纳米银在淡水沉积物中的硫化过程机制及生态毒性研究

As one of the most widely used and fastest developed nanomaterials, silver nanoparticles (AgNPs) have recently been the focus of intense research because of the potential risk they pose to humans and other biological organisms. AgNPs released into the environment will deposit and readily react with the naturally occurring sulfides to form a surface layer of Ag2S, whose very low solubility may limit the bioavailability and adverse impact of silver in the environment. However, the ability of sulfidation to significant decrease the toxicity of pristine or coated AgNPs to organisms has been ignored during the existed risk assessment of the environmental impact of AgNPs, thus the ecotoxicity of AgNPs may be overestimated. In this research, different AgNPs (such as pristine AgNPs, PVP-AgNPs and PEG-AgNPs) and bulk-Ag will be chose to investigate the sulfidation process and toxicology effects of partially or entirely sulfidized Ag-NPs (Ag2S-NPs) on different microorganisms and benthic animals. The effects of environmental related factors and characters of different types of freshwater sediments on sulfidation, as well as variation of toxicity caused by AgNPs transformation will be examined to reveal the sulfidation mechanism and toxicology effects. The combination of EDX-TEM, XRD, EXAFS, ICP-MS will be employed to characterize and determine different forms of AgNPs, and PCR-DGGE and 16SrDNA library of sediments will be used to investigate the microorganism community structure variation. Further, several benthic invertebrates with different feeding habits will be exposed to AgNPs dosing sediments to reveal the acute and chronic toxicity of different forms of AgNPs in solid and liquid phase. On these basis,the AgNPs transformations model in freshwater sediments and the interaction mechanism of biological system with AgNPs will be proposed. This research will provide a baseline for the ecological security and healthy risk assessment of AgNPs, as well as other metal-based NPs (e.g., CuO, ZnO) that have an affinity with sulfides.

纳米银作为目前应用最广、发展最快的纳米材料，其潜在生态毒性广受关注。纳米银进入水环境后最终将沉降到沉积物中，与硫化物反应是其重要的转化过程，而目前的安全性评价中对硫化过程的忽视将过高估计其生态危害。本项目拟以不同类型纳米银（AgNPs、PVP及PEG包裹AgNPs等）在不同淡水沉积物中的硫化过程及对细菌、底栖动物的影响机制为核心，研究不同环境因子、沉积环境对该过程的影响及纳米银形态改变导致的毒性变化。利用EDX-TEM、XRD、EXAFS、ICP-MS对各形态纳米银定性定量检测，通过PCR-DGGE技术和构建沉积物16SrDNA文库检测细菌群落结构变化；以不同摄食方式的底栖动物进行暴露；并通过与常规银的对照，阐明沉积物中纳米银的硫化过程及生态毒理效应,建立纳米银沉积物转化模型及与生物体系交互作用机理新方法体系。为正确评价纳米银的生态危害奠定基础，并为其它类似亲硫金属的纳米材料研究提供参考。

纳米银作为目前应用最广、发展最快的纳米材料，其潜在生态毒性广受关注。纳米银进入水环境后最终将沉降到沉积物中，与硫化物反应是其重要的转化过程，而目前的安全性评价中对硫化过程的忽视将过高估计其生态危害。本项目通过建立室内沉积物-水微宇宙模型，研究了不同粒径、包裹的纳米银在不同类型淡水沉积物中经环境转变后，其化学形态的变化及由此导致的生态毒性的改变。研究结果显示，进入水体后，大部分纳米银将在120小时内沉降，并主要积累在沉积物表层。积累在沉积物中的纳米银极易被沉积物结合，化学连续提取实验及高分辨透射电镜分析显示硫化银是纳米银在沉积物中转变后的重要存在形式。不同于水相中较高的毒性，纳米银在沉积物相中对微生物群落结构的影响相对较小，且这种影响既取决于纳米银本身性质（如涂层、粒径等），也受到沉积物沉积环境（如酸挥发性硫化物、有机质含量）的影响。尽管进入沉积物后，纳米银的毒性大幅降低，但其对氮循环仍具有不容忽视的影响。此外，沉积物中的纳米银也能够导致底栖动物如铜锈环棱螺产生氧化损伤，且银在螺体内能够显著积累。进一步的释放实验表明，沉积物中的纳米银具有向上覆水体释放的风险，释放到上覆水体中的银对水生动物如斑马鱼的毒性效应亦不容忽视。该项目的实施揭示了纳米银在沉积物中的硫化过程，基本阐明了纳米银在沉积物中的毒性机制及风险，从而为正确评价纳米银的环境行为和生态危害奠定了良好的基础。