Tempo-Spatial Variability and Health Risks of PM2.5 and Associated Metal(loid)s in Greater Cairo, Egypt

Abstract

Greater Cairo is one of the largest metropolitan areas in the world, yet the tempo-spatial trends of PM2.5 and loaded metal(loid)s) in its atmosphere, and their potential health risks, are poorly understood. We investigated the air concentrations of PM2.5, and associated Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn, in one urban and one industrial locations within Greater Cairo for one year in each location. Statistical analysis suggested that PM2.5 and its chemical composition in Greater Cairo are more influenced by land-use and local activities rather than meteorological conditions. Both annual and daily levels of PM2.5 were well above the WHO air quality guidelines, with annual averages of c. 37 and 56 µg m−3, and daily maximums of 165 and 176 µg m−3, in the urban and industrial areas, respectively. This indicates high probability of PM2.5 inflicted short- and long-term health risks to the population of Greater Cairo. Health risk modelling indicated that the residents of Greater Cairo are facing high non-carcinogenic and carcinogenic risks (up to 47 and 28 times the recommended hazard indices, respectively) from the studied 12 metal(loid)s combined. Lead (Pb) was the highest single threat to the health of Greater Cairo residents amounting up to 56% and 83% of the total non-carcinogenic and carcinogenic risks, respectively. Nevertheless, most of the exposure to Pb originated from ingestion rather than inhalation which was marginal. For all elements combined, and for some other individual elements, inhalation was a significant route of exposure but only for non-carcinogenic risks. For carcinogenic risks, the contribution of inhalation to the total risk was negligible.