Coarse Particles From Saharan Dust and Daily Mortality

Background: Winds from the Sahara-Sahel desert region regularly transport large amounts of dust to the Americas, North Africa, and Europe. The presence of high dust concentrations for long periods of time, and the interaction between dust and man-made air pollution, raise concerns about adverse health effects and appropriate interventions by health authorities. This study tested the hypothesis that outbreaks of Saharan dust exacerbate the effects of man-made pollution, specifically fine and coarse particulate matter (PM2.5 and PM10-2.5, respectively) on daily mortality. Methods: We investigated the effects of exposure to PM10-2.5 and PM2.5 between March 2003 and December 2004 in Barcelona (Spain) on daily mortality; changes of effects between Saharan and non-Saharan dust days were assessed using a time-stratified crossover design. We studied the chemical composition of particulate matter to explain changes of effects. Results: The study included 24,850 deaths. During Saharan dust days, a daily increase of 10 mu g/m(3) of PM10-2.5 increased daily mortality by 8.4% (95% confidence interval = 1.5%-15.8%) compared with 1.4% (-0.8% to 3.4%) during non-Saharan dust days (P value for interaction = 0.05). In contrast, there was no increased risk of daily mortality for PM2.5 during Saharan dust days. Although coarse particles seem to be more hazardous during Saharan dust days, differences in chemical composition did not explain these observations. Conclusions: Saharan dust outbreaks may have adverse health effects. Further investigation is needed to understand the role of coarse particles and the mechanism by which Saharan dust increases mortality.