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On the Relative Contribution of Fe and Organic Compounds, and Their Interaction in Cellular Oxidative Potential (OP) of Ambient PM2.5
YIXIANG WANG, Haoran Yu, Joseph V Puthussery, Vishal Verma, University of Illinois Urbana-Champaign
Abstract Number: 151
Working Group: Health-Related Aerosols
Abstract
Oxidative potential (OP) reflects the capability of ambient PM2.5 to cause ROS imbalance in the biological system and investigating the chemical components linked with OP has been an active area of research. However, most of the studies linking OP to chemical composition have used only the acellular OP assays, while largely ignoring the biological reactions. In this study, PM2.5 samples were collected from several Midwest US sites, and the OP of collected particles was assessed by a cellular ROS assay based on rat alveolar macrophages. Several chemical components of PM2.5 were also measured. Among all the chemical components, only water-soluble Fe and water-soluble organic carbon (WSOC) were significantly correlated with the OP at all sites. Since both of these components (i.e., Fe and WSOC) were also intercorrelated, we developed a novel mechanistic technique using a combination of solid phase extraction columns, to identify the individual contribution of these species in the macrophage ROS response. Results suggested that the hydrophobic fraction, which consists of various aromatic organic compounds was ROS-inactive in the macrophage assay. In contrast, the hydrophilic fraction, which contains most of the water-soluble metals and aliphatic organic compounds, accounted for ~80% of PM2.5 total cellular OP. To further segregate the contribution of aliphatic organic compounds with metals, we passed the hydrophilic fraction through a chelex column, which removed metals but did not affect the organic compounds. The metal-free hydrophilic fraction was ROS-inactive, while the retained fraction on chelex column, which was eluted using HCl contained most of the ROS activity. To further explore the correlation of Fe and macrophage ROS with WSOC, we investigated the water-solubility of Fe by measuring total Fe on the filters. The water-solubility of Fe was found to be tightly correlated with WSOC, indicating the indirect role of WSOC, probably through complexation of Fe, on enhancing its water-solubility and macrophage ROS activity. Our study reveals different roles of two important components of ambient PM2.5 and their interaction through effect modification on altering the cellular OP of ambient PM2.5.