The effects of lead weigh heavy on the minds of people exposed to the metal during childhood. Two new studies of adults who lived in lead-contaminated housing as kids find that higher lead levels in the blood during childhood are associated with smaller brains and with an increased risk for violent criminal behavior.
“Lead has special status as a risk factor because we can prevent it,” comments David C. Bellinger, an epidemiologist at HarvardMedicalSchool in Boston and an expert in environmental and public health. Bellinger, who was not involved in the research, wrote a commentary on the studies that appears with the new research in the May 27 PLoS Medicine. “There are a lot of risk factors for these kids and lead was one among many. It’s hard to prevent poverty,” he says. “But with lead, we know the pathways to exposure and we can prevent it.”
Mothers of the studies’ participants were recruited from 1979 to 1984 from neighborhoods in Cincinnati with a lot of old, lead-contaminated houses and historically high rates of childhood lead poisoning. Blood lead levels were measured in the pregnant moms and then, after they were born, in the children at several intervals until they were at least 6 years old. Of the children, now 19 to 24 years old, 250 participated in the study examining the association with criminal behavior and 157 participated in the brain imaging study.
MRI scans of the young adults’ brains revealed that the more lead they were exposed to as children, the smaller their adult brains were, the researchers report. The anterior cingulate cortex — a brain region associated with mood regulation, decision making and impulse control — was particularly affected, says Kim Dietrich, of the University of Cincinnati College of Medicine’s epidemiology and biostatistics division. Male brains were significantly more affected than female brains, he notes.
Childhood lead exposure has been linked to lower IQ scores and attention and hyperactivity problems, but the brain-imaging work is the first to look beyond performance to how lead affects the underlying neural substrate, Bellinger says. The studies “are red flags,” he says.
The second study looked at current arrest records and compared them with childhood levels of lead in the blood. Total arrests and arrests for violent crimes increased with each 5 micrograms per deciliter increase in blood lead level, the researchers report.
“This is a real problem for this generation,” Dietrich says. “We’re not doing a very good job right now for these kids.”
Dietrich notes that the average childhood blood lead level in the brain imaging study was about 13 μg/dl (almost everyone has background levels of 1 to 2 μg/dl). The Centers for Disease Control and Prevention “action level” for lead — the blood level that is supposed to prompt an investigation of environmental exposure — is 10 μg/dl.
“Ten is no bright line,” he says. “The real problems remain where there is still lead paint in older homes. We’re not doing a particularly good job screening, and we’re not following up,” he says.
The good news, says Bellinger, is that levels of lead in the blood have gone down a lot since the early 1980s. CDC surveillance data show that by 2006, only 2.3 percent of children in Ohio had blood lead levels of more than 10 μg/dl.
“Lead is difficult,” says Bellinger. “People refer to it as a multimedia pollutant because there are so many ways that people get exposed. There’s gasoline, paint, fallout in air. It gets into the soil and tracked into homes. It’s in interior paint, which deteriorates and gets into dust. It was used in can solder. There are lead pipes, and even when pipes are replaced with copper, it’s often in the solder for those pipes. It’s a ubiquitous and useful metal — I suppose that’s why it is still around.”