## 4 Discussion
At identical elution times ICP-MS gives higher signal intensities for Mg than MALLS does for scattered light (Figure 5). It can be concluded that signal recorded with MALLS but not with ICP-MS cannot be attributed to the presence of laponite. Thus, no release of laponite from any of the mechanical-, thermally-, or chemically-induced stress tests was detected. The signals recorded in the AF4/MALLS fractograms (black curves in Figures 8 and 9) are (again) most likely caused by abraded polymer. Both, theoretical considerations together with experimental empirical findings demonstrate that nanomaterials are immobilized in a polymer matrix and do not migrate based on Fickian law of diffusion [4; 5]. Although it is generally accepted that the limiting factor for migration is the size of the migrant and thus nanomaterials are too large to diffuse, some studies reported positive results in migration experiments from nanocomposites that contained silver [8; 9; 10; 11], clays [12; 13; 14], or titanium-based nanomaterials like titanium dioxide [15]. The reason for this might be the use of a wrong experimental design. Nanomaterials need both, a setup and analytical techniques that respect the particulate nature of the analyte throughout the experiment. However, it was recently demonstrated that common food simulants used in migration experiments for conventional polymer additives are not necessarily appropriate for nanomaterials, because nanomaterials might show weak stability and the potential to be solubilized. This way release of solubilized nanomaterials might be wrongly (false positive) interpreted as migration of particulate nanomaterials, if only element-specific detection techniques were used (e.g., detection of ionic silver with ICP-MS as a measure for release of silver nanoparticles). Furthermore, the way the samples are prepared is another crucial parameter. Some studies reported that the test samples were cut into small pieces to increase the surface (sample film) to volume (food simulant) ratio. This way the nanocomposite is damaged since at the variety of resulting cutting edges the nanomaterial might not be covered with polymer anymore. That way, no true migration under conditions as applied in practice but release of nanomaterials by dissolution of the nanomaterial itself or its surrounding polymer matrix becomes possible [16; 17]. Until now, the number of studies that investigated release of nanomaterials from consumer products after mechanical or otherwise induced stress conditions is limited. In a study of [PERSON] et al. [18], release of nanomaterials from coated cookware was only detectable after the surface was abraded with a tungsten carbide burr. As the authors stated, this condition obviously damaged the ceramic coating beyond reasonable use. Although the other abrasion conditions with scrubbing pad and steel wool can also be considered as severe, release of nanomaterials was not detected. [PERSON] et al. [19] found release of particles after abrasion and additionally weathered nanocomposites. However, no release of isolated nanoparticles was found but abrasion of polymer that contained the nanomaterial solely. In another study [PERSON] et al. [20] used an indirect measurement approach based on total Ti (ionic and particulate) without and with ultrafiltration to conclude from the difference on the potential release of particulate TiO\({}_{2}\) material. They report a correlation between mechanical stressing and release of nanomaterials [20]. In the respective study scratching of the surface of the pan coating led to higher release levels of titanium dioxide than test samples that were not stressed mechanically. It should be noted that the authors also reported release of TiO\({}_{2}\) nanomaterial from unstressed pan coatings, however, using disks punched out of the pan as test specimen with open cut edges and storing them under severe conditions in 3% acetic acid media. This way, the coating of the pan may have suffered from structural damaging as well.