No acute effects of nano-sized TiO₂ were observed in Danio rerio (zebrafish) embryos. Exposure of rainbow trout to TiO₂ NPs triggered lipid peroxidation, influence on the respiratory tract, disturbance in the metabolism of Cu and Zn, induction of intestinal erosion  and accumulation in kidney tissue. Linhua et al. exposed juvenile carp to 100 and 200 mg/ml of particles and TiO₂ observed no mortality. However, the fish suffered from oxidative stress and pathological changes in gill and liver. In the infaunal species Arenicola marina, exposure to TiO₂ NPs in sediment caused sub-lethal effects including decrease in casting rate and increase in cellular and DNA damage. Aggregated particles were visible in the lumen of the gut, but no uptake through the gut or the skin was observed.

Insolube matter in water

Why is titanium dioxide used in food, including in Skittles?

105°C volatile matter, %

Various titanium-rich minerals, including ilmenite and rutile, can serve as starting materials for the production of highly purified Titanium Dioxide. The predominant method employed in Titanium Dioxide production is the chloride process. In this process, the mineral, along with coke and chlorine, undergoes a reaction within a fluidized bed, resulting in the formation of primarily titanium tetrachloride and carbon dioxide. Subsequently, the titanium tetrachloride undergoes purification and conversion to Titanium Dioxide. Another method involves treating ilmenite with sulfuric acid to manufacture the chemical.

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.”

Genotoxicity and cytotoxicity 

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Titanium dioxide is used in a wide range of food products and consumer goods – from candy to sunscreen and house paint. The U.S. Food and Drug Administration maintains that the regulated use of titanium dioxide, specifically as a color additive in food, is safe under some restrictions.

It’s true that titanium dioxide does not rank as high for UVA protection as zinc oxide, it ends up being a small difference (think about it like being 10 years old versus 10 years and 3 months old). This is not easily understood in terms of other factors affecting how sunscreen actives perform (such as the base formula), so many, including some dermatologists, assume that zinc oxide is superior to titanium dioxide for UVA protection. When carefully formulated, titanium dioxide provides excellent UVA protection. Its UVA protection peak is lower than that of zinc oxide, but both continue to provide protection throughout the UVA range for the same amount of time.