Welding fumes contain heavy metals, such as chromium, manganese, and nickel, which cause respiratory diseases and cancer. In this study, a SiO2 precursor was evaluated as an additive to the shielding gas in an arc welding process to reduce the biotoxicity caused by welding fume particles. Transmission electron micrographic images show that SiO2 coats on the surface of welding fume particles and promotes particle agglomeration. Energy dispersive X-ray spectroscopy further shows that the relative amount of silicon in these SiO2-coated agglomerates is higher than in baseline agglomerates. In addition, Escherichia coil (E. coil) exposed to different concentrations of pure SiO2 particles generated from the arc welding process exhibits similar responses, suggesting that SiO2 does not contribute to welding fume particle toxicity. The trend of E. coil growth in different concentrations of baseline welding fume particle shows the most significant inhibition occurs in higher exposure concentrations. The 50% lethal logarithmic concentrations for E. coli in arc welding particles of baseline, 2%, and 4.2% SiO2 precursor additives were 823, 1605, and 1800 mg/L, respectively. Taken together, these results suggest that using SiO2 precursors as an additive to arc welding shielding gas can effectively reduce the biotoxicity of welding fume. (C) 2010 Elsevier B.V. All rights reserved.