A longitudinal study to assess the presence of manganese in blood and exhaled breath condensate following acute inhalation exposure to welding fumes

The association between exposure to airborne manganese (Mn) and neurotoxic outcomes is well-understood. However, the association between airborne Mn exposure and Mn uptake from the pulmonary system remains unclear. Toxicological research indicates that the chemical and physical form of Mn in exposures is a determinant of the time course of Mn uptake. The goal of this human exposure assessment study was to identify the time course of uptake and clearance of metals in the pulmonary system following inhalation exposure.Welding fume was selected as the source of Mn inhalation exposure and Mn in exhaled breath condensate (EBC Mn) and blood Mn were selected as biomarkers of internal dose. Two measures of exposure were developed and characterized for incorporation in the study: primary particle count median diameter (CMD) and Mn composition by size. In addition, a method for the collection and analysis of EBC Mn was characterized and incorporated in study measures.The following sampling strategy was applied: baseline samples of EBC and blood were collected from 17 subjects, subjects then welded in a single session and particle samples were collected, and EBC and blood samples were collected at 9 more time points within 7 days. Eight subjects repeated participation in the study as unexposed subjects by following the sampling strategy, except that they did not weld.The average Mn concentration in welding fume was 375 microg/m 3 (range 8-1800 microg/m3). The average primary particle CMD was 6.9 nm (range 3.2-14.5 nm). The average slope of Mn composition by particle size was 0.0008 nm-1 (range -0.0009--0.002 nm -1).No trend in uptake of Mn due to welding was measured in blood. Nine exposed subjects had a significant EBC Mn peak concentration following welding. Among subjects with an EBC-Mn peak, the primary particle CMD and the Mn composition by particle size slope were associated with the timing and concentration level of the maximum EBC Mn peak. Our findings, consistent with evidence from animal and nanoparticle exposure studies, suggest that an understanding of the particle size and composition is important when characterizing the impact of inhalation exposure to Mn.