At exposures far lower than the limit deemed acceptable by the U.S. government, lead can damage a young child's ability to learn and reason, researchers report this week. Moreover, a small increase in lead concentration exerts a more potent effect on the child's IQ when the blood shows a low lead concentration than when the concentration is high.
"This is a bombshell," says study leader Bruce P. Lanphear. When combined with an earlier analysis by his team, the new results indicate there is "no threshold for the adverse effects of lead on cognition," he says. An epidemiologist at Children's Hospital Medical Center in Cincinnati, Lanphear unveiled the findings Monday in Baltimore at the Pediatric Academic Societies' annual meeting.
Lanphear and his coworkers tested blood concentrations of lead in 276 children from infancy. When the children reached age 5, the team administered a standard IQ test. The researchers found a decreasing trend in IQ in 5-year-olds' whose blood l