Studies suggest link
between lead, violence
Experiment on rats indicates exposure hinders brain growth;
Analysis tracks lead, crime
By Jim Haner, Baltimore Sun Staff, May 9, 2000
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Two new studies on the effects of lead exposure to be released
this week suggest that the toxin commonly found in household
paints made before 1960 may stunt normal brain growth and
could contribute to patterns of violent crime.
The reports - to be published almost simultaneously in two
leading research journals - are the first in an expected wave
of new studies this year examining how lead exposure
influences learning disabilities in children, violent behavior
in teens and mental dysfunction in the elderly.
Researchers who have reviewed the two studies caution that
they are both preliminary and do not establish a firm causal
link between lead exposure and aberrant behavior.
But they say the results go to the heart of scientific
research on the subject.
In one of the first experiments of its kind, Baltimore's
Kennedy Krieger Institute for children found in a two-year
study that relatively low levels of lead fed to a colony of
nursing mother rats in their drinking water caused brain
abnormalities in their offspring that stunted their sensory
Experts say the research, which appears today in the
Proceedings of the National Academy of Sciences, may have
implications for human brain development, since lead tends to
have similar effects in animals and young children.
Also see Lead Paint
Full coverage of the efforts to combat lead-paint poisoning in
"We know that kids can experience permanent reductions in IQ
from lead exposure," said Mary E. Blue, a neuroscientist
involved in the study.
"And that suggests there may be physical changes in actual
brain structure - which is exactly what our research found."
In the second study, a private consulting group working under
contract for the U.S. Department of Housing and Urban
Development used computers to track lead consumption in paint
and gasoline over the past century and uncovered a striking
As the amount of lead released into the environment in paint
and auto exhaust rose and fell through the decades, so did a
broad range of reported violent crimes - including rape,
robbery, assault and murder - a researcher at ICF Consulting
in Fairfax, Va., found.
"Historians have grappled with this question for years, trying
to explain these huge arcs in the crime rate," said Rick Nevin,
an economist who authored the report appearing later this week
in the journal Environmental Research.
"But no one ever looked at the possible effects of lead
exposure. When you put that data up on the chart, the
consistency is quite astonishing."
Lead has been shown to increase aggressive behavior in humans
in repeated studies since at least 1943, when doctors at
Boston's Children's Hospital first noted a tendency toward
"cruel impulsive behavior" and "irritability" in children
exposed to lead.
But scientists have yet to establish precisely how lead fuels
anger, except that it causes humans and animals alike to have
difficulty learning and adapting to changes in the
The quest for the exact mechanism - and the lowest dosage at
which the toxin begins to cause mental problems - has been
among the most controversial in the field over the past two
"Both of these reports are striking in their general
observations about the possible gross effects of lead
exposure," said Dr. Ellen K. Silbergeld, a professor of
toxicology at the University of Maryland and an authority on
lead poisoning. "And they both fit rather nicely into the
"But they raise more questions than they answer. That said, it
doesn't make the findings any less disturbing, especially for
a city like Baltimore."
More than 7,000 children a year are exposed to highly toxic
dust from disintegrating lead paint in Baltimore, and at least
1,200 are poisoned.
Mostly poor and disproportionately African-American, they live
primarily in the dilapidated rental housing enclaves of Park
Heights, Sandtown and Middle East.
These neighborhoods have been associated with high rates of
childhood lead poisoning since at least the 1930s, according
to historical health records at the Johns Hopkins University.
Paint in old houses
While lead levels in the blood of U.S. children have declined
sharply nationwide since the 1970s - when the U.S. Congress
banned lead in gasoline and paint - kids living in older,
poorly maintained houses continue to be exposed nationwide.
In impoverished rural communities and cities such as Chicago;
Milwaukee; Providence, R.I.; Newark, N.J.; and Philadelphia,
lead paint exposure constitutes a con-tinuing public health
crisis affecting more that a million children annually,
according the U.S. Centers for Disease Control and Prevention.
In Baltimore, the Kennedy Krieger Institute on Broadway is the
primary treatment facility for the hardest-hit kids, an oasis
amid the city's worst slums.
"Their new research is totally consistent with a growing body
of literature that strongly suggests that the relatively low
levels of lead exposure now considered safe - or at least not
seriously damaging - may not be safe at all," said Dr. Deborah
Cory-Slechta of the University of Rochester in New York.
A leading expert on animal research into the hazards of lead,
Cory-Slechta has overseen multiple studies in rat colonies
demonstrating that low levels of the toxin can disrupt key
brain chemistry that controls inhibition, learning and
"We see it in rats, we see it in monkeys, and we see something
very much like it in children," Cory-Slechta said.
"There is a persistent tendency among lead-dosed organisms to
have problems of control, adaptability and discernment, even
at very low doses."
Level is key question
Just how low is the burning question that most research is
seeking to answer. Controversial in the first half of the
century, the contention that high lead doses can cause
irreparable injuries to children was firmly established by the
Until 1960, Baltimore averaged about 10 lead poisoning deaths
a year for decades, historical Health Department records show.
But improvements in early detection and treatment - and the
proximity of some of the world's most renowned medical centers
- now prevent most of lead's worst ravages.
Yet pediatricians and school officials note that subtle
behavioral effects persist long after poisoned children are
That's because even low doses of lead can cause a broad range
of functional problems, research has shown, including a loss
of self-control, shortened attention span and a host of
learning disorders that often cause lead-exposed children to
perform poorly in school and ultimately to drop out.
How it happens
What are not well understood are the precise biological
mechanisms or the minimum dosage at which lead exposure begins
to erode mental processes.
Among suspected causes are that lead inhibits the bodies of
growing children from absorbing iron, zinc and calcium,
minerals essential to proper brain and nerve development. It
disrupts the normal release of dopamine, a powerful neuro
chemical that controls an array of brain functions. And it
becomes lodged in bones and teeth, leaching into the
bloodstream for years.
"The fact that Kennedy Krieger has now seen actual physical
changes in the brain structure of rats is fairly novel, but
not surprising," Cory-Slechta said. "How that might affect
behavior or cognitive function is harder to say, except that
it's probably not good.
"It's also not much of a leap, based on what we know about the
common effects of lead exposure across species, to theorize
that it probably alters human brain structures as well. How -
and how much - is still the question."
In the Kennedy Krieger study, 17 nursing mother rats were fed
varying amounts of lead in their drinking water. Researchers
then sliced the brains of their offspring into thin sections.
Under microscopic examination, the area of the brain known as
the somatosensory cortex had shrunk in the lead-exposed rat
pups. This part of the rat's brain receives and translates
information from the animal's highly sensitive whiskers, their
primary sensory organ.
"We saw average reductions of 11 percent, and up to 16 percent
at higher levels of exposure," said Dr. Michael V. Johnston, a
pediatric neurologist involved in the study. "In layman's
terms, the rat's ability to comprehend his world has been
"We theorize that this would cause more confusion in the mind
of the rat - like static in the brain - with a whole range of
possible behavioral dysfunctions."
Dr. Gary W. Goldstein, a co-author of the study, noted that
the most severe stunting of growth seen in the rats' brains
occurred at exposure levels below the threshold at which
medical treatment is typically given to children.
"We're seeing some fairly pronounced effects at a level of 30
micrograms of lead per deciliter of blood, which isn't even
considered a treatment level right now," Goldstein said.
"That's comparable to what we see in approximately 5 percent
of the kids we treat, and that's cause for real concern."
Similar effect in monkeys
Dr. Nellie Laughlin, a senior scientist at the University of
Wisconsin Harlow Primate Laboratory, noted that the Krieger
rats' sensory functions were affected at about the same level
that monkeys in her lab begin to exhibit hearing loss.
"The disorganizing effect that they've shown in rat whiskers
could just as easily be appearing in other sensory functions
in other species," she said. "It is not hard to imagine that
eyesight, touch, hearing, smell or all the above could be
affected in other animals through a similar mechanism."
Perhaps even more troubling, the hearing loss in the
University of Wisconsin monkeys occurred more than 10 years
after they were exposed to lead in their infancy - placing
them doubly in jeopardy among their normal peers.
"We've been testing this group throughout their lives," she
said. "And they've always tended to be less successful within
the social structure. They play less, they grow up having
problems of social adaption, standing in the group.
"They tend not to be as successful in terms of their access to
food, their access to breeding opportunities ... at fighting,
predation and tool use. Obviously, these are all key behaviors
for animals operating in a hierarchical social structure.
"Basically, they have trouble competing."
These persistent long-term deficits are not unlike those seen
in children, researchers agree.
Impact on intelligence
In at least four studies conducted over the past two decades,
doctors in New Zealand, Australia, Cleveland and Boston have
tracked test scores on large groups of children exposed to low
or mild levels of lead at an early age.
"While the findings of this research have tended to be
controversial and have not been totally consistent ... when
the results from a number of studies are combined there is
evidence of a highly significant association between lead
levels and child intelligence," researchers at New Zealand's
Christchurch Hospital wrote in 1993.
In what is regarded as the most exhaustive of these studies,
the Christchurch doctors began with 1,265 children and
subjected them to a series of tests through their teen years.
That research revealed that "as lead levels increased there
was a tendency for tests scores to decline, for teacher
ratings to become less positive and for reports of
inattentive/restless behavior to increase."
Australian researchers looking at a group of 375 children in
the town of Port Pirie beginning in 1979 reported 13 years
later that IQ scores for the group declined by three points
for every 10-20 micrograms of lead exposure and persisted into
later childhood "even though blood lead concentrations ... had
These observations have been central for U.S. researchers
trying to estimate the benefits of expensive lead control
Three years ago, the U.S. Department of Housing and Urban
Development commissioned such an "econometric" study by ICF
Consulting of Fairfax, Va., as a prelude to strict new
regulations requiring the removal or repair of lead paint in
old federally funded or subsidized housing.
Set to begin in September, the program carries an estimated
price of $253 million in the first year alone.
But the ICF study predicted that the regulations would save as
much as $1.14 billion nationwide by cutting IQ deficits among
children exposed to lead paint in federal housing, improving
their ability to find and keep good-paying jobs in the future.
Criminal justice costs
Not included were the costs to the criminal justice system
associated with the increased tendency among lead-exposed
children toward aggression and violent crime in their later
"We know that lower IQ is associated with an increased
tendency toward criminality, not to mention teen pregnancy,"
said economist Rick Nevin.
"So it's reasonable to theorize that a reduction in lead
exposure would improve IQ and thereby bring reductions in both
these behaviors and further cost savings," he said.
Using historical data from the U.S. Bureau of Mines, Nevin
entered lead mining statistics into a computer model. Then, he
added crime and teen birth rate data from the FBI and the
National Center For Health Statistics.
To be sure that economic factors didn't skew his results, he
also compiled unemployment figures from the U.S. Department of
"In precisely the age groups affected, at almost every point
on the chart, we saw a startlingly consistent correlation
between lead consumption, the birth rate at the time, and the
rates of violent crime and teen pregnancy as these kids aged
into adulthood," said Nevin, who holds multiple degrees in
economics, math and management.
"I am sensitive enough to how astonishing this is that I've
devoted substantial amounts of time trying to explain the
results by other means, without much success."
Dr. Herbert L. Needleman of the University of Pittsburgh
Medical School, a pioneer in studies of the link between early
childhood lead poisoning and later aggressive behavior,
cautioned that such global studies are fraught with potential
"The biggest caveat you have to bear in mind with this kind of
broad historical study is that a lot of other things were in
play at the same time - an infinite number of major global
events - that could dramatically affect the outcome,"
"So studies of this kind can't possibly establish cause,
"What they can do rather well, when they're done right, is to
suggest avenues for further research. And I'd have to say this
one is very suggestive."