UVA irradiation influence on the acute toxicity of nanosized TiO₂ to Daphnia magna

The incorporation of engineered nanoparticles in commercial products is progressively increasing and so is the potential for release of these novel materials into the environment. In fact, some recent studies demonstrate the release of nanomaterials, in particular nano-TiO₂, from different ENP containing products such as sun-screens, paints, coatings etc. This implies that nanomaterials will reach the aquatic environment and that they could constitute a risk to aquatic organisms and humans. Common knowledge concerning photoactive nano-TiO₂ effects on freshwater organisms is largely limited to acute toxicity tests without taking into consideration the solar UVA irradiation. Our approach based on the combination of a standardized ecotoxicology method (OECD test 202) with expected solar UVA contribution will allow more realistic understanding of the toxicity of nTiO₂ to Daphnia magna. To reproduce the natural conditions of solar radiation, UVA-365 was monitored for 20 days during summer. The mean UVA intensity (0.56 mW/cm2) was chosen to reproduce the approximate radiation that the daphnids would be exposed to in a summer day. The results clearly demonstrate the higher toxicity of TiO₂ nanoparticles to Daphnia magna when they are exposed to UV-light, therefore this factor should not be neglected when studying the ecotoxicity of photocatalytic nanomaterials. While TiO₂ NPs can be classified as "harmful" to daphnids under darkness conditions (EC50 in the range 10-100 mg/L), when exposed to UVA they can be classified as "toxic" (EC50 in the range 1-10 mg/L). Water matrix was also taken into account, and thus, ecotoxicology tests were carried out in two different water matrices: river natural water and ISO test water.