Five Empa laboratories involved in the EU NanoHouse project, along with four other European research institutes and four industrial partners, have been researching the danger of nano-dust from façade paint. The aim of the project is to investigate the opportunities and risks presented by the nanomaterials used in the surface coatings applied to building façades. For the first time not only were freshly manufactured products studied to see if they set free nanoparticles, but aged samples were studies as well.

At a technology briefing about the research, Claudia Som introduced the NanoHouse project, for which she acted as Empa coordinator. This project, which is financially supported through the EU's 7th Research Framework Program, began in 2010 with the aim of investigating possible health effects caused by nanoparticles in building materials and houses. Various aspects of the research program included rubbing tests on model façades, attempts to wash out nanoparticles from surface coatings, and an analysis of the biological effects on humans and the environment.

Tina Kuenniger, an Empa expert on the protection of wood surfaces against weathering, explained how nanoparticles work in paint. Some paints containing silicon dioxide are water repellent, easy to clean and scratch resistant. Nano titanium-dioxide has photocatalytic properties and can decompose air pollutants. Nano titanium-dioxide, along with nano zinc-oxide and nano iron oxide, can be used to provide UV protection and, depending on the size of the particles used, also to protect against infrared radiation, i.e. heat. Similarly, nanoparticles can protect against attack by blue stain fungus and algae. While many laboratory studies have confirmed the effectiveness of nanoparticles, in practice one question remains open: how much of the nanomaterial does one have to mix with the paint to ensure that it functions as expected? For this reason, only a few products for external façades containing nano-materials are available on the market to date. The greatest opportunity nanoparticles offer lies in the combination of various functional properties, for example scratch resistance and easy (or self) cleaning characteristics.

Bernd Nowack, head of Empa's Environmental Risk Assessment and Management group, then presented the results of the investigations into how much nanomaterial is set free from façades. The release rate is generally very low – only one to two percent of the nanoparticles find their way into the environment. In most cases, they are released not as nanoparticles but bound to large paint particles, which significantly reduces their nano-scale effects. "We were very surprised at how few nanoparticles were actually set free," Nowack admitted. The researchers had expected that the catalytically active nanoparticles would also attack the paint surrounding them, leading to more frequent release.

Jean-Pierre Kaiser showed by means of his toxicological studies that paints containing nanoparticles have the same effect on the behavior of cells from the gastrointestinal tract and immune system as do similar paints that do not contain nanoparticles. The Empa researcher does not expect that these nanoparticle-containing paints will represent a new, acute health risk. However, the investigations did at the same time show that nanoparticles are absorbed by the cells. Whether this accumulation of nanoparticles in the cells might lead to longer-term effects cannot yet be definitively determined.

Empa environmental scientist Roland Hischier made a plea for a reasonable balance in the assessment of the possible environmental damage. For a house with an assumed lifetime of 80 years, painting the façade with nanomaterial-based paint would be more economic if this lasted for 30 percent longer than conventional coatings. Then, over the lifetime of the house, one would have to repaint the façade one time fewer, avoiding all the environmental effects caused by manufacturing the paint and disposing of the leftover material.

However, this theory remains somewhat controversial – houses are frequently repainted for aesthetic reasons and not because a new coating is strictly necessary. In this case the advantage offered by the longer lifetime of nanoparticle-based coatings becomes completely irrelevant.

Next, Ingrid Hincapie, a risk researcher on the Empa staff, reported on the results of her industrial survey. Many companies expected paint containing nanoparticles to have a longer lifetime than conventional paint. Some expected it to be easy to handle, for example because it dries faster. But exactly how one correctly disposes of leftover paint containing nanoparticles is something that only a handful of respondents knew.

Finally, André Hauser of the Swiss Federal Office of the Environment explained the current regulations covering the disposal of waste material containing nanoparticles. On its website, www.bafu.admin.ch/abfall/01472/12850, the SFOE offers tips on how to dispose of such material properly. The current regulations relating to safe working practices with nanomaterials were explained by Kaspar Schmid of the Swiss government's State Secretariat for Economic Affairs (SECO).