Nanoparticle uptake from food, the water, as well as uptake into single cells (algae and bacteria) was studied. However, the studies are not easy to compare, as particle producers and, accordingly, the titanium dioxide particle properties differ from study to study.
As example for terrestrial organisms, isopods were fed with titanium dioxide-impregnated leaves. The nanoparticles had only a minor influence on metabolic processes and no influence on feeding rate, body weight or mortality, even though the applied concentrations were very high [1,2].
Lugworms living in the seabed did not internalize particles via the skin or intestines into body tissues. Very high particle concentrations decreased the activity of the worms slightly, but this effect also occurred when worms were exposed to other metal oxides [3].
Being aquatic organisms, rainbow trouts were extensively studied and were exposed to titanium dioxide nanoparticles via water, food, and the bloodstream. Interestingly, titanium dioxide was used in a coarser form for a long time in nutritional studies in fish and is considered as not toxic. Nanoparticles ingested in smaller fractions via the food were detected in the gills, the intestine, the liver, the brain, and the spleen. The animals, however, were found to be in a healthy condition [4]. Titanium dioxide nanoparticles ingested directly from the water were internalized into the fish body only in small amounts [5]. In a further study, nanoparticles were injected directly into the bloodstream of rainbow trout (which is an unrealistic exposure scenario, yet should clarify whether very high doses have any effect e.g., after an accidental spilling) and the organ distribution was analyzed. The particles accumulated in the kidney and liver, yet the functions of these important organs were not influenced [6].
Water fleas (daphnia) are frequently used test organisms as well; here, the particle influence on mobility, heart beat, mortality, and behavior was assessed. None of these parameters was influenced by titanium dioxide, and an increased mortality only occurs in the case of very high concentrations. However, particles were shown to adhere to the exoskeleton and antennae of the animals and to be ingested from the water [7].
Several algae and bacteria showed a diminished growth only when very high concentrations of titanium dioxide nanoparticles were present in the water [8,9].
As a conclusion from the available studies, titanium dioxide nanoparticles exert a low toxicity towards environmental organisms. Still, an important limitation consists in the fact that the effects of very low concentrations applied over a long period of time, corresponding to environmental conditions, have not been assessed up to now.
Literature:
[1] Drobne, D. et al. (2009), Environ Pollut 157, 1157-1164.
[2] Jemec, A. et al. (2008), Environ Toxicol Chem 27, 1904-1914.
[3] Galloway, T. et al. (2009), Environmental Pollution, In Press
[4] Ramsden, C.S. et al. (2009), Ecotoxicology 18, 939-951
[5] Federici, G. et al. (2007), Aquat Toxicol 84, 415-430.
[6] Scown, T.M. et al. (2009), Toxicol Sci 109, 372-380.
[7] Lovern, S.B. et al. (2007), Environ Sci Technol 41, 4465-4470.
[8] Aruoja, V. et al. (2009), Sci Tot al Environ 407, 1461-1468.
[9] Heinlaan, M. et al. (2008), Chemosphere 71, 1308-1316.
[10] Baun, A. et al. (2008), Ecotoxicology 17, 387-95
