Ecotoxicological Properties of Titanium Dioxide Nanomorphologies in Daphnia magna

In this work, the structural, vibrational, morphological, and colloidal properties of commercial 15.1 nm TiO₂ nanoparticles (NPs) and nanowires (NWs, 5.6 thickness, 74.6 nm length) were studied with the purpose of determining their ecotoxicological properties. This was achieved by evaluating acute ecotoxicity experiments carried out in the environmental bioindicator Daphnia magna, where their 24-h lethal concentration (LC) and morphological changes were evaluated using a TiO₂ suspension (pH = 7) with point of zero charge at 6.5 for TiO₂ NPs (hydrodynamic diameter of 130 nm) and 5.3 for TiO₂ NWs (hydrodynamic diameter of 118 nm). Their LC values were 157 and 166 mg L^-1 for TiO₂ NWs and TiO₂ NPs, respectively. The reproduction rate of D. magna after fifteen days of exposure to TiO₂ nanomorphologies was delayed (0 pups for TiO₂ NWs and 45 neonates for TiO₂ NPs) in comparison with the negative control (104 pups). From the morphological experiments, we may conclude that the harmful effects of TiO₂ NWs are more severe than those of 100% anatase TiO₂ NPs, likely associated with brookite (36.5 wt. %) and protonic trititanate (63.5 wt. %) presented in TiO₂ NWs according to Rietveld quantitative phase analysis. Specifically, significant change in the heart morphological parameter was observed. In addition, the structural and morphological properties of TiO₂ nanomorphologies were investigated using X-ray diffraction and electron microscopy techniques to confirm the physicochemical properties after the ecotoxicological experiments. The results reveal that no alteration in the chemical structure, size (16.5 nm for TiO2 NPs and 6.6 thickness and 79.2 nm length for NWs), and composition occurred. Hence, both TiO₂ samples can be stored and reused for future environmental purposes, e.g., water nanoremediation.