The number of products containing nanomaterials is increasing this last ten years. Information and literature about the end-of-life of nanocomposites often remains partial and does not address the overall fate and transformations of nanoparticles that may affect biological responses. This paper underlines that the physico-chemical features of nanoparticles can be modified by the incineration process and the available toxicological data on pristine nanofillers might not be relevant to assess the modified nanoparticles included in soot. Combustion tests have been performed at lab-scale using a cone calorimeter modified to collect fumes (particulate matter and gas phase) and have been characterized using various techniques. Nanocomposites selected were poly(ethylene vinyl acetate) containing Al-based nanoparticles, i.e. boehmites or alumina. Evaluations of in vitro cytotoxicity responses on pristine nanofillers, soot and residual ash, show that safe boehmite nanoparticles, become toxic due to a chemical modification after incineration process.