Activity and Interaction of Iron, Copper, Lead and Other Metals in the Hydroxyl Radical and Dithiothreitol Assays under Physiological Conditions

JIAQI SHEN, Catherine Banach, Chris La, Suzanne E. Paulson, University of California, Los Angeles

     Abstract Number: 549
     Working Group: Health-Related Aerosols

Abstract
Metals have been recognized as potentially harmful components in PM_2.5 as they contribute to aerosol oxidative potential either by themselves or interactions with organic compounds. However, only a handful of studies have investigated responses in the oxidative potential assays from metals. Further, data are available mostly for iron and copper, despite numerous studies that report positive correlations between oxidative potential and other metals such as Ba, Pb, Sb, etc. In this study, we measured the activity of individual metals including Fe, Cu, Ba, Zn, Hg, Pb and Sb in the hydroxyl radical (OH) and dithiothreitol (DTT) assays in surrogate lung fluid. Some metal combinations were also tested to find out potentially important interactions of metals in aerosol oxidative potential. We found that Fe(II), Cu(II) and Cu(I) are the most active metals in the OH assay. While both Cu(II) and Cu(I) are dominant metals in the DTT assay, Cu(I) activity might be due to complex formation between Cu(I) and DTT. The complexation may also explain the low level of activity of Zn(II) in the DTT assay as a non-redox-active metal. We also observed an antagonistic effect between Pb(II) and Cu(II) in both assays. 1 μM Pb(II) decreased the DTT activity of 1 μM Cu(II) by 15% and completely suppressed OH activity of 1 μM Cu(II). While metal-organic interactions are not yet clear, this finding indicates that studies only using well-recognized active metals and organics to predict overall aerosol oxidative potential may overestimate the contribution of metals.