Cognitive functioning in lead workers

In a cross sectional study of occupational exposure to inorganic lead 91 men performed a series of microcomputer based tasks assessing sensor motor reaction time, memory, attention, verbal reasoning, and spatial processing. Performance on the tasks was studied in relation to three ranges of blood lead concentration (low, less than 20 micrograms/dl; medium, 21-40 micrograms/dl; and high, 41-80 micrograms/dl) and exposure response correlations for blood lead concentration, zinc protoporphyrin (ZPP) (range 7-210 micrograms/dl), and urinary aminolaevulinic acid (ALA) (range 0.5-22.0 mg/l). The results show that the high group were impaired on most of the tasks used and, in general, the magnitude of the impairment correlated better with blood lead concentration than ZPP or urinary ALA. An examination of the patterns of task impairment indicated a general slowing of sensory motor reaction time which was relatively independent of the nature of the cognitive functions being tested. There was some evidence, however, suggesting mild impairment of attention, verbal memory, and linguistic processing. In general, workers with high blood lead concentrations showed clear impairment of sensory motor functions in the absence of correspondingly strong evidence for impaired processing and memory functions. It is argued that a general slowness in responding may underlie many previous reports of widespread cognitive impairment in lead workers.