1. Mechanism of Action of TiO2: Recommendations to Reduce Uncertainties Related to Carcinogenic Potential
- Author
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Rob J. Vandebriel, Agnes G. Oomen, Monique Groenewold, Ilse Gosens, Hedwig M. Braakhuis, Minne B. Heringa, and Flemming R. Cassee
- Subjects
0301 basic medicine ,Pharmacology ,Inhalation exposure ,medicine.medical_specialty ,business.industry ,Mechanism (biology) ,010501 environmental sciences ,Toxicology ,01 natural sciences ,03 medical and health sciences ,030104 developmental biology ,Mechanism of action ,Adverse Outcome Pathway ,Oral route ,Medicine ,Intestinal tumors ,medicine.symptom ,business ,Intensive care medicine ,Risk assessment ,Carcinogen ,0105 earth and related environmental sciences - Abstract
The Risk Assessment Committee of the European Chemicals Agency issued an opinion on classifying titanium dioxide (TiO2) as a suspected human carcinogen upon inhalation. Recent animal studies indicate that TiO2 may be carcinogenic through the oral route. There is considerable uncertainty on the carcinogenicity of TiO2, which may be decreased if its mechanism of action becomes clearer. Here we consider adverse outcome pathways and present the available information on each of the key events (KEs). Inhalation exposure to TiO2 can induce lung tumors in rats via a mechanism that is also applicable to other poorly soluble, low-toxicity particles. To reduce uncertainties regarding human relevance, we recommend gathering information on earlier KEs such as oxidative stress in humans. For oral exposure, insufficient information is available to conclude whether TiO2 can induce intestinal tumors. An oral carcinogenicity study with well-characterized (food-grade) TiO2 is needed, including an assessment of toxicokinetics and early KEs. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 61 is January 8, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
- Published
- 2021
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