不同粒径纳米TiO2对大型溞的毒性效应及腐殖酸的调控作用

为评估纳米TiO₂在环境水体中的暴露风险，选用大型溞作为模式生物，研究了不同粒径纳米TiO₂（20、40、60和100 nm）对大型溞毒性效应的影响，并探究了腐殖酸对不同粒径纳米TiO₂毒性效应的调控作用.结果表明，粒径是影响纳米TiO₂颗粒毒性效应的重要因素，以大型溞半数致死时间（LT₅₀）为指标，不同粒径纳米TiO₂对大型溞的毒性作用强弱顺序依次为：20 nm颗粒 > 40 nm颗粒 > 60 nm颗粒 > 100 nm颗粒（p<0.05）.腐殖酸的存在可以显著降低纳米TiO₂颗粒对大型溞的毒性作用，腐殖酸对小尺寸纳米TiO₂颗粒的毒性抑制作用更为明显（p<0.05）.大型溞体内ROS水平与抗氧化系统相关酶活分析表明，纳米TiO₂导致大型溞体内活性氧自由基（ROS）浓度升高是其产生毒性作用的重要原因，腐殖酸的存在可以显著降低大型溞体内由于纳米TiO₂暴露而引起的ROS浓度上升（p<0.05），进而减轻纳米TiO₂对大型溞的毒性作用.此外，腐殖酸可以减小不同粒径纳米TiO₂之间的毒性差异.本研究结果可为纳米TiO₂在环境水体中的暴露风险评估提供参考依据.

Size-dependent toxicity of TiO2 nanoparticle to Daphnia magna and its regulation by humic acid

To investigate the potential risk of TiO₂ nanoparticles (NPs) to ecological system, Daphnia magna was adopted to assess the size-dependent toxicity of TiO₂ NPs in the absence and present of humic acids (HA). The acute toxicity results revealed that the size of TiO₂ NPs played an important role in determining their toxicity to D. magna. TiO₂ NPs with smaller size showed higher toxicity to D. magna than the larger ones (p<0.05). HA could significantly reduce the toxicity of TiO₂ NPs in a size-dependent manner, which means a more remarkable protective role of HA against TiO₂ NPs toxicity was observed for smaller sized TiO₂ NPs than the larger ones (p<0.05). Several antioxidant biomarkers results showed that the accumulation of ROS concentration induced by TiO₂ NPs was mainly responsible for the toxicity to D. magna. The presence of HA could significantly reduce the increase of ROS level caused by TiO₂ NPs exposure, and then led to alleviated toxicity. Furthermore, HA could reduce the toxicity differences between TiO₂ NPs with different size. These results highlight the importance of the physicochemical properties of TiO₂ NPs in evaluating their environmental risks.