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.