Lung Bioaccessibility of Manganese in Arc Welding Fume
Warner, Christopher K.
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Workers chronically exposed to manganese (Mn) are at increased risk for the development of a Parkinsonism syndrome called manganism. A longitudinal cohort study worked with students at a welding training school to investigate the viability of using Mn levels in various biological compartments to indicate exposure to Mn, which is a component of welding fume. Associations between airborne Mn exposure and Mn concentrations in the body were unclear. It is hypothesized that elucidation of the site of deposition of the fume particles in the respiratory tract and the degree to which the deposited particles dissolve may help to explain the lack of a stronger relationship. Mn in welding fume exists as part of complex particles, from which it must dissolve in order to pass from the lungs into the blood. Solubility depends on the physical characteristics of the particles, but is also a function of the location in the respiratory tract in which they are deposited. That location, in turn, is largely a function of particle size. Thus, to improve estimates of the potential systemic dose of Mn from welding fume, we measured particle size distributions and the solubility of Mn in fume from five types of welding (SMAW, GMAW, FCAW-dual shield, and FCAW-inner shield, and GTAW). Particle size distributions were measured by gravimetric analysis of PTFE substrates used in a 10 stage Micro-Orifice Uniform Deposit Impactor. Fume was collected for solubility tests on MCE filters. The filters were leached at 37 C in a simulated alveolar lining fluid (Hatch's solution) for 1, 24, 48, or 96 hours. Following separation of soluble Mn with a centrifugal filtering device, the dissolution of the Mn from the particles was calculated by comparing, with inductively-coupled plasma mass spectrometry, the Mn content of the solution and of the remaining filter. Mass median aerodynamic diameters (MMAD) were not statistically different between methods of welding. Average MMADs for each type ranged from 0.88 µm to 1.25 µm. Geometric standard deviations (GSD) averaged between 3.5 and 4 for all welding methods except GTAW, for which average GSD was 6.21. All five welding methods showed a tendency toward a bimodal distribution, with one mode near 0.4 µm, and a less pronounced mode in the range of 2-5 µm. A model of respiratory deposition indicated that approximately 5.7% of the mass of fume in the samples would deposit in the alveolar region. The average percent of Mn that dissolved in Hatch's solution for all samples was 3.21. A clear trend in dissolution with respect to leaching duration was seen only in the fume from GTAW, for which the percent of total Mn dissolved decreased with leaching duration. Deposition estimates and solubility together indicate that only approximately 0.2% of the Mn in inhaled welding fume will become available for uptake into the blood.
- Environmental health