Abstract
BACKGROUND: Exposure to fine particulate matter (PM(2.5)), an ambient air pollutant with mass-based standards promulgated under the Clean Air Act, and black carbon (BC), a common component of PM(2.5), are both associated with cardiovascular health effects. OBJECTIVES: To elucidate whether BC is associated with distinct, or stronger, cardiovascular responses compared to PM(2.5), we conducted a systematic review. We evaluated the associations of short- and long-term 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 PM(2.5). DATA SOURCES: We conducted a stepwise systematic literature search of the PubMed, Web of Science and TOXLINE databases and applied Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines for reporting our results. STUDY ELIGIBILITY CRITERIA: Studies reporting effect estimates for the association of quantitative measurements of ambient BC (or EC) and PM(2.5), with relevant cardiovascular endpoints (i.e. meeting inclusion criteria) were included in the review. Included studies were evaluated for risk of bias in study design and results. STUDY APPRAISAL AND SYNTHESIS METHODS: Risk of bias evaluations assessed aspects of internal validity of study findings based on study design, conduct, and reporting to identify potential issues related to confounding or other biases. Study results are presented to facilitate comparison of the consistency of associations with PM(2.5) and BC within and across studies. RESULTS: Our results demonstrate similar associations for BC (or EC) and PM(2.5) with the cardiovascular endpoints examined. Across studies, associations for BC and PM(2.5) 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 PM(2.5) within a study could be discerned, no consistent pattern across the studies examined was apparent. LIMITATIONS: We were unable to assess the independence of the effect of BC, relative the effect of PM(2.5), on the cardiovascular system, nor was information available to understand the impact of differential exposure misclassification. CONCLUSIONS: Overall, the evidence indicates that both BC (or EC) and PM(2.5) are associated with cardiovascular effects but the available evidence is not sufficient to distinguish the effect of BC (or EC) from that of PM(2.5) mass.