Associations between short-term exposure of PM2.5 constituents and hospital admissions of cardiovascular diseases among 18 major Chinese cities

Previous studies showed different risk effects on exposure of fine particulate matter (PM2.5) mass for cardio-vascular disease (CVD) globally, which is likely due to different constituents of PM2.5. This study aimed to investigate the association between short-term exposure of PM2.5 constituents and hospital admissions of CVD. Daily counts of city-specific hospital admissions for CVD in 18 cities in China between 2014 and 2017 were extracted from the national Urban Employee Basic Medical Insurance database and the Beijing Municipal Commission of Health and Family Planning Information Center database. Directly measured PM2.5 constituents, including ions and polycyclic aromatic hydrocarbons, were collected by the Chinese Environmental Public Health Tracking system. We used the time-stratified case-crossover design to estimate the association between PM2.5 constituents and hospital admissions of CVD. Concentrations of ions accounted for the majority of the detected constituents. Excess risk (ER) of average ions concentrations for CVD was highest as 2.30% (95% CI: 1.62-2.99%) for NH4+, whose major sources are residential and agricultural emissions. This was followed by 1.85% (1.30-2.41%) for NO3- (generally from vehicles), 0.95% (0.28-1.63%) for SO42-(often from fossil fuel burning) respectively. The association for ions were generally consistent with ischemic heart disease (IHD) and ischemic stroke, e.g., NH4+ was associated with IHD (2.50%; 1.52-3.48%) and ischemic stroke (1.77%; 0.65-2.9%). For polycyclic aromatic hydrocarbons (PAHs), mainly from coal and vehicle-related oil combustion, the constituents were all associated with ischemic stroke but not for IHD. The ER for ischemic stroke was highest at 1.69% (0.99-2.39%) for indeno (123-cd) pyrene. Thus, in terms of the subtypes of CVD, the risks of hospital admissions varied with exposure to different PM2.5 constituents. Exposed to NH4+ had the highest risk to IHD and ischemic stroke, whereas PAHs were predominately associated with ischemic stroke only.