A new study says homicides may be linked to high levels of lead in the air we breathe.
Criminologist Paul Stretesky looked at the murder rate between 1989 and 1991 for all 3,111 counties in the continental United States, and then he compared the number of homicides in each county to the amount of lead present in the air.
Cities with high lead levels, like Los Angeles, Detroit and Dallas, also had higher murder rates, he found. This held true even when other factors typically linked with violent crime -- such as poverty, the number of people in the "prime crime" years of 16 to 29, and low education levels -- were taken into account. While 34 percent of the counties didn't record a single homicide in 1990, large cities with high lead levels reported many.
Medical researchers have long known that high lead levels can cause hyperactivity, reduced IQ and impaired growth in children. Stretesky's research indicates that lead's legacy may last for years, predisposing some of its victims to increased aggression and violent crime.
"Poverty plays a huge role in crime and violence. I don't want to suggest they're not important," says Stretesky, an assistant professor of sociology at Colorado State University. "But the presence of lead in the air in these cities may be one of the reasons why poverty is related to crime."
Stretesky's study appears in this month's Archives of Pediatrics and Adolescent Medicine.
Lead is readily absorbed into the body through air and water and is particularly toxic to the developing brains and bodies of children under the age of 6. While lead in paint and gasoline has been banned in the United States for more than 20 years, the metal is still present in water pipes and in lead-based paint in older homes.
Lead also is found in dangerous concentrations around smelters, battery plants and factories that process lead. These factories may account for most of the lead present in the air today, Stretesky says.
An estimated 4.4 percent of American children carry dangerously high levels of lead in their blood, according to the U.S. Centers for Disease Control and Prevention. Many of those children live in poor neighborhoods and substandard housing, where lead levels in old paint are likely to be high.
Stretesky's study doesn't directly implicate lead as the cause of homicide, but the link between the two is strong, he believes.
"Reducing lead levels may be a crime-prevention strategy," Stretesky suggests. "It might work better than locking up people."
The recent drop in the violent crime rate, particularly among young adults, may be linked to a reduction in lead levels since the United States banned leaded gasoline in the 1980s, says Rick Nevin, vice president of ICF Consulting in Fairfax, Va. In a study published last year in Environmental Research, Nevin reported that the falling violent-crime rate may be related to the lead bans of the past two decades.
But not everyone is ready to jump on the lead-violence bandwagon.
Don Cherek, a professor of psychiatry at the University of Texas Health Science Center in Houston, says poverty is a stronger predictor of violence than heavy metal.
"It's well and good to get the lead out," Cherek cautions. "But doing so won't change the aggression level that much."
What To Do
While the debate over lead and violence will likely continue, some things are certain.
Parents should limit their children's exposure to lead as much as possible. Families living in pre-1978 homes should have a state-certified technician test the structures for lead. Because lead is found in soil around older homes or industrial sites, children should always wash their hands after playing outdoors. Parents of infants should avoid making formula from tap water because it may be laced with lead.