Serious questions have been raised regarding a possible causal association between neurological effects in welders and the presence of manganese in welding consumables. The objectives of the study are to: (1) construct an automated, computercontrolled welding fume generation system to simulate real workplace conditions and (2) examine the potential neurotoxic effect of manganese in rats after pulmonary exposure to different welding fumes. The systemis comprised of a programmable sixaxis robotic welding arm and a water-cooled arc welding torch.A flexible trunk has been attached to the robotic arm of the welder and is used to collect and transport fume from the vicinity of the arc to the animal exposure chamber. Of the metals measured, manganese comprised approximately 10-15% of the stainless and mild steel fume generated as determined by inductively coupled plasma atomic emission spectroscopy. Size distribution analysis indicated the mass median aerodynamic diameter of the generated particles to be approximately 0.24 mm. As determined by scanning electron microscopy, the generated aerosols were mostly arranged as chain-like agglomerates of primary particles. These fume characterization studies have indicated that particle morphology, size, and chemical composition are comparable to welding fume generated in the workplace. Initial animal inhalation studies are underway. Sprague-Dawley rats are being exposed to 15 or 40 mg/m3 of welding fume for 3 h/day for 10 or 30 days. After exposure, manganese concentrations will be determined in a number of discrete brain regions. Neurotoxicity will be detected and quantified by measuring the increased expression of glial fibrillary acidic protein and using silver degeneration staining technology. Because dopaminergic systems have been implicated as targets of manganese exposure, levels of dopamine and tyrosine hydroxylase, biomarkers of dopaminergic neuronal damage, also will be measured.With the development of this novel system, it will be possible to establish an animal model using controlled welding exposures to investigate the possible mechanisms by which welding fumes may affect the central nervous system.