 2006, John Pekkanen wrote a brilliant story about this issue for Washingtonian magazine, but we are still waiting for an answer to the question posed by his story title: “Why Is Lead Still Poisoning Our Children?”
The “pipeline” to prison has alliterative appeal, but it is a misnomer. There is a road to prison, with signs that some offenders fail to heed. A 1991 prisoner survey found that 80% of inmates had served prior sentences to probation or incarceration, including 40% with prior sentences as juveniles. Another analysis found that prisoners released in 1994 after serving sentences for nonviolent offenses had criminal records that included, on average, 9.3 prior arrests and 4.1 prior convictions. We can disagree about many criminal justice issues, but one thing we know for certain is that very few prisoners made it to age 20 before their first felony arrest. The steep declines in juvenile arrest rates and the age 18-19 incarceration rate ensure that the road to prison will be a road less traveled for many years to come.
The Supreme Court has ruled that the death penalty and life without parole are excessive sanctions for crimes committed by juveniles, citing evidence that “adolescent brains are not yet fully mature in regions and systems related to higher-order executive functions such as impulse control, planning ahead, and risk avoidance”. We now know that preschool lead exposure impairs those specific types of brain development linked to impulse control, planning, and risk avoidance; other research links those specific types of brain impairment to homicide offending; murder trends by city size have tracked lead exposure trends from 1900-2013; and murder arrest rates by race and racial disparities in death penalty sentences have tracked racial disparities in lead poisoning.
From the 1950s through the 1970s, African-Americans were disproportionately exposed to city air lead and lead paint hazards in substandard urban housing. The percent of black preschool children with blood lead over 30 mcg/dl fell from 12% in the late-1970s to less than 1% in the late-1980s, and the black juvenile murder arrest rate then fell by 83% from 1993 to 2003. Black children are still disproportionately exposed to lead contaminated dust in older homes, but the racial disparity in elevated blood lead has narrowed from the late-1980s through 2010.
There is a stale statistic that one in three black boys will end up in prison at some time in their life, based on an old analysis that assumed arrest and incarceration rates by age and race would remain unchanged at 1991 levels. Criminologists in the early-1990s used that same assumption to forecast a rising violent crime rate, largely based on projected demographic growth in the black juvenile population. Those forecasts were wildly wrong because the assumption about stable black juvenile offending was wrong. From 1991 to 2012, black juvenile arrest rates fell by 59% for violent crimes, 55% for property crimes, and 61% for weapons offenses. From 2001 to 2013, the incarceration rate for black males fell by 43% for ages 25-29, 50% for ages 20-24, and 62% for ages 18-19.
Lead exposure impacts on crime are as global as the rise and fall of leaded gasoline use. My 2007 study found that 80% to 90% of burglary rate variations in Britain, Canada, and Australia through 2002 were explained by earlier trends in lead exposure. The burglary rates in all three nations fell by more than 50% from 2002-2014, tracking earlier lead exposure trends. The title of a 2013 story in The Economist asked: “Where have all the burglars gone?” Now you know. In the future, the road to prison will be less traveled all over the world.