In recent decades the federal government has gradually reduced the threshold for acceptable blood lead levels from 60 micrograms to 10 micrograms per deciliter. However, a new study concludes that even lead levels below the 10- microgram threshold can have adverse effects on children's intelligence.
Bruce Lanphear and colleagues pooled data from seven large-scale studies in four different countries, involving more than 1,300 children, and analyzed the effects of increasing levels of lead on full-scale IQ. After adjusting for a variety of socioeconomic variables, the researchers found reductions in IQ as lead levels rose, both in children with levels considered toxic and in children with levels considered safe.
In fact, the researchers say, in accord with previous research (see related article, Crime Times, 2001, Vol. 7, No. 3, Page 2), the declines they saw in IQs as lead level rose were steeper in children with lower lead levels. Overall, the researchers found that IQ decreased 6.9 points as lead levels rose from 2.4 (the lowest level in their sampling) to 30 micrograms per deciliter. Breaking their numbers down into dose-level increments, the researchers discovered that there was a 3.9-point drop as levels rose from 2.4 to 10 micrograms; an additional 1.9-point drop as lead levels rose from 10 to 20 micrograms; and a 1.1-point drop as lead levels rose from 20 to 30 micrograms.
The researchers also found that current blood lead levels, or average lifetime estimates of lead exposure, were better predictors of lead-linked IQ deficits than were early childhood blood lead levels. "The stronger effects of concurrent and lifetime measures of lead exposure may be due to chronicity of exposure," they say.
The researchers conclude, "Although blood lead concentrations less than 10 micrograms per deciliter in children are often considered 'normal,' contemporary blood lead levels in children are considerably higher than those found in preindustrial humans. Moreover, existing data indicate that there is no evidence of a threshold for the adverse consequences of lead exposure." They note that these adverse effects include learning problems and delinquency. "Collectively," they say, "these data provide sufficient evidence to eliminate childhood lead exposure by banning all nonessential uses of lead and further reducing the allowable levels of lead in air emissions, house dust, soil, water, and consumer products."
"Low-level environmental lead exposure and children's intellectual function: an international pooled analysis," Bruce P. Lanphear et al., Environmental Health Perspectives, Vol. 113, No. 7, July 2005 (online). Address: Bruce P. Lanphear, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Mail Location 7035, Cincinnati, OH 45229-3039, firstname.lastname@example.org.