The Uptake, Accumulation And Phytotoxicity Of CuO Nanoparticles

Metal oxide nanoparticles are being widely applied and have huge development potential in high-temperature superconductivity, organocatalysis, sensors and electrode materials due to their unique electrical, magnetic and catalytic properties, which are receiving increasing attention. Efforts are underway to understand the potential eco-toxicity and environmental risks. Some kinds of nanoparticles (NPs) could be uptaken by root has been recognized by researchers, but there is still much dispute about whether the NPs could translocate up in plant. Copper oxide nanoparticles (CuONPs), as an important one of metal oxide nanoparticles, are being used in antifouling paints for boats, used in some inks, plastics, and antimicrobial coatings. In this study, the uptake, accumulation and pytotoxicity of CuONPs to plant was investigated in a hydroponic culture system. Different concentrations of CuONPs (0,100 mg/L,200 mg/L,500 mg/L and 1000 mg/L) and the comparable dose of soluble Cu (0.5 mg/L) released by CuONPs in Rorison nutrient solution were applied to Elsholtzia splendens (a Cu-accumulator and tolerance) and Cucumis sativus (a common edible plant). The main results are presented as follows:The Cu contents of both plant tissues exposed to CuONPs were higher than exposed to the 0.5 mg/L soluble Cu and the control. The Cu content in the stem and leaf of Elsholtzia splendens exposed to 1000 mg/L CuONPs were reached to 110.2 mg/kg and 90.8 mg/kg respectively, much higher than that exposed to the comparable dose 0.5 mg/L soluble Cu (32.5 mg/kg and 25.3 mg/kg respectively), not to mention the control (18.3 mg/kg and 13.8 mg/kg respectively). The result of TEM-EDS shows sediments were found in different plant cells under CuONPs treatment, and the copper concentration of the sediments were higher than the background. The sediment is suspected to be CuONPs.μ-XANES fitting imply that most accumulated Cu in both Elsholtzia splendens and Cucumis sativus tissues was CuONPs-like ligands specie under CuONPs treatment, even in leafs of Elsholtzia splendens and Cucumis sativus the proportion is as high as 43.5% and 47.2% respectively. However, there no CuONPs-like ligands specie was found in plant when treated with soluble Cu. These imply that CuONPs are able to concentrate in the rhizosphere, enter the root cells, and transport to leaf cells.The level of chlorophyll and biomass in two plants significant decreased, while MDA increased progressively stressed by CuONPs, but not in the comparable soluble Cu treatment, indicating the phytotoxicity of CuONPs is not directly from their limited dissolution in the Rorison nutrient solution, but from the nanoparticles, and CuONPs is more inhibitory than the soluble copper in the bulk solution.Comparing the Cu accumulation and growth inhibition of Elsholtzia splendens with Cucumis sativus, found that the Cu accumulation in Elsholtzia splendens tissues are higher than Cucumis sativus under the same dose of CuONPs treatment, it can be concluded that Elsholtzia splendens has higher ability of CuONPs accumulation; however, there is no significant evidence to show Elsholtzia splendens has higher ability of CuONPs tolerance than common plant, so further research is required.