Why does the exposure route matter, and what's the risk? 

Abstract

Lithopone is an inorganic white pigment, obtained from co-precipitation of Zinc sulfide (ZnS) and Barium sulfate (BaSO4). Titanium Dioxide (TiO2) has replaced Lithopone as a white pigment in majority applications as TiO2 is more durable. However, it is much cheaper than TiO2 and has advantages such as low binder requirement and good dispensability. As a white pigment, it can improve the substrate's weather resistance, and improve the fungicidal properties of paint formulations. Some of the major applications of Lithopone include manufacturing of paint pigments, plastic & rubber products, paper, printing inks, cosmetics, and leather & linoleum products. It is commercially available under names such as pigment white 5, Barium zinc sulfate sulfide, Becton White, C.I. 77115, Charlton White, Enamel White, and Zincolith. On the basis of content of ZnS, Lithopone is available at 28%-30% Lithopone and 60% Lithopone.

When manufacturers add titanium dioxide to foods and other ingestible products, it’s typically referred to as E171, which relates to food-grade purity.

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We know that there are a lot of suspended organisms and colloidal impurities in natural water. The forms of suspended solids are different. Some large particles of suspended solids can settle under their own gravity. The other is colloidal particles, which is an important reason for the turbidity of water. Colloidal particles can not be removed by natural settlement, because colloidal particles in water are mainly clay with negative electricity The Brownian motion of colloidal particles and the hydration on the surface of colloidal particles make colloidal particles have dispersion stability. Among them, electrostatic repulsion has the greatest influence. If coagulant is added to water, it can provide a large number of positive ions and accelerate the coagulation and precipitation of colloid. Compressing the diffusion layer of micelles makes the potential change into an unstable factor, which is also conducive to the adsorption and condensation of micelles. The water molecules in the hydrated film have fixed contact with the colloidal particles and have high elastic viscosity. It is necessary to overcome the special resistance to expel these water molecules. This resistance hinders the direct contact of the colloidal particles. The existence of some hydrated films depends on the electric double layer state. If coagulant is added to reduce the zeta potential, the hydration may be weakened. The polymer materials formed after coagulant hydrolysis (the polymer materials directly added into water generally have chain structure) play an adsorption bridging role between the colloidal particles. Even if the zeta potential does not decrease or does not decrease much, the colloidal particles can not contact each other and can be adsorbed through the polymer chain Colloidal particles can also form flocs.

Blanc de Comines, 27 per cent zinc sulphide, 70.5 per cent barium sulphate, 2.5 per cent zinc carbonate.

TiO2 is also used in the production of plastics, where it serves as a whitening agent and UV stabilizer. By incorporating TiO2 into plastic products, manufacturers can enhance their appearance, increase their lifespan, and improve their resistance to sunlight and weathering. Additionally, TiO2 helps prevent the degradation of plastic materials, ensuring that they retain their properties and performance over time.

In a small study published in the European Journal of Nutrition in 2020, researchers examined the effects of several food additives, including titanium dioxide, along with artificial sweeteners and cleaning products by testing the fecal samples of 13 people. Titanium dioxide was among the samples that “induced significant shifts in microbiome community structure.”  The growth of the bacterium species belonging to C. leptum, which has been shown to decrease in patients with inflammatory bowel disease, “significantly decreased in the presence of … titanium dioxide” among other additives and sweeteners tested.

While IARC listed titanium dioxide as “possibly carcinogenic to humans,” they also add that “there is inadequate evidence in humans for the carcinogenicity of titanium dioxide.” Of the four human studies that they reviewed, only one showed a potential risk for occupational workers inhaling titanium dioxide particles and lung cancer, while the other three showed no risk for cancer at all. And it’s key to note that IARC did not assess the effects of titanium dioxide found in foods.

Titanium dioxide (TiO₂). Titanium dioxide is the most common white pigment used today. As a pigment, titanium dioxide is unique because it combines both high colouring and high opacifying capacity. This is mainly due to its high refractive index (2.7). Furthermore, titanium dioxide is an excellent UV absorber (it is used in sun protective creams). Some typical properties are: density 3.3-4.25 g/cm³; pH of water suspension 3.5-10.5; particle size 8–300 nm; oil absorption 10–45 g/100 g; specific surface area 7–160 m²/g. Most titanium dioxide is produced from the rutile (TiO₂) or ilmenite (titanate of ferrous iron). Titanium dioxide can be obtained using different processes.