IDENTIFICATION,  PHYSICOCHEMICAL  CHARACTERISATION AND  PRELIMINARY RISK ANALYSIS  OF TITANIUM DIOXIDE  PARTICLES IN FACE MASKS  Intermediate report TiO2-Mask COVID-19 project  September 2021, Mast, Jan, Blaude Marie-Noelle, Siciliani Lisa, Cheyns Karlien, Waegeneers Nadia, Van Loco Joris, Vleminckx Christiane, and Verleysen Eveline , sept 2021, Elsene, Belgium, p.50, (2021)