“Protective” Effects of Titanium Dioxide Nano-particles on Daphnia magna Exposed to UV Radiation

Aims: Titanium dioxide nano-particles (nano-TiO2) have been used in sunscreen creams to protect skin againstultra violet (UV) radiation; other applications are polarized glasses, wall paints, etc., however, the ecological risks when nano-TiO2 residues reach aquatic ecosystems is not well documented; therefore, the objective of this study is to give some insight on the attenuating effects of nano-TiO2 against UV radiation on Daphnia magna and the toxicity of nano-TiO2 on this organism.
Study Design: Exposing Daphnis to UV radiation in presence and absence of nano-TiO2.
Place and Duration of Study: Biotechnology Institute, CNR, Canada and Toxicology laboratory, Faculty of Marine Sciences, University of Sinaloa Mexico; between April and July 2012.
Methodology: Daphnis (adults and neonates) were exposed to UV light for varying periods in the absence and presence of nano-TiO2. After 48 h incubation, mortalities were recorded for each experiment. Similar experiments were performed using bulk TiO2 instead of nano-TiO2, to know if protective effect is related to particles size. Finally, to know if protective effect is outer (blocking UV radiation) or interior (by cellular processes), Daphnis were pre-treated with nano-TiO2, then exposed to UV radiation, and mortalities recorded.
Results: The mortalities were significantly lower in presence than in absence of nano-TiO2. Alsomortalities were significantly higher in bulk TiO2 than in nano-TiO2, indicating that nano-TiO2 has a protective effect against UV radiation on Daphnis. Also, results indicate that protective effect is exterior, by blocking of UV rather than cellular repair mechanisms (cellular processes). However, at 100mg/L nanoTiO2 concentration, 15% mortality was observed.
Conclusion: Nano-TiO2 is a nanomaterial blocking UV radiation; however if residues reach aquatic ecosystems, could be a risk (toxic) for aquatic organisms, because the highest concentration used in this work caused mortalities in Daphnia magna.