Spatial heterogeneity of personal exposure to airborne metals in French urban areas.

The spatial distribution of urban population exposures to ambient air particles was investigated as part of the Genotox'ER study conducted in four metropolitan areas (Grenoble, Paris, Rouen and Strasbourg) in France. In each city, 60 to 90 non-smoking adult and children volunteers were selected. Subjects lived in three different urban sectors: one highly exposed to traffic emissions, one influenced by local industrial sources, and a background urban environment. The Harvard Chempass multi-pollutant personal sampler was used to sample PM10 and PM2.5 particles during 48 h during two different seasons ('hot' and 'cold'). The elemental composition of the filters was analysed by Particle-Induced X-ray Emission (PIXE). Sixteen elements were found to be over the method detection limits: Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb. The relative concentrations of elements of crustal origin (Si, Al, Ca) were higher in the coarse fraction of PM10 filters, while elements associated with combustion processes (traffic emissions or industrial combustion) presented higher relative concentrations in the PM2.5 fraction (S, Ni, V, Pb). Spatial heterogeneity of elemental exposures by urban sector is substantial for some metals of health concern, with 20% to 90% greater exposure values, on average, in the traffic proximity or industrial sectors, compared to the background sector, for Fe, Zn, Cu, V and Cr. This spatial heterogeneity should not be overlooked in epidemiological or risk assessment studies.

Can we use fixed ambient air monitors to estimate population long-term exposure to air pollutants? The case of spatial variability in the Genotox ER study.

Associations between average total personal exposures to PM2.5, PM10, and NO2 and concomitant outdoor concentrations were assessed within the framework of the Genotox ER study. It was carried out in four French metropolitan areas (Grenoble, Paris, Rouen, and Strasbourg) with the participation, in each site, of 60-90 nonsmoking volunteers composed of two groups of equal size (adults and children) who carried the personal Harvard Chempass multipollutant sampler during 48 h along two different seasons ("hot" and "cold"). In each center, volunteers were selected so as to live (home and work/school) in three different urban sectors contrasted in terms of air pollution (one highly exposed to traffic emissions, one influenced by local industrial sources, and a background urban environment). In parallel to personal exposure measurements, a fixed ambient air monitoring station surveyed the same pollutants in each local sector. A linear regression model was accommodated where the dependent pollutant-specific variable was the difference, for each subject, between the average ambient air concentrations over 48 h and the personal exposure over the same period. The explanatory variables were the metropolitan areas, the three urban sectors, season, and age group. While average exposures to particles were underestimated by outdoor monitors, in almost all cities, seasons, and age groups, differences were lower for NO2 and, in general, in the other direction. Relationships between average total personal exposures and ambient air levels varied across metropolitan areas and local urban sectors. These results suggest that using ambient air concentrations to assess average exposure of populations, in epidemiological studies of long-term effects or in a risk assessment setting, calls for some caution. Comparison of personal exposures to PM or NO2 with ambient air levels is inherently disturbed by indoor sources and activities patterns. Discrepancies between measurement devices and local and regional sources of pollution may also strongly influence how the ambient air concentrations relate to population exposure. Much attention should be given to the selection of the most appropriate monitoring sites according to the study objectives.

Pollution Atmosphérique et Santé: Corrélation ou Causalité? Le Cas de la Relation entre l'Exposition aux Particules et la Mortalité Cardio-pulmonaire.

De nombreuses études épidémiologiques ont observé dans des contextes différents une faible relation à court terme entre les particules et la mortalité cardio-pulmonaire, même quand les normes de qualité de l'air n'étaient pas dépassées. La causalité de cette relation est un enjeu de santé publique en raison de l'importance de la population exposée. Notre objectif est de faire l'inventaire critique des arguments utilisés dans 15 revues de la littérature publiées. Nous expliquons l'importance de distinguer la validité de la causalité et analysons de façon systématique les différents critères de jugement dans le contexte des études écologiques temporelles. Notre conclusion est que la relation observée est valide et que la plupart des critères de causalité sont respectés. Diminuer le niveau d'exposition des populations aux particules est souhaitable. En Europe, en agissant à la source, notamment sur les émissions Diesel, on diminuera aussi d'autres polluants qui peuvent jouer un rôle sanitaire. Aux États-Unis, la situation est plus complexe car les particules sont surtout secondaires. Il est également indispensable de poursuivre les recherches pour mieux connaître les déterminants des expositions globales des individus et mieux comprendre le rôle toxique des différents facteurs physico-chimiques des particules.