A Systematic Review of Cardiovascular Responses Associated with Ambient Black Carbon and Fine Particulate Matter
Background: Exposure to fine particulate matter (PM2.5), an ambient air pollutant with mass-based standards promulgated under the Clean Air Act, and black carbon (BC), a common component of PM2.5, are both associated with cardiovascular health effects. Objectives: To elucidate whether BC is associated with distinct, or stronger, cardiovascular responses compared to PM2.5, we conducted a systematic review. We evaluated the associations of BC, or the related component elemental carbon (EC), with cardiovascular endpoints including heart rate variability, heart rhythm, blood pressure and vascular function, ST segment depression, repolarization abnormalities, atherosclerosis and heart function, in the context of what is already known about PM2.5. Data sources: We conducted a stepwise systematic literature search of the PubMed database and applied Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines for reporting our results.
Methods: Studies reporting effect estimates for the association of quantitative measurements of ambient BC (or EC) and PM2.5, with a relevant cardiovascular endpoints were included in the review. Included studies were evaluated for risk of bias. Risk of bias evaluations assessed aspects of internal validity of study findings based on study design, conduct, and reporting and identify potential issues related to confounding or other biases. Results: Our results demonstrate similar associations for BC (or EC) and PM2.5 with the cardiovascular endpoints examined. Across studies, associations for BC and PM2.5 varied in their magnitude and precision, and confidence intervals were generally overlapping within studies. Where differences in the magnitude of the association between BC or EC and PM2.5 within a study could be discerned, no consistent pattern across the studies examined was apparent. Conclusions: Overall, the evidence indicates that both BC (or EC) and PM2.5 are associated with cardiovascular effects but the available evidence is not sufficient to distinguish the effect of BC (or EC) from that of PM2.5 mass. We were unable to assess the independence of the effect of BC, relative the effect of PM2.5, on the cardiovascular system, nor was information available to understand the impact of differential exposure misclassification.