Evaluation of δ-aminolaevulinic acid in blood of workers exposed to lead

Exposure-effect and exposure-response relation between exposure to lead and δ-aminolaevulinic acid concentration in blood (ALA-B) were examined in 238 male workers exposed to lead. Concentrations of ALA-B ranged from 26 to 352 μg/l and lead concentrations in blood (Pb-B) from 7.1 to 86.0 μg/dl. Concentrations of ALA-B correlated closely with concentrations of Pb-B (r = 0.74), and increased ALA-B concentration occurred at Pb-B concentrations of around 30 μg/dl. Exposure-response curves indicated that the 50 percentile response doses were roughly 30, 40, and 50 μg/dl Pb-B when cut off points of ALA-B were set at 50, 60, and 70 μg/l respectively. The sensitivity and specificity of measurements of ALA-B concentrations for health screening were sufficiently high when the health based exposure limits of lead were set at 30-50 μg/dl. Moreover, a pronounced increase in ALA-B concentrations occurred when the inhibition rate of erythrocyte ALA dehydratase exceeded 85%. These findings suggest that ALA-B is a useful indicator for assessing the early effects of exposure to lead on haem biosynthesis.