The Effect On The Wetland Plants And The Absorption And Transportation Of AGNPS

Silver nanoparticles(AgNPs) is the simple substance of silver with the particle size of l-100nm, which combine the characteristics of nano materials and silver. Due to their high surface activity, size effect and excellent antibacterial properties, they have become one of the most widely used and the fastest developing nano materials. However, with the accelerating production and introduction of AgNPs into commercial products, there is likelihood of release into the water, which may affect the aquatic ecosystem directly or indirectly. Therefore, it is urgent and necessary to seek an effective technology for the removal of AgNPs in water to reduce or eliminate the potential risk of AgNPs to aquatic ecosystem. In this paper, the toxicity to wetland plants, the fate and transportation of AgNPs were discussed, which will have the important practical significance and provide a theoretical basis and technical support for ecological restoration.The typical wetland plant, Eichhornia crassipes, was selected for hydroponic system under the stress of AgNPs to observe the fate and transformation process of AgNPs. The results indicated that the dissolved Ag concentration in water decreased in different degrees under the different initial concentrations of AgNPs. In the range of the experiment, there was a significant positive correlation between the initial concentration of AgNPs and the concentration of silver accumulation in roots (r=0.98,P<0.05),also in stems and leaves (r=1,p<0.001), and most of the silver was accumulated in the roots. Through the comparison between the system of AgNPs and that of AgNO3, the result showed that the removal rate and the silver concentration absorbed by the plant in the AgNPs system were both lower than that in AgNO3 system. Also, there was a significant positive correlation between the initial concentration of AgNPs and the the removal of silver (r=0.99,p<0.001). AgNPs were mainly removed by the process of aggregation and sedimentation, while the absorption capability of plants was relatively weak. In addition, under the stress of AgNPs, the germination rate, water content, soluble protein content and chlorophyll content of the plant were inhibited at different degrees.The three typical wetland plant (Iris Pseudacorus, Arundo donax var. versicolor, Typha Orientalis Presl) were selected for soil system under the stress of AgNPs, and Typha Orientalis Presl was selected for hydroponic system. The activity of three antioxidant enzymes (SOD, POD, CAT) and the content of MDA in the leaf were measured to investigate the mechanism of plant resistance. The results indicated that at the low concentrations (0.1mg/L, 1mg/L AgNPs), the activity of all the antioxidant enzymes was stable, while at the high concentrations (20mg/L,40mg/L AgNPs), the activity of the antioxidant enzymes was induced with the trend of increasing first and then slowing down the pace of increasing. It showed that AgNPs has destroyed the balance of reactive oxygen species and stimulated active the oxygen scavenging system at the beginning. In the hydroponic system, the activity of SOD and POD of Typha Orientalis Presl was inhibited under the stress of the high concentration of AgNPs (20mg/L,40mg/L AgNPs), while the activity of CAT was induced in the later period. With the accumulation of MDA in leaves of the plant, the order of the capability to resist AgNPs is Typha Orientalis Presl> Iris Pseudacorus> Arundo donax var. versicolor.The three typical wetland plant (Iris Pseudacorus, Arundo donax var. versicolor, Typha Orientalis Presl) were selected for the soil system under the stress of AgNPs. The activity of three soil enzymes in the rhizosphere (dehydrogenase, urease, phosphatase) were measured to investigate the impact of AgNPs on the soil micro environment in the rhizosphere. The results indicated that the activity of all the three soil enzymes was induced by AgNPs, especially that of dehydrogenase and urease. Compared with the other two, the rhizosphere soil dehydrogenase, urease, acid phosphatase and alkaline phosphatase of Iris Pseudacorus were inhibited by AgNPs at a relatively lower degree, which means that the impact of AgNPs on the soil micro environment in the rhizosphere of Iris Pseudacorus is milder.