Indicators Of Lead Absorption Research Articles

Assessment of Central, Peripheral, and Autonomic Nervous System Functions in Lead Workers: Neuroelectrophysiological Studies

To assess the effects of lead on central, peripheral, and autonomic nervous systems, the visual-, short-latency somatosensory-, and brainstem auditory-evoked potentials (VEP, SSEP, and BAEP), event-related potential (P300), distribution of nerve conduction velocities (DCV), and electrocardiographic R–R interval variability (CV RR), together with conventional median and radial nerve conduction velocities (NCV), were measured in the lead workers. The lead workers consisted of 22 gun metal foundry workers occupationally exposed to lead, zinc, and copper. In the lead workers with blood lead concentrations below 65 μg/dI, the latencies of the VEP (from the retina to the visual cortex), SSEP (from the brachial plexus to the brainstem). and P300 (which reflects cognitive function) were significantly prolonged when compared with the sex- and age-matched controls. All these latencies and the BAEP latencies (from the cochlear nerve to the brainstem) were significantly correlated with the indicators of lead absorption among these workers. The CV RR (especially, a component of parasympathetic activity) was significantly depressed in the lead workers. The slower (V10) velocity of the DCV, the motor, and sensory NCVs were also significantly slowed. These findings suggest that lead affects not only peripheral nerve but also the central and autonomic nervous functions at a subclinical level; zinc may antagonize the neurotoxic effects of lead.

Radial and Median Nerve Conduction Velocities in Workers Exposed to Lead, Copper, and Zinc: A Follow-Up Study for 2 Years

To evaluate the interactive effects of lead, zinc, and copper on the peripheral nervous system in man, we measured maximal motor and sensory conduction velocities (MCV and SCV) in the distal radial and median nerves in 19 gun metal foundry workers with asymptomatic increased absorption of these metals twice at a 12-month interval. The workers" initial blood lead (BPb) concentrations ranged from 16 to 64 (mean, 42) μg/dl. The principal findings in the present study indicated that (1) radial and median nerve conduction velocities were significantly slowed in the gun metal foundry workers; (2) indicators of lead absorption were inversely related to radial nerve conduction velocities, whereas indicators of copper and zinc absorption were positively correlated with the radial and median nerve conduction velocities; and (3) yearly changes in MCV in the radial nerve and in SCV in the median nerve were positively correlated with the changes in indicators of copper and zinc absorption. These findings suggest that zinc and copper antagonize the subclinical neurologic effects of lead. Also, the radial and median nerve conduction velocities provide important indicators of subclinical lead toxicity.

Auditory event-related potential (P300) in relation to peripheral nerve conduction in workers exposed to lead, zinc, and copper: effects of lead on cognitive function and central nervous system.

By measuring auditory event-related potential (P300 and N100) and peripheral nerve conduction velocities, the subclinical effects of lead, zinc, and copper on the central and peripheral nervous system were examined in 22 male gun metal foundry workers exposed to these metals. Their blood lead (BPb) concentrations ranged from 12 to 59 micrograms/dl (median 30). Control subjects were 14 healthy workers, employed at the same factory, who had never been occupationally exposed to these metals. In the gun metal foundry workers, the latencies of P300 and N100 were significantly prolonged; the latency of P300 was significantly correlated with BPb concentrations and other indicators of lead absorption. Similarly, the maximal motor and sensory conduction velocities in the radial and median nerves were significantly slowed, and were significantly correlated with indicators of lead absorption. The data suggest that lead exposure at low levels affects cognitive and central auditory nervous system function together with peripheral nerve conduction.

Short term prospective study of cognitive functioning in lead workers.

In a short term prospective study 70 male lead workers performed a series of cognitive tasks on three occasions during an eight month period. Concurrently with the cognitive testing, the concentrations of blood lead, zinc protoporphyrin (ZPP) and urinary aminolaevulinic acid (ALA) were measured. Indicators of lead absorption were stable during the study and each subject was allocated to either a low (below 20 micrograms/dl), medium (21-40 micrograms/dl), or high (41-80 micrograms/dl) group on the basis of their average blood lead concentrations. Performance deficits tended to be restricted to the high lead group and, in general, neither practice nor continued exposure during the study altered the magnitude of these deficits. The main deficit was a slowing of sensory motor reaction time, which was seen most clearly when the cognitive demands of the task were low. In the cognitively simple five choice task, blood lead concentration correlated with impaired decision making, response execution, and "lapses in concentration." In the other cognitive tasks the high blood lead group tended also to be slower by a factor of about 1.08 but the dominance of cognitive over sensory motor demands attenuated the exposure-performance correlations. The high lead group also had difficulty in recalling nouns poorly related to the focus of an earlier semantic classification task. This difficulty increased over time and was one of the few findings that correlated with all measures of lead absorption. It is concluded that the primary psychological profile of lead impairment is one of sensory motor slowing coupled with difficulties in remembering incidental information.

Central and peripheral nervous system dysfunction in workers exposed to lead, zinc and copper. A follow-up study of visual and somatosensory evoked potentials.

To evaluate the effects of lead, zinc and copper in the causation of physiological changes in the central and peripheral nervous systems, we measured the latencies of pattern-reversal, visually-evoked potential (VEP) and of short-latency, somatosensory-evoked potential (SSEP) twice at a 12-month interval in nineteen gun metal founders exposed to lead, zinc and copper. The workers' initial blood-lead (BPb) concentrations ranged from 16 to 64 (mean 42) micrograms/dl. BPb and plasma zinc and copper concentrations decreased significantly during the study period owing to the improvement in working environments. In the first examinations, we found that the N2 latency of VEP (conduction time from the retina to the visual cortex) and the N9-N13 latency of SSEP (conduction from the brachial plexus to the medulla oblongata) were both significantly prolonged in exposed workers. In the second examination, the N2 latency had returned to the "normal" level. These changes were correlated positively with changes in the indicators of lead absorption and inversely with changes in the indices of zinc and copper absorption. In the first examination, the N9 latency of SSEP (median nerve conduction) was also found to be significantly prolonged. This change also returned to normal over the study period in proportion to the reduction in BPb and the increase in intra-erythrocytic enzyme delta-aminolevulinic acid dehydratase activity. On the other hand, no significant prolongation of the N13-N20 latency of SSEP (central nerve conduction) was found in either of the two examinations; this latency and alteration over the study period were inversely correlated with the indicators of zinc and copper absorption. These data suggest that lead interferes with both peripheral and central nerve conduction. zinc and copper appear to antagonize strongly the lead-induced conduction delay in the upper central nervous system, but only weakly in the lower central and peripheral nervous systems.

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.

Psychological performance in relation to central and peripheral nerve conduction in workers exposed to lead, zinc, and copper.

Psychological performance was examined in relation to central and peripheral nerve conduction by means of the Wechsler Adult Intelligence Scale test, short-latency somatosensory-evoked potential (SSEP), and median nerve conduction velocity in 19 male gun-metal foundry workers exposed to lead, zinc, and copper. (Their blood lead concentrations--ie, 16-64 micrograms/dl with a mean of 42--and plasma zinc and copper concentrations were significantly higher than those of control subjects). In these workers, the score of picture completion (psychological performance) was significantly low; indicators of lead absorption, but no indicators of zinc and copper absorption, were significantly correlated with this score. The score of picture completion was significantly correlated with the N11-N13 latency of SSEP (conduction time in the spinobulbar region) in the workers; their N11-N13 latency, together with the N9 and N9-N11 latencies, was significantly prolonged and was significantly correlated with indicators of lead absorption. Furthermore, their maximal motor and sensory conduction velocities of the median nerve were significantly slowed. It is concluded that both psychological performance and central and peripheral nerve conduction may be impaired in lead-exposed workers with BPb's below approximately 60 micrograms/dl.

Effects of low-level lead and arsenic exposure on copper smelter workers.

An analysis of reported symptoms and their relationship with indicators of lead absorption--blood lead (Pb-B) and zinc protoporphyrin (ZPP)--and of arsenic absorption--urinary arsenic (As-U)--was undertaken among 680 active copper smelter workers. Lead and arsenic absorption in the copper smelter employees were characterized by the median values of 30.4 micrograms/dl for Pb-B, 41.5 micrograms/dl for ZPP, and 26 micrograms/L for As-U. Blood lead was 40 micrograms/dl or higher in 16.7% of cases, ZPP was 50 micrograms/dl or higher in 31.2%, and urinary arsenic was 50 micrograms/L or higher in 16.4% of currently active copper smelter workers. The number of reported symptoms (from a total of 14 symptoms) increased with ZPP levels; the relationship with Pb-B was less marked. Arsenic contributed relatively little. Mean Pb-B, ZPP, and As-U levels for subjects reporting each of the 14 symptoms were compared with those of subjects who did not report the symptoms. Mean Pb-B was found to differ significantly for one symptom, fatigue. Significant differences in mean ZPP levels were found for fatigue, sleep disturbances, weakness, paresthesia, and joint pain. Prevalence rates for these symptoms rose more markedly with increasing ZPP than with Pb-B levels. The results indicate a relationship between certain CNS and musculo-skeletal symptoms and increased lead absorption in this population. Adherence to exposure standards that preclude undue lead absorption and appropriate biological monitoring including ZPP levels, are necessary to prevent adverse, especially long-term, health effects.

Zinc protoporphyrin, blood lead and clinical symptoms in two occupational groups with low-level exposure to lead.

The results of cross-sectional clinical field surveys of 45 cable manufacturing workers and 90 telephone cable splicers are presented. Despite the rare occurrence of clinically overt lead poisoning among these occupational groups, high prevalence of lead-associated central nervous system symptoms and gastrointestinal symptoms was found. Hierarchical log-linear models for multidimensional contingency tables were fitted to those data and indicate that there is a partial correlation between reported symptoms and zinc protoporphyrin: individuals with high zinc protoporphyrin levels were more likely to report symptoms than those with low levels. No significant partial association was found between symptoms and blood lead. Because of the intermittent lead exposure encountered in one of the populations, individuals were identified with "normal" blood lead levels associated with "elevated" zinc protoporphyrin concentrations, thus indicating the difference in the biological significance between indicators of lead absorption (blood lead) and of biological response tests (ZPP). Suggestion is made that both types of diagnostic tests be utilized in the medical surveillance of lead-exposed workers.

Behavioral indicators of lead neurotoxicity: Results of a clinical field survey

Central nervous system dysfunction in workers occupationally exposed to lead was investigated by means of performance tests. The test scores of lead-exposed workers were compared with those of control groups (steel workers, papermill workers and farmers). It was found that secondary lead smelter workers showed significantly poorer performance scores than the nonexposed, control groups. The group differences between steel workers and lead workers in test scores were not attributable to differences in age or education. In the lead-exposed workers correlations between test scores and indicators of lead absorption (particularly blood lead and zinc protophyrin levels) were analyzed. Increases in zinc protoporphyrin levels were found to be highly correlated with decreases in test scores. Lower performance test scores were consistent with a sizeable prevalence of central nervous system symptoms among secondary lead smelter workers. Moreover, lead workers without central nervous system symptoms also showed decrements in performance test scores which were also correlated with elevated zinc protoporphyrin levels. The data indicate that certain behavioral tests might be important tools for studying subclinical central nervous system dysfunction due to lead toxicity; significant correlations between zinc protoporphyrin levels and behavioral test scores are considered to be consistent with an etiologic relationship between decrement in performance scores and lead effects on the central nervous system.