After adjusting for potential confounding factors, he found that an increase in childhood blood lead level of 5 micrograms per deciliter increased the rate of arrests for violent crime by about 30 percent, though the numbers varied depending on lead levels from which ages were considered. The advised action level for children set by the Centers for Disease Control is 10 micrograms per deciliter of lead, although many researchers believe that level is too high, and should be changed to at least five. "We know there are detectable and long-lasting effects for levels that go down to 2," said Ronnie Levin of the U.S. EPA, who published a review of children's lead exposures last week in Environmental Health Perspectives. Wolpaw Reyes agreed. "There is absolutely no evidence of any threshold below which lead is safe," she added. The Cincinnati team also used magnetic resonance imaging scans to compare the volume of brain regions in 157 members of the study group with a standardized brain image. Those with higher childhood lead exposure showed decreased volume in parts of the prefrontal cortex associated with judgment, reasoning, mood regulation and some components of attention, said Kim Cecil, a collaborator of Dietrich's, who lead the brain study. "The more the childhood blood level, the greater the loss was," Cecil said. The new studies help address criticisms of earlier research that the behavioral problems associated with lead exposure could be explained by differences in child rearing or socioeconomic factors that might vary together with lead exposure. "It's showing that independent of social factors, there's a biological basis," Cecil said. "When we started following this cohort in earnest in 1980, I never expected to see anything like this. I don't think anyone else did, either," Dietrich said. "It doesn't give me great pleasure in reporting these results." "We need to think about lead as a very powerful drug, in a way that even at low doses can have a major effect on brain function," he added. Although lead levels in children have declined dramatically since lead was phased out in gasoline, "That public health benefit has not been appreciated as much by children in the inner city that continue to be at risk of lead exposure," Dietrich said. Half of these children are not even screened for lead exposure as required by law, he said. "We need to be doing a better job." Related Links: Jessica Marshall's blog: EnvironMental Case |
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