Lead in Plasma and Whole Blood from Lead-Exposed Children

In 31 children exposed to lead and 13 considerably less exposed children (“unexposed”), the plasma (Pb-P) concentrations ranged from 0.46 to 18.4 (median, 2.4) and from 0.14 to 0.38 (median, 0.21) μg/L, respectively. Corresponding whole-blood concentrations (Pb-B) were 99–920 (median, 370) and 39–120 (median, 66) μg/L, respectively. The relation between Pb-B and Pb-P was nonlinear; when Pb-P rose, the Pb-B increased relatively less. There was a close association between Pb-B and log Pb-P (r=0.95;P=0.0001). When these data were compared to previous data on adults, there was no major difference between children and adults in the Pb-B/Pb-P relation. Free erythrocyte protoporphyrins in blood were associated with Pb-P (r=0.75;P=0.0001) and Pb-B (r=0.90;P=0.0001). Also, there was an association between blood–hemoglobin concentration and Pb-P in both exposed (r=−0.67;P=0.0001) and unexposed (r=−0.67;P=0.01) children; the corresponding figures for Pb-B werer=−0.42;P=0.02, andr=−0.80;P=0.001, respectively. Thus, at least with regard to toxicity on hematopoiesis at high lead levels, Pb-P may be a more relevant indicator of exposure and risk than Pb-B. Because the curved Pb-B/Pb-P relation indicates a saturation of binding sites for lead in red cells, exposure and risk at high lead levels may easily be underestimated from Pb-B data.