The Role of Particle Composition on the Association Between PM2.5 and Mortality

Abstract

Background Although the association between exposure to particulate matter (PM) mass and mortality is well established, there remains uncertainty about which chemical components of PM are most harmful to human health. Methods A hierarchical approach was used to determine how the association between daily PM2.5 mass and mortality was modified by PM2.5 composition in 25 US communities. First, the association between daily PM2.5 and mortality was determined for each community and season using Poisson regression. Second, we used meta-regression to examine how the pooled association was modified by community and season-specific particle composition. Results There was a 0.74% (95% confidence interval = 0.41%–1.07%) increase in nonaccidental deaths associated with a 10 μg/m3 increase in 2-day averaged PM2.5 mass concentration. This association was smaller in the west (0.51% [0.10%– 0.92%]) than in the east (0.92% [0.23%–1.36%]), and was highest in spring (1.88% [0.23%–1.36%]). It was increased when PM2.5 mass contained a higher proportion of aluminum (interquartile range = 0.58%), arsenic (0.55%), sulfate (0.51%), silicon (0.41%), and nickel (0.37%). The combination of aluminum, sulfate, and nickel also modified the effect. These species proportions explained residual variability between the community-specific PM2.5 mass effect estimates. Conclusions This study shows that certain chemical species modify the association between PM2.5 and mortality and illustrates that mass alone is not a sufficient metric when evaluating health effects of PM exposure.

Seasonal Variation of Airborne Particle Deposition Efficiency in the Human Respiratory System

“…The majority of this enhancement in summertime respiratory deposition was caused by an enhancement of the species concentration itself rather than from changes to size distributions. Three of these species (Al, Ni, and SO 2− 4 ) were detected as major modifiers of the PM 2.5 mass mortality association in recent epidemiological studies (Franklin et al 2008). An additional three species with a greater respiratory total deposition efficiency in the summer (V, Mn, and Fe) were identified as minor positive modifiers of PM 2.5 toxicity.…”

“…An additional three species with a greater respiratory total deposition efficiency in the summer (V, Mn, and Fe) were identified as minor positive modifiers of PM 2.5 toxicity. Six species (Na, P, Sb, Pb, NO Each of these species was shown to have weak or negative associations with health effects during the epidemiological analysis presented by Franklin et al (2008). Figure 5 shows specific deposition efficiencies (µg deposited per µg PM 1.8 species mass inhaled) in the head, tracheobronchial, and pulmonary regions of the respiratory system for all measured species during the summer and winter months.…”

“…There does not appear to be a consensus on which PM characteristics are the most important for acute and chronic health effects but numerous research studies are underway to address this question (Health Effects Institute (HEI) 2002). In one such study, Franklin et al (2008) used data from the EPA Technology Transfer Network Air Quality System and daily mortality records from the National Center for Health Statistics to demonstrate that PM 2.5 toxicity varies significantly by season and location across the United States. They went on to determine that increased proportions of PM aluminum (Al), nickel (Ni), arsenic (As), silicon (Si), and sulfate (SO 2− 4 ) enhanced the mass mortality association while nitrate (NO − 3 ) reduced the effect.…”

Semi-continuous speciation analyses for ambient air particulate matter: An urgent need for health effects studies

“…Success story from the Harvard PM center Franklin et al (2008) assembled daily mortality and PM 2.5 data for at least 4 years for 25 US cities (2000)(2001)(2002)(2003)(2004)(2005), and developed city-specific daily mortality coefficients for each city. They then used speciation data that were available for at least 2 years, plus daily weather data, to examine the possible roles of each of the available PM 2.5 components as a modifier of the apparent effect of PM 2.5 .…”

“…STN data have been sufficient to enable research investigators at NYU (Lippmann et al, 2006), and Harvard (Franklin et al, 2008) to gain new insights into the influences of PM 2.5 components (e.g., Ni, Al, and SO 4 ) and/or tracers on daily mortality and other health-related outcomes in human populations.…”