Impact of Long-term Exposures to PM2.5 Sources on Cause-Specific Mortality in U.S. Medicare Beneficiaries

Abstract

Background: While studies have demonstrated associations between long-term PM2.5 exposures and mortality, our understanding of the component(s) or sources responsible for observed mortality risks is poor. Methods: We examined the impacts of long-term PM2.5 source and component exposures on cause-specific mortality for 15.4 million Medicare beneficiaries living within the conterminous United States between 2000 to 2008. We linked Medicare beneficiary and mortality data to daily PM2.5 component concentrations from 323 stationary monitoring sites and to source-specific PM2.5 estimated using factor analysis. We analyzed these data in age-, race-, and gender-stratified log-linear regression models controlling for potential confounding by other PM2.5 components and area-level demographic and behavioral covariates. We assessed sensitivity of the mortality risk estimates to (1) variation in source estimates by urbanicity and geographical region and (2) to exposure error. Findings: We identified eight major PM2.5 source categories (and key elements): soil (Si, Ca), traffic (EC, OC, NO3 -), metals (Pb and Zn), biomass combustion (K and Cu), salt (Cl, Na), coal combustion (SO42-, Se), residual oil combustion (Ni, V) and steel (Mn, Fe). For all causes of death, we found the highest and most consistent RRs (per IQR increase) for coal combustion (MRRall-cause : 1.052 (95% CI: 1.048-1.056)) and its key tracer elements, with no evidence of confounding by behavioral covariates. Traffic PM2.5 was also significantly associated with increased risk of all-cause (MRRall-cause : 1.010; 95% CI: 1.008, 1.012), CVD- and respiratory-related, and lung cancer mortality but not all cancer-related mortality. Associations were generally null for other examined PM2.5 sources and causes of death. Conclusions: We found long-term PM2.5 exposures from coal combustion and traffic-related sources to be most strongly associated with increased mortality for all causes of death.