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Chung, Yeonseung,Dominici, Francesca,Wang, Yun,Coull, Brent A.,Bell, Michelle L. U.S. Dept. of Health, Education, and Welfare, Publ 2015 Environmental health perspectives Vol.123 No.5
<P><B>Background:</B></P><P>Several epidemiological studies have reported that long-term exposure to fine particulate matter (PM<SUB>2.5</SUB>) is associated with higher mortality. Evidence regarding contributions of PM<SUB>2.5</SUB> constituents is inconclusive.</P><P><B>Objectives:</B></P><P>We assembled a data set of 12.5 million Medicare enrollees (≥ 65 years of age) to determine which PM<SUB>2.5</SUB> constituents are <I>a</I>) associated with mortality controlling for previous-year PM<SUB>2.5</SUB> total mass (main effect); and <I>b</I>) elevated in locations exhibiting stronger associations between previous-year PM<SUB>2.5</SUB> and mortality (effect modification).</P><P><B>Methods:</B></P><P>For 518 PM<SUB>2.5</SUB> monitoring locations (eastern United States, 2000–2006), we calculated monthly mortality rates, monthly long-term (previous 1-year average) PM<SUB>2.5</SUB>, and 7-year averages (2000–2006) of major PM<SUB>2.5</SUB> constituents [elemental carbon (EC), organic carbon matter (OCM), sulfate (SO<SUB>4</SUB><SUP>2–</SUP>), silicon (Si), nitrate (NO<SUB>3</SUB><SUP>–</SUP>), and sodium (Na)] and community-level variables. We applied a Bayesian hierarchical model to estimate location-specific mortality rates associated with previous-year PM<SUB>2.5</SUB> (model level 1) and identify constituents that contributed to the spatial variability of mortality, and constituents that modified associations between previous-year PM<SUB>2.5</SUB> and mortality (model level 2), controlling for community-level confounders.</P><P><B>Results:</B></P><P>One–standard deviation (SD) increases in 7-year average EC, Si, and NO<SUB>3</SUB><SUP>–</SUP> 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 PM<SUB>2.5</SUB>. Associations between previous-year PM<SUB>2.5</SUB> and mortality were stronger in combination with 1-SD increases in SO<SUB>4</SUB><SUP>2–</SUP> and Na.</P><P><B>Conclusions:</B></P><P>Long-term exposures to PM<SUB>2.5</SUB> 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 PM<SUB>2.5</SUB> and mortality. These results provide new evidence that chemical composition can partly explain the differential toxicity of PM<SUB>2.5</SUB>.</P><P><B>Citation:</B></P><P>Chung Y, Dominici F, Wang Y, Coull BA, Bell ML. 2015. Associations between long-term exposure to chemical constituents of fine particulate matter (PM<SUB>2.5</SUB>) and mortality in Medicare enrollees in the eastern United States. Environ Health Perspect 123:467–474; http://dx.doi.org/10.1289/ehp.1307549</P>