典型纳米颗粒在人工湿地中的生态效应及迁移归趋

The potential hazards of nanoparticles on water environment and human health have obtained extensive attention. The composite ecological environment and coordinated purification mechanism of constructed wetlands provide an feasible approach for the removal of nanoparticles. This project focuses on investigating the ecological effect, transformation and fate of three typical nanoparticles (silver, zinc oxide and fullerene) in constructed wetlands. The main research contents include four parts: i) investigate the stressing effect of typical nanoparticles on the physio-ecological characteristics, antioxidant enzyme activities of wetland plants and the activity, functional diversity and community structure of wetland microbes; ii) investigate the dynamic transition of plant rhizosphere microenvironment, substrates surface microenvironment and integral wetland micro-environment under nanoparticles stressing, including dissolved oxygen and key enzyme activities; iii) investigate the distribution and transformation of nanoparticles in plant tissue and microbial cell, and moreover the migration, retention and occurrence state in different environmental layers of constructed wetlands; iv) considering the coexistent state of nanoparticles and normal pollutants, investigate the temporal and spatial distribution, transportation and transformation of various kinds of pollutants, analyze their mutual environmental behavior and coupling degrading mechanism, construct its ecological dynamic model, and propose corresponding enhancement measures incorporating stress-resistant plants, stress-resistant bacteria and high-efficient substrates. Research results will provide theoretical accordance and technology support for the ecological renovation of nanoparticles as well as the application and development of constructed wetland technology.

纳米颗粒对水环境和人类健康的潜在危害已引起广泛重视，而人工湿地的复合生态环境和协同除污机制为其去除提供了可行途径。本项目以纳米银、纳米氧化锌、富勒烯三种典型纳米颗粒为研究对象，围绕其在人工湿地中的生态效应及迁移归趋展开研究。具体内容包括：研究纳米颗粒对湿地植物生理生态特性、抗氧化酶活性和微生物活性分布、功能多样性、群落结构的胁迫效应；研究纳米颗粒胁迫下，基质界面、植物根际局部微环境及溶解氧、关键酶活性等湿地整体微环境的动态变迁；研究纳米颗粒在植物组织、微生物细胞内的迁移分布，及在湿地不同环境层中的迁移持留和赋存形态；研究纳米颗粒与常规污染物共存状态下，各类物质的时空分布和输移转化，解析纳米颗粒与常规污染物的环境共行为与耦合降解机制，构建生态动力学模型，并结合抗逆植物、抗逆菌种、高效基质等针对性地提出强化措施。本研究为纳米污染物的生态修复及人工湿地技术的应用与发展提供理论依据和技术支持。

随着纳米科技的发展，纳米颗粒不可避免地暴露于环境中，对生态环境存在风险。本项目研究了典型纳米颗粒的暴露对人工湿地生态系统中湿地植物、微生物群落及微环境特征的生态效应，解明了典型纳米颗粒在人工湿地生态系统中的迁移归趋，探讨了人工湿地生态技术去除典型纳米颗粒的可行性。研究表明，典型纳米颗粒对湿地植物生理生态指标产生影响，植物抗逆性标指标也发生明显变化；对参与地球化学循环的关键酶活性（脱氢酶、脲酶、芳基硫酸酯酶等）产生不同程度的抑制；明显改变生态系统中土壤微生物丰度及群落结构。相比于纳米氧化锌(ZnONPs)和富勒烯(nC60)，纳米银(AgNPs)对微生物群落结构的影响更为显著。人工湿地在长期运行过程中对纳米颗粒表现出高效的去除能力。进入生态系统的AgNPs绝大部分被拦截去除(92%~98%)；量化模型分析表明，AgNPs一部分滞留于土壤表层，一部分截留于下层基质，一部分被植物吸收富集，其余随出水从系统逃脱；其中，土壤表层是纳米颗粒的主要归趋。湿地植物虽然吸收富集有限，但植物的存在可明显降低纳米颗粒的生态毒性，具有解毒效应。AgNPs长期暴露下，人工湿地生态系统表现出先抑制后稳定的生态过程。暴露初期，人工湿地系统立即表现出明显的急性毒性效应，常规污染物的去除效果明显降低，尤其对含氮污染物的去除产生明显抑制，且其影响具有显著的浓度效应；随着暴露时间延长，毒性效应逐渐减弱，长期暴露450天后人工湿地运行重新趋于稳定。测序结果表明，湿地微生物群落结构及优势种群随暴露时间表现出明显变迁，同时对湿地脱氮功能基因（amoA、nxrA、nirS、nirK、nosZ和anammox bacterial 16S rRNA）产生影响，进而改变了湿地氮转化途径。为进一步强化纳米颗粒胁迫下人工湿地的稳定运行，对湿地植物进行比选发现黄菖蒲在纳米颗粒长期胁迫下表现出良好的抗逆性；通过对湿地运行方式的对比研究发现上行流运行方式明显优于下行流。人工湿地深度处理单元仍具有高效去除纳米颗粒的潜力，同时保障湿地出水水质达到一级A标准。