Seasonal Variation in the Chemical Composition and Oxidative Potential of PM2.5

Abstract

Exposure to fine particulate matter (PM2.5) has well-established systemic human health effects due in part to the chemical components associated with these exposures. Oxidative stress is a hypothesized mechanism for the health effects associated with PM2.5 exposures. The oxidative potential of PM2.5 has recently been suggested as a metric that is more indicative of human health effects than the routinely measured PM2.5 concentration. The purpose of this study was to analyze and compare the oxidative potential and elemental composition of PM2.5 collected at two locations during different seasons. PM2.5 was collected onto PTFE-coated filters (n = 16) along two highways in central Oregon, USA in the Winter (January) and Summer (July/August). PM2.5 was extracted from each filter via sonication in methanol. An aliquot of the extraction solution was used to measure oxidative potential using the dithiothreitol (DTT) assay. An additional aliquot underwent analysis via inductively coupled plasma—mass spectrometry (ICP-MS) to quantify elements (n = 20). Differences in PM2.5 elemental composition were observed between locations and seasons as well as between days in the same season. Overall, concentrations were highest in the winter samples but the contribution to total PM2.5 mass was higher for elements in the summer. Notably, the oxidative potential (nM DTT consumed/µg PM2.5/min) differed between seasons with summer samples having nearly a two-fold increase when compared to the winter. Significant negative correlations that were observed between DTT consumption and several elements as well as with PM2.5 mass but these findings were dependent on if the data was normalized by PM2.5 mass. This research adds to the growing evidence and justification for investigating the oxidative potential and composition of PM2.5 while also highlighting the seasonal variability of these factors.