Lead is a potent poison that adversely affects organs throughout the body. Recent studies have shown that higher levels not only reduce intelligence and slow development, but also can lead to behavioral problems, juvenile delinquency and even criminality.
As these studies have appeared, guidelines for exposure have continued to be lowered.
In the 1960s, doctors diagnosed lead poisoning if blood levels were above 60 micrograms per deciliter (mcg/dl), high enough to cause abdominal spasms, kidney injury and severe brain damage.
After studies in the 1980s and 1990s revealed that lower levels still damaged children's ability to think, concentrate and hear, the Centers for Disease Control and Prevention continued to reduce the allowable level -- to 30 mcg/dl in 1975, 25 mcg/dl in 1985 and to the current level of 10 mcg/dl in 1991. The last figure corresponds to about 100 parts per billion. In 1976, when lead was removed from gasoline, the average lead level in children was about 15 mcg/dl.
Today, the average is about 3. "But that's still 10 to 100 times higher than the level in preindustrial humans," said Dr. Bruce Lanphear of the Cincinnati Children's Hospital Medical Center, another study leader. "Three mcg/dl is low by current standards, but from an evolutionary perspective, it is quite high."
Canfield and Lanphear's team studied 172 children in the Rochester, N.Y., area, measuring blood lead levels at ages 6, 12, 18, 24, 36, 48 and 60 months. The children were tested for IQ at 3 and 5 years of age.
They found that a rise in lead levels from 1 mcg/dl to 10 was associated with a 7.4-point drop in IQ. An increase in lead levels from 10 to 30 mcg/dl was associated with an additional drop of only about two to three points, in line with previous studies.
"This really changes the way we think about childhood lead exposure," Lanphear said. "We have to start thinking about how we might identify hazards and reduce them before children are exposed." A 1991 study showed that lead abatement in old houses would cost about $32 billion, but would bring benefits in such areas as special education of more than $60 billion.
In the second study, EPA researchers found that a blood level of 3 mcg/dl was associated with a delay in the onset of puberty of four to six months in African American and Latina girls.
*
(BEGIN TEXT OF INFOBOX)
Childhood lead exposure
