Personal exposure to PM_2.5 emitted from typical anthropogenic sources in southern West Africa: chemical characteristics and associated health risks

Abstract

Urbanization is an issue that is strongly emerging in southern West Africa (sWA). There is a lack of full understanding on chemical compositions and personal exposure levels to fine particulate matter (hereafter defined as PE PM2.5) and its health risks related to various anthropogenic sources in this region. In this study, PE PM2.5 was studied in dry (January) and wet (July) seasons of 2016 for the first time to characterize the contributions of a domestic fire site (DF) to the exposure of women and a waste burning site (WB) to that of students in Abidjan, Côte d'Ivoire, and a motorcycle traffic site (MT) to that of drivers in Cotonou, Benin. The average PE PM2.5 mass concentrations were 331.7±190.7, 356.9±71.9 and 242.8±67.6 µg m−3 at DF, WB and MT sites for women, students and drivers, which were 2.4, 10.3 and 6.4 times the ambient PM2.5 concentrations, respectively. Elevated PE PM2.5 levels in the dry season were found at DF (358.8±100.5 µg m−3), WB (494.3±15.8 µg m−3) and MT (335.1±72.1 µg m−3) sites, on average 15 % higher than that at DF and 55 % higher at both WB and MT sites in the wet season. The seasonal variations were attributed to emission sources, meteorological factors and personal activities. In addition, the results show that geological material (35.8 %, 46.0 % and 42.4 %) and organic matter (34.1 %, 23.3 % and 24.9 %) were the major components of PE PM2.5 at DF, WB and MT sites. It is worth noting that the contribution of heavy metals was higher at WB (1.0 %) than at DF (0.7 %) and MT (0.4 %) sites, strongly influenced by waste burning emission. This results in the highest non-cancer risks of heavy metals to students, 5.1 and 4.8 times the values for women and drivers, respectively. By conducting organic speciation, fingerprints were used to access the exposure and identify the source contributions from typical local anthropogenic sources. The women's exposure concentration to particulate polycyclic aromatic hydrocarbons (PAHs) at DF (77.4±47.9 ng m−3) was 1.6 and 2.1 times, respectively, that of students at WB (49.9±30.7 ng m−3) and of drivers at MT (37.0±7.4 ng m−3). This can be associated with the higher contributions from solid fuels' burning and meat grilling activities to women, resulting in a level 5 times in exceedance of the cancer risk safety threshold (1×10-6). Phthalate esters (PAEs), commonly used as plasticizers in products, were in high levels in the student exposure PM2.5 samples (1380.4±335.2 ng m−3), owing to obvious waste burning activities nearby. The drivers' exposures to fossil fuel combustion markers of hopanes in PE PM2.5 at MT (50.9±7.9 ng m−3) was 3.0–3.3 times those for women at DF (17.1±6.4 ng m−3) and students at WB (15.6±6.1 ng m−3). Overall, the current study shows that wood combustion, waste burning, fugitive dust and motor vehicle emissions were the dominant sources of PE PM2.5 and mainly contributed to its toxicities. The exposure to the heavy metals Pb and Mn caused high non-cancer risks to students at WB, while the severe cancer risk of PAHs was found for women at DF via inhalation. The result of this study provides original data, initial perspective of PM2.5 personal exposure and health risk assessment in the developing areas. The information encourages the governments to improve the air quality and living standards of residents in this region.