AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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High Oxidative Potential of Metal Oxides in Welding and Plasma Cutting Fume Aerosols
JUN WANG, Jacob Bartels, University of Oklahoma
Abstract Number: 753 Working Group: Linking Aerosol Oxidative Potential with Chemical Composition and Biological Endpoints
Abstract Aerosols generated from metal fabrication processes (welding, plasma cutting) contain a large proportion of metal oxides that exert high oxidative potential, such as hexavalent chromium. The formation of reactive oxygen species (ROS) is a cell metabolism process in the human body, as a manifestation of reaction to these metal oxides after inhalation. In this study, aerosols were collected onto filters using a high-volume sampler in a welding fume chamber. They were then ultrasonically extracted through solvents (water and methanol). The extracted aerosols were transferred to vials and dried overnight at 37 ºC with a constant flow of pure nitrogen. Before the toxicity experiment, all extracts were resuspended with deionized water to a fixed concentration. We started with in-vitro acellular protocols developed for testing ambient particulate matter, namely the dithiothreitol (DTT) assay and ascorbic acid (AA) assay. The level of DTT and AA concentration in the protocols were modified to better suit the levels of metal fume in the occupational environment. The rate of DTT consumption was calculated using linear regression of the data from a plot of absorbance (412 nm) against concentration gradient/time. The maximum depletion rate of AA was determined similarly with absorbance at 265 nm. The results indicated AA is more suitable for metal aerosols. The reaction rates of highly oxidized metal are much rapid than the ambient particles which are relatively low in oxidative potential. Welding fume showed averaging 0.0611 nmol of AA/µg of aerosol, while plasma cutting fume had an average 0.1035 nmol of AA/µg of aerosol. The presence of shielding gas in welding operation appears to help mitigate the oxidation of metals, therefore resulted in less oxidative potential than plasma cutting which has no shielding gas. The results need to be verified with in-vitro cellular ROS assays in the future study.