In order to evaluate the penetration of the nanoparticles, eight adult male Wistar rats (3 months old) were used for the in vivo experiments. The protocol was approved by the local University Committee for animal testing and is in accordance with the Canadian Council on Animal Care (CICUAL-RD-2021–892-E-UNC-DEC#FCQ).

In a review published in 2022 in the journal Archives of Toxicology, researchers found that the ingestion of E171 is a “a definite health risk for consumers and their progeny.” After reviewing dozens of in vivo, ex vivo and in vitro studies on the toxicity of E171, the researchers wrote that two facts must be noted: “First, reprotoxicity studies show that animals of both sexes are impacted by the toxicity of these nanoparticles, underlining the importance of conducting in vivo studies using both male and female animals. Second, human exposure begins in utero via maternal-fetal transfer and continues after birth by breastfeeding. Children are then chronically re-exposed due to their food preferences. To be relevant to the human in vivo situation, experimental studies should therefore consider nanoparticle exposure with respect to the age or life period of the studied population.”

TiO₂ comes in many different forms. However, only a few of these forms are considered food-grade (acceptable to be added to food). Many studies that raised concern about the safety of TiO₂, including the concern for genotoxicity, used forms of TiO₂ that are not considered acceptable for use in food and have different properties than food-grade TiO₂. Other studies did use food-grade TiO₂, but took steps to break the material down into smaller particles than what would normally be found in food.