Frequency, duration, and severity of pulmonary infections have been shown to be increased in full-time welders. Animal studies have shown that manual metal arc, stainless steel welding fume (MMA-SS) increased susceptibility to lung infections. MMA-SS is primarily composed of iron (Fe), chromium (Cr), and nickel (Ni). The objective of this study was to determine which component of MMA-SS may alter lung defense. At day 0, male Sprague-Dawley rats were intratracheally instilled with MMA-SS at a concentration of 2 mg per rat or saline (vehicle control), or the metal constituents Fe2O3 (insoluble, 0.82 mg), NiO (insoluble, 0.06 mg), Cr2Na2O7 (soluble, 0.60 mg) at the concentration at which they are present in the dose of MMASS. Another group of rats received a mixture of the three metals. At day 3, rats were intratracheally inoculated with 5 x 103 Listeria monocytogenes. At days 6, 8 and 10, left lungs were homogenized, cultured overnight, and colony-forming units counted to assess pulmonary bacterial clearance. At day 3 (prior to infection) and at days 6, 8 and 10, right lungs were lavaged to recover cells and fluid from the airspace. Cell differentials were performed and the production of reactive oxygen species by phagocytes was measured. Lactate dehydrogenase and albumin levels were measured in lavage fluid as indicators of lung damage. Exposure to MMA-SS, the soluble Cr, or the mixture of metals before infection significantly slowed the pulmonary clearance of the bacteria and increased lung tissue damage when compared to control, and animals treated with NiO or Fe2O3 did not differ from control. Animals pre-treated with soluble Cr or the mixture of all three metals had increased cell numbers of macrophages, neutrophils, and eosinophils, and oxidant production by phagocytes was increased at all time points when compared with the saline group. The results of this study indicate that the soluble Cr present in MMASS is likely to be the primary component responsible for the suppression of lung defense in rats.
The Toxicologist. Society of Toxicology 45th Annual Meeting and ToxExpo, March 5-9, 2006, San Diego, California