The concern from animal studies is that high amounts of titanium dioxide have increased inflammation and colon tumor formation, said Dr. Johnson-Arbor. A 2021 review, meanwhile, suggested that using titanium dioxide as a food additive weakens the gut lining and worsens the progression of inflammatory bowel disease.

Skin-penetration studies 

In 2023, California and New York proposed banning several food additives that are banned in Europe but legal in the United States. Titanium dioxide was among the five proposed to be banned, but in September, the additive was removed from the list of additives from the California ban list.

References

In industrial settings, people can be exposed to titanium dioxide through inhalation. Inhalation exposure to titanium dioxide is exceedingly rare for most people. 

As a food additive, titanium dioxide and its nanoparticles in particular have been associated with DNA damage and cell mutations, which in turn, have potential to cause cancer. When used as a food coloring, it is known as E171.

In a study published in the journal Environmental Toxicology and Pharmacology in 2020, researchers examined the effects of food additives titanium dioxide and silica on the intestinal tract by grouping and feeding mice three different food-grade particles — micro-TiO2, nano-TiO2, and nano-SiO2.  With all three groups, researchers observed changes in the gut microbiota, particularly mucus-associated bacteria. Furthermore, all three groups experienced inflammatory damage to the intestine, but the nano-TiO2 displayed the most pronounced changes. The researchers wrote: “Our results suggest that the toxic effects on the intestine were due to reduced intestinal mucus barrier function and an increase in metabolite lipopolysaccharides which activated the expression of inflammatory factors downstream. In mice exposed to nano-TiO2, the intestinal PKC/TLR4/NF-κB signaling pathway was activated. These findings will raise awareness of toxicities associated with the use of food-grade TiO2 and SiO2.”

Lithopone was discovered in the 1870s by DuPont. It was manufactured by Krebs Pigments and Chemical Company and other companies. The material came in different seals, which varied in the content of zinc sulfide. Gold seal and Bronze seals contain 40-50% zinc sulfide, offering more hiding power and strength. Although its popularity peaked around 1920, approximately 223,352 tons were produced in 1990. It is mainly used in paints, putty, and in plastics.

THE OBSCURE HISTORY OF A UBIQUITOUS PIGMENT: PHOSPHORESCENT LITHOPONE AND ITS APPEARANCE ON DRAWINGS BY JOHN LA FARGE

Résumé–Cet article traite de la découverte de lithopone phosphorescent sur des dessins à l'aquarelle, datés entre 1890 et 1905, de l'artiste Américain John La Farge et de l'histoire du lithopone dans l'industrie des pigments à la fin du 19e et au début du 20e siècle. Malgré de nombreuses qualités souhaitables pour une utilisation en tant que blanc dans les aquarelles et les peintures à l'huile, le développement du lithopone comme pigment pour artistes a été compliqué de par sa tendance à noircir lorsqu'il est exposé au soleil. Sa disponibilité et son usage par les artistes demeurent incertains parce que les catalogues des marchands de couleurs n'étaient généralement pas explicites à indiquer si les pigments blancs contenaient du lithopone. De plus, lors d'un examen visuel, le lithopone peut être confondu avec le blanc de plomb et sa phosphorescence de courte durée peut facilement être ignorée par l'observateur non averti. À ce jour, le lithopone phosphorescent a seulement été documenté sur une autre œuvre: une aquarelle de Van Gogh. En plus de l'histoire de la fabrication du lithopone, cet article décrit le mécanisme de sa phosphorescence et son identification à l'aide de la spectroscopie Raman et de la spectrofluorimétrie.