title: Associations between long-term exposure to chemical constituents of fine particulate matter (PM2.5) and mortality in Medicare enrollees in the eastern United States.
abstract: BACKGROUND
  Several epidemiological studies have reported that long-term exposure to fine particulate matter (PM2.5) is associated with higher mortality. Evidence regarding contributions of PM2.5 constituents is inconclusive.
  
  
  OBJECTIVE
  We assembled a data set of 12.5 million Medicare enrollees (≥ 65 years of age) to determine which PM2.5 constituents are a) associated with mortality controlling for previous-year PM2.5 total mass (main effect); and b) elevated in locations exhibiting stronger associations between previous-year PM2.5 and mortality (effect modification).
  
  
  METHODS
  For 518 PM2.5 monitoring locations (eastern United States, 2000-2006), we calculated monthly mortality rates, monthly long-term (previous 1-year average) PM2.5, and 7-year averages (2000-2006) of major PM2.5 constituents [elemental carbon (EC), organic carbon matter (OCM), sulfate (SO42-), silicon (Si), nitrate (NO3-), and sodium (Na)] and community-level variables. We applied a Bayesian hierarchical model to estimate location-specific mortality rates associated with previous-year PM2.5 (model level 1) and identify constituents that contributed to the spatial variability of mortality, and constituents that modified associations between previous-year PM2.5 and mortality (model level 2), controlling for community-level confounders.
  
  
  RESULTS
  One-standard deviation (SD) increases in 7-year average EC, Si, and NO3- concentrations were associated with 1.3% [95% posterior interval (PI): 0.3, 2.2], 1.4% (95% PI: 0.6, 2.4), and 1.2% (95% PI: 0.4, 2.1) increases in monthly mortality, controlling for previous-year PM2.5. Associations between previous-year PM2.5 and mortality were stronger in combination with 1-SD increases in SO42- and Na.
  
  
  CONCLUSIONS
  Long-term exposures to PM2.5 and several constituents were associated with mortality in the elderly population of the eastern United States. Moreover, some constituents increased the association between long-term exposure to PM2.5 and mortality. These results provide new evidence that chemical composition can partly explain the differential toxicity of PM2.5.
authors.affiliation: Department of Mathematical Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea.
authors.forename: Yeonseung
authors.initials: Y
authors.lastname: Chung
authors.forename: Francesca
authors.initials: F
authors.lastname: Dominici
authors.forename: Yun
authors.initials: Y
authors.lastname: Wang
authors.forename: Brent A
authors.initials: BA
authors.lastname: Coull
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Bell
mesh_terms: D000368:Aged; D000397:Air Pollution / Q000009:adverse effects; D004781:Environmental Exposure / Q000009:adverse effects; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D008297:Male; D006278:Medicare; D052638:Particulate Matter / Q000633:toxicity*; D014481:United States
chemical_list: D052638:Particulate Matter