Saharan Dust and Associations between Particulate Matter and Daily Mortality in Rome, Italy
Mallone, Sandra, Stafoggia, Massimo, Faustini, Annunziata, Gobbi, Gian Paolo, Marconi, Achille, Forastiere, Francesco, Environmental Health Perspectives
BACKGROUND: Outbreaks of Saharan-Sahel dust over Euro-Mediterranean areas frequently induce exceedances of die European Union's 24-hr standard of 50 [micro]g/[m.sup.3] for particulate matter (PM) with aerodynamic diameter [greater than or equal to] than 10 [micro]m ([PM.sub.10]).
OBJECTIVES: We evaluated the effect of Saharan dust on the association between different PM fractions and daily mortality in Rome, Italy.
METHODS: In a study of 80,423 adult residents who died in Rome between 2001 and 2004, we performed a time-series analysis to explore the effects of [PM.sub.2.5], [PM.sub.2.5_10] and [PM.sub.10] on natural, cardiac, cerebrovascular, and respiratory mortality. We defined Saharan dust days by combining light detection and ranging (LIDAR) observations and analyses from operational models. We tested a Saharan dust-PM interaction term to evaluate the hypothesis that the effects of PM, especially coarse PM ([PM.sub.2.5_10]), on mortality would be enhanced on dust days.
RESULTS: Interquartile range increases in [PM.sub.2.5_10] (10.8 [micro]g/[m.sup.3]) and [PM.sub.10] (19.8 [micro]g/[m.sup.3]) were associated with increased mortality due to natural, cardiac, cerebrovascular, and respiratory causes, with estimated effects ranging from 2.64% to 12.65% [95% confidence interval (CI), 1.18-25.42%] for the association between [PM.sub.2.5_10] and respiratory mortality (0- to 5-day lag). Associations of [PM.sub.2.5_10] with cardiac mortality were stronger on Saharan dust days (9.73%; 95% CI, 4.25-15.49%) than on dust-free days (0.86%; 95% CI, -2.47% to 4.31%; p = 0.005). Saharan dust days also modified associations between [PM.sub.10] and cardiac mortality (9.55% increase; 95% CI, 3.81-15.61%; vs. dust-free days: 2.09%; 95% CI, -0.76% to 5.02%;p = 0.02).
CONCLUSIONS: We found evidence of effects of [PM.sub.2.5_10] and PMjn on natural and cause-specific mortality, with stronger estimated effects on cardiac mortality during Saharan dust outbreaks. Toxicological and biological effects of particles from desert sources need to be further investigated and taken into account in air quality standards.
KEY WORDS: air pollution, epidemiology, mortality, particulate matter, Saharan dust. Environ Health Perspect 119:1409-1414 (2011). http://dx.doi.org/10.1289/ehp.1003026 [Online 17 June 2011]
Desert dust, blown by winds thousands of kilometers away from its source, represents one of the main natural contributions to atmospheric paniculate matter (PM). Frequent events of dust advection from Sahara-Sahel deserts affect the Euro-Mediterranean region (Dulac et al. 1992; Gerasopoulos et al. 2006; Moulin et al. 1998). Events of dust advection have been shown to frequently induce exceedances of the World Health Organization (WHO) short-term guideline for PM with an aerodynamic diameter < 10 pm (PM10) of 50 ug/[m.sup.3] for a 24-hr mean, mainly in Southern Europe and with the longest duration in summer (Goudie and Middleton 2001; Rodriguez et al. 2001). The 2008 Air Quality European Union (EU) Directive (European Commission 2008) permits a maximum of 35 days exceeding the 50-pg/[m.sup.3] 24-hr level per year, but exceedances may be excluded from the total number of days per year if they are attributable to natural sources, such as the "atmospheric re-suspension or transport of natural particles from dry regions" (European Commission 2008).
To date, the impact of dust events from deserts on health has not been extensively explored, and findings from the available studies are inconsistent. Middleton et al. (2008) found an increase in hospital admissions during dust days in the city of Nicosia (Cyprus). Studies conducted in Taipei and Seoul, Korea (mineral dust originating from the Gobi desert), have suggested an increase in total mortality related to dust episodes (Chen et al. 2004; Kwon et al. 2002). In contrast, a study conducted in the region of Greater Vancouver (British Columbia, Canada) showed no association between the Gobi dust event in 1998 and hospitalizations (Bennett et al. …