Exposure to Metal Mixtures in Welding Fume and their Association with Neurological Function
Welding is a common industrial process that millions of people around the world commonly use in their primary occupation or as part of their duties in their occupation. As part of the welding process, a fume is generated. This welding fume is comprised of several metals including manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), and aluminum (Al) among many others. The metal particles are ultrafine ranging from 10 nm to 2µm in diameter. Due to the aerodynamic diameter of the welding fume particles, welders are predominately exposed through inhalation. Once inhaled, depending on the aerodynamic diameter, these particles can either penetrate deep into the alveolar regions of the lungs or deposit in the head and brain via the olfactory pathway. Welding fume metals that include Mn, Fe, Cu, Zn, and Al can be neurotoxic. Therefore, understanding which of these metals may independently, or through an interaction, cause neuropsychological deficits is critical. In the studies presented as part of this dissertation, we examined how chronic exposure to welding fume metals (Mn, Fe, Cu, Zn, and Al) results in increased levels in the human body using toenail metals as a biomarker of exposure. We further explored how the accumulation of these metals are associated with decreased neuropsychological performance. In chapter 2, we assessed the sensitivity and specificity of toenail Mn as a biomarker of Mn exposure in career welders. Utilizing a newly developed exposure model with rigorous exposure assessment techniques we assessed which exposure windows are most represented by toenail Mn concentrations. In chapter 3, we further explored the use of other toenail metals (Zn, Cu, Fe, And Al) as sensitive and specific biomarkers of exposure and assessed the exposure window which was most representative of each toenail metal. Lastly, in chapter 4, we used a cross-sectional approach to investigate if welders have significantly decreased neuropsychological performances compared to a control population. Using both modeled cumulative exposure estimates and toenail metal concentrations, we assessed if the cumulative exposure of each metal or the interaction of cumulative multi-metal exposures had a significant association with either cognition or motor function. Cumulative exposure to respirable Mn from welding fume was associated with decreased performance in several cognitive and motor function domains: cognitive flexibility and executive function, attention, processing and visuomotor tracking speed, and overall motor function. Increased toenail Mn and Cu levels were associated with decreased performance in language and verbal skills, processing and visuomotor tracking speed, attention, bilateral psychomotor speed, and increased graphomotor speed. In conclusion, we found that welders were exposed to a significantly higher concentration of Mn, Fe, Cu, Zn and Al from welding fumes. Toenail Mn, Fe, Cu, and Zn levels were found to be significantly elevated in welders. We found that toenail Mn, Cu, and Zn were significantly correlated with exposure 7-12 months prior the nail being clipped. Toenail Fe was trending towards significance with cumulative exposure. Cumulative exposure to Mn, Fe, Cu, Zn an Al was associated with neurological deficits. When further analyzed, it was found that neurological deficits are associated with increased cumulative exposure to respirable Mn, and increased toenail Mn and Cu levels. Future studies should further investigate the use of toenail Mn and Cu as biomarkers of exposure and further analyze the relationship between Cu and Mn exposure with neurological deficits in welders. (Abstract shortened by ProQuest.)
Dydak, Purdue University.
Neurosciences|Occupational safety|Environmental Health|Epidemiology
Off-Campus Purdue Users:
To access this dissertation, please log in to our