Wear particles from automotive friction brake pads of various sizes, morphology, and chemical composition are significant contributors towards particulate matter. Knowledge concerning the potential adverse effects following inhalation exposure to brake wear debris is limited. Our aim was, therefore, to generate brake wear particles released from commercial low-metallic and non-asbestos organic automotive brake pads used in mid-size passenger cars by a full-scale brake dynamometer with an environmental chamber simulating urban driving and to deduce their potential hazard in vitro. The collected fractions were analysed using scanning electron microscopy via energy-dispersive X-ray spectroscopy (SEM-EDS) and Raman microspectroscopy. The biological impact of the samples was investigated using a human 3D multicellular model consisting of human epithelial cells (A549) and human primary immune cells (macrophages and dendritic cells) mimicking the human epithelial tissue barrier. The viability, morphology, oxidative stress, and (pro-)inflammatory response of the cells were assessed following 24 h exposure to ~ 12, ~ 24, and ~ 48 µg/cm2 of non-airborne samples and to ~ 3.7 µg/cm2 of different brake wear size fractions (2-4, 1-2, and 0.25-1 µm) applying a pseudo-air-liquid interface approach. Brake wear debris with low-metallic formula does not induce any adverse biological effects to the in vitro lung multicellular model. Brake wear particles from non-asbestos organic formulated pads, however, induced increased (pro-)inflammatory mediator release from the same in vitro system. The latter finding can be attributed to the different particle compositions, specifically the presence of anatase.

BioNanomaterials Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland

BioNanomaterials Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland Chemistry Department University of Fribourg Fribourg Switzerland

BioNanomaterials Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland In Vitro Toxicology Group Swansea University Medical School Swansea Wales UK

BioNanomaterials Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland Laboratory for Materials Biology Interactions Empa Swiss Federal Laboratories for Materials Science and Technology St Gallen Switzerland

BioNanomaterials Group Adolphe Merkle Institute University of Fribourg Chemin des Verdiers 4 1700 Fribourg Switzerland Nanotechnology Centre VŠB Technical University of Ostrava Ostrava Czech Republic

Nanotechnology Centre VŠB Technical University of Ostrava Ostrava Czech Republic

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