Lead toxicity: does the critical level of lead resulting in adverse effects differ between adults and children?

OBJECTIVES: The Scientific Committee on Neurotoxicology and Psychophysiology and the Scientific Committee on the Toxicology of Metals of the International Commission on Occupational Health in 2006 recommended that the standard for blood lead (BPb) levels be reduced to 30 microg/dl for industrial workers and 5 microg/dl for children. To examine whether the critical level of lead producing adverse effects truly differs between workers and children, we provided an overview of studies addressing the critical level of lead in workers, together with a perspective on lead toxicity in children.

DATA SOURCES AND EXTRACTION: In 25 reports published in English with keywords of "benchmark dose (BMD)," "lead" and "humans," only five studies proved to be relevant to lead toxicity. Four more studies with figures illustrating significant relationships between lead and neurotoxic outcomes were selected.

DATA SYNTHESIS: Based on data from previous reports using a BMD approach, the critical organ of lead in workers was thought to be the nervous system and the critical BPb level (number-weighted mean) was between 10.7 and 17.5 microg/dl. The neurotoxic effects of lead exposure at such levels seemed reversible. The BPb level at which lead-associated intellectual deficits occurred in children was as low as the critical level of BPb (below 5 microg/dl) for inhibited heme synthesis in workers.

CONCLUSIONS: The neurotoxic effects of lead in workers appear to be initiated at BPb levels below 18 microg/dl, which are somewhat higher than the critical level of lead neurotoxicity in children. Each national institute for risk management should take evidence-based preventive action against subclinical lead poisoning in workers, as well as in children.