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BACKGROUND: Few epidemiologic studies have investigated health effects of water-soluble fractions of PM2.5 metals, the more biologically accessible fractions of metals, in their attempt to identify health-relevant components of ambient PM2.5.

OBJECTIVES: In this study, we estimated acute cardiovascular effects of PM2.5 components in an urban population, including a suite of water-soluble metals that are not routinely measured at the ambient level.

METHODS: Ambient concentrations of criteria gases, PM2.5, and PM2.5 components were measured at a central monitor in Atlanta, Georgia, during 1998-2013, with some PM2.5 components only measured during 2008-2013. In a time-series framework using Poisson regression, we estimated associations between these pollutants and daily counts of emergency department (ED) visits for cardiovascular diseases in the five-county Atlanta area.

RESULTS: Among the PM2.5 (RR) over cap components we examined during 1998-2013, water-soluble iron had the strongest estimated effect on cardiovascular outcomes [(RR) over cap =1.012 (95% CI: 1.005, 1.019), per interquartile range increase (20.46 ng/m(3))]. The associations for PM2.5 and other PM2.5 components were consistent with the null when controlling for water-soluble iron. Among PM2.5 components that were only measured during 2008-2013, water-soluble vanadium was associated with cardiovascular ED visits [(RR) over cap =1.012 (95% CI: 1.000, 1.025), per interquartile range increase (0.19 ng/m(3))].

CONCLUSIONS: Our study suggests cardiovascular effects of certain water-soluble metals, particularly water-soluble iron. The observed associations with water-soluble iron may also point to certain aspects of traffic pollution, when processed by acidifying sulfate, as a mixture harmful for cardiovascular health.