Release of TiO2 from paints containing pigment-TiO2 or nano-TiO2 by weathering.
The release of nanomaterials from products and applications that are used by industry and consumers has only been studied to a very limited extent. The amount and the characteristics of the released particles determine the potential environmental exposure. In this work we investigated the release of Ti from paints containing pigment-TiO2 and nano-TiO2. Panels covered with paint with and without nano-TiO2 were exposed to simulated weathering by sunlight and rain in climate chambers. The same paints were also studied in small-scale leaching tests to elucidate the influence of various parameters on the release such as composition of water, type of support and UV-light. Under all conditions we only observed a very low release close to background values, less than 1.5 μg l(-1) in the climate chamber over 113 irrigations per drying cycle and between 0.5 and 14 μg l(-1) in the leaching tests, with the highest concentrations observed after prolonged UV-exposure. The actual release of Ti over the 113 weathering cycles was only 0.007% of the total Ti, indicating that TiO2 was strongly bound in the paint. Extraction of UV-exposed and then milled paint resulted in about 100-times larger release of Ti from the nano-TiO2 containing paint whereas the paint with only pigment-TiO2 did not show this increase. This indicated that the release of Ti from the paints is an effect of the addition of nano-TiO2, either by photocatalytic degradation of the organic paint matrix (observed by electron microscopic imaging of the paint surface) or by direct release of nano-TiO2. Our work suggests that paints containing nano-TiO2 may release only very limited amounts of materials into the environment, at least over the time-scales investigated in this work.
Empa - Swiss Federal Laboratories for Material Science and Technology, Laboratory for Analytical Chemistry, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
Ahmed
A
Al-Kattan
Adrian
A
Wichser
Roger
R
Vonbank
Samuel
S
Brunner
Andrea
A
Ulrich
Stefano
S
Zuin
Bernd
B
Nowack
D004780:Environment, Controlled; D008855:Microscopy, Electron, Scanning; D053758:Nanoparticles / Q000032:analysis*; D010150:Paint; D014025:Titanium / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D014025:Titanium