Antimicrobial engineered nanoparticles in the built cultural heritage context and their ecotoxicological impact on animals and plants: a brief review

Nanoparticles (NPs) of metal oxides, sometimes referred to as engineered nanoparticles have been used to protect building surfaces against biofilm formation for many years, but their history in the Cultural Heritage world is rather short. Their first reported use was in 2010. Thereafter, a wealth of reports can be found in the literature, with Ti, Ag and Zn oxides being the major protagonists. As with all surface treatments, NPs can be leached into the surrounding environment, leading to potential ecotoxicity in soil and water and associated biota. Dissolution into metal ions is usually stated to be the main mode of toxic action and the toxic effects, when determined in the marine environment, decrease in the order Au > Zn > Ag > Cu > Ti > C-60, but direct action of NPs cannot be ruled out. Although ecotoxicity has been assessed by a variety of techniques, it is important that a suitable standard test be developed and the European Unions's Biocidal Product Registration group is working on this, as well as a standard test for antimicrobial efficacy to determine their impact on ecological processes of surrounding non-target organisms and their transformation products under realistic scenarios.