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1. What is titanium dioxide?

The most significant uncertainty identified by the EU experts was the concern that TiO₂ particles may have genotoxic effects. Genotoxicity refers to the ability of a chemical to directly damage genetic material within a cell (DNA), which may lead to cancer in certain situations. Although the experts did not conclude that TiO₂ particles in E171 are genotoxic, they could not rule out the concern that they might be.

As mentioned above, these oxide NPs are harmful in part because both anatase and rutile forms are semiconductors and produce ROS. Particularly, P25 kind has band-gap energies estimated of 3.2 and 3.0 eV, equivalent to radiation wavelengths of approximately 388 and 414 nm, respectively. Irradiation at these wavelengths or below produces a separation of charge, resulting in a hole in the valence band and a free electron in the conduction band, due to the electron movement from the valence to conduction bands. These hole–electron pairs generate ROS when they interact with H₂O or O₂ [43,44]. It was described that they can cause an increase in ROS levels after exposure to UV-visible light [45]. The NBT assay in the studied samples showed that bare P25TiO₂NPs produce a large amount of ROS, which is drastically reduced by functionalization with vitamin B2 (Fig. 5). This vitamin, also known as riboflavin, was discovered in 1872 as a yellow fluorescent pigment, [46] but its function as an essential vitamin for humans was established more than sixty years later, and its antioxidant capacity was not studied until the end of the XX century [47,48]. This antioxidant role in cells is partially explained because the glutathione reductase enzyme (GR) requires it for good functionality. This enzyme is the one in charge of the conversion of oxidized glutathione to its reduced form which acts as a powerful inner antioxidant and can quench the ROS [49,50]. The cost of this action is that the glutathione is converted to the oxidized form and needs to be recovered by the GR. Consequently, the cells need more vitamin B2. Another glutathione action is the protection against hydroperoxide. This activity is also mediated by riboflavin. Therefore, local delivery of this vitamin seems to significantly help the cells in their fight to keep the oxidative balance, once they are exposed to high levels of ROS.

The gravimetric determination of titanium dioxide is vital for several reasons. First and foremost, it ensures product consistency and quality, allowing manufacturers to produce coatings and plastics that meet industry standards. In industries where color consistency is crucial, such as paint production, maintaining a uniform concentration of TiO2 is essential to achieving the desired opacity and brightness.

Fig. 6. AOPP measured on samples of MSSA with: A) 0.2 mg/mL P25TiO₂NPs; B) 0.02 mg/mL P25TiO₂NPs; C) 0.2 mg/mL VitaminB2@P25TiO₂NPs; D) 0.02 mg/mL VitaminB2@P25TiO₂NPs after 3 h of irradiation (red) and 6 h (blue). SD <1 (error bars too small to be seen) and p < 0.05 between C-D and A-B.

Production

Titanium dioxide is an insoluble mineral, meaning it cannot dissolve in water. Known for its bright, white pigment, manufacturers use titanium dioxide in many different capacities, including in cosmetics, foods, and drugs.