Characterization and inflammatory potential of sub-10nm particles from Gas cooking appliances

Combustion generated ultrafine particles are believed to have an effect on human health. Their presence in the atmosphere is mainly attributed to outdoor sources, but they may also form indoor. Gas cooking is a widely diffused indoor activity commonly considered environmentally clean, and without emissions of particulate matter. However, even bluish flames of natural gas may produce considerable number concentrations of sub-10nm particles if operating conditions deviate from stoichiometry and mixing at atomic level. These particles negligibly account for particulate mass but, due to their very low sizes, they can deposit far inside the airways and on skin and potentially reach target organs being dangerous although present in low mass concentrations. We have characterized the exhausts of a domestic cooktop burner measuring stable compounds, gas-phase aromatic compounds and particulate matter and collected nanoparticles for in vitro toxicological studies and for the analysis of their possible inflammatory effects. Combustion exhausts, including polycyclic aromatic hydrocarbons (PAH) and nanoparticles, have been sampled above a mid-range cooktop burner fed with network natural gas. Tests have been performed in a free flame and by putting a pot on the burner in order to simulate operating conditions closer to those of the real life. Speciation of PAHs and the distribution of the particles generated during combustion has been measured. Results of measurements show that the cooktop burner flames produce and emit low concentrations of PAHs and huge number concentrations of sub-10nm particles. Tests on cell viability performed with crystal violet assay shows no significative reduction in cell number after 24h of treatment, both with nanoparticles collected in a "free flame" and in the operating conditions with "a pot on the fire". It is interesting to note a little positive effect in increasing cell number (+20%) at the lowest concentration. No relevant overexpression or downregulation is noted on the secretion of the 27Plex Panel of Human Cytokine, performed with Bio-Plex 200 system.