A study funded by the US National Institutes of Health concluded that titanium dioxide (TiO2) nanoparticles, found in items people all over the world use every day from cosmetics and sunscreen to vitamins and paint, caused systemic genetic damage in mice.
The study was the work of senior study author Dr Robert Schiestl from the University of California Los Angeles (UCLA) and colleagues, and was published in the journal Cancer Research on 15 November.
Schiestl, who is UCLA professor of pathology, radiation oncology and environmental health sciences and a Jonsson Cancer Center scientist, told the media this was the first study to show nanoparticles had this effect.
The manufacture of TiO2 nanoparticles is a huge industry, said Schiestl; we produce about 2 million tons of it a year. As well as paint, cosmetics, vitamins and sunscreens, they can be found in toothpaste, food colouring, nutritional supplements and hundreds of other products that we handle every day.
The body has no way of eliminating TiO2, so it accumulates in organs, and because they are so small (about 100 to 1,000 times thinner than human hair), the nanoparticles can go anywhere, penetrating cells and interfering with their internal processes.
Until now scientists thought TiO2 nanoparticles were non-toxic because they did not cause a chemical reaction. But Schiestl and colleagues suggested they cause a physicochemical reaction as opposed to a regular chemical reaction: a novel mechanism of toxicity.
“The novel principle is that titanium by itself is chemically inert,” said Schiestl.
But as the particles get smaller and smaller, the amount of surface exposed to the environment becomes progressively bigger. (Imagine the total surface area of all the particles in a handful of sand compared to the surface area of the same weight of rock, for example.)
“In the interaction of this surface with the environment, oxidative stress is induced,” Schiestl explained.
“This is the first comprehensive study of titanium dioxide nanoparticle-induced genotoxicity, possibly caused by a secondary mechanism associated with inflammation and/or oxidative stress,” he added.
For the study, Schiestl and colleagues gave mice drinking water containing TiO2 nanoparticles. Five days later, the mice began to show genetic damage.
The human equivalent of the exposure the mice underwent would be about 1.6 years exposure to nanoparticles in a manufacturing environment, said the researchers.
They said that given the increasing use of these nanoparticles, these findings should raise concerns about their potential health hazards.
Schiestl told the media that it wasn’t clear if regular everyday exposure in humans goes up exponentially with continued contact.
He suggested that a certain portion of spontaneous cancers could be due to exposure to nanoparticles.
“And some people could be more sensitive to nanoparticle exposure than others. I believe the toxicity of these nanoparticles has not been studied enough,” suggested Schiestl.
Nanoparticles can’t get into the body through the skin, said Schiestl, so he suggests people use lotion sunscreen rather than the spray-on type because the latter can be inhaled and get into the lungs, where the nanoparticles can get lodged.
In their conclusions, the authors wrote:
“These data suggest that we should be concerned about a potential risk of cancer or genetic disorders, especially for people occupationally exposed to high concentrations of titanium dioxide nanoparticles, and that it might be prudent to limit their ingestion through non-essential drug additives, food colors, etc”.
Schiestl and colleagues now plan to examine nanoparticle exposure in mice that are deficient in DNA repair, and perhaps find a way to predict which people might be particularly sensitive to them.
According to UK-based particle size specialists Malvern Instruments, although nanoparticles are currently making the headlines for health and safety reasons, we have lived with sub-micron sized particles around us “for ever”. It is the introduction of man-made versions that has “brought to light how little we know about their toxic effects”, they write on their company website.
They caution us to avoid turning the nanoparticle debate into something like the asbestos scare, where few people realize that it is only blue asbestos that is really harmful, and yet there is very little of it around, and very unlikely to be found in domestic environments. But because few people understand this, we are spending a lot of money on asbestos disposal, which is not always required.
“Nano-particles could fall in the same category if safety issues are not fully understood, and the regulations for handling them carefully drafted,” they suggested.
“Titanium Dioxide Nanoparticles Induce DNA Damage and Genetic Instability In vivo in Mice.”
Benedicte Trouiller, Ramune Reliene, Aya Westbrook, Parrisa Solaimani, and Robert H. Schiestl.
Cancer Research 69, 8784, Published Online First November 3, 2009.
Sources: UCLA, Malvern Instruments.
Written by: Catharine Paddock, PhD