A multidisciplinary study of lead-exposed subjects. I. Delayed target detection P-300 latency, an electrophysiological parameter, correlates with urinary delta-ALA.

Visual event-related potentials, generated while performing a target detection (oddball) task, were successfully evaluated in 21 out of 34 individuals occupationally exposed to lead and 40 out of 56 nonexposed controls who were examined. The blood lead level of the lead-exposed subjects ranged from a mean of 29 to 53 micrograms Pb/dl blood in three exposed subgroups, while that of the control group was 7.7 micrograms Pb/dl blood. The latencies of the N2 and P300 components of the visual event-related potential were significantly longer in the lead-exposed subjects. Both the N2 and P300 latencies significantly correlated with the blood lead levels of the subjects. In addition, the P300 latency correlated with the concentration of delta-aminolevulinic acid (delta-ALA) in urine. This in part could be due to elevated delta-ALA levels interacting with gamma-aminobutyric acid (GABA) receptor neurons. The results indicate that lead affects mental function even at permitted levels of exposure. They strengthen the conclusion, based on biochemical and hematological assays, that the maximum permitted blood lead level of 50 micrograms Pb/dl blood is not safe and should be reduced.