Association between ambient fine particulate matter constituents and mortality and morbidity of cardiovascular and respiratory diseases: A systematic review and meta-analysis

Existing studies have explored the associations between short-term or long-term exposures to PM_2.5 constituents and mortality and morbidity outcomes related to all-causes, natural causes and the cardiopulmonary system, but the results are still inconclusive. To explore the associations between short-term and long-term exposures to ambient PM_2.5 constituents with mortality and morbidity outcomes of all-cause, natural, cardiovascular and respiratory diseases. We comprehensively searched PubMed, Embase, Web of Science and Scopus electronic databases to identify studies until 28, August 2023. We estimated the pooled relative risk (RR) with 95% confidence interval (CI) using random-effect models. Then we explored potential sources of heterogeneity across different studies by subgroup and meta-regression analysis. A total of 67 articles were included in the meta-analysis. We found that short-term exposures to PM_2.5 carbon-containing constituents (black carbon and organic carbon) and metal iron showed the most consistent associations with the eight health outcomes among different PM_2.5 constituents. Meanwhile, only long-term exposures to nitrate ions and silicon in PM_2.5 showed significant positive associations with cardiovascular and natural mortality outcomes. Additionally, subgroup and meta-regression analyses highlight that geographical region and age group are primary sources of heterogeneity. The current meta-analysis reveals potential key PM_2.5 constituents associated with elevated risk of mortality and morbidity of cardiovascular and respiratory diseases. Thus, greater attention should be directed toward establishing exposure limits for specific PM_2.5 constituents to protect public health and alleviate the associated burden of diseases.