Size-, surface- and crystalline structure composition-related effects of titanium dioxide nanoparticles during their aquatic life cycle.

Nanoparticle toxicity depends amongst others on particle characteristics and nanoparticle behavior during their aquatic life cycle. Aquatic organisms may be exposed to nanoparticle agglomerates of varying size, while lager agglomerates after settling rather affect benthic organisms. In this context, the present study systematically examined the role of particle characteristics, i.e. crystalline structure composition (anatase as well as mixture of anatase-rutile), initial particle size (55-, 100-, and 140-nm) and surface area, in the toxicity of titanium dioxide nanoparticles (nTiO2) to the pelagic filter feeder Daphnia magna (n = 4) and the benthic amphipod Gammarus fossarum (n = 30). Smaller initial particle sizes (i.e. 55-nm) and anatase based particles showed an approximately 90% lower Daphnia EC50-value compared to its respective counterpart. Most importantly, particle surface normalized EC50-values significantly differed for nanoparticles equal to or below 100 nm in size from 140-nm sized particles. Hence, these data suggest that the reactive initial surface area may explain the ecotoxicological potential of different particle size classes only if their size is smaller or around 100 nm. In contrast to Daphnia, Gammarus was not affected by nTiO2 concentrations of up to 5.00 mg/L, irrespective of their characteristics. This indicates fundamental differences in the toxicity of nTiO2 during its aquatic life cycle mediated by alterations in their characteristics over time.