不同粒径纳米TiO_(2)对大型溞的毒性效应及腐殖酸的调控作用

Size-dependent toxicity of TiO_(2) nanoparticle to Daphnia magna and its regulation by humic acid

为评估纳米TiO_(2)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TiO_(2)(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TiO_(2)毒性效应的调控作用.结果表明,粒径是影响纳米TiO_(2)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TiO_(2)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TiO_(2)颗粒对大型溞的毒性作用,腐殖酸对小尺寸纳米TiO_(2)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TiO_(2)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TiO_(2)暴露而引起的ROS浓度上升(p<0.05),进而减轻纳米TiO_(2)对大型溞的毒性作用.此外,腐殖酸可以减小不同粒径纳米TiO_(2)之间的毒性差异.本研究结果可为纳米TiO_(2)在环境水体中的暴露风险评估提供参考依据.

To investigate the potential risk of TiO_(2) nanoparticles(NPs) to ecological system, Daphnia magna was adopted to assess the size-dependent toxicity of TiO_(2) NPs in the absence and present of humic acids(HA). The acute toxicity results revealed that the size of TiO_(2) NPs played an important role in determining their toxicity to D. magna. TiO_(2) NPs with smaller size showed higher toxicity to D. magna than the larger ones(p<0.05). HA could significantly reduce the toxicity of TiO_(2) NPs in a size-dependent manner, which means a more remarkable protective role of HA against TiO_(2) NPs toxicity was observed for smaller sized TiO_(2) NPs than the larger ones(p<0.05). Several antioxidant biomarkers results showed that the accumulation of ROS concentration induced by TiO_(2) NPs was mainly responsible for the toxicity to D. magna. The presence of HA could significantly reduce the increase of ROS level caused by TiO_(2) NPs exposure, and then led to alleviated toxicity. Furthermore, HA could reduce the toxicity differences between TiO_(2) NPs with different size. These results highlight the importance of the physicochemical properties of TiO_(2) NPs in evaluating their environmental risks.