Though the regulated use of titanium dioxide in food products is legal in the U.S. and Canada, it's banned in some other countries, notably throughout Europe. In May 2021, the European Food Safety Authority announced that titanium dioxide can no longer be considered safe as a food additive.

A review published in 2022 in the journal NanoImpact evaluated the latest research related to genotoxic effects of titanium dioxide through in vivo studies and in vitro cell tests. Researchers summarized the results by stating TiO2 nanoparticles “could induce genotoxicity prior to cytotoxicity,” and “are likely to be genotoxic to humans.”

What does this court ruling mean for regulation?

In the application of lithopone in ink industry, lithopone has fine particles, loose structure, good fineness and good paint adhesion, so it can be well combined with other colors in the composition of ink.

Production[edit]

A dense, white, opaque pigment composed of a mixture of Zinc sulfide (30%) and Barium sulfate (70%) with trace amounts of Zinc oxide. Lithopone, first produced in 1874, was called Orr's white. The mixture of the two components is so intimate that it is hard to distinguish microscopically. Lithopone is an inert, transparent pigment which is often used as a filler or as a base for lake pigments. Lithopone was widely used in house paints in the first half of the 20th century. It was also used for some artist grounds, inks and as a filler in Paper, Leather, and Linoleum. Now lithopone has mostly been replaced by Titanium dioxide.

Although barium sulfate is almost completely inert, zinc sulfide degrades upon exposure to UV light, leading to darkening of the pigment. The severity of this UV reaction is dependent on a combination of two factors; how much zinc sulfide makes up the pigments formulation, and its total accumulated UV exposure. Depending on these factors Lithopone B301, Lithopone B311 powder itself may vary in shade over time, ranging from pure white all the way to grey or even black. To suppress this effect, a dopant might be used, like small amount of cobalt salts, which would be added to the formulation. This process creates cobalt-doped zinc sulfide. The cobalt salts help to stabilize zinc sulfide so it will not have as severe a reaction to UV exposure.

In vitro, in the hemocytes of the marine mussel Mytilus hemocytes, suspension of TiO₂ NPs (Degussa P25, 10 μg/ml) stimulated immune and inflammatory responses, such as lysozyme release, oxidative burst and nitric oxide production. Vevers and Jha demonstrated the intrinsic genotoxic and cytotoxic potential of TiO₂ NPs on a fish-cell line derived from rainbow-trout gonadal tissue (RTG-2 cells) after 24 h of exposure to 50 μg/ml. Reeves et al. demonstrated a significant increase in the level of oxidative DNA damage in goldfish cells, and suggested that damage could not repaired by DNA repair mechanisms. Another suggestion from the mentioned study was that hydroxyl radicals are generated also in the absence of UV light. It has been shown that fish cells are generally more susceptible to toxic/oxidative injury than mammalian cells.

Overall, Chinese anatase titanium dioxide stands out as a versatile and valuable material with a wide range of applications in various industries. Its unique properties make it a popular choice for use in pigments, sunscreen, environmental remediation, and energy conversion technologies. As research into this material continues to expand, we can expect to see even more innovative uses and advancements in the field of materials science.

The author thanks Marco Leona, Scientist-in-Charge of the Department of Scientific Research at the Metropolitan Museum of Art for conducting fluorescence spectrometry on Wheel of Fortune and a valuable discussion of the research, as well as Silvia Centeno, Research Scientist at the Metropolitan Museum of Art, who performed Raman analysis on the watercolors and also contributed her insight. The phenomenon of the phosphorescing lithopone was originally discovered during the author's fellowship in the Sherman Fairchild Center for the Conservation of Works on Paper, funded by the Andrew W. Mellon Foundation. The author thanks all her colleagues for their ideas and support during the research of this paper, and special thanks to Rachel Mustalish for her assistance in editing this work.

Infrared analysis showed that the characteristics bands for the bare nanoparticles are still exhibited in the vitamins@P25TiO₂NPs spectra, such as a wide peak in 450–1028 cm⁻¹ related to the stretching vibration of Ti-O-Ti and other peaks in 1630 cm⁻¹ and 3400 cm⁻¹, which represent the surface OH groups stretching. The IR spectrum of vitaminB2@P25TiO₂NPs showed signs of binding between compounds. The OH bending peak (1634 cm⁻¹) corresponding to bare nanoparticles disappeared, and the NH₂ bending band characteristic of vitamin B2 appeared (1650 cm⁻¹). The IR spectrum of vitaminC@P25TiO₂NPs also showed signs of successful functionalization. Bands at 1075 cm⁻¹; 1120 cm⁻¹; 1141 cm⁻¹ were observed, which are originated by CO-C vibrations present in the vitamin C. The intense band at 1672 cm⁻¹ is attributed to the C = O stretching in the lactone ring while the peak at 1026 cm⁻¹ is ascribed to the stretching vibration Ti-O-C. Wide bands at 3880–3600 cm⁻¹ are related to stretching vibration OH groups, but those disappear in the modified nanoparticles spectrum. These observations confirm the interactions between the P25TiO₂NPs and the vitamins [35].

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