PPM2.5 Components Most Closely Associated with Health Effects

MORTON LIPPMANN, Lung-Chi Chen

New York University School of Medicine, Tuxedo, NY

     Abstract Number: 27
     Last modified: September 30, 2009

Abstract
There is emerging evidence that some components of ambient air PM are associated with adverse health effects when PM2.5 mass concentrations are at or near the current NAAQS. These components include EC, Ni, V, and Pb, with suggestive evidence for others, such as Al, Zn, and OC. There is also literature implicating motor vehicle-related pollution, as indexed by proximity to major roadways, and by measured concentrations of OC, NO2, and UFP. However, there are also metals in motor vehicle exhaust and in resuspended road dust that may cause traffic-related health effects at contemporary ambient air concentrations, with a suggestion that the metals in resuspended road dust may be important. Furthermore, there is some evidence that adverse health effects are significantly associated with aerosol acidity originating from fossil fuel combustion, which could be due to its irritancy, or to its role in solubilizing metals within the particles.
ROFA, which is a mixture that is similar in composition to the fly ash emitted by power plants burning residual oil, and which is notably high in the content of Ni and V, as compared to other metals, and Utah Valley dust, which is a mixture enriched in steel mill emissions, were more toxic than other source-related mixtures that have been tested in laboratory animals in vivo, or in cells in vitro. For acute pulmonary system responses, it appears, from such tests, that V and Zn may play prominent roles, and that the effects may depend on interactions among the metals. For acute cardiovascular effects, Ni appears to play a more important role. By contrast, other source-related mixtures, such as coal combustion effluents, that are notable for their content of Se, Fe, and Mn, and re-suspended soil, that contains more refractory metals, have been found to be less acutely toxic.
Aside from metals, there has been a considerable focus on motor vehicle exhaust as a source category that could account for the adverse health effects associated with PM2.5, and especially the soot in the exhaust from diesel engines.
In recent NYU studies, the cumulative effects associated with subchronic inhalation exposures to ambient air PM2.5 CAPs were directly compared in the same animal models and exposure durations to those of diluted whole diesel engine exhaust (WDE) and sidestream cigarette smoke (SS). The eastern US regional CAPs was considerably more potent, in terms of aortic plaque progression, than either WDE or SS on the basis of PM mass inhaled, even without consideration of the gaseous toxicants associated with the SS and WDE.
In summary, tailpipe emissions, while likely to play some role in causing cardiovascular and pulmonary effects associated with ambient air PM2.5, may require especially high concentrations, and may not play a dominant role in the effects in the population as a whole, where toxic metals from power plants, space heating, and possibly from resuspended road dust, are worthy of increased concern.