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Abstract
BackgroundThe 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.ResultsAmbient 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.ConclusionIn 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.
Highlights
The contribution of air particles in human cardio-respiratory diseases has been enlightened by several epidemiological studies
An experimental sampling based on the collection of the PM0.03–0.17, PM0.17–1, PM1–2.5 and PM2.5–10 aerosol fractions was developed using four using 13-stage Dekati low pressure impactors (LPI) running in parallel
In a previous pilot study with different LPI running in parallel we showed from mass determinations that particle recovery was reproducible [18]
Summary
The contribution of air particles in human cardio-respiratory diseases has been enlightened by several epidemiological studies. Surface area and pulmonary deposition efficiency increase as particle size decreases, the fine and ultrafine aerosol fractions (commonly defined as PM2.5 and PM0.1 respectively) are expected to be responsible for the most significant health effects [4]. There is still conflicting evidence from epidemiological studies and the limited number of toxicological investigations as to whether the fine aerosol fraction or the coarse one (PM2.5–10) is the most relevant fraction involved in human health effects [6,7,8,9]. The type of cells (macrophages versus epithelial cells, human versus rodent cells), the particle composition according to the sampling sites (content in metals, organic compounds, endotoxins...) as well as particle sampling mode and fractionation (filtration versus impaction, number of size fractions) could explain such discrepancies among toxicological studies
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