Abstract View
Interactions between Transition Metals in Particulate Matter and Phosphate Buffer Affect Acellular Oxidative Potential Assays
JAYASHREE YALAMANCHILI, Christopher Hennigan, Brian Reed, University of Maryland, Baltimore County
Abstract Number: 154
Working Group: Health-Related Aerosols
Abstract
Atmospheric aerosols have a deleterious effect on human health. Amongst the various constituents, transition metals are hypothesized to have enhanced toxicity based on their potential to generate reactive oxygen species (ROS). Acellular methods to measure the oxidative potential (OP) of PM commonly use a phosphate buffer matrix at pH 7.4 and 37 °C to simulate conditions in the human body. In this study, we characterize the precipitation of transition metals in the dithiothreitol (DTT) assay, one of the most widely used measures of aerosol OP. Thermodynamic modeling predicts the precipitation of Fe and Mn at low metal concentrations in the PO4 buffer matrix. Experiments were conducted at low aqueous metal concentrations (0.5- 20 µM) using individual metal salts and using urban particulate matter (NIST SRM-1648a); metal precipitation was measured via chemical analysis of dissolved metals, laser particle light scattering, and SEM analysis with EDS microscopy. The results showed unambiguous evidence for precipitation of Fe and Mn within 5 – 30 min, a timescale relevant for the DTT assay. Although thermodynamic modeling suggests Cu does not precipitate due to its high solubility, Cu removal was observed in the urban PM samples, possibly due to adsorption to Fe precipitates or co-precipitation. Finally, the DTT assay response was evaluated for metals applied in dissolved vs. solid form. The implications of this work for use of OP assays to infer PM toxicity are discussed.