Lead in blood. ICP-MS studies of lead in plasma, blood and erythrocyte proteins

Abstract: An inductively coupled plasma mass spectrometry (ICP-MS) method for the determination of lead in blood plasma has been developed. The detection limit was below 0.1 microgram/liter, and the precision 5%. There was no significant difference between levels in plasma and serum. Studies of individuals with varying lead exposure showed that in the general population the plasma concentrations were less than 1% of the levels in blood, and up to a few percent in highly lead-exposed individuals. There was a non-linear relationship between blood- and plasma-lead concentrations. The non-linearity could be described by a model based on high-affinity erythrocyte lead-binding proteins with a limited binding capacity. The association was relatively close, with an inter-individual variation in plasma lead of 30% relative standard deviation at a given blood-lead concentration. Neither age, sex, current lead exposure, nor the polymorphism in the delta-aminolevulinic acid dehydratase (ALAD) gene affected the distribution of lead between cells and plasma. Moreover, lead-binding erythrocyte proteins were studied by gel-chromatography with ICP-MS detection. The studies showed that the protein with the highest affinity for lead was ALAD. Together with a smaller protein, with an apparent molecular mass of 45 kDa, it bound more than half of the lead in the erythrocytes. There was also a small lead-binding component; the quantity of lead bound to it its not known. Lead in erythrocytes appeared not to be bound to hemoglobin.