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2772943 
Journal Article 
Associations between long-term exposure to chemical constituents of fine particulate matter (PM2.5) and mortality in medicare enrollees in the Eastern United States 
Chung, Y; Dominici, F; Wang, Y; Coull, BA; Bell, ML 
2015 
Yes 
Environmental Health Perspectives
ISSN: 0091-6765
EISSN: 1552-9924 
123 
467-474 
English 
is supplemented by 2828394 Supplemental material:
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.

OBJECTIVES: We assembled a dataset of 12.5 million Medicare enrollees (≥65 yrs) to determine which PM2.5 constituents are: 1) associated with mortality controlling for previous-year PM2.5 total mass (main effect); and 2) elevated in locations exhibiting stronger associations between previous-year PM2.5 and mortality (effect modification).

METHODS: For 518 PM2.5 monitoring locations (Eastern US, 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 (SO4(=)), 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 SO4(=) and Na.

CONCLUSIONS: Long-term exposures to PM2.5 and several constituents were associated with mortality in the elderly population of the Eastern US. 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.