Inhalation toxicity study of welding fumes: effect of single or repeated exposure on the lungs of rats.

An inhalation toxicity study of L fumes generated from the manual metal arc (MMA) welding of mild steel with a Lime electrode and S fumes generated from the MMA welding of stainless steel with a Lime-titania electrode has been carried out in rats. A method allowing continuous exposure of rats to a reasonably uniform fume concentration was established. Rats wer exposed to 1000 mg/m3 fumes for 1 h in the single exposure study and to 400 mg/m3 fumes for 30 min/day, 6 days/week, for 2 week in the repeated exposure study. Physical and chemical characteristics of the fumes, such as chemical composition, water solubility and particle size, were evaluated. Exposure to S fumes produced greater changes in lung weight and morphology than exposure to L fumes. Histopathological signs of respiratory irritation, such as mucus granules in the alveoli and hyperplasia of mucus cells in the bronchial epithelium, and bronchiectasia were observed only in the rats exposed to S fumes. Fume elements deposited in alveolar macrophages were qualitatively analyzed by means of an electron probe X-ray micro-analyzer and were essentially identical to those in the welding fumes.