纳米二氧化钛对微型生物群落的水生态效应及其作用机制

Nano-TiO2 is among the first nanomaterials made commercially available to a wide variety of applications. The high production and widespread use of nanosized TiO2 could lead to the significant release of nano-TiO2 into the aquatic environment through many pathways. And then as a nano-pollutant, nano-TiO2 could harm the aquatic organisms and ecosystems. In many ecotoxicological studies, nano-TiO2 has been shown to cause harmful effects to many freshwater organisms, such as bacteria, algae, invertebrates and fish et al. However, the existing researches mainly concern the effects to the individual organism or population cultured in the laboratory conditions.And the effect mechanisms of nano-TiO2 on the aquatic organisms have not been known clearly. Therefore, the ecological effects and their mechanism of nano-TiO2 on the microbial communities will be studied in our project, which will be useful for the water environment safety evaluation and sustainable development of nano-TiO2.. In the simulated natural environment, the effects of nano-TiO2 with different properties will be studied on the structure and functional characteristics, metabolic heat characteristics and genetic structure diversities of microbial communities collected from the natural aquatic ecosystems by the microbial monitoring, isothermal microcalorimetric and DNA fingerprint analysis technologies, expectively. In this study, we aim to clarify the ecological effects of nano-TiO2 on microbial communities, and to establish their dose-effect relationships. . In addition to that, the ecological effects on the microbial communities will be compared among micro-sized TiO2 and nano-TiO2 with different crystal types, particle sizes and surface areas. The contents, form and location of nano-TiO2 will be measured in the microbial communities. The effects of nano-TiO2 on the cell membranes will also be studied including of membrane fluidity, permeability and molecular structure. Based on the studies above, the relationships will be elucidated between properties of nano-TiO2 and their ecological effects, and the effect mechanisms of nano-TiO2 on the microbial communities will be preliminarily explored.

纳米二氧化钛是最早商业生产、产量最高、应用最广泛的纳米材料之一。随着其大量生产及广泛应用，纳米二氧化钛可通过多种途径进入水体成为纳米污染物，进而可能危害水生生物及水生态系统。然而，纳米二氧化钛可能产生的水生态效应及其作用机制尚不明确。本项目结合已有工作基础，在拟自然环境条件下，采用微型生物群落监测、等温微量热和DNA指纹分析等技术手段，研究不同性质纳米二氧化钛对微型生物群落结构与功能特征、代谢热特征、DNA指纹多样性等的影响，进而阐明纳米二氧化钛对微型生物群落的水生态效应，并建立其剂量效应关系；研究比较不同晶体类型、粒径、表面积的纳米二氧化钛以及微米二氧化钛对微型生物群落的水生态效应，阐明纳米二氧化钛性质对其水生态效应的影响；结合纳米二氧化钛在群落中含量、形态、定位及其对细胞膜影响等研究，初步探讨其作用机制。项目成果将为纳米二氧化钛的水环境安全评价及其可持续发展提供重要科学依据。

为揭示纳米二氧化钛可能产生的水生态效应及其作用机制，本项目通过研究不同性质纳米TiO2 对水体微型生物群落结构与功能、代谢热活动及其DNA指纹多态性的影响，分析了不同性质纳米二氧化钛在不同浓度、不同作用时间下对微型生物群落产生的影响，以揭示其水生态效应；同时，通过纳米二氧化钛对微型生物细胞形态、功能基团、表面电荷和吸附热以及胞外离子浓度等方面的影响研究，初步探讨了其作用机制。研究结果表明：（1）模拟自然环境条件下，纳米二氧化钛可对微型生物群落结构、代谢热活动及其DNA多态性产生影响。GLM分析显示，微型生物群落的物种数、丰度、多样性指数受纳米二氧化钛性质、浓度以及作用时间的显著影响。（2）锐钛型纳米二氧化钛影响下微型生物种类数高于金红石型，但丰度较低；25nm纳米二氧化钛影响下微型生物种类数和丰度均高于40nm、60nm，但优势种种类数最少。（3）紫外光条件下纳米二氧化钛对微型生物群落结构、代谢热及DNA多态性等均产生了较大影响，群落的种类、密度、多样性指数、代谢活性等均显著降低，体积较小的藻类细胞更易被纳米二氧化钛包围且受纳米二氧化钛光催化影响而受损。（4）紫外光条件下纳米二氧化钛使得衣藻、微囊藻等微型生物细胞形态发生显著改变甚至破裂；细胞表面C-N，-C=O，-C-O-C 和 P=O等官能团峰值下降，官能团急剧退化；细胞zeta电位值增加，阳离子的吸附热下降，说明细胞表面负电荷减少，亲水基团受损；胞外K+、Ca2+和Mg2+增加，说明细胞通透性改变，破坏了细胞内外离子平衡。由此推测，纳米二氧化钛可吸附在微型生物细胞表面，并通过光催化产生的过氧化活性物质破坏表面功能团等，从而使细胞外膜功能丧失，最终对微型生物产生直接的损伤。项目成果将为纳米二氧化钛的水生态风险评价及其可持续发展提供重要科学依据。