Comparison of the Chemical and Oxidative Characteristics of Particulate Matter (PM) Collected by Different Methods: Filters, Impactors, and BioSamplers

Abstract

In this study, we compare the chemical and oxidative characteristics of concentration-enriched PM_2.5 samples simultaneously collected by a filter, a Nano-Micro-Orifice Uniform Deposition Impactor, and a BioSampler. Gravimetric measurements showed considerable agreement in particulate matter (PM) collection efficiency for all three samplers. Accordingly, samples from the three collectors exhibited similar chemical compositions. The mass fractions of their inorganic ions, labile and nonlabile, were comparable. Moreover, the organic carbon (OC) content of the BioSampler slurry was similar to that of the filter, while water-soluble OC levels of the filter and impactor samples were close to a 100% agreement. Lastly, linear regression analyses demonstrated that the water-soluble elements existed in similar proportions for the filter and impactor samples. Their respective total components were also in very good agreement. By contrast, the recoverable elements from the BioSampler slurry, determined by high-resolution magnetic sector inductively coupled plasma mass spectrometry, were in good agreement with the water-soluble elements of the filter and impactor samples but not their corresponding total components. In spite of the overall agreement among the samples on their chemical composition, findings from a macrophage reactive oxygen species (ROS), a dithiothreitol (DTT), and a dihydroxybenzoate (DHBA) assay revealed that the oxidative potential of aqueous extracts of the filter and impactor substrates was similar yet substantially lower than that of the BioSampler slurry. However, filtering of the BioSampler slurry, i.e., removal of insoluble PM components, attenuated its ROS activity to about the same level as that of the water extracts of the filter and impactor samples. These findings first indicate that insoluble PM species are potentially redox active, and second that particle collection by the BioSampler, which circumvents the need for PM extraction, constitutes a viable alternative for collecting concentrated particles for characterization of the oxidative properties of PM.

Acknowledgments

This research was funded by U.S. EPA under the STAR program through Grant RD-8324-1301-0 to University of Southern California and by the United States Public Health service grants (NIH), R01 ES012053 and R01 ES013432. The research described herein has not been subjected to the agency's required peer and policy review and therefore does not necessarily reflect the views of the agency, and official endorsement should not be inferred. The authors gratefully acknowledge the support of the University of Southern California Provost's Ph.D. fellowship. The authors would also like to thank Debra Schmitz and Emma Di Stefano for performing the DTT and DHBA assays.