Impact of air pollution by lead on the heme biosynthetic pathway in school-age children.

Blood-lead level (Pb-B), erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity, free erythrocyte porphyrin (FEP) concentration, delta-aminolevulinic acid concentration in urine (ALAU), hematocrit value, and hemoglobin concentration were compared for groups of children 10-13 years old from areas differently polluted by lead (rural area and lead smelter area). The biological responses of the children were also compared with those observed in adults similarly exposed to lead (Pb-B: 10-40 mug/100 ml). Compared with the rural children, children living less than 1 km from the smelter exhibited a significant increase of Pb-B and FEP, a significant inhibition of ALAD, and a slight positive correlation of ALAU with Pb-B; however, they showed no biological signs of anemia. In children living approximately 1.5 km from the smelter, there was still a significant increase of Pb-B and a concomitant inhibition of ALAD, but no change in FEP concentration. Comparison of the dose-response curves between Pb-B and FEP in adult males, adult females, and children indicates that the sensitivity to lead is in the order of children larger than or equal to women greater than men. Based on the FEP response, it is proposed that 25 mug Pb/100 ml blood be regarded as the maximum biologically allowable concentration of lead in blood of school-age children.