Influence of Season and Location on Pulmonary Response to California's San Joaquin Valley Airborne Particulate Matter

Abstract

Season and location have documented impacts on particulate matter (PM)-induced morbidity and mortality. Seasonal and regional influences on the physical and chemical properties of PM_2.5 (also known as fine/ultrafine PM) contribute to differences in exposure burden and adverse respiratory health outcomes experienced in California's San Joaquin Valley (SJV), which ranks among the worst in the nation for PM pollution. Current regulations are driven by the association between mass concentrations and adverse health outcomes. However, this association is difficult to reproduce in toxicological studies and suggests a role for other parameters, such as chemical composition, involved in PM-induced adverse pulmonary health effects. Pulmonary toxicity of summer/winter and rural/urban SJV PM was evaluated given the unique geography, metereology and sources of the region. Healthy juvenile male mice inhaled summer/winter and urban/rural concentrated ambient PM (CAP) or ambient PM for 6 h/d for 10 d, and pulmonary inflammatory responses were measured 48 h postexposure. Exposure concentrations ranged from 10 to 20 μg/m³ for ambient air control mice and from 86 to 284 μg/m³. Mice exposed to rural but not urban CAP, displayed significant neutrophil influx that was more than 50-fold greater than control levels, which ranged from 21 to 60 neutrophils/ml for all experiments. Pulmonary neutrophilic inflammation was measured despite lower CAP concentrations in the rural compared to the urban location and in the absence of cytotoxicity, oxidative stress, or elevations in cytokine and chemokines expression. Further, the inflammatory responses induced by rural winter CAP were associated with the highest levels of organic carbon (OC) and nitrates (NO₃ ⁻). Evidence indicates that regional/seasonal influences on PM chemical composition rather than PM mass may be associated with increased PM-induced adverse health effects.

Acknowledgments

This study was funded in part by grants from NIOSH (U07/CCU906162) and the U.S. Environmental Protection Agency (RD-83241401-0 and R826246) to the University of California, Davis. The study has not been subject to the U.S. EPA required peer and policy review and therefore does not necessarily reflect the views of the U.S. EPA or NIOSH and no official endorsement should be inferred. We thank Suzette Smiley-Jewell for editorial assistance and Neil Willits for statistical consulting. We thank Julian Recendez, Christine Haas, Mai Ngo, Laurie Hopkins, Elizabeth Morgan, Samantha Serrano, and Vanessa Flores for their assistance in the performance of these studies at the Fresno and Westside field sites. We thank the UC Office at West Shaw Avenue as well as the Research Advisory Committee at the West Side Research Center at Westside, CA, for site access to conduct these studies. We also acknowledge Dennis Wilson for assistance with pathologic assessment of lung tissues.