Abstract for the 2017 HEI Annual Conference
Chemical and cellular oxidant production from secondary organic aerosols generated from the photooxidation of biogenic and anthropogenic volatile organic compounds
Nga L. Ng, Wing Y. Tuet, Yunle Chen, Lu Xu, Shierly Fok, Dong Gao, Rodney J. Weber, Julie A. Champion
Georgia Institute of Technology, Atlanta, GA, USA
Background Elevated particulate matter (PM) concentrations have been associated with increased cardiopulmonary morbidity and mortality in multiple epidemiological studies. Many prior health studies have focused on the effects of primary emissions even though field studies repeatedly showed that secondary organic aerosols (SOA) often dominate even in urban environments. Toxicology studies have suggested that PM-induced oxidant production may be a possible mechanism for PM-induced health endpoints. Here, we present chemical and cellular oxidant measurements from SOA generated from six common volatile organic compounds (VOC). Levels of inflammatory cytokines (TNF-α and IL-6) were also measured post SOA exposure to further understand the inflammatory response.
Methods SOA formed from the photooxidation of biogenic and anthropogenic precursors were generated in the Georgia Tech Environmental Chamber facility. Precursors were chosen to represent the main classes of hydrocarbons found in biogenic and anthropogenic emissions, including isoprene, α-pinene, β-caryophyllene, pentadecane, m-xylene, and naphthalene. Briefly, desired concentrations of ammonium sulfate seed, VOC precursor, and hydroxyl radical (OH) precursor were injected into clean chambers and the UV lights were turned on to initiate photooxidation. Teflon filters were used to collect generated SOA samples and sectioned for parallel chemical and cellular oxidant measurements. Here, we consider only the water-soluble filter extract. Dithiothreitol (DTT) was used to characterize the chemical oxidative potential of SOA. Alveolar macrophages were also exposed to SOA extracts and various cellular endpoints were measured (intracellular oxidant production: carboxy-H2DCFDA, secreted levels of TNF-α and IL-6: enzyme-linked immunosorbent assay).
Results The intrinsic DTT activity for all SOA systems investigated ranged from 9–205 pmol min-1 µg-1 and were highly dependent on the specific hydrocarbon precursor, with naphthalene and isoprene SOA generating the highest and lowest DTT activity, respectively. Dose-response curves for oxidant production and various cytokines were also obtained for each SOA sample over a wide dilution range. The area under the dose-response curve (AUC) was used to characterize each cellular endpoint for comparison with chemical oxidant production as measured by DTT activity. With the exception of naphthalene SOA, all cellular endpoints followed a trend where levels of TNF-α reached a plateau with increasing IL-6 levels. Distinct cellular response patterns were also observed for SOA systems whose reaction products shared similar functionalities and structures.
Conclusions Toxicology studies have suggested PM-induced oxidant production as a possible mechanism leading to PM-induced health effects. SOA were generated from the photooxidation of six common VOC precursors under various conditions. Multiple assays were used to measure oxidant production and characterize the inflammatory response. We found that precursor identity influenced DTT activity substantially, demonstrating the importance of sources to PM-induced health effects. Furthermore, the carbon backbone identity strongly influenced cellular responses.
Sally Ng received the 2016 Kenneth T. Whitby Award from the American Association for Aerosol Research.
See this article on the Georgia Institute of Technology website.