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children, in the us, exposed to lead at levels now deemed safe in the us scored substantially lower on intelligence tests, according to researchers who suggest that one in every 30 children in the us suffers harmful effects from the metal.
Children with lead concentration of less than 10 microgrammes per deciliter of blood scored an average of 11.1 points lower on the iq test than the mean of children with a lead concentration of one microgramme or less, the researchers found.
"There is no safe level of blood lead," said Bruce Lanphear, lead author of the study.
Lanphear said, while newborns are passed on lead contamination by the mothers, children are most commonly exposed to lead by inhaling lead-paint dust or eating paint flakes. Lead-based paint was widely used in homes inthe us throughout the 1950s and 1960s until its use was banned in 1978.
At high levels, lead can cause kidney damage, seizures, coma and death.
Before 1970, scientists believed lead poisoning took effect at 60 microgrammes per deciliter. But the toxicity standard has been lowered over the years to the point where a concentration of 10 microgrammes or less now is considered safe by experts in the us .
But this recent tests suggest that lead is a potent chemical at levels previously thought to be harmless. Lanphear's team tracked 276 children in Rochester, New York, from ages six months to five years, measuring blood lead levels every six months and administering the iq test at age 5 says an Associate Press report dated April 30, 2001.
The study also found an average 5.5-point decline in iq for every additional 10-microgramme increase in blood-lead concentration, said Lanphear. The study adjusted for other predictors of lowered iq, such as the mother's iq , tobacco exposure and intellectual environment in the home.