The gastrointestinal tract is a complex barrier/exchange system, and is the most important route by which macromolecules can enter the body. The main absorption takes place through villi and microvilli of the epithelium of the small and large intestines, which have an overall surface of about 200 m². Already in 1922, it was recognized by Kumagai, that particles can translocate from the lumen of the intestinal tract via aggregation of intestinal lymphatic tissue (Peyer’s patch, containing M-cells (phagocytic enterocytes)). Uptake can also occur via the normal intestinal enterocytes. Solid particles, once in the sub-mucosal tissue, are able to enter both the lymphatic and blood circulation.

Safety

But in the U.S., titanium dioxide is found all over the grocery shelves. Candy like Skittles, Starbursts, and Jell-O, gum like Trident White peppermint gum and Mentos Freshmint Gum, cake products like Duncan Hines Creamy Vanilla Frosting, and Nabisco Chips Ahoy! cookies are just a few of the myriad food items that contain the additive.

The principal natural source of titanium dioxide is mined ilmenite ore, which contains 45-60 percent TiO₂. From this, or an enriched derivative (known as titanium slag), pure TiO₂ can be produced using the sulphate or chloride process.