The history of titanium dioxide: a global success to date … but is its future so bright?
In our culture, the colour white is associated with purity and innocence – but in chemical circles and the coatings industry, it is primarily associated with titanium dioxide. This compound is the white pigment par excellence and can be found today in almost all products in which a white base coat is required. However, the widely used pigment has recently been struggling with a safety problem, as outlined in this article.
Successful, but toxic: titanium white’s predecessor
Let’s begin by taking a step back in time: Far back in antiquity, nobody was familiar with titanium dioxide. Instead, the pigment lead white, a basic lead carbonate with the formula 2PbCO3-Pb(OH)2, was used for white paint. For around 2000 years, it was the only white pigment worthy of the name, as it is highly opaque and extremely lightfast.
Its production from lead plates and vinegar was already known to Theophrastus (ca. 371 to 287 BC), Vitruvius (ca. 80–70 BC to ca. 15 AD) and Pliny the Elder (23 to 79 AD). Lead white was also produced in China from around 300 BC using this ancient method. [1] This pigment was not only used for oil paintings and exterior paints, but was also directly applied to the skin – for example as make-up and sun protection in ancient Egypt and Rome – which would be unthinkable today, given the toxicity of lead. Japanese geishas also used white lead to make up their faces – a deliberate contrast to their teeth, which were traditionally coloured black with vinegar and gall apples.
White lead was still used well into the 20th century, as lead poisoning was as yet unknown and there were no high-quality alternatives. It was not until 1930 that it was officially banned for painting interiors. Since 1993, it has only been authorised for the restoration of works of art and listed buildings. [1]
A new white is discovered
The ban could now be enforced not only as a result of the discovery that the lead compound was toxic, but also thanks to the availability of an alternative: titanium dioxide. It was discovered independently by two researchers: in 1791 by William Gregor in Creed, Cornwall, and in 1795 by Martin Heinrich Klaproth in Berlin. [2]
However, the industrial production of this new white pigment only began in 1916 with the sulphate process developed by Gustav Jebsen, in which the titanium ore ilmenite (FeTiO3) is broken down with concentrated sulphuric acid. This was the final starting signal for the worldwide success of this pigment. [3, 4] Today, around 70% of European TiO2 production is based on the sulphate process, with the remaining 30% coming from the chloride process, in which TiO2 is extracted from the naturally occurring mineral rutile. [4, 5]
White pigment exposes art forger
He is considered one of the most famous art forgers of modern times – Wolfgang Beltracchi spent years buying paintings by unknown artists and overpainting them in the style of famous painters. Part of the secret to his success was that he always used canvases from the same period as the copied painters and mixed his own colours – using the original techniques and materials of the copied artists as much as possible. In so doing, he deceived even art experts with his works. However, for his imitation of Heinrich Campendonk’s ‘Red Painting with Horses’, Beltracchi had used a purchased white colour that also contained traces of titanium dioxide, a pigment that was only used in the art scene after Campendonk’s creative period. When the modern white pigment was detected during an analysis of the artwork in the Art Analysis & Research laboratory, Beltracchi was convicted. He was sentenced to six years in prison in October 2011. [11]
The success of titanium dioxide in the form of ‘titanium white’ is due to the pigment’s outstanding opacity and its non-toxicity – a major advantage over the previously dominant lead white. The new white pigment is not only found in high-quality wall paint and printer ink, but also in cosmetics, toothpaste and – as the food additive E171 – in foods such as the coating of colourful chocolate lentils. [5]
Is the food colouring E171 a health hazard?
However, titanium white’s previously glowing image has recently been tarnished. In the Standing Committee on Plants, Animals, Food and Feed (PAFF Committee), representatives of the EU Member States agreed the proposal to ban the use of titanium dioxide (E171) as an additive in food from 2022. The experts based their decision on an updated safety assessment of TiO2 by the European Food Safety Authority (EFSA) in 2021. [6]
In a statement to the press, Prof. Maged Younes, Chairman of the EFSA Panel of Experts on Food Additives and Flavourings (FAF), stated “Taking into account all available scientific studies and data, the Panel came to the conclusion that titanium dioxide can no longer be considered safe as a food additive.” A decisive factor for this conclusion was that the experts could not rule out the genotoxicity of the white pigment after the consumption of titanium dioxide particles, i.e. possible damage to DNA in the cell nucleus of body cells. In the report, Younes goes on to explain: “Although the absorption of titanium dioxide particles is low after oral intake, they can accumulate in the body.” [6]
Consequently, from August 2022, foodstuffs could no longer be coloured with titanium dioxide. However, medicines and cosmetics, including toothpaste and suncream, may continue to contain titanium dioxide. [7] Is history repeating itself? Is titanium white the new lead white? Do white pigments pose a health risk to us, as was once the case for Japanese geishas?
A more in-depth look at the arguments
It is necessary to look more closely at the details in this case. The restriction imposed by the EFSA clearly distinguishes between the use of TiO2 in food and its use in other applications for good reason. The restriction applies specifically only to the oral intake of the substance and is intended as a precautionary measure because the genotoxicity of TiO2 particles cannot be ruled out and therefore no permissible daily intake level can be set for the food colouring E171. [6] There is therefore no acute health risk, but there may be a long-term risk. In contact with the skin – for example in make-up or sun cream – the pigment is considered safe, as transdermal absorption is not possible, as far as we currently know. [7]
Why is titanium dioxide still permitted in medicines?
While food may no longer be produced with titanium dioxide from 2022, there is currently no such ban for medicines. In a statement to the scientific journal, Pharmazeutische Zeitung, a spokesperson for the German Federal Institute for Drugs and Medical Devices (BfArM) explained the reason behind the different policy for medicines compared to food: “It must be taken into account that not using TiO2 in medicinal products could potentially change their efficacy, safety and pharmaceutical quality. If TiO2 were to be completely banned as an additive for medicinal products with immediate effect, this could likely cause considerable bottlenecks in the EU market.”
In tablets, titanium dioxide serves as an important excipient and, with its high opacity, protects the processed active ingredients from sunlight, thus ensuring the shelf life and safety of the medicines.
In the long term, manufacturers will have to replace TiO2 in medicines with other excipients. As there is currently no evidence of an acute health risk, but only that the occurrence of a risk can no longer be ruled out with certainty, tablets containing TiO2 will remain authorised for the time being. [12]
Risk assessment faces criticism from industry
Although titanium dioxide is currently permitted in cosmetics and medicines, the risk titanium dioxide particles by inhalation is the subject of heated debate. According to the CLP Regulation (EC, No. 1272/2008), the following classification applies: Titanium dioxide in powder form containing 1% or more of particles with aerodynamic diameter ≤10 µm shall be classified as carcinogenic category 2 and must be labelled with the hazard statement ‘May cause cancer by inhalation’. [8]
This classification has led to uncertainty for consumers, while the decision has angered manufacturers – particularly producers of paints and varnishes, in which TiO2 is often an essential component – who criticise the fact that the underlying studies on rats were not transferable to humans. In addition, extremely high concentrations of titanium dioxide in powder form were administered by inhalation in the studies, which in very few cases reflects a real exposure scenario with titanium dioxide. In a statement, the Bavarian Chemicals Associations argued that the pigment is usually bound in a matrix, such as binders and plastics, and is therefore not present in powder form, meaning that it is guaranteed safe to use. [9]
The German Paint and Printing Ink Industry Association also considered the classification to be unjustified and referred, among other things, to studies on around 24,000 workers over several decades in which no negative effects on the health of employees caused by titanium dioxide were found. [10]
It is clear that a balance remains be found between the need for risk prevention while also taking into account technical and economic interests. Additional studies on the potential toxicological properties of titanium dioxide will likely prove essential. It will then become clear what the future holds for the white pigment that has been with us for the past 100 years.
Sources:
[1] https://materialarchiv.ch/de/ma:material_982?type=all&n=Hintergrund
[2] https://www.seilnacht.com/Lexikon/Titandi.htm
[3] https://de.wikipedia.org/wiki/Titan(IV)-oxid#Zunehmend_industrielle_Herstellung_und_Nutzung
[4] https://materialarchiv.ch/de/ma:material_984?type=all&n=Grundlagen
[5] https://www.tdma.info/de/about-tio2/was-ist-titandioxid/
[8] https://www.lgl.bayern.de/lebensmittel/chemie/schwermetalle/titandioxid/index.htm
[10] https://www.lacke-und-farben.de/fileadmin/templates/img/pdf/LiG_131.pdf
[11] https://de.wikipedia.org/wiki/Wolfgang_Beltracchi
[12] https://www.pharmazeutische-zeitung.de/in-arzneimitteln-schwer-zu-ersetzen-137447/
