Black Carbon Particulate from Traffic Exhaust Linked with Stroke

A new study published in Environmental Health Perspectives suggests that long-term exposure to particulate black carbon was associated with an increase in incident stroke.

The researchers, based in Sweden, sought to assess any associations between long-term exposure to two different types of particulate matter sources, and incident ischemic heart disease and stroke. Using data from emissions databases, monitoring data, and detailed dispersion models, they looked at sources for particulate matter and black carbon from road wear, traffic exhaust, residential heating, and other sources. Drawing on data from four cohorts, the researchers examined rates of incident heart disease and stroke for first hospitalization or death, and then constructed exposure windows for same-year, 1-5y, and 6-10y averages preceding the previous year’s averages at certain residential addresses. They then calculated risk estimates based on random effects meta-analyses of cohort-specific Cox proportional hazard models.

The cohort consisted of 144,758 participants, among whom 5,166 incident heart disease and 3,119 stroke cases were reported. According to their data, the researchers did not observe many associations between differing air pollution measures and incident heart disease or stroke. They did observe, however, that same-year levels of locally emitted black carbon particulate (range, 0.01 μg/m³ to 4.6 μg/m³) was associated with a 4.0% increase in incident stroke per interquartile range 30.0 μg/m³ (95% CI, 0.04 to 7.8); they also reported that this was due primarily to traffic exhaust. Associations between incident heart disease were reported only for PM_2.5 exposure due to residential heating.

“This study identifies local traffic exhaust as a risk factor for stroke, a common disease with great human suffering, high mortality and significant costs to society,” said Petter Ljungman, researcher at the Institute of Environmental Medicine at Karolinska Institute, in a press release. “We see that these emissions have consequences even in low-pollution environments like Swedish cities.”