Zhu et al. were the first to provide evidence that TiO₂ NPs (21 nm) can transfer from daphnia to zebrafish by dietary exposure. Hence, dietary intake could be a major route of exposure to NPs for high trophic level aquatic organisms. Ecological research should therefore focus, not only on the concentration of NPs in the environment, but also on its bioconcentration, bioaccumulation and biomagnification. In addition it has been shown that TiO₂ NPs can increase accumulation of other environmental toxicants: enhanced accumulation of cadmium (Cd) and arsenic (As) was found in carp in the presence of TiO₂ NPs. The strong adsorption capacity for Cd and As was explained by the large specific surface area and strong electrostatic attraction of TiO₂ NPs that contribute to facilitated transport into different organs.

What are the forms of titanium dioxide?

Exposure routes are the pathways that allow ingredients to enter our bodies. Primary exposure routes include: 

However, the use of titanium dioxide has also raised concerns about its potential impact on human health and the environment. Some studies have suggested that titanium dioxide nanoparticles may have harmful effects when inhaled or ingested. Manufacturers of titanium dioxide are therefore taking steps to minimize the risk of exposure and develop safer products.

For research published in Archives of Toxicology in 2020, scientists fed one group of mice a solution containing titanium dioxide for one month, and compared it to those that did not receive the additive. They found “the richness and evenness of gut microbiota were remarkably decreased and the gut microbial community compositions were significantly changed” in the titanium dioxide group when compared with the control group. The tests also revealed that the titanium dioxide exposure could cause locomotor dysfunction, or mobility issues “by elevating the excitement of enteric neurons, which might spread to the brain via gut-brain communication by vagal pathway.” The researchers concluded: “These findings provide valuable insights into the novel mechanism of TiO2NP-induced neurotoxicity. Understanding the microbiota-gut-brain axis will provide the foundation for potential therapeutic or prevention approaches against TiO2NP-induced gut and brain-related disorders.”

Titanium dioxide (TiO₂) is commonly applied to enhance the white colour and brightness of food products. TiO₂ is also used as white pigment in other products such as toothpaste. A small fraction of the pigment is known to be present as nanoparticles (NPs). Recent studies with TiO₂ NPs indicate that these particles can have toxic effects. In this paper, we aimed to estimate the oral intake of TiO₂ and its NPs from food, food supplements and toothpaste in the Dutch population aged 2 to over 70 years by combining data on food consumption and supplement intake with concentrations of Ti and TiO₂ NPs in food products and supplements. For children aged 2-6 years, additional intake via ingestion of toothpaste was estimated. The mean long-term intake to TiO₂ ranges from 0.06 mg/kg bw/day in elderly (70+), 0.17 mg/kg bw/day for 7-69-year-old people, to 0.67 mg/kg bw/day in children (2-6 year old). The estimated mean intake of TiO₂ NPs ranges from 0.19 μg/kg bw/day in elderly, 0.55 μg/kg bw/day for 7-69-year-old people, to 2.16 μg/kg bw/day in young children. Ninety-fifth percentile (P95) values are 0.74, 1.61 and 4.16 μg/kg bw/day, respectively. The products contributing most to the TiO₂ intake are toothpaste (in young children only), candy, coffee creamer, fine bakery wares and sauces. In a separate publication, the results are used to evaluate whether the presence of TiO₂ NPs in these products can pose a human health risk.

Pigment grade titanium dioxide is produced at a much larger particle size than nano grade. It is used as a colourant to whiten and brighten product formulations. Nano grade titanium dioxide is manufactured into very fine (nano) particles and is transparent and colourless. It is commonly used in sunscreens to provide effective protection from potentially harmful UV rays.