A prospective study on early neurotoxic effects of lead.

A prospective follow-up study on new lead workers who entered a storage battery factory was carried out between 1975 and 1981. Nerve conduction velocities and psychological performance were recorded before the commencement of exposure and after one, two, and four years of work, respectively. Out of an initial number of 89 workers, 23 were available for the 1-year, 16 for the 2-year and 11 for the 4-year re-examination. The reference group comprised non-exposed workers of a cable manufacturing plant and an electrical power plant. Especially the sensory conduction velocities of the median nerve decreased during the 2-year follow-up. When divided into two groups according to the median Pb-B values (27-30 micrograms/100 ml), the higher exposure group showed slower values for several motor and sensory conduction velocities at the 1- and 2-year examination as compared with the lower group. Also visual intelligence and visuomotor functions had impaired significantly. The learning effect for some psychological tests which was clearly evident among the referents, was almost absent among the lead workers. After four years only 11 lead workers remained. This together with selection in the drop-out, resulted in that the group differences found for conduction velocities and psychological tests did not reach statistical significance anymore.