You may want them in your jeans, but you probably want to keep them away from your genes. They鈥檙e 鈥渘ano鈥� particles of titanium dioxide, about ten billionths of a meter in diameter that can exhibit beneficial properties not possessed by their larger cousins, but they may also have a darker side.
There are more jeans in the world than people. That stat sparked an idea in the mind of University of Sheffield chemist Tony Ryan. Why not use people鈥檚 penchant for wearing denim to help purify the air? After all, the International Agency for Research on Cancer (IARC) classifies outdoor air pollution in Group 1, reserved for substances that are known to cause cancer in humans. It estimates that there are up to seven million premature deaths in the world every year as a result of air pollution.
With thoughts of reducing pollutants such as the nitrogen oxides and volatile organic compounds emitted by vehicles, power plants, residential heating, cooking and various consumer products, Ryan, in partnership with former fashion designer Helen Storey, came聽up with the concept of 鈥淐atalytic Clothing.鈥�
鈥淐atalytic鈥� apparel uses fabric impregnated with nano-sized particles of titanium dioxide to degrade air pollutants. 鈥淣ano鈥� means small. So small that the combined surface area of the nanoparticles that are distributed through any fabric is immense. And that matters because the action takes place on the surface of the particles.
Titanium dioxide is a 鈥減hotocatalyst,鈥� meaning that it can make chemical reactions happen when exposed to the right wavelength of light, in this case ultraviolet. The light energy causes it to release electrons that then target water molecules in the air, breaking them apart to form extremely reactive hydroxyl radicals that then chop up organic compounds into simple molecules such as carbon dioxide and convert nitrogen oxides into water soluble nitric acid. This is not just theory, it is well established technology that already has commercial application, for example in 鈥渟elf-cleaning glass.鈥� A thin layer of titanium dioxide ends window cleaning worries, as long as the climate provides for sufficient sunshine and rain. The chemical can even be mixed into concrete, resulting in self-cleaning buildings such as the Jubilee Church in Rome.
Thanks to titanium dioxide we may never have to confront yellow urinals again. Coating the ceramic with a layer of titanium dioxide, about a fiftieth the thickness of human hair, prevents stains from forming. The technology also has potential in operating rooms where bacteria on floor and wall tiles can be destroyed with fluorescent light, common in hospitals, furnishing enough of the right wavelengths. And how about self-cleaning tiles for the kitchen and bathroom?
Clearly, titanium dioxide photocatalysis is sound technology. But can wearing jeans treated with this chemical actually have an impact on air pollution? According to Professor Ryan, yes. He calculates that that if a third of a million people in Sheffield wore such jeans, nitrogen oxide levels could be significantly reduced. And there is no need to buy special jeans. Titanium dioxide particles stick readily to the fabric so the idea is to add a formulation of the chemical to the water when the jeans are being laundered. The nano particles will stick until the fabric degrades.
As is often the case in science, there is a 鈥渂ut.鈥� What happens if nanoparticles enter the bloodstream? What tissues might they affect? Titanium dioxide has the potential to damage DNA, but to do that it has to enter cells. That is a possibility since nanoparticles are smaller than cells. In the lab, nano titanium dioxide has been shown to damage DNA in human intestinal cells, but only at doses far higher than what could ever be ingested.
In any case, people will not be dining on their treated jeans. But they may be gulping donuts, or a vast array of other foods such as Gobstoppers, M&Ms, pastries or soy milk that have titanium dioxide added to them to provide a more pleasing whitened appearance. Only about 5% of the titanium dioxide is made of nano sized particles, but that has raised concern because IARC has classified titanium dioxide as possibly carcinogenic to humans (Group 2B). This classification is based on inhalation of titanium dioxide dust in an occupational setting, quite a different exposure than eating a donut with a titanium dioxide enhanced white sugar coating. Nevertheless consumer activism has resulted in Dunkin Donuts removing titanium dioxide from the powdered sugar coating on its products. Maybe it can be redirected into catalyst jeans. We really don鈥檛 need to make junk food look more appealing, do we?
