No abstract

The production and use of nanoparticles (NPs), especially those of titanium dioxide (TiO(2)) have increased steadily within the last decade. Common knowledge of photoactive nanosized TiO(2) (nTiO(2)) effects on freshwater organisms is largely limited to acute toxicity tests without taking into consideration solar ultraviolet-A (UVA) irradiation. The authors' approach in the present study, based on a combination of a standardized ecotoxicology method (Organization for Economic Cooperation and Development [OECD] test 202) and the expected solar UVA contribution, will allow a more realistic understanding of the toxicity of TiO(2) to Daphnia magna. The results show that the contribution of UVA to TiO(2) toxicity cannot be ignored. The half-maximal effective concentration values (median effective concentration [EC50], immobilization as the endpoint) using Organization for Standardization (ISO) test water as well as river water decreased from 29.7 to 33.6 mg/L under dark conditions to 1.2 to 3.4 mg/L TiO(2) after exposure to 0.56 mW/cm(2) UVA radiation. The authors also discuss possible mechanisms of NPs toxicity and the accuracy of results in terms of problems observed, such as solubilization and sedimentation of NPs, in ecotoxicological testing of nTiO(2).

Rising use of nanoparticles in manufacturing as well as in commercial products bring issues related to environmental release and human exposure. A large amount of TiO nanoparticles will eventually reach wastewater treatment plants. Low pressure membrane filtration has been suggested as a feasible treatment of water streams. This study investigated first at laboratory scale the influence of: i) membrane material, ii) pore size and iii) water chemistry on nTiO removal. TiO retention was governed by the cake layer formation mechanism and significant retention of nanoparticles was observed even for filters having considerably larger pores than nTiO. PVDF showed a great potential for nTiO rejection. Additionally, filtration pilot plant experiments were carried out using PVDF membranes (0.03 and 0.4μm pore size). The release of nTiO in the pilot scale filtration system was always above the instrumental detection limit (>1.5μg/L) and in most cases below 100μg/L regardless of the pore size and applied conditions. The nTiO membrane breakthrough predominantly occurred in the first few minutes after backwashes and ceased when the cake layer was formed. Ultrafiltration and microfiltration were comparable with rejection of nTiO above 95% at similar permeate flow rates. Nevertheless, ultrafiltration is more promising than microfiltration because it allowed longer operation times between backwash cycles.