Photocatalytically active titania (TiO2) nanoparticles are applied, and considered for application, in the degradation of hazardous substances. However, these nanoparticles are also hazardous by themselves. High efficiency immobilization of TiO2 nanoparticles on large inorganic supports that are not vulnerable to photocatalytic degradation is conducive to hazard reduction. Immobilization should also aim at minimizing the release of TiO2 nanoparticles from such supports due to attrition. In doing so there may be a trade off between hazard and photocatalytic activity. (c) 2007 Elsevier B.V. All rights reserved.