Titanium dioxide nanoparticles (TiO2)

Titanium dioxide nanoparticles (TiO₂)

Why and how is TiO2 used?

The properties of titanium dioxide

Titanium dioxide has long been used on a non-nanometer scale as a white pigment (combined with other dyes, so it can also be used to decline a color palette), in many products (paints, medicines, toothpaste, make-up, food (until 2020), etc.).

In paintings for example, the so-called “pigmentary” titanium dioxide particles are often mainly between 200 and 350 nm to obtain an intense white color. Above 350 nm, the texture is no longer uniform, but “grainy”.

With advances in metrology techniques and tools, scientists have however highlighted the fact that nanoparticles are contained in the pigmentary titanium dioxide (in particular that used in the food additive E 171)¹See in particular the references cited by Bettini S and Houdeau E, Oral exposure to titanium dioxide (TiO2) nanoparticles: from crossing the oral and intestinal epithelium to fate and effects in the body, Biology today, September 2014:
- Titanium Dioxide Nanoparticles in Food and Personal Care Products, Weir A. et al., About. Science. Technology., 46 (4), 2242-2250, 2012 (36% particles with dimension <100 nm)
- Characterization of titanium dioxide nanoparticles in food products: analytical methods to define nanoparticles, Peters RJ et al., J Agric Food Chem, 62(27), 6285-6293, 2014
- Characterization of foodgrade titanium dioxide: the presence of nanosized particles, Yang Y et al., About Sci Technol, 48, 6391-6400, 2014 (17-35% particles with dimension <100 nm)
- Characterization and preliminary toxicity assay of nano-titanium dioxide additive in sugar-coated chewing gum, Chen XX et al., Small, 9, 1765-1774, 2013 (28-40% particles with dimension <100 nm)

Also to be consulted
- Detection and Characterization of SiO2 and TiO2 Nanostructures in Dietary Supplements, Lim JH et al, J Agric Food Chem., 1; 63(12), 3144-52, April 2015, without necessarily all having been intentionally produced on this scale by the manufacturers.

Questions have therefore arisen for some time about the safety of these particles contained in many food products.²Please read our What risks are associated with (nano)particles of titanium dioxide (nano TiO2)?, leading to the suspension of the E171 at the start of 2020. Over the past fifteen years, we have discovered thatat the nanometric scale, new properties appear, TiO₂ nanoparticles can therefore be used by industry in particular:

•  as bright agent : TiO₂ nanoparticles can be used to give shine to products (food, medicine, make-up, etc.), …
•  as UV barrier, in sun creams, food packaging, clothing, etc.
•  as antibacterial³See for example:
  - Nanostructured TiO2 anatase-rutile-carbon solid coating with visible light antimicrobial activity, Krumdieck SP et al., Scientific Reports, 9:1883, 2019
  - Subsurface treatment of TiO2 nanoparticles for limestone: Prolonged surface photocatalytic biocidal activities, Veltri S et al., Building and Environment, 149: 655-661, February 2019
  - Antibacterial surfaces prepared by electrospray coating of photocatalytic nanoparticles, Chemical Engineering Journal, 334: 1108-1118, February 2018, in deodorants, toothbrushes, textiles, etc.
•  as self-cleaning coating⁴See for example
  Self-cleaning materials, UVC lamps, robots… How tech will make cleaning easier, RMC, March 2023 : at less than 200 nm in diameter, TiO₂ particles lead to the oxidization (decomposition) of organic pollutants by photocatalysis (under the effect of light); deposited on surfaces made hydrophilic, they therefore allow self-cleaning (provided that the photocatalysis is complete, which is not always the case – with then bad consequences)
•  as flame retardant in some textiles
•  as a coating offering better scratch resistance

And in which products?

TiO₂ titanium dioxide nanoparticles are used in many industries and products⁵See in particular:
- Assistance in identifying nanomaterials in companies, INRS, ED 6174, June 2014
- Use of nanometric titanium dioxide – Special case of the construction industry, INRS, Occupational Health and Safety, Briefing note 2367, 4th quarter 2012:

• in the medical and pharmaceutical sector: in the pharmaceuticals as a colorant, in vaccines as an excipient
• in the food sector:
  • about food, beverages and packaging, as a dye (E171) (banned in France since 2020)
  • about packaging (cardboard, plastic) and plastic film, as a UV barrier or as an antibacterial
• in the cosmetics sector:
  •  make-up (mascara, nail polish, eye shadow, foundation, lipstick, skincare cream, hair coloring and bleaching) or the toothpaste as a colorant (CI77891)
  • about sun creams as a UV barrier
  • about déodorants as an antibacterial
  • in small care equipment, as an antibacterial: hairbrushes, electric shavers, toothbrushes, hair dryers, curling irons, etc.
• in the area textile, as an antibacterial (for medical staff gowns, fabrics used in the operating room), as a flame retardant (firefighter suits) and also as a UV barrier in clothing (for some Beach Tees for example)
• about inks as a dye (in toner type printers for example), the paintings⁶According to FIPEC, titanium dioxide provides “the whiteness, opacity, brilliance, stability and durability of colors outdoors. By the density it brings, it improves the texture, and makes it possible to limit the number of coats during application. It allows an almost infinite variation of shades » : source : http://www.fipec.org/index.php/afei/actualites-communiques-de-presse/13-sipev (last consulted December 2018), stains and varnishes as a colorant (to obtain a pearly tint⁷Pfaff, G. and P. Reynders, Angle-Dependent Optical Effects Deriving from Submicron Structures of Films and Pigments. Chemical Reviews, 1999. 99(7): p. 1963-1982 and Braun, JH, A. Baidins, and RE Marganski, TiO2 pigment technology: a review. Progress in Organic Coatings, 1992. 20(2): p. 105-138 (cited by Le Trequesser Q, Synthesis of titanium dioxide nanoparticles with controlled morphologies: localization, quantification and toxicological aspects from the cell to the multicellular organism, thesis, Material chemistry, University of Bordeaux, 2014) in particular), as an antibacterial, self-cleaning agent or agent for better UV and scratch resistance
• in the automotive sector, in catalytic converters as a depolluting agent
• in the fields of construction and roads: interior or exterior coatings of buildings and materials (concrete, cement, walls, steel, stone, glass, tiles, bitumen and roads)
• in thefurnishing and interior equipment (air purifiers) as a depollutant
• in extraction units on oil fields as a depollutant
• ...

What are the quantities on the market?

Since 2014, between 10 and 000 tonnes of titanium dioxide nanoparticles are declared every year as having been produced and/or imported in France⁸See The R-Nano register – The annual declaration of “substances with nanoparticle status” in France, mandatory since 2013,veillenanos.fr as part of the mandatory declaration of substances with nanoparticle status that feeds the r-nano register.
The vagueness is great: more or less 90 tonnes, this range illustrates the weight granted by the public authorities to the industrial and commercial secret which today prevents us from having a good understanding of the quantities and uses of these particles, despite the increasingly pressing requests for information from a growing number of players.

In France,Thann plant in the Haut-Rhin is one of the few TiO production sites₂, especially since the closure of the Tioxide plant producing TiO₂ pigmentary in Calais (Huntsman group)⁹cf. Tioxide closes its Calais plant, The New Factory, March 20, 2017. She belongs to crystal group (Saudi Arabia), the world's second largest producer of titanium dioxide after DuPont.

A wide variety of TiO2 nanoparticles

There is a wide variety of TiO₂ nanoparticle types, including differences in crystalline form (anatase, light-reactive, useful for depolluting applications / rutile, which absorbs UV), size distribution, morphology and coating:

• in food (E171), toothpaste et medication, they are overwhelmingly under anatase form (sometimes associated with the rutile form in very small proportion) and without coating

• in cosmetics (Cl 77891) and sun creams, they are mostly under rutile form (or anatase/rutile mix) and coated a layer of silica or alumina to prevent the formation of free radicals (which cause skin aging). Problem: chlorine from swimming pools can degrade this coating, but in contact with water and under the effect of light, nanoTiO₂ can then release free radicals, responsible for skin aging and the appearance of cancers¹⁰In 2012, researchers from Cincinnati in the United States showed that chlorine from swimming pools can degrade the aluminum hydroxide coating that surrounds titanium dioxide nanoparticles (TiO₂) incorporated into certain sunscreens (here Neutrogena SPF 30). In contact with water and under the effect of light, the core of the nanomaterial, nanoTiO₂ can then release free radicals, responsible for skin aging and the appearance of cancer.
  – Cf. Depletion of the protective aluminum hydroxide coating in TiO2-based sunscreens by swimming pool water ingredients, Chemical Engineering Journal, 191: 95-103, May 2012
  – See also this more recent article: UV filters interaction in the chlorinated swimming pool, a new challenge for urbanization, a need for community scale investigations, Sharifan H et al., About Res., 148:273-276, July 2016.

• in paints and cements (CI Pigment White 6), they are mainly under anatase form (or anatase/rutile mix) and without coating (to allow the photocatalysis reaction to destroy dirt / pollutants)

• for depolluting / antibacterial uses, TiO₂ is not not coated

Associated risks and regulations that are beginning to take them into account

What are the associated risks?

Titanium dioxide nanoparticles are released into the environment, with undesirable consequences for ecosystems and humans (exposed workers but also consumers and the general public).

In view of the deleterious health effects likely to be caused by nanoTiO₂ :

• the French Health Security Agency (ANSES) recommended in 2014 a classification of titanium dioxide nanoparticles as hazardous substances so that measures are put in place to restrict the use or even ban the use of certain applications for the general public
• at European level, the classification of titanium dioxide (TiO₂) as a category 2 carcinogen by inhalation was registered in the Official Journal of the European Union in February 2020.

The additive E171, food grade titanium dioxide, banned in France and then in Europe

In France, the Food law published in the official journal on November 1, 2018 stipulates that "the placing on the market of the additive E 171 (titanium dioxide-TiO2) as well as foodstuffs containing it is suspended" (section 53). This measure entered into force on January 1, 2020, before being generalized at European level in 2022, followinga long journey and collective work to which many actors contributed: NGOs (supported by Avicenn), scientists, media, parliamentarians and members of the government.

Towards the French suspension of TiO2 in certain cosmetics and medicines?

After food, several associations ask for thetitanium dioxide suspension enlargement cosmetics likely to be ingested and medicines.
Brands are now promoting TiO2-free drug coatings.
The site toothpaste.infoconso.org d'Agir pour l'Environnement was created to allow consumers to quickly identify toothpastes with or without titanium dioxide (but it has not been updated).

"If it's white, it's not nano"? Not that easy…

Below the 200 nm threshold, the titanium dioxide particles gradually lose their white appearance to become more and more transparent as they decrease in size.

They also continue to absorb ultraviolet rays below this threshold, which is why cosmetic brands use them to make sun creams both more effective, transparent while being less viscous and visible. The photos on the left show the gradient from white to transparent on two types of skin depending on the dispersion of the primary particles.
The greater the proportion of small-sized titanium dioxide particles, the more transparent the product becomes.

However, this does not mean that white titanium dioxide does not contain nanoparticles, i.e. particles with one dimension less than 100 nm, despite claims by TiO₂ makers concerned that the white dye is associated with a nanomaterial¹¹See in particular:
- Additional information regarding titanium dioxide and E171 – press release from the Titanium Dioxide Manufacturers Association (TDMA), March 23, 2015
- Statement in response to recent articles regarding removal of food grade TiO2 from food formulations – , press release from the International Association of Color Manufacturers (IACM), March 25, 015 (NB: in the USA, what is called "food grade TiO2" corresponds to the food grade titanium dioxide which is referred to as food additive E171 in Europe) (and then be subject to thereporting obligation with the national health security agency in France or even an obligation tolabeling depending on the sector).