Effects of lead, zinc and copper absorption on peripheral nerve conduction in metal workers

To examine the antagonistic effects of lead, zinc and copper on the nervous system in man, we measured maximal motor and sensory conduction velocities (MCV and SCV, respectively) in the distal radial and median nerves in 20 gun metal founders with asymptomatically increased absorption of these metals [blood lead concentrations ranged from 16 to 64 micrograms/dl (mean 42)]; and analyzed metal effects on nerve conduction by multiple regression analysis. The MCVs in the radial and median nerves and the SCV in the forearm segment of the median nerve were significantly slowed; indicators of lead absorption (urinary delta-aminolevulinic acid and coproporphyrin) were inversely correlated with the SCV in the radial nerve. The SCVs in the radial nerve and in the hand segment of the median nerve, which were not significantly slowed, were positively related to indicators of copper absorption (plasma or erythrocyte copper). The SCV in the radial nerve was also positively related to the indicator of zinc absorption (plasma zinc); similarly, the MCVs in the radial and median nerves were positively related to the indicators of zinc absorption (erythrocyte or urinary zinc). These findings suggest that copper and zinc antagonize the subclinical effects of lead on peripheral nerve conduction velocities; the conduction velocity in the distal radial nerve is sensitive not only to asymptomatic lead absorption but also to zinc and copper absorption.