PM2.5 and survival among older adults: effect modification by particulate composition.
BACKGROUND
Fine particulate (PM2.5) air pollution has been consistently linked to survival, but reported effect estimates are geographically heterogeneous. Exposure to different types of particle mixtures may explain some of this variation.


METHODS
We used k-means cluster analyses to identify cities with similar pollution profiles, (ie, PM2.5 composition) across the United States. We examined the impact of PM2.5 on survival, and its variation across clusters of cities with similar PM2.5 composition, among Medicare enrollees in 81 US cities (2000-2010). We used time-varying annual PM2.5 averages, measured at ambient central monitoring sites, as the exposure of interest. We ran by-city Cox models, adjusting for individual data on previous cardiopulmonary-related hospitalizations and stratifying by follow-up time, age, gender, and race. This eliminates confounding by factors varying across cities and long-term trends, focusing on year-to-year variations of air pollution around its city-specific mean and trend. We then pooled the city-specific effects using a random effects meta-regression. In this second stage, we also assessed effect modification by cluster membership and estimated cluster-specific PM2.5 effects.


RESULTS
We followed more than 19 million subjects and observed more than 6 million deaths. We found a harmful impact of annual PM2.5 concentrations on survival (hazard ratio = 1.11 [95% confidence interval = 1.01, 1.23] per 10 μg/m). This effect was modified by particulate composition, with higher effects observed in clusters containing high concentrations of nickel, vanadium, and sulfate. For instance, our highest effect estimate was observed in cities with harbors in the Northwest, characterized by high nickel, vanadium, and elemental carbon concentrations (1.9 [1.1, 3.3]). We observed null or negative associations in clusters with high oceanic and crustal particles.


CONCLUSIONS
To the best of our knowledge, this is the first study to examine the association between PM2.5 composition and survival. Our findings indicate that long-term exposure to fuel oil combustion and power plant emissions have the highest impact on survival.
From the Departments of aEnvironmental Health, bBiostatistics, Harvard School of Public Health, Boston, MA; and cDepartment of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA.
Marianthi-Anna
MA
Kioumourtzoglou
Elena
E
Austin
Petros
P
Koutrakis
Francesca
F
Dominici
Joel
J
Schwartz
Antonella
A
Zanobetti
D000368:Aged; D000397:Air Pollution / Q000009:adverse effects / Q000706:statistics & numerical data; D016000:Cluster Analysis; D005260:Female; D006801:Humans; D008297:Male; D009026:Mortality; D010316:Particle Size; D052638:Particulate Matter / Q000009:adverse effects*; D016016:Proportional Hazards Models; D016019:Survival Analysis; D014481:United States / Q000453:epidemiology
D052638:Particulate Matter