Attributing health effects to apportioned components and sources of particulate matter: An evaluation of collective results

It has been hypothesized that the composition of particulate matter (PM) may be a better predictor of health effects than PM mass alone. The regional differences in PM composition and the heterogeneity in PM risk estimates in large multi-city epidemiologic studies are consistent with this hypothesis. Since 2005, efforts have been made to relate apportioned components and sources of PM with human health outcomes in epidemiology, controlled human exposure and toxicology studies. We reviewed published studies that: 1) focused on short-term exposure to PM; 2) included at least five components of PM; 3) grouped them into factors or sources; and 4) used quantitative methods to examine the relationship between the factors or sources and health effects. We then examined whether specific groups of PM components or sources of PM are consistently linked to specific health effects across studies. Collectively, these studies suggest that cardiovascular effects may be associated with PM2.5 from crustal or combustion sources, including traffic, but at this time, no consistent relationships have emerged. Fewer studies evaluated respiratory health effects, and the evidence for associations was limited. Apportionment methods have linked a variety of health effects to multiple groups of PM components and sources of PM, but the collective evidence has not yet isolated factors or sources that would be closely and unequivocally related to specific health outcomes. Published by Elsevier Ltd.