Subclinical neurophysiological effects of manganese in welding workers

High-level occupational manganese (Mn) exposure has been reported to induce irreversible brain alterations determining a Parkinson-like disease. This study aimed to assess subclinical neurophysiological alterations in welding workers. They were employed in a machine building factory with an average Mn exposure <200 mg/m3. Sixty-eight workers (mean age: 34 years; mean Mn exposure duration: 16 years) and 42 flour factory workers (control group) with similar age and smoking habit were recruited. Autonomic nervous function test battery (ANSFT), composed of Valsalva maneuvre-induced heart rate variation (HR-V), heart rate variation following deep breathing (HR-DB) and heart rate variation following immediate standing up (HR-IS) was assessed. Electroencephalogram (EEG), brain electricity activity mapping (BEAM) were also performed. HR-V, HR-DB, and HR-IS were significantly lower in Mn-exposed subjects showing altered autonomic nervous system activity, parasympathetic-sympathetic imbalance and, and consequently, altered cardiovascular regulation and reactivity. The EEG of the Mn-exposed workers evidenced beta-wave rhythms significantly reduced, theta-waves markedly increased and abnormal wave activities of either localized or diffusive type. In the same workers BEAM revealed higher theta, delta and beta power values in the F7 area, lower d power values in the FP1, FP2 and C4 areas as well as dissymmetry in the central area, parietal region and occipital region. This study suggests that Mn impairs neuron activity within central nervous system. In this context, brainstem parasympathetic and sympathetic centers receiving axon projections from cortical and diencephalic areas, may reflect Mn effects on upper pathways. However, direct actions of Mn on these centers cannot be excluded.