Lead levels up to 5 mcg/dl had no obvious effect on intellectual capacity or behavior, but lead levels between 5 mcg/dl and 10 mcg/dl were tied to 49 percent lower reading scores on standardized tests and 51 percent lower writing scores, Emond's group found.
Moreover, children whose lead levels were higher than 10 mcg/dl were about three times more likely to display antisocial behavior and hyperactivity, compared with children whose blood lead levels were between 0 mcg/dl and 2 mcg/dl.
Emond's team noted that effects of lead exposure are worse when children are very young, because lead is easily absorbed and young tissues are particularly vulnerable to damage. Once lead enters the body, it is stored in the bones and can stay there for up to 30 years, the team noted.
The World Health Organization estimates that half of all children under 5 living in cities and towns have blood lead levels above 10 mcg/dl, Emond's group pointed out. Based on their data, the researchers argue that the current threshold of 10 mcg/dl should be lowered to 5 mcg/dl.
"Lead poisoning is a continuing hazard, and should be considered in children presenting with behavioral or educational difficulties," the researchers wrote. "Early childhood exposure to lead affects later educational attainment and behavior, even at low blood levels, and the level of concern should be lowered to 5 [mcg/dl]," they concluded.
While exposure to lead in the United States has dropped significantly with the banning of lead in gasoline and lead-based paint, it still remains a big problem, Dietrich said.
In the United States, lead exposure continues to come from lead-based paint, Dietrich said. "This is still a huge problem," he said. The problem is particularly acute in inner cities among people living in housing built before 1960, he noted.
Lead from paint can be found in dust in the home and in the soil around the home, Dietrich sai
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