Comparison of how ambient PM_c and PM_2.5 influence the inflammatory potential

Abstract

Airborne particulate matter (PM) is one of the six criteria air pollutants currently regulated by the U.S. Environmental Protection Agency (EPA), with existing ambient standards for PM_2.5 and PM₁₀. Currently there are no health-based regulations for the size fraction between 2.5 and 10 µm, commonly known as the coarse fraction (PM_c). The present study investigates current gaps in knowledge for PM_c including exposure toxicity and PM ratios (PM_c:PM_2.5) in PM₁₀. Throughout the world, all the three PM size fractions have been shown to be associated with adverse impacts. Recent studies have shown that PM_c can be more detrimental to susceptible populations when directly compared to PM_2.5, and that the PM_c fraction in PM₁₀ can account for the majority of the inflammatory response from PM₁₀ exposure. In our studies we utilized a bone marrow-derived mouse macrophage in vitro system to compare the inflammatory potential of PM_c, PM_2.5 and mixtures of the two. The result was a linear increase in interleukin(IL) -1β with increasing levels of exposure to winter and summer PM_c, as compared to PM_2.5, which exhibited logarithmic growth. Also, exposure to PM₁₀ as a function of PM_2.5 and PM_c mass ratios showed that IL-1β and TNF-α levels increased synergistically with a greater burden of PM_c. Endotoxin content in the PM did not correlate with these results, suggesting that other activators in PM_c are likely responsible for activating the NF-κB pathway and the inflammasome.

• Ambient particulate matter
• coarse fraction
• endotoxin
• inflammation
• IL-1β
• mixtures
• NAAQS
• NF-κB
• pulmonary macrophage
• TNF-α

Acknowledgements

We would like to thank the Montana Department of Environmental Quality (Mr Hoby Rash and Mr Dave Simonson) and the Missoula City-County Health Department (Mr Ben Schmidt) for supplying Missoula’s ambient PM data, and also Lou Herritt (University of Montana) for imaging assistance.