"Research on [lead]’s effects on the brain bolsters the hypothesis that childhood exposure is linked to criminal acts"

Regular readers know I am intrigued by the possibility that lead exposure could be a very important part of the very important modern story of US violent crime rates.  This new piece on lead and crime, appearing in Chemical & Engineering News, carries the subheadline I have used in the title of this post. Here are excerpts of a piece that merits a full read by anyone and everyone concerned about US violent crime rates and what might significantly impact them: 

When crime rates began to drop across the U.S. during the 1990s, city officials and criminologists were thrilled — but baffled.  Violent acts, most often committed by young adults, had reached an all-time high at the start of the decade, and there was no sign of a turnaround.

By the close of the ’90s, though, the homicide rate had declined more than 40% throughout the country.  Economists and criminologists have since proposed reasons for the unexpected plummet.  Some have pointed to an increase in police officers.  Others have suggested a rise in the number of offenders put behind bars.  Economist and “Freakonomics” coauthor Steven D. Levitt famously hypothesized that the legalization of abortion in 1973 even played a role....

But recently, experts have been kicking around another possible player in the crime drop of the ’90s: lead.  Cars burning leaded gasoline spewed the heavy metal into the air until 1973, when the Environmental Protection Agency mandated the fuel’s gradual phaseout. Lead-based paint was banned from newly built homes in 1978.  Because of these actions, children born in the mid- to late-1970s grew up with less lead in their bodies than children born earlier.  As a result, economists argue, kids born in the ’70s reached adulthood in the ’90s with healthier brains and less of a penchant for violence....

As the lead-crime hypothesis gains traction in economics circles, critics are invoking the “correlation does not equal causation” mantra.  But scientists argue that there is evidence that lead exposure increases aggression in lab animals.  And even though lead, one of the oldest known poisons, affects the brain in a dizzying number of ways, researchers are beginning to tease out some of the mechanisms by which it might trigger violence in humans....

Looking for explanations of the ’90s crime drop in the U.S., economists and crime experts latched onto ... epidemiology studies. “We saw these correlations for individuals and thought, ‘If that’s true, we should see it at an aggregate level, for the whole population,’ ” says Paul B. Stretesky, a criminologist at the University of Colorado, Denver.  In 2001, while at Colorado State University, Stretesky looked at data for more than 3,000 counties across the U.S., comparing lead concentrations in the air to homicide rates for the year 1990.  Correcting for confounding social factors such as countywide income and education level, he and colleague Michael J. Lynch of the University of South Florida found that homicide rates in counties with the most extreme air-lead concentrations were four times as high as in counties with the least extreme levels.

Others have found similar correlations for U.S. cities, states, and even neighborhoods. In 2000, Rick Nevin, now a senior economist with ICF International, saw the trend for the entire country.  In general, these researchers see blood-lead levels and air-lead levels increase, peak in the early 1970s, and fall, making an inverted U-shape.  About 18 to 23 years later, when babies born in the ’70s reach the average age of criminals, violent crime rates follow a similar trajectory....

Research has shown that lead exposure does indeed make lab animals — rodents, monkeys, even cats — more prone to aggression.  But establishing biological plausibility for the lead-crime argument hasn’t been as clear-cut for molecular-level studies of the brain.... On the brain development side of things, lead interferes with, among other things, the process of synaptic pruning....

“If you have a brain that’s miswired, especially in areas involved in what psychologists call the executive functions — judgment, impulse control, anticipation of consequences — of course you might display aggressive behavior,” says Kim N. Dietrich, director of epidemiology and biostatistics at the University of Cincinnati College of Medicine.

Dietrich and his colleagues have been studying lead’s effects on the developing brain for more than 30 years. In the late 1970s, he and a group of other investigators recruited some 300 pregnant women for what would become the Cincinnati Lead Study.  At the time, these women lived in parts of Cincinnati — typically the inner city — that had experienced historically high numbers of lead-poisoning cases.  Once the recruits’ babies were born, Dietrich and his group began monitoring the newborns too.

From the time they were born until they were six-and-a-half years old, the young participants had their blood-lead levels measured 23 times.  The average childhood concentration for the whole group was 13 µg/dL.  Now adults in their 30s, the subjects are having their brains scanned and behaviors analyzed.  And the results are eerie.  As of 2008, 250 members of the lead study had been arrested a total of 800 times.  The participants’ average blood-lead levels during childhood also correlated with their arrest rate, Dietrich’s team found....

Most kids in the U.S. today have a blood-lead level of 1 or 2 µg/dL.  But there are nearly a half-million children between the ages of one and five with a blood-lead level above the 5-µg/dL threshold.  These are mostly kids who are growing up in dilapidated inner-city houses with lead paint still on the walls or in neighborhoods with elevated levels of lead in the soil.

Despite progress in lowering lead levels in the environment, these kids would benefit from the reevaluation of crime policies and reinvigoration of cleanup efforts, says U of Colorado’s Stretesky. “People who are suffering the most from lead exposure are those that tend to be poor, minority, and low income.”

Some related posts:

• Should we thank unleaded gas and the EPA for the great modern crime decline?
• Effective Washington Post commentary talks up great (and still puzzling) crime decline
• Do lead exposure realities continue to best explain modern crime-rate realities?
• FBI releases 2012 crime statistics showing stability in relatively low crime rates
• New National Academy of Sciences effort seeking to unpack the crime decline 
• Fascinating lead-crime-rate forecast that incarceration levels will decline significantly in coming years