updated 5:52 p.m. ET, Thurs., Sept . 17, 2009
NEW YORK - Blood lead concentrations well below the accepted "safe" level harm youngster's intellectual and emotional development, a study released Thursday revealed.
Researchers from University of Bristol in the UK measured blood lead levels in 488 youngsters at age 2 and a half and linked these levels to scores on standardized assessment tests at age 7 to 8.
There was a clear link between blood lead levels in early childhood and academic performance by the ages of 7 and 8, the researchers report in the Archives of Disease in Childhood.
Children with blood lead levels between 2 and 5 micrograms per deciliter performed significantly better on standardized tests than those with blood lead levels above 5 micrograms per deciliter, they found.
Blood lead levels between 5 and 10 micrograms per deciliter were associated with significantly poorer scores for reading (49 percent lower) and writing (51 percent lower). A doubling of the blood lead level from 5 to 10 micrograms was associated with a 0.3 point fall in standardized test scores.
Currently, the internationally accepted "safe" threshold of blood lead is 10 micrograms per deciliter, but Dr. Alan Emond, who led the current study, is now calling for this figure to be halved to just 5 micrograms per deciliter based on his team's findings.
"Exposure to lead early in childhood has effects on subsequent educational attainment, even at low blood levels (5 to 10 micrograms per deciliter)," he noted in an email to Reuters Health. "Our results suggest that the threshold for clinical concern should be reduced to 5 micrograms per deciliter."
The researchers also talked to teachers as part of their research and found that children with blood lead levels above 10 micrograms per deciliter were nearly three times as likely to show hyperactivity and anti-social behavior as children whose blood lead levels were between 0 and 2 micrograms per deciliter.
Exposure to lead is especially risky for children, Emond noted, because lead is more easily absorbed by their growing bodies and because their tissues are especially sensitive to damage.
The chief sources of environmental lead include water supplies (lead pipes), old lead paint and soil. Blood lead levels appear to peak between the ages of 2 and 3 years — the ages when toddlers tend to put most items (including toys) in their mouths.
"While adults absorb around 10 to 15 percent of an ingested quantity of lead, this amount can increase to 50 percent in infants and young children. This lead is then absorbed into the bone where it can remain for up to 30 years," Emond said.
"Lead gets incorporated into the bones and is gradually released into the blood and circulates throughout the body. It interferes with enzymes and affects many systems — including the central nervous system," he added.
To reduce lead content in the environment, old pipes should be replaced, as should old, flaky paint, Emond said. "Any toys used in the garden, such as buggies and bikes that come into contact with soil, should be washed regularly," he added.