Combined health effects of PM components on respiratory mortality in short-term exposure using BKMR: A case study in Sichuan, China.

One of the major causes of global mortality is respiratory diseases. Fine particulate matter (PM) increased the risk of respiratory death in short-term exposure. PM is the chemical mixture of components with different health effects. The combined health effects of PM are determined by the role of each component and the potential interaction between components, but they have not been studied in short-term exposure. Sichuan Province (SC), with high respiratory mortality and heavy PM pollution, had distinctive regional differences in four regions in sources and proportions of PM, so it was divided into four regions to explore the combined health effects of PM components on respiratory mortality in short-term exposure and to identify the main hazardous components. Due to the multicollinear, interactive, and nonlinear characteristics of the associations between PM components and respiratory mortality, Bayesian kernel machine regression (BKMR) was used to characterize the combined health effects, along with quantile-based g-computation (QGC) as a reference. Positive combined effects of PM were found in all four regions of Sichuan using BKMR with excess risks (ER) of 0.0101-0.0132 (95 % CI: 0.0093-0.0158) and in the central basin and northwest basin using QGC with relative risks (RR) of 1.0064 (95 % CI: 1.0039, 1.0089) and 1.0044 (95 % CI: 1.0022, 1.0066), respectively. In addition, the adverse health effect was larger in cold seasons than that in warm seasons, so vulnerable people should reduce outdoor activities in heavily polluted days, especially in the cold season. For the components of PM, the BC and OM mainly from traffic, dominated the adverse health effects on respiratory mortality. Furthermore, NO might aggravate the adverse health effects of BC/OM. Therefore, BC/OM and NO should be focused together in air pollution control.