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BALTIMORE — Children exposed to lead at levels now considered safe scored substantially lower on intelligence tests, according to researchers who suggest one in every 30 children in the United States suffers harmful effects from the metal. 

Children with a lead concentration of less than 10 micrograms per deciliter of blood scored an average of 11.1 points lower on the Stanford-Binet IQ test than the mean of children with a lead concentration of 1 microgram or less, the researchers found. The mean is the intermediate value between the lowest and highest scores. 

“There is no safe level of blood lead,” said Dr. Bruce Lanphear, lead author of the lead study presented Monday at the Pediatric Academic Societies annual meeting. 

Lanphear said newborns have lead in their blood because of its presence in their mothers, but children are most commonly exposed to lead by inhaling lead-paint dust or eating paint flakes.  

Lead-based paint was widely used in homes throughout the 1950s and 1960s until it 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 micrograms per deciliter. But the toxicity standard has been lowered over the years to the point where a concentration of 10 micrograms or less now is considered safe. 

The researchers said their work suggests that lead is a potent toxin at levels previously thought to be harmless. 

Experts predicted the study would prompt federal regulators to lower the acceptable blood-lead standard. 

“This is a wonderful study that has very serious implications for public health in the United States and the rest of the world,” said Dr. Daniel Courey, a pediatrics and developmental behavior professor at Columbus Children’s Hospital in Columbus, Ohio. 

Lanphear’s team tracked 276 children in Rochester, N.Y., from ages 6 months to 5 years, measuring blood lead levels every six months and administering the IQ test at age 5. 

The study also found an average 5.5-point decline in IQ for every additional 10-microgram increase in blood-lead concentration, said Lanphear, a physician at Children’s Hospital Medical Center in Cincinnati. 

The study adjusted for other predictors of lowered IQ such as the mother’s IQ, tobacco exposure and intellectual environment in the home, Lanphear said. 

Lanphear’s findings confirm what those who work with “lead kids” already know, said Ruth Ann Norton, executive director of the Baltimore-based Coalition to End Childhood Lead Poisoning. 

“There are kids who are disruptive, then there are ’lead kids’ — very disruptive, very low levels of concentration,” Norton said. 

Besides affecting reading and reasoning abilities, lead also is linked to hearing loss, speech delay, balance difficulties and violent tendencies, Norton said. 

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On the Net: 

EPA: http://www.epa.gov/lead 

CECLP: http://www.leadsafe.org