Physico-chemical characterization of African urban aerosols (Bamako in Mali and Dakar in Senegal) and their toxic effects in human bronchial epithelial cells: description of a worrying situation.

BACKGROUND: The involvement of particulate matter (PM) in cardiorespiratory diseases is now established in developed countries whereas in developing areas such as Africa with a high level of specific pollution, PM pollution and its effects are poorly studied. Our objective was to characterize the biological reactivity of urban African aerosols on human bronchial epithelial cells in relation to PM physico-chemical properties to identify toxic sources. METHODS: Size-speciated aerosol chemical composition was analyzed in Bamako (BK, Mali, 2 samples with one having desert dust event BK1) and Dakar (DK; Senegal) for Ultrafine UF, Fine F and Coarse C PM. PM reactivity was studied in human bronchial epithelial cells investigating six biomarkers (oxidative stress responsive genes and pro-inflammatory cytokines). RESULTS: PM mass concentrations were mainly distributed in coarse mode (60%) and were impressive in BK1 due to the desert dust event. BK2 and DK samples showed a high content of total carbon characteristic of urban areas. The DK sample had huge PAH quantities in bulk aerosol compared with BK that had more water soluble organic carbon and metals. Whatever the site, UF and F PM triggered the mRNA expression of the different biomarkers whereas coarse PM had little or no effect. The GM-CSF biomarker was the most discriminating and showed the strongest pro-inflammatory effect of BK2 PM. The analysis of gene expression signature and of their correlation with main PM compounds revealed that PM-induced responses are mainly related to organic compounds. The toxicity of African aerosols is carried by the finest PM as with Parisian aerosols, but when considering PM mass concentrations, the African population is more highly exposed to toxic particulate pollution than French population. Regarding the prevailing sources in each site, aerosol biological impacts are higher for incomplete combustion sources resulting from two-wheel vehicles and domestic fires than from diesel vehicles (Dakar). Desert dust events seem to produce fewer biological impacts than anthropogenic sources. DISCUSSION: Our study shows that combustion sources contribute to the high toxicity of F and UF PM of African urban aerosols, and underlines the importance of emission mitigation and the imperative need to evaluate and to regulate particulate pollution in Africa.

Role of size and composition of traffic and agricultural aerosols in the molecular responses triggered in airway epithelial cells.

The increased levels of fine particles in the atmosphere are suspected of aggravating cardiopulmonary diseases, but the determinants of particle toxicity are poorly understood. This work aims at studying the role of composition and size in the toxicity of size-segregated particulate matter (PM) collected at different sites on human bronchial epithelial cells. PM were sampled at a traffic urban site (Urb S) and a rural site (Rur S) during the pesticide-spreading period. Ultrafine (UF), fine (F), and coarse (C) PM were characterized by their shape and chemical composition. Whatever the site, the finest PM (UF and F) induced the mRNA expression of CYP1A1, a biomarker of polyaromatic hydrocarbons (PAH) exposure, NQO-1 and heme HO-1, two antioxidant responsive element-driven genes; and two effect biomarkers, GM-CSF, a proinflammatory cytokine and amphiregulin (AR), a growth factor. C PM have a low or no effect. Interestingly, AR is more strongly induced by rural PM at the same mass exposure. These discrepancies suggest involvement of PM chemical composition: rural PM bearing the characteristics of aged aerosols with a high content of water-soluble components, and PM at urban kerbside sites containing mainly water-insoluble components. To conclude, we provide evidence that the finest PM fractions, whatever their origin, are more prone to induce exposure and effect biomarkers. The AR differential expression suggests a source-dependent effect requiring further investigation because of the role of this growth factor in airway remodeling, a characteristic feature of chronic lung respiratory diseases exacerbated by particulate pollution.

Size-partitioning of an urban aerosol to identify particle determinants involved in the proinflammatory response induced in airway epithelial cells.

BACKGROUND: The contribution of air particles in human cardio-respiratory diseases has been enlightened by several epidemiological studies. However the respective involvement of coarse, fine and ultrafine particles in health effects is still unclear. The aim of the present study is to determine which size fraction from a chemically characterized background aerosol has the most important short term biological effect and to decipher the determinants of such a behaviour. RESULTS: Ambient aerosols were collected at an urban background site in Paris using four 13-stage low pressure cascade impactors running in parallel (winter and summer 2005) in order to separate four size-classes (PM0.03-0.17 (defined here as ultrafine particles), PM0.17-1 (fine), PM1-2.5(intermediate) and PM2.5-10 (coarse)). Accordingly, their chemical composition and their pro-inflammatory potential on human airway epithelial cells were investigated. Considering isomass exposures (same particle concentrations for each size fractions) the pro-inflammatory response characterized by Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) release was found to decrease with aerosol size with no seasonal dependency. When cells were exposed to isovolume of particle suspensions in order to respect the particle proportions observed in ambient air, the GM-CSF release was maximal with the fine fraction. In presence of a recombinant endotoxin neutralizing protein, the GM-CSF release induced by particles is reduced for all size-fractions, with exception of the ultra-fine fraction which response is not modified. The different aerosol size-fractions were found to display important chemical differences related to the various contributing primary and secondary sources and aerosol age. The GM-CSF release was correlated to the organic component of the aerosols and especially its water soluble fraction. Finally, Cytochrome P450 1A1 activity that reflects PAH bioavailability varied as a function of the season: it was maximal for the fine fraction in winter and for the ultrafine fraction in summer. CONCLUSION: In the frame of future regulations, a particular attention should thus be paid to the ultrafine/fine (here referred to as PM1) fraction due to their overwhelming anthropogenic origin and predominance in the urban aerosol and their pro-inflammatory potential.

Wet and dry atmospheric deposition on TiO(2) coated glass.

To prevent the soiling of glass window used in the built environment, the use TiO(2) coated products appears an important application matter. To test the cleaning efficiency and the sustainability of self-cleaning glass, a field experiment was conducted under real life condition, on a site representative of the background urban pollution. Samples of float glass, used as reference, and commercialized TiO(2) coated glasses were exposed to dry and wet atmospheric deposition during two years. The crossed optical, chemical and microscopic evaluations performed, after withdrawal, allowed highlighting a sensible difference between the reference and the self-cleaning substrate in terms of accumulation, nature, abundance and geometry of the deposit. This experiment conducted in real site emphasized on the efficacy of self-cleaning glass to reduce the maintenance cost.