Neuropsychological function in manganese alloy plant workers

Objectives The objective was to investigate potential nervous system effects of manganese (Mn) exposure in workers employed in manganese-alloy-producing plants.Methods One hundred male Mn alloy plant workers were compared with 100 age-matched referents. The subjects were examined with a comprehensive neuropsychological test battery. Exposure was assessed by measurement of Mn concentrations in the workroom air, blood and urine.Results The geometric mean (GM) concentration of inhalable Mn in workroom air was 301 g/m³. The GM concentration of Mn in whole blood (181 nmol/l vs 160 nmol/l) (P=0.002) and urine (0.9 nmol/mmol creatinine vs 0.4 nmol/mmol creatinine) (P<0.001) was higher among the exposed subjects than among the referents. The Mn-exposed subjects had increased postural tremor while conducting a visually guided tremor test (static steadiness test) compared with the referents (mean number of contacts 94 vs 59 (P= 0.001); duration of contacts (in seconds) 5.1 vs 3.5 (P=0.003)). The tremor had larger frequency dispersion, indicating that the tremor included a wider variety of frequencies, among the exposed subjects than among the referents, assessed by the TREMOR test system. Smoking habits (self-reported) influenced the tremor parameters significantly, the Mn-exposed smokers having more tremor than the non-smoking Mn-exposed subjects. No differences between the groups were found in tests for cognitive functions, reaction time or in symptom reporting.Conclusion The Mn-exposed subjects had increased hand tremor compared with their referents. The tremor was related to exposure parameters. Smoking habits (self-reported) influenced the tremor parameters.