Early neurotoxic effects of occupational lead exposure: a prospective study.

A prospective follow-up study focusing on workers who entered a battery factory was started in 1975. Out of an initial number of 89 workers, 23 were available for the 1-yr, 15 for the 2-yr and 10 for the 4-yr re-examination. From an initially larger non-exposed reference group (N = 34), 23 were matched with respect to age, sex, and initial nerve conduction velocities and similarly followed. In the exposed group especially the sensory conduction velocities of the median nerve decreased during the 2-yr follow-up. Some increase in the motor distal latency of the median nerve was also noted. When the lead workers were divided into two groups according to the median Pb-B value (30 micrograms/100 ml), several motor and sensory conduction velocities were significantly slower in the lead group with the higher Pb-B levels in the 1- and 2-yr follow-up examinations as compared with those with the lower levels. Those workers whose Pb-B level hd quickly risen to over 30 micrograms/100 ml quit after one or two years. Those who continued in the battery plant for up to four years had a slower initial rise in their Pb-B levels, which rarely exceeded 30 micrograms/100 ml; this group showed no significant differences in their conduction velocities in the 4-yr re-examination in comparison with the reference group.