This study focuses on research in the area of "nanomaterials in waste" and shows the difficulty of providing quantitative data on nanomaterials in different wastes. As highlighted in the ECHA report (November 2021) and although substantial progress have been made in the characterization and measurement of nanomaterials, some challenges remain, particularly the characterization of nanomaterials in complex media. Therefore, work to improve the detection, characterization, and quantification of nanomaterials should be continued to complete the database with different types of nanowaste mixtures. The dominant end-of-life scenario for nanocomposites is the incineration. The environmental by-products impact on the soil and air have been considered from the point of view of nanoparticles partitioning and the potential toxicological synergistic effects. A specific management of nanocomposites end-of-life should be implemented as recommended by the Organization for Economic Co-operation and Development (OECD) in order to limit nanoparticles dissemination by landfilling and particularly in incineration facilities where their presence is significantly increasing. The aim of our study was to expand the current knowledge of the partition of nanowaste, mainly in case of nanocomposites mixture, and the potential synergetic or antagonistic impact of potential hazardous nanowastes on the toxicological profile. Incineration products of ethylene-vinyl acetate copolymer (EVA) and polydimethylsiloxane (PDMS) nanocomposites containing both silica and precipitated calcium carbonate, corresponding to cable sheaths compositions, were investigated in this study, using a lab-scale incineration process. Soot and residue composition were analysed using various relevant experimental techniques in order to assess the presence of initial nanoparticles. In vitro toxicological assessments were carried out and have shown that only pro-inflammatory responses seem to be affected by the presence of nanoparticles. SiO2 nanoparticles appear to have a major impact on toxicity whatever the partitioning in soot or residue. Conversely, CaCO3 as expected does not impact the nanowaste toxicity and does not seem able to mitigate the SiO2 toxicity.