纳米TiO2影响湿地挺水植物吸收磷的机制

The biological risks of nano-titanium dioxide (nTiO2) to the constructed wetland sewage treatment system are noteworthy for the researchers. The emergent aquatic plant, as the core of the constructed wetland sewage treatment system, has very significant capability to uptake phosphorus from wastewater. However, the effects and mechanisms of nTiO2 on the uptake of phosphorus by emergent aquatic plant are still not clear, and the related research work emergently needs to be carried out. Nano-titanium dioxide is selected as the research object, meanwhile Scirpus tabernaemontani (S. taber.), which is a commonly used emergent aquatic plant in constructed wetland, as the tested plant, and orthophosphate as the typical speciation of phosphorus in wastewater. Based on finding out the dominant trend of phosphorus uptake by S. taber. and related effects of water environment conditions, the rules of nTiO2 properties (including size and crystal form), concentrations of phosphorus, and water environment conditions (including pH, ion strength and concentrations of natural organic matter) on the uptake of phosphorus by emergent aquatic plant are expecting to be clear by the exposure experiment of the plant in the nTiO2 solution. In order to systematically reveal the interplay impact mechanisms of the combination between nTiO2 and phosphorus and the biological effects of nTiO2 to S. taber. on the phosphorus-uptake by S. taber., and also the adjustment mechanisms of water environment conditions affect the uptake process, the following results are analyzed together, including the adsorption characteristics of phosphorus to nTiO2, the concentration distributions of phosphorus and titanium in S. taber., physiological indicators of S. taber., enzyme activity of the plant tissue, concentrations of root exudates, and the characterizations of plant microstructure. The research results will provide a scientific proof for the precise assessment of ecological risks of nTiO2 to the constructed wetland sewage treatment system.

纳米TiO2对人工湿地污水处理系统的生态风险值得关注。作为系统核心的挺水植物，对污水中的磷有很强的吸收能力，然而纳米TiO2影响挺水植物吸收磷的机制仍不明晰，相关研究工作亟待开展。本项目以纳米TiO2为研究对象，人工湿地常用挺水植物水葱为受试植物，正磷酸盐为污水中磷的主要形态，在弄清水葱吸收磷及水环境条件影响规律的基础上，通过纳米TiO2的暴露实验，探明纳米TiO2浓度和性质（尺寸、晶型）、磷的浓度以及水环境条件（pH值、离子强度、天然有机质的浓度）影响水葱吸收磷的规律。再结合纳米TiO2对磷的吸附特性、水葱体内磷和Ti的浓度分布、水葱生理指标、组织的酶活性、根系分泌物浓度以及植物微观形貌表征结果，系统揭示纳米TiO2与磷的结合及纳米TiO2的水葱生物效应对水葱吸收磷的影响机理，以及水环境条件对吸收过程的调控机制。研究结果可为正确评价纳米TiO2的人工湿地污水处理系统生态风险提供科学依据。

纳米TiO2对人工湿地污水处理系统的生态风险值得关注，其对人工湿地中挺水植物吸收磷的影响机制是亟待探索的科学问题，相关机制的揭示是准确评价纳米TiO2人工湿地系统生态效应的基础。项目以湿地挺水植物泽泻为研究对象（浮水植物大薸为对比），在确定湿地植物水培方法、对磷吸收动力学规律和营养液水化学条件的基础上，构建了纳米TiO2对湿地挺水植物磷吸收影响的暴露实验方法体系，确定了植物组织消解和Ti、P元素浓度同步测定方法。重点开展了纳米TiO2浓度、粒径对泽泻和大薸磷吸收动力学及植物体磷吸收分配的影响研究，通过对磷吸收动力学米氏方程拟合参数的分析，植物不同组织Ti元素和P元素分布规律关系的探索，再结合植物光合作用特征参数和叶片光合色素含量测定、植物组织脂质过氧化产物浓度和自由基清除物浓度表征、泽泻植物组织的透射电镜加能量色散X射线光谱分析（TEM-EDS）的表征结果、植物根横切面细胞结构对比分析、以及基于ZrO2薄膜的纳米TiO2吸附磷酸盐能力估算结果，揭示了纳米TiO2通过载带作用促进湿地挺水植物对磷酸盐吸收的机制。最后，在纳米TiO2悬浮液中添加不同类型的溶解性有机质（DOM），结合DOM添加后纳米TiO2分散状态、ζ电位、Ti元素在植物体的富集和转移情况及Ti和P元素浓度的关系，探索了DOM影响纳米TiO2的植物转运能力和磷吸收机制。该研究的科学意义包括两个方面：第一，使用生态型污水处理工艺（人工湿地）对含纳米TiO2废水进行处理，在特定的纳米TiO2浓度、粒径和晶型条件下，系统中湿地植物的生长不会受到影响，纳米TiO2的存在可以增加植物对污水中磷的吸收；第二，由于沼生农作物（如水稻）与湿地挺水植物具有非常类似的植物生理结构，在植物营养肥中添加纳米TiO2，非常有希望提升以水稻为代表的沼生农作物生长和营养吸收状况，可开展更多的深入研究。