Health Effects of PM2.5 and Its Components on Mortality, Blood Pressure, and DNA Methylation

Epidemiological studies have examined the association between PM2.5 mass and mortality, but there remains uncertainty about the relative importance of species. PM2.5 contains various species, such as organic carbon, elemental carbon, and metals. Determining the differential toxicity of PM2.5 species and identifying species with greatest toxicity is of great importance to emission-control strategies and regulations. In the dissertation thesis, effects of PM2.5 species on health outcomes on different levels were estimated. The first study examined the association between PM2.5 species and mortality on approximately 4.5 million deaths for all causes, cardiovascular diseases, myocardial infarction, stroke, and respiratory diseases in 75 U.S. cities for 2000-2006, using city-season specific Poisson regression and multivariate meta-regression controlled for infiltration. Since cardiovascular diseases are leading causes of death within U.S. population, the second study aimed to determine which PM2.5 species are associated with blood pressure, an indicator of cardiovascular health, in a longitudinal cohort. Linear mixed-effects models with the adaptive LASSO penalty were applied to longitudinal data from 718 elderly men in the Veterans Affairs Normative Aging Study (NAS), 1999-2010. Species considered included 8 metals (Fe, K, Al, Ni, V, Cu, Zn, and Na) and 3 non-metals (S, Si, and Se). At last, the relationship between long-term exposure to PM2.5 species and epigenome-wide DNA methylation at 484 613 CpG probes in the longitudinal NAS cohort that included 646 subjects were investigated to explore the potential biological mechanisms on the epigenetic level in study 3. The studies have showed an increased risk of mortality and blood pressure associated with PM2.5, which varied with species, and differential DNA methylation linked to long-term exposure to particular components of PM2.5. In conclusion, mass alone might not be sufficient to evaluate the health effects of particles. Understanding the toxicity of particle components is crucial to public health.