Decrements in cognitive performance in metal inert gas welders exposed to aluminium

Often little has been discovered of the cognitive functions affected by occupational toxins because many functions cooperate to produce the single performance scores typically reported from neuropsychological tests. To facilitate the interpretation of neuropsychological scores, the issue of occupational exposure to aluminium was examined with an approach intended to increase understanding of those cognitive processes that may be affected.

The investigation was a cross sectional study of asymptomatic aluminium welders and a reference group of mild steel welders. Based on urinary aluminium concentrations, welders were classified into a reference (n = 28), low (n = 27), and high (n = 24) exposure group. The mean urinary aluminium concentrations were 0.46, 2.25, and 9.98 mumol/l, respectively. A comprehensive neuropsychological examination was undertaken to assess psychomotor function, simple visual reaction time, attention related tasks, verbal and visual or visuospatial abilities as well as verbal and visual learning and memory.

Aluminium welders showed no impairment on the finger tapping, Santa Ana dexterity, simple visual reaction times, any of the verbal memory tasks, the similarities subtest of Wechsler adult intelligence scale, or the Stroop task. However, the low exposed group performed poorer on the memory for designs and on more difficult block design items demanding preliminary visuospatial analysis. The time limited synonym task, embedded figures, digit symbol speed, and the backward counting component of the divided attention task showed exposure-response relations.

The impairments found were circumscribed. When the neuropsychological tasks were scored to show some of the underlying theoretical cognitive structures, the results indicated that performance difficulties were mainly detected in tasks requiring working memory, particularly that relating to processing of visuospatial information. There was also evidence that such impairments are more readily found in time limited tasks involving visually presented material, in which effective visual scanning combined with control of working memory is demanded.