Toxicity and bioaccumulation of TiO2 nanoparticle aggregates in Daphnia magna

Little is known about the potential ecotoxicity of engineered nanoparticles (NPs) to aquatic organisms. To carefully address this issue, we conducted a comprehensive toxicity assessment, including modified acute (72 h) and chronic (21 d) toxicity tests as well as nTiO2 accumulation analysis using Daphnia magna as a model organism. We found that nTiO2 exerted minimal toxicity to daphnia within the traditional 48 h exposure time, but caused high toxicity when the exposure time was extended to 72 h. This demonstrated that exposure duration may be a contributing factor in NP-mediated toxicity. Moreover, upon chronic exposure to nTiO2 for 21 d, daphnia displayed severe growth retardation and mortality, as well as reproductive defects. Interestingly, a significant amount of nTiO2 was found accumulated in daphnia. However, these daphnia displayed difficulty in eliminating nTiO2 from their body, presenting increased bioconcentration factor (BCF) values. This high level of bioaccumulation may interfere with food intake and ultimately affect growth and reproduction. In summary, long-term exposure of aquatic organisms to nTiO2 may alter the growing status of these organisms at both individual and population levels, posing risks to aquatic ecosystems.