Neurological and neurophysiological examinations of workers occupationally exposed to manganese

The nervous system is the major target of the toxic effect of manganese (Mn) and its compounds. Nowadays, neurological diagnostics is directed towards early detection of symptoms and abortive forms, and the cases of serious damage of the nervous system are no longer reported. The aim of the present study was to assess the effects of manganese on the functions of the nervous system in workers exposed to this metal in the ship and electrical industries. The study covered a selected group of 75 male workers (mean age 39.17 yr +/- 9.79; range 20-56 yr), including 62 welders and fitters, as well as 13 workers involved in the battery production. Their employment duration ranged between 1 and 41 yr (mean 17.5 yr +/- 10.81). During the welding process the air Mn concentrations varied from 0.004 to 2.67 mg/m3 (arithmetic mean, 0.399 mg/m3; geometric mean, 0.154 mg/m3; standard deviation, 0.586). Of the 62 workers, 30 worked in the area with exceeding MAC value of 0.3 mg/m3. At the battery production workposts, Mn concentrations fell within 0.086-1.164 mg/m3 (arithmetic mean, 0.338 mg/m3, geometric mean, 0.261 mg/m3; standard deviation, 0.292). The values of current Mn exposure in the study group fell within the range below 0.01 and 2.67 mg/m3 (arithmetic mean, 0.4 mg/m; geometric mean, 0.15 mg/m3). Of the 13 subjects, 6 worked at the Mn air concentration exceeding MAC values. In the exposed group, the values of cumulated exposure index ranged from 0.008 to 35.52 (arithmetic mean, 8.045; geometric mean, 4.615; standard deviation, 6.562). The control group consisted of 62 men non-occupationally exposed to Mn, matched by sex, age and work shift distribution. Clinically, the increased emotional irritability, dysmnesia, concentration difficulties, sleepiness and limb paresthesia predominated among the disorders of the nervous system functions in workers chronically exposed to manganese. Neither in the central nor in the peripheral nervous system, the objective examinations revealed organic lesions that could provide grounds for diagnosing toxic encephalopathy or polyneuropathy. Generalized and paroxysmal changes were the most common recordings in the abnormal electroencephalography. Visual evoked potentials examinations showed abnormalities in the response evoked, which could be a signal of the optic neuron disorders and their significant relationship with cumulated exposure. The results of the study demonstrate that Mn exposure within the range of <0.01-2.67 mg/m3 (arithmetic mean, 0.4 mg/m3; geometric mean, 0.15 mg/m3) induces subclinical effects on the nervous system.