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Inorganic Chemistry

The Crimes Of Lead

Research on the toxic metal’s effects on the brain bolsters the hypothesis that childhood exposure is linked to criminal acts

by Lauren K. Wolf
February 3, 2014 | APPEARED IN VOLUME 92, ISSUE 5

Credit: Courtesy of Kim Cecil
Composite MRI images of about 160 members of the Cincinnati Lead Study show that childhood exposure to element 82 causes gray matter loss (orange areas), especially in frontal areas of the brain.
Credit: Courtesy of Kim Cecil
Composite MRI images of about 160 members of the Cincinnati Lead Study show that childhood exposure to element 82 causes gray matter loss (orange areas), especially in frontal areas of the brain.

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. Once the Supreme Court decided Roe v. Wade, he argued, fewer unwanted babies grew into disturbed, crime-prone adults two decades later.

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.

Today, the Centers for Disease Control & Prevention considers 5 micrograms per deciliter of lead in a child’s blood to be abnormal. Studies have shown that people who grew up with blood-lead levels at or above this threshold are more likely to have impaired cognition than those who grew up with less lead in their blood. In 1976, the average U.S. resident had a blood-lead level of 16 µg/dL, according to the National Health & Nutrition Examination Survey. By 1991, when there was less lead in the air and in housing, the average had dropped to 3 µg/dL.

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.

During the 1960s, doctors couldn’t label a child as lead poisoned unless he or she had a blood-lead level of at least 60 µg/dL—CDC’s defined limit at the time. But researchers like University of Pittsburgh psychiatrist Herbert L. Needleman questioned the cut-off value. Surely if 60 µg/dL was toxic, 50 µg/dL couldn’t be completely harmless.

Needleman and others began observing “silent lead poisoning” in children with blood-lead levels below the established limit. Rather than overt physical symptoms like hallucinations and kidney damage, these kids had low IQ scores, attention problems, and antisocial tendencies. As more and more reports of these deficits filtered in, CDC lowered the blood-lead level it deemed acceptable for kids further and further: In 1970, the amount was 40 µg/dL, and by 1991, it was 10 µg/dL.

Some physicians noticed that children exposed to blood-lead levels below 50 µg/dL could also be aggressive or violent. In 1996, Needleman and his group followed up on these anecdotal observations by examining a few hundred 12-year-old boys in the Pittsburgh area. The researchers measured the amount of lead in the boys’ bones with X-ray fluorescence to get an idea of how much of the heavy metal their participants were exposed to during childhood. The boys rated worst by their parents and teachers in terms of aggressive and antisocial behaviors had been exposed to the highest levels of lead (J. Am. Med. Assoc. 1996, DOI: 10.1001/jama.1996.03530290033034).

Economists hypothesize that regulation of leaded gasoline and lead paint in the 1970s caused crime rates to drop in the U.S. about 20 years later.CPSC = Consumer Product Safety Commission. SOURCES: Rick Nevin, FBI Uniform Crime Reporting Statistics

In 2002, Needleman’s team delved deeper by studying 15-year-old boys who had been arrested and sentenced by the Allegheny County Juvenile Court in Pennsylvania. The kids who had been in trouble with the law had an average bone-lead level of 11 ppm—6% higher than a control group of boys without a history of arrest (Neurotoxicol. Teratol. 2002, DOI: 10.1016/s0892-0362(02)00269-6).

Looking for explanations of the ’90s crime drop in the U.S., economists and crime experts latched onto these and other 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 (Arch. Pediatr. Adolesc. Med. 2001, DOI: 10.1001/archpedi.155.5.579).

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 (Environ. Res., DOI: 10.1006/enrs.1999.4045). 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.

Still, “predicting crime trends is hard,” Stretesky says. Anything that’s followed a U-shape over the same period is going to correlate, he says. One example put forward in a 2013 Mother Jones article titled “America’s Real Criminal Element: Lead” is vinyl rec­ord sales. They rose after World War II and then declined in the 1980s and ’90s, but that doesn’t mean they’re responsible for crime trends.

Seeking to strengthen the provocative lead-crime argument, in 2007, Nevin looked abroad, at countries where the crime rates didn’t necessarily follow the inverted U pattern. In every case—New Zealand, West Germany, Italy, the U.K., and so on—the data plots for blood-lead levels overlaid with plots of violent crime rates that were shifted back about 23 years (Environ. Res. 2007, DOI: 10.1016/j.envres.2007.02.008).

“When people read about my work,” Nevin says, “they oftentimes blurt out, ‘Correlation does not mean causation.’ ” One of the key signs of causation, he argues, is biological plausibility.

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. Lead wreaks a lot of havoc on the central nervous system. So pinpointing one—or even a few—molecular switches by which the heavy metal turns on aggression has been challenging.

What scientists do know is that element 82 does most of its damage to the brain by mimicking calcium. Inside the brain, calcium runs the show: It triggers nerve firing by helping to release neurotransmitters, and it activates proteins important for brain development, memory formation, and learning. By pushing calcium out of these roles, lead can muck up brain cell communication and growth.

On the cell communication side of things, lead appears to interfere with a bunch of the neurotransmitters and neurotransmitter receptors in our brains. One of the systems that keeps popping up in exposure experiments is the dopamine system. It controls reward and impulse behavior, a big factor in aggression. Another is the glutamate system, responsible in part for learning and memory.

On the brain development side of things, lead interferes with, among other things, the process of synaptic pruning. Nerve cells grow and connect, sometimes forming 40,000 new junctions per second, until a baby reaches about two years of age. After that, the brain begins to prune back the myriad connections, called synapses, to make them more efficient. Lead disrupts this cleanup effort, leaving behind excess, poorly functioning nerve cells.

“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 (PLoS Med. 2008, DOI: 10.1371/journal.pmed.0050101).

Working with Dietrich, Kim M. Cecil, an imaging expert at Cincinnati Children’s Hospital Medical Center, has taken magnetic resonance images of the subjects’ brains and found that as childhood blood-lead levels increase, gray matter volume decreases in a handful of brain areas (PLoS Med. 2008, DOI: 10.1371/journal.pmed.0050112). Even more important, the regions with the largest gray matter loss are the ventrolateral prefrontal cortex and the anterior cingulate cortex, areas known for impulse control, emotional regulation, and decision making.

“These are the parts of the brain that say, ‘Ooh, I’ve learned from before that I shouldn’t steal that, or if I do this, then the consequences are that,’ ” Cecil says.

Still another way lead might coax the brain into committing violent acts is through IQ and learning disabilities. Although controversial when they were first reported, studies have shown that a child’s blood-lead level is inversely proportional to IQ. The extent of this relationship is still a point of contention, but most estimates have suggested that for every 10 µg/dL of blood lead, a child loses between one and 10 IQ points.

This might not seem like a lot for someone who’s been genetically gifted with an IQ around 120 or 110, Cecil contends. But for a child who might have started life with an IQ of 80, dropping to 70—a value close to impairment—is a handicap, she says.

Children who perform poorly in school and who have learning disabilities tend to have low self-esteem, get frustrated more easily, and, thus, are more likely to act out and engage in delinquent behavior, experts say.

On the molecular level, lead might be affecting learning and intellect through the N-methyl-d-aspartate receptor (NMDAR), a protein on the surface of nerve cells that gets activated when glutamate and glycine stick to it. For more than 20 years, Tomás R. Guilarte, chairman of environmental sciences at Columbia University, has been studying how NMDAR works and how it’s affected by lead.


“Lead’s a potent inhibitor of NMDAR,” Guilarte says. That’s a problem, he says, because “NMDAR is crucial for brain development, learning, and memory processes.”

Over the years, Guilarte and his team have discovered that lead somehow decreases the number of NMDARs anchored to the surfaces of nerve cells in synapses. The heavy metal binds to and disables some of the receptors, too, preventing them from ushering calcium into the nerve cells on which they reside. This in turn prevents calcium from activating enzymes such as calmodulin kinase, a protein inside the cells that goes on to participate in strengthening nerve cell connections when a person learns a fact or commits an experience to memory (Brain Res. Rev. 2005, DOI: 10.1016/j.brainresrev.2005.02.004).

“Overall, the evidence is sufficient that early exposure to lead triggers a higher risk for engaging in aggressive behavior,” says U of Cincinnati’s Dietrich. “The question now is, what is the lowest level of exposure where we might see this behavior?”

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.”



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John Duczek (February 3, 2014 5:17 PM)
If lead can cause a situation like this, then why isn't it strictly regulated. It poisoned people for years in Paint and still is poisoning them today as it flakes away. This is only one metal in the environment. For decades the USA Government has allowed Industry there to poison its people with every type of toxic material and chemical and radioactive materials in the name of $$$$$. There are so many sites where there are toxic products dumped in the ocean or in land fill leaching into water supplies or incinerated. Any wonder their are so many Americans who get cancers of all descriptions and every other malady know to Medicine. one doesn't have to be a genius to see that you can not have a situation where you poison the Countries food, water and soil and then wonder why you have so much illness in the general population. I doubt the USA has enough Money to clean up all the mess they have made to their environment in the name of Profits at any cost..... John from kapunda AUSTRALIA
Anonymous (April 3, 2014 3:27 PM)
Lead is strictly regulated as one of the six criteria pollutants in the US. I don't think the US government allowed the paint and automobile industry to "poison its the name of $$$$$." I just don't think they knew any better back then. Necessity is the mother of invention. What has "AUSTRAILIA" invented?
Nathanael (January 19, 2015 9:50 AM)
US scientists knew better back in 1920; it was known that tetraethyl lead was a deadly poison and a neurotoxin even in small doses.

However, every country in the world is guilty of allowing leaded gasoline from 1920 through the 1970s. Every single one. So no country can claim moral superiority here.
David Thompson (April 28, 2017 12:00 AM)
I agree with Nathanael. I became interested in the issue of poisoning of children by lead paint back in the 1960s. Even then, the risks to children were well known and efforts were made to require the removal of lead paint from interiors, and to ban lead paint. But the children at risk were minority children, and landlords and paint manufacturers banded together to resist legislation. The slowness of the political process in responding to this problem has been scandalous. We see the same pattern now in Flint MI, where government was slow to respond to high lead levels in the drinking water.
Environmental Biologist and RN (August 11, 2014 4:02 PM)
Hi John,
I know my comment is late but I still have to vent. You make Australia sound like some pristine, chemical free wonderland! That is absolutely amazing? Do you not have automobiles? Do you not use products containing plastic? Do you not have chemical plants and petroleum refining facilities? Do citizens in Australia live as the Amish do? No modern conveniences and thereby no pollution? I find it so amazing that other countries point their fingers at America like they are the only ones that have contributed to pollution. Take a look in your own backyard before pointing your finger.
Rita May (February 4, 2014 4:14 PM)
Thank you for this informative article. really puts a perspective on why my 22 year old daughter acts the way she does.
Anonymous (February 5, 2014 2:18 PM)
Wow, I'm in a forensic science class right now, and this is really cool stuff! Thanks I love the article!
Carmelo Barrantonio (February 5, 2014 9:27 PM)
Thank you for this article, Lauren, and for the wealth of links to researchers and their studies that you've collected together here.

I was brought to this article by a link on Kevin Drum's blog from one of his commenters. He was the author of the Mother Jones article that you mention. For those interested in reading that 2013 piece, here is the link:
Lauren Wolf (February 27, 2014 11:33 AM)
Thanks for posting this link, Carmelo. It somehow didn't get embedded in my story here. Apologies for that. But it is definitely a great read--and an inspiration for me.
Sean Costello, CIH (February 7, 2014 4:53 PM)
This correlates nicely with a study from Russia about populations living near lead smelting plants (presented @ 2013 AIHCE in Montreal).
Yjoesis (February 7, 2014 5:45 PM)
Really?? Way, way too many variables and confounders to think of this than other than a limited data relationship. Here are a couple of easy ones:

1) Y2K, end of millennia (doomsday predictions) everyone was under extreme stress that the world was going to somehow magically end or at least be severely disrupted in 1999-2001. Y2K ended up being nothing, 2000-2001 wasn't a big deal either(except the stock markets), so the stress is now less.

Blood lead and reduced IQ, several studies have followed those children with high blood leads-they are now lawyers, Drs, business owners and working well within norms. If the calculations were true some of those highly exposed individuals would have had negative IQs. This was talked about at a AIHA PDC quite a few years ago.

Of course the fact prior offenders are now incarcerated, more security, better enforcement,much better forensics(DNA info just one area) is pooh poohed as it doesn't fit the researchers model... By the way where are the ZPP results, did they test for that?? Isn't that a significant BEI to include????
David Thompson (April 28, 2017 12:12 AM)
Y2K has absolutely nothing to do with the question of lead levels causing crime. It would be helpful if Yjoesis would mention specific studies and findings that support his point. I'm not even sure what his point is, except to cast doubt on this article.
Future Chemistry Major (February 11, 2014 1:27 PM)
I'd imagine that the lowest level of exposure causing these effects could vary depending on genetic factors and perhaps even more widely due to environmental factors such as child mistreatment, nutrition, and stress level. It might not just be more lead causing more damage in the poor and minorities. The physical and mental stress of being abused, bullied, discriminated against, wondering where their next meals are coming from, etc. could lower their resistance to it and/or magnify the effects.
Howard W. Mielke, Ph.D. (February 18, 2014 1:12 PM)
Very nicely written article that extends Kevin Drums Mother Jones article. One of the critical errors is in the timeline because it misses the January 1, 1986 Rapid Phase-down. In the early 1980's as cars with catalytic converters were aging, drivers began misfueling with leaded fuel (used as a loss-leader) and the misfueling increased the amount of lead being exhausted into the environment. The January 1, 1986 Rapid Phase-down advanced the removal of lead additives to gasoline by a full decade. In 1986 the Rapid Phase-down reinforced decreases in lead aerosol emissions and the decreases corresponded with a sharp decline in blood lead of the Nation's children. The quantities of lead dust were especially large within traffic congested cities and the settled lead dust can still be measured in urban environments were it continues to expose children.
Toni Snow (February 18, 2014 1:24 PM)
Why can't someone do a prospective study of incarcerated men, to look at lead levels in the bones of deceased prisoners? I'm pretty sure lead stays in the bones forever.

Toni Snow
Program Manager
City of Lowell lead Abatement Program
Treehugger (April 17, 2014 7:12 PM)
Another chapter in this story is lead from drinking water. The EPA has no limit set for it. Lead in drinking water does not generally come from the supply, but from lead in the plumbing. There were no bans on lead in plumbing until 1983. The EPA requires water producers to maintain the water so that it is non-corrosive, however, the limits of lead in customers drinking water consist of an “Action Level” and 10% of the samples may be over this level. There is no limit on how high those 10% can be.

The Scientific Committee on Health and Environmental Risks has done a study and estimates that a 1-3 year old child drinking water at the EPA action level (15 ppb) for lead would have a blood level of 3 micro g/dL - See Table 2b of : So those 10% samples could well give such a child lead poisoning as defined by the CDC.

What’s in YOUR water?
Richard Sittel (June 5, 2014 7:41 PM)
This has me incredibly curious about several other countries in our hemisphere, Honduras and Venezuela. They both have high violent crime and murder rates, plus they were some of the last countries to eliminate lead from fuel... Then, look at the few countries on earth that STILL have leaded gas: Iraq, Afghanistan, Yemen, all at war. I also wonder what's going on in Detroit, could the crime rate there be partially caused by lead?
Environmental Scientist and RN (August 11, 2014 3:56 PM)
Interesting article. While it is true that Lead can possibly have the mentioned adverse effects on the developing human brain it cannot be blamed for all violent behavior. Sometimes human beings are just violent. If you have ever interviewed violent criminals you would be surprised at some of the things you hear. Most of them know exactly what they did and why they did it. Yes there may have been some issues with impulse control but if you are aware of something and you continue to do it over and over can you really blame it on impulse control? Especially if you are bragging about it. Treehugger mentioned lead in your drinking water. As he mentioned lead does not normally come from the drinking water source or the plant. Lead comes from the pipes in your homes. That is difficult to regulate. It would be difficult to make people replace all of the pipes and fixtures in their homes. The EPA regulations are set the way they are because of this fact. Basically the water quality parameters are set at certain levels to minimize the leaching of lead and copper from pipes and fixtures in your home. This can be a difficult task when producing millions of gallons of water a day and sending it out through miles and miles of pipes to the customer. The key is probably to ensure that there is no lead in any new fixtures or pipes used for homes. If there is no lead content then it cannot be leached out. As it stands right now the best way parents can minimize their childrens exposure to the lead from the pipes in their own homes is to flush them before use. Flushing your pipes for several minutes before use can significantly minimize the exposure. Just one more comment. Making statements that blame the government or the corporations for poisening the public for money makes absolutely no sense. Both entities rely on repeat business. So poisening them does not make any sense from a business standpoint. As another commenter stated, they didn't realize at the time how detrimental lead could be. Now they know and they are working to try to minimize our exposure.
Enkidu (November 17, 2014 6:58 AM)
The EPA leaps into action in 1973 to solve a problem which has already started diminishing in 1971 and 1972. This it is reported in several EPA and CDC documents that the peak year for tetraethyl lead usage was 1970 yet the EPA regulations did not go into effect until after the lead levels already started falling. What happened during 1971 and 1972 to make lead levels go down?
Nathanael (January 19, 2015 6:36 PM)
The EPA regs were promulgated. You forget how long it takes to finalize these things. Automakers knew well in advance that regulations were coming.
TSpencer (August 17, 2015 6:37 AM)
I pushed my Kaiser doctor to give me a blood test for lead and it showed 11g/Dl. I am 61 and was bothered by numbness in my hands and feet, and there had been a recall of some Trader Joe's Thai candied ginger. The public health people think it was more likely due to old paint in my house (Bay Area, CA). I wonder if I had high lead as a kid (seems likely). What I wonder more is how many people have high levels and aren't routinely tested so go unknown. I would imagine quite a few. Mine has come down but not to what is considered average around here (5-7g/Dl) - so I'm told.
David Lewis (February 22, 2016 1:11 AM)
Saying that there are 500,000 children in the US above the CDC 5 ug/dL "threshold" is like saying there are 12 eggs in a dozen.

The CDC publishes what it calls a "reference" level for blood lead in children which is presently 5 ug/dL. They are going to recalculate every 4 years. The definition of this reference is the 97.5 percentile of the best estimate of blood lead levels in US children. I.e. 2.5% of US children will test higher than the reference, by definition. There will always be roughly 2.5%, or about 500,000 US children testing higher than the reference, because as blood lead levels fall in response to community action, the CDC will reduce the reference.

The published CDC reference isn't a borderline between elevated and normal blood lead, and it isn't a "threshold" between harmless and harmful. The CDC has concluded that no level of lead in children is safe. The reference is published so that anyone becoming aware of children testing higher will know that 97.5% of all the other US children are testing lower. Presumably this knowledge will trigger action.

We have all been poisoned by the careless use of lead in the past.

People might want to tone down their statements about how damaged the children in Flint are. Almost every adult these children know had higher blood lead levels for far longer. I heard that kids in Flint are asking adults: "am I going to die?".

Maybe its too complicated to say that civilization blew this one and spread lead all over the place in ways that will be almost impossible to clean up. We're slowly addressing the problem, and our measure of success is declining blood lead levels in children.

The problem in Flint is the sudden spike in blood lead observed meant that the situation was going the other way, i.e. there was more lead in children, and quite rightly, Dr. Hanna-Attisha sounded the alarm.

But if we're going to say these children are permanently brain damaged and need advanced medical care for the rest of their lives, we'll all need advanced medical care for the rest of our lives. All baby boomers had three to five times the blood lead these Flint kids have, and for their entire childhoods, not just until adults told them to stop drinking the water.

We should just deal with the situation, calm the kids by telling them all adults had it worse and their children will have it better. Those officials that blundered around arrogantly turning Flint water into toxic waste need to be roasted. Our descendants will only experience less lead poisoning if we understand how pervasive lead is and if we continue to apply ourselves to reduce the threat it poses.

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