Lead is ubiquitous in the environment in many parts of the world and many people are exposed to the pollutant in their everyday lives. There is lead in automotive fuels; water pipes contain lead; paints are often tinted with lead-based pigments. As Rose Hoban reports, this is a particular problem for children, whose developing neurological systems are profoundly affected by exposure to lead.
In the 1970s, some researchers at the University of Cincinnati, in Ohio, recruited close to 400 pregnant women who lived in poor areas of the city. They wanted to see what the effects of environmental lead were on their children.
They tested the levels of lead in the women's blood while they were pregnant. Then they followed the lead levels in their children for years after birth. Environmental health professor Kim Dietrich, one of those researchers, says they took a blood test from the children every three months, all the way up to five years of age.
"The blood lead concentration in these children is a good measure, particularly when you have repeat assessments of internal dose," he explains. "So it is, in other words, a surrogate for the amount of lead that the brain is being exposed to during early development."
Researchers know that children who have blood levels as low as 10 micrograms per deciliter have neurological problems. A child who simply ingests dust from lead based paint can accumulate this miniscule amount. But Dietrich says the level at which problems start can be lower, and there is still debate over how much lead is dangerous for children and what the long term effects of that exposure are.
"There have been studies coming out from our own group here that have shown effects of lead on neurodevelopment – on such things as IQ, attention deficit hyperactivity disorder, conduct disorder – at levels below even 5 micrograms per deciliter," he says. "And I'm not sure if it will ever be resolved, I'm not sure there is a safe level of lead exposure."
The children that Dietrich's colleagues recruited are now in their 20s. He says these young adults had behavioral problems throughout their adolescence. These problems were documented in earlier studies. He says they've found the children who had higher blood lead levels are more likely to engage in criminal and violent behavior now that they're adults. More than half had at least one arrest.
"It's further evidence that lead is affecting areas of the brain that are associated with emotional regulation, impulse control, judgment," he says. "And it confirms earlier observations that have been conducted on adolescents and older children and younger children that lead is associated with behavioral difficulties that would lead to a greater risk for engaging in, for example, delinquent behaviors and perhaps extending that into an adult criminal career."
Dietrich and his colleagues report their findings in a recent issue of the online journal PLoS Medicine.