Does lead poisoning cause violence?

by Sandra Parshall

Although society seems to be reeling from the worst violence in history, the truth is that crime rates in the U.S. have dropped steadily since peaking around 1990.

Politicians and law enforcement agencies are happy to take the credit. Then-mayor of New York Rudy Guiliani and Police Commissioner Bill Bratton basked in praise when the city saw the sharpest drop in crime since the end of Prohibition. But did their get-tough policies bring about the change, or was something less obvious happening, not just in New York but across the country?

For years I’ve read off and on about scientific studies showing a link between high levels of lead in the environment and violent crime, and corresponding drops in crime when people were exposed to less lead. Yet no government body, certainly no law enforcement agency, has shown an interest in the possibility that lead poisoning is the cause of a lot of criminal behavior.

The correlation between lead exposure and crime looks strong in the statistics. For decades, the single greatest source of lead in the environment was auto exhaust. As children who were exposed to lead grew to adolescence and young adulthood, the violent crime rate increased. The phase-out of leaded gasoline in the U.S. began in 1973. When children born in the 1970s and after began to mature twenty years later, in the early 1990s, the crime rate started to decline. The turnaround has happened not only in the United States, but also in Canada, Australia, Great Britain, Finland, and West Germany, all countries that quickly and dramatically reduced the amount of lead that vehicles spewed into the air through their exhaust pipes.

The January-February 2013 issue of Mother Jones magazine has a comprehensive report on the lead-crime connection, written by investigative journalist Kevin Drum. The article contains documented information that every American, and especially those with children and grandchildren, should pay attention to, because our environment still contains far too much lead. This isn’t a matter of politics. It’s simply a question of what we’re willing to do to protect children from the brain damage lead causes – permanent, incurable damage that can result in violent behavior and uncontrollable impulses.

Scientists have long known that eating chips of lead paint causes brain damage in children – lower IQ levels, hyperactivity, behavioral problems, learning disabilities, and juvenile delinquency as the children aged. In the 1990s the U.S. Department of Housing and Urban Development decided it might be a good idea to remove lead paint from old houses, and they hired Rick Nevin as a consultant on the costs and benefits of this massive project.

Nevin followed the link between the metal and brain damage beyond paint to a far greater source of lead in the environment: gasoline. Lead isn’t a natural part of gasoline. General Motors invented tetraethyl lead in the 1920s as an additive to prevent pinging and knocking in engines. After World War II the auto industry boomed, and soon children all over the country were breathing in lead every day. Tetraethyl is doubly dangerous because, unlike the lead in paint and pipes, it’s easily absorbed through the skin. In the 1960s, twenty years after the auto boom began, crime levels started rising dramatically. The crime wave continued until the early 1990s, twenty years after the phase-out of leaded gas began.

Rick Nevin presented the results of his research in a 2000 paper, laying out  detailed evidence of the correlation between lead and criminal behavior. Children who were exposed to high levels of lead in the 1940s and 1950s were indeed more likely to become violent criminals in the period between the 1960s and 1990.

Nevin’s findings, published in the journal Environmental Research, were ignored by government bodies and law enforcement.

Nevin wasn’t the only researcher looking into the topic, though. Harvard graduate student Jessica Wolpaw Reyes investigated the connection between lead and violence for her dissertation in the late 1990s and came to the same conclusion Nevin had. She carried it further, and learned that in states where lead-free gasoline was quickly accepted, the rate of violent crime committed by young adults declined rapidly a couple of decades later. In  states where consumers were slow to begin using lead-free gasoline, the drop in crime was slower.

More recently, other researchers have published studies demonstrating the link between lead and violence at the local, state, national and international levels. “Put all this together,” Kevin Drum says in his Mother Jones article, “and you have an astonishing body of evidence.”

Using a new generation of neurological scanners, researchers have also documented the ways in which lead damages the human brain and nervous system. Lead poisoning can cause a permanent loss of gray matter in the prefrontal cortex, the part of the brain associated with reasoning, mental flexibility, attention, emotional regulation, and control of impulses and aggression.

Of course, not all crime is caused by lead poisoning, and not all of us who were exposed to lead as children (I am in that group myself) turned into violent adults. Drum points out that almost everyone in the U.S. over the age of 40 was exposed to excessive lead while growing up, and most of us probably suffered no more than the loss of a few IQ points. But millions of children already living on the margin of emotional and physical health were vulnerable to lead’s most devastating effects.

Why have criminologists, public authorities, and law enforcement agencies ignored the mountains of evidence that lead poisoning causes violent behavior? Every expert wants to explain violence in terms of his own expertise. A psychologist looks into the offender’s background for a psychological explanation. Politicians blame lax law enforcement or the  booming trade in illegal drugs. And so on. None of the criminology experts Drum contacted showed the slightest interest in the lead hypothesis.

In any case, auto fuel and house paints no longer contain lead, so the problem is solved, right? No. As Drum points out, millions of houses with leaded paint remain in the U.S., and the lead can be released to do more harm during remodeling. Airplane fuel still consists of as much as 60% tetraethyl. Small plane exhaust, by some accounts, contributes at least half of the lead remaining in our air. The lead that cars vented into the air for decades is still with us, absorbed into the soil beneath our feet. The soil our food is grown in. The soil children play on in parks. Tetraethyl, invented to stop car engines from making annoying sounds, lives on as a toxin  everywhere in our environment.

The Lead Safe America Foundation advises that if you live in an old house or neighborhood, you and your children should be tested for lead levels. If you want to renovate an old house, find out how to do it safely – or, better yet, hire a company whose workers are trained to remove lead paint.  

The cost of lead abatement nationwide would be staggering, and that, in the end, may be the reason no one wants to face the dangers of leaving it in place.

Drum concludes, “This is the choice before us: We can either attack crime at its root by getting rid of the remaining lead in our environment, or we can continue our current policy of waiting 20 years and then locking up all the lead-poisoned kids who have turned into criminals... Cleaning up the rest of the lead that remains in our environment could turn out to be the cheapest, most effective crime prevention tool we have. And we could start doing it tomorrow.”

Mother Jones, the January-February issue: buy it and read Kevin Drum’s full report. I’ve touched on only a fraction of it here.