Is TiO ₂ carcinogenic? A toxicological alert

Titanium dioxide (TiO 2 ) is a white powder used in toothpaste, pharmaceuticals, sunscreen, food additives, cosmetics, paints, decontaminants, and photocatalysts. It is produced and used in the workplace in fine and ultrafine particle sizes. International organizations set occupational exposure limits for fine and ultrafine TiO 2 particles. TiO 2 has not been confirmed to have carcinogenicity in humans, with available assessment data being limited and inconclusive owing to nonspecific effects observed from TiO 2 inhalation. The purpose of this toxicological alert is to encourage new studies to determine whether TiO 2 is a human carcinogen. TiO 2 ’s classification as a possible carcinogen was based on laboratory experiments that produced TiO 2 particles with 30–60 nm diameters. These studies assessed the potential risk of exposure to TiO 2 nanoparticles, which have diverse and atypical characteristics compared to those found in workplace settings. To date, there are no studies with sufficient data on the duration of pulmonary exposure to TiO 2 nanoparticles with significantly relevant workplace associations. Extrapolating results from rodent studies with limited parameter controls do not provide an adequate (translational) assessment of the toxicity of TiO 2 nanoparticles on the human respiratory system.