Acute respiratory tract infections are increased in terms of severity, duration, and frequency among welders as compared to the general population. The objective of this study was to determine the mechanism by which different welding fumes may affect pulmonary bacterial clearance and lung injury after infection. Fume was collected during gas metal arc (GMA) or flux-colored manual metal arc (MMA) welding using two consumable electrodes: stainless steel (SS) or mild steel (MS). The fumes were separated into water-soluble and insoluble fractions, and the metal composition determined. Sprague-Dawley rats were dosed intratracheally with saline (vehicle control) and the different welding fumes (1 mg/100 g b wt). Three days later, the rats were inoculated intratracheally with 5,000 Listeria monocytogenes. At 3, 5, and 7 days post-bacteria inoculation, left lungs were removed, homogenized, and the number of colony-forming units were counted after an overnight incubation. Animal weights and mortality were monitored over the course of the treatment period. The GMA-SS and GMA-MS fumes were found to be relatively insoluble, whereas the MMA-SS fume was highly water-soluble with the soluble fraction comprised of 87% Cr and 11% Mn. In contrast to the GMA-SS and GMA-MS groups, rats pre-exposed to MMA-SS fume lost significantly more weight and had an elevation in mortality after infection. Also, pre-exposure to the MMA-SS fume dramatically slowed the pulmonary clearance of L. monocytogenes as compared to the other groups. No difference in bacterial clearance was observed when comparing the GMA-SS, GMA-MS, and control groups. Extensive lesion formation, characterized by severe proteinaceous edema, significant inflammation, and consolidation, was present in the lungs of the MMA-SS group after infection. The significant reduction in bacterial clearance from the lungs after treatment with MMA-SS fumes is likely attributed to the presence of soluble metals and their effect on lung defense mechanisms.
The Toxicologist. Society of Toxicology 40th Annual Meeting, March 25-29, 2001, San Francisco, California