Electrophysiological study of subjects occupationally exposed to lead and with low levels of lead poisoning.

The relationship between the length of exposure to lead, blood lead level (PbB), and peripheral nerve damage in a population occupationally exposed to low lead levels was evaluated. Sixty-two foundry workers were studied whose length of exposure ranged from 5 months to 10 a; their mean PbB in the last 2 a had not exceeded 50 microgram/100 ml (2.4 mumol/l). The referents were 27 hospital employees, of comparable ages, not occupationally exposed to lead. The electrophysiological examination consisted of the determination of the motor conduction velocity (MCV) of the median, and peroneal nerves, sensory conduction velocity (SCV) of the median and sural nerves, and the latency of the T and H reflexes. The mean MCV, SCV and the amplitude of the sensory action potential (SAP) of the median nerve were significantly lower in the group of exposed workers than in the reference group. When the exposed subjects were divided into three groups according to length of exposure, no difference was observed between the three groups. When they were divided into different groups according to the maximum PbB (max PbB) value, the observed differences with respect to the reference groups were already present in those with a max PbB of less than 50 microgram/100 ml (less than 2.4 mumol/l), but were more evident in the subjects with a max PbB of greater than 70 microgram/100 ml (greater than 3.4 mumol/l). Within the group of subjects with a max PbB of 50-69 microgram/100 ml (2.4-3.3 mumol/l), the differences with respect to the reference values were more evident for subjects with a short length of exposure (less than 2 a). The MCV of the median nerve correlated with the time since the PbB exceeded 50 microgram/100 ml (2.4 mumol/l). In conclusion, the electrophysiological changes observed in lead-exposed subjects do not seem correlated with the length of exposure. Such alterations seem more evident in those subjects whose PbB has been greater than 70 microgram/100 ml (3.4 mumol/l) at least once during the preceding 2 a and in those subjects who, at the time of the neurophysiological examination, have a PbB greater than 50 microgram/100 ml (2.4 mumol/l). The apparently greater sensitivity to lead in new employees, compared to workers with a longer exposure time, remains to be clarified.