State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University , Nanjing, Jiangsu Province 210046, China.
Environ Sci Technol. 2014 Jul 1;48(13):7568-75. doi: 10.1021/es500694t. Epub 2014 Jun 18.
When nanoparticles can enter a unicellular organism directly, how may they affect the bioaccumulation and toxicity of other pollutants already present in the environment? To answer this question, we conducted experiments with a protozoan Tetrahymena thermophila. The well-dispersed polyacrylate-coated TiO2 nanoparticles (PAA-TiO2-NPs) were used as a representative nanomaterial, and Cd as a conventional pollutant. We found that PAA-TiO2-NPs could get into Tetrahymena cells directly. Such internalization was first induced by low concentrations of Cd, but later suppressed when Cd concentrations were higher than 1 μg/L. Considering its significant adsorption on PAA-TiO2-NPs, Cd could be taken up by T. thermophila in the form of free ion or metal-nanoparticle complexes. The latter route accounted for 46.3% of Cd internalization. During the 5 h depuration period, 4.34-22.1% of Cd was excreted out, which was independent of the concentrations of intracellular Cd and PAA-TiO2-NPs. On the other hand, both free and intracellular Cd concentrations only partly predicted its toxicity at different levels of PAA-TiO2-NPs. This may have resulted from PAA-TiO2-NPs' synergistic effects and the distinct subcellular distribution of Cd taken up via the two routes above. Overall, we should pay attention to the carrier effects of nanoparticles when assessing their environmental risks.
当纳米颗粒能够直接进入单细胞生物时，它们会如何影响环境中已经存在的其他污染物的生物累积和毒性？为了回答这个问题，我们用原生动物四膜虫（Tetrahymena thermophila）进行了实验。使用分散良好的聚丙烯酸酯包覆的 TiO2 纳米颗粒（PAA-TiO2-NPs）作为代表性纳米材料，Cd 作为常规污染物。我们发现 PAA-TiO2-NPs 可以直接进入四膜虫细胞。这种内化首先是由低浓度的 Cd 诱导的，但当 Cd 浓度高于 1μg/L 时，内化就会受到抑制。考虑到 Cd 对 PAA-TiO2-NPs 的显著吸附作用，Cd 可以以游离离子或金属纳米颗粒复合物的形式被 T. thermophila 吸收。后一种途径占 Cd 内化的 46.3%。在 5 小时的净化期内，有 4.34-22.1%的 Cd 被排出体外，这与细胞内 Cd 和 PAA-TiO2-NPs 的浓度无关。另一方面，自由态和细胞内的 Cd 浓度仅能部分预测在不同浓度的 PAA-TiO2-NPs 下的毒性。这可能是由于 PAA-TiO2-NPs 的协同效应以及通过上述两种途径吸收的 Cd 的不同亚细胞分布所致。总的来说，在评估纳米颗粒的环境风险时，我们应该注意到纳米颗粒的载体效应。
